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Last Updated :2024/09/16

研究者情報

マスター

アカウント（マスター）

  • 氏名

    渡部　正夫(ワタナベ　マサオ), ワタナベ　マサオ

所属（マスター）

  • 工学研究院　機械・宇宙航空工学部門　熱流体システム

所属（マスター）

  • 工学研究院　機械・宇宙航空工学部門　熱流体システム

独自項目

syllabus

  • 2021, 流体工学特論, Advanced Fluid Engineering, 修士課程, 工学院
  • 2021, 大学院共通授業科目（一般科目）：自然科学・応用科学, Inter-Graduate School Classes(General Subject):Natural and Applied Sciences, 修士課程, 大学院共通科目, Fluid engineering, Theory of thermal-fluid mechanics, Computational fluid mechanics, Flow measurement & visualization, Food Science
  • 2021, 応用数学特論, Advanced Mathematics for Applications, 修士課程, 工学院, Functional Analysis, Legesgue Integration, Hilbert Space, Operator Theory, Integral and Differential Equations
  • 2021, 流体工学特論, Advanced Fluid Engineering, 博士後期課程, 工学院
  • 2021, 応用数学特論, Advanced Mathematics for Applications, 博士後期課程, 工学院, Functional Analysis, Legesgue Integration, Hilbert Space, Operator Theory, Integral and Differential Equations
  • 2021, 機械工学概論, Introduction to Mechanical Engineering, 学士課程, 工学部, 機械工学，材料，機械力学，熱，流体，エネルギー
  • 2021, インターンシップⅠ, Internship Ⅰ, 学士課程, 工学部, 就業体験、インターンシップ
  • 2021, インターンシップⅡ, Internship Ⅱ, 学士課程, 工学部, 海外研修、Short Stay, Short Visit, SSSV、就業体験、インターンシップ
  • 2021, 流体力学Ⅰ, Fluid Dynamics Ⅰ, 学士課程, 工学部, 流体力学，検査体積，保存法則，連続の式，運動量，エネルギー，ベルヌーイの定理，渦運動，流線，ポテンシャル流れ，流れ関数
  • 2021, 流体工学, Fluid Engineering, 学士課程, 工学部, 圧縮性流れ，音波，衝撃波，完全流体の力学，物体に働く力，翼理論，層流，乱流，境界層，航空機，空力，遷音速流

researchmap

プロフィール情報

学位

  • Ph.D.（The Johns Hopkins University）
  • 工学修士（東京大学）

プロフィール情報

  • 姓

    渡部, ワタナベ

  • 名

    正夫, マサオ

  • ID各種

    200901007748840195

対象リソース

業績リスト

研究キーワード

  • 分子気体力学   extra cellular matrix   気液界面   混相流   気液二相流   Surface Tension   軟骨細胞   transport phenolnena   visualization   移流   high speed digital video   再生医療   CFD   Computational fluid dynamics   自由界面   Phase contrast   Bubble Cloud   PIV法   cell   Magnetic Resonant Angiography   bubble   モデリング   拡散   Inverse poblem   Inverse problem   Bubble generation   PIV   bovine Articular Cartilage   Finite Element Method   

研究分野

  • ものづくり技術（機械・電気電子・化学工学） / 熱工学
  • ものづくり技術（機械・電気電子・化学工学） / 流体工学

経歴

  • 2020年04月 - 現在 北海道大学 大学院工学研究院 機械・宇宙航空工学部門 教授
  • 2011年06月 - 2020年03月 北海道大学 大学院工学研究院 機械宇宙工学部門 教授
  • 2008年06月 - 2011年05月 北海道大学 工学研究院 機械宇宙工学部門 准教授
  • 1995年04月 - 2008年05月 九州大学 大学院 機械工学科 准教授

学歴

  • 1986年04月 - 1988年03月   東京大学 大学院   工学系研究科   機械工学専攻修士課程

受賞

  • 2017年10月 一般社団法人日本機械学会 日本機械学会流体工学部門貢献表彰
     
    受賞者: 渡部 正夫
  • 2014年10月 日本学術振興会 科研費審査員表彰
     
    受賞者: 渡部 正夫
  • 2013年08月 日本混相流学会 2012年度日本混相流学会 学会賞・論文賞
     気泡後部トロイダル渦の抗力への寄与 
    受賞者: 城田農;佐藤文香;真田俊之;渡部正夫
  • 2012年03月 日本機械学会 2011年度日本機械学会賞（学会賞論文）
     Unified Theory Based on Parameter Scaling for Derivation of Nonlinear Wave Equations in Bubbly Liquids 
    受賞者: 金川哲也;矢野猛;渡部正夫;藤川重雄

論文

  • Hiroyuki Fujii, Hyeonwoo Na, Jungyun Yi, Kazumichi Kobayashi, Masao Watanabe
    Colloids and Surfaces A: Physicochemical and Engineering Aspects 135208 - 135208 2024年08月
  • Hiroyuki Fujii, Hyeonwoo Na, Koyata Nishikawa, Kazumichi Kobayashi, Masao Watanabe
    Optical Review 31 3 299 - 308 2024年05月22日 
    Abstract Near-infrared spectroscopy and imaging using scattered light potentially evaluate the structural properties of the medium, like the average particle size, based on a relation between its structure and light scattering. A qualitative understanding of light scattering is crucial for developing optical imaging techniques. The scattering properties of dense colloidal suspensions have been extensively investigated using the electromagnetic theory (EMT). The colloidal suspensions are widely used in liquid tissue phantoms for optical imaging techniques and are encountered in various fields, such as the food and chemical industries. The interference between electric fields scattered by colloidal particles significantly influences the scattering properties, so-called the interference effects. Despite many efforts since the 1980s, a complete understanding of the interference effects has still not been achieved. The main reason is the complicated dependence of the interference on the optical wavelength, particle size, and so on. This paper briefly reviews numerical and theoretical studies of the interference effect based on the dependent scattering theory, one of the EMTs, and model equations.
  • Kazumichi Kobayashi, Kota Aoki, Hirofumi Tabe, Hiroyuki Fujii, Toshiki Nara, Hideyoshi Takashima, Nobuyuki Oshima, Masao Watanabe
    Physics of Fluids 35 8 2023年08月01日 
    This paper presents molecular dynamics simulations of the Couette flow of a rarefied gas between the liquid and wall boundaries and, in particular, investigates the boundary conditions for the Boltzmann equation at the liquid interface. The simulation results for various Knudsen numbers show that the slip velocity decreases at the liquid boundary and increases at the smooth wall as the Knudsen number increases, indicating that the velocity profile of the rarefied Couette flow is asymmetric. One reason for this is backscattering, in which molecules are reflected in the opposite direction to the mainstream flow, owing to molecular-scale roughness at the liquid boundary. It has also been suggested that the backscattering effect decreases when the gas density increases. This can be understood using the local Knudsen numbers near the liquid boundary.
  • Hiroyuki Fujii, Koyata Nishikawa, Hyeonwoo Na, Yuki Inoue, Kazumichi Kobayashi, Masao Watanabe
    Infrared Physics & Technology 132 104753 - 104753 2023年08月
  • Kotaro Ohashi, Kazumichi Kobayashi, Hiroyuki Fujii, Masao Watanabe
    International Communications in Heat and Mass Transfer 142 106622 - 106622 2023年03月
  • Hiroyuki Fujii, Iori Terabayashi, Kazumichi Kobayashi, Masao Watanabe
    Photoacoustics 27 100368 - 100368 2022年09月
  • Ryunosuke Adachi, Kazumichi Kobayashi, Hiroyuki Fujii, Toshiyuki Sanada, Masao Watanabe
    Physics of Fluids 34 6 062116 - 062116 2022年06月 
    A water drop impacting a dry solid surface can eject a thin liquid sheet, which is forced to expand on the surface to wet the solid surface. Wetting failure, which produces defects in applications based on the impact of drops, including coating, cooling, cleaning, and printing, may occur with a sufficiently large liquid-sheet velocity. However, the exact onset of wetting failure when a drop impacts the surface has yet to be determined. Therefore, we examine the dependence of rim instability immediately after liquid-sheet ejection on the static contact angle of the solid surface at the instant of water drop impact. This study is the first attempt to solve this problem and is made possible only by using an ultra-high-speed camera. We revealed that wetting failure can occur by investigating the rim instability of the liquid sheet.
  • Hirofumi Tabe, Kazumichi Kobayashi, Hiroyuki Fujii, Masao Watanabe
    International Journal of Heat and Mass Transfer 188 122663 - 122663 2022年06月
  • Hirofumi Tabe, Kiryu Hiramatsu, Kazumichi Kobayashi, Hiroyuki Fujii, Masao Watanabe, Tsuyoshi Totani
    Applied Thermal Engineering 212 118472 - 118472 2022年04月
  • Hiroyuki Fujii, Moegi Ueno, Yuki Inoue, Toshiaki Aoki, Kazumichi Kobayashi, Masao Watanabe
    Optics Express 30 3 3538 - 3538 2022年01月31日
  • Hiroyuki Fujii, Iori Terabayashi, Toshiaki Aoki, Yuki Inoue, Hyeonwoo Na, Kazumichi Kobayashi, Masao Watanabe
    Applied Sciences 12 3 1190 - 1190 2022年01月24日 
    Understanding light propagation in liquid phantoms, such as colloidal suspensions, involves fundamental research of near-infrared optical imaging and spectroscopy for biological tissues. Our objective is to numerically investigate light propagation in the alumina colloidal suspensions with the mean alumina particle diameter of 55 nm at the volume fraction range 1–20%. We calculated the light scattering properties using the dependent scattering theory (DST) on a length scale comparable to the optical wavelength. We calculated the steady-state radiative transfer and photon diffusion equations (RTE and PDE) using the DST results based on the finite difference method in a length scale of the mean free path. The DST calculations showed that the scattering and reduced scattering coefficients become more prominent at a higher volume fraction. The anisotropy factor is almost zero at all the volume fractions, meaning the scattering is isotropic. The comparative study of the RTE with the PDE showed that the diffusion approximation holds at the internal region with all the volume fractions and the boundary region with the volume fraction higher than 1%. Our findings suggest the usefulness of the PDE as a light propagation model for the alumina suspensions rather than the RTE, which provides accurate but complicated computation.
  • Kotaro Ohashi, Kazumichi Kobayashi, Hiroyuki Fujii, Masao Watanabe
    Physics of Fluids 33 12 122017 - 122017 2021年12月
  • 藤井 宏之, 青木 俊晃, 井上 優輝, 寺林 伊織, 小林 一道, 渡部 正夫
    Technical digest of 26th Microoptics Conference (MOC2021) PO-11 164 - 165 日本応用物理学会 2021年09月 [査読有り]
  • Hirofumi Tabe, Kazumichi Kobayashi, Hiroyuki Fujii, Masao Watanabe
    PLOS ONE 16 3 e0248660 - e0248660 2021年03月16日 [査読有り]
     
    The kinetic boundary condition (KBC) represents the evaporation or condensation of molecules at the vapor–liquid interface for molecular gas dynamics (MGD). When constructing the KBC, it is necessary to classify molecular motions into evaporation, condensation, and reflection in molecular-scale simulation methods. Recently, a method that involves setting the vapor boundary and liquid boundary has been used for classifying molecules. The position of the vapor boundary is related to the position where the KBC is applied in MGD analyses, whereas that of the liquid boundary has not been uniquely determined. Therefore, in this study, we conducted molecular dynamics simulations to discuss the position of the liquid boundary for the construction of KBCs. We obtained some variables that characterize molecular motions such as the positions that the molecules reached and the time they stayed in the vicinity of the interface. Based on the characteristics of the molecules found from these variables, we investigated the valid position of the liquid boundary. We also conducted an investigation on the relationship between the condensation coefficient and the molecular incident velocity from the vapor phase to the liquid phase. The dependence of the condensation coefficient on the incident velocity of molecules was confirmed, and the value of the condensation coefficient becomes small in the low-incident-velocity range. Furthermore, we found that the condensation coefficient in the non-equilibrium state shows almost the same value as that in the equilibrium state, although the corresponding velocity distribution functions of the incident velocity significantly differ from each other.
  • Hiroyuki Fujii, Go Chiba, Yukio Yamada, Yoko Hoshi, Kazumichi Kobayashi, Masao Watanabe
    Journal of Computational Physics 423 109825 - 109825 2020年09月 [査読有り][通常論文]
     
    A versatile and accurate treatment for the highly forward-peaked phase function in the three-dimensional (3D) radiative transfer equation (RTE) based on the discrete ordinates method (DOM) is crucial for biomedical optics. Our first objective was to compare the delta-Eddington (dE) and Galerkin quadrature (GQ) methods. The dE method decomposes the phase function into a purely forward-peaked component and the other component, and expands the other component by Legendre polynomials as well as the finite order Legendre expansion (FL) method does. The GQ method conducts the weighting procedure in addition to the Legendre expansion. Although it was reported that both methods can provide the accurate results for calculations of the RTE, the versatility of both methods is still unclear. The second objective was to examine a possibility of a conjunction of the GQ method with the dE method, called as the GQ-dE method, which has the advantages of both methods. We examined numerical errors in the moment conditions of the phase function using the FL, dE, GQ and GQ-dE methods at various types and orders of the quadrature sets, mainly in the region of the errors induced by the angular discretization using the DOM. The errors were reduced by the dE method from those by the FL method, however the error reduction depended on the types and orders of the quadrature sets. Meanwhile, the errors were significantly reduced by the GQ and GQ-dE methods, regardless of the quadrature sets. We also verified the numerical calculations of the time-dependent 3D RTE by the analytical solution of the RTE for homogeneous media in the region of the scattering length scale, where the highly forward-peaked phase function strongly influences the RTE-results. The errors in the RTE-results were similar to those in the moment conditions. Our results suggest the higher versatility and accuracy of the GQ and GQ-dE methods than those of the FL and dE methods. (C) 2020 Elsevier Inc. All rights reserved.
  • Hiroyuki Fujii, Leung Tsang, Jiyue Zhu, Koki Nomura, Kazumichi Kobayashi, Masao Watanabe
    Optics Express 2020年07月10日 [査読有り][通常論文]
  • Kotaro Ohashi, Kazumichi Kobayashi, Hiroyuki Fujii, Masao Watanabe
    Scientific Reports 10 8143  2020年05月18日 [査読有り][通常論文]
  • Hirofumi Tabe, Kazumichi Kobahashi, Hisao Yaguchi, Hiroyuki Fujii, Masao Watanabe
    International Journal of Thermal Sciences 150 106203 - 106203 2020年04月 [査読有り][通常論文]
  • Yuki FURUYA, Yuki MIZUSHIMA, Masao WATANABE, Toshiyuki SANADA
    JAPANESE JOURNAL OF MULTIPHASE FLOW 34 1 111 - 117 2020年03月15日
  • 野村 航希, 藤井 宏之, 小林 一道, 渡部 正夫, 西村 吾朗
    Proceeding of the 7th Asian NIR symposium (ANS2020) 2020 AFI-0006 12 - 13 2020年02月 [査読有り][通常論文]
  • 遠藤 茂樹, 藤井 宏之, 小林 一道, 渡部 正夫
    Proceeding of the 7th Asian NIR symposium (ANS2020) 2020 NRT-0008 60 - 61 2020年02月 [査読有り][通常論文]
  • 藤井 宏之, 西村 吾朗, 遠藤 茂樹, 野村 航希, 小林 一道, 渡部 正夫
    Proceeding of the 7th Asian NIR symposium (ANS2020) 2020 AFI-0007 14 - 15 2020年02月 [査読有り][通常論文]
  • Shinnosuke Obi, Koji Fukagata, Masaharu Kameda, Chisachi Kato, Yohei Morinishi, Yuichi Murai, Satoshi Watanabe, Masao Watanabe
    JOURNAL OF FLUID SCIENCE AND TECHNOLOGY 15 2 2020年
  • Taku Ashida, Masao Watanabe, Kazumichi Kobayashi, Hiroyuki Fujii, Toshiyuki Sanada
    Physical Review Fluids 5 1 011601  2020年01月 [査読有り][通常論文]
  • Hiroyuki Fujii, Moegi Ueno, Kazumichi Kobayashi, Masao Watanabe
    Applied Sciences 10 1 93  2019年12月 [査読有り][通常論文]
  • 藤井 宏之, 千葉 豪, 山田 幸生, 星 詳子, 小林 一道, 渡部 正夫
    Proceedings of the 9th International Symposium on Radiative Transfer, RAD-19 SM05 261 - 268 2019年09月 [査読有り][通常論文]
  • 藤井 宏之, 山田 幸生, 星 詳子, 小林 一道, 渡部 正夫
    AIP Conference Proceedings (ICNAAM2018) 2116 450037 1 - 4 2019年07月 [査読有り][通常論文]
  • 田林 孝介, 藤井 宏之, 小林 一道, 渡部 正夫
    AIP Conference Proceedings (ICNAAM2018) 2116 450052 1 - 4 2019年07月 [査読有り][通常論文]
  • Kyohei Yamamoto, Kazumichi Kobayashi, Masao Watanabe, Hiroyuki Fujii, Misaki Kon, Hiroyuki Takahira
    Physical Review Fluids 4 6 2019年06月11日 
    In this paper, the influence of a small amount of noncondensable gas on shock wave generation inside a collapsing vapor bubble is examined by combining numerical analysis of a bubble dynamics equation and of the Boltzmann equation for gas flow inside a bubble. We show the importance of the high Knudsen number in the flow, i.e., the nonequilibrium gas flow, to the temperature field inside the collapsing bubble. We also show that the maximum mean Knudsen number inside the collapsing bubble can be evaluated from the initial Knudsen number and the initial number density ratio of noncondensable gas and vapor molecules. As a result, we conclude that a small amount of noncondensable gas strongly affects the temperature field inside the collapsing bubble, preventing shock wave generation inside the bubble in the final stage of collapse.
  • 田林 孝介, 藤井 宏之, 大川 晋平, 小林 一道, 山田 幸生, 星 詳子, 渡部 正夫
    CMBE Proceedings (6th International Conference on Computational & Mathematical Biomedical Engineering) A5 161 - 164 2019年05月 [査読有り][通常論文]
  • Hirofumi Tabe, Kazumichi Kobayashi, Hisao Yaguchi, Hiroyuki Fujii, Masao Watanabe
    Heat and Mass Transfer/Waerme- und Stoffuebertragung 55 4 1005  2019年04月11日 
    During typesetting of the article, Figure 7 was changed. The correct image is shown below.
  • Hirofumi Tabe, Kazumichi Kobayashi, Hisao Yaguchi, Hiroyuki Fujii, Masao Watanabe
    Heat and Mass Transfer 55 4 993 - 1003 2019年04月 [査読有り][通常論文]
  • Yuki Furuya, Toshiyuki Sanada, Masao Watanabe
    ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference, AJKFluids 2019 5 2019年 
    Wet cleaning methods using fluid are widely applied in many industrial fields. For a cleaning inside closed-end holes, it is first necessary to fill the holes to be cleaned with the liquid. However, in structures with small holes, it is difficult to discharge inside the gas due to surface tension. In our early studies, we have found that the discharging a gas inside a closed-end hole was promoted by an impingement of droplet train. And the pressure fluctuation near the gas-liquid interface due to droplet impingement was important. In this study, we attempted the gas discharge from closed-end holes due to acoustic wave irradiation. First, we theoretically estimated the oscillation of the gas column inside the hole during acoustic wave irradiation. We modeled the natural frequency of the gas column using a spring-mass system. Then we experimentally measured the fluctuation of the gas-liquid interface for the evaluation of the model. In addition, we compared the gas discharge ratio with different frequency and pressure level. The fluctuation of gas-liquid interface and discharging the gas were observed with a high-speed video camera. As results, the natural frequencies of a gas column were depending on the length of the gas column and the diameter of the hole. From the experiments, we confirmed that the acoustic wave certainly propagated into the hole, and the frequency of the irradiated acoustic wave and the experimentally obtained natural frequency were in good agreement except for extremely low gas discharge ratio condition. Moreover, we observed gas discharge process and found that the high gas discharge ratio were achieved using the acoustic wave close to natural frequency. From these results, we concluded that the assumption based on a spring-mass system is valid.
  • Molecular Dynamics Study on Influence of Liquid-solid Intermolecular Force on Levitating Mechanism of Impacting Nanodroplet on Heated Wall
    Hirofumi Tabe, Kazumichi Kobayashi, Hisao Yaguchi, Hiroyuki Fujii, Masao Watanabe
    Surface Wettability Effects on Phase Change Phenomena(SWEP) 2019年 [査読有り][通常論文]
  • Kazumichi Kobayashi, Takahiro Nagayama, Masao Watanabe, Hiroyuki Fujii, Misaki Kon
    Journal of Fluid Mechanics 856 1045 - 1063 2018年12月 [査読有り][通常論文]
     
    This study investigates the influence of the condensation coefficient of vapour on the collapse of a bubble composed of condensable gas (vapour) and non-condensable gas (NC gas). We simulated vapour and NC gas flow inside a bubble based on the molecular gas dynamics analysis in order to replicate the phase change (viz., evaporation and condensation) precisely, by changing the initial number density ratio of the NC gas and vapour, the initial bubble radius and the value of the condensation coefficient. The results show that the motion of the bubble is unaffected by the value of the condensation coefficient when that value is larger than approximately 0.4. We also discuss NC gas drift at the bubble wall during the final stage of the bubble collapse and its influence on the condensation coefficient. We conclude that vapour molecules can behave as NC gas molecules when the bubble collapses, owing to the large concentration of NC gas molecules at the gas–liquid interface. That is, the condensation coefficient reaches almost zero when the bubble collapses violently.
  • Hiroyuki Fujii, YukioYamad, Go Chiba, Yoko Hoshi, Kazumichi Kobayashi, Masao Watanabe
    Journal of Computational Physics 371 591 - 604 2018年12月 [査読有り][通常論文]
  • Y. Tatekura, M. Watanabe, K. Kobayashi, T. Sanada
    Royal Society Open Science 5 12 181101  2018年12月 [査読有り][通常論文]
  • Toshiyuki SANADA, Yuki FURUYA, Shunsuke MURAKI, Masao WATANABE
    Journal of Fluid Science and Technology 13 3 JFST0012 - JFST0012 2018年10月 [査読有り][通常論文]
  • Hiroyuki Fujii, Yukio Yamada, Yoko Hoshi, Shinpei Okawa, Kazumichi Kobayashi, Masao Watanabe
    Reaction Kinetics, Mechanisms and Catalysis 123 2 439 - 453 2018年04月01日 [査読有り][通常論文]
     
    Constructions of numerical schemes for solving the radiative transfer equation (RTE) are crucial to evaluate light propagation inside photocatalytic systems. We develop accurate and efficient schemes of the three-dimensional and time-dependent RTE for numerical phantoms modeling aqueous titanium dioxide suspensions, in which the anisotropy of the forward-directed scattering varies and the strength of absorption is comparable to that of scattering. To improve the accuracy and efficiency of the numerical solutions, the forward-directed phase function is renormalized in the zeroth or first order with a small number of discrete angular directions. Then, we investigate the influences of the forward-directed scattering on the numerical solutions by comparing with the analytical solutions. The investigation shows that with the anisotropy factor less than approximately 0.7 corresponding to the moderate forward-directed scattering, the numerical solutions of the RTE using the both of the zeroth and first order renormalization approaches are accurate due to the reductions of the numerical errors of the phase function. With the anisotropy factor more than approximately 0.7 corresponding to the highly forward-directed scattering, the first order renormalization approach still provides the accurate results, while the zeroth order approach does not due to the large errors of the phase function. These results suggest that the developed scheme using the first order renormalization can provide accurate and efficient calculations of light propagation in photocatalytic systems.
  • 世古和也, 小林一道, 藤井宏之, 渡部正夫
    混相流 32 1 59 - 64 2018年03月 [査読有り][通常論文]
  • Influence of surface roughness of high temperature wall on levitation of impacting droplet based on molecular dynamics simulation
    Hirofumi Tabe, Kazumichi Kobayashi, Hisao Yaguchi, Hiroyuki Fujii, Masao Watanabe
    Surface Wettability Effects on Phase Change Phenomena (SWEP) workshop 2018年 [査読有り][通常論文]
  • Numerical investigation of light and pressure propagation in biological tissue for model-based photoacoustic tomography
    田林 孝介, 藤井 宏之, 小林 一道, 渡部 正夫
    Extended Abstracts of The 9th JSME-KSME Thermal and Fluids Engineering Conference TFEC9-1526 1 - 4 2017年10月 [査読有り][通常論文]
  • Misaki Kon, Kazumichi Kobayashi, Masao Watanabe
    EUROPEAN JOURNAL OF MECHANICS B-FLUIDS 64 81 - 92 2017年07月 [査読有り][通常論文]
     
    Heat and mass transfer caused by nonequilibrium phase change (net evaporation/condensation) play a major role in a vapor-liquid two-phase flow. In general, liquid temperature changes with time because of the heat and mass transfer between the vapor and liquid phases; however, a precise investigation of the transport phenomena related to this temporal evolution of liquid temperature is still lacking. The aim of this study is to examine a kinetic boundary condition, which depends on liquid temperature, for the Boltzmann equation in a vapor-liquid two-phase system with unsteady net evaporation/condensation. In this study, we confirmed whether the kinetic boundary condition follows the temporal evolution of liquid temperature attributed to unsteady net evaporation/condensation by using the molecular simulation based on mean-field kinetic theory, and then we validated the accuracy of the kinetic boundary condition by solving the initial boundary value problem of the Boltzmann equation in unsteady net evaporation/condensation. These results showed that the kinetic boundary condition follows the temporal evolution of liquid temperature in the simulation setting of this study. Furthermore, we concluded that the kinetic boundary condition that depends on liquid temperature is guaranteed to be accurate even in unsteady net evaporation/condensation by considering the temporal evolution of liquid temperature. (C) 2016 Elsevier Masson SAS. All rights reserved.
  • 森川昌太郎, 立藏祐樹, 小林一道, 藤井宏之, 渡部正夫, 佐々木浩一
    ながれ 36 2 105 - 108 日本流体力学会 2017年05月 [査読有り][通常論文]
  • H. Fujii, Y. Yamada, K. Kobayashi, M. Watanabe, Y. Hoshi
    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 33 5 e2826  2017年05月 [査読有り][通常論文]
     
    Diffuse optical tomography using near-infrared light in a wavelength range from 700 to 1000nm has the potential to enable non-invasive diagnoses of thyroid cancers; some of which are difficult to detect by conventional methods such as ultrasound tomography. Diffuse optical tomography needs to be based on a physically accurate model of light propagation in the neck, because it reconstructs tomographic images of the optical properties in the human neck by inverse analysis. Our objective here was to investigate the effects of three factors on light propagation in the neck using the 2D time-dependent radiative transfer equation: (1) the presence of the trachea, (2) the refractive-index mismatch at the trachea-tissue interface, and (3) the effect of neck organs other than the trachea (spine, spinal cord, and blood vessels). There was a significant influence of reflection and refraction at the trachea-tissue interface on the light intensities in the region between the trachea and the front of the neck surface. Organs other than the trachea showed little effect on the light intensities measured at the front of the neck surface although these organs affected the light intensities locally. These results indicated the necessity of modeling the refractive-index mismatch at the trachea-tissue interface and the possibility of modeling other neck organs simply as a homogeneous medium when the source and detectors were far from large blood vessels.
  • 村木駿介, 山本翔也, 真田俊之, 渡部正夫
    日本機械学会論文集 848 17 - 00047 2017年04月 [査読有り][通常論文]
  • Kazumichi Kobayashi, Kiyofumi Sasaki, Misaki Kon, Hiroyuki Fujii, Masao Watanabe
    MICROFLUIDICS AND NANOFLUIDICS 21 3 1 - 13 2017年03月 [査読有り][通常論文]
     
    Using molecular dynamics simulations, the present study investigated the precise characteristics of the binary mixture of condensable gas (vapor) and noncondensable gas (NC gas) molecules creating kinetic boundary conditions (KBCs) at a gas-liquid interface in equilibrium. We counted the molecules utilizing the improved two-boundary method proposed in previous studies by Kobayashi et al. (Heat Mass Trans 52: 1851-1859, 2016. doi: 10.1007/s00231-015-1700-6). In this study, we employed Ar for the vapor molecules, and Ne for the NC gas molecules. The present method allowed us to count easily the evaporating, condensing, degassing, dissolving, and reflecting molecules in order to investigate the detailed motion of the molecules, and also to evaluate the velocity distribution function of the KBCs at the interface. Our results showed that the evaporation and condensation coefficients for vapor and NC gas molecules decrease with the increase in the molar fraction of the NC gas molecules in the liquid. We also found that the KBCs can be specified as a function of the molar fraction and liquid temperature. Furthermore, we discussed the method to construct the KBCs of vapor and NC gas molecules.
  • Molecular Dynamics Study of Droplet Impact on High-Temperature Wall
    Hirofumi Tabe, Kazumichi Kobayashi, Hisao Yaguchi, Hiroyuki Fujii, Masao Watanabe
    The 7th East Asia Mechanical and Aerospace Engineering Workshop 2017年 [査読有り][通常論文]
  • Molecular Dynamics Simulation of the Role of the Wettability in the Droplet Impact on a High-temperature Wall
    Hirofumi Tabe, Kazumichi Kobayashi, Hisao Yaguchi, Hiroyuki Fujii, Masao Watanabe
    Extended Abstracts of the 9th JSME-KSME Thermal and Fluids Engineering Conference TFEC9-1492 2017年 [査読有り][通常論文]
  • Hiroyuki Fujii, Shinpei Okawa, Yukio Yamada, Yoko Hoshi, Masao Watanabe
    JOURNAL OF MATHEMATICAL CHEMISTRY 54 10 2048 - 2061 2016年11月 [査読有り][通常論文]
     
    Numerical calculation of photon migration in biological tissue using the radiative transfer equation (RTE) has attracted great interests in biomedical optics and imaging. Because biological tissue is a highly forward-peaked scattering medium, renormalization of the phase function in numerical calculation of the RTE is crucial. This paper proposes a simple approach of renormalizing the phase function by the double exponential formula, which was heuristically modified from the original one. Firstly, the validity of the proposed approach was tested by comparing numerical results for an average cosine of the polar scattering angle calculated by the proposed approach with those by the conventional approach in highly forward-peaked scattering. The results show that calculation of the average cosine converged faster using the proposed approach than using the conventional one as a total number of discrete angular directions increases. Next, the accuracy of the numerical solutions of the RTE using the proposed approach was examined by comparing the numerical solutions with the analytical solutions of the RTE in a homogeneous medium with highly forward-peaked scattering. It was found that the proposed approach reduced the errors of the numerical solutions from those using the conventional one especially at a small value of the total number of the directions. This result suggests that the proposed approach has a possibility to improve the accuracy for the numerical results of the RTE in the highly scattering medium.
  • Kazumichi Kobayashi, Kazumasa Hori, Misaki Kon, Kiyofumi Sasaki, Masao Watanabe
    HEAT AND MASS TRANSFER 52 9 1851 - 1859 2016年09月 [査読有り][通常論文]
     
    Using molecular dynamics simulations, the present study investigates the precise characteristics of evaporating and reflecting monatomic molecules (argon) composing a kinetic boundary condition (KBC) in a vapor-liquid equilibria. We counted the evaporating and reflecting molecules utilizing two boundaries (vapor and liquid boundaries) proposed by the previous studies (Meland et al. in Phys Fluids 16:223-243, 2004; Gu et al. in Fluid Phase Equilib 297:77-89, 2010). In the present study, we improved the method using the two boundaries incorporating the concept of the spontaneously evaporating molecular mass flux. The present method allows us to count the evaporating and reflecting molecules easily, to investigate the detail motion of the evaporating and reflecting molecules, and also to evaluate the velocity distribution function of the KBC at the vapor-liquid interface, appropriately. From the results, we confirm that the evaporating and reflecting molecules in the normal direction to the interface have slightly faster and significantly slower average velocities than that of the Maxwell distribution at the liquid temperature, respectively. Also, the stall time of the reflecting molecules at the interphase that is the region in the vicinity of the vapor-liquid interface is much shorter than those of the evaporating molecules. Furthermore, we discuss our method for constructing the KBC that incorporates condensation and evaporation coefficients. Based on these results, we suggest that the proposed method is appropriate for investigating KBC in various nonequilibrium states or multi-component systems.
  • Misaki KON, Kazumichi KOBAYASHI, Masao WATANABE
    International Journal of Heat and Mass Transfer 99 317 - 326 2016年08月 [査読有り][通常論文]
     
    For the accurate description of heat and mass transfer through a vapor-liquid interface, the appropriate modeling of the interface during nonequilibrium phase change (net evaporation/condensation) is a crucial issue. The aim of this study is to propose a microscopic interfacial model which should be imposed at the interface as the kinetic boundary condition for the Boltzmann equation. In this study, we constructed the kinetic boundary condition for monoatomic molecules over a wide range of liquid temperature based on mean field kinetic theory, and we validated the accuracy of the constructed kinetic boundary condition by solving the boundary value problem of the Boltzmann equation. These results showed that we can impose the kinetic boundary condition at the interface by simply specifying liquid temperature and simulate the complex vapor-liquid two-phase flow induced by net evaporation/condensation. Furthermore, we applied the constructed kinetic boundary condition to the boundary condition for the fluid-dynamic type equations. This application enables us to deal with a large spatio-temporal scale of the interfacial dynamics in the vapor-liquid two-phase system with net evaporation/condensation. (C) 2016 Elsevier Ltd. All rights reserved.
  • 真田 俊之, 野崎 紘史, 渡部 正夫
    日本機械学会論文集 82 838 2016年06月 [査読有り][通常論文]
  • Kazumichi Kobayashi, Kazuki Konno, Hisao Yaguchi, Hiroyuki Fujii, Toshiyuki Sanada, Masao Watanabe
    PHYSICS OF FLUIDS 28 3 2016年03月 [査読有り][通常論文]
     
    In this study, we investigated nanodroplet spreading at the early stage after the impact using molecular dynamics simulations by changing the magnitude of the intermolecular force between the liquid and wall molecules. We showed that the droplet deformation after the impact greatly depends on the intermolecular force. The temporal evolution of the spreading diameters was measured by the cylindrical control volume for several molecular layers in the vicinity of the wall. At the early stage of the nanodroplet impact, the normalized spreading radius of the droplet is proportional to the square root of the normalized time, (t) over cap. This result is understood by the geometrical consideration presented by Rioboo et al. ["Time evolution of liquid drop impact onto solid, dry surfaces," Exp. Fluids 33, 112-124 (2002)]. In addition, we found that as the intermolecular force between the liquid and wall becomes stronger, the normalized spreading diameter of the first molecular layer on the wall remains less dependent on the impact velocity. Furthermore, the time evolution of the droplet spreading changes from root(t) over cap to log (t) over cap with time. (C) 2016 AIP Publishing LLC.
  • 藤井 宏之, 西村 吾朗, 服部 聖仁, 小林 一道, 渡部 正夫
    Proceeding of the fifth Asian NIR symposium (ANS2016) 2016 P-86 288 - 289 2016年 [査読有り][通常論文]
  • 服部 聖仁, 藤井 宏之, 西村 吾朗, 小林 一道, 渡部 正夫
    Proceeding of the fifth Asian NIR symposium (ANS2016) 2016 O-6 72 - 73 2016年 [査読有り][通常論文]
  • Hiroyuki Fujii, Shinpei Okawa, Yukio Yamada, Yoko Hoshi, Masao Watanabe
    Proceedings of the International Conference of Computational Methods in Sciences and Engineering 2016 (ICCMSE-2016) 1790 050002 1 - 4 2016年 [査読有り][通常論文]
     
    Numerical calculation of photon migration in biological tissue using the radiative transfer equation (RTE) has attracted great interests in biomedical optics and imaging. Because biological tissue is a highly forward-peaked scattering medium, a normalization of scattering phase function in the RTE is crucial. This paper proposes a simple way of normalizing the phase function by the double exponential formula, which is heuristically modified from the original one. The proposed method is validated by the agreement between the numerical solution of the RTE with the proposed method and analytical solution of the RTE for the case of a highly forward-peaked scattering medium, while the numerical solutions with conventional normalization methods disagree with the analytical solution. This result suggests the proposed method is accurate in numerical calculation of the RTE.
  • Erina Miyakawa, Hiroyuki Fujii, Kiyohito Hattori, Yuki Tatekura, Kazumichi Kobayashi, Masao Watanabe
    Proceedings of the International Conference of Computational Methods in Sciences and Engineering 2016 (ICCMSE-2016) 1790 050003  2016年 [査読有り][通常論文]
     
    Diffuse optical tomography (DOT), which is still under development, has a potential to enable non-invasive diagnoses of thyroid cancers in the human neck using the near-infrared light. This modality needs a photon migration model because scattered light is used. There are two types of photon migration models: the radiative transport equation (RTE) and diffusion equation (DE). The RTE can describe photon migration in the human neck with accuracy, while the DE enables an efficient calculation. For developing the accurate and efficient model of photon migration, it is crucial to investigate a condition where the DE holds in a scattering medium including a void region under the refractive-index mismatch at the void boundary because the human neck has a trachea (void region) and the refractive indices are different between the human neck and trachea. Hence, in this paper, we compare photon migration using the RTE with that using the DE in the medium. The numerical results show that the DE is valid under the refractive-index match at the void boundary even though the void region is near the source and detector positions. Under the refractive-index mismatch at the boundary, the numerical results using the DE disagree with those using the RTE when the void region is near the source and detector positions. This is probably because the anisotropy of the light scattering remains around the void boundary.
  • Kazumichi Kobayashi, Kiyofumi Sasaki, Misaki Kon, Hiroyuki Fujii, Masao Watanabe
    30TH INTERNATIONAL SYMPOSIUM ON RAREFIED GAS DYNAMICS (RGD 30) 1786 110002  2016年 [査読有り][通常論文]
     
    The aim of this study is to construct the kinetic boundary condition for Ar-Ne binary mixture in equilibrium using molecular dynamics (MD) simulations. The temperature of the MD simulation system is 85 K; Ar molecules behave as condensable gas (vapor), and Ne molecules behave as non-condensable gas (gas). In this simulation, we utilize the two-boundary method improved by our previous study to investigate behaviors of Ar and Ne molecules at the interface. From the results, we can obtain the molecular mass fluxes at the interface, and evaluate the values of evaporation and condensation coefficients of Ar (vapor) and Ne (gas) molecules.
  • Misaki Kon, Kazumichi Kobayashi, Masao Watanabe
    30TH INTERNATIONAL SYMPOSIUM ON RAREFIED GAS DYNAMICS (RGD 30) 1786 110001  2016年 [査読有り][通常論文]
     
    To examine the transport phenomena in a vaporliquid two-phase system attributed to the phase change, a proper specification of the mass flux at a vaporliquid interface is crucial. Since the mass flux induced by the phase change originates from the motion of molecules in the vicinity of the vaporliquid interface, a continuum description such as the fluid dynamic based approach is inappropriate. An essential way to obtain this mass flux is the analysis of the Boltzmann equation with a certain boundary condition, that is, the kinetic boundary condition. In this study, we examined the definition and the estimation procedure of the evaporation coefficient, which is included in the kinetic boundary condition, at the vaporliquid interface with phase change, especially at higher temperature for hard-sphere molecules. As the result, we confirmed that a conventional definition of the evaporation coefficient is accurate even if liquid temperature is higher. Moreover, we also confirmed that the evaporation coefficient is only the function of liquid temperature by counting the number of molecules passing through the two boundaries which are placed near the vaporliquid interface.
  • Hiroyuki Fujii, Shinpei Okawa, Ken Nadamoto, Eiji Okada, Yukio Yamada, Yoko Hoshi, Masao Watanabe
    Journal of Applied Nonlinear Dynamics 5 1 117 - 125 2016年 [査読有り][通常論文]
     
    Biomedical optical imaging has a possibility of a comprehensive di- agnosis of thyroid cancer in conjunction with ultrasound imaging. For improvement of the optical imaging, this study develops a higher order scheme for solving the time-dependent radiative transport equa- tion (RTE) by use of the finite-difference and discrete-ordinate meth- ods. The accuracy and efficiency of the developed scheme are ex- amined by comparison with the analytical solutions of the RTE in homogeneous media. Then, the developed scheme is applied to de- scribing photon migration in the human neck model. The numerical simulations show complex behaviors of photon migration in the hu- man neck model due to multiple diffusive reflection near the trachea.
  • 今 美沙紀, 小林 一道, 佐々木 清文, 渡部 正夫
    混相流 29 5 493 - 500 日本混相流学会 2015年11月 [査読有り][通常論文]
     
    The aim of this study is to confirm the existence of a spontaneous evaporation molecular mass flux which takes a constant value independent of the degree of net evaporation/condensation. We carried out the numerical simulation based on the mean field kinetic theory during net evaporation/condensation and estimated the evaporation and reflection molecular mass fluxes by using a pair of boundaries. The simulation results showed that the reflection molecular mass flux varies with the increase of the degree of nonequilibrium, and the evaporation molecular mass flux takes a constant value during net evaporation and condensation.
  • Junya Kawahara, Masao Watanabe, Kazumichi Kobayashi
    Mechanical Engineering Letters 1 115-00464-15-00464 2015年10月 [査読有り][通常論文]
  • 加藤昌也, 渡部正夫, 小林一道, 真田俊之
    混相流 28/29 5/1 531 - 537 2015年03月15日 [査読無し][通常論文]
  • 今 美沙紀, 小林 一道, 渡部 正夫
    日本物理学会講演概要集 70 2975 - 2975 一般社団法人日本物理学会 2015年
  • Hiroyuki Fujii, Shinpei Okawa, Yukio Yamada, Yoko Hoshi, Masao Watanabe
    Progress in Biomedical Optics and Imaging - Proceedings of SPIE 9792 2015年 [査読有り][通常論文]
     
    Development of a physically accurate and computationally efficient photon migration model for turbid media is crucial for optical computed tomography such as diffuse optical tomography. For the development, this paper constructs a space-time coupling model of the radiative transport equation with the photon diffusion equation. In the coupling model, a space-time regime of the photon migration is divided into the ballistic and diffusive regimes with the interaction between the both regimes to improve the accuracy of the results and the efficiency of computation. The coupling model provides an accurate description of the photon migration in various turbid media in a wide range of the optical properties, and reduces computational loads when compared with those of full calculation of the RTE.
  • Kiyohito Hattori, Hiroyuki Fujii, Yuki Tatekura, Kazumichi Kobayashi, Masao Watanabe
    Progress in Biomedical Optics and Imaging - Proceedings of SPIE 9792 2015年 [査読有り][通常論文]
     
    An accurate determination of optical properties of agricultural products is crucial for non-destructive assessment of food quality. For the determination, light intensity is measured at the surface of the product then, inverse analysis is employed based on a light propagation model such as the radiative transfer equation (RTE). The inverse analysis requires high computational loads because the light intensity is numerically calculated using the model every time the optical properties are changed. For the calculation, we propose an efficient technique by combining a numerical solution with an analytical solution of the RTE, and investigate the validity of the technique in a two-dimensional homogeneous circular medium which is regarded as a light propagation model with optical properties of kiwifruit. The proposed technique can provide accurate results of the light intensity in change of the optical properties, and the accuracy is less dependent on the boundary conditions and source-detector angles. In addition, the technique can reduce computation time compared with that for numerical calculation of the RTE. These results indicate usefulness of the proposed technique for the inverse analysis.
  • Hiroyuki Fujii, Shinpei Okawa, Ken Nadamoto, Eiji Okada, Yukio Yamada, Yoko Hoshi, Masao Watanabe
    Progress in Biomedical Optics and Imaging - Proceedings of SPIE 9333 2015年 [査読有り][通常論文]
     
    Accurate modeling and efficient calculation of photon migration in biological tissues is requested for determination of the optical properties of living tissues by in vivo experiments. This study develops a calculation scheme of photon migration for determination of the optical properties of the rat cerebral cortex (ca 0.2 cm thick) based on the three-dimensional time-dependent radiative transport equation assuming a homogeneous object. It is shown that the time-resolved profiles calculated by the developed scheme agree with the profiles measured by in vivo experiments using near infrared light. Also, an efficient calculation method is tested using the delta-Eddington approximation of the scattering phase function.
  • Hiroyuki Fujii, Shinpei Okawa, Ken Nadamoto, Eiji Okada, Yukio Yamada, Yoko Hoshi, Masao Watanabe
    BIOMEDICAL APPLICATIONS OF LIGHT SCATTERING IX 9333 933313 1 - 6 2015年 [査読有り][通常論文]
     
    Accurate modeling and efficient calculation of photon migration in biological tissues is requested for determination of the optical properties of living tissues by in vivo experiments. This study develops a calculation scheme of photon migration for determination of the optical properties of the rat cerebral cortex (ca 0.2 cm thick) based on the three-dimensional time-dependent radiative transport equation assuming a homogeneous object. It is shown that the time-resolved profiles calculated by the developed scheme agree with the profiles measured by in vivo experiments using near infrared light. Also, an efficient calculation method is tested using the delta-Eddington approximation of the scattering phase function.
  • Hiroyuki Fujii, Shinpei Okawa, Yukio Yamada, Yoko Hoshi, Masao Watanabe
    BIOPHOTONICS JAPAN 2015 9792 979214 1 - 5 2015年 [査読有り][通常論文]
     
    Development of a physically accurate and computationally efficient photon migration model for turbid media is crucial for optical computed tomography such as diffuse optical tomography. For the development, this paper constructs a space-time coupling model of the radiative transport equation with the photon diffusion equation. In the coupling model, a space-time regime of the photon migration is divided into the ballistic and diffusive regimes with the interaction between the both regimes to improve the accuracy of the results and the efficiency of computation. The coupling model provides an accurate description of the photon migration in various turbid media in a wide range of the optical properties, and reduces computational loads when compared with those of full calculation of the RTE.
  • Kiyohito Hattori, Hiroyuki Fujii, Yuki Tatekura, Kazumichi Kobayashi, Masao Watanabe
    BIOPHOTONICS JAPAN 2015 9792 97921A  2015年 [査読有り][通常論文]
     
    An accurate determination of optical properties of agricultural products is crucial for non-destructive assessment of food quality. For the determination, light intensity is measured at the surface of the product; then, inverse analysis is employed based on a light propagation model such as the radiative transfer equation (RTE). The inverse analysis requires high computational loads because the light intensity is numerically calculated using the model every time the optical properties are changed. For the calculation, we propose an efficient technique by combining a numerical solution with an analytical solution of the RTE, and investigate the validity of the technique in a two-dimensional homogeneous circular medium which is regarded as a light propagation model with optical properties of kiwifruit. The proposed technique can provide accurate results of the light intensity in change of the optical properties, and the accuracy is less dependent on the boundary conditions and source-detector angles. In addition, the technique can reduce computation time compared with that for numerical calculation of the RTE. These results indicate usefulness of the proposed technique for the inverse analysis.
  • Y. Jinbo, K. Kobayashi, M. Watanabe, H. Takahira
    9TH INTERNATIONAL SYMPOSIUM ON CAVITATION (CAV2015) 656 1 - 5 2015年 [査読有り][通常論文]
     
    The ghost fluid method is improved to include heat and mass transfer across the gas-liquid interface during the bubble collapse in a compressible liquid. This transfer is due to both nonequilibrium phase transition at the interface and diffusion of the noncondensable gas across the interface. In the present method, the ghost fluids are defined with the intention of conserving the total mass, momentum, and energy, as well as the mass of each component while considering the heat and mass fluxes across the interface. The gas phase inside the bubble is a mixture of vapor and noncondensable gas, where binary diffusion between the mixture components is taken into account. The gas diffusion in the surrounding liquid is also considered. This method is applied to a simulation of a single spherical bubble collapse with heat and mass transfer across the interface in a compressible liquid. When noncondensable gas is present, it accumulates near the interface due to vapor condensation, thereby preventing further condensation. This results in a weaker bubble collapse than the case without noncondensable gas.
  • Toshiyuki Sanada, Masao Watanabe
    JOURNAL OF PHOTOPOLYMER SCIENCE AND TECHNOLOGY 28 2 289 - 292 2015年 [査読有り][通常論文]
  • Y. Tatekura, T. Fujikawa, Y. Jinbo, T. Sanada, K. Kobayashi, M. Watanabe
    ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY 4 9 N117 - N123 2015年 [査読有り][通常論文]
     
    A two-fluid spray cleaning technique has been gaining popularity as a cleaning process in the semiconductor industry. The most essential physical process in this technique is the impact of droplets with a velocity of O(10 m/s) on a solid surface. This study aims to experimentally and numerically investigate water-droplet impacts with velocities of up to 50 m/s and their subsequent flow fields, especially the gas flow field in the strictly limited area in the vicinity of the contact line. First, we experimentally evaluated the velocity of the splash and numerically calculated the gas velocities. Comparison of these velocities supported our assumption that the maximum gas velocity may be on approximately the same order as the velocity of the splash. Therefore, we concluded that the gas velocity field of the order of 500 m/s indeed develops at the impact of droplet with a velocity of the order of 50 m/s. Moreover, we determined that the gas pressure was of the order of 1.0 MPa by numerical analysis. Such a high pressure leads to shock wave propagation, which can contribute to the cleaning process in semiconductor production. (C) 2015 The Electrochemical Society. All rights reserved.
  • Junya Kawahara, Masao Watanabe, Kazumichi Kobayashi
    9TH INTERNATIONAL SYMPOSIUM ON CAVITATION (CAV2015) 656 1 - 5 2015年 [査読有り][通常論文]
     
    Pressure wave propagation in a liquid containing several bubbles is numerically investigated. We simulate liner plane wave propagation in a liquid containing 10 spherical bubbles in a rectangular duct with the equation of motion for N spherical bubbles. The sound pressures of the reflected waves from the rigid walls are calculated by using the method of images. The result shows that the phase velocity of the pressure wave propagating in the liquid containing 10 spherical bubbles in the duct agrees well with the low-frequency speed of sound in a homogeneous bubbly liquid.
  • Misaki Kon, Kazumichi Kobayashi, Masao Watanabe
    PHYSICS OF FLUIDS 26 7  - 072003 2014年07月 [査読有り][通常論文]
     
    The aim of the present study is to develop the method of determining the kinetic boundary condition (KBC) at a vapor-liquid interface in net evaporation/condensation. We proposed a novel method for determining the KBC by combining the numerical simulations of the mean field kinetic theory and the molecular gas dynamics. The method was evaluated on steady vapor flow between two liquid slabs at different temperatures. A uniform net mass flux in the vapor phase induced by net evaporation and condensation is obtained from the numerical simulation of the mean field kinetic theory for both vapor and liquid phases. The KBC was specified by using the uniform net mass flux, and the numerical simulation of the molecular gas dynamics was conducted for the vapor phase. Comparing the macroscopic variables in the vapor phase obtained from both numerical simulations, we can validate the KBC whether the appropriate solutions are obtained. Moreover, the evaporation and condensation coefficients were estimated uniquely. The results showed that the condensation and evaporation coefficients were identical and constant in net evaporation. On the other hand, in net condensation, the condensation coefficient increased with the collision molecular mass flux. We also presented the applicable limit of the KBC which is assumed to be the isotropic Gaussian distribution at the liquid temperature. From these results, the KBCs in net evaporation and condensation, which enable the exact macroscopic variables to be determined, were proposed. (C) 2014 AIP Publishing LLC.
  • Kazumichi Kobayashi, Kazumasa Hori, Hisao Yaguchi, Masao Watanabe
    PROCEEDINGS OF THE 29TH INTERNATIONAL SYMPOSIUM ON RAREFIED GAS DYNAMICS 1628 404 - 410 2014年 [査読有り][通常論文]
     
    By using molecular dynamics simulations of argon molecules, the present study investigates molecular evaporation and reflection in equilibrium at a vapor liquid interface, which involves the kinetic boundary condition (KBC) of the Boltzmann equation. The present method allows evaporation and reflection molecules to be selected naturally at the vapor-liquid interphase. Based on the results, we confirm that the evaporation molecules in the equilibrium state behave almost similar to spontaneous evaporation molecules (as determined by virtual vacuum evaporation simulations). Furthermore, we find that the velocity distribution of reflection molecules in the normal direction to the boundary is lower than the Maxwell distribution at the liquid temperature.
  • Misaki Kon, Kazumichi Kobayashi, Masao Watanabe
    PROCEEDINGS OF THE 29TH INTERNATIONAL SYMPOSIUM ON RAREFIED GAS DYNAMICS 1628 398 - 403 2014年 [査読有り][通常論文]
     
    This study aims to investigate the liquid temperature dependency of the kinetic boundary condition at a vapor-liquid interface in net evaporation/condensation. The numerical simulations based on the mean-field kinetic theory and the molecular gas dynamics in the cases of various liquid temperatures were carried out. We focused on two important issues for the kinetic boundary condition; one is to investigate the applicable limit of the kinetic boundary condition which is assumed to be the isotropic velocity distribution at the liquid temperature and the other is to estimate the value of the condensation coefficient included in the kinetic boundary condition. The simulation results showed that the applicable limit of the isotropic velocity distribution in net evaporation/condensation practically independent from the liquid temperature. Furthermore, the condensation coefficients in net evaporation/condensation depend significantly on the liquid temperature; the condensation coefficient is constant and equal to the evaporation coefficient in net evaporation, while, in net condensation, the condensation coefficient increases with the increase of the degree of nonequilibrium.
  • 真田俊之, 渡部正夫
    エアロゾル研究 29 4 236-240 (J-STAGE)  2014年 [査読無し][通常論文]
  • 川原 潤也, 小林 一道, 渡部 正夫
    数理解析研究所講究録 1847 10 - 15 京都大学 2013年08月 [査読無し][通常論文]
  • 小林一道, 毛利信吾, 渡邉優介, 渡部正夫, 藤川重雄
    熱物性 27 1 9 - 14 JAPAN SOCIETY OF THERMOPHYSICAL PROPERTIES 2013年02月28日 [査読無し][通常論文]
     
    衝撃波管内で蒸気中を伝播する衝撃波が管端で反射した際に管端面で生ずる膜状凝縮について，液膜の成長速度を光多重反射干渉計で測定し，測定結果を分子気体力学で解析することにより，常温でのメタノールの蒸発係数及び凝縮係数を決定した．測定は気液界面での蒸気の非平衡度σ/ρ*が1≤σ/ρ*<1.3の範囲でなされた．その結果，凝縮係数は気液界面での蒸気の非平衡度が1≤σ/ρ*<1.05の領域では蒸発係数（＝0.86）とほぼ同じ値をとること，σ/ρ*＞1.05の領域では非平衡度の増大とともに蒸発係数よりも小さくなっていくこと，さらに著者らが用いてきた気体論境界条件はσ/ρ*<1.05の領域で有効であることを明らかにした．
  • T. Yano, T. Kanagawa, M. Watanabe, S. Fujikawa
    Bubble Dynamics and Shock Waves 107 - 140 2013年
  • Molecular Dynamics Study of Nano-scale Liquid-gas Interface Inspired by Fuel Cell Catalyst Layer
    Youngmin Kim, Hisao Yaguchi, Nobuyuki Oshima, Masao Watanabe, Kazumichi Kobayashi
    ASME 2013 11th International Conference on Nanochannels 2013年 [査読有り][通常論文]
  • 稲葉匡司, 矢野猛, 小林一道, 渡部正夫
    ながれ 31 6 487 - 490 日本流体力学会 2012年12月25日 [査読無し][通常論文]
  • 真田俊之, 橋本健太郎, 林田充司, 小林一道, 渡部正夫
    混相流 26 2 172 - 177 THE JAPANESE SOCIETY FOR MULTIPHASE FLOW 2012年06月15日 [査読無し][通常論文]
     
    We have been developing a novel surface cleaning technique using steam and water mixed spray. Our technique shows great efficiency in removing thin surface film such as photo-resist film. However, the film-removal mechanism has not been clarified yet. One possible film-removal mechanism is the local heat expansion due to the difference of coefficients of linear expansion between film and substrate. In this study, we studied the removal characteristics of deposited aluminum film on a glass surface by spraying steam-water or air-water mixed spray. The surface temperature changes caused by the spray were carefully measured. We found that the steam and water mixed spray that increases the surface temperature can remove the film while the air and water mixed spray cannot. These results indicate that the difference of coefficients of linear expansion between film and substrate may not be the dominant factor in the film removal by the steam and water mixed spray.
  • 櫻井泰貴, 小林一道, 藤川俊秀, 真田俊之, 渡部正夫
    混相流 26 2 164 - 171 THE JAPANESE SOCIETY FOR MULTIPHASE FLOW 2012年06月15日 [査読無し][通常論文]
     
    In the cleaning processes of manufacturing semiconductor devices, two-fluid spray cleaning technique is widely used: however, the detailed cleaning mechanism has not been clarified yet. In this study, we focus our attention to the elementary process of this cleaning technique, i.e. a single droplet impact on a solid surface. We experimentally observe impact of single droplet on a rigid solid surface with the use of high-speed photography, and we discuss the deformation of the droplet. Especially we focus on the effects of surfaces tension, surface roughness and surrounding pressure. Water droplets always create lamella during spreading after the impact on a smooth surface in the atmospheric pressure condition. Either decrease of the surface tension or increase of the surface roughness causes droplet splash. However, decrease of the surrounding gas pressure makes droplets always create lamella even in the cases with low surface tension and rough surfaces.
  • 真田 俊之, 橋本 健太郎, 林田 充司, 小林 一道, 渡部 正夫
    混相流 = Japanese journal of multiphase flow 26 2 172 - 177 THE JAPANESE SOCIETY FOR MULTIPHASE FLOW 2012年06月15日 [査読無し][通常論文]
     
    We have been developing a novel surface cleaning technique using steam and water mixed spray. Our technique shows great efficiency in removing thin surface film such as photo-resist film. However, the film-removal mechanism has not been clarified yet. One possible film-removal mechanism is the local heat expansion due to the difference of coefficients of linear expansion between film and substrate. In this study, we studied the removal characteristics of deposited aluminum film on a glass surface by spraying steam-water or air-water mixed spray. The surface temperature changes caused by the spray were carefully measured. We found that the steam and water mixed spray that increases the surface temperature can remove the film while the air and water mixed spray cannot. These results indicate that the difference of coefficients of linear expansion between film and substrate may not be the dominant factor in the film removal by the steam and water mixed spray.
  • 櫻井 泰貴, 小林 一道, 藤川 俊秀, 真田 俊之, 渡部 正夫
    混相流 = Japanese journal of multiphase flow 26 2 164 - 171 THE JAPANESE SOCIETY FOR MULTIPHASE FLOW 2012年06月 [査読有り][通常論文]
     
    In the cleaning processes of manufacturing semiconductor devices, two-fluid spray cleaning technique is widely used: however, the detailed cleaning mechanism has not been clarified yet. In this study, we focus our attention to the elementary process of this cleaning technique, i.e. a single droplet impact on a solid surface. We experimentally observe impact of single droplet on a rigid solid surface with the use of high-speed photography, and we discuss the deformation of the droplet. Especially we focus on the effects of surfaces tension, surface roughness and surrounding pressure. Water droplets always create lamella during spreading after the impact on a smooth surface in the atmospheric pressure condition. Either decrease of the surface tension or increase of the surface roughness causes droplet splash. However, decrease of the surrounding gas pressure makes droplets always create lamella even in the cases with low surface tension and rough surfaces.
  • Masashi Inaba, Takeru Yano, Masao Watanabe
    FLUID DYNAMICS RESEARCH 44 2 2012年04月 [査読有り][通常論文]
     
    An asymptotic analysis of a boundary-value problem of the Boltzmann equation for small Knudsen number is carried out for the case when an unsteady flow of polyatomic vapour induces reciprocal evaporation and condensation at the interface between the vapour and its liquid phase. The polyatomic version of the Boltzmann equation of the ellipsoidal statistical Bhatnagar-Gross-Krook (ES-BGK) model is used and the asymptotic expansions for small Knudsen numbers are applied on the assumptions that the Mach number is sufficiently small compared with the Knudsen number and the characteristic length scale divided by the characteristic time scale is comparable with the speed of sound in a reference state, as in the case of sound waves. In the leading order of approximation, we derive a set of the linearized Euler equations for the entire flow field and a set of the boundary-layer equations near the boundaries (the vapour-liquid interface and simple solid boundary). The boundary conditions for the Euler and boundary-layer equations are obtained at the same time when the solutions of the Knudsen layers on the boundaries are determined. The slip coefficients in the boundary conditions are evaluated for water vapour. A simple example of the standing sound wave in water vapour bounded by a liquid water film and an oscillating piston is demonstrated and the effect of evaporation and condensation on the sound wave is discussed.
  • Tetsuya Kanagawa, Takeru Yano, Junya Kawahara, Kazumichi Kobayashi, Masao Watanabe, Shigeo Fujikawa
    FLUID MEASUREMENTS AND INSTRUMENTATION CAVITATION AND MULTIPHASE FLOW ADVANCES IN FLUIDS ENGINEERING EDUCATION MICROFLUIDICS, VOL 2 237 - 241 2012年 [査読有り][通常論文]
     
    Nonlinear propagation of weakly diffracted sound beams in a weakly nonuniform bubbly liquid is analytically studied based on the method of multiple scales and scaling relations of some physical parameters. The system of basic equations consists of the conservation equations of mass and momentum for gas and liquid in a two-flui model, the Keller equation for bubble wall, the state equations for gas and liquid, and so on. The compressibility of liquid is taken into account and this leads to the wave attenuation due to bubble oscillations. It is assumed that the spatial distribution of the number density of bubbles in an initial state at rest is a slowly varying function of space coordinates and the amplitude of its variation is small compared with a mean number density. As a result, a Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation with dispersion and nonuniform effects for a low frequency and long wavelength case and a nonlinear Schrodinger (NLS) equation with dissipation, diffraction, and nonuniform effects are derived from the basic equations.
  • Junya Kawahara, Tetsuya Kanagawa, Takeru Yano, Kazumichi Kobayashi, Masao Watanabe, Shigeo Fujikawa
    FLUID MEASUREMENTS AND INSTRUMENTATION CAVITATION AND MULTIPHASE FLOW ADVANCES IN FLUIDS ENGINEERING EDUCATION MICROFLUIDICS, VOL 2 251 - 256 2012年 [査読有り][通常論文]
     
    A weakly diffracted ultrasound beam radiated from a circular piston placed in a bubbly liquid is formulated in terms of a wave equation based on scaling relations of physical parameters [1]: typical propagation speed, period, wavelength, and diameter of beam. We derive a nonlinear evolution equation for the modulation of quasi-monochromatic waves for the case of a short wavelength with a moderately high frequency from a set of basic equations for bubbly flows: conservation equations of mass and momentum for gas and liquid in a two-fluid model, Keller's equation for bubble wall motion, state equations for gas and liquid, and so on. The compressibility of liquid is taken into account, and thus the waves are attenuated due to bubble oscillations. The viscosity of gas, heat conduction in gas and liquid, and phase change across bubble wall are ignored. As a result, the nonlinear Schrodinger equation for the envelope of the beam with diffraction effect is derived from the basic equations. For plane waves the diffraction term does not appear, and hence our equation is reduced to the original nonlinear Schrodinger equation [1].
  • 櫻井泰貴, 小林一道, 藤川俊秀, 真田俊之, 渡部正夫
    日本混相流学会精選論文集 98 6 515 - 521 THE JAPANESE SOCIETY FOR MULTIPHASE FLOW 2012年 [査読有り][通常論文]
     
    In the cleaning processes of manufacturing semiconductor devices, two-fluid spray cleaning technique is widely used: however, the detailed cleaning mechanism has not been clarified yet. In this study, we focus our attention to the elementary process of this cleaning technique, i.e. a single droplet impact on a solid surface. We experimentally observe impact of single droplet on a rigid solid surface with the use of high-speed photography, and we discuss the deformation of the droplet. Especially we focus on the effects of surfaces tension, surface roughness and surrounding pressure. Water droplets always create lamella during spreading after the impact on a smooth surface in the atmospheric pressure condition. Either decrease of the surface tension or increase of the surface roughness causes droplet splash. However, decrease of the surrounding gas pressure makes droplets always create lamella even in the cases with low surface tension and rough surfaces.
  • Masao Watanabe, Toshiyuki Sanada, Takashi Mashiko, Atsushi Hayashida
    ULTRA CLEAN PROCESSING OF SEMICONDUCTOR SURFACES X 187 141 - + 2012年 [査読有り][通常論文]
     
    We have been developing an innovative ultra-low environmental load cleaning technique by the use of steam-water mixed spray. We showed that this technique is quite effective in both cleaning and photo-resist stripping. We also found that the physical force associated with steam-water mixed spray is greater than that with air-water mixed spray; hence we proposed that the condensation plays an important role in this cleaning technique. In order to discuss further this mechanism, we perform the order estimation of physical processes in dynamics of liquid droplet moving in vapor flow impacting on a solid interface in this study. Results show that droplet impact velocity can be reduced while the droplet approaches to the solid surface. However, the vapor in the gap can condensate to either the liquid droplet or the solid surface with the velocity whose order of magnitude cannot be negligible compared to the impact velocity; hence the amount of vapor that should be pushed out from gap can be drastically reduced, This condensation results in the significant reduction of viscous force. This reduction of force with the existence of condensation reduces the impact velocity deceleration. Consequently significantly large impact pressure is generated.
  • Takashi Mashiko, Toshiyuki Sanada, Hideo Horibe, Itsuo Nishiyama, Masao Watanabe, Atsushi Hayashida
    ULTRA CLEAN PROCESSING OF SEMICONDUCTOR SURFACES X 187 85 - + 2012年 [査読有り][通常論文]
     
    We performed two experiments on resist-coated wafers. In the measurement of the resist-wafer adhesivity, we confirmed that it is significantly increased by an HMDS layer in between. In the resist-removal experiment using steam-water mixed spray, we found that the area of resist removal is limited within the area of spray application if HMDS is used, otherwise the former can be larger than the latter. These results suggest that the resist removal from a wafer surface by steam-water mixed spray is essentially a peel-off process.
  • Tetsuya Kanagawa, Takeru Yano, Junya Kawahara, Kazumichi Kobayashi, Masao Watanabe, Shigeo Fujikawa
    NONLINEAR ACOUSTICS: STATE-OF-THE-ART AND PERSPECTIVES (ISNA 19) 1474 144 - 147 2012年 [査読有り][通常論文]
     
    Weakly nonlinear propagation of diffracted ultrasound beams in a nonuniform bubbly liquid is theoretically studied based on the method of multiple scales with the set of scaling relations of some physical parameters. It is assumed that the spatial distribution of the number density of bubbles in an initial state at rest is a slowly varying function of space coordinates and the amplitude of its variation is small compared with a mean number density. As a result, a Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation with dispersion and nonuniform effects for a low frequency case and a nonlinear Schrodinger (NLS) equation with dissipation, diffraction, and nonuniform effects for a high frequency case, are derived from the basic equations of bubbly flows.
  • Masashi Inaba, Takeru Yano, Masao Watanabe, Kazumichi Kobayashi, Shigeo Fujikawa
    NONLINEAR ACOUSTICS: STATE-OF-THE-ART AND PERSPECTIVES (ISNA 19) 1474 80 - 83 2012年 [査読有り][通常論文]
     
    Resonant gas oscillation in a closed tube bounded by an oscillating plate and a vapor-liquid interface is theoretically analyzed by applying the asymptotic theory to the ES-BGK Boltzmann equation for the case of M-2 similar or equal to Kn << 1 and a small evaporation coefficient alpha = O(Kn), where M and Kn are the typical Mach number and the Knudsen number, respectively. As a result, we derive a nonlinear integro-differential equation for determining the wave profile with the evaporation and condensation in the form including alpha.
  • Kazumichi Kobayashi, Kotaro Ohashi, Masao Watanabe
    28TH INTERNATIONAL SYMPOSIUM ON RAREFIED GAS DYNAMICS 2012, VOLS. 1 AND 2 1501 1145 - 1151 2012年 [査読有り][通常論文]
     
    In this study, equilibrium and nonequilibrium numerical simulations for vapor-liquid two-phase systems were performed by using the Enskog-Vlasov equation. The kinetic boundary condition (KBC) at the interface was investigated. The simulation results showed that at a low or slightly high liquid temperature, the velocity distribution of the KBC obtained by our simulation is anisotropic Gaussian; this result agrees qualitatively with the results of the MD simulation performed by Ishiyama et al. (PRL, 2005). Also, the nonequilibrium nature of KBC becomes larger with the increase of liquid temperature.
  • Masashi Inaba, Takeru Yano, Kazumichi Kobayashi, Masao Watanabe
    28TH INTERNATIONAL SYMPOSIUM ON RAREFIED GAS DYNAMICS 2012, VOLS. 1 AND 2 1501 53 - 58 2012年 [査読有り][通常論文]
     
    Resonant gas oscillation in a closed tube bounded by an oscillating plate and a vapor-liquid interface is theoretically analyzed by applying the asymptotic theory to the ES-BGK Boltzmann equation for the case of M-P similar to Kn << 1 and a small evaporation coefficient alpha = O(root Kn), where M-P and Kn are the Mach number of the plate and the Knudsen number, respectively. As a result, we derive a nonlinear integro-differential equation for determining the wave profile with the evaporation and condensation including alpha. We numerically solve the integro-differential equation with the method of Fourier series, and obtain a parameter plane for shock formation conditions and also the prediction of critical condition for shock formation.
  • 真田俊之, 渡部正夫, 関映子, 林田充司
    砥粒加工学会誌 55 11 640-643 - 643 砥粒加工学会 2011年11月01日 [査読無し][通常論文]
  • 真田 俊之, 渡部 正夫, 関 映子, 林田 充司
    砥粒加工学会誌 = Journal of the Japan Society of Grinding Engineers 55 11 640 - 643 砥粒加工学会 2011年11月01日 [査読無し][通常論文]
  • Tetsuya Kanagawa, Masao Watanabe, Takeru Yano, Shigeo Fujikawa
    Journal of Fluid Science and Technology 6 6 838 - 850 The Japan Society of Mechanical Engineers 2011年08月 [査読有り][通常論文]
     
    Based on the unified theory by the present authors (Kanagawa et al., J. Fluid Sci. Tech., 5, 2010), the Korteweg-de Vries-Burgers (KdVB) equation and the nonlinear Schrödinger (NLS) equation with an attenuation term for weakly nonlinear waves in bubbly liquids are re-derived from a system of bubble-liquid mixture model equations composed of the conservation equations of mass and momentum, the Keller equation for bubble dynamics, and supplementary equations. We show that the re-derived KdVB equation and NLS equation are essentially the same as those derived from a system of two-fluid model equations except for the coefficients of nonlinear, dissipation, and dispersion terms. The differences in these coefficients are studied in detail, and we find that for the case of KdVB equation, the mixture model is valid only for sufficiently small initial void fractions. On the other hand, for the case of NLS equation, the range of validity of the mixture model depends on not only the initial void fraction but also the wavenumber concerned.
  • 城田農, 佐藤文香, 真田俊之, 渡部正夫
    混相流 24 5 531 - 537 THE JAPANESE SOCIETY FOR MULTIPHASE FLOW 2011年03月15日 [査読無し][通常論文]
     
    Droplet impacts on solid surfaces are key elements in technical applications, such as semiconductor cleaning, rapid spray cooling and ink-jet printing. There exist varieties of physical parameters proposed that control the droplet impact although they are not thoroughly explored; hence, dynamics of the droplet after the impact are yet fully understood. In this study, we experimentally observed the high-speed droplet impact on acrylic surfaces in a vacuum chamber with a high-speed photography, in order to clarify the effects of both the ambient gas pressure around the droplet and the impact velocity. The results show that the splash does not occur under the reduced ambient gas pressure even when the impact velocity becomes much higher than in the conventional experiments, in the range of the present experimental conditions.
  • 益子 岳史, 真田 俊之, 橋本 健太郎, 堀邊 英夫, 林田 充司, 渡部 正夫
    混相流 = Japanese journal of multiphase flow 24 5 703 - 709 日本混相流学会 2011年03月15日 [査読無し][通常論文]
  • 城田 農, 佐藤 文香, 真田 俊之, 渡部 正夫
    混相流 = Japanese journal of multiphase flow 24 5 531 - 537 日本混相流学会 2011年03月15日 [査読無し][通常論文]
     
    Droplet impacts on solid surfaces are key elements in technical applications, such as semiconductor cleaning, rapid spray cooling and ink-jet printing. There exist varieties of physical parameters proposed that control the droplet impact although they are not thoroughly explored; hence, dynamics of the droplet after the impact are yet fully understood. In this study, we experimentally observed the high-speed droplet impact on acrylic surfaces in a vacuum chamber with a high-speed photography, in order to clarify the effects of both the ambient gas pressure around the droplet and the impact velocity. The results show that the splash does not occur under the reduced ambient gas pressure even when the impact velocity becomes much higher than in the conventional experiments, in the range of the present experimental conditions.
  • 矢口久雄, 藤川重雄, 矢野猛, 渡部正夫
    アンサンブル 13 1 7 - 11 分子シミュレーション研究会 2011年01月31日 [査読無し][通常論文]
  • KANAGAWA Tetsuya, YANO Takeru, WATANABE Masao, FUJIKAWA Shigeo
    Journal of Fluid Science and Technology 6 2 279 - 290 The Japan Society of Mechanical Engineers 2011年 
    In our previous paper (Kanagawa et al., J. Fluid Sci. Tech., 5, 2010), we have proposed a systematic method for derivation of various types of nonlinear wave equations for plane waves in bubbly liquids. The method makes use of an asymptotic expansion with multiple scales in terms of a small wave amplitude as an expansion parameter and a set of scaling relations of physical parameters, based on basic equations of two-fluid model of bubbly flows. In this paper, we extend the method so as to handle a weakly diffracted ultrasound beam in a quiescent liquid containing a number of spherical gas bubbles distributed with a weak nonuniformity. Because of the high expandability of the original method, the extension can be accomplished by adding a scaling relation of the diameter of the beam to the original set of scaling relations. As a result, we derive a generalized Khokhlov—Zabolotskaya—Kuznetsov (KZK) equation [or a generalized Kadomtsev—Petviashvili (KP) equation] for a long wave and low frequency case.
  • 澤江 義則, 渡部 正夫, 小俣 誠二, 村上 輝夫
    バイオエンジニアリング講演会講演論文集 2010 0 181 - 182 一般社団法人 日本機械学会 2011年 [査読有り][通常論文]
  • T. Fujikawa, Y. Tatekura, K. Kobayashi, T. Sanada, A. Hayashida, M. Watanabe
    SEMICONDUCTOR CLEANING SCIENCE AND TECHNOLOGY 12 (SCST 12) 41 5 67 - 74 2011年 [査読無し][通常論文]
     
    In the steam-water mixed spray-cleaning technique, droplet impact on the solid surface is the one of the primarily important physical processes. We experimentally studied a droplet impact on a solid place that moves with a speed ranging from 1 to 50 m/s using high-speed video camera. We observed that high-speed liquid film flows radially outward along the surface just after the impact. In addition, we also observed that liquid turns into corona splash in the cases of higher impact velocities. These flows with large velocities can generate huge shear stress on the solid surface, which may contribute to cleaning. Furthermore, we numerically studied the velocity field development and found that gas flow field may also contribute in advecting removed particles or stripped resists away from the original place.
  • A. Sato, M. Shirota, T. Sanada, M. Watanabe
    PHYSICS OF FLUIDS 23 1 013307  2011年01月 [査読有り][通常論文]
     
    Bouncing of a rectilinearly rising bubble on a free surface is modeled with the use of a simple mass-spring system. The most striking characteristic of the present model is that it is based on an equation of motion of the system that consists of two springs connected in series; hence, we can account for the restoring forces of both the bubble and free surfaces. This equation of motion is coupled with a conservation equation of energy that is taking into account an exchange between the surface energy due to deformations of both the bubble and free surfaces and the kinetic energy of the bubble. With the use of these equations, the contact time, i.e., the time duration of a bubble contacting a free surface, is determined to be a half of the characteristic period of the oscillator. We also conducted experiments of a single clean bubble in ultrapure water bouncing on a flat free surface in order to verify the present model. We found that results obtained from the model agree well with the experimentally obtained results, even in cases with significant surface deformations. When bubbles are smaller than 0.6 mm in radius, the deformations of both the bubble and free surfaces play important roles in bouncing. In case of larger bubbles, on the other hand, bouncing is dominated by the free surface deformation since the bubble has already been highly deformed before collision. We conclude that bouncing of a bubble on a free surface can be explained clearly by the present model based on a simple mass-spring system. (c) 2011 American Institute of Physics. [doi:10.1063/1.3546019]
  • 益子岳史, 真田俊之, 渡部正夫, 林田充司, 関映子
    クリーンテクノロジー 20 8 65 - 69 2010年08月10日 [査読無し][通常論文]
  • 金川 哲也, 矢野 猛, 渡部 正夫, 藤川 重雄
    数理解析研究所講究録 1701 40 - 46 京都大学 2010年08月 [査読無し][通常論文]
  • Tetsuya KANAGAW, Takeru YANO, Masao WATANABE, Shigeo FUJIKAWA
    Journal of Fluid Science and Technology 5 3 351 - 369 The Japan Society of Mechanical Engineers 2010年07月 [査読有り][通常論文]
     
    We propose a systematic derivation method of the Korteweg-de Vries-Burgers (KdVB) equation and nonlinear Schrödinger (NLS) equation for nonlinear waves in bubbly liquids on the basis of appropriate choices of scaling relations of physical parameters. The basic equations are composed of a set of conservation equations for mass and momentum and the equation of bubble dynamics in a two-fluid model. The scaling of parameters is related to the wavelength, frequency, propagation speed, and amplitude of waves concerned. With the help of the method of multiple scales, appropriate choices of the parameter scaling allow us to derive various nonlinear wave equations systematically from a set of basic equations. The result shows that the one-dimensional nonlinear propagation of a long wave with a low frequency is described by the KdVB equation, and that of an envelope of a carrier wave with a high frequency by the NLS equation. Thus, we establish a unified theory of derivation of nonlinear wave equations in bubbly liquids.
  • Shigeto NAKAMURA, Takeru YANO, Masao WATANABE, Shigeo FUJIKAWA
    Journal of Fluid Science and Technology 5 1 26 - 34 The Japan Society of Mechanical Engineers 2010年02月 [査読有り][通常論文]
     
    A new method for measurement of evaporation coefficient using sound resonance experiment is proposed on the basis of a theory of molecular gas dynamics, by which the evaporation coefficient is expressed as a function of the amplitude of standing sound wave between a planar sound source and a vapor-liquid interface facing against it. To demonstrate the applicability of this method, we carried out test experiments under the condition of neither evaporation nor condensation for several initial pressures, 30, 50, 80 and 101 kPa, at room temperature. In the experiments, we measure the amplitude of standing wave with a resonant frequency generated in a cylindrical space filled with air and closed by liquid water. We utilize the second harmonics component excited by the nonlinearity of sound to determine the evaporation coefficient, thereby eliminating the electromagnetic noises from measured signals. We find that the amplitude of the second harmonics at sound resonance decreases with the decrease in the initial pressure.
  • Ayaka SATO, Masumi AOKI, Masao WATANABE
    Journal of Fluid Science and Technology 5 1 14 - 25 The Japan Society of Mechanical Engineers 2010年02月 [査読有り][通常論文]
     
    Effects of electrolytes on bubble coalescence are investigated experimentally from fluid dynamic point of view. Collisions of a bubble with free surface in two kinds of liquids, namely, ultrapure water and sodium chloride solution, are observed using a high speed camera. It is found that the repetitive number of bubble bounces on a free surface in electrolyte solution is larger than that in ultrapure water when the equivalent bubble radii are the same. This result qualitatively shows that electrolyte works to prevent bubbles from coalescing. It is also revealed that the bubbles can coalesce if their Weber numbers, which are based on the radius of curvature of the front side of the bubble and the approach velocity just before the collision with the free surface, are less than a critical Weber number. Furthermore, the critical Weber number decreases with the increase in the concentration of the electrolyte solutions despite the fluid dynamic characteristics, such as bubble rise velocity and bubble shape, are not affected by the addition of the electrolytes. It is concluded that Weber number is the most important parameter to specify the effects of electrolytes on bubble coalescence.
  • 真田俊之, 渡部正夫, 益子岳史, 林田充司, 駒野秀男
    空気清浄 47 5 31 - 36 日本空気清浄協会 2010年01月31日 [査読無し][通常論文]
  • 毛利 信吾, 小笠原 俊樹, 矢口 久雄, 渡部 正夫, 藤川 重雄
    年次大会講演論文集 2010 239 - 240 一般社団法人日本機械学会 2010年 
    The condensation coefficients of water and methanol, i.e., the ratios of condensation mass flux of vapor molecules to their mass flux colliding on the interface, are evaluated by combining the experiment conducted by a shock tube and the numerical simulation of Gaussian-BGK Boltzmann equation applicable to polyatomic gases. Film condensation occurs on the endwall of vapor filled shock-tube, when a shock wave is reflected at the endwall and the vapor eventually becomes supersaturated there. The formed liquid film grows with the lapse of time. The time evolution in thickness of the liquid film is measured by an optical interferometer, and thereby the growth rate of the film is obtained. The rate is incorporated into the kinetic boundary condition at the interface for the Gaussian-BGK Boltzmann equation, the solution of which is in consequence obtained uniquely. The condensation coefficients in nearequilibrium states for water and methanol are found to be close to those evaluated by molecular dynamics simulations at equilibrium states.
  • 矢口 久雄, 矢野 猛, 渡部 正夫, 藤川 重雄
    年次大会講演論文集 2010 237 - 238 一般社団法人日本機械学会 2010年 
    Nonequilibrium molecular dynamics simulation is carried out to study weak condensation of argon vapor into its nanodroplet. Temperature of the nanodroplet is kept at 90 K by using the velocity scaling method. The nanodroplet grows steadily ranging from about 3.3 to 3.4 nm in the radius R_m which is defined as the radius of the center of transition layer in density profile. The mass fluxes at the vapor-nanodroplet interface are investigated and condensation coefficient of the nanodroplet is successfully determined. As a result, the condensation coefficient is almost equal to the evaporation coefficient obtained by our previous study. The rate of change of R_m can be predicted by the mass fluxes and evaporation/condensation coefficients within about 16 percent error.
  • Molecular Dynamics Study of Vapor-liquid Equilibrium Condition for Nanodroplet
    Hisao Yaguchi, Takeru Yano, Masao Watanabe, Shigeo Fujikawa
    Proceedings of 7th International Conference on Multiphase Flow 2010年 [査読有り][通常論文]
  • 金川 哲也, 渡部 正夫, 矢野 猛, 藤川 重雄
    日本機械学會論文集. B編 76 771 1802 - 1810 一般社団法人日本機械学会 2010年 [査読無し][通常論文]
     
    Based on the unified theory by the present authors (T. Kanagawa, et al., J. Fluid Sci. Tech., 5, 2010), the Korteweg-de Vries-Burgers (KdVB) equation and the nonlinear Schrodinger (NLS) equation with an attenuation term for weakly nonlinear waves in bubbly liquids are re-derived from a system of bubble-liquid mixture model equations composed of the conservation equations of mass and momentum, the Keller equation for bubble dynamics, and supplementary equations. We show that the re-derived KdVB equation and NLS equation are essentially the same as those derived from a system of two-fluid model equations except for the coefficients of nonlinear, dissipation, and dispersion terms. The differences in these coefficients are studied in detail, and we find that for the case of KdVB equation, the mixture model is valid only for sufficiently small initial void fractions. On the other hand, for the case of NLS equation, the range of validity of the mixture model depends on not only the initial void fraction but also the wavenumber concerned.
  • 金川哲也, 金川哲也, 渡部正夫, 矢野猛, 藤川重雄
    日本機械学会論文集 B編 76 771 1802 - 1810 2010年 [査読無し][通常論文]
     
    Based on the unified theory by the present authors (T. Kanagawa, et al., J. Fluid Sci. Tech., 5, 2010), the Korteweg-de Vries-Burgers (KdVB) equation and the nonlinear Schrödinger (NLS) equation with an attenuation term for weakly nonlinear waves in bubbly liquids are re-derived from a system of bubble-liquid mixture model equations composed of the conservation equations of mass and momentum, the Keller equation for bubble dynamics, and supplementary equations. We show that the re-derived KdVB equation and NLS equation are essentially the same as those derived from a system of two-fluid model equations except for the coefficients of nonlinear, dissipation, and dispersion terms. The differences in these coefficients are studied in detail, and we find that for the case of KdVB equation, the mixture model is valid only for sufficiently small initial void fractions. On the other hand, for the case of NLS equation, the range of validity of the mixture model depends on not only the initial void fraction but also the wavenumber concerned.
  • 佐藤文香, 青木真澄, 渡部正夫
    混相流研究の進展 4 103 - 110 THE JAPANESE SOCIETY FOR MULTIPHASE FLOW 2009年12月 [査読有り][通常論文]
     
    Effects of electrolytes on bubble coalescence are investigated experimentally. Collisions of bubbles with free surface of three kinds of liquids, namely, super purified water, NaCl solution and KCl solution, are observed by using a high speed camera. It is found that the numbers of bounces on a free surface in electrolyte solution are larger than those in super purified water with the same equivalent bubble radius. This result qualitatively indicates that electrolyte works to prevent bubbles from coalescing. It is also revealed that a bubble can coalesce if the Weber number, which is based on radius of curvature of fore side of the bubble and approach velocity just before collision with free surface, is less than a critical value. The decrease of the critical Weber number, which corresponds to the inhibition of the coalescence, is observed with the increase in the concentration of the electrolyte solutions.
  • Toshiyuki Sanada, Ayaka Sato, Minori Shirota, Masao Watanabe
    CHEMICAL ENGINEERING SCIENCE 64 11 2659 - 2671 2009年06月 [査読有り][通常論文]
     
    Bouncing and coalescence of a pair of slightly deformed bubbles rising side by side in a quiescent liquid are experimentally studied. The trajectories and shapes of the bubbles are investigated in detail by using a high-speed video camera. The wakes of bubbles are visualized by using a photochromic dye that is colored with UV light irradiation. We observe that the patterns of the trajectories of rising bubbles are strongly dependent on the Reynolds number. When the Reynolds number is over the critical region, two bubbles approach each other and then collide. After the collision, two types of motions are observed-coalescence and bouncing. We investigate the critical Reynolds number and Weber number over which the bubbles bounce. In the definitions of these numbers, we use vertical velocity, instead of horizontal one, as the characteristic velocity. We clarify that the critical Weber number is around 2 regardless of the Morton number. The critical Reynolds number decreases with an increase in the Morton number. Moreover, the visualization of the wake of bubbles enables us to observe the vortex separation from the rear surface of the bubbles on collision. We find that the vortex separation from the rear of bouncing bubbles causes a decrease in the rising velocity and an increase in the horizontal speed after their collision. We also observe that the behavior of repeatedly bouncing bubbles is significantly influenced by the wake instability of a single bubble rather than by the bubble-bubble interaction. By applying an existing model for spherical bubble-bubble interaction, we clarify that the revised model accurately describes the trajectory of a pair of slightly deformed bubbles using the restitution coefficient and velocity fluctuation from the experimental results. (C) 2009 Elsevier Ltd. All rights reserved.
  • A. Hayashida, A. Seki, T. Mashiko, T. Sanada, M. Watanabe
    ECS Transactions 25 5 249 - 256 2009年 
    A novel ultra low environmental load removal technique of post-dry etch residue is developed, by applying physical force cleaning technique using high-speed steam-water mixture spray. It is found that the removal rate of the proposed technique depends on the dry-etch processes, and that the steam-water mixture spray almost completely removes the post-dry etch residue from some kinds of dry etched wafers without help of any chemicals. It is also found that the proposed technique requires very dilute concentration of inorganic solution, if necessary, to remove post-dry etch residue completely from other kinds of wafers and that removal process using amine compound with isopropyl alcohol is unnecessary. By contrast, air-water mixture spray could not remove the dry-etch residue at all even with some chemicals. Therefore it is understood that steam atmosphere significantly contributes the proposed technique. The characteristic feature and efficiency of the proposed technique are discussed.
  • 今井 亮介, 中川 浩哉, 桜井 康介, 渡部 正夫, 藤川 重雄
    年次大会講演論文集 2009 107 - 108 一般社団法人日本機械学会 2009年 
    In the field of medical engineering, the application of bubbles of nanometer size to Drug Delivery System (DDS) has attracted great attention as the administration of next generation. DDS with bubbles is expected to be a noninvasive clinical treatment. As the transport carrier of DDS, there exists bubble encapsulated in a lipid bilayer, generally called as a lipid bubble. However, dynamic properties of these lipid bubbles are not yet made clear. In this study, acoustic characteristics of lipid bubbles are experimentally investigated. The resonant frequencies of lipid bubbles are evaluated from attenuation of ultrasound pulse propagating through the experimental cell filled with lipid bubble solution. It is found that the attenuation spectrum has two dominant peaks in the frequency range of 1.0 through 14.0 MHz due to the acoustic energy absorbed by lipid bubble with resonant oscillations.
  • 矢口 久雄, 田中 綾一, 矢野 猛, 渡部 正夫, 藤川 重雄
    年次大会講演論文集 2009 115 - 116 一般社団法人日本機械学会 2009年 
    Molecular dynamics simulations of an argon nanodroplet evaporating into vacuum are carried out to investigate time development of its temperature. Configuration in vaporliquid equilibrium state of the nanodroplet with 3.6 nm in radius at 105 K is adopted as initial configuration of the evaporation. Although the temperature of nanodroplet decreases with time because of the loss of latent heat for evaporation, rapid temperature rise has been observed at about 8.0 ns. Radial distribution function of molecules inside the nanodroplet suggests that phase change from liquid to solid has been occurred. Recovery from the supercooling consequent to release of latent heat for solidification is thought to be cause of this rapid temperature rise.
  • 小笠原 俊樹, 山野 大吾, 渡部 正夫, 藤川 重雄
    年次大会講演論文集 2009 113 - 114 一般社団法人日本機械学会 2009年 
    The condensation coefficient of water, ie., the ratio of condensation mass flux of vapor molecules to incoming mass flux at the interface, is evaluated by combining the experiment conducted by a shock tube and the numerical simulation of Gaussian-BGK Boltzmann equation applicable to polyatomic gases. Film condensation occurs on the endwall of a vaporfilled shock-tube, when a shock wave is reflected at the endwall and the vapor becomes supersaturated there. The formed liquid film grows with the lapse of time. The time evolution in thickness of the liquid film is measured by an optical interferometer, and thereby the growth rate of the film is obtained. The rate is incorporated into the kinetic boundary condition at the interface for the Gaussian-BGK Boltzmann equation, and the unique numerical solution of the vaporliquid system is obtained. Values of condensation coefficient in near equilibrium state are found to be close to that evaluated by molecular dynamics simulations at the equilibrium state.
  • T. Mashiko, A. Hayashida, Y. Yamada, T. Sanada, M. Watanabe
    ECS Transactions 25 5 233 - 240 2009年 [査読有り][通常論文]
     
    Performance of photoresist stripping using steam-water mixed spray is quantitatively investigated with water flow rate as the operating parameter. The most striking and the most important finding is that air-water mixed spray turns out hardly effective. This result shows the peculiar superiority of the proposed technique. As we found that the prominently excessive long time of spraying of steam-water mixture on metal surface results in surface abrasion, this result strongly suggests that both the resist stripping and metal surface abrasion are dominated by essentially the same mechanism. We speculate that our proposing technique is categorized in the physical force cleaning. We discuss the role of the water flow rate in this cleaning technique and the validity of the assumption of physical force cleaning.
  • Toshiyuki Sanada, Masao Watanabe, Atsushi Hayashida, Yoichi Isago
    ULTRA CLEAN PROCESSING OF SEMICONDUCTOR SURFACES IX 145-146 273 - + 2009年 [査読有り][通常論文]
  • Masao Watanabe, Toshiyuki Sanada, Atsushi Hayashida, Yoichi Isago
    ULTRA CLEAN PROCESSING OF SEMICONDUCTOR SURFACES IX 145-146 43 - + 2009年 [査読有り][通常論文]
  • Toshiyuki Sanada, Masao Watanabe, Atsushi Hayashida, Yoichi Isago
    Solid State Phenomena 145-146 273 - 276 2009年 [査読有り][通常論文]
     
    It is well-known that ion-implant doses greater than 5E14 atoms/cm 2 can create an amorphous carbon-like layer "crust", and also that this crust is extremely difficult to dissolve with wet chemicals. In practice, a combination of dry plasma ashing and wet chemical removal is used to eliminate the photoresist. In this study, a novel photoresist stripping technique is proposed. We have improved wet vapor photoresist stripping technique [1] using the mixture of high-speed steam flow and purified water droplets. Relatively low pressure clean steam is mixed with purified water in the nozzle, and sprayed on a photoresist coated Si wafer. We have also developed a pre-treatment method in a chamber with keeping both temperature and humidity constant, in order to strip post ion-implanted photoresit. The most significant feature of this proposed technique is that we use water only hence we are able to strip photoresist without chemicals. © (2009) Trans Tech Publications.
  • 松原瑞浦, 渡部正夫
    日本臨床バイオメカニクス学会誌 29 99 - 106 2008年11月01日 [査読無し][通常論文]
  • 渡部 正夫, 真田 俊之, 山瀬 雅男
    日本機械学會論文集. B編 74 744 1717 - 1724 一般社団法人日本機械学会 2008年08月25日 [査読無し][通常論文]
     
    Our experimental results [T. Sanada, et. al., ASME-FEDSM 2007-37129] showed that spraying relatively low pressure stream (0.1MPa-0.2MPa), mixed with super-purified water in the nozzle, on a solid surface, caused harsh erosion. We turned our attention to the occurrence of a strong focused rarefaction wave in the middle of the droplet, possibly cavitation. Experimental results that the degrees of the erosion are heavily dependent on temperature also may support the existence of cavitation. We numerically studied the dynamics of high speed liquid droplet impacts on a solid surface by solving the Euler equation of gas-liquid two phase compressible flow. We discuss the possibility of cavitation as the primary cause of the experimentally observed harsh erosion on the solid surface.
  • 渡部正夫, 真田俊之, 山瀬雅男
    日本機械学会論文集 B編 74 744 1717 - 1724 一般社団法人日本機械学会 2008年08月25日 [査読無し][通常論文]
     
    Our experimental results [T. Sanada, et. al., ASME-FEDSM 2007-37129] showed that spraying relatively low pressure stream (0.1MPa-0.2MPa), mixed with super-purified water in the nozzle, on a solid surface, caused harsh erosion. We turned our attention to the occurrence of a strong focused rarefaction wave in the middle of the droplet, possibly cavitation. Experimental results that the degrees of the erosion are heavily dependent on temperature also may support the existence of cavitation. We numerically studied the dynamics of high speed liquid droplet impacts on a solid surface by solving the Euler equation of gas-liquid two phase compressible flow. We discuss the possibility of cavitation as the primary cause of the experimentally observed harsh erosion on the solid surface.
  • Toshiyuki Sanada, Keiji Sugihara, Minori Shirota, Masao Watanabe
    Fluid Dynamics Research 40 7-8 534 - 545 2008年07月 
    We experimentally study the motion and shape of a single rising bubble in super-purified water. We develop an apparatus that is equipped with a measurement system for monitoring both the resistivity and amount of total organic carbon of water in order to evaluate the purity of water. We investigate the critical Reynolds number above which the rising bubble motion changes from rectilinear to zigzag or spiral motion. It is revealed that the critical Reynolds number is susceptible to the range of observation height in the experimental tank. Next, we investigate the effects of the amount of contaminant on bubble motion. The drag coefficient of bubbles in the case of low Reynolds numbers is greatly affected by a small amount of contaminant. We also compare the experimental results of both the terminal rising velocity and drag coefficient with theoretical results for ellipsoidal bubble obtained for high Reynolds number. For smaller bubbles, good agreement is found between the experimental and theoretical results. For larger bubbles, however, discrepancies are prominent. Finally, we examine the effects of the bubble shape on its motion. There exist significant discrepancies between the experimental and theoretical results of aspect ratio as a function of Weber number, even in the range where the experimental and theoretical results in both the terminal velocity and drag coefficient show good agreement. © 2008 The Japan Society of Fluid Mechanics and Elsevier B.V.
  • 佐藤文香, 城田農, 真田俊之, 渡部正夫
    混相流研究の進展 3 2008 35 - 41 THE JAPANESE SOCIETY FOR MULTIPHASE FLOW 2008年06月15日 [査読無し][通常論文]
     
    Relations between drag coefficients CD and bubble shapes are investigated by comparing our experimental results with both analytical [Moore, J. Fluid Mech., 23, 749-766 (1965)] and numerical results [Blanco & Magnaudet, Phys. Fluids, 7(6), 1265-1274(1995)] on ellipsoidal bubbles rising in a quiescent clean liquid. We clarify that the analytically obtained CD overestimates the experimental results especially in the case of either high aspect ratio or low Reynolds number, and that numerically obtained results for ellipsoidal bubbles well predict our experimental results. We also show that the effect of the deviation in the shape from the ellipsoid, i.e., fore-aft asymmetry, on CD is negligible; CD for fore-aft asymmetry bubbles is in good agreement with the numerically obtained CD for ellipsoidal bubbles.
  • Minori Shirota, Toshiyuki Sanada, Ayaka Sato, Masao Watanabe
    PHYSICS OF FLUIDS 20 4 043301  2008年04月 [査読有り][通常論文]
     
    The mechanism of a bubble production method using pulsed acoustic pressure waves in gas phase is investigated using high-speed photography. The acoustic characteristics of the present bubble generator are also investigated. We found out the optimal acoustic waveform for producing only one bubble per one action; the bubble detachment radius is accurately controlled by first applying the positive onset-assistance acoustic pressure wave and then the negative detachment-assistance acoustic pressure wave with an accurately controlled time lapse. From an orifice with a radius of 0.09 mm submerged in water, bubbles with radii in the range of 0.28-0.78 mm with an extremely small standard deviation of less than 1 mu m are obtained. The shrinking and pinch-off motions of a capillary bridge connecting the bubble and orifice at the time of bubble detachment are observed in detail. The balancing force on a growing bubble, which is based on a spherical bubble formation model is also estimated. As a result, we reveal that when the gas pressure is decreased due to a negative pressure wave, the capillary bridge submerges into the orifice and an upward added mass force is applied on the bubble, both of which cause the detachment of the bubble from the orifice. (C) 2008 American Institute of Physics.
  • 真田俊之, 齋藤隆之, 林田充司, 斉藤輝夫, 山瀬雅男, 渡部正夫
    噴流工学 24 3 4-10  2008年01月18日 [査読無し][通常論文]
  • 中村 勇揮, 渡部 正夫, 入部 昌樹, 松原 瑞浦
    年次大会講演論文集 2008 21 - 22 一般社団法人日本機械学会 2008年 
    Nailfold video capillaroscopy (NVC) can observe the micro vascular structure non-invasively. We developed NVC by using high speed digital video camera to evaluate both micro vascular structure and red blood cell movement quantitatively The objects of this study are to evaluate the radius distribution of micro vascular by level-set method and also the red blood cell velocity by tracing plasma gap between blood cells.
  • 野林 真, 北島 洋佑, 渡部 将平, 澤江 義則, 渡部 正夫
    年次大会講演論文集 2008 73 - 74 一般社団法人日本機械学会 2008年 
    Engineered cartilages are expected to be used for the treatment of cartilage defects. Cartilage tissue is avascular; hence transport phenomena are controlled by diffusion and also advection by so called "pumping mechanism" of tissue. The objective of present paper is to evaluate the contribution of both diffusion and advection in engineered tissue for the control of transport phenomena.
  • Motion and drag of single bubbles in super-purified water
    Toshiyuki Sanada, Keiji Sugihara, Minori Shirota, Masao Watanabe
    FLUID DYNAMICS RESEARCH 40 534 - 545 2008年01月 [査読有り][通常論文]
  • Impact of High-speed steam-droplet spray on solid surface
    Toshiyuki Sanada, Masao Watanabe, Minori Shirota, Masao Yamase, Takayuki Saito
    FLUID DYNAMICS RESEARCH 40 627 - 636 2008年01月 [査読有り][通常論文]
  • Toshiyuki Sanada, Minori Shirota, Masao Watanabe
    CHEMICAL ENGINEERING SCIENCE 62 24 7264 - 7273 2007年12月 [査読有り][通常論文]
     
    Wake structure of a single "clean bubble", rising in rectilinear, zigzagging or spiraling path, is experimentally investigated. A single nitrogen gas bubble was produced in a silicone oil pool and the wake structure development in the rear of the rising bubble was visualized by using photochromic dye. The flexibility of this visualization method enabled us to distinguish wake from drift easily. Both bubble motion and wake structure were recorded by using stereo high-speed video camera simultaneously. We present the first experimental support for the existence of the standing eddy at the rear of the clean bubble, as predicted by a previous numerical study by Ryskin and Leal [1984. Journal of Fluid Mechanics 148, 19-35], Dandy and Leal [1986. Physics of Fluids 29(5), 1360-1366] and Blanco and Magnaudet [1995. Physics of Fluids 7(6), 1265-1274]. We study motion of a pair of vortex filaments, which is called double-threaded type wake, in the case of bubble rising in an axi-asymmetric path. Visualization results of multiple formations of horse-shoe type vortices in one period of zigzag motion of rising bubble with shape oscillations, which has not been observed in previous studies are also presented. (C) 2007 Elsevier Ltd. All rights reserved.
  • 杉原慶治, 真田俊之, 城田農, 渡部正夫
    化学工学論文集 33 5 402 - 408 2007年09月 [査読無し][通常論文]
     
    We experimentally studied the motion and shape of single rising bubbles in superpurified water. We developed an apparatus, which was equipped with a measurement system of both resistance and TOC value of water, in order to maintain water purity by monitoring it during the experiment. We investigated the critical Reynolds number over which the rising bubble motion changed front rectilinear motion to zigzag or spiral motion. In the case of Re=650, the bubble reached the terminal velocity at the height of 40 mm and the onset of transition to zigzag or spiral motion was observed at the height of 140 mm. Oil the other hand, in the case of Re 700, both the terminal velocity and onset of transition were observed at the approximately same height; hence the critical Reynolds number was unable to be uniquely determined. The height of the onset of transition increased with the decrease in Reynolds number. We also compared experimental results of both the terminal rise velocities and drag coefficients with those obtained theoretically for ellipsoidal bubble in the limit of potential flow theory. For smaller bubbles, experimental values of the terminal velocities and drag coefficients showed good agreement with those obtained theoretically. For larger bubbles, however, the deferences between experimental and theoretical values in the terminal velocities and drag coefficients became prominent. Finally we quantitatively evaluated the bubble shapes by expanding them in terms of Legendre's polynomials and proposed the new correlations of the aspect ratio with either Weber number or Eotvos number.
  • 城田農, 小野友輝, 杉原慶治, 真田俊之, 渡部正夫
    混相流研究の進展 2 125 - 132 2007年04月01日 [査読無し][通常論文]
  • 城田農, 真田俊之, 荒田康弘, 渡部正夫, 亀田正治
    日本機械学会論文集 B編 73 726 467 - 473 一般社団法人日本機械学会 2007年02月25日 [査読無し][通常論文]
     
    The mechanism of a bubble production method using controlled gas pressure fluctuation, originally developed by Kariyasaki and Osaka [Trans. JSME, Series B, Vol.68, No.674, (2002)1, is further investigated using high-speed photography. We found out more appropriate pressure fluctuation than that of Kariyasaki and Osaka in producing single bubble. The radius of bubbles can be varied from about 0.3 to 0.8 mm with extremely small standard deviation of less than 1μm. Shrinking motion of a capillary bridge connecting a bubble and a nozzle was observed in detail. Force balance on a growing bubble which is based on a spherical bubble formation model is also estimated. As a result, we reveal that when gas pressure is decreased the capillary bridge is sucked down into a nozzle and upward added mass force is applied on a bubble, both of which cause the detachment of a bubble from a nozzle.
  • 渡部正夫, 真田俊之, 城田農, 松隈洋介
    日本機械学会論文集 B編 73 726 459 - 466 一般社団法人日本機械学会 2007年02月25日 [査読無し][通常論文]
     
    A new treatment of no slip boundary condition on complex geometry in a lattice Boltzmann method is proposed. We developed Space-Time Bounce-Back (STBB) method, which evaluate distribution functions in the vicinity of the solid boundary whose geometry described in the scale less than the lattice size. The STBB method is based on not only the spatial distribution but also the temporal distribution of distribution functions, in order to satisfy both the complete reflection on the solid boundary and the second order accuracy in the spatial discretization. Two-dimensional channel flow is calculated by using the proposed method, and both the accuracy and the stability are examined by comparing with the analytical solution.
  • WATANABE Masao, MATSUBARA Mizuho, SANADA Toshiyuki, KURODA Hiroaki, IRIBE Masaki, FURUE Masutaka
    Journal of Biomechanical Science and Engineering 2 2 81 - 92 The Japan Society of Mechanical Engineers 2007年 
    Nailfold capillaroscopy has been shown to reflect microvascular disturbances mainly in connective tissue diseases, and the development of video capillaroscopy made it possible to determine capillary red blood cell velocity by measuring the displacement of plasma gaps between red cells. We improved both temporal and spatial resolutions of video capillaroscopy by developing the high speed digital video capillaroscopy, integrating high speed digital video camera, deep-focus zoom lens, appropriate light source and light collecting adaptor. The first objective of this study is to present the novel method for quantitative capillary shape analysis by using the level-set method. The capillary radius distribution along the capillary center line is obtained and described by the level-set function. Based on this mathematical description of capillary shape, more rigorous definition of the capillary red blood cell velocity than the conventional method is discussed. The second objective of this study is to propose the innovative measurement method of red blood cell velocity in nailfold capillary, and then the possibility of tracking the individual red blood cell movement, not only in the axial direction but also lateral direction, in human nailfold capillary is discussed
  • MATSUBARA Mizuho, WATANABE Masao, WATANABE Satoshi, KONISHI Kozo, YAMAGUCHI Shohei, HASHIZUME Makoto
    Journal of Biomechanical Science and Engineering 2 2 69 - 80 The Japan Society of Mechanical Engineers 2007年 
    Budd-Chiari syndrome (BCS) is a symptomatic complete or partial occlusion of the hepatic vein and/or the inferior vena cava. The cause of BCS is not well known yet, however; abnormal vessel wall shear stress caused by blood flow is thought to increase the likelihood of developing BCS. We investigate the blood flow field in the vicinity of the junction of the inferior vena cava and hepatic veins by using numerical simulation based on medical imaging. However, there exist inaccuracies in computational vessel models. The sensitivities of flow characteristics to vessel shape have not been fully investigated. In this study, the characteristics of the blood flow in the vicinity of the junction of the hepatic vein and the inferior vena cava are discussed based on the numerical results obtained by several reconstructed vessel models which are slightly different in shapes and surface smoothness. It is also demonstrated that relatively small differences in the shapes and surface smoothness of the reconstructed vessel model cause noticeable effects on the flow characteristics in the vicinity of the junction of the inferior vena cava and large hepatic veins.
  • 入部 昌樹, 黒田 寛顕, 渡部 正夫, 松原 瑞浦, 真田 俊之
    年次大会講演論文集 2007 87 - 88 一般社団法人日本機械学会 2007年 
    Nailfold video capillaroscopy (NVC) examines the micro vascular structure noninvasively and aids in the diagnosis of capillary disease, such as Raynaud's phenomenon. We developed high speed digital video capillaroscopy which is composed of high speed digital video camera, deep-focus lens, metal halide light source, and light collecting adaptor. We obtained sequential images of nailfold microcirculation loop with much higher temporal resolution than conventional capillaroscopy. The high speed digital video capillaroscopy enabled us to evaluate quantitatively both micro vascular structure and red blood cell movement. The objects of this study are to measure the radius distribution of micro vascular by Level Set method and also the red blood cell velocity by tracing plasma gap between blood cells.
  • 武富 祐太, 佐藤 文香, 城田 農, 真田 俊之, 渡部 正夫
    年次大会講演論文集 2007 133 - 134 一般社団法人日本機械学会 2007年 
    The structure of the flow around a rising bubble in silicone oil was visualized by using photochromic dye. We present the first experimental evidence of the existence of the standing eddy, which was predicted numerically by Blanco & Magnaudet[Phys. Fluids, Vol.7, 1265-1274(1995)]. We also experimentally evaluated two kinds of critical aspect ratios over which the standing eddy or three dimensional wake exists. It was found that experimentally obtained critical aspect ratios were smaller than those obtained numerically, however both experimental and numerical results qualitatively agree that critical aspect ratios were bigger in lower Reynolds number.
  • 松原 瑞浦, 渡部 正夫, 渡邉 聡, 小西 晃造, 山口 将平, 橋爪 誠
    年次大会講演論文集 2007 93 - 94 一般社団法人日本機械学会 2007年 
    Budd-Chiari syndrome (BCS) is one of the vessel disorders caused by thrombosis which occlude partially or completely hepatic veins (HVs) and the inferior vena cava (IVC). It has been demanded to model the blood flow fields in the IVC and HVs to study the cause of formation of thrombosis. In order to analyze the blood flow fields, we carried out medical vessel segmentation of HVs and IVC using level set method, constructed 3D vessel model, and conducted computational fluid dynamics simulation by using velocity profile of the analytical solution for pulsatile flow in the IVC.
  • 真田 俊之, 城田 農, 小野 友輝, 渡部 正夫
    化学工学会 研究発表講演要旨集 2007 288 - 288 公益社団法人 化学工学会 2007年
  • 真田 俊之, 城田 農, 杉原 慶治, 渡部 正夫
    化学工学会 研究発表講演要旨集 2007 289 - 289 公益社団法人 化学工学会 2007年
  • 真田俊之, 城田農, 小野友輝, 渡部正夫
    可視化情報学会論文集 27 7 47 - 52 The Visualization Society of Japan 2007年01月 [査読有り][通常論文]
     
    ジグザグもしくはらせん運動を行う上昇気泡の後流について，実験的に調査した．単一の気泡をシリコンオイル中に発生させ，その後流をフォトクロミック染料を用いることで可視化した．気泡の挙動と後流は，高速度ビデオカメラを用いて同時にステレオ撮影した．その結果，気泡がらせん運動を開始する際には，ダブルスレッド型と思われる二本の渦構造が観察された．また気泡が形状振動を伴いながらジグザグ運動を行う際には，複数の馬蹄形の渦構造が観察された．
  • M Watanabe, T Sanada
    JSME INTERNATIONAL JOURNAL SERIES B-FLUIDS AND THERMAL ENGINEERING 49 2 410 - 418 2006年05月 [査読有り][通常論文]
     
    We study the motion of a pair of bubbles rising in the vertical line, at intermediate Reynolds number (5 < Re < 150), both numerically and experimentally. It has been predicted, by analytical and numerical studies, that there exists a stable equilibrium distance between a pair of bubbles due to the balance between the potential repulsive and viscous atractive forces. However, no experimental results have ever confirmed the existence of an equilibrium distance between bubbles rising in a vertical line. Most experimental results indicated that a pair of bubbles collided. We solve this paradox and answer the question: "Is there an equilibrium distance?" by presenting both experimental evidence of an existence of the equilibrium distance and the detailed numerical results of a deforming-spatial-domain/space-time finite element method, taking bubble surface deformation effects into account.
  • 藤野 真聡, 城田 農, 真田 俊之, 松下 大介, 渡部 正夫, 松宮 [ヒカル]
    年次大会講演論文集 2006 271 - 272 一般社団法人日本機械学会 2006年 
    In order to measure a wind turbine performance on a complex terrain that fails to satisfy the IEC standard, we should evaluate a flow correction factor which is the ratio of wind speeds between two points. In this study, we have compared the flow correction factors for 16 principal azimuthal directions between actual measurements and CFD results. From March in 2005 to February in 2006, wind speed and wind direction were measured by using two meteorological. And we calculate unsteady wind fields using highly accurate CFD method combined with both large eddy simulation and geographical information system. As a result, in 6 of 16 directions, the flow correction factors obtained from measurements differ from that obtained using CFD by only 〜10%.
  • 真田 俊之, 城田 農, 荒田 康弘, 渡部 正夫
    年次大会講演論文集 2006 273 - 274 一般社団法人日本機械学会 2006年 
    A method of a bubble production, originally developed by Kariyasaki and Osaka [Trans. JSME, 68-674B (2002)], is further investigated experimentally. First, the acoustic characteristic of the pipe between audio speaker and nozzle is investigated. Then, a new type of fluctuation consisted of both increase and decrease in gas pressure is used to clarify the effect of the fluctuation. Shrinking motion of a capillary bridge connecting a bubble and a nozzle was observed in detail using high-speed photography. We also estimate the force balance on a bubble center based on a spherical bubble formation model. As results, it is clarified that the pipe between speaker and nozzle could regard as acoustic tube. Moreover, when gas pressure is decreased the capillary bridge is sucked down into a nozzle and upward added mass force is applied on a bubble center, both of which cause the detachment of a bubble from a nozzle.
  • 杉原 慶治, 小野 友輝, 城田 農, 真田 俊之, 渡部 正夫
    年次大会講演論文集 2006 445 - 446 一般社団法人日本機械学会 2006年 
    We experimentally studied both bouncing and coalescence of a pair of bubbles rising side by side in a quiescent liquid. At high Reynolds number, a pair of bubbles approached each other and then collided. After the collision, bubbles either coalesced or bounced. We visualized flow field formed in the vicinity of bubbles by irradiating photochromic dye with UV light sheet, and observed wake of bubbles both before and after the collision. We discuss wake development of bubbles as bubbles collided and the relation between wake structure and bubble motion after the collision. We also investigated the critical Reynolds number and Weber number of coalescence of bubbles. We clarified that the critical Weber number is approximately two regardless of Morton number and that the critical Reynolds number decreases with the increase in Morton number.
  • 杉野 翔一, 北島 洋佑, 渡部 正夫, 澤江 義則, 真田 俊之, 村上 輝夫
    年次大会講演論文集 2006 215 - 216 一般社団法人日本機械学会 2006年 
    Articular cartilage is charactericstic tissue which is mainly composed of avascular extracellular matrix. Solute transport in articular cartilage is to mainly by diffusion across the articular surface. We engineered regenerated cartilage by seeding bovine chondrocyte into agarose gel as scaffold. We evaluate diffusion coefficient by using fluorescent molecular with image process and to examine the effect of molecular weight and electric property of fluorescent labeled dextran on diffusion process in regenerated cartilage tissue.
  • 松原 瑞浦, 渡部 正夫, 渡邉 聡, 小西 晃造, 山口 将平, 橋爪 誠
    年次大会講演論文集 2006 109 - 110 一般社団法人日本機械学会 2006年 
    Budd-Chiari syndrome (BCS) is one of vessel disorders caused by thrombosis which occlude partially or completely hepatic vein and inferior vena cava. The cause of BCS has not been revealed yet, but it has been indicated that there are some relationships between BCS and blood flow fields in the vicinity of the confluence of hepatic vein with inferior vena cava. In order to analyze the blood flow fields, we carried out medical vessel segmentation of hepatic vein and vena cava using level set method with high accuracy, constructed 3D vessel model, and conducted computational fluid dynamics (image-based CFD).
  • 真田 俊之, 城田 農, 渡部 正夫
    化学工学会 研究発表講演要旨集 2006 163 - 163 公益社団法人 化学工学会 2006年
  • 真田 俊之, 渡部 正夫
    化学工学会 研究発表講演要旨集 2006 166 - 166 公益社団法人 化学工学会 2006年
  • T. Sanada, M. Watanabe, T. Fukano
    Multiphase Science and Technology 18 2 155 - 174 2006年 [査読有り][通常論文]
     
    Interaction effects on the bubble motion and consequently induced coalescence were experimentally studied. A high accuracy bubble production control device enabled us to experiment various spatial configurations of a pair of bubbles. Among them, we focused on the cases where either bubbles rose in vertical line and side by side in silicone oil pool. Bubble diameter and liquid kinematic viscosity were taken as the experimental parameters. The motion of bubbles was recorded by a high-speed video camera. We observed that the Reynolds number Re significantly affected the motion of a pair of bubbles rising in both vertical line and side by side. When a pair of bubbles rose in vertical line, the trailing bubble was attracted by the wake of the leading bubble, and then it collided with leading bubble, in the case of low Re. On the other hand, in the case of intermediate Re, a pair of bubbles kept a mutual equilibrium distance due to the balance between the leading bubble wake attractive force and potential repulsive force. As Re further increased, the trailing bubble deformed and then escaped from the vertical line. When a pair of bubbles rose side by side, they separated from each other as they rose in the case of low Re. On the contrary, in the case of large Re, they attracted each other and then collided if the initial bubble horizontal distance was smaller than a critical value. At the moment of the collision of a pair of bubbles, we did not observe the significant deceleration of the bubble rising velocity. It should be noted that they collided with each other with asymmetric shape deformation. In addition, we investigate the criteria of either bouncing or coalescence of bubbles. Our experimental results show that the approach velocity is important parameter on coalescence of a pair of bubbles.
  • T. Sanada, M. Watanabe, Y. Sawae, M. Furue
    PROCEEDINGS OF THE 5TH WORLD CONGRESS OF BIOMECHANICS 451 - + 2006年 [査読有り][通常論文]
     
    We developed high-speed video capillaroscopy and observed the capillary loops of blood vessels in finger skin nail fold. Deep-focus high magnification zoom lens and high speed video camera allowed us to observe the motion of red blood cells, white blood cells and plasmas. It should be emphasized that this method is non-invasive and non-blood observing diagnosis. Quantitative analysis of blood flow allowed us to observe the motion of red blood cell in a capillary vessel with the diameter from 10 micron to 20 micron with recording rate from 500 to 1000 Hz. We also conducted shape analysis of the capillary vessel, by using level set method. By analyzing the obtained level set function, quantitative evaluation of capillary blood shape, such as characteristic diameter and curvature are carried out.
  • T Sanada, M Watanabe, T Fukano
    CHEMICAL ENGINEERING SCIENCE 60 19 5372 - 5384 2005年10月 [査読有り][通常論文]
     
    Effects of liquid viscosity on coalescence of a bubble upon impact with a free surface were studied both experimentally and numerically. Experiments were conducted in a pool filled with silicone oil by generating a nitrogen gas bubble and observing it with a high-speed video camera. Full Navier-Stokes equations were solved with two level set functions for a bubble and a free surface. As a result, the Weber number was the most important parameter determining the coalescence time in low viscosity liquids. in contrast, the coalescence time in a high viscosity liquid was much greater than that of a low viscosity liquid with the same Weber number. In addition, the thresholds between bubble coalescence and bouncing were affected by liquid viscosity. For the differences in coalescence time, foam was observed at the free surface in the case of high viscosity case only the difference of liquid viscosity in the non-polar liquid. By examining the pressure distribution of the liquid film between the bubble and the free surface and the downward liquid flow, we conclude that not only the liquid film but also the liquid flow field underneath the bubble was important for bubble coalescence or bouncing. (c) 2005 Elsevier Ltd. All rights reserved.
  • 渡部正夫, 真田俊之, 沢江義則, 古江増隆
    日本臨床バイオメカニクス学会誌 26 91 - 96 2005年10月01日 [査読無し][通常論文]
  • 渡部正夫, 真田俊之, 沢江義則, 増田禎一, 古江増隆
    西日本皮膚科 67 5 546  2005年10月01日 [査読無し][通常論文]
  • T Sanada, M Watanabe, T Fukano, A Kariyasaki
    CHEMICAL ENGINEERING SCIENCE 60 17 4886 - 4900 2005年09月 [査読有り][通常論文]
     
    The motion of a single nitrogen gas bubble chain and the structure of water flow field surrounding the chain were experimentally studied. We developed a bubble generator that can control both the bubble diameter and the generation frequency independently. Experimental conditions of bubble Reynolds number and bubble distance divided by bubble diameter were from 300 to 650 and from 6.5 to 300, respectively. We discuss the interaction effects on the motion of each bubble rising in a chain, as compared to the effects of a single rising bubble. The bubble trajectories and the surrounding water flow fields in the state of bubbles rising in a chain were investigated using a high-speed digital video camera and an analog single-lens-reflex camera. We observed two important physical phenomena. First, bubbles passed through a nearly identical path in the case of low frequency of bubble production. On the contrary, at a height of approximately 50 turn from the nozzle, the bubbles in the case of high frequency deviated and scattered from this path due to bubble-bubble interaction. Second, with higher bubble production frequency, coherent bubble chain and the characteristic structure of the surrounding water flow called "liquid jet" were observed near the nozzle. The direction of liquid jet flow differed from the bubble trajectory. We theoretically investigated the relation of coherent bubble chain and liquid jet by applying the conservation of liquid momentum. (c) 2005 Elsevier Ltd. All rights reserved.
  • 古江増隆, 増田禎一, 渡部正夫, 真田俊之, 沢江義則
    福岡医学雑誌 96 6 277 - 277 福岡医学会 2005年06月25日 [査読無し][通常論文]
     
    人の末梢血管は皮膚表層の表皮下真皮乳頭層の血管を最小血管とする血流網を形成している.乳頭層の細小血管は皮膚表面を拡大すると,そのループの頂点を観察できるわけであるが,指爪郭の爪上皮(あまかわの所)部では,その全容を観察することが可能である.たとえば皮膚筋炎では,毛細管の拡張や出血が認められるが,爪郭の毛細管ではその病態がはっきりと可視化されている.本研究では,皮膚毛細管動静脈ループを流れる血流の血行動態を,毛細血管顕微鏡と高速度ビデオカメラとを組み合わせることにより,非侵襲・非観血で高時空間分解能に観察する手法を開発した.
  • 藤野 真聡, 真田 俊之, 松下 大介, 内田 孝紀, 渡部 正夫, 松宮 輝
    風力エネルギー利用シンポジウム 27 265 - 268 一般社団法人 日本風力エネルギー学会 2005年
  • 真田 俊之, 渡部 正夫, 澤江 義則, 古江 増隆
    バイオエンジニアリング学術講演会・セミナー講演論文集 2004 57 - 58 一般社団法人日本機械学会 2005年
  • 渡部 正夫, 澤江 義則, 真田 俊之, 羽有 健太, 村上 輝夫
    バイオエンジニアリング学術講演会・セミナー講演論文集 2004 279 - 280 一般社団法人日本機械学会 2005年
  • 渡部正夫, 真田俊之
    日本機械学会論文集 B編 71 702 389 - 396 2005年 [査読無し][通常論文]
     
    We study the motion of a pair of bubbles rising in the vertical line in intermediate Reynolds number, both numerically and experimentally. It has been predicted by the analytical and numerical studies that the trailing bubble approaches the leading bubble and then a pair of bubbles keeps the mutual equilibrium distance. However, no experimental results have ever confirmed the existence of the equilibrium distance between a pair of bubbles rising in the vertical line. Most of experimental results reported that a pair of bubbles collided. We solve this paradox and answer the question : "If there is an equilibrium distance?" by presenting the first experimental evidence of the existence of the equilibrium distance. Moreover we show that the equilibrium distance is considerably unstable by experimental results.
  • 渡部正夫, 姫野龍太郎
    日本機械学会論文集 A編 70 697 1276 - 1283 一般社団法人日本機械学会 2004年09月25日 [査読無し][通常論文]
     
    Quantitative evaluation of level set contour segmentation method applied to three dimensional images detecting image edge based on threshold is discussed. The integration of two popular level set methods, i.e., reinitialization method and geodesic active contour method, leads to success in development of robust, with high accuracy, level set based segmentation method. The applications of this method to both synthetic and clinical medical images are shown. Accuracy of the propose method, in the view of both averaged contour location and standard deviation of curvature in the vicinity of contour, calculated using obtained level set function is discussed.
  • Sanada Toshiyuki, Watanabe Masao, Sato Ayaka, Fukano Tohru
    アジア・太平洋化学工学会議発表論文要旨集 2004 709 - 709 公益社団法人 化学工学会 2004年 
    Effects of liquid viscosity on coalescence of a pair of bubbles were experimentally studied by generating nitrogen gas bubbles in a pool filled with silicon oil. We focused on two types of coalescence/bouncing of bubbles. The first type was those between a rising bubble and a free surface, and the second type was those between of a pair of bubbles rising side by side. The former is considered as the extreme case, which is equivalent to coalescence/bouncing between bubbles with finite and infinite diameters. The later is more practical. That is, bubbles were generated simultaneously from a pair of pin-holes on a pipe horizontally placed. We studied the viscosity effects on coalescence of bubbles by investigating behavior of bubbles with both liquid viscosity and bubble diameter as the parameters. Previous studies reported that We number based on approach velocity could predict whether two bubbles would bounce or coalesce in super purified water. Our experimental results show that the threshold We number in the case of low viscosity liquid indicates same order as the one in the case of super purified water. On the other hand, in the case of large viscosity liquid, the threshold We number differs significantly from the one in the super purified water.
  • 渡部 正夫, 真田 俊之
    年次大会講演論文集 2004 355 - 356 一般社団法人日本機械学会 2004年 
    Behavior and shapes of a pair of bubbles rising in a viscous liquid were numerically analyzed by using DSD/ST (Deforming-Spatial-Domain/Space-Time) Finite Element Method in the cylindrical coordinate system. It has been predicted by the analytical and numerical studies that the trailing bubble approaches the leading bubble and then a pair of bubbles rising in the vertical line keeps the mutual equilibrium distance. However, no experimental results have ever confirmed the existence of the equilibrium distance between a pair of bubbles. In this study, we investigated the effects of bubble deformation on behavior of a pair of bubbles rising in line. We clarified that a pair of deformable bubbles reaches an equilibrium distance and the equilibrium distance is considerably unstable.
  • 真田 俊之, 佐藤 文香, 渡部 正夫, 深野 徹
    年次大会講演論文集 2004 351 - 352 一般社団法人日本機械学会 2004年 
    Effects of liquid viscosity on the coalescence of a pair of bubbles were experimentally studied by generating nitrogen gas bubbles in a pool filled with silicon oil. We focused on two types of coalescence/bouncing of bubbles, i.e., those between a rising bubble and a free surface, and between a pair of bubbles rising side by side. The former is considered as the extreme case, which is equivalent to coalescence/bouncing between bubbles with finite and infinite diameters. The later is more practical. That is, bubbles were generated simultaneously from a pair of pin-holes on a pipe horizontally placed. We studied the viscosity effects on coalescence of bubbles by investigating the behavior of bubbles with both liquid viscosity and bubble diameter as the parameters. Previous studies reported that We number based on approach velocity could predict whether two bubbles would bounce or coalesce in superpurified water. Our experimental results show that the threshold in the case of low viscosity liquid indicates the same order as the one in the case of superpurified water. On the other hand, in the case of a large viscosity liquid, the threshold differs significantly from the one in the superpurified water.
  • 渡部正夫, PROSPERETTI A
    日本機械学会論文集 B編 70 691 636 - 643 2004年 [査読無し][通常論文]
     
    The purpose of this study is to explore the validity of the continuum model by treating the bubbles individually accounting for their interaction exactly by numerical means. Using the equation set describing the bubble behavior including interactions in the bubble cloud, we simulate the acoustical characteristics of the bubble cloud. We compare eigenfrequencies and eigenvectors obtained from these equations with the continuum model results. We discuss the limits of the validity of the continuum model in detail, and answer the question "How many bubbles can generate a bubble cloud from the acoustical point of view ?".
  • 真田俊之, 渡部正夫, 湯田朋寛, 深野徹
    日本機械学会論文集 B編 70 692 863 - 870 2004年 [査読無し][通常論文]
     
    Bouncing and coalescence between single rising bubble and free surface were experimentally and numerically studied. In experimental study, with Weber number of O (10-2) ∼1.7 and Morton number of O(10 -9)O(10-4), it was observed that both liquid viscosity and bubble diameter are playing the dominant role in coalescence time and bounce/coalescence condition. It was clarified that Weber number is the important parameter in the coalescence, time of bubble with free surface in low viscosity liquid. However, in high viscosity liquid, scale of coalescence time was observed significantly different from the one of low viscosity liquid. In numerical study, the full Navier-Stokes equation was solved, by defining two Level Set functions for bubble and free surface respectively. The pressure of liquid film between bubble and free surface, bouncing mechanism and difference of coalescence time scales are discussed.
  • 真田俊之, 渡部正夫, 佐藤文香, 深野徹
    日本機械学会論文集 B編 70 700 3128 - 3135 2004年 [査読無し][通常論文]
     
    Effects of liquid viscosity on the coalescence of a pair of bubbles were experimentally studied by generating nitrogen gas bubbles in a pool filled with silicone oil. We focused on two types of coalescence/bouncing of bubbles, i.e., those between a rising bubble and a free surface, and between a pair of bubbles rising side by side. The former is considered as the extreme case, which is equivalent to coalescence/bouncing between bubbles with finite and infinite diameters. The later is more practical. That is, bubbles were generated simultaneously from a pair of pin-holes on a pipe horizontally placed. We studied the viscosity effects on coalescence of bubbles by investigating the behavior of bubbles with both liquid viscosity and bubble diameter as the parameters. Previous studies reported that We number based on approach velocity could predict whether two bubbles would bounce or coalesce in superpurified water. Our experimental results show that the threshold in the case of low viscosity liquid indicates the same order as the one in the case of superpurified water. On the other hand, in the case of a large viscosity liquid, the threshold differs significantly from the one in the superpurified water.
  • Toshiyuki Sanada, Tohru Fukano, Masao Watanabe
    Proceedings of the ASME/JSME Joint Fluids Engineering Conference 2 1489 - 1496 2003年 
    The behaviors of single nitrogen gas bubble chains, with diameters of from 0.5 mm to 2.5 mm, in stagnant water were experimentally studied. We developed an innovative acoustic bubble generator, which can precisely control both bubble diameter and generation frequency in an independent manner. We discuss the effects of interactions between bubbles in bubble chains on the behaviors of each bubble quantitatively, comparing to those of single rising bubble. Bubble trajectories and surrounding water flow field generated by the bubble chains were carefully investigated by applying the image processing technique to the high-speed video camera data. We analyzed the experimental data and identified the following two significant physical phenomena. (1) Under the condition of bubble radii kept unchanged, while bubbles passed almost the same path in the current measurement region in the case of low generation frequency, they deviated from this path and scattered about 30 mm from the generator with the increase of bubble generation frequency. (2) With higher bubble generation frequency, characteristic structures of the surrounding flow fields were clearly observed. These flow fields possessed the planer structure which could be spanned by the bubble trajectory direction and vertical axis through bubble generator.
  • 真田俊之, 渡部正夫, 仮屋崎侃, 深野徹
    日本機械学会論文集 B編 69 678 307 - 314 2003年 [査読無し][通常論文]
     
    The effects of both generation frequency and bubble diameter on the behaviors of single bubble chains in stagnant water were experimentally investigated. We developed the bubble generator equipment to control precisely both bubble generation frequency and bubble diameter, independently. Bubbles were generated with diameters from 1.0 mm to 2.5 mm, and generation frequencies from 1 Hz to 20 Hz. We investigated bubble chain patters developments in stagnant water, by taking both generation frequency and diameter as parameters. Two types of bubble chain patterns were investigated carefully. The first type was the bubbles rising in zig-zag or helical. In this case the behaviors of bubbles with l/d > 100 (l : mutual distance d : diameter) were observed to be identical to those of single bubbles, on the contrary, those of bubbles with l/d < 50 ∼ 100 were influenced by the interaction by the other bubbles. The second type was the bubbles rising in line. The behavior of bubbles with l/d > 200 were indistinguishable from those of single bubble.
  • 真田俊之, 渡部正夫, 野田瞳, 深野徹
    日本機械学会論文集 B編 69 687 2446 - 2452 2003年 [査読無し][通常論文]
     
    The behavior of single nitrogen gas bubble chains and the structures of flow field in the vicinity of a nozzle were experimentally studied. Both bubble diameters and bubble generation frequencies were precisely controlled independently to be 2.2 mm, and from 1 Hz to 10 Hz (corresponding bubble distance 300∼30 mm), respectively, by using innovative acoustic device. Careful investigations of flow field in the vicinity of a nozzle by using Particle Image Velocimetry enabled us to investigate the following two significant physical phenomena. First, The lift forces acting on bubbles in the bubble chains were observed to increase as bubble generation frequency increases, and were largely affected by the preceding bubbles. Second, developments of characteristic liquid jet were identified to play a dominant role in generation of lift forces on each bubble in single bubble chains, and were theoretically investigated by applying the conservation of liquid momentum.
  • 渡部正夫, KIKINIS R, WESTIN C‐F
    日本機械学会論文集 B編 69 687 2408 - 2415 2003年 [査読無し][通常論文]
     
    A novel approach to correct magnetic resonance phase contrast angiography (MR-PCA) based on the coupling computational fluid dynamics (CFD) to vessel segmentation in the level set methodology. MR-PCA data is supplied not only to partial differential equation based fast local level set vessel segmentation as the initial condition, but also to CFD code using level set ghost fluid method as the initial and boundary conditions. These procedures are integrated to provide with the corrected velocity field in the most optimal vessel geometry. The application of this system to both synthetic and clinical data are shown and validity is discussed.
  • 渡部正夫, PROSPERETTI A
    日本機械学会論文集 B編 69 688 2612 - 2619 2003年 [査読無し][通常論文]
     
    A mathematical model discribing the acoustical characteristics of a bubble cloud containing N bubbles is derived taking bubble interaction effects into account. The method of multipole expansion, by using both singular perturbation method and the matching procedure, is carried out to determine the coefficients of the spherical harmonics expansion to satisfy boundary conditions of both on the bubble surfaces and at the infinity. Discrete characteristic equations are obtained from a set of N algebraic equations, under the assumption of potential flow and spherical bubble shape of bubbles.
  • WATANABE M.
    CD-ROM of 3rd ASME-JSME Joint Fluid Eng. Conf., FEDSM 99 - 7101 1999年 [査読無し][通常論文]
  • Numerical Analysis of Bubble Motion Using Finite Element Method with Time Dependent Non-Structured Interface Capturing Mesh
    Masao Watanabe, Rajendra Shrestha, Tohru Fukano
    Proceedings of 4th International Joint Symposium between Kyushu University and Chungnam National University 96  1999年 [査読無し][通常論文]
  • WATANABE Masao, SHRESTHA Rajendra, FUKANO Tohru
    九州大学工学紀要 59 4 243 - 261 九州大学 1999年 [査読無し][通常論文]
  • Bubble Cloud Collapse in an Inviscid and Incompressible Liquid
    Masao Watanabe, Tohru Fukano
    Proceedings of ASME/JSME Fluids Engineering Division Summer Meeting CA, USA. F. EDSM99-6771 1999年 [査読無し][通常論文]
  • 稲冨 誉也, 深野 徹, 渡部 正夫
    日本機械学会論文集(B編) 65 638 3252 - 3259 1999年 [査読無し][通常論文]
     
    Viscous waves are generated on the gas-liquid interface of thin liquid film flowing concurrently with high speed gas flow in a horizontal rectangular duct when the flow rates of both gas and liquid are relatively small. It is well known that waves on the thin liquid film, such as viscous waves, play important roles on the breakdown and formation of liquid film. In the present paper we numerically investigate the nonlinear behavior and the flow conditions of generation of the viscous waves by solving two-dimensional incompressible Navier-Stokes equations of both phases with the Level Set method to capture the gas-liquid interface.
  • M Watanabe, T Fukano
    JSME INTERNATIONAL JOURNAL SERIES B-FLUIDS AND THERMAL ENGINEERING 41 2 480 - 485 1998年05月 [査読無し][通常論文]
     
    A new method is developed to solve the three-dimensional hydrodynamic field generated by multiple bubbles, which are arbitrarily configured at low Reynolds number, taking the effects of both bubble interactions and the slight deformation of the bubble surface into consideration, for the case of epsilon=We/Re<<1. The numerical results for the case of two equi-radial bubbles confirm the validity of this method with the restriction that the gap between the two bubbles is to be not less than half of the radius. It is shown that the hydrodynamic force acting as drag is smaller in the case of a bubble moving away from another stationary bubble than in the case of one bubble approaching another. This difference is explained as the nonlinear effect originating from the bubble surface deformation.
  • Complex Motions of Bubbles in Periodically Driven Pressure Field
    Masao Watanabe, Tohru Fukano
    Proceedings of International Conference of Multiphase Flow '98, Lyon, France 1998年 [査読無し][通常論文]
  • M Watanabe, A Prosperetti, H Yuan
    JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 102 6 3484 - 3496 1997年12月 [査読無し][通常論文]
     
    A simplified quasi-one-dimensional model of thermoacoustic devices is formulated by averaging the conservation equations over the cross section. Heat transfer and drag effects are introduced by means of suitable coefficients. While the primary motivation for this work is the development of a model approximately valid in the nonlinear regime, the focus of this paper is the proper formulation of the transfer coefficients and the analysis of the linear problem. The accuracy of the model is demonstrated by comparison with existing more precise theories and data. Examples of devices with variable cross section demonstrate the flexibility of the approach. (C) 1997 Acoustical Society of America. [S0001-4966(97)01412-4].
  • T Fukano, H Nakagawa, Y Mori, M Watanabe
    NUCLEAR ENGINEERING AND DESIGN 175 1-2 3 - 13 1997年11月 [査読有り][通常論文]
     
    In a horizontal channel a separated how usually occurs if the size of the channel is not as small as a capillary tube and the flow rates of both phases of gas and liquid are low. If the how rate of gas exceeds a certain value, liquid begins to climb up the inner surface of the channel. The higher the gas velocity, the higher the film climbs up toward the top of the channel cross section. The present paper is concerned with the experimental investigation of the role of large scale waves, or disturbance waves, in the formation of liquid film on the side wall of a horizontal channel. The thinning process of liquid film thickness as the function of time is also investigated by a simple liquid flow model. (C) 1997 Elsevier Science S.A.
  • M WATANABE, A PROSPERETTI
    JOURNAL OF FLUID MECHANICS 274 349 - 381 1994年09月 [査読無し][通常論文]
     
    The propagation of weak shock waves in liquids containing a small concentration of gas bubbles is studied theoretically on the basis of a mathematical model that contains all - and only - the effects that contribute to first order in the gas volume fraction. In particular, the thermal exchange between the gas bubbles and the liquid is described accurately. This aspect of the theory emerges:as its most significant component, relegating effects such as the relative motion between the phases to roles of minor importance. Comparison with experimental results substantiates the accuracy of the model for shock waves that have had time to broaden from an initial sharp front to a more diffuse profile. For shock waves closer to inception, marked differences are found between theory and experiment. The same problem affects all other published theoretical treatments. It is concluded that some as yet poorly understood mechanism governs the early-time behaviour of shock waves in bubbly liquids.
  • The Effect of Gas Diffusion on the Nuclei Population Downstream of a Cavitation Zone
    Masao Watanabe, Andrea Prosperetti
    Proceedings of the Symposium on Cavitation and Gas-Liquid Flow in Fluid Machinery and Devices, FED-Vol. 190 211  1994年 [査読無し][通常論文]
  • Mass Diffusion Effects on Cavitation Nuclei
    Masao Watanabe, Andrea Prosperetti
    Proceedings of 2nd International Symposium and Cavitation, Tokyo Japan 321  1994年 [査読無し][通常論文]
  • Yoichiro MATSUMOTO, Masao WATANABE
    TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series B 55 519 3282 - 3287 1989年 [査読無し][通常論文]
  • 松本 洋一郎, 渡部 正夫
    日本機械学会論文(B編) 55 519 3282 - 3287 1989年 [査読無し][通常論文]
  • Yoichiro Matsumoto, Masao Watanabe
    JSME International Journal, Series II 32 2 157  1988年 [査読無し][通常論文]
  • 松本 洋一郎, 渡部 正夫
    日本機械学会論文集 B編 54 501 1051 - 1057 The Japan Society of Mechanical Engineers 1988年 [査読無し][通常論文]
     
    The pressure response of a small air bubble in water is calculated numerically in an oscillatory pressure field. The following phenomena are taken into account in the calculation ; mist formation inside the bubble due to homogeneous condensation, diffusion between vapor and noncondensable gas inside the bubble and so on. The internal condition adapts itself easily to the oscillatory pressure field by the internal phenomena, which includes mist formation, evaporation and deposition onto the bubbler wall, so that the bubble tends to oscillate synchronously. The frequency response curves for bubbles are calculated. The curve is shifted towards low frequency, and the maximum bubble radius becomes large. When the pressure amplitude is increased, the periodic bubble oscillation bifurcates to non-periodic oscillation, which is a deterministic chaos.
  • 松本 洋一郎, 渡部 正夫
    日本機械学会論文集(B編) 54 501 1051 - 1057 The Japan Society of Mechanical Engineers 1988年 [査読無し][通常論文]
     
    The pressure response of a small air bubble in water is calculated numerically in an oscillatory pressure field. The following phenomena are taken into account in the calculation ; mist formation inside the bubble due to homogeneous condensation, diffusion between vapor and noncondensable gas inside the bubble and so on. The internal condition adapts itself easily to the oscillatory pressure field by the internal phenomena, which includes mist formation, evaporation and deposition onto the bubbler wall, so that the bubble tends to oscillate synchronously. The frequency response curves for bubbles are calculated. The curve is shifted towards low frequency, and the maximum bubble radius becomes large. When the pressure amplitude is increased, the periodic bubble oscillation bifurcates to non-periodic oscillation, which is a deterministic chaos.

MISC

講演・口頭発表等

所属学協会

  • American Physical Society   日本流体力学会   日本混相流学会   日本機械学会   

Works（作品等）

  • 生体力学シミュレーション研究プロジェクトにおけるMRAデータからの循環器系シミュレーション
    2002年 -2003年

共同研究・競争的資金等の研究課題

  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2024年04月 -2028年03月 
    代表者 : 小林 一道, 藤井 宏之, 渡部 正夫
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2024年04月 -2026年03月 
    代表者 : 渡部 正夫, 小林 一道, 藤井 宏之, 真田 俊之
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2020年04月 -2023年03月 
    代表者 : 小林 一道, 藤井 宏之, 渡部 正夫
     
    本提案研究は，混合気体に接した気液界面における気体論境界条件を構築し，様々な分野に本研究成果を展開することである．2021年度は主に以下の３つの研究を行った． １．分子計算（分子運動論および分子動力学シミュレーション）を用いて，非平衡気液界面における気体論境界条件の構築を行った．その結果，気体論境界条件に含まれる二つの未知パラメータ（蒸発係数および凝縮係数）を決定した．本結果より，非平衡気液界面における蒸発係数と凝縮係数の値は，平衡状態および非平衡状態においてほぼ変わらないことが明らかとなった．これにより，初期液体温度などの条件にもよるが，平衡状態の蒸発係数および凝縮係数を求めておけば気体論境界条件を構築できることが示唆された． ２．分子動力学解析を用いて，固体壁と液体に挟まれた気体のクエット流れについて解析を行った．この研究より，気液界面における気体論境界条件の位置を検証した．本研究より，１の研究で指定していた気体論境界条件の位置は妥当であることが示唆された．また，高クヌーセン数流れになるほど，気液界面の境界条件が平衡状態の関数形から異なることが示唆された．これについてはさらなる検討が必要である． ３．分子動力学解析を用いて，混合液体（エタノール・イソオクタン）の蒸発について検証した．分子動力学計算を用いてエタノール・イソオクタンの気液平衡系を作り出し，１の研究で提案した方法によって，液体から蒸発する分子の成分について調べた．その結果，エタノールの濃度が低い混合液体においても，蒸発するエタノール分子の割合は高くなることが示された．今後はこの知見を用いて実験結果を整理する予定である．
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2020年04月 -2023年03月 
    代表者 : 藤井 宏之, 西村 吾朗, 渡部 正夫, 小林 一道
     
    本研究の目的は、「生体を模擬した高密度なコロイド溶液に対して、輻射（ふくしゃ）の干渉効果を組み込んだ輻射輸送モデル(輸送モデル)を新たに構築した上で、干渉効果が及ぼす光伝播への影響を明らかにすること」である。生体光イメージングや光治療において、生体内の光伝播を定量的に把握することが必要であり、光を輻射と捉えた輸送モデルが活用されている。しかし、従来の輸送モデルには、生体のような高密度な散乱媒体において重要となる干渉効果が考慮されていない。本研究では電磁波の散乱理論より干渉効果を考慮した散乱特性を計算し、輸送モデルに組み込んだ上で光強度の時間分解波形を数値計算する。また、短パルスレーザー光源による光強度計測も実施する。干渉効果が光伝播へ影響を及ぼす時空間スケールについて、散乱係数などで表される無次元数を用いて解析し、理論、数値計算、実験より体系的に明らかにする。この目的を達成するため、本年度は以下の３項目について研究を実施した。 １．光散乱特性を簡潔に記述するモデル式を開発した。モデル式により、単一散乱の寄与と干渉効果の寄与を分離して評価することに初めて成功した。 ２．分担研究者の西村吾朗助教の波長可変の光計測システムを利用して、コロイド溶液（脂質エマルジョン）において、濃度20%まで21条件、720 nmから860 nmまでの6条件で光計測を実施した。光計測データを逆解析することで算出した光学特性値をモデル式より解析し、干渉効果の波長依存性を明らかにした。 ３．分子動力学シミュレーションにより構造特性を計算し、干渉散乱理論に組み込んで散乱特性を計算した。粒子間の引力相互作用が散乱特性に強く影響を及ぼすことを明らかにした。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2020年04月 -2023年03月 
    代表者 : 渡部 正夫, 小林 一道, 藤井 宏之, 真田 俊之
     
    本研究の目的は，「高Oh液滴の固体面衝突直後に発生するcorona splashとprompt splashの発生条件を明らかにし，二つのsplashの発生メカニズムを説明する理論モデルを構築すること」である．この目的を達成するために，本年度は以下の２項目について研究を行った． １．固体表面に滴衝する高Oh液滴の観察：自由落下するシリコンオイルを用いて衝突実験を行い，高Oh液滴のsplash発生条件を探索した．高粘度液滴衝突ではあるOhを閾値としてsplashとreceding break-upの２種類の不安定性が観察されること, 閾値Oh数以上ではreceding break-upのみが観察されさらにOh数を大きくすると不安定性が観察されないこと，receding break-upはある衝突速度以上では観察されないことを明らかにした． ２．粗い表面に衝突する液滴の観察：低圧力環境下の高速液滴衝突 (50m/s程度) 実現を行い，固体表面粗さの効果を検討するために，減圧チャンバ内での粗い固体表面への高速液滴衝突を観察した．平滑表面および粗い固体表面においてsplashの発生閾値を検討した．低Oh液滴衝突においては，これまで観察されていたcorona splashとprompt splashに加えて衝突直後極短時間にのみ観察されるsplashが存在することが発見され，これまでに提案されたsplash発生閾値モデルは，粗い表面には適用できないことを明らかにした． ３．高速度カラー光干渉計による気液界面計測システムによる観察：固体表面に衝突する液滴の固体面衝突直前に，固体表面と液滴との間に形成される薄空気膜はsplash発生に大きな影響を与える．この薄空気膜厚さの空間分布の時間変化が，固体表面電位と液体の誘電率によって大きく変化することを明らかにした．
  • 表面プラズモン共鳴観察によるアクティブマターのメカニズムの解明
    日本学術振興会：科学研究費補助金(挑戦的研究(萌芽))
    研究期間 : 2018年04月 -2020年03月 
    代表者 : 渡部 正夫
  • 高速射出液膜流れの固気液三相接触線近傍流れ場の不安定現象に及ぼす周囲気体効果
    日本学術振興会：科学研究費補助金(基盤研究(B))
    研究期間 : 2017年04月 -2020年03月 
    代表者 : 渡部 正夫
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2016年04月 -2019年03月 
    代表者 : 小林 一道, 藤井 宏之, 渡部 正夫, 今 美沙紀
     
    本研究は蒸気(凝縮性気体)と気体(非凝縮性気体)の混合気体に対する気体論境界条件を決定し，その境界条件を利用して，混相流れの解析，特に気泡の崩壊問題の解析に適用することである．本研究期間では，分子動力学法を用いて平衡状態における混合気体の気体論境界条件を構築した．また，得られた境界条件を用いて，気泡の崩壊問題に適用した．その結果，気泡が崩壊する際には，気液界面近傍に薄い非凝縮性気体の層が形成され，この層の影響で，蒸気の凝縮係数が著しく低くなることが示唆された．また，崩壊時の気泡内部の温度分布は，その内部に含まれるほんのわずかな非凝縮性気体の量に応じて変化することが明らかとなった．
  • 文部科学省：科学研究費補助金(基盤研究(B))
    研究期間 : 2014年 -2016年 
    代表者 : 渡部 正夫
     
    固体表面への液滴衝突は噴霧冷却，インクジェット印刷，超清浄洗浄等の技術応用において重要な技術的要素である．本研究では，Xuら（Phys. Rev. Lett, 184505, 2005）の液滴衝突後に発生する高速液膜の不安定現象発生閾圧力についてのモデルが，周囲気体温度の寄与を予測することが可能であることを示した．さらに周囲気体が凝縮性気体の場合には，高速液膜の不安定現象発生閾圧力がXuらのモデルでは予測できず，不安定現象発生閾圧力はより高く，すなわち安定化することを示した．
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2011年04月 -2015年03月 
    代表者 : 大島 伸行, 渡部 正夫, 栗原 央流, 矢口 久雄
     
    燃料電池システムの性能にかかわるマルチスケール流動現象の予測に焦点を当てて，分子動力学・非平衡熱力学モデル・非定常流動シミュレーションを連成する階層型連成シミュレーションの各階層，および，それらの連成に対して数理モデルの検討・改良を進めて，１）非定常連成シミュレーションによるセル，スタックレベルでの電池性能予測の実用性検証，２）格子ボルツマン法（LBM）に基づく気液界面シミュレーションの構築と検証，および，触媒層の水輸送モデルの構築，３）水分子ポテンシャルモデルとして6-siteモデルを用いた混合流体の気液相分子シミュレーションの構築，などの成果を得た．
  • 文部科学省：科学研究費補助金(挑戦的萌芽研究)
    研究期間 : 2014年 -2015年 
    代表者 : 渡部 正夫
     
    本研究の目的は，平均場運動論理論から得られるEnskog-Vlasov方程式を用いて，強い非平衡状態にある気液界面近傍での非定常熱・物質輸送現象を解明することである．運動論理論の数値解析手法の一つであるEV-DSMC法を用いて，強い非平衡状態の気液界面近傍の非定常熱・物質輸送現象の数値解析を行い，流体力学の枠組み内で使用可能な，気液界面近傍の熱・物質輸送を記述する境界条件を構築した．この境界条件を用いて相変化を含んだ気泡運動を表す数理モデルを提案し，物理過程を調査した．
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2011年04月 -2014年03月 
    代表者 : 矢野 猛, 青木 一生, 髙田 滋, 渡部 正夫
     
    蒸発・凝縮をともなう気液界面およびその近傍に対する分子動力学と、それを取り囲む大きなスケールの非平衡現象を記述する分子気体力学との包括的統合を行い、非線形非平衡流体力学を確立することが本研究の目的であった。これを実現すべく、１．凝縮相と接する蒸気の非定常非平衡流動に対する一般的な定式化、２．線形化されたBoltzmann方程式に内在する双対性に関する理論研究の非定常問題への深化、３．ナノスケールの液体の流動現象への巨視的流体力学の適用可能性の問題の精密化、４．混合流体の気液界面の分子動力学解析などを行なって、重要な成果を得た。これらの成果を基礎として、非線形非平衡流体力学の構築を継続している。
  • 文部科学省：科学研究費補助金(基盤研究(B))
    研究期間 : 2010年 -2012年 
    代表者 : 渡部 正夫, 真田 俊之, 小林 一道, 矢口 久雄
     
    半導体デバイス製造工程における洗浄工程において,二流体ジェット洗浄呼ばれる,高速な気流に液体を混合し,微細液滴を高速で衝突させ表面を洗浄する技術が多く利用されている.本研究課題では,この洗浄技術の素過程である液滴衝突現象に着目し,固体表面への衝突過程を観察した.特に表面張力,固体表面粗さ,および周囲圧力に着目し,周囲圧力が低下すると,低表面張力液体/粗い固体表面における液滴衝突においても,衝突後の液滴の飛散が抑えられることを確認した.
  • 文部科学省：科学研究費補助金(挑戦的萌芽研究)
    研究期間 : 2011年 -2011年 
    代表者 : 渡部 正夫, 小林 一道, 矢口 久雄
     
    液体燃料ロケットエンジンの信頼陸の向上のために,燃料混合気の濃度分布の高精度予測のための,気液混合界面での輸送現象の解明を目的としている.相変化が存在する気液界面における輸送現象を評価するために,平均場運動論理論から得られるEnskog-Vlasov方程式を用いることにより,界面の物理特陸を評価するために数値解析手法を解析し,分子動力学シミュレーション結果と比較することにより,混合界面での熱・物質輸送現象を検討する.
  • 文部科学省：科学研究費補助金(基盤研究(A))
    研究期間 : 2009年 -2011年 
    代表者 : 藤川 重雄, 渡部 正夫, 矢野 猛, 彭 國義, 小林 一道
     
    当初の計画どおりに研究を進め、以下の成果を得た。(1)凝縮係数の非平衡度依存性の解明:衝撃波管と分子気体力学解析によって決定された水蒸気とメタノール蒸気の凝縮係数の非平衡度依存性について考察を行い、凝縮係数は気液界面での蒸気分子の反射率により支配され、界面での液体分子の自発蒸発にはほとんど影響を受けないことを明らかにした。(2)蒸発係数を測定するための音波共鳴法の開発・実験・解析:蒸気を満たした管内で音波の共鳴を起こさせ、音圧振幅から蒸発係数を求める方法を開発し、296～306Kの温度範囲で水の蒸発係数を測定した。水の蒸発係数は1.0であることが明らかとなった。この結果は、蒸発係数が平衡状態近傍での凝縮係数と一致しするという蒸発係数の定義と整合し、(1)の衝撃波管による平衡状態近傍での凝縮係数の値と一致している。これにより(1)および(2)の方法による蒸発係数と凝縮係数測定法の正しさが明らかにされた。(3)アルゴン液滴に対する気液界面での蒸発係数の計算:アルゴン液滴の気液界面での蒸発係数を分子動力学法により計算し、蒸発係数に及ぼす曲率の影響を明らかにして、結果を陽的な式の形で表現した。(4)以上の(1)～(3)の成果を組み入れることにより、流体力学方程式系に対する正確な気液境界条件を提示した。
  • 文部科学省：科学研究費補助金(挑戦的萌芽研究)
    研究期間 : 2009年 -2010年 
    代表者 : 渡部 正夫, 小林 一道
     
    本研究では,研究代表者らが提案した水蒸気と水を混合しノズルから噴射する革新的混相噴流洗浄方法の基本原理を解明することを目的としている.具体的には,水蒸気中の水液滴が固体表面上の水液膜に衝突することにより発生する衝突圧力に着目する.この衝突圧力は,液滴衝突速度に大きく左右されるため,衝突速度を正確に見積もる必要があり,液滴界面および固体表面での凝縮効果を高精度で解析することが必要である.従って,分子気体力学を用いることが必要不可欠である.本年度は,昨年度構築した気体分子力学と連続体数値流体力学を融合させた数値解析スキーム開発のための基礎モデルの評価を行った.球対称一次元座標系を用いて,Gaussian-BGK-Boltzmann方程式に従う多原子分子気体が,球形液滴に凝縮する過程の数値シミュレーションを行った.液滴周囲の圧力分布を観察することにより液滴に働く抗力を算出した.気液界面の境界条件を支配する蒸発・凝縮係数に液滴抗力は大きく依存し,蒸発・凝縮が発生することにより液滴抗力が低下することを確認した.さらに,より現実的な系を取り扱うために,気体中に分子の占める体積が無視できないような高密度の気体に対して有効である,Enskog-Vlasov方程式を用いることを試みた.Boltzmann方程式の直接解法であるDSMC法を拡張したParticle Scheme法を用いて,単純な系...
  • 文部科学省：科学研究費補助金(基盤研究(B))
    研究期間 : 2008年 -2010年 
    代表者 : 澤江 義則, 渡部 正夫, 坂井 伸朗
     
    単離軟骨細胞をアガロースゲルに播種した再生軟骨組織モデルを用い,関節摺動に伴い組織に付加される繰り返し圧縮,せん断,摩擦といった力学的刺激が,組織内での物質輸送や細胞代謝に与える影響を実験的に評価した.その結果を基に,関節軟骨組織がその最表層部に備えるきわめて洗練された生体潤滑機能が,摺動による力学的刺激に対する適応により構築されるプロセスを実験的に検証した.
  • 文部科学省：科学研究費補助金(基盤研究(B))
    研究期間 : 2007年 -2009年 
    代表者 : 渡部 正夫, 坂井 伸朗, 真田 俊之, 澤江 義則, 坂井 伸朗, 真田 俊之
     
    再生軟骨組織発達における輸送現象の可視化および定量化を行った.細胞が試験片に存在することにより,物質輸送が促進されることが観察された.これは,細胞代謝活動により拡散輸送が増大したためであると考える。細胞代謝の結果,負の電荷を有するケラタン硫酸等の細胞外マトリックスを構成する高分子の産出が拡散輸送を制限することがわかった.また,圧縮により発生する移流現象が拡散現象へ及ぼす影響を明らかにした.
  • 文部科学省：科学研究費補助金(基盤研究(C))
    研究期間 : 2006年 -2007年 
    代表者 : 澤江 義則, 渡部 正夫
     
    生体関節の表面を覆う関節軟骨は,滑らかな関節運動を実現する軸受の役割を果たしており,その表面には摩擦を低く保つための高度な潤滑機能が備わっている.本研究では,関節軟骨組織に潤滑機能が発現するメカニズムについて,まず次のような仮説を立てた.「軟骨組織内部に存在する軟骨細胞が組織に負荷される流体せん断や,摩擦により誘起される圧縮,せん断ひずみといったトライボ刺激(Tribological Stimulation)に応答し,細胞外マトリックスの産生と組織構造形成を制御することで,関節内のトライボ環境に適応した関節潤滑機構を構築する」.この仮説を証明するため,三次元担体に播種された軟骨細胞に,任意の転がり滑り運動を負荷しながら培養することが可能な実験システムを構築した.このシステムを用い,アガロースを三次元担体とした培養組織試験片に転がり滑り運動を負荷し,細胞外マトリックスによる組織構造形成に及ぼす影響を評価した.その結果,3日間の静置培養の後,試験片表面に純滑りを加えながら更に5日間培養した試験片では,表層部に存在する軟骨細胞による細胞外マトリックス産生が促進され,培養組織表面近傍に糖タンパク複合体が高濃度に蓄積されることが示された.これは,培養中のトライボ刺激負荷により,生体軟骨類似の潤滑性表層構造が,再生組織に形成される可能性を示すものと思われる.また,培養中の細胞への物質供給...
  • 文部科学省：科学研究費補助金(基盤研究(B))
    研究期間 : 2005年 -2006年 
    代表者 : 渡部 正夫, 真田 俊之, 澤江 義則, 杉村 丈一
     
    気泡流動を用いたエアリフト型動物培養細胞槽の生産性向上のために,(1)「上昇気泡挙動」と(2)「細胞の輸送現象」の見地から研究を行った.均一気泡流動を実現するためには,最適な気泡数密度すなわち,気泡径および気泡間隔を決定する必要がある.界面活性剤の影響が気泡挙動には非常に重要となってくるために,超純水中における気泡挙動を観察した.自由界面と上昇気泡の反発においては接触時間は突入速度によらず一定であり,反発過程におけるエネルギー散逸は非常に小さいことがわかった.超純水中における並行して上昇する2気泡問に働く相互作用に関しては,2気泡が合体する場合には気泡形状変化を伴って速度低下が見られた.反発する場合にも大きな速度低下が観察された.また,シリコンオイル中に紫外線誘起フォトクロミック染料を溶解し,気泡の後流の可視化観察を行った.並行して上昇する2気泡が衝突後に反発する場合には,気泡後部に発達した後流が衝突と同時に剥離し,2気泡問に入り込み衝突後の気泡挙動に大きな影響を与えることがわかった.また,繰り返し反発する場合には,気泡後部に発達するdouble thread型およびhorse-shoe型後流が観察され,単一上昇気泡の挙動との類似を観察した.さらに,細胞活動と細胞外マトリックスにおける輸送現象に着目し,細胞周囲における物質輸送現象を解明するために,ジェル内に懸架された動物細胞...
  • 文部科学省：科学研究費補助金(萌芽研究)
    研究期間 : 2005年 -2005年 
    代表者 : 渡部 正夫, 真田 俊之, 澤江 義則, 古江 増隆
     
    本研究の目的は,ヒト皮膚毛細管動静脈ループに注目し,血流動態と血管形状の非侵襲・高時空間解像度解析を行うシステムを開発することである.まず,ヒト爪郭皮膚毛細管動静脈ループを観測するために,計測システムを構築した.特に,被写体から対物レンズまでの距離を固定し,被写体のブレを抑えるために光学アタッチメントの開発を行い,実用に耐えうることを確認した.また,高速度カメラで被写体を撮影し,画像のブレを抑制するためにシャッタースピードを上げる必要があるために光源の高光度が要求されるが,光源は熱源となるために過度の光量は被写体の熱損傷を引き起こす.光源・レンズ・光学系の設計・開発を行い,照射面積を大幅に減じ効率の向上を図った結果,鮮明な画像取得と被写体の低侵襲観察の相反する要求を満足させることに成功した.さらに,フレキシブルアームスタンドによりカメラを固定することにより,光軸に空間自由度を与えることに成功し,ヒト皮膚毛細管動静脈ループに限定されない他の皮膚毛細血管,特に血管腫等の観察の臨床応用に適用可能であることを示した.得られた画像には,Matlabを用いて様々な画像処理を施すことにより画像強調を行い,生画像に比して格段の視認性を得られることを確認した.10μm程度の径を持つ細小動静脈管内を流れる赤血球,白血球および血漿の非定常挙動の観察に成功した.また,医療画像認識工学で用いられるレベ...
  • 文部科学省：科学研究費補助金(基盤研究(B))
    研究期間 : 2003年 -2004年 
    代表者 : 渡部 正夫, 松下 大介, 古川 明徳
     
    1.単一のノズルから発生し,曲りながら上昇する気泡列の周囲には特徴的な流れ場が存在することが確認されたので,この特徴的な気泡列の生成週程を水プール中に連続して気泡径と発生頻度を制卸した気泡列を生成させ観察した気泡列中の気泡がより大きな揚力を受けるのは,先行気泡によって形成された流れ場の影響であり,先行気泡の後流が後続気泡の不安定性,特に気泡形伏の変形を生じ,気泡が曲がったと考察した.2.気泡列の周囲に発生する特徴的な流れ場をPIVを用いて可視化した.気泡列まわりの液体流れ場に検査体積をとり,運動量理論を用いることにより,気泡列には液ジェットの形成により働く特徴的な力が存在することを示し,液ジェットの形成に関する理論モデルを構築し,実験結果と比較することにより,その妥当性を評価した.3.上昇する2気泡間での相互干渉現象に関して,実験的および数値的に考察した.気泡レイノルズ数が平衡距離に関しては支配的であることがわかった.実験的に2気泡間に平衡距離が存在することを確認した.また,数値的にはレイノルズ数を減少させることにより,平衡距離が減少し2気泡の接触にいたることを確認した.4.相互作用下の気泡挙動を顕微鏡カメラで観察し,得られた画像に対してフーリエ記述子を用いて定量化し,気泡重心位置の高精度算出および気泡形状と気泡挙動との相関について考察を行った.気泡が衝突するような場合には大...
  • 文部科学省：科学研究費補助金(萌芽研究)
    研究期間 : 2003年 -2004年 
    代表者 : 渡部 正夫
     
    1.磁気共鳴位相コントラスト血管撮像法(MR-PCA)において,数値流体力学の手法を用いることにより,得られた血流流れ場を修正すると共に,より高精度の血管形状の認識・輪郭抽出を行うための手法を提唱し,高制度化をはかった。特に本手法は初期の血管セグメンテーションに精度が依存するために,より高精度化をはかるため,レベルセット法を用いた三次元医療イメージングの輪郭抽出において,閾値法に基づく手法を検討した.レベルセット法の中で適用例の多い再初期化法と測地的動的輪郭法とを組み合わせることにより,再初期法の堅牢性・収束性の良さと,測地的動的輪郭法の解曲面の平滑性とを併せ持つ手法を開発した.この手法のパラメータ強度を調査するために,MRデータのみならず,毛細血管データにも適用し複雑血管形状を抽出した.血管壁認識力の高い再初期化法と血管壁再構成力の高い測地的動的輪郭法との混合を単一のパラメータで制御することが可能であることを認識した.さらに,測地的動的輪郭法の特徴を生かすことにより,従来は画像幾何より求められていた血管の管径・曲率等の特徴値をレベルセット関数を用いて解析的に求める手法を提唱した.2.複雑な3次元血管内の血流をシュミレートするためには,単純な境界条件と並列化の容易さが要求される.そこで,血流流れソルバを従来の差分法から格子ボルツマン法へと改良するための検討を行った.特に境界条...
  • 文部科学省：科学研究費補助金(基盤研究(B))
    研究期間 : 2002年 -2003年 
    代表者 : 深野 徹, 渡部 正夫
     
    沸騰水型原子炉の熱工学的な設計上の制約は燃料棒支持用スペーサ近傍での熱除去によることが、実規模実験より確認されている。しかしスペーサ近傍の冷却材(水)の挙動と加熱管がバーンアウトへ至る機構は明確ではない。このような現状をふまえ、本研究ではスペーサ近傍における液膜の消失およびバーンアウトへ至る機構を実験的に明らかにすることを目的とした。本研究で得られたおもな知見は以下の通りである。1.スペーサ近傍で発生するバーンアウト発生のトリガとなるドライアウトの発生は、じょう乱波間隔が大きくなった場合にじょう乱波間の基底液膜部の蒸発により発生すること、スペーサ下流側では、じょう乱波の到達とともに液膜が再付着しやすく、バーンアウトは全く発生しないことがわかった。特にドライアウト発生にはじょう乱波が支配的役割を果たすことを明らかにした。2.じょう乱波により変動するスペーサ部の差圧を測定し、以下の重要な結果を得た。すなわちスペーサ上流側は、一旦ドライアウトが発生すると液膜が再付着しにくいため、バーンアウトが発生しやすく、その反対にスペーサ内部ではドライアウトが発生しても、じょう乱波の通過により液膜が付着しやすいため、バーンアウトの発生確率は低い、などである。また時々刻々のドライアウト発生を説明するには、二相流に特有の『非定常性』を考慮する必要があること、などを明らかにした。3.供試部に2個のスペ...
  • 文部科学省：科学研究費補助金(萌芽研究)
    研究期間 : 2002年 -2002年 
    代表者 : 渡部 正夫, 松下 大介
     
    血管が存在しない軟骨組織を対象として,生体組織における組織レベルのマクロスケールなマクロな輸送現象輸送現象に関して研究を行った.軟骨組織内には血管細胞が欠如しているため,組織内の輸送現象は主に拡散・浸透によるものであると考えられる.本研究では分子量の異なる蛍光マーカーを培地に混入し,牛関節軟骨より切り出した軟骨微小組織切片を一定期間培養し,蛍光マーカーが拡散した軟骨組織の,連続凍結切片の蛍光顕微鏡像に画像処理を施し,蛍光マーカー空間分布を定量化することにより,細胞組織内への輸送現象を観察した.その結果,以下の知見を得た.1.軟骨組織内の物質輸送は,組織の幾何学的構造,生物理学的特徴の異方性により大きく影響を受ける.軟骨組織の加重方向に輸送されるマーカー量は,加重方向の直交方向に輸送されるマーカー量に卓越している.特に軟骨組織表層部よりのマーカーの浸入が顕著であることが観察された.2.分子量の異なるマーカーを用いることにより,拡散速度および拡散量に大きな違いが観察された.特に,分子量500kD程度のマーカーの場合には,組織内部への侵入がほとんど観察されなかった.3.分子量の等しいFITC-dextranとRITC-dextranをマーカーとして用い,12時間培養を行った結果,拡散様式に大きな違いが観察された.FITCは負に荷電され,RITCは中性であることが,電気泳動を用いて確...
  • 文部科学省：科学研究費補助金(基盤研究(B))
    研究期間 : 2001年 -2002年 
    代表者 : 深野 徹, 宮原 雅晴, 渡部 正夫
     
    現在ノート型パソコンの小型化・高性能化は著しく、それに伴ってMPU(超小型中央処理装置)は益々集積度が上がり、近未来においてはMPUからの発熱量が現在の30Wの2〜3倍に達すると考えられ、この業界の発展の速度から、このことを視野においた展開が必要である。最近の検討ではMPUから発生する熱は一旦ヒートパイプで拡散させ得ると見られるが、パソコン函体内部に蓄積していく熱の処理は、結局ファンで外部へ放出する方式が最も安価であろうという結論に至った。ディスプレイが15〜17インチサイズの机上用ノート型パソコンにはスペースにいくぶん余裕があることから、この方式がとれるがその最大の問題は低騒音化である。本研究では、そのような要求を満たすターボ型ファンの開発を目的とした。予備実験により、発生騒音が現在市販されているシステムでは騒音が超低レベルであること、ならびにファンの圧力上昇および軸トルクなど空力特性値がきわめて小さいことなど、騒音と空力の両特性のいずれの測定にも問題が生じること、測定の規定があいまいであること、などの問題が明らかになった。この対策を講じる中でメーカおよび本研究者らが中心となって、本研究で対象とする程度のファンの騒音・空力の測定に関する規定作成委員会が設立され鋭意検討されている。一方本研究で用いた供試ファンでの空力性能については軸流タイプ、遠心タイプ、横流ファンタイプは超小...
  • 文部科学省：科学研究費補助金(奨励研究(A))
    研究期間 : 2000年 -2001年 
    代表者 : 渡部 正夫
     
    気泡運動を利用したマイクロポンプの作動原理を理解するためには,気泡運動により誘起される周囲流体挙動を解析することが必要である.特に,今年度は気泡運動が比較的単純な場合についてのみ検討することにより,基礎的データを取得することを目的とした.そのため,モノポールとダイポールがそれぞれ支配的な流れ場について考察を行なった.気泡運動として径方向運動(モノポール)が支配的な流れ場に関しては,より複雑な流れ場を形成し得る気泡群の挙動により誘起される周囲流体,特に形成される圧力場に関して考察した.多数の気泡が液体中のある領域内に高い密度で存在する気泡群の場の圧力の変動に対する挙動を,多重極展開法・摂動展開法に基づく数学モデルを構築し数値計算を行なった.気泡群の線形圧力応答を解析することにより,少数の気泡が存在すれば,連続体モデルにより予測される音響特性を生じることが確認された.また,離散モデルを用いて,気泡群周囲圧力を急激に上昇させることにより気泡群内の気泡を収縮させる,キャビテーション気泡群崩壊の単純モデルを提案した.並進運動(ダイポール)が支配的な流れ場を解析するためには,最も単純な場合であると考えられる同一直線上を上昇する気泡による流れ場解析を有限要素法による数値シミュレーションにより行なった.DSD/ST(deforming-spatial-domain/space-time)有限...
  • 文部科学省：科学研究費補助金(基盤研究(B))
    研究期間 : 2000年 -2001年 
    代表者 : 深野 徹, 渡部 正夫
     
    狭い環状流路内沸騰二相流中に設置した流動障害物近傍の発熱管表面温度変動特性とその流動様相とを同時計測した。供試管の熱流束、質量速度、入口クオリテイがそれぞれ独立に急変する場合の過渡変動が流動障害物近傍の壁温変動に与える影響ならびに供試管上流側にエルボ部を有する場合における不安定流動の影響について詳細に調査した結果、次の結論を得た。(1)熱流束急増および流量急減の過渡変化の場合、過渡変化の影響は小さく、変化後の条件が定常BTとほぼ同じ条件の場合にのみBTが発生する。また低流量の場合(j_L=0.1m/s)、BTの開始がスペーサ下部か内部にかかわらず発生するが、スペーサ下流ではBTは発生しない。(2)熱流束急減による過渡変化ではその変動幅によってドライパッチがスペーサ内部およびその上流側にまで及び、温度上昇幅は20K〜30Kに及ぶ。(3)供試管入口クオリテイを急増させる場合には安定に遷移するが、逆に急減させる場合には擾乱波の通過頻度が急減後に少なくなり、スペーサ近傍でBTが発生する。(4)過渡変化により流動様相が変化しても、流速が速くなりせん断力が増す方向に変化する場合には比較的安定に遷移するが、反対に速度が低下する方向に変わる場合には、定常BT条件以下でもBTが発生することが有り、注意が必要である。(5)本実験のように、供試管上流側にエルボ部を有する場合にはそのエルボ部のクオリ...
  • MRアンギオグラフィーにおける血流流れ場シミュレーションと血管セグメンテーションとのレベルセット法による統合
    研究期間 : 2001年
  • 文部科学省：科学研究費補助金(基盤研究(B))
    研究期間 : 1998年 -1999年 
    代表者 : 深野 徹, 渡部 正夫
     
    BWR型原子炉燃料棒支持用スペーサを模擬した円筒型の障害物を環状流路内に設置し、その近傍の加熱された内管表面上でのドライパッチ生成の状況を高速度ビデオを用いて詳細に観察し、同時にスペーサ近傍の加熱表面温度の時間的変動を管軸方向に異なる6断面で計測した。本年度は特に熱流束q、入口クオリテイxが急変する場合の過渡的温度変動挙動をバーンアウト発生に関連して調査し、以下の結論を得た。(1)加熱壁面上の大振幅の温度変動は、液膜の薄層化による熱伝達の向上に伴う温度の急低下と、それに引き続く液膜のドライアウトによる伝熱劣化による温度の急上昇に因る。(2)加熱部ヘサブクール水が流入する場合には、ドライアウト発生に因る温度変動はみかけの蒸気速度j_Gが15〜20m/sで増大し、最大5°Kに達する。j_G>20m/sでは熱流束の増加にもかかわらず減少する。これは環状流が発達し平均的な流れになるからである。ドライアウト発生は、前者の条件下ではドレーニジによるもの、後者では基底液膜の蒸発によるものが支配的である。(3)加熱部入り口でボイドを持っている場合には、低液流量(j_L=0.1m/s)で入口の流動様式がスラグ流であると、その圧縮性によって系全体の流れが不安定になり、ドライアウト発生時の最高温度はスペーサ上流側で140℃に達することがある。以上をqとxとでまとめたドライパッチ発生領域の線図を得た...
  • 文部科学省：科学研究費補助金(奨励研究(A))
    研究期間 : 1997年 -1998年 
    代表者 : 渡部 正夫
     
    多数の気泡を含んだ液体(気泡群)の流体力学的挙動をモデル化するために気泡相互作用・気泡変形を考慮に入れたマクロモデルの基礎となる,ミクロ要素モデルを構築することを目的とした.今年度は特に静止流体中を上昇する気泡および気泡列の挙動および周囲液体へ及ぼす影響を解明するための,基礎実験および数値解析を行った.実験においては,気泡周りの流れ場を計測するために,様々なトレーサと光源を用いることにより得られた二次元流体画像に対して,昨年度購入したグラフィックワークステーション上で開発されたPIV法による流れ場計測用処理プログラムを用いて,静止流体中における単一上昇気泡および上昇気泡列まわりの流れ場に適用した.ステレオ画像を用いることにより気泡後流の発達過程と気泡の上昇過程との相互作用を観察し,気泡変形および放出渦の相互干渉に関して知見を得た.数値計算によるアプローチにおいては,DSD/ST有限要素法を用いることにより,気泡を含む軸対称二次元流れ場を解析するための計算コードを解析し,気泡形状の変形および境界の影響に関してして調査を行った.特に可視化実験の比較対照モデルとなる2気泡の運動に関して詳細な検討を行い,同一直線上を上昇する二気泡の運動に関して数値シミュレーションを行い,気泡変形が気泡相互作用に及ぼす影響を様々な表面張力係数を用いることにより解析を行い,また,界面活性剤の影響を計算コ...
  • 文部科学省：科学研究費補助金(一般研究(B), 基盤研究(B))
    研究期間 : 1995年 -1996年 
    代表者 : 深野 徹, 大田 治彦, 後藤 昭和, 渡部 正夫
     
    本年度は、BWR燃料棒支持用スペ-サのうちの代表的なものであるRing Type SpaserとGrid Type Spacerとを環状流路内に設置して、そのスペ-サ周辺の熱・流動現象、すなわち加熱された管表面上でのドライアウト生成の状況を高速度カメラを用いて詳細に観察する一方、スペ-サ近傍における管壁面温度を測定し、上記二つのスペ-サを実用化するための問題点について検討して、以下の結論を得た。(1)Grid Type Spacerではスペ-サと加熱壁面との間のすき間がくさび状であるため、表面張力が働き、液体が狭いすき間の方へ引っぱられてそこで停留しやすく、スペ-サ上流からの液体の供給を阻害する。一方Ring Type Spacerの場合も狭いすき間内での液体の停留現象はあるが、管周方向にすき間が一様であるため表面張力の効果は小さい。其の結果、Grid Type Spacerの方がスペ-サ直下の加熱表面での液膜の消失(ドライパッチの生成)が激しく起こる。従来からRing Type SpacerよりGrid Type Spacerの方が限界熱流束が小さくBWR燃料棒支持用スペ-サとしては不利であるという実規模の実験があったが、本研究における詳細な流動の観察によって、この理由を始めて明らかにすることができた。(2)上記の2種類のスペ-サを用いて、ドライパッチの生成が激しく起こるス...
  • 気泡群の音響特性の直接シミュレーション
  • 気泡運動の数値解析
  • Dynamic Simulation of the Acoustic Characteristics of Bubble Clouds
  • Thermo-Fluid Mechanical Study of the Thermoacoustic Devices
  • Numerical Simulation of Bubble Motions

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