Category Archives: Seminars

分科会「非平衡流体への運動学的アプローチ」（第7回）

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日時： 2022年9月9日（金）　17:30-18:30
場所： オンライン開催
講演： Spectroscopy of the asteroid Ryugu: Access to the records of our ancient Solar System
  Dr. Eri Tatsumi (Instituto de Astrofísica de Canarias, Spain)
巽 瑛理 氏 （カナリア天体物理学研究所）
要旨： Asteroids are building blocks of planets and keep the compositional information of the early Solar System. Especially the primitive asteroids, which are characterized by dark surfaces, are the key for water and organics on the Earth. My approach to constrain the composition and its evolusion on asteroids is the telescopic and remote-sensing observations. Recently the Hayabusa2 spacecraft by JAXA brought the sample materials from the primitive asteroid (162173) Ryugu. The sample return mission can connect the spectroscopic information to the compositional information directly, which gives strong constrains to our knowledge of the ancient Solar System.
In this talk, the spectroscopic results of Ryugu from the Hayabusa2 remote-sensing observations and ground-based observations will be discussed. The Hayabusa2 spacecraft equipped the multi-band Optical Navigation Camera (ONC) which mapped the whole surface of Ryugu up to 5 cm/pix in visible wavelengths. Using the images obtained by ONC, we could extract the evolutional history of Ryugu such as the parent body history, the impact history, and the recent trajectry changes. Besides, it is important to put the asteroid in the context of the Solar System. To do this, we investigated the distribution of the asteroids which have the similar spectral feature to Ryugu. Especially the UV region is useful to characterize hydrated minerals on asteroids. We found the very peculiar distribution of the asteroid with the spectral feature similar to Ryugu. Connecting the spectra to the material information which will be brought from the Ryugu sample analyses will make a new compositional map of the Solar System.

分科会「非平衡流体への運動学的アプローチ」（第6回）

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日時： 2021年10月25日（月）　16:45-17:45
場所： オンライン開催
講演： New lattice Boltzmann model for simulating compressible flows
  Prof. Takeshi Kataoka (Department of Mechanical Engineering, Kobe University, Japan)
片岡 武 准教授 （神戸大学大学院 工学研究科 機械工学専攻）
要旨： We have developed a new type of simple lattice Boltzmann (LB) model for the compressible Euler and NS equations based on the kinetic-equation approach proposed by Sone in 2002. The model uses the kinetic equation of the free-molecular type in the streaming process, and modifies the distribution function to its Chapman-Enskog type in the collision process. Compared with the conventional LB models which solve the kinetic equation of the BGK type, the proposed model is superior in the following two points: (i) any flow parameters, including the specific-heat ratio and three transport coefficients, can be chosen freely according to our convenience; (ii) there are no inherent errors associated with the Knudsen number. Numerical tests and error estimates confirm these merits.

分科会「非平衡流体への運動学的アプローチ」（第5回）

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日時： 2021年8月11日（水）　16:30-17:30
場所： オンライン開催
講演： Mathematical analysis of Chorin’s projection method
  Prof. Kohei Soga (Department of Mathematics, Faculty of Science and Technology, Keio University, Japan)
曽我 幸平 准教授 （慶應義塾大学 理工学研究科 基礎理工学専攻）
要旨： Chorin’s projection method, originally introduced by Alexandre Joel Chorin in 1969, is a numerical technique of computational fluid dynamics. The method can be seen as the most elementary and direct approach to solve the incompressible Navier-Stokes equations in a general setting. Nowadays, many versions of the original method are known. In this talk, we revisit Chorin’s original projection method and discuss its potential to be a mathematical tool beyond a computational technique for smooth solutions. We first observe that the method yields a Leray-Hopf weak solution. Then, we apply the method to investigate time-periodic solutions, which is an attempt to capture qualitative features of flows through discrete approximation. Finally, we investigate the accuracy of the method.

分科会「非平衡流体への運動学的アプローチ」（第4回）

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日時： 2021年8月10日（火）15:00-16:00
場所：オンライン開催
講演：物理ゲルの構造、弾性、振動特性：分子動力学シミュレーションを用いた研究
Prof. Hideyuki Mizuno (Graduate School of Arts and Sciences, The University of Tokyo, Japan)
水野　英如　助教　（東京大学 大学院総合文化研究科 広域科学専攻）

分科会「非平衡流体への運動学的アプローチ」（第3回）

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日時： 2020年12月16日（水）　16:15-17:15
場所： オンライン開催
講演： Recent Developments of Nonequilibrium Thermodynamic Theories of Gases
Prof. Takashi Arima (Department of Engineering for Innovation, National Institute of Technology, Tomakomai College, Japan)
有馬 隆司 准教授 （苫小牧工業高等専門学校 創造工学科 総合自然科学系）
要旨： Nonequilibrium thermodynamic theories of continuous media of which applicable range goes beyond the local thermodynamic equilibrium have been developed. Starting from the pioneering works of Grad in the context of kinetic theory, of Cattaneo for a rigid heat conductor, and of Müller for the first phenomenological version of extended thermodynamics, several attempts have been made, for example, Rational Extended Thermodynamics, Extended Irreversible Thermodynamics, General Equation for the Nonequilibrium Reversible–Irreversible Coupling, the regularized moment approach, and others. In this talk, we present the state of the art on these modern nonequilibrium theories focusing on Rational Extended Thermodynamics. In particular, we consider rarefied gases and discuss the linkage with the kinetic theory. Conceptual discussions of the differences among these nonequilibrium theories are also summarized.

分科会「非平衡流体への運動学的アプローチ」（第2回）

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日時： 2020年11月27日（金）　16:15-17:15
場所： オンライン開催
講演： Some formulations of the volume force in the immersed boundary method and a new approach in combination with the lattice Boltzmann method
Prof. Kosuke Suzuki (Institute of Engineering, Academic Assembly, Shinshu University, Japan)
鈴木 康祐 准教授 （信州大学 学術研究院 (工学系) ）
要旨： One of the important issues in computational fluid dynamics is to simulate moving-boundary flows efficiently. The immersed boundary method (IBM), which was proposed by Peskin in 1970s in order to simulate blood flows in the heart, has been reconsidered as an efficient method for simulating moving-boundary flows on a fixed Cartesian grid. In the IBM, it is assumed that the boundary is regarded as an infinitely thin shell, an incompressible viscous fluid fills in both inside and outside of the boundary, and the no-slip condition on the boundary is satisfied by volume force applied only near the boundary. The way to determine the volume force is the key concept of the IBM. In this talk, I introduce some formulations of the volume force in the IBM. Then, I present a new approach in combination with the lattice Boltzmann method (LBM). In this approach, the volume force of the IBM is regarded as the discontinuity of the stress tensor, and the stress tensor is calculated from the desired particle distribution functions of the LBM. This approach enables us to calculate the stress tensor on the boundary which is blurred by the volume force.

分科会「非平衡流体への運動学的アプローチ」（第1回）

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日時： 2020年7月22日（水）　15:00-16:00
場所： オンライン開催
講演： Mathematical Analysis of Moving Boundary Problems in the Kinetic Theory of Gases （分子気体力学における移動境界問題の数学解析）
Dr. Kai Koike (Department of Aeronautics and Astronautics, Graduate School of Engineering, Kyoto University, Japan)
小池 開 氏 （日本学術振興会 特別研究員(PD)）
要旨： Moving boundary problems for kinetic equations have become an active area of research mainly due to its importance in MEMS applications. It has also proved to be a source of interesting mathematical problems. Despite this, it’s mathematical theory has not developed to a satisfactory level although there are some recent progresses. In this talk, I would like to review these results hoping to stir interaction between the engeneering and the mathematical community further, which has always been an important element in this field.

分科会「運動論方程式，流体力学とその周辺」（第11回）

日時： 2019年12月19日（木）16:15-17:15
場所： 京都大学 桂キャンパスCクラスタ総合研究棟III（C3棟）3階　b3n03室（航空宇宙工学専攻会議室）
講演： Solid-state physics of glasses
Hideyuki Mizuno, PhD (Graduate School of Arts and Sciences, The University of Tokyo, Japan)
水野　英如　助教　（東京大学 大学院総合文化研究科 広域科学専攻）
要旨： In our lives, there are two types of solid-states materials. One is crystals, and the other is noncrystalline, glasses. We already have a good level of understanding of crystals. Their thermal and transport properties can be described in terms of phonons; their heat capacity and thermal conductivity are well described by the Debye theory and the phonon-gas theory, respectively. By contrast, we have only a limited understanding of glasses that exhibit fundamentally different properties from those of crystals. Because glasses are materials commonly encountered in our daily lives and are widely employed in modern technologies (examples include silicate glasses, metallic glasses, plastic materials, ceramics, and many other rigid, disordered materials), their understanding is crucial not only in physics and materials science but also in engineering. In this seminar, I would introduce the latest progress in understanding of glasses.

分科会「運動論方程式，流体力学とその周辺」（第10回）

普段とは違い，場所は吉田キャンパスです．ご注意ください．

日時： 2019年11月1日（金）16:30-17:30
場所： 京都大学 吉田キャンパス 工学部総合校舎 111講義室
講演： On the homogenization problem for the linear Boltzmann equation
Prof. Francesco Salvarani (Léonard de Vinci School of Engineers, France & Dipartimento di Matematica, Università di Pavia, Italy)
要旨： In this talk, we study the homogenization problem for the linear Boltzmann equation when the optical parameters are highly heterogeneous in the energy variable. We employ the method of two-scale convergence to arrive at the homogenization result. In doing so, we show the induction of a memory effect in the homogenization limit and we discuss its link with the self-shielding effect in nuclear reactor physics. The results presented here have been obtained in collaboration with Harsha Hutridurga and Olga Mula.

分科会「運動論方程式，流体力学とその周辺」（第9回）

日時： 2019年7月23日（火）16:15-17:15
場所： 京都大学 桂キャンパスCクラスタ総合研究棟III（C3棟）3階　b3n03室（航空宇宙工学専攻会議室）
講演： Compressible fluid approximation for rarefied gases in bounded domains
Prof. Renjun Duan (Department of Mathematics, The Chinese University of Hong Kong, Hong Kong)
要旨： In this talk I will talk about two recent results on the mathematical justification of the compressible viscous fluid approximation of solutions to the Boltzmann equation in bounded domains when the Knudsen number is small. The first result is concerned with the situation where the diffusive reflection boundary condition is considered and the fluid equations are solved under the non-slip boundary conditions. The second result is focused on a specific case of the one-dimensional heat transfer for a steady rarefied gas flow between two parallel plates with diffusive reflection boundaries of different temperatures where the temperature difference is small but does not depend on the Knudsen number, and we show the existence of steady solutions by taking the approximation of fluid equations with slip boundaries together with the Knudsen layer equations.