谷口 隆晴 | ![]() |
ヤグチ タカハル | |
大学院システム情報学研究科 計算科学専攻 | |
准教授 | |
工学その他 |
2021年08月 日本応用数理学会, 日本応用数理学会論文賞 理論部門, 波動方程式と弾性方程式からなる連成系のシンプレクティック性について
2017年09月 日本応用数理学会, 日本応用数理学会論文賞(理論部門), ハミルトン方程式に対する離散勾配法のRiemann構造不変性
学会誌・学術雑誌による顕彰
2016年06月 日本応用数理学会, 日本応用数理学会研究部会連合発表会優秀講演賞, 第12回日本応用数理学会研究部会連合発表会における講演「自動離散微分とその応用」
国内学会・会議・シンポジウム等の賞
2014年09月 日本応用数理学会, 日本応用数理学会論文賞(理論部門), コンパクト差分に基づく離散変分導関数法
2012年08月 日本応用数理学会, 日本応用数理学会若手優秀講演賞, ホロノミック系に対するラグランジュ力学的離散勾配法
2011年07月 SciCADE 2011 (the International Conference on Scientific Computation And Differential Equations 2011), SciCADE 2011 New Talent Award, A Lagrangian Approach to Deriving Energy-Preserving Numerical Schemes for the Euler-Lagrange Partial Differential Equations and Its Applications
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In a secret communication system using chaotic synchronization, the communication information is embedded in a signal that behaves as chaos and is sent to the receiver to retrieve the information. In a previous study, a chaotic synchronous system was developed by integrating the wave equation with the van der Pol boundary condition, of which the number of the parameters are only three, which is not enough for security. In this study, we replace the nonlinear boundary condition with an artificial neural network, thereby making the transmitted information difficult to leak. The neural network is divided into two parts; the first half is used as the left boundary condition of the wave equation and the second half is used as that on the right boundary, thus replacing the original nonlinear boundary condition. We also show the results for both monochrome and color images and evaluate the security performance. In particular, it is shown that the encrypted images are almost identical regardless of the input images. The learning performance of the neural network is also investigated. The calculated Lyapunov exponent shows that the learned neural network causes some chaotic vibration effect. The information in the original image is completely invisible when viewed through the image obtained after being concealed by the proposed system. Some security tests are also performed. The proposed method is designed in such a way that the transmitted images are encrypted into almost identical images of waves, thereby preventing the retrieval of information from the original image. The numerical results show that the encrypted images are certainly almost identical, which supports the security of the proposed method. Some security tests are also performed. The proposed method is designed in such a way that the transmitted images are encrypted into almost identical images of waves, thereby preventing the retrieval of information from the original image. The numerical results show that the encrypted images are certainly almost identical, which supports the security of the proposed method.
MDPI AG, 2021年07月16日, Entropy, 23 (7), 904 - 904, 英語[査読有り]
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Recently, soft robots that consist of soft and deformable materials have received much attention for their adaptability to uncertain environments. Although these robots are difficult to control with a conventional control theory owing to their complex body dynamics, research from different perspectives attempts to actively exploit these body dynamics as an asset rather than a drawback. This approach is called morphological computation, in which the soft materials are used for computation that includes a new kind of control strategy. In this article, we propose a novel approach to analyze the computational properties of soft materials based on an algebraic method, called the input–output equation used in systems analysis, particularly in systems biology. We mainly focus on the two scenarios relevant to soft robotics, that is, analysis of the computational capabilities of soft materials and design of the input force to soft devices to generate the target behaviors. The input–output equation directly describes the relationship between inputs and outputs of a system, and hence by using this equation, important properties, such as the echo state property that guarantees reproducible responses against the same input stream, can be investigated for soft structures. Several application scenarios of our proposed method are demonstrated using typical soft robotic settings in detail, including linear/nonlinear models and hydrogels driven by chemical reactions.
SAGE Publications, 2020年03月20日, The International Journal of Robotics Research, 40 (1), 027836492091229 - 027836492091229, 英語[査読有り]
研究論文(学術雑誌)
In this paper, we propose a method for deriving energetic-property-preserving numerical schemes for coupled systems of two given natural systems. We consider the case where the two systems are interconnected by the action–reaction law. Although the derived schemes are based on the discrete gradient method, in the case under consideration, the equation of motion is not of the usual form represented by using the skew-symmetric matrix. Hence, the energetic-property-preserving schemes cannot be obtained by straightforwardly using the discrete gradient method. We show numerical results for two coupled systems as examples; the first system is a combination of the wave equation and the elastic equation, and the second is of the mass–spring system and the elastic equation.
MDPI AG, 2020年02月14日, Mathematics, 8 (2), 249 - 249, 英語[査読有り][招待有り]
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Aim: A number of interventions have been undertaken to develop and promote social networks among community dwelling older adults. However it has been difficult to examine the effects of these interventions, because of problems in assessing interactions. The present study was designed to quantitatively measure and visualize face-to-face interactions among elderly participants in an exercise program. We also examined relationships among interactional variables, personality and interest in community involvement, including interactions with the local community. Methods: Older adults living in the same community were recruited to participate in an exercise program that consisted of tour sessions. We collected data on face-to-face interactions of the participants by using a wearable sensor technology device. Results: Network analysis identified the communication networks of participants in the exercise program, as well as changes in these networks. Additionally, there were significant correlations between the number of people involved in face-to-face interactions and changes in both interest in community involvement and interactions with local community residents, as well as personality traits, including agreeableness. Conclusions: Social networks in the community are essential for solving problems caused by the aging society. We showed the possible applications of face-to-face interactional data for identifying core participants having many interactions, and isolated participants having only a few interactions within the community. Such data would be useful for carrying out efficient interventions for increasing participants' involvement with their community.
WILEY, 2017年10月, GERIATRICS & GERONTOLOGY INTERNATIONAL, 17 (10), 1752 - 1758, 英語[査読有り]
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In this contribution, we propose a new framework to derive energy-preserving numerical schemes based on the variational principle for Hamiltonian mechanics. We focus on Noether's theorem, which shows that the symmetry with respect to time translation gives the energy conservation law. By reproducing the calculation of the proof of Noether's theorem after discretization using the summation by parts and the discrete gradient, we obtain the scheme and the corresponding discrete energy at the same time. The significant property of efficiency is that the appropriate choice of the discrete gradient makes our schemes explicit if the Hamiltonian is separable.
一般社団法人 日本応用数理学会, 2016年09月, JSIAM Letters, 8, 53 - 56, 英語[査読有り]
研究論文(学術雑誌)
研究論文(研究会,シンポジウム資料等)
We consider invariance of schemes derived by using the discrete gradient method for the Webster equation under change of Riemannian structures. In our previous research we expected that Furihata's discrete gradient method for the Webster equation has invariance under change of Riemannian structures. In this paper we prove this conjecture.
AMER INST PHYSICS, 2015年, PROCEEDINGS OF THE INTERNATIONAL CONFERENCE OF NUMERICAL ANALYSIS AND APPLIED MATHEMATICS 2014 (ICNAAM-2014), 1648, 英語[査読有り]
研究論文(国際会議プロシーディングス)
As it is widely accepted, for differential equations that reflect some physical properties it is preferable to use numerical schemes that inherit these properties. Many of such schemes are designed for Hamiltonian equations and are derived by using the Hamiltonian structures of the equations. In this paper, we formulate Hamiltonian structures for a class of wave-type equations that are compatible with the finite element exterior calculus. The finite element exterior calculus is a unified approach to designing finite element schemes for discretizing the scalar Laplacian and the vector Laplacian. In this theory, the stability result is obtained by using the Hodge theory and the Poincare inequality. We provide Hamiltonian structures for the wave-type equations for which the schemes derived with the help of the finite element exterior calculus can be employed and thereby make combinations of structure-preserving methods and the finite element exterior calculus possible.
AMER INST PHYSICS, 2015年, PROCEEDINGS OF THE INTERNATIONAL CONFERENCE OF NUMERICAL ANALYSIS AND APPLIED MATHEMATICS 2014 (ICNAAM-2014), 1648, 英語[査読有り]
研究論文(国際会議プロシーディングス)
We consider application of the discrete gradient method for the Webster equation, which models sound waves in tubes. Typically Hamilton equations are described by the use of gradients of the Hamiltonian and it is indispensable to introduce an inner product to define a gradient. We first apply the discrete gradient method to design an energy-preserving method by using a weighted inner product. Comparing with another scheme that is derived by a standard inner product, we show that the discrete gradient method has a geometric invariance, which implies that the method reflects the symplectic geometric aspect of mechanics.
The Japan Society for Industrial and Applied Mathematics, 2015年01月, JSIAM Letters, 7, 17 - 20, 英語[査読有り]
研究論文(学術雑誌)
We propose a Lagrangian approach to deriving energy-preserving finite difference schemes for the Euler-Lagrange partial differential equations. Noether's theorem states that the symmetry of time translation of Lagrangians yields the energy conservation law. We introduce a unique viewpoint on this theorem: "the symmetry of time translation of Lagrangians derives the Euler-Lagrange equation and the energy conservation law, simultaneously." The proposed method is a combination of a discrete counter part of this statement and the discrete gradient method. It is also shown that the symmetry of space translation derives momentum-preserving schemes. Finally, we discuss the existence of discrete local conservation laws.
EDP SCIENCES S A, 2013年09月, ESAIM-MATHEMATICAL MODELLING AND NUMERICAL ANALYSIS-MODELISATION MATHEMATIQUE ET ANALYSE NUMERIQUE, 47 (5), 1493 - 1513, 英語[査読有り]
研究論文(学術雑誌)
ソリトン方程式のように保存量を持つ偏微分方程式に対しては,それらを保つ「構造保存数値解法」が適している.一方数値流体の分野では,波動現象の記述に適した「コンパクト差分法」がよく用いられる.本論文では,構造保存数値解法の一種である「離散変分導関数法」において両手法を組み合わせられること,すなわちコンパクト差分に基づく離散変分導関数法を構成できることを述べ,数値例によりその有効性を示す.
一般社団法人 日本応用数理学会, 2013年06月, 日本応用数理学会論文誌, 23 (2), 203 - 232, 日本語[査読有り]
研究論文(学術雑誌)
本論文ではEuler-Lagrange偏微分方程式に対し,局所的エネルギー保存則を保つ有限差分スキーム導出法を提案する.この保存則はLagrangianの局所的時間対称性から導出されるが,本論文では,この対称性からEuler-Lagrange方程式自体も導出できることに着目し,これと離散勾配法を組み合わせる.応用として,線形波動方程式に対する無反射境界条件の離散化法についても論じる.
一般社団法人 日本応用数理学会, 2012年09月, 日本応用数理学会論文誌, 22 (3), 143 - 169, 日本語[査読有り]
研究論文(学術雑誌)
As is well known, for PDEs that enjoy a conservation or dissipation property, numerical schemes that inherit this property are often advantageous in that the schemes are fairly stable and give qualitatively better numerical solutions in practice. Lately, Furihata and Matsuo have developed the so-called "discrete variational derivative method'' that automatically constructs energy preserving or dissipative finite difference schemes. Although this method was originally developed on uniform meshes, the use of non-uniform meshes is of importance for multi-dimensional problems. On the other hand, the theories of discrete differential forms have received much attention recently. These theories provide a discrete analogue of the vector calculus on general meshes. In this paper, we show that the discrete variational derivative method and the discrete differential forms by Bochev and Hyman can be combined. Applications to the Cahn-Hilliard equation and the Klein-Gordon equation on triangular meshes are provided as demonstrations. We also show that the schemes for these equations are H-1-stable under some assumptions. In particular, one for the nonlinear Klein-Gordon equation is obtained by combination of the energy conservation property and the discrete Poincare inequality, which are the temporal and spacial structures that are preserved by the above methods. (C) 2012 Elsevier Inc. All rights reserved.
ACADEMIC PRESS INC ELSEVIER SCIENCE, 2012年05月, JOURNAL OF COMPUTATIONAL PHYSICS, 231 (10), 3963 - 3986, 英語[査読有り]
研究論文(学術雑誌)
We consider structure preserving numerical schemes for the Ostrovsky equation, which describes gravity waves under the influence of Coriolis force. This equation has two associated invariants: an energy function and the L-2 norm. It is widely accepted that structure preserving methods such as invariants-preserving and multi-symplectic integrators generally yield qualitatively better numerical results. In this paper we propose five geometric integrators for this equation: energy-preserving and norm-preserving finite difference and Galerkin schemes, and a multi-symplectic integrator based on a newly found multi-symplectic formulation. A numerical comparison of these schemes is provided, which indicates that the energy-preserving finite difference schemes are more advantageous than the other schemes. (C) 2012 Elsevier Inc. All rights reserved.
ACADEMIC PRESS INC ELSEVIER SCIENCE, 2012年05月, JOURNAL OF COMPUTATIONAL PHYSICS, 231 (14), 4542 - 4559, 英語[査読有り]
研究論文(学術雑誌)
We propose a new structure-preserving integrator for the Korteweg-de Vries (KdV) equation. In this integrator, two independent structure-preserving techniques are newly combined; the "discrete variational derivative method" for constructing invariants-preserving integrator, and the "compact finite difference method" which is widely used in the area of numerical fluid dynamics for resolving wave propagation phenomena. Numerical experiments show that the new integrator is in fact advantageous than the existing integrators.
The Japan Society for Industrial and Applied Mathematics, 2012年03月, JSIAM Letters, vol. 4, 5-8., 5 - 8, 英語[査読有り]
研究論文(学術雑誌)
We consider systems of ordinary differential equations with known first integrals. The notion of a discrete tangent space is introduced as the orthogonal complement of an arbitrary set of discrete gradients. Integrators which exactly conserve all the first integrals simultaneously are then defined. In both cases we start from an arbitrary method of a prescribed order (say, a Runge-Kutta scheme) and modify it using two approaches: one is based on projection and the other on local coordinates. The methods are tested on the Kepler problem.
IOP PUBLISHING LTD, 2011年07月, JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL, 44 (30), 英語[査読有り]
研究論文(学術雑誌)
We consider structure-preserving integration of the Ostrovsky equation, which for example models gravity waves under the influence of Coriolis force. We find a multi-symplectic formulation, and derive a finite difference discretization based on the formulation and by means of the Preissman box scheme. We also present a numerical example, which shows the effectiveness of this scheme.
The Japan Society for Industrial and Applied Mathematics, 2011年06月, JSIAM Letters, vol. 3, 41-44., 41 - 44, 英語[査読有り]
研究論文(学術雑誌)
In this paper, we consider a random field, which is a generalization of Voronoi diagrams to probabilistic metric spaces. This random field is defined at each point of the space as a random variable that represents the nearest generator. As an application, relation to the post office problem for fuzzy point sets that was posed by Aurenhammer-Stockl-Welzl is investigated. This problem is also considered on digital pictures and an efficient numerical method to compute the probabilities is provided. The proposed method gives the probabilities of the random field in O (M-2 + MN) time, where M is the number of pixels in the input pictures and N is the number of generators, while a straightforward calculation takes O ((MN2)-N-3) time.
KINOKUNIYA CO LTD, 2010年12月, JAPAN JOURNAL OF INDUSTRIAL AND APPLIED MATHEMATICS, 27 (3), 425 - 441, 英語[査読有り]
研究論文(学術雑誌)
The Ostrovsky equation describes gravity waves under the influence of Coriolis force. It is known that solutions of this equation conserve the L(2) norm and an energy function that is determined non-locally. In this paper we propose four conservative numerical schemes for this equation: a finite difference scheme and a pseudospectral scheme that conserve the norm, and the same types of schemes that conserve the energy. A numerical comparison of these schemes is also provided, which indicates that the energy conservative schemes perform better than the norm conservative schemes. (C) 2009 Elsevier B.V. All rights reserved.
ELSEVIER SCIENCE BV, 2010年06月, JOURNAL OF COMPUTATIONAL AND APPLIED MATHEMATICS, 234 (4), 1036 - 1048, 英語[査読有り]
研究論文(学術雑誌)
The discrete variational method is a method used to derive finite difference schemes that inherit the conservation/dissipation property of the original equations. Although this method has mainly been developed for uniform grids, we extend this method to multidimensional nonuniform meshes. (C) 2010 Elsevier Inc. All rights reserved.
ACADEMIC PRESS INC ELSEVIER SCIENCE, 2010年06月, JOURNAL OF COMPUTATIONAL PHYSICS, 229 (11), 4382 - 4423, 英語[査読有り]
研究論文(学術雑誌)
As is well known, for PDEs that enjoy conservation properties, numerical schemes that inherit the properties are advantageous in that the schemes give qualitatively better solutions in practice. Lately Furihata and Matsuo have developed "the discrete variational method" that automatically constructs conservative finite difference schemes on uniform meshes for a class of PDEs with certain variational structures. We extend this method to mixed meshes and derive a numerical scheme that conserves the energy and the density for the nonlinear Schrodinger equation on such meshes.
AMER INST PHYSICS, 2009年, NUMERICAL ANALYSIS AND APPLIED MATHEMATICS, VOLS 1 AND 2, 1168, 892 - 895, 英語[査読有り]
研究論文(国際会議プロシーディングス)
離散変分法は,解が保存・散逸的性質を持つ偏微分方程式に対し,元の方程式と同様に数値解が保存・散逸的性質を持つように差分スキームを導出するための方法である.離散変分法はこれまで等間隔格子上での利用が主であったが,本論文ではこれを多次元の非一様格子へと拡張する.
一般社団法人 日本応用数理学会, 2009年, 応用数理学会論文誌,, 19 (4), 371-431 - 431, 日本語[査読有り]
研究論文(学術雑誌)
計算機資源は有限のため,無限領域上における波動シミュレーションでは領域の打ち切りが必要となるが,このときに生じた打ち切り断面上で与える境界条件は,得られる数値解の質に大きな影響を与える,本論文では,非粘性圧縮流体の等エントロピー流れに対し,ある人工的境界条件を導出し,その境界条件のもとで解の評価を与える.さらに,得られた境界条件はよく知られたThompsonの無反射境界条件と等価であることを示す.
一般社団法人 日本応用数理学会, 2008年, 日本応用数理学会論文誌, 18 (3), 447 - 471, 日本語[招待有り]
記事・総説・解説・論説等(学術雑誌)
Nonreflecting boundary conditions for numerical simulations of waves are reviewed. We describe the idea of the classical Engquist-Majda boundary condition for linear wave equations and the Hedstrom boundary condition for quasilinear hyperbolic systems. Some comments on the theoretical aspects of the boundary treatments such as the validity of the nonreflecting boundary conditions are provided. The recent developments on this subject are also discussed.
日本シミュレーション学会, 2007年06月15日, シミュレーション, 26 (2), 84 - 89, 日本語空力学の諸問題を扱った数値シミュレーションにおいては, 広大な現実の空間に比べ計算機の中で扱うことのできる領域は高々有限であるため, 計算対象となる空間の打ち切りが必要となる.このとき, 打ち切られた断面という人工的な境界が生じてしまうが, そのような人工的な境界上で特別な取り扱いをしなければ, 現実には存在しない反射波が生成されてしまい, 現実的な解を得ることはできない.そこで, 無反射境界条件, すなわち, 人工的な境界上で反射が起こらないようにするための境界条件の設定が重要となる.無反射境界条件は既にいくつか提案されているが, 特にPoinsot-Leleの境界条件は, その頑健性と実装の容易さから現在広く利用されている手法のひとつとなっている.しかし, Poinsot-Leleの手法の基礎となったThompsonの境界条件の有効性が理論的に保証されているのは波が境界に対して垂直に入射している場合のみである.この問題点は以前から指摘され, その改善が望まれていた.本論文ではこの要望に答える.すなわち, 数値計算時のデータを利用することによって, 流れの向きに対する仮定をおかないEuler方程式に対する無反射境界条件を提案し, そのNavier-Stokes方程式への拡張法について述べる.
日本流体力学会, 2005年02月25日, ながれ : 日本流体力学会誌, 24 (1), 81 - 91, 日本語Because the computational resources are finite, one needs to truncate the computational domain when he/she simulates a physical problem. This truncation gives rise to non-physical artificial boundaries and one cannot obtain proper solutions without appropriate boundary conditions on such boundaries. Practically nonreflecting boundary conditions, which are boundary conditions that prevent the generation of reflections, are of great importance. Most popular methods for the Navier-Stokes equations right now are boundary conditions by Poinsot and Lele. However, their methods are based on Thompson's boundary condition for the Euler equations, which are essentially one-dimensional, and hence are valid only when the flow is perpendicular to the boundary. Here we propose a boundary condition for the Navier-Stokes equations which does not require the assumption for the direction of flow. Our basic idea is to estimate the direction of the flow with numerical data.
日本流体力学会, 2004年, 日本流体力学会年会講演論文集, 2004, 456 - 457, 日本語[招待有り]
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口頭発表(一般)
口頭発表(一般)
口頭発表(一般)
口頭発表(一般)
[招待有り]
口頭発表(一般)
[招待有り]
口頭発表(一般)
口頭発表(一般)
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シンポジウム・ワークショップパネル(指名)
口頭発表(一般)
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ポスター発表
口頭発表(一般)
口頭発表(一般)
口頭発表(一般)
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口頭発表(一般)
口頭発表(一般)
口頭発表(一般)
[招待有り]
口頭発表(招待・特別)
口頭発表(一般)
口頭発表(一般)
口頭発表(一般)
口頭発表(一般)
口頭発表(一般)
口頭発表(一般)
口頭発表(一般)
ポスター発表
口頭発表(一般)
口頭発表(一般)
口頭発表(一般)
口頭発表(一般)
口頭発表(一般)
口頭発表(一般)
[招待有り]
口頭発表(招待・特別)
口頭発表(一般)
[招待有り]
口頭発表(招待・特別)
口頭発表(一般)
口頭発表(一般)
[招待有り]
口頭発表(招待・特別)
口頭発表(一般)
口頭発表(一般)
口頭発表(一般)
[招待有り]
口頭発表(招待・特別)
[招待有り]
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[招待有り]
口頭発表(招待・特別)
[招待有り]
口頭発表(招待・特別)
口頭発表(一般)
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口頭発表(一般)
その他
口頭発表(一般)
口頭発表(招待・特別)
[招待有り]
口頭発表(招待・特別)
Institute of Electrical and Electronics Engineers
2020年05月 - 現在情報処理学会
2020年02月 - 現在Society for Industrial and Applied Mathematics
2017年01月 - 現在American Institute of Aeronautics and Astronautics
日本流体力学会
Mathematical Association of America
日本数学会
日本応用数理学会
競争的資金
競争的資金
競争的資金
競争的資金
本研究プロジェクトでは,構造保存型の数値解法として理工学各分野で広く応用されている有限体積法に対する数学的な基盤理論の開発とその現実問題への応用を行なった。基礎的な面では、離散ソボレフの不等式、補間誤差不等式の最良定数、離散Rellichの定理、離散最大値の定理、離散微分形式などについて応用指向の進んだ結果を得ることができた。応用面では、細胞性粘菌の数理モデルに対して、構造保存型の有限体積法を開発し、いままで未解決だった離散エネルギー不等式の証明に成功した。また、離散微分形式の応用としてLagrange力学に基づくエネルギー保存型数値解法の有限体積法への拡張を行なった。
競争的資金
圧縮流体シミュレーションで重要となる無反射境界条件について、Riemann不変量多様体に基づいた無反射境界条件を導出した。また、得られた方法は安定性に問題があったため、それを改善する修正を行ったところThompsonの無反射境界条件と呼ばれる既存の方法に一致し、その結果、Thompsonの境界条件に関する知見を得た。また、安定な実装法の開発を目指して離散変分法についての研究も行った。その結果、離散変分法をいくつかの点で拡張することに成功した。