2024/05/26 更新

写真a

テラハラ タクヤ
寺原 拓哉
所属
理工学術院 理工学術院総合研究所
職名
次席研究員(研究院講師)
 

論文

  • A computational model of red blood cells using an isogeometric formulation with T-splines and a lattice Boltzmann method

    Yusuke Asai, Shunichi Ishida, Hironori Takeda, Gakuto Nakaie, Takuya Terahara, Yasutoshi Taniguchi, Kenji Takizawa, Yohsuke Imai

    Journal of Fluids and Structures   125  2024年03月

     概要を見る

    The red blood cell (RBC) membrane is often modeled by Skalak strain energy and Helfrich bending energy functions, for which high-order representation of the membrane surface is required. We develop a numerical model of RBCs using an isogeometric discretization with T-splines. A variational formulation is applied to compute the external load on the membrane with a direct discretization of second-order parametric derivatives. For fluid–structure interaction, the isogeometric analysis is coupled with the lattice Boltzmann method via the immersed boundary method. An oblate spheroid with a reduced volume of 0.95 and zero spontaneous curvature is used for the reference configuration of RBCs. The surface shear elastic modulus is estimated to be Gs=4.0×10−6 N/m, and the bending modulus is estimated to be EB=4.5×10−19 J by numerical tests. We demonstrate that for physiological viscosity ratio, the typical motions of the RBC in shear flow are rolling and complex swinging, but simple swinging or tank-treading appears at very high shear rates. We also show that the computed apparent viscosity of the RBC channel flow is a reasonable agreement with an empirical equation. We finally show that the maximum membrane strain of RBCs for a large channel (twice of the RBC diameter) can be larger than that for a small channel (three-quarters of the RBC diameter). This is caused by a difference in the strain distribution between the slipper and parachute shapes of RBCs in the channel flows.

    DOI

    Scopus

  • Isogeometric boundary element analysis of creasing of capsule in simple shear flow

    Hironori Takeda, Yusuke Asai, Shunichi Ishida, Yasutoshi Taniguchi, Takuya Terahara, Kenji Takizawa, Yohsuke Imai

    Journal of Fluids and Structures   124  2024年01月

     概要を見る

    Wrinkling and creasing of an elastic membrane are post-buckling processes induced by in-plane compression. When a hyperelastic capsule is suspended in a simple shear flow, its membrane forms several wavy patterns. To elucidate the post-buckling behavior of a capsule in a Stokes shear flow, we investigated the effects of the shear rate and membrane thickness on capsule deformation by performing numerical analysis to capture the wrinkling and creasing of the capsule membrane. The deformation of the capsule was formulated based on the Kirchhoff–Love shell theory and the Stokes flow was calculated using the boundary integral equation. The capsule shape was represented by a T-spline surface. The isogeometric boundary element analysis showed that the capsule in the shear flow formed wrinkles and creases. Whereas wrinkling occurred at low shear rates, both wrinkling and creasing occurred at high shear rates depending on the membrane thickness. Based on the geometrical consistency of the capsule surface, we suggest that the deformation type can be determined by mechanical and geometrical effects of the membrane thickness, that is, the bending rigidity and ease of self-contact, respectively. This approach will be useful for investigating the geometrical consistency for further understanding the post-buckling behavior of capsules in Stokes flows.

    DOI

    Scopus

    2
    被引用数
    (Scopus)
  • T-splines computational membrane–cable structural mechanics with continuity and smoothness: II. Spacecraft parachutes

    Takuya Terahara, Kenji Takizawa, Reha Avsar, Tayfun E. Tezduyar

    Computational Mechanics   71 ( 4 ) 677 - 686  2023年04月

     概要を見る

    In this second part of a two-part article, we present spacecraft parachute structural mechanics computations with the T-splines computational method introduced in the first part. The method and its implementation, which was also given in the first part, are for computations where structures with different parametric dimensions are connected with continuity and smoothness. The basis functions of the method were derived in the context of connecting structures with 2D and 1D parametric dimensions. In the first part, the 2D structure was referred to as “membrane” and the 1D structure as “cable.” The method and its implementation, however, are certainly applicable also to other 2D–1D cases, and the test computations presented in the first part included shell–cable structures. Similarly, the spacecraft parachute computations presented here are with both the membrane and shell models of the parachute canopy fabric. The computer model used in the computations is for a subscale, wind-tunnel version of the Disk–Gap–Band parachute. The computations demonstrate the effectiveness of the method in 2D–1D structural mechanics computation of spacecraft parachutes.

    DOI

    Scopus

    7
    被引用数
    (Scopus)
  • T-splines computational membrane–cable structural mechanics with continuity and smoothness: I. Method and implementation

    Takuya Terahara, Kenji Takizawa, Tayfun E. Tezduyar

    Computational Mechanics   71 ( 4 ) 657 - 675  2023年04月

     概要を見る

    We present a T-splines computational method and its implementation where structures with different parametric dimensions are connected with continuity and smoothness. We derive the basis functions in the context of connecting structures with 2D and 1D parametric dimensions. Derivation of the basis functions with a desired smoothness involves proper selection of a scale factor for the knot vector of the 1D structure and results in new control-point locations. While the method description focuses on C and C1 continuity, paths to higher-order continuity are marked where needed. In presenting the method and its implementation, we refer to the 2D structure as “membrane” and the 1D structure as “cable.” It goes without saying that the method and its implementation are applicable also to other 2D–1D cases, such as shell–cable and shell–beam structures. We present test computations not only for membrane–cable structures but also for shell–cable structures. The computations demonstrate how the method performs.

    DOI

    Scopus

    9
    被引用数
    (Scopus)
  • Computational flow analysis with boundary layer and contact representation: II. Heart valve flow with leaflet contact

    Takuya Terahara, Takashi Kuraishi, Kenji Takizawa, Tayfun E. Tezduyar

    Journal of Mechanics   38   185 - 194  2022年

     概要を見る

    In this second part of a two-part article, we provide an overview of the heart valve flow analyses conducted with boundary layer and contact representation, made possible with the space-time (ST) computational methods described in the first part. With these ST methods, we are able to represent the boundary layers near moving solid surfaces, including the valve leaflet surfaces, with the accuracy one gets from moving-mesh methods and without the need for leaving a mesh protection gap between the surfaces coming into contact. The challenge of representing the contact between the leaflets without giving up on high-resolution flow representation near the leaflet surfaces has been overcome. The other challenges that have been overcome include the complexities of a near-actual valve geometry, having in the computational model a left ventricle with an anatomically realistic motion and an aorta from CT scans and maintaining the flow stability at the inflow of the ventricle-valve-aorta sequence, where we have a traction boundary condition during part of the cardiac cycle.

    DOI

    Scopus

    26
    被引用数
    (Scopus)
  • Computational flow analysis with boundary layer and contact representation: I. Tire aerodynamics with road contact

    Takashi Kuraishi, Takuya Terahara, Kenji Takizawa, Tayfun E. Tezduyar

    Journal of Mechanics   38   77 - 87  2022年

     概要を見る

    In computational flow analysis with moving solid surfaces and contact between the solid surfaces, it is a challenge to represent the boundary layers with an accuracy attributed to moving-mesh methods and to represent the contact without leaving a mesh protection gap. The space-time topology change (ST-TC) method, introduced in 2013, makes moving-mesh computation possible even when we have contact between moving solid surfaces or other kinds of flow-domain TC. The contact is represented without giving up on high-resolution flow representation near the moving surfaces. With the ST-TC and other ST computational methods introduced before and after, it has been possible to address many of the challenges encountered in conducting this class of flow analysis in the presence of additional complexities such as geometric complexity, rotation or deformation of the solid surfaces and the multiscale nature of the flow. In this first part of a two-part article, we provide an overview of the methods that made all that possible. We also provide an overview of the computations performed for tire aerodynamics with challenges that include the complexity of a near-actual tire geometry with grooves, road contact, tire deformation and rotation, road roughness and fluid films.

    DOI

    Scopus

    22
    被引用数
    (Scopus)
  • Space-Time Flow Computation with Contact Between the Moving Solid Surfaces

    Kenji Takizawa, Takuya Terahara, Tayfun E. Tezduyar

    Current Trends and Open Problems in Computational Mechanics     517 - 525  2022年01月

     概要を見る

    In computation of flow problems with moving boundaries and interfaces, including fluid-structure interaction, moving the fluid mechanics mesh to follow the fluid-solid interface enables mesh-resolution control near the interface. Therefore moving-mesh methods, such as the Space-Time Variational Multiscale (ST-VMS) method, enable high-resolution boundary-layer representation near fluid-solid interfaces and thus higher accuracy in such critical flow regions. In flow problems with contact between solid surfaces, until recently, one had to either give up on representing the actual contact and leave a small gap or give up on using a moving-mesh method and thus give up on having high-fidelity flow solution near the solid surfaces. The ST Topology Change (ST-TC) method changed all that. Now we can both represent the actual contact and have high-fidelity flow solution near the solid surfaces. With the ST-VMS, which serves as the core method, and the ST-TC and two other special methods, the ST Slip Interface method and ST Isogeometric Analysis, we have created a powerful computational framework. The new framework is enabling high-fidelity computational flow analysis of some of the most complex problems, such as the ventricle-valve-aorta sequence. This chapter is a description and demonstration of that framework.

    DOI

    Scopus

    13
    被引用数
    (Scopus)
  • Ventricle-valve-aorta flow analysis with the Space–Time Isogeometric Discretization and Topology Change

    Takuya Terahara, Kenji Takizawa, Tayfun E. Tezduyar, Atsushi Tsushima, Kensuke Shiozaki

    Computational Mechanics   65 ( 5 ) 1343 - 1363  2020年05月

     概要を見る

    We address the computational challenges of and presents results from ventricle-valve-aorta flow analysis. Including the left ventricle (LV) in the model makes the flow into the valve, and consequently the flow into the aorta, anatomically more realistic. The challenges include accurate representation of the boundary layers near moving solid surfaces even when the valve leaflets come into contact, computation with high geometric complexity, anatomically realistic representation of the LV motion, and flow stability at the inflow boundary, which has a traction condition. The challenges are mainly addressed with a Space–Time (ST) method that integrates three special ST methods around the core, ST Variational Multiscale (ST-VMS) method. The three special methods are the ST Slip Interface (ST-SI) and ST Topology Change (ST-TC) methods and ST Isogeometric Analysis (ST-IGA). The ST-discretization feature of the integrated method, ST-SI-TC-IGA, provides higher-order accuracy compared to standard discretization methods. The VMS feature addresses the computational challenges associated with the multiscale nature of the unsteady flow in the LV, valve and aorta. The moving-mesh feature of the ST framework enables high-resolution computation near the leaflets. The ST-TC enables moving-mesh computation even with the TC created by the contact between the leaflets, dealing with the contact while maintaining high-resolution representation near the leaflets. The ST-IGA provides smoother representation of the LV, valve and aorta surfaces and increased accuracy in the flow solution. The ST-SI connects the separately generated LV, valve and aorta NURBS meshes, enabling easier mesh generation, connects the mesh zones containing the leaflets, enabling a more effective mesh moving, helps the ST-TC deal with leaflet–leaflet contact location change and contact sliding, and helps the ST-TC and ST-IGA keep the element density in the narrow spaces near the contact areas at a reasonable level. The ST-SI-TC-IGA is supplemented with two other special methods in this article. A structural mechanics computation method generates the LV motion from the CT scans of the LV and anatomically realistic values for the LV volume ratio. The Constrained-Flow-Profile (CFP) Traction provides flow stability at the inflow boundary. Test computation with the CFP Traction shows its effectiveness as an inflow stabilization method, and computation with the LV-valve-aorta model shows the effectiveness of the ST-SI-TC-IGA and the two supplemental methods.

    DOI

    Scopus

    58
    被引用数
    (Scopus)
  • Heart valve isogeometric sequentially-coupled FSI analysis with the space–time topology change method

    Takuya Terahara, Kenji Takizawa, Tayfun E. Tezduyar, Yuri Bazilevs, Ming Chen Hsu

    Computational Mechanics   65 ( 4 ) 1167 - 1187  2020年04月

     概要を見る

    Heart valve fluid–structure interaction (FSI) analysis is one of the computationally challenging cases in cardiovascular fluid mechanics. The challenges include unsteady flow through a complex geometry, solid surfaces with large motion, and contact between the valve leaflets. We introduce here an isogeometric sequentially-coupled FSI (SCFSI) method that can address the challenges with an outcome of high-fidelity flow solutions. The SCFSI analysis enables dealing with the fluid and structure parts individually at different steps of the solutions sequence, and also enables using different methods or different mesh resolution levels at different steps. In the isogeometric SCFSI analysis here, the first step is a previously computed (fully) coupled Immersogeometric Analysis FSI of the heart valve with a reasonable flow solution. With the valve leaflet and arterial surface motion coming from that, we perform a new, higher-fidelity fluid mechanics computation with the space–time topology change method and isogeometric discretization. Both the immersogeometric and space–time methods are variational multiscale methods. The computation presented for a bioprosthetic heart valve demonstrates the power of the method introduced.

    DOI

    Scopus

    71
    被引用数
    (Scopus)
  • Mesh refinement influence and cardiac-cycle flow periodicity in aorta flow analysis with isogeometric discretization

    Kenji Takizawa, Tayfun E. Tezduyar, Hiroaki Uchikawa, Takuya Terahara, Takafumi Sasaki, Ayaka Yoshida

    Computers and Fluids   179   790 - 798  2019年01月

     概要を見る

    We present detailed studies on mesh refinement influence and cardiac-cycle flow periodicity in aorta flow analysis with isogeometric discretization. Both factors play a key role in the reliability and practical value of aorta flow analysis. The core computational method is the space–time Variational Multiscale (ST-VMS) method. The other key method is the ST Isogeometric Analysis (ST-IGA). The ST framework, in a general context, provides higher-order accuracy. The VMS feature of the ST-VMS addresses the computational challenges associated with the multiscale nature of the unsteady flow in the aorta. The ST-IGA provides smoother representation of the aorta and increased accuracy in the flow solution. We conduct the studies for a patient-specific aorta geometry. We determine the level of mesh refinement needed and assess the nature of the flow periodicity reached.

    DOI

    Scopus

    64
    被引用数
    (Scopus)
  • Heart valve flow computation with the space-time slip interface topology change (ST-SI-TC) method and isogeometric analysis (IGA)

    Kenji Takizawa, Tayfun E. Tezduyar, Takuya Terahara, Takafumi Sasaki

    Lecture Notes in Applied and Computational Mechanics   84   77 - 99  2018年

     概要を見る

    We present a heart valve flow computation with the Space-Time Slip Interface Topology Change (ST-SI-TC) method and Isogeometric Analysis (IGA). The computation is for a realistic heart valve model with actual contact between the valve leaflets. The ST-SI-TC method integrates the ST-SI and ST-TC methods in the framework of the ST Variational Multiscale (ST-VMS) method. The STVMS method functions as a moving-mesh method, which maintains high-resolution boundary layer representation near the solid surfaces. The ST-TC method was introduced for moving-mesh computation of flow problems with TC, such as contact between the leaflets of a heart valve. It deals with the contact while maintaining highresolution representation near the leaflet surfaces. The ST-SI method was originally introduced to addresses the challenge involved in high-resolution representation of the boundary layers near spinning solid surfaces. The mesh covering a spinning solid surface spins with it, and the SI between that mesh and the rest of the mesh accurately connects the two sides. This maintains the high-resolution representation near solid surfaces. In the context of heart valves, the SI connects the sectors of meshes containing the leaflets, enabling a more effective mesh moving. In that context, the ST-SI-TC method enables high-resolution representation even when the contact is between leaflets that are covered by meshes with SI. It also enables dealing with contact location change or contact and sliding on the SI. With IGA, in addition to having a more accurate representation of the surfaces and increased accuracy in the flow solution, the element density in the narrow spaces near the contact areas is kept at a reasonable level. Furthermore, because the flow representation in the contact area has a wider support in IGA, the flow computation method becomes more robust. The computation we present for an aortic-valve model shows the effectiveness of the ST-SI-TC-IGA method.

    DOI

    Scopus

    50
    被引用数
    (Scopus)
  • Aorta flow analysis and heart valve flow and structure analysis

    Kenji Takizawa, Tayfun E. Tezduyar, Hiroaki Uchikawa, Takuya Terahara, Takafumi Sasaki, Kensuke Shiozaki, Ayaka Yoshida, Kenji Komiya, Gaku Inoue

    Modeling and Simulation in Science, Engineering and Technology     29 - 89  2018年

     概要を見る

    We present our computational methods for and results from aorta flow analysis and heart valve flow and structure analysis. In flow analysis, the core method is the space–time Variational Multiscale (ST-VMS) method. The other key methods are the ST Slip Interface (ST-SI) and ST Topology Change (ST-TC) methods and the ST Isogeometric Analysis (ST-IGA). The ST framework, in a general context, provides higher-order accuracy. The VMS feature of the ST-VMS addresses the computational challenges associated with the multiscale nature of the unsteady flows in the aorta and heart valve. The moving-mesh feature of the ST framework enables high-resolution computation near the valve leaflets. The ST-SI connects the sectors of meshes containing the leaflets, enabling a more effective mesh moving. The ST-TC enables moving-mesh computation even with the TC created by the contact between the leaflets. It deals with the contact while maintaining high-resolution representation near the leaflets. Integration of the ST-SI and ST-TC enables high-resolution representation even though parts of the SI are coinciding with the leaflet surfaces. It also enables dealing with leaflet–leaflet contact location change and contact sliding. The ST-IGA provides smoother representation of aorta and valve surfaces and increased accuracy in the flow solution. With the integration of the ST-IGA with the ST-SI and ST-TC, the element density in the narrow spaces near the contact areas is kept at a reasonable level. In structure analysis, we use a Kirchhoff–Love shell model, where we take the stretch in the third direction into account in calculating the curvature term. The computations presented demonstrate the scope and effectiveness of the methods.

    DOI

    Scopus

    46
    被引用数
    (Scopus)
  • Heart valve flow computation with the integrated Space–Time VMS, Slip Interface, Topology Change and Isogeometric Discretization methods

    Kenji Takizawa, Tayfun E. Tezduyar, Takuya Terahara, Takafumi Sasaki

    Computers and Fluids   158   176 - 188  2017年11月

     概要を見る

    Heart valve flow computation requires accurate representation of boundary layers near moving solid surfaces, including the valve leaflet surfaces, even when the leaflets come into contact. It also requires dealing with a high level of geometric complexity. We address these computational challenges with a Space–Time (ST) method developed by integrating three special ST methods in the framework of the ST Variational Multiscale (ST-VMS) method. The special methods are the ST Slip Interface (ST-SI) and ST Topology Change (ST-TC) methods and ST Isogeometric Analysis (ST-IGA). The computations are for a realistic aortic-valve model with prescribed valve leaflet motion and actual contact between the leaflets. The ST-VMS method functions as a moving-mesh method, which maintains high-resolution boundary layer representation near the solid surfaces, including leaflet surfaces. The ST-TC method was introduced for moving-mesh computation of flow problems with TC, such as contact between the leaflets of a heart valve. It deals with the contact while maintaining high-resolution representation near the leaflet surfaces. The ST-SI method was originally introduced to have high-resolution representation of the boundary layers near spinning solid surfaces. The mesh covering a spinning solid surface spins with it, and the SI between the spinning mesh and the rest of the mesh accurately connects the two sides. In the context of heart valves, the SI connects the sectors of meshes containing the leaflets, enabling a more effective mesh moving. In that context, integration of the ST-SI and ST-TC methods enables high-resolution representation even when the contact is between leaflets that are covered by meshes with SI. It also enables dealing with contact location change or contact and sliding on the SI. By integrating the ST-IGA with the ST-SI and ST-TC methods, in addition to having a more accurate representation of the surfaces and increased accuracy in the flow solution, the element density in the narrow spaces near the contact areas is kept at a reasonable level. Furthermore, because the flow representation in the contact area has a wider support in IGA, the flow computation method becomes more robust. The computations we present for an aortic-valve model with two different modes of prescribed leaflet motion show the effectiveness of the ST-SI-TC-IGA method.

    DOI

    Scopus

    90
    被引用数
    (Scopus)
  • Turbocharger flow computations with the Space–Time Isogeometric Analysis (ST-IGA)

    Kenji Takizawa, Tayfun E. Tezduyar, Yuto Otoguro, Takuya Terahara, Takashi Kuraishi, Hitoshi Hattori

    Computers and Fluids   142   15 - 20  2017年01月

     概要を見る

    We focus on turbocharger computational flow analysis with a method that possesses higher accuracy in spatial and temporal representations. In the method we have developed for this purpose, we use a combination of (i) the Space–Time Variational Multiscale (ST-VMS) method, which is a stabilized formulation that also serves as a turbulence model, (ii) the ST Slip Interface (ST-SI) method, which maintains high-resolution representation of the boundary layers near spinning solid surfaces by allowing in a consistent fashion slip at the interface between the mesh covering a spinning surface and the mesh covering the rest of the domain, and (iii) the Isogeometric Analysis (IGA), where we use NURBS basis functions in space and time. The basis functions are spatially higher-order in all representations, and temporally higher-order in representation of the solid-surface and mesh motions. The ST nature of the method gives us higher-order accuracy in the flow solver, and when combined with temporally higher-order basis functions, a more accurate representation of the surface motion, and a mesh motion consistent with that. The spatially higher-order basis functions give us again higher-order accuracy in the flow solver, a more accurate, in some parts exact, representation of the surface geometry, and better representation in evaluating the second-order spatial derivatives. Using NURBS basis functions with a complex geometry is not trivial, however, once we generate the mesh, the computational efficiency is substantially increased. We focus on the turbine part of a turbocharger, but our method can also be applied to the compressor part and thus can be extended to the full turbocharger.

    DOI

    Scopus

    102
    被引用数
    (Scopus)
  • Ram-air parachute structural and fluid mechanics computations with the Space–Time Isogeometric Analysis (ST-IGA)

    Kenji Takizawa, Tayfun E. Tezduyar, Takuya Terahara

    Computers and Fluids   141   191 - 200  2016年12月

     概要を見る

    We present a method for structural and fluid mechanics computations of ram-air parachutes. A ram-air parachute is a parafoil inflated by the airflow through the inlets at the leading edge. It has better control and gliding capability than round parachutes. Reliable analysis of ram-air parachutes requires accurate representation of the parafoil geometry, fabric porosity and the complex, multiscale flow behavior involved in this class of problems. The key components of the method are (i) the Space–Time Variational Multiscale (ST-VMS) method, (ii) the version of the ST Slip Interface (ST-SI) method where the SI is between a thin porous structure and the fluid on its two sides, (iii) the ST Isogeometric Analysis (ST-IGA), and (iv) special-purpose NURBS mesh generation techniques for the parachute structure and the flow field inside and outside the parafoil. The ST-VMS method is a stabilized formulation that also serves as a turbulence model and can deal effectively with the complex, multiscale flow behavior. With the ST-SI version for porosity modeling, we deal with the fabric porosity in a fashion consistent with how we deal with the standard SIs and how we enforce the Dirichlet boundary conditions weakly. The ST-IGA, with NURBS basis functions in space, gives us, with relatively few number of unknowns, accurate representation of the parafoil geometry and increased accuracy in the flow solution. The special-purpose mesh generation techniques enable NURBS representation of the structure and fluid domains with significant geometric complexity. The test computations we present are for building a starting parachute shape and a starting flow field associated with that parachute shape, which are the first two key steps in fluid–structure interaction analysis. The computations demonstrate the effectiveness of the method in this class of problems.

    DOI

    Scopus

    86
    被引用数
    (Scopus)

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共同研究・競争的資金等の研究課題

  • 高度個別医療に向けた心臓弁まわりの流体解析手法の構築

    日本学術振興会  科学研究費助成事業 若手研究

    研究期間:

    2022年04月
    -
    2027年03月
     

    寺原 拓哉

  • 接触を伴う流体現象の解明のためのT-spline動的細分化による計算手法の構築

    日本学術振興会  科学研究費助成事業 研究活動スタート支援

    研究期間:

    2020年09月
    -
    2022年03月
     

    寺原 拓哉

     概要を見る

    物体同士が接触する際の流れは,押し出されるようにして速い流れが生じ,周囲の流体場や物体そのものへ影響を及ぼす.この把握することの難しい接触する物体近傍の流れ場を,理論に基づく数値解析により明らかにする.本研究では,この流体現象を多くの問題に適用可能な手法にするため,高次の基底関数で表現した空間の局所的な細分化技術を本手法に導入した.最終的には実問題への適用例として,開閉する人工心臓弁周囲の流体場を解析し,弁が開く,閉じる瞬間,開いている時の複雑な流れ場の様子を効率よく明らかにした.

  • 流体構造連成解析のための特殊格子移動法

    日本学術振興会  科学研究費助成事業 特別研究員奨励費

    研究期間:

    2017年04月
    -
    2020年03月
     

    寺原 拓哉

     概要を見る

    令和元年度はまず流体構造連成解析による複雑な動作を伴う心臓弁の高精度流体解析を実現し、査読付き国際ジャーナル論文の一本目を執筆した。
    さらには実際の問題への適用のため、心臓弁を有する心血管系を対象とし、境界適合格子での流体解析を行った。本問題に取り組むにあたって、流入口および流出口にトラクション条件を課す手法を提案した。通常流体解析では流入口には流速、流出口にはトラクション条件を課す。一方で実際の心血管系では流体は圧力により駆動される。さらに、流入境界において流入出が起こる問題では、流入量を規定することが適さない。ここで、トラクション条件を課した境界から流入する場合、速度プロファイルに対して、流入するエネルギーが一意に定まらないため、安定的に解くことが難しいという問題がある。流出境界で用いられる安定化手法は研究されているが、流入するエネルギーを減らす方法であるため流入境界には適さない。この課題に対して、本研究では二次のB-splineを応用することで解決した。二次のB-splineで構築された一要素を流入口に設け、計算ドメインと不連続な基底関数を許す方法により接続する方法を提案した。二次のB-splineの一要素は流入境界を三点の制御点で表現し、そのうち二点の端点は壁であるため流速が規定される。よって中央の一点のみでパラボラ型の速度プロファイルが決定される。本手法を用いたテスト計算では、流出境界で用いられる安定化手法と比較を行い、より理論解に近い結果を得られていることを確認した。また本手法を適用した心血管系の流体解析では、左心室内部で作られる大きな渦流が、らせん流となって大動脈内に流入する様子や、大動脈弁が左心室内部の乱れた流れに影響され非対称な壁面せん断応力を受けていることが確認できた。本研究内容をまとめ、査読付き国際ジャーナル論文の二本目を執筆した。

 

現在担当している科目

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他学部・他研究科等兼任情報

  • 理工学術院   創造理工学部

特定課題制度(学内資金)

  • 接触を伴う流体現象の解明のためのT-spine動的細分化による計算手法の構築

    2021年   滝沢研二, Tezduyar Tayfun E.

     概要を見る

    本研究では接触を伴う流体現象を高精度に解析する流体解析手法において、空間の基底関数にNURBSの上位互換であるT-splineを採用し、局所的な動的細分化を行うことで本手法をより信頼のできる手法にアップデートすることを目的とした。本年度は目的に向け、T-splineによる細分化を3次元の解析格子に対して実現し、実用例として人工心臓弁の流体解析において心臓弁近傍の境界付近を細分化した計算を行った。流体解析の結果から渦構造を可視化し、細分化による効果を確認した。壁近傍のみならず弁が開く瞬間の流れが高解像となることがわかった。本研究に関して国内学会にて研究成果を発表し、研究の一部は既に主著1本、共著1本を国際論文誌に投稿し採択されている。