1. |
Daniel S. Morikawa, Mitsuteru Asai, Coupling total Lagrangian SPH-EISPH for fluid-structure interaction with large deformed hyperelastic solid bodies, *Computer Method in Applied Mechanics and Engineering*, https://doi.org/10.1016/j.cma.2021.113832, 2021.08, 粒子法による流体構造連成解析をする際，特に構造解析の大変形解析が不安定になり，ロバストに解析が実施することが困難であった。そこで、超弾性体モデルの範囲内であれば、初期配置と現配置の間に1対1の関係があることを利用し、固体のつり合い問題を初期配置で解くTotalラグランジュ記述によるSPH粒子法を利用した新しい流体構造連成解析法を提案した。. |

2. |
Mitsuteru Asai，Li Yi, Bodhinanda Chandra, Masaharu Isshiki, Fluid-rigid body interaction simulations and validations using a coupled stabilized ISPH-DEM incorporated with the energy tracking impulse method for multiple body contacts, *Computer Method in Applied Mechanics and Engineering*, https://doi.org/10.1016/j.cma.2021.113681, 2021.04, 流体構造連成解析手法はいくつか提案されているものの、複数固体間での接触摩擦を含む問題を安定して解く方法はいまだ確立していない。そこで、流体、剛体の両者を粒子で離散化した上で、安定した流体剛体連成解析を実施とした。著者らが前報で提案した撃力で接触を表現するEnergy-tracking impulse法をベースとし、ISPH法による流体解析との連成させた新手法を提案した。. |

3. |
Daniel Shigueo Morikawa, Harini Senadheera, Mitsuteru Asai, Explicit Incompressible Smoothed Particle Hydrodynamics in a multi-GPU environment for large scale simulations, *Journal of Computational Particle Mechanics*, 2020.06, GPUの性能向上により、コードによってはCPUと比較してかなり高速な演算が可能となっている．研究対象とした非圧縮性流体の粒子法では、演算時間よりも使用メモリの制限のため、大規模な計算をGPU上で実施することは困難であった．そこで、計算アルゴリズムを見直し、陽解法化（連立一次方程式を厳密に解かず、近似解で与える）することで、使用メモリを大幅に減らし、1GPUで2000万～3000万粒子を使った演算が可能とした．さらに大規模な演算を実施するため、1ノードに搭載できる複数のGPUを使用することで、1億粒子以上の計算を可能とし、またGPUを使った従来研究と比べても高速な演算が実施できてることを示した．. |

4. |
Zehba Raizah, Mitsuteru Asai, Abdelraheem M. Aly, Incompressible smoothed particle hydrodynamics simulations of natural convection flow resulting from embedded Y-fin inside Y-shaped enclosure filled with a nanofluid, *International Journal of Numerical Methods for Heat and Fluid Flow*, 10.1108/HFF-02-2020-0094, 31, 1, 154-173, 2020.05, © 2020, Emerald Publishing Limited. Purpose: The purpose of this study is to apply the incompressible smoothed particle hydrodynamics (ISPH) method to simulate the natural convection flow from an inner heated Y-fin inside Y-shaped enclosure filled with nanofluid. Design/methodology/approach: The dimensionless governing partial differential equations are described in the Lagrangian form and solved by an implicit scheme of the ISPH method. The embedded Y-fin is kept at a high temperature Th with variable heights during the simulations. The lower area of Y-shaped enclosure is squared with width L = 1 m and its side-walls are kept at a low temperature Tc. The upper area of the Y-shaped enclosure is V-shaped with width 0.5 L for each side and its walls are adiabatic. Findings: The performed simulations revealed that the height of the inner heated Y-fin plays an important role in the heat transfer and fluid flow inside the Y-shaped enclosure, where it enhances the heat transfer. Rayleigh number augments the buoyancy force inside the Y-shaped enclosure and, consequently, it has a strong impact on temperature distributions and strength of the fluid flow inside Y-shaped enclosure. Adding more concentration of the nanofluid until 10% has a slight effect on the temperature distributions and it reduces the strength of the fluid flow inside Y-shaped enclosure. In addition, the average Nusselt number is measured along the inner heated Y-fin and it grows as the Rayleigh number increases. The average Nusselt number is decreasing by adding more concentrations of the nanofluid. Originality/value: An improved ISPH method is used to simulate the natural convection flow of Y-fin embedded in the Y-shaped enclosure filled with a nanofluid.. |

5. |
Li Yi, Mitsuteru Asai, Bodhinanda Chandra, Masaharu Isshiki, Energy-tracking impulse method for particle-discretized rigid-body simulations with frictional contact, *Journal of Computational Particle Mechanics*, https://doi.org/10.1007/s40571-020-00326-5, 2020.04, 剛体接触解析を行う常套手段としては、バネとダッシュポットで簡易的に表現するペナルティ法が良く採用されるが、時間増分が小さくなる、また人工パラメータの設定方法が曖昧であるなどの、問題点があった。そこで、適切な力（撃力：インパルス）で接触を表現するインパルス法に着目し、特にエネルギー保存性を担保できるEnergy-tracking impulse法をベースとし、これをDEMなどの粒子離散化された剛体の解析へと適用した。. |

6. |
Zehba Raizah, Mitsuteru Asai, Abdelraheem M. Aly, Incompressible smoothed particle hydrodynamics simulations of natural convection flow resulting from embedded Y-fin inside Y-shaped enclosure filled with a nanofluid, *International Journal of Numerical Methods for Heat and Fluid Flow*, 10.1108/HFF-02-2020-0094, 2020.01, Purpose: The purpose of this study is to apply the incompressible smoothed particle hydrodynamics (ISPH) method to simulate the natural convection flow from an inner heated Y-fin inside Y-shaped enclosure filled with nanofluid. Design/methodology/approach: The dimensionless governing partial differential equations are described in the Lagrangian form and solved by an implicit scheme of the ISPH method. The embedded Y-fin is kept at a high temperature with variable heights during the simulations. The lower area of Y-shaped enclosure is squared with width L = 1 m and its side-walls are kept at a low temperature . The upper area of the Y-shaped enclosure is V-shaped with width 0.5 L for each side and its walls are adiabatic. Findings: The performed simulations revealed that the height of the inner heated Y-fin plays an important role in the heat transfer and fluid flow inside the Y-shaped enclosure, where it enhances the heat transfer. Rayleigh number augments the buoyancy force inside the Y-shaped enclosure and, consequently, it has a strong impact on temperature distributions and strength of the fluid flow inside Y-shaped enclosure. Adding more concentration of the nanofluid until 10% has a slight effect on the temperature distributions and it reduces the strength of the fluid flow inside Y-shaped enclosure. In addition, the average Nusselt number is measured along the inner heated Y-fin and it grows as the Rayleigh number increases. The average Nusselt number is decreasing by adding more concentrations of the nanofluid. Originality/value: An improved ISPH method is used to simulate the natural convection flow of Y-fin embedded in the Y-shaped enclosure filled with a nanofluid.. |

7. |
Abdelraheem M. Aly, Zehba Raizah, Mitsuteru Asai, Natural convection from heated fin shapes in a nanofluid-filled porous cavity using incompressible smoothed particle hydrodynamics, *International Journal of Numerical Methods for Heat and Fluid Flow*, 10.1108/HFF-03-2019-0270, 29, 12, 4569-4597, 2019.12, Purpose: This study aims to focus on the numerical simulation of natural convection from heated novel fin shapes in a cavity filled with nanofluid and saturated with a partial layer of porous medium using improved incompressible smoothed particle hydrodynamics (ISPH) method. Design/methodology/approach: The dimensionless of Lagrangian description for the governing equations were numerically solved using improved ISPH method. The current ISPH method was improved in term of wall boundary treatment by using renormalization kernel function. The effects of different novel heated (Tree, T, H, V, and Z) fin shapes, Rayleigh number Ra, porous height H (0.2-0.6), Darcy parameter and solid volume fraction ϕ(0.0-0.05) on the heat transfer of nanofluid have been investigated. Findings: The results showed that the variation on the heated novel fin shapes gives a suitable choice for enhancement heat transfer inside multi-layer porous cavity. Among all fin shapes, the H-fin shape causes the maximum stream function and Z-fin shape causes the highest value of average Nusselt number. The concentrations of the fluid flows in the nanofluid region depend on the Rayleigh and Darcy parameters. In addition, the penetrations of the fluid flows through porous layers are affected by porous heights and Darcy parameter. Originality/value: Natural convection from novel heated fins in a cavity filled with nanofluid and saturated with a partial layer of porous medium have been investigated numerically using improved ISPH method.. |

8. |
Masao Ogino, Takuya Iwama, Mitsuteru Asai, Development of a Partitioned Coupling Analysis System for Fluid-Structure Interactions Using an In-House ISPH Code and the Adventure System, *International Journal of Computational Methods*, 10.1142/S0219876218430090, 16, 4, 2019.06, © 2019 World Scientific Publishing Company. In this paper, a partitioned coupling analysis system is developed for a numerical simulation of 3-dimensional fluid-structure interaction (FSI) problems, adopting an incompressible smoothed particle hydrodynamics (SPH) method for fluid dynamics involving free surface flow and the finite element method (FEM) for structural dynamics. A coupling analysis of a particle-based method and a grid-based method has been investigated. However, most of these are developed as a function-specific application software, and therefore lack versatility. Hence, to save cost in software development and maintenance, the open source software is utilized. Especially, a general-purpose finite element analysis system, named ADVENTURE, and a general-purpose coupling analysis platform, named REVOCAP-Coupler, are employed. Moreover, techniques of an interface marker on fluid-structure boundaries and a dummy mesh for fluid analysis domain are adopted to solve the problem that the REVOCAP-Coupler performs to unify two or more grid-based method codes. To verify a developed system, the dam break problem with an elastic obstacle is demonstrated, and the result is compared with the results calculated by the other methods.. |

9. |
Daniel Morikawa, Mitsuteru Asai, Yusuke Imoto, Masaharu Isshiki, Bingham flow model by fully implicit SPH and its application to reinforce underground caves, *Proceedings of the 2019 Rock Dynamics Summit (RDS 2019)*, 10.1201/9780429327933-48, 2019, 299-304, 2019.05. |

10. |
Daniel Morikawa, Mitsuteru ASAI, Nur' Ain Idris, Yusuke Imoto, Masaharu Isshiki, Improvement in highly viscous fluid simulation using a fully implicit SPH method, *Journal of Computational Particle Mechanics*, 10.1007/s40571-019-00231-6, 2019.03, 土石流あるいは火砕流などの災害シミュレーションへ向けた高粘性流体のシミュレーションのために、独自に開発してきた粒子法（ISPH法）を改良し、 安定かつ高精度に解析可能な手法を開発した。. |

11. |
Masao OGINO, Takyuya IWAMA, Mitsuteru ASAI, Development of an ISPH-FEM Weak Coupling Analysis System for 3-dimensional Fluid-Structure Interaction Problems, *Teroretical and Applied Mechanics Japan*, 2018, 2018.08. |

12. |
Masaharu Isshiki, Mitsuteru Asai, Shimon Eguchi, Yoshiya Miyagawa, An Offline-Based On-Demand Visualization System of Large-Scale Particle Simulation for Tsunami Disaster Prevention, *Electronics and Communications in Japan*, 10.1002/ecj.12050, 101, 4, 55-62, 2018.04, © 2018 Wiley Periodicals, Inc. After the Great East Japan Earthquake Tsunami, new Tsunami disaster-prevention and mitigation methods for the next millennium Tsunami are actively being discussed. Consequently, the methods have highlighted the importance of both hard disaster-prevention method, which means direct prevention using infrastructure such as breakwater, and soft disaster-prevention method, including disaster-prevention education. In this paper, a visualization and polygonization system that can be effectively utilized for Tsunami disaster prevention is proposed for large-scale particle simulation. The system includes two important features, such as engineering-purposed visualization and polygonization for hard and soft tsunami disaster-prevention methods, respectively. Moreover, the system can handle the large-scale particle simulation data that are computed by a high-performance computer via an offline on-demand tool without data transfer.. |

13. |
Masao OGINO, Takyuya IWAMA, Mitsuteru ASAI, Development of a partitioned coupling analyssis system for fluid-structure interactions using an in-house ISPH code and the ADVENTURE system, *International Journal of Computational Methods*, 2018, 2018.03. |

14. |
DIFFERENCES ON DIFFERENT FIDELITY LEVEL IN MODELING OF BUILDING AND EMBANKMENT HEIGHT ON TSUNAMI RUN UP SIMULATION BY 2D FINITE DIFFERENCE METHOD. |

15. |
Li Yi, Mitsuteru ASAI, Fluid-rigid body interaction simulation based on a stabilized ISPH method incorporated with the impulse-based rigid body dynamics, *日本計算工学論文集*, https://doi.org/10.11421/jsces.2018.20182010, 2018, 2, p.20182010, 2018.02. |

16. |
Masao Ogino, Takuya Iwama, Mitsuteru Asai, Development of an ISPH-FEM Weak Coupling Analysis System for 3-Dimensional Fluid -Structure Interaction Problems, *THEORETICAL AND APPLIED MECHANICS JAPAN*, 10.11345/nctam.64.143, 64, 143-153, 2018.01, This paper focuses on a weak coupling analysis system of 3-dimensional fluid structure interaction problems. As the numerical discretization scheme, the stabilized incompressible smoothed particle hydrodynamics (ISPH) method is adopted for fluid dynamics involving free surface flow and the finite element method (FEM) is used for structural dynamics. To save cost in software developments maintenance, the open source software is utilized. Especially, a general-purpose finite element analysis system, named ADVENTURE Solid, and a general-purpose coupling analysis platform, named REVOCAP Coupler, are employed. Moreover, techniques of an interface marker on the fluid-structure boundary and a dummy mesh for a fluid analysis domain is adopted to solve the problem that the REVOCAP Coupler performs to unify two or more grid-based method codes. To verify a developed system, the dam break problem with an elastic obstacle is demonstrated. Moreover, the effect of a relaxation parameter in the ISPH method is studied.. |

17. |
Abdelraheem M. Aly, Mitsuteru Asai, Water Entry of Decelerationg Spheres Simulaitons using Improved ISPH method, *Journal of Hydrodynamivs*, 2017.03. |

18. |
3次元離散型有限要素モデルによる石造アーチ橋の静的・動的強度解析. |

19. |
Keita Ogasawara, Mitsuteru Asai, Mikito Furuichi, Daisuke Nishiura, PERFORMANCE OF LARGE SCALED TSUNAMI RUN-UP ANALYSIS USING EXPLICIT ISPH METHOD, *V INTERNATIONAL CONFERENCE ON PARTICLE-BASED METHODS - FUNDAMENTALS AND APPLICATIONS (PARTICLES 2017)*, 162-171, 2017.01, The tsunami run-up simulation by the particle method at city level needs to huge number of particle at least 1 billion particles. The conventional particle simulation method is not easy to solve these huge problem even on the premise of using super-computer. Then, a new particle method 'fully explicit Incompressible SPH' is developed that takes into consideration both calculation efficiency and accuracy. Finally, we demonstrate the future plan how to use our simulation resultes for a practical 'Soft' disaster mitigation method through the evacuation education with the Virtual Reality(VR) system.. |

20. |
Abdelraheem M. Aly, Mitsuteru Asai, ISPH method for double-diffusive natural convection under cross difussion effects in an anisotropic porous cavity/annulus, *International Journal of Numerical Methods for Heat & Fluid Flow*, 26, 1, 235-268, 2016.10. |

21. |
Masaharu Isshiki, Mitsuteru Asai, Shimon Eguchi, Hideyuki O-tani, 3D tsunami run-up simulation and visualization using particle method with GIS-based geography model, *Journal of Earthquake & Tsunami*, 2016.06. |

22. |
Mitsuteru Asai, Yoshiya Miyagawa, Nur'Ain Idris, Abdul Muhari, Fumihiko Imamura, Coupled tsunami simulation based on a 2D shallow-water equation-based finite difference method and 3D incompressible smoothed particle hydrodynamics, *Journal of Earthquake & Tsunami*, 2016.06. |

23. |
Yoshiya Miyagawa, Mitsuteru Asai, Multi-scale bridge wash out simulation during tsunami by using a particle method, *MATEC Web of Conferences*, 10.1051/matecconf/20164702019, 47, 2016.04, © Owned by the authors, published by EDP Sciences, 2016. In 2011, the huge tsunami caused by the great east Japan earthquake devastated many infrastructures in pacific coast of north eastern Japan. Particularly, collapse of bridges caused a traffic disorder and these collapse behaviors led to delay of recovery after the disaster. In this study, the bridge wash away accident is selected as a target issue, and it is represented by a numerical simulation. For this purpose, Smoothed Particle Hydrodynamics (SPH) Method, which is one of the pure mesh free methods, is utilized for the rigid body motion simulation. In this study, rigid body motion is introduced for the fluid-rigid interaction behavior during bridge wash away simulation. In the numerical analysis, the upper bridge structure is washed away by receiving an impact fluid force. The wash away simulation of two types of the bridge girder showed good agreement with the real accident on the great east Japan earthquake tsunami.. |

24. |
Tomotaka Nogami, Mitsuteru Asai, Kiyonobu Kasama, Taro Arikawa, A Coupling Simulation Between Soil Scour and Seepage Flow by Using a Stabilized ISPH Method, *3RD INTERNATIONAL CONFERENCE ON CIVIL AND ENVIRONMENTAL ENGINEERING FOR SUSTAINABILITY (ICONCEES 2015)*, 10.1051/matecconf/20164703019, 47, 2016.01, In 2011, the example that breakwaters collapsed because of the basic ground's destabilization was reported by Tohoku-Kanto earthquake tsunami. Fluid-Structure-Soil coupling simulation is desired for a systematic comprehension of the breakwater collapse mechanism, and it may help to develop next disaster prevention method. In this study, A particle simulation tool based on the SPH has been modified and improved to analyze seepage flow and soil scouring. In seepage flow analysis, as a first step, this simulation treat the surface flow and seepage flow interactions by using governing equation. In the scouring analysis, soil scour is judged by an empirical criteria based on quicksand quantity formula.. |

25. |
Abdelraheem M. Aly, Mitsuteru Asai, A. Chamkha, Analysis of Unsteady Mixed Convection in Lid-Driven Cavity Included Circular Cylinders Motion Using an Incompressible Smoothed Particle Hydrodynamics Method, *International Journal of Numerical Mechods for Heat and Fluid Flow*, 25, 2014.12. |

26. |
3次元粒子法による橋桁に作用する津波外力評価とその精度検証. |

27. |
Abdelraheem M. Aly, Mitsuteru Asai, Incompressible smoothed particle hydrodynamics simulations of fluid-structure interaction on free surface flows, *International Journal of Fluid Mechanics Research*, 10.1615/InterJFluidMechRes.v41.i6.10, 41, 6, 471-484, 2014.01, In this paper, fluid-structure interaction (FSI) on free surface flows has been simulated using ISPH method. The governing equations are discretized and solved with respect to Lagrangian moving particles filled within the mesh-free computational domain and the pressure was evaluated by solving pressure Poisson equation using a semi-implicit algorithm based on the projection scheme to ensure divergence free velocity field and density invariance conditions. In this study, the structure is taken as a rigid body and it modeled using ISPH method by two different techniques. In the first technique, the solid particles are treated initially as fluid particles and after corrector step in projection method, the solid constraint is applied to get the rigid body motion. In the second technique, we computed the motions of a rigid body by direct integration of fluid pressure at the position of each particle on the body surface. Then, the equations of translational and rotational motions were integrated in time to update the position of the rigid body at each time step. The applicability and efficiency of current ISPH method with the two different treatment of rigid body are tested by comparison with reference experimental results.. |

28. |
Abdelraheem M. Aly, Mitsuteru Asai, Yoshimi Sonda, Modelling of surface tension force for free surface flows in ISPH method, *International Journal of Numerical Methods for Heat and Fluid Flow*, 10.1108/09615531311301263, 23, 3, 479-498, 2013.12, Purpose - The purpose of this paper is to show how a surface tension model and an eddy viscosity based on the Smagorinsky sub-grid scale model, which belongs to the Large-Eddy Simulation (LES) theory for turbulent flow, have been introduced into ISPH (Incompressible smoothed particle hydrodynamics) method. In addition, a small modification in the source term of pressure Poisson equation has been introduced as a stabilizer for robust simulations. This stabilization generates a smoothed pressure distribution and keeps the total volume of fluid, and it is analogous to the recent modification in MPS. Design/methodology/ approach - The surface tension force in free surface flow is evaluated without a direct modeling of surrounding air for decreasing computational costs. The proposed model was validated by calculating the surface tension force in the free surface interface for a cubic-droplet under null-gravity and the milk crown problem with different resolution models. Finally, effects of the eddy viscosity have been discussed with a fluid-fluid interaction simulation. Findings - From the numerical tests, the surface tension model can handle free surface tension problems including high curvature without special treatments. The eddy viscosity has clear effects in adjusting the splashes and reduces the deformation of free surface in the interaction. Finally, the proposed stabilization appeared in the source term of pressure Poisson equation has an important role in the simulation to keep the total volume of fluid. Originality/value - An incompressible smoothed particle hydrodynamics is developed to simulate milk crown problem using a surface tension model and the eddy viscosity.. |

29. |
Abdelraheem M. Aly, Mitsuteru Asai, YOSHIMI SONODA, Modelling of surface tension force for free surface flows in ISPH method, *International Journal of Numerical Methods for Heat and Fluid Flow*, 23, 3, 479-498, 2013.04. |

30. |
Coupling simulator between chemical diffusion and crack propagation by a Voxel FEM incorporated with the Damage Mechanics Alkali Silica Reaction (ASR), chloride damage of reinforced steel and other aging degradations in concrete structures are strongly dependent on both of chemical phenomena and mechanical behavior including fracture. In this study, a coupling simulator has been developed in order to investigate the degradation mechanism of these concrete aging damages. In the coupling simulator, non-stationary diffusion analysis for Alkali ion is solved firstly, and then the expansion force act on the aggregate is evaluated by referring consistency of the alkali ion. In the second step, nonlinear damage analysis is conducted. The nonlinear damage analysis evaluates cracking region with the damage parameter. The following diffusion analysis changes diffusion coefficient in the cracking region by referring the damage parameter. The above procedures are coupled at each time step. © 2013 by the Japan Society for Computational Engineering and Science.. |

31. |
Slip and no-slip boundary treatment for particle simulation model with incompatible step-shaped boundaries by using a virtual maker Particle method such as Smoothed Particle Hydrodynamics (SPH) and Moving Particle Semi-implicit method (MPS) can handle quite complicated physical problems involving dynamic changes of free surface and crack propagation, and it is wildly expanding its applications not only in the fluid dynamics but also in the solid mechanics. Beside of these advantages, particle methods are not so easy to treat boundary conditions, like pressure Neumann condition and slip or no-slip condition in fluid dynamics. This is one of the typical difficulties in mesh-less type method. In addition, particle simulation model may include an incompatible step-shaped boundary line, which is made by using a simple pre-processing of particle model. Although the simple and robust pre-processing is one of the advantage of particle simulation, the step-shaped boundary may generate un-realistic numerical solution across the real boundary line especially in the fluid dynamics. Recently, pressure Neumann condition in SPH is re-focused with fixed ghost boundary method using virtual makers. In this paper, the fixed ghost boundary method is modified to treat the incompatible step-shaped boundary particles by referring the real physical boundary line. The accuracy and efficiencies of proposed method are validated by comparison between a numerical solution and experimental results. © 2013 by the Japan Society for Computational Engineering and Science.. |

32. |
Coupling simulator between chemical diffusion and crack propagation by a Voxel FEM incorporated with the Damage Mechanics Alkali Silica Reaction (ASR), chloride damage of reinforced steel and other aging degradations in concrete structures are strongly dependent on both of chemical phenomena and mechanical behavior including fracture. In this study, a coupling simulator has been developed in order to investigate the degradation mechanism of these concrete aging damages. In the coupling simulator, non-stationary diffusion analysis for Alkali ion is solved firstly, and then the expansion force act on the aggregate is evaluated by referring consistency of the alkali ion. In the second step, nonlinear damage analysis is conducted. The nonlinear damage analysis evaluates cracking region with the damage parameter. The following diffusion analysis changes diffusion coefficient in the cracking region by referring the damage parameter. The above procedures are coupled at each time step. © 2013 by the Japan Society for Computational Engineering and Science.. |

33. |
Slip and no-slip boundary treatment for particle simulation model with incompatible step-shaped boundaries by using a virtual maker Particle method such as Smoothed Particle Hydrodynamics (SPH) and Moving Particle Semi-implicit method (MPS) can handle quite complicated physical problems involving dynamic changes of free surface and crack propagation, and it is wildly expanding its applications not only in the fluid dynamics but also in the solid mechanics. Beside of these advantages, particle methods are not so easy to treat boundary conditions, like pressure Neumann condition and slip or no-slip condition in fluid dynamics. This is one of the typical difficulties in mesh-less type method. In addition, particle simulation model may include an incompatible step-shaped boundary line, which is made by using a simple pre-processing of particle model. Although the simple and robust pre-processing is one of the advantage of particle simulation, the step-shaped boundary may generate un-realistic numerical solution across the real boundary line especially in the fluid dynamics. Recently, pressure Neumann condition in SPH is re-focused with fixed ghost boundary method using virtual makers. In this paper, the fixed ghost boundary method is modified to treat the incompatible step-shaped boundary particles by referring the real physical boundary line. The accuracy and efficiencies of proposed method are validated by comparison between a numerical solution and experimental results. © 2013 by the Japan Society for Computational Engineering and Science.. |

34. |
Naoki Takano, Mitsuteru Asai, Kohta Okamoto, Monte Carlo simulation of dynamic problem using model order reduction technique highlighting on tail probability, *Journal of Solid Mechanics and Materials Engineering*, 6, 3, 169-181, 2012.09. |

35. |
Mitsuteru Asai, Multi-scale modeling in heterogeneous material properties, *MI Lecture Note Series*, 39, 84-95, 2012.09. |

36. |
Mitsuteru Asai, Keisuke Fujimoto, Abdelraheem M. Aly, Yoshimi Sonoda, Fluid-Soil-Structure coupling analysis for tsunami disaster simulation, *Proceeding of KSME-JSME joint symposium on computational mechanics & CAE 2012*, 11-16, 2012.09. |

37. |
Mitsuteru ASAI, Abdelraheem M. ALY, Yoshimi SONODA, Yuzuru SAKAI
, A stabilized incompressible SPH method by relaxing the density invariant condition, *Journal of Applied Mathematics*, Volume 2012 (2012), Article ID 139583, 24 pages, 2012.04. |

38. |
Abdelraheem M. ALY, Mitsuteru ASAI, Yoshimi SONODA
, A study of violent water induced impact problems using ISPH method , *Proceeding of 9th International Conference on Shock & Impact Loads on Structures*, 217-224, 2011.11. |

39. |
Nobutaka ISHIKAWA, Masuhiro BEPPU, Tsutomu MIKAMI, Hiroshi TATESAWA, Mitsuteru ASAI
, Collapse mechanism of seawalls by impulsive load due to the March 11 tsunami , *Proceeding of 9th International Conference on Shock & Impact Loads on Structures*, 1-12, 2011.11. |

40. |
Mitsuteru Asai, Hiroki Iida, Norliyati M. Amin and Yoshimi Sonoda
, Fast dynamic solver for the design of bridge using a model order reduction , *Proceeding of 9th International Conference on Shock & Impact Loads on Structures*, 225-234, 2011.11. |

41. |
Abdelraheem M. ALY, Mitsuteru ASAI and Yoshimi SONODA, Floating rigid body simulation in free surface flow using a stabilized incompressible SPH method, *Proceedings of the 2011 World Congress on Advances in Structural Engineering and Mechanics*, 4460-4469, 2011.09. |

42. |
Mitsuteru ASAI, Akane WATANABE, Yoshimi SONODA, Development of a 3D coupling simulator between chemical diffusion and nonlinear mechanics in meso-scopic concrete, *Proceedings of the 2011 World Congress on Advances in Structural Engineering and Mechanics*, 3515-3523, 2011.09. |

43. |
Abdelraheem M. Aly, Mitsuteru Asai, Yoshimi Sonoda, Simulation of free falling rigid body into water by a stabilized incompressible SPH method, *Ocean Systems Engineering*, Vol. 1, No. 3, 2011.08. |

44. |
Mitsuteru Asai，Norliyati M. Amin, Yoshimi Sonoda, Practical determination of an effective reduced order in a model order reduction of dynamic FEM via Krylov subspace, *応用力学論文集*, Vol.14, 2011.08. |

45. |
Mitsuteru Asai, Abdelraheem M. Aly, Yoshimi Sonoda, ISPH-FEM coupling simulator for the FSI problems, *Proceeding of the 6th SPHERIC SPH workshop*, pp.201-208, 2011.06. |

46. |
Constitutive modeling for texture reinforced rubber by using an anisotropic visco-hyperelastic model Fabric reinforced rubber shows an anisotropy and viscosity in wide strain range. In this paper, an anisotropic visco-elastic model based on Mooney-Rivlin model is developed for fabric reinforced rubber. Anisotropy is introduced, in this constitutive model, by using a structure tensor that shows direction of reinforced fiber. A new strain energy density function for anisotropic elasticity is proposed to improve accuracy associated with shear behaviors. After developing an elastic model, an anisotropic viscosity is modeled by a kind of Maxwell viscosity model at large strains. In addition to the development of constitutive model, a simple fracture prediction method, which refers to the finite element solution incorpolated with our proposed constitutive model, is proposed. Finally, our proposed constitutive model and fracture prediction method are validated with comparisons of uni-axial tension tests with fabric reinforced rubber.. |

47. |
Constitutive modeling for texture reinforced rubber by using an anisotropic visco-hyperelastic model Fabric reinforced rubber shows an anisotropy and viscosity in wide strain range. In this paper, an anisotropic visco-elastic model based on Mooney-Rivlin model is developed for fabric reinforced rubber. Anisotropy is introduced, in this constitutive model, by using a structure tensor that shows direction of reinforced fiber. A new strain energy density function for anisotropic elasticity is proposed to improve accuracy associated with shear behaviors. After developing an elastic model, an anisotropic viscosity is modeled by a kind of Maxwell viscosity model at large strains. In addition to the development of constitutive model, a simple fracture prediction method, which refers to the finite element solution incorpolated with our proposed constitutive model, is proposed. Finally, our proposed constitutive model and fracture prediction method are validated with comparisons of uni-axial tension tests with fabric reinforced rubber.. |

48. |
Norliyati Mohd Amin, Mitsuteru Asai, Yoshimi Sonoda, Fast transient structural FE analysis imposing prescribed displacement condition by using a model order reduction method via Kryrov subspace, *応用力学論文集*, 13, 159-167, 2010.08. |

49. |
Norliyati Mohd Amin, Mitsuteru Asai, Yoshimi Sonoda, Application of a model order reduction based on the Kryrov subspace to finite element transient analysis imposing several kinds of boundary condition, *IOP conf. ser. : Material Science and Engineering,*, 10, 012118, 2010.05. |

50. |
Mitsuteru Asai, Takanori Hayashi, Yoshimi Sonoda, Numerical estimation of water-induced impact pressure by using a smoothed particle hydrodynamics for incompressible flow, *Proceedings of Protect2009*, 2009.08. |

51. |
高野 直樹, Reduction of Finite Element Mesh and Model Order for Fast Dynamic Analysis of Global/Local Problem, *Jurnal of Solid Mechanics and Materials Engineering*, 3, 3, 572-583, 2009.03. |

52. |
高野 直樹, Reduction of Finite Element Mesh and Model Order for Fast Dynamic Analysis of Global/Local Problem, *Jurnal of Solid Mechanics and Materials Engineering*, 3, 3, 572-583, 2009.03. |

53. |
Mitsuteru ASAI, Kenjiro TERADA and Atsushi MARUYAMA, Eulerian Finite Cover Method for multi-scale analysis of large deformed composites, *8 th World Congress on Computational Mechanics*, 2008.07. |

54. |
Mitsuteru Asai, Naoki Takano, Yasutomo Uetsuji, Kunihiko Taki, An iterative solver applied to strongly coupled piezoelectric problems of porous Pb(Zr,Ti)O-3 with nondestructive modelling of microstructure, *MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING*, 10.1088/0965-0393/15/6/002, 15, 6, 597-617, 2007.09, A new preconditioned iterative solver based on the Kryrov subspace method is developed for solving large-scale finite element (FE) models of piezoelectric problems. The system matrix of piezoelectric FE analysis has negative eigenvalues because of coupling terms between mechanical and electrical fields. A general preconditioned iterative solver is ineffective for large-scale piezoelectric FE analysis due to the indefinite system matrix. A block diagonal preconditioner for the piezoelectric finite element method (FEM) is proposed by grouping nodal values as a block. Then the proposed solver is applied to the homogenization method, which can evaluate the effective macroscopic material properties by using FEM. In the FE modelling of complex microstructures, a semi-automatic technique with nondestructive observation provides reasonable 3D micrographs of porous Pb(Zr, Ti)O-3 (PZT). The efficiency of the proposed solver is investigated through the homogenization analysis of real porous PZT samples.. |

55. |
Mitsuteru Asai, Naoki Takano, Yasutomo Uetsuji, Kunihiko Taki, An iterative solver applied to strongly coupled piezoelectric problems of porous Pb(Zr,Ti)O-3 with nondestructive modelling of microstructure, *MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING*, 10.1088/0965-0393/15/6/002, 15, 6, 597-617, 2007.09, A new preconditioned iterative solver based on the Kryrov subspace method is developed for solving large-scale finite element (FE) models of piezoelectric problems. The system matrix of piezoelectric FE analysis has negative eigenvalues because of coupling terms between mechanical and electrical fields. A general preconditioned iterative solver is ineffective for large-scale piezoelectric FE analysis due to the indefinite system matrix. A block diagonal preconditioner for the piezoelectric finite element method (FEM) is proposed by grouping nodal values as a block. Then the proposed solver is applied to the homogenization method, which can evaluate the effective macroscopic material properties by using FEM. In the FE modelling of complex microstructures, a semi-automatic technique with nondestructive observation provides reasonable 3D micrographs of porous Pb(Zr, Ti)O-3 (PZT). The efficiency of the proposed solver is investigated through the homogenization analysis of real porous PZT samples.. |

56. |
S. Manchiraju, Mitsuteru Asai, S. Ghosh, A dual-time-scale finite element model for simulating cyclic deformation of polycrystalline alloys, *Journal of Strain Analysis for Engineering Design*, 10.1243/03093247JSA233, 42, 4, 183-200, 2007.08, A dual-time-scale finite element model is developed in this paper for simulating cyclic deformation in polycrystalline alloys. The material is characterized by crystal plasticity constitutive relations. The finite element formulation of the initial boundary-value problems with cyclic loading involves decoupling the governing equations into two sets of problems corresponding to two different time-scales. One is a long-time-scale (low-frequency) problem characterizing a cycle-averaged solution, while the other is a short-time-scale (high-frequency) problem for a remaining oscillatory portion. Cyclic averaging together with asymptotic expansion of the variables in the time domain forms the basis of the multitime-scaling. The crystal plasticity equations at the two scales are used to study cyclic deformation of a titanium alloy Ti-6Al. This model is intended to study the fatigue response of a material by simulating a large number of cycles to initiation.. |

57. |
Mitsuteru Asai, Naoki Takano, Yasutomo Uetsuji, Kunihiko Taki, An iterative solver applied to strongly coupled piezoelectric problems of porous Pb(Zr.Ti)O3 with nondestructive modeling of microstructure, *Modeling and Simulation in Metarial Science and Engineering*, Vol. 15, pp. 597-617, 2007.07. |

58. |
S. Manchiraju, M. Asai, S. Ghosh, A dual-time-scale finite element model for simulating cyclic deformation of polycrystalline alloys, *JOURNAL OF STRAIN ANALYSIS FOR ENGINEERING DESIGN*, 10.1243/03093247JSA233, 42, 4, 183-200, 2007.04, A dual-time-scale finite element model is developed in this paper for simulating cyclic deformation in polycrystalline alloys. The material is characterized by crystal plasticity constitutive relations. The finite element formulation of the initial boundary-value problems with cyclic loading involves decoupling the governing equations into two sets of problems corresponding to two different time-scales. One is a long-time-scale (low-frequency) problem characterizing a cycle-averaged solution, while the other is a short-time -scale (high-frequency) problem for a remaining oscillatory portion. Cyclic averaging together with asymptotic expansion of the variables in the time domain forms the basis of the multitime- scaling. The crystal plasticity equations at the two scales are used to study cyclic deformation of a titanium alloy Ti-6Al. This model is intended to study the fatigue response of a material by simulating a large number of cycles to initiation.. |

59. |
S. Manchiraju, M. Asai, S. Ghosh, A dual-time-scale finite element model for simulating cyclic deformation of polycrystalline alloys, *JOURNAL OF STRAIN ANALYSIS FOR ENGINEERING DESIGN*, 10.1243/03093247JSA233, 42, 4, 183-200, 2007.04, A dual-time-scale finite element model is developed in this paper for simulating cyclic deformation in polycrystalline alloys. The material is characterized by crystal plasticity constitutive relations. The finite element formulation of the initial boundary-value problems with cyclic loading involves decoupling the governing equations into two sets of problems corresponding to two different time-scales. One is a long-time-scale (low-frequency) problem characterizing a cycle-averaged solution, while the other is a short-time -scale (high-frequency) problem for a remaining oscillatory portion. Cyclic averaging together with asymptotic expansion of the variables in the time domain forms the basis of the multitime- scaling. The crystal plasticity equations at the two scales are used to study cyclic deformation of a titanium alloy Ti-6Al. This model is intended to study the fatigue response of a material by simulating a large number of cycles to initiation.. |

60. |
Image-Based Multi-Scale Analysis for Porous Piezoelectric Materials Based on the Homogenization Method This paper presents an image-based multi-scale analysis in order to evaluate macroscopic properties of heterogeneous porous piezoelectric materials by finite element calculations. The multi-scale analysis is based on the mathematical homogenization theory. Material heterogeneity is represented as a micro structure FE model that is automatically generated from the cross-sectioned images by high resolution X-ray CT. The high resolution X-ray measurement for porous PZT is compared with the digital image of SEM. Radius of pore is quantified from their images to compare these images. Nodal blocking preconditioned iterative solver is developed for piezoelectric FEM with high degree of freedom. In the numerical examples, material properties of porous PZT materials with different porosity are evaluated by the image-based multi-scale analysis to show the applicability and efficiency. Image-based multi-scale analysis with one million elements can be conducted by conventional PC with help of the proposed iterative solver.. |

61. |
Image-Based Multi-Scale Analysis for Porous Piezoelectric Materials Based on the Homogenization Method This paper presents an image-based multi-scale analysis in order to evaluate macroscopic properties of heterogeneous porous piezoelectric materials by finite element calculations. The multi-scale analysis is based on the mathematical homogenization theory. Material heterogeneity is represented as a micro structure FE model that is automatically generated from the cross-sectioned images by high resolution X-ray CT. The high resolution X-ray measurement for porous PZT is compared with the digital image of SEM. Radius of pore is quantified from their images to compare these images. Nodal blocking preconditioned iterative solver is developed for piezoelectric FEM with high degree of freedom. In the numerical examples, material properties of porous PZT materials with different porosity are evaluated by the image-based multi-scale analysis to show the applicability and efficiency. Image-based multi-scale analysis with one million elements can be conducted by conventional PC with help of the proposed iterative solver.. |

62. |
Multi-Scale Stress Analysis of Trabecular Bone Considering Trabeculae Morphology and Biological Apatite Crystallite Orientation This paper presents the multi-scale stress analysis of trabecular bone by the homogenization method bridging nano-micro-macro scales. Three-dimensional microstructure of trabeculae is obtained by the X-ray CT and the image-based modeling technique. Biological apatite (BAp) crystallite orientation is considered in the microstructure model by means of the anisotropic mechanical properties. The c-axis of BAp is set up as the maximum principal stress direction under the long term macroscopic stress condition. These properties are automatically assigned to each voxel element. To determine appropriately the microstructure model, the trabeculae morphology is analyzed and quantified as the trabecular density distribution. The proposed method is applied to pig's femur. It was revealed by the morphology analysis and homogenized macroscopic properties that the trabecular bone has plate-like characteristics. The predicted anisotropic level of the macroscopic properties was quantitatively coincident with the measured value by the X-ray diffraction analysis.. |

63. |
Multi-Scale Stress Analysis of Trabecular Bone Considering Trabeculae Morphology and Biological Apatite Crystallite Orientation This paper presents the multi-scale stress analysis of trabecular bone by the homogenization method bridging nano-micro-macro scales. Three-dimensional microstructure of trabeculae is obtained by the X-ray CT and the image-based modeling technique. Biological apatite (BAp) crystallite orientation is considered in the microstructure model by means of the anisotropic mechanical properties. The c-axis of BAp is set up as the maximum principal stress direction under the long term macroscopic stress condition. These properties are automatically assigned to each voxel element. To determine appropriately the microstructure model, the trabeculae morphology is analyzed and quantified as the trabecular density distribution. The proposed method is applied to pig's femur. It was revealed by the morphology analysis and homogenized macroscopic properties that the trabecular bone has plate-like characteristics. The predicted anisotropic level of the macroscopic properties was quantitatively coincident with the measured value by the X-ray diffraction analysis.. |

64. |
Composites Science/Technology and New Challenges for Tomorrow's Applications : II : Simulation-Based Design of Composite Materials and Structures. |

65. |
Composites Science/Technology and New Challenges for Tomorrow's Applications : II : Simulation-Based Design of Composite Materials and Structures. |

66. |
Finite cover method for physically and geometrically nonlinear problems. |

67. |
Kenjiro Terada, Mitsuteru Asai, Finite cover method for physically and geometorically nonlinear problems, *Lecture Notes on Computaional Science and Engineering*, Vol.43, pp.169-190, 2005.01. |

68. |
Mitsuteru Asai, Somnath Ghosh, Temporal homogenization for crystal plasticity, *AIP Conference Proceedings*, Vol. 712, pp.1725-1730, 2004.06. |

69. |
A NON-LOCAL VOXEL FINITE ELEMENT METHOD AND ITS APPLICATION TO FAILURE ANALYSES A non-local voxel FEM is developed for simulating the failure phenomena of heterogeneous brittle materials. The micro-scale or meso-scale morphology of heterogeneous materials is realized by the image-based modeling technique, whereas the cracking is simulated by the element vanish technique. Also, the nonlocal technique of integral-averaging type is effectively utilized to avoid both the stress oscillation errors on the material interfaces and the spurious dependency on the voxel size for crack propagation problems. The three-dimensional numerical simulations successfully demonstrate the cracking phenomena induced by the micro-scale heterogeneities and the so-called biaxial effect that is typical in the strength characteristics of concrete.. |

70. |
Kenjiro Terada, Mitsuteru Asai, Michihiro Yamagishi, Finite cover method for linear and nonlinear analysis of heterogeneous solids, *International Journal of Numerical Methods in Engineering*, Vol.58, pp.1321-1346, 2003.11. |

71. |
K Terada, M Asal, M Yamagishi, Finite cover method for linear and non-linear analyses of heterogeneous solids, *INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING*, 10.1002/nme.820, 58, 9, 1321-1346, 2003.11, We introduce the finite cover method (FCM) as a generalization of the finite element method (FEM) and extend it to analyse the linear and non-linear mechanical behaviour of heterogeneous solids and structures. The name 'FCM' is actually an alias for the manifold method (MM) and the basic idea of the method has already been established for linear analyses of structures with homogeneous materials. After reviewing the concept of physical and mathematical covers for approximating functions in the FCM, we present the formulation for the static equilibrium state of a structure with arbitrary physical boundaries including material interfaces. The problem essentially involves the discontinuities in strains, and possibly has the discontinuities in displacement caused by interfacial debonding or rupture of material interfaces. We simulate such non-linear mechanical behaviour after presenting simple numerical examples that demonstrate the equivalence between the approximation capabilities of the FCM and those of the FEM. Copyright (C) 2003 John Wiley Sons, Ltd.. |

72. |
Mitsuteru Asai, Kenjiro Terada, Kiyohiro Ikeda, Hiroyuki Suyama, Katashi Fujii, Meso-scopic numerical analysis of concrete structures by a modified lattice model, *土木学会論文集I*, Vol.20, No.1, pp.43-54, 2003.04. |

73. |
K Terada, M Asal, M Yamagishi, Finite cover method for linear and non-linear analyses of heterogeneous solids, *INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING*, 10.1002/nme.820, 58, 9, 1321-1346, 2003.11, We introduce the finite cover method (FCM) as a generalization of the finite element method (FEM) and extend it to analyse the linear and non-linear mechanical behaviour of heterogeneous solids and structures. The name 'FCM' is actually an alias for the manifold method (MM) and the basic idea of the method has already been established for linear analyses of structures with homogeneous materials. After reviewing the concept of physical and mathematical covers for approximating functions in the FCM, we present the formulation for the static equilibrium state of a structure with arbitrary physical boundaries including material interfaces. The problem essentially involves the discontinuities in strains, and possibly has the discontinuities in displacement caused by interfacial debonding or rupture of material interfaces. We simulate such non-linear mechanical behaviour after presenting simple numerical examples that demonstrate the equivalence between the approximation capabilities of the FCM and those of the FEM. Copyright (C) 2003 John Wiley Sons, Ltd.. |

74. |
Mitsuteru Asai, Kenjiro Terada, Kiyohiro Ikeda, Hiroyuki Suyama, Katashi Fujii, Meso-scopic numerical analysis of concrete structures by a modified lattice model, *Structural Engineering/Earthquake Engineering*, 10.2208/jsceseee.20.43s, 20, 731, 19-30, 2003.04, Realistic simulation of the mechanical behavior of concrete and reinforced concrete structures is performed by using a lattice type numerical model. Five different types of lattice members with simple constitutive models are introduced for mortar, coarse aggregate, steel, aggregate-mortar interface and steel-concrete interface. The meso-scopic morphology of concrete, which can be realized by the image-based geometry modeling technique, is taken into account. By the incorporation of the accurate meso-scopic morphology into the lattice type numerical modeling, the cracking behavior induced by the meso-scopic heterogeneities has been successfully captured.. |

75. |
Mitsuteru Asai, Kenjiro Terada, Kiyohiro Ikeda, Hiroyuki Suyama, Katashi Fujii, Meso-scopic numerical analysis of concrete structures by a modified lattice model, *Structural Engineering/Earthquake Engineering*, 10.2208/jsceseee.20.43s, 20, 731, 19-30, 2003.04, Realistic simulation of the mechanical behavior of concrete and reinforced concrete structures is performed by using a lattice type numerical model. Five different types of lattice members with simple constitutive models are introduced for mortar, coarse aggregate, steel, aggregate-mortar interface and steel-concrete interface. The meso-scopic morphology of concrete, which can be realized by the image-based geometry modeling technique, is taken into account. By the incorporation of the accurate meso-scopic morphology into the lattice type numerical modeling, the cracking behavior induced by the meso-scopic heterogeneities has been successfully captured.. |

76. |
浅井 光輝, 寺田 賢二郎, 池田 清宏, ラチスモデルによるコンクリート構造のメゾレベル解析, *土木学会論文集*, 10.2208/jscej.2003.731_19, 731, 19-30, 2003.04. |

77. |
Mitsuteru Asai, Kenjiro Terada, Kiyohiro Ikeda, Meso-scopic concrete analysis with a lattice model, *Proceeding of FRAMCOS-4*, A.A. Publishers, pp.757-764, 2001.05. |