| 1. |
Kumpei Tsuji, Mitsuteru Asai, Kiyonobu Kasama, Seepage failure prediction of breakwater using an unresolved ISPH-DEM coupling method enriched with Terzaghi’s critical hydraulic gradient, Advanced Modeling and Simulation in Engineering Sciences, https://doi.org/10.1186/s40323-022-00239-3, 10, 2023.01. |
| 2. |
Daniel Shigueo Morikawa, Kumpei Tsuji, Mitsuteru Asai, Corrected ALE-ISPH with novel Neumann boundary condition and density-based particle shifting technique, Journal of Computational Physics: X, https://doi.org/10.1016/j.jcpx.2023.100125, 17, 2023.03. |
| 3. |
Daniel S. Morikawa, Mitsuteru Asai, A phase-change approach to landslide simulations: Coupling finite strain elastoplastic TLSPH with non-Newtonian IISPH, COMPUTERS AND GEOTECHNICS, 10.1016/j.compgeo.2022.104815, 148, 2022.08, The present work shows a novel phase-change concept for simulating landslides using the smoothed particles hydrodynamics (SPH) method. The idea is to initiate the simulation of a slope stability problem with a Solid Mechanics-based SPH, modeling the soil as an elastoplastic material at finite strain. Next, if a particle exceeds a certain level of plastic strain, such particle changes its phase to a fluid state with non-Newtonian rheology, which is then solved with a Fluid Dynamics-based SPH method. We use the total Lagrangian SPH (TLSPH) method to solve the Solid Mechanics phase to avoid problems related to particle distribution (such as the tensile instability), while the implicit incompressible SPH (IISPH) to solve the Fluid Dynamics part to avoid the restriction on time increment in relation to high values of viscosity. The coupling between the two phases is treated as a conventional fluid-solid interaction (FSI) problem. We verified the proposed TLSPH method with the triaxial compression problem and demonstrated the robustness of the proposed phase-change TLSPH-IISPH coupled method in the simulation of the Aso landslide. Specifically, it may be the first time to simulate the Aso landslide from its initiation to its propagation in a single numerical simulation.. |
| 4. |
Daniel S. Morikawa, Mitsuteru Asai, Soil-water strong coupled ISPH based on u-w-p formulation for large deformation problems, Computers and Geotechnics, https://doi.org/10.1016/j.compgeo.2021.104570, 2022.02, 豪雨時の斜面崩壊など、地盤における水と土の連成問題の予測が求められている。粒子法の一つであるISPH法は、これまで主に水のみを対象とした解析技術として発展してきたが、この解析手法の拡張し、水と土の連成現象を強連成の定式化で解析できる手法を構築した。. |
| 5. |
Daniel S. Morikawa, Mitsuteru Asai, Soil-water strong coupled ISPH based on u - w - p formulation for large deformation problems, COMPUTERS AND GEOTECHNICS, 10.1016/j.compgeo.2021.104570, 142, 2022.02, This paper is dedicated to the introduction of a strong coupled soil-water interaction formulation based on an incompressible smoothed particle hydrodynamics (ISPH) framework. The method is based on the u-w-p Biot's formulation and adapted to a semi-implicit projection method for incompressibility condition of pore water and soil grains. The SPH Lagrangian particles move according to the soil velocity, while water variables are embedded into such soil particles. This allows to solve the pressure Poisson equation in a strong coupling way, in addition to enable to update the Darcy's drag force implicitly. A simple boundary treatment on natural boundary conditions for soil particle is proposed to take into account both non-penetration and friction effects. The proposed method was verified and validated through a series of numerical tests resulting in good agreements with both theoretical and experimental results. Finally, we show the applicability of the proposed method in the famous Selborne experiment, a full-scale slope failure problem.. |
| 6. |
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。. |
| 7. |
Daniel S. Morikawa, Mitsuteru Asai, Coupling total Lagrangian SPH-EISPH for fluid-structure interaction with large deformed hyperelastic solid bodies, COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING, 10.1016/j.cma.2021.113832, 381, 113832-113832, 2021.08, In this work, we propose a two-way coupling technique between a total Lagrangian smoothed particle hydrodynamics (SPH) method for Solid Mechanics and the explicit incompressible SPH (EISPH) to simulate fluid-structure interaction problems. In the solid part, the total Lagrangian framework guarantees that the particle distribution keep stable to correctly calculate the deformation gradient and thus the elastic forces. The constitutive model follows hyperelastic formulations, and the stability of the method is enforced by a Jameson-Schmidt-Turkel (JST) stabilization procedure. For the fluid part, we applied an EISPH formulation, which is a fully explicit incompressible scheme based on a projection method capable of providing accurate pressure distributions for free-surface flows, while avoiding costly linear equations. The coupling scheme follows the same manner as the fixed wall ghost particle (FWGP) approach, which was here adapted to include moving walls. In addition, the non-penetration condition is rigorously reinforced through a numerical algorithm to avoid penetration of every fluid particle, including free-surface particles. Our method for solid is then verified through a large deformed tension plate numerical test, and our coupling forces through a series floating tests and hydrostatic water column over a thin infinite plate. Then, the method is validated comparing it with experimental data of a dam break test in which the water column attacks a thin rubber plate. (C) 2021 Elsevier B.V. All rights reserved.. |
| 8. |
Daniel Morikawa, Harini Senadheera, Mitsuteru Asai, Explicit incompressible smoothed particle hydrodynamics in a multi-GPU environment for large-scale simulations, COMPUTATIONAL PARTICLE MECHANICS, 10.1007/s40571-020-00347-0, 8, 3, 493-510, 2021.05, © 2020, OWZ. We present an explicit incompressible smoothed particle hydrodynamics formulation with stabilized pressure distribution and its implementation in a multiple graphics processing unit environment. The pressure Poisson equation is stabilized via both pressure invariance and divergence-free conditions, and its explicit formulation is derived using the first step of the Jacobi iterative solver. Also, we show how to adapt the fixed wall ghost particle for the boundary condition into our explicit approach. Verification and validation of the method include hydrostatic and dam break numerical tests. The computational performance in the multi-GPU environment was notably high with reasonable speedup values compared to our single-GPU implementation. In particular, our code allows simulations with very large number of particles reaching up to 200 million per GPU card. Finally, to illustrate the potential of our formulation in simulating natural disasters, we present a simulation of the famous Fukushima Dai-ichi Power Plant inundation by the tsunami from The Great East Japan Earthquake in 2011, in Japan.. |
| 9. |
Mitsuteru Asai, Yi Li, Bodhinanda Chandra, Shinsuke Takase, 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 Methods in Applied Mechanics and Engineering, 10.1016/j.cma.2021.113681, 377, 113681-113681, 2021.04, © 2021 The Author(s) In this paper, a new particle-based fluid–rigid-body interaction simulator for violent free-surface flow problems is developed. The incompressible Smoothed Particle Hydrodynamics (ISPH) method has been proven to produce a smooth and accurate pressure distribution of free-surface fluid flow with breaking and fragmentation. Computed hydrodynamic forces can be applied onto rigid bodies, which may simultaneously experience contact or impact with the surrounding wall boundaries or another rigid body. Modeled by using the discrete element method (DEM), the contact force between rigid bodies is traditionally calculated employing the penalty approach, where a spring-based repulsive force is approximated at the vicinity of contact points depending on the deepest penetration depth. However, for high-speed collision problems involving a system of many rigid bodies, the values of approximated repulsive forces may be highly overestimated, and thus, a much smaller time step and an excessive damping parameter are often required to stabilize the approximated forces. This problem is highly inefficient for the computational resources of the fluid–rigid body interaction simulation since the computational cost at each time step is mostly dominated by the incompressible fluid simulation. The capability to increase the time increment following the critical time step of the fluid solver is, therefore, strongly demanded to increase the simulation efficiency. The current paper incorporates the usage of the energy-tracking impulse (ETI) method as an alternative approach to handle contact accurately. To achieve better energy conservation and enhance stability, Stronge's hypothesis is considered instead of the generally assumed Newton's contact law. The current work also covers three experimental validation tests, which were conducted to assure the quality and robustness of the coupled ISPH–DEM implementation.. |
| 10. |
Yi Li, Mitsuteru Asai, Bodhinanda Chandra, Masaharu Isshiki, Energy-tracking impulse method for particle-discretized rigid-body simulations with frictional contact, COMPUTATIONAL PARTICLE MECHANICS, 10.1007/s40571-020-00326-5, 8, 2, 237-258, 2021.03, © 2020, OWZ. Simulations of multi-body dynamics for computer graphics, 3D game engines, or engineering simulations often involve contact and articulated connections to produce plausible results. Multi-body dynamics simulations generally require accurate contact detection and induce high computational costs because of tiny time increments. As higher accuracy and robustness are continually being sought for engineering purposes, we propose an improved multi-body dynamics simulator based on an impulse method, specifically an energy-tracking impulse (ETI) algorithm that has been modified to handle particle-discretized rigid-body simulations. In order to decrease the computational costs of the simulations, in the current work, we assume a fixed moderate time increment, allowing multiple-point contacts within a single time increment. In addition to that, we distinguish the treatment between point-to-point and multiple-point contacts, which include edge-to-surface and surface-to-surface contacts, through an additional sub-cycling iterations. The improved ETI method was verified with analytical solutions of examples with single-body contact, a frictional slip, and a rolling contact. Moreover, the method was also validated with an experimental test of a line of dominoes with multiple-point contacts. Finally, a demonstration simulation with bodies of complicated shape subjected to a large number of constraints is given to show the optimum performance of the formulation.. |
| 11. |
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。. |
| 12. |
Estimation on collapse mechanism of Aso-bridge during the 2016 Kumamoto earthquakes using ASI-Gauss code
Many bridges and infrastrucutures were damaged by the seismic waves in the 2016 Kumamoto Earthquakes, and in this research, we focused on the Aso-bridge which collapsed immediately after the main shock. A huge landslide happened after the earthquakes and Aso-bridge, which was constructed in the same location of the landslide, totally collapsed. There are a couple of reports that four main factors might have contributed to this collapse; (1) seismic wave, (2) ground deformation, (3) landslide material load increase on the bridge, (4) basement ground collapse. In this paper, a numerical analysis of the Aso-Bridge collapse was conducted using the ASI-Gauss code, which is one of the finite element method utilizing beam elements. Then, we have discussed the main factor of the Aso-bridge collapse. . |
| 13. |
SPH-DEM COUPLING SIMULATION WITH A LIQUID BRIDGE FORCE FOR THE REPRESENTATION OF GROUND COLLAPSE PHENOMENON
Recently, the ground collapse caused by deterioration of sewer pipes, which is constructed during the period of high economic growth, has occurred frequently. In this study, 3-dimensional numerical analysis is conducted to understand the mechanism of ground collapse. As an analysis method, we developed a fluidsoil multi-phase flow analysis method based on particle method that can follow large deformation and discontinuous motion. By introducing the liquid bridging force, which has been studied in the field of powder engineering, the apparent cohesion due to water content was taken into consideration and improvements were made to adapt to unsaturated ground. We succeeded in reproducing the qualitative collapse phenomenon by the analysis of the depression phenomenon using this method. . |
| 14. |
Daniel Morikawa, Mitsuteru Asai, NurAin Idris, Yusuke Imoto, Masaharu Isshiki, Improvements in highly viscous fluid simulation using a fully implicit SPH method, COMPUTATIONAL PARTICLE MECHANICS, 10.1007/s40571-019-00231-6, 6, 4, 529-544, 2019.10, © 2019, OWZ. This study describes the application of two main improvements in highly viscous fluid simulations using the smoothed particle hydrodynamics (SPH) method: an implicit time integration scheme to overcome the problem of impractically small time step restriction and the introduction of air ghost particles to fix problems regarding the free surface treatment. This study adopts the incompressible SPH as a basis for the implementation of these improvements, which guarantees a stable and accurate pressure distribution. We verified the proposed implicit time integration scheme with simulations of pipe flow and the free surface treatment with a simple hydrostatic problem. As a result, the free surface of the hydrostatic problem became very smooth and stable. In addition, we conducted a variety of dam-break simulations to validate this proposed SPH method, as well as to analyze the density and divergence error. Finally, we demonstrate the potential of this method with the highly viscous vertical jet flow over a horizontal plate test, which features a complex viscous coiling behavior.. |
| 15. |
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。. |
| 16. |
Daniel Morikawa, Mitsuteru Asai, Nur’Ain Idris, Yusuke Imoto, Masaharu Isshiki, Improvements in highly viscous fluid simulation using a fully implicit SPH method, Computational Particle Mechanics, 10.1007/s40571-019-00231-6, 6, 4, 1-16, 2019.03, This study describes the application of two main improvements in highly viscous fluid simulations using the smoothed particle hydrodynamics (SPH) method: an implicit time integration scheme to overcome the problem of impractically small time step restriction and the introduction of air ghost particles to fix problems regarding the free surface treatment.. |
| 17. |
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. |
| 18. |
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. |
| 19. |
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. |
| 20. |
Abdelraheem M. Aly, Mitsuteru Asai, Water Entry of Decelerationg Spheres Simulaitons using Improved ISPH method, Journal of Hydrodynamivs, 2017.03. |
| 21. |
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. |
| 22. |
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. |
| 23. |
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. |
| 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. |
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. |
| 27. |
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. |
| 28. |
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. |
| 29. |
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. |
| 30. |
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. |
| 31. |
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. |
| 32. |
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. |
| 33. |
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. |
| 34. |
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. |
