| 1. |
♯Shota Deguchi, Mitsuteru Asai, Dynamic & norm-based weights to normalize imbalance in back-propagated gradients of physics-informed neural netwroks, Journal of Physics Communications, 10.1088/2399-6528/ace416, 7, 7, 2023.06. |
| 2. |
Yifang Qin, Shunhua Chen, Mitsuteru Asai, A nodal-based Lagrange multiplier/cohesive zone approach for three-dimensional dynamic crack simulations of quasi-brittle materials, Engineering Fracture Mechanics, https://doi.org/10.1016/j.engfracmech.2023.109637, 2023.09. |
| 3. |
Daniel Morikawa, Mitsuteru Asai, Surface tension simulations with corrected ALE-ISPH and density-based shifting technique, COMPUTATIONAL PARTICLE MECHANICS, https://doi.org/10.1007/s40571-023-00666-y, 2023.10. |
| 4. |
Mitsuteru Asai, Shujiro Fujioka, Yusuke Saeki, Daniel Morikawa Shigueo, Kumpei Tsuji, A class of second derivatives in the Smoothed Particle Hydrodynamics with 2nd-order accuracy and its application to incompressible flow simulations, Computer Method in Applied Mechanics and Engineering, https://doi.org/10.1016/j.cma.2023.116203, 415, 2023.10. |
| 5. |
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. |
| 6. |
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. |
| 7. |
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.. |
| 8. |
Masashi Watanabe, Taro Arikawa, Naoto Kihara, Chiaki Tsurudome, Koichi Hosaka, Tatsuto Kimura, Takayuki Hashimoto, Fumitaka Ishihara, Takemi Shikata, Daniel Shigueo Morikawa, Taiga Makino, Mitsuteru Asai, Yu Chida, Yoichi Ohnishi, Simone Marras, Abhishek Mukherjee, Juan Carlos Cajas, Guillaume Houzeaux, B. D. Paolo, Javier L. Lara, Gabriel Barajas, Inigo J. Losada, Masanobu Hasebe, Yoshinori Shigihara, Tatsuya Asai, Tsuyoshi Ikeya, Shusaku Inoue, Hideo Matsutomi, Yoshiaki Nakano, Yasuo Okuda, Shunya Okuno, Takayuki Ooie, Gaku Shoji, Tomokazu Tateno, Validation of tsunami numerical simulation models for an idealized coastal industrial site, COASTAL ENGINEERING JOURNAL, 10.1080/21664250.2022.2072611, 64, 2, 302-343, 2022.04, Numerous tsunami numerical models have been proposed, but their prediction accuracies have not been directly compared. For quantifying the modeling uncertainties, the authors statistically analyzed the prediction results submitted by participants in the tsunami blind contest held at the 17th World Conference on Earthquake Engineering. The reproducibility of offshore water level generated due to the tsunami with soliton fission significantly decreased when the nonlinear shallow water equation models (NSWE) was used compared to three-dimensional (3D) models. The inundation depth was reproduced well in 3D models. However, the reproducibility of wave forces acting on the structure and velocities over land was lower in 3D models than that in NSWE models. For cases where the impulsive tsunami wave pressure generated could not be calculated based on the hydrostatic assumption, the prediction accuracy of the NSWE models was higher than that of the 3D models. The prediction accuracies of both models were not improved at small grid-cell sizes. The NSWE model cannot simulate the short-wave component and vertical pressure distribution. Therefore, further developments in 3D models and smoothed particle hydrodynamics methods (SPH) are needed. The presented results contribute to the future development of tsunami numerical simulation tools.. |
| 9. |
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。. |
| 10. |
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.. |
| 11. |
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。. |
| 12. |
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.. |
| 13. |
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.. |
| 14. |
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.. |
| 15. |
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.. |
| 16. |
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 & FLUID FLOW, 10.1108/HFF-02-2020-0094, 31, 1, 154-173, 2021.01, © 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.. |
| 17. |
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。. |
| 18. |
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. . |
| 19. |
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.. |
| 20. |
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. . |
| 21. |
A RATIONALE OF THE STABILIZED ISPH METHOD II -AN OPTIMIZATION OF RELAXATION COEFFICIENT BASED ON ERROR ESTIMATES-
The stabilized ISPH method is a particle method for the incompressible Navier–Stokes equations and has a characteristic of adding a relaxation term with respect to a particle density in the pressure Poisson equation. The relaxation term contributes to keeping uniformness of particle distribution, then, enhancements of stability, volume conservation, and accuracy are confirmed by numerical results. For the stabilized ISPH method, it was shown by our previous study that the stabilization term is theoretically derived as an approximate solution of an energy minimization problem with respect to errors of incompressibility of fluid and uniformness of particle distributions weighted by a relaxation coefficient. However, a theoretical derivation of the optimal value of the relaxation coefficient remained unsolved. Then, this paper derives an optimal relaxation coefficient in the sense that minimizing an upper bound of errors derived by error analysis. Moreover, it is shown that the value and tendency of the optimal relaxation coefficient coincide with experimental results. . |
| 22. |
A VALIDATION FOR SOIL SCOURING SIMULATION BASED ON AN ISPH-DEM COUPLING METHOD
The mechanisms of the seawall destruction have been studied and the following three causes have been investigated in general; 1) horizontal force due to the water level difference, 2) soil scour and erosion behind the seawall during overflow, 3) seepage failure associated with the reduction of the bearing capacity. Whereas, the collapse predictions by complex destruction factors have not ever been realized. Hence, to predict various destruction due to interaction between water and soil, a multiphase flow simulator utilizing the Incompressible Smoothed Particle Hydrodynamics method (ISPH method) for water and Discrete Element method (DEM) for soil is developed in our research group. In this research, we simulated scouring phenomena due to vertical jet experiment for a validation test. In our SPH model, a turbulence model is adopted, and the velocity in the vicinity of the gravel DEM particles may decrease because of the eddy viscosity effect of the turbulent model. Then, we propose a modification to take into account the influence of unresolved turbulent flow. The modified drag force model shows a better performance to represent the gravel movement during this vertical jet simulation. Consequently, the result in this research indicate possibility that the gravel movement force needs to be supplemented energy. . |
| 23. |
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.. |
| 24. |
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, © 2019, Emerald Publishing Limited. 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(103 – 106), porous height Hp (0.2-0.6), Darcy parameter Da(10−5 − 10−1) 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.. |
| 25. |
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.. |
| 26. |
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.. |
| 27. |
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. |
| 28. |
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。. |
| 29. |
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.. |
| 30. |
A RATIONALE OF THE STABILIZED ISPH METHOD-A DERIVATION OF A STABILIZATION TERM FROM AN ENERGY MINIMIZATION PROBLEM-. |
| 31. |
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. |
| 32. |
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.. |
| 33. |
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. |
| 34. |
DIFFERENCES ON DIFFERENT FIDELITY LEVEL IN MODELING OF BUILDING AND EMBANKMENT HEIGHT ON TSUNAMI RUN UP SIMULATION BY 2D FINITE DIFFERENCE METHOD. |
| 35. |
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. |
| 36. |
Fluid-rigid body interaction simulation based on a stabilized ISPH method incorporated with the impulse-based rigid body dynamics
© 2018 by the Japan Society for Computational Engineering and Science. In fluid-rigid body interaction simulation based on the particle method, incompressible Smoothed Particle Hydrodynamic (ISPH) method is used to resolve the problem of fluid particles’ motion and impact load on the structure in the meanwhile DEM based on the penalty method is commonly applied to deal with the contact problem of rigid bodies. However, the accuracy of penalty method relies on a relatively small time increment. In this paper, the impulse-based rigid body dynamics is applied to deal with the collision contact problem instead of the conventional penalty method for robust and faster computation.. |
| 37. |
Validation of a fluid-solid multiphase flow simulation by a SPH-DEM coupled method and soil foundation scour simulation with a coarse graining particle model
© 2013 by the Japan Society for Computational Engineering and Science.. Disasters, such as sediment disaster caused by heavy rain and Tsunami disaster caused by an earthquake, are multiphase flow phenomena of fluid (water) and solid (soil). For damage prediction and countermeasure, fluid-solid analysis method is necessary since there is a scale limitation for an experiment. In this study, we develop multiphase simulator utilizing the Incompressible Smoothed Particle Hydrodynamics method (ISPH method) for fluid and Discrete Element Method (DEM) for solid. The interaction between ISPH method and DEM is implemented by considering an interaction force between fluid and solid. Free surface judgement is an important factor to obtain a good fluid analysis result. We utilize a method proposed by Marrone et al. to improve the free surface detection in a solid domain. In a simple validation test, dam break flow of water and glass beads, we validate and verify our method. At last, the method is applied to scouring analysis with a coarse graining particle model.. |
| 38. |
An offline based on-demand visualization system of large-scale particle simulation for tsunami disaster prevention
© 2017 The Institute of Electrical Engineers of Japan. 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 is computed by a high-performance computer via an offline on-demand tool without data transfer.. |
| 39. |
Masao Ogino, Takuya Iwama, Mitsuteru Asai, Development of an ISPH-FENI 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.. |
| 40. |
Abdelraheem M. Aly, Mitsuteru Asai, Water Entry of Decelerationg Spheres Simulaitons using Improved ISPH method, Journal of Hydrodynamivs, 2017.03. |
| 41. |
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. |
| 42. |
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.. |
| 43. |
Kensuke Harasaki, Mitsuteru Asai, DEVELOPMENT OF A FLUID-SOLID MULTIPHASE FLOW SIMULATOR BY A SPH-DEM COUPLED METHOD FOR SIMULATING A SEAWALL DESTRUCTION DUE TO SOIL FOUNDATION SCOUR, V INTERNATIONAL CONFERENCE ON PARTICLE-BASED METHODS - FUNDAMENTALS AND APPLICATIONS (PARTICLES 2017), 135-145, 2017.01, In 2011, Tohoku-Kanto earthquake tsunami caused serious damage to the port and coastal structures such as breakwaters and seawalls. The damage mechanism of these structures has been studied in the past, and it is found that there are some causes. In this study, a new simulation tool taking account of the soil scouring and seepage flow phenomena is developed to represent and predict the collapse of the breakwater with SPH-DEM coupled method.. |
| 44. |
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 AND TSUNAMI, 10.1142/S1793431116400200, 10, 5, 2016.12, The 2011 off the Pacific coast of Tohoku Earthquake was one of the most powerful earthquakes on record in Japan and the huge tsunami caused by the earthquake inflicted extensive damage to the coastal areas of the Tohoku region. To form safe coastal areas, countermeasures against disaster should be developed considering not only tangible infrastructures including breakwater and bridges but also intangible measures including education on disaster prevention and the development of hazard maps. The tsunami run-up analysis is expected to play a role as one of the countermeasures against tsunami. In this research, we aim to establish a tool to effectively analyze the tsunami run-up in urban areas based on the Smoothed particle hydrodynamics (SPH) method. And then, we propose a series of pre-process procedures to develop a detailed geography analysis model that reflects the geography, elevation, and exterior shapes of buildings by referring to 3D location information and digital elevation model data obtained from a geographical information system. Finally, we established a photorealistic visualization method so that citizen can understand the tsunami phenomenon intuitively.. |
| 45. |
Mitsuteru Asai, Yoshiya Miyagawa, Nur'ain Idris, Abdul Muhari, Fumihiko Imamura, Coupled Tsunami Simulations Based on a 2D Shallow-Water Equation-Based Finite Difference Method and 3D Incompressible Smoothed Particle Hydrodynamics, JOURNAL OF EARTHQUAKE AND TSUNAMI, 10.1142/S1793431116400194, 10, 5, 2016.12, In 2011, the tsunami generated by the Great East Japan Earthquake devastated infrastructure along the Pacific coast of northeastern Japan. In particular, the collapse of bridges resulted in much disruption to traffic, which led to delays in recovery after the disaster. We are developing a multi-scale and multi-physics tsunami disaster simulation tool to evaluate the safety and damage of infrastructure from huge tsunami. Multistage zooming tsunami analysis is one of the possible methods for implementing a high-resolution three-dimensional (3D) tsunami inundation simulation for a city. In this research, a virtual wave source that includes transition layers is proposed for a coupled simulation based on 3D particle simulation. The zooming analysis has been undertaken using the same particle method and a two-dimensional (2D) finite difference simulation. The 3D particle coupled simulation has been examined and validated.. |
| 46. |
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. |
| 47. |
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. |
| 48. |
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. |
| 49. |
Yoshiya Miyagawa, Mitsuteru Asai, Multi-Scale Bridge Wash Out Simulation During Tsunami by Using a Particle Method, 3RD INTERNATIONAL CONFERENCE ON CIVIL AND ENVIRONMENTAL ENGINEERING FOR SUSTAINABILITY (ICONCEES 2015), 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.. |
| 50. |
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.. |
| 51. |
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. |
| 52. |
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
On March 11, 2011, the huge tsunami caused by the great east Japan earthquake devastated the Pacific coast of north-eastern Japan. Many infrastructures including bridges were collapsed by the tsunami. New generation of tsunami disaster prevention and mitigation method should be reconsidered toward the next millennium Tsunami. In this study, a new boundary treatment using a virtual marker and the fixed boundary particle is developed to control the slip and no-slip boundary condition for the velocity field and to satisfy the pressure Neumann condition at the same time. Finally, the accuracy and efficiencies of our proposed method are validated by comparison between a numerical solution and experimental results.. |
| 53. |
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.. |
| 54. |
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.. |
| 55. |
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. |
| 56. |
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.. |
| 57. |
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.. |
| 58. |
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.. |
| 59. |
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.. |
| 60. |
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. |
| 61. |
Mitsuteru Asai, Multi-scale modeling in heterogeneous material properties, MI Lecture Note Series, 39, 84-95, 2012.09. |
| 62. |
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. |
| 63. |
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. |
| 64. |
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. |
| 65. |
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. |
| 66. |
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. |
| 67. |
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. |
| 68. |
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. |
| 69. |
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. |
| 70. |
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. |
| 71. |
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. |
| 72. |
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.. |
| 73. |
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.. |
| 74. |
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. |
| 75. |
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. |
| 76. |
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. |
| 77. |
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. |
| 78. |
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, 10.1299/jmmp.3.572, 3, 3, 572-583-583, 2009.03, MEMS structures and machines fabricated by photolithography and/or etching have often repeated unit microstructure. We need to design not only the global parameters but also microscopic and local parameters. In pursuit of this, a dynamic analysis of global/local problem is essential, and especially fast computational method and convenient modeling technique are both required for the MEMS design. Hence, this paper presents the application of model order reduction (MOR) for fast dynamic analysis combined with the finite element mesh superposition (FEMS) technique for practical and convenient modeling of the above-mentioned microstructures. Through two examples, the accuracy is carefully investigated for both global and local responses associated with the base vectors in MOR algorithm. The first example is analyzed by a kind of homogenization technique and MOR. The number of DOFs was finally reduced by a factor of approximately 1/6 (47,362/296,268). In addition, MOR enabled us to reduce the coefficient matrix size to only 300. The second example is analyzed by both FEMS and MOR, and it was found that MOR is also applicable to an unusual matrices generated by FEMS.. |
| 79. |
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. |
| 80. |
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.. |
| 81. |
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.. |
| 82. |
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.. |
| 83. |
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. |
| 84. |
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.. |
| 85. |
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.. |
| 86. |
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.. |
| 87. |
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.. |
| 88. |
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.. |
| 89. |
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.. |
| 90. |
Composites Science/Technology and New Challenges for Tomorrow's Applications : II : Simulation-Based Design of Composite Materials and Structures. |
| 91. |
Composites Science/Technology and New Challenges for Tomorrow's Applications : II : Simulation-Based Design of Composite Materials and Structures. |
| 92. |
Finite cover method for physically and geometrically nonlinear problems. |
| 93. |
Mitsuteru Asai, Somnath Ghosh, Temporal homogenization for crystal plasticity, AIP Conference Proceedings, Vol. 712, pp.1725-1730, 2004.06. |
| 94. |
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. |
| 95. |
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. |
| 96. |
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.. |
| 97. |
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.. |
| 98. |
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.. |
| 99. |
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. |
| 100. |
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.. |
| 101. |
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.. |
| 102. |
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. |
| 103. |
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. |
