Moving Particle Simulation Method Research Articles

Numerical simulation of interaction between organs and food bolus during swallowing and aspiration

The mechanism of swallowing is still not fully understood, because the process of swallowing is a rapid and complex interaction among several involved organs and the food bolus. In this work, with the aim of studying swallowing and aspiration processes noninvasively and systematically, a computer simulation method for analyzing the involved organs and water (considered as the food bolus) is proposed. The shape and motion of the organs involved in swallowing are modeled in the same way as in our previous study, by using the Hamiltonian moving particle simulation (MPS) method and forced displacements on the basis of motion in a healthy volunteer. The bolus flow is simulated using the explicit MPS method for fluid analysis. The interaction between the organs and the bolus is analyzed using a fluid-structure coupling scheme. To validate the proposed method, the behavior of the simulated bolus flow is compared qualitatively and quantitatively with corresponding medical images. In addition to the healthy motion model, disorder motion models are constructed for reproducing the aspiration phenomenon by computer simulation. The behaviors of the organs and the bolus considered as the food bolus in the healthy and disorder motion models are compared for evaluating the mechanism of aspiration.

Estimation of oil overflow due to sloshing from oil storage tanks subjected to a possible Nankai Trough earthquake in Osaka bay area

Sloshing of oil storage tanks is a great threat to industrial complexes when huge earthquakes occur. Overflow of oil due to sloshing could lead to serious tank fire and to oil dispersion due to Tsunamis. Since liquid sloshing is characterized as a highly nonlinear free-surface flow, numerical approaches are more suitable than theoretical ones to estimate the overflow from oil storage tanks caused by sloshing. The moving particle simulation (MPS) method, which is a mesh-free and Lagrangian particle method, is applied to the sloshing simulation. Thanks to the perfect mass conservation of the particle method, the overflow amount of oil can be accurately estimated by simply counting the number of overflowed fluid particles.There is high-possibility of occurrence of huge earthquakes along the Nankai Trough subduction zone, and the worst scenario is presumed as MW9.0, which is the same as the 2011 Tohoku earthquake. In order to simulate sloshing of oil storage tanks subjected to a possible Nankai Trough earthquake, ground shaking characteristics of the site need to be evaluated. Therefore we carried out microtremor measurements with high density in an industrial complex in Osaka bay area. A strong ground motion during a scenario earthquake with MW9.0 along the Nankai Trough is estimated based on the SMGA models considering the empirical site amplification and phase effects.Fully nonlinear sloshing simulations, using an in-house GPU computing code based on the explicit MPS method, are performed for a large-size oil storage tank installed with a floating roof by imposing the estimated strong ground motion of Nankai Trough earthquake as the external oscillation. As a result, significant amount of oil flows onto the floating roof and large amount of oil overflow from the tank is confirmed. The numerical result suggests the entire fire is one of major concerns for the assumed earthquake scenario. Finally sloshing simulations are repeated for small- and medium-size tanks, and then the total amount of outflow oil is estimated for the industrial complex of interest in the estimated Nankai Trough earthquake.

Second order accurate particle-based formulations

Purpose– The purpose of this paper is to present new implementation aspects of unified explicit time integration algorithms, called the explicit GS4-II family of algorithms, of a second-order time accuracy in all the unknowns (e.g. positions, velocities, and accelerations) with particular attention to the moving-particle simulation (MPS) method for solving the incompressible fluids with free surfaces.Design/methodology/approach– In the present paper, the explicit GS4-II family of algorithms is implemented in the MPS method in the following two different approaches: a direct explicit formulation with the use of the weak incompressibility equation involving the (modified) speed of sound; and a predictor-corrector explicit formulation. The first approach basically follows the concept of the explicit MPS method, presented in the literature, and the latter approach employs a similar concept used in, for example, a fractional-step method in computational fluid dynamics.Findings– Illustrative numerical examples demonstrate that any scheme within the proposed algorithmic framework captures the physics with the necessary second-order time accuracy and stability.Originality/value– The new algorithmic framework extended with the GS4-II family encompasses a multitude of pastand new schemes and offers a general purpose and unified implementation.

Performance improvements of differential operators code for MPS method on GPU

In the present study, performance improvements of the particle search and particle interaction calculation steps constituting the performance bottleneck in the moving particle simulation method are achieved by developing GPU-compatible algorithms for many core processor architectures. In the improvements of particle search, bucket loops of the cell-linked list are changed to a loop structure having fewer local variables and the linked list and the forward star of particle search algorithms within a bucket are compared. In the particle interaction calculation, the problem of the ratio of particles within the interaction domain to the neighboring particle candidates being quite low is improved. By these improvements, a performance efficiency of 24.7 % can be achieved for the first-order polynomial approximation scheme using NVIDIA Tesla K20, CUDA-6.5, and double-precision floating-point operations.

Deformation analysis for earth structure based on Moving Particle Simulation method

Deformation analysis for earth structure based on Moving Particle Simulation method

Accuracy of Rayleigh wave analysis using the moving particle simulation method

Accuracy of Rayleigh wave analysis using the moving particle simulation method

20208 液体入り容器の運搬軌道計画

This paper describes the transport of a liquid container by a robot, due to the demand for the conveyance of molten metal in casting processes, for the tray service by robots, and so on. Since liquid in a container can wave greatly by changes of transport velocity due to the inertial force acting on its own, robots are not able to carry the container as a rigid box. Therefore, the transportation of one or more liquid containers using a robot requires a carrying method which prevents content fluid from being spilled from the container. The proposed method, the TGCW (Trajectory Generation to Control Wave) method, is a feed-forward control to realize the prevention of the spillover of content fluid. To reveal the performance of the TGCW method, we perform the verification by simulation using the explicit MPS (Moving Particle Simulation) method and by experiment.

MPS–FEM PARTITIONED COUPLING APPROACH FOR FLUID–STRUCTURE INTERACTION WITH FREE SURFACE FLOW

Fluid–structure interaction analysis involving free surface flow has been investigated using mesh-based methods or mesh-free particle methods. While mesh-based methods have several problems in dealing with the fragmentation of geometry and moving interfaces and with the instability of nonlinear advective terms, mesh-free particle methods can deal with free surface and moving boundary relatively easily. In structural analyses, the finite element method, which is a mesh-based method, has been investigated extensively and can accurately deal with not only elastic problems but also plastic and fracture problems. Thus, the present study proposes a partitioned coupling strategy for fluid–structure interaction problems involving free surfaces and moving boundaries that calculates the fluid domain using the moving particle simulation method and the structure domain using the finite element method. As the first step, we apply a conventional serial staggered algorithm as a weak coupling scheme. In addition, for the verification of the proposed method, the problem of a breaking dam on an elastic wall is calculated, and the results are compared with the results obtained by other methods.

Development of Moving Particle Simulation Method for Multiliquid-Layer Sloshing

The mixed oil and gas including water and sand are extracted from well to offshore structure. This mixed fluid must be separated for subsequent processes by using wash tanks or separators. To design such a system, a proper numerical-prediction tool for multiphase fluids is required. In this regard, a new moving particle simulation (MPS) method is developed to simulate multiliquid-layer sloshing problems. The new MPS method for multifluid system includes extra search methods for interface particles, boundary conditions for interfaces, buoyancy-correction model, and surface-tension model for interface particles. The new particle interaction models are verified through comparisons with published numerical and experimental data. In particular, the multiliquid MPS method is verified against Molin et al’s (2012) experiment with three liquid layers. In case of excitation frequency close to one of the internal-layer resonances, the internal interface motions can be much greater than top free-surface motions. The verified multiliquid MPS program is subsequently used for more nonlinear cases including multichromatic multimodal motions with larger amplitudes, from which various nonlinear features, such as internal breaking and more particle detachment, can be observed. For the nonlinear case, the differences between with and without buoyancy-correction and surface-tension models are also demonstrated.

Numerical prediction of oil amount leaked from a damaged tank using two-dimensional moving particle simulation method

When an oil-spilling accident occurs at sea, it causes tremendous economic loss and environmental damages. To minimize these marine disasters, predicting the amount of oil-leaking is one of the most important things for the quick response and decision making in the early stage of the accident. In the present study, numerical investigation on the oil-leaking phenomena from a two-dimensional damaged tank was carried out to predict the amount of the oil leaking from a leakage hole of a rectangular tank by using the PNU-MPS(Pusan-National-University-modified Moving Particle Simulation) method (Lee et al., 2011). As a preliminary test to confirm the accuracy of the PNU-MPS method for the two-phase problem and to investigate the influence of the gradient model, numerical simulations for the Rayleigh–Taylor(R–T) instability were carried out By using an appropriate gradient model and applying a high-order time integration scheme, i.e. 4th-order Runge–Kutta scheme, it was found that the simulation results became closer to the experimental ones (Kim and Lee, 2001), by which the oil-leaking speed and Torricelli's factor relating the speed predicted by using the hydrostatic balance and the real leakage speed were measured and assessed.

係留浮体の波浪中応答解析に対するMPS法の適用性に関する研究（第二報）

For advancing ocean development, it is important to estimate response of moored floating structures in order to ensure the safety because they are placed on severe environment for a long time. Moored floating structures show complex motion at offshore ocean. The moving particle simulation (MPS) method is suitable to simulate the non-linear phenomena and the interaction of fluid and structures. In this study a improved MPS method which has an algorithm to solve pressure oscillation of particles and attenuation of wave height has been developed. The authors examined the applicability of the two-dimensional MPS method to response analysis of moored floating structure in regular waves. The numerical results have good agreement with laboratory data in term of time histories, spectra and frequency response, and the allow ability of the improved MPS method is indicated.

Optimizing Particle Simulation for Kepler GPU

We optimized Moving Particle Simulation (MPS) method for Kepler GPU. Solving sparse matrix occupies a large portion of particle simulation because it is a casus of performance bottlenecks. We reported at NVIDIA's GPU Technology Conference 2012 that we achieved to accelerate MPS method about 7x faster on NVIDIA Tesla C2070 compared with on Intel Core i7 920 (4 cores). Last year, NVIDIA released the latest GPU, Kepler. We optimized and accelerated particle simulation on Kepler GPU by using new shuffle instruction and read-only data cache. We obtained to accelerate Sparse Matrix-Vector multiplication operation 1.48x faster on Kepler (Tesla K20c) compared with on Fermi (Tesla C2075).

CM-JP-10 Hierarchical domain decomposition explicit MPS method for a billions-of-particle analysis

In this research,a new distributed memory parallel algorithm of the explicit MPS(Moving Particle Simulation) method is presented.An analysis region is divided for a distributed memoiy parallel computation using ParMETIS.As a result,we have been able to do the MPS analysis of 523 million particles using 23,040 cores in 5.4 seconds per one time step.In the performance,we has achieved near 5% of the peak performance,16.65 teraflops at maximum and 13.24 speed -up from 480 cores to 7,680 cores.

1403 10億粒子解析のためのマルチスケールグリッドを用いた階層型領域分割MPS陽解法と津波解析への応用(OS14-1.メッシュフリー/粒子法とその関連技術(1),OS・一般セッション講演)

In this research, a new distributed memory parallel algorithm of the explicit MPS (Moving Particle Simulation) method is presented. An analysis region is divided for a distributed memory parallel computation using ParMETIS. As a result, we have been able to do the MPS analysis of 523 million particles using 23,040 cores in 5.4 seconds per one time step. In the performance, we has achieved near 5% of the peak performance, 16.65 teraflops at maximum and 13.24 speed-up from 480 cores to 7,680 cores. Performance during large scale simulation is examined by computing tsunami wave run-up on a virtual gulf area using up to 58 million particles.

슬로싱 해석을 위한 CCUP 기반 시뮬레이션 기술 개발

A new computational program, which is based on the CIP/CCUP(Constraint Interpolation Profile/CIP Combined Unified Procedure) method, has been developed to numerically analyse sloshing phenomena dealt as multiphase-flow problems. For the convection terms of Navier-Stokes equations, the RCIP(Rational function CIP) method was adopted and the THINC-WLIC(Tangent of Hyperbola for Interface Capturing-Weighted Line Interface Calculation) method was used to capture the air/water interface. To validate the present numerical method, two-dimensional dam-breaking and sloshing problems in a rectangular tank were solved by the developed method in a stationary Cartesian grid system. In the case of sloshing problems, simulations by using a improved MPS(Moving Particle Simulation) method, which is named as PNU-MPS(Pusan National University-MPS), were also carried out. The computational results are compared with those of experiments and most of the comparisons are reasonably good.

Moving Particle Simulation for Mitigation of Sloshing Impact Loads Using Surface Floaters

The violent free-surface motions and the corresponding impact loads are numerically simulated by using the refined Moving Particle Simulation (MPS) method, which was originally proposed by Koshizuka and Oka (1996) for incompressible flows. In the present method, accuracy and efficiency are significantly improved compared to the original MPS method by using optimal source term, optimal gradient and collision models, and improved solid-boundary treatment and search of free-surface particles. The refined MPS method was verified through comparisons against Kishev et al.'s (2006) sloshing experiment. It is also demonstrated that the refined MPS method is excellent in mass conservation regardless of length of simulation time. The developed simulation tool is applied to an interesting idea of using surface floaters to reduce sloshing-induced impact loads. It is seen by a series of simulations that the maximum impact loads can be effectively reduced by using properly chosen floater density. Copyright 2011 Tech Science Press.

Numerical Simulation of Three-Dimensional Free-Surface Flows with Explicit Moving Particle Simulation Method

In nuclear engineering, fluid flows involving free surface were well studied, e.g., pipe thinning produced by liquid droplet impingement, and steam explosion triggered by molten metal immersed in water. The moving particle simulation (MPS) method was often used in past studies. In this method, the Poisson equation was solved to obtain the pressure field. Solving the Poisson equation becomes a dominant process. Reducing the time of calculation of the Poisson equation is important for using the CFD in the engineering fields. Thereat, we propose a new MPS method by which the pressure field is calculated explicitly. We call it the explicit (E-)MPS method. The E-MPS method was applied to a static water and dam break problem to show its adequacy. Besides, we compare the calculation time between the E-MPS method and traditional one.

515 粒子法における安定化(OS5.メッシュフリー/粒子法とその関連技術(4),OS・一般セッション講演)

Although the MPS (Moving Particle Simulation) method has been expected to prevail in wide industrial applications, the numerical instability of pressure remains a serious problem. This paper shows that the modification in a Poisson equation using hybrid source terms and the optimization of those parameters reduce the instability. At the same time, this optimization method is effective to prevent the volume compression of the MPS particles, which has the trade-off against the stability.