Particle Method for Incompressible Flow With Free Surface

Coupling of rigid body dynamics and moving particle semi-implicit method for simulating isothermal multi-phase fluid interactions

Simulation on mass transfer at immiscible liquid interface entrained by single bubble using particle method

Comparison of MPS and SPH methods for solving forced motion ship flooding problems

This paper proposes a control method for swarm robots to avoid collisions via fluid dynamics. MPS (Moving Particle Semi-implicit) method, which is a type of particle method, is used to reflect fluid dynamics to swarm robots. To adapt the MPS method to swarm robots, we consider distributed calculation of the MPS method. Specifically, the simultaneous equations for pressure calculation in the MPS method are solved by DCG (Distributed Conjugate Gradient) method. Since the DCG method is a distributed iterative solution method, the trade-off between computational complexity and communication traffi is important. We cluster swarm robots to reduce the total communication traffic, taking into account the relationship between distributed calculation and communication traffic. Numerical experiments are conducted to demonstrate the effectiveness of fluid collision avoidance against various shaped obstacles.

Core melting and molten migration behavior are hot and difficult issues in the field of nuclear reactor severe accident research. The Moving Particle Semi-implicit (MPS) meshless method has potential to simulate free-surface and multiphase flows. In this study, the MPS method was utilized to simulate the melting process of UO2-Zr rod-type fuel elements. The models of heat conduction with phase change, simplified UO2-Zr eutectic reaction, viscous flow and surface tension were implemented with the framework of standard MPS method. Then, the improved MPS code was used to simulate and analyze the process of high-temperature melting and characteristics of molten migration and solidification in the coolant channel, aiming at revealing the severe accidents for light water reactors (LWR), particularly the early core damage. The results showed that compared with the case of higher initial temperature, when the initial temperature of molten UO2 is lower, more molten UO2 will solidify on the surface of rod cluster, and the blockage of upper flow channel caused by molten UO2 is more serious. In addition, this study also demonstrated the potential of the MPS method for the study of complicated severe accident phenomena in not only traditional LWR but also advanced nuclear reactors in the future.

In this paper, the dam-break problem is numerically simulated using two-phase moving particle semi-implicit (MPS) method. Firstly, the two-phase MPS method is extended from single-phase MPS method. The present method treats the multiphase system as a multi-density and multi-viscosity fluid, and a single set of equations could be used for the whole system. The interaction between particles of different phases is considered through the applications of inter-particle viscosity and density smoothing technique. The two-phase MPS method is then successfully applied to violent dam-break problem. The numerical results obtained by single-phase and two-phase method are both compared with experimental results in the open literature. The characteristics of air cavity are analyzed, including the pressure inside the cavity and the cavity shape deformation.

The energetic fuel-coolant interaction (FCI) has been one of the primary safety concerns in nuclear power plants. Graphical processing unit (GPU) implementation of the moving particle semi-implicit (MPS) method is presented and used to simulate the fuel coolant interaction problem. The governing equations are discretized with the particle interaction model of MPS. Detailed implementation on single-GPU is introduced. The three-dimensional broken dam is simulated to verify the developed GPU acceleration MPS method. The proposed GPU acceleration algorithm and developed code are then used to simulate the FCI problem. As a summary of results, the developed GPU-MPS method showed a good agreement with the experimental observation and theoretical prediction.

In this paper, a new multiphase MPS-GPU method is proposed through the combination of moving particle semi-implicit (MPS) method and Graphics Processing Unit (GPU) acceleration technique. The new method not only inherits the advantage of MPS method in capturing complex interface deformations, but also overcomes the limitations of huge computational cost in three-dimensional MPS simulation. By this method, both the two-layer-liquid and three-layer-liquids sloshing problems are simulated three-dimensionally on the GPU device, in which more than one million of particles are included. In simulations, the sloshing patterns of each liquid layer under different external excitations are accurately captured. From the interface elevations and impacting pressures calculated by present method, it is found that an obvious discrepancy exists between the deformations of free surface and phase interfaces. Then, the results obtained by multiphase MPS-GPU method are compared with experimental data and other numerical results in open literature and a good agreement is achieved, which validates the accuracy and applicability of the present method in three-dimensional simulations of multi-layer-liquid sloshing flows.

Comparison investigations of numerical simulations of incompressible viscous flows by the SPH (smoothed particle hydrodynamics) and the MPS (moving particle semi-implicit) are presented. A dam-break problem is chosen as the test case. In the calculation with the SPH method, weakly compressible model is used, i.e. WCSPH, which describes water as a nearly incompressible fluid, while in MPS method, the pressure Poisson equation is introduced to keep the density of fluid to be constant. The numerical results show that the two particle methods are robust and flexible, numerical results qualitatively agree with the experimental data. It can be seen that both the SPH method and the MPS method can be easily applied to the complex free surface flow problems.

A higher-order moving particle semi-implicit (MPS) method was developed to solve water entry problems. The Wendland kernel function was applied in the particle interaction model. Various models for pressure gradient were investigated. To overcome the inconsistency in the original MPS methods, a pressure gradient correction was implemented to guarantee the first-order consistency of gradient. The corrective matrix was modified by using the derivative of the kernel function. A particle shifting technique was also applied to improve the numerical stability. Validation studies were carried out for water entry of a rigid wedge with the tilting angles of 0°, 10° and 20°, and a rigid ship section. The solutions by the present method are generally in good agreement with experimental data and other published numerical results.

Sponsored by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan, a computer code, named COMPASS, has been developed employing the Moving Particle Semi-implicit (MPS) method for various complex phenomena of core disruptive accidents (CDAs) in sodium-cooled fast reactors (SFRs). The COMPASS is designed to analyze multi-physics problems involving thermal hydraulics, structure and phase change, in a unified framework of MPS method. In this and the following five papers [1–5], the outcomes of the project in FY2006 are presented. In FY2006, development of the basic functions of the COMPASS was completed and fundamental verification calculations were carried out. In this paper, the outline of the project and a part of COMPASS, the structural mechanics part, are described, including formulation of MPS method and the conceptual design of COMPASS, and the results of the basic verification calculations for structural mechanics module.

A conservative finite volume-particle hybrid method for simulation of incompressible interfacial flow

The reliability of a micro-solder joint in a semiconductor structure depends on its solder shape. Therefore, many methods of predicting the molten-solder shape have been proposed. However, conventional methods cannot be used to accurately predict the shape of a miniaturized solder. In a miniaturized solder joint, molten solder greatly changes its shape during the reflow process, and even topology changes (e.g., merging with another solder in a neighboring joint or splitting into several pieces) might occur. Conventional methods cannot be used for expressing these phenomena. To predict a miniaturized solder shape, we developed a new shape-prediction method based on the moving-particle semi-implicit (MPS) method. In the MPS method, a continuum is expressed as an assembly of particles. In contrast to finite element analysis (FEA), our new method can easily express large deformation and topology changes because the continuum does not need to be divided into elements. Moreover, we evaluated the fracture life of a solder joint with the predicted solder shape by coupling our shape-prediction method with a crack-propagation analysis method that we also developed. The crack-propagation is used for automatically calculating a crack-initiation point and crack-propagation paths, and the fracture life is evaluated quantitatively. We applied this coupling method to evaluate fracture lives of various solder joints and found that a difference in solder shape caused a difference in crack-initiation points, crack-propagation paths, and fracture lives.

Numerical simulation of the SURC-2 and SURC-4 MCCI experiments by MPS method

When a liquid droplet impacts on a solid surface, it recoils to the center of that surface after reaching its maximum spreading diameter. The mechanism of droplet recoiling is not fully understood. To simulate this recoiling of a droplet, a particle method is a good choice because it does not require grids for simulating fluid motions, and can easily handle a large deformation of fluid. In this study, the coupled method of rigid body dynamics and the moving particle semi-implicit (MPS) method (Park and Jeun, 2011) was used to calculate three-dimensional droplet impingement. Also, the previous surface tension model for MPS (Nomura et al., 2001) was revised to get a more realistic surface tension force. A two-step calculation was performed. In the first step, a MPS calculation was performed with particles that were considered to have no mass or volume. In the second step, rigid body dynamics came into the calculation and considered the diameters of particles being slightly lesser than the initial distance between particles. In this study, the calculated results were compared with the measured data (Kim and Chun, 2000) and the recoiling lengths of droplets for the various initial impingement speeds were estimated.