Moving Particle Semi-implicit Method Research Articles

Numerical Simulations on the Flooding into a Damaged Cabin with a Flexible Bulkhead Based on the Mixed-Mode Function-Modified MPS Method

Floodwater entering the damaged cabin and impacting the bulkhead can cause damage to the watertight compartment and affect the survival of the ship. The elastic deformation of the bulkhead can slow down the impact and affect the flow field, which affects the hydrodynamic distribution inside the cabin. In this work, numerical simulations on the flooding phenomena into the damaged cabin with various stiffness, watertight bulkheads are carried out by using the mixed-mode function-modified moving particle semi-implicit (MPS) method, with the objective of investigating the influence of the stiffness of the watertight bulkheads on the structural impact load. Firstly, the numerical model based on the MPS method is set up to predict the dam-break wave impact load on an elastic plate and compared with the experimental measurements to verify the feasibility of the method. Then, the evolution of the flooding process of the damaged cabin with four different stiffnesses are simulated and the impact pressure on the bulkhead is predicted and compared. It is found that the flexible watertight bulkheads not only can reduce the peak pressure acting on it, but also have an effect on the hydrodynamic pressure distribution of the entire cabin. This implies that properly selected stiffness and material properties of watertight bulkheads can mitigate the impact of flooding on the damaged cabin’s bulkheads.

Potential of Computer-Aided Engineering in the Design of Ground-Improvement Technologies

The progress status of jet-grouting construction during the construction phase is difficult to verify and even after the completion of construction, it can be verified only by empirical methods. This study attempted to recreate a realistic simulation result of the middle-pressure jet-grouting method by establishing a computer-aided engineering (CAE) system from the planning/design stage of the ground model and verifying the validity of the construction process after the model was analyzed by the moving particle semi-implicit (MPS) method. The governing parameters for the ground were determined by the MPS simulation of the unconfined compression test. The construction simulation was analyzed and the results were validated by visual confirmation of the related phenomena, such as the soil-improved body formation and mud discharge. To verify the accuracy of the mud discharge phenomenon, three different probe regions were set above the model ground and the amount of mud discharge generated in each region was computed before drawing an overall conclusion of the study. A soil-improvement body of approximately 0.38 m3 was observed to have formed at the end of the study and the highest mud discharge particle number measured, for instance, was 896. This study is expected to serve as a guideline for further studies on simulation-based research.

Numerical investigation of gas entrapment in metal additive manufacturing using a quasi-sharp-interface particle method

Porosity is a key issue for the parts fabricated by selective laser melting. However, the porosity formation mechanisms have not been fully clarified. In particular, the formation of small pores in fabricated parts from the gas among granules is controversial. The existence of sharp corners among molten granules is a key numerical challenge because the conventional diffusive interface model (DIM) might trigger spurious gas entrapment. To solve the problem, a quasi-sharp-interface model (QSIM) was proposed for the moving particle semi-implicit (MPS) method in this study. A new approach to calculate the interface area based on the local triangularization was proposed to accurately impose the surface-tension force in the QSIM. The bubble-rising simulation verified the capability of the QSIM to simulate topological changes of interfaces. The sharp-corner deformation problem demonstrated that the QSIM could effectively prevent unphysical breakup and the spurious gas entrapment. Thus, the QSIM was indispensable for reliably simulating the gas entrapment from the gaps among granules in SLM. Finally, the QSIM results indicated that the gas among granules was completely discharged when the granules melted. This suggested that the gas among granules did not cause small pores in the fabricated parts. This observation correlated with an experimental composition analysis of gas in pores.

Turbulence analysis for vertical baffle configurations on prismatic tanks by the MPS method

A series of conceptual baffles have been proposed to attenuate pressure effects provoked by sloshing on the walls of Liquefied Natural Gas (LNG) tanks. However, these structures provoke turbulent behavior that need to be analyzed to avoid non-desired fluid effects. In this work, numerical sloshing analyses are developed by a two dimensional Moving Particle Semi-implicit (MPS) method applying the Sub-Particle-Scale Large Eddy Simulation (SPS-LES) turbulent model to identify the turbulent effects due to global motions on a prismatic LNG tank for two filling fractions. The impact pressure, total force, and total moment on tank walls are compared to a prismatic tank without baffles, one configuration with one baffle and two configurations with two baffles. The results illustrate the turbulence effects generated by the three baffle configurations on partially filled tanks (25% and 50% of filling fraction) showing that the effect of the baffles to reduce sloshing effects is more significant for low filling levels (25% of filling fraction), and also, there is a small difference on the sloshing reduced effects between one baffle or two baffles at different separations. However, important turbulent effects appear for high filling levels (50% of filling fraction) specially at roll motion.

The stability criterion based on the spurious pressure oscillation analysis of MPS method

The Moving Particle Semi-implicit (MPS) method has been widely used in nuclear engineering due to its unique advantages in capturing moving interfaces. However, the unphysical numerical oscillation in MPS method is still a hotspot and difficulty in current study, and also a bottleneck hindering its high-accuracy numerical simulation of nuclear engineering. To obtain more accurate and stable numerical simulation, the spurious pressure oscillation behavior is studied theoretically and numerically. Through theoretical analysis, it is found that the incompressible compensation term is the main cause of spurious pressure oscillation. Besides, three mainstream forms of PPE are analyzed in detail. The simulations are carried out to study the effects of corrective matrix, time step, external force, numerical resolution and velocity on pressure oscillation. Finally, the stability criterion of spurious oscillation phenomenon is newly proposed to determine the time step, and reliable simulation results are obtained as well.

Numerical study of gas-injection induced pool sloshing behavior using MPS method

When a Core Disruptive Accident (CDA) occurs in a Sodium-cooled Fast Reactor (SFR), as the accident progresses, its core may form a pool of molten fuel. When the molten fuel pool expands, a certain amount of coolant may be entrained in it. Because of the Fuel-Coolant Interaction (FCI), the molten fuel pool will have centralized sloshing behavior, making the fuel distribution more dense, leading to the risk of re-criticality, therefore, the study of centralized sloshing behavior is of great significance for evaluating the impact of the CDA. Under various experimental conditions, the sloshing experiment of gas injection can effectively simulate the mechanism and characteristics of centralized sloshing behavior. In this study, numerical simulation of gas-injection induced sloshing behavior is performed based on the Moving Particle Semi-implicit (MPS) method. Simulation results are compared with the experimental results. The results show that the deformation of bubble shape and liquid level in the sloshing characteristics are in good agreement with the experimental results. Therefore, the numerical simulation method established in this study can be used to study the pool sloshing characteristics induced by gas injection.

A multi-resolution particle method with high order accuracy for solid-liquid phase change represented by sharp moving interface

This paper develops a highly accurate, multi-resolution particle method to simulate solid-liquid phase change coupled with the thermal flow. Instead of including the latent heat in the governing equation, the heat equations for solid and liquid phases are solved separately. A sharp interface model is proposed to represent the solid-liquid interface explicitly. The sharp interface, represented by discrete nodes, provides the Neumann boundary condition for pressure and the Dirichlet boundary condition for velocity/temperature, respectively. Based on temperature gradients in the solid and liquid phases, the positions of these interface nodes are updated every time step. The Eulerian-based formulation, rather than the conventional Lagrangian-based one, is utilized to minimize time step-dependent error. Up to 4th order spatial discretization scheme is adopted based on the Least Square Moving Particle Semi-implicit (LSMPS) scheme. Moreover, a geometry-based multi-resolution scheme is introduced to dynamically refine the spatial resolution near the interface for saving computational cost. The 1-D Stefan problem is firstly simulated to verify the accuracy of the proposed sharp interface model. Then, the consistency of the multi-resolution scheme is investigated by a convergence study of the Taylor-Green vortex problem. After that, numerical simulations of natural convection in a cavity are performed with different spatial resolutions and high order schemes. Resulted computational costs are compared and discussed. Finally, the problems of melting by natural convection with different Rayleigh numbers are investigated. The results achieved so far indicate that the multi-resolution and high order schemes have great potential to save computational cost.

Study on Oil Distribution and Oil Content of Oil Bath Lubrication Bearings Based on MPS Method

Bearings are a core component of high-end equipment. Bearings need to be lubricated by oil and remove heat during operation. Lubrication is key to the stable operation of bearings. The moving particle semi-implicit (MPS) method is a numerical calculation method based on the Lagrange method. The oil distribution and content of oil bath–lubricated bearings are numerically simulated by the MPS method. A visual test bed for the oil bath lubrication flow field is established. The accuracy of the simulation results is verified. The distribution and total content of oil in the bearing cavity of oil bath–lubricated bearings at different speeds and oil levels are analyzed. The results show that when the rotation speed is low, the area with low lubricating oil content is 160°–200°, and the area with high lubricating oil content is 100°–140°. As the immersion height increases, the content of oil in the bearing cavity increases. As the rotation speed increases, the total content of oil in the bearing cavity decreases. The article offers a numerical simulation method for oil bath–lubricated bearings and has important guiding significance for the effective lubrication of bearings.

Numerical study of gas bubble rising in liquid sodium using advanced MPS method

In Sodium cooled Fast Reactor (SFR), study on the behavior of gas bubble is very crucial to the safety of SFR. In this study, an advanced Moving Particle Semi-implicit (MPS) method, the least square MPS (LSMPS), is used to study the rising behavior of gas bubble in liquid sodium. To improve the calculation, modified multiphase model is developed for the purpose of clear interface capture. The accuracy of LSMPS with modified multiphase model in simulate single rising bubble behavior is verified by several benchmarks with available experiment results. Then LSMPS is used to study single gas bubble rising in liquid sodium pool with different diameters. Velocity and shape of gas bubble is predicted using the LSMPS method. Side wall effects is also investigated.

An efficient MPS refined technique with adaptive variable-size particles

For the single-resolution particle method, large computation demand with high accuracy commonly requires enormous number of particles, which becomes greatly time-consuming. The moving particle semi-implicit (MPS) method with variable-size particles (VSP) has been proposed to refine particles in local domain. However, in VSP-MPS method, the refined area is fixed in the calculation, which makes it difficult to precisely capture flow near moving and deformable boundaries. This study develops a MPS method with adaptive variable-size particles model, called AVSP-MPS. In this method, by capturing moving and deformable boundaries, the objective computational domain can be dynamically refined. A new criterion, that splitting and coalescing only happen when the entire particle crosses the refined interface, is proposed to avoid unnecessary chain reactions of particle splitting and coalescing. The stability of the method is therefore improved. The district resolution is not a specific value, but a range in VSP model. An inappropriate selection of resolution range would cause repetitive splitting and coalescing, leading to low efficiency of the computation. In this research, the new maximum and minimum volumes in the region with different resolutions, as an optimized result, are obtained to improve convergence near the multi-resolution boundaries. Several cases as dam break and water entry are verified. The numerical results show that the AVSP-MPS method has an efficient, flexible and stable refinement technique in treating complex flow with large deformation.

Numerical investigation of sediment transport mechanism under breaking waves by DEM-MPS coupling scheme

Plunging waves generate vortices that suspend significant amounts of sediment in the key sediment transport mechanism in the surf and swash zones of beaches, causing major changes in the beach morphology over time. The intermittency and locality of vortices and sediment transport make it difficult to measure the flow fields and sediment concentrations in laboratory experiments or field investigations, making such studies of limited value for studying the sediment transport at beaches or as a basis for predicting changes in beach morphology. An attempt is made in this study to overcome these shortcomings through a particle-scale numerical investigation of sediment transport mechanisms under breaking waves. The numerical simulation was performed using three-dimensional coupling of the discrete element method (DEM) and moving particle semi-implicit (MPS) method, with the validity of the numerical model confirmed by comparison with experimental results obtained in a small wave flume. The numerical results revealed the intra-wave sediment motion and the contribution of the wave-generated pressure gradient to the sediment transport near the ripple crest. Sediment transport mechanisms was investigated at the spatial scale of the individual sediment grains by associating it with the vortices, turbulence, and exerted forces near the ripple trough. The results revealed that vortices generated at the water surface by plunging waves affected the bed material motions mainly through the action of a large pressure gradient force that arises near the bed surface owing to a local minimum of pressure, which can be associated with a vortex region.

Splitting of a three-dimensional liquid plug at an airway bifurcation.

Employing the moving particles' semi-implicit (MPS) method, this study presents a numerical framework for solving the Navier-Stokes equations for the propagation and the split of a liquid plug through a three-dimensional air-filled bifurcating tube, where the inner surface is coated by a thin fluid film, and surface tension acts on the air-liquid interface. The detailed derivation of a modified MPS method to handle the air-liquid interface of liquid plugs is presented. When the front air-liquid interface of the plug splits at the bifurcation, the interface deforms quickly and causes large wall shear stress. We observe that the presence of a transverse gravitational force causes asymmetries in plug splitting, which becomes more pronounced as the capillary number decreases or the Bond number increases. We also observe that there exists a critical capillary number below which the plug does not split into two daughter tubes but propagates into the lower daughter tube only. In order to deliver the plug into the upper daughter tube, the driving pressure to push the plug is required to overcome the hydrostatic pressure due to gravity. These tendencies agree with our previous experimental and theoretical studies.

Oil injection lubrication analysis of a silent chain drive system

Previous investigations on oil lubrication have mainly focused on gear transmission systems. There has been little research on injection lubrication of silent chain drive systems. In this study, a high-fidelity 3D model of a silent chain drive system is established, and the stability of the model is verified through simulation analysis. Using the moving particle semi-implicit (MPS) method, the flow field distribution of the silent chain drive system under the coupling of multiple fields is obtained through co-simulation with RecurDyn and Particleworks. The effects of key parameters, including sprocket speed, injection quantity, lubricant viscosity, and injection angles, on the lubrication performance of the silent chain drive system are investigated. These results provide a reference for future practical application and theoretical research of oil injection lubrication for chain drive systems.

Review of the State-of-Art of MPS Method in Ocean Engineering

When dealing with the complex deformation of free surface such as wave breaking, traditional mesh-based Computational Fluid Dynamics (CFD) methods often face problems arising alongside grid distortion and re-meshing. Therefore, the meshless method became robust for treating large displaced free surface and other boundaries caused by moving structures. The particle method, which is an important branch of meshless method, is mainly divided into the Smoothed Particle Hydrodynamics (SPH) and Moving Particle Semi-implicit (MPS) methods. Different from the SPH method, which involves continuity and treat density as a variable when building kernel functions, the kernel function in the MPS method is a weight function which treats density as a constant, and the spatial derivatives are discretized by establishing the gradient operator and Laplace operator separately. In other words, the first- or second-order continuity of the kernel functions in the MPS method is not a necessity as in SPH, though it might be desirable. At present, the MPS method has been successfully applied to various violent-free surface flow problems in ocean engineering and diverse applications have been comprehensively demonstrated in a number of review papers. This work will focus on algorithm developments of the MPS method and to provide all perspectives in terms of numerical algorithms along with their pros and cons.

An improved MPS-DEM numerical model for fluid–solid coupling problem in nuclear reactor

Compared with the grid method, the moving particle semi-implicit method (MPS) has prominent advantages in capturing the phase interface and avoiding grid distortion at the interface. However, MPS method is not particularly effective in dealing with the fluid–solid coupling problems including the interaction between discrete solid elements. Therefore, the PArticle method software for Nuclear reactor thermal hyDraulic Analysis (PANDA) is developed based on the MPS method and coupled Discrete Element Method (DEM) by introducing the idea of multiphase flow into the MPS-DEM coupling method. In this paper, the model is validated by reappearing the phenomena of DKT(drafting, kissing, and tumbling), and the problems of the slide of dry granular material and the underwater landslide are simulated as well. The numerical results are in good agreement with the experimental results, and the relative error of the leading edge distance is less than 6.12%. Finally, numerical simulation is carried out by taking molten pool accumulation in sereve accident of nuclear reactor as an example, which further confirms the good application prospects of PANDA in engineering problems.

An accurate and stable alternating directional moving particle semi-implicit method for incompressible flow simulation

As a Lagrangian mesh free method, Moving Particle Semi-implicit (MPS) method can easily handle complex incompressible flow with free surface. However, some deficiencies of MPS method such as inaccurate results, unphysical pressure oscillation and particle thrust near free surface still required to be further resolved. In this paper, an improved MPS method based on Crank-Nicolson time scheme, named Alternating Direction Moving Particle Semi-implicit (ADMPS) method, is proposed. In addition, a time integral source term (TIS) is developed to suppress unphysical pressure oscillation and a free-surface revise (FR) technique is proposed to avoid particle thrust near free surface. Enhancement of accuracy and stability by these improvements is proved by hydrostatic and dam breaking benchmarks, and the numerical results of the ADMPS-FR-TIS model show good agreement with the hydrostatic analytical solution and the dam breaking experiment data.

THE STRATIFICATION BEHAVIOR OF REACTOR MATERIALS IN THE FRAMEWORK OF MOVING PARTICLE SEMI-IMPLICIT

In reactor research, the safety of the reactor plays an important role. Besides the experiment research, computational simulation can also provide important information about the behavior of materials inside the reactor core. The Moving Particle Semi-Implicit (MPS) method assists in providing information about the reactor material computationally. In this study, the stratification process of several materials, i.e. the melts of PbBi, PbLi, and Pb in combination with Al, have been investigated by simulation. The time to achieve stratified conditions for each material has been obtained where each paired material needs 0.5 seconds to reach the stratified condition. It is also obtained that the Pb-Al is the fastest in reaching the stratified condition among the other used materials.

Experimental and Numerical Studies on Flowing Properties of Grouting Mortar Based on the Modified MPS Method

Grouting mortar has widespread application in engineering because of the advantages of good durability, low cost, and environmental friendliness. To study the flowing properties of grouting mortar, laboratory minislump tests taking different rheological parameters of grouting mortar into consideration were conducted to obtain the flow time and flow pattern of grouting mortar. A modified MPS method (moving-particle semi-implicit method) introduced two sections of Bingham rheological, and segregation was proposed. The effects of the plastic viscosity on the flow state of mortar were studied, and the relationship between the plastic viscosity and the flowing time was established. The numerical results show that the modified MPS method can be used to predict the flow time and flow pattern of mortar in the template, and plastic viscosity has a great influence on the flow time of concrete, and with the increase of plastic viscosity, the time to flow to the specified area also increases. Moreover, the analysis of the rheological parameters can provide the basis for the design of mix ratio in the construction practice.

Analysis of churning losses distribution of hydraulic pump in engineering vehicles using MPS method

The power losses of the hydraulic pump in engineering vehicle include mechanical losses, churning losses, and volume losses. The proportion of churning losses to power losses increases markedly, with the continuous improvement of the rotating speed of the hydraulic pump. The churning losses of the hydraulic pump are calculated by moving particle semi-implicit (MPS) method. It indicates that the inclination angle, speed, and oil content will significantly influence the churning losses. The churning torque and power losses of each rotating part increase with the pump speed. The churning losses of the cylinder block are the largest, followed by the retainer and slippers. The churning losses of pistons and shaft are small. With the decrease of oil volume, the churning losses decrease. With the decrease of the inclined angle of the swashplate, the total churning losses decreases. When the oil content is 70% of the full oil, the churning losses of the hydraulic pump is reduced by 57.4%. It provides guidance for the design of the hydraulic pump of high-power density for engineering vehicles and a new numerical calculation method for churning losses of the hydraulic pump.

Numerical investigation of fluid–solid interaction during debris bed formation based on MPS-DEM

The core may melt down and a debris bed with specific shape may be formed on the lower head of Reactor Pressure Vessel (RPV). The solid-to-solid collision has not been concerned thoroughly in the previous studies. In order to solve the problems of fluid–solid interaction and solid collision, the MPS-DEM code is developed based on Moving Particle Semi-implicit (MPS) method and Discrete Element Method (DEM). In this paper, the MPS models, DEM models are introduced, and the coupling method is validated by particle flow and collapse tests. Besides, the two-dimensional (2D) and three-dimensional (3D) simulations of the QUEOS-Q21 test are performed. The results of numerical simulation are in accordance with that of experiments, which indicates that the MPS-DEM method has the potential to be applied to study the movement characteristics of the debris particles during the debris bed formation without heat transfer, and has application prospect in the severe accident analysis.