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A wall boundary condition represented by polygons was presented by Harada et al.(31) based on the moving particle semi-implicit (MPS)(1) method to reduce the memory cost and calculation time for the wall particles. However, the inaccuracy of the wall weight function near a non-planar wall boundary causes the unphysical motion of the fluid. Therefor...
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Citations
... the contribution to a particle's particle number density and the boundary force based on the interpolated value of the SDF. Zhang et al. (2015) improved the accuracy of the model when curvature is present. ...
Computational fluid dynamics has been widely used in the design and analysis of various fluid systems. The proper treatment of boundary conditions is crucial for the accurate simulation of fluid flow. However, in particle methods, such as smoothed particle hydrodynamics method and moving particle semi-implicit method, the treatment of boundary conditions has been a challenging problem. In this paper, starting from the incompressibility condition, we present a new theory for the unified treatment of both rigid bodies and wall boundaries, which allows the strong coupling of rigid bodies and incompressible fluids. Because the boundary models are based on signed distance functions and do not use particles, these models can avoid several problems, such as resolution dependence of particle representations, and unavoidable unevenness of surfaces. We also provide a way to efficiently handle rigid-body boundaries and wall boundaries without particles by finding the fundamental boundary weight function that does not change with time. Several numerical examples are presented to demonstrate the capability of our models and to compare them with theoretical and experimental results.
... However, severe pressure fluctuation was induced. Zhang et al. (2015) modified the weight function for nonplanar boundaries, which significantly suppressed the pressure fluctuation. Zhang et al. (2016) proposed the boundary particle arrangement technique to make the PND near the nonplanar wall boundaries more accurate. ...
With the significant development of computer hardware, many advanced numerical techniques have been proposed to investigate complex hydrodynamic problems. This article aims to provide a detailed review of moving particle semi-implicit (MPS) techniques and their application in ocean and coastal engineering. The achievements of the MPS method in stability and accuracy, boundary conditions, and acceleration techniques are discussed. The applications of the MPS method, which are classified into two main categories, namely, multiphase flows and fluid-structure interactions, are introduced. Finally, the prospects and conclusions are highlighted. The MPS method has the potential to solve practical problems.
... For FSI problems in ocean engineering [1][2][3][4], aerodynamics etc., handling actual geometry with complex shapes is one of the challenges of wall boundary conditions in particle methods. The current research studies corresponding to wall boundary conditions in particle methods could range from dummy particle boundary [5][6][7], ghost particle model [8][9][10], unified semi-analytical wall (USAW) boundary [11][12][13][14], repulsive force boundary [15], wall potential particle boundary [16], immersed boundary model [17], polygon wall model [18][19][20][21] and generalized wall boundary [22]. ...
... In 3-D, an approximate equation is applied to reduce the computational cost. A polygon wall (PW) boundary condition was applied in MPS method by Zhang et al. [21][22][23][24]. Polygon meshes, instead of wall particles, are applied in to represent wall boundaries. ...
Dealing with complex geometry boundaries is a challenge for particle boundary conditions. Since the effective area of the fluid particle is cut off by the boundary, it is difficult to obtain accurate results near the boundary, especially for complex geometry shapes. Things become more complicated when dealing with multiple sizes of particles in multi-resolution particle methods. In this paper, a generic smoothed wall (GSW) boundary is proposed by using single layer particles to accurately discretize the boundary. The boundary weight function is transformed to a distance function to fill the vacancy of the particle number density of fluid particles. The GSW boundary can be applied in the static, moving and non-linear deforming wall conditions. It also can be used to effectively handle complex geometric boundaries, since simulation results are not affected by changes in the number and size of wall particles. In addition, the GSW boundary also shows good results when combined with multi-resolution methods solving problems with multiple sizes of particles. In this paper, the MPS–DEM coupling method with GSW boundary model is applied to solve non-linear FSI problem. Several cases have been calculated to validate the accuracy, convergency and stability of the GSW boundary model. Compared with dummy particle boundary, results show that the proposed GSW boundary model can improve the numerical accuracy near the boundary, and handle arbitrary moving boundaries with high efficiency.
... On the other hand, in the particle methods deformable geometry with a reasonable cost, unphysical behaviors are often observed. 27 Zhang et al 28 has proposed a remedy for this issue, although auxiliary boundary particles are needed. ...
Numerical treatment of complicated wall geometry has been one of the most important challenges in particle methods for computational fluid dynamics. In this study, a novel wall boundary treatment using analytical volume integrations has been developed for two‐dimensional (2D) incompressible flow simulations with the moving particle semiimplicit method. In our approach, wall geometry is represented by a set of line segments in 2D space. Thus, arbitrary‐shaped boundaries can easily be handled without auxiliary boundary particles. The wall's contributions to the spatial derivatives as well as the particle number density are formulated based on volume integrations over the solid domain. These volume integrations are analytically solved. Therefore, it does not entail an expensive calculation cost nor compromise accuracy. Numerical simulations have been carried out for several test cases including the plane Poiseuille flow, a hydrostatic pressure problem with complicated shape, a high viscous flow driven by a rotating screw, a free‐surface flow driven by a rotating cylinder and a dam break in a tank with a wedge. The results obtained using the proposed method agreed well with analytical solutions, experimental observations or calculation results obtained using FVM, which confirms that the proposed wall boundary treatment is accurate and robust.
... The polygon wall model developed by Harada et al. (2008) is necessary to simulate complicated shapes of actual products in practical calculation times; therefore, the polygon wall model has become important for industrial applications. Zhang et al. (2015) and Matsunaga et al. (2018) improved the polygon wall model of Harada et al. (2008). Studies of wettability on the polygon wall without using wall particles have been performed by Murozono et al. (2009), Ishii andSugii (2012), and Hattori et al. (2016); these researchers successfully reproduced static wettability in the equilibrium state by using the MPS method. ...
This paper presents the numerical simulation methods used to reproduce droplet retention and sliding on an inclined surface by using the Moving Particle Semi-implicit (MPS) method. The MPS method is useful for simulating free surface flows with highly deformed gas–liquid interfaces, such as the behavior of condensed water in an evaporator. However, the existing MPS method cannot correctly reproduce the behavior of a droplet retention and droplet sliding on an inclined surface. In the simulation of a droplet on a wall using the existing MPS method, the simulated droplet starts sliding as soon as the wall is inclined even slightly and falls down at a very high speed. In this study, the details of the forces acting from the wall to a droplet are considered, and the boundary condition models that contain the resistance forces acting on the contact line of a droplet are proposed. Droplet retention and droplet sliding on an inclined plate are successfully simulated by using the proposed models. Furthermore, the simulation results are compared with the experimental results reported in literature. The relationship between the droplet volume and critical sliding angle and that between the inclination angle of a slope and droplet sliding velocity are each compared using the experimental results and evaluated both qualitatively and quantitatively; they show good agreement with the experimental results.
... There are some other methods in which walls are represented by polygons (or a group of triangles) so that wall particles can be neglected [9,34,64]. However, these methods are based on the traditional MPS method and they calculate the particle number density of the wall from the distance between a particle and a wall. ...
... In other words, the number of particles used in the simulation was able to be reduced by 59.4% throughout the simulation. Additionally, the time step for the multi-resolution simulation, which is determined by the Courant condition from Eq. (64), was about twice larger than that for the single resolution simulation because the larger particles were located in the higher velocity region. As a result, the computational time was able to be reduced by 86.0% by using the multi-resolution discretisation. ...
In this work, the Moving Particle Semi-implicit (MPS) method is enhanced for multi-resolution problems with different resolutions at different parts of the domain utilising a particle splitting algorithm for the finer resolution and a particle merging algorithm for the coarser resolution. The Least Square MPS (LSMPS) method is used for higher stability and accuracy. Novel boundary conditions are developed for the treatment of wall and pressure boundaries for the Multi-Resolution LSMPS method. A wall is represented by polygons for effective simulations of fluid flows with complex wall geometries and the pressure boundary condition allows arbitrary inflow and outflow, making the method easier to be used in flow simulations of channel flows. By conducting simulations of channel flows and free surface flows, the accuracy of the proposed method was verified.
... The polygon wall boundary model was firstly proposed by Harada et al. [27] and modified by Zhang et al. [30] to accurately represent the smooth wall boundary and improve the efficiency. Different from the widely used particle wall boundary, which is shown in Figure 2, the wall boundaries are treated as a set of arbitrary planes instead of using particles. ...
The Fukushima nuclear accident raised the importance of flooding study in nuclear reactor buildings. It is known that the external flooding can be attributed to natural causes, while the internal flooding is caused by the piping ruptures, tank failure or the actuation of fire suppression systems. The building flooding process can damage the safety-related components and systems, which needs to study carefully. In order to simulate this phenomenon which is accompanied by complex flow with free surface, a particle method based on Lagrangian approach named explicit moving particle simulation (EMPS) method, is employed in this analysis. Verification and validation analyses are carried out. The verification problems are a hydrostatic analysis and a water spreading to investigate the differences of the particle wall and polygon wall boundary models, while the validation studies of two experiments of dam-break induced flooding show good agreements. Afterwards, the internal flooding process in AP1000 is simulated by assuming a break of the in-containment refueling water storage tank as an example. The results achieved so far indicate that the EMPS method is capable to simulate the internal flooding process in the nuclear reactor buildings.
The paper aims to provide a comprehensive review on the achievements made on moving particle semi-implicit (MPS) method and the applications in nuclear engineering. The state-of-the-art advancements in stability and accuracy, boundary conditions, surface tension, multiphase flow, fluid–structure interaction and multi-resolution technique are discussed. The applications in nuclear reactor fundamental thermal hydraulics and melt behaviors in severe accident are summarized. The drawbacks, current challenges, future developments and potential application areas of MPS method are highlighted.
As a Lagrangian meshless method, moving particle semi-implicit (MPS) method has been proven useful in the analysis of the free-surface flow, especially accompanied by the large deformation and fragmentation of fluids. The improvement of pressure distribution in three dimensions is an important aspect to verify the effectiveness of MPS. The accurate representation of 3-D geometries especially complex geometries is the premise of obtaining convincing pressure distribution. However, most of MPS applications cannot accurately represent complex wall geometries, which highly affects the reliability of MPS. For this reason, the triangle meshes are used to accurately represent the complex wall geometries in this research. The polygon wall boundary condition (PW) is adopted to enforce the wall boundary condition to the triangle meshes. The pressure of the wall boundaries is derived from the Neumann boundary condition to improve the velocity distribution of fluid particles near the wall boundaries. A first-order gradient model is presented to improve the accuracy and stability of the PW. Our approach can enhance the numerical stabilization to arbitrary geometries. We simulate several 3-D examples such as the classic hydrostatic simulation and the complex 3-D geometries with sharp angles and curved surfaces to demonstrate the general applicability of our new model.
The particle methods are suited to simulate fluid flow problems with large boundary deformation. The moving particle semi-implicit (MPS) method is one of the representative particle methods for incompressible flow. In recent years, the MPS method has received a great deal of attention in various fields of science and engineering. However, the numerical treatment of complicated wall geometry is still an open question. The conventional approaches have severe issues in handling arbitrary shape or calculation accuracy. In these circumstances, this study has been done to propose a novel numerical treatment of solid wall boundary in the MPS method. In this approach, the wall contribution in the discretization scheme is described in a form of volume integral over object domain. Thus, arbitrary-shaped boundaries represented by a polygon mesh can faithfully be considered. Moreover, since the distribution of physical quantity inside object is given by linear extrapolation, it satisfies the prescribed boundary condition with high accuracy. While the volume integral cannot be numerically evaluated with affordable computational cost, it can be transformed into a boundary integral form based on the divergence theorem. The derived boundary integral can be calculated with reasonable cost and acceptable accuracy using a projection technique and the Gaussian quadrature. The proposed method has been examined through several numerical test cases in 2D and 3D. As a result of the numerical tests, the present method is shown to have considerably higher accuracy compared to conventional methods, and its validity is verified.
