关于流体模拟细节增强技术的研究

基于物理的流体动画技术一直是计算机图形学领域研究的重点,但是之前大多数研究一直针对的是如何对流体模拟进行加速,而文章对于如何更加精细的模拟流体做了全面的综述,重点从模拟方法、界面重构、边界控制及算法优化方面做了介绍与分析.     

Automotive fuel cell sloshing under temporally and spatially varying high acceleration using GPU-based Smoothed Particle Hydrodynamics (SPH)

Understanding how fuel sloshes in a fuel cell, as a vehicle races around a circuit, is an important but mostly unexplored factor when designing fuel containment systems. Cell designs are based on knowledge of how liquids slosh in other containers, with the design and placement of structures, such as weirs, based on engineering judgement.This work aims to provide better understanding for this difficult problem with a view to improve future designs. A Graphics Processing Unit (GPU) based Smoothed Particle Hydrodynamics (SPH) model is presented to simulate the fuel sloshing problem, with results from a simplified and real fuel cell geometry shown and compared against real data recorded in a vehicle. The vehicle motion and accelerations are included in the SPH simulations using a body force within the momentum equation. Results show good agreement between the simulation and the real fuel movement, with bulk motion captured well for accelerations up to 5 times gravity.Focus is placed on the practicality of the method for use as part of an industrial design process, therefore the amount of time needed to compute results is considered throughout. Computational performance is found to be within acceptable limits, while numerical accuracy is actively considered through the use of Kahan compensated summation. It is concluded that the model is successful in capturing the necessary fluid dynamics for it to be useful in fuel cell design. It is expected that the method will provide insight into current cell designs and highlight where improvements can be made.     

高可扩展可容错的无网格/粒子程序petaPar及其测试

petaPar 粒子模拟程序面向千万亿次级计算,在统一框架下实现两种广受关注的粒子模拟算法：光滑粒子流体动力学（Smoothed Particle Hydrodynamics,SPH）和物质点法（Material Point Method,MPM)。代码支持多种材料模型、强度模型和失效模型,适合模拟大变形、高应变率和流固耦合问题。支持纯 MPI 和 MPI+X 混合两种并行模型。系统具有可容错性,支持无人值守变进程重启。在Titan 上测试表明,petaPar 可线性扩展到 26 万 CPU 核,SPH 和 MPM 算法并行效率相对 8 192 核分别为 87% 和 90%。     

Dynamic flow‐based particle splitting in smoothed particle hydrodynamics

In this work, a dynamic procedure for local particle refinement to be used in smoothed particle hydrodynamics (SPH) is presented. The algorithm is able to consistently produce successive levels of particle splitting in accordance to a flow‐based criterion. It has been applied together with accurate and robust formulations for variable spatial resolution in the framework of a semi‐implicit, truly incompressible scheme for SPH. Different test cases have been considered to assess the capabilities and advantages of the proposed procedure, namely, the laminar flow around circular and square obstacles in a plane channel for various regimes. Such flow cases entail the simulation of attached and separated shear layers, recirculating flow, vortex shedding and surface discontinuities. The results obtained for two levels of particle splitting have demonstrated that significant improvements may be obtained with respect to uniform particle spacing solutions in a variety of situations, thus presenting an excellent trade‐off between accuracy and computational cost. Copyright © 2015 John Wiley & Sons, Ltd.     

Modelling elastoplastic frictional collisions of ellipsoidal granules with collisional-SPH

The Collisional-SPH method models the combined evolution of deformation and frictional contact forces in elastoplastic granular collisions. However, there are many applications in which the granules are not spherical. In this paper, CSPH is extended to model an impact of an ellipsoidal granule on a flat deformable substrate. The CSPH spring-stiffness formulation is developed to account for the contact area eccentricity. Validation for different granule orientations and aspect-ratios are presented. The combined effect of substrate deformation and non-spherical granule shape on the contact-zone mechanics is investigated for different granule orientations and aspect ratios. It is found that the granule’s orientation and aspect ratio influences the interdependence between substrate deformation and contact-force distribution and should be accounted for in collision models.     

Local Poisson SPH For Viscous Incompressible Fluids

Enforcing fluid incompressibility is one of the time‐consuming aspects in SPH. In this paper, we present a local Poisson SPH (LPSPH) method to solve incompressibility for particle based fluid simulation. Considering the pressure Poisson equation, we first convert it into an integral form, and then apply a discretization to convert the continuous integral equation to a discretized summation over all the particles in the local pressure integration domain determined by the local geometry. To control the approximation error, we further integrate our local pressure solver into the predictive‐corrective framework to avoid the computational cost of solving a pressure Poisson equation globally. Our method can effectively eliminate the large density deviations mainly caused by the solid boundary treatment and free surface topological change, and show advantage of a higher convergence rate over the predictive‐corrective incompressible SPH (PCISPH).     

模拟突放水体问题的SPH方法

采用SPH方法数值模拟了二维方形水箱突放水体各时刻流动的情况,计算结果表明:模拟过程中,整个水体的密度和速度值变化不大,而压强值变化比较大。数值模拟粒子分布图可以显示出各时刻整个水体的流态、各时刻闸门开启情况及闸门对周围水体流态的影响等,闸门开启的1.460 3 s时刻,闸门左侧部分水体有相对下降缓慢的特殊流态。     

On the Galerkin formulation of the smoothed particle hydrodynamics method

In this paper, we propose a Galerkin‐based smoothed particle hydrodynamics (SPH) formulation with moving least‐squares meshless approximation, applied to free surface flows. The Galerkin scheme provides a clear framework to analyse several procedures widely used in the classical SPH literature, suggesting that some of them should be reformulated in order to develop consistent algorithms. The performance of the methodology proposed is tested through various dynamic simulations, demonstrating the attractive ability of particle methods to handle severe distortions and complex phenomena. Copyright © 2004 John Wiley & Sons, Ltd.     

A robust weakly compressible SPH method and its comparison with an incompressible SPH

This paper presents a comparative study for the weakly compressible (WCSPH) and incompressible (ISPH) smoothed particle hydrodynamics methods by providing numerical solutions for fluid flows over an airfoil and a square obstacle. Improved WCSPH and ISPH techniques are used to solve these two bluff body flow problems. It is shown that both approaches can handle complex geometries using the multiple boundary tangents (MBT) method, and eliminate particle clustering‐induced instabilities with the implementation of a particle fracture repair procedure as well as the corrected SPH discretization scheme. WCSPH and ISPH simulation results are compared and validated with those of a finite element method (FEM). The quantitative comparisons of WCSPH, ISPH and FEM results in terms of Strouhal number for the square obstacle test case, and the pressure envelope, surface traction forces, and velocity gradients on the airfoil boundaries as well as the lift and drag values for the airfoil geometry indicate that the WCSPH method with the suggested implementation produces numerical results as accurate and reliable as those of the ISPH and FEM methods. Copyright © 2011 John Wiley & Sons, Ltd.     

Addendum to “On the consistency of MPS” [Comput. Phys. Comm. 184 (3) (2013) 732–745]

The analogies between the Moving Particle Semi-implicit method (MPS) and Incompressible Smoothed Particle Hydrodynamics method (ISPH) are established in this note, as an extension of the MPS consistency analysis conducted in Souto-Iglesias et al. (2013).