A flexible multiscale algorithm based on an improved smoothed particle hydrodynamics method for complex viscoelastic flows

Viscoelastic flows play an important role in numerous engineering fields,and the multiscale algorithms for simulating viscoelastic flows have received significant attention in order to deepen our understanding of the nonlinear dynamic behaviors of viscoelastic fluids.However,traditional grid-based multiscale methods are confined to simple viscoelastic flows with short relaxation time,and there is a lack of uniform multiscale scheme available for coupling different solvers in the simulations of viscoelastic fluids.In this paper,a universal multiscale method coupling an improved smoothed particle hydrodynamics(SPH)and multiscale universal interface(MUI)library is presented for viscoelastic flows.The proposed multiscale method builds on an improved SPH method and leverages the MUI library to facilitate the exchange of information among different solvers in the overlapping domain.We test the capability and flexibility of the presented multiscale method to deal with complex viscoelastic flows by solving different multiscale problems of viscoelastic flows.In the first example,the simulation of a viscoelastic Poiseuille flow is carried out by two coupled improved SPH methods with different spatial resolutions.The effects of exchanging different physical quantities on the numerical results in both the upper and lower domains are also investigated as well as the absolute errors in the overlapping domain.In the second example,the complex Wannier flow with different Weissenberg numbers is further simulated by two improved SPH methods and coupling the improved SPH method and the dissipative particle dynamics(DPD)method.The numerical results show that the physical quantities for viscoelastic flows obtained by the presented multiscale method are in consistence with those obtained by a single solver in the overlapping domain.Moreover,transferring different physical quantities has an important effect on the numerical results.

Simulation of mould filling process using smoothed particle hydrodynamics

The implementation of high pressure die casting （HPDC） filling process modeling based on smoothed particle hydrodynamics （SPH） was discussed. A new treatment of inlet boundary was established by discriminating fluid particles from inlet particles. The roles of artificial viscosity and moving least squares method in the present model were compared in the handling pressure oscillation. The final model was substantiated by simulating filling process in HPDC in both two and three dimensions. The simulated results from SPH and finite difference method （FDM） were compared with the experiments. The results show the former is in a better agreement with experiments. It demonstrates the efficiency and precision of this SPH model in describing flow pattern in filling process.

Numerical Simulation of Dam Breaking Using Smoothed Particle Hydrodynamics and Viscosity Behavior

Smoothed particle hydrodynamics (SPH) is a Lagrangian meshless particle method. It is one of the best method for simulating violent free surface flows in fluids and solving large fluid deformations. Dam breaking is a typical example of these problems. The basis of SPH was reviewed, including some techniques for governing equation resolution, such as the stepping method and the boundary handling method. Then numerical results of a dam breaking simulation were discussed, and the benefits of concepts like artificial viscosity and position correction were analyzed in detail. When compared with dam breaking simulated by the volume of fluid (VOF) method, the wave profile generated by SPH had good agreement, but the pressure had only reasonable agreement. Improving pressure results is clearly an important next step for research.

Numerical Simulation of Water Mitigation Effects on Shock Wave with SPH Method

The water mitigation effect on the propagation of shock wave was investigated numerically. The traditional smoothed particle hydrodynamics (SPH) method was modified based on Riemann solution. The comparison of numerical results with the analytical solution indicated that the modified SPH method has more advantages than the traditional SPH method. Using the modified SPH algorithm, a series of one-dimensional planar wave propagation problems were investigated, focusing on the influence of the air-gap between the high-pressure air and water and the thickness of water. The numerical results showed that water mitigation effect is significant. Up to 60% shock wave pressure reduction could be achieved with the existence of water, and the shape of shock wave was also changed greatly. It is seemly that the small air-gap between the high-pressure air and water has more influence on water mitigation effect.

Multi-resolution technique integrated with smoothed particle element method (SPEM) for modeling fluid-structure interaction problems with free surfaces

Free-surface flows, especially those associated with fluid-structure interactions(FSIs), pose challenging problems in numerical simulations. The authors of this work recently developed a smoothed particle element method(SPEM) to simulate FSIs. In this method, both the fluid and solid regions are initially modeled using a smoothed finite element method(S-FEM) in a Lagrangian frame, whereas the fluid regions undergoing large deformations are adaptively converted into particles and modeled with an improved smoothed particle hydrodynamics(SPH) method. This approach greatly improves computational accuracy and efficiency because of the advantages of the S-FEM in efficiently treating solid/fluid regions showing small deformations and the SPH method in effectively modeling moving interfaces. In this work, we further enhance the efficiency of the SPEM while effectively capturing local fluid information by introducing a multi-resolution technique to the SPEM and developing an effective approach to treat multi-resolution element-particle interfaces. Various numerical examples demonstrate that the multiresolution SPEM can significantly reduce the computational cost relative to the original version with a constant resolution.Moreover, the novel approach is effective in modeling various incompressible flow problems involving FSIs.

Modelling incompressible flows and fluid-structure interaction problems with smoothed particle hydrodynamics:Briefing on the 2017 SPHERIC Beijing International Workshop

The 2017 SPHERIC Beijing International Workshop（or SPHERIC Beijing 2017） was held at Peking University, in China,on October 17-20, 2017. This is the first time that the SPHERIC Workshop was held out of Europe. We are delighted to present nine contributions in this Special Column of the Journal of Hydrodynamics, and take this opportunity to announce that the 13 th SPHERIC Workshop（or SPHERIC 2018） will be held in Galway, Ireland in 2018 by the National University of Ireland, and the SPHERIC International Workshop in Harbin, China in 2019 by the Harbin Engineering University.

基于SPH方法的叶片鸟撞数值模拟研究

基于显式碰撞动力分析软件PAM-CRASH及其提供的SPH方法,建立了鸟撞平板叶片数值分析模型。通过SPH方法、Lagrange方法结果和实验结果三者对比,指出SPH方法比Lagrange方法的数值计算结果更贴近试验结果。还应用SPH方法,研究了圆柱体、两端带半球的圆柱体、椭球体三种不同几何构型的鸟体对计算结果的影响。最后,计算了实验条件下易出现损伤的叶片根部不同时刻的应变分布及应力分布。

基于FEM与SPH耦合算法的单颗磨粒切削玻璃的动态过程仿真

采用有限元法(FEM)与光滑质点流体动力学法(SPH)耦合算法,假设以圆锥作为磨粒的形状,以玻璃为工件材料,进行了单颗金刚石磨粒的三维磨削仿真。仿真结果表明:磨粒的挤压使工件材料向前方及两侧流动而产生隆起,且磨屑发生粉末化现象;沟槽的实际宽度远大于磨粒的切削宽度,断裂裂纹向沟槽两侧扩张,裂纹扩展一段后就停止不前而残留下来,成为残留裂纹。该方法可以较好地解决传统有限元法进行脆性材料磨削仿真时容易发生单元畸变的问题,验证了FEM与SPH耦合算法应用于脆性材料磨削仿真研究的可行性。

基于SPH的边坡稳定性计算中失稳判据研究

在用强度折减法进行边坡稳定性分析时,失稳判据的选择对安全系数有着直接的关系。光滑粒子流体动力学法(SPH)是一种新型的无网格法,由于其在大变形等领域的优势而逐渐发展起来,并扩展至边坡稳定性分析领域。然而,目前对于该方法在边坡稳定性分析中失稳判据的研究尚未见报道。首先通过Fortan语言编写了基于SPH强度折减法的边坡稳定性分析程序,然后通过一个经典边坡案例,讨论了不同失稳判据对安全系数的影响,并提出了一种新的位移变化失稳判定方法。结果表明,在基于SPH的边坡稳定性分析中,以塑性区贯通或以位移变化为判定准则时各有优劣,但得到的安全系数均与极限平衡法及有限元法得到的安全系数十分接近,均可作为失稳判据。而当采用位移变化准则进行分析时,采用"两步走"的方法即可以减小计算量,又可以得到较准确的安全系数,是一种值得推荐的方法。

基于SPH方法的立面二维涌浪数值模拟

基于无网格SPH法模拟块体下滑所引起的涌浪流动过程,并将模拟得到的自由表面速度、高度变化结果与解析解以及VOF紊流模型计算结果进行比较。在此基础上,计算滑块下滑速度分别为0.2,0.6,1.0 m/s时的自由面变化。结果表明:滑块下滑引起水槽自由液面变化并形成卷碎波,并有水气混掺现象。自由面孤立波波形、水平速度与解析解以及VOF紊流模型计算结果吻合较好。下滑速度较慢时波形平坦,无卷碎波产生;滑速大时水气完全分离;涌浪形成的波峰峰值随滑块入水速度增大而增加。SPH方法可进一步用于模拟水体中由大型崩岸产生的高速远程滑坡涌浪或复杂的海啸模拟。

基于SPH方法的二维矩形舱液体晃荡数值研究

储液舱内液体晃荡是当外激激励频率与容器内部液体自由液面的固有频率接近时,液体产生的剧烈共振运动.采用光滑粒子流体动力学(SPH)方法,在二维矩形舱低载液率横荡和横摇激励下,自由液面共振频率附近4个激励频率处开展数值研究.对比数值和对应实验中全局自由液面波形和冲击压力时程发现,SPH方法可以很好地模拟液体晃荡时的波形,如水跃、破碎波等自由液面的大变形运动.此外,该方法可用于模拟和评估非共振区域晃荡荷载的特性.建议采用两相流来模拟共振频率下液体剧烈的晃荡运动.

光滑质点流体动力学(SPH)及其算法特性

基于Lagrange观点的无网格方法计算是建立在一群可移动的自适应性的质点基础之上,对特大变形区域和自由表面的捕捉有着较高的精度。光滑质点流体动力学(SPH)是无网格方法的一种,本文阐述其理论基础和计算方法,主要包括:SPH的基本概念、核近似和粒子近似的基本原理、核函数的构造方法、SPH形式的流体运动方程、边界处理方法和数值算例等多方面内容。研究工作在了解SPH方法的理论特点和潜在优势的同时,也为相关问题的深入研究和改进奠定了理论和算法基础。

基于SPH的土质边坡稳定性及失稳后大变形数值模拟

本文采用光滑粒子流体动力学(SPH)法对土质边坡稳定性及其失稳后的大变形进行数值模拟研究。该方法既可以分析边坡的稳定性系数和潜在滑移面,又可以对土质边坡失稳后的大变形过程进行模拟,从而弥补了传统数值模拟分析方法的不足,为土质边坡稳定性及失稳后滑坡大变形分析提供了一种新的方法。首先,采用Fortran语言编写了模拟土质边坡稳定性及失稳后滑坡大变形分析的SPH程序;其次,采用一个经典算例,验证了本文程序和方法在进行边坡稳定性分析时的准确性;最后,为验证该法模拟黏性土质边坡滑坡大变形的准确性,笔者自行设计了一组黏性土体滑坡大变形物理实验并与SPH模拟结果进行了对比。研究成果表明,基于弹塑性本构模型及D-P屈服准则的SPH方法可以较准确的模拟稳定性系数及潜在滑移面,并且可以较准确地模拟失稳后的滑坡大变形发展过程,弥补了目前数值模拟方法的不足,是一种值得推广的新型稳定性及滑坡大变形分析方法。

基于SPH-DEM流-固耦合算法的滑坡涌浪模拟

采用光滑粒子流体动力学(SPH)方法和离散单元法(DEM),并基于达西渗透试验原理,提出一种SPH-DEM耦合算法用于处理宏观尺度下离散体与流体之间的相互作用问题,并基于该流-固耦合方法采用FORTRAN语言建立滑坡涌浪数学模型。模拟了块体滑坡问题,并与试验数据进行对比以验证该耦合方法的有效性。模拟分析了离散体滑坡产生涌浪以及涌浪传播的过程,分析比较了数值模拟得到的最大涌浪高度与经验公式结果间的关系。研究表明:采用该耦合方法模拟水下块体滑坡问题得到的结果与试验数据吻合良好;模拟离散体滑坡涌浪问题时,较清晰地反映了滑坡体对水的排挤到涌浪的产生过程、水在滑坡体中的渗透过程和滑坡体与水耦合作用发生变形的过程;不同公式分析方法得到的最大涌浪高度之间均有一定差别,算例中滑坡体受重力作用沿倾斜坡面滑动入水过程更接近于潘家铮法的垂直运动模式,因此,模拟结果与之最为接近。

基于SPH结合FEM的喷丸残余应力数值模拟

针对以往有限元模型中弹丸数量较少且为规则阵列排布的缺陷,采用光滑粒子流体动力学法(Smoothed particle hydrodynamics,SPH)与有限元法(Finite element method,FEM)相结合的方法,对喷丸过程进行数值模拟;使用MATLAB对弹丸空间位置坐标进行随机化处理,形成了大量丸粒冲击工件表面的随机喷丸仿真模型。通过分析确定了喷丸饱和时间,研究了喷射角度、弹丸流量对残余应力场的影响。结果表明:在喷丸参数一定的条件下,存在相应的饱和喷丸时间;研究喷丸参数对残余应力的影响时,应在喷丸达到饱和时间之后提取残余应力值;喷射角度增大,残余压应力增大;开始时弹丸流量增大,残余压应力会有所增大,但当其达到饱和值后,残余压应力不再变化。

SPH法数值仿真三维切削破岩和切削力估算

以Mohr-Coulomb模型描述岩石,在LS-DYNA中用SPH(Smootheed Particle Hydrodynamics)法模拟三维刀齿切削破岩,探讨切削参数和岩石性质对切削力的影响.基于切削力随各切削参数和岩石性质的变化规律,建立切削力估算公式.用所得公式计算切削力,并与实验值进行比较.仿真结果表明:切削厚度、切削前角、切削宽度、岩石的内聚力和内摩擦角对切削力影响显著,切削速度在较低范围内变化时对切削力影响非常小.三维切削仿真能够较好地反映刀齿两侧岩石颗粒对切削的影响,比二维理论模型更接近实际.所得切削力估算公式能准确计算仿真中的平均切向力,且其计算值能与实验吻合较好.验证了基于SPH法的数值仿真用于研究刀齿切削破岩的可靠性.

SPH方法在剪切式碰撞能量吸收器中的应用

剪切式碰撞能量吸收器是提高汽车被动安全性的一种实用新型设计。建立了剪切式碰撞能量吸收器数值分析模型,采用SPH方法数值模拟了碰撞吸能器的碰撞过程,研究了其碰撞吸能特性,并通过不同碰撞速度的台车碰撞试验进行了试验验证研究。数值模拟结果同试验结果相符,表明SPH方法在碰撞吸能器性能研究中是行之有效的数值计算方法。同时分析了在碰撞吸能器的复杂碰撞情况下,SPH方法相比有限元法的优势。

SPH-DEM流固耦合方法模拟金沙江白格滑坡应用研究

从力学本质来讲,滑坡属于滑坡动力学和水动力学复杂流固耦合问题。采用离散元方法(DEM)模拟滑坡体大变形、不连续问题,以光滑粒子流方法(SPH)模拟水体的流体动力学特性,充分利用不同数值计算方法的特点,构建SPH-DEM流固耦合算法,并应用于2018年10月10日西藏白格滑坡堵江的灾害模拟中。结果显示计算模型能较为准确地捕捉滑坡碎屑体入江激起水砂射流的规模以及范围,再现主堆积区向次堆积区产生二次滑移的动力过程,完整刻画堆积体的厚度、几何形态和断面特征。仿真结果有助于进一步深化对高速高位滑坡产生堵江过程和机理的认识,为后续进行抢险施工组织设计,制定防灾减灾策略提供参考。

基于溃坝模型的SPH方法光滑函数模拟

为研究光滑函数对溃坝数值模拟结果的影响,基于光滑粒子流体动力学(Smoothed Particle Hydrodynamics,SPH)法的基本原理,选取三次样条型和Wendland型两种光滑函数对溃坝进行数值模拟,并以高斯型光滑函数为基准,从流体压力云图、粒子压强来比较溃坝数值模拟结果。研究发现:三次样条型和Wenland型光滑函数都能较好地模拟溃坝流体的整个流动过程;三次样条型光滑函数计算精度较低,但计算时间较短,Wenland型光滑函数既可以保证计算精度又可以有效地减少计算时间。为采用SPH方法进行流体动力研究时,光滑函数的选取提供依据。

基于SPH-FEM方法的舷侧与冰山碰撞结构响应

传统的有限元数值仿真对于研究高速碰撞大变形等问题具有一定的局限性,建立一套基于光滑粒子流体动力学(SPH)的水介质中小型冰山与船舶舷侧碰撞数值模拟方法,验证SPH模拟冰材料与船-水-冰耦合的合理性,对不同舷侧部位与不同冰山碰撞工况进行数值模拟,分析碰撞形状、面积和速度等对舷侧结构的应力、应变、结构损伤等的影响规律。研究表明,提出的冰山与舷侧碰撞数值模拟方法具有较高的计算精度,对冰山-船舶碰撞的研究具有重要的参考价值。