Numerical modeling of sediment transport based on unsteady and steady flows by incompressible smoothed particle hydrodynamics method

The purpose of the present paper is to introduce a simple two-part multi-phase model for the sediment transport problems based on the incompressible smoothed particle hydrodynamics(ISPH) method. The proposed model simulates the movement of sediment particles in two parts. The sediment particles are classified into three categories, including the motionless particles, moving particles behave like a rigid body, and moving particles with a pseudo fluid behavior. The criterion for the classification of sediment particles is the Bingham rheological model. Verification of the present model is performed by simulation of the dam break waves on movable beds with different conditions and the bed scouring under steady flow condition. Comparison of the present model results, the experimental data and available numerical results show that it has good ability to simulate flow pattern and sediment transport.     

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.     

Numerical simulation of hydro-elastic problems with smoothed particle hydrodynamics method

Violent free surface flows with strong fluid-solid interactions can produce a tremendous pressure load on structures, resu-lting in elastic and even plastic deformations. Modeling hydro-elastic problem...     

基于光滑粒子流体动力学方法的溃坝水流模拟

受全球气候变暖的影响,由极端天气引发的类似溃坝等问题发生的概率大大增加,深入研究溃坝水流的水动力特性势在必行。在分析光滑粒子流体动力学基本原理的基础上,提出了一种改进的边界处理方法,即将接近壁面的流体视为层流,在耦合动力边界附近引入层流黏性近似边界层理论。采用该方法对溃坝水流进行数值模拟,将SPH数值模拟得到的外轮廓、自由液面高度以及压力与实验结果进行了比较和分析。结果表明：改进的边界处理方法较完整地得到了水流与壁面相互作用而产生的多种复杂的物理现象,其外部轮廓与实验非常吻合;自由表面融合过程中液面间冲击的能量耗散会导致融合后的液面高度存在一些差异;不同监测点处压力随时间的变化基本落在置信区间之内。数值模拟结果与实验结果吻合度较高,验证了改进方案的可靠性和计算结果的准确性。     

液滴冲击固体表面的光滑粒子动力学模拟

液滴冲击固体表面的现象广泛地存在于自然界和工业生产中,深入研究液滴冲击固体表面现象对环境工程、微纳米工程以及医药工程等领域有着十分重要的指导作用.该文采用光滑粒子动力学方法(SPH)对液滴冲击固体表面的现象进行了数值模拟.SPH方法是一种纯拉格朗日形式的无网格粒子方法,可以很容易的处理大变形、可变形边界、追踪自由表面以及运动界面.为了提高传统SPH方法的计算精度和数值稳定性,该文在传统SPH方法的基础上对粒子方法中的核梯度进行了修正,采用粒子间相互作用力的形式来模拟表面张力,应用改进的SPH方法对液滴冲击固体表面进行了数值模拟.计算结果表明,改进的SPH方法能够精细地描述液滴冲击固体表面所产生的铺展和飞溅等动力学特性,得到了稳定精确的结果,数值模拟结果与实验观察结果吻合较好.     

光滑粒子水动力学在水利与海洋工程中的应用研究进展

将光滑粒子水动力学(smoothed particle hydrodynamics,SPH)在水利及海洋工程中的应用分为纯水流模拟、流固耦合模拟、泥沙模拟和水气两相流模拟4大类问题,系统地介绍了SPH在解决这些问题时的技术手段与研究现状,指出了SPH独特的计算方法及其在处理无反射造波、进出流边界、流固界面运动、底床冲刷等问题中面临的困难,阐述了不同类型的SPH模型的优缺点,总结了SPH在过去十几年的发展特点,并提出未来SPH在水动力学领域的发展方向应该集中在开发高精度与高效率的新算法模型、成熟的紊流模型和高效的并行计算模型方面。     

Integrated rainfall-runoff process with shallow water model by mass varied smoothed particle hydrodynamics:Infiltration effect implementation

Rainfall-runoff modeling is essential for addressing a wide range of issues in urban drainage system design and operation in both scientific research and engine...     

辽东湾区域性漂移海冰的SPH数值模拟

在海冰动力过程的数值模拟中引入SPH法，采用Hibler的粘塑性海冰本构方程，并考虑海冰的热力过程，对辽东湾海域区性漂移海水进行了96h数值模拟，计算结果与海冰的实际演化过程吻合，分析表明，海冰内力对冰速、冰厚和密集度的分布有较大影响，在区域性在海冰数值模拟中应予以考虑。     

Comparison of two projection methods for modeling incompressible flows in MPM

Material point method(MPM)was originally introduced for large deformation problems in solid mechanics applications.Later,it has been successfully applied to solve a wide range of material behaviors.However,previous research has indicated that MPM exhibits numerical instabilities when resolving incompressible flow problems.We study Chorin's projection method in MPM algorithm to simulate material incompressibility.Two projection-type schemes,non-incremental projection and incremental projection,are investigated for their accuracy and stability within MPM.Numerical examples show that the non-incremental projection scheme provides stable results in single phase MPM framework.Further,it avoids artificial pressure oscillations and small time steps that are present in the explicit MPM approach.     

Parametric study on smoothed particle hydrodynamics for accurate determination of drag coefficient for a circular cylinder

Simulations of two-dimensional (2D) flow past a circular cylinder with the smoothed particle hydrodynamics (SPH) method were conducted in order to accurately determine the drag coefficient. The fluid was modeled as a viscous liquid with weak compressibility. Boundary conditions, such as a no-slip solid wall, inflow and outflow, and periodic boundaries, were employed to resemble the physical problem. A sensitivity analysis, which has been rarely addressed in previous studies, was conducted on several SPH parameters. Hence, the effects of distinct parameters, such as the kernel choices and the domain dimensions, were investigated with the goal of obtaining highly accurate results. A range of Reynolds numbers (1–500) was simulated, and the results were compared with existing experimental data. It was observed that the domain dimensions and the resolution of SPH particles, in comparison to the obstacle size, affected the obtained drag coefficient significantly. Other parameters, such as the background pressure, influenced the transient condition, but did not influence the steady state at which the drag coefficient was determined.     

螺旋桨非定常力的黏性数值分析

基于黏流的数值模拟技术在非均匀来流情况下对DTMB P4119桨所受的非定常力进行了分析.该桨已在DTMB用给定的非均匀轴向进流场做过非定常水动力测量,故本文计算用该进流场作为进流条件并把该试验结果用来验证.计算过程分析了网格数的收敛性. 非定常力的计算的预报结果,明显地反映了1阶,2阶及3阶叶频的轴承力幅值与进流阶调的耦合效应.通过计算结果与试验结果的对比,不论是非定常力的演变特征还是脉动幅度都与试验结果吻合良好.通过简单定性分析认为通过计算得到的非定常力预报螺旋桨线谱噪声误差将在3dB以内,比较理想.     

黏性流场中鱼类胸鳍的水动力性能分析

针对刚性胸鳍建立了二自由度、三自由度的运动模型.在此基础上,通过对基于求解雷诺平均纳维-斯托克斯(RANS)方程的商用计算流体力学(CFD)软件FLUENT的二次开发,采用其先进的动网格技术以及强大的后处理系统,详细计算了刚性胸鳍在黏性流场中的水动力性能.数值计算结果与最近物理实验结果进行详细比较和讨论.通过研究发现摆动胸鳍产生的独特表面压力分布以及尾涡变化方式是其产生较高推进性能的内在原因.     

粘性泥石流产流机理探讨

粘性泥石流产流是斜坡或沟床中粘粒含量较高的松散土体与入渗为主的水体结合,产生容重和起始静力分别大于1.8-1.9t/m3和30Pa的土水混合流。产流包括两个紧密相连的过程:含水量饱和或局部饱和土体的起动过程;动起后的流体化过程。本文首先阐述粘性泥石流产流的4种理想化情况及其相应的公式和4类流体化方式;然后结合泥石流活动的实际状况,提出粘性泥石流产流的4种常见类型,从而综合探讨粘性泥石流的产流机理。     

大涡模拟在水下航行体周围黏性流场计算中的初步应用

在空间过滤得到的不可压缩流动的大涡模拟控制方程基础上,利用基于三阶迎风偏置格式的混合差分及二阶中心差分离散控制方程的对流项及耗散项,离散得到的线性方程组通过无矩阵计算的隐式LU-SGS（Lower-Upper Symmetric Gauss Seidel）分步迭代方法求解.利用大涡模拟（Large Eddy Simulation-LES）方法对水下航行体周围的黏性流场及水动力进行了定常数值模拟,计算得到的速度、压力分布及阻力值与试验吻合较好.     

二维非恒定粘性泥石流运动堆积的数值模拟

以结构二相流模型为基础,建立了二维粘性泥石流运动堆积的数学模型。模型采用三角网格的有限差分方法,具有计算效率高、边界处理精度高的优点。针对粘性泥石流运动速度快、龙头部位前缘坡度陡的特性,简述了计算中的动边界处理及泥石流停积条件的处理方法。以云南东川蒋家沟泥石流堆积试验为例,模拟了不同来流补给量下粘性泥石流的运动堆积过程。     

三维方腔拖曳流的数值模拟

本文推导出一种适用于定常和不定常粘性不可压缩Navier-Stokes方程的分裂步方法。采用Taylor-Galerkin有限元格式进行求解，对有限元等式中关于速度的时间项进行三点向后差分，深入考虑粘性不可压缩流Navier-Stokes方程中对流项的作用，利用二阶Taylor展开完成时间项向空间项的转化，采用张量分析的方法推导了N-S方程分裂步方法的有限元离散格式，并采用低Reynolds数三维方腔拖曳粘性流^[23][24]作为基本算例，检验了这种分裂步方法的稳定性和有效性，同时与大涡模拟相结合对Reynolds数为10000的三维方腔拖曳湍流流场进行了相关的分析，进一步揭示了方腔回流运动的非定常非对称性、流动结构表现为竖轴环流与立面环流相叠加、流速沿垂线分布相对均匀等流动规律，显示了该方法与大涡模拟相结合能够有效地捕捉涡系及其时变过程。     

基于SPH的自由表面流动数值模拟

光滑粒子流体动力学方法是一种新近发展的无网格数值方法,在处理自由表面等复杂边界、流体大变形方面具有显著优势.应用该方法求解了拉格朗日形式的Navier-Stokes方程,为提高计算精度,本文通过采用两种粒子模拟固壁边界,改进了计算方法.并对湍流、粘性流体、不可压缩问题进行求解.通过二维和三维算例对近岸水动力学中波浪传播、变形、与建筑物的相互作用问题进行了数值计算,验证了其可行性,并为SPH的进一步扩展和应用奠定了基础.     

有蒸发的气－水二维湍流流动的数值模拟

对水面蒸发问题的研究，过去一直是仅仅依赖于实验的手段．本文在国内首次提出了有蒸发的气－水二维湍流流动的理论模型，用Ｓｔｅｆａｎ流的概念，采用Ｋ－ε湍流模型及ＳＩＭＰＬＥ算法，进行了　　数值模拟，分析了风速、水气温差和相对湿度等各个物理因素对蒸发的影响，并就蒸发对流体流　动和传热的影响进行了探讨．计算结果和实验结果作了比较，大部分参数变化规律在趋势上与实验吻合，亦有某些参数的变化规律与实验有出入，其原因尚待进一步研究．本研究工作在冷却水工程和水资源的开发利用中具有广泛的实际意义．