光滑粒子模拟方法在超高速碰撞现象中的应用

简要介绍了基于黎曼解的光滑粒子法,并将改进的SPH方法应用于超高速碰撞,对二维轴对称条件下的弹丸超高速碰撞薄板问题进行了数值模拟,研究了靶板厚度、弹丸速度、弹丸形状等因素对形成碎片云的影响。通过与实验数据比较,该算法模拟的碎片云的形状及特征与实验相吻合,验证了光滑粒子法对冲击动力学问题数值模拟的有效性。     

12.7 mm弹侵彻不同强度钢靶的数值模拟

针对12.7 mm弹侵彻不同强度钢靶时可能出现子弹保持完整或发生破碎的情况,过去的数值模拟仅限于模拟单一模式的子弹侵彻行为。为了克服这种数值模拟的局限性,开展了模型算法、网格尺寸对模拟结果影响的研究,并将模拟结果与实验结果进行了对比,提出了一种能够用于模拟子弹保持完整或破碎的弹靶模型。研究结果表明,为模拟子弹保持完整状态,子弹和靶板应分别采用基于Lagrange算法的有限元法和光滑粒子算法,而且子弹网格尺寸和靶板粒子间距之比应至少保持在5.3左右,否则弹头会产生与实验结果不符合的异常变形。但是,在模拟子弹发生破碎侵蚀时,该比例的网格/粒子尺寸比会引起计算中止。为了克服该问题,进一步建立了一种弹体表面采用大尺寸网格、内部采用细化小尺寸网格的有限元/光滑粒子法耦合弹靶模型。计算结果表明,改进的弹靶模型可模拟子弹保持完整或者发生破碎的情况。     

NUMERICAL SIMULATION OF WIND-BLOWN SAND MOVEMENT BASED ON SPH

运用光滑粒子流体动力学(smoothed particles hydrodynamics, SPH)方法对沙粒和气流的相互耦合运动特性进行了分析,研究提出了风沙流的SPH数值方法并进行了数值模拟. 首先提出了风沙流的SPH建模方法和基本理论,建立了风沙流动的SPH数值模拟平台. 其次通过建立风沙流的SPH 模型并施加边界条件,对自然风作用下沙粒的运动情况进行了数值模拟,详细分析了沙粒运动轨迹及特性,最后通过与相关研究成果对比分析,验证了完善后的SPH方法有效性. 通过考虑气流场的可变性,在风沙流SPH计算模型中引入了加载(起风)和卸载(停风)方式,观察并对比分析了沙粒的运动轨迹和特性. 为进一步研究风沙流的实时动态非线性行为提供了SPH理论基础和数值分析方法.     

爆炸焊接界面波的数值模拟

借助动力学分析软件ANSYS/LS-DYNA 11.0,运用光滑粒子流体动力学方法(SPH方法),建立以Johnson-Cook材料模型和Grüneisen状态方程为基础的热塑性流体力学模型,对同种钢板爆炸焊接界面波进行了数值模拟.结果表明,运用SPH方法可以得到清晰的爆炸焊接界面波形貌.与实验结果的比较表明:模拟误...     

Numerical simulation of plunging wave breaking by the weakly compressible smoothed particle hydrodynamic method

In this paper, a numerical meshless method called the weakly compressible smoothed particle hydrodynamic (WCSPH) method, which is a two-dimensionalmodel of a weakly compressible fluid, is applied to simulate the plunging wave breaking process. This model solves the viscous fluid equations to obtain the velocity and density fields and also solves the equation of state to obtain the pressure field. The WCSPH method is demonstrated to have a higher computational efficiency than the basic SPH model. To simulate the turbulent behavior of the fluid flow in the wave breaking procedure, a sub particle scale (SPS) model is used, which is obtained from the Large eddy simulation (LES) theory. To consider the accuracy of the standard WCSPH model (WCSPH model without considering the turbulent effect), a dam break test is performed, and model results are compared with available experimental data.     

GPU-accelerated smoothed particle hydrodynamics modeling of jet formation and penetration capability of shaped charges

The prediction of the penetration of three-dimensional (3D) shaped charge into steel plates is a challenging task. In this paper, the smoothed particle hydrodynamics (SPH) method is applied to simulate the jet formation generated by the shaped charge detonation and its damage to steel plates. The Jones–Wilkins–Lee (JWL) equation of state (EOS), Tillotson EOS, and elastic–perfectly plastic constitutive model were incorporated into SPH for the modeling of explosive detonation and dynamic behavior of metal material. The compute unified device architecture (CUDA) parallel programming interface has been employed in SPH to improve the computational efficiency of SPH. Firstly, the constitutive models and EOSs are validated by 3D TNT slab detonation and aluminum–aluminum (Al–Al) high velocity impact. Then the jet formation of the shaped charge detonation and its penetration into the steel plates are investigated using the graphics processing unit (GPU)-accelerated SPH methodology. The numerical results of these test cases are compared against the published experimental data or analytical result, which shows that the GPU-accelerated SPH methodology is capable of tackling the 3D shaped charge detonation and penetration involving millions of particles with high computational efficiency.     

基于修正光滑粒子流体动力学算法的低能量耗散数值波浪水池开发

目前, 无网格光滑粒子流体动力学SPH粒子法在波浪与结构物相互作用研究方面得到广泛应用, 但该方法模拟波浪远距离传播时, 常常面临严重的能量耗散问题, 导致波高非物理性降低, 给大范围海域、长时间作用下的波-物耦合作用研究带来一定困难. 对此, 本文采用一种核函数修正算法, 在确保粒子间相互作用对称性的同时, 改进压力梯度离散项的计算精度, 设法解决SPH方法中能量非物理性耗散的难题. 相较于前人减缓能量非物理性衰减的方法, 本文的修正SPH算法避免了自由液面搜索等复杂处理过程, 并能保证动量守恒特性. 数值结果中, 采用振荡液滴、规则波、不规则波等算例, 验证本修正SPH算法的准确性和有效性. 结果表明, 该修正SPH算法能准确模拟振荡液滴形态变化, 且动能保持较好守恒性. 通过数值水池与物理水池两者规则波与不规则波结果的对比分析表明, 基于本文修正SPH算法建立的数值波浪水池具有较好的抗能量衰减效果, 能实现长时间、远距离波浪传播的准确模拟. 此外, 本算法能在低光滑长度系数条件下, 实现精确模拟, 将极大缩减三维SPH模拟的时间, 从而节约计算成本.      

非等温黏弹性复杂流动的改进SPH方法模拟

非等温黏弹性流体广泛存在于自然界和工业生产中,准确预测黏弹性流体的非等温流动机理和复杂流变特性有着重要的应用价值.文章提出一种改进的光滑粒子流体动力学(smoothed particle hydrodynamics,SPH)方法对非等温黏弹性复杂流动进行了数值模拟,其中流体的黏弹特性通过eXtended Pom-Pom本构模型来表征.为了提高模拟结果的精度,采用了一种核函数梯度的修正算法;为了灵活地施加边界条件,发展了边界粒子和虚拟粒子相联合的边界处理方法;为了消除流动过程中的拉伸不稳定性,施加了粒子迁移技术.运用改进SPH方法数值模拟了液滴撞击固壁和F型腔注塑成型问题,通过与Basilisk软件得到的结果进行比较验证了改进SPH方法求解非等温黏弹性流体的有效性.通过利用不同粒子初始间距进行计算,评价了改进SPH方法的数值收敛性.研究了非等温流动相较于等温流动的不同流动特征,深入分析了不同热流变参数对流动过程的影响.数值结果表明,文章提出的改进SPH方法可稳定、准确地描述非等温黏弹性复杂流动的传热机理、复杂流变特性和自由面变化特性.     

Simulating bubble dynamics in a buoyant system

Multiphase flows are critical components of many physical systems; however, numerical models of multiphase flows with large parameter gradients can be challenging. Here, two different numerical methods, volume of fluid (VOF) and smoothed particle hydrodynamics (SPH), are used to model the buoyant rise of isolated gas bubbles through quiescent fluids for a range of Bond and Reynolds numbers. The VOF is an Eulerian grid–based method, whereas the SPH is Lagrangian and mesh free. Each method has unique strengths and weaknesses, and a comparison of the two approaches as applied to multiphase phenomena has not previously been performed. The VOF and SPH simulations are compared, verified, and validated. Results using two-dimensional VOF and SPH simulations are similar to each other and are able to reproduce numerical benchmarks and experimental results for sufficiently large Morton and Reynolds numbers. It is also shown that at low Reynolds numbers, the two methods, SPH and VOF, diverge in the transient regime of the bubble rise. Regimes that require simulations capable of representing three-dimensional drag are identified as well as regimes in which results from VOF and SPH diverge.     

Numerical simulation of landslide impulsive waves by incompressible smoothed particle hydrodynamics

An incompressible‐smoothed particle hydrodynamics (I‐SPH) formulation is presented to simulate impulsive waves generated by landslides. The governing equations, Navier–Stokes equations, are solved in a Lagrangian form using a two‐step fractional method. Landslides in this paper are simulated by a submerged mass sliding along an inclined plane. During sliding, both rigid and deformable landslides mass are considered. The present numerical method is examined for a rigid wedge sliding into water along an inclined plane. In addition solitary wave generated by a heavy box falling inside water, known as Scott Russell wave generator, which is an example for simulating falling rock avalanche into artificial and natural reservoirs, is simulated and compared with experimental results. The numerical model is also validated for gravel mass sliding along an inclined plane. The sliding mass approximately behaves like a non‐Newtonian fluid. A rheological model, implemented as a combination of the Bingham and the general Cross models, is utilized for simulation of the landslide behaviour. In order to match the experimental data with the computed wave profiles generated by deformable landslides, parameters of the rheological model are adjusted and the numerical model results effectively match the experimental results. The results prove the efficiency and applicability of the I‐SPH method for simulation of these kinds of complex free surface problems. Copyright © 2007 John Wiley & Sons, Ltd.     

Modeling air entrainment and transport in a hydraulic jump using two-fluid RANS and DES turbulence models

Both RaNS (Reynolds-averaged Navier–Stokes) and DES (Detached Eddy Simulation) type turbulence models were used in conjunction with a two-fluid model of bubbly flow and a new subgrid air entrainment model to predict air entrainment and transport in a hydraulic jump. It was found that the void fraction profiles predicted by both methods are in agreement with the experimental data in the lower shear layer region, which contains the air bubbles entrained at the so-called toe of the hydraulic jump. In contrast, in the upper roller region behind the toe, the averaged results of the DES turbulence model gives accurate predictions while a RaNS turbulence model does not. This is because the DES turbulence model successfully captures the strong fluctuations on the free surface which allows it to entrain air near the top of the roller region. In contrast, RaNS type turbulence model results in a steady, smooth interface which fails to capture the wave-induced bubble sources in that region. To our knowledge, this study is the first successful quantitative numerical simulation of the overall void fraction profiles in a hydraulic jump.     

An SPH pressure correction algorithm for multiphase flows with large density ratio

In this paper, we propose an interfacial pressure correction algorithm for smoothed particle hydrodynamics (SPH) simulation of multiphase flows with large density ratios. This correction term is based on the assumption of small deformation of the interface, and derived from perturbation expansion analysis. It is also proven to be applicable in cases with complex interfaces. This correction algorithm helps to overcome the discontinuities of the pressure gradient over the interfaces, which may cause unphysical gap between different phases. This proposed correction algorithm is implemented on a recent multiphase SPH model, which is based on the assumption of pressure continuity over the interfaces. The coupled dynamic solid boundary treatment is used to simulate solid walls; and a cut‐off pressure is applied to avoid negative particle pressure, which may cause computational instabilities in SPH. Three numerical examples of air–water flows, including sloshing, dam breaking, and water entry, are presented and compared with experimental data, indicating the robustness of our pressure correction algorithm in multiphase simulations with large density ratios. Copyright © 2015 John Wiley & Sons, Ltd.     

基于表面力模型的液滴冲击弹性基底SPH模拟

采用光滑粒子动力学SPH方法建立液滴冲击弹性基底的流固耦合数值模型,给出描述粘性流体和弹性固体运动的SPH离散方程和数值处理格式,引入人工耗散项来抑制标准SPH方法的数值震荡。为模拟液滴的表面张力效应,通过精确检测边界粒子,采用拉格朗日插值方法计算表面法向量和曲率,结合界面理论中的连续表面力CSF方法,建立了适用于自由表面液滴的表面力模型,方形液滴变形的模拟结果与拉普拉斯理论解吻合较好。随后,采用SPH流固耦合模型模拟1.0 mm直径水滴以不同速度(0.2 m/s～3.0 m/s)冲击两种薄板型基底,分析了基底弹性变形对液滴铺展、收缩以及回弹行为的影响。     

SPH方法研究空气在平板入水中的影响

飞机水上迫降以及船体在高速行驶时,均会发生结构物砰击水面的现象,当结构物底面较为平坦,砰击水面时会捕获空气,在板底形成空气垫。研究空气垫的形成及影响,有助于对结构物进行更准确的载荷分析。该问题的研究涉及到气固液三相的相互作用,在数值模拟中仍是一个挑战,本文使用光滑粒子流体动力学(SPH)方法对该问题进行模拟。首先,与实验结果进行对比;其次,系统地研究了平板形成空气垫以及砰击水面的过程,考查了空气、水和平板的动能变化。对比了在SPH模拟中考虑空气与不考虑空气得到的水压力场和平板所受压力,说明了空气对结果的影响;最后,研究了平板宽度对空气垫形成的影响,从而进一步影响加速度。     

长杆弹撞击陶瓷靶的一种数值模拟方法

陶瓷材料具有高强度和低密度等特点，抗弹性能优越，被广泛用于各类装甲中。长杆弹撞击陶瓷靶时会发生径向流动、质量显著侵蚀而无明显侵彻的界面击溃现象，是陶瓷抗侵彻性能研究中具有重要研究价值的特殊现象。利用有限元软件AUTODYN建立了长杆弹撞击陶瓷靶的二维轴对称计算模型，采用Lagrange和光滑粒子流体动力学（smooth particle hydrodynamics, SPH）算法，模拟了柱形钨合金长杆弹撞击带盖板的碳化硅陶瓷，通过改变长杆弹的撞击速度，得到了界面击溃、驻留转侵彻和直接侵彻3个不同现象。讨论了不同建模算法、边界条件以及材料参数对模拟结果的影响。通过网格收敛性验证和与实验结果进行拟合，综合验证了计算模型中算法、边界条件和参数设定的可靠性。结果表明，在建模中若同时使用SPH算法和Lagrange算法，需要考虑粒子和网格大小对于模拟结果的影响。针对长杆弹撞击陶瓷靶的界面击溃模拟，不建议对陶瓷材料采用SPH粒子建模。相关建模和参数选择方法对后续陶瓷抗侵彻/界面击溃的数值模拟具有重要的指导意义。     

水底管道抛石加固过程的DEM-SPH耦合分析

水底管道的抛石加固过程是典型的颗粒-流体耦合问题.采用DEM-SPH耦合方法模拟颗粒-流体系统,其中离散元方法(DEM)用于模拟落石,光滑粒子流体动力学方法(SPH)用于模拟流体.通过三维Voronoi切割算法生成不规则形状的多面体,并基于闵可夫斯基原理构造扩展多面体形态的落石单元.通过SPH的边界排斥力模型计算颗粒与流体间的作用力,从而建立DEM-SPH耦合方法.采用该方法模拟溃坝与楔形块入水的过程,将计算结果与试验结果及其他数值结果进行对比分析,分别验证了 SPH与DEM-SPH耦合方法的合理性.建立锥形结构模拟卸料斗和水底管道,采用DEM-SPH耦合方法模拟落石通过卸料斗入水并与水底管道相互作用的过程,确定了落石和水对管道的作用力,并分析了卸料斗静止与运动时的落石堆积情况.以上研究表明,DEM-SPH方法可有效模拟颗粒材料、水和工程结构的相互作用,可进一步应用于水下抛石过程的结构和参数设计.     

基于拟流体模型的SPH新方法及其在弹丸超高速碰撞薄板中的应用

引入颗粒动力学理论(拟流体模型)建立了适用于超高速碰撞的SPH新方法。将超高速碰撞中处于损伤状态的碎片等效为拟流体,在描述其运动过程中引入了碎片间相互作用和气体相对碎片的作用。采用该方法对球形弹丸超高速碰撞薄板形成碎片云的过程进行了数值模拟,得到了弹坑直径、外泡碎片云和内核碎片云的形状、分布,并与使用传统SPH方法、自适应光滑粒子流体动力学(ASPH)方法的模拟结果进行对比,结果显示:新方法在内核碎片云形状和分布上计算结果更加准确。同时对Whipple屏超高速碰撞问题进行了研究,分析了不同撞击速度下防护屏弹坑尺寸及舱壁损伤特性等特性,计算结果与实验吻合较好且符合Whipple防护结构的典型撞击极限曲线。     

Modified incompressible SPH method for simulating free surface problems

An incompressible smoothed particle hydrodynamics (I-SPH) formulation is presented to simulate free surface incompressible fluid problems. The governing equations are mass and momentum conservation that are solved in a Lagrangian form using a two-step fractional method. In the first step, velocity field is computed without enforcing incompressibility. In the second step, a Poisson equation of pressure is used to satisfy incompressibility condition. The source term in the Poisson equation for the pressure is approximated, based on the SPH continuity equation, by an interpolation summation involving the relative velocities between a reference particle and its neighboring particles. A new form of source term for the Poisson equation is proposed and also a modified Poisson equation of pressure is used to satisfy incompressibility condition of free surface particles. By employing these corrections, the stability and accuracy of SPH method are improved. In order to show the ability of SPH method to simulate fluid mechanical problems, this method is used to simulate four test problems such as 2-D dam-break and wave propagation.     

穿甲燃烧弹侵彻陶瓷复合装甲和玻璃复合装甲的FEM-SPH耦合计算模型

为了提高小口径穿甲燃烧弹侵彻陶瓷复合装甲和玻璃复合装甲（透明装甲）的仿真分析精度,本文将传统的FEM（finite element method）-SPH（smooth particle hydrodynamics）耦合计算模型中穿甲燃烧弹弹芯的有限元模型和JC（Johnson-Cook）材料模型分别替换为SPH模型和JH2（Johnson-Holmquist-ceramics）材料模型,提出了新型FEM-SPH耦合计算模型。研究表明,新型FEM-SPH耦合计算模型可以有效模拟弹芯碎裂现象,减少SPH粒子和有限元耦合计算量,进而显著提高仿真模型的计算精度和计算效率,并给出了新型FEM-SPH耦合计算模型的有限元/粒子尺度和建模尺寸的优选结果。