核电厂房安全壳流固耦合动力响应分析

在地震荷载作用下,核电厂房安全壳水箱内水会发生晃动,这种流固耦合作用会影响到安全壳的动力响应。采用简化附加质量法和光滑粒子流体动力学(SPH)法,分别对应不考虑和考虑水体晃动的效应,选取常用自然波Northridge波和上海人工合成波作为地震动输入,获取了7个水位工况下包括基底剪力、位移和加速度的动力响应。通过对比两种方法的模拟结果,发现考虑水体流动的SPH法要比不考虑水体晃动的简化附加质量法的动力响应要小,水箱内水的晃动对结构整体的动力响应起到了减震的作用;并分析SPH法各水位工况下的动力响应,结果表明:水位高度4.0 m时,安全壳动力响应相对较小,是水箱较为合理的储水水位。     

基于FEM-SPH耦合法的弹丸侵彻钢纤维混凝土数值模拟

针对有限元法(FEM)处理超大变形问题时所存在的困难,基于有限元与光滑粒子流体动力学(Smoothed Particle Hydrodynamics:SPH)的耦合方法模拟了弹丸对钢纤维混凝土的侵彻破坏过程。其中弹丸作为刚体处理并划分成Lagrange标准有限元网格,而靶体中心部分划分成光滑粒子并经历大应变、高应变率和高压作用。为了描述钢纤维混凝土的非线性变形及断裂特性,在计算中引入了Holmquist-Johnson-Cook累积损伤材料模型。数值模拟结果形象再现了弹丸冲击作用下靶体材料破碎、飞溅成坑的物理过程,尤其靶表面碎片飞散的模拟情况与高速摄影照片符合较好,并且侵彻深度计算结果与实验数据具有较好的一致性,FEM-SPH耦合方法显示出了模拟侵彻问题的有效性。研究表明钢纤维能明显增强混凝土基体的抗侵彻性能,且随纤维含量的提高增强效果更佳。     

基于有限元与边界元耦合法的波浪力分析

利用有限元与边界元耦合法对三维无界区域中直立圆柱所受的波浪力进行进行计算,把整个求解区域分成内域或外域两部分,在内域采用有限元法,对外域采用边界元法,数值计算的结果与理论解吻合良好,表明该方法有效。     

基于边光滑有限元法的结构振动与稳定性研究

用一种新型的数值方法-边光滑有限元方法（edge-based smoothed finite element method, ES-FEM）对梁、板等简单结构的振动与稳定性问题进行分析与研究。光滑有限元方法在计算系统总体刚度矩阵时在构造的光滑域内对应变进行光滑操作,这样得到的刚度矩阵改善了有限元方法过刚的数值缺陷。对梁和板结构在一定边界条件下的振动与稳定性问题的分析结果表明：与其它有限元方法相比,光滑有限元方法提高了数值计算结果的精确度和收敛性。     

基于细分粒子的刚体破裂动画

为了模拟固体在外力作用下产生的破裂现象,提出一种采用细分粒子的刚体破裂的模拟算法.该算法首先将固体的四面体网格绑定到一系列离散的粒子上;再利用光滑粒子流体动力学（SPH）对线弹性力学方程进行离散求解;并采用粒子细分的算法来进行开裂面的生成和延展.最后实现了多个固体现象的模拟,如砖块碎落、砖墙受力倒塌等.文中算法可适用于刚体脆性破碎的动画应用.     

改进迭代过程的车轨耦合振动数值解法及应用

针对列车-轨道耦合振动迭代求解过程,结合Newmark-β 积分格式,提出一种基于有限元法与非线性接触理论的改进迭代过程数值解法。考虑分别建立车辆系统和轨道系统振动方程,在耦合和解耦迭代过程中,构造松弛因子函数和收敛准则函数,简化轮轨界面协调适应条件,利用轮轨相互作用力在两子系统之间的快速迭代实现动态耦合关系的高效求解。此算法增强了对迭代收敛精度、迭代过程稳定性的控制,同时也减小了程序设计的难度。应用此算法分别对竖错和路基沉降两类典型线路缺陷引起的车轨振动响应进行了算例对比和分析,计算结果表明,改进解法在迭代速度和迭代稳定性上具有优势,可广泛应用于高速铁路车辆运行和轨道结构动力学问题的分析中。     

基于罚函数SPH新方法的水模拟充型过程的数值分析

同传统的网格法相比,光滑粒子流体动力学(SPH)方法非常适合于求解大变形和自由表面流动问题.阐述了SPH理论及其应用,并用罚函数处理流体与壁面的相互作用,以解决传统SPH本质边界条件不易施加的问题.对水模拟的允型过程实验进行数值分析,并和文献实验结果以及传统SPH进行对比,最终表明仿真结果与实验非常吻合,比传统SPH方...     

动态镦粗过程的动力显式有限元分析

为了研究金属的三维动态锤锻成形过程,基于连续介质力学及有限变形理论,建立了一种有限元模型.采用动力分析方法,在运动方程中加入惯性力项考虑锤锻中显著的惯性效应;根据设备的工作原理按照能量守恒定律计算变形期间的锤头速度;同时,将变形视为一个绝热过程计算变形期间试样内部的温度升高.基于建立的模型开发了动力显式有限元分析程序,模拟了铅块试样在落锤打击下的动态镦粗过程,给出了试样内部的位移、等效应变、等效应力和温度分布规律.将变形后试样几何形状、成形载荷-时间曲线和锤头速度-时间曲线的计算结果与实验结果相对比,表明了开发程序计算结果的准确性.     

基于SPH方法的油箱抗冲击有限元分析

目的验证SPH方法在流固耦合问题上的适用性。方法采用SPH方法(光滑粒子流体动力学方法)模拟无人机油箱抗冲击过程,并与采用CEL方法(耦合欧拉-拉格朗日方法)模拟得到的结果进行对比。结果 2种模拟方法得到的燃油晃荡情况、油箱应力分布及地面支反力结果接近。结论 SPH方法在流固耦合问题上是适用的。     

基于有限元与宽频快速多极边界元的二维流固耦合声场分析

采用有限元/快速多极边界元法进行水下弹性结构的辐射和散射声场分析。Burton-Miller法用于解决传统单Helmholtz边界积分方程在求解外边界值问题时出现的非唯一解的问题。该文采用GMRES和快速多极算法加速求解系统方程。针对传统快速算法在高频处效率低和对角式快速算法在低频处不稳定这一问题,该文通过结合这两种快速算法形成宽频快速算法来克服。同时该文通过观察不同参数条件设置下,宽频快速多极法得到的数值结果在计算精度和计算时间上的变化,得到最优的参数组合值。最后通过数值算例验证该文算法的正确性和有效性。     

坡膛结构变化对弹带挤进过程影响的研究

基于弹塑性有限元接触理论,引入了弹带材料的初始损伤及累计损伤模型,对弹带挤进、冲击坡膛的过程进行了理论分析,建立了弹带挤进、冲击坡膛的显式非线性有限元模型。对在两种不同结构坡膛条件下的弹带挤进过程进行了分析计算,得到了挤进过程弹丸及弹带的动力学响应,并通过计算分析了坡膛结构变化对挤进冲击力的影响,揭示了坡膛裂纹的形成机理。     

典型民机机身段水上冲击数值模拟方法及其耐撞性研究

为了改善民机在紧急迫降情况下的安全性能,对典型机身段水上冲击数值模拟方法及其冲击特性进行了研究。通过合理的简化建立了机身段有限元模型,对有限元方法(FEM)、任意拉格朗日/欧拉方法(ALE)和光滑粒子方法(SPH)水体模型进行了研究,探讨了水体材料模型对机身段结构动态响应特性的影响。在7 m/s垂向冲击速度下,对比分析了水面和刚性地面情况下的机身段结构的耐撞性能。结果表明ALE方法具有最佳计算精度和计算效率。由于忽略了偏应力,采用空材料得到的机身结构响应与弹性流体和弹塑性水体材料有明显不同。在水上冲击过程中,由于水体耗散了大量冲击动能,因此机身加强框变形较小。机身底部蒙皮结构承受较大的均布载荷,因此蒙皮吸能结构吸收了较多的冲击动能,是最重要的吸能结构之一。相对于刚性地面,水面冲击情况下机身具有更小的加速度过载。在紧急迫降情况下,选择湖泊或者江河等水域作为迫降地点可以减小乘员承受加速度过载。     

A saturated discrete particle model and characteristic-based SPH method in granular materials

Based on the discrete particle model for solid-phase deformation of granular materials consisting of dry particulate assemblages, a discrete particle–continuum model for modelling the coupled hydro-mechanical behaviour in saturated granular materials is developed. The motion of the interstitial fluid is described by two parallel continuum schemes governed by the averaged incompressible N–S equations and Darcy's law, respectively, where the latter one can be regarded as a degraded case of the former. Owing to the merits in both Lagrangian and mesh-free characters, the characteristic-based smoothed particle hydrodynamics (SPH) method is proposed in this paper for modelling pore fluid flows relative to the deformed solid phase that is modelled as packed assemblages of interacting discrete particles. It is assumed that the formulation is Lagrangian with the co-ordinate system transferring with the movement of the solid particles. The assumed continuous fluid field is discretized into a finite set of Lagrangian (material) points with their number equal to that of solid particles situated in the computational domain. An explicit meshless scheme for granular materials with interstitial water is formulated. Numerical results illustrate the capability and performance of the present model in modelling the fluid–solid interaction and deformation in granular materials saturated with water. Copyright © 2007 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.     

充液容器跌落过程的SPH模拟方法

采用SPH和FEM耦合的方法,考虑流固耦合效应的影响,对典型矩形薄壁充液容器的跌落过程进行数值仿真。通过对容器的变形、自由液面的运动、液体对容器的动压变化、容器的应力状态和所受动态激励的情况进行分析,说明SPH方法在充液容器的冲击问题研究中是行之有效的数值计算方法。同时数值算例的结果对充液容器的设计和试验具有一定的参考价值。     

液压锤打桩动态过程有限元分析

摘 要：液压锤打桩过程是由多结构组成的冲击过程。对其复杂的相互作用进行动态分析,对实现液压锤打桩效果及桩的设计有着指导作用。针对锤头、锤垫、砧座、桩垫、桩与土组成的锤击系统,建立有限元模型,采用罚函数法处理接触,对工业试验进行模拟。打击软土层与持力层时,测试点应力的计算结果与实测值吻合较好,验证了模型的正确性。在此基础上,分析了不同打击层应力沿桩长和桩径的分布,得到了桩上的应力分布规律,指导桩的设计。使用持力层打击模型,就垫层弹性模量比对桩顶锤击应力的影响进行了分析,得到了垫层材料的选择依据。     

Waterjet penetration simulation by hybrid code of SPH and FEA

The creativity of this work is combining finite element analysis (FEA) and smoothed particle hydrodynamics (SPH) methods to simulate the waterjet (WJ) penetration process. In WJ penetration, the waterjet undergoing extremely large deformation will introduce the distortion of mesh in FEA. To overcome this difficulty, the coupled method of SPH and FEA was developed, in which the waterjet was modeled by SPH particles and the target material was modeled by finite elements. The two parts interacted by contact algorithm of “nodes-to-surface”. Utilizing this hybrid model, waterjet with high velocity penetrating the target materials was calculated and the mechanism of erosion was depicted. The computation result gives the relationship between the jet velocity and the erosion capacity, including the depth of penetration and mass removal, which was compared with the experimental data.     

Rigid body water impact-experimental tests and numerical simulations using the SPH method

Statistics show that water impact of an aircraft in emergency is likely to have tragic consequences and therefore new researches on this topic are recommendable. In 2005, the GARTEUR AG15 was established to improve the SPH method for application to helicopter ditching. As a contribution, water impact drop tests using rigid bodies were performed at the Politecnico di Milano LAST Crash Lab to collect data and validate the numerical models. During the tests, impact decelerations were measured and suitably pressure transducers were developed to measure the impact pressures. Numerical simulations were carried out by adopting the SPH method to model the fluid region. A close experimental-numerical correlation was obtained. Findings are reported and guidelines for further investigations are proposed.     

FEM and BEM coupling in elastostatics using localized Lagrange multipliers

The equations produced by the finite and boundary element methods in structural mechanics are expressed in different variables and cannot be linked without modifications. Conventional coupling methods of these numerical techniques have traditionally been based on the use of classical Lagrange multipliers making a direct connection of the two solids through their common interfaces using matching meshes and altering the formulation of one of the methods to make it compatible with the other. In this work, a discrete surface called frame is interposed between the connected subdomains to approximate their common interface displacements, it is treated using a finite element discretization and connected to each substructure using localized Lagrange multipliers collocated at the interface nodes. This methodology facilitates the connection of non‐matching finite and boundary element meshes avoiding modifications to the numerical methods used and providing a partitioned formulation, which preserves software modularity. Copyright © 2006 John Wiley & Sons, Ltd.     

结构动应力分析的FEM-BEM耦合方法

本文提出了利用结构的有限元结点位移响应(或结点力)的计算值作为子域的边界条件,然后利用边界元方法计算子域内各瞬时的动应力的FEM-BEM耦合方法.文中给出了薄板在简谐激励下动应力响应的计算实例并与分析解进行了比较,结果表明,FEM-BEM耦合法比常规有限元法对结构动应力的计算精度有大幅度的提高.