强激波与流-固界面相互作用的数值模拟

1 引言强激波与流-固界面相互作用的数值模拟在实际问题中具有重要的应用,比如水下炸弹爆炸时产生的强大的冲击波对附近的舰船或水下潜艇会造成非常大的破坏,造成舰体严重变形甚至断裂．在此类问题中,界面两边的流体具有完全不同的特性,流体的密度、     

水下爆炸气泡与复杂弹塑性结构的相互作用研究

计及结构的弹塑性,将边界元法(BEM)与有限元法(FEM)耦合提出了气泡与弹塑性结构耦合动力学计算方法,并开发了全套的三维水下气泡分析程序（UBA）,计算值与实验值之间误差在10%以内．以水面舰船为例,将三维计算程序工程化．并分析了水下爆炸气泡载荷作用下船体的弹塑性响应,从船体结构典型单元上的应力时历曲线可以看出,在气泡坍塌时出现应力峰值,证实了气泡坍塌压力及射流引起的压力对舰船等结构造成严重毁伤．从气泡与舰船的相互作用中可以看出,舰船低阶垂向振型被激起,在气泡作用下呈鞭状运动,同时舰船随着气泡的膨胀和收缩作升沉运动,通过本文的分析得到了适合于工程应用的规律及结论．     

基于MPS-FEM耦合方法对比研究刚性与弹性挡板对液舱晃荡的抑制作用

由流体冲击载荷引起的流固耦合问题广泛存在于船舶与海洋工程领域.例如:在特定激励频率下载液货舱内流体的非线性运动引起对舱壁的砰击作用,进而可能影响液舱围护系统的安全性.由于此类流固耦合问题通常涉及多学科知识,且流体自由面的变化具有强非线性特征,对研究人员带来较大挑战.考虑到Lagrange类方法在处理结构和流体自由面大变形问题上的优势,基于MPS-FEM耦合方法开发了流固耦合求解器.其中,采用MPS方法来数值模拟流体场瞬态变化,FEM方法来分析结构场的变形问题.此外,该求解器采用了弱耦合的方式来实现流体场和结构场之间的数据传递.为了验证该方法在处理流固耦合问题上的可靠性,首先数值研究了溃坝泄洪流与弹性挡板之间的流固耦合标准算例,数值结果与实验标准结果能够较好地吻合.此后,采用该求解器数值研究了带刚性挡板和弹性挡板的液舱晃荡问题,对比分析了多种激励频率下两种挡板对液舱内流体运动及舱壁上冲击压力的抑制效果.     

基于MPS-FEM耦合方法对比研究刚性与弹性挡板对液舱晃荡的抑制作用（英文）

由流体冲击载荷引起的流固耦合问题广泛存在于船舶与海洋工程领域.例如:在特定激励频率下载液货舱内流体的非线性运动引起对舱壁的砰击作用,进而可能影响液舱围护系统的安全性.由于此类流固耦合问题通常涉及多学科知识,且流体自由面的变化具有强非线性特征,对研究人员带来较大挑战.考虑到Lagrange类方法在处理结构和流体自由面大变形问题上的优势,基于MPS-FEM耦合方法开发了流固耦合求解器.其中,采用MPS方法来数值模拟流体场瞬态变化,FEM方法来分析结构场的变形问题.此外,该求解器采用了弱耦合的方式来实现流体场和结构场之间的数据传递.为了验证该方法在处理流固耦合问题上的可靠性,首先数值研究了溃坝泄洪流与弹性挡板之间的流固耦合标准算例,数值结果与实验标准结果能够较好地吻合.此后,采用该求解器数值研究了带刚性挡板和弹性挡板的液舱晃荡问题,对比分析了多种激励频率下两种挡板对液舱内流体运动及舱壁上冲击压力的抑制效果.     

论理想流体与线弹性结构的耦联振动

本文对理想流体与线弹性结构的耦联振动问题作理论分析和数值分析.文中证明了耦联振动的固有频率存在并且均为正实数.将流-固耦合系统分析转化为单一结构物在真空中的自由振动分析后,频率方程中不再含有流体变元.使问题得以大大简化.给出了数值解的收敛性证明,以保证解的可靠性.文中还综合里兹法、边界元和有限元方法,提出一种分析转化后结构的混合算法.利用该算法,只需对现有结构分析程序稍作改进,就可分析那些理想流场与结构的耦合问题.一些数例说明了算法的有效性.     

无锚固储液罐提离的流-固多种非线性耦合的三维移动边界问题统一分析格式*

本文建立了在地震作用下无锚固储液罐提离的流-固多种非线性耦合的移动边界问题的统一格式的三维分析方法,其中建立了任意四边形标薄板壳拟协调非线性有限元的列式和分析移动边界问题的线性互补方程;提出了在ALE标架下用带压力项的时间分裂步法求解储液罐内含自由液面大幅晃动(移动边界问题)的非定常的三维粘性流体(N-S)问题的方法;其中没有利用轴称性和梁式模态假定等条件及未曾利用势函数理论;该方法适用于一般板壳-流体多种非线性耦合的多种移动边界问题.     

直管束流固耦合振动的数值模拟

为了研究反应堆结构中的诸如燃料棒、蒸汽发生器和其它换热器传热管束等的流体-结构交互作用问题,利用有限体积法离散大涡模拟(large eddy simulation, LES)的流体控制方程,用有限元方法求解结构动力学方程,并结合动网格技术,建立三维流体诱发振动的数值模型,模拟直管束中流体的流动及结构振动,实现计算结构动力学(computational structure dynamics, CSD)与计算流体力学(computational fluid dynamics, CFD)之间的联合仿真．首先,基于流固耦合方法对单管的流致振动特性进行了详细分析,得到了其动力学响应与流场特性;其次基于建立的传热管束流致振动计算模型,研究了两并列管、两串列管以及3×3正方形排列管束的流致振动行为．     

黏性不可压流体的自适应网格技术和基本特性方程分离算法的联合分析

组合基本特性方程分离算法和自适应网格技术,分析二维黏性不可压流体.该方法使用3节点三角单元,对速度分量和压力等变量分析,使用等阶次的插值函数.组合解法的主要优点在于,在自适应网格技术中,对解梯度变化大的区域,通过耦合误差估计生成小的单元,利于提高解的精度,在其它区域生成大单元,可以节省时间.最后,通过对一个黏性流体圆柱体绕流问题的瞬态和稳态特性分析,给出了组合解法性能的评价.     

地下结构物在爆炸冲击波作用下的动力分析

提出了一种求解任意形地下结构物在爆炸冲击波作用下的动应力集中问题的半解析方法．爆炸冲击波以平面SH波的形式入射,并用Fourier变换方法将其转换到频域,不同形状地下结构物的导纳函数由复变函数和保角映射的方法求得．利用Fourier逆变换,进一步合成得到时域中的地下结构的动力响应,最后,对正方形、三角形及马蹄形孔洞附近的动应力集中系数作了数值计算,并给出了具体结果．     

爆炸冲击载荷下航空铝合金平板动态响应数值分析方法

为得到适用于爆炸冲击载荷下航空铝合金平板动态响应的数值分析方法,采用LS-DYNA显式动力学分析软件对爆炸冲击载荷下的铝合金平板进行数值仿真计算.主要研究了不同的任意Lagrange-Euler(拉格朗日-欧拉)网格（ALE）输运步算法、流固耦合方式、流固耦合点数量、网格尺寸、有限元单元类型对计算结果的影响.通过计算结果与实验结果的分析对比,表明采用van Leer+HIS输运步算法、罚函数耦合方式、在流体网格与结构网格之间采用3个耦合点、结构网格尺寸与空气域网格尺寸比例设为2∶1、结构单元采用163号壳单元时可以较为准确地计算航空铝合金平板在爆炸冲击载荷下的动态响应,并且能提高计算效率,节约计算时间.     

Damage analysis of arch concrete dams subjected to underwater explosion

The nonlinear behavior of arch concrete dams subjected to underwater explosions was investigated. Pressure waves were spherically modeled using a 3-D finite element method. The nonlinear behavior of concrete was modeled using the concrete damage plasticity model. In addition, absolute wave formulation was used to develop a fully-coupled model incorporating the propagation of the shock wave and water–dam interaction. Analysis of an arch concrete dam subject to underwater explosion was performed upon model verification. The dynamic response of the dam subject to the underwater explosion was studied for different sizes of explosions at different depths. The results showed that the closer the point to the explosive source, the sooner the impression and damage was caused by the blast. It was clear that the middle part of the dam facing the explosion was the first location to incur damage and then cracks extended to the downstream face and abutments. Finally, cracks extended to the bottom of the dam. The results of the dynamic analysis and dissipated energy by the loss of elements’ resistance indicated that the time slice of 150 ms was appropriate to analyze arch concrete dam structure subject to an underwater explosion. In addition, for a given amount of explosives, an increase in the depth of explosion corresponded to an increase in the maximum displacement of the upstream face of the dam. The results also confirmed that the damage distribution to the arch concrete dam subject to an underwater explosion depended upon the amount and depth of explosive materials.     

Behavior of laterally and vertically loaded piles in multi-layered transversely isotropic soils

In this paper, a coupled approach of the finite element method (FEM) and the analytical layer-element method (ALEM) is proposed to conduct a research on vertically and laterally loaded piles. The FEM is used to model the pile, and the ALEM is utilized to solve the multi-layered transversely isotropic soils. Then with the assumption of force equilibrium and deformation compatibility, the interaction equation of pile and soils is obtained. Finally, the behavior of piles simultaneously subjected to lateral and vertical loads in layered transversely isotropic soils is investigated by considering the influence of lateral–vertical loads interaction and soft soil stratum.     

Vibrational analysis of electrostatically actuated microstructures considering nonlinear effects

The vibrational behavior of electrostatically actuated microstructures subjected to nonlinear squeeze film damping and in-plane forces is investigated. First-Order Shear Deformation Theory is used to model dynamical system by means of finite element method, while finite difference method is applied to solve the nonlinear Reynolds equation of squeeze film damping simultaneously. Vibrational analysis of microplates is performed by solving eigenvalue problem, after validating the model by pull-in phenomenon and transient behavior. In addition, considering nonlinear squeeze film damping and step-input actuations, response frequencies of microplates are calculated. Effect of ambient pressure and in-plane forces on dynamic pull-in phenomenon is also studied. Results for simplified models are verified and are in good agreement with the published literature. This investigation can reveal nonlinear vibrational behavior of microstructures.     

船体梁在水下近距爆炸作用下反直观动力行为的相似分析

针对漂浮船体梁结构在船舯底部近距爆炸作用下最终呈现的反直观中垂破坏现象进行了研究．首先以单发MK48鱼雷击沉DD973驱逐舰的实船打靶试验为例,建立了该问题的物理仿真模型,将水下爆炸冲击载荷的指数衰减段、倒数衰减段、倒数衰减后段和负压段压力精确加载到梁单元节点上进行求解,其中考虑了流固耦合效应、附连水质量以及重力和浮力变化的影响．之后利用相似理论对实船结构和箱型梁实验模型在中部下方近距爆炸作用下的整体动力响应进行分析,得到了决定船体梁中垂和中拱变形的相似参数及采用Rn数表示的理论预报公式,同时分析了各相似参数的物理意义和影响规律．     

Coupled fluid-solid thermal interaction modeling for efficient transient simulation of biphasic water-steam energy systems

This paper proposes a fluid-solid coupled finite element formulation for the transient simulation of water-steam energy systems with phase change due to boiling and condensation. As it is commonly assumed in the study of thermal systems, the transient effects considered are exclusively originated by heat transfer processes. A homogeneous mixture model is adopted for the analysis of biphasic flow, resulting in a nonlinear transient advection-diffusion-reaction energy equation and an integral form for mass conservation in the fluid, coupled to the linear transient heat conduction equation for the solid. The conservation equations are approximated applying a stabilized Petrov-Galerkin FEM formulation, providing a set of coupled nonlinear equations for mass and energy conservation. This numerical model, combined with experimental heat transfer coefficients, provides a comprehensive simulation tool for the coupled analysis of boiling and condensation processes. For the treatment of enthalpy discontinuities traveling with the flow, a novel explicit-implicit time integration method based on Crank-Nicolson scheme is proposed, analyzing its accuracy and stability properties. To reduce problem size and enhance numerical efficiency, a modal superposition method with balanced truncation is applied to the solid equations. Finally, different example problems are solved to demonstrate the capabilities, flexibility and accuracy of the proposed formulation.     

泡沫覆盖层对水下爆炸气泡射流防护机理缩比试验研究

水下爆炸会对水中结构物造成严重威胁。柔性覆盖层或夹层板能够降低水中结构物水下爆炸冲击响应，因此成为研究的热点。以往的研究多集中于覆盖层对冲击波的防护机理，适用于较远距离的水下爆炸情况。近距离水下爆炸除了冲击波外，爆炸气泡溃灭时产生的朝向结构物的高速水射流更为致命。该文针对这种情况，基于量纲原理，推导缩比相似关系，通过缩比模型水下爆炸试验发现了覆盖层表面空化微气泡群对爆炸气泡形成高速水射流过程产生干扰，提出了泡沫覆盖层钢板水下爆炸气泡射流防护机理。     

The finite element solution of a quasi-linear elliptic equation governing non-Newtonian flows through rectangular ducts

A Rayleigh-Ritz finite element method (FEM) using quadratic, cubic and quartic elements has been used to solve the steady laminar flow of a non-Newtonian fluid through rectangular ducts. Different iterative approaches were investigated to solve the large system of linear equations resulting from the discretization of the quasi-linear partial differential equation. The performance of the FEM incorporating the method of variation of parameters (Davidenko path procedure) was compared with the finite difference method in terms of speed, accuracy and the capability of handling the very pronounced nonlinearity. From the convergent solutions obtained, some flow parameters were investigated. The results presented agree well with other published work.     

A General Cavitation Model for the Highly Nonlinear Mie-Grüneisen Equation of State

A general one-fluid cavitation model is proposed for a family of Mie-Grüneisen equations of state (EOS), which can provide a wide application of cavitation flows, such as liquid-vapour transformation and underwater explosion. An approximate Riemann problem and its approximate solver for the general cavitation model are developed. The approximate solver, which provides the interface pressure and normal velocity by an iterative method, is applied in computing the numerical flux at the phase interface for our compressible multi-medium flow simulation on Eulerian grids. Several numerical examples, including Riemann problems and underwater explosion applications, are presented to validate the cavitation model and the corresponding approximate solver.     

基于时域精细积分算法的瞬态传热多宗量反演

基于有限元法和精细积分算法,提出了一种求解瞬态热传导多宗量反演问题的新方法．采用有限元法和精细积分算法分别对空间、时间变量进行离散,可以得到正演问题高精度的半解析数值模型,由此建立了多宗量反演的计算模式,并给出敏度分析的计算公式．对一维和二维的热物性参数、热源项、边界条件等进行了单宗量和多宗量的反演求解,初步考虑了初值和噪音等对反演结果的影响,数值算例验证了该方法的有效性．