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.     

计入气穴的水下爆炸作用下结构流固耦合三维数值模拟

水下爆炸在结构物面附近产生的气穴现象,严重影响水下爆炸作用下的流固耦合动响应,是舰船水下爆炸领域的难点,传统的边界元方法、有限元方法(FEM)难以解决水下爆炸气穴现象这类强非线性问题．针对此问题,计及流体中的气穴现象,考虑流体的可压缩型,忽略流体粘性,建立水下爆炸瞬态强非线性流固耦合三维数值模型,采用流体谱单元方法(SEM)和结构有限元方法求解该模型．计算结果表明:相对有限元法,谱单元法具有更高的计算精度,且谱单元解与解析解、试验值吻合良好．在此基础上,结合ABAQUS软件,分别探讨三维球壳、船体板架在水下爆炸作用下的瞬态流固耦合机理,给出气穴区域及其对水中结构物动响应的影响特征,旨在为舰船水下爆炸瞬态流固耦合问题的相关研究提供参考．     

爆炸和冲击载荷下金属材料及结构的动态失效仿真

通过数值模拟研究爆炸冲击载荷下金属材料和结构的动态失效规律对表征爆炸冲击毁伤效应及设计新型抗冲击结构具有重要意义.强动载下金属材料失效涉及材料大变形、热力耦合、材料状态变化等多个复杂物理过程,给数值仿真带来了极大挑战,其中包括裂纹、剪切带等复杂失效模式的几何描述、动态失效准则的确定、塑性与损伤耦合演化的描述等问题.针对这些挑战性问题,基于能量变分建立描述金属动态失效过程的热弹塑性相场理论和计算模型,实现了断裂与剪切带失效模式的统一描述,并提出了其显式有限元高效求解策略.进一步将该模型应用于爆炸冲击载荷下金属脆韧失效模式转变、绝热剪切带（ASBs）自组织及冲击波作用下薄壁圆盘失效形式转变三个典型金属动态失效问题,验证了理论模型的准确性及计算模型的稳健性.该工作为后续开展基于仿真的爆炸冲击毁伤评估及防护结构设计研究奠定了基础.     

芳纶纤维平纹织布在爆炸载荷下的动态响应与失效行为的数值分析

为了研究柔性纤维织布的抗爆性能,通过数值模拟的方法对芳纶纤维织布在爆炸冲击下的响应与失效行为进行了分析。对国产芳纶纤维织布H1000D-AP220进行了力学性能试验,建立了柔性平纹织布的本构模型和爆炸冲击数值分析模型,对不同厚度不同铺层角度织布进行了爆炸冲击数值分析,获得了织布在不同爆炸载荷下的动态响应和失效模式。结果表明,织布在爆炸冲击载荷下主要表现为中心撕裂破孔和简支边界处拉伸撕裂2种典型的失效模式,并伴有明显褶皱,宽度方向出现织布向内侧收缩翻转现象;相比于中间层织布,迎爆面和背爆面吸能较多;在计算分析中改变了织布的层叠角度,获得了更好的抗爆效果。     

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

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.     

钢管混凝土柱抗爆性能数值模拟与实验验证

利用LS-DYNA非线性有限元程序,基于多物质流固耦合方法,建立了爆炸荷载作用下钢管混凝土柱的动态响应数值模型.对比分析了模拟结果与足尺构件的爆炸破坏实验结果,验证了数值模型和计算方法的有效性,并运用参数化分析方法,研究了截面形式、比例距离、混凝土强度及钢材等级、截面形状特性等关键参数对钢管混凝土柱抗爆性能的影响.研究结果表明:钢管混凝土柱具有优越的抗爆性能,所建立的数值模型能够有效地分析钢管混凝土柱在爆炸荷载作用下的动态影响及破坏形态;圆形截面钢管混凝土柱的抗爆性能优于方形截面;提高材料等级、减小圆形截面钢管混凝土柱的径厚比、增大矩形截面钢管混凝土柱的长宽比,均有利于提升钢管混凝土柱的抗爆特性.     

二维八次对称准晶的断裂动力学问题

基于准晶弹性流体动力学模型,采用有限差分法研究了含Griffith裂纹八次对称准晶在不同冲击载荷下的动态响应,得到了应力、位移和应力强度因子的数值结果,讨论了不同冲击载荷对动力学行为的影响.     

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．     

Blast Damage Simulation With the Discontinuous Galerkin Finite Element Method of Bond⁃Based Peridynamics北大核心CSCD

近场动力学是一种积分型非局部的连续介质力学理论,已广泛应用于固体材料和结构的非连续变形与破坏分析中,其数值求解方法主要采用无网格粒子类的显式动力学方法.近年来,弱形式近场动力学方程的非连续Galerkin有限元法得到发展,该方法不仅可以描述考察体的非局部作用效应和非连续变形特性,还可以充分利用有限单元法高效求解的特点,并继承了有限元法能直接施加局部边界条件的优点,可有效避免近场动力学的表面效应问题.该文阐述了键型近场动力学的非连续Galerkin有限元法的基本原理,导出了计算列式,给出了具体算法流程和细节,计算模拟了脆性玻璃板动态开裂分叉问题,并对爆炸冲击荷载作用下混凝土板的毁伤过程进行了计算分析.研究结果表明,该方法能够再现爆炸冲击荷载作用下结构的复杂破裂模式和毁伤破坏过程,且具有较高的计算效率,是模拟结构爆炸冲击毁伤效应的一种有效方法.     

炸药爆轰物质点法三维数值模拟

炸药爆轰以及多点起爆所产生的爆轰波汇聚问题很难应用有限元法进行模拟分析,尤其当网格发生畸变时,导致有限元法计算效率和数值精度严重下降,甚至无法得到正确结果.为此,该文应用显式积分算法的物质点法对炸药两点起爆和按时间序列的多点起爆的爆轰过程进行数值模拟,与炸药爆轰的理论计算结果相吻合.物质点法不但可以有效地避免网格畸变问题,而且为炸药爆轰的数值模拟提供了新的思路.     

Construction of locally conservative fluxes for the SUPG method

We consider the construction of locally conservative fluxes by means of a simple postprocessing technique obtained from the finite element solutions of advection diffusion equations. It is known that a naive calculation of fluxes from these solutions yields nonconservative fluxes. We consider two finite element methods: the usual continuous Galerkin finite element method for solving nondominating advection diffusion equations and the streamline upwind/Petrov‐Galerkin method for solving advection dominated problems. We then describe the postprocessing technique for constructing conservative fluxes from the numerical solutions of the general variational formulation. The postprocessing technique requires solving an auxiliary Neumann boundary value problem on each element independently and it produces a locally conservative flux on a vertex centered dual mesh relative to the finite element mesh. We provide a convergence analysis for the postprocessing technique. Performance of the technique and the convergence behavior are demonstrated through numerical examples including a set of test problems for advection diffusion equations, advection dominated equations, and drift‐diffusion equations. © 2015 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 31: 1971–1994, 2015     

Numerical–analytical model for transient dynamics of elastic-plastic plate under eccentric low-velocity impact

The aim of this study is to present an efficient model for the analysis of complicated nonlinear transient dynamics of an elastic-plastic plate subjected to a transversely eccentric low-velocity impact. A mixed numerical–analytical model is presented to predict the transient dynamic behaviours consisting of either plate impact responses or wave propagations induced by the impact in a plate with an arbitrary shape and support. This hybrid approach has been validated by comparison with results of laboratory tests performed on an elastic-perfectly plastic narrow plate eccentrically struck by an elastic sphere, and results of a three-dimensional finite element (FE) analysis for an elastic-perfectly plastic simply-supported rectangular plate eccentrically struck by an elastic sphere. The advantages of this hybrid approach are in the simplification of local contact force formulation, computational efficiency over the FE model, and convenient application to parametric study for eccentric impact behaviour. The hybrid approach can provide accurate predictions of the plate impact responses and plate wave propagations.     

Discontinuous Galerkin finite element heterogeneous multiscale method for advection–diffusion problems with multiple scales

A discontinuous Galerkin finite element heterogeneous multiscale method is proposed for advection–diffusion problems with highly oscillatory coefficients. The method is based on a coupling of a discontinuous Galerkin discretization for an effective advection–diffusion problem on a macroscopic mesh, whose a priori unknown data are recovered from micro finite element calculations on sampling domains within each macro element. The computational work involved is independent of the high oscillations in the problem at the smallest scale. The stability of our method (depending on both macro and micro mesh sizes) is established for both diffusion dominated and advection dominated regimes without any assumptions about the type of heterogeneities in the data. Fully discrete a priori error bounds are derived for locally periodic data. Numerical experiments confirm the theoretical error estimates.     

基于浸入边界-有限元法的流固耦合碰撞数值模拟方法

针对流固耦合碰撞问题,建立了流体中固体与固体碰撞界面解析直接模拟方法,采用清晰界面浸入边界法模拟流体中的动边界问题,避免了传统贴体网格方法在求解流体中存在固体间碰撞问题时网格出现负体积的问题,采用基于罚函数的有限元方法对固体的运动和碰撞进行求解,以分域耦合方式实现流体域和固体域的耦合求解.通过与静止流体中球形颗粒与壁面正碰撞和斜碰撞的实验数据对比,验证了建立的数值模拟方法对流体中固体与固体碰撞数值模拟的正确性,获得了流体域流场在碰撞前后随时间的变化,同时通过该文建立的数值模拟方法也获得了固体域中固体的碰撞力和应力.未来,将把该数值模拟方法应用到流体流动环境中,如固体颗粒对管道的冲蚀、流体诱导海洋立管之间的碰撞、坠物对海底管道的撞击等.     

A new stabilized finite element method for advection‐diffusion‐reaction equations

In this article, a new stabilized finite element method is proposed and analyzed for advection‐diffusion‐reaction equations. The key feature is that both the mesh‐dependent Péclet number and the mesh‐dependent Damköhler number are reasonably incorporated into the newly designed stabilization parameter. The error estimates are established, where, up to the regularity‐norm of the exact solution, the explicit‐dependence of the diffusivity, advection, reaction, and mesh size (or the dependence of the mesh‐dependent Péclet number and the mesh‐dependent Damköhler number) is revealed. Such dependence in the error bounds provides a mathematical justification on the effectiveness of the proposed method for any values of diffusivity, advection, dissipative reaction, and mesh size. Numerical results are presented to illustrate the performance of the method. © 2015 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 32: 616–645, 2016     

Rail-bridge coupling element of unequal lengths for analysing train-track-bridge interaction systems

This paper presents a rail-bridge coupling element of unequal lengths, in which the length of a bridge element is longer than that of a rail element, to investigate the dynamic problem of train-track-bridge interaction systems. The equation of motion in matrix form is given for a train-track-bridge interaction system with the proposed element. The first two numerical examples with two types of bridge models are chosen to illustrate the application of the proposed element. The results show that, for the same length of rail element, (1) the dynamic responses of train, track and bridge obtained by the proposed element are almost identical to those obtained by the rail-bridge coupling element of equal length, and (2) compared with the rail-bridge coupling element of equal length, the proposed element can help to save computer time. Furthermore, the influence of the length of rail element on the dynamic responses of rail is significant. However, the influence of the length of rail element on the dynamic responses of bridge is insignificant. Therefore, the proposed element with a shorter rail element and a longer bridge element may be adopted to study the dynamic responses of a train-track-bridge interaction system. The last numerical example is to investigate the effects of two types of track models on the dynamic responses of vehicle, rail and bridge. The results show that: (1) there are differences of the dynamic responses of vehicle, rail and bridge based on the single-layer and double-layer track models, (2) the maximum differences increase with the increase of the mass of sleeper, (3) the double-layer track model is more accurate.     

解Stokes特征值问题的一种两水平稳定化有限元方法

基于局部Gauss积分,研究了解Stokes特征值问题的一种两水平稳定化有限元方法．该方法涉及在网格步长为H的粗网格上解一个Stokes特征值问题,在网格步长为h=O(H2)的细网格上解一个Stokes问题．这样使其能够仍旧保持最优的逼近精度,求得的解和一般的稳定化有限元解具有相同的收敛阶,即直接在网格步长为h的细网格上解一个Stokes特征值问题．因此,该方法能够节省大量的计算时间．数值试验验证了理论结果．     

A constitutive model for the flow stress behavior and microstructure evolution in aluminum alloys under hot working conditions – with application to AA6099

A constitutive model for aluminum alloys under hot working conditions is proposed. The elastic-viscoplastic model is implemented in a finite strain continuum mechanical framework. The model accounts for the interplay between dynamic recovery and recrystallization during hot working of aluminum alloys and central aspects of microstructure evolution such as grain/subgrain size and dislocation density. The proposed model is generic in the sense that it can be used for arbitrary aluminum alloys, but in order to demonstrate its capabilities, the model is calibrated to a newly developed AA6099 alloy in the present study. The model is thoroughly discussed and details on the numerical implementation as well as on the calibration of the model against experimental data are provided.