水下爆炸应力波在含声学覆盖层结构中的传播规律

 针对舰船的含声学覆盖层结构,对水下爆炸作用下应力波在该结构中的传播规律进行研究。采用二阶Godunov方法,建立水下爆炸应力波在多层介质中传播的计算模型,并与经典Taylor平板解析解进行对比验证;通过对不同工况下的应力波传播规律分析,获得边界条件、声学覆盖层厚度等参数对其影响规律,可为舰艇抗冲击设计、研究提供参考。     

非饱和地基中Love波的传播特性

基于非饱和多孔介质的波动方程,考虑了土中水,气体与土骨架之间的粘性耦合作用,建立了弹性半空间上非饱和土层中Love波的弥散方程。首先分析了饱和度与频率对非饱和孔隙介质中剪切波速的影响。然后运用数值方法得到了不同饱和度下土层中多种Love模态波的弥散特性和位移分布情况,并用图表的形式给出。数值计算结果表明,上覆非饱和土层中Love波的传播速度和衰减系数不仅具有频散性,而且与土层的饱和度有关。在不同饱和度时的高模态(n≥2)的Love波的截止频率值不同。此外,讨论了饱和度对Love波水平位移幅值的影响。     

软弱夹层对爆炸应力波传播过程的影响研究

针对含软弱夹层岩体爆炸应力波的传播过程,采用数值模拟的方法,探讨了软弱夹层厚度、位置及角度对爆炸应力波传播的影响规律。研究结果表明:爆炸应力波在软弱夹层界面处发生反射,产生的拉伸应力波使应力波能量在迎波面汇聚,加剧该部分岩体的破坏程度。随着软弱夹层厚度的增加,前方岩体拉应力峰值增长作用由近迎波面岩体向炮孔周边岩体传播,拉应力峰值增长率逐渐提高;同时,夹层阻隔作用增强,后方岩体有效应力峰值衰减加快。软弱夹层与起爆中心的间距减小使得夹层前方岩体拉应力峰值显著增长,而对夹层后方岩体的阻隔作用逐渐减弱。应力波能量主要汇聚在软弱夹层的垂直方向,致使岩体爆破产生的裂缝偏离水平测线方向而向软弱夹层法线方向发展。研究成果可用于指导类似地层隧道爆破施工设计。     

梁撞击弹塑性波传播的动态子结构方法的研究

该文针对简支梁横向弹塑性撞击问题,建立动态子结构模型,推导了相应的动力学控制方程,并采用Newmark隐式积分法进行求解,将动态子结构方法应用于撞击激发弹塑性波传播问题的研究。考虑局部弹塑性接触变形,通过对撞击激发的弹塑性波传播,包括弯矩波、挠曲波、速度波和应力波传播过程的计算,研究动态子结构法分析弹塑性波的传播特征,弯曲波的弥散特征,以及塑性铰形成机理等的合理性。经过与三维动力有限元计算结果的比较表明,动态子结构方法可以合理地应用于柔性梁中弹塑性撞击瞬态波传播问题的研究。     

基于谱元法的复合材料裂纹梁Lamb波传播特性研究

基于谱元法提出了一种弹簧元来模拟复合材料梁由于横向裂纹导致的轴弯耦合效应,分析复合材料裂纹梁中Lamb波的传播特性。由断裂力学的相关知识求得弹簧元的刚度,建立复合材料裂纹梁的损伤谱元模型。通过模拟复合材料裂纹梁内Lamb波传播,并和传统的有限元结果进行比较,验证了所提出模型的可行性和有效性。推导了频域内Lamb波各模态的能量计算公式,裂纹处的能量守恒证明了所提出模型的正确性,同时计算表明复合材料梁中裂纹处反射与透射的Lamb波各模态能量随着裂纹深度的变化规律具有单调性,结论可以为定量识别复合材料梁裂纹提供实用依据。     

一种基于本征波匹配的EMD边界处理方法

希尔伯特-黄变换(Hilbert-Huang Transform,简称HHT)是上世纪末出现的一种处理非线性非平稳信号的新方法 ,EMD边界处理是其中的关键技术之一。着重介绍了一种基于本征波匹配的EMD边界处理方法——本证波匹配预测法,特别是介绍了将该方法和其他两种有代表性的EMD边界处理方法应用于仿真信号和和实测信号的算例对比,从而验证了本证波匹配预测法的先进性。本文工作使得相关研究得到较大程度地深化和完善。     

基于微平面弹塑性应力-应变关系的混凝土本构模型

在B.P. Bazant等人提出的混凝土微平面本构模型M2的基础上,将微平面上的应力分解为体、偏、剪三个分量,根据各个分量的物理意义定义了相应的应力-应变关系函数,即理想弹塑性函数。引入了破断应变的概念,当微平面应变达到破断应变后应力减为零。介绍了模型参数的确定方法。最后通过三个算例初步验证了本文所建议模型的合理性和正确性。     

非对称周期结构中耦合波的传播特性

为了揭示周期结构中纵向波和弯曲波的耦合作用,设计了对称和非对称周期结构。考虑子结构中的纵向和弯曲耦合运动,利用导纳法和传递矩阵法,得到了周期单元的传递方程。由于结构中存在多种波的耦合作用,在求解周期单元的传播系数时将出现变态矩阵,采用波型分组法,求得了周期结构中多种波型的传播系数。推导了半无限长和有限长周期结构在纵向力、横向力和弯矩作用下的动态响应。数值计算结果表明,对称周期结构中纵向波和弯曲波的带隙结构相互独立;非对称周期结构中纵向波和弯曲波的耦合明显改变了两种波的带隙结构,只有在两种波阻带重叠的频段内结构上的振动响应才存在衰减。     

基于杆系模型的磁流变阻尼结构弹塑性动力反应分析

磁流变阻尼器(MRD)是一种性能优越的半主动控制装置。首先推导了设置有MRD框架结构中MRD的位置矩阵,然后将框架结构简化为杆系模型,用MATLAB编制了加入MRD的框架结构的弹塑性动力时程分析程序,分别计算并对比了框架结构在未控和有控下各层的位移、加速度响应和各杆端塑性铰分布情况。结果表明,设置MRD的框架结构各层位移和加速度响应显著减小,其中位移的减震效果优于加速度的减震效果,同时杆件屈服数量相应减少。     

畸形波作用下二阶波浪载荷对张力腿平台动力响应的影响

畸形波易对海上的建筑物造成极大的危害。为研究畸形波作用下张力腿平台的动力响应特性,考虑张力腿平台的六自由度运动与张力腿非线性恢复刚度,建立非线性耦合运动方程。结合随机频率相位角调制法生成的畸形波波面时历,计算在畸形波条件下平台所受的一阶及二阶和、差频波浪载荷,并采用数值方法求解平台六自由度的运动。结果表明,在畸形波作用下,一阶、二阶波浪载荷均受到畸形波的影响,但各波浪载荷成分的增幅在不同自由度上并不相同。以纵荡为代表的低频运动主要受二阶差频波浪载荷影响,以垂荡、纵摇为代表的高频运动受二阶和频波浪载荷的影响。而由平台水平面内运动引发的下沉运动在二阶差频波浪载荷的作用下显著增大,从而诱发了垂荡运动产生了显著增加,因此在畸形波作用下垂荡运动同时受到二阶和频及差频波浪载荷的影响。此外,由于畸形波具有冲击载荷的特性,不同自由度运动幅值出现时刻并不相同。     

Dynamic flow‐based particle splitting in smoothed particle hydrodynamics

In this work, a dynamic procedure for local particle refinement to be used in smoothed particle hydrodynamics (SPH) is presented. The algorithm is able to consistently produce successive levels of particle splitting in accordance to a flow‐based criterion. It has been applied together with accurate and robust formulations for variable spatial resolution in the framework of a semi‐implicit, truly incompressible scheme for SPH. Different test cases have been considered to assess the capabilities and advantages of the proposed procedure, namely, the laminar flow around circular and square obstacles in a plane channel for various regimes. Such flow cases entail the simulation of attached and separated shear layers, recirculating flow, vortex shedding and surface discontinuities. The results obtained for two levels of particle splitting have demonstrated that significant improvements may be obtained with respect to uniform particle spacing solutions in a variety of situations, thus presenting an excellent trade‐off between accuracy and computational cost. Copyright © 2015 John Wiley & Sons, Ltd.     

On the Galerkin formulation of the smoothed particle hydrodynamics method

In this paper, we propose a Galerkin‐based smoothed particle hydrodynamics (SPH) formulation with moving least‐squares meshless approximation, applied to free surface flows. The Galerkin scheme provides a clear framework to analyse several procedures widely used in the classical SPH literature, suggesting that some of them should be reformulated in order to develop consistent algorithms. The performance of the methodology proposed is tested through various dynamic simulations, demonstrating the attractive ability of particle methods to handle severe distortions and complex phenomena. Copyright © 2004 John Wiley & Sons, Ltd.     

SPH原理、发展现状及热传导问题模型

对光滑粒子流体动力学方法（smoothed particle hydrodynamics,SPH）的基本技术原理及发展现状进行了综述,利用SPH方法对两个典型二维非线性动力学算例进行了数值模拟。同时,利用国外学者提出的方法初步探索了有关热传导问题的SPH模型。     

Simulation of high velocity impact in fluid-filled containers using finite elements with adaptive coupling to smoothed particle hydrodynamics

This paper presents a numerical study on the simulation of impacts of projectiles on fluid-filled containers. The type of impact investigated leads to hydrodynamic ram (HRAM) and complete failure of the container shell. Two different numerical approaches are compared which are both implemented in a research hydrocode: a pure Lagrangian discretization with Finite Elements (FE) and element erosion, and a coupled adaptive FE/SPH discretization. The numerical results are compared with two reference experiments. The principal phenomenology including the container deformation could be modeled well with both methods. The coupled FE/SPH approach was superior in the reproduction of the projectile’s observed residual velocity, it is, however, computationally more expensive.     

Transient Fokker–Planck–Kolmogorov equation solved with smoothed particle hydrodynamics method

Probabilistic theories aim at describing the properties of systems subjected to random excitations by means of statistical characteristics such as the probability density function ψ (pdf). The time evolution of the pdf of the response of a randomly excited deterministic system is commonly described with the transient Fokker–Planck–Kolmogorov (FPK) equation. The FPK equation is a conservation equation of a hypothetical or abstract fluid, which models the transport of probability. This paper presents a generalized formalism for the resolution of the transient FPK equation by using the well‐known mesh‐free Lagrangian method, smoothed particle hydrodynamics). Numerical implementation shows notable advantages of this method in an unbounded state space: (1) the conservation of total probability in the state space is explicitly written; (2) no artifact is required to manage far‐field boundary conditions; (3) the positivity of the pdf is ensured; and (4) the extension to higher dimensions is straightforward. Furthermore, thanks to the moving particles, this method is adapted for a large kind of initial conditions, even slightly dispersed distributions. The FPK equation is solved without any a priori knowledge of the stationary distribution, just a precise representation of the initial distribution is required.Copyright © 2013 John Wiley & Sons, Ltd.     

Topology optimization of plane structures using smoothed particle hydrodynamics method

This paper presents an alternative topology optimization method based on an efficient meshless smoothed particle hydrodynamics (SPH) algorithm. To currently calculate the objective compliance, the deficiencies in standard SPH method are eliminated by introducing corrective smoothed particle method and total Lagrangian formulation. The compliance is established relative to a designed density variable at each SPH particle which is updated by optimality criteria method. Topology optimization is realized by minimizing the compliance using a modified solid isotropic material with penalization approach. Some numerical examples of plane elastic structure are carried out and the results demonstrate the suitability and effectiveness of the proposed SPH method in the topology optimization problem. Copyright © 2016 John Wiley & Sons, Ltd.     

Development of smoothed particle hydrodynamics method for modeling active nematics

This article proposes a novel graphics processing unit-based active nematic flow solver based on the smoothed particle hydrodynamics (SPH) method. Nematohydrodynamics equations are discretized using the SPH algorithm. Flow behavior, nematic ordering, topological defects, and vorticity correlation are calculated and discussed in detail. The spectrum of the kinetic energy with respect to the wavenumber is calculated at high particle resolution, and its slope at the different length scales is discussed. To exploit the SPH capabilities, pathlines of nematic particles are evaluated during the simulation. Finally, the mixing behavior of the active nematics is calculated as well and described qualitatively. The effects of two important parameters, namely, activity and elastic constant are investigated. It is shown that the activity intensifies the chaotic mixing nature of the active nematics, while the elastic constant behaves oppositely.     

Numerical modeling of Kelvin–Helmholtz instability using smoothed particle hydrodynamics

This paper presents a Smoothed Particle Hydrodynamics (SPH) solution for the Kelvin–Helmholtz Instability (KHI) problem of an incompressible two‐phase immiscible fluid in a stratified inviscid shear flow with interfacial tension. The time‐dependent evolution of the two‐fluid interface over a wide range of Richardson number (Ri) and for three different density ratios is numerically investigated. The simulation results are compared with analytical solutions in the linear regime. Having captured the physics behind KHI, the effects of gravity and surface tension on a two‐dimensional shear layer are examined independently and together. It is shown that the growth rate of the KHI is mainly controlled by the value of the Ri number, not by the nature of the stabilizing forces. It was observed that the SPH method requires a Richardson number lower than unity (i.e. Ri?0.8) for the onset of KHI, and that the artificial viscosity plays a significant role in obtaining physically correct simulation results that are in agreement with analytical solutions. The numerical algorithm presented in this work can easily handle two‐phase fluid flow with various density ratios. Copyright © 2011 John Wiley & Sons, Ltd.     

Development of smoothed particle hydrodynamics method and its application in the hydrodynamics of condensed matter

An improved smoothed particle hydrodynamics (SPH) method is described; in this method, the solution to the Riemann problem in strength media is described. Generalization of this approach to solving heat conduction problems is performed. The improved SPH method is used to solve a wide range of problems. Problems of heat conduction and volume energy release accompanied by spallation effects, simulation of high speed perforation, and propagation of failure waves in brittle materials are considered. Shock wave compression of porous materials and diffraction of detonation waves in heterogeneous explosives are simulated on the mesostructure scale.     

Search algorithm,and simulation of elastodynamic crack propagation by modified smoothed particle hydrodynamics (MSPH) method

We first present a nonuniform box search algorithm with length of each side of the square box dependent on the local smoothing length, and show that it can save up to 70% CPU time as compared to the uniform box search algorithm. This is especially relevant for transient problems in which, if we enlarge the sides of boxes, we can apply the search algorithm fewer times during the solution process, and improve the computational efficiency of a numerical scheme. We illustrate the application of the search algorithm and the modified smoothed particle hydrodynamics (MSPH) method by studying the propagation of cracks in elastostatic and elastodynamic problems. The dynamic stress intensity factor computed with the MSPH method either from the stress field near the crack tip or from the J-integral agrees very well with that computed by using the finite element method. Three problems are analyzed. One of these involves a plate with a centrally located crack, and the other with three cracks on plates’s horizontal centroidal axis. In each case the plate edges parallel to the crack are loaded in a direction perpendicular to the crack surface. It is found that, at low strain rates, the presence of other cracks will delay the propagation of the central crack. However, at high strain rates, the speed of propagation of the central crack is unaffected by the presence of the other two cracks. In the third problem dealing with the simulation of crack propagation in a functionally graded plate, the crack speed is found to be close to the experimental one.