高压泄爆导致的二次爆炸

基于计算结果和相关实验结果，通过理论分析，对高压泄爆导致的二次爆炸机理进行了系统的阐述。泄爆后，泄出的高压可燃气体在泄爆口附近形成可燃云团，由于欠膨胀，云团内存在稀疏波低压区和Mach干高压区。火焰射流泄出后，在一定条件下，可使Mach干高压区内的可燃云团爆炸式燃烧，压力迅速上升，以致产生二次爆炸。     

水介质初始参数设置对水下爆炸载荷的影响

针对数值计算中水介质初始参数设置对水下爆炸载荷特性的影响开展了深入分析。基于参考状态参数确定了水介质状态方程形式;从热力学角度分析了常用的两种初始参数设置方式,提出了一种按等温假设设置初始参数的方式,并对LS-DYNA中INITIAL_EOS_ALE关键字给出的参数设置结果进行了分析;采用LS-DYNA程序进行一维球形装药水下爆炸数值计算,分析了3种设置方式下爆炸载荷特性的差异,并与已有研究成果进行了对比。结果表明:当仅改变水介质内能项时,参数按等容过程变化,流场压力源于外界传热,与实际深水环境严重不符;INITIAL_EOS_ALE关键字给出的参数设置结果与仅改变水介质密度（等内能过程）接近,水温变化规律与真实环境不符;按等内能过程和等温过程设置初始参数时,水下爆炸载荷特性计算结果基本相同,与已有成果吻合;综合分析认为,按等温形式进行初始参数设置方式较优。研究成果可为水下爆炸尤其是深水爆炸数值仿真提供参考。     

PBX-01炸药水中爆轰产物状态方程研究

提出通过水中实验确定炸药的水中爆轰产物JWL状态方程参数的方法;选择PBX-01高能炸药进行水中实验,利用ANSYS/LS-DYNA程序建立炸药的水中实验模型,将实验结果与数值计算结果进行对比,确定PBX-01炸药水中爆轰产物的JWL状态方程参数。研究结果显示,圆筒实验确定的JWL参数在反映炸药水中爆轰产物的膨胀状态时有所不足,水中实验确定的JWL状态方程参数能够更准确地描述PBX-01炸药水中爆轰产物的膨胀过程,因此对水中爆炸的研究需要通过水中爆炸实验建一套状态方程参数。     

开放空间H2/CH4/空气爆炸实验与数值模拟研究

近年来氢的使用范围逐渐发展到各个领域, 含氢多元混合物气体在工业生产及生活燃料中被普遍使用. 为了保障含氢气体在生产、运输、使用等各个环节的安全性, 构建了开放空间混合气体爆炸测试实验系统, 研究了H₂/CH₄/空气混合气体爆炸压力及火焰传播特性, 给出了不同氢摩尔分数(100%, 75%, 66.67%, 50%, 33.33%)、混合气体当量比(0.8, 1.0, 1.1, 1.2, 1.4)、可燃云团尺寸(1 m3, 4 m3, 8 m3)及障碍物约束等因素对混合气体爆炸压力及火焰的影响规律. 基于经典TNT当量法, 建立了考虑混合气体组分比及可燃云团尺寸的最大爆炸超压预测模型, 修正了爆炸火焰传播半径理论模型. 结合高精度数值模拟技术揭示了加气站内建筑结构对混合气体爆炸的影响. 研究表明, 氢气的加入能够明显增强气体爆炸强度, 最大爆炸超压、火焰传播速度均随氢摩尔分数的增加而增大, 随当量比的增大先增大后减小, 当量比为1.1~1.2时最大; 通过对大尺度混合气体爆炸数值仿真与分析发现, 加气站内不同建构筑物条件下爆炸火焰传播距离、传播速度、最大爆炸超压等关键参数明显不同, 顶部和背部同时约束时, 爆炸伤害范围及事故后果最严重, 因此在划定加气站安全距离时, 应充分考虑不同建筑结构的影响.      

水下接触爆炸下沉箱码头毁伤效应

为研究水下接触爆炸下沉箱码头毁伤效应和毁伤机理,通过LS-DYNA有限元软件建立沉箱码头水下接触爆炸模型,进行数值模拟研究,并通过试验验证模型准确性。结果表明:运用有限元方法能够较好地模拟水下接触爆炸作用下沉箱码头的毁伤效应,沉箱码头的破坏过程可分为两个阶段:冲击波阶段,沉箱外墙产生初始破口和环状裂缝;气泡膨胀阶段,爆轰产物从破口涌入仓格加速了仓格的变形和毁伤,仓格顶部变形严重导致码头面板破坏,气泡由于冲出水面提前溃灭,码头毁伤在0.14倍的气泡第一次脉动周期基本停止。对比不同爆炸深度,水域中部接触爆炸下沉箱毁伤最为严重,近水面接触爆炸对码头面板的毁伤作用更强。     

含铝炸药水下滑移爆轰实验研究

为了研究含铝炸药水中爆炸近场范围内沿装药径向的冲击波特性及爆轰产物的膨胀规律,设计了水下滑移爆轰实验装置。采用高速扫描相机和阴影照相技术记录了一种RDX基含铝炸药的水下滑移爆轰过程,获得了清晰的水下滑移爆轰过程的扫描图像。通过对图像进行分析,得到了水中爆炸近场范围内沿装药径向冲击波的传播迹线及爆轰产物气泡的膨胀迹线,进而分析出冲击波传播速度、阵面压力及爆轰产物气泡的膨胀位移等参数的变化规律。此外,根据气泡的膨胀迹线,标定了该含铝炸药爆轰产物的JWL状态方程参数,并将其与Φ50mm圆筒实验确定的参数值在p-V图上进行了对比。结果显示,两者偏差较小,证实了该方法的可行性。     

燃料爆炸抛撒成雾的实验与数值研究

为了合理设计云雾爆轰装置 ,对液体燃料爆炸抛撒规律作了实验与数值模拟研究。获得 6～ 2 5 0kgFAE装置云雾形成的若干重要实验数据。通过实验数据分析给出了云雾膨胀的相似律 ,并研究了爆炸抛撒过程中近场与远场阶段特性 :用一个简化的解析模型描述了液体燃料的近场膨胀 ,给出了液体燃料在加速阶段的极限速度 ;用数值方法研究了远场云雾的物理特性 ,给出了云雾速度场及云雾内部燃料浓度与燃料蒸汽浓度的分布。     

壳体对燃料近区抛散速度的影响

通过建立力学模型 ,分析了燃料空气炸药 ( FAE)装置壳体对燃料近区抛散过程的影响规律 ,给出了考虑壳体时燃料近区 (加速阶段 )抛散速度的计算方法。为 FAE爆炸云雾及战斗部弹壳碎片的杀伤作用分析奠定了力学基础。     

水中爆炸气泡脉动流场的数值计算

由一维不可压流体力学理论，考虑到爆轰产物的等熵膨胀，建立了水中爆炸气泡脉动流场的基本方程。采用龙格－库塔数值方法计算了气泡脉动半径、周期及水中压力，计算结果与实测数据吻合较好。     

柱形装药条件下锥形水中爆炸激波管内的冲击波特性

锥形水中爆炸激波管是进行水中爆炸实验的一种装置,该装置能够通过较小装药量在相同距离处实现自由场水中较大装药量爆炸的冲击波峰值。为了获得柱形装药条件下锥形水中爆炸激波管内的冲击波特性,本文通过数值计算的方式,对不同圆锥角和不同柱形装药质量下锥形激波管内的冲击波传播过程进行了模拟,通过对不同工况下激波管内冲击波特性进行分析,发现其初始冲击波的衰减规律符合自由场水中的指数衰减形式,并拟合得到了与自由场水中爆炸相容的冲击波峰值、比冲量和能流密度经验公式;发现其二次脉动压力周期与炸药质量呈反常规的变化规律,并引入等效静水压深度解释了这一现象;发现其二次脉动压力幅值与初始冲击波幅值之比比自由场水中更大,而二次脉动压力的比冲量与初始冲击波冲量之比与自由场水中相当。     

Stabilized finite element method for simulation of freeway traffic

The modeling of traffic flow is a key tool to simulate and predict the behavior of traffic systems. Macroscopic traffic simulation models are based on advection dominated coupled non-linear partial differential equations. The solution of such advection dominated equations with the method of finite elements is leading to the development of stabilization techniques. The choice of suitable stabilization parameters is often application-dependent. A stabilized finite element procedure on the basis of a Galerkin/least-square approximation is presented for systems of transient advection-dominated equations. A general rule for computing suitable element stabilization parameters is outlined which uses the spectral radius of the differential operators and the specific element expansion. The application of this approximation to a macroscopic traffic model shows the applicability of this approach. Simulation results of typical phenomena of jam formation in freeway traffic are presented.     

周边嵌入弹性圆薄板非线性自由振动直接摄动解法

采用弹性圆薄板中心无量纲振幅和板厚与半径的比值为参数。将挠度、应力函数对半径的导数以及自由振动频率展开为双参数的幂级数。用直接摄动法获得各级递推线性偏微分方程。应用变分法求得各级递推方程的近似解，从而给出弹性圆薄板非线性自由振动频率的基本公式。     

Singular perturbation of initial value problem for a nonlinear second order systems

In this paper,the singular perturbation of initial value problem for nonlinearsecond order vector differential equationsε~rx″=f(t,x,x′,ε)x(0,ε)=a,x′(0,ε)=βis discussed,where r>0 is an arbitrary constant,ε>0 is a small parameter,x,f,aandβ∈R~n.Under suitable assumptions,by using the method of many-parameterexpansion and the technique of diagonalization,the existence of the solution of pertur-bation problem is proved and its uniformly valid asymptotic expansion of higher order isderived.     

含初缺陷复合材料圆柱曲板的动力屈曲分析

基于修正的一阶剪切变形理论，利用Ｈａｍｉｌｔｏｎ原理导出包含横向剪切变形和转动惯量的复合材料长圆柱曲板的非线性动力方程，通过将位移和载荷展开为Ｆｏｕｒｉｅｒ级数，把非线性偏微分方程组转化为二阶常微分方程组，并可由四阶Ｒｕｎｇｅ－Ｋｕｔｔａ方法数值求解，通过算例，讨论了有关因素对迭层复合材料圆柱曲板动力屈曲的影响。     

Analytical solutions for finite cylindrical dynamic cavity expansion in compressible elastic-plastic materials

Analytical solutions for the dynamic cylindrical cavity expansion in a com-pressible elastic-plastic cylinder with a finite radius are developed by taking into account of the effect of lateral free boundary, which are different from the traditional cavity expan-sion models for targets with infinite dimensions. The finite cylindrical cavity expansion process begins with an elastic-plastic stage followed by a plastic stage. The elastic-plastic stage ends and the plastic stage starts when the plastic wave front reaches the lateral free boundary. Approximate solutions of radial stress on cavity wall are derived by using the Von-Mise yield criterion and Forrestal’s similarity transformation method. The effects of the lateral free boundary and finite radius on the radial stress on the cavity wall are discussed, and comparisons are also conducted with the finite cylindrical cavity expansion in incompressible elastic-plastic materials. Numerical results show that the lateral free boundary has significant influence on the cavity expansion process and the radial stress on the cavity wall of metal cylinder with a finite radius.     

Flapwise bending vibration analysis of a rotating double-tapered Timoshenko beam

In this study, free vibration analysis of a rotating, double-tapered Timoshenko beam that undergoes flapwise bending vibration is performed. At the beginning of the study, the kinetic- and potential energy expressions of this beam model are derived using several explanatory tables and figures. In the following section, Hamilton’s principle is applied to the derived energy expressions to obtain the governing differential equations of motion and the boundary conditions. The parameters for the hub radius, rotational speed, shear deformation, slenderness ratio, and taper ratios are incorporated into the equations of motion. In the solution, an efficient mathematical technique, called the differential transform method (DTM), is used to solve the governing differential equations of motion. Using the computer package Mathematica the effects of the incorporated parameters on the natural frequencies are investigated and the results are tabulated in several tables and graphics.     

A boundary value method for the singular behavior of bimaterial systems under inplane loading

Based on the governing equations of linear elasticity, this paper develops a novel boundary value method to study the singular behavior of elastic stress fields at the corners of bimaterial wedges and junctions by using the eigenfunction expansion technique. The resulted one-dimensional differential system, which consists of the reduced equilibrium equations and boundary conditions, just relates to an angular coordinate in the polar coordinate system. Implementing discretization of this differential system by the finite cloud method, we readily derive the so-called generalized eigenproblem in the singular eigenvalue. The performance of the methodology is subsequently verified through the well-known crack and interface crack problems, demonstrating high accuracy and quick convergence characteristics. In addition, a selected set of practically useful models is numerically analyzed to examine the angular variations of the displacement and stress fields, and the influences of wedge-side boundary conditions to singular behavior are also studied.     

Homotopy analysis solution for micropolar fluid flow through porous channel with expanding or contracting walls of different permeabilities

The flow of a micropolar fluid through a porous channel with expanding or contracting walls of different permeabilities is investigated. Two cases are considered, in which opposing walls undergo either uniform or non-uniform motion. In the first case,the homotopy analysis method (HAM) is used. to obtain the expressions for the velocity and micro-rotation fields. Graphs are sketched for some parameters. The results show that the expansion ratio and the different permeabilities have important effects on the dynamic characteristics of the fluid. Following Xu's model, in the second case which is more general, the wall expansion ratio varies with time. Under this assumption, the governing equations are transformed into nonlinear partial differential equations that can also be solved analytically by the HAM. In the process, both algebraic and exponential models are considered to describe the evolution of α(t) from the initial state α0 to the final state α1. As a result, the time-dependent solutions are found to approach the steady state very rapidly. The results show that the time-dependent variation of the wall expansion ratio can be ignored because of its limited effects.     

相同子结构串的本征对问题及展开解法

本文讲述了串连式子结构的分析计算方法,它相当于结构分析中按横截面展开的方法。文中讲述了移位不变法以及初参数与传递矩阵法两个方面,并指明了两种方法的联合运用及相互关系,截面上本征值问题的计算以及按本征向量展开等问题。     

圆柱壳的塑性膨胀和变形

根据材料不可压缩假设,适当选取材料塑性本构关系,将圆柱壳塑性膨胀运动简化为以圆柱壳内 半径为因变量的常微分方程初值问题。对3种初始内外半径比纯铜厚壁圆柱壳膨胀过程的计算表明,应变率 硬化阻碍圆柱壳的塑性膨胀运动,应变硬化和温度效应的影响可以忽略,而与圆柱壳的厚度无关。