A new formulated method of a quasi-compatible finite-element and its application in fracture-mechanics

Based on the local properties of a singular field, the displacement pattern of an isoparametric element is improved and a new formulated method of a quasi-compatible finite element is proposed in this paper. This method can be used to solve various engineering problems containing singular distribution, especially, the singular field existing at the tip of cracks. The singular quasi-compatible element (SQCE) is constructed. The characteristics of the elements are analysed from various angles and many examples of calculations are performed. The results show that this method has many significant advantages, by which, the numerical analysis of brittle fracture problems can be solved.

Non-linear theory of a positive-column in a magnetic-field

A nonlinear theory of an intermediate pressure discharge column in a magnetic field is presented. Motion of the neutral gas is considered. The continuity and momentum transfer equations for charged particles and neutral particles are solved by numerical methods. The main result obtained is that the rotating velocities of ionic gas and neutral gas are approximately equal. Bohm's criterion and potential inversion in the presence of neutral gas motion are also discussed.

采用分布式压电驱动器升力面的颤振主动抑制

对采用分布式压电驱动器升力面的颤振主动抑制进行了理论与试验研究。应用LQG最优控制法设计了主动控制律，在控制律降阶时提出了平衡实现与LK法结合使用的新途径，在对不定常气动力进行有理函数拟合时对LS法进行了改进。试验中利用激光测速仪非接触测量模型的速度响应并在地面共振试验中用压电驱动器激振模型。颤振风洞试验结果表明，理论计算合理并与试验结果吻合良好。

导弹水下潜射过程的流体—固体耦合仿真

导弹潜射是集高速流动、冲击、结构响应于一体的流体—固体—气体三态非线性耦合复杂过程,是决定潜射导弹发射成败的关键环节。本文应用LS-DYNA显式程序建立了三种包含水体、空气、导弹、发射井和筒盖的多物质耦合ALE网格模型,使用罚函数流体—固体耦合方法对导弹水下无攻角潜射过程进行了数值模拟,给出了弹体质心的轴向加速度、轴向流体阻力及阻力系数、空泡区压力分布。仿真结果表明,模型2的仿真过程与实际导弹潜射过程最为相符。同时总结介绍了LS-DYNA程序中流体—固体耦合计算的相关设定原则和方法。本文可为潜射导弹的水动力载荷设计和数值仿真提供有益的参考。

高能气动喷丸致纯铜细晶化的实验与模拟

高能气动喷丸是通过剧烈塑性变形产生细晶材料的方法之一.用纯铜作为实验材料在高能气动喷丸实验机上作喷丸实验,利用表面形貌仪、显微硬度仪以及电子背散射衍射方法对经喷丸处理的试样进行表面粗糙度、硬度及晶粒尺度的测量.结果表明,表面粗糙度随处理时间的增长呈指数衰减趋势;晶粒尺度细化了一个量级,由初始的25.48μm细化至2.52μm;且显微硬度由原来的0.58GPa增加到1.25GPa.量纲分析得到喷丸过程的5个无量纲参数,利用有限元模拟研究了无量纲参数的影响.自编制程序产生丸粒的随机碰撞并调用Ansys/ls-dyna模拟碰撞过程,并将模拟1000次碰撞的结果与相应的实验值进行了比较.

冷弯成型过程的有限元模拟

概述了冷弯成型过程有限元数值模拟的基本原理和基本算法,利用ANSYS/LS-DYNA分析软件对冷弯过程进行有限元数值模拟,并对模拟结果进行受力和应变分析以验证其可行性和正确性,为冷弯成型的工程设计提供了科学依据,从而降低设计风险。

钠离子与电子复合电离动力学的激波管研究

利用反射激波加热使试验气体电离,继之以强稀波快速冷却,构成一种新的激波管方法,并测定了在氩气氛中钠离子与电子三体复合速率系数。由于稀疏波冷却速度达10~6K/s,电离过程处于非平衡状态。选用氨基钠作为向实验体系中引入钠离子的源物质。用压电传感器和Langmuir静电探针分别监测反射激波后5区压力和离子浓度变化。稀疏波的冷却过程被视为绝热的。分析了探针工作状态,引入了探针鞘层内的弹性散射修正。测定了在800~2 600K温度范围内以惰性气体氩为碰撞第三体的钠离子与电子离复合速率系数k_r=3.43×10~(-14)T~(-3.77)cm~6s~(-1)。

水中悬浮隧道在冲击载荷作用下的计算模型与数值模拟

建立了水中悬浮隧道在冲击载荷作用下的简化计算模型。用等效质量法将圆柱壳分布质量折算成冲击点处的集中质量,模型中考虑流体附加质量和系统阻尼的影响。根据碰撞过程中的动量守恒、变形过程中的能量守恒以及结构的位移与内力关系,得到问题的解析解。为验证解析解,在ANSYS/LS-DYNA中建立了动态冲击有限元分析模型。通过算例分别考察了在忽略和考虑流体附加质量两种情况下,冲击点位置和冲击速度对冲击点处最大径向位移的影响,将解析解与数值解进行对比,结果吻合较好。然后采用数值模拟方法得到了系统阻尼对计算结果的影响规律。数值模拟过程中还可以得到冲击点处的最大Mises应力。

一种岩石概率型本构及其应用

在岩石材料非均匀特性的基础上,建立了弹塑性概率材料本构.认为材料单元的切线模量与破坏强度都是服从二参数Weibull分布的随机量,通过用户材料子程序将该本构导入到LS-DYNA3D中,推导了程序流程,分析了导入过程中的关键技术.算例验证表明,应用该本构模拟得出的现象与实验观测完全一致,这是确定性本构无法实现的.

爆破近区地质结构特性对震动信号传播的影响研究

基于文献〔1〕提出的“爆破震动弹性区的信号是经过震源邻近区域等效地质结构滤波后传出的”观点,利用LS-DYNA程序对岩土介质中存在软弱夹层时的爆破震动过程进行了一系列数值计算,讨论了存在软弱地质结构面时自由表面震动信号频率特征的变化规律。比如:爆破点和软弱结构面的相对位置以及软弱结构面分布范围和刚度改变时,爆破地震信号频率特征的演化规律。这些规律说明了爆破邻近区域的结构特征对震动信号频率特征有着显著的影响,同时为各种工程地质结构(如地下裂隙、软弱夹层等)的识别提供了一种新的思路。现场爆破实验的结果也定性地验证了这些规律。

高温非平衡条件下氟原子亲电动力学的激波管研究(英文)

用激波管方法研究了氟原子亲电动力学.利用反射激波加热获得离子化气体,随后经冷却速度达106K/s的强稀疏波冷却,离化气体将经历以电子复合为主的非平衡过程.用Langmuir静电探针监测反射激波后离子浓度随时间的演变,分析了探针工作状态,引入了探针鞘层内的弹性散射修正.测定了温度在1200～2200K以氩气为碰撞第三体的F原子与电子复合速率系数,讨论了温度依赖关系.

Propagation of Explosion Wave in Hard-Soft-Hard Layered Media

The paper presents a reasonable analysis for dynamic response and failure process of a plane multi-layered media, which are subjected to a blast loading. This blast loading is induced by a cylindric explosive put on the center of top surface of the layered media. With the help of numerical simulation technique provided by LS-DYNA software, the whole process of explosion wave propagation and attenuation can be revealed. The feature of local failure around the blasting site is also discussed in some detail. Our focus will be on the explosion wave attenuation for the hard-soft-hard sandwich layers. As seen in the paper, the computational results are delivered in a feasible way by comparing with experimental data.

A Semi-Empirical Equation of Penetration Depth on Concrete Target Impacted by Ogive-Nose Projectiles

In this paper, the penetration process of ogive-nose projectiles into the semi-infinite concrete target is investigated by the dimensional analysis method and FEM simulation. With the dimensional analysis, main non-dimensional parameters which control the penetration depth are obtained with some reasonable hypothesis. Then, a new semi-empirical equation is present based on the original work of Forrestal et al., has only two non-dimensional combined variables with definite physical meanings. To verify this equation, prediction results are compared with experiments in a wide variation region of velocity. Then, a commercial FEM code, LS-DYNA, is used to simulate the complex penetration process, that also show the novel semi-empirical equation is reasonable for determining the penetration depth in a concrete target.

Measurement and Calculation of Vibrational Temperature behind Strong Shock Waves

In the present paper the measured values of vibrational temperature behind strong shock waves are compared with theoretical ones. The histories of vibrational temperature behind strong shock waves in a shock tube were measured using two monochromators. The test gas was pure nitrogen at 100-300Pa, and the speeds of shock waves were 5.0-6.0km/s. The electronic temperature of N-2(+) was also approximately determined from experiment and compared with the experimental vibrational temperature. The results show that the presented calculational method is effective, and the electronic energy of N2+ is excited much faster than its vibrational energy. One Langmuir probe was used to determine the effective time of region 2. The influence of viscosity in the shock tube is also analyzed.

桩靴贯入对固定平台基础扰动的数值模拟

利用有限元软件LS-DYNA对桩靴贯入产生临近主平台基础的扰动问题进行了数值模拟。研究了桩靴贯入过程中土体和临近主平台桩基础的变形和应力变化,从而分析主平台基础承载力的变化。结果表明,土体表面沉陷区为失效区周围两倍半径区域;桩靴压入到一定深度后,上部土体发生回弹,且由于桩基的影响,桩靴左右两侧土体竖向和横向位移不对称,埋有桩基侧的土体竖向位移略小。