X形夹芯激光焊接夹层板碰撞性能分析

基于传统加筋板架设计出一种新的能量吸收单元——X形夹层板,用Dytran分析X形夹层板在低速冲击载荷作用下的碰撞损伤特性;通过分析结构的极限撞深、碰撞力及能量吸收等结果,与传统加筋板进行比较分析,评估夹层板的耐撞性能;同时分析不同结构型式和结构尺寸参数(蒙皮板厚度、夹芯层壁厚、夹芯层高度及夹芯层的夹角等)对夹层板结构耐撞性能的影响.     

多层金字塔夹芯结构在冲击载荷作用下的动态响应

金属材料点阵夹芯结构能量吸收效率较高,为得到多层金字塔点阵夹芯结构在冲击载荷作用下的动态响应,利用Patran建立多层金字塔点阵夹芯结构在冲击载荷作用下的数值模拟模型,通过Dytran计算分析质量为25 kg的钢板以30 m/s, 60 m/s和90 m/s的速度冲击时模型的应力、应变、变形以及变形能,研究随着冲量的增加,模型的应力、应变、变形和变形能的变化规律.     

基于MSC Dytran的潜艇结构撞击强度分析

提出潜艇碰撞问题,对其碰撞特征进行分析,并针对某型潜艇舯部典型结构的撞击极限强度特性进行数值计算,结果表明由于准静压载荷的附连耦合作用,随着静水压力的增加,潜艇舯部耐压壳体结构的防撞能力大幅下降,而耐压壳体内部的平台和舱壁结构能有效提高壳体结构的横向失稳临界应力,改善潜艇结构的径向耐撞能力.     

基于主S-N曲线法的地铁制动箱焊接疲劳分析

为研究地铁车辆制动箱焊接接头的疲劳寿命,根据实际结构建立4节点壳单元有限元模型,给出搭接焊和T型焊的焊缝建模方法.在3种振动工况下,运用主S N曲线法计算焊缝的等效结构应力和对应损伤比.结果表明：该地铁车辆制动箱焊接结构设计合理可靠;通过与实体单元模型计算结果进行对比证明壳单元模拟焊缝的合理性;在不同尺寸单元下对比2种疲劳评估方法,结果表明名义应力法预测疲劳寿命的准确性较低.     

带防撞设施的船桥碰撞数值模拟

采用LS-DYNA对一座带防护设施的斜拉桥进行船桥碰撞模拟. 防护设施为钢套箱. 通过对单元和材料本构关系的合理选取、接触和摩擦的处理,实现采用合理的全桥模型进行船桥碰撞模拟,并研究船撞桥的碰撞细节和桥梁动力反应.     

摄像头也能看星空（中）——DIY天体摄影利器

经过换芯的900NC需要专门针对黑白CCD进行EEPROM刷新。很多人或许分不清EEPROM．EPROM、FLASH这三者到底是什么。其实它们都是基于浮栅管单元（Floating Gate Transister）的结构。EPROM的浮栅处于绝缘的二氧化硅层中．要改写EPROM数据只能采用紫外线的能量，对硬件设施和技术的要求较高。EEPROM的单元采用双管结构．     

基于角点检测的铝蜂窝芯层拉伸力学性能研究

铝蜂窝夹芯结构材料在航空航天和建筑等领域已被大量采用,发挥着重要作用.材料中的蜂窝芯层,是空心区域占绝大部分的六边形结构.针对该特殊结构对传统电测法不易贴片的限制,首次采用CCD拍摄的数字图像测量方法,对铝蜂窝芯层进行了拉伸试验研究.试验得到了铝蜂窝芯层在整个过程中力-位移的拉伸曲线,用角点检测法得到了拉伸线弹性范围的弹性模量和泊松比,和基于Y模型的蜂窝芯层等效模型理论计算值做了比较,为研究蜂窝夹芯结构整体的力学性能和结构设计提供了参考依据.     

阻尼对泡沫夹芯梁非线性振动响应的影响

基于Euler—Bernoulli梁理论、Hamilton原理以及Galerkin方法，建立了大变形悬臂夹芯梁在横向周期载荷作用下的二阶动力学方程；通过考虑外周期激励的不同频率与幅值，详细分析了材料阻尼比对泡沫铝夹芯梁的振动响应的影响．结果表明，泡沫夹芯结构具有较好的阻尼性能，可有效抑制梁的混沌振动．     

机床整机振型与连接模型的影响研究

一、连接件模型采用有限元模型构造分析对象时，对于基于线弹性小变形假设的单个零部件静、动态分析技术已完全解决。但是，对整机的分析处理尚存在以下两方面的问题：①如何采用现有商品化软件（如Ansys、Nastran、Algor、Adina等）进行产品整机性能的分析。这首先需要解决部件与部件之间的连接处理问题。如图1（a）为C616车床床身和主轴箱的主视图，当以板壳单元建模时，若采用图1（b）的分析模型，这时即使A、B两个部件的材料不同，但由于在边界1-1′上是通过逐个节点连接了两个相邻的部件，根据单元节点的位移协调条件，得到的模型事…     

微型客车正面碰撞特性建模及仿真研究

该文利用Pam—Crash对某微型客车及乘员约束系统进行了建模及仿真研究，全面研究了该微型客车的正面碰撞特性，包括结构耐撞性和乘员安全性。整个建模过程分三个阶段：白车身建模；整车建模；整车及乘员约束系统建模，每个阶段都参照相应的试验条件进行了仿真计算，所得计算结果与试验结果基本吻合，表明所建立的微型客车及乘员约束系统模型是可信的、采用的建模和计算方法是正确的。这些仿真方法可为企业改善汽车的碰撞安全性或开发新产品提供参考。     

Evaluation of modeling accuracy of 20-node solid elements by statistical factorial design

Many complex engineering structures consist of plates and shells. When applying finite element methods to a plate or shell, how can a design engineer choose an initial mesh and decide the integration order? The statistical design of experiments is employed to investigate the influence of three relevant modeling factors—aspect ratio, number of elements per edge of model and integration order on the accuracy of applying 20-node solid elements to plates and shells. In addition to the main effects of individual factors, the effects of multiple-factor interactions among factors are addressed. Given a certain aspect ratio and integration order for a structure under a specific load, a minimum number of elements per edge of model can be predicted with a given statistical confidence coefficient in modeling.     

An open platform of shape design optimization for shell structure

A general platform built on a computer-aided design (CAD) system is developed for parameterized shape design optimization of shell structure. Within the platform, parameterized surface modeling and computer-aided engineering (CAE) applications are embedded and seamlessly integrated with the CAD system through its application programming interface (API). Firstly, instead of the CAD system inherent surface modeling, a parameterized surface modeling for shell structure is fulfilled through integrating with parametric solid modeling of the CAD system. Thus, any dimensions for parametric solid modeling can be used to control shape modification of shell structure and serve as design variables for shape design optimization. Secondly, seamless integration of geometry modeling and finite-element modeling for shell structure is implemented. Finally, with integrated procedures of finite-element analysis and optimization algorithms, a general platform for parameterized shape optimization of shell structure is realized. Numerical examples are presented, and the results validate the effectiveness and efficiency of the platform. A shorten version of this paper was presented to the 7th World Congress of Computation Mechanics (WCCM 2006), July 16–22, 2006, Los Angeles, CA, USA.     

On design optimization for structural crashworthiness and its state of the art

Optimization for structural crashworthiness and energy absorption has become an important topic of research attributable to its proven benefits to public safety and social economy. This paper provides a comprehensive review of the important studies on design optimization for structural crashworthiness and energy absorption. First, the design criteria used in crashworthiness and energy absorption are reviewed and the surrogate modeling to evaluate these criteria is discussed. Second, multiobjective optimization, optimization under uncertainties and topology optimization are reviewed from concepts, algorithms to applications in relation to crashworthiness. Third, the crashworthy structures are summarized, from generically novel structural configurations to industrial applications. Finally, some conclusions and recommendations are provided to enable academia and industry to become more aware of the available capabilities and recent developments in design optimization for structural crashworthiness and energy absorption.

     

Computer modeling for the coupled stress-wave and structural response

The mesh density and the time-step size requirements of a Finite Element Model used to predict the coupled stress-wave and the structural response to dynamic loading are discussed. The problem chosen for this study is a long cylindrical shell containing a bonded annular solid core subjected to external uniform radial impulse. This shell-core system represents the case and solid propellant of a solid rocket motor. Depending on the geometry and the mechanical properties of the shell-core system, the coupling between the radial stress-waves in the core and the gross structural breathing mode of the shell-core system could be either strong or weak.

When the time required for a through the thickness round trip of radial stress waves in the core is of the same order of magnitude as the gross structural breathing mode period of the whole system, the coupling between the stress-wave propagation and the structural response is strong. A finer mesh of solid elements (NASTRAN HEXA elements) for modeling the solid core is required to predict correctly the peak hoop strains and stresses in the shell. A coarser mesh gives erroneous results.

On the other hand, when the time required for a through the thickness round trip of radial waves is small compared to the structural breathing mode period of the system, the coupling between the wave propagation and the structural response is weak and the two are decoupled. In this case, a coarser mesh of solid elements gives a good estimate of the peak hoop stresses in the shell. These values are not significantly changed if the mesh is made finer.     

Wave propagation simulation in an electrically open shell reinforced with multi-phase nanocomposites

Wave propagation simulation in a multi-hybrid nanocomposite (MHC)-reinforced doubly curved open shell covered with piezoelectric actuator is examined for the first time. The third-order shear deformation theory (third-order SDT) is applied to formulate the stress–strain relations. Rule of the mixture and modified Halpin–Tsai model are engaged to provide the effective material constants of the MHC-reinforced open shell. By employing Hamilton’s principle, the governing equations of the structure are derived. Via the compatibility rule, the bonding between the smart layer and sandwich open shell is modeled. Also, with the aid of Maxwell's equation, the mechanics of the piezoelectric layer are formulated. Afterward, a parametric study is carried out to investigate the effects of the CNTs’ weight fraction, various FG face sheet patterns, small radius to total thickness ratio, the thickness of the smart layer, externally applied voltage, and carbon fiber angle on the phase velocity of the MHC-reinforced open shell. Another necessary consequence is that as the externally applied voltage to the piezoelectric layer of the smart open shell increases, there will be seen an enhancement on the phase velocity or wave response of the system and without a doubt this issue is much more substantial at the lower wave number. It is also observed that when the applied voltage is more than zero, we can find a range for the fiber angle that these values are the critical fiber angle and this critical range will expand by increasing the external electrical load. The useful suggestion of this study is that for designing the structure, we should attention to the FG pattern and higher value of the wavenumber, simultaneously. The presented study outputs can be used in ultrasonic inspection techniques and structural health monitoring.

     

Analysis and optimal design of plates and shells under dynamic loads – I: finite element and sensitivity analysis

In this paper we consider the development, integration, and application of reliable and efficient computational tools for the geometry modeling, mesh generation, structural analysis, and sensitivity analysis of variable-thickness plates and free-form shells under dynamic loads. A flexible shape-definition tool for surface modeling using Coons patches is considered to represent the shape and the thickness distribution of the structure, followed by an automatic mesh generator for structured meshes on the shell surface. Nine-node quadrilateral Mindlin–Reissner shell elements degenerated from 3D elements and with an assumed strain field, the so-called Huang–Hinton elements, are used for the FE discretization of the structure. The Newmark direct integration algorithm is used for the time discretization of the dynamic equilibrium equations for both the structural analysis and the semi-analytical (SA) sensitivity analysis. Alternatively, the sensitivities are computed by using the global finite difference (FD) method. Several examples are considered. In a companion paper, the tools presented here are combined with mathematical programming algorithms to form a robust and reliable structural optimization process to achieve better dynamic performance on the shell designs.     

Revit API在空间网格结构参数化建模中的应用

为将参数化建模技术应用于Revit Structure平台,充分发挥Revit三维建模平台的强大功能,采用Revit API类库在Revit平台上进行二次开发.通过参数化生成空间网格结构模型,实现在Revit平台下空间结构模型的参数化生成程序的开发,完成典型空间网格结构和载荷、支座等结构分析模型要素在Revit平台下的创建.该方法结合API的灵活性和Revit参数化建模的强大功能,比界面交互建模方式效率更高、实用性更强.     

Efficient modeling of panel-like structures in perforation simulations

This paper presents results of numerical simulations for impact effects in panel-like structures using solid and shell element modeling techniques. Three examples from experiments in literature have been numerically analyzed. The nonlinear transient dynamic analysis code, LS-DYNA is used in the simulations to model projectiles and panel-like targets. It is found that models established for panel-like targets using solid shell elements cannot only save significant computational effort, but also produce good results as long as the panel-like targets satisfy certain conditions. A criterion that governs the validity of modeling panel-like targets with shell elements is proposed in the paper.     

Optimization of inelastic conical shells with cracks

Inelastic conical shells loaded by the central rigid boss with vertical load are studied. The thickness of the conical part of the structure is piecewise constant. The connection between the shell and the boss is weakened with a stable crack. The designs with the maximal load-carrying capacity are established under a given material consumption of the shell. Material of the shell wall obeys the von Mises yield condition.