基于快速建立四面体网格的有限元心脏建模

针对目前通过医学成像技术获得心脏序列图像来提取相关心脏结构参数,判断心脏的功能的三维心脏建模技术的热点问题.提出了一种基于快速建立四面体网格的有限元心脏建模的方法,结合心脏这种形变模型的各种约束条件,模拟心脏的动态形变,利用有限元与生物力学原理构建心脏表面重建的有限元方程,由心脏表面三角网格数据点快速构建一系列不相重叠的四面体网格单元,以满足单元的应力矢量及单元节点位移矢量计算的需要,为模拟重建心脏运动奠定基础.实验结果表明了有效性和可行性.     

利用带标记线核磁共振图像的左心室力学形态分析

为直观地分析左心室在心脏收缩期的形变情况，提出一种左心事力学形态分析方法．首先利用带标记线的心脏核磁共振图像数据针对左心室建立系数可变的物理可形变模型，并在所建模型的基础上，利用心脏收缩期各个时刻的左心室轮廓点数据恢复三维外形；然后利用心脏收缩期各相邻时刻的标记点数据计算左心室模型外力；最后将模型外力转换为收缩应力分量、切向应力分量和拉伸应力分量，并将各个应力分量用彩色云图显示．实验结果表明，文中方法能直观、有效地反映左心室内外表面在整个心脏收缩期的应力分布及形变趋势，获取的力学形态变化云图将成为重要的医学诊断依据．     

结合有限元和非刚体运动估计的左心室应变分析

提出一种直观地分析左心室在心脏收缩期的应变情况的方法.首先利用心脏核磁共振图像数据对左心室进行三维实体建模,再进行有限元单元划分;然后,使用非刚体运动估计算法--单位法线及高斯曲率混合算法,在左心室收缩期相邻时刻的有限元模型表面上寻找最相似单元结点作为对应单元结点,计算各对应结点间的位移,并用α剪枝平均对位移过大的可疑结点进行处理;最后,利用弹塑性力学中应变与位移间的几何关系求解左心室表面各单元结点的应变,获得位移和应变的彩色云图.实验结果表明,该方法能直观、有效地反映左心室表面在整个心脏收缩期的形变情况和应变分布.     

高铬铸铁件成型过程三维热应力数值模拟

应用大型通用有限元分析软件ANSYS,在高铬铸铁应力框温度场模拟的基础上进行了三维热应力场数值模拟,得到应力框的定量的、动态的变形及应力变化,其模拟计算结果与实测结果基本吻合,本文工作为今后高铬铸铁件残余应力的研究提供了重要的参考价值.     

基于CATIA的机械手装置的运动仿真及有限元分析

对一种机械手装置利用CATIA进行三维建模、动态模拟仿真、分析计算.通过动态虚拟仿真、观察、改进机械手运动规则.对其进行空间分析、应力分析,为其优化设计奠定了理论基础.     

基于LS-DYNA刨刀刨削煤岩的模拟研究

利用有限元分析软件LS-DYNA,建立刨煤机刨刀刨削煤层的三维模型,模拟刨刀刨削煤层的动态过程。研究中,获取了刨刀刨削阻力、应力分布等时间历程曲线,分析了刨刀不同刨削深度、刨刀间距和刨刀宽度对刨削能耗的影响。     

基于三角网格模型的心脏超声图像三维表面重建

心脏超声图像三维表面重建方法的研究对心血管疾病诊断有重要意义,传统方法受医学超声图像噪声影响较难获得准确的表面重建结果。本文研究提出三角网格模型,通过对初始三角网格进行形变,逐渐逼近目标腔体边缘,实现三维表面重建。本文方法重建后的三维表面整体形态上较接近真实心脏腔体,本文方法为心脏超声图像三维表面重建开辟了一条新的途径。     

基于视频的树木运动信息提取和动画生成技术研究

为了快速模拟树木在风中的运动和形变,提出了一种基于视频的树木运动信息提取和动画生成方法,可以在虚拟场景中快速绘制具有动态效果的三维树木模型.该方法首先将含有树木运动的视频转化为多个关键帧,以提取树木的形态和运动信息,并通过数据最小二乘拟合方法计算出其运动轨迹,然后对其进行三维模型重建和运动模拟.实验表明,该方法可以快速地建立树木的三维模型,并能较好地模拟树木的运动和形变.     

一种三维有限元应力分析的可视化方法

提出了一种三维有限元分析结果可视化方法,采用透明效果,将高应力区表示为不透明实体,低应力区表示为透明实体。这样我们能够直接观察高应力区的三维图象,即高应力区的表面形状及其深度。     

基于刚柔耦合模型的仿生鸭机器人运动分析

通过Hypermesh有限元软件及Adams动力学软件建立了所设计的一种仿生鸭机器人的刚柔耦合模型以更好地模拟真实的运行工况.计算了小腿的动态受力及形变情况,并分析了影响蹼足运动参数的两种因素,即小腿结构是否形变及腿部关节摩擦系数.结果表明：在机器人运行过程中,小腿满足强度和刚度要求；小腿形变导致的蹼足运动学参数误差会使机器人运行时的精确性变差；对关节进行润滑可以减小机器人移动时受到的冲击.仿真计算结果可为后续机器人结构优化提供数据参考.     

反应堆堆芯围筒结构热流固耦合热变形分析

针对反应堆堆芯围筒热流固耦合问题,采用三维有限元法研究堆芯围筒的热变形.考察ANSYS的三维实体热单元SOLID 70,三维实体单元SOLID 45,三维表面热效应单元SURF 152和三维热-流耦合管单元FLUID 116等单元类型的特点和实用性.建立堆芯围筒、吊篮和冷却剂的温度分析有限元模型：堆芯围筒和吊篮采用SOLID 70,结构表面与冷却剂的对流传热表面采用SURF152,堆芯围筒与吊篮之间冷却剂采用FLUID 116.采用SOLID 45建立堆芯围筒有限元模型,根据得到的堆芯围筒、吊篮和冷却剂的温度场结果分析堆芯围筒热变形.结果表明,在考虑堆芯围筒及吊篮固体和流体的交叉耦合的基础上,采用三维有限元法能比较客观地模拟反应堆堆芯处的复杂运行环境.     

Fast generation of 3-D deformable moving surfaces

Dynamic surface modeling is an important subject of geometric modeling due to their extensive applications in engineering design, entertainment and medical visualization. Many deformable objects in the real world are dynamic objects as their shapes change over time. Traditional geometric modeling methods are mainly concerned with static problems, therefore unsuitable for the representation of dynamic objects. Apart from the definition of a dynamic modeling problem, another key issue is how to solve the problem. Because of the complexity of the representations, currently the finite element method or finite difference method is usually used. Their major shortcoming is the excessive computational cost, hence not ideal for applications requiring real-time performance. We propose a representation of dynamic surface modeling with a set of fourth order dynamic partial differential equations (PDEs). To solve these dynamic PDEs accurately and efficiently, we also develop an effective resolution method. This method is further extended to achieve local deformation and produce n-sided patches. It is demonstrated that this new method is almost as fast and accurate as the analytical closed form resolution method and much more efficient and accurate than the numerical methods.     

基于刚体运动与弹性运动的机械系统动力学建模研究

讨论了具有刚体运动与柔性变形的机械系统的动力学建模,将刚体自由度与弹性变形自由度看作广义坐标,利用有限元法对具有刚性运动与弹性变形的机械系统的运动与变形进行了描述,得到了以刚体位移与弹性变形位移表示的单元的广义惯性力;从应力应变入手,得到了表示单元弹性变形与几何非线性变形的结构刚度矩阵与几何非线性刚度矩阵,使用Kane方程推导了弹性连杆机构的单元运动方程,这种建模方法,可以使用在任意结构的机械系统。     

The research of load spectrum between flexible gear and wave generator of harmonic drive

The harmonic drive is a kind of gear transmission that uses wave generator to produce controllable soft round elastic deformation and engages with rigid gear to transmit motion and power.The load distribution on the surface of the flexible gear and wave generator is an important parameter of studying the deformation of flexible gear and flexible bearing outside the wave generator and is also a necessary condition for studying the fatigue damage of flexible gear under alternating load.In this paper,a 3D model of 32-type 80:1 harmonic drive is build.Based on the generalized Hooke law,a hypothesis of load distribution which is proved to be validity by using finite element simulation is proposed on the interface of flexible gear and wave generator.On this base,the mathematic model and the quantitative calculation formula of the load distribution on the surface of the flexible gear and wave generator are proposed which provide a basis for the dynamic analysis and the fatigue damage of harmonic gear drive.     

An efficient computational method for dynamic stress analysis of flexible multibody systems

This paper presents an efficient computational method of dynamic stress history calculation for a general three-dimensional flexible body by combining flexible multibody dynamic simulation and quasi-static finite element analysis (FEA). In the dynamic simulation of flexible multibody systems, flexible components can undergo nonsteady gross motion and small elastic deformation that is described with respect to the body reference frame by using the assumed mode method. D'Alembert inertia loads from the gross body motion and the elastic deformation are expressed as a combination of space-dependent and time-dependent terms that are obtained from the dynamic simulation. D'Alembert inertia loads that are associated with each unit value of the time-dependent terms are then distributed to all finite element nodes in order to compute a corresponding stress influence coefficient through quasi-static structural analyses. Total dynamic stresses due to D'Alembert inertia loads are obtained by multiplying actual magnitude of time-dependent terms with the associated stress influence coefficients. By the proposed method, it is shown that, for a general three-dimensional component, the required number of FEAs can be significantly reduced.     

Dynamic modeling of butterfly subdivision surfaces

The authors develop integrated techniques that unify physics based modeling with geometric subdivision methodology and present a scheme for dynamic manipulation of the smooth limit surface generated by the (modified) butterfly scheme using physics based “force” tools. This procedure based surface model obtained through butterfly subdivision does not have a closed form analytic formulation (unlike other well known spline based models), and hence poses challenging problems to incorporate mass and damping distributions, internal deformation energy, forces, and other physical quantities required to develop a physics based model. Our primary contributions to computer graphics and geometric modeling include: (1) a new hierarchical formulation for locally parameterizing the butterfly subdivision surface over its initial control polyhedron, (2) formulation of dynamic butterfly subdivision surface as a set of novel finite elements, and (3) approximation of this new type of finite elements by a collection of existing finite elements subject to implicit geometric constraints. Our new physics based model can be sculpted directly by applying synthesized forces and its equilibrium is characterized by the minimum of a deformation energy subject to the imposed constraints. We demonstrate that this novel dynamic framework not only provides a direct and natural means of manipulating geometric shapes, but also facilitates hierarchical shape and nonrigid motion estimation from large range and volumetric data sets using very few degrees of freedom (control vertices that define the initial polyhedron)     

Real-time simulation of large-scale dynamic river water

The real-time modeling and rendering of large-scale dynamic river motion phenomenon is one of the most challenge problems in the research field of simulation, the river water is the most important component in the virtual flood routing process, the simulation should realistically represent its dynamic behavior. This paper embraces a number of techniques covering all the steps of water motion simulation and focuses on the dynamic river surface generation and animation, we describes a combination of modeling methods for flood routing process simulation: FFT-based (Fast Fourier Transform) large-scale water surface modeling and dynamic flood peak generation on water surface using a physically based approach. The real-time rendering techniques for the large-scale 3D scene rendering such as LOD and seamless tiling of LOD patches were discussed in detail, we have adapted them to the rendering of flowing river, new method called template culling for fast clipping were also developed. The methods allow the user to interactively fly over a virtual valley, and there are presented results of implementation of the 3D visualization for river flood routing simulation.     

基于Inventor的产品外观设计与实现

随着计算机技术的发展,计算机辅助设计(CAD)的水平有了很大的提高,CAD已不仅仅局限于进行二维图纸设计,而是能够建立真实地反映系统的三维实体模型,并且可以将多个三维实体模型装配为系统进行机构动态分析。Inventor是以实体建模为主,兼顾基础曲面建模的混合型三维建模的通用CAD软件系统。其核心组成部分为零件设计、装配设计、工程图纸;此外,Inventor还有一些特定行业的功能:动力学仿真模块、有限元应力分析模块、管路设计模块等。