爆炸冲击波对桥梁毁伤的实时模拟

文章介绍了一种模拟爆炸冲击波对桥梁毁伤过程的方法。该方法用3DMAX建立桥梁的表面模型并用VRML格式保存，然后使用Delaunay三角剖分算法对表面模型进行三角剖分，并构造出一种由三菱柱组成的三维实体模型来模拟桥梁的断裂及碎片的产生和运动，文中采用了简单的冲击波－球形冲击波，结合随机函数求解各碎片的初始速度，计算出每帧内各碎片的位置，最后生成桥梁毁伤的动画效果，该方法能逼真地表现出桥梁受冲击波毁的效果，并能满足虚拟战场的实时性要求。     

航空发动机叶片非线性动力学分析

论文研究了航空发动机叶片的非线性振动问题,将叶片简化为功能梯度材料薄壁悬臂梁,考虑几何大变形的影响,基于一阶活塞气动力理论,利用Hamilton原理建立了叶片的非线性偏微分运动方程.综合运用Galerkin方法、多尺度方法和数值方法对叶片模型进行了非线性动力学分析,通过相图、波形图和频谱图分析了不同气流流速情况下旋转叶片的动态响应.结果表明:随着气流流速的增加,系统呈现倍周期运动和混沌运动等多种复杂动力学行为.     

摄像机简化模型对三维重构的影响--分析与实验

讨论了摄像机简化模型对三维重构的影响．主要结论有：当摄像机在两幅图像间的运动为纯平移运动时,从理论上证明了使用摄像机简化模型重构空间点与实际空间点之间满足仿射变换;当摄像机在两幅图像间的运动为一般刚体运动时,使用简化模型的重构只有在一定条件下才能较好地保持原物体的形状;在简化模型下,基于Kruppa方程的方法所估计的焦距精度不能满足三维重构的要求．实验结果表明：在三维重构中不能盲目地使用简化模型,必须对摄像机内参数进行全面标定．     

核爆炸外观景象实时模拟

根据核爆炸的基本表现过程,建立了一个综合的爆炸模型,可以实现实时的核爆炸景象模拟。通过球形扩张建立冲击波的冲击模型,并实现了快速的碰撞检测;使用视角范围内的粒子抛撒,表现核爆炸产生的飞溅物;利用适当简化后的Navier-Stokes方程,优化求解策略,实现具有复杂运动形式的蘑菇状烟云模拟。实验结果表明,采用该模型可以实现实时的核爆炸效果模拟,通过控制和调整参量,可以获得多种不同类型的核爆炸效果。     

基于二参数Antoine方程的石油物系汽-液平衡模型

石油物系汽-液平衡计算在石油蒸馏计算过程中至关重要,本文应用一种简化的汽.液平衡模型对石油物系进行相平衡计算。通过引入简化的蒸汽压方程简化了计算步骤,进而大幅度的降低了计算时间,最终达到提高计算效率的目的。该方法与广泛应用的严谨汽.液平衡计算的SRK方程对比,具有结构简单、迭代步骤少等优点。通过实验,将该简化模型应用于大庆石油、胜利石油等5种石油的石油物系中,经过对比PT闪蒸的仿真结果得到,该简化模型与应用SRK方程方法相比,在0.002 MPa-0.5MPa下的汽化分率的绝对误差约为1%,故该方法与严谨算法的误差在一个较小的范围内,证明了该简化模型的有效性。同时,通过应用简化模型可将计算速度提升98倍,证明模型具有较强的实用价值。     

土壤水盐运移的简化数学模型在水盐动态预报上的应用研究

对土壤水盐运移的确定性数学模型 ,采用数值模拟的简化法 ,实现对方程的求解。并引入水分运动原理、质量守恒原理 ,根据地下水、土壤水盐运动的特点 ,建立土壤剖面含水量分布的概化模型和土壤盐储量的预报模型。以期从土壤水盐运动的机制出发 ,提出一种应用简化数值模拟方法来预报土壤水盐动态的途径。同时为适应大面积田间土壤盐分预报的特点 ,希望不通过方程的求解来达到应用简化数学模型实现水盐动态预报的目的。所建简化数学模型可为田间大面积土壤水盐动态预测预报提供参考     

人体运动仿真建模方法研究

为了研究人体在运动过程中的力学行为,探讨人体运动仿真的建模方法,运用多体系统动力学的建模方法建立了17刚体,55自由度的人体动力学模型,模型对人体颈部和下躯干的柔性效应给予了充分考虑,基于第一类Lagrange方程推导了系统的动力学方程,并以某人体为例,利用该模型对人体的行走过程进行了仿真计算,计算结果表明:采用所建立的人体动力学模型进行人体步态仿真、碰撞仿真等研究是现实可行的,最后结合对人体运动仿真的未来发展趋势的展望,说明人体动力学模型有待进一步完善.     

平移初值操作的基于Kruppa方程的自标定方法

针对传统的基于Kruppa方程的摄像机自标定算法鲁棒性差的情况提出了一种新的二步式标定方法。首先对Kruppa方程进行简化,确定了经简化后的目标函数,再通过摄像机的三次线性无关的任意平移运动确定初值,然后用非线性优化目标函数法精化初值。实验结果表明,该方法可以大大提高基于Kruppa方程标定算法的鲁棒性及标定精度。     

基于滑模趋近律的防空导弹垂直发射姿态控制研究

为了实现一种针对光纤制导的低空战术防空导弹垂直发射过程的姿态控制,首先利用四元数在弹体坐标系下对垂直发射的防空导弹建立了运动方程,并在纵向通道利用小扰动线性化理论将运动方程简化为状态空间模型,然后设计了基于滑模趋近律的姿态控制律,最后建立了Simulink六自由度弹道仿真模型并进行了数字仿真验证,结果表明:基于四元数的运动方程形式运行有效,基于滑模趋近律的姿态控制律可实现对防空导弹垂直发射的有效控制.     

气相色谱分离过程的模拟

建立了描述多组分气相色谱柱内运动过程的数学模型 ,模型包括物料平衡方程、吸附方程和传质方程 ,采用数值方法求解。对多种操作条件及色谱柱特征参数对色谱分离过程的影响进行模拟 ,为色谱过程的应用提供设计和优化的基本条件 ;模拟结果与实验结果一致 ,表明本文所建立的模型能够正确描述各种条件下的色谱过程。该模型还可以推广用于各种不同的色谱程序操作     

基于Smoothed Particle Hydrodynamics方法的实时流体模拟

提出基于物理的、实时的技术模拟水体,根据Smoothed Particle Hydrodynamics方法求解流体动力学的Navier-Stokes方程,并运用Marching Cubes体绘制算法重建流体表面.实验表明基于粒子的方法能模拟流体所特有的飞溅、漩涡等现象,Marching Cubes在表面重建的高效性使模拟达到实时、交互的应用.     

三维实时云建模与渲染在工业仿真中的应用

在云建模方面,提出一种基于物理仿真和艺术可控性相结合的方法,利用Navier-Stokes流体动力学公式描述单一云朵的聚散和运动,通过盒子的堆积来描述云朵的初始轮廓,最终在盒子内部按流体动力学规律填充粒子生成三维云模型.为了满足实时性要求,在可编程图形芯片上求解Navier-Stokes等式,以便利用图形芯片的并行处理能力加快求解速度.在云的实时渲染方面,基于太阳光照方向和天气状况提出了一种简单的光照模型,大幅度地提高了云的渲染速度.此外,还提出一种改进的环状Impostor技术来提高大范围云层的渲染速度,并通过Shader编程的方法解决了应用Impostor技术到Alpha融合场景中所出现的问题.基于所描述的理论模型,利用三维图形API开发了一套三维云仿真系统,并广泛应用于各种工业仿真和科技娱乐展示项目中,取得了较好的效果.利用该方法生成的云模型具有真实感强、渲染速度快等特点.     

Mathematical modeling of the MHD pump in view of the external circuit

This article presents spatially a 2D cylindrically symmetrical, mathematical model of the MHD pump that is not stationary in time. To describe electromagnetic fields, the MHD approximation of Maxwell’s equations is used; to describe the motion of heat-transfer fluid in the pump channel, the Navier-Stokes equations written in terms of vortex and flow function are used. The fluid consumption is calculated from the equation of fluid motion in a closed circuit. The calculations of different pump operating modes are presented.     

On a method for direct numerical simulation of shear layer/compression wave interaction for aeroacoustic investigations

Direct numerical simulation (DNS) of a spatially developing mixing layer was performed. The compressible three-dimensional Navier-Stokes equations were solved for pressure, velocities and entropy for this flow using a compact finite-difference scheme of sixth-order accuracy in space, combined with Runge-Kutta three-step time advancement. On one of the transverse boundaries of the box-shaped domain, a compression wave profile was imposed in pressure and velocity components via a wave decomposition of the governing equations, in order to study the interaction of an isolated weak shock wave entering the domain with the mixed subsonic/supersonic shear layer. This flow situation is found along the shear layer of supersonic, imperfectly expanded jets containing a shock cell structure. In the present work, an isolated compression-expansion structure constitutes the model problem. The domain setup and the boundary conditions were chosen such as to allow analysis of the sound field generated by the turbulent flow and the shock-turbulence interaction. The numerical method used to impose the boundary conditions and solve the compressible Navier-Stokes equations, and the choice of numerical parameters, are described in detail. Some results on the two-dimensional and three-dimensional flow field computed are presented as well.     

Multigrid solutions of steady two-dimensional flow past a cascade of sudden expansions

In the steady laminar flow past a sudden expansion the motion is assumed to be two-dimensional and to be governed by the Navier-Stokes equations for incompressible fluids. In this work the multigrid method is employed to obtain finite-difference solutions to the steady Navier-Stokes equations, which are in terms of the vorticity and stream function, up to Re = 1000 for a uniform inflow past a cascade of expansions. The calculations show that, for both small and large values of the expansion ratio, the eddy length increases linearly with Re, which is in good agreement with recent theoretical work but contradicts some previously published Navier-Stokes computations.     

Computation of shape and drag of a deforming elastic body under fluid dynamic force

This paper describes numerical simulations for the shape and its drag of an elastic body deforming under the fluid dynamic force. The simulations were carried out by coupling the Navier-Stokes equations and the equations of motion of the elastic body. The equations of motion are formulated for an elastic shell model which is composed of material particles connected with elastic springs and dampers. The relation between deforming elastic body shape in response to the fluid dynamic force and its drag force was investigated under the constraint of constant volume and fixed center of gravity of the elastic body for incompressible and compressible supersonic flows. In these simulations, an initial shape of the elastic body is a circular cylinder and starts deformation under the fluid dynamic force.     

Boussinesq systems in two space dimensions over a variable bottom for the generation and propagation of tsunami waves

Considered here are Boussinesq systems of equations of surface water wave theory over a variable bottom. A simplified such Boussinesq system is derived and solved numerically by the standard Galerkin-finite element method. We study by numerical means the generation of tsunami waves due to bottom deformation and we compare the results with analytical solutions of the linearized Euler equations. Moreover, we study tsunami wave propagation in the case of the Java 2006 event, comparing the results of the Boussinesq model with those produced by the finite-difference code MOST, that solves the shallow water wave equations.     

Particle Monte Carlo and lattice-Boltzmann methods for simulations of gas-particle flows

A numerical solution concept is presented for simulating the transport and deposition to surfaces of discrete, small (nano-)particles. The motion of single particles is calculated from the Langevin equation by Lagrangian integration under consideration of different forces such as drag force, van der Waals forces, electrical Coulomb forces and not negligible for small particles, under stochastic diffusion (Brownian diffusion). This so-called particle Monte Carlo method enables the computation of macroscopic filter properties as well the detailed resolution of the structure of the deposited particles. The flow force and the external forces depend on solutions of continuum equations, as the Navier-Stokes equations for viscous, incompressible flows or a Laplace equation of the electrical potential. Solutions of the flow and potential fields are computed here using lattice-Boltzmann methods. Essential advantage of these methods are the easy and efficient treatment of three-dimensional complex geometries, given by filter geometries or particle covered surfaces. A number of numerical improvements, as grid refinement or boundary fitting, were developed for lattice-Boltzmann methods in previous studies and applied to the present problem. The interaction between the deposited particle layer and the fluid field or the external forces is included by recomputing of these fields with changed boundaries. A number of simulation results show the influence of different effects on the particle motion and deposition.     

Transient state analysis of separated flow around a sphere

Transient state solutions of the Navier-Stokes equations were obtained for incompressible flow around a sphere accelerating from zero initial velocity to its terminal free falling velocity. By assuming rotational symmetry about the axis in the direction of motion, the Navier-Stokes equations and the continuity equation were simplified in terms of vorticity and stream function. The instantaneous acceleration of the falling sphere was calculated by considering the difference between the gravitational force and the drag force in a transient state. A set of implicit finite difference equations was developed. In order to obtain accurate information around the body, an exponential transformation along the radial direction was used to provide finer meshes in the vicinity of the surface of the sphere. The vorticity equation was solved by an alternating direction implicit (ADI) method while the stream function equation was solved by a successive over-relaxation (SOR) method. Simultaneous solutions were obtained. Transient state solutions were compared with steady state solutions for Reynolds numbers up to 300. Separations first occurred at a Reynolds number 20 for steady state flows and at Reynolds numbers 22·46 and 28·24 for transient state flows with terminal Reynolds numbers of 100 and 300, respectively. Separation angles, sizes of separation regions, and drag coefficents were calculated for both steady and unsteady states. Good agreement was obtained with existing experimental data in the steady state.