基于虚拟响应信号的结构参数时域辨识研究

在充分考虑线性动力系统的时域响应特性以及小波包分析的频率空间剖分特性的基础上,提出了一种基于虚拟响应信息提取的信号去噪新方法.虚拟响应虽然没有在结构动力检测过程中真实发生,但却是在某种激励下可以实现的一个响应,因此,根据虚拟响应信息同样可以进行结构系统的动力识别.数值研究表明,对于地脉动响应这种有效信号频带与噪声频带相互覆盖的低信噪比信号而言,小波阈值去噪法已无能为力,而基于虚拟响应信息提取的信号去噪方法则有较好的去噪效果.     

隐式Newmark法分析波动问题精度的探讨

本文研究了用平均加速度的Newmark积分格式求解一维平面弹性波动问题的精度。由于平均加速度的Newmark积分格式没有振幅衰减、不产生数值阻尼,因此采用此法分析波动问题会产生较强的高频振荡,尤其是加速度的计算值误差甚大。本文对防护工程中常见的平台型荷载和升压三角形荷载作用下的波动问题,应用有限元分析的实例表明:采用有数值阻尼的Newmark积分格式是改进有限元求解波动问题的一个有效方法,可以大大地提高应力和加速度求解精度。文中推荐的有数值阻尼Newmark积分格式的积分参数(=0.9,=0.49)可供工程中土与结构动力分析时参考使用。     

在微粗糙平面上滚动的Chaplygin球的稳定性

本文利用文献[1]的结果,继续讨论 Chaplygin 球在微粗糙平面上滚动的稳定性。严格证明了在粘性和库仓两种磨擦条件下球绕最大惯量主轴滚动的一致稳定性,和在粘性摩擦条件及球的最大与中间主惯量矩十分接近的前提下球绕最小惯量主轴滚动的不稳定性。     

Averaging methods for numerical simulations of flows through heterogeneous porous media

Many natural rock systems contain small patches of different permeability which affect the flow of fluids through them. As these heterogeneities become smaller and more numerous, they become harder to model numerically. We consider how to reduce the computational effort required in simulations by incorporating their effects in the boundary conditions at the edges of each grid block. This is in contrast with current methods which involve often arbitrary changes in the fluid properties. The method is restricted to the case of widely-spaced patches, which simplifies interaction effects. The system then reduces to an array of dipoles, and two averaging methods are proposed for finite grid blocks. Several infinite systems, including vertical and horizontal bands, are also considered as further approximations. There is a great wealth of existing results from different fields which lead to identical mathematical problems and which can be used in these cases. Finally, we consider how to use these techniques when the precise configuration of the grid block is not known, but only its statistical properties. This can lead to results which are very different from the deterministic case.     

The low Reynolds number turbulent flow and mixing in a confined impinging jet reactor

Turbulent mixing takes an important role in chemical engineering, especially when the chemical reaction is fast compared to the mixing time. In this context a detailed knowledge of the flow field, the distribution of turbulent kinetic energy (TKE) and its dissipation rate is important, as these quantities are used for many mixing models. For this reason we conduct a direct numerical simulation (DNS) of a confined impinging jet reactor (CIJR) at Re = 500 and Sc = 1. The data is compared with particle image velocimetry (PIV) measurements and the basic flow features match between simulation and experiment. The DNS data is analysed and it is shown that the flow is dominated by a stable vortex in the main mixing duct. High intensities of turbulent kinetic energy and dissipation are found in the impingement zone which decrease rapidly towards the exit of the CIJR. In the whole CIJR the turbulence is not in equilibrium. The strong mixing in the impingement zone leads to a rapid development of a monomodal PDF. Due to the special properties of the flow field, a bimodal PDF is generated in cross-sections downstream the impingement zone, that slowly relaxes under relaminarising conditions. The time required for meso-mixing is dominating the overall mixing performance.     

考虑膨胀力的非饱和介质热-水-应力耦合二维有限元分析

从建立应力平衡方程、水连续性方程、能量守恒方程和弹塑性矩阵入手,使用Galerk in方法,将各控制方程分别在空间域和时间域进行离散,开发出了一个可考虑膨胀力的用于分析非饱和介质中热-水-应力耦合弹塑性问题的二维有限元程序.通过对一个假定的核废料地下处置库的热-水-应力耦合问题的数值计算,比较了无、有膨胀力时的情况,在定性上验证了该程序的正确性.     

粘性可压混合层时间稳定性对称紧致差分求解

基于可压扰动方程组的一阶改型 ,将高精度对称紧致格式引入边值法数值线性稳定性分析。对所获非线性离散特征值问题给出了一个通用形式二阶迭代局部算法 ,实现了时间模式和空间模式的统一求解 ,并将扰动特征值及其特征函数同时得到。据此分析了可压平面自由混合层时间稳定性 ,涉及二维 /三维扰动波、粘性 /无粘扰动波、第一 /第二模态、特征函数、伪特征值谱等。研究表明 ,压缩性效应和粘性效应对最不稳定扰动波数和增长率呈相似的减抑作用 ;在 Mc=1附近 ,从高波数段开始 ,粘性效应可强化二维不稳定扰动波由第一模态向第二模态的过渡     

岩体质量分级的风险分析方法

提出了基于RMR岩体质量分级系统的岩体质量研究风险分析方法。该方法分析步骤如下 :(1)通过岩芯样品的现场观测和实验室试验获得分类所需的变量 ;(2 )统计分析拟合得出各变量的分布函数及参数 ;(3)运用Monte Carlo模拟方法获得 2万个RMR值 ,并将结果绘成岩体质量描述图 ;(4)利用以上结果作出岩体质量风险分析评价。该方法用于润扬长江公路大桥岩体质量评价研究获得良好效果     

生物瓣膜应力的数值模拟

应用有限元方法分析了瓣架的材料特性、瓣叶的材料特性和瓣叶的钙化等因素对瓣叶的应力分布的影响。分析结果表明：采用全弹性材料的瓣架将改善瓣叶的应力分布，最大应力区域将远离接缝部位；将生物瓣瓣叶材料简化为拟线弹性材料时，对瓣叶最大主应力等值线的分布影响不大，计算结果在一定范围内存在差异；当瓣叶出现钙化时，钙化点及其周围产生应力集中，促进钙化的进一步加剧。     

爆轰波拐角传播三维数值模拟

为了研究爆轰波在拐角中的传播特性以及拐角爆轰低压流场现象,用LSDYNA 3D程序对三种常见的拐角装药的爆轰波传播特性进行了数值模拟,清晰显示了爆轰波因拐角处爆轰波传播面积的变化而产生的衰减 增长过程,讨论了侧向三通中爆速的变化情况,并得到了拐角处低压爆轰区的尺寸。