基于特征正交分解的梁结构损伤识别

介绍了特征正交分解（Proper Orthogonal Decomposition, POD）的相关理论和一种基于特征正交分解的结构损伤识别方法的基本原理,并利用该识别方法对简支梁结构进行了损伤识别数值研究。研究结果发现：基于特征正交分解的结构损伤识别方法能较好地识别出梁结构的损伤位置,并具有一定的抗噪能力。     

结构风振分析中的脉动风荷载频率补偿方法

以风洞试验相似理论和随机振动理论为基础,提出了风振分析中的脉动风荷载频率补偿问题,即根据已有的测点风压数据重构脉动风荷载的高频部分,其目的是解决由于缩尺比导致的试验采样频率转化为原型荷载频率后所存在的高频截断问题。对脉动风荷载频率补偿的必要性进行了探讨,指出被截断的高频信号可能导致结构风振响应分析结果失真;结合脉动风荷载能谱理论和本征正交分解(POD)技术提出了一种实用的频率补偿方法;结合一风洞试验分析了考虑频率补偿与否对单层网壳结构风振响应分析结果的影响,验证了方法的有效性。     

基于奇异值分解及特征正交分解的结构损伤检测方法

为直接通过结构振动响应提取损伤特征参数,将奇异值分解和特征正交分解运用到结构响应分析中。该方法首先通过对结构响应功率谱矩阵的奇异值分解,获得模态频率,然后在模态频率处计算互相关矩阵,利用特征正交分解获得收敛于结构模态向量的特征正交模态,进而构建了损伤定位向量,最后通过结构单元应力的不同分布准确定位了损伤位置。实验数据分析结果表明,该方法能有效的进行损伤检测和定位。     

Modified smoothed particle hydrodynamics method and its application to transient problems

A modification to the smoothed particle hydrodynamics method is proposed that improves the accuracy of the approximation especially at points near the boundary of the domain. The modified method is used to study one-dimensional wave propagation and two-dimensional transient heat conduction problems.This work was supported by the ONR grant N00014-98-1-0300 and the ARO grant DAAD19-01-1-0657 to Virginia Polytechnic Institute and State University, and the AFOSR MURI grant to Georgia Tech that awarded a subcontract to Virginia Polytechnic Institute and State University. Opinions expressed in the paper are those of authors and not of the funding agencies.     

POD-based identification approach for powder mixing mechanism in Eulerian–Lagrangian simulations

Numerous products are manufactured through powder mixing. Understanding the mixing mechanism is essential to improve product quality. Convection, diffusion, and shear are well-known classifications in the powder mixing mechanism. During powder mixing, plural mixing mechanisms may occur simultaneously. In this study, to identify the main mixing mechanisms and investigate the transition of the main mixing mechanisms, an advanced identification technique is developed by incorporating the proper orthogonal decomposition (POD) method into numerical modeling for powder mixing. The discrete element method (DEM) coupled with computational fluid dynamics (CFD) is employed to simulate powder mixing. Several investigations are performed to show the adequacy of the developed technique. First, numerous CFD–DEM simulations for solid–liquid flows are performed in a rotating paddle mixer. Next, an efficient Lanczos-based POD (LPOD) method is proposed to characterize the main features of powder mixing via the POD analysis. The results show that the mixing mechanism is dominated by convection in the early stage and by diffusion in the late stage. Besides, a novel mixing identification technique is established by giving the relation between POD modes and mixing mechanisms, namely, clumped and random spatial distributions of the POD modes appear in convective and diffusive mixing, respectively. Consequently, it is shown that combining the CFD–DEM simulation with the LPOD method is effective to identify the main mixing mechanism and to explain the time transition of mixing mechanisms between convective and diffusive mixing.     

Wave characteristic of femtosecond heat conduction in thin films

The hyperbolic heat conduction equation (HHC) is solved for submicrometer gold film irradiated with a short-pulse laser. The transient temperature profiles are calculated. It is shown that the solutions of HHC and standard heat diffusion equation are significantly different for submicrometer films.Paper presented at the Third Workshop on Subsecond Thermophysics, September 17–18, 1992, Graz, Austria.     

POD法在定日镜风振响应计算中的应用

定日镜结构风振响应中有多个振型参与,利用完全二次型组合法(CQC)可以考虑各振型间的耦合作用,得到精确结果,但计算量很大,因此提出将随机风场本征正交分解(POD)技术运用到定日镜结构响应计算中.首先给出了POD法原理,讨论了如何将POD法与CQC法结合进行结构脉动响应的频域分析;然后利用POD法分解风洞试验中多通道电子式压力扫描阀系统同步采集到的定日镜表面风压时程,分析了其本征向量的分布特点,以及各阶模态的贡献情况;最后计算出定日镜风致位移响应的均方根,并且对比采用不同阶数模态缩减得到均方根响应的误差.结果表明将POD法引入到风振响应分析中可以大大减少计算工作量并且能保证足够的精度.     

POD‐based model reduction with empirical interpolation applied to nonlinear elasticity

The constantly rising demands on finite element simulations yield numerical models with increasing number of degrees‐of‐freedom. Due to nonlinearity, be it in the material model or of geometrical nature, the computational effort increases even further. For these reasons, it is today still not possible to run such complex simulations in real time parallel to, for example, an experiment or an application. Model reduction techniques such as the proper orthogonal decomposition method have been developed to reduce the computational effort while maintaining high accuracy. Nonetheless, this approach shows a limited reduction in computational time for nonlinear problems. Therefore, the aim of this paper is to overcome this limitation by using an additional empirical interpolation. The concept of the so‐called discrete empirical interpolation method is translated to problems of solid mechanics with soft nonlinear elasticity and large deformations. The key point of the presented method is a further reduction of the nonlinear term by an empirical interpolation based on a small number of interpolation indices. The method is implemented into the finite element method in two different ways, and it is extended by using different solution strategies including a numerical as well as a quasi‐Newton tangent. The new method is successfully applied to two numerical examples concerning hyperelastic as well as viscoelastic material behavior. Using the extended discrete empirical interpolation method combined with a quasi‐Newton tangent enables reductions in computational time of factor 10 with respect to the proper orthogonal decomposition method without empirical interpolation. Negligibly, orders of error can be reached. Copyright © 2015 John Wiley & Sons, Ltd.     

使用特征正交分解型谱表示法的汽车受路面激励随机模拟

将特征正交分解型谱表示法用于模拟汽车受路面激励。首先给出了路面不平度对汽车输入的位移随机激励的谱描述。基于路面激励的功率谱矩阵,结合特征正交分解（POD,Proper Orthogonal Decomposition,）型谱表示法的模拟表达式,给出了路面激励的显式POD分解,定义了汽车的“路面激励模态”,推导了路面对汽车输入激励随机模拟的简化计算公式。该方法可用FFT来减少计算量以提高计算速度。它由于完全消除掉了原型谱表示法的Cholesky分解过程而具有较高的计算效率和更明确的物理意义。最后,通过对一个四轮轿车在国标GB7031—87中的A级路面不平度下受到的位移随机激励进行模拟,说明了该方法的有效性。