三截面法在光弹图像处理中的应用

为了适应光弹图像自动处理的需要,本文采用 SHIBUYA 等人提出的一种计算方法——三截面法,将模型光弹应力分析程序化.这种方法只需利用等差线条纹,避开了等倾线,减少了误差来源,并且可以只求出某一指定截面上的应力,不必将全场应力求出,计算量小,速度快,对其提供的条纹级次精度愈高,计算结果的精确度愈好。为了获取较高精度的条纹级数,本文提出了一个用以确定整、半数级次的干涉条纹细化法,以及求取分数级条纹级次的曲线拟合法,方法简单,速度快,精度高。     

全息动光弹性旋光法研究

本文提出了一个在全息动光弹性瞬态平面应力问题中同时获得分离的等差线及等和线条纹并分解平面瞬态应力的方法。文中给出了框架在冲击荷载作用下不同时刻等差线及等和线的分离条纹图和某个截面不同时刻的动态应力分布。     

固体火箭发动机燃烧室光弹性分析

本文运用光弹性法研究了某型固体火箭发动机燃烧室内端燃型药柱和星柱型药柱两种形状的固体复合推进剂的残余应力场,测定了光弹材料的弹性模量、泊松比、线胀系数、材料条纹值和冻结温度,获得了光弹材料在压应力和温度应力下的等差线条纹图,分析了应力分布情况.     

爆破等差与等和条纹图分析方法探讨

在一次加载同时得到爆破模型的动态等差线与等和线条纹的基础上，采用部分改变物光光程的方法求得等和条纹的级次，它对今后的爆破条纹判读具有重要意义；并以此为据证实了目前采用的爆破等差条纹判读方法的正确性；发现在两种条纹图上存在着特殊的条纹对应区域，它有益于更方便地进行几种条纹图的判读。     

改进的六步相移法确定等倾角与等差线相位

光弹性应力分析是一种重要的实验方法,确定等倾线参数和等差线参数是光弹法的关键。常用的六步相移法可以自动确定等倾线和等差线参数,但在求解等倾角时,由于不能避免等倾线相位图中耦合等差线的影响,会造成误差。针对这个问题,本文提出优化方案--多次载荷-六步相移法,实现在等倾线相位图求解中消除等差线的影响。通过处理对称受压圆盘在不同载荷、不同光场下得到的光弹图像,实现光弹性等倾线和等差线的自动判读,验证了所提方法的可行性。     

光弹等差线与等倾线参数的全场检测法

本文研究了一种自动获得全场等差线级数与等倾线参数角的方法.该方法是根据“相移”思想,利用数字图像处理技术,对光弹等差线图与等倾线图进行位相检测,经过去包裹处理,确定出全场各点的等差条纹级次与主应力方向角.最后通过典型实验,考核了这种方法的正确性与处理精度。     

爆破动态应力场量化研究原理与初步实验

以近年发展的激光动光弹与全息干涉法相结合,进行实验室二维爆破模型的全场动应力求解研究。在一次加载中可同时获得四个不同时刻的等和线与等差线条纹,从而在较为一般情况下完整地给出模型的全场动应力,解决了以往爆破模型全场主应力无法获得的难题。还阐述了主应力分离的理论公式;建立了相关的实验系统;用光程变化原理研究等和条纹的级次,作为实例,对双孔迭加应力场进行了定量研究。     

获取光弹性全视场n+(1/4)级和n+(3/4)级等差线的方法

经典的光测弹性力学,均推导有出现整数级和半级等差线条纹的理论公式,从而成为光弹性试验观测、计算结构应力的重要依据。但是,在实际的光弹试验的全场分析中,常感到此种条纹数的不足。特别是发展到今天,大量的三维应力工程问题中,往往在三向切片上的条纹甚少,有相当的部位根本没有等差线通过,而造成计算分析上极大的困难。因而如何加密等差 ...     

边界元法与光弹性实验相结合的应力分析法

本文介绍了边界无法与光弹性实验相结合进行应力分析的方法。叙述了用边界无法求解主应力的基本原理。结合光弹性实验等差线条纹图,可分离出主应力。     

应力波传播规律研究中的一种快速分析方法

本文提出了一种能快速、简便、直观地分析了应力波传播状况的方法。该方法利用可视化计算并绘制流前图，而后将其与动光弹条纹图相比较，进而利用所推导的应力波迭加分析式判断出物体边界或其内部的应力波迭加效果。文中对圆盘中的几个典型区域进行了实例分析。     

The inverse identification problem and its technical application

This paper presents an overview of a loading force identification technique. Load identification methods are based on the solution of the inverse identification problem. Many different approaches for linear systems have been developed in this area. For both linear and nonlinear systems, methods based on the minimization of assumed objective functions are formulated. The least square error between the simulated and measured system responses is mainly used as the objective function. The dynamic programming optimization method formulated by Bellman is commonly used for the minimization of the objective function to estimate the excitation forces. The inverse identification problem in most practical cases is ill-posed because not all the state variables or initial conditions are known. Ill-posed inverse identification problems can be solved using several techniques, the most useful of which are: the generalized cross-validation method, the dynamic programming technique and Tikhonov’s method. This article presents the theoretical background and main limits to the application of inverse identification methods. Numerical and experimental tests on a laboratory rig were made to verify the formulated procedures. The method is applied to the identification of wheel–rail contact forces during rail vehicle operation. The method can be applied for indirect measurements of contact forces in railway equipment testing.     

优化方法用于模型校核

在工程实际中,常常会遇到需要选择本构模型和校准参数的模型校核问题。文中采用优化方法实现了复杂模型校核的自动化。文中,首先将各种本构模型映射为整数编号,并根据这些编号来激活相应的本构模型和本构模型参数,解决了本构模型的参数化问题;另外,根据模型校核问题的特点选择了试验结果和计算结果相对误差的平方和作为目标函数。通过这些步骤,用实现了优化方法模型校核自动化。     

Impact of node dynamics parameters on topology identification of complex dynamical networks

This paper aims at investigating the topology identification problem of complex dynamical networks with varying node dynamics parameters and fixed inner coupling matrices. In particular, by employing the unified chaotic system as node dynamics, this work further explores the influence of continuously changing node dynamics parameters on topology identification of complex dynamical networks with different coupling strengths. Results show that for sufficiently small or large coupling strengths, the performance of topology identification is not affected by the change of node parameters. Specifically, for small enough coupling strengths, the topological structure can be completely identified regardless of the change of node parameters, while for sufficiently large coupling strengths, the connectivity (presence and absence of connections) cannot be successfully identified. Furthermore, for certain coupling strengths, with the increase of node dynamics parameters, the topology identification varies from completely unidentifiable to partially or event completely identifiable. Therefore, the synchronization-based topology identification depends on node dynamics. Even for the same node dynamical model, different parameters can have a significant impact on identification results. Furthermore, for networks consisting of chaotic oscillators defining node dynamics, small coupling strengths are conducive to topology identification. A broader conclusion is that projective synchronization, rather than just complete synchronization, is an obstacle to the network topology identification. The findings in this paper will add to our understanding of conditions for identifying topologies of complex networks.     

转子系统模态参数现场识别技术研究

基于时域振动参数识别理论,本文讨论了由转子和油膜轴承构成的转子系统的模态参数现场识别问题。本文所述方法不需要施加人工激振,仅在轴承座处测量轴承座的振动和转子的绝对振动,可以在线应用。     

动荷载反分析的模态选择方法

提出了动态载荷识别中新的确定模态的准则与实施方法.提出了模态选取概念,在此基础上提出了反分析中模态选取的准则,并给出了相应的公式.大量算例表明,采用该文准则和公式可以防止因模态选取不当而产生的伪解,避免计算中的数值病态,明显提高了动态载荷识别的成功率和精度.     

A perspective on regression and Bayesian approaches for system identification of pattern formation dynamics

We present two approaches to system identification, i.e. the identification of partial differential equations(PDEs) from measurement data. The first is a regression-based variational system identification procedure that is advantageous in not requiring repeated forward model solves and has good scalability to large number of differential operators. However it has strict data type requirements needing the ability to directly represent the operators through the available data.The second is a Bayesian inference framework highly valuable for providing uncertainty quantification, and flexible for accommodating sparse and noisy data that may also be indirect quantities of interest. However, it also requires repeated forward solutions of the PDE models which is expensive and hinders scalability. We provide illustrations of results on a model problem for pattern formation dynamics, and discuss merits of the presented methods.     

基于应变脉冲响应协方差的损伤识别方法研究

基于振动参数的结构损伤识别,是近年来土木工程的热点研究课题,振动参数包括频率、振型、频响函数、模态应变能、应变响应和加速度响应等,当结构损伤时,损伤位置附近将产生应力重分布,从而引起应变的变化,因此对比损伤前后的应变或者应变响应参数,可以用来识别结构损伤.提出了一种应变脉冲响应协方差参数,它是应变脉冲响应在时间区间上的能量积分;推导并证明了该参数是结构模态参数(频率,位移模态,应变模态,阻尼等)的函数,可用来表征结构状态.相比于传统的模态参数识别方法,可以保留更高阶的模态参数,而且避免了模态识别可能引起的误差;基于简支钢梁的多种损伤工况,研究和展示了该参数的特性,通过数值模拟发现,该参数能简单直观地判定损伤发生和识别损伤位置,无需建立结构分析模型,只需比较结构损伤前后的应变脉冲响应协方差参数即可;该参数简便易算,具有较好的抗噪性能,对结构损伤敏感,而且对结构刚度减少呈现一致变化特性,所以适合实际工程结构的健康监测和损伤识别.     

基于贝叶斯理论的恢复力模型参数识别方法

提出了基于贝叶斯理论的恢复力模型参数识别方法,该方法考虑了模型误差的影响,结合实测滞回曲线数据,不仅可以得到模型参数的最有可能值,而且可以得到模型参数的定量的不确定性。以密肋复合墙体在低周反复荷载作用下所得滞回曲线为例,提出了可考虑刚度降低、捏拢滑移及极限荷载后强度降低现象的恢复力模型,建立了基于贝叶斯理论的恢复力模型参数识别计算框架,推导得到了模型参数的负对数似然函数,据此可得到模型参数的最有可能值及协方差矩阵。对标准密肋复合墙体预制试件和现浇试件的恢复力模型参数进行了识别,将根据模型参数最有可能值得到的滞回曲线及根据模型参数最有可能值及协方差矩阵得到的骨架曲线,与相应的实测值进行了对比,验证了所提方法的可行性及识别结果的合理性,更新的模型参数概率分布可用于后续的抗震风险评估。     

基于模态数据的长细结构小损伤精确识别研究

本文针对现有的损伤识别方法不能满足部分结构损伤识别精度要求的现状，对结构的小损伤精确识别方法开展研究．以长细结构为研究对象，对具有不同损伤位置和损伤程度的圆柱形的轻阻尼梁结构进行了数值分析和实验研究，应用数值计算方法和实验确定的特征向量和特征频率对长细结构裂缝参数进行识别计算．本文在研究过程中编制了一个创新性的预测程序，通过其一次性生成目标函数图来选择合适的初始参数，从而对识别结果进行分析．研究结果表明，应用本文提出的识别方法，裂缝位置的识别误差可以控制在0.05 %~0.28 %范围内，裂缝深度识别误差低于7 %．     

Modal Model Identification with Unknown Nonstationary Base Motion

Techniques developed for structural identification are typically devoted to obtaining a model, parametrical or not, on the basis of information on the structural response and on the forcing action, both assumed as known from experimental tests. In many situations, however, it may be necessary, or simply useful, to refer only to the measured response. In this paper we describe the theoretical aspects of a technique we have recently developed to identify the modal model in the frequency domain when the input is unknown. To simplify, we refer to unknown nonstationary base motion, but many of our conclusions can be extended to different situations. We show that, from a theoretical point of view, the identification problem has a unique solution, for this kind of input, when at least three time histories are known, and this circumstance had never been pointed out before. Because the theoretical analysis furnishes only necessary conditions for the existence of a unique solution, an extensive numerical analysis is reported in the second part of the paper, which also shows the sensitivity of the identification procedure.