Proper application of a kind of matrix construction method in physical parameter identification of dynamic model

ＩｎｔｒｏｄｕｃｔｉｏｎＴｈｅｐｈｙｓｉｃｓｐａｒａｍｅｔｅｒｉｄｅｎｔｉｆｉｃａｔｉｏｎｐｒｏｂｌｅｍｓａｒｅｆｒｅｑｕｅｎｔｌｙｅｎｃｏｕｎｔｅｒｅｄｉｎｔｈｅｆｉｅｌｄｓｏｆａｖｉａｔｉｏｎ,ｓｐａｃｅ,ｍｅｃｈａｎｉｓｍａｎｄｃｉｖｉｌｅｎｇｉｎｅｅｒｉｎｇ .Ｆｏｒｅｘａｍｐｌｅ ,ｄｕｅｔｏｔｈｅｃｏｍｐｌｅｘｉｔｙｏｆｍａｔｅｒｉａｌｐｒｏｐｅｒｔｉｅｓｉｎｃｉｖｉｌｅｎｇｉｎｅｅｒｉｎｇ ,ｔｈｅｐｈｙｓｉｃｓｐａｒａｍｅｔｅｒｓｕｓｕａｌｌｙａｒｅｉｄｅｎｔｉｆｉｅｄｂｙｔｅｓｔｄａｔ…     

自由-自由运行体系动态载荷反演问题研究

对自由-自由运行体系动态载荷识别问题进行深入研究,将自由-自由运行体系振动积分方程时域离散化,建立了体系动态载荷反演的力学模型。在动态载荷反演模型求解过程中,由于结构矩阵的病态特性以及测量噪声的影响,常规最小二乘法往往失效;通过对载荷反演模型进行奇异值分解,指出该病态问题的本质,并提出相应的正则化求解方法。数值仿真表明了本文方法能够得到满足工程要求的稳定近似解。本文研究对于实际飞行器运行过程所受动载荷评估具有一定的意义。     

基于遗传算法的低压液压管路模型参数识别

为了合理预测伴随气泡和气穴的低压液压管路压力瞬态脉动,提出了用改进遗传算法对低压液压管路压力瞬态脉动模型进行参数辨识的新方法.给出了用来描述管路流动特性的瞬态脉动数学模型,建立了用来计算伴随气泡和气穴的液压管路瞬态下气泡体积和气穴体积的数学模型.构造了基于最小二乘法的适应度模型,探讨了遗传操作方式及算法终止准则,采用了算术交叉同线性逼近相结合的改进算术交叉算子进行交叉操作,给出了模型参数寻优的算法流程.实现了对低压液压管路压力瞬态脉动数学模型的参数识别,得到了参数优化后的低压液压管路压力瞬态脉动模型.仿真结果与实验数据的比较表明在低压液压管路瞬态模型中,用改进遗传算法来识别模型中的未知参数的方法是可行的、有效的.     

Parameter identification in a soil with constant diffusivity

We consider infiltration into a soil that is assumed to have hydraulic conductivity of the form K = K = K_se^h and water content of the form = K – _r. Here h denotes capillary pressure head while K_s, , and _r represent soil specific parameters. These assumptions linearize the flow equation and permit a closed form solution that displays the roles of all the parameters appearing in the hydraulic function K and . We assume K_s and _r to be known. A measurement of diffusivity fixes the product of and resulting in a parameter identification problem for one parameter. We show that this parameter identification problem, in some cases, has a unique solution. We also show that, in some cases, this parameter identification problem can have multiple solutions, or no solution. In addition it is shown that solutions to the parameter identification problem can be very sensitive to small changes in the problem data.     

Stability analysis of abnormal multiplication of plankton using parameter identification technique

This paper presents the mathematical approach for the abnormal multiplication of plankton. An abnormal multiplication can be expressed as an unstable problem and the stability of the system is investigated by introducing eigenvalues of a mathematical equation. The stability of the system can be judged by an eigenvalue based on the Lyapunov's stability theory. In this paper, the Arnoldi‐QR method is used to obtain eigenvalues and eigenvectors of the system. The mode superposition method is employed to create spatial distribution needed to analyse the stability. To obtain the objective eigenvalue, the parameter identification technique is employed. The finite element method is used for the discretization in space. Lake Kasumigaura, which is located in Ibaraki Prefecture in Japan, is selected and actual data in 1975, 1976, 1991 and 2000 are used in order to investigate the stability of the specified lake in Japan. Copyright © 2004 John Wiley & Sons, Ltd.     

An experimental study of nonlinear dynamic system identification

A technique for robust identification of nonlinear dynamic systems is developed and illustrated using both digital simulations and analog experiments. The technique is based on the Minimum Model Error optimal estimation approach. A detailed literature review is included in which fundamental differences between the current approach and previous work is described. The most significant feature of the current work is the ability to identify nonlinear dynamic systems without prior assumptions regarding the form of the nonlinearities, in contrast to existing nonlinear identification approaches which usually require detailed assumptions of the nonlinearities. The example illustrations indicate that the method is robust with respect to prior ignorance of the model, and with respect to measurement noise, measurement frequency, and measurement record length.     

Navier solution for the elastic equilibrium problems of rectangular thin plates with variable thickness in linear and nonlinear theories

This paper discusses the elastic equilibrium problems of rectangular thin plates of varying thickness and simply supported on all four sides by linear and nonlinear theory. using the Navier method to seek an approach to the problem, and illustrates the solution with two examples. In conclusion, mention in made of scope of application and the convergency of the solution.     

Bayesian parameter identification in dynamic state space models using modified measurement equations

When Markov chain Monte Carlo (MCMC) samplers are used in problems of system parameter identification, one would face computational difficulties in dealing with large amount of measurement data and (or) low levels of measurement noise. Such exigencies are likely to occur in problems of parameter identification in dynamical systems when amount of vibratory measurement data and number of parameters to be identified could be large. In such cases, the posterior probability density function of the system parameters tends to have regions of narrow supports and a finite length MCMC chain is unlikely to cover pertinent regions. The present study proposes strategies based on modification of measurement equations and subsequent corrections, to alleviate this difficulty. This involves artificial enhancement of measurement noise, assimilation of transformed packets of measurements, and a global iteration strategy to improve the choice of prior models. Illustrative examples cover laboratory studies on a time variant dynamical system and a bending–torsion coupled, geometrically non-linear building frame under earthquake support motions.     

考虑关节摩擦的空间机器人动力学建模与参数辨识

研究了考虑关节摩擦影响的空间机器人系统的动力学建模与参数辨识问题．采用单向递推组集方法和虚功率原理建立了含有关节摩擦的多体系统动力学方程,推导了关节摩擦对系统动力学方程的贡献,采用基于腕力传感器信号和最小二乘法的辨识方法进行了系统惯性参数的辨识．数值仿真结果验证了数学模型的正确性与辨识方法的有效性．     

Estimation of boundary values and identification of boundary type for numerical models of aquifer flow

Inverse methods which focus on aquifer properties implicitly assume that boundary conditions are known with certainty and can therefore lead to biased results. An inverse procedure is described which allows the simultaneous estimation of not only spatially varying aquifer storage coefficients and transmissivities, but also model parameters which represent both boundary type and boundary values. The weighted least-squares procedure is based on either Bayesian or maximum likelihood arguments and requires both measurements of transient piezometric heads and prior information on all model parameters. Prior estimates and their covariance can be nonconditioned (e.g. a stationary mean and covariance structure) or conditioned on direct measurements (e.g. a kriged transmissivity field with its estimation covariance). Hypothetical examples are presented using an unsteady finite element model. In some cases, with weak prior information on the boundary type, it is possible to distinguish between prescribed head, prescribed flux and mixed boundaries. Simultaneous estimates of aquifer properties and boundary values are always possible, although their accuracy depends on the relative magnitudes of model sensitivities and prior information.     

一种调整线性振动系统特征参数的方法

在设计一个线性振动系统时,为了获得某些希求的特征参数;或者为了调整数学模型的特征值,使能与试验值更好地符合,往往需要对原数学模型作些修改。利用线性规划,本文给出了一种求解逆特征值问题的迭代方法。通过算例说明本文方法是对线性振动系统进行再设计的一种有效和可靠的方法。     

Parameter identification in offshore platform using arma moded and technology of extracting free vibration signal

A procedure for identifying the dynamic parameter of offshore platform is presented. The present procedure consists of two key features. First uses random decrement (RD) technology to extract free vibration signal in strong noise environment in which it may not white noise. Second technology which called autoregressive moving average (ARMA) was used to model the data treated by the random decrement method. In order to get rid of the color noise in the output signal response from the offshore platform an imaginary system is added in RD system and make the course of extracting performed under the state of color input by choosing the breakover condition and lead time. For eliminating multi-values of parameters identified, an updating moving average method is used. The dynamic parameters of structure under arbitrary input are identified. Example of the method as applied to a scale-model offshore platform was used to evaluate the technology of efficiency and the value of on-line. Foundation items: the National Outstanding Youth Science Foundation of China (59625815); the Applied Development Foundation of National High Technology Biography: OU Jin-ping (1959-), Professor, Vice-President, Doctor     

平稳随机振动荷载识别的逆虚拟激励法（二）

本文将逆虚拟激励法（ＩＰＥＭ）用于求解平稳随机振动的荷载谱识别问题，已知部分结构应变（或部分应变及部分位移）响应的自谱与互谱，反求多点激励间的自谱与互谱。     

平稳随机振动荷载识别的逆虚拟激励法（一）

本文将虚拟激励法作了逆向推广，从而用确定性方式求解了平稳随机振动的荷载谱识别问题。即已知部分响应的自谱与互谱，反求多点激励间的自谱与互谱。并通过计算机模拟，讨论了识别的精度及影响因素等问题。     

Modal parameter identification of flexible spacecraft using the covariance-driven stochastic subspace identification (SSI-COV) method

In this paper, the on-orbit identification of modal parameters for a spacecraft is investigated. Firstly, the cou-pled dynamic equation of the system is established with the Lagrange method and the stochastic state-space model of the system is obtained. Then, the covariance-driven stochas-tic subspace identification (SSI-COV) algorithm is adopted to identify the modal parameters of the system. In this algo-rithm, it just needs the covariance of output data of the system under ambient excitation to construct a Toeplitz matrix, thus the system matrices are obtained by the singular value decom-position on the Toeplitz matrix and the modal parameters of the system can be found from the system matrices. Finally, numerical simulations are carried out to demonstrate the validity of the SSI-COV algorithm. Simulation results indi-cate that the SSI-COV algorithm is effective in identifying the modal parameters of the spacecraft only using the output data of the system under ambient excitation.     

界面连接刚度参数辨识的子结构分析法

以试验模态参数为基础,提出一种通过特征方程反问题辨识子结构界面连接刚度参数的子结构分析法。新方法以子结构动柔度矩阵特征方程为基础,建立求解界面结点内力和位移的方程,从而由子结构内部结点可测自由度上的位移用广义逆理论估计界面结点内力和位移。并通过迭代修正内部结点可测自由度上的试验值,以提高界面内力和位移的估计精度。最后通过连接子结构刚度矩阵建立的平衡方程求解相应的刚度参数。文中以太阳电池阵板间铰链副刚度参数辨识为例,将铰链副简化为两端结点各有6个自由度的弹簧连接元,考虑到自由度之间的耦合,推导了连接元的刚度矩阵。用上述方法辨识了铰链副6个自由度的刚度参数,得到满意的辨识结果。     

振动系统动力学设计迭代算法及解的存在性讨论

振动系统动力学设计被抽象为高维广义非线性特征值反问题。若系统构成以可变参数表示，则可构造一个非线性多元函数。基于多元函数极小原理，提出了一套求解这一特征值反问题的迭代算法。该算法不受系统给定阶数和给定方向的限制，也适用于具有重特征值的退化情况，系统或结构的构成材料可以是任意的。文中同时讨论了解的存在条件，且以显式表达，可方便地应用于工程实际。结合某直升机旋翼桨叶的动力学设计，给出了应用的数值算例。大量数值仿真结果及应用实践表明，本文算法具很好的收敛性，并有较高的计算精度。     

Bammann-Chiesa-Johnson粘塑性本构模型材料参数的一种识别方法

粘塑性本构模型能否成功模拟金属高应变率大应变变形过程依赖于材料参数识别结果的好坏。由于BCJ模型考虑了应变率、温度与材料硬化之间的耦合效应以及应变率、温度历史效应,同时模型中包含了多个材料参数,因此很难通过试验直接识别模型的材料参数。本文针对BCJ模型中的耦合效应和历史效应,基于对模型中材料参数物理涵义的界定,给出了一种对材料参数解耦、分离并进行估计的方法,获得了模型材料参数估计公式,估计了材料参数的取值范围。在此基础上,编制了BCJ模型应力积分径向返回算法和粒子群优化算法的计算程序,应用重新设计了BCJ模型耦合效应和历史效应的反分析方法,在参数取值范围内对材料参数进行了优化识别。以OFHC Cu为例,应用提出的识别方法对BCJ模型的材料参数进行了识别,计算结果和试验结果符合较好。     

激光刻痕聚丙烯塑料失效破坏的参数识别

采用等效截面积法建立了激光加工微孔的有限元模型及带激光刻痕聚丙烯塑料板的冲击模型,并 通过参数识别方法确定了材料的失效应变。通过极差分析得出该塑料材料的冲击断裂强度随撕裂线直径的 增大而增大,随冲击速度的增大而减小。这与实验结果一致。     

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。