Derivatives of repeated eigenvalues and corresponding eigenvectors of damped systems

A procedure is presented for computing the derivatives of repeated eigenvalues and the corresponding eigenvectors of damped systems. The derivatives are calculated in terms of the eigenvalues and eigenvectors of the second-order system, and the use of rather undesirable state space representation is avoided. Hence the cost of computation is greatly reduced. The efficiency of the proposed procedure is illustrated by considering a 5-DOF non-proportionally damped system.     

Fast stochastic analysis for non-proportionally damped system

Fundamental principles from structural dynamics, pseudo excitation method and pseudo force method are used to develop a new fast stochastic method for seismic response analysis of non-proportionally damped system. In the method, the mathematical equation of non-proportionally damped system is expressed in the iterative form, based on which the inverse operation of the matrices is avoided. Moreover, the new method does not need the solution of any complex eigenvalue problem, in contrast to other methods found in the literature.     

非比例阻尼线性体系平稳随机地震响应计算的虚拟激励法

应用复振型分解方法,将非比例阻尼线性体系在地震作用下的动力方程求解问题转化为若干个广义复振子的求解与叠加问题。通过假定地震地面运动为一零均值的平稳随机激励,应用虚拟激励法原理,推导得到了广义复振子动力坐标的解析计算公式,进而得到了以复振型为基础的非比例阻尼线性体系随机地震响应计算的一般实数解析解答。算例证实了这种方法的可靠性及高效率。     

一类结构的（n－3）重根及其非退化性

基于陀螺模态综合法，从总装阵的块式结构出发，构造性地证明了具有ｎ片桨叶的旋翼型结构陀螺特征值问题存在一系列的（ｎ－３）重特征根，得到了对应的（ｎ－３）个完备的振型．结论进而推广到有阻尼的旋翼型结构．继续研究证明过程表明：结论适用于更广泛的一类具有重复子结构的结构系统，结果表明这类结构几何上的重复性或对称性导致的重根不会引入退化性．不同类型的算例验证了所得到的解析结果．本文还试图说明动力子结构法的定性性质保持特性是值得继续探讨的课题     

粘弹性阻尼修改后结构系统动特性的预测

无阻尼或比例阻尼结构系统经粘弹阻尼修改后,可变为粘弹性阻尼系统。要获得其动特性,需求解复特征值问题。但是,随之带来了计算量大、费用高等问题。尤其是粘弹性材料特性随频率而变化,需求解高阶非线性复特征值问题,这对于一个自由度较大的结构,计算量太大,通常较难实现。本文在特征值修改方法的基础上,提出粘弹性阻尼局部动力修改方法,即仅需已知原结构系统的实模态参数,就可求出粘弹阻尼修改后系统的复模态参数。还发展了特征值和修改量同时迭代方法,有效地解决了粘弹材料复模量随频率变化引起的非线性复特征值问题。     

多自由度参激系统稳定性的数值分析

提出多自由度周期参激系统稳定性的数值直接法。通过将扰动方程表示成状态方程形式,再根据Flo-quet理论将扰动解表示成指数特征分量与周期分量之积,并将其周期分量与系统周期系数展成Fourier级数,导出一系列代数方程,建立矩阵特征值问题,从而由数值求解特征值可直接确定参激系统的稳定性。该方法可用于一般周期参激阻尼系统,特征值矩阵不含逆子阵。应用于斜拉索在支座周期运动激励下的参激振动不稳定性分析,数值结果表明该方法的有效性。     

An iterative approach for nonproportionally damped systems

Modal analysis of nonproportionally damped linear dynamic systems is considered. Dynamic response of such systems can be expressed by a modal series in terms of complex modes. Normally state-space based methods or approximate perturbation methods are necessary for the computation of complex modes. In this paper, an iterative method to calculate complex modes from classical normal modes for general linear systems is proposed. A simple numerical algorithm is developed to implement the iterative method. The new method is illustrated using a numerical example.     

An acceleration for the eigensystem realization algorithm with partial singular values decomposition

The real-time identification of dynamic parameters is important for the control system of spacecraft. The eigensystem realization algorithm (ERA) is currently the typical method for such application. In order to identify the dynamic parameter of spacecraft rapidly and accurately, an accelerated ERA with a partial singular values decomposition (PSVD) algorithm is presented. In the PSVD, the Hankel matrix is reduced to dual diagonal form first, and then transformed into a tridiagonal matrix. The eigenvalues are computed by the bisection method in terms of the Sturm property, and the corresponding eigenvectors are obtained by the inverse iteration method. Finally, the eigenvalues and the eigenvectors are transformed into the singular values and the singular value vectors of the original matrix. An example for space station is presented to demonstrate the efficacy and accuracy of the proposed algorithm.     

接近亏损系统的矩阵摄动法

随着系统参数的变化，带有重频的系统可转变成带有密集频率的系统，反之亦然．本文讨论了亏损系统与接近亏损系统之间的关系．并提出了接近亏损系统的平均移位的摄动方法．算例表明了此方法的有效性．     

黏性阻尼系统时域响应灵敏度及其一致性研究

时域响应灵敏度分析是时域梯度优化算法的基础. 灵敏度分析通常只涉及对设计变量的微分运算, 但时域响应灵敏度问题还涉及时间域的离散化. 因此, 微分和离散的先后顺序可能对时域响应灵敏度结果产生影响. 针对黏性阻尼系统时域响应灵敏度求解问题, 基于改进精细积分方法, 分别推导了先微分后离散和先离散后微分两种伴随变量方法. 其中, 先微分后离散法首先对由伴随变量构造的增广函数微分, 再利用改进精细积分方法在各离散时间点求解时域响应灵敏度; 而先离散后微分方法则首先在各离散时间点引入残值方程构造增广函数, 再对各增广函数进行微分以求解时域响应灵敏度. 通过数值算例验证了所提出方法的有效性和准确性, 并与传统基于Newmark的方法进行比较. 结果表明, 积分方案、数值离散误差以及离散和微分的先后顺序共同影响灵敏度的一致性误差. 综合考虑精度、效率和一致性问题, 基于改进精细积分的先微分后离散伴随变量法表现更优, 最适合应用于黏性阻尼系统时域梯度优化算法.      

Complexity of chaotic binary sequence and precision of its numerical simulation

Numerical simulation is one of primary methods in which people study the property of chaotic systems. However, there is the effect of finite precision in all processors which can cause chaos to degenerate into a periodic function or a fixed point. If it is neglected the precision of a computer processor for the binary numerical calculations, the numerical simulation results may not be accurate due to the chaotic nature of the system under study. New and more accurate methods must be found. A quantitative computable method of sequence complexity evaluation is introduced in this paper. The effect of finite precision is evaluated from the viewpoint of sequence complexity. The simulation results show that the correlation function based on information entropy can effectively reflect the complexity of pseudorandom sequences generated by a chaotic system, and it is superior to the other measure methods based on entropy. The finite calculation precision of the processor has significant effect on the complexity of chaotic binary sequences generated by the Lorenz equation. The pseudorandom binary sequences with high complexity can be generated by a chaotic system as long as the suitable computational precision and quantification algorithm are selected and behave correctly. The new methodology helps to gain insight into systems that may exist in various application domains such as secure communications and spectrum management.     

Zur Eigenformmethode nichtproportional gedämpfter Schwingungssysteme

Übersicht Das Differentialgleichungssystem eines gedämpften Mehrmassenschwingers konnte bisher nur dann in reeller Schreibweise mit der Eigenformmethode exakt gelöst werden, wenn die Bequemlichkeitshypothese erfüllt ist. Diese Einschränkung setzt eine Darstellbarkeit der Dämpfungsmatrix aus der Massen- und Steifigkeitsmatrix voraus. Die vorgestellte Weiterentwicklung der Eigenformmethode ermöglicht, diese Bedingung fallenzulassen. Das allgemeine gekoppelte, lineare Schwingungsdifferentialgleichungssystem 2. Ordnung wird in reelle entkoppelte Differentialgleichungen 1. und 2. Ordnung überführt. Hiermit wird auch für nichtproportional gedämpfte Systeme die ganze Bandbreite der für den Einmassenschwinger entwickelten Lösungen verfügbar.

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On the modal superposition method of non-proportionally damped systems

Summary The modal superposition method in its real form could up to now only be applied to proportionally damped MDOF systems. The damping matrix of such a system has to be a combination of the mass and stiffness matrices. The development presented here allows that condition to be disposed of. The general coupled linear system of differential equations of second order is transformed to decoupled differential equations of first and second order. All solutions of the SDOF system can now be applied to the non-proportionally damped systems too.

     

A new matrix perturbation method for analytical solution of the complex modal eigenvalue problem of viscously damped linear vibration systems

A new matrix perturbation analysis method is presented for efficient approximatesolution of the complex modal quadratic generalized eigenvalue problem of viscouslydamped linear vibration systems.First,the damping matrix is decomposed into the sum of aproportional-and a nonproportional-damping parts,and the solutions of the real modaleigenproblem with the proportional dampings are determined,which are a set of initialapproximate solutions of the complex modal eigenproblem.Second,by taking thenonproportional-damping part as a small modification to the proportional one and using thematrix perturbation analysis method,a set of approximate solutions of the complex modaleigenvalue problem can be obtained analytically.The result is quite simple.The new methodis applicable to the systems with viscous dampings-which do not deviate far away from theproportional-damping case.It is particularly important that the solution technique be alsoeffective to the systems with heavy,but not over,dampings.The solution formul     

结构动力响应数值算法耗散和超调特性设计

对结构动力响应数值计算问题提出引入多个自由参数来获得所希望的算法特性. 多参数的一个明显的好处就是在算法设计上有更大的自由空间. 利用这些自由参数获得了两个新的无条件稳定、有二阶精度的、有好的耗散和没有超调的单步时间直接积分算法. 在存在阻尼情况下基于有限差分分析理论证明了新算法的这些特性. 其中一个有高频渐进消去特性，且在有阻尼情况下与Houbolt方法相比对高频有更强的耗散. 另一个在低频极限无耗散，高频耗散可以用一自由参数控制. 超调分析结果显示两个新算法都不显示超调，而HHT方法不仅有速度超调，还有位移超调. 最后使用一些算例并通过与传统方法的比较数值地验证了理论分析结果.     

Modalsynthese — Viskoelastische Kopplung von nichtproportional gedämpften Substrukturen

Übersicht Es wird eine Methode für die viskoelastische Kopplung von Substrukturen mit nichtproportionaler Dämpfung vorgestellt, bei der die Modalparameter der Substrukturen im Zustandsraum berechnet und das Kopplungsverfahren direkt im Zustandsraum durchgeführt wird. Das Verfahren beinhaltet im wesentlichen zwei Transformationen. Durch die erste werden mit einer reellen Modalmatrix die Bewegungsgleichungen in Modalkoordinaten in reeller Form transformiert. Durch die zweite Transformation mit einer komplexen Modalmatrix werden die Gleichungen des gekoppelten Systems vollständig entkoppelt. Die Modalparameter des Gesamtsystems sind dann komplex, können aber so direkt für die Berechnung der Übertragungsfunktion und von erzwungenen Schwingungen verwendet werden. Anhand eines Beispieles wird die relativ hohe Genauigkeit der vorgestellten Methode gezeigt.

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Modal synthesis — Viscoelastic coupling procedure for non-proportionally damped substructures

Summary A method for the viscoelastic coupling of non-proportionally damped substructures is introduced in which the modal parameters of the substructures are determined in the state space and the coupling process is directly made in the state space. The approach consists of two transformations. The first is made with a real modal matrix and transform the equations into modal coordinates in a real form. The second is with a complex modal matrix and discouples the equations of coupled systems. Then the modal parameters are complex, but they can be directly used for the calculation of the frequency response function and forced response function. An example demonstrates that this method give a relativ good approximation.

     

连续时间系统的混沌同步

本文讨论混沌连续时间系统的完全同步问题，提出一个构造混沌同步系统的新方法。这个方法基于线性系统的稳定性分析准则。通过对系统线性项与非线性项的适当分离，当系统的雅可比矩阵的所有特征值都具有负实部时，同步误差e(t)的线性系统是渐进稳定的，即可实现新系统和原系统的完全同步。新方法不需计算条件Lyapunov指数以作为判定同步的条件，因而比通用方法更为简单有效。新方法适用于自治或非自治系统，尤其适用于具有多于两个正Lyapunov指数的超混沌系统。甚至当初始同步误差极大时，也能实现理想的混沌同步。以Lorenz系统，耦合Duffing振子系统和超混沌Roessler系统作为算例。数值计算结果证实所提出方法的有效性和鲁棒性。     

基于奇异值分解的复模态矩阵摄动法

对非自伴随系统的振动重分析问题,提出了一种简单的通用方法。从子空间缩聚出发,基于复矩阵的奇异值分解定理,推导了同时适用于孤立 特征值,相重特征值和相近特征值三种复特征值情况的一阶和二阶摄动公式。算例表明,该方法通用性好,且具有足够的精度。     

非线性振动系统周期运动及其稳定性的数值研究

§1引言确定型非线性振动系统的运动可分类如下: 1.非定常运动;2.定常运动:(1)周期运动,(2)各态历经运动,(3)浑沌运动。其中非定常运动是一暂态过程,会随着时间的增长逐步衰减乃至实际上消失。定常运动中的各态历经运动,指系统至少有两个互不通约(即其比值为无理数)的振动频率,因此运动虽然局      

Updated numerical integration method for stability calculation of Mathieu equation with various time delays

The determination of the stability of systems with time delays is of high importance in many industrial and research applications. In this study, we improve the numerical integration method (NIM) by using the Lagrange form interpolating polynomial to approximate the delayed terms and construct a periodic discrete dynamical map for the damped Mathieu equation with time delays. Hence, we can obtain the Floquet transition matrices without matrix multiplication, which can reduce calculation time when the matrix inversed has a small bandwidth according to the computation based on MATLAB. To compare the calculation efficiency and computational accuracy between the updated and original methods, we compare the stability charts calculated by using three NIM methods for a damped Mathieu equation with multiple delays. To further confirm the efficiency of the presented method, we calculate the stability of the Mathieu equation with distributed delays and time-periodic delays, and then we compare the computational accuracy and calculation time with those of the semi-discretization method.     

大型非比例阻尼线性系统的地震反应复振型分析方法

对于大型非比例阻尼线性系统,当采用基于复振型的振型叠加方法进行动力反应分析时,按照通用算法(例如雅克比法)求解结构全部振型向量的计算工作量很大,甚至是不现实的.本文将经典阻尼系统中行之有效的Lanczos法和子空同迭代法加以推广和改进,给出了一组可对原来的方程进行自由度缩减的实向量基,然后与Foss变换相结合,得到一组实用的复向量基,使之适用于求解复杂非比例阻尼线性系统的任意低阶复振型和相应的复特征值,适用于任意扰力作用下的动力反应分析.理论推导和实例计算表明,本文所给出的复向量基概念清晰,计算效率高,能够适应对具有非比例阻尼特性的大型复杂结构进行动力分析的实际需要,其中包括地震作用下的时程分析和反应谱振型叠加分析.