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对于具有非比例阻尼的多自由度线性振动系统的研究需要用到复模态理论.本文根据复模态有关理论,分析了复模态传递函数和频响函数的特性,定义了模态固有频率和模态阻尼比,导出了频响函数与复模态参数的解析关系式。在此基础上,介绍了由频响数据识别复模态参数的导纳圆拟合法.为了进一步提高模态识别精度,还论述了由加速度频响数据识别复模态参数的两种迭代方法:分步迭代法和整体迭代法.文中还以某航天器刚性太阳电池板模态试验为例,介绍了利用导纳圆拟合法联机模态识别枝术,给出了两种方法的模态识别结果,并进行了比较. 相似文献
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本文采用以模态迭加原理为基础的实模态分析技术及初参数优选法对汽车车架的模态参数进行了识别,讨论了振动特征值问题中关于非重特征值和重特征值的矩阵摄动法,提出了利用有弹性元件悬挂的结构振动测试数据来得到自由——自由结构的模态参数的摄动修正方法.文中还给出了一些数值例子来说明此方法的应用,同时得到了一些重要结论. 相似文献
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基于不完备频响函数数据,结合概率统计方法,提出了一种能同时考虑模型参数不确定性和测试噪声影响的结构损伤统计识别方法。首先,基于频响函数某一行向量在不同频率下的幅值数据,利用矩阵拉直运算建立了关于损伤系数的确定性识别方程。其次,假设模型参数误差和测试噪声为零均值的高斯随机变量,根据摄动理论,推导了损伤后结构刚度参数的前二阶矩。随后,利用结构损伤前后的概率分布得到了结构损伤存在概率。最后,通过一个平面桁架结构模型验证了本文方法的有效性。数值算例的研究结果表明,损伤单元的损伤存在概率远大于非损伤单元;测试噪声对识别结果的影响比模型参数不确定性的影响更为显著。 相似文献
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结构动力学中传递函数与模态参数识别 总被引:2,自引:1,他引:2
本文从任意粘性阻尼离散化线性结构系统的复模态理论出发,建立了结构系统传递函数与模态参数的一般解析关系式.在最优化方法基础上提出了两种传递函数和模态参数识别方法.用计算机试验、检验了两种识别算法的精度和使用范围.给出了真实结构识别全过程的实例. 相似文献
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结构动力学模型中阻尼特性参数的修正 总被引:1,自引:0,他引:1
将结构分析计算的稳态位移响应和相应实测数据的差异映射为具有能量意义的误差范数,通过最小化该误差范数来修正与结构系统有关的阻尼特性参数.通过计算的或实测的频响函数获得稳态响应数据,使用的幅值在理论上完全包含了所有的复模态信息,参数值正过程采用迭代的方式.给出仿真算例,并对实验数据有噪声和无噪声两种情况进行了研究,结果表明方法合理且可行. 相似文献
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对随机减量技术的数学表示 总被引:1,自引:0,他引:1
自1973年Cole提出随机减量技术,1977年Ibrahim加以发展推广,之后,在振动模态参数识别方面得到了成功的应用.本文推导了随机减量特征信号的数学表达式,这个表达式表明,随机减量特征信号和方差函数是完全等价的.本文计算了一个三自由度系统的例子来验证所导出的结论.还介绍了在振动参数识别中使用随机减量技术和方差函数的理论基础.对在不同场合使用的一些时域识别方法之间的关系给了证明. 相似文献
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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. 相似文献
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基于线黏弹性球面波Laplace域的理论解, 得到了不同传播距离处粒子速度、粒子位移、应力、应变等力学量的传递函数。以标准线性固体模型为例, 重点讨论了粒子速度频率响应函数的传播特征, 指出随着传播距离的增加, 粒子速度幅频响应函数的高频响应会低于低频响应, 而在理想弹性条件下, 粒子速度幅频响应函数的高频响应一直高于低频响应。以弹性半径为0.025 m的空腔爆炸为例, 采用Laplace数值逆变换方法对粒子速度波形的演化进行了分析, 给出了粒子速度强间断幅值及粒子速度峰值随传播距离变化的衰减规律曲线, 指出黏弹性介质中粒子速度幅值的衰减曲线介于理想弹性介质中粒子速度幅值衰减曲线和黏弹性介质中粒子速度强间断幅值衰减曲线之间。 相似文献
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密集模态挠性结构的模态不仅阻尼小而且耦合程度高,给模型辨识带来了很大困难.频域辨识是获取空间挠性结构模型的一个有效方法,但是目前频域辨识要么模型结构定义有缺陷,要么是集中在单变量情形,不适合作大型空间挠性结构多变量模型的辨识.本文提出了多变量极大似然频域辨识,给出了其模型结构定义、算法推导及实现,并将其应用于H型密集模态挠性板的模型辨识,根据辨识结果,设计主动控制律,实现了对密集模态挠性板振动的有效抑制,表明了辨识算法及主动控制的可行性. 相似文献
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This study is devoted to the experimental validation of a theoretical model of large amplitude vibrations of thin spherical
shells described in a previous study by the same authors. A modal analysis of the structure is first detailed. Then, a specific
mode coupling due to a 1:1:2 internal resonance between an axisymmetric mode and two companion asymmetric modes is especially
addressed. The structure is forced with a simple-harmonic signal of frequency close to the natural frequency of the axisymmetric
mode. The experimental setup, which allows precise measurements of the vibration amplitudes of the three involved modes, is
presented. Experimental frequency response curves showing the amplitude of the modes as functions of the driving frequency
are compared to the theoretical ones. A good qualitative agreement is obtained with the predictions given by in the model.
Some quantitative discrepancies are observed and discussed, and improvements of the model are proposed. 相似文献
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Pravesh Kumar 《基于设计的结构力学与机械力学》2020,48(1):48-67
AbstractHere, investigation to explore the effect of generic payload and externally applied asymmetric load on the calculation of modal parameters and dynamic performance of a rotating flexible manipulator under prismatic motion has been established. We thus have developed a dynamic model of a rotating Cartesian manipulator with a payload whose center of gravity doesn’t coincide with the point of attachment, to determine the modal parameters i.e., natural frequency and corresponding mode-shape. These modal parameters are then illustrated graphically upon varying parameters like offset parameters (i.e., offset mass, offset inertia, offset length), mass and stiffness of rotary actuator, and amplitude and frequency of asymmetric load. An investigation into the nonlinear dynamics of the system accounting of geometric nonlinearity has been executed while obtained results have been validated numerically within the permissible error at the assorted critical points in frequency characteristic curves. Current research further investigates the influences of offset parameters, mass and stiffness of the actuator, frequency and amplitude of axial force on the steady state responses for the primary and sub-harmonic resonance conditions to reveal the built-in saddle-node and pitchfork bifurcation due to which the system losses its structural stability. This work enables an insight into the modal characteristics and nonlinear behavior of a rotating-Cartesian manipulator with a generic payload under asymmetric axial force and prismatic motion. 相似文献
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Hassan Jalali Hamid Ahmadian John E. Mottershead 《International Journal of Solids and Structures》2007,44(25-26):8087-8105
Joints and fasteners often have a significant effect on the dynamical behaviour of assembled mechanical structures and the analytical prediction of structural responses therefore depends upon the accuracy of joint modelling. Detailed constitutive models that fully describe the behaviour of frictional interfaces are often unduly complicated; in which case simpler phenomenological models having parameters identified from vibration tests may be preferable. Unfortunately the direct measurement of forces transmitted between two contacting surfaces and their relative displacements are not possible in practice and it is therefore necessary to rely on measurements remote from joints. In this paper, the parameters of an assumed nonlinear joint model are identified by force-state mapping from time-domain acceleration records in response to single-frequency excitation close to the first natural frequency. The problem of lack of accessibility for measurement at the joint is overcome by casting the governing equation of the system in modal coordinates so that modal parameters are identified to represent the nonlinear behaviour of the joint. A particular result from the experimental programme is the identification of viscous damping coefficients dependent upon displacement amplitude. The significance of this result is that the complex phenomenon of energy dissipation in lap joints can be represented by a simple analytical model capable of producing accurate results. 相似文献
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Large amplitude periodic forced vibration of curved beams under periodic excitation is investigated using a three-noded beam element. The element is based on the higher-order shear deformation theory satisfying interlayer continuity of displacements and transverse shear stress, and top-bottom conditions on the latter. The periodic responses are obtained using shooting technique coupled with Newmark time marching and arc length continuation algorithm developed. The second order governing differential equations of motion are solved without transforming to the first order differential equations thereby resulting in a computationally more efficient algorithm. The effects of excitation amplitude, support conditions and beam curvature on the frequency versus response amplitude relation are highlighted. The typical frequency response curves for isotropic and cross-ply laminated curved beams are presented. Phenomenon of strong modal interactions is observed. 相似文献
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The frequency response characteristics of MIMO systems are investigated by using harmonic balance equations. For this purpose,
the algorithm for the automatic generation of harmonic balance equations is extended to include MIMO systems. Then the method
is applied to obtain the frequency response of an example model having two-input and two-output. Both the frequency response
and its harmonics are validated by numerical solutions. The effect of input amplitude variations and phase differences of
inputs on the frequency response are investigated. Direct computation of the resonance parameters depending on input amplitude
and phase variations are also obtained for the example system. 相似文献
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N. Nematipoor M. R. Ashory E. Jamshidi 《Archive of Applied Mechanics (Ingenieur Archiv)》2012,82(5):631-642
Vibration absorbers are usually designed using the finite element (FE) model of structures. It is generally believed that
the modal models are more accurate than FE models, because in modal testing the model is built by direct measurement of the
test structure. In this paper, a method is proposed to design a translational vibration absorber using the measured frequency
response functions of a primary structure. The designed vibration absorber imposes a node on the structure when it is excited
by a harmonic force. The method is based on the structural modification using experimental frequency response functions technique
and determines the required receptance of the absorber at the excitation frequency. Moreover, a procedure is developed to
suppress the vibration amplitude of two arbitrary points on a linear structure subjected to harmonic excitations by attaching
two sprung mass absorbers. A cantilever beam is considered for the numerical case study, and the sprung masses are designed
to suppress the vibration amplitude of the beam at the selected arbitrary points. A U-shape plate was considered for the experimental
validation of the method for imposing a node using one absorber. Also, a beam was tested to demonstrate the effectiveness
of method for imposing two nodes on the structures. The experimental results show that the designed absorbers can considerably
suppress the vibration amplitude at the selected points on the structure. 相似文献
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