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1.
One of the present barriers to the realization of structural health monitoring is the lack of efficient and general identification methodologies for dealing with nonlinearity, because a priori knowledge of the nature and mathematical form of the nonlinearities of typical engineering structures are usually unknown. The studies on the identification of restoring force, which can be considered as a direct indicator of the extent of the nonlinearity, have received increasing attention in recent years. In this paper, the nonlinear restoring force (NRF) was estimated by using a power series polynomial, and each coefficient of the polynomial was identified by means of standard least-square techniques. No information about the system was needed, and only the applied excitations and the corresponding response time series were used for the identification. Two different cases, in which the system was under complete and incomplete excitations, were investigated. Moreover, the effect of noise level was also taken into consideration. The feasibility and robustness of the proposed approach were verified via a 2-degree-of-freedom (DOF) lumped-mass numerical model, and experimental tests on a 4-story shear building with magneto-rheological (MR) dampers which served to simulate nonlinear behavior. The results show that the proposed data-based method is capable of identifying the NRF in a chain-like multi-degree-of-freedom engineering structures without any assumptions on the structural parameters, and provides a promising way for damage detection in the presence of structural nonlinearities.  相似文献   

2.
《Comptes Rendus Mecanique》2017,345(6):386-398
Vibrations are classified among the major problems for engineering structures. Anti-vibration isolators are used to absorb vibration energy and minimise transmitted force which can cause damage. The isolator is modelled as a parallel combination of stiffness and damping elements. The main purpose of the model is to enable designers to predict the dynamic response of systems under different structural excitations and boundary conditions. A nonlinear identification method, discussed in this paper, aims to provide a tool for engineers to extract information about the nonlinear dynamic behaviour using measured data from experiments. The proposed method is demonstrated and validated with numerical simulations. Thus, this technique is applied to determine the nonlinear parameters of a commercial metal mesh isolator. Nonlinear stiffness and nonlinear damping can decrease with the increase in the amplitude of the base excitation. The softening behaviour of the mesh isolator is clearly visible.  相似文献   

3.
A new procedure for designing optimal bounded control of stochastically excited multi-degree-of-freedom (MDOF) nonlinear viscoelastic systems is proposed based on the stochastic averaging method and the stochastic maximum principle. First, the system is formulated as a quasi-integrable Hamiltonian system with viscoelastic terms and each viscoelastic term is replaced approximately by an elastically restoring force and a visco-damping force based on the randomly periodic behavior of the motion of quasi-integrable Hamiltonian system. Thus, a stochastically excited MDOF nonlinear viscoelastic system is converted to an equivalent quasi-integrable Hamiltonian system without viscoelastic terms. Then, by applying stochastic averaging, the system is further reduced to a partially averaged system of less dimension. The adjoint equation and maximum condition for the optimal control problem of the partially averaged system are derived by using the stochastic maximum principle, and the optimal bounded control force is determined from the maximum condition. Finally, the probability and statistics of the stationary response of optimally controlled system are obtained by solving the Fokker–Plank–Kolmogorov equation (FPK) associated with the fully averaged Itô equation of the controlled system. An example is worked out to illustrate the proposed procedure and its effectiveness.  相似文献   

4.
Health monitoring and damage detection strategies for base-excited structures typically rely on accurate models of the system dynamics. Restoring forces in these structures can exhibit highly non-linear characteristics, thus accurate non-linear system identification is critical. Parametric system identification approaches are commonly used, but require a priori knowledge of restoring force characteristics. Non-parametric approaches do not require this a priori information, but they typically lack direct associations between the model and the system dynamics, providing limited utility for health monitoring and damage detection. In this paper a novel system identification approach, the intelligent parameter varying (IPV) method, is used to identify constitutive non-linearities in structures subject to seismic excitations. IPV overcomes the limitations of traditional parametric and non-parametric approaches, while preserving the unique benefits of each. It uses embedded radial basis function networks to estimate the constitutive characteristics of inelastic and hysteretic restoring forces in a multi-degree-of-freedom structure. Simulation results are compared to those of a traditional parametric approach, the prediction error method. These results demonstrate the effectiveness of IPV in identifying highly non-linear restoring forces, without a priori information, while preserving a direct association with the structural dynamics.  相似文献   

5.
建筑结构爆破地震反应弹塑性精细时程分析   总被引:1,自引:0,他引:1  
针对爆破地震作用下建筑结构的安全评估问题,提出利用时程分析方法全面评估爆破地震波的安全度;建立了基于精细积分算法的结构弹塑性动力分析架构模式,编制了建筑结构爆破地震反应弹塑性精细时程分析程序;通过算例验证了该算法的准确性与高效性,弹性时程分析与不同恢复力模型弹塑性时程分析的结果曲线具有类似特征和数值差异;建议选择合理的恢复力模型,使用弹塑性时程分析方法模拟爆破地震作用下结构的动力响应,全面评估爆破地震波的安全性。  相似文献   

6.
The detection of structural damages real-time on-line, based on vibration data measured from sensors, is an important but challenging research topic, and it has received considerable attentions recently. Due to practical limitations, it is highly desirable to install as few sensors as possible in the structural health monitoring system, leading to incomplete measurements of structural responses and excitations. The traditional time-domain analysis techniques, such as the least-square estimation (LSE) method and the extended Kalman filter (EKF) approach, require that all the external excitations (inputs) be available, which may not be the case for most structural health monitoring systems. Recently, the adaptive sequential non-linear least-square estimate (SNLSE) method has been proposed for the on-line identification of structural damages. In this paper, we extend the SNLSE method to cover the general case with unknown (unmeasured) excitations (inputs) and unknown (unmeasured) acceleration responses (outputs) in order to reduce the number of sensors required in the structural health monitoring system, referred to as the SNLSE-UI-UO. Analytic recursive solutions for the new approach are derived and presented. The accuracy and effectiveness of the proposed approach have been demonstrated using the Phase I ASCE structural health monitoring benchmark building, a 5-degree-of-freedom non-linear hysteretic building model, and a 3-story steel frame finite-element model. Simulation results indicate that the proposed approach is capable of tracking the changes of structural parameters leading to the identification of damages.  相似文献   

7.
基于残余力向量法和改进遗传算法的结构损伤识别研究   总被引:2,自引:0,他引:2  
提出了一种基于残余力向量法和改进遗传算法的结构损伤识别方法。文中首先对残余力向量法和遗传算法的基本理论进行了介绍。在无噪声的情况下,使用任意一阶模态数据,残余力向量法都能够对损伤进行准确定位。但是,振动测试数据中往往包含噪声,导致运用残余力向量法进行损伤识别完全不可行。考虑到这个问题,在常规模态分析的基础上,以节点的残余力向量构造用于遗传搜索优化的目标函数形式,然后利用改进的遗传算法重点进行了噪声条件下的结构损伤定位和定量研究。最后,本文用一个平面桁架模型进行了数值模拟,验证了所提出方法的有效性,并对方法应用中存在的一些问题进行了深入分析,得出了一些有益的结论。  相似文献   

8.
姜潮  刘宁宇  倪冰雨  韩旭 《力学学报》2016,48(2):447-463
提出了一种非随机振动分析方法,可给出系统在不确定性激励下的动态响应边界,从而为实验信息相对缺乏的不确定性振动分析及未来的可靠性设计提供一种新的计算工具.采用非概率凸模型过程而非传统的随机过程描述不确定性动态激励,仅需知道激励在任意时刻点的边界信息而非精确概率分布,从而有效降低对大样本量的依赖性.针对单自由度和多自由度系统,建立了相应的非随机振动分析算法,以求解系统在不确定性动态激励下的响应区间;另外,也给出了蒙特卡罗仿真方法,为非随机振动提供一种最为一般的分析工具.最后,通过3个数值算例验证了本文方法的有效性.非随机振动分析方法可以作为传统随机振动理论的补充,在工程不确定性结构动力学分析及结构可靠性设计领域发挥作用.  相似文献   

9.
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。  相似文献   

10.
In this paper describing functions inversion is used and the restoring force of a nonlinear element in a MDOF system is characterized. The describing functions can be obtained using linearized frequency response functions (FRFs). The response of the system to harmonic excitation forces at distinct frequencies close to the resonant frequency results in linearized FRFs. The nonlinear system can be approximated at each excitation frequency by an equivalent linear system. This approximation leads to calculation of the first-order describing functions. By having the experimental describing functions calculated and the system’s responses corresponding to the nonlinear element (measured or interpolated), nonlinear parameter identification can be performed. Two numerical and experimental case studies are provided to show the applicability of this method.  相似文献   

11.
随机最优控制方法识别动力学系统局部非线性   总被引:1,自引:0,他引:1  
利用随机动态规划方法可以得到线性二次型高斯问题的最优控制解.基于这一结果与系统辨识问题最优控制解的概念,将动力学系统中局部非线性结构参数的辨识问题转化为求解对应线性系统的最优控制问题,利用线性系统随机最优控制的理论与方法,结合FSM(ForceStateMapping)方法,提出了识别动力学系统中局部非线性回复力类型及结构参数的新方法.所研究系统由大的线性子结构与一个或多个非线性子结构组成,其中线性结构的模型参数已知,待辨识量为局部非线性结构参数.  相似文献   

12.
Based on the elasto-plastic mechanics, the damage analysis and dynamic response of an elasto-plastic laminated composite shallow spherical shell under low velocity impact are carried out in this paper. Firstly, a yielding criterion related to spherical tensor of stress is proposed to model the mixed hardening orthotropic material, and accordingly an incremental elasto-plastic damage constitutive relation for the laminated shallow spherical shell is founded when a strain-based Hashin failure criterion is applied to assess the damage initiation and propagation. Secondly, using the presented constitutive relations and the classical nonlinear shell theory, a series of incremental nonlinear motion equations of orthotropic moderately thick laminated shallow spherical shell are obtained. The questions are solved by using the orthogonal collocation point method, Newmark method and iterative method synthetically. Finally, a modified elasto-plastic contact law is developed to determine the normal contact force and the effect of damage, geometrical parameters, elasto-plastic contact and boundary conditions on the contact force and the dynamic response of the structure under low velocity impact are investigated.  相似文献   

13.
残余力向量法是一类常用的损伤识别方法,现有的残余力向量法都是基于动力测试的模态参数,和动力测试数据相比,静力测试数据往往精度更高,且无需模态分析等复杂操作.鉴于此,本文提出一种静力残余力向量法用于结构损伤评估.所提方法利用静力测试位移数据,并结合结构有限元模型的刚度矩阵,定义了静力残余力向量,根据该向量中不为零的元素来判断损伤自由度,再根据自由度和单元之间的对应关系来确定发生损伤的位置,并进一步提出一种求解损伤参数的代数解法.另外,针对实践中角位移难以测量的情况,进一步提出了一种静力缩聚残余力向量法,拓宽了所提方法的应用范围.以桁架结构和梁结构模型为例对所提方法进行了验证,数值算例结果说明所提方法合理有效.  相似文献   

14.
张颖  王伟  曹军义 《力学学报》2021,53(11):2984-2995
混沌和分岔使得多稳态俘能系统的非线性动力学响应对系统结构参数非常敏感, 导致了系统的非线性特性正向设计比较困难. 为了定量地表征非线性恢复力与结构参数的关系, 提出了一种多稳态俘能系统的准确磁力建模方法. 推导了多稳态俘能系统端部磁铁和外部磁铁的相对距离和转角位置, 并采用磁荷理论建立了多稳态系统的非线性磁力模型. 通过搭建实验平台测量了不同结构参数条件下多稳态系统的非线性磁力, 并对比了本方法与传统方法和实验测量的结果. 结果表明: 本方法的磁力计算结果与实验测量值吻合较好, 双稳态系统和三稳态系统的磁力峰值误差分别仅为4.3%和6.49%, 验证了本方法计算多稳态系统非线性磁力的有效性. 此外, 基于本方法探究了多稳态系统结构参数对系统势阱的影响机理, 获取了多稳态系统的稳态临界位置, 研究了双稳态和三稳态系统在不同结构参数下的响应电压规律. 参数优化结果表明, 双稳态系统在竖直距离为34 mm时, 均方电压最大为10.22 V; 三稳态系统在竖直距离为28 mm且水平距离为8 mm时, 均方电压最大为12.7 V. 该研究提出的模型以期为多稳态系统的输出性能优化设计提供借鉴.   相似文献   

15.
Taking into account surface coatings painted on disc and casing, a nonlinear rotor system is established for simulating unbalance-rubbing coupled fault. During the modeling process of shaft, the nonlinear geometric relation between displacement and strain is considered. According to the Hamilton's principle, the restoring force between disc and shaft is described by the equivalent spring and the equivalent damper, and then the equivalent dynamic model is further set up. For contact analysis, the novel contact force model is employed to describe the impact force between disc and casing. Meanwhile, the Coulomb model is used to simulate the frictional force. The motion equations of the equivalent dynamic model are solved numerically and the corresponding dynamic behaviors are analyzed by bifurcation diagram, whirl orbit and Poincaré map. The relationship between equivalent linear/nonlinear stiffness and structural parameters is analyzed in detail. Moreover, the effects of eccentricity of disc, surface coatings and radius of shaft on the dynamic characteristic of the equivalent model are discussed.  相似文献   

16.
A stochastic minimax semi-active control strategy for multi-degrees-of-freedom (MDOF) strongly nonlinear systems under combined harmonic and wide-band noise excitations is proposed. First, a stochastic averaging procedure is introduced for controlled uncertain strongly nonlinear systems using generalized harmonic functions and the control forces produced by Magneto-rheological (MR) dampers are split into the passive part and the active part. Then, a worst-case optimal control strategy is derived by solving a stochastic differential game problem. The worst-case disturbances and the optimal semi-active controls are obtained by solving the Hamilton–Jacobi–Isaacs (HJI) equations with the constraints of disturbance bounds and MR damper dynamics. Finally, the responses of optimally controlled MDOF nonlinear systems are predicted by solving the Fokker–Planck–Kolmogorov (FPK) equation associated with the fully averaged Itô equations. Two examples are worked out in detail to illustrate the proposed control strategy. The effectiveness of the proposed control strategy is verified by using the results from Monte Carlo simulation.  相似文献   

17.
For the difficulty that the information vector in the identification model contains the unknown variables, we substitute these unknown variables with the outputs of the auxiliary model and then develop an auxiliary model based recursive least squares algorithm, an auxiliary model based least squares iterative (AM-LSI) algorithm, and derive an equivalent matrix decomposition based AM-LSI algorithm for input nonlinear controlled autoregressive systems based on the auxiliary model. The simulation results show that the proposed algorithms can estimate the parameters of a class of input nonlinear systems.  相似文献   

18.
给出了一种基于系统能量函数辨识的静电致动微薄板系统自由度缩减建模方法.从Von Karman应变-位移关系式出发,推导出以广义模态坐标为变量的系统动能、应变能以及电容函数的函数表达式.为了将应变能以及电容函数写成广义模态坐标的多变量多项式形式,利用一系列经静态非线性结构有限元计算的结果,拟合得到多变量多项式的未知系数.由Lagrangian方程获得原系统的自由度缩减模型.利用该模型对器件的静/动态特性进行仿真,其计算费用很低.与有限元结果比较,验证了建模方法的正确性.  相似文献   

19.
Mechanical systems are often nonlinear with nonlinear components and nonlinear connections, and mechanical damage frequently causes changes in the nonlinear characteristics of mechanical systems, e.g. loosening of bolts increases Coulomb friction nonlinearity. Consequently, methods which characterize the nonlinear behavior of mechanical systems are well-suited to detect such damage. This paper presents passive time and frequency domain methods that exploit the changes in the nonlinear behavior of a mechanical system to identify damage. In the time domain, fundamental mechanics models are used to generate restoring forces, which characterize the nonlinear nature of internal forces in system components under loading. The onset of nonlinear damage results in changes to the restoring forces, which can be used as indicators of damage. Analogously, in the frequency domain, transmissibility (output-only) versions of auto-regressive exogenous input (ARX) models are used to locate and characterize the degree to which faults change the nonlinear correlations present in the response data. First, it is shown that damage causes changes in the restoring force characteristics, which can be used to detect damage. Second, it is shown that damage also alters the nonlinear correlations in the data that can be used to locate and track the progress of damage. Both restoring forces and auto-regressive transmissibility methods utilize operational response data for damage identification. Mechanical faults in ground vehicle suspension systems, e.g. loosening of bolts, are identified using experimental data.  相似文献   

20.
Unified 2D continuum formulation of the nonlinear dynamic problem for a von Kármán shear indeformable symmetric cross-ply composite plate in a thermomechanical environment is presented, along with the ensuing reduction procedure ending up to a three-mode discretized model with unknown transverse displacement and membrane/bending temperatures. Systematic numerical analyses in the case of thermal dynamics passively entrained by the solely active mechanical excitations allow to unveil the main features of the nonlinear response, while highlighting fundamental aspects associated with the thermomechanical coupling. Local and global dynamics of a single-layer orthotropic plate are investigated under varying in-plane/transverse excitations or thermal property of the material. Comparison with the response provided by partially coupled models and the uncoupled mechanical oscillator enables to identify situations in which thermomechanical coupling affects the nonlinear response even in the solely passive thermal setting and to frame the relevant effects within known literature results.  相似文献   

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