Simulation of spatially coupling dynamic response of train-track time-variant system

There exist three problems in the calculation of lateral vibration of the train-track time-variant system athome and abroad and the method to solve them is presented. Spatially coupling vibration analysis model of train-track time-variant system is put forward. Each vehicle is modeled as a multi-body system with 26 degrees of freedomand the action of coupler is also considered. The track structure is modeled as an assembly of track elements with 30degrees of freedom, then the spatially coupling vibration matrix equation of the train-track time-variant system is es-tablished on the basis of the principle of total potential energy with stationary value and the "set-in-right-position"rule. The track vertical geometric irregularity is considered as the excitation source of the vertical vibration of thesystem, and the hunting wave of car bogie frame is taken as the excitation source of lateral vibration of the system.The spatially coupling vibration matrix equation of the system is solved by Wilson-θ direct integration method. Theapproximation of the calculated results to the spot test results demonstrates the feasibility and effectiveness of thepresented analysis method. Finally, some other vibration responses of the system are also obtained.

Analytical Modeling and Mechanism Analysis of Time-Varying Excitation for Surface Defects in Rolling Element Bearings

Surface defects,including dents,spalls,and cracks,for rolling element bearings are the most common faults in rotating machinery.The accurate model for the time-varying excitation is the basis for the vibration mechanism analysis and fault feature extraction.However,in conventional investigations,this issue is not well and fully addressed from the perspective of theoretical analysis and physical derivation.In this study,an improved analytical model for time-varying displacement excitations(TVDEs)caused by surface defects is theoretically formulated.First and foremost,the physical mechanism for the effect of defect sizes on the physical process of rolling element-defect interaction is revealed.According to the physical interaction mechanism between the rolling element and different types of defects,the relationship between time-varying displacement pulse and defect sizes is further analytically derived.With the obtained time-varying displacement pulse,the dynamic model for the deep groove bearings considering the internal excitation caused by the surface defect is established.The nonlinear vibration responses and fault features induced by surface defects are analyzed using the proposed TVDE model.The results suggest that the presence of surface defects may result in the occurrence of the dual-impulse phenomenon,which can serve as indexes for surface-defect fault diagnosis.

New Robust Exponential Stability Analysis for Uncertain Neural Networks with Time-varying Delay

In this paper,the global robust exponential stability is considered for a class of neural networks with parametric uncer- tainties and time-varying delay.By using Lyapunov functional method,and by resorting to the new technique for estimating the upper bound of the derivative of the Lyapunov functional,some less conservative exponential stability criteria are derived in terms of linear matrix inequalities (LMIs).Numerical examples are presented to show the effectiveness of the proposed method.

A New Robust Stabilization Analysis Result for Uncertain Systems with Time-Varying Delay

The robust stabilization problem for uncertain systems with time-varying delay has been discussed. A new sufficient criterion is obtained to guarantee the closed-loop system robust stabilizable. The controller gain matrix is included in a Hamiltonian matrix. The Hamiltonian matrix can be constructed by the boundedness of the uncertainties. Some examples are given to illustrate the feasibility of the criterion.

Nonlinear parametrically excited vibration and active control of gear pair system with time-varying characteristic

In the present work, we investigate the nonlinear parametrically excited vibration and active control of a gear pair system involving backlash, time-varying meshing stiffness and static transmission error. Firstly, a gear pair model is established in a strongly nonlinear form, and its nonlinear vibration characteristics are systematically investigated through different approaches. Several complicated phenomena such as period doubling bifurcation, anti period doubling bifurcation and chaos can be observed under the internal parametric excitation. Then, an active compensation controller is designed to suppress the vibration, including the chaos. Finally, the effectiveness of the proposed controller is verified numerically.

Science Letters:A minimax optimal control strategy for uncertain quasi-Hamiltonian systems

A minimax optimal control strategy for quasi-Hamiltonian systems with bounded parametric and/or external disturbances is proposed based on the stochastic averaging method and stochastic differential game. To conduct the system energy control,the partially averaged It stochastic differential equations for the energy processes are first derived by using the stochastic averaging method for quasi-Hamiltonian systems. Combining the above equations with an appropriate performance index,the proposed strategy is searching for an optimal worst-case controller by solving a stochastic differential game problem. The worst-case disturbances and the optimal controls are obtained by solving a Hamilton-Jacobi-Isaacs(HJI) equation. Numerical results for a controlled and stochastically excited Duffing oscillator with uncertain disturbances exhibit the efficacy of the proposed control strategy.

船舶推进轴系振动的不确定性分析

[目的]针对传统的船舶推进轴系确定性振动分析存在安全性与可靠性不足的问题,开展轴系在不确定性激励下的振动响应分析。[方法]采用基于非概率凸模型过程的非随机振动分析方法,以区间上下界的形式描述不确定性激励和振动响应,降低对大量激励样本数据的依赖。与相关文献的计算结果对比,验证所编求解二自由度系统响应边界程序的正确性,并基于在此,探究轴系的不确定振动问题。[结果]当轴系受到螺旋桨[-30 N,30 N]的横向激励力激励时,在轴承处产生了量级约为10-6m的位移响应,表明轴系受到某一区间的激励,则必会产生某一区间的响应。[结论]将基于非概率凸模型过程的非随机振动分析方法应用于船舶推进轴系不确定性振动分析领域,可求得轴系受到不确定性激励时的振动位移响应边界,并可在激励样本较少的情况下为提高轴系系统动态响应预测的稳健性提供有益参考。

Modal Parameter Identification Method of Jacket Platform Structure Based on AFDD and Optimized FBFFT

Offshore platforms are susceptible to structural damage due to prolonged exposure to random loads,such as wind,waves,and currents.This is particularly true for platforms that have been in service for an extended period.Identifying the modal parameters of offshore platforms is crucial for damage diagno sis,as it serves as a prerequisite and foundation for the process.Therefore,it holds great significance to prioritize the identification of these parameters.Aiming at the shortcomings of the traditional Fast Bayesian Fast Fourier Transform(FBFFT) method,this paper proposes a modal parameter identification method based on Automatic Frequency Domain Decomposition(AFDD) and optimized FBFFT.By introducing the AFDD method and Powell optimization algorithm,this method can automatically identify the initial value of natural frequency and solve the objective function efficiently and simply.In order to verify the feasibility and effectiveness of the proposed method,it is used to identify the modal parameters of the IASC-ASCE benchmark model and the j acket platform structure model,and the Most Probable Value(MPV) of the modal parameters and their respective posterior uncertainties are successfully identified.The identification results of the IASC-ASCE benc hmark model are compared with the identification re sults of the MODE-ID method,which verifies the effectivene ss and accuracy of the proposed method for identifying modal parameters.It provides a simple and feasible method for quantifying the influence of uncertain factors such as environmental parameters on the identification results,and also provide s a reference for modal parameter identification of other large structures.

自适应逆推励磁控制器设计

发电机的阻尼系数通常难以准确测量,使得电力系统是一个典型的参数不确定非线性系统。通过对含励磁控制的单机无穷大电力系统的精确反馈线性化,利用逆推控制与自适应机制相结合设计了逆推自适应励磁控制器。其所含的自适应增益控制可以对未知参数进行实时的估计, 该控制器能使参数不确定的电力系统保持在Lyapunov意义下的渐近稳定。仿真结果表明,该控制器能有效地稳定电力系统,维持机端电压。

相关激励作用下随机结构振动响应的统计分析

应用随机过程理论,以能量为变量,分析了随机结构振动响应的统计特性。结构受相关激励作用时,通过输入激励的解相关方法,将作用在结构上的相关激励转变为各个不相关激励的作用;分析结构的振动响应的统计特性时,计及响应特征频率的相关性,在响应特征频率满足高斯正交总体的假设下,推导出了随机结构振动响应分析的统计分析表达式。应用设计的实验件和试验验证了所提出的统计分析的正确性,通过和已存在的统计分析结果的比较,表明了统计分析具有更高的分析精度,能够定性和定量的给出随机结构振动响应的统计变化情况。

地震激励下参数不确定的相邻建筑结构重叠分散保性能混合控制方法

研究阐述了具有不确定结构参数的两个相邻建筑物在地震激励下的混合控制方法。利用包含原理和具有保证性能控制算法的重叠分散控制策略,提出了一种不确定参数结构系统的重叠分散保性能混合控制算法。基于包含原理,将一个大尺度结构分为一组具有共同部分的成对子结构,其共同部分即重叠的部分。使用保性能算法设计每个成对子结构的控制器,然后利用收缩原理,形成原系统的控制器。将重叠分散保性能混合控制算法应用于具有不确定参数的12层和9层两个相邻建筑物的振动控制问题,并与集中的保性能振动控制方法进行了比较,两种方法下结构层间位移的最大控制率分别为50%~60%和60%~70%。数值结果表明:对于具有不确定结构参数的两个相邻建筑物,该方法可以有效地抑制结构的动力响应,确保控制系统稳定性,提高了控制器设计的灵活性和可靠性。

随机过程激励下随机结构系统可靠度分析的一种方法

提出了随机过程荷载激励下，具有随机参数的结构系统可靠度分析的一种方法．该方法基于首次超越破坏机制，分析随机过程荷载激励下，结构参数（随机变量）取某一确定向量时的条件失效概率，采用ＭｏｎｔｅＣａｒｌｏ技术模拟结构参数的随机性，由条件失效概率给出随机结构的无条件失效概率．最后对文中方法和程序作了检验，并进行了实际计算．

给出不确定性激励下的动态响应边界--一种非随机振动分析方法

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.

参数不确定结构动态输出反馈重叠分散保性能控制方法

针对参数不确定建筑结构在地震激励下控制方法,采用重叠分散控制策略,提出了动态输出反馈的重叠分散保性能控制算法。基于包含原理,一个大尺度结构分为一组具有共同部分的成对子系统,使用保性能算法和线性矩阵不等式设计了子系统的控制器,然后利用收缩原理,形成原系统的控制器。利用提出的动态输出反馈重叠分散保性能控制方法,对20层Benchmark结构模型进行数值模拟分析,并与采用重叠分散LQG、状态反馈重叠分散、输出反馈集中保性能控制方法进行了分析对比。结果表明,提出控制算法能够降低地震激励下结构动力响应且保证了控制系统在结构参数摄动下的鲁棒性。

区间参数结构谐振载荷识别方法

将结构体系中的不确定性参数描述为区间变量,基于频域方法对在简谐激励作用下的不确定性结构进行了载荷识别。区间参数结构动态载荷识别过程包含两个层面,内层需要对不确定性参数单个样本作用下的结构进行载荷识别,而外层需要处理不确定性带来的影响以获得待识别载荷的上下界值。结果表明,基于确定性方法获得的载荷识别结果是考虑不确定性时载荷识别结果的子集,在结构设计时使用基于不确定性载荷识别结果将能够给出更为安全的结构设计方案。

不确定微分代数系统的多指标非线性鲁棒自适应控制方法

针对含不确定因素的多输入多输出微分代数系统,提出一种多指标非线性鲁棒自适应控制方法(multi-index nonlinear robust adaptive control,MINRAC),并将其应用于汽门开度与发电机励磁的协调控制上。数字仿真表明:在系统参数不确定和存在外部扰动的情况下,该方法能够使得系统的多个指标都运行在期望的工作点上而不发生静态偏移。对于不同类型的扰动,如有功功率阶跃,三相短路,该控制方法都能很好地镇定系统,并且能够消除机端电压偏差。与多指标非线性控制(multi-index nonlinear control,MINC)和多指标非线性鲁棒控制(multi-index nonlinear robust control,MINRC)相比,该文提出的方法能更好地兼顾系统的动静态性能。

参数不确定结构平稳随机响应虚拟激励摄动方法

基于虚拟激励法建立了平稳随机荷载作用下参数不确定结构随机响应分析的虚拟激励摄动方法.首先应用虚拟激励法将原复合随机问题精确地转化为单随机问题,进而推导了随机响应对不确定参数的灵敏度计算公式.随后由Taylor级数展开得到结构平稳随机响应对不确定性参数的摄动列式,并按数理统计方法得到响应的概率特征.最后应用建立的摄动方法计算了参数不确定空间桁架结构平稳随机响应方差的概率特征,与蒙特卡罗数值模拟进行对比验证了方法的正确性.

不确定性激励下碰摩转子的振动响应识别

应用伪周期替代数据算法分析受不确定性激励的碰摩故障转子振动响应,对故障信号进行识别和分类。在考虑非线性油膜力及碰摩力作用的基础上,建立有界噪声激励作用下碰摩故障转子系统动力学模型,对系统振动响应信号及其相应替代数据进行对比分析与识别,应用关联维数作为检验假设的判别统计量,并结合Poincaré截面图、最大Lyapunov指数及分岔图进行验证。结果表明,替代数据算法能够有效识别此类受随机不确定激励转子系统的周期占优与混沌占优响应信号,可进一步应用于受不确定性激励转子系统的信号识别与故障诊断研究。

Dynamic Characteristics Analysis with Multi-Directional Coupling in a TBM Mainframe

The cutterhead of a full-face rock tunnel boring machine(TBM)is constantly subjected to varying impact and dynamic loads during tunneling processes,resulting in relatively large vibrations that could easily lead to fatigue cracking of the entire machine and a ect the tunneling performance and efficiency.To explore the dynamic characteristics of the TBM mainframe,a TBM from a water-diversion project is investigated in this research.According to the TBM vibration transmission route,an equivalent dynamic model of the TBM mainframe is established using the lumped-mass method in which the relevant dynamic parameters are solved.Additionally,the dynamic response characteristics of the TBM mainframe are analyzed.The results indicate that the vibration levels in three directions are approximately the same,the multi-directional vibration of the cutterhead is more intense than that of other components,and the vibration and external excitation exhibit identical change trends.A set of vibration field tests is performed to analyze the in situ dynamic responses of the mainframe and verify the correctness of the dynamic model.The theoretical and measured acceleration values of the TBM mainframe have the same magnitude,which proves the validity of the dynamic model and its solution.The aforementioned results provide an important theoretical value and practical significance for the design and assessment of the TBM mainframe.

不确定结构非线性随机最优控制的鲁棒性

对地震地面运动引起的不确定剪切结构振动的非线性随机最优控制的鲁棒性进行了研究.基于系统参数不确定性与激励随机性的独立性假定,将具平均参数的名义结构进行模态变换解耦,运用拟可积哈密顿系统随机平均法与随机动态规划原理得到非线性随机最优控制力;利用随机平均法与概率分析估算受控的具有不确定参数结构的均方根响应、控制效果与控制效率的均值和标准差;以受控结构均方根响应、控制效果与控制效率的变差系数对不确定参数变差系数的敏感度作为鲁棒性评价指标,对非线性随机最优控制进行评价.通过对一个承受宽带随机基础激励的含不确定参数的三层剪切结构的数值计算与分析表明,该非线性随机最优控制策略对不确定参数具有很好的鲁棒性.