自参数动力系统临界状态减振的非光滑方法

系统在达到稳态运动前通常要经历瞬态振动过程。瞬态振动对系统的影响是不可忽略的。在这个过程中作用于系统的激振力频率实际上是由零开始增加到某一工作频率。当激振力频率接近或超过系统的临界频率。系统发生共振，同时振幅达到峰值，并且此共振振幅通常要比系统的稳态振幅大的多。考虑到上述问题。文中分析了两种通过调制激振频率来实现降低临界振幅的方法，即让激振频率按单调线性增加或者分段线性增加到系统工作频率，通过系统相位的调制来实现减振。数值仿真结果表明上述方法能有效地降低临界振幅。同时上述方法工程实际应用中易于实现。     

大型离心叶轮振动模态局部化特性研究

为了研究目前工程中大型流体机械离心叶轮出现的局部疲劳破坏的机理,基于现有的有限元分析方法,结合模态分析等动力学理论以及叶轮所承受的气流激励,对其动力学特性进行了研究。着重研究了离心叶轮这类周期循环对称性结构具有的不同于非周期循环结构的特殊动力学性质以及该特殊的动力学特性与叶轮疲劳破坏的联系。研究发现其存在频率通带(passbands)、频率禁带(stopbands)现象,并出现了振动模态局部化现象。另外,叶轮的动力学特性对其周期性结构失谐特别敏感,该类失谐可来自由制造误差、材料和使用中磨损出现的不均匀等多种因素。对于协调结构,在一定条件下(如系统具有高密集模态),很小的失谐量(1%)就可使结构振动模态产生急剧变化,从而出现振动模态局部化现象。对于所研究的机组,当进口预旋器导致的流体激振频率(1166.7Hz)接近叶轮的由第12阶～18阶固有频率组成的禁带(1020.3～1054.5 Hz)时,数值分析结果显示叶片进口部位出现了振幅较大的振动,与该机组实际破坏的部位相符。研究结果表明所使用的振动模态局部化分析方法能够揭示叶轮发生疲劳破坏的原因,即是一类共振型疲劳破坏现象。     

斜拉索模态试验参数研究

试验模态分析是斜拉桥索力测试中广泛应用的方法。该方法的关键之一是采取合理的试验方案获取可靠的响应信号以识别出正确的索振动频率。本文通过试验,详细讨论了斜拉索模态测试中若干试验参数,如激振类型、激振位置、传感器位置以及频率分辨率对试验结果的影响;比较环境激励与锤击激励的效果,验证了环境激励的方法也可以准确识别索的频率;最后给出了较为合理的斜拉索模态试验方案,用该方案确定的索力与理论计算结果相差不超过 1. 5%。     

简谐荷载下橡胶隔震渡槽-水耦合体共振响应机理分析

采用计算流体力学（CFD）方法分析了在简谐激振作用下橡胶支座隔震渡槽槽-水耦合体的共振响应特性,并通过基于水体小幅晃动假设的槽水动力响应理论解进行了验证。结果表明：橡胶支座能将激振的高频分量隔离掉,使得槽-水耦合体不存在理论解所显示的高频共振问题;在接近水体一阶晃动频率的情况下容易发生共振响应;在以一阶水体自振频率的激振作用下,液面波高、动水压力、倾覆力、倾覆力矩均表现出随时间增长的共振放大现象,并且橡胶支座对耦合体的动力响应周期有一定的延长作用。本文对渡槽隔震设计选择隔震周期时,需要避开水体一阶晃动频率提供了参考依据。     

离心式叶轮流体激振响应及动态疲劳的研究

研究离心式叶轮的动力特性及流体激振下的稳态响应。讨论结构动态疲劳理论,认为流体激振激起了叶轮的共振,是动态疲劳,特点是激励频率高,幅值低,能量小,激起结构多个固有模态,主要是局部模态的共振。通过一个工程实际叶轮算例,研究动态疲劳破坏的机理。采用循环对称理论,计算叶轮的模态及离心力作用下的应力分布,对流体的压力脉动进行了频谱分析。将叶片表面的静压脉动作为载荷施加于叶轮上进行频率响应分析,得到叶轮在各频率成分激振力作用下的响应,最后根据频率响应的结果计算了叶轮的疲劳寿命,为叶轮疲劳破坏提供了分析依据和计算方法。     

与应变模态分析有关的若干问题

本文阐述了应变模态分析的基本原理及相应的参数识别方法，讨论了应变传递函数与应变模态振型、应变传递函数的性质，模态参数的识别以及应变传递函数与激振力谱、应变响应谱之间的关系。     

失谐整体叶盘多模态振动抑制的吸振器阵列方法

整体叶盘是新一代高性能航空发动机的关键部件,具有结构紧凑、重量轻和推重比高等优点,但也存在结构阻尼低、模态密度高和随机失谐问题,导致其通过共振区域时振幅大,显著影响整体叶盘结构的可靠性和疲劳寿命.为有效抑制失谐整体叶盘的多模态振动,提出一种由一系列吸振器环状布置而成的吸振器阵列减振方法,通过设置多组匹配不同模态的吸振器,实现对多模态共振峰值的抑制.为揭示吸振器阵列方法的多模态减振机理,采用具有代表性的集中参数模型构建整体叶盘-吸振器阵列系统的动力学分析模型,结合解析形式的功率流分析方法,分析吸振器质量、频率调谐精度、阻尼水平以及吸振器个数等关键参数对吸振器阵列减振性能的影响.搭建了吸振器阵列方法验证实验台,并通过实验验证了吸振器阵列方法的效果.分析结果表明:吸振器阵列方法能够有效控制叶片主导与叶片-轮盘耦合型模态,能够以较小的质量实现对谐调与失谐整体叶盘多模态共振的高效抑制,减振性能的鲁棒性较好.     

光纤传感器和压电作动片对薄板振动控制的分析

利用双模模态域光纤传感器的模间干涉感知薄板结构中应变的变化、获得薄板结构振动变化状况，进一步利用压电体作为动元件，减小振幅，实现振动的主动控制，采用振型叠加法和直接积分相结合的方法，从理论上论证薄板分别受到正弦波激振力，脉冲激振力和方波激振力时的振动主动控制，并由脉冲激振下的响应得到控制前后的幅频特性曲线和相频特性曲线．。     

汽车动力总成悬置系统振动解耦计算方法研究

目前,汽车发动机动力总成悬置系统设计的主要任务是选择悬置元件的刚度、位置和角度,使悬置系统自由振动模态频率避开发动机怠速激励力频率与车身自振频率,并尽量提高各模态振型的解耦程度,从而提高悬置系统隔振效果。悬置系统按预定频率严格解耦设计是使设计出的悬置系统模态频率完全等于按汽车设计频率规划预定的频率,并使各模态的振型严格解耦,即各向振动能量的解耦度等于1。本文从悬置系统的自由振动方程出发给出了对悬置系统按预定频率严格解耦设计的方程组,通过方程组构造函数进而求出该方程组的解,从而提供比当前的悬置系统模态优化设计更为简便高效的优化设计方法。相应的算例验证了本文提出的按预定频率严格解耦设计方程和求解方法的正确性。     

磁橡胶约束阻尼壳的宽频振动控制能力研究

不同于传统被动约束阻尼处理(PCLD),磁橡胶约束阻尼处理(MRLD)采用磁化的铁-橡胶混合粉末替代PCLD的粘弹性材料,不是通过粘结而是磁力吸附在钢制振动体上,在振动时交界面处发生滑移使部分能量转化为热能,从而降低振动.采用假设模态法计算PCLD的频率响应,再基于周期耗能相等原理.将MRID与PCLD等价,得到MRLD壳的模态损耗因子,研究了MRLD处理对简支壳阻尼的影响.分析结果表明:对于1000～3365Hz间前11阶模态频率的MRLD壳振动,当激振力低于16～20倍的起滑激励力F0时,MRLD均可获得比PCLD更好的阻尼;但各模态的F0的差异仅在3～4倍内;因此在前11阶模态频率范围内,激振力可以存在一个交集,在此交集内可同时引起各阶模态的阻尼层发生滑移,从而能控制壳的宽频振动.     

Convergence predictions for aeroelastic calculations of tuned and mistuned bladed disks

Mistuning changes the dynamics of bladed disks significantly. Frequency domain methods for predicting the dynamics of mistuned bladed disks are typically based on iterative aeroelastic calculations. Converged aerodynamic stiffness matrices are required for accurate aeroelastic results of eigenvalue and forced response problems. The tremendous computation time needed for each aerodynamic iteration would greatly benefit from a fast method of predicting the number of iterations needed for converged results. A new hybrid technique is proposed to predict the convergence history based on several critical ratios and by approximating as linear the relation between the aerodynamic force and the complex frequencies (eigenvalues) of the system. The new technique is hybrid in that it uses a combined theoretical and stochastic/computational approach. The dynamics of an industrial bladed disk is investigated, and the predicted convergence histories are shown to match the actual results very well. Monte Carlo simulations using the new hybrid technique show that the aerodynamic ratio and the aerodynamic gradient ratio are the two most important factors affecting the convergence history.     

失谐叶片-轮盘结构系统振动局部化问题的研究进展

对近２０年来国内外关于失谐叶片－轮盘结构系统振动局部化问题研究的进展进行了较为详细的评述和讨论,文中首先说明了振动局部化问题的基本概念,然后对失谐叶片－轮盘结构系统模态局部化和动态响应局部化在分析模型、求解方法及其基本性质和规律等方面的研究进展进行了较为全面的评述,最后提出了今后应深入研究的问题．     

Localization in Nonlinear Mistuned Systems with Cyclic Symmetry

In forced systems with cyclic symmetry localization can occur due toparameter uncertainties. Often, Monte-Carlo simulations are used to findregions, where the system response is sensitive to parameteruncertainties. These simulations require a large computation time.Therefore, an approximate method to calculate the envelopes of thefrequency response functions is developed in this paper. An example of anonlinear system with cyclic symmetry is a bladed disk assembly withfriction dampers. Friction dampers can be installed underneath the bladeplatforms of turbine blades. Due to dry friction and the relative motionbetween blades and dampers, energy is dissipated, which results in areduction of blade vibration amplitudes. By optimizing the mass of thefriction dampers, the best damping effects are obtained, which lead toan increase in the reliability of the turbine. In this paper, thecalculated response of a mistuned bladed disk assembly with frictiondampers is discussed. An approximate method is developed to calculatethe envelopes of the corresponding frequency response function forstatistically varying eigenfrequencies of the blades. Regions wherelocalization can occur with a high probability, are calculated by thismethod.     

The worst response of mistuned bladed disk system using neural network and genetic algorithm

The objective of this paper is to develop an integrated approach using artificial neural networks (ANN) and genetic algorithms (GA) for predicting the worst response of mistuned bladed disk. ANN is used to predict the responses of bladed disk system which are used further in evaluation of fitness and constraint violation in GA process. A multilayer back-propagation neural network is trained with the results obtained from finite element model for different bladed disk configurations. Subsequently, GA is employed for arriving at optimum configuration of the bladed disk system by maximizing the blade responses. By integrating ANN with GA, the computational time required for obtaining optimal solution could be reduced substantially. The efficacy of this approach is demonstrated by carrying out studies on mistuned bladed disk systems for different sets of mistuning parameters, namely mistuning in modulus of elasticity and length of blades. Finally, the effect of adding shroud at the tip of blades in reducing the maximum response of the bladed disk system was investigated.     

Nonlinear dynamics of mistuned bladed disks with ring dampers

In turbomachinery applications, rotating bladed disks (blisks) are often subject to high levels of dynamic loading, such as traveling wave excitations, which result in large response amplitudes at resonance. To prevent premature high cycle fatigue, various dry friction dampers are designed for blisk systems to reduce the forced responses. Ring dampers are located in the disk, underneath the blades, and are held in contact with the blisk by centrifugal loading. Energy is dissipated by nonlinear friction forces when relative motions between the ring damper and the blisk take place. To investigate the dynamic responses of blisk–damper systems in the presence of the nonlinear frictional contacts, conventional methods based on numerical time integration are not suitable since they are computationally expensive. This paper presents a reduced-order modeling technique to efficiently capture the nonlinear dynamic responses of the blisk–damper systems. Craig–Bampton component mode synthesis (CB-CMS) serves as the first model reduction step. A novel mode basis that mimics the contact behavior under sliding and sticking conditions is developed to further reduce the CB-CMS model while maintaining its accuracy. The resulting reduced nonlinear equations of motion are solved by a hybrid frequency/time domain (HFT) method. In the HFT method, the contact status and friction forces are determined in the time domain by a three-dimensional contact model at each contact point, whereas the reduced equations of motion are solved in the frequency domain according to a harmonic balance formulation. Moreover, to investigate the effects of blade mistuning, which can lead to drastic increase of forced responses, an extension of the reduced-order models (ROMs) is developed based on component mode mistuning. Forced responses computed by the proposed ROMs are validated for both tuned and mistuned systems. A statistical analysis is performed to study the effectiveness of ring dampers under random blade mistuning patterns.     

Fully suspended, five-axis, three-magnetic-bearing dynamic spin rig with forced excitation

A significant advancement in the dynamic spin rig (DSR), i.e., the five-axis, three-magnetic-bearing DSR, is used to perform vibration tests of turbomachinery blades and components under rotating and non-rotating conditions in a vacuum. The rig has three magnetic bearings as its critical components: two heteropolar radial active magnetic bearings and a magnetic thrust bearing. The bearing configuration allows full vertical rotor magnetic suspension along with a feedforward control feature, which enables the excitation of various modes of vibration in the bladed disk test articles. The theoretical, mechanical, electrical, and electronic aspects of the rig are discussed. Also presented are the forced-excitation results of a fully levitated, rotating and non-rotating, unbladed rotor and a fully levitated, rotating and non-rotating, bladed rotor in which a pair of blades were arranged 180° apart from each other. These tests include the “bounce” mode excitation of the rotor in which the rotor was excited at the blade natural frequency of 144 Hz. The rotor natural mode frequency of 355 Hz was discerned from the plot of acceleration versus frequency. For non-rotating blades, a blade-tip excitation amplitude of approximately 100 g A⁻¹ was achieved at the first-bending critical (≈144 Hz) and at the first-torsional and second-bending blade modes. A blade-tip displacement of 1.778×10⁻³m (70 mils) was achieved at the first-bending critical by exciting the blades at a forced-excitation phase angle of 90° relative to the vertical plane containing the blades while simultaneously rotating the shaft at 3000 rpm.     

Qualitative analysis of forced response of blisks with friction ring dampers

A damping strategy for blisks (integrally bladed disks) of turbomachinery involving a friction ring is investigated. These rings, located in grooves underside the wheel of the blisks, are held in contact by centrifugal loads and the energy is dissipated when relative motions between the ring and the disk occur. A representative lumped parameter model of the system is introduced and the steady-state nonlinear response is derived using a multi-harmonic balance method combined with an AFT procedure where the friction force is calculated in the time domain. Numerical simulations are presented for several damper characteristics and several excitation configurations. From these results, the performance of this damping strategy is discussed and some design guidelines are given.     

CFRP索斜拉桥的结构动态测试研究与分析

为获知CFRP索斜拉桥的动力特性,推动CFRP索斜拉桥在我国的发展并积累经验,对国 内首座CFRP索斜拉桥分别进行了基于环境激励和锤击激励的结构动态特性测试研究,对不同 测试方案的试验结果进行了对比分析,结果表明脉动测试与锤击激励测试结果在对应的频率 值误差小、振型相似;环境激励测试法从测试的可行性、方便性及测试所得频率成分的组成 上较锤击激励测试法更为丰富.     

A new study of chaotic behavior and the existence of Feigenbaum’s constants in fractional-degree Yin–Yang Hénon maps

hing dynamics in a square tank are numerically investigated when the tank is subjected to horizontal, narrowband random ground excitation. The natural frequencies of the two predominant sloshing modes are identical and therefore 1:1 internal resonance may occur. Galerkin’s method is applied to derive the modal equations of motion for nonlinear sloshing including higher modes. The Monte Carlo simulation is used to calculate response statistics such as mean square values and probability density functions (PDFs). The two predominant modes exhibit complex phenomena including “autoparametric interaction” because they are nonlinearly coupled with each other. The mean square responses of these two modes and the liquid elevation are found to differ significantly from those of the corresponding linear model, depending on the characteristics of the random ground excitation such as bandwidth, center frequency and excitation direction. It is found that the direction of the excitation is a significant factor in predicting the mean square responses. The frequency response curves for the same system subjected to equivalent harmonic excitation are also calculated and compared with the mean square responses to further explain the phenomena. Changing the liquid level causes the peak of the mean square response to shift. Furthermore, the risk of the liquid overspill from the tank is discussed by showing the three-dimensional distribution charts of the mean square responses of liquid elevations.