基于Hoff夹层板理论计算约束阻尼结构的结构损耗因子

利用Hoff夹层板理论研究约束阻尼结构的固有频率和模态损耗因子的计算问题.计算结果表明,利用Hoff理论计算约束阻尼结构固有频率和模态损耗因子方法具有较高的计算精度,与Ansys计算结果较为接近,可用于约束阻尼结构固有频率和结构损耗因子计算.     

Identification of modal parameters of unmeasured modes using multiple FRF modal analysis method

Current modal analysis methods seek to identify the modal parameters of some or all of the modes in the measured frequency range of interest. In many applications however, it will be very useful if modal parameters of some of the out-of-range modes can be identified during modal analysis. Such a goal is obviously theoretically possible since the raw measured frequency response functions (FRFs), upon which modal analysis is performed, do contain adequate information about the out-of-range modes in the form of residue contributions. In this paper, a new method for the estimation of modal parameters using multiple FRFs analysis is presented. In the process of modal identification, the proposed method not only presents accurate modal parameters of the modes which are present in the measurement frequency range, but also quite accurately identifies some of the modes which are not measured. The method calculates the required modal parameters by solving eigenvalue problem of an equivalent eigensystem derived from those measured FRF data. All measured FRFs are used simultaneously to construct the equivalent eigensystem matrices from which natural frequencies, damping loss factors and modeshape vectors of interest are solved. Since the identification problem is reduced to an eigenvalue problem of an equivalent system, natural frequencies and damping loss factors identified are consistent. Applications of the method to both numerically simulated and practically measured FRF data are given to demonstrate the practicality of the proposed method and the results have shown the method is capable of accurately identifying modal parameters of out-of-range modes.     

基于传递率函数的运行模态分析方法

传统的运行模态分析方法在推导过程中多假设激励为白噪声,造成在应用上有一定的局限性。提出了一种基于传递率函数的运行模态分析方法,无需采用白噪声假设,利用两种不同载荷情况下的传递率函数构造有理函数,通过有理分式Forsythe正交多项式法对其进行拟合,得到模态频率、阻尼和振型参数。最后,采用机翼模型仿真算例和悬臂梁实验,验证了在非白噪声激励情况下该方法的有效性与可靠性。     

汽车水泵总成的动态特性研究

利用有限元软件Ansys模态分析功能,在对某汽车水泵总成建立三维实体模型的基础上,对其进行约束模态分析,计算汽车水泵总成的前7阶固有频率和相应振型,并与试验模态相比较,证明计算模型的合理性。通过模态分析为该水泵的结构优化提供理论依据,并为解决汽车水泵总成的泄漏问题提出改进措施。     

A DUAL FITTING ALGORITHM FOR MODAL PARAMETERS IDENTIFICATION

A dual fitting algorithm (DFA) for modal parameters identification is presented. The method is implemented in three steps: first, the coefficients of the Forsythe orthogonal polynomials for the rational fraction of the frequency response functions (FRFs) are obtained by fitting the experimental FRF data; then the coefficients of the orthogonal polynomials are converted into the coefficients of ordinary power polynomials by the fitting method again; and finally, the poles and residues of the rational fraction of FRFs in ordinary power polynomials are extracted to identify the modal parameters. Some notes to the definition and use of the recurrence formulation for the real half-function Forsythe orthogonal polynomials are introduced. An example is given to show the aspects of the present method.     

登高消防车臂架的有限元分析与优化研究

针对传统力学方法校核登高消防车臂架的强度和刚度计算繁琐且精度低、臂架设计过厚、登高消防车上装系统笨重、在使用过程中容易出现倾翻等问题,对臂架的静动态特性和臂架的截面参数化优化进行了研究,提出了将有限元法应用到臂架的静力学分析和模态分析中,快速精确地计算臂架在两种极限恶劣工况下的强度和臂架的前4阶固有频率及其对应的振型;将参数化有限元法与多约束非线性二次规划法有机结合应用到臂架的截面参数化优化中,让优化迭代算法融入有限元分析的全过程,快速搜索全局的最优解。研究结果表明,臂架截面参数化优化后最大等效应力减少了7.3 MPa,臂架体积减少了16.5%,实现了臂架的轻量化。     

基于信号时频分析理论识别时变模态参数的实验

为研究温度对结构模态参数的影响设计了一套温度可控的实验设备。在这套实验设备提供的可控温度环境中采集悬臂梁结构的加速度响应信号,利用基于信号时频分析的模态参数辨识算法处理实验数据,得到其时变模态参数,包括固有频率和振型,以此研究温度对其模态参数的影响。分析结果显示了基于信号时频分析的模态参数辨识算法在处理非平稳信号以得到结构的时变模态参数上的应用前景,更重要的是实验数据的分析结果较好地反映了温度对结构模态参数的影响,为热环境下结构振动特性分析提供了可靠而且有价值的分析方法和实验依据。     

一种新的固有频率跟踪及虚假频率剔除方法

针对时变参数辨识中常见的固有频率辨识和虚假频率剔除问题,引入了一种基于新信息准则的子空间跟踪辨识算法,结合实验提出了一种消除虚假固有频率的后处理方法。首先,利用基于新信息准则的子空间跟踪算法辨识出伪时变模态参数;其次,通过聚类方法估计各阶伪固有频率;最后,利用滑动的数据窗比对数据剔除虚假频率。该方法仅需要给出预估的活动模态数即可。不同频率变化形式的仿真算例结果证明了本研究方法较其他辨识算法在信号信噪比较低时具有较高的辨识精度。高温环境下的时变模态实验也验证了该方法的可行性,说明该方法在实际工程中具有较高的应用价值。     

Scaling-factor estimation using an optimized mass-change strategy

In operational modal analysis, only unscaled mode shapes can be obtained. The mass-change method is in many cases the simplest way to estimate the scaling factors, which involves repeated modal testing after changing the mass at different points of the structure where the mode shapes are known. With this method, the scaling factors are determined using the natural frequencies and mode shapes of both the modified and the unmodified structure. However, the uncertainty on the scaling-factor estimation depends on the modal-analysis accuracy and the mass-change strategy (number, magnitude, and location of the masses) used to modify the dynamic behavior of the structure. In this paper, a procedure to optimize the mass-change strategy is proposed, which uses the modal parameters (natural frequencies and mode shapes) of the original structure as the basic information.     

轴向运动简支-固支梁的横向振动和稳定性

研究一端简支一端固支轴向运动梁的横向振动和稳定性。提出在给定边界条件下确定一匀速运动梁固有频率和模态函数的方法。当轴向运动速度在其常平均值附近作简谐波动时,应用多尺度法给出轴向变速运动梁参数共振时的不稳定条件。用数值仿真说明相关参数对固有频率和不稳定边界的影响。     

Modal identification of spindle-tool unit in high-speed machining

The accurate knowledge of high-speed motorised spindle dynamic behaviour during machining is important in order to ensure the reliability of machine tools in service and the quality of machined parts. More specifically, the prediction of stable cutting regions, which is a critical requirement for high-speed milling operations, requires the accurate estimation of tool/holder/spindle set dynamic modal parameters. These estimations are generally obtained through Frequency Response Function (FRF) measurements of the non-rotating spindle. However, significant changes in modal parameters are expected to occur during operation, due to high-speed spindle rotation.The spindle's modal variations are highlighted through an integrated finite element model of the dynamic high-speed spindle-bearing system, taking into account rotor dynamics effects. The dependency of dynamic behaviour on speed range is then investigated and determined with accuracy. The objective of the proposed paper is to validate these numerical results through an experiment-based approach. Hence, an experimental setup is elaborated to measure rotating tool vibration during the machining operation in order to determine the spindle's modal frequency variation with respect to spindle speed in an industrial environment. The identification of natural frequencies of the spindle under rotating conditions is challenging, due to the low number of sensors and the presence of many harmonics in the measured signals. In order to overcome these issues and to extract the characteristics of the system, the spindle modes are determined through a 3-step procedure. First, spindle modes are highlighted using the Frequency Domain Decomposition (FDD) technique, with a new formulation at the considered rotating speed. These extracted modes are then analysed through the value of their respective damping ratios in order to separate the harmonics component from structural spindle natural frequencies. Finally, the stochastic properties of the modes are also investigated by considering the probability density of the retained modes. Results show a good correlation between numerical and experiment-based identified frequencies. The identified spindle-tool modal properties during machining allow the numerical model to be considered as representative of the real dynamic properties of the system.     

Measurements of dynamic properties of a medium span suspension bridge by using the wavelet transforms

The aim of this paper is to show the capabilities of the real-time kinematic (RTK) global positioning network system (GPS) to measure the low-frequency vibration of a medium span suspension bridge. In particular, this paper presents the results of studies conducted on the identification of modal parameters including natural frequencies, damping coefficients and mode shapes of a suspension bridge using ambient excitation loads. A real-time kinematic (RTK) global positioning system (GPS) was designed and installed on the Nottingham Wilford Bridge to provide long-term and real-time measurement of bridge deck movement. An approach to estimate modal parameters, from only output data in the time domain using the wavelet transform, is presented. Displacements responses of the bridge are used in the wavelet transform to identify its dynamic characteristics. The modal properties were extracted using a two-step methodology. In the first step, the random decrement method was used to transform random signals in free vibration responses. Secondly, a wavelets-based technique was used to extract natural frequencies and to determine the mode shapes of the structure. This method was compared with the well-established techniques eigensystem realisation algorithm showing a difference of 1% in the estimated first natural frequency.The efficiency of RTK–GPS was demonstrated in the full-scale measurement. In particular, the results showed that the RTK–GPS data can be used for extracting modal properties from in-service-loads induced low-frequency vibration (<5 Hz) by processing the signal with the wavelets transform.     

Erratum to “Scaling-factor estimation using an optimized mass-change strategy” [Mech. Syst. Signal Process. 24(5) (2010) 1260–1273]

In operational modal analysis, only unscaled mode shapes can be obtained. The mass-change method is in many cases the simplest way to estimate the scaling factors, which involves repeated modal testing after changing the mass at different points of the structure where the mode shapes are known. With this method, the scaling factors are determined using the natural frequencies and mode shapes of both the modified and the unmodified structure. However, the uncertainty on the scaling-factor estimation depends on the modal-analysis accuracy and the mass-change strategy (number, magnitude, and location of the masses) used to modify the dynamic behavior of the structure. In this paper, a procedure to optimize the mass-change strategy is proposed, which uses the modal parameters (natural frequencies and mode shapes) of the original structure as the basic information.     

Adaptive arrival cost update for improving Moving Horizon Estimation performance

Moving horizon estimation is an efficient technique to estimate states and parameters of constrained dynamical systems. It relies on the solution of a finite horizon optimization problem to compute the estimates, providing a natural framework to handle bounds and constraints on estimates, noises and parameters. However, the approximation of the arrival cost and its updating mechanism are an active research topic. The arrival cost is very important because it provides a mean to incorporate information from previous measurements to the current estimates and it is difficult to estimate its true value. In this work, we exploit the features of adaptive estimation methods to update the parameters of the arrival cost. We show that, having a better approximation of the arrival cost, the size of the optimization problem can be significantly reduced guaranteeing the stability and convergence of the estimates. These properties are illustrated through simulation studies.     

柴油机机体三维建模及有限元模态分析

应用有限元理论模态分析,对SF480型发动机的机体进行了动态特性研究.首先,在Pro/E中建立机体的三维实体模型,再导入ANSYS中进行网格划分,得到其有限元模型,采用子空间迭代法进行模态求解得到前10阶固有频率和振型;其次,通过理论模态与实验模态参数的对比,验证了结果的有效性,并分析了机体模态的规律,为该类型发动机的机体结构优化提供了一定的参考依据.     

On the estimate of the FRFs from operational data

In this paper, the effects of different mass loadings required for the estimation of the frequency response functions, FRFs, from data gained by the emerging technique of operational modal testing, is proposed. This technique allows the evaluation of the natural frequencies, mode shapes and damping ratios from operational data achieved from a first session of tests, then the scaling factors are derived from a further experimental investigation. The approach is based on the sensitivity of the eigenproperties to structural modifications, such as the mass and stiffness distribution. It is shown that the generalized modal parameters could be derived by the measurements of the natural frequency shifts due to a controlled mass variation in the structure, assuming negligible changes in the mode shapes. Such generalized modal parameters are finally used to estimate the FRFs. This mode shape scaling technique, together with the investigation of the effects of the mass positioning on the uncertainties in the estimates of the scaling factors will be experimentally investigated on simple aerospace structures.     

基于遗传算法的梁结构边界条件识别

利用波动理论建立梁结构振动的行波模型,并基于遗传算法提出了一种识别梁结构边界条件的新方法。该方法直接利用结构振动的频响函数,将边界条件的识别问题转化为优化问题,然后利用遗传算法的全局优化特性得到全局最优解。实验结果表明,本文提出的方法能够很好的识别结构的边界条件。     

卫星相机快门装置的模态分析及刚度优化

为了研究卫星相机快门装置动态结构刚度,利用ANSYS Workbench对快门装置进行了有限元模态分析,得出该装置的固有频率和模态.在有限元建模中采用以弹簧单元代替滚珠的滚动轴承部件的简化建模方法,通过对简化样机进行模态试验,验证了简化建模方法的准确性.根据模态分析结果,以快慢盘的6个尺寸参数为设计变量,以其基频为目标函数,进行了快门装置的刚度优化设计,提高了装置的基频,使装置结构达到了设计性能指标.