Experimental determination of damping of plate vibrations in a viscous fluid

A method of determining the aerodynamic-drag coefficient of flat vibrating plates from the vibrogram of free damping vibrations of cantilever-fixed duralumin samples has been developed. From the results of our experiments, simple approximating formulas determining the decrement of damping vibrations and the aerodynamic-drag coefficient through the dimensionless vibration amplitude and the Stokes parameter are proposed. The approach developed in this study for determining the aerodynamic-drag coefficient of a vibrating plate can be a useful alternative to purely hydrodynamic methods of finding the drag of vibrating solids.     

Effect of viscous damping on power transmissibility for the vibration isolation of building services equipment

Vibration isolation plays an important role in both the vibration and noise control of building services equipment. To evaluate vibration isolation performance, the force transmissibility method is commonly adopted. However, increasing the damping effect in the force transmissibility method reduces both the resonance peak value and the isolation performance in the “isolation region”. The limitation of the method is that the transmitted displacement of a floor structure and the interaction of mounting points are neglected. To include the floor displacement and the interaction of mounting points, Mak and Su recently proposed the power transmissibility method to assess the performance of vibration isolation. In this paper, the effect of viscous damping on power transmissibility is investigated. A practical procedure for experimentally determining the damping ratio is also given.     

利用阻尼振动测量气垫导轨阻尼系数的新思路

利用气垫导轨上两根弹簧连接滑块做阻尼振动的模型,通过求解阻尼振动方程推算得到了滑块运动的最大速度衰减式,从而求得气垫导轨的阻尼系数.此外,从品质因数的角度推算阻尼系数的计算式,在阻尼很小时,该方法可视为最大速度衰减法的近似.通过气垫导轨阻尼振动实验,测量振幅、周期和光电门遮光时间等物理量,利用最大速度衰减和品质因数法得出阻尼系数的值非常接近.进一步对做阻尼振动的滑块拍摄视频,通过慢放视频得到其振动过程中振幅的衰减值,利用最大振幅衰减法计算出阻尼系数,所得结果与上述两种方法的数值符合较好,从另一个角度证明了本文提出的最大速度衰减法和品质因数法测阻尼系数的可靠性,该类方法在实验中易于操作、实践性强、所得结论可靠,为气垫导轨阻尼系数的测量提供了一种新的思路.     

Complex modal analysis of rods with viscous damping devices

The complex modal analysis of rods equipped with an arbitrary number of viscous damping devices is addressed. The following types of damping devices are considered: external (grounded) spring-damper, attached mass-spring-damper and internal spring-damper. Within a standard 1D formulation of the vibration problem, the theory of generalized functions is used to model axial stress and displacement discontinuities at the locations of the damping devices. By using the separate variable approach, a simple solution procedure of the motion equation leads to exact closed-form expressions of the characteristic equation and eigenfunctions, which inherently fulfill the required matching conditions at the locations of the damping devices. Based on the characteristic equation, a closed-form sensitivity analysis of the eigensolution is implemented. The displacement eigenfunctions exhibit orthogonality conditions. They can be used with the complex mode superposition principle to tackle forced vibration problems and, in conjunction with the stress eigenfunctions, to build the exact dynamic stiffness matrix of the rod for complex modal analysis of truss structures. Numerical results are discussed for a variety of parameters.     

阻尼贴片式高速列车车轮振动声辐射试验分析

为了研究辐板不同阻尼贴片装置对高速列车车轮的减振降噪效果,在半消声室内进行标准车轮与阻尼贴片式车轮自由状态下的振动声辐射试验研究,并基于有限元法对车轮模态进行了仿真计算。研究结果表明：施加辐板阻尼贴片后,两种阻尼贴片车轮的固有频率与标准车轮相比变化不大,但对于频率在1600Hz以上各阶模态阻尼比显著增加。径向与轴向激励下的降噪效果均达到10dB(A)以上,可见两种阻尼贴片装置均具有良好的降噪效果。其中在多了0.3mm铝合金薄板的情况下,W2车轮的降噪效果要略优于W1车轮,轴向激励下更加明显。     

动力吸振器中库仑阻尼对吸振性能的影响

研究了动力吸振器中库仑阻尼(干摩擦)对吸振性能的影响。给出了库仑摩擦模型,在考虑了吸振器中的库仑阻尼的情况下,分析了库仑阻尼引起的主振动系统与附加质量块的2种相对运动状态(滑移和粘滞)以及它们存在和转换的条件,讨论了因库仑阻尼引起的吸振器自由度冻结现象;用Simulink仿真工具对非线性吸振器进行了数值仿真,研究了谐波和白噪声激励下库仑阻尼对吸振器吸振性能的影响以及库仑阻尼与线性阻尼的等效问题。结果显示:弱激励条件下,非线性吸振器减弱吸振效果,强激励条件下增强吸振效果。     

动力吸振器中库仑阻尼对吸振性能的影响

研究了动力吸振器中库仑阻尼（干摩擦）对吸振性能的影响。给出了库仑摩擦模型,在考虑了吸振器中的库仑阻尼的情况下,分析了库仑阻尼引起的主振动系统与附加质量块的2种相对运动状态（滑移和粘滞）以及它们存在和转换的条件,讨论了因库仑阻尼引起的吸振器自由度冻结现象;用Simulink仿真工具对非线性吸振器进行了数值仿真,研究了谐波和白噪声激励下库仑阻尼对吸振器吸振性能的影响以及库仑阻尼与线性阻尼的等效问题。结果显示：弱激励条件下,非线性吸振器减弱吸振效果,强激励条件下增强吸振效果。     

Collisional damping of Bernstein linear echoes

A Fokker Planck collisional model is used to study the time evolution of Bernstein linear wave echoes. It is shown that a very small amount of collision destroys efficiently the upper echoes.     

Mechanical analysis of active vibration damping in continuous structures

The aim of this work is to solve problems of active damping of vibrations in some given domain of a continuous viscoelastic structure. A mathematical model of the mechanical system, the sources of perturbing vibrations, the control system, and the different absorption criteria to be compared are defined. The problems are set in infinite dimension spaces, and the approximate problems are derived in finite dimension spaces. Two methods of resolution are proposed and the solutions are compared. Numerical results simulating the response of a square plate submitted to flexural vibrations are presented for three different absorption criteria, thus permitting a quick evaluation of the comparative effectiveness of the chosen criteria.     

数码相机在研究阻尼振动中的应用

介绍一种采用数码相机来研究阻尼振动的特性参数及其运动规律的方法.     

Quantification of non-viscous damping in discrete linear systems

The damping forces in a multiple-degree-of-freedom engineering dynamic system may not be accurately described by the familiar ‘viscous damping model’. The purpose of this paper is to develop indices to quantify the extent of any departures from this model, in other words the amount of ‘non-viscosity’ of damping in discrete linear systems. Four indices are proposed. Two of these indices are based on the non-viscous damping matrix of the system. A third index is based on the residue matrices of the system transfer functions and the fourth is based on the (measured) complex modes of the system. The performance of the proposed indices is examined by considering numerical examples.     

复测法测定气轨的粘性阻尼常量

运用解决天平不等臂的复称法的思想，设计了复测法测定气轨的粘性阻尼常量的方法。     

Power law damping parameter identification

The parameter estimation of a nonlinear power damping system is studied. The parameter identification method used here assumes a priori the equation of motion describing the system dynamics. The method, which is based on the measured data (acceleration), was applied to the free and forced vibrations.The identification procedure was found to be robust on the guessed value of parameters at the numerical experimentation. The parameter values were estimated with a good accuracy for both modes of system operation (free and forced) if only the measured time history was sampled at a high enough rate for the noise level contained within. It was shown that the steady state of the harmonically excited system is not the best region for the parameter identification with this method.During the experimentation the method was applied to the free vibrations in different media (air and water). The results obtained by the parameter identification method were compared to the ones obtained by separate tests and good agreement was found. The identification procedure was found to work fine for all models under consideration and the models' responses correspond well to the measured acceleration time histories.     

Modeling of viscous damping of perforated planar microstructures. Applications in acoustics

The paper contains an analysis of the viscous damping in perforated planar microstructures that often serve as backplates or protecting surfaces in capacitive microsensors. The focus of this work is on planar surfaces containing an offset system of periodic oval holes or its limit cases: a system of circular holes or of slits. The viscous damping is calculated as the sum of squeeze film and the holes' resistances. The optimum number of holes is determined which minimizes the total viscous damping for a given percentage of open area. Graphs and formulas are provided for designing these devices. In the case the open area is higher than 15% the numerical results show that the influence of the holes' geometry (circular or oval) has a slight influence on viscous damping. As the planar structures containing oval holes assure a better protection against dust particles and water drops, they should be preferred in designing protective surfaces for microphones working in a natural environment. The obtained results also can be applied in designing other MEMS devices that use capacitive sensing such as accelerometers, micromechanical switches, resonators, and tunable microoptical interferometers.