Coupled bending-torsion vibration of a homogeneous beam with a single delamination subjected to axial loads and static end moments

Delaminations in structures may significantly reduce the stiffness and strength of the structures and may affect their vibration characteristics. As structural components, beams have been used for various purposes, in many of which beams are often subjected to axial loads and static end moments. In the present study, an analytical solution is developed to study the coupled bending-torsion vibration of a homogeneous beam with a single delamination subjected to axial loads and static end moments. Euler–Bernoulli beam theory and the free mode assumption in delamination vibration are adopted. This is the first study of the influences of static end moments upon the effects of delaminations on natural frequencies, critical buckling loads and critical moments for lateral instability. The results show that the effects of delamination on reducing natural frequencies, critical buckling load and critical moment for lateral instability are aggravated by the presence of static end moment. In turn, the effects of static end moments on vibration and instability characteristics are affected by the presence of delamination. The analytical results of this study can serve as a benchmark for finite element method and other numerical solutions.     

Electromechanical coupled nonlinear dynamics for microbeams

In this paper, an electromechanical coupled nonlinear dynamic equation of a microbeam under an electrostatic force is presented. Using the nonlinear dynamic equations and perturbation method, we investigated nonlinear free vibrations, forced responses far from and near to natural frequency, respectively. Nonlinear natural frequencies and vibrating amplitudes of the electromechanical coupled microbeam are dependent on the mechanical and electric parameters. Compared with linear forced responses, the obvious shift of the mean dynamic response occurs. Under certain condition, the jump phenomenon will occur. The studies can be used to design parameters of the microbeam and remove undesirable dynamic behavior such as jump phenomenon, etc.     

动圈传声器振动膜的工艺分析

振动膜的工艺及设计，是动圈传声器设计中的主要技术，文中论述了振动膜的设计及压制工艺，并介绍了几种优良的振动系统。     

Nonlinear dynamic strain analysis on rotor bladestructures with embedded piezoceramic sensors for activevibration control

In this paper, a relative index method is proposed to analyze the nonlinear VonKarman strain effects on a rotor blade structure with embedded piezoceramic sensors. Althoughother qualitative and quantitative methods are available for nonlinear strain analysis, thesemethods have inherent drawbacks. The proposed relative index method circumvents thedrawbacks of both qualitative and quantitative methods. Firstly, it measures the nonlinear effectand converts it into a numerical value. The value is in the range of zero to one in which zerocorresponds to negligible effects and one indicates the highest severity of the nonlinear effects. Inaddition, to generate the index value, this method takes the whole picture of nonlinear effectresponse into consideration.

The results of using the relative index method show that at any given mode of vibrationthe nonlinear effect on the sensor is relatively negligible at a high rate of rotation rather than onlow. The results also indicate that the nonlinear effect increases at lower modes of vibration butits effect on the sensor almost levels off at higher modes. Moreover, if comparing index value ofgiven modes of vibration with the index value of its preceding modes, the effect of nonlinearitydecreases. In addition, the results also suggest that at any given instantaneous speed of rotationthe level of the nonlinear effect diminishes with the higher accelerationdeceleration operation ofthe blade.     

Exact controllability of a spherical cap: Numerical implementation of HUM

This paper deals with the numerical implementation of the exact boundary controllability of the Reissner model for shallow spherical shells (Ref. 1). The problem is attacked by the Hilbert uniqueness method (HUM, Refs. 2–4), and we propose a semidiscrete method for the numerical approximation of the minimization problem associated to the exact controllability problem. The numerical results compare well with the results obtained by a finite difference and conjugate gradient method in Ref. 5.This work was done when the first two authors were at CNR-IAC, Rome, Italy as Graduate Students.     

A linear motor damper for vibration control of steel structures

A hybrid mass damper based on the linear motor principle is developed to suppress structural vibration. We will call it a linear motor damper in this paper. This paper deals with the design, analysis, and manufacture of the linear motor damper. It consists of the NdFeB permanent magnets, a coil-wrapped nonmagnetic hollow rectangular structure, an iron core, mechanical springs, and so on. It is designed to be able to move the auxiliary mass of 1500 kg, up to ±250 mm stroke. A series of performance tests for the linear mass damper with H_∞ robust controller are carried out on a steel frame structure. Through performance tests, it is confirmed that the developed hybrid mass damper has reliable feasibility as a control device for structural control. In addition, the linear motor damper is more economical than both hydraulic and electric motor driving mass damper with respect to simple structure and low maintenance cost.     

Parametric excitation of waves on a free boundary of a horizontal fluid layer

We consider the dynamical stability of horizontal fluid layer, performing harmonic oscillations in vertical direction. The continued fractions approach allowed us to avoid the conventional restriction to the case of small viscosity and almost-resonant frequencies. Our numerical results cover a wide range of the parameters (viscosity, amplitude and frequency of the oscillation, and depth of the layer). To cite this article: V.I. Yudovich et al., C. R. Mecanique 332 (2004).     

Static and free vibration analysis of laminated glass beam on viscoelastic supports

Static behavior and free vibration analysis of laminated glass beam on viscoelastic supports are performed. For the static case, an analytical way is developed for analyzing and optimization of laminated glass beam with general restraints at the boundaries. In the case of free linear vibrations, the modal properties of the glass are determined using a finite element method which is a powerful tool in the design of support damping treatment of a sandwich glass for passive vibration control.     

A new interferometric method for vibration measurement by electronic holography

Electronic holography is a well-established technique used in real-time, non-contact, whole-field displacement measurements. When using the real-time, time-averaged method for vibration measurments, the quantitative interpretation of dense fringe patterns is difficult because of speckle noise. Even when speckle-reducing procedures are used, such as multiple-frame averaging or rotation of the illumination beam, the remaining speckles and decreasing visibility of higher-order Bessel fringes are serious limitations. The primary objective of this paper is to present a new realtime, interferometric method for mechanical vibration measurements and the associated quantitative interpretation. The fringe pattern obtained by this method is quasi-binary and half as dense as in the time-averaged method. The method greatly improves the overall visibility (contrast, resolution) of vibration fringe patterns without any sacrifice in the real-time capabilities. Quantitative fringe interpretation is straightforward and based on binary fringe tracking. It allows quantitative measurements in situations where the time-averaged fringe processing fails.     

The effect of friction reduction in the presence of in-plane vibrations

A reduction of friction by vibrations has been observed in various experiments. This effect can be applied to actively control frictional forces by modulating vibrations. Moreover, common methods of controlling friction rely on lubricants and suitable material combinations. The superimposition of vibrations can further reduce the friction force. This study presents a theoretical approach based on the Dahl friction model that describes the friction reduction observed in the presence of the tangential vibrations at an arbitrary angle. Analysis results indicated that the tangential compliance should be considered in modeling the effect of vibrations in reducing friction. At any vibration angle, the tangential compliance of the contacts reduces the friction reduction effect. The vibrations parallel to the macroscopic velocity are most effective for friction reduction.