Effect of thermal gradient on frequencies of an orthotropic rectangular plate whose thickness varies in two directions

A simple model is presented for the use of research workers in space technology, mechanical sciences and nuclear energy where certain components of the structures have to operate under elevated temperatures. The effect of a constant thermal gradient on the free vibrations of an orthotropic rectangular plate whose thickness varies linearly in two directions is considered. An approximate but quite convenient frequency equation is derived by using Rayleigh-Ritz techniques with a two-term deflection function. The upper bound on the frequency corresponding to the first mode of vibrations is obtained for various boundary conditions, and for various values of the length to width ratio, two paper constants and the temperature gradient.     

Estimation and correction of the influence of an IR spectometer on mechanical vibrations

The problem of influence of mechanical vibrations on a measurement is well known and analyzed for ground conditions. However, the problem becomes quite essential and difficult to solve in space conditions. The influence of vibrations on accuracy of the measurement was observed on MIPAS – ENVISAT and in PFS Mars Express.This paper presents an experimental and theoretical investigation on sensitivity to mechanical disturbances of the Fourier-transform infrared spectrometer PFS.A theoretical analysis has been performed in order to highlight the expected effect of the vibration, then laboratory tests have been designed and carried out for instrument characterization.The theoretical investigation has been confirmed by experimental tests.The data were distorted by errors that reflect the influence of vibrations on the instrument and temperature instability of the reference source.The considerations are a perfect example presenting the scale of vibrations problem and the instability of the reference source in assessing accuracy of the measurement in space.     

Resonance breakdown of a Coulomb blockade due to the mechanical vibrations of a quantum dot

The effect of forced mechanical vibrations of a suspended single-electron transistor on Coulomb-blockade limited electron tunneling through a quantum dot has been studied. The mechanical vibrations of the quantum dot have been shown to result in the Coulomb blockade breakdown, which is manifested by narrow resonance peaks of the transistor conductance as a function of the excitation frequency at the frequencies corresponding to the eigenmodes of the mechanical vibrations. The mechanism of the observed effect presumably associated with the oscillations of the mutual electrical capacitances between the quantum dot and the surrounding electrodes is discussed.     

气动弹性能量采集系统空气动力建模研究综述

气动弹性能量采集旨在将结构气动弹性振动机械能转化为可利用的电能, 近年来引起了国内外学者的关注.在气动弹性能量采集系统理论建模的过程中, 空气动力建模至关重要, 显著影响系统的动力学响应和能量输出分析结果.文章针对当前各类气动弹性能量采集系统的气动建模,对其研究现状进行了综述.首先介绍气动弹性能量采集的研究背景; 随后, 分别针对基于翼段非流线体平板和机翼结构气动弹性振动的能量采集系统, 对相关气动模型进行了总结和讨论; 最后, 结合现有气动建模的待完善之处,给出了未来可能的发展方向.      

Effect of geometrical and material imperfections on damping flexural vibrations in plates with attached wedges of power law profile

In the present paper, an efficient method of damping structural vibrations using the acoustic black hole effect is further investigated experimentally. This method is based on some specific properties of flexural wave propagation in tapered plates (wedges) of power-law profile that have to be partially covered by narrow thin strips of absorbing layers. Ideally, if the power-law exponent of the profile is equal or larger than two, the flexural wave never reaches the sharp edge and therefore never reflects back, which constitutes the acoustic black hole effect. It has been previously established theoretically and confirmed experimentally that this method of damping structural vibrations is very efficient even in the presence of edge truncations. The present work describes the results of the experimental studies of the effects of manufacturing intolerances on damping flexural vibrations in wedge-like structures of power-law profile. In particular, the effect of mechanical damage resulting from the use of cutting tools to wedge tips is investigated, including tip curling and early truncation, as well as the placement of absorbing layers on different wedge surfaces. Also, the effects of welded and glued bonding of wedge attachments to basic rectangular plates (strips) are investigated. The results show that, although the above-mentioned geometrical and material imperfections reduce the damping efficiency by varying degrees, the method of damping structural vibrations using the acoustic black hole effect is robust enough and can be used widely without the need of high precision manufacturing.     

The determination of electrical parameters of quartz crystal resonators with the consideration of dissipation

Recently, as the dissipation of quartz crystal through material viscosity is being considered in vibrations of piezoelectric plates, we have the opportunity to obtain electrical parameters from vibration solutions of a crystal plate representing an ideal resonator. Since the solutions are readily available with complex elastic constants from Mindlin plate equations for thickness-shear vibrations, the calculation of resistance and other parameters related to both mechanical deformation and electrical potential is straightforward. We start with the first-order Mindlin plate equations of a piezoelectric plate for the thickness-shear vibration analysis of a simple resonator model. The electrical parameters are derived with emphasis on the resistance that is related to the imaginary part of complex elastic constants, or the viscosity. All the electrical parameters are frequency dependent, enabling the study of the frequency behavior of crystal resonators with a direct formulation. Through the full consideration of complications like partial electrodes and supporting structures, we should be able obtain electrical parameters for practical applications in resonator design.     

Elasticity and inelasticity of biomorphic carbon,silicon carbide,and SiC/Si composite produced on the basis of medium density fiberboard

The amplitude and temperature dependences of the Young’s modulus and the internal friction (ultrasonic absorption) of biomorphic carbon, silicon carbide, and SiC/Si composite produced from medium density fiberboard (MDF) by pyrolysis (carbonization), followed by infiltration of molten silicon into the prepared carbon preform have been studied in the temperature range 100–293 K in air and under vacuum. The measurements have been performed by the acoustic resonance method with the use of a composite vibrator for longitudinal vibrations at frequencies of approximately 100 kHz. The data obtained by acoustic measurements of the amplitude dependences of the elastic modulus have been used for evaluating the microplastic properties of samples under study. It has been shown that the Young’s modulus, the decrement of elastic vibrations, and the conventional microyield strength of the MDF samples differ from the corresponding data for previously studied similar materials produced from natural eucalyptus, beech, sapele, and pine woods. In particular, the desorption of environmental molecules at small amplitudes of vibrations, which is typical of biomorphic materials based on natural wood, is almost absent for the MDF samples. The results obtained have been explained by different structures and the influence of pores and other defects, which, to a large extent, determine the mechanical characteristics of the biomaterials under investigation.     

Dynamic performance of the beam position monitor support at the SSRF

Electron beam stability is very important for third‐generation light sources, especially for the Shanghai Synchrotron Radiation Facility whose ground vibrations are much larger than those for other light sources. Beam position monitors (BPMs), used to monitor the position of the electron beam, require a greater stability than other mechanical structures. This paper concentrates on an investigation of the dynamic performance of the BPM support prototype. Modal and response analyses have been carried out by finite‐element (FE) calculations and vibration measurements. Inconsistent results between calculation and measurement have motivated a change in the soft connections between the support and the ground from a ground bolt in the initial design to full grout. As a result the mechanical stability of the BPM support is greatly improved, showing an increase in the first eigenfrequency from 20.2 Hz to 50.2 Hz and a decrease in the ratio of the root‐mean‐square displacement (4–50 Hz) between the ground and the top of the support from 4.36 to 1.23 in the lateral direction. An example is given to show how FE analysis can guide the mechanical design and dynamic measurements (i.e. it is not just used as a verification method). Similar ideas can be applied to improve the stability of other mechanical structures.     

Influence of wall vibrations on the behavior of a simplified wind instrument

The issue of the influence of wall vibrations on the behavior of wind instruments is still under debate. The mechanisms of vibroacoustic couplings involved in these vibrations are difficult to investigate, as fluid-structure interactions are weak. Among these vibroacoustic interactions, the present study is focused on the coupling between the internal acoustic field and the mechanical behavior of the duct. For this purpose, a simplified single reed instrument consisting of a brass tube connected to a clarinet mouthpiece has been studied. A theoretical model of coupling between the plane inner acoustic wave and mechanical modes is developed and suggests that in order to obtain measurable effects of wall vibrations, the geometrical parameters of the studied tube have to be unusual compared to that of real instruments. For a slightly oval-shaped and very thin brass tube, it is shown theoretically and experimentally that a coupling between the inner plane acoustic wave and ovalling mechanical modes occurs and results in disturbances of the input impedance, which can slightly affect the tone color of the sound produced. It is concluded that the reported effects are unlikely to occur in real instruments except for some organ pipes.     

Investigations of mechanical vibrations for beamlines at the Canadian Light Source

Vibration is often a problem causing poor quality of photon beams at synchrotron radiation facilities, since beamlines are quite sensitive to vibrations. Therefore, vibration analysis and control at synchrotron radiation facilities is crucial. This paper presents investigations on mechanical vibrations at four beamlines and endstations at the Canadian Light Source, i.e. the Canadian Macromolecular Crystallography Facility 08ID‐1 beamline, the Hard X‐ray MicroAnalysis 06ID‐1 beamline, the Resonant Elastic and Inelastic Soft X‐ray Scattering 10ID‐2 beamline, and the Scanning Transmission X‐ray Microscope endstation at the Spectromicroscopy 10ID‐1 beamline. This study identifies vibration sources and investigates the influence of mechanical vibrations on beamline performance. The results show that vibrations caused by movable mechanical equipment significantly affect the data acquired from beamlines.     

Nonlinear vibrations of loudspeaker-like structures

During high amplitudes of vibration, nonlinearities affect the electroacoustical behavior of electrodynamic transducers and are responsible for audible distortions. We distinguish two types of nonlinearities: electrical and mechanical. In this study, attention is paid to the mechanical and geometrical properties of loudspeaker-like structures. The loudspeaker is viewed as a combination of an annular plate with a circular plate. Nonlinear vibrations of such a structure are investigated, using the dynamic analog of the Von-Kármán equations. Furthermore, the influence of both material properties and geometrical parameters is studied. It is shown that nonlinear effects can be substantially reduced by choosing appropriate material and geometrical parameters.     

New method of determining the young’s Modulus of (Ga,Mn)As nanowhiskers with a scanning electron microscope

Arrays of (Ga,Mn)As nanowhiskers have been grown by molecular-beam epitaxy. The scanning electron microscopy study of the surface morphology of the samples has revealed the appearance of mechanical vibrations of individual nanowhiskers. To describe the vibrations, a model has been developed for the determination of the Young’s modulus of (Ga,Mn)As nanowhiskers.     

Field emission of electrons from a single carbon fiber with a nanostructured emitting surface

The field emission of electrons from a single fine carbon fiber with a nanostructured emitting surface is studied experimentally. It is found that the fiber can serve as an effective field emitter of electrons at voltages of ∼10²–10³ under the conditions of technical vacuum and the emission current density may reach ∼10² A/cm². At a certain threshold voltage, the fiber starts executing flexural mechanical vibrations. The onset of mechanical vibrations is accompanied by a change in the field emission conditions. Namely, in the absence of vibrations, the mode of steady current extraction is observed. When mechanical vibrations set in, the field emission switches to the mode of current periodic oscillations with a constant component.     

Deciphering vibration holograms

In vibration holography one measures the temporal Fourier coefficients of the complex amplitude emanating from the vibrating object. However, the user wants to know the temporal Fourier coefficients of the mechanical vibration itself. The mechanical vibrations are proportional to the phase of the complex light amplitude. Hence, the temporal Fourier coefficients of the mechanical vibrations depend in a complicated manner on the temporal Fourier coefficients of the complex amplitude itself. So far, either narrow approximations or complicated Bessel algorithms were used for deducing the mechanical Fourier coefficients from the optical Fourier coefficients. In other words, deciphering the mechanical data from the optical measurements was not easy.We propose a simple and rigorous algorithm for this deciphering project. In addition we outline a holographic experiment that allows one to reconstruct a space- and time-dependent complex amplitude and also its temporal derivative. This experiment is capable of displaying the mechanical velocity distribution as image brightness. Also the spatial distribution of mechanical acceleration can be displayed.     

Vibration transmission from internal structures to the tank of an oil-filled power transformer

The vibration of a transformer tank is related to the transformer’s noise radiation and health condition. Therefore, it is important to understand the transmission of vibration from internal vibration sources in the windings and core to the transformer tank. The characteristics of this transmission are determined by direct mechanical coupling between the internal structures and the tank, and by indirect coupling through fluid–structure interaction induced by the transformer’s cooling oil. In this paper, the transmission of vibration is examined experimentally in a 110-kV power transformer with and without cooling oil. Under respective mechanical and electrical excitations, vibrations of the internal structures and transformer tank are measured simultaneously. The results allow an evaluation of the transmission efficiency of vibration from the internal structures to the tank, and the effects of fluid–structure coupling on the transmission. This experimental work improves understanding of vibration transmission in oil-filled power transformers, and explains the characteristics of a transformer’s on-line vibration.     

The effect of mechanical vibrations on holograms

The effect of mechanical vibrations on hologram recording is discussed, with emphasis on sinusoidal vibrations. A simple method for evaluating this effect is presented.     

Spin-controlled nanomechanics induced by single-electron tunneling

We consider dc-electronic transport through a nanowire suspended between normal- and spin-polarized metal leads in the presence of an external magnetic field. We show that magnetomotive coupling between the electrical current through the nanowire and vibrations of the wire may result in self-excitation of mechanical vibrations. The self-excitation mechanism is based on correlations between the occupancy of the quantized electronic energy levels inside the nanowire and the velocity of the nanowire. We derive conditions for the occurrence of the instability and find stable regimes of mechanical oscillations.     

Vibration suppression of a cantilever beam using magnetically tuned-mass-damper

Eddy currents are induced by the movement of a conductor through a stationary magnetic field or a time varying magnetic field through a stationary conductor. These currents circulate in the conductive material and are dissipated, causing a repulsive force between the magnet and the conductor. These electromagnetic forces can be used to suppress the vibrations of a flexible structure. A tuned mass damper is a device mounted in structures to reduce the amplitude of mechanical vibrations and is one of the effective vibration suppression methods. In the present study, an improved concept of this tuned mass damper for the vibration suppression of structures is introduced. This concept consists of the classical tuned mass damper and an eddy current damping. The important advantages of this magnetically tuned mass damper are that it is relatively simple to apply, it does not require any electronic devices and external power, and it is effective on the vibration suppression. The proposed concept is designed for a cantilever beam and the analytical studies on the eddy current damping and its effects on the vibration suppression. To show the effectiveness of the proposed concept and verify the eddy current damping model, experiments on a cantilever beam are performed. It is found that the proposed concept could significantly increase the damping effect of the tuned mass damper even if not adequately tuned.     

Interpretation of vibrational spectra of a closed form of indoline spirophenanthroxazine

We have measured IR and Raman spectra of molecules of a closed form of the photochromic compound indolinespirophenanthroxazine. Using the density-functional method, we have optimized the structures of the closed and open forms of this molecule and calculated its normal vibrations. Based on these calculations, we propose an interpretation of the obtained vibrational spectra. We have determined the spectral range of manifestation, 700–900 cm^?1, and have found wavenumbers of normal vibrations through which the spiro structure of the indolinespirophenanthroxazine molecule in an excited state is likely to be rearranged into a merocyanine structure.     

Prediction of vibrations induced by underground railway traffic in Beijing

This paper examines the problem of subway induced vibrations on line 4 of Beijing metro, which is currently under construction and is planned to pass in close proximity of the Physics Laboratory of Beijing University. The laboratory has a lot of equipment that is very sensitive to traffic induced vibrations and future operation of metro line 4 is a matter of concern. Hence, it is important to study the influence of subway induced vibrations inside the laboratory and to propose a viable solution to mitigate the vibrations. In this paper, the tunnel north of Chengfulu station is modelled using a coupled periodic FE-BE model and the free-field response due to moving trains is predicted. In addition, vibration measurements have been performed on the site of the Physics Laboratory to estimate the existing vibration levels due to road traffic. The predicted and measured vibrations are superimposed to assess the vibrations due to the combined effect of road and railway traffic in the vicinity of the Physics Laboratory. Apart from the numerical investigations, vibration measurements have also been performed on a similar site at line 1 of Beijing metro to substantiate the estimated results on metro line 4. Finally, it is studied how the vibrations can be controlled using a floating slab track, which is widely used as an effective measure of vibration isolation in tunnels. The efficiency of a 7.9 Hz floating slab track as a vibration countermeasure is assessed in this paper. This study demonstrates the applicability of the numerical model for the relevant assessment of subway induced vibrations and its use to study the performance of different track structures in the tunnel.