Showing papers on "Dynamic Vibration Absorber published in 2010"

Metamaterial-based Broadband Elastic Wave Absorber:

Abstract: This article presents modeling and analysis techniques for and reveals the actual working mechanism of longitudinal metamaterial bars as elastic wave absorbers. A metamaterial-based elastic wave absorber can be a uniform isotropic bar with many tiny spring-mass subsystems attached at separated longitudinal locations. In the literature, each cell that consists of a bar segment and an attached spring-mass subsystem is modeled as a discrete system of two degrees of freedom by integration and/or finite difference, and the idealized model becomes a dispersive medium for elastic waves and has a stop band that allows no waves to propagate forward. This work shows that these idealized models can be used only for elastic waves having wavelengths much longer than the unit cell’s length. Moreover, it is revealed that a metamaterial-based elastic wave absorber is actually based on the concept of conventional mechanical vibration absorbers, which uses the local resonance of subsystems to generate inertia forces to wor...

MRE properties under shear and squeeze modes and applications

Abstract: Magnetorheological elastomers (MREs) are smart materials whose mechanical properties, like their modulus and elasticity, can be controlled by an external magnetic field. This feature has resulted in a number of novel applications, such as adaptive tuned dynamic vibration absorbers for suppressing unwanted vibrations over a wide frequency range. MRE-based devices operate in different modes, such as shear mode and squeeze mode; however, the study of mechanical performances of MREs under squeeze mode is very rare. This article aims to investigate MRE performances under both shear and squeeze modes. Experimental studies and simulations were conducted to analyze the MR effect in both modes. These studies indicate a different working frequency ranges for both modes. In a case study, a MRE-based vibration absorber was built up in a simulation and its mechanical performances were analyzed, which demonstrated good capabilities in reducing vibrations.

An Active-damping-compensated Magnetorheological Elastomer Adaptive Tuned Vibration Absorber

Abstract: This article presents the development of an active-damping-compensated magnetorheological elastomer (MRE) adaptive tuned vibration absorber (ATVA). The principle and the vibration attenuation performance of the proposed active-damping-compensated ATVA were theoretically analyzed. Based on the analysis, a prototype was designed and manufactured. Its dynamic properties and vibration attenuation performances were experimentally investigated. The experimental results demonstrated that the damping ratio of the prototype was significantly reduced by the active force. Consequently, its vibration attenuation capability was significantly improved compared with a conventional MRE ATVA.

Reduction of bending vibration in railway vehicle carbodies using carbody–bogie dynamic interaction

Abstract: This paper presents a theory to utilise the longitudinal vibration in bogies as a dynamic vibration absorber (DVA) to reduce the vertical bending vibration of railway vehicle carbodies in a simple and easy way. This study focuses upon the interaction between carbody vertical bending and bogie longitudinal motion, and the condition for tuning the natural frequency of the bogie motion to the target carbody vibration is derived theoretically using a very simple formula. Numerical and experimental studies are then outlined to validate the theory and formula, and the DVA effects are observed from both of them. The effectiveness of the method is also confirmed from a running test with a Shinkansen train on a commercial line.

Optimal design of damped dynamic vibration absorber for damped primary systems

Abstract: This study focuses on the optimum design of the damped dynamic vibration absorber (DVA) for damped primary systems. Different from the conventional way, the DVA damper is connected between the absorber mass and the ground. Two numerical approaches are employed. The first approach solves a set of nonlinear equations established by the Chebyshev’s equioscillation theorem. The second approach minimizes a compound objective subject to a set of the constraints. First the two methods are applied to classical systems and the results are compared with those from the analytical solutions. Then the modified Chebyshev’s equioscillation theorem method is applied to find the optimum damped DVAs for the damped primary system. Various results are obtained and analyzed.

A tunable magneto-rheological fluid-filled beam-like vibration absorber

Abstract: Tuned vibration absorbers (TVAs) are often used to suppress unwanted vibrations. If the excitation frequency is time harmonic but the frequency changes with time, it is desirable to retune the TVA so that the natural frequency of the TVA always coincides with the excitation frequency. One way of achieving this is to adjust the stiffness of the TVA. The key challenge is to change the stiffness quickly in real time. In this paper a magneto-rheological (MR) fluid in its pre-yield state is used as the core of a three-layer beam-like TVA. The shear stiffness of the MR fluid is adjusted by varying the magnetic field to which it is exposed by changing the current supplied to the electromagnets. Hence the stiffness of the TVA can be varied. The vibration characteristics of the TVA as a function of the magnetic field strength are predicted using a finite element model together with an empirical model for the shear modulus of the MR fluid and a model for the magnetic field applied to the fluid. An MR fluid-filled TVA was manufactured and tested to validate the predictions. This TVA design allows the natural frequency to be changed by about 40%.

Mitigation of Pedestrian-induced Vibrations in Suspension Footbridges via Multiple Tuned Mass Dampers

Abstract: The dynamic response of suspension footbridges to pedestrian-induced excitations and its passive mitigation, via multiple tuned mass dampers (TMDs), are investigated. First, the nonlinear equations of motion are obtained assuming finite planar motions of the suspension bridge. A suitable approximate version of the equations of motion is shown to be in agreement with existing theories and its linearization is then employed in the structural dynamics analyses. A Galerkin discretization is exploited to calculate both the free and forced dynamic response towards the design of the vibration control system. First, the leading characteristics of the bridge dynamic response are outlined. Resonant vibrations induced by the passage of pedestrians are shown to be effectively reduced using viscoelastic TMDs. As the frequencies of the lowest two modes in suspension footbridges can be very close in the proximity of the crossover phenomenon, three different design scenarios are considered: below, near and above the crossover. In particular, the influence of these scenarios on the passive control architecture is investigated.

A shape memory alloys based tuneable dynamic vibration absorber for vibration tonal control

Abstract: This paper examines a novel model of an Adaptive Tuneable Dynamic Vibration Absorber (ATDVA), based on the use of Shape Memory Alloy materials (SMA). Being adaptive, the absorber is able to track variation of the structural dynamic response. The absorber architecture is extremely simple: it consists of a clamped SMA wire and a concentrated mass. Two reference structures have been considered: a typical aeronautical aluminium panel and a fibreglass panel. In the first part, the investigated concept is introduced with a short presentation about the SMA main properties. The realisation and experimental characterisation of the device are then presented. Its implementation, a report on the experimental campaign and the presentation of the attained results conclude the work, together with a discussion on the achieved results and the next investigation steps.

On Magnetorheologic Elastomers for Vibration Isolation, Damping, and Stress Reduction in Mass-varying Structures

Abstract: This article considers two devices based on a magnetorheological elastomer (MRE): an MRE isolator under a frequency-varying harmonic excitation and a MRE Dynamic Vibration Absorber (DVA) mounted on a frequency-varying structure under a random excitation. In the first case, it is shown that the commandability of the elastomer improves the reduction of the RMS value of the body displacement by 10%. In the second case, it is shown on a simple example that a MRE DVA, while not optimal, can reduce the stress in the structure about 50% better than a classical DVA when the mass of the structure changes 35%. This makes them suitable to avoid high stress in mass-varying structures, and delay some damage mechanisms like the emergence of cracks and fatigue.

Power-amplifying strategy in vibration-powered energy harvesters

Abstract: A new cantilevered piezoelectric energy harvester (PEH) of which the additional lumped mass is connected to a harmonically oscillating base through an elastic foundation is proposed for maximizing generated power and enlarging its frequency bandwidth. The base motion is assumed to provide a given acceleration level. Earlier, a similar energy harvester employing the concept of the dynamic vibration absorber was developed but the mechanism of the present energy harvester is new because it incorporates a mass-spring system in addition to a conventional cantilevered piezoelectric energy harvesting beam with or without a tip mass. Consequently, the proposed energy harvester actually forms a two-degree-of-freedom system. It will be theoretically shown that the output power can be indeed substantially improved if the fundamental resonant frequencies of each of the two systems in the proposed energy harvester are simultaneously tuned as closely as possible to the input excitation frequency and also if the mass ratio of a piezoelectric energy harvesting beam to the lumped mass is adjusted below a certain value. The performance of the proposed energy harvester is checked by numerical simulation.

On interaction of vibrating beam with essentially nonlinear absorber

Abstract: The paper deals with interaction of elastic beam with essentially nonlinear vibration absorber. Forced vibrations of the beam are described by 2DOF model. We treat the motions favorable for vibration absorption as nonlinear modes in a configuration space and compute them by a modification of Rausher method. Stability of these modes is analyzed numerically with the help of the Floquet theory.

Vibration element coupled with non-linear force to improve non-resonant frequency response

Abstract: Embodiments of the invention couple a non-linear force to a vibration element such as a piezoelectric cantilever to introduce chaotic, i.e., non-resonant vibration in the vibration element and thereby improve the non-resonant response of the vibration element. By doing so, the vibration element is responsive to a wider frequency range of vibrations and thus may be more efficient in scavenging energy in environments where the vibration frequency is not constant, e.g., in environment subject to multi-mode or random vibration sources.

Passive tuned vibration absorber

Abstract: A passive tuned vibration absorber is used to attenuate unwanted vibrations in the spokes of a non-pneumatic tire and wheel assembly. Each spoke has a cutaway central portion having a tuned vibration absorber n the form of a protruding member having an axial width and a radial height and the radial height of the protruding member is less than a radial height of the spoke. Additionally, a method of determining the vibrational characteristics of the spokes of a non-pneumatic tire and wheel assembly is included.

Structure and Performance Analysis of Regenerative Electromagnetic Shock Absorber

Abstract: This paper analyze d the structure and principle of a regenerative electromagnetic shock absorber in detail. The innovative shock absorber resembles linear generator in principle and can generate electric power through the relative reciprocating motion between coil assembly and permanent magnet assembly . A t the same time, the damping can remove discomfort caused by road roughness. The regenerated electric power can be recovered through battery. Analysis of magnetic flux density of the permanent magnet array of the innovative shock absorber was performed using ANSYS software based on the structure parameters given in the paper,then the performance parameters of the shock absorber was determined . Analysis and calculation results prove the viability of this shock absorber .

Electrohydraulic energy regenerative vibration absorber

Abstract: The invention relates to an electrohydraulic energy regenerative vibration absorber, which comprises a piston, a hydraulic check bridge, an accumulator, a hydraulic motor and a rotary generator. A vibration absorber cavity is divided into a rodless cavity (11) and a rod cavity (12) by a piston and a piston push rod (16); the two cavities are provided with an oil outlet and an oil inlet respectively; each oil outlet and each oil inlet are provided with a one-way valve; the one-way valve and a pipeline which is connected with the one-way valve form the hydraulic check bridge; the accumulator is connected in parallel on a connecting pipeline between two oil outlets and an oil inlet of the hydraulic motor; a volume conversion bridge (5) is connected in parallel on a pipeline between the oil outlet of the hydraulic motor and two oil inlets of the vibration absorber cavity; and the volume conversion bridge consists of two one-way valves and an oil tank which is connected with the one-way valves. The electrohydraulic energy regenerative vibration absorber meets the damping force requirement of an automobile vibration absorber, and can convert the ground vibration into direction-invariable rotary movement to drive the generator to generate power and actively control the damping of the vibration absorber by controlling the generator load.

Proportional and derivative control for steady-state vibration mitigation in a piecewise linear beam system

Abstract: A control using Proportional and/or Derivative feedback (PD-control) is applied on a piecewise linear beam system with a flushing one-sided spring element for steady-state vibration amplitude mitigation. Two control objectives are formulated: (1) minimize the transversal vibration amplitude of the midpoint of the beam at the frequency where the first harmonic resonance occurs, (2) achieve this in a larger (low) excitation frequency range, where the lowest nonlinear normal mode dominates the response. Experimentally realizable combinations of PD-control are evaluated for both control objectives. Eventually objective (1) is realized by applying proportional control only, whereas derivative control is selected to realize objective (2). The vibration reduction that is achieved in simulations and validated by experiments is very significant for both objectives. Current results obtained with active PD-control are compared with earlier results obtained using a passive dynamic vibration absorber.

Self-adaptive damping variable ultra-precise vibration absorber

Abstract: The invention discloses a self-adaptive damping variable ultra-precise vibration absorber, which has the following structure: the exterior of a metal shell is in an upper end-opened cylinder shape; the metal shell is hollow, is divided into an upper hollow part and a lower hollow part by a clapboard, has an H-shaped section; a lower cavity is formed in the hollow part on the lower part; an upper cavity is formed by connecting the upper hollow part and a piston mechanism through a film structure in a sealed mode; an air inlet is formed at the bottom of the lower cavity; a communicating pipeline with a throttling valve is arranged between the lower cavity and the upper cavity; a load connecting plate is fixedly connected with the upper end face of the piston mechanism; an absolute velocity sensor is arranged on the load connecting plate; a non-contact eddy current proximity sensor is arranged on the upper end part of the metal shell; an active actuator is arranged between the metal shell and the load connecting plate; and the load connecting plate is used to be fixedly connected with load. The self-adaptive damping variable ultra-precise vibration absorber can well attenuate vertical vibration and perform on-line self-adaptation without off-line debugging, and can provide hyperstatic environment for a photoetching machine and other precision equipment.

A vibration absorber for motorcycle handles

Abstract: This paper describes the application of a vibration absorber to ameliorate the comfort of motorcycle handles. The concept of dynamical absorber is briefly summarised and a frequency response function is expressed as the ratio of vibration amplitudes (transmissibility). Some practical hints on the tuning strategy are also suggested in order to correctly define the absorber and then achieve the most effective vibration reduction. A specifically designed item is presented, with the peculiar characteristic of taking advantage of the damping properties of viscoelastic material undergoing shear deformations. An experimental verification of the good performances of the absorber is eventually given on the basis of both a modal analysis of a motorbike and the testing of its handle on an electrodynamical shaker.

An elastic damping element and mounting method thereof

Abstract: The invention discloses an elastic damping element and a mounting method thereof, which are applied to the field of elastic damping. The elastic damping element comprises two vibration absorber main bodies, an outer limit sleeve and an inner limit sleeve, wherein the two vibration absorber main bodies are symmetrically installed at two ends of a central pore canal of an mounting support; the outer and inner limit sleeves are coaxially installed in the central pore canal of the mounting support; and the vibration absorber main bodies are fixed between a mounting bracket and a mounting plate through a screw. Before the mounting process, radial pre-compression is supplied by extruding the inner sleeve of each vibration absorber main body. In the mounting process, axial stress and axial pre-compression are supplied. The outer and inner limit sleeves are mounted coaxially, different radial rigidities are realized under different vibration frequencies and limiting effect is acted when excessive load occurs. The elastic damping element mounted by the mounting method has variable rigidity and plays limiting effects along axial and radial direction when excessive load occurs. The elastic damping element has simple structure, large load capacity, high maintenance-free reliability and long service life.

Robust Optimal Design of a Nonlinear Dynamic Vibration Absorber Combining Sensitivity Analysis

Abstract: Dynamic vibration absorbers are discrete devices developed in the beginning of the last century used to attenuate the vibrations of different engineering structures. They have been used in several engineering applications, such as ships, power lines, aeronautic structures, civil engineering constructions subjected to seismic induced excitations, compressor systems, etc. However, in the context of nonlinear dynamics, few works have been proposed regarding the robust optimal design of nonlinear dynamic vibration absorbers. In this paper, a robust optimization strategy combined with sensitivity analysis of systems incorporating nonlinear dynamic vibration absorbers is proposed. Although sensitivity analysis is a well known numerical technique, the main contribution intended for this study is its extension to nonlinear systems. Due to the numerical procedure used to solve the nonlinear equations, the sensitivities addressed herein are computed from the first-order finite-difference approximations. With the aim of increasing the efficiency of the nonlinear dynamic absorber into a frequency band of interest, and to augment the robustness of the optimal design, a robust optimization strategy combined with the previous sensitivities is addressed. After presenting the underlying theoretical foundations, the proposed robust design methodology is performed for a two degree-of-freedom system incorporating a nonlinear dynamic vibration absorber. Based on the obtained results, the usefulness of the proposed methodology is highlighted.

Vibration isolation strategies using magneto-rheological elastomer for a miniature cryogenic cooler in space application

Abstract: Miniature cryogenic coolers are widely used to cool down sensitive image sensors in observation and surveillance satellites. The linear actuator in the cooler compressor operates at a relatively constant rate and this is the main source of vibration disturbance transmitted to the imaging sensor. Passive vibration isolation with and without an absorber, and a semi-active tuned vibration absorber are studied and compared to make a guidance of choosing the appropriate isolation system. This paper newly proposes the use of magneto-rheological elastomer (MRE) for vibration isolation of a cryogenic cooler. MRE is a smart material that changes its stiffness and damping rapidly and reversely under magnetic field. This tunable property is investigated and experimented to determine the feasibility of MRE application for vibration mitigation of a cryogenic cooler.

Vibration sensor film, vibration actuator film, vibration reduction film, and multilayer film using them

Abstract: A vibration reduction system has a vibration reduction film and a control unit. The vibration reduction film is constituted of a vibration sensor film, an insulating layer, and a vibration actuator film that are stacked in this order. In each of the vibration sensor film and the vibration actuator film, two pairs of electrodes are formed on both surfaces of a piezoelectric polymer film into a pattern based on a particular mode of vibration. The electrodes of the vibration sensor film overlap with the electrodes of the vibration actuator film. In response to electric charge signals from the electrodes of the vibration sensor film, the particular mode of vibration is detected. By application of voltages into the electrodes of the vibration actuator film, a vibration of opposite phase is generated to counteract the detected vibration.

Passive control of seismically excited structures by the liquid column vibration absorber

Abstract: The potential of the liquid column vibration absorber (LCVA) as a seismic vibration control device for structures has been explored in this paper. In this work, the structure has been modeled as a linear, viscously damped single-degree-of-freedom (SDOF) system. The governing differential equations of motion for the damper liquid and for the coupled structure-LCVA system have been derived from dynamic equilibrium. The nonlinear orifice damping in the LCVA has been linearized by a stochastic equivalent linearization technique. A transfer function formulation for the structure-LCVA system has been presented. The design parameters of the LCVA have been identified and by applying the transfer function formulation the optimum combination of these parameters has been determined to obtain the most efficient control performance of the LCVA in terms of the reduction in the root-mean-square (r.m.s.) displacement response of the structure. The study has been carried out for an example structure subjected to base input characterized by a white noise power spectral density function (PSDF). The sensitivity of the performance of the LCVA to the coefficient of head loss and to the tuning ratio have also been examined and compared with that of the liquid column damper (LCD). Finally, a simulation study has been carried out with a recorded accelerogram, to demonstrate the effectiveness of the LCVA.