Showing papers on "Dynamic Vibration Absorber published in 2011"

The design of an active–adaptive tuned vibration absorber based on magnetorheological elastomer and its vibration attenuation performance

Abstract: This paper presents an active–adaptive tuned vibration absorber (AATVA) which is based on magnetorheological elastomer (MRE). A voice coil motor is attached to a conventional MRE adaptive tuned vibration absorber (ATVA) to improve its performance. In this study, two feedback types of the activation force were analyzed and the stability condition was obtained. In order to eliminate the time delay effect during the signal processing, a phase-lead compensator was incorporated. Based on the analysis, an MRE AATVA prototype was designed and its dynamic properties were experimentally investigated. The experimental results demonstrated that its resonant frequency could vary from 11 to 18 Hz and its damping ratio decreased to roughly 0.05 from 0.19 by adding the activation force. Besides, its vibration reduction abilities at the first two resonant frequencies of the experimental platform could reach 5.9 dB and 7.9 dB respectively. (Some figures in this article are in colour only in the electronic version)

An adaptive tunable vibration absorber using a new magnetorheological elastomer for vehicular powertrain transient vibration reduction

Abstract: During the transient stage of acceleration, the powertrain experiences a period of high level vibration because the engine speed passes through one or several powertrain natural frequencies. This paper presents a concept design of an adaptive tuned vibration absorber (ATVA) using a new magnetorheological elastomer (MRE) for powertrain transient vibration reduction. The MRE material used to develop the ATVA is a new one, which is synthesized from a highly elastic polymer and carbonyl iron particles of 3–5 and 40–50 µm. Under a magnetic field of 0.3 T, the MRE material has a giant increase, which is more than two orders, in both the storage and loss moduli. To facilitate the ATVA design, effective formulae for the storage modulus and loss factor were derived as explicit functions of the applied magnetic field density. With the derived formulae, ATVA parameters such as the stiffness and damping coefficients were converted effectively from the magnetic field density. Thus, the ATVA frequency can be tuned properly according to the excitation frequency. Numerical simulations of a powertrain system fitted with the ATVA were conducted to examine the ATVA proposed design. By using the MRE-based ATVA, the powertrain natural frequencies can be actively tuned far away from the resonant area of excitation frequency. Also, the time histories of powertrain frequencies depending on the magnetic field density before and after installing the ATVA have been compared to show that the resonant phenomena have been dealt with completely. As a result, the powertrain transient vibration response is significantly suppressed. In addition, the effect of the ATVA's moment of inertia, stiffness and damping on the ATVA's effectiveness during the transient stage was investigated to choose the ATVA's optimal parameters. The MRE-based ATVA will be a novel device for powertrain vibration control not only for the steady stage but also for transient vibration.

Theory of Vibration: An Introduction

Abstract: 1 Introduction.- 1.1 Basic Definitions.- 1.2 Elements of the Vibration Models.- 1.3 Particle Dynamics.- 1.4 Systems of Particles.- 1.5 Dynamics of Rigid Bodies.- 1.6 Linearization of the Differential Equations.- 1.7 Idealization of Mechanical and Structural Systems.- Problems.- 2 Solution of the Vibration Equations.- 2.1 Homogeneous Differential Equations.- 2.2 Initial Conditions.- 2.3 Solution of Nonhomogeneous Equations with Constant Coefficients.- 2.4 Stability of Motion.- Problems.- 3 Free Vibration of Single Degree of Freedom Systems.- 3.1 Free Undamped Vibration.- 3.2 Analysis of the Oscillatory Motion.- 3.3 Stability of Undamped Linear Systems.- 3.4 Continuous Systems.- 3.5 Equivalent Systems.- 3.6 Free Damped Vibration.- 3.7 Logarithmic Decrement.- 3.8 Structural Damping.- 3.9 Coulomb Damping.- 3.10 Self-Excited Vibration.- 3.11 Motion Control.- 3.12 Impact Dynamics.- Problems.- 4 Forced Vibration.- 4.1 Differential Equation of Motion.- 4.2 Forced Undamped Vibration.- 4.3 Resonance and Beating.- 4.4 Forced Vibration of Damped Systems.- 4.5 Rotating Unbalance.- 4.6 Base Motion.- 4.7 Measuring Instruments.- 4.8 Experimental Methods for Damping Evaluation.- Problems.- 5 Response to Nonharmonic Forces.- 5.1 Periodic Forcing Functions.- 5.2 Determination of the Fourier Coefficients.- 5.3 Special Cases.- 5.4 Vibration Under Periodic Forcing Functions.- 5.5 Impulsive Motion.- 5.6 Response to an Arbitrary Forcing Function.- 5.7 Frequency Contents in Arbitrary Forcing Functions.- 5.8 Computer Methods in Nonlinear Vibration.- Problems.- 6 Systems with More Than One Degree of Freedom.- 6.1 Free Undamped Vibration.- 6.2 Matrix Equations.- 6.3 Damped Free Vibration.- 6.4 Undamped Forced Vibration.- 6.5 Vibration Absorber of the Undamped System.- 6.6 Forced Vibration of Damped Systems.- 6.7 The Untuned Viscous Vibration Absorber.- 6.8 Multi-Degree of Freedom Systems.- Problems.- 7 Continuous Systems.- 7.1 Free Longitudinal Vibrations.- 7.2 Free Torsional Vibrations.- 7.3 Free Transverse Vibrations.- 7.4 Orthogonality of the Eigenfunctions.- 7.5 Forced Longitudinal and Torsional Vibrations.- 7.6 Forced Transverse Vibrations.- Problems.- References.- Answers to Selected Problems.

Numerical Investigation of an Adaptive Vibration Absorber Using Shape Memory Alloys

Abstract: The tuned vibration absorber (TVA) is a well-established passive vibration control device for achieving vibration reduction of a primary system subjected to external excitation This contribution deals with the non-linear dynamics of an adaptive tuned vibra- tion absorber (ATVA) with a shape memory alloy (SMA) element Initially, a single-degree of freedom oscillator with an SMA element is analyzed showing the general characteristics of its dynamical response Then, the analysis of an ATVA with an SMA element is carried out Initially, small amplitude vibrations are considered in such a way that the SMA element does not undergo a stress-induced phase transformation Under this assumption, the SMA influ- ence is only caused by stiffness changes corresponding to temperature-induced phase trans- formation Afterwards, the influence of the hysteretic behavior due to stress-induced phase transformation is considered A proper constitutive description is employed in order to cap- ture the general thermomechanical aspects of the SMAs The hysteretic behavior introduces complex characteristics to the system dynamics but also changes the absorber response allow- ing vibration reduction in different frequency ranges Numerical simulations establish com- parisons of the ATVA results with those obtained from the classical TVA

A magnetorheological fluid embedded pneumatic vibration isolator allowing independently adjustable stiffness and damping

Abstract: A magnetorheological (MR) fluid embedded pneumatic vibration isolator (MrEPI) with hybrid and compact connection of pneumatic spring and MR damping elements is proposed in this study. The proposed MrEPI system allows independent nonlinear stiffness and damping control with considerable maneuverable ranges. Meanwhile, it allows convenient switching between different passive and active vibration control modes, thus providing more flexibility and versatility in applications. To demonstrate the advantageous dynamic performance of the MrEPI, a nonlinear non-dimensional dynamic model is developed with full consideration of the nonlinear elements involved. A systematic analysis is therefore conducted which can clearly reveal the influence on system output performance caused by each physically important parameter and provide a useful insight into the analysis and design of nonlinear vibration isolators with pneumatic and MR elements.

Control of torsional rotor vibrations using an electrorheological fluid dynamic absorber

Abstract: Torsional rotor vibrations are undesirable phenomena which are very difficult to control in rotating systems. A common method for reducing vibrations involves the use of dynamic absorbers. However, if their physical parameters are constant, the frequency range of efficiency of dynamic absorbers is tight, making them unsuitable for systems with variable speeds. The use of smart materials, due to their variable and controllable mechanical properties, may be a powerful tool for increasing the frequency range. Electrorheological (ER) fluids are attractive materials that undergo very fast reversible changes in their rheological properties upon the application of an electric field. In this study, an electrorheological dynamic torsional absorber, called the Smart ER Dynamic Absorber, has been designed in order to reduce torsional rotor vibrations. Under shear mode, the ER absorber can exhibit various torsional damping and stiffness characteristics when an electric field is applied. A nonlinear empirical model of...

Suppressing harmonic vibrations of a miniature cryogenic cooler using an adaptive tunable vibration absorber based on magneto-rheological elastomers

Abstract: This paper presents dynamic performances of an adaptive tunable vibration absorber (TVA) designed to suppress the main harmonic disturbance of a miniature linear cryogenic cooler, which is being used in space applications such as an observation satellite. The adaptive TVA employs a magneto-rheological elastomer (MRE) for a variable stiffness element. This study first investigates the shear modulus change of MRE samples with respect to the magnetic flux density, which varies through the alignment of particle chains. The MRE with the maximal shear modulus change is mounted for the TVA on a prototype cooler, which emulates the characteristics of a miniature cryogenic cooler. Using the test setup, a series of vibration tests are performed to evaluate the performance and efficacy of the MRE TVA and its re-tuning ability. The experimental results show that the MRE TVA is able to robustly suppress the vibration of the cooler even when the frequency of resonant vibration is changed up to 87% from its initial frequency.

Flutter Control of a Lifting Surface via Visco-Hysteretic Vibration Absorbers

Abstract: In this paper, a visco-hysteretic vibration absorber (VA) is proposed to increase the flutter speed of an airfoil and enhance damping in the pre- and post-flutter regimes. The passive system consists of a parallel arrangement of a dashpot and a rateindependent hysteretic element, represented by the Bouc-Wen differential model. The equations of motion are obtained and various tools of linear and nonlinear dynamics are employed to study the effects of the visco-hysteretic VA in the pre- and postflutter ranges.

Comparison of negative and positive position feedback control of a flexible structure

Abstract: Two modal control techniques, negative position feedback (NPF) and positive position feedback (PPF), are applied to reduce multi-mode vibration of a lightly damped flexible beam using a piezoelectric sensor and piezoelectric actuators. The NPF and PPF controllers are constructed by respectively feeding back the generalized displacement response from the sensor in a negative and a positive sense to the actuators through second order high pass and low pass filters. PPF is well known while NPF is new for this application and is in fact an electrical realization of a dynamic vibration absorber. The choice of the parameters for controllers of both types is made easy by a robust modal control technique that offers an optimal performance for NPF control and a near-optimal performance for PPF control. Explicit forms of the controller parameters are presented. Experiments are conducted on a cantilever beam embedded with a matched pair of PZT (lead zirconate titanate) patch actuators and a collocated PVDF (polyvinylidene fluoride) patch sensor. The experiments demonstrate that it is possible to realize an electrical dynamic absorber using the generalized displacement sensor. It is further demonstrated that NPF can be a good alternative control strategy particularly when multiple modes are to be controlled.

Optimal and robust modal control of a flexible structure using an active dynamic vibration absorber

Abstract: This paper is concerned with feedback vibration control of a lightly damped flexible structure that has a large number of well-separated modes. A single active electrical dynamic absorber is used to reduce a particular single vibration mode selectively or multiple modes simultaneously. The absorber is realized electrically by feeding back the structural acceleration at one position to a collocated piezoceramic patch actuator via a controller consisting of one or several second order lowpass filters. A simple analytical method is presented to design a modal control filter that is optimal in that it maximally flattens the mobility frequency response of the target mode, as well as robust in that it works within a prescribed maximum control spillover of 2 dB at all frequencies. Experiments are conducted with a free–free beam to demonstrate its ability to control any single mode optimally and robustly. It is also shown that an active absorber with multiple such filters can effectively control multiple modes simultaneously.

Fluid transmission apparatus

Abstract: A fluid transmission apparatus including a pump impeller that is connected to an input member coupled to a motor; a turbine runner that is rotatable together with the pump impeller; a damper mechanism that includes an input element, an intermediate element engaged with the input element via a first elastic body and an output element engaged with the intermediate element via a second elastic body; a lock-up clutch mechanism; a dynamic damper that includes a mass body and a third elastic body engaged with the mass body; and a centrifugal pendulum vibration absorber that includes a support member and a plurality of mass bodies each oscillatable with respect to the support member. The third elastic body of the dynamic damper is engaged with one of the intermediate element and the output element. The centrifugal pendulum vibration absorber's support member is connected to the intermediate element or the output element.

Machinery-electric-hydraulic Coupling Vibration Control of Hot Continuous Rolling Mills

Abstract: Thin slab continuous-casting and continuous-rolling mill appear different degree of serious vibration phenomenon when rolling thin strip in the world.The vibration phenomenon lead the strip and rolls to generate obvious stripe,which affects product quality and enterprise external image and economic benefits.Using self-made comprehensive telemetry system test the rolling mills vibration parameters,force and energy parameters,electric parameters and technological parameters in the site.Analysing the test signal in the time and frequency domain,characteristics and rules of vibration can be obtain.Through the theoretical and simulation research,it is found that rolling mill do exist vertical-twist coupling vibration,electro-mechanical coupling vibration and liquid-mechanical coupling vibration phenomenon.So confirming the nature of the rolling mill vibration is mechanical-electrical-liquid coupling vibration.Based on modification and optimization of the electric drive control system and AGC system,applying the designing second order torsional vibration observer in the main drive control system and optimizing AGC parameters,the main drive system of the second order torsional vibration is restrained effectively.By site assessment,the roll system vibration is reduced obviously,and it is inhibited rolling mill mechanical-electronic-liquid coupling vibration phenomenon,so it has obtained the remarkable economic and social benefits.

Development of a Mechanical Semi-Active Vibration Absorber

Abstract: A Semi-Active Vibration Absorber (SAVA) can suppress the vibration with time-varying frequency by tuning its natural frequency to track the excitation frequency. This paper presents the development of a mechanical SAVA whose natural frequency can be adjusted in real time by adjusting its geometry parameters. The principle and dynamic properties of the SAVA were theoretically analyzed. Based on these analyses, a prototype SAVA was designed and implemented. An optimum variable step-size control strategy of the SAVA was investigated. This control strategy is made up by two stages: the roughly tuning stage and the optimization stage. Some experiments were conducted to evaluate the dynamic properties and vibration attenuation performance of the SAVA. The experimental results indicate that the developed SAVA can tune its natural frequency in a large frequency range and its vibration attenuation effect is significantly improved compared with a Tuned Vibration Absorber (TVA).

A Novel Semiactive Variable Stiffness Device and Its Application in a New Semiactive Tuned Vibration Absorber

Abstract: An innovative design for a semiactive variable stiffness (SAVS) device is presented in this paper. This beamlike device is capable of altering its stiffness in a smooth manner between minimum and maximum levels by using the variations of moment of inertia of an area as it rotates around a normal axis passing through its centroid. Analytical expressions for the stiffness of the proposed device have been derived. As an application of the SAVS device in engineering, a semiactive tuned vibration absorber (SATVA) is developed that is capable of real-time retuning and operates effectively in broadband frequency excitations. A single-degree-of-freedom (SDOF) system coupled with the SATVA is considered. The excitation force is assumed to arise from a rotating unbalance whose frequency varies with a constant acceleration and then reaches a steady-state operating condition. The absorber stiffness is varied to tune the absorber's natural frequency to the forcing frequency in real time. The effectiveness of SATVA is evaluated by comparing the system's responses with those of the system with passive vibration absorber. The results show the salient features of the proposed SATVA in transient response reduction compared with the traditional passive vibration absorber.

A new isolator for vibration control

Abstract: This study presents the feasibility of a new variable stiffness and damping isolator (VSDI) in an integrated vibratory system. The integrated system comprised of two VSDIs, a connecting plate and a mass. The proposed VSDI consists of a traditional steel-rubber vibration absorber, as the passive element, and a magneto-rheological elastomer (MRE), with a controllable (or variable) stiffness and damping, as the semi-active element. MREs' stiffness and damping properties can be altered by a magnetic field. Dynamic testing on this integrated system has been performed to investigate the effectiveness of the VSDIs for vibration control. Experimental results show significant shift in natural frequency, when activating the VSDIs. Transmissibility and natural frequency of the integrated system are obtained from properties of single device. The experimental and predicted results show good agreement between the values of the natural frequency of the system at both off and on states. However, system damping predictions are different from experimental results. This might be due to unforeseen effects of pre-stressed MREs and nonlinear material properties.

Adaptive Tuned Vibration Absorbers: Design Principles, Concepts and Physical Implementation

Abstract: The tuned vibration absorber (TVA) has been used for vibration control purposes in many sectors of civil/automotive/aerospace engineering for many decades since its inception by (Ormondroyd & Den Hartog, 1928). A tuned vibration absorber (TVA), in its most generic form, is an auxiliary system whose parameters can be tuned to suppress the vibration of a host structure. The auxiliary system is commonly a spring-mass-damper system (or equivalent) and the TVA suppresses the vibration at its point of attachment to the host structure through the application of an interface force. The tuned frequency a  of the TVA is defined as its undamped natural frequency with its base (point of attachment) blocked. The TVA can be used in two distinct ways, resulting in different optimal tuning criteria and design requirements (von Flotow et al., 1994): a. It can be tuned to suppress (dampen) the modal contribution from a specific troublesome natural frequency s  of the host structure over a wide band of excitation frequencies. b. It can be tuned to suppress (neutralise) the vibration at a specific troublesome excitation frequency  , in which case it acts like a notch filter. When used for application (a), the TVA referred to as a “tuned mass damper” (TMD). a  is optimally tuned to a value slightly lower than that of the targeted mode s  and an optimal level of damping needs to be designed into the absorber. When used for application (b), the TVA is referred to as a “tuned vibration neutraliser” (TVN) (Brennan, 1997, Kidner & Brennan, 1999) or “undamped TVA”. The optimal tuning condition is in this case is a    and the TVN suppresses the vibration over a very narrow bandwidth centred at the tuned frequency. Total suppression of the vibration at this frequency is achieved when there is no damping in the TVN. Deviation from the tuned condition (mistuning) degrades the performance of either variant of the TVA (von Flotow et al., 1994) and it can be shown that a mistuned vibration neutraliser could actually increase the vibration of its host structure (Brennan, 1997). To avoid mistuning, smart or adaptive tunable vibration absorbers (ATVAs) have been developed. Such devices are capable of retuning themselves in real time. Adaptive technology is especially important in the case of the TVN since the low damping requirement in the spring element can raise the host structure vibration to dangerous levels

Optimization of anisotropic sandwich beams for higher sound transmission loss

Abstract: This study aims to predict the vibration damping and sound transmission properties of composite laminated thin-walled structures with the attached dynamic vibration absorbers systems. In this paper, the effective stiffness constants (the equivalent Timoshenko beam) of sandwich type laminates and their damping properties have been determined by using a procedure based on multi-level numerical schemes. Numerical evaluations obtained for the vibration of the laminates have been used to determine the displacement field for the analysis of the vibration and sound transmission properties of laminated composite beams in the lower frequency range.

Developing a real time controlled adaptive MRE-based tunable vibration absorber system for a linear cryogenic cooler

Abstract: To cool down image sensors in observation satellites, a miniature linear cryogenic cooler is used. The cooler operates at a constant frequency and it creates the main vibration disturbance that is transmitted to the image sensors, causing poor image quality. A semi-active vibration system using a tuned vibration absorber (TVA) has shown to be effective for suppressing the cooler vibrations. However, if the cooler operating frequency changes, the off-tuned TVA loses its effectiveness. To automatically retune the TVA to the varying disturbance frequency, this paper proposes a control strategy of the TVA using magnetorheological elastomer(MRE). It focuses on the development of a real time control system for an 2-DOF MRE based TVA applied on a linear cooler.

Earthquake resistnat type switchgear using elastic supporting element providing kinesis

Abstract: PURPOSE: An earthquake proof type distribution panel equipped with a non-direction elastic support board is provided to protect a closure body and devices within the enclosure body by installing a vibration absorber absorbing the vibration of the seismic wave delivered from the ground CONSTITUTION: An upper channel(310), coupled to a base, supports a distribution panels A lower channel(320) is installed on the ground or a floor side of a building in order to cope with the upper channel A plurality of coil spring mounts(330), installed between the upper channel and the lower channel, absorbs the vibration and the impact transferred from the ground A plurality of revolution support members(400), installed between the upper channel and the lower channel, support the upper channel and eliminates the support force by revolving when a vibration occurs A plurality of hydraulic cylinders(500), installed on the ground or the floor side of the building, transfers the upper channel up and down within a set section