Tuned Vibration Absorber Research Articles

When things go crunch: Gap length effects on a magnetorheological tunable vibration absorber

A tunable vibration absorber (TVA), where the tunable element is a magneto-rheological (MR) elastomer spring, has demonstrated up to a 460% change on tuning frequency. A frequency increase is associated with a significant decrease in the springs static equilibrium length, referred hereto as a crunch. The crunch is caused by magnetic attractive forces across the spring. The spring, an iron-doped silicone gel, is placed between two halves of a low-carbon steel loop. One loop half behaves as an absorber mass, and has approximately 200 turns of magnet wire around it. Driving current through this wire generates a magnetic flux around the steel path and through the MR spring. Beyond a threshold, the magnetic field induces a large frequency shift in the absorber, with a crunch observed across the elastomer. The crunch can occur when the static equilibrium length is unconstrained by geometry, thus a magnetic attractive force shortens the spring length. The relationship between the magnitude of the crunch and the frequency shift will be presented. Additionally, the impact of different initial MR spring lengths on the frequency behavior will be considered. Finally, the frequency variability achievable by MR-spring-based TVAs with and without the crunch will be assessed.

State Space Implementation of the Algorithm of Mode Isolation

The Algorithm of Mode Isolation (AMI) extracts modal properties from complex frequency response data. Previous work used classic undamped modes as the analytical framework for the algorithm. The present work extends the algorithm to implement damped modal analysis, in which the eigenvalues and eigenvectors are complex. In order to assess how well this reformulation performs when natural frequencies are close and drive point mobilities are low, a prototypical system consisting of a cantilever beam with attached subsystems is introduced. One of these subsystems is selected to be a tuned vibration absorber for the isolated beam, so the system features a combination of modes whose natural frequencies are close and modes whose drive point mobility is low. The time domain response of this system is evaluated, contaminated with substantial white noise, and then FFT processed in order to obtain synthetic complex frequency response data. The performance of AMI is evaluated by comparing extracted values for natural frequency, modal damping ratio, and complex normal mode vectors to the analytical values. The results reveal that the pair of modes having proximite natural frequencies are accurately identified. Natural frequencies and damping ratios for those modes whose drive mobility is low are identified by processing the ensemble of frequency response functions, but identification of normal mode coefficients for such modes remains problematic.

A qualitative analysis of groundhook tuned vibration absorbers for controlling structural vibrations

The primary purpose of this study is to investigate the dynamic characteristics of semi-active groundhook tuned vibration absorbers (TVAs), using closed-form equivalent models of such systems. Closed-form, equivalent models of groundhook TVAs are developed and compared analytically with those for passive TVAs. Additionally, closed-form solutions of groundhook equivalent TVA models are obtained and are used for a parametric study to evaluate the dynamic characteristics of such systems as various parameters change. The numerical results are compared with passive TVAs which have been studied extensively in the past. The results indicate tat groundhook TVAs, with off-state damping levels within a critical value, are capable of lowering the magnitude of resonant peaks without increasing vibration. In contrast, increasing damping in passive TVAs results in a reduction in the amplitude of resonant peaks, at the expense of increased vibrations at the tuned frequency. The results further indicate that increasing the mass ratio between the TVA and the structure increases the effectiveness of groundhook TVAs, in a manner much similar to passive TVAs. However, increasing off-state damping decreases the effectiveness of groundhook TVAs.

PI Control with Anti-Windup in a Nonlinear Phase-Locked Loop

A simple PI controller with anti-windup (PIAW controller) has been developed to control the relative phase between the vibrations of an adaptive tuned vibration absorber (ATVA) and a primary mass to which the ATVA has been attached. The controller and dynamic system combination acts as a phase-locked loop (PLL). This paper compares the PIAW controller with a traditional PLL. In both cases, the forward loop contains a static nonlinearity in series with a linear plant. A benefit of the PIAW controller is that if high gains are used to achieve rapid response times, stability is still guaranteed. While PIAW controller usage has so far been restricted to the ATVA problem in the area of adaptive-passive vibration control, it is anticipated that the controller will have further application in other areas of vibration and motion control research.

Design and Dynamic Analysis of an Adjustable Inertia Absorber for Semiactive Structural Vibration Attenuation

A new class of adaptive tuned vibration absorber, a variable effective inertia absorber, is presented to impart optimum vibration absorption. The tuning scheme has two facets: spectral analysis of the excitation and a concurrent in situ tuning of the absorber. The spectral analysis reveals the frequency content of the excitation. The online tuning uses the frequency content of the excitation to reposition a moving mass and change the damping coefficient of a variable rate damper for optimal (broadband) or tonal vibration suppression. The nonlinear differential equations of motion are linearized and then utilized to develop the online tonal and the broadband tuning of the variable effective inertia absorber. A case study is presented to demonstrate the novelty of the concept. The results show that the retuned absorber delivers considerable vibration suppression improvement over the detuned one.

GLOBAL CONTROL OF STRUCTURAL VIBRATION USING MULTIPLE-TUNED TUNABLE VIBRATION NEUTRALIZERS

Tunable vibration absorbers are used to control vibration due to time-varying harmonic disturbances. Either vibration which is local to the neutralizer, or global vibration of the host structure can be chosen as the quantity to be suppressed. In this paper, the latter is the subject of investigation, but using multiple neutralizers rather than a single device. It is shown that by positioning these devices carefully, the global vibration of a structure (as characterized by its kinetic energy) can be effectively reduced at each single frequency in the frequency range of interest, and is comparable to the performance of active control. A methodology on how to correctly position the devices, an on how to determine their optimum mass is suggested.

The analysis of a state-switched absorber design concept

A tuned vibration absorber (TVA) is a spring-damper-mass system used in many industries for the suppression of a specific vibration frequency, and has application for the suppression of aircraft fuselage vibration. A state-switched absorber (SSA) is similar to a TVA, except that one or more components in the SSA is able to instantaneously and discretely change properties, thus increasing the effective bandwidth of vibration suppression. In order to design a replacement SSA for the classic TVA, the SSA must operate in the appropriate frequency range, be lightweight, and compact. An optimal SSA will also have a maximal frequency range between which it can switch. This paper discusses the development of a magnetorheological (MR) silicone gel used as the SSA switching element, the shape required to maintain a magnetic flux path, and the contribution of the magnet-mass to frequency shifting. The MR gel is iron-doped silicone, cured in the presence of a magnetic field. During operation, the applied magnetic flux is modified to change the natural frequency. The applied flux requirement forces the SSA to be a small ring. The SSA is designed to operate below 100 Hz.

Vibration attenuation of tennis racquets using tuned vibration absorbers

Modern tennis racquets are made of advanced composite materials resulting in significantly lighter and stiffer structures than traditional wooden or metal racquets. While these high-tech structures have had a profound effect on improving the performance of tennis players, modified structural dynamic behaviour and in particular the vibrational response felt by the players has caused some concern thus raising particular interest in vibration attenuation and the application of dynamic vibration absorbers in modern tennis racquet technology. The use of dynamic vibration absorbers is common in engineering applications where there is a need to attenuate high vibration levels caused by resonant response. The effect of using tuned vibration absorbers to attenuate certain key modes of vibration of a tennis racquet is examined in this paper. Attachment of tuned absorbers has traditionally been affected by attaching to antinodal locations of the primary structure. This does not necessarily convey the effectiveness of attachment at other available locations. To overcome this, an effectiveness criterion is formulated and used to indicate the most beneficial attachment location for the devices. The impulse responses obtained from the model are indicative, if not absolute, that tuned vibration absorbers with small mass values could prove effective in the attenuation of key structural modes of the racquet.

Development of a new damper to reduce resonant vibrations in lightweight steel joist floors

Floor vibrations annoying to humans often occur in lightweight constructions. A number of methods to solve the problem of resonant vibrations are reported in the literature. Tuned mass damper, semi-active tuned vibration absorber and active control system are all examples of existing methods. A new method has been tested in laboratory environment on a prefabricated floor containing a resilient ceiling with a size up to 6.8×4.8 m 2. The method takes advantage of small pieces of visco-elastic material connected between the ceiling joists and the primary beams. A finite element model is used to calculate the correct amount of visco-elastic material. The new damper is especially effective in damping mode shapes where the ceiling oscillates out of phase relative to the floor but shows improvements for other mode shapes as well.

Optimally tuned vibration absorbers to control sound transmission

A design optimization method is proposed for controlling broadband vibration of a structure and it concomitant acoustic radiation using multiple-tuned absorbers. A computationally efficient model of a structure is developed and coupled with a nonlinear optimization search algorithm. The eigenvectors of the original structure are used as repeated basis functions in the analysis of the structural dynamic re-analysis problem. The re-analysis time for acoustic power computations is reduced by calculating and storing modal radiation resistance matrices at discrete frequencies. The matrices are then interpolated within the optimization loop for eigenvalues that fall between stored frequencies. The method is demonstrated by applying multiple-tuned vibration absorbers to an acoustically-excited composite panel. The absorber parameters are optimized with an objective of maximizing the panel’s sound power transmission loss. It is shown that in some cases the optimal solution includes vibration absorbers that are tuned very closely in frequency, thus acting effectively as a broadband vibration absorber (BBVA). The numerical model and design optimization method are validated experimentally, and the BBVA is found to be an effective noise abatement tool.

On the Stability of a Tuned Vibration Absorber for Time Varying Multiple Frequencies

A class of actively tuned vibration absorbers is presented. The absorber substructure is controlled using an unconventional position feedback with multiple, unrelated time delays. This control sensitizes the absorber at a number of time-varying frequencies concurrently. It converts the absorber into a multi-frequency resonator (the Multiple Frequency Delayed Resonator or MFDR). The resonator, in turn, acts as a perfect absorber of vibration at its resonance frequencies when it is attached to a harmonically excited primary system. This tuning scheme offers some practical benefits. The highlight of the paper is on the stability analysis of such systems with multiple, unrelated time delays. A new strategy to achieve this, the Directional Stability Chart Method (DSCM), is presented, which is based on a one-dimensional search. A complementary method is also explained, the Local Stability Radius Method (LSRM), which results in a regional stability understanding. Examples are given to demonstrate the capabilities of these methods. Tunability feature to the time varying frequencies is also shown through simulations. A single degree of freedom (SDOF) primary system and a two-degrees-of-freedom (TDOF) absorber are considered for dual frequency suppression as a case study.

Floor vibration control using semi-active tuned mass dampers

This paper discusses the application of a new class of semi-active tuned mass dampers, called ground-hook tuned mass dampers (GHTMD), for the reduction of floor vibrations due to human movements. The TMD introduced uses a continuously variable semi-active damper (ground-hook damper) to achieve reduction in the floor acceleration. Here, the GHTMD is applied to a single degree of freedom system representative of building floors. The GHTMD design parameters are defined in terms of non-dimensional values. The optimum values of these parameters are found based on the minimization of the acceleration response of the floor for different GHTMD mass ratios and floor damping ratios. The performance of the GHTMD is compared to that of the equivalent passive TMD. In addition, the effects of off-tuning due to variations in the mass ratios and frequency ratios of the TMD and GHTMD are studied. Comparison of the results demonstrates the efficiency and robustness of GHTMD with respect to equivalent TMD. Finally, a guide for the design of GHTMDs is presented.Key words: floor vibrations, semi-active tuned mass dampers, tuned vibration absorbers, vibration control, ground-hook dampers, human-induced vibrations, annoying vibrations, optimum design parameters.

Adaptive tuned vibration absorber, system utilizing same and method of controlling vibration therewith

A flex-plate tuned vibration absorber (35) including a tuned mass (43) flexibly suspended by one or more flex plates (58). In one aspect the Tunable Vibration Absorber (TVA) (35) is adaptive in that the position of the mass is adaptively moveable with respect to its initial position, thereby effectuating a change in the TVA's resonant frequency. In one embodiment, the tuned mass (43) moves along a rigid frame (53). In another, movement of the mass (43) statistically stresses a preferably disc-shaped flexible plate (58) thereby changing its stiffness. Preferably, a reducer (78) gears down the speed of the motor (64). In another aspect, a TVA system includes a base sensor (40) providing a base vibration signal, a mass sensor (38) for providing a vibration signal of the tuned mass (43), and an electronic controller (42) for generating a control signal to the TVA (35). The TVA finds application for absorbing vibration in vibrating structures, such as in aircraft.

NON-LINEAR VIBRATION ABSORBER FOR A SYSTEM UNDER SINUSOIDAL AND RANDOM EXCITATION: EXPERIMENTS

A system consisting of a primary structure coupled with a passive tuned vibration absorber is experimentally studied. The primary structure consists of four flexible columns with a mass, while the absorber consists of a beam with a tip-mass. The system, which is a coupled non-linear oscillator, is subjected to sinusoidal and random excitation. The effects of the forcing frequency, forcing amplitude, mass ratios and frequency ratios on the displacement response of the system in the neighborhood of the autoparametric region are studied. Control parameters related to effectiveness of the absorber are determined. The objective of this study is to experimentally define an absorption region for the passive vibration absorber and to determine the parameters that influence the effectiveness of the vibration absorber.

ADAPTIVE-PASSIVE ABSORBERS USING SHAPE-MEMORY ALLOYS

The adaptive-passive vibration absorber shows promise for combining the stability and low complexity of passive tuned absorbers with the robust performance of active vibration control schemes. Previous adaptive tuned vibration absorbers (ATVA) had been complex and bulky. Shape memory alloys (SMA), with their variable material properties, offer an alternative adaptive mechanism. Heating an SMA causes a change in the elastic modulus of the material. An ATVA using spring elements composed of three pairs of SMA wires and one pair of steel wires was constructed and tested. On–off actuation of the SMA elements created an ATVA with four discrete tuned frequencies. Characterization testing of the absorber showed variation of the natural frequency of the ATVA of approximately 15%. The ATVA was applied to a primary system and the frequency response of the system at various states of ATVA actuation was determined. Manual tuning of the ATVA actuation during a stepped-sine base excitation of the primary system showed a wider notch of attenuation than was possible with a non-adaptive absorber. Results of the tests indicate that an adaptive absorber incorporating SMA as a tuning element has potential as a simple, high-performance adaptive-passive technique for vibration control.

Experimental validation of the state-switched absorber for two-component harmonic forcing

A state-switched vibration absorber (SSA) is a semiactive device that is capable of instantaneously changing its dynamical state by altering its stiffness. However, the SSA can switch between more than one resonance frequency, providing a greater bandwidth as compared to classical tuned vibration absorbers. Modeling predictions indicate that with appropriate logic for switching between states, the SSA is more effective at vibration suppression than classical tuned vibration absorbers, when the system to be controlled is subject to a disturbance with more than one spectral component. This presentation considers the experimental validation of SSA performance for the suppression of vibration on a driven elastically mounted lumped mass system. The SSA considered here is implemented in a dynamical proof-of-concept demonstrator. State switching is effected through the use of a magneto-rheological fluid clamp to connect or disconnect a coil spring in parallel with another coil spring. The two coil springs, one switchable, the other not, constitute the spring element of an otherwise passive mass-spring-damper vibration absorber. The stiffness state is controlled by actuation of the MR clamp. The experimentally observed performance of the SSA will be presented and compared to modeling predictions. [This work is based upon work supported by, or in part by, the U.S. Army Research Laboratory and the U.S. Army Research Office under Grant No. 38955-EG, Dr. Gary Anderson, Technical Monitor.]

Damping characteristics of particle dampers—some preliminary results

Particle dampers offer considerable potential for suppressing structural resonant conditions over a wide frequency range compared with tuned mass dampers or tuned vibration absorbers. However, they exhibit non-linear behaviour which relates to the motion of the particles that in turn is dependent on the excitation level. This communication describes some preliminary experimental results on the damping characteristics of a particle damping device which clearly show that the damping levels are dependent on the geometry of the device and the resulting motion of the particles arising from the level of the input excitation.

High Bandwidth Tunability in a Smart Vibration Absorber

An electrically tunable vibration absorber based on the strong δ E effect of Terfenol-D has been developed. A general description of tuned vibration absorbers is presented along with a description of the magnetostrictive effects that make an electrically tunable Terfenol-D vibration aborber function. It is emphasized that the large modulus changes achievable with the proposed magnetostrictive vibration absorber arise as a consequence of the stiffening of the crystal lattice as the magnetic field is increased from the demagnetized state to magnetic saturation. This is in contrast to the small modulus changes often reported in the literature which are achieved by operating smart materials between their open- and short-circuit states. Experimental results are presented that show agreement with prior art and demonstrate control of a magnetostrictive actuator resonant frequency between 1375 Hz and 2010 Hz by electrically varying the elastic modulus of a magnetostrictive material. This operating principle is then implemented to obtain high bandwidth tunability in a Terfenol-D vibration absorber.

Chatter suppression in turning operations with a tuned vibration absorber

In this paper, a piezoelectric inertia actuator is mounted on the cutting tool and acted as a tuned vibration absorber for the suppression of chatter in turning operations. It is shown that the tuned vibration absorber can modify the frequency response function of the cutting tool so as to improve cutting stability in turning operations. Chatter can then be effectively suppressed due to the increase of cutting stability. Theoretical studies and experimental results performed in turning operations are presented to illustrate this approach.

A STANDING-WAVE-TYPE SLOSHING ABSORBER TO CONTROL TRANSIENT OSCILLATIONS

The primary purpose of this study is to introduce a sloshing absorber as a practical alternative to the damped tuned absorber. In addition, a numerical simulation procedure is introduced as a computer-aided design tool. The problem of interest is the control of excessive oscillations of a mechanical oscillator in response to an initial displacement. Tuned vibration absorbers are frequently used for this purpose, and if damping is included in the tuned absorber, control action is quite effective. The problem, however, is that inclusion of an energy dissipation element necessitates frequent maintenance in practice. The suggested control technique here is a sloshing absorber, in place of the damped tuned vibration absorber. In contrast to a tuned absorber, a sloshing absorber accomplishes energy dissipation through sloshing. Therefore, it may be virtually maintenance free. Also for practical applications, this type of absorber can be an advantage where existing water storage tanks can be modified to control vibrations of the supporting structure.