State-switched Absorber Research Articles

Experimental Vibration Control of a Single-Degree of Freedom System Using a State-Switched Absorber

A state-switched absorber (SSA) is a device capable of instantaneously switching between resonance frequencies, increasing its effective bandwidth as compared to classical tuned vibration absorbers (TVAs) for vibration control. Previous simulations show that for a system subjected to a multi-harmonic disturbance, the SSA reduces vibration more effectively than classical TVAs. This study considers the experimental performance of the SSA for vibration suppression of an elastically mounted lumped mass base. State switching is achieved using a clutch to connect or disconnect a coil spring in parallel with other coil springs. An SSA system outperforms a classical TVA system for several combinations of forcing frequencies.

Investigation of the Two-state, Maximum Work Extraction Switching Rule of a State-switched Absorber for Vibration Control

A state-switched absorber (SSA) is a derivative of a classical tuned vibration absorber (TVA). An SSA is a mass-spring-damper system that is capable of instantaneously changing its stiffness, thus is capable of instantaneously changing its resonance frequency. Between instantaneous switch events, the absorber is a passive device, acting similarly to a classical TVA. When a switch event occurs, the SSA instantly changes its stiffness, effectively `retuning' its resonance frequency. At this point, the SSA remains tuned to this new frequency until the next switch event, where it changes frequencies again. Previous research has shown that applying a maximum work extraction switching rule to a two-stiffness-state absorber results in improved performance of the SSA over classical vibration absorbers. The article at hand investigates the two-state, maximum work extraction switching rule in more detail. Specifically, the explanation of how the switching rule reduces the vibration of the base to which it is attached is considered. The article also details the stability of such a switching rule.

Application of dynamic vibration absorbers in structural vibration control under multi-frequency harmonic excitations

In this research, the response properties of a single-degree-of-freedom system under dual harmonic excitation are analyzed to provide some principles for the choice of time span and step in the simulations. The performances of dynamic vibration absorber (DVA) and state-switched absorber (SSA) are compared. The results indicate that dual DVAs almost have the same performance as the SSA. Moreover, dual DVAs compared with the SSA have some advantages such as lower ratio of tuning frequencies, more rapid optimization process and lower requirement for the anti-fatigue property of the material. Furthermore, the performances of different frequency-tuning methods are investigated. It is shown that the one–one method almost has the same performance as the optimization method and it does not need time-consuming optimization process.

A State-Switched Absorber Used for Vibration Control of Continuous Systems

A state-switched absorber (SSA) is a device that is capable of switching between discrete stiffnesses; thus, it is able to instantaneously switch between resonance frequencies. The state-switched absorber is essentially a passive vibration absorber between switch events; however, at each switch event the SSA instantly “retunes” its natural frequency and maintains that frequency until the next switch event. This paper considers the optimization of the state-switched absorber applied to a continuous vibrating system and details the experimental validation of these simulation results. A simulated annealing optimization algorithm was utilized to optimize the state-switched absorber. For the most part, the SSA performed only marginally better than a classical tuned vibration absorber (TVA). However, for a select few cases considered, the SSA was able to reduce the kinetic energy of the plate to which it is attached by 12.9dB over that of a classical tuned vibration absorber. The optimal SSA location on a clamped square plate was near the center of the plate for the vast majority of the forcing cases considered. To experimentally validate the simulation, a SSA was fabricated by employing magnetorheological elastomers to achieve a stiffness change. For several two-force component excitations, several tuning configurations of the SSA were applied and the kinetic energy of the system was found and optimized. As with the majority of the optimization cases, the experiments showed the SSA outperforming the TVA by only 2dB. When comparing the observed results to those found via simulation, the simulations accurately predicted the performance of the SSA in the experiments.

Quarter-Cycle Switching Control for Switch-Shunted Dampers

Significant interest has been generated by the possibilities of active vibration control through the implementation of state switching, with a specific implementation embodied through piezoceramic shunting. A state-switched absorber (SSA) is a vibration absorber that has the unique ability to change its resonant state amongst multiple distinct resonant states while in motion, thereby increasing the effective bandwidth over that of a single frequency device and thereby allowing control of multi-frequency, transient, and time-varying disturbances. In contrast, a switch-shunted damper (SSD) is a variant of an SSA that is used to increase the damping of the structure to which the damper is applied. Active vibration control applications discussed in the literature indicate the potential advantages of SSDs which employ piezoelectric ceramics as switchable springs with control algorithms that require switching states at points of non-zero strain. However, consideration of the constitutive equations for piezoelectric materials indicates a discontinuity in the electrical and mechanical conditions imposed by switching the stiffness at non-zero strains. A prototype SSD has been built and tested to experimentally investigate switching control logic and electrical and mechanical discontinuities at switching points; experimental measurements with this prototype SSD indicate that quarter-cycle switching algorithms which include switching states at a condition of maximum strain yield enhanced damping effectiveness but also leads to the generation of potentially undesirable mechanical transients.

Damping Effects on the State-Switched Absorber Used for Vibration Suppression

A state-switched device is conceptually capable of instantaneously changing its mass, stiffness, or damping. Such a device will exhibit different dynamical response properties (modes and resonance frequencies) depending on its current state. A state-switched vibration absorber exploits the state-switching concept for the purposes of enhanced vibration suppression. Between each state switch, it is fundamentally a passive vibration absorber, but one which exhibits a different tuning frequency for each possible state. A state-switched vibration absorber therefore has a greater effective bandwidth than a classical passive absorber. This paper considers the role of damping in the state-switching concept for a simple one-degree of freedom system and for a two-degree of freedom system. Certain values of damping in the system improve performance, while other values hinder the performance of the state-switched absorber, as compared to classical absorbers. The predicted performance of the system also depends upon the particular damping model used, such as viscous absorber or system modal damping. Damping values also affect the frequency of switch events that occur during the response of the system. In general, the highest relative performance of the state-switched absorber as compared to a classical vibration absorber occurs at low values of damping.

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.

State-Switched Absorber for Vibration Control of Point-Excited Beams

A system that has the capability to make instantaneous changes in its mass, stiffness, or damping may be termed a state-switchable dynamical system. Such a system will display different dynamical responses dependent upon its current state. State-switchable stiffness may be practically obtained through the control of the termination impedance of piezoelectric stiffness elements. If such a switchable stiffness element is incorporated as part of the spring element of a vibration absorber, the change in stiffness causes a change in the resonance frequencies of the system, thereby instantaneously ‘retuning’ the state-switched absorber to a new frequency. In between state switches, the operation of such a device is passive, being fundamentally a passive vibration absorber. This concept has improved performance over classical passive vibration absorbers or dampers, particularly for disturbances with multiple spectral components. This paper considers the application of such a device for the purpose of vibration control on beams subjected to harmonic point-force excitation.

State-Switched Absorber for Semi-Active Structural Control

A system that has the capability to make instantaneous changes in its mass, stiffness, or damping may be termed a state-switchable dynamical system. Such a system will display different dynamical responses dependent upon its current state. For example, state-switchable stiffness may be practically obtained through the control of the termination impedance of piezoelectric stiffness elements. If such a switchable stiffness element is incorporated as part of the spring element of a vibration absorber, the change in stiffness causes a change in the resonance frequencies of the system, thereby instantaneously “retuning” the state-switched absorber to a new frequency. This paper briefly develops the fundamental analysis tools for a Single-Degree-of-Freedom state-switchable device, and then considers the application of such a device for the purpose of vibration control in a 2-DOF system. Simulation results indicate that state-switched vibration absorbers may be advantageous over classical passive tuned vibration absorbers under certain conditions.