Tuned Vibration Absorber Research Articles

Lever-Based Semiactive Inerter and Its Application in Vibration Absorbers

In this paper, a lever structure is proposed to enlarge the range of inertances of existing semiactive inerters. A semiactive inerter with the lever structure would be called lever-based semiactive inerter. The transmission ratio of the lever-based semiactive inerter can be changed by setting a different ratio of the arm of force of the lever, and then the range of inertance of the lever-based semiactive inerter can be enlarged. This paper also presents the mechanical model of the proposed lever-based semiactive inerter. The lever-based semiactive inerter is applied to an adaptive tuned vibration absorber. The frequency-tracker-based control algorithm is derived to maximize vibration reduction of the absorber. It can be shown that the vibration absorber with the lever-based semiactive inerter can adapt to a broader range of frequencies of vibration compared with that of the classical semiactive inerter.

Adaptive Electromagnetic Vibration Absorber for a Multimode Structure

All structures experience vibrations due to external dynamic force excitations, such as earthquakes and wind loadings. At resonance, the impact of this natural dynamic force on structures may lead to structural failures. Hence, an absorber is mounted to absorb vibrations from the primary system. Unfortunately, passive tuned mass absorbers can only target a single frequency. Since structural buildings possess multiple modes, an adaptive or tune-able vibration absorber is needed to attenuate the vibration in a multi-degree of freedom (MDOF) system. In this work, an adaptive electromagnetic vibration absorber (AEMVA) is proposed to eliminate the effects of vibrations and is dynamically tuned using electromagnets. By varying the current supplied to the coil, the stiffness of the AEMVA can be adjusted, resulting in a varying absorber frequency. A mathematical description of the AEMVA on a three-story prototype model building is also presented. The three-story benchmark model was used to demonstrate the effectiveness of AEMVA in absorbing multiple vibration modes, both analytically and experimentally. It is shown that 68.81 %, 50.49 %, and 33.45 % of vibration amplitude reductions were achieved at the first, second, and third modes, respectively.

Adaptively tunable magnetorheological elastomer-based vibration absorber for a propeller aircraft seat

In this study, a simple but effective design of an adaptively tunable magnetorheological elastomer (MRE)-based seat vibration absorber (SVA) is presented to achieve better vibration reduction of a propeller aircraft seat. In order to effectively concentrate the magnetic field generated from the electromagnet into the MRE pad areas, an electromagnetic finite element analysis (FEA) was also conducted. Based on this FEA, the MRE-based SVA was fabricated. The damping force characteristics of the MRE-based SVA were experimentally evaluated using an Instron testing machine. The dynamic stiffness and loss factor of the MRE-based SVA were obtained using this test data. In order to confirm the tunability of the MRE-based SVA, the transmissibility with respect to a range of applied input currents was experimentally obtained via vibration testing.

Online Frequency Estimation on a Building-like Structure Using a Nonlinear Flexible Dynamic Vibration Absorber

The online frequency estimation of forced harmonic vibrations on a building-like structure, using a nonlinear flexible vibration absorber in a cantilever beam configuration, is addressed in this article. Algebraic formulae to compute online the harmonic excitation frequency on the nonlinear vibrating mechanical system using solely available measurement signals of position, velocity, or acceleration are presented. Fast algebraic frequency estimation can, thus, be implemented to tune online a semi-active dynamic vibration absorber to obtain a high attenuation level of undesirable vibrations affecting the main mechanical system. A semi-active vibration absorber can be tuned for application where variations of the excitation frequency can be expected. Adaptive vibration absorption for forced harmonic vibration suppression for operational scenarios with variable excitation frequency can be then performed. Analytical, numerical, and experimental results to demonstrate the effectiveness and efficiency of the operating frequency estimation, as well as the acceptable attenuation level achieved by the tunable flexible vibration absorber, are presented. The algebraic parametric estimation approach can be extended to add capabilities of variable frequency vibration suppression for several configurations of dynamic vibration absorbers.

Sensitivity Analysis of Suppressing Vibration by Inducing a Node on a Harmonically Forced Euler–Bernoulli Beam

Abstract In this paper, a properly tuned vibration absorber (spring-mass system) is used to induce a point of zero vibration, or node, anywhere along an arbitrarily supported beam for the purpose of suppressing vibration. Other benefits of enforcing a node include the ability to place a sensitive instrument near or at a point where there is little or no vibration and to keep any point along the beam stationary without using a rigid support. The assumed-modes method is used to discretize the equations of motion, which conveniently leads to the beam displacement at the node location in matrix form. Exploiting the Sherman–Morrison inverse formula, one can obtain compact, closed-form expressions for the beam deflection at the node location and the displacement of the absorber mass, explicitly in terms of the absorber parameters, attachment location, excitation frequency, forcing location and the node location. The resulting expressions can then be used to systematically perform a parameter sensitivity analysis and rapid design modifications. The proposed work contributes to the parametric study of Euler–Bernoulli beams by leveraging closed-form sensitivity expressions to rapidly account for inverse problems involving parameter tolerances and perturbations. The method introduced in this paper can also be easily extended to accommodate changes in attachment location and the tolerable deflection of the absorber mass without the need to perform a potentially expensive and time-consuming re-analysis. Numerical examples are presented to illustrate the utility of using the sensitivity expressions in designing an accurate and robust vibration absorber when slight modifications are introduced.

Design of a tunable electromagnetic vibration absorber for transient vibration suppression under impulse

Vibration absorbers usually aim to control the steady-state vibration of harmonic excitation based on the traditional fixed point theory, but few efforts focus on suppressing the transient vibration caused by impulse excitation. In this paper, the excitation is regarded as impulse in modeling, and it can be used for impulse excitation. Thus, the transient vibration absorber is designed to control the transient vibration, and the stiffness of the absorber is a key factor to control the response of the primary system. This paper presents a tunable electromagnetic transient vibration absorber to avoid direct mechanical contact for the absorber. The analytical results of the transient response indicate that the vibration can be attenuated by adjusting the stiffness of the absorber. In order to establish the model of the electromagnetic stiffness, the absorber is divided into three equivalent virtual springs. The circular current loop is equivalent to the rectangular current loop to show the spatial distribution of the magnetic flux density in the air gap. The experimental tests demonstrate that the transient vibration of the primary system can be attenuated by 13% when the current of the coil is 6 A.

Analysis, optimization and control of an adaptive tuned vibration absorber featuring magnetoactive materials

Excessive vibration may cause premature fatigue failure on structural components if it is not properly controlled. One effective way to attenuate vibration is to attach a tuned vibration absorber to the main structural component. Passive tuned vibration absorbers are mainly effective to attenuate vibration at a specific range of frequencies and thus they become infective under varied environmental conditions which can significantly alter the tuning frequencies. The present study aims at development of a wide-bandwidth and light-weight adaptive tuned vibration absorber (ATVA) featuring a magnetorheological elastomer (MRE) which is tuned to absorb the vibrations of a flexible beam. The accelerance transfer function is derived for both beam with and without ATVA. The effectiveness of the ATVA to control vibration of the flexible beam caused by external excitation under wide range of frequencies is demonstrated. The proposed ATVA consists of C-Shape frame with winding coils, two isometric MRE specimens with 40% volume fraction, and active mass. An empirical model for the MRE has been developed through an experimental identification method in order to predict the MRE's elastic modulus under various levels of excitation frequencies and applied magnetic fields. Using MRE models and magneto-circuit analysis, the frequency bandwidth of the ATVA is analytically obtained. The analytical model is then used to develop a multidisciplinary design optimization formulation to minimize the mass and maximize the frequency bandwidth of an ATVA featuring MRE given several geometrical and physical constraints. Finally, a tuning algorithm has been presented to determine the required applied magnetic flux density to the MRE layers based on the identified phase difference between the absolute acceleration of the host and relative acceleration of the host and ATVA's resonator.

A standalone tunable vibration absorber with self-sensing magnetorheological elastomer

This study proposed a standalone module of a tunable vibration absorber (TVA) using a self-sensing magnetorheological elastomer (MRE) that replaced accelerometer sensors required for the automatic tuning of a TVA. The manufactured self-sensing MRE can estimate the frequency of the input vibration and change its stiffness to tune the absorber system. Unlike previous MRE-based TVAs, the proposed TVA module is free from external sensors and is designed as a compact system to be easily attached to the target application, such as a linear compressor. In this paper, a self-sensing MRE of 10 mm in thickness was manufactured for rigid support of the absorber mass, allowing the electrical resistance to change by 1,375% from 20.6 to 283 kΩ owing to a compression strain of 2.5 mm. In addition, test results showed that the self-sensing MRE can estimate the vibration frequency within the error of 0.04 Hz. Under a magnetic field of 232 mT, the designed self-sensing MRE achieves a stiffness variation of approximately 125% for tuning the absorber frequency from 39 to 45 Hz. Thus, based on a series of experiments, the vibration sensing and control performance of the proposed self-sensing MRE TVA was validated.

Rotational Vibration Test Apparatus for Laser Vibrometer Verification

<div class="section abstract"><div class="htmlview paragraph">Prior to making rotational vibration measurements with a laser vibrometer, it is good practice to establish that the instrument is operating properly. This can be accomplished by comparative measurement of a rotational vibration source with known amplitude and frequency. This paper describes the design and development of a rotational vibration apparatus with known amplitude and frequency to be used as a reference for comparison to concurrent and co-located measurements made by a rotational laser vibrometer (RLV). The comparative measurements acquired with the apparatus are helpful to verify proper laser vibrometer operation in between regular calibration intervals, and/or whenever the functionality of the vibrometer is suspect. In the subject apparatus, a Cardan shaft with variable input speed and angle is used to provide output torsional vibration with variable frequency and amplitude. Previously derived equations of motion for Cardan joints are used to estimate operating amplitude versus speed relationship for the apparatus. To provide an independent rotational vibration measurement for comparison to the laser, a ferromagnetic toothed wheel and magnetic pickup are used. The design of the Cardan shaft and adjustable support table are described, followed by the design of the variable speed electric drive system and controller. For the finished apparatus, example operating data from the reference sensor are compared to laser vibrometer data, and to the theoretical prediction of output torsional velocity from the Cardan joint equations of motion. Finally, suggestions for future work are provided. The development and verification of rotational tuned vibration absorbers is provided as a potential additional application of the apparatus.</div></div>

Nonlinear Optimal-Based Vibration Control of a Wind Turbine Tower Using Hybrid vs. Magnetorheological Tuned Vibration Absorber

This paper presents an implementation of a nonlinear optimal-based wind turbine tower vibration control method. An NREL 5.0 MW tower-nacelle model equipped with a hybrid tuned vibration absorber (HTVA) is analysed against the model equipped with a magnetorheological TVA (MRTVA). For control purposes, a 3 kN active actuator in parallel with a passive TVA is used in the HTVA system, while an MR damper is built in the MRTVA instead of a viscous damper, as in a standard TVA. All actuator force constraints are embedded in the implemented nonlinear control techniques. By employing the Pontryagin maximum principle, the nonlinear optimal HTVA control proposition was derived along with its simplified revisions to avoid a high computational load during real-time control. The advantage of HTVA over MRTVA in vibration attenuation is evident within the first tower bending frequency neighbourhood, with HTVA also requiring less working space. Using the appropriate optimisation fields enabled an 8-fold reduction of HTVA energy demand along with a (further) 29% reduction of its working space while maintaining a significant advantage of HTVA over the passive TVA. The obtained results are encouraging for the assumed mass ratio and actuator force limitations, proving the effectiveness and validity of the proposed approaches.

Seismic response control of bridges with nonlinear tuned vibration absorbers

The paper investigates seismic response control of bridges with nonlinear tuned vibration absorbers (n-TVAs). A three-span continuous bridge is used as case study. The n-TVAs are designed to act in both longitudinal and transverse directions of the bridge. The n-TVAs are modelled as inelastic springs with bilinear hysteretic behavior. A simple and effective method to design the parameters of the n-TVAs for controlling structural displacement is presented. The performance of the proposed n-TVAs is compared with the optimum linear TVAs (o-TVAs) and elasto-plastic bilinear TVAs (bn-TVAs). The results show that the n-TVAs are at least as effective as o-TVAs in controlling structural response. Because the n-TVAs do not require additional dashpots like the o-TVAs, they provide a more economical solution. It is observed that although effective in controlling structural response, their stroke is of the same order as that of o-TVAs. Addition of a viscous dashpot to the device is found to reduce their stroke, although accompanied by an inherent detrimental effect on the structural control performance.

Modifications on F 2 MC tubes as passive tunable vibration absorbers

This paper presents new parameters for damping improvement in F2MC tubes performance as tunable vibration absorbers. They offer very good performance with environments having susceptibility to high frequency vibration noise. This study highlights the behavior of changing some parameters of F2MC tubes which never have been studied before. These parameters include thickness ratio between each two respective layers and fluid type that the tubes are filled with. In this paper the beam governing equations with the tube's stress analyses equations are solved for finding the combined system's response by MATLAB® software function solvers. To ensure accuracy of modifications, validations have been proposed by performing illustrative examples and comparing the results with the existing data available in literature. The results showed improvements of F2MC tubes performance 20% over previous studies achievements by studying the thickness ratio, and another 12.82% can be added by using glycerin instead of water under the same conditions. Finally, the reduction of 34.34 dB in first mode amplitude of vibration was achieved in the beam's frequency response function plot.

Optimization of the frequency tracking scheme for an adaptively tuned vibration absorber

Vibration absorbers can absorb vibration energy and reduce the vibration amplitude of the primary system. With adaptive tuning, an adaptively tuned vibration absorber (ATVA) can track the dominant frequency of the external excitation, and reduce the vibration response amplitude of the primary system under variable-frequency external excitation. To realize the optimal vibration reduction performance, the 100% frequency tracking scheme of the adaptively tuned absorber must be optimized. In this regard, a dynamic model of an undamped primary system and a vibration absorber is established based on vibration absorption theory, and alternative tuning schemes for these absorbers are investigated in this paper. Using ATVA with the 100% frequency tracking scheme as a reference, a frequency tracking scheme is optimized by the segmented intercept optimization method. This optimization method continuously tunes the ratio of the absorber natural frequency and external excitation frequency to minimize the response in the variable-frequency vibration regions. Hilbert-Huang transform (HHT) time-frequency analysis is performed on the vibration response to reveal the vibration reduction mechanism of the improved vibration absorber. The vibration reduction effects are verified by comprehensive analysis results and experimental results.

Studies on the damping mechanism of shape memory alloy-spring tuned vibration absorber attached to a multi-degree-of-freedom structure

To mitigate the adverse structural responses, an improved version of the traditional tuned vibration absorber has been proposed based on the shape memory alloy spring, referred as the shape memory alloy-spring tuned vibration absorber. The finite element numerical models of the multi-degree-of-freedom structure (e.g., transmission tower) and shape memory alloy-spring tuned vibration absorber are developed by using the commercial software ANSYS, and the nonlinear behavior of the shape memory alloy spring is validated based on a previous experimental study. The damping mechanism of the shape memory alloy-spring tuned vibration absorber attached to a multi-degree-of-freedom structure under seismic excitations is investigated, and the nonlinear hysteretic behavior of the shape memory alloy spring is also discussed. The results show that the proposed damper has a two-stage damping mechanism, and its control performance is remarkable. Because the coupled system response is sensitive to the amplitude level, the optimal configuration of the shape memory alloy-spring tuned vibration absorber can be obtained by parametric analysis. Particularly, because of the nonlinear target energy transfer and transient resonance capture mechanism, the shape memory alloy-spring tuned vibration absorber exhibits stable control ability under different seismic waves, indicating a good stability in vibration control of a multi-degree-of-freedom system.

A New Tuned Vibration Absorber Based on One-Degree-of-Freedom of Translational Motion

A New Tuned Vibration Absorber Based on One-Degree-of-Freedom of Translational Motion

On the vibration suppression of power lines using mobile damping robots

Fixed passive tuned vibration absorbers (TVA) are ineffective in controlling wind induced vibration of continuous systems (e.g., power lines). This is because fixed passive TVAs are not only narrowband, but they are also unable to adapt to changing wind characteristics, and thus are unable to reposition themselves at antinodes of the vibrating loop. To tackle this issue, this paper proposes a mobile vibration absorber (i.e, mobile damping robot) capable of self-adjustment to antinodes. The study focuses on power lines vibration suppression, but it can be extended to other continuous systems. The mobile damping robot is connected to a single conductor that is subjected to a pretension and a wind force. The governing equations of motion are obtained using Hamilton's principle. A control force is incorporated in the mathematical formulation for driving the robot to the antinode location based on the wind excitation frequency. Also, the two-way nonlinear coupling between the robot and cable is considered. Numerical simulations indicate that the mobile damping robot significantly improves the vibration suppression of the power line. Parametric studies are carried out to determine the influence of key design parameters on the performance of the mobile damping robot.

Design of model-free reinforcement learning control for tunable vibration absorber system based on magnetorheological elastomer

This paper proposes a novel model-free reinforcement learning (RL) for vibration control of a magnetorheological elastomer (MRE)-based application. Because the modeling of the MRE stiffness is nonlinear and time-varying depending on various environmental factors, this paper approached the MRE control issue via a model-free learning based method. In this study, an RL model is designed for the MRE-based tunable vibration absorber (TVA) which can control the optimal stiffness of MRE to maximize the vibration suppression. The designed RL algorithm continuously learns and updates the optimal control input of the MRE stiffness adaptively to the dynamic environment without using any prior knowledge of the MRE modeling. From analyzing the mechanism of MRE TVA, the RL algorithm and parameters are carefully designed for a high vibration performance. Also, this study proposed several ideas to make the RL model simpler and converge at a high rate. The experiments confirmed that the proposed RL model showed a rapid convergence to the optimal policy which could minimize the vibration level with respect to the dynamic excitation disturbance. Results showed that the RL model had a similar performance as the conventional tuning method and suppressed the vibration level as much as 57% compared to the one without the controller. Also, the proposed RL algorithm was able to estimate the actual dynamics of the MRE TVA by learning from the environment. Thus, this study showed the feasibility of implementing a model-free RL model to realize an adaptive controller for applications based on highly nonlinear MRE.

Dynamic Balance of the Head in a Flexible Legged Robot for Efficient Biped Locomotion

In the biped robotics domain, head oscillations may be extremely harmful, especially if the robot is teleoperated, since vibrations strongly reduce the operator’s spatial awareness. In particular, undesired head oscillations occur in under-actuated robots, where springs and passive mechanisms are used to achieve a human-like motion. This paper proposes an approach to reduce the vibrations of a biped robot’s head; the proposed solution does not affect the dynamic locomotion properties, on which specific control logic could have been already tuned. The approach is tested on Rollo, a flexible-biped-wheeled robot, whose head vibrates throughout the robot locomotion. The two requirements, i.e., head vibration reduction and unchanged Rollo locomotion properties, are traduced in constraints to the robot possible modifications. Based on a 1D finite element model of the robot, tuned on experimental modal analysis, the undesired vibration causes are detected, and a solution for their reduction is proposed. Rollo’s head vibration amplitude is attenuated using a tuned vibration absorber, which achieves impressive performance in the robot. An archetype of the proposed vibration absorber is tailored designed on Rollo, without invasive changes to the robot structure. The proposed approach solves a significant problem in the biped robotic research community. The approach used to reduce the Rollo head oscillations may be utilized in other biped robot machines with or without flexible legs.

Magnetorheological elastomers — An underestimated class of soft actuator materials

In this paper, the results of various investigations on the viscoelastic and magnetic properties of magnetorheological elastomers (MRE) in magnetic fields of variable strength, are reported. These characteristics have a strong influence on the behavior of MRE in various applications such as vibration damping and tunable vibration absorbers. Moreover, the actuation capabilities of MRE with different kinds of deformation in a magnetic field are considered. The degree of deformation depends on the magnetic field strength and its gradient and can reach about 10%. When removing the magnetic field, the MRE body relaxes back to its initial shape. MRE materials can be used for linear actuators, where the MRE body is deformed due to the attraction by a magnetic circuit acting from one side. Such linear actuators may be applied for haptic feedback and pumps. However, ring-shaped MRE bodies can also deform radially around their cylindrical axis, if the magnetic field is oriented correspondingly. This unusual type of deformation allows the realization of a proportional valve, whose opening is controlled by the magnetic field strength. Similar configurations can be used for controllable seals, for locking devices and even for inchworm drives. Various versions of this actuation principle are discussed in the paper.

Modeling of Magnetic Properties of Magnetorheological Elastomers Using JA Hysteresis Model

Magnetorheological elastomers (MREs) are composite materials that consist of magnetically permeable particles in a nonmagnetic polymeric matrix. Under the influence of an external magnetic field, a reversible deformation change occurs in the mechanical properties of these materials. Due to their coupled magnetomechanical response, these materials have been found suitable for a range of applications including tunable vibration absorbers, sensors, and actuators. Notably, improvement of such devices are prerequisites to efficient energy conversion systems, hence the need to understand further the MRE technology. The Jiles-Atherton (JA) theory takes into consideration the magneto-coupling experienced by effective domains in a magnetic material. Algorithm based on the theory yields five model parameters; saturation magnetization (M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> ), domain density (a), domain coupling (α), loss coefficient (k), and reversibility (c). Using JA theory, model parameters were calculated and linked to the physical attributes of Fe powder and isotropic MRE. The results show that the calculated Ms for the MRE is reasonably related to that of the Fe powder by a factor of the particle's volume fraction used in the MRE. The calculated k, a, and α provided support for the reduced pinning factor, domain density, and increased domain coupling in the MRE due to the changes in the domain structure between the two materials. From the calculated JA parameters, finite-element modeling (FEM) of the MRE hysteresis loop was performed. The analysis showed that the modeled magnetic properties including coercivity, remanence, and coordinates of the hysteresis loop tip vary with geometric position.