Tuned Vibration Absorber Research Articles

Progress in studying passive and active devices for fuselage noise reduction for next generation turboprop

Over the years, the interior noise levels have been improved, and nowadays a high acoustical comfort is of major importance for the commercial success of propeller aircraft. The use and development of high vibro-acoustic performance devices and their integration on the primary structure are, therefore, among the most critical topics in the greening of the next generation air transportation. The purpose of this research was properly focused on the analysis of a dynamic control system appointed to increase the noise attenuation transmitted in the propeller aircraft fuselage. Passive and active dynamic devices have been studied and characterized in this work. Simulations and tests performed on the first stage demonstrator structure highlighted how the passive tuned vibration absorber increases the comfort controlling the structural behaviour of the fuselage at the first blade pass frequency. Further improvements of fuselage comfort can be reached using active devices. A conceptual design of a hybrid active device able to act on the first three blade pass frequencies has been outlined. The characterization of the whole active noise control system has been described and its effect on noise reduction in fuselage of propeller aircraft has been evaluated.

Chatter mitigation using the nonlinear tuned vibration absorber

A passive vibration absorber, termed the nonlinear tuned vibration absorber (NLTVA), is designed for the suppression of chatter vibrations. Unlike most passive vibration absorbers proposed in the literature for suppressing machine tool vibrations, the NLTVA comprises both a linear and a nonlinear restoring force. Its linear characteristics are tuned in order to optimize the stability properties of the machining operation, while its nonlinear properties are chosen in order to control the bifurcation behavior of the system and guarantee robustness of stable operation. In this study, the NLTVA is applied to turning machining.

Shunted piezoelectric patch vibration absorber on two-dimensional thin structures: Tuning considerations

This paper investigates the flexural vibration control effects produced on a distributed two-dimensional thin structure by an electrically shunted piezoelectric patch tuned vibration absorber. The study highlights how the high modal overlap factors that characterise the response of thin two-dimensional distributed structures and the electro-mechanical, capacitive, stiffening and inertial, inherent properties of the piezoelectric patch transducer substantially influence the tuning of the electrical shunt and consequently the vibration control effects produced at frequencies near a given resonance frequency of the structure. In particular, the study shows that the classical approach considering a simplified two degrees of freedom equivalent model of the structure and shunted piezoelectric patch is inadequate to identify the optimal tuning parameters of the shunt. The study, also provides general guidelines for the dimensioning of the piezoelectric patch transducer and electrical shunt in order to maximise the electro-mechanical vibration absorption.

Dynamical Behavior of a Pseudoelastic Vibration Absorber Using Shape Memory Alloys

The tuned vibration absorber (TVA) provides vibration reduction of a primary system subjected to external excitation. The idea is to increase the number of system degrees of freedom connecting a secondary system to the primary system. This procedure promotes vibration reduction at its design forcing frequency but two new resonance peaks appear introducing critical behaviors that must be avoided. The use of shape memory alloys (SMAs) can improve the performance of the classical TVA establishing an adaptive TVA (ATVA). This paper deals with the nonlinear dynamics of a passive pseudoelastic tuned vibration absorber with an SMA element. In this regard, a single degree of freedom elastic oscillator is used to represent the primary system, while an extra oscillator with an SMA element represents the secondary system. Temperature dependent behavior of the system allows one to change the system response avoiding undesirable responses. Nevertheless, hysteretic behavior introduces complex characteristics to the system dynamics. The influence of the hysteretic behavior due to stress-induced phase transformation is investigated. The ATVA performance is evaluated by analyzing primary system maximum vibration amplitudes for different forcing amplitudes and frequencies. Numerical simulations establish comparisons of the ATVA results with those obtained from the classical TVA. A parametric study is developed showing the best performance conditions and this information can be useful for design purposes.

Actively Tuned Vibration Absorber using Smart Adaptive Composites

Shape memory materials (SMMs) are known for their excellent vibration absorption properties. The current work is focused on study of vibration absorption characteristics of Smart Adaptive Composites (Shape Memory Composites) (SACs), as tuned vibration absorbers. Thin cantilever plate of SAC works as the absorber system in the configuration.

Optimum LCVA for suppressing harmonic vibration of damped structures

Explicit design formulae of liquid column vibration absorber (LCVA) for suppressing harmonic vibration of structures with small inherent structural damping are developed in this study. The developed design formulae are also applicable to the design of a tuned mass damper (TMD) and a tuned liquid column damper (TLCD) for damped structures under harmonic force excitation. The optimum parameters of LCVA for suppressing harmonic vibration of undamped structures are first derived. Numerical searching of the optimum parameters of tuned vibration absorber system for suppressing harmonic vibration of damped structure is conducted. Explicit formulae for these optimum parameters are then obtained by a series of curve fitting techniques. The analytical result shows that the control performance of TLCD for reducing harmonic vibration of undamped structure is always better than that of non-uniform LCVA for same mass and length ratios. As for the effects of structural damping on the optimum parameters, it is found that the optimum tuning ratio decreases and the optimum damping ratio increases as the structural damping is increased. Furthermore, the optimum head loss coefficient is inversely proportional to the amplitude of excitation force and increases as the structural damping is increased. Numerical verification of the developed explicit design expressions is also conducted and the developed expressions are demonstrated to be reasonably accurate for design purposes.

Semiactive Inerter and Its Application in Adaptive Tuned Vibration Absorbers

This brief presents a novel framework to realize the semiactive inerter, and proposes a novel semiactive-inerter-based adaptive tuned vibration absorber (SIATVA). The proposed semiactive inerter can be realized by replacing the fixed-inertia flywheel in the existing flywheel-based inerters with a controllable-inertia flywheel. Then, by using the proposed semiactive inerter, an SIATVA is constructed, and two control methods, that is, the frequency-tracker-based (FT) control and the phase-detector-based (PD) control, are derived. The experimental results show that both the FT control and the PD control can effectively neutralize the vibration of the primary mass, although the excitation frequency may vary. The proposed SIATVA can also tolerate the parameter variation of the primary system. As a result, it can be applied to a variety of primary systems without resetting the parameters. The performance degradation by the inherent damping is also demonstrated.

Experimental Passive Flutter Suppression Using a Linear Tuned Vibration Absorber

The current drive for increased efficiency in aeronautic structures such as aircraft, wind-turbine blades, and helicopter blades often leads to weight reduction. A consequence of this tendency can be increased flexibility, which in turn can lead to unfavorable aeroelastic phenomena involving large-amplitude oscillations and nonlinear effects such as geometric hardening and stall flutter. Vibration mitigation is one of the approaches currently under study for avoiding these phenomena. In the present work, passive vibration mitigation is applied to a nonlinear experimental aeroelastic system by means of a linear tuned vibration absorber. The aeroelastic apparatus is a pitch and flap wing that features a continuously hardening restoring torque in pitch and a linear restoring torque in flap. Extensive analysis of the system with and without absorber at precritical and postcritical airspeeds showed an improvement in flutter speed of around 36%, a suppression of a jump due to stall flutter, and a reduction in limit-cycle oscillation amplitude. Mathematical modeling of the experimental system is used to demonstrate that optimal flutter delay is achieved when two of the system modes flutter at the same flight condition. Nevertheless, even this optimal absorber quickly loses effectiveness as it is detuned. The wind-tunnel measurements showed that the tested absorbers were much slower to lose effectiveness than those of the mathematical predictions.

Stiffness control of magnetorheological gels for adaptive tunable vibration absorber

In this study, a stiffness feedback control system for magnetorheological (MR) gel—a smart material of variable stiffness—is proposed, toward the design of a tunable vibration absorber that can adaptively tune to a time varying disturbance in real time. A PID controller was designed to track the required stiffness of the MR gel by controlling the magnitude of the target external magnetic field pervading the MR gel. This paper proposes a novel magnetic field generator that could produce a variable magnetic field with low energy consumption. The performance of the MR gel stiffness control was validated through experiments that showed the MR gel absorber system could be automatically tuned from 56 Hz to 67 Hz under a field of 100 mT to minimize the vibration of the primary system.

Implementation of the LQG controller for a wind turbine tower-nacelle model with an mr tuned vibration absorber

Vibration of a wind turbine tower is related to fatigue wear, influencing reliability of the whole structure. The current paper deals with the problem of Linear-Quadratic-Gaussian (LQG) tower vibration control using specially designed and built simulation and laboratory tower-nacelle models with a horizontally aligned, magnetorheological (MR) damper based tuned vibration absorber located at the nacelle. Force excitation applied horizontally to the tower itself, or to the nacelle, is considered. The MR damper LQG control algorithm, including the Kalman state observer and LQR (Linear-Quadratic-Regulator) controller is analysed numerically and implemented on the laboratory ground, in comparison with the system with a deactivated absorber. Simulation and experimental results are presented.

Incorporating piezoelectric energy harvester in tunable vibration absorber for application in multi-modal vibration reduction of a platform structure

Tunable vibration absorber is an effective device to reduce the vibration of structure subjected to harmonic excitation. The vibration energy is transferred mostly to the absorber when the natural frequency of the absorber is tuned to the excitation frequency. In this study, a piezoelectric (PZT) transducer was incorporated into the absorber in order to harvest the vibration energy and still alleviate the vibration of a platform structure. The tuning in dynamic characteristics of the absorber was facilitated by controlling its tip mass. The design formulation of the absorber was presented with a single degree-of-freedom (SDOF) model having the equivalent parameters. In the meantime, an optimal electric load resistor was determined to maximize the power output from the PZT transducer. The experimental measurement validated the SDOF model with good accuracy both in the vibration response and the output electric voltage. Finally, the absorber was installed on a platform structure to investigate its vibration reduction and energy harvesting capability for the external disturbance frequency covering certain frequency span. With three resonance modes of the platform studied, the absorber was able to reduce more than 80% of its original vibration and harvest several folds of electric power comparing with the untuned absorber. Although the performance in vibration reduction was slightly influenced (<6%), the great increase in the electric energy harvested revealed the absorber design a good potential toward self-powered sensor or actuator applications.

Magnetic (ethylene-octene) elastomer composites obtained by extrusion

Most research on magnetorheological elastomer (MRE) composites is focused on achieving the best magnetic and magnetorheological properties of composites. Less attention is paid to obtain adequate strength properties. The aim of this study was to receive MRE composites with the best mechanical characteristics. Thermoplastic ethylene–octene rubber composites, filled with different magnetoactive particles were reported. The use of extrusion method instead of traditional preparation processes (two-roll mill, mixer) of composites was also presented. Ferromagnetics: micro- and nano-sized iron oxides, as well as gamma iron oxide and carbonyl iron powder were found to be an active fillers improving both mechanical and magnetic properties of rubber. Application of extrusion process affected mechanical properties of MRE composites and the dispersion of magnetic fillers. Dynamic mechanical analysis (DMA) indicates the presence of strongly developed secondary structure in vulcanizates. Studies investigated by vibration sample magnetometer (VSM) proved that all composites exhibit adequate magnetic properties, predispose them for plenty of applications with the most promising being nowadays tunable vibration absorbers. POLYM. ENG. SCI., 57:520–527, 2017. © 2016 Society of Plastics Engineers

Active Structural Acoustic Control in an Original A400M Aircraft Structure

Low frequency noise has always been a challenge in propeller driven aircraft. At low frequencies passive noise treatments are not as efficient as active noise reduction systems. The Helmut-Schmidt-University has built up a full-scale test rig with an original A400M aircraft structure. This provides a good opportunity to develop and test active noise reduction systems in a realistic environment. The currently installed system consists of mechanical actuators and acoustical sensors. The actuators are called TVAs (Tuneable Vibration Absorber) and contain two spring-mass systems whose natural frequencies are adjusted to the BPFs (Blade Passage Frequency) of the propellers. The TVAs are mounted to the frames and the force direction is normal to the skin. The sensors are condenser microphones which are attached to the primary structure of the airframe. The TVAs are equipped with signal processing devices. These components carry out Fourier transforms and signal amplification for the sensor data and actuator signals. The communication between the TVAs and the central control unit is implemented by the CAN Bus protocol and mainly consists of complex coefficients for the sensor and actuator data. This paper describes the basic structure of the system, the hardware set-up and function tests of the controller.

Optimization of a tuned vibration absorber in a multibody system by operational analysis

Mechanical vibration in a drive-train can affect the operation of the system and must be kept below structural thresholds. For this reason tuned vibration absorbers (TVA) are usually employed. They are optimally designed for a single degree of freedom system using the Den Hartog technique. On the other hand, vibrations can be used to produce electrical energy exploitable locally avoiding the issues to transfer it from stationary devices to rating parts. Thus, the design of an integrated device for energy harvesting and vibration reduction is proposed to be employed in the drive-train. By investigation of the dynamic torque in the system under real operation, the accuracy of a numerical model for the multibody is evaluated. In this study, this model is initially used for the definition of the TVA. An energetic procedure is applied in order to reduce the multibody in an equivalent single degree of freedom system for a particular natural mode. Hence, the design parameters of the absorber are obtained. Furthermore, the introduction of the TVA in the model is considered to evaluate the vibration reduction. Finally, an evaluation of the power generated by the piezo transducer and its feedback on the dynamic of the drive-train is performed.

Coarse-fine adaptive tuned vibration absorber with high frequency resolution

The speed fluctuation of satellite-rotary-mechanisms causes vibration of slightly different frequencies. The critical requirements of satellites need a vibration control device with high frequency resolution to suppress the vibration. This paper presents a coarse-fine adaptive tuned vibration absorber (ATVA) with high frequency resolution. The coarse-fine ATVA which simultaneously satisfies the requirements of high resolution and relatively wide effective bandwidth is capable of tracking the variable exciting frequency adaptively to suppress the vibration of the primary system. The coarse-fine ATVA is divided into a coarse tuning segment and a fine tuning segment. The coarse tuning segment is used to tune the required natural frequency in a relatively wide effective bandwidth and the fine tuning segment can achieve precise tune in a tiny-scale bandwidth. The mathematical model of the coarse tuning and the fine tuning is proposed to design the parameters of the coarse-fine ATVA. The experimental test results indicate the coarse tuning bandwidth of the coarse-fine ATVA is 8.7Hz to 29Hz and the minimum resolution of the fine tuning is 0.05Hz. Moreover, a significant vibration attenuation of 15dB is verified in the effective bandwidth.

Tremor Reduction at the Palm of a Parkinson's Patient Using Dynamic Vibration Absorber.

Parkinson’s patients suffer from severe tremor due to an abnormality in their central oscillator. Medications used to decrease involuntary antagonistic muscles contraction can threaten their life. However, mechanical vibration absorbers can be used as an alternative treatment. The objective of this study is to provide a dynamic modeling of the human hand that describes the biodynamic response of Parkinson’s patients and to design an effective tuned vibration absorber able to suppress their pathological tremor. The hand is modeled as a three degrees-of-freedom (DOF) system describing the flexion motion at the proximal joints on the horizontal plane. Resting tremor is modeled as dual harmonic excitation due to shoulder and elbow muscle activation operating at resonance frequencies. The performance of the single dynamic vibration absorber (DVA) is studied when attached to the forearm and compared with the dual DVA tuned at both excitation frequencies. Equations of motion are derived and solved using the complex transfer function of the non-Lagrangian system. The absorber’s systems are designed as a stainless steel alloy cantilevered beam with an attached copper mass. The dual DVA was the most efficient absorber which reduces 98.3%–99.5%, 97.0%–97.3% and 97.4%–97.5% of the Parkinson’s tremor amplitude at the shoulder, elbow and wrist joint.

A principle of similarity for nonlinear vibration absorbers

This paper develops a principle of similarity for the design of a nonlinear absorber, the nonlinear tuned vibration absorber (NLTVA), attached to a nonlinear primary system. Specifically, for effective vibration mitigation, we show that the NLTVA should feature a nonlinearity possessing the same mathematical form as that of the primary system. A compact analytical formula for the nonlinear coefficient of the absorber is then derived. The formula, valid for any polynomial nonlinearity in the primary system, is found to depend only on the mass ratio and on the nonlinear coefficient of the primary system. When the primary system comprises several polynomial nonlinearities, we demonstrate that the NLTVA obeys a principle of additivity, i.e., each nonlinear coefficient can be calculated independently of the other nonlinear coefficients using the proposed formula.

Study of vibration control using laboratory test rig of wind turbine tower-nacelle system with MR damper based tuned vibration absorber

Abstract Wind turbine tower dynamic stress is related to the fatigue wear and reliability of the whole wind turbine structure. This paper deals with the problem of tower vibration control using a specially designed and built laboratory model. The considered wind turbine tower-nacelle model consists of a vertically arranged stiff rod (representing the tower), and a system of steel plates (representing nacelle and turbine assemblies) fixed at its top. The horizontally aligned tuned vibration absorber (TVA) with magnetorheological (MR) damper is located also at the top of the rod (in nacelle system). Force excitation sources applied horizontally to the tower itself and to the nacelle were both considered. The MR damper real-time control algorithms, including ground hook control and its modification, sliding mode control, linear and nonlinear (cubic and square root) damping, and adaptive solutions are compared to the open-loop case with various constant MR damper input current values and system without MR TVA (i.e., MR TVA in “locked” state). Comprehensive experimental analyses and their results are presented.

An innovative MRE absorber with double natural frequencies for wide frequency bandwidth vibration absorption

A new design of adaptive tuned vibration absorber was proposed in this study for vibration reduction. The innovation of the new absorber is the adoption of the eccentric mass on the top of the multilayered magnetorheological elastomer (MRE) structure so that this proposed absorber has two vibration modes: one in the torsional direction and the other in translational direction. This property enables the absorber to expand its effective bandwidth and to be more capable of reducing the vibrations especially dealing with those vibrations with multi-frequencies. The innovative MRE absorber was designed and tested on a horizontal vibration table. The test results illustrate that the MRE absorber realized double natural frequencies, both of which are controllable. Inertia’s influence on the dynamic behavior of the absorber is also investigated in order to guide the design of the innovative MRE absorber. Additionally, the experimentally obtained natural frequencies coincide with the theoretical data, which sufficiently verifies the feasibility of this new design. The last part in terms of the vibration absorption ability also proves that both of these two natural frequencies play a great role in absorbing vibration energy.

Design of a magnetic vibration absorber with tunable stiffnesses

The design and characterisation of a magnetic vibration absorber (MVA), completely relying on magnetic forces, is addressed. A distinctive feature of the absorber is the ability of tuning the linear stiffness together with the nonlinear cubic and quintic stiffnesses by means of repulsive magnets located in the axis of the main vibrating magnetic mass, together with a set of corrective magnets located off the main axis. The tuning methodology is passive and relies only on three geometrical parameters. Consequently the MVA can be adjusted to design either a nonlinear tuned vibration absorber (NLTVA), a nonlinear energy sink (NES), or a bi-stable absorber with negative linear stiffness. The expressions of the stiffnesses are given from a multipole expansion of the magnetic fields of repulsive and corrective magnets. A complete static and dynamic characterisation is performed, showing the robustness of the modelling together with the ability of the MVA to work properly in different vibratory regimes, thus making it a suitable candidate for passive vibration mitigation in a wide variety of contexts.