Structural Vibration Reduction Research Articles

Vibroacoustics behavior of self-similarly loaded sandwich structures

The reduction of structural vibrations and acoustic radiation is increasingly challenging due to lightweight material use driven by mass reduction, particularly in the aerospace industry. Trim panels are well-known materials with high acoustic transmission and radiation. This study combines semi-analytical modeling, numerical simulations and experiments on the vibroacoustic behavior of sandwich constructions locally overloaded by a pre-fractal mass distribution. The research originality lies in the overload distribution (a self-similar pattern inspired by the Cantor set) which is directly slotted within the honeycomb core, so that the structure load-bearing capability is not altered. As the mass effect spatially localizes the vibrations, the pre-fractal pattern focuses the effect of localization on some specific frequency band gaps, which reduces the total vibrational energy and thus the acoustic radiation. Before the extension to composite plates, simulations of a homogenized beam model have been computed to form a numerical modal database. Experiments have been conducted to compare and tune the mechanical model parameters. Satisfying agreement has been obtained between simulations and experiments. Finally, acoustic radiation simulations of self-similarly loaded structures have been conducted and radiation coefficients are expected to be weaker than for classical bending beams.

Selective modal control for vibration reduction in flexible structures

The design of a controller for selective reduction of vibrations in flexible low-damped structures is presented. The objective of the active feedback control law is to increase damping of selected modes only, in frequency regions where a disturbance is likely to produce largest effect. Moreover, the stabilizing controller is required to be band-pass, in order to filter out high-frequency sensor noise and low-frequency accelerometer drift, and stable to increase robustness to uncertain parameters. The control design is based on the Inverse Optimal Design approach, through the solution of a matrix Stein equation, resulting in the solution of an optimal H∞ control problem. A grey-box identification approach of the authors is employed for obtaining the model from experimental data or from detailed Finite Element Model (FEM) simulators. The problem of optimal actuator/sensor location is also addressed. Detailed simulation results are provided to show the effectiveness of the strategy.

Parameter Identification of Long Stroke and Short Stroke MR Damper for its Use in Semi-Active Vibration Control

Magnetorheological (MR) dampers are devices that can be used for structural vibration reduction under seismic excitation. These devices are used in semi-active control which require less power compared to active devices and offer high reliability compared to passive devices. Despite the advantages of MR damper, use of these dampers in an effective way in a structure is highly challenging and a precise modelling is required as these dampers are highly non-linear. Among the parametric models available, Bouc–Wen model is widely used because of its effective modelling of the hysteretic force–velocity curve of MR damper. The parameters of Bouc–Wen model are damper dependent and hence need to be identified before utilising the damper for further simulation studies. In this work, the parametric identification of Bouc–Wen model for commercially available long stroke and short stroke MR damper (RD 8040-1 and RD 8041-1) is done. For this, experimental characterization of the dampers are carried out using hydraulic actuators mounted on a self-restraining frame. The damper is driven harmonically in the testing setup at various combinations of frequency, amplitude, current and displacement. Using the experimental characterization, parameters of Bouc–Wen model are identified by Levenberg–Marquardt optimization Algorithm (LMA). The identified parameters are validated by comparing with the experimental results. The identified parameters are believed to be worthwhile for the use of these MR dampers in further studies of real-time semi-active vibration control of structures.

Vibration Reduction Design with Hybrid Structures and Topology Optimization

Abstract The hybrid structures show excellent performance on vibration reduction for ship, aircraft and spacecraft designs. Meanwhile, the topology optimization is widely used for structure vibration reduction and weight control. The design of hybrid structures considering simultaneous materials selection and topology optimization are big challenges in theoretical study and engineering applications. In this paper, according to the proposed laminate component method (LCM) and solid isotropic microstructure with penalty (SIMP) method, the mathematical formulations are presented for concurrent materials selection and topology optimizations of hybrid structures. Thickness distributions of the plies in laminate components are defined as materials selection design variables by LCM method. Relative densities of elements in the components are defined as topology design variables by SIMP method. Design examples of hybrid 3-bar truss structures and hybrid floating raft with vibration reduction requirements verified the effectiveness of the presented optimization models.

Nonlinear targeted energy transfer of two coupled cantilever beams coupled to a bistable light attachment

In order to control the sound radiation by a structure, one aims to control vibration of radiating modes of vibration using “Energy Pumping” also named “Targeted Energy Transfer”. This principle is here applied to a simplified model of a double leaf panel. This model is made of two beams coupled by a spring. One of the beams is connected to a nonlinear absorber. This nonlinear absorber is made of a 3D-printed support on which is clamped a buckled thin small beam with a small mass fixed at its centre having two equilibrium positions. The experiments showed that, once attached onto a vibrating system to be controlled, under forced excitation of the primary system, the light bistable oscillator allows a reduction of structural vibration up to 10dB for significant amplitude and frequency range around the first two vibration modes of the system.

MODELING AND OPTMIZATION POWER REQUIREMENTS OF ACTIVE ACOUSTIC LOUVRES

The development of new technologies for ventilated facades is within the context of energy efficiency of buildings , including the compatibility of the dichotomy between natural ventilation and soundproofing in tropical countries . Given this perspective, this work proposes the application of techniques for active noise control in acoustic louvers . One limitation of the spread of technical active noise control in buildings is the energy inherent in the technique. Thus, the proposed system is based on the reduction of structural vibrations of the shutter blades by using piezoelectric actuators . The acoustic transmission loss and energy requirements for active shutters are investigated from numerical modeling . The results suggest their technical feasibility with superior soundproofing to 30 dB and power consumption less than 35 W. Thus , the active noise control using piezoelectric actuators is presented as a promising technology , aligning soundproofing with low energy consumption Type the text of the abstract here, Times New Roman, 9, lower case letters, justified paragraphs, 1.0 line spacing. The abstract should state the objectives, methodology and main conclusions in 200 to 300 words. No not divide into paragraphs.

Multi positive feedback control method for active vibration suppression in flexible structures

This paper presents a novel controller for active vibration reduction in piezoelectric-actuated flexible structures. The new Multi Positive Feedback (MPF) control consists of two sections where each operates using a set of actuators. One section uses position and the other uses velocity feedback to perform real-time vibration control. The 90° phase difference between the feedbacks leads to non-zero resultant control output. This property results in a more effective operation of the available actuators. Sections of the MPF controller are designed based on the concept of the Modified Positive Position Feedback (MPPF) control approach, where the damping of the control system is increased by addition of a first-order term parallel to a second-order compensator. The controller is designed to simultaneously control single or multi resonant frequency vibrations. Due to the high influence of gain values on the control performance, H2 and H∞ norms are used to optimize these gains. For validation purposes, the controller is verified here numerically and experimentally for vibration control of a clamped–clamped beam and a cantilever at resonance. According to the results, the MPF controller has a superior performance compared to the MPPF controller, in addition to effective suppression on both vibration displacement and velocity. Using the MPF controller in multimode and by utilizing the H∞ gain optimization method, vibration displacement amplitudes were reduced to 19.4% of the uncontrolled state for the beam.

Vibration reduction in aerospace structures via an optimized modified positive velocity feedback control

In this paper, an optimized positive feedback based control approach is developed for unwanted resonant vibration attenuation of flexible lightweight aerospace structures. A modified form of the positive velocity feedback control (MPVF) is implemented, where the resonant compensator of each mode is enhanced with a parallel lossy integrator. For multi-mode control purpose and to control n-modes, n sets of parallel compensators are required. A focus of this paper is on development of effective gain optimization methods in order to improve the multi-mode suppression performance of the vibration controller. The optimization problem is addressed via the M-norm optimization method and the Linear Quadratic Regulator (LQR). A flexible clamped-free beam is considered as a sample aerospace structure, and the controller verification is performed experimentally. Results show that vibration velocity is well reduced, which is important in preventing fatigue failures in aerospace structures. The LQR-optimized MPVF provides a compensated result between vibration amplitude reduction and the consumed control power. The M-norm approach, on the other hand, aims to directly suppress each mode based on the assigned weighting coefficients. Since an M-norm-optimized MPVF controller focuses on modes with higher amplitudes of velocity, it provides a higher level of vibration suppression than LQR-optimized method.

Experimental application of a vibration absorber in structural vibration reduction using tunable fluid mass driven by micropump

A new design of tuned mass damper was proposed in this study to reduce the structural vibration of a machine platform subjected to varying excitation frequency, e.g. disturbance from the unbalance mass of motor in different rotational speeds. The absorber mass was changed by pumping of fluid between the liquid chambers of the vibration absorber. With the stiffness remained unchanged, the absorber׳s natural frequency could be tuned accordingly. Thus, reduction in machine vibration could be obtained by tuning the natural frequency of the absorber according to the frequency of external harmonic disturbance. Firstly, the variations of natural frequency and damping ratio of the absorber with different tuned masses were measured experimentally. The natural frequency results showed that the adjustable ranges for the first two modes could all reach more than 30%. Then, the absorber was installed on a machine platform and its performance was investigated under external disturbance at the natural frequency of the platform. It was found that, due to the effect of damping increase originated from the fluid sloshing inside liquid chamber, the vibration reduction effect from the absorber was limited. To improve this situation, we added a horizontal separation panel inside the liquid chambers, and the experimental results showed that the liquid sloshing was alleviated, and effectively reduced the damping ratio of absorber. Thus, the system became more stable and the control efficiency was effectively improved.

Black-box MIMO model identification for structural vibration reduction in helicopters

This work addresses the identification of a control-oriented multivariable model of the structural response of a helicopter, with reference to the Agusta A109 helicopter. The estimated model will be used to design an active vibration control system to reduce the vibrations transmitted to the cabin by the main gearbox. The considered system consists of a set of piezoelectric actuators mounted at the interface between the gearbox and the cabin and accelerometers located on the cabin roof. Identification data are generated by independent excitation of each individual actuator. Model identification is carried out using a subspace identification algorithm.

Synchronized Control for Five-Story Building under Earthquake Loads

Synchronized control is implemented for a five-story building under earthquake loads and its capabilities are investigated for protection of building under earthquake. In this regard, we appliedH2/LQGcontrol algorithm in form of synchronized control for structural vibration reduction. Simulation results of modeling indicated that not only the provided control is able to reduce the responses of vibrations for the structure, but also it is even capable of supplying the objectives of synchronized control at the same time. Numerical results for uncontrolled, traditionalH2/LQGcontrol and synchronized control coupled withH2/LQGalgorithm are presented. It is shown that for El Centro and Bam earthquakes the synchronized control is more efficient to reduce damage to the given structures.

Robust harmonic control: an application to structural vibration reduction in helicopters

This work addresses the problem of designing robust multivariable controllers for the attenuation of the structural response of a helicopter, with reference to the Agusta A109 helicopter. The considered configuration consists of a set of piezoelectric actuators and accelerometers located on the fuselage of the helicopter. The robust harmonic control approach is adopted, based on an data-driven mathematical model of the system.

Multiobjective optimization of viscoelastic laminated sandwich structures using the Direct MultiSearch method

A multiobjective approach for optimization of passive damping for vibration reduction in sandwich structures is presented in this paper. Constrained optimization is conducted for maximization of modal loss factors and minimization of weight of sandwich beams and plates with elastic laminated constraining layers and a viscoelastic core, with layer thickness and material and laminate layer ply orientation angles as design variables. The problem is solved using the Direct MultiSearch (DMS) solver for derivative-free multiobjective optimization and solutions are compared with alternative ones obtained using genetic algorithms.

Topology optimization of shunted piezoelectric elements for structural vibration reduction

Passive structural vibration reduction by means of shunted piezoelectric patches is addressed in this article. The concept of topology optimization, based on the solid isotropic material with penalization method, is employed in this work to optimize, in terms of damping efficiency, the geometry of piezoelectric patches, as well as their placement on the host elastic structure. The proposed optimization procedure consists of distributing the piezoelectric material in such a way as to maximize the modal electromechanical coupling factor of the mechanical vibration mode to which the shunt is tuned. An original finite element formulation, suitable to any elastic structures with surface-mounted piezoelectric patches, is proposed to solve the electromechanical problem. Numerical examples validate and demonstrate the potential of the proposed approach for the design of piezoelectric shunt devices.

Fabrication and characterization of magnetorheological elastomer with carbon black

In this study, the isotropic magnetorheological elastomer samples are fabricated with and without addition of carbon blacks into the silicon rubber matrix and carbonyl iron particles in the absence of magnetic field. Microscopic and morphological analyses, thermo-gravimetric analysis, MH measurements, thermomechanical analysis, dynamic mechanical analysis, tensile test and magnetorheological test of magnetorheological elastomers are performed to characterize the fabricated magnetorheological elastomers. The experimental results demonstrate that the addition of carbon black improves the mechanical properties of the magnetorheological elastomer. The fabricated magnetorheological elastomers can be used in applications such as adaptive tuned vibration absorbers and vibration reduction in sandwich structures.

Kenneth McKechnie Eldred—A distinguished noise control engineer II

Ken's accomplishments in noise control engineering cover the spectrum from basic engineering research to recommendations for noise control in six areas: measurement of industrial noise; measurement and reduction of structural vibration in space vehicles; noise radiation from jet flow; noise reduction of jets by multiple nozzles and turbofans; vibroacoustic environmental simulation for aerospace vehicles; and community and transportation noise control. Some of these areas are discussed in consulting reports, and others in papers published in the open literature. He was a consultant at Bolt Beranek and Newman from 1973 until 1982 when he formed Ken Eldred Engineering. His publications appeared in the journal NOISE Control, several NOISE-CON and INTER-NOISE Proceedings, Noise Control Engineering Journal, and the Journal of the Acoustical Society of America. Representative samples of his accomplishments taken from the above sources will be presented.

Reduction of Structural Vibrations by Passive and Semiactively Controlled Friction Dampers

Reduction of structural vibrations is of major interest in mechanical engineering for lowering sound emission of vibrating structures, improving accuracy of machines, and increasing structure durability. Besides optimization of the mechanical design or various types of passive damping treatments, active structural vibration control concepts are efficient means to reduce unwanted vibrations. In this contribution, two different semiactive control concepts for vibration reduction are proposed that adapt to the normal force of attached friction dampers. Thereby, semiactive control concepts generally possess the advantage over active control in that the closed loop is intrinsically stable and that less energy is required for the actuation than in active control. In the chosen experimental implementation, a piezoelectric stack actuator is used to apply adjustable normal forces between a structure and an attached friction damper. Simulation and experimental results of a benchmark structure with passive and semiactively controlled friction dampers are compared for stationary narrowband excitation. For simulations of the control performance, transient simulations must be employed to predict the achieved vibration damping. It is well known that transient simulation of systems with friction and normal contact requires excessive computational power due to the nonlinear constitutive laws and the high contact stiffnesses involved. However, commercial finite-element codes do not allow simulating feedback control in a general way. As a remedy, a special simulation framework is developed which allows efficiently modeling interfaces with friction and normal contact by appropriate constitutive laws which are implemented by contact elements in a finite-element model. Furthermore, special model reduction techniques using a substructuring approach are employed for faster simulation.

REDUCCIÓN DEL RUIDO ESTRUCTURAL Y LA VIBRACION EN UN PROTOTIPO DE CABINA DE ASCENSOR MEDIANTE LA UNIÓN ADHESIVA DE PANELES

Abstract This paper presents an experimental study for the structural noise and vibration reduction in a cabin elevator by means of adhesive bonded joints of panels. For that noise and vibration measurements are carried out on two prototypes: one of them built with classical panel joining technologies and the other one with adhesive joints. First of all the mechanical properties (relaxation and complex moduli) of two low modulus materials are compared: a silane and a modified silane adhesives. These properties are obtained for both materials by means of dynamic mechanical thermal analysis technique (DMTA), the master curves under direct strain being built-up through a procedure based on the time-temperature superposition (TTS) principle. Next, the influence that these two materials have on the dynamic response of an adhesively bonded metallic beam is investigated, in order to select the right candidate according to design criteria. Finally, an application for an elevator cabin prototype is presented, in which noise and vibration are measured in order to put into evidence the benefits of joining panels by means of adhesive bonded joints in contrast to the traditional joining technologies. Keywords: Noise and vibration reduction; adhesive bonded joints; cabin elevator

The Operational Modal Analysis of an Industrial Sewing Machine

The operational modal analysis (OMA) was conducted on a certain industrial sewing machine to identify its modal parameters. Harmonic analysis was carried out through the OP.Synthesis method and false modes were removed according to the Modal Assurance Criterion, finally the natural frequency, damping ratio and modal shape were obtained. The vibration in the low frequencies is mainly nodding and shaking, while that in the high frequencies is local expansion of the head and motor end. The result shows that, the modal parameters of the industrial sewing machine can be well identified by the OMA method. This paper provides a valuable reference for the vibration source identification and structural vibration reduction.

TRANSDUCER FOR VIBRATION ABSORBING, SENSING, AND TRANSMITTING

A hermetically sealed actuator design for absorbing and reducing the ef- fect of sound or vibration energy from a vibrating surface. The device comprises a body (1) containing a magnetostrictive core (2-6) a reaction mass (7) for en-5 ergising the actuator by compression, and a bearing or lever system to control the movement of the reaction mass. The actuator has a foot (11) for receiving the vibration from the structure into the device and a sensor (13) for monitoring vibration levels. The device can also function as an audio transmitter whereby it vibrates the surface onto which it is mounted and can be used for audio trans-10 mission through the structure or noise and vibration reduction by driving the sur- face out of phase with the vibration received from the structure.