Constrained-layer damping

About: Constrained-layer damping is a research topic. Over the lifetime, 795 publications have been published within this topic receiving 15758 citations.

Topology Optimization of a Constrained Layer Damping Plate Coupled with an Acoustical Cavity

Abstract: An acoustical topology optimization of a constrained layer damping (CLD) plate coupled with a rigid acoustical cavity is presented to minimize the sound radiation power. A mathematical model is developed to simulate the sound radiation based on the theories of the finite element and boundary element methods together. The model is integrated with the acoustical topology optimization approach, which utilizes the genetic algorithm with an elitist strategy. The obtained results demonstrate the effectiveness of the proposed approach in attenuating the sound radiation power and the sound pressure inside the acoustical cavity simultaneously by proper layout of the CLD materials. Furthermore, experimental verification is carried out by manufacturing topology optimized CLD/plate and monitoring the sound pressure in the acoustical cavity. The experimental results are a good match with the predictions of the mathematical model. The study shows that the proposed acoustical topology optimization approach can be an effective tool in the design of a wide variety of critical structures, which is lightweight and operates quietly, such as the panels in the vehicle body and aircraft cabin.

High Damping Characteristics of an Elastomer Particle Damper

Abstract: Research testing has led to the development of an Elastomer Particle Damper (EPD), which can add considerable damping to a structure by directing the vibration to a set of interacting elastomer particles through a rigid connection. This vibration treatment presents highly nonlinear behavior that is strongly dependent on both the vibration amplitude and frequency. Curves of damping loss factor (DLF) of an EPD system with vertical motion as a function of frequency and acceleration are reported herein. The results show that the elastomer particle damper has two distinct damping regions. The first region is related to the fluidization state of the particles, as described in the literature, obtained when the damper is subjected to vertical acceleration close to 1 g and frequencies below 50 Hz. The second region presents high values of DLF to acceleration values lower than 1 g, and the frequency range is dependent upon the stiffness of the particles. A high degree of effectiveness is achieved when the working frequency of the elastomer particle dampers is tuned to a natural frequency of a plate and when they are strategically located at points having large displacement. The performance of EPDs was compared with that of a commercial constrained layer damping installed in an aircraft floor panel. The EPDs achieved an acceleration level attenuation in the aircraft floor panel similar to that of the commercial constrained layer damping system.

Active damping for the control of flexible structures

Abstract: Active damping can be generated in a number of ways, the most obvious one being applying a force to the structure which is proportional to the velocity at a point on the structure. Another technique is to actively increase the damping of a structure by using a passive damping element i.e. dissipate the energy of vibration by increasing the relative motion of the structure with respect to the passive damping element. A practical way to achieve this is by using constrained layer damping (CLD). It is well known that CLD is effective because of the relative motion of the structure and the constraining layer which produces extra shear in a layer of viscoelastic material. The work described in this paper is concerned with controlling the strain of the constraining layer of a composite structure in such a way as to enhance the shear generated in the viscoelastic material and hence improve the overall damping of the composite structure. If the control law selected forces the constraining layer to move 180 degrees out of phase with the structure then the viscoelastic damping layer undergoes maximum shear and active damping is achieved. The results have indicated that this concept of active damping produces very effective levels of vibration suppression. In the case of cantilever beams the first two modes can be almost eliminated when velocity feedback of the beam tip is used. The results show that the addition of active control and passive damping in a single structure combines the advantages of passive damping in the higher modes and active control in the lower modes. In addition active damping as defined in this paper produces a fail safe mechanism in case of instability occurring in the feedback system since passive damping is always present.

A matrix method for analyzing vibration of a circular cylindrical shell with partially constrained layer damping treatment

Abstract: Based on the linear theories of thin cylindrical shells and viscoelastic materials,the governing equation generally describing vibration of a sandwich circular cylindrical shell with partially constrained layer damping treatment under harmonic excitation,which can be written in a matrix differential equation of first order,is derived by considering the energy dissipation due to the shear deformation of the viscoelastic layer and the interaction between all layersAfter that a semi-analytical and semi-numerical method for solving this governing equation is presented by means of the extended homogeneous capacity precision integration approachIts essential difference from the recent works on transfer matrix method is that the state vector in governing equation is composed of the twelve displacements and internal forces of the sandwich shell rather than of the displacements and their derivativesAs a result,the present method can be applied to solve the dynamic problems of the kind of sandwich shell with various boundary conditions and partially constrained layer dampingNumerical examples show that the proposed approach is very effective and reliable,compared with the existing analytical solutionsFurthermore,the effects of PCLD coverage percents and locations on FRF are then discussed