Showing papers on "Constrained-layer damping published in 1995"

Optimum Design and Control of Active Constrained Layer Damping

Abstract: Conventional Passive Constrained Layer Damping (PCLD) treatments with viscoelastic cores are provided with built-in sensing and actuation capabilities to actively control and enhance their vibration damping characteristics. The design parameters and control gains of the resulting Active Constrained Layer Damping (ACLD) treatments are optimally selected, in this paper, for fully-treated beams using rational design procedures. The optimal thickness and shear modulus of the passive visco-elastic core are determined first to maximize the modal damping ratios and minimize the total weight of the damping treatment. The control gains of the ACLD are then selected using optimal control theory to minimize a weighted sum of the vibrational and control energies. The theoretical performance of beams treated with the optimally selected ACLD treatment is determined at different excitation frequencies and operating temperatures. Comparisons are made with the performance of beams treated with optimal PCLD treatments and untreated beams which are controlled only by conventional Active Controllers (AC). The results obtained emphasize the potential of the optimally designed ACLD as an effective means for providing broad-band attenuation capabilities over wide range or operating temperatures as compared to PCLD treatments.

Use of active constrained-layer damping for controlling resonant vibration

Abstract: 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. The results have indicated that this concept of active damping produces very effective levels of vibration suppression. In the case of cantilever beams the vibration levels in 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 loop since a considerable level of passive damping is always present.

Performance Characteristics of Active Constrained Layer Damping

Abstract: Theoretical and experimental performance characteristics of the new class of actively controlled constrained layer damping (ACLD) are presented. The ACLD consists of a viscoelastic damping layer sandwiched between two layers of piezoelectric sensor and actuator. The composite ACLD when bonded to a vibrating structure acts as a “smart” treatment whose shear deformation can be controlled and tuned to the structural response in order to enhance the energy dissipation mechanism and improve the vibration damping characteristics. Particular emphasis is placed on studying the performance of ACLD treatments that are provided with sensing layers of different spatial distributions. The effect of the modal weighting characteristics of these sensing layers on the broad band attenuation of the vibration of beams fully treated with the ACLD is presented theoretically and experimentally. The effect of varying the gains of a proportional and derivative controller and the operating temperature on the ACLD performance is determined for uniform and linearly varying sensors. Comparisons with the performance of conventional passive constrained layer damping are presented also. The results obtained emphasize the importance of modally shaping the sensor and demonstrate the excellent capabilities of the ACLD.

Vibration control of plates with active constrained-layer damping

Abstract: Bending vibration of flat plates is controlled using patches of active constrained layer damping (ACLD) treatments. Each ACLD patch consists of a visco-elastic damping layer which is sandwiched between two piezo-electric layers. The first layer is directly bonded to the plate to sense its vibration and the second layer acts as an actuator to actively control the shear deformation of the visco-elastic damping layer according to the plate response. With such active/passive control capabilities the energy dissipation mechanism of the visco-elastic layer is enhanced and its damping characteristics of the plate vibration is improved. A finite element model is developed to analyze the dynamics and control of flat plates which are partially treated with multi-patches of ACLD treatments. The model is validated experimentally using an aluminum plate which is 0.05 cm thick, 25.0 cm long, and 12.5 cm wide. The plate is treated with two ACLD patches. Each of which is made of SOUNDCOAT (Dyad 606) visco- elastic layer sandwiched between two layers of AMP/polyvinylidene fluoride (PVDF) piezo- electric films. The piezo-electric axes of the patches are set at zero degrees relative to the plate longitudinal axis to control the bending mode. The effect of the gain of a proportional control action on the system performance is presented. Comparisons between the theoretical predictions and the experimental results suggest the validity of the developed finite element model. Also, comparisons with the performance of conventional passive constrained layer damping clearly demonstrate the merits of the ACLD as an effective means for suppressing the vibration of flat plates.

Bending and torsional vibration control of composite beams through intelligent constrained-layer damping treatments

Abstract: This paper aims to develop a mathematical model to predict whether or not intelligent constrained-layer (ICL) damping treatments could simultaneously reduce bending and torsional vibrations of composite beams having bending-torsion coupling stiffness. The ICL composite-beam model is obtained by integrating the existing ICL composite-plate model proposed by Shen (1994). When the plate width (along the x-axis) is much smaller than the plate length (along the y-axis), integration of the ICL composite-plate equations and linearization of displacement fields with respect to x will lead to a set of equations that couple bending, torsional, and axial vibrations of a composite beam. The equations of motion and associated boundary conditions are normalized and rearranged in a state-space matrix form, and the vibration response is predicted through the transfer function approach developed by Yang-Tan (1992). A numerical example is illustrated on a composite beam with bending-torsion coupling stiffness.

Design and Analysis of Fiber Enhanced Viscoelastic Damping Polymers

Abstract: A new composite damping material is investigated, which consists of a viscoelastic matrix and high elastic modulus fiber inclusions. This fiber enhanced viscoelastic damping polymer is intended to be applied to lightweight flexible structures as a surface treatment for passive vibration control. A desirable packing geometry for the composite material is proposed, which is expected to produce maximum shear strain in the viscoelastic damping matrix. Subsequently, a micromechanical model is established in which the effect of fiber segment length and relative motion between neighboring fibers are taken into account. Based on this model, closed form expressions for the effective storage and loss properties of the damping material are developed, and an optimal relation between design parameters, such as the length, diameter spacing, and Young's modulus of fibers and the shear modulus of viscoelastic matrix, is derived for achieving maximum damping performance. To address the verification of the development, the theoretical results are compared with NASTRANfinite element results. Upon comparison of an enhanced viscoelastic damping treatment with a conventionally constrained layer damping treatment, it is found that the enhanced polymer provides a significant improvement in damping performance.

Optimal Constrained Layer Damping of Beams: Experimental and Numerical Studies

Abstract: This article deals with the optimal damping of beams constrained by viscoelastic layers when only one or several portions of the beam are covered. The design variables are the dimensions and locations of the viscoelastic layers and the objective function is the maximum damping factor. The discrete design variable optimization problem is solved using a genetic algorithm. Numerical results for minimum and maximum damping are compared to experimental results. This is done for a various number of materials and beams. © 1995 John Wiley & Sons. Inc.

Modeling active constrained-layer damping using Golla-Hughes-McTavish approach

Abstract: Viscoelastic material (VEM) adds damping to structures. In order to enhance the damping effects of the viscoelastic material, a constraining layer is attached. If this constraining layer is a piezoelectric patch, the system is said to have active constrained layer damping (ACLD). In this paper, the damping effects due to viscoelastic material which has an active constraining layer is modeled using the Golla-Hughes-McTavish (GHM) damping method. The piezoelectric patch and structure are modeled using a Galerkin approach in order to account for the effect of the constraining layer on the beam.

Placing small constrained layer damping patches on a plate to attain global or local velocity changes

Abstract: Experimental results show how structural intensity can predict where to locate small constrained layer damping patches to attain either local or global velocity changes on a plate. If damping is applied to a region of low shearing reactive structural intensity magnitude, a local velocity change is seen. If damping is applied to a region of high shearing reactive structural intensity magnitude, a global velocity change is seen. In addition, the researchers noted that large damping patches produce global velocity changes. The filtering process needed to calculate the structural intensity was partially automated to reduce computational time.

Bending and torsional vibration control of composite beams through intelligent constrained-layer damping treatments

Abstract: This paper is to develop a mathematical model to predict bending, twisting, and axial vibration response of a composite beam with intelligent constrained layer (ICL) or active constrained layer (ACL) damping treatments. In addition, preliminary experiments are conducted on composite beams to evaluate this new technique. The ICL composite beam model is obtained by integrating the existing ICL composite plate model proposed by Shen. When the plate width (along the x-axis) is much smaller than the plate length (along the y-axis), integration of the ICL composite plate equations and linearization of displacement fields with respect to x leads to a set of equations that couples bending, tosional, and axial vibrations of a composite beam. The equations of motion and associated boundary conditions are normalized and rearranged in a state-space matrix form, and the vibration response is predicted through the distributed transfer function method developed by Yang and Tan. A numerical example is illustrated on a composite beam with bending-torsion coupling stiffness. Numerical results show that ICL damping treatments may or may not reduce coupled bending and torsional vibrations of a composite beam simultaneously. When the deflection is fed back to actuate the ICL damping treatment, a sensitivity analysis shows that only those vibration modes with significant bending response are suppressed simultaneously with their torsional components. In the preliminary experiments, two different ICL setups are tested on a composite beam without bending-torsion coupling. Damping performance of both ICL setups agrees qualitatively with existing mathematical models and experimental results obtained from other researchers. The damping performance, however, is not optimized due to the availability of materials and their dimensions in the laboratory. An optimization strategy needs to be developed to facilitate design of ACL damping treatments with maximized damping performance.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Experimental comparison of piezoelectric and constrained-layer damping

Abstract: A qualitative comparison between a piezoelectric vibration absorber and a constrained layer damping treatment is presented. Piezoelectric materials convert mechanical strains into electrical charge. Dissipation of the charge results in attenuation of vibration. The damping is concentrated to a single mode by constructing a piezoelectric absorber. The damped vibration absorber is comprised of the piezoelectric material and a passive electronic shunt. Previous research has applied the piezoelectric absorber to one-dimensional structures. This paper applies the absorber to a two-dimensional planar problem. The simple mathematical description of the absorber is modified for the two-dimensional problem. An analytical means of estimating the effectiveness of the piezoelectric absorber is derived. The effectiveness is estimated for an electronics chassis box subjected to random excitation. A typical constrained layer damping treatment is also analytically designed for the problem. The piezoelectric absorber and the constrained layer damping treatment are experimentally applied to identical boxes. Results show that the piezoelectric absorber can provide vibration suppression comparable to that obtained by the constrained layer damping treatment.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Optimum Design and Control of Active Constrained Layer Damping

Abstract: Conventional Passive Constrained Layer Damping (PCLD) treatments with viscoelastic cores are provided with built-in sensing and actuation capabilities to actively control and enhance their vibration damping characteristics. The design parameters and control gains of the resulting Active Constrained Layer Damping (ACLD) treatments are optimally selected, in this paper, for fully-treated beams using rational design procedures. The optimal thickness and shear modulus of the passive visco-elastic core are determined first to maximize the modal damping ratios and minimize the total weight of the damping treatment. The control gains of the ACLD are then selected using optimal control theory to minimize a weighted sum of the vibrational and control energies. The theoretical performance of beams treated with the optimally selected ACLD treatment is determined at different excitation frequencies and operating temperatures. Comparisons are made with the performance of beams treated with optimal PCLD treatments and untreated beams which are controlled only by conventional Active Controllers (AC). The results obtained emphasize the potential of the optimally designed ACLD as an effective means for providing broad-band attenuation capabilities over wide range or operating temperatures as compared to PCLD treatments.

Optimal design of structures with active constrained-layer damping

Abstract: A piezoelectric element and a constrained layer damping element are combined to allow for an active constrained layer damping treatment. The development of these elements is reviewed and results are compared with the literature to insure that the elements work together. A procedure for placing patches damping treatments or other material anomalies on structures is introduced. The patch placement process uses a grid deformation procedure to realign elements with the patch boundaries. This makes the process of optimally locating the damping treatment one of continuous variables. The patch placement process is used in conjunction with the combined elements and an optimization algorithm to design an active constrained layer damping treatment and the beam to which it is attached.

Slit-tube replicated in-place constrained layer damper and method

Abstract: An economic and efficient method for providing an inner constrained layer damping system to a tubular structure by inserting an inner damping tube that has been substantially slit along its length at several places around its circumference and then wrapped in a viscoelastic tape to cover the slits, or just plain tape to just cover the slits, with a viscoelastic layer thereupon with the tape inserted within and coextensively along the inside of the outer structural beam to be damped, and with the space between the two filled with a replicating material such as epoxy, cement grout, rubber, or other pourable or injectable material, which must have high shear damping properties if the latter tape-just- covering-the-slit option is used, to couple in shear the outer structural beam to the inner slit damping tube and cause shear strains to be transmitted across the viscoelastic boundary between the two tubes.

Optimum design and control of partial active constrained layer damping treatments

Abstract: Passive constrained layer damping (PCLD) treatments with visco-elastic cores are augmented with sensing and actuation capabilities to actively control and improve their vibration damping characteristics. The design parameters and control gains of the resulting active constrained layer damping (ACLD) treatments are optimally selected in this paper, for partially-treated beams. The theoretical performance of beams treated with the optimally selected ACLD treatments is determined at different excitation frequencies and compared with optimal PCLD treatments.

Barberpole: constrained-layer damping for bending and torsion

Abstract: In this paper, a new constrained layer damping configuration is proposed for beams of circular cross section that may experience both bending and torsional vibrations. The `barberpole' configuration consists of narrow strips of damping treatment oriented at a pitch angle relative to lines parallel to the beam centerline. The individual damping strips may be continuous over the length of the beam, or periodically segmented along the strip length. A quasistatic analysis is developed to evaluate the effectiveness of the barberpole configuration for damping bending and torsional vibrations. It is shown that damping for both bending and torsion is attainable with the same damping treatment if the constraining layer strips are periodically segmented. It is also shown that for the pure bending problem, the unsegmented barberpole geometry provides an improvement in damping over unsegmented straight strips. At each crossing of the beam neutral plane, the constraining layer is free of extensional stress, which provides a `virtual segmentation' effect. This virtual segmentation provides an alternative to conventional segmentation of the damping layer when the more conventional approach is undesirable due to environmental or operational reasons.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Bending and twisting vibration control of a cantilever plate via electromechanical surface damping

Abstract: The electromechanical surface damping technique (EMSD) is applied to suppress the bending and twisting peak vibration amplitudes of a cantilever plate. The technique is a combination of the constrained layer damping (CLD) and the shunted piezoelectric methods in which the constraining layer of the CLD is replaced by a shunted piezoelectric ceramic. The frequency responses, to a white noise random base excitation, of the EMSD-treated plate at the vicinity of the first and second bending and twisting resonant frequencies are determined and compared with the corresponding responses of the CLD-treatment. It is shown that, in general, the EMSD treatment provides more suppression of the bending and twisting peak vibration amplitudes than the conventional CLD treatment. The EMSD treatment, however, is more effective at higher frequencies and lower temperatures, which suggests that the EMSD method can be applied to extend the effective range of frequencies and/or temperatures of the conventional CLD method. The work presented is primarily analytical, however crude and preliminary experimental results are presented in order to demonstrate the feasibility of the EMSD technique.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Single-element modeling of multilayer constrained-layer damping treatments

Abstract: The use of multi-layer constrained layer damping treatments on plate-like structures provides broadband vibration damping over a wide temperature range. A difficulty with the design of such treatments is their modeling. The current state of the art requires a separate plate element for each constraining layer plus a solid element for each viscoelastic layer in the thickness direction. The number of degrees of freedom is large conflicting with the iterative approach necessitated by the frequency and temperature dependance of the material properties which dictates that a small model size must be maintained. The large model size also slows optimization. The goal of this research was to produce a true plate finite element model which uses only a few degrees of freedom per node. This model is obtained by using a variational asymptotical theory to correctly capture the layerwise jumps in the stress and strain fields. A model is developed for simply supported plates which can later be extended to a more general finite element. Results are compared with the exact elasticity solution of Pagano. They show an excellent match exists in the predicted stress and strain field. The model is also compared with RKU analysis for plates again demonstrating its accuracy. A future finite element model based on this theory would require only six extra degrees of freedom per node with only one element in the thickness direction, thus simplifying the modeling of constrained layer damping treatments.

Prediction and Measurement of the Vibration and Acoustic Radiation of Panels Subjected to Acoustic Loading

Abstract: Interior noise and sonic fatigue are important issues in the development and design of advanced subsonic and supersonic aircraft. Conventional aircraft typically employ passive treatments, such as constrained layer damping and acoustic absorption materials, to reduce the structural response and resulting acoustic levels in the aircraft interior. These techniques require significant addition of mass and only attenuate relatively high frequency noise transmitted through the fuselage. Although structural acoustic coupling is in general very important in the study of aircraft fuselage interior noise, analysis of noise transmission through a panel supported in an infinite rigid baffle (separating two semi-infinite acoustic domains) can be useful in evaluating the effects of active/adaptive materials, complex loading, etc. Recent work has been aimed at developing adaptive and/or active methods of controlling the structural acoustic response of panels to reduce the transmitted noise1. A finite element formulation was recently developed to study the dynamic response of shape memory alloy (SMA) hybrid composite panels (conventional composite panel with embedded SMA fibers) subject to combined acoustic and thermal loads2. Further analysis has been performed to predict the far-field acoustic radiation using the finite element dynamic panel response prediction3. The purpose of the present work is to validate the panel vibration and acoustic radiation prediction methods with baseline experimental results obtained from an isotropic panel, without the effect of SMA.

Minimizing the Radiated Sound Power with Minimal Structural Modification

Abstract: In cases where a structure's excitation cannot be altered, the sound radiation from the structure must be minimized by modifying the structure within given design constraints. This dissertation considers minimizing sound radiated by an existing structure with minimal changes to the structure itself. To accomplish this the sound power radiated by a structure was written as a function of the normal surface velocity using the boundary element method. The feasibility of reducing radiated sound power with small patches of constrained layer damping material is proved. Small patches of constrained layer damping material are placed on the structure to effectively reduce radiated sound using reactive structural shearing intensity. The size, shape, and number of patches is explored. Two gradient methods are then used to minimize sound power radiated by a structure as a function of the area covered by constrained layer damping. The method of simulated annealing was used to minimized sound power as a function of damping patch area in cases where gradient methods proved unsuccessful. Reductions in sound power radiated at a single frequency of over 10 dB were achieved by covering just 1.1 percent of the total structural surface area with constrained layer damping material.