Showing papers on "Constrained-layer damping published in 1998"

Control of sound radiation from a plate into an acoustic cavity using active piezoelectric-damping composites

Abstract: Sound radiation from a plate into an acoustic cavity is controlled using patches of active piezoelectric-damping composites (APDC) The APDC under consideration consists of piezoelectric fibers embedded across the thickness of a visco-elastic matrix in order to control the compressional damping characteristics of the composite The effectiveness of the APDC treatments in attenuating the sound radiation from thin plates into cavities is demonstrated theoretically and experimentally A finite element model (FEM) is developed in order to describe the dynamic interaction between the plate, the APDC patches and the acoustic cavity The FEM is used to predict the dynamics of the plate/acoustic cavity and the sound pressure distribution for different control strategies The predictions of the FEM are validated experimentally using a square aluminum plate whose sides are 298 cm long and have a thickness of 004 cm The plate is mounted on a cavity The test plate is treated with a single APDC patch placed at the plate center The patch is and is made of 15-25% lead zirconate titanate (PZT) fibers embedded in soft and hard polymeric resin matrices and provided with silver-epoxy electrodes Vibration and sound pressure level attenuations of about 70% are obtained, at the plate/cavity first mode of vibration, with a maximum control voltage of 330 V using a derivative feedback controller Such attenuations are attributed to the effectiveness of the APDC treatment in increasing the modal damping ratios by about a factor of four over those of conventional passive constrained layer damping (PCLD) treatments Comparisons between the theoretical predictions of the FEM and the experimental results indicate close agreement between theory and experiments The obtained results suggest the potential of the APDC treatments in controlling the sound radiation from plates into acoustic cavities Such potential can be exploited in many critical applications such as cabins of aircrafts and automobiles to ensure a quiet environment for the occupants

Characteristics of Enhanced Active Constrained Layer Damping Treatments With Edge Elements, Part 1: Finite Element Model Development and Validation

Abstract: This paper is concerned with the enhanced active constrained layer (EACL) damping treatment with edge elements. A finite element time-domain-based model (FEM) is developed for the beam structure with partially covered EACL. The edge elements are modeled as equivalent springs mounted at the boundaries of the piezoelectric layer. The Golla-Hughes-McTavish (GHM) method is used to model the viscoelastic layer. The GHM dissipation coordinates can describe the frequency-dependent viscoelastic material properties. This model becomes the current active constrained layer (ACL) system model as the stiffness of the edge elements approaches zero. Without the edge elements and viscoelastic materials, the purely active system model can also be obtained from the EACL model as a special case. Lab tests are conducted to validate the models. The frequency responses of the EACL, current ACL, and purely active systems predicted by the FEM match the test results closely. Utilizing these models, analysis results are illustrated and discussed in Part (2) of this paper.

Constrained layer damping compositions

Abstract: A constrained layer damping structure is provided, including a panel to be damped, a constraining layer and a layer of foam vibration damping material sandwiched therebetween. The foam vibration damping material is provided from a composition including 1-20 weight percent elastomeric polymer, 20-60 weight percent thermoplastic polymer, 0.5-18 weight percent tackifier, 4-23 weight percent asphalt filler, 20-50 weight percent inorganic filler and 0.2-7 weight percent blowing agent.

Characteristics of Enhanced Active Constrained Layer Damping Treatments With Edge Elements, Part 2: System Analysis

Abstract: This paper presents some important characteristics of enhanced active constrained layer damping (EACL) treatments for vibration controls. Specific interests are on understanding how the edge elements will influence the active action authority, the passive damping ability, and their combined effects in EACL. Analysis results indicate that the edge elements can significantly improve the active action transmissibility of the current active constrained layer damping (ACL) treatment. Although the edge elements will slightly reduce the viscoelastic material (VEM) passive damping, the EACL will still have significant damping from the VEM. Combining the overall active and passive actions, the new EACL with sufficiently stiff edge elements not only could achieve better performance with less control effort compared to the current ACL system, but also could outperform the purely active system. With careful analysis, we can map out the required critical edge element stiffness for successful designs. In addition, analysis also shows that the EACL treatment is a more robust design. That is, it could outperform both the purely active and passive systems throughout a much broader design space than the current ACL configuration. With these desirable characteristics, the EACL could be used to realize an overall optimal active-passive hybrid system.

Variations of hybrid damping

Abstract: Damping is important to structures and can be achieved through the addition of viscoelastic materials (VEM). The dampingof the VEM is enhanced if a constraining layer is attached to the VEM. If this consiraining layer is active, the treatment iscalled active constrained layer damping (ACLD). In the last few years, ACiD has proven to be superior in vibration conirolto active or passive damping. The active element makes ACLD more effective than passive constrained layer damping. Italso provides a fail-safe in case of breakdown of the active element that is not present for purely active control. It is shownthat the conirol effort needed to damp vibration using ACLD can be significantly higher than purely active control. In orderto combine the inherent damping of passive control with the effectiveness of the active element, this paper will exploredifferent variations of active, passive and hybrid damping. Some of the variations include: passive constrained layerdamping (PCLD) separate from active element but on the same side ofbeam, PCLD separate from active on the opposite sideof the beam, and active element underneath PCLD. The discreUzed system equations will be obtained using assumed modesmethod and Lagrange's equation. The damping will be modeled using the Golla-Hughes-McTavish (GHM) method. Theoptimal placement and size of the active, passive, ACLD and hybrid treatments will be found using different schemes. Theissue of overshoot and setthng time of the output and control force using LQR will be addressed, as well as the control effort,passive and active vibration suppression, and LQR cost function. It will be shown that the hybrid treatments are capable ofgreater vibration control for lower control effort for different optimization schemes.Keywords: passive damping, active damping, ACLD, optimal control, hybrid damping, optimal placement and size

Optimum placement and control of active constrained layer damping using the modal strain energy approach

Abstract: Active Constrained Layer Damping (ACLD) treatment has been used successfully for controlling the vibration of various flexible structures It provides an effective means for augmenting the simplicity and reliability of passive damping with the low weight and high efficiency of active controls to attain high damping characteristics over broad frequency bands In this paper, optimal placement strategies of ACLD patches are devised using the modal strain energy (MSE) method These strategies aim at minimizing the total weight of the damping treatments while satisfying constraints imposed on the modal damping ratios A finite element model is developed to determine the modal strain energies of plates treated with ACLD treatment The treatment is then applied to the elements that have highest MSE in order to target specific modes of vibrations Numerical examples are presented to demonstrate the utility of the devised optimization technique as an effective tool for selecting the optimal locations of the ACLD treatment to achieve desired damping characteristics over a broad frequency band

Analytical model for a passive stand-off layer damping treatment applied to an Euler-Bernoulli beam

Abstract: Passive constrained layer (PCL) damping treatments have been shown to be a very effective and reliable method for the damping of structures and have been implemented successfully in many commercial and defense designs for the aerospace and automotive industries. A conventional passive constrained layer damping treatment consists of a viscoelastic layer sandwiched between the vibrating structure and a cover layer. In a passive stand-off layer (PSOL) damping treatment, a stand-off or spacer layer is added to a conventional passive constrained layer damping treatment between the vibrating structure and the viscoelastic layer. The addition of this stand-off layer increases the distance of the viscoelastic and constraining layers from the neutral axis of the vibrating structure. This is thought to enhance damping by increasing the shear angle of the viscoelastic layer. To investigate how the bending and shearing rigidities of the stand-off layer (SOL) affect the damping performance, an analytical model has been developed for a PSOL damping treatment applied to an Euler-Bernoulli beam. In this paper, the equations of motion are derived and solved. The resulting simulations of the frequency response are then discussed.

Vibration control of plates using magnetic constrained layer damping

Abstract: A new class of surface treatment is proposed to provide effective means for attenuating undesirable structural vibrations. The proposed treatment relies in its operation on the use of smart damping treatments which consists of integrated arrays of constrained visco-elastic damping layers that are controlled passively by a specially arranged network of permanent magnets. The interaction between the magnets and the visco-elastic layers aims at enhancing the energy dissipation characteristics of the damping treatment. In this manner, it would be possible to manufacture structures that are light in weight which are capable of meeting strict constraints on structural vibration when subjected to unavoidable disturbances. This new treatment will be called Magnetic Constrained Layer Damping (MCLD) treatment. A finite element modeling of a plate treated with MCLD treatments is developed. This model describes the dynamics and the damping characteristics of this structure. The numerical results are verified experimentally using a cantilever plate fully treated with MCLD with the magnets placed at the root of the plate. Close agreement is obtained between theory and experiments. Also the performance characteristics of the MCLD is compared with the corresponding performance of the conventional Passive Constrained Layer Damping (PCLD). The effectiveness of the MCLD in attenuating structural vibration of the plate has been clearly demonstrated in the frequency domain. The developed theoretical and experimental techniques present invaluable tools for designing and predicting the performance of plates treated with MCLD.

Enhanced active constrained layer damping treatment with symmetrically and nonsymmetrically distributed edge elements

Abstract: This paper is concern with the effects of edge element symmetry on the Enhanced Active Constrained Layer (EACL) treatment. The research characterizes the relationship among the edge element stiffness distribution, the strain field of the base structure, and the system active, passive, and hybrid damping abilities. The results could provide good insights and guidelines for EACL designers.

Optimization of energy dissipation characteristics of active constrained layer damping

Abstract: The energy dissipation characteristics of Active Constrained Layer Damping (ACLD) treatments, consisting of visco-elastic cores constrained by active piezo-electric layers, is optimized using rational design procedures. The optimal lengths and control gains of these ACLD treatments are determined when a globally stable boundary control strategy is utilized to control the longitudinal strain of the active piezo-electric layers in response to the structural vibrations. The optimal parameters are obtained such that the sum of the passive and active loss coefficients of the ACLD treatments is maximized. The effect of the visco- elastic loss factor on the performance and the optimal parameters of the ACLD treatments is determined. Comparisons with optimal ACLD is more effective in dissipating vibrational energy particularly for visco-elastic cores with low loss factors.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Damping of patched structures subjected to acoustic fatigue : A numerical study

Abstract: This numerical study seeks to evaluate a set of reinforcement/damping treatment options to alleviate the acoustic fatigue damage ofthe nacelle panel ofthe F/A-18 aircraft. This study focuses on the use of constrained layer damping to increase the structural loss factor in the nacelle region in a bid to reduce the incidence of acoustic fatigue. The findings of this report show that where add-on damping material is to be implemented on a repair/reinforcement, orthotropic material, (e.g. boron/epoxy), is a more appropriate material to use as a repair/reinforcement material than isotropic material, e.g. aluminium. In addition, the results presented in this paper revealed that boron/epoxy laminate can be used as an alternative constraining layer for the damping treatment in regions of intense acoustic excitation.

Coil springs with constrained-layer viscoelastic damping for passive isolation

Abstract: This paper summarizes the design, optimization, development, fabrication, and testing of a vacuum compatible coil spring with embedded constrained layer visco-elastic damping. The spring is developed as part of the NSF funded LIGO (Laser Interferometer Gravity Wave Observatory) project. Large numbers of those springs are the primary components of multi- stage, in-vacuum, passive seismic isolation stacks that provide high attenuation (-160 dB/decade above 15 Hz) of floor vibrations for ultra-sensitive (better than 10-18 m/(root)Hz noise floor between 40 and 1000 Hz) laser interferometers. The spring design addresses both requirements for passive isolation within a single, self- contained, vacuum tight envelope: low stiffness for maximum attenuation and non-viscous damping to limit resonant amplitudes in the stack. This is achieved with a tubular coil spring design with an internal torsional constrained layer damping structure. The paper presents the analysis of this spring using closed-form analytical expressions, trend studies showing the strong dependence of spring performance on key design parameters, and explicit numerical design optimization. Manufacturing issues are briefly discussed. Finally, experimental results from static and dynamic tests performed on prototype units are presented. Results show loss factors of the order of 1.5% in the transverse direction to 3% in the axial direction, at frequencies from 1 to 2 Hz.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Experimental Determination of the Dynamic Properties of a Soft Viscoelastic Material

Abstract: Diminishing the vibration level in industrial structures becomes an essential point. both to avoid fatigue failure and to improve the comfort, from a vibratory or an acoustical point of view . This goal is generally fulfilled through the use of damping treatments. These can be single layer or constrained layer damping treatments. In both case, the efficiency of these methods is closely related to the knowledge of the dynamical characteristics of the applied material. Indeed, for successful results, the damping treatment should suit the vibratory problem. For a reliable prediction of the vibratory response of the damped system, one needs accurate values of the damping material physical characteristics. These are the complex moduli, which are temperature and frequency dependent ([3]).

Passive and active damping of a large composite panel

Abstract: A study was undertaken to investigate low frequency vibration suppression of a large composite panel under acoustic excitation. Both passive and active techniques are examined. Passive damping is achieved with a peel and stick constrained layer damping treatment. The treatment uses a constraining layer with a stand-off spacer to increase damping performance. Active damping is achieved with surface bonded piezoceramic wafer actuators and a closed-loop controller. This paper will discuss the analytical modeling of both damping techniques and show comparisons with test data. The reduced vibration resulted in noise attenuation at panel resonance. This phenomenon will also be discussed with the presentation of accelerometer and microphone test data.

Life extension of F/A 18 intake nacelle using add-on dampers

Abstract: Acoustic fatigue is due to very high intensity excitation as a result of pressure waves caused by either engine/or aerodynamic effects Currently a large portion of the F/A-18 fleet has suffered from acoustic fatigue cracking in skin panel on the lower external surface of the inlet nacelle There has been a long history of cracking in this region, which is attributed to fatigue caused by acoustic excitation of the panel during the operation of the aircraft Efforts to alleviate these fatigue crack growth with traditional boron/epoxy patches was not successful This paper seek to select a set of damping material suitable for the reinforcement/damping treatment to alleviate the acoustic fatigue damage of the nacelle panel of the F/A-18 aircraft This experimental study will address the relevance of constrained layer damping reducing the incidence of acoustic fatigue problems in the nacelle region