Showing papers on "Constrained-layer damping published in 2000"

Dynamics of active piezoelectric damping composites

Abstract: A finite element model is developed to investigate the dynamic characteristics of beams treated with discrete patches of Active Piezoelectric Damping Composites (APDC) The APDC patches, under consideration, consist of piezoelectric rods that are obliquely embedded in a viscoelastic matrix to actively control its shear and compression damping characteristics With such active and passive control capabilities, the energy dissipation mechanism of the viscoelastic layer can be enhanced and the dynamic behavior of the system can be improved The effectiveness of the APDC in damping the vibration of beams is compared with the performance of the conventional Passive Constrained Layer Damping (PCLD) The effect of the inclination angle of the piezoelectric rods on the performance of the APDC is presented The results obtained demonstrate that the APDC, with their inherent active and passive capabilities, are an effective means for controlling structural vibrations over a broad frequency band

Control of axi-symmetric vibrations of cylindrical shells using active constrained layer damping

Abstract: Distributed-parameter modeling of thin cylindrical shells which are fully treated with active constrained layer damping (ACLD) is presented. Hamilton's principle is utilized to develop the shell/ACLD model as well as the associated boundary conditions. A globally stable boundary control strategy is developed to damp out the vibration of the shell/ACLD system. The devised boundary controller is compatible with the operating nature of the ACLD treatments where the strain induced, in the active constraining layer, generates a control force acting at the boundary of the treated shell. As the boundary control strategy is based on a distributed-parameter model of the shell/ACLD system, the classical spillover problems resulting from using “truncated” finite element models is eliminated. Also, such an approach makes the boundary controller capable of controlling all the modes of vibration of the shell/ACLD and guarantees that the total energy norm of the system is continuously decreasing with time. Numerical examples are presented to demonstrate the effectiveness of the ACLD in damping out the vibration of cylindrical shells. Such effectiveness is determined for different control gains and compared with the performance of conventional passive constrained layer damping (PCLD). The results obtained demonstrate the high damping characteristics of the boundary controller particularly over broad frequency bands.

Hybrid damping models using the Golla-Hughes-McTavish method with internally balanced model reduction and output feedback

Abstract: Viscoelastic materials (VEMs) are used to increase passive damping in structures. The damping capabilities of the VEM can be enhanced by attaching a constraining layer to the VEM. If this constraining layer is active, the treatment is called active constrained layer damping (ACLD). In the last few years, ACLD has proven to be superior in vibration control to active or passive damping. The active element allows for more effective vibration suppression than purely passive constrained layer damping. On the other hand, the VEM provides a fail-safe in case of breakdown of the active element that is not present for purely active control. It has been shown that the control effort needed to damp vibration using ACLD can be significantly higher than purely active control. In order to combine the inherent damping of passive control with the effectiveness of the active element, different variations of active, passive and hybrid damping are explored. Some of the variations included in this paper are passive constrained layer damping (PCLD) separate from the active element, but on the same side of beam and PCLD separate from the active element on the opposite side of the beam. The discretized system equations are obtained using the assumed modes method and Lagrange's equation. The damping is modeled using the Golla-Hughes-McTavish (GHM) method. This method adds `dissipation coordinates' to the structure in order to account for the damping present. These additional modes are eliminated using a reduction method, rendering the method more practical. A linear quadratic regulator and output feedback are used to actively control vibration.

Spectral finite-element modeling of the longitudinal wave propagation in rods treated with active constrained layer damping

Abstract: A spectral finite-element model (SFEM) is developed to describe the propagation of longitudinal waves in rods treated with active constrained layer damping (ACLD) treatments. The model is formulated in the frequency domain using dynamic shape functions that capture the exact displacement distributions of the different ACLD layers. In this manner, a small number of elements is needed to accurately model the wave propagation dynamics, particularly in rods with discontinuities and partial ACLD treatments. Numerical examples are presented to illustrate the accuracy of the SFEM as compared to the exact solutions. Application of the SFEM to beams, plates and shells treated with ACLD treatments is a natural extension of the present work.

Active constrained layer damping of plate vibrations: a numerical and experimental study of modal controllers

Abstract: In this paper the authors address the problem of suppressing the vibrations of a clamped-clamped plate using an active constrained layer damping treatment. This treatment involves adding viscoelastic and metallic constraining layers to the host plate and then augmenting this arrangement with an active feedback scheme using piezoelectric actuators. The basis of the control strategy is an effective model of the plate together with the passive damping treatment. The paper summarizes the modelling procedures including the finite-element formulation, model reduction and model updating. By this means a low-order model, capable of accounting for the observed behaviour, is developed. Emphasis is placed upon the design and implementation of active modal controllers based upon the reduced and updated model. Four actuator/sensor configurations are examined in both numerical and experimental studies. It is shown that effective control of the first two modes of vibration (bending and torsion) can be achieved using only a single actuator and single sensor. However, the most effective configuration involves two actuators and two sensors operating as two independent control channels. It is shown that through suitable design, the active constrained layer damping treatment is capable of avoiding problems due to spillover effects.

H ∞ Control of Active Constrained Layer Damping

Abstract: Conventional passive constrained layer damping treatments with viscoelastic cores are provided with built-in sensing and actuation capabilities to actively control and enhance their vibration damping charac teristics. Two configurations of the resulting hybrid treatment are considered in this paper. In the first configuration, the active control and passive operate separately, whereas in the second configuration, the two operate in unison to maximize the energy dissipation characteristics. In this study, three objectives are accomplished. The first objective aims at the design and implementation of robust H∞) controllers for the separated and unified control strategies. In the second, the performance of the H∞ controllers at different operating frequencies and temperatures is compared with that of a conventional proportional/derivative controller to demonstrate robustness. Finally, a control effort study involving the H∞ controllers for the separated and unified control strategies is shown to assess the e...

Finite element modeling of vibration and sound radiation from fluid-loaded damped shells

Abstract: The vibration and noise radiation from fluid-loaded cylindrical shells are controlled by using multiple stiffeners and passive constrained layer damping treatment. Dynamic and fluid finite elements are developed to study the fundamental phenomena governing the coupling between the stiffened shell, with and without damping, and the fluid domain surrounding it. The models are used to predict the response of the shell and to evaluate the effect of stiffening rings and damping treatment on both the structural vibration and noise radiation in the fluid domain. The geometry of the shell and fluid domain allows the formulation of a harmonic-based model, which uncouples the fluid–structural response of modes corresponding to different numbers of circumferential nodes. In this study, it is shown that stiffening of the shell reduces the amplitude of the vibration and noise radiation, particularly for high-order lobar modes. The attenuation of the shell response and sound radiation can be increased significantly through the application of passive constrained layer damping treatments on the inner surface of the stiffening rings.

Finite element analysis of frequency- and temperature-dependent hybrid active-passive vibration damping

Abstract: A new finite element is formulated and used for the analysis of sandwich damped beams with laminate piezoelectric faces. The viscoelastic damping of the core is accounted for using three models, namely Golla-Hughes-McTavish, Anelastic Displacement Fields and Iterative Modal Strain Energy. Since the first two models increase much the system dimension, a modal reduction is proposed. The reduced models are then applied to the analysis of active constrained layer damping treatments of a cantilever beam, using a constrained input optimal control algorithm. Furthermore, the effect of temperature variations on the control performance is studied

SMA Hybrid Composites for Dynamic Response Abatement Applications

Abstract: A recently developed constitutive model and a finite element formulation for predicting the thermomechanical response of SMA hybrid composite (SMAHC) structures is briefly described. Attention is focused on constrained recovery behavior in this study, but the constitutive formulation is also capable of modeling restrained or free recovery. Numerical results are shown for glass/epoxy panel specimens with embedded Nitinol actuators subjected to thermal and acoustic loads. Control of thermal buckling, random response, sonic fatigue, and transmission loss are demonstrated and compared to conventional approaches including addition of conventional composite layers and a constrained layer damping treatment. Embedded SMA actuators are shown to be significantly more effective in dynamic response abatement applications than the conventional approaches and are attractive for combination with other passive and/or active approaches.

Vibration Control of Beams Using Electro-Magnetic Compressional Damping Treatment

Abstract: A new class of structural damping treatments is introduced. This class is the electro-magnetic damping treatment (EMDT) which relies in its operation on a viscoelastic damping layer sandwiched between two magnetic layers. Interaction between the magnets generates magnetic forces that enhance the compressional damping mechanism of the viscoelastic layer. With proper tuning of the magnetic forces, in response to the structural vibration, undesirable resonances and catastrophic failures can be avoided. The fundamentals and the underlying phenomena associated with the EMDT are investigated theoretically and experimentally. A finite element model is developed to describe the interaction between the dynamics of flexible beams, the viscoelastic damping layer and the magnetic layers. The validity of the developed finite element model is checked experimentally using aluminum beams treated with EMDT patches. The beam/EMDT system is subjected to sinusoidal excitations and its multi-mode response is monitored when the magnetic layers are activated or not. Several control strategies are considered to activate the magnetic layers including simple PD controllers. The performance of the uncontrolled and controlled system is determined at various operating conditions. Attenuation of 49.4 percent is obtained for the amplitude of. first mode of vibration (5.2 Hz) with control voltage of 0.2 volts. The attenuation increases to 72.56 percent for the second mode of vibration (28.6 Hz) with a control voltage of 1.68 volts. Comparisons with conventional Passive Constrained Layer Damping (PCLD) treatments emphasize the potential of the EMDT treatment as an effective means for controlling structural vibrations.

Performance Characteristics of the Magnetic Constrained Layer Damping

Abstract: A new class of surface damping 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 consist 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 treatments. In this manner, it would be possible to manufacture structures that are light in weight which are also capable of meeting strict constraints on structural vibration when subjected to unavoidable disturbances.

Use of segmented constrained layer damping treatment for improved helicopter aeromechanical stability

Abstract: The use of a special type of smart material, known as segmented constrained layer (SCL) damping, is investigated for improved rotor aeromechanical stability. The rotor blade load-carrying member is modeled using a composite box beam with arbitrary wall thickness. The SCLs are bonded to the upper and lower surfaces of the box beam to provide passive damping. A finite-element model based on a hybrid displacement theory is used to accurately capture the transverse shear effects in the composite primary structure and the viscoelastic and the piezoelectric layers within the SCL. Detailed numerical studies are presented to assess the influence of the number of actuators and their locations for improved aeromechanical stability. Ground and air resonance analysis models are implemented in the rotor blade built around the composite box beam with segmented SCLs. A classic ground resonance model and an air resonance model are used in the rotor-body coupled stability analysis. The Pitt dynamic inflow model is used in the air resonance analysis under hover condition. Results indicate that the surface bonded SCLs significantly increase rotor lead-lag regressive modal damping in the coupled rotor-body system.

Design of a railway wheel with acoustically improved cross-section and constrained layer damping

Abstract: The rolling-noise generating characteristics of a railway wheel design have been studied theoretically. Two aspects of design for reducing noise have been investigated, optimisation of the cross-sectional shape of the wheel and addition of a constrained layer damping treatment. In this the thermo-mechanical behaviour of tread-braked wheels must be taken into account. To produce significant noise reduction, the damping achieved by the constrained layer treatment must exceed the effective ’rolling damping’. A finite element model is used to produce the modal basis of the wheel and to predict the modal damping of a wheel with visco-elastic layers a method of complex eigenvalue analysis has been used. The analysis indicates that the wheel component of rolling noise from the UIC standard tread-braked freight wheel can be reduced by more than 5 dB(A) by a combination of the two measures.

Improved Helicopter Aeromechanical Stability Analysis Using Segmented Constrained Layer Damping and Hybrid Optimization

Abstract: Aeromechanical stability plays a critical role in helicopter design and lead-lag damping is crucial to this design. In this paper, the use of segmented constrained damping layer (SCL) treatment and composite tailoring is investigated for improved rotor aeromechanical stability using formal optimization technique. The principal load-carrying member in the rotor blade is represented by a composite box beam, of arbitrary thickness, with surface bonded SCLs. A comprehensive theory is used to model the smart box beam. A ground resonance analysis model and an air resonance analysis model are implemented in the rotor blade built around the composite box beam with SCLs. The Pitt-Peters dynamic inflow model is used in air resonance analysis under hover condition. A hybrid optimization technique is used to investigate the optimum design of the composite box beam with surface bonded SCLs for improved damping characteristics. Parameters such as stacking sequence of the composite laminates and placement of SCLs are us...

Passive Damping of Spinning Disks

Abstract: An investigation of the application of constrained-layer damping to computer disk drives is pre sented. Nine constrained-layer disks were manufactured and tested to determine their modal parameters...

Improved helicopter aeromechanical stability analysis using segmented constrained layer damping and hybrid optimization

Abstract: Aeromechanical stability plays a critical role in helicopter design and lead-lag damping is crucial to this design. In this paper, the use of segmented constrained damping layer (SCL) treatment and composite tailoring is investigated for improved rotor aeromechanical stability using formal optimization technique. The principal load-carrying member in the rotor blade is represented by a composite box beam, of arbitrary thickness, with surface bonded SCLs. A comprehensive theory is used to model the smart box beam. A ground resonance analysis model and an air resonance analysis model are implemented in the rotor blade built around the composite box beam with SCLs. The Pitt-Peters dynamic inflow model is used in air resonance analysis under hover condition. A hybrid optimization technique is used to investigate the optimum design of the composite box beam with surface bonded SCLs for improved damping characteristics. Parameters such as stacking sequence of the composite laminates and placement of SCLs are used as design variables. Detailed numerical studies are presented for aeromechanical stability analysis. It is shown that optimum blade design yields significant increase in rotor lead-lag regressive modal damping compared to the initial system.

Hybrid Active/Passive Control of Sound Radiation From Panels With Constrained Layer Damping and Model Predictive Feedback Control

Abstract: Feedback control of aircraft sidewall panels has been studied for reducing interior noise due to turbulent boundary layer excitation of the fuselage. Online adaptation of the feedback controller parameters can be used to track pressure, temperature, and structural variations, but the associated computational burden can be overwhelming. This work describes a hybrid active/passive control approach, where the passive components reduce the complexity of the active system. Constrained layer damping provides damping at high frequencies, and a generalized predictive controller is used at low frequencies. Experiments were conducted on a panel subjected to broadband speaker excitation in a transmission loss facility. A piezoelectric actuator provided control input to the panel, accelerometers provided error feedback. Two sensing configurations were studied: one used full-state feedback to control radiated sound power, estimated from 15 accelerometers on the panel; the other used dynamic output feedback to control the summed responses of 4 accelerometers. Active noise reduction from different locations of constrained layer damping is discussed. The addition of the constrained layer damping makes it possible to achieve good noise reduction with the simpler 4-accelerometer sensing configuration.

Comparison of the mechanism and effectiveness of position and velocity feedback in active constrained-layer damping treatments

Abstract: In active constrained layer (ACL) damping treatments there are two distinct physical mechanisms that contribute to the damping of resonant oscillations -- increased passive damping due to increased shear in the viscoelastic material (VEM) layer, and damping due to transmission of active forces to the host structure. The present study demonstrates that the first mechanism is dominant when proportional feedback is used while the second mechanism is dominant when derivative feedback is used. In the case of proportional feedback, the shear in the VEM increases considerably so that the passive damping is significantly larger than that obtained for zero-voltage (PCL case), but the active action is actually slightly detrimental. In the case of derivative feedback, the shear strain levels in the VEM are virtually unchanged, and all of the damping augmentation is due to the active action. While previous studies have suggested that a high VEM shear modulus would enhance the active damping augmentation due to improved transmissibility of active forces from the piezoelectric layer to the host structure, voltage (or electric field) limits on the piezoelectric layer were never directly considered. In the present study it is concluded that for high VEM shear modulus the low inherent damping results in large resonant response amplitudes. In such a case, the allowable control gains (so as not to exceed the piezoelectric voltage limits) would be reduced, and the damping increases predicted previously (without considering the voltage limits) are no longer available. The present results indicate that when voltage limits are considered, the maximum damping augmentation is available in the VEM shear modulus range that provides optimal passive damping, since these allow the largest control gains.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Improved constrained-layer damping treatment design for high damping and low interlaminar stresses

Abstract: The purpose of this research is to investigate and improve constrained layer (CL) damping treatment for high damping and low interlaminar stresses (better durability). In this paper a mathematical model is developed to calculate interlaminar stresses in a CL treatment. The model is based on the Built-Up Bar (BUB) theory but includes numerous fundamental modifications to handle the behavior of various coversheet and viscoelastic materials. A parametric study is conducted. It is shown that the interlaminar peeling and shearing stresses in a CL treatment could be very high, especially at the free edges due to discontinuities in the material properties. It is also illustrated that these interlaminar stresses are of local type, i.e. the high stresses are limited to a region that is close to the free edge and is of the same order-of-magnitude in length as the layer thickness. The observation is that the designs that provide high damping usually have high interlaminar stresses. This means that the existing high performance CL designs that provide high damping usually have high interlaminar stresses.This means that the existing high performance CL designs could fail, especially under high load operations. From this research, it is shown that through some simple yet innovative modifications (e.g., slightly tapering the constraining layer at the free ends), the interlaminar stresses in the CL treatment can be significantly reduced while maintaining high levels of damping.

Enhanced damping of hat-stiffened panels using continuous wave fiber composites

Abstract: A unique composite material called Continuous Wave Fiber Composite (CWFC) or wavy composite has shown great promise in improving damping properties of composite structures. In wavy composites, the fiber is oriented in a continuous sine wave which produces a varying fiber angle. This new material has exhibited high levels of damping when two layers, with wave patterns 180 degrees out of phase, surround a layer of viscoelastic material. This research investigated the acoustic transmission loss and flexural damping of hat-stiffened panels produced with graphite/epoxy wavy composite material. The 22- panel test matrix included sixteen exploratory panels used to determine the most highly damped design, four optimized panels based on the best exploratory design, and two control panels including one panel without CWFC and another without VEM or CWFC. The panels were tested to quantify the acoustic transmission loss and flexural damping under free-free boundary conditions. Hat-stiffened panels produced with graphite/epoxy wavy composites provide 17% higher damping than constrained layer damping and slightly higher transmission loss over panels made with conventional unidirectional materials.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Analytical model for a one-dimensional slotted stand-off layer damping treatment

Abstract: Passive stand-off layer and slotted stand-off layer damping treatments are presently being implemented in many commercial and defense designs. In a passive stand-off layer damping treatment, a stand-off or spacer layer is added to a conventional passive constrained layer damping treatment. Additionally, this stand-off layer can be slotted in order to reduce the bending rigidity and total mass of the damping treatment. A preliminary analytical model has being developed for a slotted stand-off layer damping treatment applied to a beam. This mathematical model is based on Euler-Bernoulli beam theory, and may be able to provide an analytical solution of the frequency response for a beam treated with slotted stand- off layer damping.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Application of constrained-layer damping to a precision kinematic coupling

Abstract: This paper addresses the need to support a very precise optical instrument while causing essentially no influence to its natural shape. Such influences could come from a number of sources, such as manufacturing tolerances, temperature changes, over-constrained structural members, or ground motion. Kinematic couplings have long been used for purposes of repeatable location and minimal influence to the supported object, however these couplings typically offer very little damping. This paper presents a kinematic coupling that utilizes constrained-layer damping techniques to damp out the first three modes of vibration of a precision optical instrument. Finite element analysis was used to aid in the design and tuning of the dampers for the kinematic coupling. Experimental tests were conducted and confirmed the effectiveness of the dampers. The quality factor (Q), which measure the amplification at resonance, dropped from 33.3 to 5.9 on the first mode, from 156.3 to 7.1 on the second mode, and from 147.1 to 18.5 on the third mode. These dampers help to ensure that the stringent vibration requirements necessary to produce high quality optical images are met.

Model-based control of plate vibrations using active constrained layer damping

Abstract: In this thesis, the author presents a numerical and experimental study of the application of active constrained layer damping to a clamped-clamped plate. Piezoelectric actuators with modal controllers are used to improve the performance of vibration suppression from the passive constrained layer damping treatment. Surface damping treatments are often effective at suppressing higher frequency vibrations in thin-walled structures such as beams, plates and shells. However, the effective suppression of lower frequency modes usually requires the additional of an active vibration control scheme to augment the passive treatment. Advances in the technologies associated with so-called smart materials are dramatically reducing the cost, weight and complexity of active structural control and make it feasible to consider active schemes in an increasing number of applications. Specifically, a passive constrained layer damping treatment is enhanced with an active scheme employing a piezoceramic (PZT) patch as the actuator. Starting with an established finite element formulation it is shown how model updating and model reduction are required to produce a low-order state-space model which can be used as the basis for active control. The effectiveness of the formulation is then demonstrated in a numerical study. Finally, in the description of the experimental study it is shown how modes in the frequency range from 0 to 600 Hz are effectively suppressed: the two lowest modes (bending and torsional) through active control, the higher modes (around ten in number) by the passive constrained damping layer. The study'S original contribution lies in the experimental demonstration that given a sufficiently accurate model of the plate and passive constrained damping layer, together with a suitable active feedback control algorithm, spillover effects are not significant even when using a single sensor and single actuator. The experimental traces show, in some instances, minor effects due to spillover. However, it can be concluded that the presence of the passive layer introduces sufficient damping into the residual modes to avoid any major problems when using only the minimum amount of active control hardware.

High passive damping in a NiTi shape memory alloy fiber aluminum metal matrix composite

Abstract: Vibration control in structures often requires the addition of viscoelastic constrained layer damping treatments. In critical applications, however, the low strength of the viscoelastic material and the threat of delamination prevent the use of these treatments. In this paper we present a means of how to overcome these difficulties by using high strength shape NiTi fibers to increase the damping of aluminum structures. Specifically, we show that the introduction of high strength, shape memory alloy fibers into an aluminum beam can result in a significant increase in the passive damping response of the beam. The objective of our research is to develop passive and active structural materials that can be sued in applications that demand high loss factors, strength, and high reliability. The development of the NiTi fiber reinforced aluminum matrix composite beam is a first important step towards achieving this objective.