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.

The Hubble Space Telescope (HST) is currently operating with two flexible solar arrays (or 'wings'), referred to as SA2, that were installed during Servicing Mission 1. These flexible solar arrays are to be replaced with two rigid solar arrays, SA3, during Servicing Mission 3B which is currently scheduled for May, 2001. The key requirements for these arrays are to: (1) increase long term power to support the HST mission, (2) improve the jitter performance while maintaining stability margin requirements, and (3) withstand re-boost loads without astronaut or ground intervention. Analysis of the original SA3 design showed that the Pointing Control System (PCS) stability margin requirements would be violated because of the modal characteristics of the SA3 fundamental bending modes. One of the options to regain the stability margins was to increase the damping of these modes. Damping of 1.5% of critical of the SA3 fundamental bending modes, at the HST system level, is needed to meet stability margin requirements. Therefore, the development of a discrete damping device was undertaken to provide adequate damping of the SA3 fundamental bending modes for all operational conditions.

Considerable attention has been devoted to actively and passively control of the sound radiating from vibrating plates into closed cavities. With the advent of smart materials, extensive efforts have been exerted to control the vibration and sound radiation from flexible plates using smart sensors/actuators. Active Constrained Layer Damping (ACLD) treatment has been used successfully for controlling the vibration of various flexible structures. The treatment 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. The proposed study is investigated using a numerically simulated example consisting of an ACLD treated plate/acoustic cavity system excited by a point harmonic force. In this study, an ACLD treated plate/acoustic cavity coupled finite element model is utilized to calculate the structural intensity and sound pressure radiated by vibrating plates. In the passive control, the optimum placements of ACLD patches are determined by structural intensity of ACLD treated plates and compared to the results obtained by modal strain energy approach. The influence on structural intensity of plate due to damping treatment is investigated.

Vibration suppression of a flexible four-bar mechanism is investigated. A generic four-bar mechanism, with flexible coupler, is considered for the investigation. Passive and active constrained layer damping techniques are adopted for the vibration suppression. The equations of motion are developed using the assumed mode method and the constrained Lagrange's equations, and are manipulated and solved using Maple and Matlab. Two types of responses are investigated: the free decay response due to an initial midpoint deflection of the flexible coupler, and the forced transient response due to an applied crank pulse torque. Effects of the application of passive and active constrained layer damping on the responses are discussed.

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.

A new configuration of surface damping treatments, Active- Passive Hybrid Constrained Layer (HCL) damping, is analyzed and experimentally investigated. The purpose is to improve the performance of the current active constrained layer (ACL) and passive constrained layer (PCL) treatments by mixing passive and active materials in the constraining layer. In HCL, the viscoelastic material is constrained by an active-passive hybrid constraining layer -- the active part is made of PZT ceramics, and the passive part can be selected by the designer to meet different requirements, such as higher damping performance or lighter weight. The active and passive constraining parts are mechanically connected such that the displacement and force are continuous at the connecting surface, but are isolated electrically so the passive constraining part will not affect the function of its active counterpart. Following a generic study of the HCL concept by the authors earlier, the purpose of this paper is to illustrate and validate the HCL performance through both numerical and experimental investigations on a beam structure. The governing equations and boundary conditions of an HCL treated beam are derived and a finite element model is formulated. Tabletop tests with cantilever beam specimens are used for the experimental study. The new hybrid constrained layer is found to have the advantages of both ACL and PCL. By selecting a stiffer passive constraining material and an optimal active-to-passive length ratio, the HCL can achieve better closed-loop and open-loop performances than the treatment with a pure active constraining layer.

We use two constitutive relations to analyze finite simple shearing, simple extensional and torsional deformations of a viscoelastic body. One of these constitutive relations is a linear relationship between the second Piola-Kirchhoff stress tensor and the history of the rate of change of the Green-St. Venant strain tensor. The other is a linear relationship between the Cauchy stress tensor and the rate of change of the relative Green-St. Venant strain tensor. It is found that only predictions from the latter constitutive relation agree with the test findings. This constitutive relation is used to analyze damping in steady state torsional oscillations of a cylinder, and slow finite shearing deformations of a constrained viscoelastic layer.

When the vibration of a structure is considerably magnified by resonance effects, adding of damping is an effective method to reduce the level of vibration. Viscoelastic materials are generally used as an instrument to increase the amount of damping in the structure. The constrained-layer damping (CLD) method involves sandwiching a viscoelastic damping medium between two outer layers. The most important parameters which influence the dynamic behavior of a CLD system are the geometrical dimensions and the frequency dependent material properties of the viscoelastic material. Therefore, a direct solution of the equation of motion in the frequency domain seems to be the only valid solution technique. However, this method has to be rejected from a computational point of view when dealing with large structures. The mode superposition method is a powerful solution method to characterize the dynamic response of a large structure. The two basic assumptions to apply this method are that the material properties are constant and that the damping is proportional which is not the case for a CLD system. In the paper, four different solution techniques based on the solution of a (non- linear) eigenvalue problem are presented to predict the dynamic behavior of a simple supported sandwich layer system due to a uniform base excitation. The damping ratio of each eigenmode is calculated by the Modal Strain Energy method. Each proposed technique is validated in terms of accuracy and computational effort.

Golla-Hughes-McTavish (GHM) method has been shown to be an effective approach to model viscoelastic materials (VEMs). In the GHM model, a mini-oscillator has been used as the mechanical analogy to illustrate the relation of GHM parameters. However, the GHM mini-oscillators have not been studied in depth so far. In this paper, the damping and isolation characteristics of this two degree-of-freedom mini- oscillator are analyzed. Those characteristics are crucial to the effectiveness and limitations of the passive and hybrid (active-passive) vibration suppression techniques employing VEMs. Under harmonic excitations, the corresponding nondimensional relationships among parameters are derived. The transmissibility due to force and base excitations is investigated with respect to various parameters. The damping ability of the mini-oscillator is also evaluated. For those critical points and special cases, their conditions are identified and discussed. Several unique distinctions are observed when compared to previous studies on vibration absorbers and isolators. The analysis results of this research provide more understanding and physical insight to designers when considering VEM-based configurations including passive and hybrid systems for the purpose of vibration isolation and control.

A new finite element type, compound beam element, is derived for sandwich beam by considering the effects of both shear and thickness deformation in the adhesive layer. The new element type overcomes some limitations with the conventional finite element method, in which modal strain energy method is normally used for structural damping analysis. Modal strain energy method becomes quite inaccurate when the damping of the structure becomes high because it is always assumed that the structural modal shapes are real while actual modal shapes of the damped structures are quite complex. For achieving the best damping effect, the thickness of the damping layer is normally very thin, which requires great amount of elements in conventional finite element modeling to get a proper aspect ratio for accurate prediction. In compound beam element, all base beam layers and adhesive layer are modeled into a single element. The use of the element will result in significant simplification of sandwich beam modeling and dramatic reduction of element density while maintaining the desired accuracy. The use of the element also allows consideration of complex modulus of the adhesive material in the analysis and calculation of complex modal shapes of the damped structure.

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.

The chief tool for design of viscoelastic-based damping treatments over the past 20 years has been the modal strain energy (MSE) approach. This approach to damping design traditionally has involved a practitioner to vary placement and stiffness of add-on elements using experience and trial and error so as to maximize the add-on element's share of system MSE in modes of interest. In this paper we develop a new technique for maximizing strain energy as a function of stiffness for add-on structural elements modeled as rank r perturbations to the original stiffness matrix. The techniques is based on a constrained substructure approach allowing us to parameterize strain energy in terms of the eigenvalues of the perturbed structure. An optimality condition is derived that relates the input-output response at the attachment location of the add-on elements to the maximum achievable strain energy. A realizability condition is also derived which indicates whether or not the optimal solution is achievable with passive structural elements. This method has applications in the design of structural treatments for controlling sound and vibration and promises an efficient means of determining the limits of performance of passive structural treatments. An advantage of our approach over existing methods is that the maximum achievable strain energy fraction in the add-on elements is directly computable with the realizability condition then indicating whether the optimal solution is achievable.

Composite joints with specially designed viscoelastic inserts could act as effective vibration absorbers. The damping performance of a novel viscoelastic material used as an interlayer in a composite Top-hat stiffener is studied following experimental and FE modal analysis. The damping performance of the same material embedded inside Aluminum Beams in different shapes but constant volume is also evaluated. Results from the experimental and numerical analysis are discussed.

Recently, Nishihara and Matsuhisa have proposed a new theory for attaining the H_(infinity) optimization of a dynamic vibration absorber (DVA) in the linear vibratory systems. The H_(infinity) optimization of DVA is a classical optimization problem, and already solved more than 50 years ago. All of us know the solution through the textbook written by Den Hartog. The new theory proposed them gives us the exact algebraic solution of the problem. In the first report, we have expounded the theory and showed the procedure of finding the algebraic solution to a typical performance index (compliance transfer function) of the viscous damped system. In this paper, we will apply this theory to another performance indexes: mobility and accelerance transfer functions for force excitation system, and the absolute and relative displacement responses to acceleration, velocity or displacement input to foundation for motion excitation system. We apply this theory not only the viscous damped system but also the hysteretic damped system. As a result, we found the closed-form exact solutions in every performance indexes when the primary system has no damping. The solutions obtained here are compared with the classical ones solved by the fixed-points theory. We further apply this theory to design of DVAs attached to damped primary systems, and found the closed-form exact solutions to some performance indexes of the hysteretic damped system.

Emerging digital image processing techniques are utilized to demonstrate their potential applications in earthquake engineering, particularly in the area of system identification. In this respect, the objectives of this research are to demonstrate the underlying principle that permits nonlinear system identification, non-intrusively and remotely, with the aid of CCD camera and, for the purpose of the proof-of-concept, to apply the principle to an identification problem involving friction forces, a simple but not necessarily easy problem to solve, on the basis of the image captured by a CCD camera. On the one hand, intricate micromechanic interpretation of friction phenomena is prevalent and necessary in the area of Tribology and similarly detailed analysis of friction is performed as the extension of contact problem in continuum mechanics. On the other hand, the practice in the structural dynamics dealing with the friction issue is such that the Coulomb friction model is widley used for its mathematical expedience and ease of application. In this study, the method of digital image processing is applied to the identification of friction behavior between two solids with the aid of the Coulomb friction model. For this purpose, a pendulum is used which has a metal weight hung by a metal wire from a fixed point on a slant solid board and sliding on the board. The algorithm developed for this problem can be extended to identify, simultaneously and in near real-time, the friction coefficient and the relative motion between the model structure and the base in a shaking table test of a structure base-isolated by a sliding system. The proof-of- concept experiment was successfully carried out to show that the proposed identification method based on digital image processing can be used with appropriate modifications to identify many other engineering-wise significant quantities remotely. For example, the system in principle can be used to identify the friction coefficient of friction base-isolators of model or actual buildings during strong earthquakes.

It is now well established that magnetorheological (MR) fluids can provide the basis for constructing controllable vibration damping devices. Moreover, the characteristics of MR fluids are generally compatible with industrial requirements and there is enormous scope for commercial exploitation. In this paper the authors describe the design and construction of a vibration isolator which incorporates an MR damper. The damper is unusual in that it operates in the squeeze-flow mode. A quasi-steady model of the MR damper is summarized and then extended to include the vibration isolator dynamics. Model predictions are compared with experimental results. It is shown that by employing the MR damper a wide range of control can be exercised over the transmissibility of the vibration isolator. Numerical experiments are used to show that a feedback control strategy can provide even more control over transmissibility.

Two kinds of Magneto-rheological fluid damper (MRF damper) have been designed and manufactured. One has a nominal capacity of 2kN and the other 20kN. A bypass flow system is adopted for both dampers and each has the same capacity of electromagnet attached to the bypass portion. The effective fluid orifice is the rectangular space and the magnetic field is applied from the outside. A test was performed by applying different magnetic fields to the orifice portion of the rectangular space. The damping force and the force- displacement loop were evaluated. The test results yielded the following: (1) Two type's of dampers functioned by using one unit of the electromagnet under an appropriate electrical current control. (2) The magnitude of the damping force depends on the input magnetic field, but it has an upper limit. (3) Without an applied magnetic field, the MRF damper exhibits viscous-like behavior, while with a magnetic field it shows friction-like behavior. A mechanical model of the damper is estimated by taking account of the force-displacement loop. It is clarified that MRF dampers provide a technology that enables effective semi-active control in real building structures.

This paper presents the development and evaluation of a controllable, semi-active magneto-rheological fluid (MRF) shock absorber for a High Mobility Multi-purpose Wheeled Vehicle (HMMWV). The University of Nevada, Reno (UNR) MRF damper is tailored for structures and ground vehicles that undergo a wide range of dynamic loading. It also has the capability for unique rebound and compression characteristics. The new MRF shock absorber emulates the original equipment manufacturer (OEM) shock absorber behavior in passive mode, and provides a wide controllable damping force range. A theoretical study is performed to evaluate the UNR MRF shock absorber. The Bingham plastic theory is employed to model the nonlinear behavior of the MR fluid. A fluid-mechanics-based theoretical model along with a three-dimensional finite element electromagnetic analysis is utilized to predict the MRF damper performance. The theoretical results are compared with experimental data and are demonstrated to be in excellent agreement.

The hysteresis behavior of a linear stroke magnetorheological damper is characterized for several magnetic fields and sinusoidal excitations over a nominal operational frequency range of 1.0 - 3.0 Hz. The behavior of the damper is inadequately modeled using the equivalent viscous damping and the complex modulus. Therefore, four different non-linear modeling perspectives are discussed for purposes of system identification procedures, including: (1) nonlinear Bingham plastic model, (2) nonlinear biviscous model, (3) nonlinear hysteretic biviscous model, and (4) nonlinear viscoelastic plastic model. The first three nonlinear models are piecewise continuous in velocity. The fourth model is piecewise smooth in velocity. The parameters for each model are identified from an identification set of experimental data, these parameters are then used to reconstruct the force vs. displacement and the force vs. velocity hysteresis cycles for the respective model. Model performance is evaluated by calculating equivalent viscous damping and force time history errors between the model fit and the experimental data. In addition to the identification study, a validation study was done. Model parameters were calculated for offset values of current and frequency. These intermediate parameters were used to calculate hysteresis cycles which were compared with a second set of experimental data, a validation data set. The results from both identification and validation studies of the MR damper behavior are presented in this paper, including calculated damping and force time history errors.

The Bingham plastic constitutive model has been widely used to predict the post-yield behavior of electro- and magneto- rheological fluids (ER and MR fluids). However, if these fluids experience shear thinning or shear thickening, the Bingham plastic model may not be an accurate predictor of behavior, since the post-yield plastic viscosity is assumed to be constant. In a recent study, it was theoretically and experimentally demonstrated that the Herschel-Bulkley fluid model can be successfully employed when evaluating non- Newtonian post-yield behavior of ER and MR fluids. In this paper, the Herschel-Bulkley model is employed to include a detailed analysis of ER and MR fluid dynamics through pipes and parallel plates. Simplified explicit expressions for the exact formulation are also developed. It is shown that the proposed simplified model of the Herschel-Bulkley steady flow equations for pipes and parallel plates can be used as an accurate design tool while providing a convenient and generalized mathematical form for modeling ER and MR fluids. Theoretical and experimental analyses are presented for a MR fluid damper, which is designed, developed, and tested at the University of Nevada, Reno (UNR).

Electrorheological (ER) and magnetorheological (MR) fluid- based dampers are typically analyzed using Bingham-plastic shear flow analysis under quasi-steady fully developed flow conditions. An alternative perspective, supported by measurements reported in the literature, is to allow for post- yield shear thinning and shear thickening. To model these, the constant post-yield plastic viscosity in Bingham model can be replaced with a power law model dependent on shear strain rate that is known as the Herschel-Bulkley fluid model. Depending on the value of the flow behavior index number, varying degrees of post-yield shear thickening or thinning behavior can be analyzed. A nominal ER bypass damper is considered. Damping forces in the damper are analyzed by approximate parallel plate geometry. The impacts of flow behavior index on shear stress-strain relationship and velocity profile for variable electric field are also examined numerically. Then, analytical damping predictions of ER/MR flow mode dampers are compared using the nonlinear Bingham-plastic and nonlinear Herschel-Bulkley analyses.

A preliminary experimental investigation on the problem of viscous heating of fluid dampers that find applications in the vibration reduction of civil engineering structures is presented in this paper. Time histories of the temperatures are recorded near the piston head and at the outer surface of a 3-kip fluid damper that undergoes harmonic loading. The experimental results uncover some of the limitations of simple analytical expressions that have been derived in the past based on one-dimensional approximations of the energy balance equation.

This paper studies the optimization of the orifice's flow in shock absorber using shape memory alloys (SMA) wire. The motivation for this optimization is to ensure that the damping properties of shock absorber remained intact over the longer period of operating time and hence to maintain the overall energy dissipating performance of the damping system. The temperature of hydraulic fluid in a shock absorber increases every time when high-energy impacts have to be absorbed by the system. This in turn will lead to drop of viscosity of the fluid. Thus at the fixed size of orifice's opening, the fluid's flow rate through the orifice is significantly higher compare to the rate at lower temperature. The high flow rate through the orifice will impose in the end a negative impact to the energy dissipating capability of the shock absorber. In other words, the high flow rate through the orifice will induce the degeneration of damping constant and hence shorten the lifetime of the shock absorber. The paper discussed the possibility of varying the size of orifice's opening in order to reduce the volume flow rate through the orifice. For the purpose of varying the size of orifice's opening a piece of SMA wire was placed in the proximity of the orifice. The SMA wire was in such a way configured that at low temperature it will let the fluid flow through the orifice without hindrance and at high temperature it closes part of orifice's opening, so that the fluid flows through the orifice with significant amount of resistance. Although, the viscosity of fluid decreases, consequently the cross sectional area of orifice also decreases and the damping constant will improve. The application of this device has been experimentally and analytically studied. The study included component testing over a range of temperature, modeling of the orifice flow of absorber's fluid, analytical prediction of response and development of simplified analysis procedures. Experimental results demonstrate a significant improvement of damping constant due to the reduction of volume flow rate through the orifice at high temperature.

At last year's SPIE symposium, we reported results of an experiment on structural vibration damping of an F-15 underbelly panel using piezoelectric shunting with five bonded PZT transducers. The panel vibration was induced with an acoustic speaker at an overall sound pressure level (OASPL) of about 90 dB. Amplitude reductions of 13.45 and 10.72 dB were achieved for the first and second modes, respectively, using single- and multiple-mode shunting. It is the purpose of this investigation to extend the passive piezoelectric shunt- damping technique to control structural vibration induced at higher acoustic excitation levels, and to examine the controllability and survivability of the bonded PZT transducers at these high levels. The shunting experiments was performed with the Thermal Acoustic Fatigue Apparatus (TAFA) at the NASA Langley Research Center using the same F-15 underbelly panel. The TAFA is a progressive wave tube facility. The panel was mounted in one wall of the TAFA test section using a specially designed mounting fixture such that the panel was subjected to grazing-incidence acoustic excitation. Five PZT transducers were used with two shunt circuits designed to control the first and second modes of the structure between 200 and 400 Hz. We first determined the values of the shunt inductance and resistance at an OASPL of 130 dB. These values were maintained while we gradually increased the OASPL from 130 to 154 dB in 6-dB steps. During each increment, the frequency response function between accelerometers on the panel and the acoustic excitation measured by microphones, before and after shunting, were recorded. Good response reduction was observed up to the 148dB level. The experiment was stopped at 154 dB due to wire breakage from vibration at a transducer wire joint. The PZT transducers, however, were still bonded well on the panel and survived at this high dB level. We also observed shifting of the frequency peaks toward lower frequency when the OASPL was increased. Detailed experimental results will be presented.

The SSD technique proposed here addresses the problem of resonance damping on a mechanical structure. SSD stands for Synchronized Switch Damping. Apart from active techniques, passive ones consist in connecting a piezoelectric insert attached to the structure to a passive electric network in which the energy generated by the piezoelectric inserts is degraded. In the semi passive approach, the piezoelectric inserts are continuously switched from open circuit to short circuit synchronously to the structure motion. Due to this switching mechanism, a phase shift appears between the piezoelectric strain and the resulting voltage, thus creating energy dissipation. For the new technique proposed here, instead of discharging the piezoelectric inserts during a brief short circuit, they are connected on a small inductor, allowing the inversion of the voltage and then released to open circuit. In this case the voltage amplitude is optimized and is 90 degrees out of phase with the motion then enhancing the damping mechanism. The technique is applicable at any frequency without the need for a large tuned inductor, especially for low frequency applications. There is no need for external power supply unless for the low power circuitry of the switch device. The implementation of the switch drive with a very cheap micro-controller is described. Experimental results measured on cantilever beams made with different materials are proposed. Damping ability ranges from 6 dB on a very viscoelastic epoxy beam to nearly 20 dB on a steel beam. Harmonic excitation and transient results are both proposed and compared. Finally, an electromechanical model is proposed, giving an interpretation of the damping mechanism. Theoretical predictions are in good agreement with the experiments.

Vibration damping of a cantilever plate is achieved by using a piezoelectric element simultaneously as passive single-mode device and active broad-band actuator. Control strategies are designed on the basis of a modal model of the coupled electro- mechanical structure. This model is obtained by using a suitable finite-element formulation together with a modal analysis. A purely passive single-mode control composed of an optimally tuned external RL shunt circuit and a purely active control based on classical LQG techniques are compared to a semi-active control obtained by tuning the external shunt circuit on the second vibration mode of the structure and using a LQG controller designed on the only first-mode model.

A design method of hybrid damping is proposed here. Values of design parameters of hybrid damping: active control gain, number and location of piezo-elements to be used to passive damping, are determined under equal vibration suppression performance condition. Vibration suppression performance is evaluated by using the gain of the accelerance transfer function of the closed loop system in modal space. According to the proposed design method, the equal vibration suppression performance with less active control power is achieved by hybrid damping. Availability of the proposed design method is experimentally demonstrated by using a flexible cantilever beam. The experimental results indicate that hybrid damping is effective comparing with fully active damping from the viewpoint of active control power under the equal vibration suppression performance condition.

A series of mechanism-based phenomenological models, comprising of springs and friction elements, are presented for the pseudoelastic damping behavior of Shape Memory Alloys. The constitutive equations and a method for identifying the parameters from experimental hysteresis cycles are presented for each of the models. Comparisons are made with an existing phenomenological model. Unlike the thermodynamic-based models, the present models do not require calculation of austenite- martensite phase transformations. The mechanical analogies provide a strong physical basis to the models, and clear relationships are established between the unlocking of the friction elements and the occurrence of phase transformation.

Auxetic (negative Poisson's ratio) cellular materials expand in all direction when pulled in only one, thus behaving in an unusual manner compared to 'classical' materials. Negative Poisson's ratio honeycombs and open cell foams have shown increased shear modulus, indentation resistance and low cut- off frequency acoustic properties. In this paper FEM microstructure models are used to compute the static and viscoelastic properties of closed-cell and two-phase foam composites. The complex modulus of the materials is calculated making use of the correspondence principal and evaluating the strain energy distributions for the different phases. The results are compared to the ones given by models representing a global in-plane uniaxial loading. The static and storage modulus values of two-phase composite foam are significantly enhanced by the presence of a re-entrant (auxetic) skeleton layout. The loss factor shows also a significant sensitivity on the volume fraction and strain energy distribution on the microstructure unit cells. Static and free-vibration simulations on sandwich beams with different core cellular materials show that it is possible to obtain both enhanced stiffness per unit weight values and modal loss factors using two-phase cellular solids with a re-entrant skeleton.

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.

In this paper, recent results of ongoing studies into the effectiveness and predictability of particle damping are discussed. Efforts have concentrated on characterizing and predicting the behavior of a wide range of potential particle materials, shapes, and sizes in the laboratory environment, as well as at elevated temperature. Methodologies used to generate data and extract the characteristics of the nonlinear damping phenomena are illustrated with interesting test results. Experimental results are compared to predictions from analytical simulations performed with an explicit code, based on the particle dynamics method, that has been developed in support of this work.

The work describes the attenuation problem of vibrations affecting a nonlinear oscillatory mechanical system using passive and active vibration control methods based on nonlinear techniques. The mechanical system consists of an oscillating rigid bar coupled to a passive absorber. The undesirable vibration is a harmonic torque, with variable frequency, applied to the bar. The main goal consists of the design of feedback and feedforward control laws, employing information of the open-loop frequency response parameterized in terms of a new coordinate in order to tune appropriately the system. Physically, this coordinate stand for the position the passive absorber along the bar, implying the addition of a degree of freedom and enabling the horizontal motion of the absorber. With the measurement of the excitation frequency it can be computed the optimal attenuation position (minimal disturbance-output gain). Then, the application of a control law that asymptotically reach such position yields indirectly reduction of the angular motion of the bar to the minimum. The control scheme is designed using partial feedback linearization and output regulation techniques. Both cases lead to a fourth order zero dynamics (passive absorber), which is globally asymptotically stable. Some numerical simulations illustrate the resulting dynamic behavior and performance.

The present paper proposes the retrofit use of dynamic restrainers at the expansion joint for preventing the collapse of bridges in the event of a severe earthquake. The proposed dynamic restrainer consists of a nonlinear viscous damper and an elastic spring connected in parallel. Two-dimensional nonlinear finite element analysis using bilinear hysteretic models for RC bridge substructure joints and nonlinear gap elements for expansion joints is performed on example bridges with one or two expansion joints. The numerical simulation study indicates that the dynamic restrainers are substantially effective in reducing the relative opening displacements and impact forces due to pounding at the expansion joints. It is also found that the dynamic restrainer can be installed at expansion joint in abutment as well as between adjacent bridge frames to avoid a possible increase of ductility demands in the bridge substructures.

This paper considers the dynamic performance of systems of centrifugal pendulum vibration absorbers that are used to attenuate torsional vibrations in rotating systems. These absorbers, which can be found in certain IC engines and helicopter rotors, consist of movable masses whose centers of mass are kinematically restricted to move along prescribed paths relative to the rotor of interest. The most common choice for absorber paths are simple circles that are slightly mistuned from the desired order, so that undesirable nonlinear behaviors are avoided when the absorbers undergo large amplitude motions. In this work we consider a range of different path types and tunings, with the goal of optimizing performance over a wide operating range. This analytical study relies on a mathematical model of a rotor fitted with N identical, general-path absorbers, and utilizes perturbation techniques to obtain analytical estimates for the response of the rotor and the absorbers. The results are used to select path parameters based on selected performance measures, and the results are verified via simulation studies. It is shown that slightly overtuned cycloidal paths provide excellent vibration reduction characteristics and prevent the occurrence of nonlinear instabilities and vibration localization in the response of the absorbers.

Passive energy dissipation systems have long been used in industrial, military and aerospace applications but only more recently in bridges. This paper will review the first use of dampers on a new concrete bridge in the United States. Dampers were incorporated into the design of a pair of 1270-foot long bridges to absorb energy induced by earthquakes and reduce seismic movements. The bridges are located on the Eastern Transportation Corridor, a 27-mile long design/build toll road in Orange County, California. The two-level seismic design criteria required consideration of seismic movements in sizing the joints and backwall gaps. The intent of the criteria is to maintain toll road traffic following the lower level earthquake by preventing damage to the abutments and joint seal assemblies. Each bridge was fitted with three 160-kip, 0.4 exponent, nonlinear fluid viscous dampers. The units reduce the lower level longitudinal seismic movement by approximately forty-five percent allowing the use of smaller joint seals. Because nonlinear devices were used, the structures will also see significant reductions in upper level forces and displacements as well. The design principles, applicable design codes, analysis requirements, detailing and design specifications will be discussed. The benefits and potential cost savings of dampers will also be reviewed.

The concept and the functionality of the Stiffness Decoupler for Base Isolation of Structures, (SDFBIS, U.S. patent No. 5,660,007, August 1997, and No. 5,386,671, February 1995), and the methodology for the numerical simulation of the dynamic responses of structures, the computer simulated accelerogram and the recorded time histories of the response accelerations of the 14' by 9' by 18' tall model steel structure under the application of an 88% of the ground motion of the Northridge 1994 Earthquake, (shaken by the KSU shaking table), will be presented for comparison. The performance of the SDFBIS system, the efficiency of the numerical algorithm and the sensitivity of accelerometer s Model 799M and 731A model of Wilcoxon Research will be presented in the concluding remarks.

ESPA, the Secondary Payload Adapter for Evolved Expendable Launch Vehicles, addresses two of the major problems currently facing the launch industry: the vibration environment of launch vehicles, and the high cost of putting satellites into orbit. (1) During the 1990s, billions of dollars have been lost due to satellite malfunctions, resulting in total or partial mission failure, which can be directly attributed to vibration loads experienced by payloads during launch. Flight data from several recent launches have shown that whole- spacecraft launch isolation is an excellent solution to this problem. (2) Despite growing worldwide interest in small satellites, launch costs continue to hinder the full exploitation of small satellite technology. Many small satellite users are faced with shrinking budgets, limiting the scope of what can be considered an 'affordable' launch opportunity.

Small launch vehicles historically provide a very rough ride to spacecraft during launch. This is particularly true of solid-fueled launch vehicles. In order for the spacecraft to survive such a trip to orbit, one of two choices must be made: (1) design all structure, payloads, and systems on the spacecraft to be strong enough to survive the high launch loads, or (2) reduce the magnitude of the high launch loads. The former is not a good choice because it typically requires additional cost, schedule, and weight. The latter is the preferred choice because it allows the focus of the spacecraft design to be primarily for on-orbit performance rather that for launch survival. Under a number of contrasts from the Air Force Research Laboratory, Space Vehicles Directorate, whole- spacecraft vibration isolation systems have been in development since 1993. This work has resulted in two whole- spacecraft isolation systems (SoftRide) that have been flown on Taurus launch vehicles, the first in February 1998 with the GFO spacecraft and the second in October 1998 with the STEX spacecraft. Both of these isolation systems were designed primarily to reduce axial dynamic responses on the spacecraft due to resonant burn excitations from the motors of the solid- fueled booster. Full coupled-loads analyses were used to predict the performance of the SoftRide systems. Using the isolation requirements derived from these analyses, hardware having the correct damping and stiffness was designed to implement the isolation system. All isolation system components were extensively tested and characterized. Typical results show 85% attenuation (i.e., only 15% of original) for the worst case resonant burn condition and 59% attenuation for a combination of static plus worst case resonant burn condition in the axial spacecraft c.g. location. No detrimental effects from the SoftRide system were observed. Limited flight data from the two flights agree with the predictions. SoftRide systems are now under development for the first and second OSP launches and for the Taurus/MTI launch. Additionally, isolation systems are being designed for larger liquid-fueled launch vehicles. This isolation system technology will greatly further the goal of better, faster, cheaper, and lighter spacecraft.

Research to create advanced vibration isolator designs and practical design techniques for Launch Vehicle (LV) manufacturers is discussed. Avionics of launch vehicles have unique requirements for isolation since many generate heat and cannot use convection cooling for dissipation. Nearly all isolation systems are ineffective thermal conductors unless expensive custom modifications are performed. The cost of a custom isolation design can rarely be justified, particularly with expendable vehicles. While viscoelastic isolators offer simplicity and affordability, such materials with high loss factors (greater than 0.25) also exhibit aggressive changes in stiffness with both temperature and frequency. Materials having new and unique formulations are introduced which have an order of magnitude higher thermal conductivity than today's materials of similar stiffness. This enables appreciable heat conduction with nominal temperature increases to isolated packages. The formulation of nearly all elastomeric vibration isolators creates heavy coupling between their loss factors and the rate of change in their storage moduli. High loss factors result in an aggressive temperature-dependent shift in the resonant frequencies of an isolated element. New compounds introduced in this paper address this limitation. A software utility has also been developed that greatly simplifies isolation design. The utility solves the equations of motion for a rigid body on flexible mounts and allows performance predictions using base vibration inputs. New progress in material technology and design techniques enables LV manufacturers to implement affordable designed vibration isolation systems on avionics and similar systems.

Airborne optical or electro-optical systems may be too large for all elements to be mounted on a single integrating structure, other than the aircraft fuselage itself. An active system must then be used to maintain the required alignment between elements. However the various smaller integrating structures (benches) must still be isolated from high- frequency airframe disturbances that could excite resonances outside the bandwidth of the alignment control system. The combined active alignment and vibration isolation functions must be performed by flight-weight components, which may have to operate in vacuum. A testbed system developed for the Air Force Airborne Laser program is described. The payload, a full-scale 1650-lb simulated bench, is mounted in six degrees- of-freedom to a vibrating platform by a set of isolator- actuators. The mounts utilize a combination of pneumatics and magnetics to perform the dual functions of low-frequency alignment and high-frequency isolation. Test results are given and future directions for development are described.

This paper presents the results of a study in which a semi- active vibration suppression system is used to control vibrations in a machine excited by impulsive forces. The problem involves a machine, which is mounted to a flexible foundation, that sees an impulse excitation force. Given the flexibility of the foundation, the excitation causes significant vibrations in the machine. If the foundation could be sufficiently stiffened, the vibrations could be reduced to acceptable levels. However, such changes to the foundation are not possible for this application. Therefore the system is being redesigned to include a vibration suppression system. Because of the high forces and strokes involved, a semi-active system is studied and compared to a fully active optimal control approach to determine its limitations and feasibility for this application.

This paper is a follow-up of a presentation at the Smart Structures Symposium of 1998. There we described an innovative technical solution which provides a combined passive damping and isolation interface with the appropriate transmissibility characteristics between a vibrating base and a sensitive payload, typically an optical terminal/telescope. The particularity of the solution is primarily found in the implementation of energy dissipation by means linear electromagnetic linear motors leveraged by means of flexure elements, to constitute an integrated resistor-damped electromechanic lever block, which we called MEDI (Mechanical Elastic element for Damping and Isolation). Passive viscous damping with attenuation of the order of -20 dB at 50 Hz with respect to a hard fixation, is obtained by simply short- circuiting the electro-magnetic motor. The study and test program presented here extends the application of MEDIs to active vibration reduction systems. The study, contracted by the European Space Agency, aimed at investigating the possibility of using the MEDI as an active isolator for scientific experiments in the International Space Station. By controlling the current in the electromagnetic motor in closed loop with the signal from specially designed force sensor (with extremely low noise), we achieved attenuation of the order of -15 dB at 1 Hz, -30 dB at 10 Hz, -50 dB at 30 Hz, with the isolation slope starting as low as 0.1 Hz.

The fixed-points method for the dynamic vibration absorber (DVA) is widely accepted and the results are prevalent for practical applications. However, they usually have to fall back to a heuristic approach from the point of view of its optimization criterion. A typical design problem to minimize the maximum amplitude magnification factor of the primary system, for which the fixed-points method was originally developed, is an example of such common cases. In the present paper, a new algebraic formulation is developed to this classic problem and closed-form exact solutions to both the optimum tuning ratio and the optimum damping parameters are derived, on the assumption of undamped primary system. This algebraic approach is based on an observation of trade-off between two resonance amplitude magnification factors. Thus, the problem reduces to a solution of an algebraic equation, which is derived as a discriminant of quartic algebraic equation. In undamped case, it was proven that the optimum parameters, the minimum amplitude magnification factor, the resonance and antiresonance frequencies, and sensitivities of the amplitude magnification factors are totally algebraic. A numerical extension enables efficient solutions for the damped primary system and has more direct applicability.

In this paper, an efficient piezoelectric passive damper is newly devised to suppress the multi-mode vibration of plates. To construct the passive damper, the piezoelectric materials are utilized as energy transformer, which can transform the mechanical energy to electrical energy. To dissipate the electrical energy transformed from mechanical energy, multiple resonant shunted piezoelectric circuits are applied. The dynamic governing equations of a coupled electro-mechanical piezoelectric with multiple piezoelectric patches and multiple resonant shunted circuits is derived and solved for the one edge clamped plate. The equations of motion of the piezoelectrics and shunted circuits as well as the plate are discretized by finite element method to estimate more exactly the effectiveness of the piezoelectric passive damper. The method to find the optimal location of a piezoelectric is presented to maximize effectiveness for desired modes. The electro-mechanical coupling term becomes important parameter to select the optimal location.

The effect of temperature on the behavior of nonlinear viscoplastic, low-concentration suspensions of diatomite in transformer oil in strong electric fields in the presence of vibration is investigated experimentally. Temperature has proved to control the electrophysical and cross-linking properties of the test fluids.

In this paper, a passive damping enhancement of piezoelectric smart structures is studied. A conventional parameter tuning method of the passive damping using piezoelectric smart materials, so called a mechanical vibration absorber method, is reviewed and a new method for determining the optimal shunting parameters using electric impedance is developed. The electric impedance method determines the optimal parameters by maximizing the dissipated energy at the load resistor. To see the validity of this approach, a mechanical vibration absorber is taken as an example and the shunting parameters tuned by proposed method agree with those of conventional tuning method. A piezoelectric cantilevered beam for single mode shunt and plate for multiple-mode shunt are taken as examples for real implementation. The simulation and experiment are conducted and they show remarkable vibration reductions at targeted modes. This method can be applied to arbitrary piezoelectric smart structures such that it will increase the applicability of smart structures to noise and vibration reductions.

Fluid disperse systems, sensitive to the external electric field-electrorheological fluids, are finding increasing use in various areas of industry and technology. Their physicomechanical, electrophysical characteristics determine the valuable specific properties of the materials with assigned structure, obtainable with everwide use of electric fields, which makes it possible to substantially enhance efficiency and productiveness of technological processes and to improve the control of operational regimes of the equipment which employ fluid disperse media. The present investigations has been undertaken with the aim of studying thermophysical properties and rheophysical behavior of low-concentration ER- fluid (diatomite in transformer oil) at different temperatures. It was shown that the electric field, which changes considerably the structure of electrorheological fluid, influences effective thermal conductivity and diffusivity coefficients. Their increase with electric field intensity and the increase of the effective viscosity with temperature are connected with the increase of the conductive component of the overall heat transfer through the contact spots between the solid particles, and with intensification of electric convection in the spaces between the dispersed particles.

Rubber is commonly added to composites to increase the toughness. This research investigates adding toughening particles to graphite/epoxy composites for the purpose of increasing the vibrational damping. Adding toughening particles to the interlaminar regions of graphite/epoxy is shown to significantly increase the loss factor, although the increase is much less than can be achieved by embedding a viscoelastic damping layer. The bending stiffness and shear modulus, however, are much higher for the samples with embedded particles than samples with a viscoelastic layer. The addition of damping particles could therefore be used for stiffness-critical parts.

This paper is a continuation of previously presented research work involving the dynamic characterization of automotive shock absorbers. The objective was to develop new testing and analysis methodologies for obtaining equivalent linear stiffness and damping of the shock absorbers for use in CAE- NVH low-to-mid frequency chassis models. It is well known that a hydraulic actuated elastomer test machine is not suitable for testing shocks in the mid-to-high frequency range where the typical road input displacements fall within the noise floor of the hydraulic machine. Hence, initially in this project, an electrodynamic shaker was used for exciting the shock absorbers under displacements less than 0.05 mm up to 500 Hz. Furthermore, instead of the swept sine technique, actual road data were used to excite the shocks. Equivalent linear spring-damper models were developed based on least- squares curve-fitting of the test data. The type of road profile did not influence the stiffness and damping values significantly for the range of amplitudes and frequencies considered. The success of the characterization of shock absorbers on the electrodynamic shaker using non-sinusoidal input has led to the development of a similar methodology to be employed on the hydraulic actuated elastomer test machine.

Cryocoolers are well known sources of harmonic disturbance forces. In this paper two miniaturized, add-on, vacuum compatible, active vibration control systems for cryocoolers are discussed. The first, called VIS6, is an active/passive isolation hexapod and has control authority in all six degrees of freedom. This capability is desirable when reduction of all cryocooler disturbance loads, including the radial loads, is required. Each of the six identical hexapod struts consists of a miniature moving coil electromagnetic proof mass actuator, custom piezoelectric wafer load cell, viscoelastic passive isolation stage, and axial end flexures. The first five disturbance tones are reduced over a bandwidth of 250 Hz using a filtered-x least mean square algorithm. Load reductions of 30 - 40 dB were measured both axially and radially. The second system, called VRS1, is a pure active control system designed to reduce axial expander head disturbance loads. It works on the basis of a counter-force developed from an electromagnetic proof mass actuator. Error signals are provided from a commercial accelerometer to a standalone digital signal processor, on which a filtered-x least means square control algorithm is implemented. Over the 500 Hz control bandwidth, the 11 disturbance tones were reduced on between 14 to 40 dB.