The hysteresis type of material specific damping capacity (SDC) of a unidirectional hybrid fibre reinforced smart composite has been studied in the present work using a multi-cell method.To do this, as a first step, we reviewed various micromechanics modelling for the mechanical properties in general and material damping in particular in order to compare the theoretical capabilities and limitations of the existing analytical models. A new refined unit cell featuring a more realistic fibre-matrix domain has then been proposed for the present modelling. SDC equations corresponding to all the six directions were derived using the strain energy concept within the framework of mechanics of material approach. The generality of the present model in terms of the range of fibre volume ratio, different combinations of fibre-matrix systems etc., has been verified by comparing the present results with the literature including available experimental results. An important merit of the present theory that has to be emphasized over other available theories is the accurate prediction of the transverse and shear directions SDC for composites having a high fibre/matrix modulus ratio. Further, the scope of the present model to the practical applications of a typical shape memory alloy hybrid composite has also been demonstrated through numerical simulations.

Researchers have been seeking the best combinations of active and passive damping since the mid 1980's. Much of this work has centered around classical control schemes and has assumed real- or complex-valued approximations of the viscoelastic material properties. The time dependence of viscoelastic materials has been addressed effectively by several researchers using internal variable methods. Most of these methods do yield simple entries in existing mass and stiffness matrices. Rather, the time dependence of the system is represented by coupling of the physical and internal degrees of freedom in a set of first-order equations. Just as with many of the physical states, the internal degrees of freedom are not measurable. This work explores the implications of reconstructing these states through an observer for the purpose of feedback control. After reviewing some basic theory for internal variables, the effect on control effort is demonstrated for systems using output feedback versus full state feedback. This work is a preliminary step toward better accounting for the time dependencies of viscoelastic materials in systems with active control.

A new procedure is developed to identify damping in a dynamic system as damping matrices in the equation of motion from the dynamic stiffness matrix, which is obtained by inverting the measured frequency response function matrix. It is shown that the method provides the most direct and shortest path to finding dampened matrices. The procedure is applied to a theoretical example and two real structures for its validation, which also reveals unique measurement and signal processing issues related to the technique. Potential applications and possible improvement of the identification method are discussed.

Over the past ten years, space structures such as optical systems, large antennae or sensitive microgravity payloads have increased their stability requirements. To answer this need, prediction and reduction of vibration levels have been widely studied. The 'CASTOR' truss experiment (French acronym for ChAracterization of STructures in ORbit) is mainly dedicated to the investigation of the dynamic behaviour -in zero g conditions- of a truss mock-up with various damping technologies. The performances of various dampers have been validated in flight, measurements compared with the predictions and the results analysed for different technological solutions. This project was developed under CNES management, and the final experimental work was performed in orbit by a French cosmonaut on MIR station during the summer of 1999. In the first place, the French space agency's interest in structural dynamics behind the CASTOR experiment will be recalled. The flight hardware will then be fully described and a short clip filmed during the PERSEUS mission in MIR will supported this. The truss test bench will be presented, together with the design drivers for damping the first structural modes below 100Hz. The dampers -which are efficient- are located in some strategic bars in the truss. Their performance has been optimized using an energetic criterion. This paper will then focus on the design of the damping, using either piezoelectric active control or passive energy dissipation in elastomer or fluid devices. Particular emphasis will be laid upon the excellent flight results obtained with all the various damping systems, and on the effect of in-orbit conditions. A comparison between the different technologies here tested will also be made with regards to performances achieved and their suitability for space applications. In conclusion, lessons learned during the development process will be highlighted and further work on spacecraft applications discussed.

Engineered Damping Treatments (EDT) that have high damping characteristics per unit volume are presented. The EDT's under consideration, consist of cellular viscoelastic damping matrices with optimally selected cell configuration, size and distribution. The cellular topology of the EDT's is designed using Computer-Aided-Design (CAD) strategies and the obtained optimal configurations will be manufactured using the state-of-the-art technology of Rapid Prototyping (RP). The EDT's are modeled using the finite element method in an attempt to determine the optimal topologies that maximize the strain energy, maximize the damping characteristics and minimize the total weight. The CAD files of the prototypes of the EDT's. The damping characteristics of the manufactured EDT's are evaluated and compared with the corresponding characteristics obtained by conventional solid damping treatments in order to emphasize the importance of using optimally configured damping treatment to achieve high damping characteristics. The presented procedures are invaluable for designing efficient damping treatments for many military and civilian structures whose vibrations and noise must be effectively controlled.

Hybrid vibration control of laminated composite beams has been carried out using piezoceramic sensor/actuator and viscoelastic material. Collocated piezoceramic sensor/actuator is mainly used to control the first bending mode and the viscoelastic material is used to control the second bending mode by passive constrained-layer damping. The passive constrained-layer damping has been analyzed by formulating the equations of motion through the use of extended Hamiltoní»s principle. The dynamic characteristics such as damping ratio and modal damping of the beams are calculated for various fiber orientations by means of iterative complex eigensolution method based on finite element method. Active control of vibration of the cantilevered laminated composite beams using collocated piezoceramic sensor/actuator is analyzed theoretically and verified experimentally for various fiber orientations. Impact on the stiffness and damping properties by varying stacking sequence is studied. This paper addresses a design strategy of laminated composite under vibrations to design a structure with maximum possible damping capacity.

The Stratospheric Observatory For Infrared Astronomy, SOFIA is being developed by NASA and the German space agency, Deutschen Zentrum fur Luft- und Raumfahrt (DLR), with an international contractor team. The 2.5-meter reflecting telescope of SOFIA will be the world's largest airborne telescope. Flying in an open cavity on a modified 747 aircraft, SOFIA will perform infrared astronomy while cruising at 41,000 feet and while being buffeted by a 550- mile-per-hour slipstream. A primary system requirement of SOFIA is tracking stability of 0.2 arc-seconds, and a 3-axis pointing control model has been used to evaluate the feasibility of achieving this kind of stability. The pointing control model shows that increased levels of damping in certain elastic modes of the telescope assembly will help achieve the tracking stability goal and also expand the bandwidth of the attitude controller. This paper describes the preliminary work that has been done to approximate the reduction in image motion yielded by various structure configurations that use reaction masses to attenuate the flexible motions of the telescope structure. Three approaches are considered: passive tuned-mass dampers, active-mass dampers, and attitude control with reaction-mass actuators. Expected performance improvements for each approach, and practical advantages and disadvantages associated with each are presented.

The objective of the research is to investigate an effective method of using servo control through the use of a fast steering mirror and/or acoustic actuators and sensors for optical jitter suppression. The experimental testbed is built in an anechoic chamber at Duke University. Two optical benches are used to isolate metrology components from vibrating optical elements. A Helium-Neon laser and a position sensor are mounted on one optical bench and a turning flat mirror and a 3-axis fast steering mirror are on the other optical bench. External acoustic disturbances from the speaker are used to generate vibration in the optical components. A speaker housed within an enclosure and a fast steering mirror are the two allowable control actuators and external microphones are used for reference measurement, microphones/accelerometers mounted on or nearby the optical elements and the optical sensor are the three allowable control sensors in the experiment. The generalized predictive controller is used to conjugate the process of the system identification algorithm and the process of the controller design, and can be updated adaptively in the changes of the operating environment. The generalized predictive controllers are designed for each actuator and each sensor: Case 1) Fast steering mirror and position detector, Case 2) Control speaker and position detector, Case 3) Fast steering mirror and external microphones. The generalized predictive controller for all control actuators and sensors is also designed.

This study focuses on a fluid mechanics approach utilizing the Herschel-Bulkley constitutive equation to develop a theoretical model for predicting the behavior of field- controllable electro-rheological (ER) and magneto- rheological (MR) fluid dampers. The aim of this research is to provide an accurate theoretical model for analysis, design, and development of control algorithms for ER/MR fluid dampers. The Herschel-Bulkley quasi-steady analysis is extended to include the effect of fluid compressibility. The major advantage of the proposed model is its dependency on only the geometric and material properties of the device. The theoretical results are validated by an experimental study. It is demonstrated that the proposed fluid mechanics- based dynamic model can effectively predict the behavior of field-controllable fluid dampers.

Electrorheological (ER) and magnetorheological (MR) fluids show similar field-dependent rheological characteristics from a bulk fluid perspective. However, the implementation of ER and MR fluids in devices may require different strategies because of the inherent properties of ER and MR fluids such as density, viscosity and the strength of the yield stress. Therefore, in this study, we explore the dynamic performance ranges and time response characteristics of ER and MR fluid-based systems in order to comprehensively understand each system. So far, quasi-steady fluid flow model has been widely used in the performance evaluation of ER and MR fluid-based systems. However, the quasi-steady fluid flow model can predict the dynamic performance range of the system, but does not give any information about time response characteristics of the system. Moreover, research on comparative analysis between ER and MR fluid-based systems is considerably rare. Therefore, in this study, comparative analysis for the characteristics of ER and MR fluid-based systems is undertaken based on considering the time response phenomena. For doing so, a set of nondimensional analysis based on parallel plate geometry to characterize the field-dependent properties of ER and MR fluid-based systems is developed and experimental test for ER and MR dampers are done in order to evaluate the validity of the analysis.

Filling an elastomeric material with magnetizable particles leads to mechanical properties -shear moduli, tensile moduli, and magnetostriction coefficients - that are reversibly and rapidly controllable by an applied magnetic field. The origin of the field dependence of these properties is the existence of field-induced dipole magnetic forces between the particles. These 'smart' composites, which are sometimes termed magnetorheological (MR) elastomers, have been explored for use in a number of components, including automotive suspension bushings. In these and other applications, the tunability of the stiffness can enhance the compliance-control or vibration-transfer performance of the complex mechanical systems in which they are used. In the present study, we have constructed a simple one-degree-of-freedom mass-spring system - an adaptive tuned vibration absorber - that utilizes MR elastomers as variable-spring-rate elements. This device was used not only to explore the performance of such tunable components, but also to extend measurements of the shear moduli of these materials to higher frequencies than has previously been reported. We find that the field-induced increase in moduli of these materials is effective to mechanical frequencies well above 1 kHz, and that the moduli are consistent with the behavior expected for filled elastomers.

Ongoing research at the University of Sheffield is currently concerned with the design and construction of magneto- rheological (MR) squeeze-flow vibration damper. Previous work has demonstrated the feasibility of employing such a device as the key component in a controllable vibration isolator. The work also demonstrated the inadequacies of existing mathematical models which do not account for the observed behavior of MR fluids in squeeze flow. In parallel with investigations into the behavior of MR dampers, a collaborative programme between the Universities of Liverpool and Sheffield is also in progress. Here attention is focussed on ER fluids in squeeze-flow and a new test facility has been constructed for use in the development and validation of mathematical models. It is anticipated that this collaborative programme will assist in the development of both ER and MR squeeze-flow models. In this paper, the authors present a summary of progress to date.

A disk-type MR fluid damper based on shear mode has been developed and the experimental results show that the dynamic characteristics of a disk-type MR fluid damper can be controlled by the application of an external magnetic field with a low voltage. In this paper, the effectiveness of on-off control based on feedback of rotational speed, proportional (P) control and proportional-integral (PI) control, both based on feedback of disk vibration eccentricity, on controlling the rotor vibration are experimentally studied. It is shown that the simple on-off control was the most effective method in attaining the required objective, but as expected requires pre-knowledge of the switching speeds and there is a transient response with large amplitude at switching speeds. P and PI control can control the rotor vibrations, but both exhibit significant chattering which can adversely affect the control performance and still require to properly choose the controller parameters.

It has been shown that piezoelectric materials can be used as passive electromechanical vibration absorbers by shunting them with electrical networks. Semi-active piezoelectric absorbers have also been proposed for suppressing harmonic excitations with varying frequency. However, these semi- active devices have limitations that restrict their applications. In a previous study, the authors have developed a high performance active-passive alternative to the semi-active absorber that uses a combination of passive electrical circuit and active control actions. The active control consists of three parts: an adaptive inductor tuning action, a negative resistance action, and a coupling enhancement action. This new device has been shown, both analytically and experimentally, to be very effective for the suppression of harmonic disturbances with time-varying frequency. In the present paper, the adaptive active-passive piezoelectric absorber configuration is modified so that it can track and suppress multiple harmonic excitations. The effectiveness of this new multi-frequency absorber design is demonstrated by comparing its performance and control power requirement to a start-of-the-art adaptive feedforward control law.

Active vibration isolation of automotive seats requires actuators that achieve millimeter-range displacements and forces on the order of 300 N. Recent developments in piezoceramic actuator technology provide a means for achieving these force and displacement levels in a compact device. This work demonstrates that prestressed, curved piezoceramic actuators achieve the force and displacement levels required for active isolation of automotive seats. An estimate of the force and displacement requirements are obtained from numerical simulations on a four-degree-of- freedom car and seat model that utilize representative road accelerations as inputs. An actuator that meets these specifications is designed using piezoceramic materials. Free displacement of 4.4 mm and blocked force greater than 300 N are measured. The actuator is integrated within a dead mass setup that simulates the isolation characteristics of an automotive seat. Control experiments demonstrate that active vibration is achievable with realistic road disturbances. Feedback control is able to eliminate any amplification due to mechanical resonance and reduce the isolation frequency from 9.5 Hz to 2 Hz.

Small launch vehicles present an economically viable method for placing small satellites into orbit. These launch vehicles would be even more attractive to satellite customers if they could provide a softer ride to orbit. Passive whole-spacecraft vibration isolation systems have been developed for small launch vehicles to greatly reduce the dynamic launch loads. To date, two types of isolation systems have been designed.

The Department of Defense has identified launch vibration isolation as a major research interest. Reducing the loads a satellite experiences during launch will greatly enhance the reliability and lifetime and decrease the payload structural mass. DoD space programs stand to benefit significantly from advances in vibration isolation technology. This study explores potential hybrid vibration isolation using adaptive control with a passive isolator. Lyapunov analysis is used to develop the structural adaptive control scheme. Simulink and Matlab simulations investigate these control methodologies on a lumped mass dynamic model of a satellite and its representative launch vehicle. The results are compared to Proportional-Integral-Derivative (PID) control and skyhook damper active control methods. The results of the modeling indicate adaptive control achieves up to a 90 percent reduction in loads on the payload when compared to the conventional active control methods. The adaptive controller compensated for the loads being transmitted to the payload from the rest of the launch vehicle. The current adaptive controller was not able to effectively control the motion of a vibrating subcomponent within the payload or the subcomponent's effect on the overall payload itself.

Supplemental energy dissipation devices have been proven in applications worldwide to be an effective means of mitigating seismic hazard. This work offers a comparison of viscous fluid dampers and metallic yielding dampers in a Steel Moment Frame. A computer-simulated building frame model, with and without supplemental energy dissipation devices, is subjected to three levels of ground motion. The simulated building is then fitted with four combinations of metallic yielding dampers, with varying stiffness ratio, and viscous fluid dampers, with 10%, 20%, and 30% of critical damping. One additional combination of dampers is examined with varying ductility ratio to demonstrate its effect on the metallic dampers. Comparison and analysis of the simulation results reveals that the viscous fluid dampers are more flexible in their suitability for a wider range of applications, but that metallic dampers are perhaps more suitable for situations involving large seismic input requiring early energy dissipation. The comparison of the response of the frame with different values of ductility ratio with respect to the metallic dampers reveals that it is the stiffness ratio rather than the ductility ratio that has a greater effect on the performance of the devices under seismic loading.

Focused research in the area of Multi-Particle Impact Damping (MPID) has resulted in new methods of characterization and prediction. An analytical method has been developed, based on the particle dynamics method, that uses characterized particle damping data to predict damping in structural systems. A methodology to design particle damping for dynamic structures will be discussed. The complete design methodology has been validated in proof-of-methodology testing on a structural component in the laboratory.

One of the highly effective Layered damping methods is Constraining Layer Damping (CLD), wehrein a layer of viscoelastic (VE) material is sandwiched between the host structure and a stiff Constraining Layer (CL). Traditional CLD uses metallic Cls and hence all the damping comes from the VE layer. However, Cls of certain nonmetallic and/or anisotropic materials with significant inherent damping can be considered to enhance the net damping performance. A single degree of freedom (SDOF) model is presented here to investigate the performance of layered damping coatings comprising a VE layer and a stiff CL. The proposed model considers both the bending and extensional stiffness of the host structure and constraining layer separately, in addition to the shear stiffness of the VE layer. This facilitates the incorporation of some anisotropic stiffness effects and a study of its influence on the damping. The Complex stiffness is used to model the damping in individual components. Structural loss factors are obtained as a function of suitable dimensionless stiffness parameters. The useful range of modulus and the thickness of the layers/coatings are identified to obtain desired level of damping for different material loss factors enabling proper choice of the materials and/or thickness of damping treatments. The model can be reduced to represent conventional free or CLD coatings. The proposed model is validated by comparing the results with those from closed form solutions for traditional CLD systems and finite element results for anisotropic systems.

Recent developments in the new field of auto-adaptive materials offer promising opportunities for developing radically new fastening mechanisms. One of the classes of materials in this category is Shape Memory Alloys (SMAs). SMAs are very attractive for structural application because of their major constitutive behaviors such as pseudoelastic characteristic. Pseudoelastic behavior of NiTi SMAs is a unique hysteretic energy dissipation behavior that combined with a very long fatigue life makes SMAs a viable candidate for developing new fasteners. Pseudoelastic behavior of Shape Memory Alloys, particularly NiTI, can be used for developing passive fastening-mechanisms and tendon-systems. In case of coastal structures, where hurricane destruction inflicted upon residential structures results in million of dollar in financial damages and loss of lives each year, development of more effective fastening-mechanisms and tendon-systems for the connections between the walls and the roofs will aid in damage reduction. A study carried out by the authors has shown that the extent of damping effect of a hybrid tendon-system, made of rigid NiTi sections directly depends on the length-ratio of the rigid NiTi section, tendon diameter and the amount of pre-strain on the tendon. Moreover, because of tendon-system passive design the nature of excitation has a profound effect on its activation and damping capability. In this paper effectiveness of a hybrid NiTi tendon-system for damage mitigation of coastal structures and optimal hybrid tendon length-ratio are studied.

Shunted piezoelectric patches are periodically placed along rods to control the longitudinal wave propagation in these rods. The resulting periodic structure is capable of filtering the propagation of waves over specified frequency bands called stop bands. The location and width of the stop bands can be tuned, using the shunting capabilities of the piezoelectric materials, in response to external excitations and to compensate for any structural uncertainty. A mathematical model is developed to predict the response of a rod with periodic shunted piezoelectric patches and to identify its stop band characteristics. The model accounts for the aperiodicity, introduced by proper tuning of the shunted electrical impedance distribution along the rod. Disorder in the periodicity typically extends the stop-bands into adjacent propagation zones and more importantly, produces the localization of the vibration energy near the excitation source. The conditions for achieving localized vibration are established and the localization factors are evaluated for different levels of disorder on the shunting parameters. The numerical predictions demonstrated the effectiveness and potentials of the proposed treatment that requires no control energy and combines the damping characteristics of shunted piezoelectric films, the attenuation potentials of periodic structures, and the localization capabilities of aperiodic structures. The theoretical investigations presented in this work provide the guidelines for designing tunable periodic structures with high control flexibility where propagating waves can be attenuated and localized.

A new multi-mode semi-active shunt technique for controlling vibration in piezoelectric laminated structures is proposed in this paper. The effect of the ``negative capacitor'' controller is studied theoretically and then validated experimentally on a piezoelectric laminated simply-supported beam. The negative capacitor controller is similar in nature to passive shunt damping techniques, as a single piezoelectric transducer is used to dampen multiple modes. While achieving comparable performance to that of the purely piezoelectric passive shunt schemes, the negative capacitor controller has a number of advantages. It is simpler to implement, less sensitive to environmental variations, and can act as a multiple mode and broadband vibration controller. Experimental resonant amplitudes for the piezoelectric laminated simply-supported beam 1st, 2nd, 3rd, 4th and 5th modes were successfully reduced by 6.1, 16.3, 15.2, 11.7 and 10.2dB.

This paper reports an advanced passive piezoelectric shunt damping technique called broadband piezoelectric shunting. The shunt circuit for the broadband shunting is built with a reactance neutralizing circuit, which is designed with operational amplifier circuits to maximize the parallel reactance of the shunt circuit over a wide frequency band. It is different from the earlier shunt circuits, either used for the single- or multiple-mode shunting, which were built with inductors or simulated inductor circuits. In these earlier shunt circuits the anti-resonant frequency of the shunt circuit, with the inclusion of the piezoelectric transducer, was tuned with the inductor to a specific frequency to match with the natural frequency of the mode to be controlled. We first describe how the concept of the broadband shunt circuit was conceived and developed. We next report the shunt damping experiments performed on three difference structures: a thin aluminum cantilever beam, a two-wing aluminum cantilever beam, and a small-scale thermoplastic composite fairing. We have successfully demonstrated broadband amplitude reduction of structural vibration modes over a wide frequency band using the broadband shunt-damping technique. More detailed experimental results will be presented.

In this paper, the performances of two novel low frequency piezoceramic shunt techniques for structural damping are compared to the traditional passive tuned resonant shunt circuit techinque. The first novel technique, state switching, is a semi-active variable stiffness technique in which bonded piezoceramic actuators are switched from the short circuit to open circuit states. This technique changes the stiffness of the structure for two quarters of its vibration period, thus dissipating energy. The second novel technique, synchronized switching, is a semi-active continuous switching technique in which a resistor/inductor shunt circuit is periodically connected to the bonded piezoceramic actuators. This technique applies charges to the piezoceramic actuators in a manner similar to the Direct Velocity Feedback and Bang-Bang time optimal control techniques. A brief description of each of the damping techniques is given. Numerical simulations of the switching techniques are shown and compared to the resonant shunt damping technique. Finally, preliminary experimental results are presented for the resonant shunt, state, and synchronized switching techniques on a simply supported beam.

The application of electrically shunted piezoceramic materials (PZTs) for increasing transmission loss is studied. A test setup in an SAE J1400 facility is used to analyze the sound transmission loss due to a test plate with shunted PZTs, and to compare the results with an undamped plate and a plate with constrained-layer damping materials. The test results indicate that shunted PZTs can increase sound transmission loss by approximately 6 dB for a pure tune input at 162 Hz, and 7 dB for a broad band input of 10 - 10000 Hz. The test results further show that, compared to the constrained layer damping materials that are commonly used in the automotive industry, PZTs provide a substantially higher sound transmission loss-to-weight ratio.

The application of electrically shunted piezoceramic materials (PZTs), commonly known as 'smart damping materials,' for reducing noise and vibrations in damped and undamped structures is examined, using a specially designed test stand. The 'smart damping' technique used in this study involves attaching PZTs that are shunted with electrical circuits, consisting of resistors, capacitors, and inductors. The shunted PZTs are simple, do not require any external power, and can be easily and cost-effectively applied in practice. The test results indicate that the shunted PZTs can dissipate vibration energy, much the same way as adding viscoelastic damping materials to the structure, without adding any significant amount of weight to the structure. The results further indicate that the shunt circuits can be tuned to specific vibration frequencies, in the lower frequency ranges. The results presented here include a comparison between smart and passive damping materials, in terms of the noise and vibration reduction performance.

This paper presents a study of dissipation mechanisms of the Non-Obstructive Particle Damping (NOPD), based on a discrete element method (DEM). The goal of the work is to provide a theoretical basis for engineering applications of NOPD technology. Computer simulation is carried out for the coupled movement model of a single degree of freedom system of NOPD. A quantitative analysis describes the energy transference and energy dissipation of the particles in a collision process of the particle-primary system and the particle-particle system. The analysis reveals that the effectiveness of frictional dissipation is on the same numerical scale as that of collision energy dissipation. The energy dissipation by friction is greater for smaller size of particles. Furthermore, the NOPD technique has a wide frequency band for vibration reduction. The theoretical findings of the work are found to be in a good agreement with the previous experiment results.

Piezoelectric materials are an important class of smart materials for the generation of mechanical ultrasonic vibrations. In industrial applications (for example ultrasonic cutting) the frictional contact of the vibrating tool with the workpiece is of special importance. A common observation at the contact zone is that frictional forces can be significantly reduced by superposition of ultrasonic vibrations. In this report we present a theoretical explanation for the reduction of friction. A basic system, consisting of a longitudinal ultrasonic vibrator sliding on a plane, is investigated. It is shown that a modification of Coulomb's friction law can be applied to this kind of vibrating friction contact. The macroscopically observed friction-force with ultrasonic vibration depends on the sliding velocity and the velocity of vibration: For sliding velocities higher than the vibration-amplitude the frictional force is not changed by vibration. But for small sliding velocities the friction-coefficient is significantly reduced and almost approaches zero for very slow sliding-velocity. The theoretical results were confirmed systematically by experimental investigations done on a specially designed test-rig. Energy considerations are used to calculate the ultrasonic energy which is required to achieve a prescribed reduction of the frictional forces. The model is also used for sensing the vibration-amplitude as well as the sliding-velocity without an additional sensor.

Sensitive mechanical or electrical components often require protection from the potentially damaging effects of vibration and shock loading. High-damping viscoelastic materials are usually used in the design of impact-absorbent components. Since shock transients are characterized by a broad frequency spectrum, it is imperative to properly model frequency dependence of material parameters over the frequency range of interest. The Anelastic Displacement Fields (ADF) method is used to incorporate frequency-dependence within a finite element formulation. This method considers the effect of material anelasticity on the displacement field, as opposed to directly modeling physical damping mechanisms. ADF-based, plane-stress, and plane-strain finite elements are developed in order to facilitate the modeling of complex viscoelastic structures. The governing equations and assumptions underlying the various finite element developments are presented. In this paper, corresponding finite element models are used to model shock propagation and absorption through viscoelastic beams. The model predictions are validated against wave propagation theory, which shows that ADF-based finite element models are capable of capturing wave propagation phenomena, such as geometric dispersion, and viscoelastic attenuation and dispersion of longitudinal waves in beams. The behavior of mechanical filters in realistic shock conditions is also investigated. ADF three-dimensional finite element models could thus be successfully employed to design mechanical filters, or compare the benefits of using one viscoelastic material over another for a given shock-mitigating task.

Achieving guaranteed behavior after many years in the high temperature phase should consolidate the potential capability of SMA in damping of series of oscillation cycles followed by long periods of inactivity. To use an appropriate model in simulation of the material behavior they have been carried out three types of experimental analysis. The first one focuses on the remnant after quench effects. The second one centers on the parent phase and its time-temperature dependence. The third one shows the changes on transformation temperature and on hysteretic width related to the cycling and on the two-phase coexistence.

An efficient method of modeling the rheological behavior of viscoelastic dampers is discussed and illustrated. The method uses the standard mechanical model composed of linear springs and dashpots, which leads to a Prony series representation of the corresponding material function in the time domain. The computational procedure used is simple and straightforward and allows the linear viscoelastic material functions to be readily determined from experimental data in the time or frequency domain. Some existing models including the fractional derivative model and modified power-law are reviewed and compared with the standard mechanical model. It is found the generalized Maxwell and generalized Voigt model accurately describe the broadband rheological behavior of viscoelastic dampers commonly used in structural and vibration control. While a cumbersome nonlinear fitting technique is required for other models, a simple collocation or least-squares method can be used to fit the standard mechanical model to experimental data. The remarkable computational efficiency associated with the exponential basis functions of the Prony series greatly facilitates fitting of the model and interconversion between linear viscoelastic material functions. A numerical example on a viscoelastic fluid damper demonstrates the advantages of the use of the standard mechanical model over other existing models. Details of the computational procedures for fitting and inter-conversion are discussed and illustrated.

This study focuses on an experimental study of heat transfer from magneto-rheological fluid (MRF) dampers. Two semi- active automotive size MRF dampers, one with fins and the other without fins, were constructed and tested. The experimental results were compared with those of a previously developed theoretical model. It is demonstrate that especially at high peak velocities, the temperature rise is significant and heat transfer from these devices can be enhanced considerably by utilizing fins.

High-strength, stable, magnetorheological (MR) fluids and devices such as rotary brakes and linear vibration dampers that enable the benefits of controllable fluid technology are now commercially available. Recently, a new way of using MR fluids in which the fluid is contained in an absorbent matrix has been developed. Such MR fluid sponge devices enable the benefits of controllable MR fluids to be realized in cost sensitive applications. Most of the high-cost components normally associated with a fluid-filled device can be eliminated with this approach. Low-cost, controllable MR sponge dampers are particularly appropriate for moderate-force vibration control problems where a high degree of control authority is desired. One attractive area for their application is in next-generation high-performance home washing machines. These new machines operate under varying agitation rates, load imbalances, and often at very high speeds, and as such require varying damping charateristics. Test results have shown the MR sponge damper to be an ideal way to control vibration in these new washing machines.

A disk-type MR fluid damper based on shear operation mode is presented in this paper. The magnetic field of the disk-type MR fluid damper is analysed by the finite element method. The effect of excitation current in the coil on the magnetic flux density in the axial gaps filled with MR fluid is studied both theoretically and experimentally. Finally, the effectiveness of the disk-type MR fluid damper for attenuating vibration of rotor systems and of a simple open-loop on-off control based on the feedback of rotational speed on controlling vibration of rotor systems are experimentally studied. It is shown that the dynamic characteristics of the disk-type MR fluid damper can be controlled by a simple magnetic coil with a low voltage, and the disk-type MR fluid damper is very effective to attenuate vibration of rotor systems.

The present paper is devoted to de3velopment and testing of an active vibration system. The system is intended for providing efficient motion of a piston in a hydraulic channel for creation of shocks and periodic vibrations in a low frequency range by means of the ER-valves based on an electrosensitive working me dium, i.e. electrorheological fluids. The latter manifests the electrorheological (ER) effect, i.e. a reversible change in the rheological characteristics of weak-conducting disperse compositions in the presence of constant and alternating electric fields. As a result of the experimental study of the dependence of viscoelastic properties of the ER-fluid on the magnitude and type of an electric field, the optimum dimensions of the vibrator and the its valves characteristics of the optimal electrical signal are determined. For control of an ER- vibrator having several valves we have designed a special type of a high-voltage two-channel impulse generator. Experiments were conducted at the frequencies ranged from 1- 10 Hz. It has been shown, that a peak force made 70% of the static force exercised by the vibrator rod. A phase shift between the input voltage and the load acceleration was less than 45 degree(s)C which allowed servocontrol and use of the vibrator for attendant operations. It was noted that a response of the vibrator to a stepwise signal has a delay only of several milliseconds.

Smart laminated composites with layers of magnetostrictive and/or piezoelectric materials have been explored for active damping applications. Active vibration control in laminated structures with low inherent damping, may lead to instability. In some other cases like flexible appendages of satellites, design considerations may impose constraints in collocated sensing and actuation in structure which would also cause degradation in system performance if only active control is used. Ideally, both structural damping and active control are desirable to achieve good dynamic performance. Of late, hard ceramic materials with hysteretic stress- strain behavior are used in passive vibration control. Because of high strain dependency of the damping in these materials, especially near the high damping regime, it is possible to enhance the amount of passive damping by active control of strain in the passive layer. Because of the layered structure in laminates, several interesting possibilities for hybrid damping exist and a few of them are proposed and explored in the present study. Smart composites are magnetostrictive (Terfenol-D) layers and strain dependent ceramic and/or ferroelectric Passive Damping (PD) layers are considered. The damping achieved in the PD layers is controlled by varying their location and/or the amount of gain in the active controller. Both frequency and time domain studies are carried out to investigate the performance of proposed hybrid damping systems. Simulations using recently developed smart beam elements are carried out to investigate the performance of proposed hybrid damping systems. Simulations using recently developed smart beam elements are carried out on laminates with several configurations of active and passive layers. The simulation brings out the significance and the exploitation of strain dependency of passive damping on the overall damping of the hybrid system.

A new hybrid piezoelectric damping system with switching control are proposed here in order to reduce the control power requirement of piezoelectrical damping augmentation for flexible structures. There are two types of hybrid piezoelectric damping; one is a series type (integrated type, type I) where piezoelectric actuators are actively driven by the external voltage source with the passive tuned RL shunting circuit in series. The other is a separated type in collocated condition (type II) where the external voltage sources and the passive tuned RL shunting circuits are separated from each other, and both piezoelectric actuators to be used to the active and passive dampings are collocated on the host structure. The types I - II switching rule of the variable hybrid piezoelectric damping is determined by the vibration condition on the host structure. Availability of the proposed variable hybrid piezoelectric damping system is experimentally demonstrated by using a simple cantilever beam example with surface bonded piezo-elements. The experimental results indicate that the variable hybrid piezoelectric damping system is effective comparing the single type of hybrid piezoelectric damping system (type I or type II) from the viewpoint of active control power requirement.

Different techniques, both active and passive, are available to reduce the noise. Usually the energy associated to the noise is dissipated; anyway it may be recovered and stored, or used to drive other devices to counteract noise, without additional active electrical components. The energy can be directly converted from mechanical into electrical form using thin piezoelectric patches making a complete self-supplied system for noise control. The basics of this principle are here reported. In order to prove the goodness of the principle, a deep investigation using FEM tools has been performed. Some FE commercial software allow to take into account the interaction between fluid and piezoelectric structure and make possible to introduce in the model an electrical network. An original complete fully coupled (Fluid-Piezo Structure-Electrical Network) FE model is presented and different layouts for piezo panel absorbers are investigated. Together with the simulations, experimental trials have also been made. The experiments validate the model and the results are reported. Both the simulations and the experiments show clearly that the proposed solution can be a smart and inexpensive alternative to the classical systems. Moreover many interesting applications can be based on this system.

In this paper, multi-mode piezoelectric shunt damping and the damping performance comparison according to different piezoelectric materials are studied. Multi-mode damping is tried by using a newly proposed tuning method. This method is based on electrical impedance model and maximizing the dissipated energy at the shunt circuit. By measuring the electrical impedance at the piezoelectric patch bonded on a structure, an equivalent electrical model is constructed near the system resonance frequency. After shunting elements are connected to the equivalent circuit, the shunt parameters are optimally searched based on the criterion of maximizing the dissipated energy at the shunt circuit. This is for a single mode and it is expanded to multi-mode damping. Cantilever beam is taken as examples. Piezoceramics are bonded near root of the beam and electrical impedance is measured using HP 4192 impedance analyzer. Small electronic shunt circuits are made according to the found optimal shunt parameters. The first and second vibration modes are damped out independently. However, it was found that the presence of the shunt circuit tuned for the second resonance deteriorates the electrical impedance near the first resonance. Discussion on this fact is provided. The piezoelectric damping performance is compared according to different piezoelectric materials. Three piezoelectric materials are selected: PZT-5, PZN-PT single crystal and QuickPack IDE actuator. When resonant shunt circuit is considered, the use of PZN-PT single crystal exhibited the best piezoelectric damping performance. When IDE actuator is used with resistive shunt, although the tip displacement reduction is not so large, the first and second resonance modes can be damped out by a simple passive electronics- a resistor.

The work presented in this paper is concerned with the application of embedded piezo-electric actuators in model helicopter rotor blades. The paper outlines techniques to define the optimal location of actuators to excite particular modes of vibration whilst the blade is rotating. Using composite blades the distribution of strain energy is defined using a Finite Element model with imposed rotor-dynamic and aerodynamics loads. The loads are specified through strip theory to determine the position of maximum bending moment and thus the optimal location of the embedded actuators. The effectiveness of the technique is demonstrated on a 1/4 scale fixed cyclic pitch rotor head. Measurement of the blade displacement is achieved by using strain gauges. In addition a redundant piezo-electric actuator is used to measure the blades' response characteristics. The addition of piezo-electric devices in this application has been shown to exhibit adverse aeroelastic effects, such as counter mass balancing and increased drag. Methods to minimise these effects are suggested. The outcome of the paper is a method for defining the location and orientation of piezo-electric devices in rotor-dynamic applications.

The wave propagation in sandwich beams with cellular core is analyzed and controlled. The material properties of cellular cores are highly dependent on the geometry of the cell composing the honeycomb structure. Core materials of different geometry placed periodically along the beam length introduce the proper impedance mismatch necessary to impede the propagation of waves along the beam. A Spectral Finite Element model is developed to describe the wave propagation characteristics and the vibration of the sandwich beam. The model uses dynamic shape functions obtained from the solution of the corresponding distributed parameter model and thus allows for predicting the dynamic behavior of the structure with a significantly reduced number of elements as compared with the conventional FEM. The model is used to derive the transfer matrix of the sandwich beam, which identifies the location of the frequency bands where traveling waves are attenuated. The influence of core geometry and periodicity on the location and extension of these stop bands is assessed through a series of simulations. The effect of the periodicity of the structure is also evaluated by considering the vibration response of a clamped free beam excited by the harmonic motion of the base. The results demonstrate the simplicity and the effectiveness of the proposed treatment whereby the transmission waves and the vibration over specified frequency bands can be significantly reduced without requiring additional passive or active control devices. The unique characteristics of cellular solids therefore can be used to design light-weight composite panels that behave as mechanical filters. The filtering capabilities of such passive composite panels may be easily changed and optimized to reduce their transmissibility over a desired frequency range without compromising the size and the weight of the structure.

Internal damping of hollow structures, particularly retrospectively, is often difficult and expensive. The nature of the damping material and how it will be used will also be relevant if weight penalties are of significance. It would seem advantageous to establish how effective a damping treatment will be before deciding whether or not to use it. This paper presents an investigation into different methods of applying passive damping treatments to such structures. The merits of three treatments, extensional, constrained-layer, and visco-sphere in-fill damping are discussed. Using the dynamic properties of the viscoelastic damping material, the effect of the individual damping treatments are modelled using MATLAB, for the optimised treatments are applied to the box beam. This allowed for thickness optimisation of the layers of viscoelastic material, particularly for the constrained layer damping. The effectiveness of these treatments in damping the lowest flexural modes present in a steel box beam is investigated using hammer and electromagnetic shaker excitation. These results are then compared with predicted values and each other.

In a self-sensing actuator, a single piece of piezoelectric element is used simultaneously as a sensor and an actuator. Since the sensor and actuator are placed at the same location, they are truly collocated. Recently, a self-sensing active constrained layer (ACL) damping treatment has been introduced. This work has shown that a self-sensing ACL will eliminate system instability. However, while the viscoelastic layer of the ACL treatment will enhance damping, it will also reduce the control authority from the active source to the host structure. In this study, an enhanced self-sensing ACL treatment is proposed. The viscoelastic layer is still sandwiched between the host structure and the piezoelectric constraining layer. The single piezoelectric element is used as an actuator and a sensor simultaneously. By adding two edge elements onto the boundaries of the piezoelectric cover sheet, the actuator authority can be increased due to the direct transmissibility from the piezoelectric layer to the host structure. On the other hand, the sensing capability of the piezoelectric element can also be increased because the converse transmissibility from the host structure to the piezoelectric layer is enhanced. A beam structure with a partially covered enhanced self-sensing ACL is implemented to investigate the system characteristics. Both actuating and sensing abilities are evaluated. Their concurrent sensing/actuating performance is also investigated. Experimental results show that the two-way bypass effect via the edge elements can significantly improve the piezoelectric actuating/sensing abilities, and the overall performance. Therefore, this enhanced self-sensing ACL damping treatment can provide an effective means for structural vibration control.

In this paper, viscoelastic properties of MR fluids under oscillatory shear were experimentally studied using a rheometer with parallel-plate geometry. The experiments were conducted with amplitude sweep mode and frequency sweep mode. For the amplitude sweep mode, the driving frequency is fixed at a given value of (omega) rad/s and the strain amplitude, (gamma) ₀, is swept from 0.01% to 100$; For the frequency sweep mode, the strain amplitude is fixed at a certain strain, (gamma) ₀, and driving frequency is swept from 1 to 11 Hz. Consequently, the effects of strain amplitude, frequency, magnetic field strength, and temperature on the viscoelastic properties of MR fluids were investigated. MR fluid behaves as a linear viscoelastic body for sufficiently small strain amplitude ((gamma) ₀<EQ(gamma) _lin), while nonlinear viscoelastic behavior is observed for high strain ranges ((gamma) ₀>(gamma) _lin). At small strain amplitudes, the storage modulus and the loss modulus are independent of strain amplitude. At high strain amplitudes, the storage modulus is independent of the frequency and approaches plateau values at low frequencies. With increasing frequency, the storage modulus shows a decreasing trend before increasing again. The loss modulus varies slightly with frequency. MR fluid shows elastic-dominated properties in a magnetic field. Both the storage modulus and the loss modulus increase significantly with increasing field of strength. The temperature dependence of viscoelastic properties is also discussed. For the experimental temperature range of 20 degree(s)C to 60 degree(s)C, the storage modulus shows a slightly decreasing trend with temperature.