Materials that exhibit controllable modulus variations will enable new developments in applications in vibration suppression and shape change. In this paper we analyze a class of materials that exhibits reversible modulus variations due to solvent incorporation or removal. These materials, known as ionomeric polymers, have been shown previously to exhibit 20X changes in modulus depending on the hydration state of the material. A test fixture that allows a ionomeric polymer sample to be placed in a hydration controlled environment is developed. The Young's modulus of unplated materials and materials plated with metal is measured as a function of hydration level. A change of 2.56 and 3.89 times in modulus is obtained for the unplated and plated material, respectively. Experiments are performed to determine the ability to increase the stiffening rate of the polymer using applied electrical energy. Square input signals are applied to increase the elastic modulus of these materials. The rate of modulus change is higher or lower depending on the voltage amplitude and the forcing frequency of the input signal. Different kinds of solvents are used to control the modulus of the ionomer plated with platinum. Glycerol is the solvent with the highest modulus reduction (88.87%) and water is the smallest (67.71%). In addition, a test fixture consisting of a mass on a plate is built and modeled as moving-base. The change in stiffness is explored as a method to reduce unwanted vibration. The displacement transmissibility versus frequency is measured for water and acetonitrile solvents. The stiffness of Nafion 117 is computed when the solvents are applied and after they dry. The steady state response of the system is measured by applying a sinusoidal input signal. A forcing frequency of 94 Hz near the natural frequency is selected to produce a high amplitude. The displacement amplitude is reduced 5 times in 10 seconds after the application of the acetonitrile to the ionomeric polymer. These results demonstrate the basic feasibility of controlling the modulus in real time and quantify the time constants associated with hydration and dehydration of the material.

Some harsh environments, such as those encountered by aerospace vehicles and various types of industrial machinery, contain high frequency/amplitude mechanical vibrations. Unfortunately, some very useful components are sensitive to these high frequency mechanical vibrations. Examples include MEMS gyroscopes and resonators, oscillators and some micro optics. Exposure of these components to high frequency mechanical vibrations present in the operating environment can result in problems ranging from an increased noise floor to component failure. Passive micromachined silicon lowpass filter structures (spring-mass-damper) have been demonstrated in recent years. However, the performance of these filter structures is typically limited by low damping (especially if operated in near-vacuum environments) and a lack of tunability after fabrication. Active filter topologies, such as piezoelectric, electrostrictive-polymer-film and SMA have also been investigated in recent years. Electrostatic actuators, however, are utilized in many micromachined silicon devices to generate mechanical motion. They offer a number of advantages, including low power, fast response time, compatibility with silicon micromachining, capacitive position measurement and relative simplicity of fabrication. This paper presents an approach for realizing active micromachined mechanical lowpass vibration isolation filters by integrating an electrostatic actuator with the micromachined passive filter structure to realize an active mechanical lowpass filter. Although the electrostatic actuator can be used to adjust the filter resonant frequency, the primary application is for increasing the damping to an acceptable level. The physical size of these active filters is suitable for use in or as packaging for sensitive electronic and MEMS devices, such as MEMS vibratory gyroscope chips.

In the fields of high-resolution metrology and manufacturing, effective anti-vibration measures are required to obtain precise and repeatable results. This is particularly true when the amplitudes of ambient vibration and the dimensions of the investigated or manufactured structure are comparable, e.g. in sub-micron semiconductor chip production, holographic interferometry, confocal optical imaging, and scanning probe microscopy. In the active anti-vibration system examined, signals are acquired by extremely sensitive vibration detectors, and the vibration is reduced using a feedback controller to drive electrodynamic actuators. This paper deals with the modeling of this anti-vibration system. First, a six-degree-of-freedom rigid body model of the system is developed. The unknown parameters of the unloaded system, including actuator transduction constants, spring stiffness, damping, moments of inertia, and the location of the center of mass, are determined by comparing measured transfer functions to those calculated using the updated model. The model is then re-updated for the case of an arbitrarily loaded system. The responses predicted by the final updated model agree well with the experimental measurements, thereby giving confidence in the model and the updating procedure.

Payloads, such as satellites or spacecraft, which are mounted on launch vehicles, are subject to severe vibrations during flight. These vibrations are induced by multiple sources that occur between liftoff and the instant of final separation from the launch vehicle. A direct result of the severe vibrations is that fatigue damage and failure can be incurred by sensitive payload components. For this reason a payload adapter has been designed with special emphasis on its vibration isolation characteristics. The design consists of an annular plate that has top and bottom face sheets separated by radial ribs and close-out rings. These components are manufactured from graphite epoxy composites to ensure a high stiffness to weight ratio. The design is tuned to keep the frequency of the axial mode of vibration of the payload on the flexibility of the adapter to a low value. This is the main strategy adopted for isolating the payload from damaging vibrations in the intermediate to higher frequency range (45Hz-200Hz). A design challenge for this type of adapter is to keep the pitch frequency of the payload above a critical value in order to avoid dynamic interactions with the launch vehicle control system. This high frequency requirement conflicts with the low axial mode frequency requirement and this problem is overcome by innovative tuning of the directional stiffnesses of the composite parts. A second design strategy that is utilized to achieve good isolation characteristics is the use of constrained layer damping. This feature is particularly effective at keeping the responses to a minimum for one of the most important dynamic loading mechanisms. This mechanism consists of the almost-tonal vibratory load associated with the resonant burn condition present in any stage powered by a solid rocket motor. The frequency of such a load typically falls in the 45-75Hz range and this phenomenon drives the low frequency design of the adapter. Detailed finite element analysis is used throughout to qualify the design for vibration isolation performance as well as confirm its static and dynamic strength.

Different factors cause vibration. These vibrations make the voyages difficult and reduce comfort and convenience in passenger ships. In this paper, the creating factors of vibration have discussed first, then with mathematical modelling it will be attempted to minimize the vibration over the crew's seat. The modelling consists of a system with two degrees of freedom and by using vibration\isolation with passive method of Tuned Mass Damper (TMD) it will be tried to reduce the vibration over personnel. Moreover using active control systems will be compared with passive systems.

The design of the control devices for the control system of adjacent structures connected with control devices involves two aspects: the number and placement of the control devices and the control law or the parameters of the control devices. The performance index increment equation is established in this paper by using the conclusions of LQG problem at the condition of the control gain unchanged. Hence the optimum placement method is proved. The step reduced order method is used to overcome the defect of the control gain unchanging and it can be applied to the case in which only a few control devices are to be placed into the building with a large number of story units. The method proposed in this paper gives the optimum design of the number, the placement and the control law of the control devices at the same time.

This study intends to identify the behavior of MR fluid subject to high rates of shear and high flow velocities. A high shear rheometer is built which allows for the high velocity testing of MR fluids. The rheometer is capable of fluid velocities ranging from 1 m/s to 37 m/s, with corresponding shear rates ranging from 0.14x10⁵ s^-1 to 2.5x10⁵ s^-1. Fluid behavior is characterized in both the off-state and the on-state. In the off-state, the MR fluid was shown to exhibit nearly Newtonian post-yield behavior. A slight thickening was observed for growing shear rates. This slight thickening can be attributed to the behavior of the carrier fluid. The purpose of the on-state testing was to characterize the MR effect at high flow velocities. MR fluid was run through the rheometer at various flow velocities and a number of magnetic field strengths. The term "dwell time" is introduced and defined as the amount of time the fluid spends in the presence of a magnetic field. Two active valve lengths were considered, which when coupled to the fluid velocities, generated dwell times ranging from 12 ms to 0.18 ms. The yield stress was found from the experimental measurements and the results indicate that the magnitude of the yield stress is sensitive to fluid dwell time. The results from the on-state testing imply that high velocity applications may be subject to diminished controllability for falling dwell times.

The objective of this paper is to develop a pressurized magnetorheological (MR) damper which is suitable for train suspension in order to improve the ride comfort of passengers. A double-ended MR damper is designed and fabricated. The custom-made MR damper is pressurized in order to eliminate the force-lag problem. Then the MR damper is mathematically modeled with experimental validation and then integrated with the railway vehicle model. An on-off semi-active control strategy based on the measurement of the absolute lateral velocity of the car body is adopted for the semi-active suspension system. The performances of the semi-active train suspension system using MR dampers are evaluated by comparing with the passive, passive-on-H and passive-on-L suspension systems. The results indicate that when the human sensation of ride comfort is considered, the semi-active suspension with the developed MR dampers can substantially improve the ride quality of the passengers.

The primary objective of this study is to experimentally implement semi-active control to a Magneto-Rheological Tuned Vibration Absorber (MRTVA) and evaluate the dynamic performance of the MRTVA. The MRTVA is a semi-active TVA that employs an MR damper as its damping element. A test apparatus was built to represent a two-degree-of-freedom system-a primary structure coupled with an MRTVA. Using this test setup, a series of tests were performed to assess the dynamics of the MRTVA and to compare them with those of a passive TVA. The TVA used displacement-based, on-off groundhook (on-off DBG) control to regulate the MR damper. Unlike a passive TVA, the MRTVA was able to effectively control the resonant vibrations without sacrificing the isolation valley at high damping. To interpret the dynamics of the passive and semi-active system, the damper lock-up dynamics were investigated. The lock-up analysis further explains the actual implementation of the on-off DBG control policy in the system. The results of the lock-up analysis indicated that the dynamics of the control logic prevented lock-up in the MRTVA. This paper demonstrates that the MRTVA with the on-off DBG semi-active control can offer the benefits of high damping at the resonant peaks while still maintaining good isolation at the natural frequency of the structure. In other words, the semi-active TVA that employed an MR damper was more effective than an equivalent passive system in reducing vibrations of the primary structure.

Magnetorheological (MR) fluids provide a novel solution to adapt damping levels in aircraft landing gear, so that optimal performance can be achieved over a wide range of conditions. The present study helps to demonstrate the feasibility of this solution by sizing an MR valve within the constraints of an existing commercial (passive) oleopneumatic shock strut. Previous work on MR landing gear has tended to focus on potential control strategies rather than design and sizing issues. However these latter aspects are of great importance in aircraft systems, where space and weight are vital design constraints. To aid the sizing analysis performed in this study, accurate quasi-steady and dynamic impact models of passive and MR oleopneumatic landing gears are developed. The model is validated against experimental data incorporating the passive device, which is then used as a benchmark for the MR designs and to assess fail safety. The dynamic model is particularly important as it incorporates fluid compressibility, which may be a significant contributor to the overall response of the device in an impact scenario. The present study also aims to give further insight into high velocity MR valve flow, which will be inevitable during impulsive loading. This area remains largely unexplored and particular importance is given to valve Reynolds number since turbulent values are known to reduce device performance. The feasibility of an MR landing gear will be largely dependant on these factors.

Passive stand-off layer (PSOL) and slotted stand-off layer (SSOL) damping treatments are presently being implemented in many commercial and defense designs. In a PSOL damping treatment, a stand-off or spacer layer is added to a conventional passive constrained layer damping treatment. In an SSOL damping treatment, slots are included in the stand-off layer. A set of experiments using PSOL and SSOL beams in which the geometric properties of the stand-off layer were varied was conducted to analyze the contribution of the stand-off layer to the overall system damping. This set of experiments measured the frequency response functions for a series of beams in which the total slotted area of the stand-off layer was held constant while the number of slots in the stand-off layer was increased for a constant stand-off layer material. Finite element analysis models were developed in ANSYS to compare the predicted frequency response functions with the experimentally measured frequency response functions for the beams treated with PSOL and SSOL damping treatments. In these beams, the bonding layers used to fabricate these treatments were found to have a measurable and significant effect on the frequency response of the structure. The finite element model presented here thus included an epoxy layer between the base beam and the stand-off layer, a contact cement layer between the stand-off layer and the viscoelastic layer, and a method for modelling delamination.

Significant damping can be introduced to a closed structure by filling the structure with a moderately lossy, low-wave-speed medium, such as a foam or a low-density powder. In this paper, we study the damping in long, thin-walled, cylindrical tubes filled with a low-density powder. Experimental results show that significant damping can be attained in tube bending (n=1) modes as well as shell bending (n=2 and higher) modes. To predict the damping in such systems, we develop a model based on three-dimensional shell equations including shear deformation and in-plane inertia, and treat the powder as a compressible fluid with a complex speed of sound. By studying the spatial decay of steady harmonic motion in an infinitely long tube, we obtain estimates for the loss factor of vibration for various numbers of circumferential nodes as a function of driving frequency.

Recent research into the use of thermal barrier coatings has shown that they can provide sufficient additional damping, reducing vibration levels and significantly extending the life of the coated component. Various deposition techniques may be employed to apply ceramic coatings with Air Plasma Spraying (APS) and Electron Beam - Physical Vapour Deposition (EB-PVD) being the most widely used. However, one has to take into account that even when the starting ceramic material is the same, the microstructures of the resultant coatings depend strongly on the deposition technique. The objective of this paper is to study of the differences in the damping behaviour and stiffness of an yttria-stabilised zirconia (YSZ with 8%wt yttria) coating deposited by APS and by EB-PVD. Both damping and stiffness of these two YSZ coatings were estimated from tests performed at room and high temperatures. Moreover, this paper presents the microstructural characterisation of these two YSZ coatings using scanning electron microscopy, and attempts a correlation of the differences in their properties to their microstructure.

Ionomeric polymers are a promising class of intelligent material which exhibit electromechanical coupling similar to that of piezoelectric bimorphs. Ionomeric polymers are much more compliant than piezoelectric ceramics or polymers and have been shown to produce actuation strain on the order of 2% at operating voltages between 1 V and 3 V. Their high compliance is also advantageous in low force sensing configurations because ionic polymers have a very little impact on the dynamics of the measured system. This paper presents a variational approach to the dynamic modeling of ionic polymer actuators and sensors. The approach requires a priori knowledge of three empirically determined material properties: elastic modulus, dielectric permittivity, and effective strain coefficient. Previous work by Newbury and Leo has demonstrated that these three parameters are strongly frequency dependent in the range between less than 1 Hz to frequencies greater than 1 kHz. A model of a cantilever beam incorporating this frequency dependence has been developed. The variational method produces a second-order matrix representation of the structure. The frequency dependence of the material parameters is incorporated using a complex-property approach similar to the techniques for modeling viscoelastic materials. A transducer was manufactured and the method of material characterization is outlined. Additional experiments are performed on this transducer and both the material and structural model are validated. The modeling method is then used to simulate the performance of actuators and sensors in a cantilever configuration.

This paper addresses the theory and finite element analysis of the transient large amplitude vibration response of thin composite structures and its control by integrated piezoelectric layers. A geometrically nonlinear finite shell element for the coupled analysis of piezolaminated structures is developed that is based on the first-order shear deformation (Reissner-Mindlin) hypothesis and the assumptions of small strains and moderate rotations of the normal. The finite element model can be applied to smart structures consisting of a composite laminated master structure with arbitrary ply lay-up and integrated piezoelectric sensor and actuator layers or patches attached to the upper and lower surfaces.

It is well known that both martensite and austenite (superelastic) Nitinol Shape Memory Alloys (SMAs) have damping capacities, benefiting from their hysteretic stress-strain relationships. In general, for SMA devices for passive vibration control, martensite SMA has a larger damping capacity; however, it requires external heat to cause a phase transformation to restore its original shape. On the other hand, superelastic SMA has less damping capacity, but it has a strong re-centering force to restore its initial shape and there is little residual strain of the superelastic SMAs. This paper researches the damping capacity of Nitinol in martensite and austenite co-existence phase. Nitinol with the co-existence of both martensite and austenite phases combines advantages of martensite SMAs and superelastic SMAs and has a large damping capacity with self-shape restoring ability. To quantitatively study the damping effect of Nitinol in martensite and austenite co-existence phase, a setup is designed and fabricated. This setup involves a cantilevered steel beam with pre-stressed SMA wires attached to each surface at the remote end of the beam. The SMA wires function as a damper to the cantilevered beam. A piezoceramic patch sensor attached to the beam near its cantilevered end is used to record the data of the vibration of beam and the data is then used to estimate the damping ratio of the system. The percentage of the martensite phase in the Nitinol SMA wires is controlled by electrically heating the wires via a closed-loop control system. Experimental results verify that the Nitinol wires with the co-existence of the both martensite and austenite have the best damping property for vibration suppression. For practical implementation, the transformation temperate of the SMA wire damper can be chosen as the room temperature so that both martensite and austenite co-exist.

Vibration control and suppression in structures plays a central role in the extension of their service life and improvement of their reliability. While in many cases the solution of this problem implies the introduction of external damping devices, it is also conceivable to adaptively modify their vibratory properties, so that the occurrence of severe vibrations due to resonance phenomena can be curbed at its origin. The modification of the shear stress transfer at the interface between the core and the faces of a sandwich beam has been shown to have a remarkable effect on the bending stiffness of the structure. Such modification can be obtained by applying a normal stress between the core and the un-bonded, electrically insulated faces of the sandwich by means of a strong electrical field. An intermediate behavior between fully bonded and un-bonded layers in terms of inter-laminar shear stress can be achieved by temporary electrostatic bonding of the components. The outlined approach to the reduction of transversal vibrations in thin multi-layer beams is promising and can in principle be applied to multi-layer plates.

Multiwalled carbon nanotubes are dispersed in polycarbonate matrices using a novel solution mixing technique and dynamic load tests are performed to characterize the storage and loss modulus. Tests are also performed with pristine polycarbonate (no carbon fillers), to compare the response of the two materials. The test results indicate that as the strain amplitude is increased, the storage modulus decreases in conjunction with an increase in the loss modulus. This suggests that at large strain levels the adhesion between the nanotubes and polymer is not strong enough to prevent interfacial slip, resulting in frictional sliding at the tube-polymer interfaces. This debonding at the filler-matrix interface is responsible for the observed decrease in storage modulus and increase in loss modulus. The nanotube-polymer sliding energy dissipation mechanism shows potential to reliably and efficiently deliver high levels of structural damping to polymer structures.

This paper presents the results of an investigation of the structural damping characteristics of polymeric composites containing randomly oriented nanoropes. The SWNT (single-walled nanotube) rope is modeled as a closed-packed lattice consisting of seven nanotubes in hexagonal array. The composite is described as a three-phase system consisting of a resin, a resin sheath acting as a shear transfer zone, and SWNT ropes. The "stick-slip" mechanism is proposed to describe the load transfer behavior between a nanorope and a sheath and between individual SWNTs. The analytical results indicate that both the Young’s modulus and loss factor of the composite are sensitive to stress magnitude. Also, to address the orientation effect on inter-tube sliding and tube/sheath sliding, the Young’s moduli and loss factors of composites filled with aligned nanoropes and randomly oriented nanoropes are compared.

Topology optimization has been successfully used for improving vibration damping in constrained layer damping structures with viscoelastic materials. Reinforcing carbon nanotubes in a polymer matrix greatly influences the mechanical properties of the polymer. Such nanotube-reinforced polymers (NRP) can be used to further enhance the damping properties of the constrained layer structures. The effects of nanotube inclusions on the damping properties of polymers and applicability of NRP for damping in structures have been studied previously. The inclusion of nanotubes into a polymer matrix provides new design variables in the topology optimization studies on such structures. The aim of this research is to determine the optimal topology and the optimal constituent make-up of the constrained NRP layer, where the volume fraction of the nanotubes in the constrained layer is optimized to maximize the system loss factor.

Resistance exercise has been widely reported to have positive rehabilitation effects for patients with neuromuscular and orthopaedic conditions. This paper presents an optimal design of magneto-rheological fluid dampers for variable resistance exercise devices. Adaptive controls for regulating the resistive force or torque of the device as well as the joint motion are presented. The device provides both isometric and isokinetic strength training for various human joints.

The primary purpose of this study is to provide a comprehensive experimental analysis of how various popular semiactive control methods perform when used with magneto rheological dampers. Specifically, the performance of five different skyhook control methods is studied experimentally, using a single suspension test rig. The control methods that are analyzed include: skyhook control, groundhook control, hybrid control, displacement skyhook, and relative displacement skyhook. For a MR damper, this paper provides an in-depth analysis of how these semiactive control methods perform at the sprung and unsprung mass natural frequencies, using the single suspension test rig. Upon evaluating the performance of each control method in frequency domain for various conditions, they are compared with each other as well as with passive damping. The results indicate that no one control method outperforms others at both the sprung and unsprung mass natural frequencies. Each method can perform better than the other control methods in some respect. Hybrid control, however, comes close to providing the best compromise between different dynamic demands on a primary suspension. The results indicate that hybrid control can offer benefits to both the sprung and unsprung mass with control gain settings that provide equal contributions from skyhook control and groundhook control.

A magneto-rheological (MR) fluid-elastomer vibration isolator is constructed by encapsulating a MR fluid inside an elastomer. The structural properties of this system are controllable by an applied magnetic field. Previous studies have shown that the damping capacity of this MR fluid-elastomer vibration isolator is a function of strain amplitude and field strength, and weakly dependent on the excitation frequency. The energy-dissipated mode, subjected to a magnetic field during oscillatory motion, is similar to a combined viscous and frictional damping. In this paper, a mechanical model is presented to account for the dynamic behavior of the MR fluid-elastomer vibration isolators under oscillatory compressive deformations. This model is a two-element analogy comprised of a variable friction damper and a nonlinear spring. The parameters of the model have been identified by a series of harmonic loading tests. The theoretical and experimental results are in excellent agreement.

Magnetorheological elastomer (MRE) is a solid-state smart material with field-dependant dynamic shear modulus. But, its lower shear modulus, which is about 0.388MPa, does prevent its application. Sandwich configuration is an alternative to apply MRE in engineering since the outer thin skins will strengthen the bulk flexural stiffness and the transverse flexibility of the MRE core will affect the bulk flexural dynamic performance. In this paper, the field-dependant dynamic property of MRE-based sandwich beams, composed of conductive skins or non-conductive skins, is addressed theoretically through a high order model. By defining the maximum field-induced relative change of the bulk flexural dynamic stiffness as controllability index, structure designs to yield maximum controllability are presented through a non-dimensional analysis. The simulation on simply supported MRE-based sandwich beam indicates: (1) the anti-resonant frequencies and resonant frequencies of the sandwich beam change with applied magnetic fields up to 30%; (2) the bulk field-dependant flexural dynamic property is mainly depended on the field-dependant shear modulus of the MRE core; and, (3) there is an optimal combination of the thickness of the core and the thickness of the skins for maximum controllability; (4) around the optimal combination point, the controllability/mass ratio can be enhanced dramatically though decreasing the core thickness; (5) the normalized density of the skins affects the controllability slightly when the Young's modulus of the skins is low. This work indicates that sandwich structures can well utilize the controllable property of MRE to realize applicable stiffness changeable devices.

An automotive suspension strut is proposed that utilizes compressible magnetorheological (CMR) fluid. A CMR strut consists of a double ended rod in a hydraulic cylinder and a bypass comprising tubing and an MR valve. The diameter on each side of the piston rods are set to be different in order to develop spring force by compromising the MR fluid hydrostatically. The MR bypass valve is adopted to develop controllable damping force. A hydro-mechanical model of the CMR strut is derived, and the spring force due to fluid compressibility and the pressure drop in the MR bypass valve are analytically investigated on the basis of the model. Finally, a CMR strut, filled with silicone oil based MR fluid, is fabricated and tested. The spring force and variable damping force of the CMR strut are clearly observed in the measured data, and compares favorably with the analytical model.

The primary purpose of this paper is to present the theories leading to the development of a semiactive adaptive controller for nonlinear systems. The adaptive algorithm developed in this paper is applied to one class of nonlinear vibration systems, namely semiactive base-excited vibration isolation systems. The algorithm includes the on-line system identification and the adaptation of the control signal. Finally, the stability of the semiactive adaptive system is presented.

A Bouc-Wen element has been employed by a number of researchers to model magnetorheological (MR) linear dampers with success. In this work, a modified commercial MR brake was modeled using a Bouc-Wen element and experimental data gathered on the torque response of the brake to oscillation. An optimization was undertaken using torque and displacement time-series data to determine the parameters of the brake model, and comparisons were made between experimental and predicted torque response.

Since the development of the vehicle suspension system, designers have been faced with the conflict of vehicle safety versus ride comfort. Originally, this trade-off was minimized by optimally adjusting a passive damper. In the recent years, the development of computer-controlled suspension dampers and actuators has improved the trade-off between the vehicle handling and ride comfort, and has led to the development of various damper control policies. In this study, the vehicle handling and ride comfort trade-off is studied for a vehicle suspensions with semiactive fuzzy control. The proposed semiactive fuzzy control is based on the control policies that are commonly known as "skyhook" and "groundhook". After describing the mathematical details of the proposed semiactive fuzzy control, it is applied to a roll-plane model of a heavy truck in order to compare its performance with conventional passive suspensions. The results of the study show that semiactive suspensions with fuzzy logic control could improve rollover characteristics during vehicle maneuvers. The results, however, show that for road inputs at the tire, the semiactive suspensions can cause larger body acceleration peaks and a harsher ride.

Analytical and experimental work has been performed on the use of a magneto-rheological (MR) fluid brake for controlling torsional vibrations in rotating systems. In this paper, two different strategies are examined for controlling the MR brake in such applications. First, implementation of the MR fluid brake as a passive friction damper with a variable friction torque is presented. In that application, fixed currents were applied to the electromagnets in the MR brake. As a result, the dominant behavior of the brake was as a dry friction damper whose friction was a function of applied current. The second approach was the implementation of the MR brake in a modified skyhook damping control approach. In that application, the friction in the MR brake was adjusted according to a comparison between the sign of absolute velocity of the primary system and the sign of the relative velocity between the MR brake and the primary system in order to add effective damping to the system. Characterization of the MR brake was an essential part of both control strategies. This work includes the results of system identification performed on the MR fluid brake, along with experimental performance results of the system under the different control strategies.

A damping effect can be induced on a conductive structure that is vibrating in a magnetic field. This damping effect is caused by the eddy currents that are induced in the material due to a time varying magnetic field. The density of these currents is directly related to the velocity of the conductor in the magnetic field. However, once the currents are formed the internal resistance of the conductive material causes them to dissipate into heat, resulting in a removal of energy from the system and a damping effect. In a previous study, a permanent magnetic was fixed in a location such that the poling axis was perpendicular to the beam's motion and the radial magnetic flux was used to passively suppress the beam’s vibration. Using this passive damping concept and the idea that the damping force is directly related to the velocity of the conductor, a new semi-active damping mechanism will be created. This new damper will function by allowing the position of the magnet to change relative to the beam and thus allowing the net velocity between the two to be maximized and the damping force significantly increased. Using this concept, a model of both the passive and active portion of the system will be developed, allowing the beams response to be simulated. To verify the accuracy of this model, experiments will be performed that demonstrate both the accuracy of the model and the effectiveness of this semi-active control system for use in suppressing the transverse vibration of a structure.

Using self-sensing in an electrodynamic actuator for broadband active vibration damping requires compensation of the actuator resistance and of the self-inductance of the actuator with an appropriate shunted circuit. In order to reduce power consumption the actuator resistance should be small, but for robustness of self-sensing and a large bandwidth a large resistance is required. A high transducer coefficient is important to get high sensitivity of the induced voltage that is proportional to the vibration velocity of an attached mechanical structure. However, a large transducer coefficient implies a strong magnetic field that also increases the self-inductance so that the measurement bandwidth potentially is reduced. In this study, in order to eliminate the first trade-off between power consumption and robustness, an actuator with a primary driving coil and a secondary measurement coil is proposed. The primary coil is optimized for driving by choosing a small resistance, whereas the secondary coil is optimized for sensing by choosing a large resistance. It has been shown that the transformer coupling between the two coils could be reduced by decreasing the cross section of the secondary coil, but there is a geometric limit on the reduction of the cross section of the secondary coil. Therefore an analogue electronic compensation scheme is proposed to compensate for the transformer coupling between the primary and the secondary coil. Feedback of the sensed velocity in the secondary coil is implemented and experimental vibration damping results at a plate are presented. Results are compared to self-sensing vibration damping, active vibration damping using a velocity sensor and passive damping means of the same weight as the actuator.

Vibrations of structures equipped with a piezoelectric actuator can be damped by connecting the electrodes of the actuator to a suitable electric circuit. The insertion of a negative capacitance in the electric circuit, able to compensate the reactive impedance of the piezoelectric actuator, rise up the damping performance of the device. In this paper different circuits containing a negative capacitance are proposed and optimized for both single-mode and multi-mode damping. A theoretical analysis is performed in the former case, yielding closed-form expressions for the achieved exponential time-decay rate of vibrations, whereas a numerical optimization is employed in the latter case. The proposed circuits show good performances in simulation for both single-mode and multi-mode damping.

The goal of this study is to reduce the bending vibration of railway vehicles by applying a vibration suppression technique. The technique utilizes piezoelectric elements that are electrically shunted by an external circuit. This paper presents an investigation by using a scale model of a Shinkansen vehicle with a length of about 5m, mainly focused on implementation of shunt circuits. Small pieces of piezoelectric elements are bonded to its floor structure and electrically connected to a shunt circuit. The authors propose a new method to implement shunt circuits, a part of which is virtually realized. The circuits are designed for practical use under the condition of high voltage generated by the elements. Two types of shunt circuits are tested in this study. One is equivalent to an inductor and a resistor in series, and the other consists of a negative capacitor and a resistor. In actuality, the inductor and the negative capacitor are replaced by virtually realized impedance components. Results of excitation tests show that the circuits implemented based on the proposed method function as expected and bending vibration of the carbody can be reduced successfully.

Terfenol-D is one of magnetostrictive materials with the property of converting the energy in magnetic field into mechanical motion, and vice versa. We designed and fabricated a linear magnetostrictive actuator using Terfenol-D as a control device. In order to grasp the dynamic characteristics of the actuator, a series of experimental and numerical tests were performed. Induced-strain actuation displacements of the actuator measured by the test and predicted by magnetic analysis agreed well. And blocked forces according to the input currents were estimated from the testing results. Modeling method representing the exerting force of the actuator was confirmed through some testing results. We also explored the effectiveness of the linear magnetostrictive actuator as a structural control device. A series of numerical and experimental tests was carried out with simple aluminum beam only supported at each end by the actuator. After the equation of motion of the controlled system was obtained by the finite element method, a model reduction was performed to reduce the numbers of degree of freedom. A linear quadratic feedback controller was realized on a real-time digital control system to damp the first four elastic modes of the beam. Through some tests, we confirmed the possibility of the actuator for controlling beam-like structures.

It has been well established that using viscoelastic damping materials in structural applications can greatly reduce the dynamic response and thus improve structural fatigue life. Previously these materials have been used to solve vibration problems in metallic structures, where the damping material is attached to the structure and then a stiff outer layer is attached to promote shear deformation in the damping material. More recently, these materials have been used successfully in expensive aerospace composite structures, where the damping material is embedded between plies of prepreg graphite/epoxy prior to being cured in a high-temperature, high-pressure autoclave. The current research involves embedding these damping layers into low-cost composite structures fabricated using the Vacuum Assisted Resin Transfer Molding (VARTM) process. The damping layers are perforated with a series of small holes to allow the resin to flow through the damping layer and completely wet-out the structure. Experimental fabrication, vibration testing, and stiffness testing investigate the effect of hole diameter versus hole spacing. Results show that the damping and stiffness can be very sensitive to perforation spacing and size. It is shown that for closely spaced perforations (95% damping area) that damping increases by only a factor of 2.2 over the undamped plate. However, for greater perforation spacing (99.7% damping area) the damping is increased by a factor of 14.3. Experimental results as well as practical design considerations for fabricating damped composite structures using the VARTM process are presented.

Extreme noise and vibration levels at lift-off and during ascent can damage sensitive payload components. Recently, the Air Force Research Laboratory, Space Vehicles Directorate has investigated a composite structure fabrication approach, called chamber-core, for building payload fairings. Chamber-core offers a strong, lightweight structure with inherent noise attenuation characteristics. It uses one-inch square axial tubes that are sandwiched between inner and outer face-sheets to form a cylindrical fairing structure. These hollow tubes can be used as acoustic dampers to attenuate the amplitude response of low frequency acoustic resonances within the fairing’s volume. A cylindrical, graphite-epoxy chamber-core structure was built to study noise transmission characteristics and to quantify the achievable performance improvement. The cylinder was tested in a semi-reverberant acoustics laboratory using bandlimited random noise at sound pressure levels up to 110 dB. The performance was measured using external and internal microphones. The noise reduction was computed as the ratio of the spatially averaged external response to the spatially averaged interior response. The noise reduction provided by the chamber-core cylinder was measured over three bandwidths, 20 Hz to 500 Hz, 20 Hz to 2000 Hz, and 20 Hz to 5000 Hz. For the bare cylinder with no acoustic resonators, the structure provided approximately 13 dB of attenuation over the 20 Hz to 500 Hz bandwidth. With the axial tubes acting as acoustic resonators at various frequencies over the bandwidth, the noise reduction provided by the cylinder increased to 18.2 dB, an overall increase of 4.8 dB over the bandwidth. Narrow-band reductions greater than 10 dB were observed at specific low frequency acoustic resonances. This was accomplished with virtually no added mass to the composite cylinder.

We propose a modified LMS algorithm for adaptive feedforward control with actuator limits. Unlike the leaky LMS method, which limits the controller effort by introducing an auxiliary cost, in the proposed algorithm we maintain the cost as the performance measurement. We derive the true stochastic gradient of the cost for systems with saturation with respect to the filter coefficients and obtain an adaptation rule very close to that of the filtered-x algorithm, but in the proposed algorithm, the reference filter is a time-varying modification of the secondary channel. In simulations of an active vibration isolation system with actuator limits, the proposed algorithm attains better performance than that attained by the leaky LMS algorithm.

The objective of this research is to investigate the feasibility of utilizing left eigenvector assignment for vibration disturbance rejection. In the previous study, it has been shown that through right eigenvector assignment and modal confinement, one can enhance the performance of periodic vibration isolators. However, it was also recognized that since vibration mode confinement is based on the concept of modal response, it does not guarantee that vibration will always be reduced in a forced excitation scenario. In this research, the left eigenvector assignment technique is utilized to achieve vibration suppression throughout a broad frequency range. The principle is to alter the left eigenvectors of the closed-loop system so that the system's forcing vectors are as closely orthogonal to each left eigenvector as possible. With such an approach, one can directly attack the forced response problem. A new formulation is developed so that the desired left eigenvectors of this integrated system are selected through solving a generalized eigenvalue problem, where the orthogonality indices between the forcing vector and the left eigenvectors are minimized. The integrated system with assigned left eigenvectors achieves to reject external disturbance of the complete electromechanical system. An integrated closed-loop system with state estimator is also developed so that the algorithm can be implemented realistically. Numerical simulations are performed to evaluate the effectiveness of the proposed method on disturbance rejection for an isolator design example. Frequency responses of the isolator in the selected frequency range are illustrated. It is shown that with the left eigenvector assignment technique, the system’s external disturbances are rejected and vibration amplitude of the isolated regions can be effectively suppressed.

We present a multivariable controller architecture that is a hybrid combination of a classically designed controller and an observer-based controller. The design process starts with a classical multivariable feedback controller, designed by any convenient method, such as sequential SISO loop closing. After designing the classical controller, an observer-based modern controller is designed to be stable in parallel combination with the classical controller. The hybrid configuration is realized by introducing an additional feedback path between the two feedback controllers, to subtract the effects of the classical controller from the observer-state estimate. All of the controller gains are re-tuned to improve a variety of performance measures. The additional feedback path does not increase the number of states in the controller but allows significantly higher gains to be used in the observer-based controller, resulting in better isolation from input disturbances. A six-input, nine-output lightweight space structure (LSS) provides a working example. The classical controller was implemented as six 40th-order SISO feedback controllers, at a sample rate of 20 kHz, closed in parallel around the six main mount struts, achieving very good isolation across the struts. A 240th-order observer-based modern controller, also at a 20 kHz sample rate, was designed to work with the classical closed loops and has been implemented in the hybrid configuration described. This non-square modern controller uses feedback signals from three non-collocated sensors, in addition to the six used by the classical SISO controllers, and improves isolation by about 5 dB in the most critical regions of the controller bandwidth.

Various techniques that involve switching a piezoelectric shunt have been studied for overcoming the shortcomings of purely passive piezoelectric shunts, including so-called "state-switching" (switching between short and open circuit conditions on the piezoelectric) and various forms of short-duration switching, called "pulse-switching" or "synchronized switching". Pulse-switching can be done with a simple resistor shunt, but is more effective with an RL shunt. Previous research has shown that not only can the pulse-switched RL shunt provide very effective vibration control performance, but it eliminates much of the shunt parameter tuning required by the passive shunt approach, and can be done with a simple control circuit using very little power. In addition, it has been shown that a single switched shunt can simultaneously control multiple vibration modes. This paper illustrates that switch timing is important in the performance of these systems. A numerical simulation study is presented in which the switch time and duration are varied in a multi-degree of freedom system, and the controller performance is quantified. In addition, a group of performance indices are analyzed for their potential to be used in a real-time tuning system for optimizing switch timing.

This paper develops an averaging analysis for qualitative and quantitative study of switched piezostructural systems. The study of piezostructural systems including passive and active shunt circuits has been carried out for some time. Far less is known regarding analytical methods for the study of switched piezostructural systems. The technique developed in this paper is motivated by the success of averaging methods for the analysis of switched power supplies. In this paper it is shown that averaging analysis provides a means of determining time domain as well as frequency domain response characteristics of switched piezostructural systems that include switched capacitive shunt circuits. The time domain and frequency domain performance of a tunable piezoceramic vibration absorber is derived via averaging in this paper. The proposed switching architecture provides an essentially continuous range of tunable notch frequencies, in contrast to a finite and fixed collection of discrete notch frequencies available in some implementations of capacitively shunted piezostructures. The technique for analysis appears promising for the study of vibration damping and energy harvesting piezostructures whose underlying operating principle is similar.

This paper presents a new design of piezoelectric friction damper, which consists of tube piezoceramic stack actuators, load cells, preload bolts, brass sheets, spring washers and slotted bolted connection. A semi-active control strategy for variable friction dampers based on an improved suboptimal Bang-Bang control algorithm presented in this paper is also developed. By using genetic algorithm, the amplitudes of the control and preloading friction forces in the control system are obtained for enhancing the seismic performance of the controlled structures. The proposed approach is applied to a three-story building with a variable friction damper installed in the first story. The numerical results indicate that more reduction of the peak accelerations under seismic excitations and a better adaptability can be achieved than those of the unmodified controller.

This work examines the friction factor of magneto-rheological (MR) fluids in channel flow, where the channel walls are porous surfaces impregnated with MR fluid. There is no flow through the porous walls. Various porosity sizes and different impregnation techniques are utilized in this study. The results are compared to those of a smooth surface. From the experimental results it has been found that under an applied magnetic field, the impregnated porous wall surface would increase the friction factor of MR fluid flow significantly when compared to the smooth surface with the same dimensions. It is also concluded that the impregnation technique affects the amount of iron particles trapped inside the porosities, thus affecting the friction factor. In addition, scanning electron microscopy images of the impregnated samples are taken to qualitatively examine the penetration of MR fluid into porosities. Based on the experimental results a non-dimensional relation for friction factor of MR fluids is developed as a function of Mason number and porosity size. By using this relation, the pressure loss of a MR fluid flowing through a channel with MR impregnated porous walls can be determined without using a constitutive model for MR fluids.

This paper presents an effective design strategy for a magnetorheological (MR) damper using a nonlinear flow model. The MR valve inside a flow mode MR damper is approximated by a rectangular duct and its governing equation of motion is derived based on a nonlinear flow model to describe a laminar or turbulent flow behavior. Useful nondimensional variables such as, Bingham number, Reynolds number, and dynamic (controllable) range are theoretically constructed on the basis of the nonlinear model, so as to assess damping performance of the MR damper over a wide operating range of shear rates. First, the overall damping characteristics of the MR damper are evaluated through computer simulation and, second, the effects of important design parameters on damping performance of the MR damper are investigated. Finally, the effective design procedure to meet a certain performance requirement is proposed. A high force-high velocity damper is fabricated and tested, and the resulting model and design procedure are experimentally validated.

This paper concerns the transient response of MR fluids and factors that can influence the response performance of the material. In this study, the MR fluid is subjected to a constant shear between two parallel discs, one of which is rotating at a constant speed and the other fixed. When a step current is applied, the closed-loop controller increases the torque delivered to the rotating disc in order to maintain the speed. By examining the transient response of this delivered torque, the relative response time and rise time for the MR fluid can be determined. Results showing the relative response time dependency on five variables, (i) applied current (from 0.25 A to 2.00 A), (ii) shear rate (from 50 rpm to 300 rpm), (iii) particle volumetric concentration (from 10% to 40%), and (iv) particle properties, are presented. It was found that the rate of shear does not have much influence on the relative response time, but the other four factors can affect the response characteristics quite significantly. For example, the relative response time increases with a decrease in concentration of the material, and using silicone oxide-coated magnetically active particle improves the response of the material.

Tuned Liquid Dampers (TLD) are used to limit horizontal vibrations in structures, and offer practical alternatives to Tuned Mass Dampers (TMD). However, to our knowledge, liquid damping systems have not been developed to reduce vertical vibrations. In this work, we develop a model for a Vertical Motion Liquid Damper (VMLD), idealized as a discrete, two degree of freedom system. One degree of freedom represents the 'target' structure that is to be damped, and the other represents the approximate, one-dimensional motion of a liquid in a U-shaped tube. Internal losses due to the fluid oscillation serve to limit and control motions of the target structure. The U-shaped tube has a flexible joint such that one vertical portion and the horizontal portion of the tube remain fixed, and the remaining vertical portion of the tube is affixed to the vibrating structure, allowing the liquid to become excited. The equations of motion are derived using Lagrange's Equations, and are integrated using Runge-Kutta algorithms that are available in Matlab. An experimental model was built in the laboratory, consisting of a mass attached to the end of a cantilevered beam (corresponding to the target structure), and a U-tube made from PVC pipe. The various damping and stiffness parameters of the system were calibrated independently based on experimental data. Measured data from the experimental model show reasonable agreement with numerical simulations.

This paper proposes a new modeling scheme to describe the hysteresis and the preload characteristics of piezoelectric stack actuators in the inchworm. From the analysis of piezoelectric stack actuator behavior, the hysteresis can be described by the functions of a maximum input voltage and the preload characteristics are identified by the preload weight. The dynamic characteristics are also identified by the frequency domain modeling technique based on the experimental data. For the motion control, the hysteresis is compensated by the inverse hysteresis model. Since the dynamic stiffness of an inchworm is generally low compared to its driving condition, the mechanical vibration may degrade accuracy of the inchworm. Therefore, the SMC (Sliding Mode Control) and the Kalman filter are developed for the precision motion control of the inchworm. The feasibility of the proposed modeling scheme and the control algorithm is tested and verified experimentally.

This article deals with the fully coupled electromechanical responses of an infinitely long piezoelectric tube as a sensor or an actuator. By adopting the variational approach for generalized loading conditions and utilizing Hamilton's principal, the governing differential equations of an infinitely long piezoelectric tube subjected to natural boundary conditions are derived. For studying the direct and converse effect of the piezoelectric tube, the obtained governing equations are solved to give the exact solutions corresponding to different boundary conditions prescribed for the tube functioning as a sensor or an actuator. For numerical illustrations of our analysis, polyvinylidene difluoride and lead zirconate titanate, which are widely used in industries nowadays, are chosen as the materials for our investigations. The piezoelectric tubes made of these materials are investigated with thorough discussions over their different electromechanical responses.

A novel tunable mass damper (TMD) is developed using the sensitivity of transversal bending stiffness and resonance frequencies of a beam to its axial force. This smart TMD consists of a force actuator-sensor unit suspended in a rigid frame by two flexible beams coupled to the axial ends of the unit and the frame. The force actuator-sensor unit is composed of a giant magnetostrictive composite-based force actuator for producing an axial force to the beams and a pair of piezoelectric ceramic-based force sensors for generating a tuning signal. Through adjusting the magnetic field strength applied to the force actuator to change the axial force exerted on the beams, the transversal bending stiffness of the beams and hence the natural frequency of the smart TMD is tuned. In this paper, the design, fabrication, and characterized of the smart TMD is described. The measured resonance frequency of the smart TMD is 65 Hz at zero magnetic tuning field and 50 Hz at an applied magnetic field of 686 Oe. Tunability of the resonance frequency as high as 23 % is achieved with the reasonably low magnetic tuning field. The frequency response functions as measured using the force sensors agree well with those obtained using a commercial accelerometer, indicating a great possibility of directly deploying the force sensors for active or semi-active tuning or control purposes.

This paper presents the application of Lightweight Piezo-composite Curved Actuator (LIPCA) to suppress vibration as actuator. LIPCA is composed of a piezoelectric layer, a carbon/epoxy layer and glass/epoxy layers. When compared to the bare piezoelectric ceramic (PZT), LIPCA has advantages such as high performance, durability and reliability. In this study, performances of LIPCA are estimated in an active vibration control system. Experiments are performed on an aluminum beam by cantilever configuration. In this test, strain gages and single LIPCA are attached on the aluminum beam with epoxy resin in order to investigate their performance. Comparison of actuation force between LIPCA and bare PZT showed that performance of LIPCA was better than that of bare PZT. In addition, digital on-off control algorithm is applied into the system to exhibit performance of LIPCA as actuator in active vibration control system. The results showed LIPCA could suppress free vibration of the aluminum beam. It is possible to apply LIPCA as actuator to control vibration of dynamic structures.

This work presents the experimental investigations of wave propagation in two-dimensional (2D) periodic lattice structures. Periodic structures in general feature unique wave propagation characteristics, whereby waves are allowed to propagate only in specific frequency bands, while they are attenuated at frequencies belonging to the so-called "band gap". This behavior makes periodic structures attractive candidates as passive vibration isolators. The band-gap characteristics of a rectangular lattice are here investigated. An optimized configuration is found through a numerical model previously developed and presented. An aluminum specimen is manufactured by machining, and tested for validation and demonstration purposes. The wave field in the lattice is generated by a point harmonic excitation at various frequencies, and it is measured through a Scanning Laser Vibrometer. The objective of the tests is the validation of the numerical model and the demonstration of the unique filtering properties of the considered structural assembly.

Customer awareness and sensitivity to noise and vibration levels have been raised through increasing television advertisement, in which the vehicle noise and vibration performance is used as the main market differentiation. This awareness has caused the transportation industry to regard noise and vibration as important criteria for improving market shares. One industry that tends to be in the forefront of the technology to reduce the levels of noise and vibration is the automobile industry. Hence, it is of practical interest to reduce the vibrations induced structural responses. The automotive vehicle engine is the main source of mechanical vibrations of automobiles. The engine is vulnerable to the dynamic action caused by engine disturbance force in various speed ranges. The vibrations of the automotive vehicle engines may cause structural failure, malfunction of other parts, or discomfort to passengers because of high level noise and vibrations. The mounts of the engines act as the transmission paths of the vibrations transmitted from the excitation sources to the body of the vehicle and passengers. Therefore, proper design and control of these mounts are essential to the attenuation of the vibration of platform structures. To improve vibration resistant capacities of engine mounting systems, vibration control techniques may be used. For instance, some passive and semi-active dissipation devices may be installed at mounts to enhance vibration energy absorbing capacity. In the proposed study, a radically different concept is presented whereby periodic mounts are considered because these mounts exhibit unique dynamic characteristics that make them act as mechanical filters for wave propagation. As a result, waves can propagate along the periodic mounts only within specific frequency bands called the "Pass Bands" and wave propagation is completely blocked within other frequency bands called the "Stop Bands". The experimental arrangements, including the design of mounting systems with plain and periodic mounts will be studied first. The dynamic characteristics of such systems will be obtained experimentally in both cases. The tests will be then carried out to study the performance characteristics of periodic mounts with geometrical and/or material periodicity. The effectiveness of the periodicity on the vibration levels of mounting systems will be demonstrated theoretically and experimentally. Finally, the experimental results will be compared with the theoretical predictions.

An approach for introducing damping to the flexural vibration of rotating shafts is presented. The idea of the approach is simple and the implementation is novel. The idea is to introduce viscoelastic angular spring at the boundaries. The spring would stiffen up and damp out the bending fluctuation, and therefore would increase the frequency range of operation and alleviate the vibration amplitudes in the vicinity of resonance of the shaft. The idea is implemented by introducing carbon/polyurethane composite hyperboloid couplings at the boundaries (ends) of the shaft. The mathematical model of the coupling is developed and solved, using finite element, for the fundamental flexural natural frequency and associated loss factor. From the results, the merits and feasibility of applying the flexible coupling to alleviate the flexural vibration of rotating shafts are addressed.

In this work we describe the vibroacoustic behavior of a novel concept of core for sandwich structures featuring auxetic characteristics, enhanced shear stiffness and compressive strength compared to classical cellular cores in sandwich components for sandwich applications. The out-plane properties and density values are described in terms of geometric parameters of the honeycomb unit cells. Opposite to classical honeycomb cellular applications, the hexagonal chiral structure presents a noncentresymemetric configuration, i.e., a "mirror" symmetrical topology. The derived mechanical properties are used to assess the modal behaviour and modal densities of sandwich plate elements with chiral and standard cellular cores. The analytical findings are backed up by structural tests on chiral honeycomb plates and sandwich beams.

The work described in this paper relates to the evaluation of some of the parameters determining the impact response properties of flexible beams made from a foam-filled fluid which is a blend of elastomeric capsules or beads in a matrix fluid. When these composites are impacted, the pressure that develops inside the beam plays a role in the shock absorbing properties of the composite. The beam composition could vary as to the volume of beads, the type of beads, the viscosity and the volume of the matrix fluid. For this work the same type of beads and fluid are used for all the tests. However, different levels of constraint are applied on the flexible and expandable material used for the skin of the beams. This is done by increasing the number of layers of skin material. In this way a higher pressure is allowed to develop inside the beam at different increments of constraint levels. It is shown that as the level of constraint is increased, so does the pressure that develops inside the beam, and so do the shock absorption characteristics of the composite.

This paper looks at the use of viscoelastic damping pockets in the suppression of structural vibration. These are in the form of cavities filled with a viscoelastic material. The benefits and uses of these designed-in damping treatments are highlighted. The vibration responses of viscoelastically-damped beams are predicted using the finite element method. A series of cantilevered beams are considered and the damping performance of several configurations of designed-in dampers are predicted and compared to that of a traditional CLD treatment. It is shown that the effectiveness of the damping pockets and sinks depends on their location and size with respect to the highly stressed regions of the beams. Although there is a practical limit on the sizes of the geometrical features that can be designed-in, it is shown that if located correctly the damping pockets and sinks can be more effective at suppressing structural vibration than traditional CLD treatments.

This paper presents the mathematical modeling and predictive control of a magnetorheological fluid damper system. For the development of an effective controller precise modeling of the force-velocity characteristics of the MR damper is needed. Based on experimental data first the mathematical model for the MR damper is developed. Then a predictive controller is designed for the shock isolation of the payload mass. The design of the predictive controller is based on the optimization of a judiciously chosen performance index. The control input (electric current) is assumed to be bounded and positive for all time. Simulation results are presented which show that the developed mathematical model is effective in characterizing the behavior of the MR damper and the designed predictive controller is effective in the shock isolation of the payload.

Due to their character of low power requirement, rapid-response and large force, the dampers that made based on the special rheologic performance of magnetorheological fluid (MRF) have shown to be one kind of ideal semi-active vibration control devices for civil engineering structures and vehicles. In this paper, the character of magnetic circuit of MRF damper was firstly studied; based on above results, a large-scale MRF damper whose adjustable multiple is about 16 and maximum damping force is about 170kN was then designed and tested. Experimental results show that, under lower electrical current, same or opposite of electric current direction of multi-coils winding on the piston do not influence damping performance of MRF damper; however, under higher electrical current, inverse connecting of adjacent coils is apt to improve damping force of MRF damper.