Mechanical cryocoolers represent a significant enabling technology for precision space instruments by providing cryogenic temperatures for sensitive infrared, gamma-ray, and x-ray detectors. However, the vibration generated by the cryocooler's refrigeration compressor has long been identified as a critical integration issue. The key sensitivity is the extent to which the cooler's vibration harmonics excite spacecraft resonances and prevent on-board sensors from achieving their operational goals with respect to resolution and pointing accuracy. To reduce the cryocooler's vibration signature to acceptable levels, a variety of active vibration suppression technologies have been developed and implemented over the past 15 years. At this point, nearly all space cryocoolers have active vibration suppression systems built into their drive electronics that reduce the peak unbalanced forces to less than 1% of their original levels. Typical systems of today individually control the vibration in each of the cryocoolers lowest drive harmonics, with some controlling as many as 16 harmonics. A second vibration issue associated with cryocoolers is surviving launch. Here the same pistons and coldfingers that generate vibration during operation are often the most critical elements in terms of surviving high input acceleration levels. Since electrical power is generally not available during launch, passive vibration suppression technologies have been developed. Common vibration damping techniques include electrodynamic braking via shorted motor coils and the use of particle dampers on sensitive cryogenic elements. This paper provides an overview of the vibration characteristics of typical linear-drive space cryocoolers, outlines their history of development, and presents typical performance of the various active and passive vibration suppression systems being used.

This paper describes the application of active damping systems to the reduction of weight of aerospace electronics. Aerospace electronics are subject to extremely harsh vibratory environments throughout their service lives. Present methods of protecting and reinforcing circuit boards from vibration and their associated stresses and strains in such applications add significant weight to these electronic systems. The vibration protection they provide is crucial, however, as the nature of aerospace vehicles requires an extremely robust, durable design to prevent premature failure of any of the components of the electronics system. By directly mounting an active mass damping system onto each circuit board, it is possible to reduce significantly the weight and volume of the complete electronic circuit board system, while maintaining equal or superior vibration protection. This paper presents results of electronic circuit board active vibration reduction of damping sinusoidal excitations near resonance, free vibration damping, as well as future strategies for the active vibration control system.

A broad survey of current literature detailing the current state-of-the-art and future research trends in vibration isolation for current and proposed space systems is presented. Terminology for vibration control is first defined. Next, the vibration isolation problem is discussed taking into account nonlinearities of variable parameters. It is followed by a discussion of some current space specific applications, illustrating the tremendous importance of vibration control technology for space and the challenges these applications present. Next, a discussion of vibration control elements is provided. Finally, a summary of semi-active control strategies is presented and conclusions are drawn about the state of the art.

This paper is concerned with the development of an active vibration isolation device using PZT wafers. The main task of the device is to protect vibration-sensitive instruments from hazardous environments. The device developed in this study consists of S-shaped supporters bonded with PZT wafers, passive damping materials and piezoceramic sensors that can measure the relative motion between the base and the platform. The newly developed device can produce discernible displacement thus providing a way of counteracting external disturbances. Control techniques, which can fully utilize the functions of the device, are also developed. The experimental results show that the proposed device and the control techniques are capable of isolating vibrations thus useful in protecting sensitive instruments from external vibrations.

A tuned vibration absorber (TVA) is a spring-damper-mass system used in many industries for the suppression of a specific vibration frequency. A state-switched absorber (SSA) is similar to a TVA, except that one or more components in the SSA is able to instantaneously and discretely change properties, thus increasing the effective bandwidth of vibration suppression. The components responsible for bandwidth increase are called switching elements. In order to design a replacement SSA for the classic TVA, the SSA must operate in the appropriate frequency range, be lightweight and compact. An optimal SSA will also have a maximal frequency range that it can switch between. This paper discusses the development of a magnetorheological (MR) silicone gel used as the SSA switching element, the SSA geometry selected to maintain a magnetic flux path, and the contribution of the magnet-mass to frequency shifting. The MR gel is iron-doped silicone, cured in the presence of a magnetic field. During operation, the applied magnetic flux is modified to change the natural frequency. Since a flux path through the switching element is required, a steel flux path was incorporated as part of the SSA design. The SSA is desgined to operate below 100 Hz. An MR elastometer with 35% iron by volume yielded the most tunable results, where the minimum natural frequency was found to be 45 Hz, and the natural frequency was tunable up to 183 Hz.

This paper presents the design, testing, and application of a thin-film Magnetorheological (or simply MR) fluids damper/lock. This MR damper/lock is designed for the use in a model adaptive fan nozzle system actuated by shape memory alloy wires. The MR damper/lock (a total of 8 in the fan nozzle system) will lock the opening size of the fan nozzle and provides damping when the system vibrates. For this purpose, the MR damper/lock has to have the following characteristics: 1) The device is in lock position when power is off. 2) The device has a small static friction force (less than 1 lbf) when power is on. 3) The device generates a small kinetic friction force when it slides during power-on period. 4) Its damping coefficient can be adjusted. 5) Being compact. To meet these requirements, a new design of a damper/lock using thin MR fluid film is employed. The device consists of five major components: two soft steel bars, two stacks of permanent magnets, two groups of magnetic wires, a soft steel slider, and MR fluid. Utilizing the permanent magnets, the MR fluid is trapped and the device is always in lock position. When the device is powered on, the flux of the electrical magnets partially cancels and re-directs the rest of the flux from the permanent magnets, and then the slider is free to move. In this design, MR fluid reduces the air gap and increases locking force when it is powered off. On the other hand, it also functions as a lubricant to reduce the kinetic friction forces when it is powered on. Extensive tests of the MR damper/lock are conducted to reveal its force-displacement curves and force-velocity curves under different applied voltages. Utilizing these testing results, the MR damper/lock is applied to the model adaptive fan nozzle system to perform both locking and damping tasks with a feedback control. Experimental results show that these tasks are successfully achieved.

Dampers based on electrorheological (ER) and magnetorheolgical (MR) fluids can be analyzed under assumptions of quasi-steady, fully developed flow behavior. Models that have been used to characterize ER and MR dampers include the Bingham-plastic, the Herschel-Bulkley and biviscous models. In the Bingham-plastic and the Herschel-Bulkley models, the fluid exhibits rigid behavior in the preyield flow region. The difference between these two models lie in the modeling of the postyield behavior. In the case of the Bingham-plastic model, the postyield behavior is such that the shear stress is proportional to the shear rate. In contrast, the Herschel-Bulkley model assumes that the shear stress is proportional to a power law of the shearrate. In the biciscous model, the relationship between the shear stres and shear rate is linear in both the preyield and postyield regions with constant values of viscosities for the two regions. However, the preyield flow behavior exhibits a much high viscosity than that in the postyield. In the propose model, the assumption of preyield rigid behavior within the Herschel-Bulkley model has been relaxed while the postyield relationship based on the power law has been retained. Here the fluid undergoes Newtonian preyield viscous flow and has a non-Newtonian postyield behavior. Based on this model, we have analyzed the performance of a rectangular duct ER or MR valve. Typical results include shear stress and velocity profiles across the valve gap, equivalent damping and damping coefficients.

A key aspect of application of electrorheological (ER) and magnetorheological (MR) fluids is the characterization of rheological properties. For this purpose, two rotational viscometers are theoretically analyzed. One is a rotational coaxial cylinder viscometer, and the second is a rotational parallel disk viscometer. A key goal is to determine the shear stress and shear rate of ER/MR fluids for both viscometers from the torque and angular velocity data. To do this, the equations between shear stress and torque as well as shear rate and angular velocity are derived on the basis of the Bingham-plastic, biviscous, and Herschel-Bulkley constitutive models. For simplicity in mathematical form, the Bingham-plastic model is used to describe the flow behavior of ER/MR fluids. The biviscous model characterized by static and dynamic yield stresses is used to capture the preyield behavior. The preyield region where the local shear stress is smaller than the static yield stress has much larger viscosity than the postyield region. In order to account for the shear thinning or thickening in postyield region, the Herschel-Bulkley constitutive model is used in this study. The shear stress for a rotational coaxial cylinder viscometer can be calculated directly from measured torque. However, three approximation methods are applied to determine the shear rate. For rotational parallel disk viscometers, the shear rate and shear stress can be obtained directly from the torque and angular velocity data. In order to comprehensively understand the flow behavior of ER/MR fluids with respect to the constitutive models, the nondimensional analyses are undertaken in this study.

The main purpose of this study is to experimentally evaluate the dynamic performance of a semi-active Tuned Vibration Absorber (TVA) with a Magneto-Rheological (MR) damper. To this end, a test apparatus was built to represent a two-degree-of-freedom primary structure model coupled with a MR TVA. The primary structure mass, which is modeled with steel plates, was excited by a hydraulic actuator through four air springs. The air springs represent the stiffness of the primary structure and offer the ability to change the stiffness. The semi-active TVA consists of a steel plate, a MR damper, and four coil springs for physical representation of the mass, the damping element, and the stiffness of the TVA, respectively. Mounted on top of the primary structure, the TVA is connected to the primary structure plates by hardened linear bearing shafts. A series of transducers along with a data acquisition system was used to collect sensory information and implement real time control of the MR TVA. Using this test rig setup, a parametric study was performed to analyze the dynamics of the semi-active TVA and to compare the performance of the semi-active TVA with a passive TVA. Displacement based on-off groundhook (on-off DBG) control was used as the control policy for the semi-active TVA. In the parametric study, the effects of on/off-state damping of the MR damper were investigated and compared with a passive TVA to analyze the relative benefits of a semi-active TVA. When damping increased in the passive TVA, the two resonant peaks merge into one peak, and the peak grows. This indicates that the primary structure and TVA are linked together, disabling the TVA, and it eventually magnifies the vibrations. For a semi-active TVA, however, the two resonant peaks decrease as on-state damping increases (keeping low off-state damping), indicating reduction of vibrations. It is shown that semi-active TVAs outperform passive TVAs in reducing the peak transmissibility, implying that semi-active TVAs are more effective in reducing the vibrations of the primary structure.

Ferromagentic shape memory alloy composites exhibit good qualities as vibration absorbers. Loss ratios in excess of 25% have been measured in polymer samples containing 20 vol% Ni-Mn-Ga. The ability to dissipate large amounts of energy is due to the same mechanism that is also responsible for the large strains observed in single crystals used as actuators, namely twin-boundary motion. The loss ratios of the FSMA-loaded composites are compared to those for pure polymer samples and polymer loaded with inert filler. The effects of the pre-processing of the filler material on its performance are also shown.

A metallic closed cellular material containing organic materials for the smart materials has been developed. Powder particles of polystyrene coated with a nickel-phosphorus alloy layer using electroless plating were pressed into green pellets and sintered at high temperatures. A metallic closed cellular material containing organic materials was then fabricated. On the fabricated metallic closed cellular materials, compressive properties, Young's modulus, ultrasonic attentuation coefficient internal friction were measured. The compressive tests shows that this material has the different stress-strain curves among the specimens that have different thickness of the cell walls. Each stress-strain curve has a long plateau region, the sintering temperatures of the specimens affect the compressive strength of each specimen, and energy absorbing capacity is very high. Young's modulus of this material depends on the thickness of the cell walls and the sintering temperature. The attenuation coefficient of this material observed by ultrasonic measurement is very large. Internal friction of this material is very large and depends on the sintering temperaturer. These results indicate that this metallic closed cellular material can be utilized as energy absorbing material and passive damping material.

The paper presents a theoretical model of a passive magnetic suspension based on rare-earth permanent magnets; the aim is to minimize the dependence of the natural frequency of a single degree of freedom system on mass. In order to estimate magnetic interactions, the gradient of magnetic induction is evaluated by using a magnetic model based on the analogy of the equivalent currents method in a quasi-static open-circuit-type configuration. Therefore magneto-elastic forces between permanent magnets can be determined and compared with empirical formulas, applied in practical uses, and with experimental static tests. For a single degree of freedom system with variable mass, static configuration and dynamic behavior are evaluated for classic linear elastic systems, for purely magnetic suspensions and for a combination of the two. In particular the dynamics of the magneto-mechanic interaction by use of nonlinear and linearized models are investigated for non-zero initial conditions, in order to underline the influences of nonlinearities on the system response. Finally, the single degree of freedom system frequency response is presented for different values of the geometrical and inertial properties of the system, thus demonstrating the insensibility of resonance with respect to mass.

The study of piezoceramic and piezoelectric transducers behavior by finite element method (FEM) shows an important influence of viscous damping. Damping values for piezoceramic materials are not provided by manufacturers. In addition, damping values for non-piezoelectrics materials, such as, resins, steel, aluminum, etc, which are usually applied to assemble these transducers are not appropriately given for FEM simulations. Therefore, the objective of this work is to determine damping values of these materials so they can be used in a FEM software, such as, the ANSYS, which has four different ways for damping input. Damping values are determined by combining experimental and numerical techniques. For piezoceramics the damping is determined through the quality factor (Qm) by measuring the admittance curve which are influenced by damping. By using these damping values, harmonic and transient FEM simulations of piezoceramics and piezoelectric transducers are performed and the simulated admittance curve is compared with the measured one, as well as, displacement results are compared with laser interferometer measurements. Damping determination for non-piezoelectric materials are done by comparing experimental and simulated results. By using the obtained damping values, experimental measurements and simulated results for different piezoelectric transducers show a very good agreement.

During the March 2002 Servicing Mission by Space Shuttle (STS 109), the Hubble Space Telescope was refurbished with two new solar arrays that now provide all of its power. These arrays were built with viscoelastic/titanium dampers, integral to the supporting masts, which reduce the interaction of the wing bending modes with the Telescope. Damping of over 3% of critical was achieved. To assess the damper's ability to maintain nominal performance over the 10-year on-orbit design goal, material specimens were subjected to an accelerated life test. The test matrix consisted of scheduled events to expose the specimens to pre-determined combinations of temperatures, frequencies, displacement levels, and numbers of cycles. These exposure events were designed to replicate the life environment of the damper from fabrication through testing to launch and life on-orbit. To determine whether material degradation occurred during the exposure sequence, material performance was evaluated before and after the accelerated aging with complex stiffness measurements. Based on comparison of pre- and post-life-cycle measurements, the material is expected to maintain nominal performance through end of life on-orbit. Recent telemetry from the Telescope indicates that the dampers are performing flawlessly.

Multiwalled carbon nanotube thin films were fabricated using catalytic chemical vapor deposition of xylene-ferrocene mixture precursor. The nanotube films were employed as inter-layers within composite systems to reinforce the interfaces between composite plies, enhancing laminate stiffness as well as structural damping. Experiments conducted using a piezo-silica composite beam with an embedded nano-film sub-layer indicated up to 200% increase in the inherent damping level and 30% increase in the baseline bending stiffness with minimal increase in structural weight. Scanning Electron Microscopy (SEM) characterization of the nano-film was also conducted to investigate the mechanics of stiffness and damping augmentation. The study revealed a fascinating network of densely packed, highly interlinked multiwalled nanotubes (MWNTs). This inter-tube connectivity resulted in strong interactions between adjacent nanotube clusters as they shear relative to each other causing energy dissipation within the nano-film. Molecular Dynamics (MD) simulations confirmed that inter-tube interaction was the dominant mechanism for damping within the nano-film layer. The cross-links between nanotubes also served to improve load transfer within the network resulting in improved stiffness properties.

Space systems comprise sensitive electronics and delicate mechanical instruments that need to be protected against harsh vibration and shock loads encountered during launch or landing. High damping viscoelastic materials are often used in the design of geometrically complex, shock and vibration isolation components. Since shock transients are characterized by a broad frequency spectrum, and since viscoelastic materials are characterized by frequency-dependent mechanical properties, it is necessary to properly model this behavior over the frequency domain of interest. The Anelastic Displacement Fields (ADF) method is employed herein to model frequency-dependence of material properties within a time-domain finite element framework. A solid, four-node tetrahedron, ADF-based finite element is developed for single and multiple ADF. This particular element is then validated and used for the general purpose of investigating damping in given structures that employ viscoelastic materials. The new three-dimensional finite element may also be used to investigate the potential phase dependence of the Poisson's ratio for such materials. The model predictions are compared against theory.

Smart fluid dampers offer an attractive solution to vibration damping problems where there is a need for variable damping behaviour. In recent years there has been a great deal of research effort in developing these dampers, and implementing appropriate control strategies. Consequently a wide range of modelling techniques have been proposed, for both device design and controller design processes. In general, however, the development of modelling and control techniques has proceeded in parallel to the development of laboratory-based devices. Consequently the techniques become well suited to those particular devices, and their performance in a more generic device design process may not be guaranteed. A more thorough method of illustrating the performance of models would be to investigate their performance when based upon different devices. This would help to emphasise the strengths and potential weaknesses of the model when used in a generic device design process. In this paper, the authors will seek to assess the robustness of a modelling technique by assessing its performance when based upon an 'unrelated' damper design from a different research group.

Conventional magnetorheological fluids are suspensions of micron sized particles in a hydraulic or silicone oil medium. Recently, research has been conducted into the advantages of using bidisperse fluids, which is a mixture of two different powder sizes in the MR suspension. The MR fluids investigated here use a mixture of conventional micron sized particles and nanometer sized particles. The settling rate of such bidisperse fluids using nanometer sizes particles is reduced because of thermal convection and Van der Waals experienced by the nanometer sized particles compete favorably with gravitational forces. This reduction in the settling rate comes at a cost of a reduction in the maximum yield stress that can be manisfested by such an MR fluid. There is a measurable and predictable variation in rheological properties as the weight percent of the nanometer sized particles is increased, relative to the weight percent of micron sized particles, while maintaining the solids loading in the MR fluid as a constant. In this context, this study investigates the effect of varying the weight percent of nanometer sized particles on rheological characteristics such as yield stress and postyield viscosity. The goal of this study is to find an optimal composition of the bidisperse fluid to obtain best combination of high yield stress and low settling rates based on empirical measurements. The applicability of rheological models, such as the Bingham-plastic and the Hershel Buckley models, to the measured flow curves of these MR fluids is also presented.

Magnetorheological (MR) fluid damper design typically constitutes a piston/dashpot configuration. During reciprocation, the fluid is circulated through the device with the generated pressure providing viscous damping. In addition, the damper is also intended to accommodate off-axis loading; i.e., rotation moments and lateral loads orthogonal to the axis of operation. Typically two sets of seals, one where the piston shaft enters and exits the device and one between the piston and the cylinder wall, maintain alignment of the damper and seal the fluid from leaking. With MR fluid, these seals can act as sources of non-linear friction effects (stiction) and oftentimes possess a shorter lifespan due to the abrasive nature of the ferrous particles suspended in the fluid. Intelligently controlling damping forces must also accommodate the non-linear stiction behavior, which degrades performance. A new, unique MR fluid isolator was designed, fabricated and tested that directly addresses these concerns. The goal of this research was the development of a stiction-free MR isolator whose damping force can be predicted and precisely controlled. This paper presents experimental results for a prototype device and compares those results to model predictions.

Theoretical and experimental studies are performed for the design, development and testing of a new fail-safe semiactive magneto-rheological fluid (MRF) damper for a high-mobility multi-purpose wheeled vehicle (HMMWV). A fail-safe MRF damper is referred to as a device, which retains a minimum damping capacity required in the event of a power supply or electronic system failure. The proposed MRF damper is designed using a disk shape magneto-rheological (MR) valve. The MR valve occurs in the space between two fixed parallel disks with radial flow. Bingham plastic fluid model and a three-dimensional finite element electro-magentic analysis are employed to theoretically analyze the proposed MRF damper. Experimental and theoretical results are presented for force-displacement and force-time behavior of the damper under different harmonic input motion and various input magnetic fields.

Passive shunt damping involves the connection of an electrical shunt network to a structurally attached piezoelectric transducer. In recent years, a large body of research has focused on the design and implementation of shunt circuits capable of significantly reducing structural vibration. This paper introduces an efficient, light weight, and small-in-size technique for implementing piezoelectric shunt damping circuits. A MOSFET half bridge is used together with a signal processor to synthesize the terminal impedance of a piezoelectric shunt damping circuit. Along with experimental results demonstrating the effectiveness of switched-mode shunt implementation, we discuss the design of a device aimed at bridging the gap between research in this area and practical application.

The characteristics of multiple tuned-mass dampers (MTMDs) attached to a single-degree-of-freedom primary system have been examined by many researchers, and several papers have included some parameter optimization. In this paper, we propose an efficient numerical algorithm to optimize the stiffness and damping of each of the tuned-mass dampers (TMDs) in such a system directly. We formulate the parameter optimization as a decentralized H2 control problem where the block-diagonal feedback gain matrix is composed of the stiffness and damping coefficients of the TMDs. The gradient of the root-mean-square (RMS) response with respect to the design parameters is evaluated explicitly, and the optimization can be carried out efficiently. The effects of the mass distribution, number of dampers, total mass ratio, and uncertainties in system parameters are studied. Numerical results indicate that the optimal designs have neither uniformly spaced tuning frequencies nor identical damping coefficients, and that optimization of the individual parameters in the MTMD system yields a substantial improvement in performance. We also find that the distribution of mass among the TMDs has little impact on the performance of the system provided that the stiffness and damping can be individually optimized.

Several electric vibration absorbers based on distributed piezoelectric control of beam vibrations are studied. The damping devices are conceived by interconnecting with different modular electric networks an array of piezoelectric transducers uniformly distributed on a beam. Five different vibration absorbers made of five different network interconnecting topologies are considered and their damping performances are analyzed and compared. The analysis is based on homogenized models of modular piezo-electromechanical systems. The optimal parameters of these absorbers are found by adopting the criterion of critical damping of waves with a single wave number. We show that: i) there is an interconnecting network providing an optimal multimodal damping; ii) the performances required to the electr(on)ic components can be significantly decreased by increasing the number (and decreasing the dimensions) of the piezoelectric transducers.

Piezoelectric transducers are known to exhibit less hysterisis when driven with current or charge rather than voltage. Despite this advantage, such methods have found little practical application due to the poor low frequency response of present current and charge driver designs. This paper introduces the compliance feedback current driver containing a secondary voltage feedback loop to prevent DC charging of capacitive loads and to compensate for any voltage or current offsets in the driver circuit. Low frequency bandwidths in the milli-Hertz range can be achieved.

A 400kN magnetorheological damper (MR damper) for a real base-isolated building was developed and its dynamic characteristics were verified by experimental tests. The MR damper has 950mm (+/-475mm) stroke and by-pass flow potion. A new type of Magneorheological fluid is also developed in order to apply to the MR damper. MR fluid had a property of the settlement of particles in dampers. Authors developed a new MR fluid, which keeps the particles in the fluid adequately enough for usual use of MR damper. Analytical model was discussed in this paper. The force by the bingham visco-plastic model was compared with the results of experimental tests. It was found that this analytical model is useful to predict the capacity of the MR damper.

In this paper, a seismic control method of structures with the tuned liquid column damper (TLCD) is presented by using artificial neural networks. The passive TLCD in the approach is converted into a semi-active variable damping system. The equation of motion for the TLCD-structure interactive system are derived and relevant control algorithm is developed by adjusting the area of orifice-opening in the TLCD and making use of neural networks with BP algorithm. The numerical results of system subjected to earthquake excitations show that the intelligent control approach introduced herein is effective.

The shaking table tests are carried out to examine the seismic responses of rocking structural systems with yielding base plates (base plate yielding systems). When subjected to a strong earthquake ground motion, these systems can cause rocking vibration with base plate yielding to reduce the seismic responses of buildings. In the tests, the seismic responses of test frames are compared with those of fixed-base systems and simple rocking systems. The test frames are the steel frames of one-third scale which have one bay and five stories. The total height and width are 5 and 2 meters, respectively. In tests of the base plate yielding systems, the yielding base plates are attached at the bases of these frames. Furthermore, to predict the seismic responses of base plate yielding systems, such as up-lift displacements, base shears and roof displacements, we propose a simple prediction method using an equivalent single degree-of-freedom (SDOF) system. It is concluded that the base plate yielding systems can reduce effectively the seismic response of building structures and their seismic responses are predicted by the proposed method appropriately.

We are now developing the rocking structural system that can reduce earthquake responses of building structures by causing rocking vibration on them under appropriate control. This paper examines applicability of this system to building structures based on case studies using four realistic steal planer frame models which have 5 stories and 1 bay. All models have the same height and width, which are 18 m and 6 m respectively. But they have the different first natural period. These values range from 0.384 s to 0.729 s. The case studies are executed using a numerical simulation method. Furthermore, we propose simple prediction method for earthquake responses of the rocking structural systems using the equivalent one mass model. It is concluded that the rocking structural systems can reduce seismic responses of building structures effectively, and these response values can be predicted by the proposed method appropriately.

The resonance phenomenon often imposes limitations in structural design when loads have variable frequency. Components exhibiting variable stiffness allow enlarging the range of frequencies that the structures can undergo without the risk of resonance. The layout of tunable-stiffness bushing system proposed in this paper consists of a typical rubber silent-block working in parallel to a circular array of Ni-Ti wires which, changing from their martensitic state to the austenitic one, induce significant variations in the load-displacement response of the entire supporting system. The versatility of the configuration is due to the possibility to activate the wires in various combinations, extending the range of stiffness values obtainable with respect to the case of a single Ni-Ti component. Both numerical simulations and experimental tests conducted on a prototype of the support indicated that interesting performances could be achieved with the proposed bushing structure.

A hexapod strut at the University of Wyoming currently exhibits high resonant modes at 3 kHz and above. To reduce these resonant peaks, the current aluminum rod of one of the struts was redesigned. A graphite/epoxy granularly filled composite tube was designed and incorporated into the strut. Reduction in the resonant peaks of up to 32 dB’s was achieved. Six of the above mentioned composite tubes were fabricated and incorporated into the hexapod. Testing showed considerable improvement in overall damping for the hexapod.

The active silicon microstructures known as Micro-Electromechanical Systems (MEMS) are improving many existing technologies through simplification and cost reduction. Many industries have already capitalized on MEMS technology such as those in fields as diverse as telecommunications, computing, projection displays, automotive safety, defense and biotechnology. As they grow in sophistication and complexity, the familiar pressures to further reduce costs and increase performance grow for those who design and manufacture MEMS devices and the engineers who specify them for their end applications. One example is MEMS optical switches that have evolved from simple, bistable on/off elements to microscopic, freelypositionable beam steering optics. These can be actuated to discrete angular positions or to continuously-variable angular states through applied command signals. Unfortunately, elaborate closed-loop actuation schemes are often necessitated in order to stabilize the actuation. Furthermore, preventing one actuated micro-element from vibrationally cross-coupling with its neighbors is another reason costly closed-loop approaches are thought to be necessary. The Laser Doppler Vibrometer (LDV) is a valuable tool for MEMS characterization that provides non-contact, real-time measurements of velocity and/or displacement response. The LDV is a proven technology for production metrology to determine dynamical behaviors of MEMS elements, which can be a sensitive indicator of manufacturing variables such as film thickness, etch depth, feature tolerances, handling damage and particulate contamination. They are also important for characterizing the actuation dynamics of MEMS elements for implementation of a patented controls technique called Input Shaping®, which we show here can virtually eliminate the vibratory resonant response of MEMS elements even when subjected to the most severe actuation profiles. In this paper, we will demonstrate the use of the LDV to determine how the application of this compact, efficient algorithm can improve the performance of both open- and closed-loop MEMS devices, eliminating the need for costly closed-loop approaches. This can greatly reduce the complexity, cost and yield of MEMS design and manufacture.

Wave-absorption control with online simulation of an imaginary system is applied to 1-dimensional periodic body-and-spring system and flexible structures, rope and beam, approximating as lumped systems by using the finite difference method. Wave-absorption control with imaginary system, where the controller is installed near fixed boundary, is effective and practical to suppress the vibration, which is not realized by conventional mode-based vibration control method. Experimental results on rope system have shown the effectiveness of the present method.

This paper introduces electromagnetic shunt damping (EMSD) which is similar to piezoelectric shunt damping. EMSD has four major advantages over piezoelectric shunt damping; simple transducer manufacturing, smaller shunt voltages, long stroke and larger control forces. A novel single mode shunt control strategy is validated through experimentation on a simple electromagnetic mass spring damper system. Theoretical results are also presented.

This paper introduces a new multiple mode passive piezoelectric shunt damping technique. The robust passive piezoelectric shunt controller is capable of damping multiple structural modes and maybe less susceptible to variations in environmental conditions that can severely effect the performance of other controllers. The proposed control scheme is validated experimentally on a piezoelectric laminated plate structure.

The power requirements imposed on an active vibration control system are quite important to the overall system design. In order to improve the efficiency we analyze different feedback control strategies which will provide electrical energy regeneration. The active isolation system is modeled in a state-space form for two different types of actuators: a piezoelectric stack actuator and a linear electromagnetic (EM) actuator. During regenerative operation, the power is flowing from the mechanical disturbance through the electromechanical actuator and its switching drive into the electrical storage device (batteries or capacitors). We demonstrate that regeneration occurs when controlling one or both of the flow states (velocity and/or current). This regenerative control strategy affects the closed loop dynamics of the isolator which sees its damping reduced.

Recently the concept of Piezo-Electro-Mechanical (PEM) structural member has been developed. Given a structural member, a set of piezoelectric actuators if uniformly distributed on it and electrically interconnected by one of its analog circuits. In this way it is obtained a high-performances piezoelectric structural-modification aiming to multimodal mechanical vibrations control. In the present paper it is addressed the problem of synthesizing an electrically dissipative PEM Kirchhoff-Love (K-L) plate by using completely passive electric networks.

An intelligent control system has the ability to learn about its environment, process the information to reduce uncertainty, plan, generate and execute actions to either control or reduce to a minimum the undesired motion of all or some of its parts. It generally incorporates sensors, actuators, a controller and a power supply unit. Most of the previous work has focused on active control in which electric power is supplied to the actuators that exert actions on the host structure to suppress its vibrations. Alternatively, undesired mechanical energy of a host structure could be converted into electrical energy that can be dissipated through a set of resistor. This does not require an external power unit and is a more economical means of controlling vibrations of a structure, but an effective transduction of mechanical energy into electric energy has to be guaranteed. Such an effective transduction can be achieved imposing to the electric controller to be resonant at all the mechanical resonance frequencies, and to mimic all the mechanical modal shapes, i.e. to be the analog of the host structure. In this paper we synthesize a completely passive electric circuit analog to an Euler beam, aimed for distributed vibration control.

In this paper, we study vibration damping in structures coupled to low-density media (such as powder or foam) in which the speed of sound propagation is relatively low. The results of several experiments in which flexural vibration of aluminum beams over a broad frequency range is damped by the introduction of a layer of lossy low-wave-speed foam are presented. We find that at frequencies high enough to set up standing waves through the thickness of the foam, damping coefficients as high as 0.07 can be obtained with a foam layer whose mass is 3.9% of that of the beam. Next, a model is presented for the flexural dynamics of coupled beam-foam systems in which we treat the foam material as a continuum in which waves of dilatation and distortion can propagate. Approximate solutions for the frequency response of the primary beam are obtained by means of a modal expansion, and the results are in close agreement with the measured responses.

A new way to perform vibration control on a single-degree-of-freedom system using a piezoelectric friction damper is developed. The damper consists of an actuator, which is based on a piezoelectric stack with a mechanical amplifying mechanism that provides symmetric forces within the isolator. The advantages of such an actuator are its high bandwidth, actuating response and its ability to operate in vacuum environments such as in space. The damper is constrained to move using an air bearing that produces a virtually ideal single-degree-of-freedom spring-mass system. Within this work, the actuating ability of the friction-based actuator is characterized. The relationship between the force generated by the actuator and the applied voltage was found to be linear. The maximum force generated by the friction damper in this study is 85 N for the specific friction pads used.

In this paper, the governing equations of space nonlinear vibration for a stay-cable with viscous dampers are first derived. Bending stiffness, static sag and geometric non-linearity of cable are taken into account. The partial differential equations are discretized in space by the finite center difference approximation, then the nonlinear ordinary differential equations are obtained. A hybrid method involving the combination of the Newmark method and the pseudo-force strategy is proposed to analyze the nonlinear transient response of stay-cable with viscous dampers under arbitrary dynamic loading. The proposed method offers some advantages of accuracy and efficiency to deal with nonlinearity. Numerical examples including the short cable and the long cable under arbitrary loads are carried out to demonstrate the applicability of the proposed method and to verify the control efficiency of in-plane and out-of-plane coupling vibration of stay-cable attached viscous dampers

The data of previous researchers on the structure formation of electrosensitive suspensions under the action of an external electric and on the resulting changes in the mechanical parameters of the medium (viscosity, plasticity, resilience) were used to develop a method of damping in a special cluthes, which were used for fixing thin-wall constraction, that surfaces are to undergo fine turning. As demonstrated, the use of a fluid, the structure of which responds to an electric field, as a cluthing layer improves the technological characteristics of the product and increase its reliability.

In this paper we present a digital control system designed to damp the mechanical motion of a suspended mass. The control system is based on optical levers for reading the position of the mass with respect to some fixed references. The reading system was implemented by using a laser beam, produced by a commercial laser diode, and two position sensing photodiodes as components. The laser light is reflected from the suspended mass and the reflected beam is sent to the position sensing photodiode. Each beam can be used to control more than one degree of freedom of the mass by simply using a suitable optical arrangement to uncouple translation and rotational motions. The digital control system is based on both standard linear signal filtering and on a non linear section. The latter is necessary to solve particular situations, like the very large motion, a situation in which standard control system techniques are often not adequate. Moreover the control system has to take into account all the degree of freedom of the suspended mass, also to avoid the excitation of some extra resonance due to the coupling of the different motions.

This study deals with a shake table test on a three-story base-isolated steel frame. The frame rests on four roller bearings for isolation and is equipped with four laminated rubbers as shear spring. An MR damper is used in the test to perform semi-active seismic response control. The basic control algorithm applied in the study is to simulate the load-deflection of an origin-restoring friction damper (ORFD) which is a sort of friction damper that looses its resistance when it moves toward the origin, making sure for the base-isolated system to minimize residual displacement even after an extremely strong ground motion. Also attempted is a hybrid type control that superposes viscous damping on the ORFD when the damper moves from the peak displacement toward the origin.

This paper presents an experimental investigation on the acoustic properties of a novel concept of auxetic (Negative Poisson's ratio) open cell polyurethane gray foam for dynamic crash loading applications. The acoustic absorption coefficients and real and imaginary part of the specific acoustic impedance have been measured with an ASTM standard impedance tube using a transmissibility technique. The foam shows a significant increase of the absorption properties in the low frequency range compared to equivalent conventional open cell foams. The acoustic properties of the foams are identified using an empirical model to describe their structural characteristic.

Space flight experiment test results of a Space Station Active Rack Isolation System (ARIS) are presented. The purpose of ARIS is to isolate microgravity sensitive science experiments mounted in Space Station racks from structural vibrations present on the large Space Station orbital structure. The overall objectives of the experiment were 1) to test and evaluate the ARIS design modifications made from 1997 to 2000 as a result of prototype flight testing performed on the Space Shuttle Atlantis, 2) to characterize isolation performance on the International Space Station, 3) to assess the impact that rack payload disturbances have on the microgravity environment, 4) to test alternative umbilicals designed to improve isolation performance, and 5) to gain on-orbit operational experience and validate procedures. The scope of the material presented is limited to microgravity performance issues, so only results related to the first four objectives are presented. Over a year of flight testing was completed, and ARIS consistently has performed extremely well such that station vibrations were isolated to levels well below the science requirement.