Spacecraft are subjected to shock loads in the several thousands of g's level during their trip to orbit. These high shock loads usually result from some separation event, such as staging, spacecraft separation, and fairing separation. Shock loads are very detrimental to spacecraft components, instruments and electronics. A new type of shock isolation system is discussed. This shock system, referred to as the SoftRide ShockRing, is a whole-spacecraft isolation system, i.e., it shock isolates the complete spacecraft from the launch vehicle. Seven whole-spacecraft vibration isolation systems (SoftRide) have flown to date and flight data confirms large reductions of the dynamic loads on the spacecraft. The standard SoftRide system is a lower frequency isolation system than the ShockRing, vibration isolating the spacecraft starting in the approximately 25 Hz range. The ShockRing is targeted at shock loads and is set to isolate above approximately 75 Hz. Component tests have been performed on the ShockRing using a specially built pneumatic gun that can generate 10,000 g's on the test article. Results from these tests demonstrate substantial reductions of the shock being transmitted to the payload. Results from a system test consisting of a spacecraft simulator, payload attachment fittings, avionics section, and shock plate are discussed. In the system tests, pyrotechnic devices were used to obtain the high levels of shock for the tests.

An analytical beam-type model of an inflatable, piezoactuated, cantilever tube is developed. Perturbation methods are utilized to determine the system response. The results are compared to experimental data.

A NASA research program is underway to develop fan blades that have significantly greater propulsive efficiency, lower acoustic noise, and lower weight. These blades have a large internal manifold and open trailing edge that is used to blow air in the downwash. The blades are composed of a titanium root and composite internal manifold with an outer graphite/epoxy shell. Due to the complex internal structure and open-cell design, these blades have low natural frequencies and bending-torsion coupled mode shapes that could potentially lead to aeroelastic instabilities. Increasing the damping levels in these blades will improve the fatigue life and reduce aeroelastic instability concerns. The vibratory modes of interest include the first and second bending modes as well as first torsion mode. Due to the geometric constraints of the outer blade shape and large internal manifold very little room is available for damping treatment placement. Results from the analysis study reveal that (1) significantly more damping can be obtained by embedding the material in the outer shells than within the manifold vanes, (2) carefully designing a patch that fills approximately 29% of the surface area and is only 0.005' thick will produce a loss factor of at least 0.01 for the first three structural modes, and (3) a patch that fills approximately 45% of the surface area will produce a loss factor of at least 0.02 for the first three structural modes.

In this paper different numerical techniques are suggested to improve the prediction of natural frequencies and modal loss factors of structures with viscoelastic damping. The suggested methods involve the use of classical Finite Element mass and stiffness matrices and the knowledge of the undamped modal basis of the system. One technique is based is based on a dyadic matrix perturbation approach that gives control over the approximation sought for the natural frequencies and modal loss factors. Unlike other perturbation techniques, the proposed method does not involve the solution of linear system equations. Two other methods suggested involve IRS techniques that use either static or low frequency reduction with weighted damping to condense the full complex eigenvalue system into a real one. During the solution spurious modes are eliminated via a modified Modal Assurance Criteria. All the proposed methods give good approximations of the exact complex solutions without the need for a complex eigensolver and therefore can be used with existing eigensolution routines available in commercial FE codes.

In traditional modal strain energy method, the real eigen-vector of each mode obtained from finite element analysis of the corresponding undamped structure is used to calculate modal strain energy in each material layer, and an iterative approach is used in dealing with the frequency dependency of viscoelastic materials. In this paper, a revised modal strain energy method is presented to significantly improve analysis accuracy of the structural natural frequencies and modal loss factors when the material loss factor is high, and a simplified approach is recommended to replace the iterative analysis to avoid tremendous amount of computational effort.

Constrained layer damping (CLD) methods provide significant damping in laminated composite materials in bending modes. CLD treatments also provide damping mechanisms in axial modes in structures with significant free edges. Where free-edges are absent such as in cylinders or plates with fixed edges, the damping of axial modes in the structure is limited and damping of bending modes is reduced. This paper investigates an alternate passive geometric treatments that improve damping in constrained layer composite materials. In particular, the effect of including strategically-placed geometric anomalies or wrinkles in laminated composite materials is presented. Correct placement of the anomalies result in increased damping in axial modes due to the three-dimensional stress state created in the viscoleastic layer near the anomaly. Because this method does not depend on strain energies created at the free edge, effective damping of axial modes in cylinders may be realized. A closed-form solution is derived that can be used to conduct parametric design studies. Design parameters include defect placement, defect geometry, and composite material properties.

A finite element model is developed to study the dynamics properties, vibration, shock and acoustics performance of constrained layer damping treated covers for hard disk drives (HDD). The ever-increasing storage density of HDD requires smaller vibration level of HDD components, especially the storage disks inside. In the mean time, tighter vibration, shock and acoustics specifications are required by customers. In practice, it is found that the vibration of the storage disks and the shock/vibration and acoustics performance of HDD are closely related to the properties of the HDD covers. The existence of viscoelastic materials (VEM) inside the HDD covers makes them hard to analyze and the complex modulus provided by VEM manufactures can only be utilized in frequency domain. In this paper, the VEM properties are fitted with GHM (Golla, Hughes and McTavish) parameters so that a complex eigenvalue analysis can be performed to extract modal frequencies and damping of the cover. Parametric study is conducted to understand how some essential design parameters affect the dynamics properties of the cover. Vibration/shock and acoustics responses of the cover are also simulated to provide insights for HDD cover design.

Cellular structures like honeycombs or reticulated micro-frames are widely used in sandwich construction because of their superior structural static and dynamic properties. Aim of this study is to evaluate the dynamic behavior of bi-dimensional cellular structures, with focus on the effect of the geometry of the unit cell composing the solid on the dynamics of the propagation of elastic waves within the structure. The characteristics of wave propagation for the considered class of cellular solids are analyzed through the Finite Element model of the unit cell and the application of the theory of periodic structures. This combined analysis yields the phase constant surfaces, which define the directions of wave propagation in the plane of the structure for assigned frequency values. The analysis of iso-frequency contour lines in the phase constant surfaces allows predicting the location and extension of angular ranges, and therefore regions within the structures, where waves do not propagate. The performance of honeycomb grids of regular hexagonal topology is compared with that of grids of various geometries, with emphasis on configurations featuring a negative Poisson's ratio behavior. The harmonic response of the considered structures at specified frequencies confirms the predictions from the analysis of the phase constant surfaces and demonstrates the strongly spatial dependent characteristics of periodic cellular structures. The presented numerical results indicate the potentials of the phase constant surfaces as tools for the evaluation of the wave propagation characteristics of this class of two-dimensional periodic structures. Optimal design configurations can be identified in order to achieve desired transmissibility levels in specified directions and to obtain efficient vibration isolation capabilities. The findings from the presented investigations and the described analysis methodology will provide invaluable guidelines for the prototyping of future concepts of honeycombs or cellular structures with enhanced vibro-acoustics performance.

The dynamic vibration absorber (DVA) is a passive vibration control device which is attached to a vibrating body (called a primary system) subjected to exciting force or motion. In this paper, we will discuss an optimization problem of the three- element-type DVA on the basis of the H₂ optimization criterion. The objective of the H₂ optimization is to reduce the total vibration energy of the system for overall frequencies; the total area under the power spectrum response curve is minimized in this criterion. If the system is subjected to random excitation instead of sinusoidal excitation, then the H₂ optimization is probably more desirable than the popular H_(infinity ) optimization. In the past decade there has been increasing interest in the three-element type DVA. However, most previous studies on this type of DVA were based on the H_(infinity ) optimization design, and no one has been able to find the algebraic solution as of yet. We found a closed-form exact solution for a special case where the primary system has no damping. Furthermore, the general case solution including the damped primary system is presented in the form of a numerical solution. The optimum parameters obtained here are compared to those of the conventional Voigt type DVA. They are also compared to other optimum parameters based on the H_(infinity ) criterion.

Modern tank guns, such as the one on the Abrams, are stabilized to allow fire on the move while traversing uneven terrain. The current barrel is short enough that treating as a rigid beam allows engagement of another tank at ranges of over a kilometer. However, as the length of the tube is extended, to meet required muzzle exit velocities, the terrain induced vibrations lead to increased muzzle pointing errors. A method to reduce these vibrations is to use the forward thermal shroud as part of a mass tuned damper. In this case the system under study is an extended length version of the gun currently fielded. This extended length increases its susceptibility to terrain-induced vibrations. The forward thermal shroud has been shortened and additional mass has been added onto its forward collar. This collar is then supported by springs, which are preloaded so that they stay in contact through the full range of the shroud's movement. Varying the stiffness of these springs allows for tuning of the absorber. Different types of springs and attachments have been tried. The current version uses leaf springs and a wedge collar. This system has been modeled and experiments conducted to validate the model.

Many methods have been developed for the design of a single-degree-of-freedom (SDOF) vibration absorber to damp SDOF vibration since Den Hartog presented his fixed points method in 1928. But a rigid body employed as a vibration absorber will in general have six degrees of freedom relative to a structure. By taking full advantage of the inertia of the body, we can damp as many as six modes, or make the system more robust or compact. In this paper, we present a two-step method for optimization of the stiffness and damping of a multi-degree-of-freedom connection between a reaction mass and a vibrating structure: First, treating the reaction mass as a perturbation to the vibrating structure, we obtain an approximate design. Second, we adapt a descent-subgradient method to fine-tune the design by maximizing the minimal damping over a prescribed frequency range.

The power requirements imposed on a active vibration isolation system are quite important to the overall system design. In order to improve the efficiency of an active isolation system we analyze different feedback control strategies which will provide an electrical energy regeneration. In this case, 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 current). This regenerative control strategy also affects the closed loop dynamics. The regenerative control applied to a voice-coil actuator results in a closed loop system which has a reduced amount of damping compared to the initial system. In fact the regenerative control strategy will increase the level of vibration compared to the closed electrical circuit boundary condition in order to make the system absorb more energy, of which a part is transferred to an electrical storage device.

A new concept, the Passive Remote Electromechanical Dynamic Absorber (RDA) is investigated. The current design utilizes piezoelectric elements to convert the mechanical strain energy of a parent system into electrical energy, which is fed into the RDA. The RDA similarly uses piezoelectric elements to convert the applied electrical energy into mechanical self-excitation and vice versa. A lumped-system model of the coupled system is developed, accounting for the stiffness and mass of both the parent and RDA systems, along with a coupling stiffness term. Additionally, a three dimensional coupled-system finite element model is developed in ANSYS/Multiphysics. Experimental work is conducted to validate the concept of the lumped system model and to validate the finite element modeling technique. A reasonable correlation exists between the experimental results and the analytical predictions. Finite Element Analysis (FEA) provides a reasonable prediction of the RDA performance. Furthermore, analytical predictions of the RDA show a successful reduction of the parent response by up to ~30 db, in a narrow frequency band around its uncoupled resonant frequency. The overall qualitative agreement between the analytical and the experiment confirm the validity and potential of the proposed RDA for vibration suppression of dynamic systems.

It is common to use piezoelectric materials to reduce vibrations or otherwise alter the dynamics of structures made of metal or composite materials. In contrast, this work addresses modeling of piezoelectric patches applied to a rubber substrate. An underlying goal of modeling, however, is to represent the significant physics of a problem with the simplest model possible. There were several simplified approaches to modeling piezoelectric actuation on classical beam and plate elements developed in the late 1980's and early 1990's. Of these, the pin force, extended pin force, and Euler-Bernoulli methods are assessed in this study. The basic concepts of the three approximation methods are developed, and the curvatures predicted by each is compared to predictions from a special-purpose finite element code. The final conclusion is that the constant-strain approaches (pin force and enhanced pin-force) are not accurate for very soft substrates. Future work includes adding the time dependence of rubber materials as well as the possibility of material of geometric nonlinearities.

It is now widely accepted that smart fluids in the so-called squeeze-flow mode have many potential applications in vibration damping and isolation. In squeeze-flow the fluid is subjected to forces imposed by oscillating electrodes (or poles) which alternatively subject the fluid to tensile and compressive loading. Consequently displacement levels are limited to a few millimeters but large force levels are available. Modeling of smart fluid squeeze-flow devices is a complex process, primarily since the fluid is liable to be subjected to simultaneous changes in the inter-electrode gap and the strength of the applied electric (or magnetic) field. Consequently the authors have developed a comprehensive test facility dedicated to the study of smart fluids in dynamic squeeze-flow operation. In the present paper, the authors will describe a new approach to modeling smart fluids in squeeze-flow. The analysis relates specifically to an electrorheological fluid modeled using a bi- viscous shear stress/shear strain characteristics. By assuming that the electrically stressed fluid has a yield stress which is dependent on the strain direction, it will be shown how the model is able to account for observed experimental behavior.

This paper theoretically presents Bingham characteristics of ER (electrorheological)/MR (magnetorheological) fluids with respect to different rotational viscometers through comparative analysis. For doing so, two different types of rotational viscometers are introduced and configured for ER/MR fluids; one is a rotational coaxial cylinder viscometer and the other is a rotational parallel disk viscometer. In order to determine the shear stress and shear rate of fluids tested in both viscometers, the fundamental equations between shear stress and torque as well as shear rate and angular velocity are derived on the basis of the biviscous constitutive model. The biviscous model is characterized by a yield stress: when the shear stress is less than this yield stress, the preyield viscosity is relatively large compared to the postyield viscosity when shear stress is greater than the yield stress. For rotational coaxial cylinder viscometers, the shear stress can be calculated directly from the measured torque. However, for the determination of the shear rate, some strategies are required. In this study, different methods of determining the shear rate are developed and their accuracy is assessed. In the case of rotational parallel disk viscometers, the calculation of the shear rate is straightforward from angular velocity measurements, but the shear stress requires a relatively complicated calculation. In this study, for simplicity, the shear stress is approximated and the error of this approximation is evaluated with respect to important rotational parallel disk viscometer geometry. Finally, the Bingham characteristics of ER/MR fluids at two different rotational viscometers are theoretically presented and compared in the shear stress vs. shear rate response.

Heavy structures (such as machine-tool bases) are sometimes filled with granular materials (such as sand, gravel, or lead shot) to increase their damping. Traditionally, relatively dense granular fills have been selected for such applications in order to obtain strong coupling between the structure and the granular material. But recent experiments indicate that a low-density granular fill can provide high damping of structural vibration if the speed of sound in the fill is sufficiently low. We describe a set of experiments in which aluminum beams are filled with a granular material whose total mass is three per cent of that of the unfilled beam and damping coefficients as high as 0.04 are obtained. The experiments indicate that the damping at high frequencies is essentially a linear phenomenon. We present a simple model that qualitatively explains the essentially linear high-frequency damping observed in the experiments.

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. The density of this metallic closed cellular material was measured. The density of this material is smaller than that of other structural metals. On the fabricated metallic closed cellular materials, compressive properties, Young's modulus and ultrasonic attenuation coefficient were measured. The compressive tests showed 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. These results indicate that this metallic closed cellular material can be utilized as energy absorbing material and passive damping material.

The wave propagation in and the vibration of sandwich plates with cellular core are analyzed and controlled. Negative Poisson's ratio (auxetic) core materials of different geometry placed periodically in the plate introduce the proper impedance mismatch necessary to obstruct the propagation of waves over specified frequency bands (stop bands) and in particular directions. The location and the extension of the stop bands and the directions of wave propagation can be modified by proper selection of the periodicity and of the geometrical and physical properties of the core. A Finite Element model is developed to predict the dynamic response of three-layered sandwich panels with honeycomb core. The Finite Element model along with the theory of periodic structures is used to evaluate the influence of core materials of different geometry placed periodically along the two dimensions of the structure. This combined analysis yields the phase constant surfaces for the considered sandwich plates, which define location and extension of the stop bands, as well as the directions of wave propagation at assigned frequency values. The analysis of the phase constant surfaces and the evaluation of the harmonic response at specified frequencies indicate that the plates are characterized by dynamic behaviors with directional properties, with spatial patterns strongly dependent on the configuration of the periodic core and on the excitation frequency. Auxetic honeycombs are considered as core materials in order to obtain maximum design flexibility. The elastic and inertial characteristics of auxetic honeycombs in fact vary substantially with their internal geometry and for given configurations outcast up to five times the corresponding properties of traditional hexagonal honeycombs. The presented numerical results demonstrate the unique characteristics of this class of two-dimensional periodic structures, which behave as directional mechanical filters. The findings of this study suggest that optimal configurations for the periodic cellular core can be identified in order to design passive composite panels, which are stable and quiet over desired frequency bands and which fit desired transmissibility levels in particular directions. Such unique filtering capabilities are achieved without requiring additional passive or active control devices and therefore without compromising the size and the weight of the layered structure.

The recursive generalized predictive control algorithm, conjugating the process of system identification and the process of the controller design, is presented and applied to real time. In the control design process, there are three parameters to be chosen: the prediction horizon, the control horizon, and the input weighting factor. The prediction horizon and the control horizon are the finite horizons of the system output and control input predictions. Two practical parameters are defined to express effects of the prediction horizon and the control horizon. A time varying algorithm for the input weighting factor and a dual-sampling-rate algorithm are presented. A time varying input weighting factor algorithm allows the recursive generalized predictive controller to be designed aggressively. A dual-sampling-rate algorithm between data acquisition and control design allows higher-order controllers to be designed. The recursive generalized predictive control algorithm is applied to two different systems: a sound enclosure and an optical jitter suppression testbed. For each experiment, the estimation of the frequency response magnitude corresponding to the open loop identified system and the closed loop identified system is shown and compared. The advantages of the proposed recursive generalized predictive control algorithm are: no prior system information is required since the process of the system identification is performed recursively from real time system input and output data, and the controller is updated adaptively in the presence of a changing operating environment.

A jet turbine engine compressor disk is modeled as a rotationally periodic structure. An adaptive parameter estimator was used to eliminate the inter-blade coupling forces. The individual blade vibrations were then suppressed using a positive position feedback method. The resulting control law was tested on a simulated four and eight bladed system.

This paper introduces a new type of passive piezoelectric shunt controller which is capable of damping multiple modes of a flexible structure using one piezoelectric transducer. The current flowing shunt technique has a number of advantages over comparable techniques; it is simpler to implement and requires less discrete circuit elements. The passive control strategy is validated through experimental work on a piezoelectric laminated simply supported beam.

It has been shown that passive electronic damping can be successfully achieved using tuned RL circuits to shunt piezoelectric materials on structures. These designs provide electronic equivalents of tuned-vibration dampers where the coupling coefficient plays the role of the mass ratio in similar mechanical devices and is the primary factor in determining performance. However, in many applications the coupling coefficient is too small to produce desired or acceptable changes in performance. In addition, changes in system parameters, such as the piezoelectric's capacitance, detune the system also limiting performance. A sensoriactuator circuit offers the ability to eliminate the effects of the piezoelectric's capacitance and improve the coupling coefficient. Thus, electronic dampers built with a sensoriactuator circuit could see improved performance over their strictly passive counterparts. A cantilevered beam test article is modeled with a sensoriactuator attached. The sensoriactuator and appropriate control filter are used in place of the passive shunt circuitry. An optimal circuit design criteria somewhat analogous to that of the resonant shunt damper is developed. The sensoriactuator circuit is built using this design criteria, and the effects of the sensoriactuator electronic damping scheme are included in the model.

The low structural damping of large space structures and the stringent positioning requirements in missions demand effective vibration suppression. The semi-active approach at hand is based on friction damping due to interfacial slip in semi-active joints which can be controlled by varying the normal pressure in the contact area using a piezo-disc actuator. This paper focuses on the optimal placement of semi-active joints for vibration suppression. The proposed method uses optimality criteria for actuator and sensor locations based on eigenvalues of the controllability and observability gramians. It is stated as a nonlinear multicriteria optimization problem with discrete variables which is solved by a stochastic search algorithm. As final step in the design procedure, parameters of the local feedback controllers assigned to each adaptive joint are optimized with respect to transient response of the structure. The present method is applied to a 10-bay truss structure. Simulation runs of the controlled structure are used to verify the optimization results.

This paper presents an analytical and experimental study of a novel, patent pending, semi-active piezoelectric coulomb damper. A piezoelectric stack actuator is used to modulate the friction force of a passive coulomb damper resulting in high ranges of controllable friction forces. First, the piezoelectric coulomb damper is introduced and its method of operation is described. Experimental results are presented that reveal the static and dynamic frictional force behavior of the damper. An analytical model is developed and the results are compared with the experimental data. The force range of the piezoelectric coulomb damper was observed to be between approximately 890 N to 11 kN. It has a total stroke of +/- 13 mm and requires less than 0.5 W power. For a relatively small volume device, 10 cm x 6.3 cm x 6.3 cm, it is able to provide a large range of forces exceeding the capabilities of many other types of semi-active dampers.

This paper presents experimental and theoretical analysis of a vibration isolation system using MR fluid-based semi-active isolators. In doing so, a vibration isolator using MR fluids is designed and manufactured in this study. A new nonlinear hysteresis model with simplicity in form is proposed to describe the hysteresis force characteristics of the MR isolator. The damping forces of the MR isolator with different excitation frequency and current input are measured and compared with that resulting from the hysteresis model for the verification of the theoretical analysis. A vibration isolation system with the MR isolator is constructed and its dynamic equation of motion is derived. A simple skyhook controller is formulated to attenuate the vibration of the system. Controlled performances of the vibration isolation system are experimentally and theoretically evaluated in the frequency and time domains.

This paper is concerned with the development of the passive-active vibration absorber using piezoelectric actuators. The active vibration absorber system consists of 2 pairs of PZT actuators bonded on aluminum plates making s- shaped device. Hence, the active system is directly connected to the passive system. The rubber attached to the end of the beam is connected to the upper base as a structural member. It allows bending thus maximizing the vertical movement generated by the piezoceramic actuators. This paper also presents the development and the verification of the control techniques for the passive-active vibration absorber. The vibration absorber can be utilized as a passive vibration absorber when the controller is off. It is shown that vibrations can be reduced by 20dB for the first mode, when the SISO PPF controller is operated. The advantage of PPF controller provides us the most effective way of increasing damping for the particular mode of interest. However, the natural mode should be computed in the process of design, to maximize the performance. In reality the target natural frequency is estimated by the frequency response of the vibration-absorbing device and is later applied to the PPF controller as a filter frequency. In this paper, the adaptive PPF controller is considered to cope with the structural change, so that it can modify the filler frequency based on the measurement. It is found that the adaptive PPF controller is effective for the active vibration absorber when the external disturbance is applied with various excitation frequencies. It can be concluded that the proposed passive-active vibration absorber is an effective way of reducing the vibration amplitude of the precise devices in the harsh environments thus enhancing the precision.

This paper aims at proposing an integrated design method of the active/passive hybrid type of the piezoelectric damping system for reducing the dynamic response of the flexible structures due to external dynamic loads. The design method is based on the numerical optimization technique whose objective function is the active control power requirement of the damping system. The vibration suppression performance, which is evaluated by the maximum value of the gain of the frequency response function of the structure, is constrained. In order to demonstrate the effectiveness of the proposed integrated design method, numerical simulation and laboratory experiment will be done using a three-story structure model equipped with 12 surface bonded PZT tiles pairs. The results indicate that the optimally designed hybrid piezoelectric damping system successfully achieves excellent performance comparing with the pure active piezoelectric damping system from the viewpoint of the control power requirement.

Smart fluid devices are now seen as an attractive solution to vibration damping problems. They offer superior performance compared to passive devices, without involving the cost, weight and complexity of fully active damping strategies. However, the inherent non-linearity of smart fluid dampers makes it difficult to fully exploit their capabilities, due the problems in applying an effective control strategy. In the past much of the research focused on complex controllers involving techniques such as neural networks and fuzzy logic. In recent years, however, an alternative approach has been adopted, whereby classical control techniques are used to linearise the damper's response. As a result some applications for smart fluid damping now use combinations of proportional, integral, or derivative control methods. However, it appears that these controllers can become unstable in much the same way as for a truly linear system. In order to investigate this instability it is suggested that a sufficiently accurate model of the damper's response is required, so that the onset of instability can be reproduced numerically. In this contribution, a model updating technique is described whereby an existing ER damper model is updated in line with experimental data. The paper begins with an overview of the experimental test facility and the modeling approach. The updating algorithm is then described, and it is shown how the updated model improves significantly on the accuracy of the model predictions.

This paper presents experimental and theoretical analysis of an electrorheological (ER) damper. To describe the practical damper characteristics on force vs. velocity and force vs. displacement responses, a new alternative to existing models is proposed. On the basis of an Eyring model, Eyring-plastic model is constructed by the combination of simple nonlinear functions. Therefore, the Eyring-plastic model has the advantage to be simple in its design and formulation, even though it is in the form of a nonlinear function. In addition, the Eyring-plastic model can capture quite well the practical damper responses, particularly, in both the preyield and the postyield states. An ER damper is configured and its damping force under various electric fields and excitation frequencies is experimentally tested. On the basis of the damper response tested, the Eyring-plastic model is constructed and its validation is proved by comparing the experimental and predicted damper data on force vs. velocity and force vs. displacement responses.

Lead attracts large attentions for its applications in Civil Engineering as constitutive element in base isolators. However, the mechanical properties of this material are still not well known. This is due to its typical behavior in testing characterized by the large strain generated (more than 10%), the strain rate dependency, the growth of voids inside the material, the necking after the peak of the stress and the localization of deformations. In this research, tests are performed to collect data for the development of lead constitutive model. The localization of deformations is analyzed by applying the image processing technique, which is improved with respect to previous study as concerning the perspective definition of the material point initial grid, the detailed mesh in the stress concentration area, the increased efficiency and accuracy in calculating the strain field, the new deformation modes for the template used in matching two pictures and the attention to local torsional effect. After the post-processing of the data, the 3D displacement field is visualized and the stress-strain relation is calculated.

An undamped SDOF system with a pseudoelastic SMA restoring force is investigated to find the optimal shape of the hysteresis loop of SMA elements which provides the maximum damping performance. The performance of the device is evaluated by the steady-state response at the resonance point in order to focus on the damping effect. Dynamic analysis utilizing the equivalent linearization approach results in two major findings: (a) for a given excitation amplitude, the scale of the hysteresis loop, which is a measure of displacement and restoring force, needs to be adjusted so that the response sweeps the maximum loop but does not exceed it; (b) the ratio of the area confined within the hysteresis loop, to the area of a corresponding envelope of triangular shape, should be as large as possible. Numerical study is carried out to verify the performance of the optimized devices subject to harmonic and random excitation. A simple mechanism that realizes the quasi-optimal hysteresis curve is shown as an example of possible devices.

The use of seismic isolation rubber bearings in bridges and buildings provides a very effective passive method to suppress hazard from earthquake-induced vibration. Carbons filled natural rubber and high damping rubber (HDR) are smart civil engineering materials especially used in those bearings. This study is to develop algorithms for large strain field measurements in rubber material by image analysis and to experimentally investigate temperature dependency on rubber behavior under cyclic loadings by thermal image analysis. A correlation-based template-matching algorithm is developed in displacement field measurements in continua so that a large strain field can be measured. Possible unrealistic displacement vectors present in measured displacement fields are eliminated by new algorithm in which the deformation should satisfy the continuity condition. The algorithms are successfully employed in strain field measurement of rubber materials reported here as experimental verification. Local deformational characteristics of rubber were also studied; results are shown by the analysis. Finally, a failure criterion was proposed for the rubber. The use of infrared thermographs to measure temperature field is described. This paper will discuss its application in HDR temperature field measurements under cyclic loadings. In HDR, various changes of properties were investigated with respect to the frequencies of loadings and its body temperature; results are shown by the analysis.

Semi-active control systems are becoming more popular because they offer both the reliability of passive systems and the versatility of active control systems without imposing heavy power demands. In particular, it has been found that magnetorheological (MR) fluids can be designed to be very effective vibration control actuators, which use MR fluids to produce controllable damping force. The objective of this paper is to study a single-degree-of-freedom (SDOF) isolation system with a MR fluid damper under harmonic excitations. A mathematical model of the MR fluid damper with experimental verification is adopted. The motion characteristics of the SDOF system with the MR damper are studied and compared with those of the system with a conventional viscous damper. The energy dissipated and equivalent damping coefficient of the MR damper in terms of input voltage, displacement amplitude, and frequency are investigated. The relative displacement with respect to the base excitation is also quantified and compared with that of the conventional viscous damper through updating equivalent damping coefficient with changing driving frequency. In addition, the transmissibility of the MR damper system with semi-active control is also discussed. The results of this study are valuable for understanding the characteristics of the MR damper to provide effective damping for the purpose of vibration isolation or suppression.

Despite its great potentials, having a large displacement and force compared to traditional electro-hydraulic servo mechanical actuators or to PZT actuators, there are not so many studies on SMA active actuator. The main reasons are considered as following; (1) SMA has transformation only in one direction, (2) the response is quite slow, and (3) vibration control requires punctual thermo control in real time. In the study at our laboratory, the vibration can be clearly separated into different modes by distributed cluster system. SMA actuators are, then, proposed to use with PZT actuators for control of low and high frequency modes, respectively, to realize all-round actuation. The purpose of this paper is to realize SMA active actuator for low frequency modes. First of all, actuators using SMA wires, partly embedded in CFRP, were fabricated in consideration of SMA/FRP interfacial strength. Their thermo-mechanical behavior had been studied with cooling system. These lightweight actuators were placed on beam structure made of CFRP. Recovery force of beam structure itself was used as reactive force against force generated by SMA. As a result, actuator which is favorable for low frequency vibration modes control, i.e. having a large displacement and a large force, was obtained.

This study focuses on the design and characterization of a radial double-plate magneto-rheological fluid (MRF) clutch. The clutch's torque output can be controlled by adjusting the applied magnetic field. Electromagnetic finite element analysis (FEA) is performed to design and optimize the clutch. The shear stress distribution in MRF between the plates is theoretically predicted using the magnetic flux density distribution evaluated from the FEA. The output torque of the clutch is derived by using the Bingham plastic constitutive model. The output torque values are recorded for different input velocities and applied magnetic fields, and they are compared with the theoretical results. It was demonstrated that the clutch is capable of producing high controllable torques.

For the purpose of reducing the cost, a control system for a truss structure with a simplified controller equipped with amplifying function alone is proposed. In order to realize a sensor in consideration of system stability, the sensor is provided with multiplication-addition capability and a distributed modal filter capable of isolating multiple vibration modes. Then, a control system is built up to amplify the sensor output through a power amplifier, by using a moment actuator which can exert actuation comparable to that of the velocity feedback for damping the system. Finally, the control system is incorporated to the truss structure and the vibration control effect through direct feedback is studied.

The paper presents a comparison between the theoretical dynamic model of systems made of structures of paramagnetic or diamagnetic conductible materials interacting with rare-earth passive magnetic elements and the relative experimental outcomes. The magnetic effects are characterized by a viscous-type damping, and by an interesting dynamic effect of stiffening of the structure called phantom effect, modeled adding an imaginary term in the damping coefficient of a single degree of freedom system. The theoretical model finds a proper application in case of a uniform cantilever clamped-free beam of different kinds of paramagnetic or diamagnetic conductible materials, whose frequency response is modified by the presence of a pair of concordant or discordant magnets settled at the free end. Through the comparison between theoretical and experimental results, the paper demonstrates the validity of the model; besides, the model points out the above mentioned effect of dynamic stiffening of the structure and, finally, the considerable localized damping properties in paramagnetic or diamagnetic materials with low electric resistivity, when interacting with permanent magnets of high residual induction.

The paper studies the influence of a shape memory alloy (SMA) element on the dynamic response of a single-degree-of-freedom- system, representing a structural building under earthquake excitation. Variations of the SMA geometry are studied by numerical simulation, and a value for the SMA radius is determined, which provides optimal system performance. In particular do we focus on the role of hysteresis-induced passive damping, which can potentially be exploited for the development of SMA-based semi-active control schemes.