Interferometric fiberoptic sensor (FOS) is immune from electromagnetic influence and provides a useful tool for vibration monitoring. In this paper, some problems associated with the vibration sensing for structures are analyzed. A phase drift model was developed and used to investigate the experimental phenomena occurring at the test. This simpler method was utilized to detect the exciting frequency without complicated signal demodulation. The obtained FOS was used to control the vibration of the structure subjected to a random external excitation.

Advanced rotor systems including hingeless and bearingless rotors have air and ground resonance instabilities due to coalescence of low-frequency rotor modes with landing gear and fuselage modes, respectively. This coalescence is of difficulty due to the direct connection of the rotor blade in these advanced rotor systems to the rotor hub using a flexure or flexbeam. We are currently exploring the mitigation of this modal coalescence through the use of active damping techniques and electro-rheological fluid technology.

Electrorheological (ER) fluids are typically nonaqueous suspensions that show a reversible viscosity increase upon application of an external electric field. There has been some important basic work on the stress-transfer mechanisms in ER fluids but little work on actual particle size effects. Several ER fluids were characterized with a modified Brookfield viscometer; field strengths up to about 0.5 kV/mm may be employed with this setup. The ER fluids consisted of various synthetic precipitated and fumed silicas suspended in a 50-cStk. or 200- cStk. silicone oil at levels up to 9% by weight. Apparent viscosity and shear stress were measured as a function of shear rate and field strength employing several silicas with different primary particle size and composition. The data show a dependence of primary and agglomerated particle sizes on the electrorheological behavior. However, all of the data for these three systems could be combined onto one scaling plot of relative viscosity versus Mason number, Mn. The crossover from electrostatic to hydrodynamic control for the stress transfer in these systems occurred at a Mn of 1.5. A fumed silica with a smaller primary particle size, and no significant agglomeration was also examined. It showed similar behavior to the previous silicas.

A multiobjective optimization procedure is developed for rotating composite box beams with discrete piezoelectric actuators. A rotating composite cantilever box beam model is presented that includes piezoelectric elements used as induced-strain actuators for vibration control. The model is implemented using the finite elements method. Multiple design objectives are efficiently combined using a multiobjective optimization formulation. Actuator locations and ply-stacking sequences are represented with discrete (0,1) variables while structural/control parameters such as box beam dimensions are continuous design variables. A transformation technique is used to formulate the combined continuous/discrete problem. This allows both optimal actuator locations and structural/control parameters to be determined inside a closed loop procedure. A technique based on simulated annealing is used for optimization in conjunction with an approximate analysis technique to reduce computational effort.

An integrated distributed actuator design methodology based upon the converse piezoelectric effect and aimed at actively controlling the in-vacuo flapping and lagging eigenvibration characteristics of rotating blades carrying a tip mass is presented. The system of piezoelectric actuators bonded or embedded into the structure produces a localized strain field in response to an applied voltage, and as a result, an adaptive change of dynamic response characteristics is generated. The helicopter blade is modeled as a thin/thick-walled closed cross- section untwisted cantilevered beam rotating with constant angular velocity. The considered numerical illustrations reveal the power of the adaptive technology to control the dynamic characteristics of rotating blade structures and, as a result, to avoid their structural resonance as well as any of their dynamic instabilities.

This paper presents an analytical-experimental study on dynamic response of open-section composite beams with actuation by piezoelectric devices. The analysis includes the essential features of open-section composite beam modeling, such as constrained warping and transverse shear deformation. A general plate segment of the beam with and without piezoelectric ply is modeled using laminated plate theory and the forces and displacement relations of this plate segment are then reduced to the force and displacement of the one-dimensional beam. The dynamic response of bending-torsion coupled composite beams excited by piezoelectric devices is predicted. In order to validate the analysis, kevlar-epoxy and graphite-epoxy beams with surface mounted pieziceramic actuators are tested for their dynamic response. The response was measured using accelerometer. Good correlation between analysis and experiment is achieved.

We develop electromechanical actuators based on the concept of mechanical amplification with piezo and electrostrictive stacks as drivers to achieve high force and high displacement actuation. The actuators were designed for two different applications. Experiments were performed on both stacks to evaluate their important characteristics such as block force, free displacement, and stiffness that were essential in the design of the actuators. The results showed that the block force obtainable from piezo stack was higher and that of electrostrictive stack was lower than that specified by the respective manufacturers while the free displacements are about the same. The dynamic response of the actuators over a frequency range of 33 Hz was evaluated. Results showed that the actuation force of 7 lbs was obtainable in both cases with flaperon actuator producing 15 mils of dynamic displacement at 15 Hz and droop flap actuator producing about 6 mils of displacement at 16 Hz. The results were inconclusive beyond 16 Hz due to the setup resonance. Droop flap actuator did not achieve the desired performance because the design calculations were based on block force listed by the manufacturer which was about 20% higher than the measured value. This led to the conclusion that before design process begins, the stack alone performance should be carefully measured to achieve required performance. Thus, a simple actuator based on mechnaical amplification concept could be effectively designed to produce high force and high displacements.

Integral control surfaces in rear sections of airfoils can be used to actively control camber. This has potential applications in individual blade cyclic control of helicopters and in aeroelastic control of fixed-wing aircraft. When analyzed as actuators, integral control surfaces will have a characteristically misbehaved frequency response function (FRF). Taking tip displacement as a result of a force input, one would expect either highly peaked resonances characteristic of such a substructure or large areas of very low response depending on what part of the frequency domain the observation is made. In this paper, active control is used locally to convert the FRF of a proposed integral actuator into a more favorable flat-gain FRF in a frequency range of interest. This is accomplished while still exploiting at least some of the gain of the open loop first structural resonance. Both experiment and analysis are presented.

Rotor blade vibration reduction based on higher harmonic control - individual blade control (HHC-IBC) principles is presented as a possible area of application of induced strain actuator (ISA). Recent theoretical and experimental work on achieving HHC-IBC through conventional and ISA means is reviewed. Though the force- displacement and power-energy estimates vary significantly, some common-base values are identified. Hence, a benchmark specification for a tentative HHC-IBC device based on the aerodynamic servo-flap principle operated through ISA means is developed. Values for the invariant quantities of energy, power, and force-displacement product are identified, along with actual displacement and force values of practical interest. The implementation feasibility of this specification into an actual ISA device is then discussed. It is shown that direct actuation is not feasible due to the large required length of the ISA device, resulting in excessive compressibility effects (displacement loss and parasitic strain energy). Indirect actuation through a displacement amplifier was found to be more feasible, since it allows for matching the internal and external stiffness. A closed-form formula was developed for finding the optimal amplification gain for each required value of the closed- loop amplification ratio. Preliminary studies based on force, stroke, energy, and output power requirements show that available ISA stacks coupled with an optimally designed displacement amplifier might meet the benchmark specifications.

The objective of this research is to develop a dynamically scaled (Froude scale) helicopter rotor blade with embedded piezoceramic elements as sensors and actuators to control blade vibrations. A 6-ft-diameter two-bladed bearingless rotor model was built, where each blade is embedded with banks of piezoelectric actuators at +/- 45-degree angles with respect to the beam axis on the top and bottom surfaces. A twist distribution along the blade span is achieved through in-phase excitation of the top and bottom actuators at equal potentials, while a bending distribution is achieved through out-of-phase excitation. In order to fix design variables and to optimize blade performance, a uniform strain beam theory is formulated to analytically predict the static bending and torsional response of composite rectangular beams with embedded piezoelectric actuators. Parameters such as bond thicknesses, actuator skew angle, and actuator spacing are investigated by experiments and then validated by theory. The static bending and torsional response of the rotor blades is experimentally measured and correlated with theory. Dynamic torsional and bending responses are experimentally determined for frequencies from 2-120 HZ to assess the viability of a vibration reduction system based on piezoactuation of blade twist. Although the magnitudes of blade twist attained in this experiment were small, it is expected that future models can be built with improved performance.

We present a theoretical approach for investigating the response of an active composite plate system containing elastic nonlinear actuation devices undergoing small strains. the model satisfies the equations of elasticity and Maxwell's governing equation by assuming that the flux through the thickness is a constant and that Kirchhoff-Love assumptions are applicable. This yields an electric field which varies linearly through the thickness and is consistent with the results of thin plate analysis for linear actuation materials. The analysis presented here is meant to provide an initial framework for modeling generic actuation systems behaving in a elastic nonlinear fashion. The model is presently coupled with a micro solution also incorporating a general set of constitutive relations. These two modeling efforts provide a means to optimize actuator geometry and architecture for specific applications. Preliminary results are presented for optimizing a simple linear active bimorph laminated plate system.

The transient response and the damping of a cantilevered adaptive beam is explored in this paper. The adaptivity of the beam comes from embedded piezoelectric actuators which are used to enhance the damping of the beam. The dynamic model is based on Hamilton's variational principle and the interactions between the beam and the devices are modeled using Eshelby's equivalent inclusion method. The Rayleigh-Ritz technique is used to obtain the approximate behavior of the structure.

The thrust of this research has been to develop powerful models for characterizing sensor and actuator behavior, and to construct demonstration articles for assessing and quantifying the performance of advanced embedded actuators and sensors. Powerful finite elements have been developed to model the sensor and actuator behavior for use in designing smart systems. The capability exists to accurately model fiberoptic sensors, piezoelectric material behavior, and shape memory alloy material behavior in both static and dynamic applications. These finite elements were written for use with the ABAQUS computer code. Real-time data interaction with the code allows active control simulations to be conducted. Existing control theories have been used to analytically simulate response control of randomly excited structures. In addition, both thermoset and thermoplastic composite structures with embedded piezoelectric actuators were fabricated. These structures will be used as benchmarks to evaluate our smart structure manufacturing capabilities. The manufacturing methods presented here have addressed the issues of sensor / actuator survivability, sensor / actuator integration, and process conditioning. Finally, the results for all tests are qualified and compared, and the implications for their relationship to future platforms are discussed.

A variational statement of the nonlinear boundary value problem of magneto-mechanical interactions in magnetostrictive materials is presented. Some of the complexities arising out of the nature of these interactions are pointed out. A finite element code developed on the basis of a linearized version of the above variational statement is used to model the behavior of an idealized magnetostrictive actuator. The strong influence of coupling constants on the induced magnetic field is demonstrated through our coupled finite element analysis. Errors that are possible in uncoupled analyses are illustrated and the need for fully coupled analyses of general two or three dimensional actuator configurations is brought out.

An ab initio model describing the nonlinear behaviors of polycrystalline piezoceramics during polarization reversal is proposed. The model is based on a description of polarization reversal behaviors of a single piezoelectric crystallite in a piezoceramic. The polarization of the single crystallite can be switched among the six allowable directions in the lattice if the work done by the external electrical and/or mechanical loads exceeds the internal energy barriers. The piezoceramic is then modeled as an aggregate of these crystallites rotated into random orientations. The macroscopic responses of the piezoceramic were calculated in two ways. The first method is to calculate the average crystallite response in global coordinates. The second is to use Taylor expansions of the macroscopic strain and electrical displacement in terms of external loads and the internal alignment of the crystallites. Finally, the experimental results from free and clamped PZT wafers were compared with the model predictions.

This paper is concerned with the mathematical modeling of a nonlinear laminated anisotropic piezoelectric structure in which geometric nonlinearity induced by large deformations is considered. A generic theory is proposed and its nonlinear thermo-electromechanical equations are derived based on the variational principle. Thermo-electromechanical couplings among the elastic, electric, and temperature fields are discussed, and nonlinear components identified. Applications of the nonlinear theory to other materials, continua, and linear cases are discussed.

Magnetostrictive Terfenol-D transducers are an attractive alternative to viscoelastic dampers, and electrodynamic and piezoelectric actuators for damping and self-sensing. These advantages include high stiffness and primary load carrying capability, high power density, low voltages, and low temperature sensitivity. Terfenol-D converts 50 percent of the transducer strain energy into magnetic field energy. Because the Terfenol-D transducer is a primary load carrying member, large amounts of structural energy are converted into magnetic field energy. This magnetic field energy is converted into electric energy by a surrounding coil and dissipated in a resistor to provide damping. The voltage developed in the surrounding coil is proportional to the strain rate of the magnetostrictive material, thus producing a velocity signal. This velocity signal can be used for colocated active damping by controlling coil current based on coil voltage induced by transducer velocity. Experiments using a Terfenol-D actuator capable of 65 microns motion and 1,000 N force showed modal loss factors to 0.22 (relative damping to 0.11) and velocity sensing scale factors to 183 volts/(meter/sec). Room temperature tests of a transducer designed for 77 degree(s)K use showed only 20 percent reductions in damping and velocity signals. Magnetic modeling supports the damping and sensing observations.

Recently, more attention has been focused on improving open-loop performance characteristics of smart actuator materials. The impetus in pursuing this course of research is reducing the need for oftentimes costly and obtrusive independent sensors used for feedback to the actuator. Self-sensing actuation is a control technique that can be applied to many smart materials including piezoceramics. It involves extracting a sensing signal from the actuating material by use of a bridge circuit, then properly feeding this signal back to improve the actuator's performance. The research presented in this paper is concerned with the feasibility of applying this technique to a soft PZT stacked actuator used as a micropositioner. The result of applying this control technique was a reduction of the micropositioner's decay time from over 1 ms to under 0.3 ms. A major contributor to the success of this research was the insertion of a nonlinear capacitive element in the self-sensing bridge which negated the nonlinear effects of the PZT stack thus enabling an increase in the self-sensing signal to noise ratio.

This paper presents a modal analysis technique based on the measurement of electric admittance of collocated actuator/sensors. The technique utilizes thin piezoelectric patches bonded on structures as both sensor and actuator. A commercial electrical impedance analyzer is used to measure the electrical admittance of the PZT patch. An SDOF model governing the electromechanical interaction is derived and then used to extract the mechanical impedance of the structures from the measured electrical admittance. Two corresponding algorithms, revised inverse Nyquist plane curve fitting and admittance matching-half power bandwidth approaches are presented for the extraction of modal parameters. Both approaches exclude the stiffening effect of PZT on structure yielding better estimations of extracted structure natural frequencies. The placement of PZT on structure is also studied. An experimental example is given on a small flexible beam. The results show the advantages of this technique in modal test of lightweight and flexible structures whose modal parameters are extremely sensitive to the stiffening of the transducers and shaker.

Piezoelectric ceramics have become an area of interest in the smart structures arena during the past several years. They have shown promise in the area of structures control because of their simplicity, low power consumption, application to wide frequency range, and ability to be attached to structures in a distributed nature. In addition, an attractive feature of piezoceramics is that they have the ability to act as both as a sensor and/or an actuator. In fact, a piezoelectric element can act in both capacities simultaneously. This is particularly attractive to the controls designer because a self-sensing piezoactuator can be considered to be a collocated sensor-actuator pair. This paper deals with the comparisons between analytical and experimental results of piezoelectrics as both sensors and actuators. It contains a survey of some of works conducted in the area of self- sensing actuators, and briefly discusses their results. It also contains analytical and experimental results of work conducted at the United States Air Force Academy with a two meter aluminum beam instrumented and actuated with piezoelectric patches. Results include comparisons of transfer functions for various collocated sensor/actuator pairs to numerical results.

Actuator power factor, defined as the ratio of structural dissipative mechanical power to apparent supplied electrical power, describes the effectiveness of the integrated actuators to convert supplied electrical power to mechanical power which creates the intended structural response. A large actuator power factor in the frequency range of application indicates that the corresponding actuator (position) has a higher authority to excite its host structure in that frequency range than positions with a lower power factor. The use of acutator power factor provides an alternate tool in the determination of the optimal actuator locations and dimensions to theoretical calculations. More importantly, the power factor can be experimentally measured on large-scale complex structures, thereby eliminating the need for sophisticated theoretical modeling. The concept of an actuator power factor was first introduced by the authors (Liang et al., 1993a) and will be briefly described herein. The utility of using the actuator power factor in optimizing an actuator system will then be illustrated using a numerical case study. The hardware development of the actuator power factor meter will be presented. The application of actuator power factor meter for optimal experimental actuator placement will be discussed.

The next generation of materials will contain many embedded or attached actuators and/or sensors. They will also contain support electronics including power electronics and a computer processor with a communication network along with the `smarts' to respond to their environment. Current research is also directed toward miniaturization of the components, particularly the sensor and actuators with the idea of incorporating large numbers of actuators and sensors into the material. In keeping with this trend, the electronics should also be miniaturized along with the sensors and actuators. In this paper we discuss miniaturized power converters and power systems with potential applications to materials with miniaturized sensors and actuators.

In developing intelligent structures in which actuation, sensing, and processing elements are physically integrated within the structure, the use of piezoelectric actuators places certain requirements on the electronic components which drive them. Applications may impose strict limitations on power consumption and heat dissipation, and structural integration brings an added requirement for component miniaturization. An understanding of the power flow behavior of piezoelectric actuators in controlled structure applications is therefore important. This paper addresses power issues in the application of piezoelectric actuators and embedded electronic components. The power flow characteristics of piezoelectric actuators are examined in closed-loop control applications. An analysis is presented of the power flow and voltage and current requirements of a piezoelectric actuator in a simple system, along with implications for the design of linear amplifiers. The contributions of various elements to average and peak power flow levels are identified, as is the effect of loop closure on the impedance which the actuator presents to the amplifier.

This paper describes a method for improving convergence of actuator or damper placement algorithms that employ randomized search techniques. An easily computed scalar measure of effectiveness is calculated for each possible location independently from damper properties. This quantity is then used to weight the random selection or mutation. Simulated annealing or genetic search algorithms optimizing damper placement to minimize RMS displacement benefit from the weighted selection. Two models of controlled structures testbeds are used to show improvements in convergence. Optimal or near-optimal sets of five member dampers are found in fewer iterations and with greater frequency using the new method.

Distributed control of a cantilever beam using a fully distributed piezoelectric layer has been a classical problem for years. In general, the equivalent actuation is introduced at the free end of the cantilever beam, and the control action is equivalent to an (electric) counteracting moment. The control effect is proportional to the feedback voltage, if the system is considered linear. If the feedback voltage is continuously increased, what would happen to the cantilever beam was not investigated. In this study, nonlinear control effects and boundary transition of the cantilever beam with large feedback voltages are studied. Analytical solutions are compared with finite element simulations.

This paper focuses on the development of an approximate time- optimal feedback strategy for conducting rest-to-rest maneuvers of a magnetically levitated table. Classical switching curves are modified to account for the complexities of magnetic actuation as well as the coupling of the rigid body modes through the control. A smooth blend of time-optimal and proportional-derivative controls is realized near the destination point to correct for inaccuracies produced by the approximate time-optimal strategy. Detailed computer simulations of the system indicate that this hybrid control strategy provides a significant reduction in settling time as compared to proportional-derivative control alone.

A design technique is presented to improve the overall performance of a structural system by simultaneously optimizing the design of the structure and an associated controller. This procedure requires the minimization of a single objective function, subject to dimensional or mass constraints. This is done by including the control and disturbance forces in the equations of motion for the structure and using the eigenfunctions of a uniform structural design as a basis for the eigenfunctions of the optimally designed, nonuniform structure. The results of the concurrent optimization of an Euler-Bernoulli beam and H₂ controller are presented. More complicated structures/controllers can be designed using this technique, provided the structure can be modeled as a linear time-invariant plant and the controller synthesis technique involves a single cost functional.

The design of spatially shaped distributed sensors for the control of infinite order structural systems has become a topic of interest in recent years. Sensor shape optimization techniques were developed for the design of optimal controllers on infinite order structural systems. In this paper, we investigate methods for the implementation of distributed sensors using polyvinylidene flouide (PVDF) film. The complexity of the sensor shapes depends on the mode shapes of the flexible structure and the performance measure of the controllers. The sensitivity of the sensor shape on the performance of the controller is being investigated. The problems associated with the practical implementation of distributed sensors with PVDF film are also identified. The shapes of the distributed sensors for the implementation of a linear quadratic regulator (LQR) and a pole- placement controller have been determined. These sensors are implemented on simple cantilever beam test articles using PVDF film. The details of hardware implementation of the controllers are presented. The closed loop performance of the controllers are compared with simulation studies. The sensitivity of the shapes of the distributed sensors for the LQR and pole-placement controllers is discussed.

A modeling technique is presented for transducer spatial design applicable to discrete and distributed transducers with arbitrary one-dimensional shading (spatial gain weighting). The technique accommodates finite element models (FEM) composed of beamlike elements yielding modal displacements and rotations at element node locations. An example is presented: transducer spatial design for a 56-in. by 59-in. nine-bay aluminum grillage. Locations and distributions were chosen in order to shape the system's transducer-augmented forward loop transfer function, making the modal coefficients as large as possible within the eight-mode control bandwidth, and minimizing the coefficients associated with higher frequency modes of vibration. The transducer suite includes accelerometers and the piezoelectric polymer polyvinylidene-fluoride (PVDF) for sensors with lead- zircon-titanate piezoelectric ceramic and PVDF actuators. Modal coefficients employing the three aforementioned techniques are presented showing an average deviation in coefficient magnitude between different methods of calculation of 1.16% over the first 24 modes of vibration.

We describe a design technique for optimal control in active structural vibration damping using smart materials. The vibration of a cantilever beam is stabilized by feedback the weighted integration of vibration velocity in the closed loop system through the application of distributed sensors and actuators made of smart materials. We model the beam by the Timoshenko beam model embedded with the distributed sensors and actuators to account for the shear and inertial effects on the structures. We propose an algorithm to find the optimal placement of the actuators and sensors so as to maximize the damping effect. An objective functional is defined based on the vibration energy of the system. The optimal shapes of the sensor and actuator are determined through minimizing the energy functional of the beam over the admissible shape function space subject to certain constraints. This approach can be generalized to cases of plate damping and active control of more complicated smart structures as well.

An important development in future aerospace applications is the use of thick-wall composite material high-pressure vessels. While polymer matrix composite vessels are already widely used in low- pressure applications, because of reliability and fabrication issues, composite materials have not found use in high-pressure applications. Replacing current steel pressure vessel designs with polymer matrix composite pressure vessels for high pressure applications will yield significant weight reductions. High- pressure composite pressure vessels can reduce the size and weight of fuel, hydraulic, and auxiliary systems in aerospace vehicle applications. Presented here is an investigation of adaptive hybrid composite cylinders utilizing active shape memory alloy (SMA) composite layers for use in high-pressure vessel applications. An analytical analysis using an elasticity formulation shows that the adaptive composite cylinders can carry greater pressures with thinner walls than conventional composite and metal cylinders. A more reliable pressure vessel design is attained due to lower peak stresses in the adaptive composite material vessels. With the adaptive hybrid composite material concept, cylinders which can carry greater pressure with less radial expansion can also be produced. A model for the adaptive composite material cylinder and representative stress states for various composite materials is presented.

Composite material impact damage tolerance and resistance are often limiting criteria when composites are considered for critical load bearing applications. Often undetectable to visual inspection, foreign object impact causes varying degrees of damage to composite structures which can initiate fatal material failures under various operating loads. This paper examines a new concept of composite material toughening by embedding small amounts of fibrous superelastic shape memory alloy (SMA) materials into brittle composite materials. In this preliminary study, a 2.8-percent volume fraction of activated (i.e. superelastic) shape memory alloy fibers were embedded within G40- 600/5245C graphite/bismaleimide to create a hybridized composite material. Impact test results show that with the SMA fibers, impact resistance of the hybrid composite materials was increased. At impact energies that perforate the standard graphite/bismaleimide, the SMA fibers stopped perforation of the hybridized composite. Preliminary results show that composite-ply delamination was reduced as much as 25 percent because of the embedded SMA fibers.

The instability of elastic tubes conveying fluids is controlled by manufacturing these tubes from a nickel-titanium alloy (NITINOL) which has unique shape memory characteristics. A mathematical model is developed to describe the fundamentals governing the operation of this class of actively controlled NITINOL tubes while conveying fluids. The model describes the interaction between the fluid flow, the elastic behavior of the tubes, and the thermal activation of the shape memory effect. The predictions of the model are validated experimentally using a 0.58-m-long NITINOL-55 tube that has outer diameter of 2.134 mm and inner diameter of 1.778 mm. The effect of varying the activation strategy of the shape memory effect on the critical flow velocity, at which flow-induced instabilities occur, is determined theoretically and experimentally. It is shown that the shape memory controller can significantly increase these critical flow velocities as it stiffens the tubes by virtue of the strain energy imparted by the shape recovery process. Furthermore, the effectiveness of the controller is demonstrated also by its speed of response as it brings the unstable tubes back to their undeflected shape while conveying fluids at velocities equal to their uncontrolled critical velocities. Close agreement is obtained between the theoretical predictions and the experimental results. The results presented suggest the potential of the shape memory controller as a viable means for enhancing the elastic stability of tubes conveying fluids.

Shape memory alloys exhibit several characteristics which make these materials particularly attractive for modal modification of structures: a large change in modulus upon heating through the phase transformation temperature, an exceptionally high specific damping capacity, and an ability to generate large forces through the shape recovery mechanism. Used as either embedded members in a composite structure, or as an external actuator when caused to undergo the shape transformation by heating, these actuators can provide a significant change in acoustic response of the structure. The paper describes shape memory alloy characterization and the design of an actuator system for modifying the acoustic response of a clamped plate.

The problem of plane deformations of flexible rods with embedded SMA line actuators is considered. A simple formula for calculating the shape change of flexible rods under uniform prestrain of an embedded actuation wire is given. The results are compared with previously obtained results based on a shear-lag model for the evaluation of actuation force, a finite element solution and experimental data. It is shown that the present model gives very good accuracy and simplicity. A thermal analysis of the SMA cool-down from the austenitic finish temperature is also considered in this paper. A solution for heat conduction in a cylindrical rod with off-center heat source is presented. The results show that for common elastomeric flexible materials the rate of heat conduction is slow. As a result frequency control of the thermal cycle in flexible rods is not as efficientas the mechanical shape control.

The shape of composite beams is controlled by sets of flat strips of a shape memory nickel-titanium alloy (NITINOL). A mathematical model is developed to describe the behavior of this class of SMART composites. The model describes the interaction between the elastic characteristics of the composite beams and the thermally- induced shape memory effect of the NITINOL strips. The effect of various activation strategies of the NITINOL strips on the shape of the composite beams is determined. The theoretical predictions of the model are validated experimentally using a fiberglass composite beam made of 8 plies of unidirectional BASF 5216 prepregs which are 9.75-cm wide and 21.20 cm long. The beams are provided with four NITINOL-55 strips which are 1.2 mm thick and 1.25 cm wide. The time response characteristics of the beam are monitored and compared with the corresponding theoretical characteristics. Close agreement is obtained between the theoretical predictions and the experimental results. The obtained results suggest the potential of the NITINOL strips in controlling the shape of composite beams without compromising their structural stiffness.

The use of piezoceramics in micropositioning is increasing tremendously. Deformable and segmented optical reflectors are examples where the micropositioning is critical to system performance. In addition to correcting for mirror flaws and the effects of gravity, the actuators in adaptive segmented reflectors can constantly correct each of the segmented reflector surfaces to compensate for the disturbances in the atmosphere. This task requires the piezoceramic actuator, used to position the mirror, which operates over a large bandwidth with very high resolution. However, the hysteresis associated with piezoceramics hampers its application in optical micropositioning where nanometer resolution and wide bandwidth is required. Clearly, there is a need to compensate for these hysteretic effects to make piezoceramics more suitable for such high resolution applications. This paper presents an investigation of the linear performance of piezoceramic materials. The investigation is made to study the level of precision that can be attained for a broad- band amplification of an open loop micro-positioner. Direct compensation is introduced that can enhance the open loop dynamics of the actuator.

Future technologies in microsensing, microactuation, active changes in shapes of aerofoils and turbine blades justify and necessitate a comprehensive study of piezoactuators for shape control of structures. Piezo materials have the property to develop strain on applying voltage and voltage on applying strain, hence, these materials are useful both as sensors and actuators. If a piezoactuator is bonded to a substrate plate, on applying voltages, the resulting strain in the actuator induces a deflection in the plate. This deflection is a function of geometry, material properties of actuator and substrate, layout of piezoactuators, and voltage inputs to the actuators. The objectives of this paper are: (a) to develop a mathematical model for deflection of a thin plate embedded with piezo actuators using elastic plate theory, (b) to compute plate deflection by solving the mathematical model using finite difference technique, and (c) to estimate optimal actuation voltages to match the deflection of the plate to a desired deflection.

An adaptive sandwich reflector of composite material has been designed and manufactured in the in-situ technique. The deformation profile of the structure is experimentally verified by speckle interferometry and mechanical measurements using strain gages. To enforce defined deformation patterns to change the overall geometry (contur), the shape of the reflector can be adapted by actuating embedded piezoceramic patches. The fabrication process of the reflector does not require additional machining for the electrical wiring. The results of numerical simulations with respect to the out-of-plane deformations are verified by different measurement techniques.

We will describe an effort that to date has produced a working prototype of a micropatch antenna incorporating a single-dollar- per-bit phase shifter. In this paper we will describe a method of controlling a micropatch antenna to provide phase only variation of the antenna characteristics using a similar device to that used for the frequency control experiments. We have successfully varied the phase of the antenna element without significantly changing the operating frequency. This work has led us to pursue further the design and fabrication of an array of such phase adjustable element to test the hypothesis that such phase- controlled micropatch elements can be used to fabricate a low- cost phased-array antenna.

The reliability with bounded distribution parameters (mean, standard deviation, etc.) is maximized and the reliability-based cost is minimized for adaptive intraply hybrid fiber composites using a probabilistic method. The probabilistic method accounts for all naturally occurring uncertainties including those in constituent material properties, fabrication variables, structure geometry and control related parameters. Probabilistic sensitivity factors are computed and used in optimization procedures. The reliability for actuated change in the angle of attack of an airfoil-type composite shell structure with an adaptive torque plate is maximized to 0.9999 probability with constraints on mean and standard deviation of control volume ratio (percentage of actuation composite material in a ply) and control strain coefficient. The reliability-based cost for an airfoil-type composite shell structure with adaptive skin is minimized with mean control volume ratio as the design parameter. It is found that at 0.91 mean control volume ratio, the balance between maximum reliability and minimum cost is achieved.

Anthropomorphic exoskeletal systems with full-force feedback are desired for intuitive telemanipulation. Current dexterous force- reflecting hand masters are fundamentally limited by available force actuators. Multiple-degree-of-freedom dexterous exoskeletal systems are especially sensitive to mass, volume, force, velocity, and geometric constraints. This project discusses desired operational parameters and targets for ideal dexterous- force feedback actuation. New resistive and active actuators, using Terfenol-D magnetostrictive driven elements, are proposed. Simple resistive and active magnetostrictive concepts, prototypes, and devices are demonstrated and evaluated.

Magnetostrictive and piezoelectric materials were used to create a linear motor operating on the inchworm principle. This motor operates at an electrical resonance, switching power internally between inductive and capacitive components. Magnetic coils surrounding the two Terfenol-D rods which drive the inchworm's center expanding element form the inductive component. Piezoelectric stacks that control the end clamping action are the capacitive components. The normal electrical phase relationship between these components provides natural drive timing for the inchworm. The motor direction can be easily reversed by changing the magnetic bias on the Terfenol. A prototype motor was built that achieved a stall load of 26 lb and no-load speed of 1 inch/sec vs the design of 30 lb and 1.3 inch/sec. A new type of power supply that switches power from a dc source was built for the motor. This power supply uses a small number of components to exactly supply the energy used in each inchworm cycle. It tracks the motor circuit resonance and is not affected by frequency shifts.

A piezoelectric rotary ultrasonic motor is modeled for the purpose of predicting, a priori, motor performance as a function of design parameters. The Rayleigh-Ritz assumed mode energy method is used to model the distributed piezoceramics and the traveling-wave dynamics of the stator. Natural frequencies and dynamic modeshapes are obtained for a generally configured motor. Nonlinear normal and tangential interface forces between the rotor and stator are incorporated into the forcing function along with the linear piezoelectric forcing. Given the applied torque, applied axial loading, and piezo drive voltages as inputs to the model, general motor performance measures are obtained--namely speed, input power, output power, and efficiency. The approach presented here provides a general framework for modeling these motors as well as a design tool for optimizing prototypes with the added flexibility of allowing for a wide variety of geometries and materials.

This paper details the design and development of an inchworm-type linear piezomotor that consists of three piezoelectric actuators, a monolithic flexure frame, and a guideway. The design is accomplished using the finite element methods to optimize the stiffness of elastic hinges and to calculate the stress-strain field of the flexure frame. The buckling of the bolted joints and interface stiffness of the quideway, and jerking of the linear piezomotor motion, are discussed. The linear piezomotor is capable of traveling speed of 1.6 mm/s over a travel range of 300 mm with a positioning resolution of 5 nm. It also provides a stiffness of 90 N/micrometers and an output force of 200 N.

Longitudinal and shear waves are produced in structure by using piezoceramic transducers. These elastic waves have been used to obtain effective elastic properties of the medium or are used to detect localized damage. Elastic wave generation in a beam by surface-mounted piezoceramic patches is described in this paper. Preliminary experimental and analytical results are presented and discussed qualitatively. Longitudinal and flexural waves are generated by surface mounted piezoceramic patches. Numerical procedures are developed and preliminary simulation results are presented and qualitatively compared with experimental observation.

This paper presents the theoretical development and the experimental verification of a dynamic model of distributed piezoelectric (PZT) actuators locally coupled with 2D structures. The model includes the dynamic interaction between PZT actuators and their host structures. An analytical solution of the moment (or force) outputs of the PZT patch actuators has been developed based upon the input impedance of the piezoelectric actuator and the mechanical impedance of host structures. A simply-supported thin plate with surface-bonded PZT patches was built and tested so that the ability of the impedance approach to predict the dynamic performance of the actuator and intelligent structures has been verified. When compared with conventional static models or quasi-static models, the impedance modeling method offers insight into the dynamics and electromechanical coupling of the integrated PZT/substrate systems and more accurately predicts the actuation of induced-strain actuators.

Based on the thin-shell Donnel theory, a model to represent the action of discrete induced strain actuator patches bonded to the surface of a circular cylindrical shell has been developed. The model provides estimates of the curvature due to the out-of-phase actuation and the in-plane strains due to the in-phase actuation of the bonded actuator patches. The magnitudes of the induced curvature and the in-plane strain are found to be identical to those of plates; however, due to the cylindrical strain- displacement relations, the in-plane and out-of-plane displacements are coupled. Expressions for the equivalent forces and moments that represent the action of the actuator patches have been developed. Due to the curvature of the shell, the representation of the in-phase actuation with an equivalent in- plane line force applied along the edge of the actuator results in the application of erroneous rigid-body transverse forces. To avoid these rigid body forces, a method to represent the in-phase actuation with a system of self-equilibrating forces is proposed. The action of the actuator is then represented by an equivalent in-plane force and a transverse distributed pressure applied in the region of the actuator patch. Finite element verification of the proposed model is presented. The displacements due to the actual actuator actuation are compared with the proposed model, and very good agreement is found.

This paper develops a model for the behavior of an electrostrictively coupled electromechanical system. The framework for the derivation of the governing equations is sufficiently general to model the dynamics of any nonlinear electroceramic actuated system which can be described by a set of constitutive relationships. The constitutive relations for electrostrictors are reviewed and are simplified to contain a single quadratic nonlinearity. By introducing the constitutive relations into Hamilton's equation and then assuming mode shapes, the general system equations are derived. Experimental validation of the equations is accomplished with an electrostrictive wafer surface-bonded to a cantilevered beam. The range of validity of the simplified constitutive relationships is also experimentally investigated.

The ability of the adhesive in a piezoceramic actuator to effectively transfer strain between the ceramic and the metal structure is critical as piezoceramics become popular as elements in mechanical actuators. As motion requirements increase, the strain transfer must be maximized from the ceramic to the metal. The objective of this work is to develop guidelines for designing metal-ceramic actuator systems using piezoceramic motor elements. Both analytical and experimental methods were employed to investigate strain transfer between the piezoceramic element and the metal. Taguchi methods were used to select optimum adhesive and base metal combinations. Following these optimum parameters, single-layer piezoceramic elements were bonded to cantilevered beams to investigate the strain transfer from an actuator to a beam. An existing analytical model of the bond layer was modified for use with the metal-ceramic actuators being tested. The strain and deflection predicted by this model were compared to the experimental results.

While the phenomenon of shifts in the poles of flexible structures caused by local stiffening due to bonded piezoceramic actuators is well documentated, shifts in the zeros associated with the distorted mode shapes due to localized stiffening has yet to be investigated. The finite element method in conjunction with state space models was used to derive transfer functions for both collocated and noncollocated sensor/actuator pairs. Models that considered the mode shape distortions compared favorably with experimental measurements. With the numerical models validated by experiments, state variable feedback control gains were determined using linear quadratic regulator design for noncollocated and collocated sensor/actuator pairs for the cases of classical mode shapes and distorted mode shapes. It is demonstrated that lack of consideration of distorted mode shapes can lead to a loss of performance of the control systems.

An integrated induced-strain actuator/substructure system requires a third-phase adhesive layer to provide bond between the adherends. The presence of the adhesive, which in general has relatively low stiffness and strength, brings about concern regarding losses in transferring the actuation mechanism from the actuator to the substructure and bonding failure regarding structural integrity. In this paper, an analytical model for an integrated actuator/adhesive/substructure system is developed to study the adhesive layer effects. The model is formulated on the basis of the theory of elasticity and solved by the principle of stationary complementary energy. The solution obtained is, in an approximate manner, in closed form. The results show that a relatively thick and/or compliant adhesive causes noticeable losses in the transfer of the actuation mechanism, particularly in the end zone near the actuator edges. Nevertheless, such an adhesive yields low interfacial shear and peeling stresses which are beneficial to the structural integrity.

In this paper, the refined model presented currently by the authors (Lin and Rogers, 1993a) for the induced-strain actuation mechanism of the actuators is extended to include external loads. The same stress field obtained for the actuation mechanism is used to model the external loading with different end traction condition and the solutions are superimposed to yield the complete solution for the combined loading condition. The results obtained from the current analysis agree very well with those obtained from the finite element model on the prediction of the effective force/moment induced on the substrate. The interfacial shear and peeling stresses are shown to be altered noticeably with the application of external loads, and the maximum interfacial shear and peeling-stress level appears to vary linearly with the external loads. The influence of the external bending moments on the optimum actuator-to-substructure thickness ratio that induced maximum bending curvature on the substrate is also discussed.

This paper presents a control scheme based on fuzzy logic and neural network algorithms and its application to vibration damping of slewing flexible structures with piezoceramic sensors and actuators. In particular, the algorithms are implemented on a flexible-link manipulator. Here, a fuzzy-based adaptive controller is considered due to its simplicity and the fact that it does not require expressing the controller in terms of the system parameters, as is necessary in the case of self-tuning regulators. This controller is based on a functional fuzzy model where the consequents are crisp functions of the system states and/or inputs; these functions represent controllers designed for different operating regimes. The premise is constituted by the fuzzy subsets corresponding to the process parameters estimated in real time. The neural network is utilized for two different purposes: (1) derivation of a fuzzy model of the system (fuzzy system identification), and (2) derivation of the rule base for the fuzzy logic controller through training. The effectiveness of this new scheme is verified on a clamped-free beam and a flexible-link manipulator instrumented with piezoceramic sensors and actuators. It will be shown that robust performance may be achieved in face of large parameter variations.

This paper addresses the implications of spurious nonminimum phase zeros for design of control systems with noncollocated sensors and actuators. The relationship between the finite- element model and the control system model is examined in detail, with particular emphasis on the physical analogies of nonminimum phase zeros in the finite-dimensional representation of the system. Finite element models of constrained systems may be used to determine which zeros are spurious. Synthesis of accurate transfer functions is demonstrated using the idea of constrained modes. By considering the infinity norm of the undermodelling, the exact residue model even with spurious nonminimum phase zeros is the preferred model for control system design.

The objective of this study is to provide experimental data on bending oscillation of a deploying or retrieving beam cantilevered by a clamping device with three pairs of rollers and springs, and to formulate a finite element analysis for treating the corresponding oscillation of the axially moving beam by using beam elements of varying length. The equation of motion of the beam derived is numerically solved with the aid of the modified Newmark method, the so-called (alpha) -method, to simulate the transitional motion of the beam measured experimentally.

A system for active suppression of structural vibrations has been developed. The system consists of piezoelectric ceramic actuator and sensor elements which can be either bonded on to or embedded in structural components. For active damping, these are placed at locations of high modal strain energy. For active isolation, locations of high disturbance transmissibility are chosen. Small analog and digital control electronics units have been developed which include all sensing, processing, and actuator drive electronics. The analog unit is appropriate for active damping using strategies such as positive position and integral force feedback. Damping levels in structures has been increased from 0.1% to 100% using a single analog controller. The digital system is capable of executing any algorithm having two inputs and two outputs. Active damping using feedback and active force cancellation using feedforward have been demonstrated. Block diagrams, specifications, photographs, and test results describing the elements of the modular vibration suppression system are presented.

Presented is a novel design of a composite linear actuator utilizing a parallel array of contractile shape-memory alloy (SMA) wires. The fiber bundle of SMA wires is either circumscribed inside a helical compression spring with flat heads or are in parallel with a number of helical compression springs, end-capped by two parallel circular plates with embedded electrodes to which the ends of the SMA wires are secured. Thus, the wires can be electrically heated and subsequently contracted to compress the helical compression spring. Upon cooling the SMA wires expand and allow the helical compression spring to tightly stretch them to their initial length. Design details are first fully described. Steps involved in the fabrication of a number of these composite SMA actuators are then elaborated on. A number of interesting heat transfer phenomena are observed. In essence the dynamic behavior of the actuator depends on the interaction between the current supplied to the wires and the rate of heat transfer from the wires due to convection and radiation. A design model is finally presented for the dynamic response of contractile fiber bundles embedded in or around elastic springs that are either linear helical compression springs, hyperelastic springs such as rubberlike materials, or nonlinear springs such as air. The fiber bundle is assumed to consist of a parallel array of contractile fibers made from contractile shape-memory alloy (SMA) wires. The proposed model considers the temperature- induced contraction of the fibers due to resistive heating of the shape-memory wires. Results of both dynamic computer simulation and dynamics of a prototype model built in our laboratory indicate a fairly good comparison.

Presented is a novel design of an active crawling robotic annelid capable of autonomously moving in a preferred direction. This preferential motion is achieved by continuous contraction and expansion of its wormlike body just like the motion of an annelid. A set of resilient cilia mounted on the outer body of the robotic annelid act as one-way motion cilia. The basic design of the robotic crawling annelid is based on a novel fibrous shape-memory alloy (SMA) actuator which utilizes a parallel array of contractile SMA wires. The fiber bundle of SMA wires is either circumscribed inside a helical compression spring with flat heads or are in parallel with a number of helical springs, end-capped by two parallel circular plates with embedded electrodes to which the ends of the SMA wires are secured. Thus, the wires can be electrically heated and subsequently contracted to compress the helical spring back and forth. This causes the body of the robotic annelid to contract and expand. If the robotic annelid is placed on a flat surface it would tend to move in a preferred direction dictated by a set of elastic one-way cilia. On the other hand, if the robotic annelid is placed inside a long passage of round cross-sections, it would still move in a preferred direction. A design model is first presented for the dynamic response of contractile fiber bundles embedded in or around elastic springs that are either linear helical compression springs, hyperelastic springs such as rubberlike materials, and nonlinear springs such as air. The fiber bundle is assumed to consist of a parallel array of contractile fibers made from contractile SMA wires. The proposed model considers the temperature-induced contraction of the fibers due to resistive heating of the SMA wires. Results of both dynamic computer simulation and dynamics of a prototype model built in our laboratory indicate a fairly good comparison.

Excessive deceleration forces experienced during high speed deployment of parachute systems can cause damage to the payload and the canopy fabric. Conventional reefing lines offer limited relief by temporarily restricting canopy inflation and limiting the peak deceleration load. However, the open-loop control provided by existing reefing devices restrict their use to a specific set of deployment conditions. In this paper, the sensing, processing, and actuation that are characteristic of adaptive structures form the basis of three concepts for active control of parachute inflation. These active control concepts are incorporated into a computer simulation of parachute inflation. Initial investigations indicate that these concepts promise enhanced performance as compared to conventional techniques for a nominal release. Furthermore, the ability of each controller to adapt to off-nominal release conditions is examined.

This paper describes the results of current research being carried out at McDonnell Douglas Aerospace (MDA) to develop a flight-ready vibration isolation system for possible use on shuttle or space station. Measurements and predictions indicate that the natural vibration modes of these vehicles may be excited by on-board equipment and astronaut activities. These disturbances may be enough to upset the desired levels of microgravity. The MDA system consists of a very low frequency, flexible interface between a scientific payload and the orbiting host platform augmented by active acceleration feedback. The design of a system that will accommodate materials and biological experiments must take into account predicted input vibration levels, experiment services requirements, and logistic considerations. It must accommodate all these requirements while consuming the absolute minimum of the space available to the payload itself. The MDA isolator concept has been demonstrated in 3-axis testing in the laboratory and nearly meets the desired space station specifications. However, the design needs on-orbit testing to verify its performance in true space environment. This paper discusses some of the practical aspects of the design and operation of the system. NASA has notified MDA that a Phase A award for the development of a flight demonstration of our experiment will be made under its IN-Space Technology Experiment Program (IN-STEP).

This paper examines the design of a linear motor combining piezoceramic actuation with viscoelastic damping. The actuator consists of aluminum discs alternately treated with piezoceramics and viscoelastic material. The discs are joined together by a rod through their center and cantilevered inside a cylinder to form a linear motor. This configuration offers increased design flexibility. The issues of a combined passive/active actuator design are discussed in terms of vibration isolation.

A finite element model is developed for the active control of thermally induced vibration of laminated composite plates with piezoelectric sensors and actuators. The present model takes into account the mass, stiffness and thermal expansion of the piezoelectric patches. A C degree(s) continuous nine-noded shear flexible element is implemented to model the plate. The piezoelectric sensing layer monitors the structural oscillation due to the direct piezoelectric effect and the actuator suppresses the oscillation via the converse piezoelectric effect. These two effects are then coupled with a constant gain negative velocity/positive position feedback control algorithm to actively control the dynamic response of the plate in a closed loop. Numerical results indicate that thermally induced deformation of a laminated plate can be suppressed through the application of electrical potential to the piezoelectric patches.

In this paper a new method of distributed parameter control of flexible structures is considered. It is based on finite element approximation, from which the auto-regressive moving average representation of the distributed parameter system is derived. First, a discrete-time recursive least squares estimation algorithm is designed to estimate mass, stiffness and damping coefficient of the structure. It is then combined with a continuous time linear quadratic regulator algorithm, to form a hybrid distributed adaptive control system for the suppression of vibration in flexible structures. Simulation results are furnished to demonstrate the performance of the estimation algorithm and the adaptive controller.

Frequently in designing a structure to incorporate integrated sensors the stiffness of the system is sacrificed to improve sensitivity. By incorporating finite length measurement paths that tessellate throughout the volume of a structure, a measurement's sensitivity can be optimized while retaining structural rigidity. Thus the transducer element can be utilized as a critical load-bearing structure. Within the framework of linear elastostatics, the normal, transverse, and shear components of strain along a path can be integrated over a finite length to separate and yield external loading components. These measurements over a long distance accommodate the use of fiber- optic displacement sensors. The use of interferometric sensors in contrast with electrical strain gauges allows the precision and range of the component measurements to scale with the geometry of the device rather than the maximum strain in the structure. It becomes possible by virtue of these scaling properties to construct a stiff yet sensitive device. The design of stiff structures that measure all six resultant-load-components using both piezo-resistive and interferometric sensors is described. An advanced torsion sensor and a linear acceleration transducer are also discussed. In addition, invariant paths have been found that allow the in-situ integrity of a structural volume to be monitored with a single pair of displacement sensors. Finally, practical considerations in the design of finite length sensor path transducers are noted.

Distributed control of elastic continua using distributed piezoelectric actuators posts a problem when the environmental temperature also changes in time. In this paper, an open-loop distributed control of a circular ring subjected to combined mechanical and thermal excitations is studied. One electric charge is tuned to control the mechanical excitation, and the other to compensate the temperature induced oscillation. Control effectiveness is evaluated.

The feasibility of implementing embedded magnetostrictive mini actuators (MMA) for smart structure applications, such as vibration suppression of beams, is investigated in this paper. Based on the Euler-Bernoulli's beam theory and previously reported magnetothermoelastic theory of MMA, an integrated mathematical model of the beam embedded with MMA is formulated. In addition, different forms of control schemes for MMA are investigated. Simulation results, based on the open-loop control, shows that it is possible to attenuate the vibration by embedding MMA in the beam. Further work on the investigation of the merits of nonlinear closed-loop control is in progress.

In order to develop effective controllers for active vibration control of complex flexible structural systems, it is imperative to be thorough with vibratory transmission analysis in such systems. This paper addresses the interpretation of vibration behavior in active structures in the form of modal synthesis and waveform propagation, from which control architectures for vibration reduction are developed and specialized. Multi-input multi-output robust control methods for actively controlling vibration transmission of narrow-band disturbances, based on modal vibration characteristics in a typical beam structure bonded with piezoelectric sensors and actuators are presented. The development of compensators based on wave-propagation techniques for active control of stationary and propagating wave- forms in an active beam structure is also discussed. Vibration transmission in the structure in the form of intensity and energy density is investigated for effective vibration minimization. A LMS-based adaptive feedforward algorithm, and nonlinear feedback gain scheduling of wave parameters targeting transient and steady state vibration isolation is presented. Numerical and experimental results obtained from the implementation of the active control techniques from analysis of the modal based, and wave-type vibration transmission characteristics for an aluminum and a composite active structure is presented.

Damage in the form of local cracks or distributed microcracks causes a reduction of natural frequencies and increase in vibration damping. Natural frequency measurements are a very attractive form of damage detection tests since they can be made at a single point on the component and are independent of position chosen. Since this change in natural frequencies is due a localized reduction of stiffness due to damage anywhere in the structure, if the natural frequencies are shifted back to their undamaged values, it can be said that the local stiffness in the damaged region should be increased to the stiffness of the undamaged region. So damage mitigation can be taken as a dynamic pole placement problem. Considerable work has been done and very good results have been obtained in detecting damage by analyzing the modal test data from a bonded piezoceramic sensor after the structure has been excited with a sine sweep using a bonded piezoceramic actuator. Now work is going on in actuating the piezoceramic patches to reduce the dynamic moment in the damaged region for stress alleviation.

The University of Dayton Research Institute (UDRI) is teamed with McDonnell Douglas Aerospace (MDA) to develop and fly a NASA IN- STEP experiment entitled Jitter Suppression Experiment (JSX). The JSX will demonstrate a combined active/passive vibration control system on an actual full scale space structure. This paper will present the impact of the JSX system requirements on the passive and active vibration control system and verification that these requirements were met. The basic JSX system requirements are broken down into two categories, shuttle requirements and experiment requirements.

The University of Dayton Research Institute (UDRI) is teamed with McDonnell Douglas Aerospace (MDA) to develop and fly a NASA IN- STEP experiment entitled Jitter Suppression Experiment (JSX). The JSX will demonstrate a combined active/passive vibration control system on an actual full-scale space structure. This paper presents various mechanical considerations in the design of the active control system. This includes evaluating different sensor and actuator types and evaluating applicable control theories and control implementations.

Inthe realm of SemI-acth,e" suspension systems, this paper descilbes a truly "active damping" system. Thorough research and development of low voltage Electro-Rheological Magnetic (ERM) flus, a revived rotary shock absorber suspenon phiosophy and a newv developed control algorithm have resulted in an active damping system that resolves the selection between ilde comfcwt and handling performance. The ERM fluid technology, rotary shock absorber configuration and Digital Signal Processor (DSP) technology have advantages oftransmithng high forces in a small compact package. The DSP controls the eIemen that digitize analog sensor signals and through software, result in active damping. We call the actuator e Rotary Active Control Damper (RACD, pronounced ack-dee"). The variety of on-board sensors makes it possible to adjust vehicle performance through software. Mathematical analysis, computer simulations, iind actual vehicle testing of the developed algorithm in which RACD is the damping actuator have shown the advantage of the developed technology. The system can be operational in either an open or closed-loop form for o4imum continuous control of the active damper. Actual vehicle Eistallation of RACD's with extensive testing have shown that this is a practical alternative to todays multidamping shock absorbers.