Showing papers in "Journal of Intelligent Material Systems and Structures in 1991"

Static Aeroelastic Control Using Strain Actuated Adaptive Structures

Abstract: In this study, the feasibility of using representative box wing adaptive structures for static aeroelastic control is examined. A deformable typical section is uti lized to derive the optimal and suboptimal relations for induced strain actuated adaptive wings, and the relations developed are used to design representative adaptive lifting sur faces which are assessed in trade studies. The optimal relations developed showed that op timal adaptive airfoil designs are possible for some realistic configurations, and effective sub-optimal designs can be achieved for others. In addition, the important parameters associated with inducing curvature and twist, thereby altering the lifting forces on the air foil, are determined. The most important of which were found to be the airfoil thickness ratio, the actuation strain produced by the induced strain actuators, and the relative stiff ness ratio of the actuator to the wing skin for both camber and twist control. The stiffness coupling parameter and the wing aspect ...

Bending and Shape Control of Beams Using SMA Actuators

Abstract: Two new configurations for enhanced bending control of beams with in duced strain actuators are presented. In the first configuration the actuator is external to the beam and passes through selective points on the beam. Since the actuator is outside the beam, differential movement between the actuator and the beam is possible; this results in enhanced bending due to the buckling action of the actuator force. Before actual buckling, there is a fairly large useful range of enhanced bending. In this range the beam displace ments are much greater than can be obtained by embedded or surface bonded actuators. The theoretical formulation for this configuration and its experimental verification is pre sented.

Modeling of Finite-Length Spatially-Distributed Induced Strain Actuators for Laminate Beams and Plates

Abstract: A model for laminate beams and plates with attached or embedded finite- length spatially-distributed induced strain actuators has been formulated and is presented. A conservation of strain-energy model was developed by equaling the applied moment on the cross section of the edges of actuators to determine the induced linear strain distribu tion and the equivalent axial force and bending moment induced by the actuators. Results show that the strain-energy model for a thin laminate beam agrees well with the pin-force madel. In addition, more general conditions were included in this work; for example, mul tiple actuators can be embedded in any layer of laminate. The concept of the conservation of strain-energy model for beams was also extended to a two-dimensional problem- plates. Classical laminate plate theory for spatially-distributed induced strain actuators de veloped previously by the authors is revised here to include the use of the strain-energy model. This work also compares several developed models...

Complete phase-strain model for structurally embedded interferometric optical fiber sensors

Abstract: The relation between a three-dimensional state of strain and the optical phase retardation in a single mode optical fiber is formalized by drawing together classical three-dimensional crystal optics and classical waveguide theory. Neumann's strain optic relations are described in a form usable in optical fiber sensor design. These relations are then combined with weakly guiding fiber theory to develop an integral which relates the optical phase shift in a structurally embedded interferometric optical fiber strain sensor to the induced three-dimensional strain field. This process leads to a previously undisclosed, additional waveguide dispersion term which contributes on the same order to the total strain induced phase retardation as does the term derived by Butter and Hocker (1978). Still, however, waveguide dispersion effects are found to be negligibly small, even in three- dimensional loading. Butter and Hocker's equation and the complete phase-strain model developed herein can give very similar results...

Control of Sound Radiation with Adaptive Structures

Abstract: Active control of sound radiation from a vibrating simply supported rec tangular plate excited by a steady state harmonic point force disturbance is experimentally studied A variety of test cases were studied for controlling sound radiation due to a distur bance both on and off structural resonance Control structural inputs are achieved by three piezoceramic actuators bonded to the surface of the plate The control approach is based upon a Filtered-X version of the adaptive LMS algorithm Error information for the con troller was taken from two sensor formats, either microphones placed in the acoustic far- field, or polyvmylidene fluoride (PVDF) piezoelectric distributed sensors bonded to the surface of the structure The two narrow strip PVDF sensors were positioned on the plate such that the dominant observed response was due to the odd-odd and to a lesser degree, the odd-even modes (ie, the more efficient acoustic radiators) Results from these experi ments indicate that piezoceramic elements provi

Trussarm—A Variable-Geometry-Truss Manipulator:

Abstract: An overview is given of recent work done in Canada on "trussarms"—truss structures of high aspect ratio and variable geometry, suitable for use as manipulator arms. Four possible truss topologies are compared, and the "standard" octahedral topology is shown to be superior, largely on the basis of simplified hinge design. A preliminary com parison is also made between the Canadarm (the current Shuttle manipulator arm) and two trussarms. Some of the key issues in the kinematics, dynamics and control of truss arms are discussed, and the paper closes with a brief description of laboratory trussarm models currently under development.

Wave Propagation in Piezoelectric Layered Media with Some Applications

Abstract: In this article we introduce a systematic methodology to investigate wave propagation in piezoelectric layered media. It is based on a matrix formalism and the con cept of the surface impedance tensor which relates the components of particle displace ment and the normal component of the electric displacement along a surface to the electric potential and the components of traction acting along the same surface. Once the surface impedance tensor for a single layer is calculated, a simple recursive algorithm allows the evaluation of the surface impedance tensor for any number of layers. As an example, the surface impedance tensor is used to find the dispersion curves for a bilaminated piezoelec tric plate. Also the dispersion curves for the subsonic interfacial waves when the plate is in contact with a nonconducting acoustic fluid is investigated. Floquet theory is also ap plied to study wave propagation when the layered medium is periodic.

Modeling of a Shape Memory Integrated Actuator for Vibration Control of Large Space Structures

Abstract: Martin Marietta is developing a shape memory material actuator to pro vide active vibration and shape control for large, adaptive space structures. An important facet of this work is the development of analytical modeling capabilities for shape memory material behavior. These alloys exhibit a very interdependent force-length-temperature (FLT) response, which must be understood to best exploit their behavior for the efficient and timely conversion of heat into mechanical work. Also, the modal response of large, flexible space structures will be affected by the use of inherently non-linear, hysteretic shape memory actuators, and specialized control methodologies need to be developed spe cific to this application. In this work, Cory and McNichols' theory of non-equilibrium thermostatics (NET) was modified to account for the multiple quadrant (i.e., tension and compression) hysteretic behavior of shape memory alloys. Experimental results were used to provide the basis for spatial mapping of the austenite-to-m...

Observations on the nature of transfer functions for control of piezoelectric laminates

Abstract: In this paper, some fundamental relationships for beams incorporating piezoelectric film actuators and sensors are examined. The differential equation of motion for a beam with piezoelectric film bonded to both sides is used to develop Laplace domain transfer function models of the system. These transfer functions are exact Laplace domain representations of the system equations of motion. The transfer functions are cast into a closed rational form using Maclaurin series expansions representing a specific number of modes. In this form, the transfer functions lend themselves to classical control analysis. It is shown that the transfer function relating a voltage applied to a full coverage actuating layer, to the voltage induced in a full coverage sensing layer on the opposite beam face, be haves like a classic colocated system with alternating poles and zeros and accordingly the system is easy to stabilize with low order compensation. In contrast to this result, it is shown that in spite of the effective co...

Application of Smart Structures to Aircraft Health Monitoring

Abstract: Research efforts at Innovative Dynamics have produced sensors and signal processing software that can be integrated into an advanced Health Monitoring System (HMS) to increase the safety of aging aircraft. HMS is a unique distributed system based on "smart structures" technology. By monitoring the vibration signature of a structure, HMS determines structural abnormalities using a network of sensor arrays and distributed processors. Pattern recognition techniques are utilized to classify the sensor signals and determine the type of defect. The memory of the system is formed through a learning pro cess in which a systematic series of experiments is presented to the system.

Analysis of Laminated Composites Containing Distributed Piezoelectric Ceramics

Abstract: A finite element formulation was developed for modeling the dynamic as well as static response of laminated composites containing distributed piezoelectric ceram ics subjected to both mechanical and electrical loadings. The formulation was derived from the variational principle with consideration for both the total potential energy of the structures and the electrical potential energy of the piezoceramics. An eight-node three- dimensional composite brick element was implemented for the analysis, and three- dimensional incompatible modes were introduced to take into account the global bending behavior resulting from the local deformations of the piezoceramics. Experiments were also conducted to verify the analysis and the computer simulations. werall, the compari sons between the predictions and the data agreed fairly well.

Adaptive active control of instabilities

Abstract: This article reports the results of an experimental investigation in which adaptive methods are applied to various situations of active control of flow instabilities: combustion instabilities, flow-excited cavity oscillations, and compressor surge. The pres ent work draws attention especially to the adaptive controller behaviour and capacities. The main results are as follows: 1) The adaptive controller manages to automatically find its optimal characteristics in order to cancel the instability in the three experiments under consideration; 2) It is able to cope with time-dependent changes in the operating condi tions such as flow velocity sweeps for the oscillating cavity and air and propane mass flow rate variations in the combustion instability experiment; and 3) In the case of the Helmholtz cavity resonator, the algorithm has also exhibited capacity to recover effective control even when initially set such that artificial closed-loop instabilities induced by the control system occurred.

Damping and Structural Control of the JPL Phase 0 Testbed Structure

Abstract: This paper describes recent advances in structural quieting technology as applied to active truss structures intended for high precision space based optics applications. The active structure incorporates piezoelectric active members which exert control forces internal to the structure and thereby improve the structure's dimensional stability. The control architecture involves two layers of feedback control. The first utilizes collocated measurements of force and velocity at the active member to achieve active damping, the second utilizes noncollocated measurements of acceleration at the location of a simulated optical component to achieve structural stabilization. The local control loops are based on the concept of impedance matching, the global control loops are designed using robust control methods. These two levels of control are intended to operate simultaneously; however, in this paper each approach is applied individually. The combined implementation is left for future work.

Development of a Shape Memory Material Actuator for Adaptive Truss Applications

Abstract: A shape memory material actuator is being developed to provide active vibration and shape control for large, adaptive space structures. Shape memory alloys have the ability to generate high recovery stresses (>700 MPa) over large strains (> 6 % ), providing potential payoffs for their use in lightweight actuator designs and adaptive com posite structures. However, the utility of these alloys has been limited in past programs due to lack of adequate material characterization studies to optimize mechanism or composite performance, lack of material property stability during transformational cycling, and the dependence on heat transfer rates for rapid cycling capability. In this study, Cory and McNichols' theory of nonequilibrium thermostatics (NET) was applied to quantify and correlate shape memory material behavior for a binary NiTi alloy. NET was then em ployed as a design tool to develop an actuator, utilizing 24 0.5 mm dia. wires (280 mm long) acting against a biasing spring (with stiffness of 305 N/mm),...

Intelligent Chemical Systems Based on Conductive Electroactive Polymers

Abstract: Conductive, electroactive polymers provide a unique platform upon which to construct intelligent materials. These polymers are capable of monitoring and respond ing to the chemical environment in w...

Structural Acoustic Control of a Shape Memory Alloy Composite Beam

Abstract: Active control of sound radiation from a clamped, baffled, composite beam with embedded Shape Memory Alloy (SMA) fibers was demonstrated using two dif ferent control strategies. The unique behavior of the SMA reinforced composites was uti lized to allow minimization of radiated sound for harmonic beam vibration and placement of peak radiation response at specified frequencies within a controllable range.

Shape Control of Flexible Structures

Abstract: A shape control algorithm for a large flexible structure is proposed: (a) a reduced order model, which represents the precise shape of a structure; (b) a shape esti mation filter, which reduces the estimation error caused not only by the white noises of sensor measurements but also by the variation of the D.C. offsets of sensors; (c) a simple and robust controller to regulate many state variables by using many sensors and actuators. The controller is realized by a zero proportional, integral, derivative controller (zero P-ID controller) with the concept of low authority control/high authority control (LAC/HAC). The proposed shape control algorithm is illustrated through applications to a numerical model of an experimental setup.

Vibration Suppression of Flexible Linkage Mechanisms Using Piezoelectric Sensors and Actuators

Abstract: This paper presents a theoretical and experimental study on the vibration suppression of the elastodynamic response of high-speed flexible linkage mechanisms by incorporating smart materials featuring piezoceramic actuators and sensors into the mech anism systems. A mixed variational principle is developed to provide the basis for the deri vation of the finite element equations governing the dynamic responses of the flexible links, the behaviors of the piezoelectric materials and their coupling relationships. The mathematical models of the piezoelectric sensors and actuators are then developed and employed in the finite element analysis and the control system design. To ensure the robust stability, the classical control approach is utilized to design the control system for actively suppressing the vibratory motions of the flexible links. An experimental study on a four- bar linkage mechanism with one flexible link is performed in order to verify the mathe matical model and the results of computer simulati...

Modern Adaptive Real-Time Controllers for Actively Reacting Flexible Structures.

Abstract: This paper describes modern controllers which are based on digital real-time filters, powerful adaptation algorithms and high speed signal processor systems. Such controllers are required for active shape and vibration control on large flexible space structures. Within the framework of the DLR program ARES (Actively Reacting Flexible Structures) - which is an attempt to develop systems capable of changing their characteristics in orbit in order to fulfil essential operational requirements, efforts are specially focused on adaptive signal processing. The hitherto achieved results are presented. The philosophy and capabilities of such controllers are demonstrated, referring to the process of adaptive system identification and inverse modeling. In addition, different types of filtering techniques and adaptation algorithms are theoretically and experimentally discussed concerning structural dynamic requirements.

An application of genetic algorithms to active vibration control

Abstract: A genetic algorithm is developed for the calculation of the time-optimal control force for flexible systems. The algorithm is a robust random-search method which uses a simple and compact coding of the control signal as a binary string of maximum positive and negative forces. A random population of admissible strings is allowed to evolve through the three processes of selection, reproduction and mutation to produce strings with increasing fitness and optimality. The introduction of stop characters allows the time optimal control problem to be solved in one procedure. A simulation is presented to illustrate the behavior of the algorithm. 10 refs.

Polarization controlled ferroelectric high strain actuators

Abstract: The simple phenomenological relation which relates elastic and dielectric properties in an insulating crystalline dielectric takes the form

Kinematics of Adaptive Truss Permitting Nodal Offset(Configuration and Workspace Reach)

Abstract: The adaptive truss structure of statically determinate topology has a capa bility to perform the required task and to meet the environment by adapting its geometrical configuration and mechanical properties. This article discusses the configuration and workspace reach of the practical model of the geometry adaptive truss of helical mast. At the preliminary stage, the kinematics of the ideal truss model is described. Then, the prac tical structure is investigated for the adaptive truss permitting the offsets at the truss nodes. The kinematics are formulated in the context of incremental analysis. The procedures to analyze the configuration and workspace reach are described in the context of the in cremental kinematics. Some illustrative case studies are also conducted.

Control of Position and Bending-Torsion-Coupled Vibration of Rotating Elastic Plate Using Double Tendon Mechanisms

Abstract: For a control method of position and bending-torsion-coupled vibration of a rotating plate, a control method using double trapezoid tendon mechanisms is presented in this study. The proposed trapezoid tendon mechanisms consist of two control sticks, two pairs of wires and two driving sticks individually driven by motors.First, the modeling of the proposed mechanism is carried out by applying the Lagrange's equation method and the modal expansion technique. Secondly, by formulating the crite rion function to take into account the square sum of the rotation angle, the bending, stress and the torsion angle of a thin plate, the optimal control law is derived. Finally, in order to investigate the usefulness of the mechanism, computer simulations and experiments were carried out. To summarize the results, it was demonstrated that the proposed control mechanism is useful for the controls of both the positioning and the vibrations.

Dynamic strain sensing of a composite lattice with an integrated optical fiber

Abstract: A fiber-optic sensor was used to investigate the modal response of a highly-flexible graphite/bismaleimide lattice structure. The natural frequencies and modal amplitudes were determined based on strain readings taken from the structurally- integrated fiber-optic sensor. The advanced composite lattice structure to which the sensor was attached is a half-scale model of the aluminum grid currently being used for active control studies at the Air Force Astronautics Laboratory. The dynamically-scaled compos ite lattice structure, which employs 2.604-cm (1.025-inches) wide strips to form a five-by- five grid, is 76.52-cm (30.125-inches) square overall with a nominal thickness of 0.094 cm (0.037 inches). The longitudinal and transverse members employ the same seven-ply [O3/90] s stacking sequence with reference to their local coordinate system, except at the intersections, where the layers are alternated. The scaled lattice structure was fabricated from G40-600/5245C graphite/bismaleimide prepreg tape. The firs...

A Unified Control Strategy for the Active Reduction of Sound and Vibration

Abstract: The generalized minimum variance (GMV) control strategy is proposed as an effective strategy for active sound and vibration control systems. The GMV strategy is shown to unify well-known adaptive filtering approaches based on LMS-type algorithms and purely feedback strategies as used in other types of control systems. The shortcomings of the LMS adaptive filtering systems for active sound control are clearly uncovered. Pure adative filtering emerges from the GMV strategy merely when the extraneous noise at the error sensor is Gaussian noise, the controller complexity is restricted and no fast tracking of system changes is required The necessary additional identification of the secondary acoustic path is an extra problem of the adaptive fittering approach. Simulation experiments with real and synthetic data verify the wide appticability of the GMV control strategy and the limited efficacy of (LMS) adapive filters for use in active sound reduction systems.

Eigenproperties of Feedforward Controlled Flexible Structures

Abstract: Adaptive feedforward algorithms have been successfully applied in the ac tive control of sound and vibration. However, the actual mechanisms of control inherent in the technique remain an area of much interest. The main objective of this research is to study the dynamic characteristics of a feedforward controlled elastic system. An en tirely new mathematical approach to predicting the dynamic characteristics of the con trolled structure is presented. It is shown that the controlled system effectively behaves as having new eigenproperties. The controlled eigenvalues and eigenfunctions are func tions of the control force and error sensor locations, and independent of the input disturbance.

Identification and Adaptive Control of Flexible Truss Structures

Abstract: This paper describes investigations on adaptive vibration control and shape adjustment of truss structures making use of the active member actuator. The actua tor was manufactured in an attempt to achieve these functions by linear actuating. Funda mental characteristics were examined statically and dynamically. Numerical simulations of planar truss model with the configuration of one pair of collocated actuator and sensor shows that a state observer can estimate truncated modes well and the excited vibration can be controlled rapidly.

Exploitation of chaos for active control : an experiment

Abstract: We have implemented a control scheme to exploit chaotic behavior in a physical system. The method of control requires only small time-dependent perturbations of a single system parameter and does not require model equations for the dynamics. We have demonstrated the power of the method by controlling an experimental chaotic system around unstable periodic orbits and exploiting the underlying chaos to switch the motion between these orbits at will. The robustness of the method is tested by adding white noise to our experimental system during control to obtain information on the effect of noise on control failures.

Use of Robustness Constraints in the Optimum Design of Space Structures

Abstract: This paper describes an optimization procedure to design a minimum weight structure and optimum control system with constraints on the eigenvalues and robustness parameter for structured uncertainties in the closed-loop plant matrix. The design variables are the cross-sectional areas of the members and the elements of the state and control weighting matrices. The optimization problem was solved by using a nonlinear mathematical optimization technique based on the interior penalty functions. The numeri cal results are presented for the ACOSS-FOUR structure. This example illustrates how the use of optimization techniques can reduce the weight of the nominal structure, make the control system more robust and Improve the response due to the external disturbance.

Algorithm-based method for suppressing the transmission of sound in a water-filled waveguide

Abstract: Harmonic waves propagating in a water-filled cylindrical waveguide are suppressed by an actuator-sensor combination. The actuator and sensor are made from a material consisting of piezoelectric particles suspended in an elastomer matrix. The feed back mechanism is based on an algorithm originating in the evaluation of complex roots of an analytic function. It does not depend on a model for the experimental arrangement. Results are presented for frequencies varying from 100 to 5000 Hz. Although it is not needed for the operation of the method, a mathematical model is offered that illustrates the wave interaction and provides a comparison of the merits of the active material used with other candidates.