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Integration of autonomous fatigue crack detection and vibration control in smart plates

Proceedings of SPIE - The International Society for Optical Engineering 2000年 3985卷 629-639页

作者： Ray, Laura R. Koh, Bong-Hwan Dartmouth Coll Hanover United States

This paper develops and demonstrates performance analysis of vibration suppression and damage detection control laws on structures with fatigue cracks. State feedback control laws for the individual tasks of vibration suppression and autonomous damage detection are designed based on low-order models of a damaged structure. These control laws are applied to finite-element models of structures with through-surface and surface cracks. The analysis ascertains the ability of feedback control to enhance sensitivity of modal frequency shifts due to realistic damage and the potential for using the same sensors and actuators for implementing vibration damping control laws that are insensitive to damage. In the control model, damage consists of simple reductions in thickness over a small area of the structure. Finite-element models to which control laws are applied are developed using commercial software (ABAQUS) that more accurately models the crack by releasing element connections or by using line spring elements. Results show that feedback control laws can be designed for either crack detection or vibration suppression using identical hardware. In addition, we demonstrate that simple models of damaged structures are suitable for designing control laws for detecting more complex damage conditions, and we demonstrate the use of commercial software for model-based simulation of controlled structures.

关键词： Intelligent structures

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Vibration control of a flexible beam with integrated actuators and sensors

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smart materials & structures 2000年第6期9卷 932-939页

作者： Manning, WJ Plummer, AR Levesley, MC Univ Leeds Sch Mech Engn Leeds LS2 9JT W Yorkshire England

The use of system identification to determine linear Auto Regressive Moving Average eXogenous inputs (ARMAX) models for smart structures has been scarcely reported in the literature. However, these models can be used as a basis for a Linear discrete-time controller design. This work presents a smart structure vibration control scheme developed using an ARMAX model of the structure and compares its performance to an empirically designed velocity feedback controller. The smart structure is comprised of piezoceramic (such as PZT) actuators and strain gauge sensors attached to a cantilever beam and interfaced to a PC, which provides the control software platform. System identification is carried out in three phases: data collection, model characterization and parameter estimation. Input-output data are collected by stimulating the piezoactuators with a bipolar square wave signal and monitoring the strain gauge response. The model is characterized with second-order plant dynamics and a least-squares estimation algorithm calculates the model parameters. The controller is designed using pole placement to achieve the desired closed-loop response. The ARMAX model is used to calculate the pole placement controllers by solution of the Diophantine equation for the prescribed closed-loop pole positions. Results show that the pole placement controller can match the performance of a velocity feedback controller and maintain this performance when the sampling rate is greatly reduced.

关键词： Intelligent structures

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Active structural acoustic control of a thick-walled cylindrical shell

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Proceedings of SPIE - The International Society for Optical Engineering 2000年 3984卷 112-124页

作者： Song, Kyungyeol Atalla, Mauro J. Hall, Steven R. Massachusetts Inst of Technology Cambridge United States

We consider the problem of reducing the noise radiation from a thick-walled cylindrical shell by actively controlling the motion of the shell's outer surface. Because the shell is very stiff, it is difficult to directly control the shell deflections. Instead, the proposed approach is to cover the shell's outer surface with curved active composite panels. Each panel contains several embedded accelerometers mounted to its outer and inner surfaces, which can sense both the motion of the panel base (i.e., the outer motion of the shell) and the outer surface of the panel (i.e., the radiating surface). The accelerometers are used in both feedback and feedforward architectures, in which the accelerometer signals are used to command the panel displacement, in order to reduce the motion of the panel outer surface, reducing the radiated noise. Experimental results show that, in the best case, 10-30 dB of surface vibration reduction can be achieved in the frequency range of interest, which is 250-2000 Hz.

关键词： Acoustic variables control

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Seismic control of civil structures utilizing semi-active MR bracing systems

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Proceedings of SPIE - The International Society for Optical Engineering 2000年 3988卷 217-228页

作者： Hiemenz, Gregory J. Choi, Young-Tai Wereley, Norman M. Univ of Maryland College Park United States

Magnetorheological (MR) dampers are a promising class of devices for the control of civil structures for earthquake hazard mitigation. MR dampers exhibit both viscous damping and friction damping, where the friction damping level is controlled by an applied magnetic field. This unique characteristic, as well as low power requirements, high force capacity, and mechanical simplicity, lends them to be very suitable devices for the semi-active control of such seismically loaded structures. This study investigates semi-active control methods and their application to MR dampers. Skyhook control and a `clipped' Continuous Sliding Mode (CSM) control are simulated both numerically and experimentally. The results show that control of civil structures with semi-actively controlled MR braces is very effective.

关键词： Structural analysis

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Natural frequencies of a smart plate with segmented piezoelectric patches

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Proceedings of SPIE - The International Society for Optical Engineering 2000年 3984卷 468-477页

作者： Gopinathan, Senthil V. Varadan, Vasundara V. Varadan, Vijay K. Pennsylvania State Univ University Park United States

Classical Plate Theory (CPT) has been applied successfully in the past to the plates with distributed piezoelectric patch bonded to the surface or embedded within the layers [1-7]. In all earlier models the mass and stiffness' contributions from sensor and actuator patches were neglected for estimating the natural frequencies of the smart plate. Also the thickness direction electric fields and strain fields inside the patches are assumed to be constant over the entire area of the patch. The validity of these assumptions depends on the size and relative stiffnesses of the patches and is not investigated before. In this paper the CPT is used to estimate the natural frequencies of a plate structure with surface bonded piezoelectric patches without the above-mentioned assumptions. A detailed modeling of the patches is developed by expressing the electric potential inside the patch as a quadratic function of thickness coordinate. The equations of motion are derived for a generally isotropic plate with surface bonded segmented patches. Solution to the dynamic equation of motion are obtained using Fourier series method for a plate with collocated piezoelectric actuator/sensor patches. The effect of the passive and active stiffness' of the surface bonded actuator and sensor patches on the dynamic characteristics of host plate structure is investigated.

关键词： Plates (structural components)

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Active deformable sheets: prototype implementation, modeling and control

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Proceedings of SPIE - The International Society for Optical Engineering 2000年 3985卷 572-582页

作者： Lind, Robert J. Johnson, Norbert Doumanidis, Charalabos C. Tufts Univ

Active deformable sheets are integrated smart planar sheet structures performing off-plane deformations under computer actuation and control, to take up a desired dynamic morphology specified in CAD software or obtained by 3-D scanning of a solid surface. The sheet prototypes are implemented in the laboratory by elastic neoprene foil layers with embedded asymmetric grids of SMA wires (Nitinol), which upon electrical contraction bend the sheet to the necessary local curvature distribution. An analytical model of such prototypes, consisting of an electrical, a thermal, a material and a mechanical module, as well as a more complex finite element thermomechanical simulation of the sheet structure have been developed and validated experimentally. Besides open-loop control of the sheet curvatures by modulation of the SMA wire actuation current, a closed-loop control system has been implemented, using feedback of the wire electrical resistance measurements in real time, correlating to the material transformation state. The active deformable sheets are intended for applications such as reconfigurable airfoils and aerospace structures, variable focal length optics and electromagnetic reflectors, flexible and rapid tooling and microrobotics.

关键词： Intelligent structures

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Vibration distribution reconstruction and control of a thin plate by using distributed PVDF sensors affixed to the plate

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Proceedings of SPIE - The International Society for Optical Engineering 2000年 3984卷 576-586页

作者： Nagayasu, Katsuyoshi Uchida, Norio Hayashi, Takuro Takahashi, Hiroshi Toshiba Corp Kanagawa Japan

In this study, vibration distribution of a thin plate is detected using outputs from a number of long-span piezoelectric films that serve as distributed vibration sensors affixed on the plate. Using long-span piezoelectric films, only the integrated strains along the direction of the sensor span could be obtained. However, in the case that plural sensors were affixed and a kind of transformation was used, the vibration distribution could be obtained. We are considering applying the method for vibration control of space structures, namely antennas and/or solar battery paddles. In this study, basic technology for realizing the applications is presented. The strain distributions and the sensor outputs are predicted and calculated using NASTRAN (Finite Element Method). The strain distributions of a vibrating rectangular thin plate to which a number of long-span PVDF films were affixed are detected by experiment. These PVDF films are cut into several kinds of sinusoidal shapes and the outputs of the films are composed to the vibration distribution. This method is based on the theory that waves of any kind are composed by the sum of trigonometric function series. The usefulness of this approach is confirmed by comparing the calculational and experimental results.

关键词： Sensors

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Properties of interfacial adhesion for vibration controllability of composite materials as smart structures

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COMPOSITES SCIENCE AND TECHNOLOGY 2000年第10期60卷 1953-1963页

作者： Park, JM Kim, DS Han, SB Gyeongsang Natl Univ Res Ctr Aircraft Parts Technol Dept Polymer Sci & Engn Chinju 660701 South Korea Kyungnam Univ Div Mech Engn Masan 630701 South Korea

The performance of smart structures depends on the quality of the bonding along the: interface between the main structure and the attached sensing and actuating elements. By using interfacial adhesives providing optimum bonding conditions between them, vibrational properties of the composite beams with attached sensor and actuator were investigated. Three different adhesives, i.e. ethyl-2-cyanoacrylate adhesive (type A), toughness and stiffness controlled epoxy adhesives (types B and C) were compared with each other. An optimal type adhesive was chosen, based on its mechanical and wetting properties. Under severe loading condition, type C was found to be most suitable for the vibrational structure system, assuming that the composite beam/adhesive layer/PZT system can deform with the same curvature. In addition, type C adhesive can provide the optimized bonding for manufacturing the smart structure and transfer the elastic behavior precisely. In addition, the beam with type C adhesive provided the fastest response time for the vibration control. This means that the optimum bonding between composite beam and PZT was formed comparatively using this interfacial adhesive. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.

关键词： smart materials interphase surfaces vibration stress transfer

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Active control system for a rotor blade trailing-edge flap

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Proceedings of SPIE - The International Society for Optical Engineering 2000年 3985卷 52-61页

作者： Duvernier, Marc Reithler, Livier Guerrero, Jean Yves Rossi, Rinaldo AEROSPATIALE MATRA CCR Suresnes France

Reducing the external noise is now a major issue for helicopter manufacturers. The idea beyond this goal is to reduce or even avoid the blade vortex interaction (BVI). EUROCOPTER is currently investigating several strategies to reach this goal. One such strategy is to control the local incidence of the blade by a direct lift flap. AEROSPATIALE MATRA Corporate Research Center and AEROSPATIALE MATRA MISSILES provide the actuator system for the direct lift flap.

关键词： Actuators

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The control of the post-buckling response in thin composite plates using smart technology

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THIN-WALLED structures 2000年第4期36卷 231-263页

作者： Thompson, SP Loughlan, J Cranfield Univ Cranfield Coll Aeronaut Struct & Mat Technol Grp Cranfield MK43 0AL Beds England

Restoration forces, associated with embedded activated pre-strained shape memory alloy wires, have successfully been employed to enhance the post-buckling behaviour of various laminated plate structures. An extensive experimental and numerical programme has been conducted, the results of which will be presented. The manufacturing methodology of the hybrid SMA/carbon/epoxy plates is outlined. Such specimens feature 0.4-mm diameter shape memory alloy wires located within tubing at desired locations. Numerical thermal analysis has been employed to predict the non-uniform temperature profile, attributed to shape memory alloy activation through resistive heating, within the laminates. Structural finite element analysis has been employed to determine the hybrid plates' adaptive response while under the influence of a uniaxial compressive load in excess of its critical buckling value. It is shown that, utilising the considerable control authority generated, even for a small actuator volume fraction, the out-of-plane displacement of the post-buckled laminates can be significantly reduced. Such displacement alleviation allows for load redistribution away from the specimens' unloaded edges. With the increase in use of composite materials within aerospace platforms, it is envisaged that the hybrid adaptive SMA/laminate configuration will extend the operational performance over conventional materials and structures, particularly when the structure is exposed to an elevated temperature. (C) 2000 Elsevier Science Ltd. All rights reserved.

关键词： adaptive control shape memory alloy actuators post-buckling composite plates smart technology

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