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smart structures and materials 2000 - Industrial and Commercial Applications of smart structures Technologies

作者： Ninneman, R.Rory Denoyer, Keith K. Air Force Research Lab Kirtland Air Force Base United States

The Air Force Research Laboratory (AFRL) is sponsoring the Middeck Active control Experiment Reflight (MACE II) Program. MACE II is a manned space experiment (requires astronaut assembly and operations) that evaluates the capabilities of adaptive control of flexible structures in the zero-g environment of the Space Shuttle's Middeck. MACE II has grown out of lessons learned from the original MACE flight and from AFRL sponsored structural control experiments. Previous experiments required extensive testing and `tuning' for their particular test environment to meet their performance expectations. Such a process is too inefficient to be seriously considered for operational systems, especially space-based systems were access is limited. MACE II takes the next logical step by evaluating the capability of adaptive structural control algorithms. AFRL has assembled a team of five small businesses and Universities to develop and evaluate several adaptive control methodologies. In addition, AFRL has recruited a second science team led by the Massachusetts Institute of Technology (MIT) to evaluate control systems for time-varying and geometrically nonlinear systems. This paper is an overview of the AFRL science team only.

关键词： Intelligent structures

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Active structural acoustic control of a thick-walled cylindrical shell

Active structural acoustic control of a thick-walled cylindr...

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smart structures and materials 2000 - mathematics and control in smart structures

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

Seismic control of civil structures utilizing semi-active MR...

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smart structures and materials 2000: smart Systems for Bridges, structures, and Highways

作者： Hiemenz, Gregory J. Choi, Young-Tai Wereley, Norman M. Univ of Maryland College Park MD 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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Recent advances in Active Fiber Composites for structural control

Recent advances in Active Fiber Composites for structural co...

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smart structures and materials 2000 - Industrial and Commercial Applications of smart structures Technologies

作者： Bent, Aaron A. Pizzochero, Alessandro E. Continuum Control Corp Billerica United States

Active Fiber Composites (AFCs) provide a novel method for large scale actuation and sensing in active structures. The composite comprises unidirectionally aligned piezoelectric fibers, a resin matrix system, and interdigital electrode. AFCs have demonstrated distinct advantages over current monolithic piezoceramic actuators, including: higher planar actuation strains, tailorable orthotropic actuation, robustness to damage, conformability to curved surfaces, and potential for large area distributed actuation/sensing systems. This manuscript focuses on recent developments in three key areas. The first area describes the completion of a standard AFC baseline material. The baseline AFC consists of 5.5 mil diameter PZT-5A fibers laminated with an epoxy film adhesive and silver screen-printed electrodes. A scalable fabrication process based on lamination industry equipment has been implemented. Baseline AFC performance has been characterized, including free strains (1200 μS) and blocked force (70 lbs). The send area describes continued work in developing optimized geometry/materials for future AFCs. AFC performance and efficiency can be affected significantly by changes in electrode pitch and fiber diameter and/or cross-sectional geometry. Various improved designs have been identified. Third is a review of application demonstrations that exploit the benefits of AFCs to solve structural control problems.

关键词： Composite structures

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Static shape control of composite plates using a slope-displacement based algorithm

Static shape control of composite plates using a slope-displ...

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AIAA/ASME/ASCE/AHS/ASC 41st structures, Structural Dynamics, and materials Conference

作者： Chee, C Tong, L Steven, GP Univ Sydney Dept Aeronaut Engn Sydney NSW 2006 Australia

An intuitive approach for the determination of voltage distribution in the application to shape control of smart structures using piezoelectric actuators is presented here. This novel approach introduces slope as the fine-tuning criteria on top of the common displacement based shape control. The algorithm called the Perturbation Buildup Voltage Distribution (PBVD) is based on an iterative approach inspired by a previous algorithm BVD on displacement control. This method aims to provide a means of targeting the desired shape of a structure with a higher order criteria such as slope. A natural consequence of this method is the smoothing of the resultant structure. This effect will be illustrated by numerical examples. Iterative parameters are varied to investigate favorable choices of the parameters. Results show that the slopes of the structure can be improved but at a tolerable expense of the displacement criteria. Another result of practical interest is the reduction of internal stresses compared to cases using pure displacement shape control.

关键词： Iterative methods

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Natural frequencies of a smart plate with segmented piezoelectric patches

Natural frequencies of a smart plate with segmented piezoele...

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smart structures and materials 2000 - mathematics and control in smart structures

作者： Gopinathan, Senthil V. Varadan, Vasundara V. Varadan, Vijay K. Pennsylvania State Univ University Park PA 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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Artificial muscles versus natural actuators from frogs to flies

Artificial muscles versus natural actuators from frogs to fl...

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smart structures and materials 2000 Conference

作者： Full, RJ Meijer, K Univ Calif Berkeley Dept Integrat Biol Berkeley CA 94720 USA

ISBN: (纸本)0819436054

When is a human-made actuator an artificial muscle? Natural actuators in the animal kingdom vary greatly in their capacity and role (Full, 1997 Handbook of Physiology). Maximum stress varies by 100-fold (0.7 to 80 Ncm(-2)) as does the velocity at which muscles contract (0.3 to 17 lengths/sec). Some muscles generate near maximum force over broad strain ranges, while others function over only the narrowest ranges. Frequencies of operation range from less than 1 Hz to 1000 Hz. Mass-specific power output can reach over 250 W/kg muscle. Muscles function not simply as force generators, but as springs and dampers. Our isolated muscle experiments on insects show that some muscles function primarily as energy absorbers and have a role in control, while others are effective at power generation. At present, we are evaluating EAPs to see where these actuators fit in the functional space of nature's muscles. EAPs appear particularly promising as artificial muscles for insect-sized robots.

关键词： Actuators Electroactive polymers Artificial muscles Dielectrics control systems Electrodes Carbon Kinematics Polymers Robots

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Implementation and testing of passive control devices based on shape memory alloys

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EARTHQUAKE ENGINEERING & STRUCTURAL DYNAMICS 2000年第7期29卷 945-968页

作者： Dolce, M Cardone, D Marnetto, R Univ Basilicata Dept Struct Geotech & Appl Geol I-85100 Potenza Italy TIS SPA I-00128 Rome Italy

Two families of passive seismic control devices exploiting the peculiar properties of shape memory alloy (SMA) kernel components have been implemented and tested within the MANSIDE project (Memory Alloys for New Seismic Isolation and Energy Dissipation Devices). They are special braces for framed structures and isolation devices for buildings and bridges. Their most important feature is their extreme versatility, i.e. the possibility to obtain a wide range of cyclic behaviour - from supplemental and fully re-centring to highly dissipating - by simply varying the number and/or the characteristics of the SMA components. Other remarkable properties are their extraordinary fatigue resistance under large strain cycles and their great durability and reliability in the long run. In this paper, the working mechanisms of the SMA based devices are outlined and the experimental tests carried out to verify the above-mentioned properties are extensively described. Copyright (C) 2000 John Wiley & Sons, Ltd.

关键词： passive seismic control energy dissipation systems isolation systems smart materials shape memory alloys superelasticity

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Adaptive control of radiated noise from a cylindrical shell using Active Fiber Composite actuators

Adaptive control of radiated noise from a cylindrical shell ...

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smart structures and materials 2000 - Industrial and Commercial Applications of smart structures Technologies

作者： Goddu, Gregory McDowell, Donald Bingham, Brian Naval Undersea Warfare Cent Newport United States

This paper describes the application of Active Fiber Composite actuators, a hybrid piezoelectric device, to the reduction of acoustic radiation from a cylindrical shell by active control methods. Active Fiber Composites were developed to provide a mechanically robust method for large-area, orthotropic actuation and sensing in active structures. The actuation layer is formed by small diameter piezoelectric fibers that are unidirectionally aligned and imbedded in a resin matrix system. By the nature of its structure, an Active Fiber Composite actuator allows use of the primary piezoelectric effect in the plane of the composite. A cylindrical shell testbed is used for this experiment due to the predominance of this structure, and the resulting general interest, within the field of underwater acoustics. To control acoustic radiation from the cylindrical shell, the Active Fiber Composite actuators, placed at optimal locations determined using numerical models, are used to generate a strain field that counteracts the strain associated with acoustically efficient shell motions. Using an end-mounted accelerometer as the error measurement, an adaptive LMS algorithm is used to minimize the error signal in real-time. Experimental are supplied to validate both the device and the methodology in a complex, real-world environment.

关键词： Intelligent structures

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Placement of feedback controllers on civil structures using genetic algorithms

Placement of feedback controllers on civil structures using ...

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smart structures and materials 2000: smart Systems for Bridges, structures, and Highways

作者： Abdullah, Makola M. Richardson, Andy Hanif, Jameel Florida State Univ Coll of Engineering FL United States

Genetic algorithms will be used for the optimization of feedback gains and controller placement for discrete building structures. The optimal design and placement of controllers at discrete locations is an important problem that will have impact on the control of civil engineering structures. Though algorithms exist for the placement of sensor/actuator systems on continuous structures, the placement of controllers on discrete civil structures is a very difficult problem. Became of the nature of civil structures, it is not possible to place sensors and actuators at any location in the structure. This usually creates a nonlinear constrained mixed integer problem that can be very difficult to solve. Using genetic algorithms in conjunction with gradient based optimization techniques will allow for the simultaneous placement and design of an effective structural control system. The introduction of genetic-based algorithms should increase the rate of convergence and thus reduce the computational time for solving the difficult control problem.

关键词： Structural analysis

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