This paper presents some of the results of an experimental and analytical study of a controllable electrorheological device configured to induce an adjustable amount of dynamic shear force in response to an applied vo...
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This paper presents some of the results of an experimental and analytical study of a controllable electrorheological device configured to induce an adjustable amount of dynamic shear force in response to an applied voltage. Maps of the force-deformation characteristics of the aluminosilicate based ER material are developed over a relatively wide frequency range, and approximating analytical expressions are obtained for the force-deformation-frequency-voltage characteristics of the material. Subsequently, an evaluation is made of the efficiency of using on line control of an electrorheological actuator to emulate the operation of an optimally tuned auxiliary mass damper attached to a primary system subjected to arbitrary dynamic environments. It is shown through numerical simulation studied that the proposed parameter control algorithm provides an efficient means for the on line control of the primary system under a wide range of excitations. An experimental study is presented in which an ER device is used, in conjunction with a small laboratory building model, as a semiactive element in an on line structural control approach using pulse control techniques.
One major problem in magnetic resonance image (MRI) equipment is the high-level noise borne by the vibration of the cylindrical shell to support the coils for gradient magnetic fields. The vibration of the shell is ex...
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One major problem in magnetic resonance image (MRI) equipment is the high-level noise borne by the vibration of the cylindrical shell to support the coils for gradient magnetic fields. The vibration of the shell is excited by the Lorentz force between the pulse current applied to the coils and the main magnetic field. In order to suppress the noise inside the cylindrical shell, it is aimed to control the vibration of the shell. In this paper, simulation is carried out on the vibration control of the shell by using distributed piezoelectric actuators. The actuators produce a bending moment or an in plane force when pulse voltages are applied synchronously with the pulse current of the coils. Coupling of actuators and vibration modes, and parameter optimization are also discussed. The simulation results show that the vibration level is successfully reduced in the frequency range of 400-1200 Hz.
The aim of this paper is to study how much adaptive semiactive control improves the seismic behaviour of base isolated buildings. The semiactive force at any instant is determined on line by minimizing a quadratic per...
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The aim of this paper is to study how much adaptive semiactive control improves the seismic behaviour of base isolated buildings. The semiactive force at any instant is determined on line by minimizing a quadratic performance index based on a weighting of the building's response and the control effect. This method requires precise knowledge of the building's behavior, but in practice this may be impractical or impossible, such as when certain non-linear components have no known analytical form, or when a system's properties are time varying. The principle presented here is to use a neural network to build an adaptive semiactive control method whereby non-linear distributed systems are identified by their dynamic response. After recalling the principles of active and semiactive control, an application to a eight-storey building is proposed and the numerical results are analysed.
The work described in this paper is concerned with controlling the strain of the constraining layer of a composite structure In such a way as to enhance the shear generated in the viscoelastic material and hence impro...
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The linear quadratic regulator has been used extensively in many control systems designed for structural control applications due to its stability and robustness. Recent results obtained from simulation, model experim...
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The linear quadratic regulator has been used extensively in many control systems designed for structural control applications due to its stability and robustness. Recent results obtained from simulation, model experiments, and full-scale structural applications, however, show that it is difficult to employ linear feedback control laws to produce a significant peak response reduction when the peak response occurs during the first few cycles of the time history. In this paper, based on the fact that minimizing the maximum response can be approximated by minimizing a higher-order performance index, a higher-order performance criterion is introduced and an optimal non-linear feedback control law is derived based upon this criterion. It is shown that this non-linear control law can significantly improve peak response reduction under the same constraints imposed on the control resources as in the linear quadratic regulator case.
Instruments and machines requiring very high stability should be isolated from their normally less stable environment. Exact constraint mounting using six, single-constraint flexures provides a stiff connection betwee...
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ISBN:
(纸本)0819417947
Instruments and machines requiring very high stability should be isolated from their normally less stable environment. Exact constraint mounting using six, single-constraint flexures provides a stiff connection between the instrument and its environment while isolating the instrument from low frequency deformations of the environment, such as thermal expansion. Higher frequency disturbances, however, transfer through the flexures and excite vibration modes of the instrument. Traditionally, passive or active vibration isolation is employed to attenuate environmental disturbances reaching the instrument. However, strict alignment requirements for the instrument preclude the use of low-frequency isolation, unless active methods are used. Therefore, the solution is to provide damping in parallel with the flexures to reduce the vibration amplitudes of the instrument. Flexures concentrate strain energy in blades making them excellent candidates for damping treatments. A properly designed damping treatment across the flexures can provide as much as 8% to 10% viscous damping to the isolation modes and will also help attenuate the instrument vibration modes. Thus, through the use of six damped single-constraint flexures the instrument's requirements for stability, alignment, stress, and vibration may be met. An application of this approach will be employed on the Reflection Grating Array (RGA) for the X-ray Multi-mirror Mission for the European Space Agency. The RGA is an array of 200 diffraction gratings aligned to sub-micron and sub-arc-second tolerances relative to each other. This produces a coherent wavefront for spectrum analysis. The launch vehicle will be an Ariane 5 scheduled for 1998.
Let a structural system be operating under a natural hazard. The time history of the loading acting on it during its lifetime cannot be foreseen but only recorded on line. The system can be equipped by appropriate dev...
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Let a structural system be operating under a natural hazard. The time history of the loading acting on it during its lifetime cannot be foreseen but only recorded on line. The system can be equipped by appropriate devices for the control of its dynamics. The general switch of the control process should be operated by a decisional link where the records, coming from the sensors which monitor the external excitation, are put in relation with the expected performance, and/or safety, of the structure. The actuators will be turned on only in the case where the uncontrolled response is predicted to express undesired features. The problem is to recognize from the very first sampled values of any excitation pulse the effectiveness which the preselected control scheme will exhibit once adopted. The present paper deals with the design of such a decisional link in a neural-network framework. The resulting tool is restricted to operate under stationary forms of excitation. Non-stationarity due to signal modulation, however, is covered by the approach, provided that local considerations offer a demodulation rule.
About eight years have passed since the authors promoted full-time research and development of the structural response control systems which aimed at a 'safer and more comfortable' building structure. Up to no...
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About eight years have passed since the authors promoted full-time research and development of the structural response control systems which aimed at a 'safer and more comfortable' building structure. Up to now, various types of passive and active structural response control systems have been developed and practically applied to actual buildings with a good success rate. The emphasis had been placed especially on the active and hybrid type structural response control systems which resulted in the 'first in the world' practical application of an active mass driver (AMD) system to an actual building in 1989. At present, three different types of active or hybrid control systems, which are applicable for earthquakes of moderate to high intensities, as well as strong winds, have been successfully developed and practically applied: (1) Active mass driver (AMD) system;(2) Active variable stiffness (AVS) system;(3) Hybrid mass damper (HMD) system. In this report, the R&D motivation of the authors and the development are first described. Then the developed passive control systems concentrating on the application to high-rise buildings are explained. Finally an introduction to the basic principles and the composition of the active control systems, and the control effects on the buildings' response based on actual observations, as well as the numerical simulation under real earthquakes and strong winds, are presented.
smartmaterials such as piezoceramics and shape memory alloys (SMAs) exhibit significant hysteresis and in order to estimate the effect on open and closed loop control a suitable model is needed. One promising candida...
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smartmaterials such as piezoceramics and shape memory alloys (SMAs) exhibit significant hysteresis and in order to estimate the effect on open and closed loop control a suitable model is needed. One promising candidate is the Preisach independent domain hysteresis model that is characterized by the congruent minor loop and wiping out properties. Comparable minor loop and decaying oscillation test data for a multi-sheet piezoceramic actuator (made of lead zirconate titanate) attached to a flexible beam are presented and are seen to be very consistent with the two Preisach model properties. The commanded parameter is the sheet transverse electric field while the measured parameter is an approximately colocated strain induced in the beam. Equivalent data for a Nitinol SMA wire muscle, attached to the same beam, are also presented. The input and output parameters are the SMA current and a beam strain respectfully. The minor loop and wiping out evidence is less strong than that of the piezoceramic case, but encouraging. In all experiments the quasi-steady state responses were generated in order to avoid exciting beam flexible modes which would complicate the analysis.
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