Active control of structures against environmental loads such as those due to wind and earthquakes has received much attention recently. Feasibility studies, numerical and experimental, have shown that it is a viable ...
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Active control of structures against environmental loads such as those due to wind and earthquakes has received much attention recently. Feasibility studies, numerical and experimental, have shown that it is a viable alternative to conventional methods in enhancing the performance of structures under such loadings. Most of the research thus far has concentrated on developing mathematical models and algorithms based on optimal control theory and the necessary hardware to implement the control. Research on control based on neural networks has been very limited in spite of the potential advantages of this method such as its inherent ability to handle non-linear systems, incorporate leads or delays, and recover from partial system failure. This paper presents a method of control of structures based on neural networks. The rationale for neural network-based control is first outlined, followed by a brief description of the analytical and experimental investigations, and finally illustrative numerical examples are given of control of a non-linear single-degree-of-freedom structure by neural net.
The paper presents some results from the application of a set-theoretic bounded-state control strategy to active structural control problems. This particular control strategy, never before applied to structural proble...
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The paper presents some results from the application of a set-theoretic bounded-state control strategy to active structural control problems. This particular control strategy, never before applied to structural problems, has many features that are very suited for structural control: among them, the possibility of prescribing and guaranteeing exact bounds on the state and on the control forces, while taking into account the uncertainty on the external forces (in a non-probabilistic way). After a brief presentation of the control strategy, two examples are discussed, showing the applicability of the proposed control strategy to general structural systems. The interpretation of the results throws light on some limitations of the original approach, and suggests possible extensions of the concept, in view of the application to real problems.
In this paper, some important issues regarding the active and passive vibration control of long-span cable-supported bridges are presented. Such structures present unique features that need to be specifically addresse...
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In this paper, some important issues regarding the active and passive vibration control of long-span cable-supported bridges are presented. Such structures present unique features that need to be specifically addressed in order to provide meaningful results. First, the problem of control systems in the seismic analysis of long-span bridges is analysed. It is shown that the spatial variability of the ground motion strongly affects the structural response and it must be considered in the analysis of appropriate control systems. Then, the problem of monitoring of bridge vibrations, whether to provide control of subsequent, potentially damaging motions or for detection of hidden damage that may already have occurred, is addressed. Several examples involving analysis, monitoring and control for seismic and wind-induced motion are presented, as well as laboratory studies for damage detection.
Bending vibration of flat plates is controlled using patches of active constrained layer damping (ACLD) treatments. Each ACLD patch consists of a visco-elastic damping layer which is sandwiched between two piezo-elect...
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ISBN:
(纸本)0819417947
Bending vibration of flat plates is controlled using patches of active constrained layer damping (ACLD) treatments. Each ACLD patch consists of a visco-elastic damping layer which is sandwiched between two piezo-electric layers. The first layer is directly bonded to the plate to sense its vibration and the second layer acts as an actuator to actively control the shear deformation of the visco-elastic damping layer according to the plate response. With such active/passive control capabilities the energy dissipation mechanism of the visco-elastic layer is enhanced and its damping characteristics of the plate vibration is improved. A finite element model is developed to analyze the dynamics and control of flat plates which are partially treated with multi-patches of ACLD treatments. The model is validated experimentally using an aluminum plate which is 0.05 cm thick, 25.0 cm long, and 12.5 cm wide. The plate is treated with two ACLD patches. Each of which is made of SOUNDCOAT (Dyad 606) visco- elastic layer sandwiched between two layers of AMP/polyvinylidene fluoride (PVDF) piezo- electric films. The piezo-electric axes of the patches are set at zero degrees relative to the plate longitudinal axis to control the bending mode. The effect of the gain of a proportional control action on the system performance is presented. Comparisons between the theoretical predictions and the experimental results suggest the validity of the developed finite element model. Also, comparisons with the performance of conventional passive constrained layer damping clearly demonstrate the merits of the ACLD as an effective means for suppressing the vibration of flat plates.
This paper is to develop a mathematical model to predict bending, twisting, and axial vibration response of a composite beam with intelligent constrained layer (ICL) or active constrained layer (ACL) damping treatment...
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ISBN:
(纸本)0819417947
This paper is to develop a mathematical model to predict bending, twisting, and axial vibration response of a composite beam with intelligent constrained layer (ICL) or active constrained layer (ACL) damping treatments. In addition, preliminary experiments are conducted on composite beams to evaluate this new technique. The ICL composite beam model is obtained by integrating the existing ICL composite plate model proposed by Shen. When the plate width (along the x-axis) is much smaller than the plate length (along the y-axis), integration of the ICL composite plate equations and linearization of displacement fields with respect to x leads to a set of equations that couples bending, torsional, and axial vibrations of a composite beam. The equations of motion and associated boundary conditions are normalized and rearranged in a state-space matrix form, and the vibration response is predicted through the distributed transfer function method developed by Yang and Tan. A numerical example is illustrated on a composite beam with bending-torsion coupling stiffness. Numerical results show that ICL damping treatments may or may not reduce coupled bending and torsional vibrations of a composite beam simultaneously. When the deflection is fed back to actuate the ICL damping treatment, a sensitivity analysis shows that only those vibration modes with significant bending response are suppressed simultaneously with their torsional components. In the preliminary experiments, two different ICL setups are tested on a composite beam without bending-torsion coupling. Damping performance of both ICL setups agrees qualitatively with existing mathematical models and experimental results obtained from other researchers. The damping performance, however, is not optimized due to the availability of materials and their dimensions in the laboratory. An optimization strategy needs to be developed to facilitate design of ACL damping treatments with maximized damping performance.
A servoflap that uses a piezoelectric bender to deflect a trailing edge flap for use on a helicopter rotor blade was designed, built, and tested. This servoflap design is an improvement over a design developed previou...
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ISBN:
(纸本)0819417750
A servoflap that uses a piezoelectric bender to deflect a trailing edge flap for use on a helicopter rotor blade was designed, built, and tested. This servoflap design is an improvement over a design developed previously at MIT. The design utilizes a new flexure mechanism to connect the piezoelectric bender to the control surface. The efficiency of the bender was improved by tapering its thickness with length. Also, the authority of the actuator was increased by implementing a nonlinear circuit to control the applied electric field, allowing a greater range of actuator voltages. Experiments were carried out on a bench test article to determine the frequency response of the actuator, as well as hinge moment and displacement capabilities. Flap detections of 11.5 deg or more were demonstrated while operating under no load conditions at frequencies up to 100 Hz. The data indicate that if properly scaled, the actuator will produce flap deflections greater than 5 deg at the 90% span location on a full- scale helicopter. In addition, the first mode of the actuator was at 7/rev frequency of the target model rotor. Proper inertial scaling of this actuator could raise this modal frequency to greater than 10/rev on an operational helicopter, which is adequate for most rotor control purposes. A linear state space model of the actuator was derived. Comparisons of this model with the experimental data highlighted a number of mild nonlinearities in the actuator's response. However, the agreement between the experiment and analysis indicate that the model is a valid tool for predicting actuator performance.
The relationship between the strain and the feedback voltage to a PZT. phase modulator in an active homodyne Mach-Zehnder interferometric fibre optic sensor operating beyond the limit of the feedback electronics was l...
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The relationship between the strain and the feedback voltage to a PZT. phase modulator in an active homodyne Mach-Zehnder interferometric fibre optic sensor operating beyond the limit of the feedback electronics was linearized. Strain in carbon fibre/epoxy composite bar during uniaxial tensile loading was measured in two ways: interferometrically, using an embedded optical fibre as sensor, and secondly, with conventional resistance strain gauges mounted on the specimen surface. The optically measured strain and resistively measured strain was in good agreement when the optical fibre was oriented parallel to the carbon fibres. An instrument that combined high resolution with large range was developed.
The dynamic characteristics of a flexible 3DOF structural model, namely the stiffness and damping ratios, are identified by using the extended Kalman filtering technique. Two types of structural response datum are use...
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The dynamic characteristics of a flexible 3DOF structural model, namely the stiffness and damping ratios, are identified by using the extended Kalman filtering technique. Two types of structural response datum are used for the identification. These are the structural response under base excitation generated by a shaking table and the forced vibration response due to an active mass damper (AMD) installed at the top of the model. Using the identified structural parameters, experimental results of the earthquake response of the model with the AMD control are compared with those of analytical simulation. Fairly good agreement between the experiment and the numerical simulation suggests the accuracy of the identification and the effectiveness of the vibration control by the AMD.
Active control of a slightly sagged cable using actuator motion in the cable axial direction is studied. Two active control schemes are proposed: (i) active stiffness control and (ii) active sag-induced force control....
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Active control of a slightly sagged cable using actuator motion in the cable axial direction is studied. Two active control schemes are proposed: (i) active stiffness control and (ii) active sag-induced force control. They are verified experimentally, and good agreement between experiments and predictions is shown. Next, using the direct method of Liapunov, a stable control scheme to control multimodal response of a cable is proposed. An uncontrollable motion is identified as a circular swirling motion of the cable that is formed by two closely spaced antisymmetric modes. The simulation results show that the controller suppresses free vibration of a cable efficiently whenever the cable motion is controllable and stops when uncontrollable. It is observed that control spillovers occur but their effects are not significant. The vibration energy of the multimodal response of a cable under random excitation is shown to be reduced effectively by the proposed control scheme.
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