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作者： Kim, Myung-Hyun Virginia Polytechnic Institute and State University

学位级别：Ph.D.

A robust nonlinear observer, utilizing the sliding mode concept, is developed for the dynamic positioning of ships. The observer provides the estimates of linear velocities of the ship and bias from the slowly varying environmental loads. It also filters out wave frequency motion to avoid wear of actuators and excessive fuel consumption. Especially, the observer structure with a saturation function makes the proposed observer robust against neglected nonlinearties, disturbances and uncertainties. A direct adaptive neural network controller is developed for a model of an underwater vehicle. Radial basis neural network and multilayer neural network are used in the closed-loop to approximate the nonlinear vehicle dynamics. No prior off-line training phase and no explicit knowledge of the structure of the plant are required, and this scheme exploits the advantages of both neural network control and adaptive control. A control law and a stable on-line adaptive law are derived using the Lyapunov theory, and the convergence of the tracking error to zero and the boundedness of signals are guaranteed. Comparison of the results with different neural network architectures is made, and performance of the controller is demonstrated by computer simulations. The sliding mode observer is used to eliminate observation spillovers in the vibration control of flexible structures. It is common to build a state feedback controller and a state estimator based on the mathematical model of the system with a finite number of vibration modes, but this may cause control and observation spillover due to the residual (uncontrolled) modes. The performance of a sliding mode observer is compared with that of a conventional Kalman filter in order to demonstrate robustness and disturbance decoupling characteristics. Simulation and experimental results using the sliding mode observer are presented for the active vibration control of a cantilever beam using smart materials.

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Model-based control of plate vibrations using active constrained layer damping

Model-based control of plate vibrations using active constra...

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作者： Chantalakhana, Chak University of Sheffield

学位级别：博士

In this thesis, the author presents a numerical and experimental study of the application of active constrained layer damping to a clamped-clamped plate. Piezoelectric actuators with modal controllers are used to improve the performance of vibration suppression from the passive constrained layer damping treatment. Surface damping treatments are often effective at suppressing higher frequency vibrations in thin-walled structures such as beams, plates and shells. However, the effective suppression of lower frequency modes usually requires the additional of an active vibration control scheme to augment the passive treatment. Advances in the technologies associated with so-called smart materials are dramatically reducing the cost, weight and complexity of active structural control and make it feasible to consider active schemes in an increasing number of applications. Specifically, a passive constrained layer damping treatment is enhanced with an active scheme employing a piezoceramic (PZT) patch as the actuator. Starting with an established finite element formulation it is shown how model updating and model reduction are required to produce a low-order state-space model which can be used as the basis for active control. The effectiveness of the formulation is then demonstrated in a numerical study. Finally, in the description of the experimental study it is shown how modes in the frequency range from 0 to 600 Hz are effectively suppressed: the two lowest modes (bending and torsional) through active control, the higher modes (around ten in number) by the passive constrained damping layer. The study'S original contribution lies in the experimental demonstration that given a sufficiently accurate model of the plate and passive constrained damping layer, together with a suitable active feedback control algorithm, spillover effects are not significant even when using a single sensor and single actuator. The experimental traces show, in some instances, minor effects due to s

关键词： Piezoelectric actuators Vibration suppression

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Adaptive structures and coupled multi-field problems

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Stahlbau 2000年第6期69卷 446-454页

作者： Grohmann, Boris A. Wallmersperger, Thomas Kröplin, Bernd Leiter Instituts Statik/Dynam. L. Stuttgart Germany

The present paper deals with adaptive structures from the perspective of coupled multi-field problems. First, the characteristic capabilities of adaptive structures in aerospace engineering are introduced. Subsequently, four basic mechanisms of adaptive structures applications are given, namely shape adaptation, counteraction, energy absorption and active control of the energy exchange with the environment. Furthermore, adaptive materials are presented and compared concerning potential application areas and limitations. Thereafter, stimulated polymer gels are discussed in consideration of their application as artificial muscles or actuators with large active strains. The corresponding electro-chemo-mechanical multi-field problem and a suitable coupling strategy for its numerical solution are presented. Finally, the application of active materials to the adaptive camber control of helicopter rotor blades is treated. Coupled numerical simulations of the aeroelastically unbalanced smart structure concept are conducted.

关键词： Intelligent structures

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Detecting damage in non-uniform beams using the dereverberated transfer function response

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smart materials & structures 2000年第4期9卷 429-444页

作者： Purekar, AS Pines, DJ Univ Maryland Dept Aerosp Engn Smart Struct Lab College Pk MD 20742 USA

Delamination damage in composite rotorcraft flexbeams caused by excessive vibratory and fatigue loads can lead to degradation in flapwise and lagwise performance of the rotor blade. In addition, delaminations can result in rapid fatigue failure of these tailored composite elements leading to catastrophic results. A novel damage detection strategy is evaluated in this work which attempts to exploit the dereverberated transfer function response of beams with tapered geometries. This approach avoids high fidelity finite element models of damaged one-dimensional beams with non-uniform geometries. To obtain the dereverberated transfer function response, a virtual control force is applied to the reverberated transfer function response to remove resonant and anti-resonant dynamics associated with the beam's boundary conditions. Magnitude and phase characteristics between each actuator and sensor can then be used to infer changing structural properties. Analytical and experimental results suggest that this approach can be used to quantitatively and qualitatively infer delamination damage in non-uniform beams. Experimental results are displayed for beams with varying thickness and width tapers.

关键词： Composite beams and girders

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Localized Effects of Piezopolymer Devices on the Dynamics of Inflatable Space-Based structures

Localized Effects of Piezopolymer Devices on the Dynamics of...

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作者： Robert Brett Williams Virginia Polytechnic Institute and State University

学位级别：硕士

Inflatable space-based devices have become popular over the past three decades, as they offer minimized launch-mass and launch-volume. Since some satellites have mirror sections over fifty feet in diameter and struts with lengths over ninety feet, inflation while in orbit has become a necessary procedure. Once inflated, these space structures are subject to two types of vibrations: those induced mechanically by guidance systems and space debris and those induced thermally from variable amounts of direct sunlight as they orbit about earth. controlling vibrations of spaced-based structures is critical to ensuring optimal performance. The focus of this research is derived from an Air Force program to develop and model an active control system using smart materials to suppress the vibrations of inflatable communication satellites. When small piezoceramic devices are attached to an aluminum or steel structure, the effects of the piezo on the dynamic properties of the host are typically ignored. However, the inflatable satellites of interest to this project are manufactured from Kapton, a thin, light polyimide film. Therefore, even a piezopolymer film actuator, such as PVDF, could greatly change the mass and stiffness values in the area under and around the patch, altering the dynamic behavior of the satellite. Thin-walled pressure vessel theory was employed to assess the state of stress at any location on an inflated torus. A flat, rectangular coupon was selected at a general point on the structure and modeled as a membrane. The equation of motion for this membrane with clamped edges was derived and a closed-form solution for the natural frequencies and mode shapes was presented. The Rayleigh-Ritz and finite element methods were then seen to numerically approximate the natural frequencies and mode shapes for the bare membrane with a high degree of accuracy. A passive PVDF patch was then attached to the base membrane and the equation of motion derived using an energy appr

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Optimal piezo-actuator locations/lengths and applied voltage for shape control of beams

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smart materials & structures 2000年第2期9卷 205-211页

作者： Bruch, JC Sloss, JM Adali, S Sadek, IS Univ Calif Santa Barbara Dept Mech & Environm Engn Santa Barbara CA 93106 USA Univ Calif Santa Barbara Dept Math Santa Barbara CA 93106 USA Amer Univ Sharjah Dept Comp Sci Math & Stat Sharjah U Arab Emirates

Shape control of beams under general loading conditions is implemented using piezoceramic actuators to provide the control forces. The objective of the shape-control is to minimize the maximum deflection of the beam to obtain a min-max deflection configuration with respect to loading and piezo-actuators. In practice, the loading on a beam is a variable quantity with respect to its magnitude, and this aspect can be handled easily by optimizing the magnitude of the applied voltage to achieve the min-max deflection. This property of the smart materials technology overcomes the problem of one-off conventional optimal designs which become suboptimal when the loading magnitude changes. In addition to the magnitude of the applied voltage, the optimal values for the locations and the lengths of the piezo-actuators are determined to achieve the min-max deflection. Due to the complexity of the governing equations involving finite length piezo patches, the numerical results are obtained by the finite-difference method. The analysis of the problem shows the effect of the actuator locations, lengths and the applied voltage on the maximum deflection. The optimal Values for the actuator locations and the voltage are determined as functions of the load locations and load magnitudes, respectively. The effect of the actuator length on the min-max deflection is investigated and it is observed that the optimal length depends on the applied voltage. Finally, it is shown that using multiple actuators are more effective than a single actuator in the cases of complicated loading.

关键词： Beams and girders

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Development of active six-degrees-of-freedom microvibration control system using giant magnetostrictive actuators

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smart materials & structures 2000年第2期9卷 175-185页

作者： Nakamura, Y Nakayama, M Masuda, K Tanaka, K Yasuda, M Fujita, T Fujita Corp Tech Res Inst Kanagawa Japan Tokkyokiki Corp Amagasaki Hyogo Japan Univ Tokyo Inst Ind Sci Minato Ku Tokyo 106 Japan

An active six degrees-of-freedom microvibration control system using giant magnetostrictive actuators is developed in order to realize a microvibration-free space for precision instruments which hate vibration. A giant magnetostrictive actuator is suitable as a displacement actuator for active microvibration control, because it is both compact and durable and also its response against input is fast and reliable. The developed device consists of a table, six air springs, eight magnetostrictive actuators and six accelerometers on the table. Four actuators are set in the horizontal directions, and another four in the vertical direction. Since air springs and actuators as a unit of vertical support system are arranged in parallel, readjustment of the system is quite easy, even when the operating load an the table is changed. The dimensions of the table are 2000 mm length, 1400 mm width, 230 mm height and a weight of about 2 tons. The operating load on the table is 2 tons. A giant magnetostrictive rod is 6 mm in diameter and 50 mm long. The actuators operate within the stroke range of +/-25 Cc m. A feedback control strategy using only six components of table acceleration on the table is adopted and the controller is designed by a model matching method. The obtained control performance of the system through two vibration control tests can be summarized as follows (1) Root-mean-square values of the table accelerations under micro-tremor are reduced to one-third to one-tenth of the floor accelerations, and kept less than 0.008 cm s(-2) (2) Induced vibrations by impacts acting on the table disappear in less than 0.05 s.

关键词： Intelligent structures

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The optimal design of piezoelectric actuators for plate vibroacoustic control using genetic algorithms with immune diversity

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smart materials AND structures 2000年第4期9卷 485-491页

作者： Gao, F Shen, YP Li, LX Xi An Jiao Tong Univ Dept Mech Xian 710049 Shaanxi Peoples R China

This paper studies the optimal design of piezoelectric actuators for suppressing noise transmission of a vibration plate. The optimal placement of the actuators to reduce the global noise levels is still a significant design problem, especially placement limited to discrete locations. With the increase of the alternative locations and number of actuators, a large number of placement possibilities exist. These multi-dimensional nonlinear problems are very difficult for traditional optimization methods. In this paper, genetic algorithms have introduced to solve the problem of optimal discrete placement of piezoelectric patches. In order to improve the diversity of the population, a new selection factor is presented that is based on immune diversity, which is dependent on the string denseness and its function value. The survivor probability of the string with higher denseness will be reduced. Several cases for a simple supported plate under different load conditions show that the improved algorithms are efficient.

关键词： Genetic algorithms

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Active position control of a shape memory alloy wire actuated composite beam

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smart materials & structures 2000年第5期9卷 711-716页

作者： Song, GB Kelly, B Agrawal, BN Univ Akron Dept Mech Engn Akron OH 44325 USA USN Postgrad Sch Dept Aeronaut & Astronaut Monterey CA 93943 USA

This paper presents the design and the experimental result of the active position control of a shape memory alloy (SMA) wire actuated composite beam. The composite beam has a honeycomb structure with SMA wires embedded in one of its face sheets for the active actuation. The potential applications of this experiment include thermo-distortion compensation for precision space structure, stem shape control for submarines, and flap shape control for aeronautical applications. SMA wires are chosen as the actuating elements due to their high recovery stress (>500 MPa) and tolerance to high strain (up to 6%). However, SMA wires are inherently nonlinear and pose a challenge for control design. A robust controller is designed and implemented to actively control the tip position of the composite beam. The experiment set-up consists of the composite beam with embedded SMA wires, a programmable current/voltage amplifier to actuate the SMA wires, an infrared laser range sensor to detect the beam tip displacement, and a real-time data acquisition and control system. The experimental result demonstrates the effectiveness of the robust control.

关键词： Composite beams and girders

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Dynamic responses of smart composites using a coupled thermo-peizoelectric-mechanical model

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AIAA JOURNAL 2000年第10期38卷 1939-1948页

作者： Zhou, X Chattopadhyay, A Gu, HZ Arizona State Univ Dept Mech & Aerosp Engn Tempe AZ 85287 USA

A completely coupled thermo-piezoelecltic-mechanical theory is developed to model the dynamic: response of composite plates with surface-bonded piezoelectric actuators. A higher-order laminate theory is used to describe the displacement fields of both composite laminate and piezoelectric actuator layers to accurately model the transverse shear deformation, which is significant in moderately thick constructions. A higher-order temperature field is used to accurately describe the temperature distribution through the thickness of composite plates. A finite element model is developed to implement the theory. Thermal and piezoelectric loads are considered. The results obtained using this coupled theory are compared with those obtained using an uncoupled theory. Numerical results indicate that the thermo-piezoelectric-mechanical coupling has significant effect on the dynamic response of composite plates. Furthermore, coupling also affects the control authority of piezoelectric actuators.

关键词： Structural Damping Piezoelectric Actuators Stiffness Matrices Piezoelectric materials Electric Potential Vibration Amplitude Permittivity Thermal Conductivity Transverse Shear Thickness Ratio

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