Model and experimental investigations of electrodynamic properties of tunable structures from liquid-impregnated porous magnetic media are presented. Microwave spectra of complex permittivity and permeability of dry a...
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Model and experimental investigations of electrodynamic properties of tunable structures from liquid-impregnated porous magnetic media are presented. Microwave spectra of complex permittivity and permeability of dry and liquid-impregnated media with ethyl alcohol or water-alcohol mixtures were measured Real and imaginary parts of permittivity were found to exceed the upper Wiener boundary. Dielectric and magnetic properties of liquid-impregnated porous ferrite media were modeled using non-local volume averaging theory (VAT). This approach accounts for several hierarchical levels and morphology of the system.
This paper is concerned with designing an optimum flexible wing structure to enhance roll maneuver capability at high dynamic pressures using embedded actuating system. A wing optimized to minimize the weight, with co...
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This paper is concerned with designing an optimum flexible wing structure to enhance roll maneuver capability at high dynamic pressures using embedded actuating system. A wing optimized to minimize the weight, with constraints on strength for symmetric pull up maneuver and constraints on the frequency distribution was used for this study. Elastic twist and camber is achieved by providing a system of actuating elements distributed within the internal substructure of the wing to provide control forces. The equilibrium equations were developed for the steady roll maneuver of a wing subjected to aerodynamic loads and actuating forces. Optimal control design approach was used to determine the distribution of actuating forces. The total strain energy was calculated as a measure of power requirement to produce twist and camber, to achieve specified flexible roll rate at different Mach numbers.
The paper discusses feedback control strategies for the reduction of helicopter vibration using a trailing edge flap located at the outer part of the rotor blades. The problem of reducing rotor-induced vibration is co...
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The paper discusses feedback control strategies for the reduction of helicopter vibration using a trailing edge flap located at the outer part of the rotor blades. The problem of reducing rotor-induced vibration is considered as a disturbance rejection control problem where robust servomechanism control is applied in combination with optimal constant output feedback. This control scheme is examined in the view of limitations in the transient performance by investigating the zeros of the multivariable system. Local control strategies in the rotating system are developed for active damping enhancement. Simulations are presented based on a BO105 helicopter.
The problems of the mathematical modeling and dynamical response of thin-walled beam structures including a number of non-classical features and incorporating adaptive capabilities are considered. The theory of thin-w...
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The problems of the mathematical modeling and dynamical response of thin-walled beam structures including a number of non-classical features and incorporating adaptive capabilities are considered. The theory of thin-walled beams as considered in this study encompasses non-classical features such as anisotropy, transverse shear and secondary warping, whereas the adaptive capabilities are provided by a system of piezoelectric devices whose sensing and actuating functions are combined and which are bonded or embedded into the host structure. The synergistic implications of the application of both tailoring and collocated sensing-actuating capabilities upon the closed-loop dynamic response are presented and pertinent conclusions are outlined.
Distributed vibration control of an elastic beam is analyzed. The elastic beam is sandwiched between two thin layers of mono-axially oriented piezoelectric material. One layer acts as a distributed sensor while the ot...
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Distributed vibration control of an elastic beam is analyzed. The elastic beam is sandwiched between two thin layers of mono-axially oriented piezoelectric material. One layer acts as a distributed sensor while the other behaves as an actuator. A displacement feedback control with a time delay is implemented. In this feedback, the distributed sensor signal which is proportional to strains is amplified and applied to the actuator after a time delay. Because of the nature of the problem the control action enters as a boundary control. An evaluation of the control effectiveness, natural frequency and damping is made for the case of a cantilever beam. Comparisons are given with the uncontrolled cases and zero-delay systems.
This paper is concerned with the real-time automatic tuning of the positive position feedback controller for smartstructures by the genetic algorithms. The genetic algorithms have proven its effectiveness in searchin...
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This paper is concerned with the real-time automatic tuning of the positive position feedback controller for smartstructures by the genetic algorithms. The genetic algorithms have proven its effectiveness in searching optimal design parameters without falling into local minimums thus rendering globally optimal solutions. The advantage of the positive position feedback controller is that if it is tuned properly it can enhance the damping value of a target mode without affecting other modes. In this paper, we develop a real-time algorithm for determining a tuning frequency of the PPF controller based on the genetic algorithm. Hence, the traditional positive position feedback controller can be used in adaptive fashion in real time. To this end, the digital PPF control law is downloaded to the DSP chip and a main program, which runs genetic algorithms in real time, updates the parameter of the controller in real time. The real-time tuning of the PPF controller is applied to cases of initial disturbance and persistent harmonic disturbance. In both cases, the real-time tuning is achieved successfully. Hence, vibrations are suppressed satisfactorily. The experimental results also show that the PPF controller tuned by GA gives better performance than the manually tuned PPF controller for accommodating harmonic disturbances did.
In this paper the design of an optimal controller using discretely placed collocated sensor/actuator pairs to control the vibration of a plate structure is presented. Three-dimensional finite elements are used to mode...
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In this paper the design of an optimal controller using discretely placed collocated sensor/actuator pairs to control the vibration of a plate structure is presented. Three-dimensional finite elements are used to model the smart structure containing discrete piezoelectric sensors and actuators by the use of a combination of solid, transition, and shell elements. Since several discrete piezoelectric patches are spatially distributed in the structure to effectively observe and control the vibration of a structure, the system model is thus utilized to design multi-input-multi-output (MIMO) controller. The output feedback controller is then employed to emulate the optimal controller by solving the Riccati equations from modal space model. An optimal controller design for the vibration suppression of a clamped plate is presented for the steady state excitation case. The reduction in the sound pressure level inside an enclosure radiated from this optimally controlled vibrating plate is also estimated.
The strain-temperature hysteresis for shape memory alloy (SMA) actuators has been shown to undergo large changes according to the applied load. This paper provides an adaptive hysteresis model capable of accounting fo...
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The strain-temperature hysteresis for shape memory alloy (SMA) actuators has been shown to undergo large changes according to the applied load. This paper provides an adaptive hysteresis model capable of accounting for a time-varying hysteresis, specifically SMA hysteresis under a varying applied stress. Previous research has established excellent performance, in both numerical and laboratory experiments, of the adaptive hysteresis model for actuators with fixed hysteresis. In this paper, the performance of the adaptive model when there are significant changes in the hysteresis characteristics is examined in laboratory tracking experiments.
Dynamic behaviors of a 1-story and 4-story steel structures subject to multi-dimensional ground motion excitations were experimentally investigated by using a shaking table. Linear and nonlinear structural responses w...
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Dynamic behaviors of a 1-story and 4-story steel structures subject to multi-dimensional ground motion excitations were experimentally investigated by using a shaking table. Linear and nonlinear structural responses were obtained as observation data for the identification. Dynamics characteristics of the model structures were identified using the adaptive H∞ filter, which was developed for identifying structural systems with non-stationary dynamic characteristics by adding the function of memory fading (forgetting factor) for past observation data to the H∞ filter. Identification results show that the H∞ filtering technique are very efficient for identifying linear and nonlinear structural systems. Especially, the nonlinear behavior of the model can be traced effectively.
New class of automobiles has structural skins that are quite different from their current designs. Particularly, new families of composite skins are developed with new injection molding processes. These skins while su...
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New class of automobiles has structural skins that are quite different from their current designs. Particularly, new families of composite skins are developed with new injection molding processes. These skins while support the concept of lighter vehicles of the future, are also susceptible to damage up on impact. It is important that their design should be based on a better understanding on the type of impact loads and the resulting strains and damage. It is possible that these skins can be integrally designed with active materials to counter damages. This paper presents a preliminary analysis of a new class of automotive skins, using piezoceramic as a smart material. The main objective is to consider the complex system with, the skin to be modeled as a layered plate structure involving a lightweight material with foam and active materials imbedded on them. To begin with a cantilever beam structure is subjected to a load through piezoceramic and the resulting strain at the active material site is predicted accounting for the material properties, piezoceramic thickness, adhesive thickness including the effect of adhesives. A finite element analysis is carried out to compare experimental work. Further work in this direction would provide an analytical tool that will provide the basis for algorithms to predict and counter impacts in the future class of automobiles.
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