Adaptive Materials Technology Research Articles

Comparative study on vibration control methodologies applied to adaptive thin-walled anisotropic cantilevers

Abstract A study of the vibrational control of adaptive doubly-tapered cantilevered beams, simulating an aircraft wing, exposed to time-dependent external pulses is presented. Whereas the beam structure encompasses non-classical properties such as transverse shear and anisotropy of their constituent materials, the active control capabilities are based upon the implementation of the adaptive materials technology. Herein, the adaptive feature is achieved through the converse piezoelectric effect that consists of the generation of localized strains in response to an applied voltage. Piezoactuators in the form of patches or spread all over the beam span are considered. The active control involves the dynamic response to arbitrary time-dependent external pulses. The closed-loop dynamic response time-histories are obtained via the use of the piezoelectrically induced moment control, and through the implementation of a modified bang–bang control strategy that involves a maximum value constraint imposed on the input voltage. In addition to this active feedback control methodology, a passive one based upon the use of the directionality property of anisotropic composite material structures is also implemented. Moreover, the results are compared to those obtained via the implementation of other two feedback control methodologies, namely the Linear Quadratic Regulator (LQR) and the Fuzzy Logic Control (FLC). Numerical simulations emphasizing the performance of the adopted control strategies intended to contain and even suppress the oscillations when time unfolds are presented, and pertinent conclusions are outlined.

Optimal Dynamic Response Control of Elastically Tailored Nonuniform Thin-Walled Adaptive Beams

A dual approach based on structural tailoring and adaptive materials technology aimed at controlling the dynamic response of tapered thin-walled beams exposed to external pressure pulses is presented. Whereas structural tailoring uses the directionality properties of advanced composite materials, the adaptive materials technology exploits the actuating and sensing capabilities of piezoelectric material systems bonded or embedded into the host structure. The structure is modeled as a doubly tapered composite thin-walled beam incorporating a number of nonclassical features such as transverse shear, warping inhibition, anisotropy of constituent materials, and rotatory inertias. The cases of piezoactuators spread over the entire span of the structure or in the form of a patch are considered, and issues related to the influence of patch location and size on the control efficiency are discussed. Other issues related to the implications of the inclusion/discard in the quadratic performance index of time-dependent external excitations are also addressed. The displayed numerical results provide a comprehensive picture of the synergistic implications of the application of both techniques, namely, the tailoring and optimal control on vibration response of nonuniform thin-walled beam structures exposed to external time-dependent excitation.

Dynamic response of elastically tailored adaptive cantilevers of nonuniform cross section exposed to blast pressure pulses

The main purpose of this paper is to assess the implications of a number of effects of geometric and physical nature on dynamic response control of adaptive cantilevers modeled as composite thin-walled beams. It is considered that the cantilevered beam is exposed to pressure pulses generated, among others, by an explosive blast or sonic-boom. The features on which preponderance will be given in this study are related to the non-uniformity of the beam cross-section, anisotropy of constituent materials, transverse shear and warping inhibition. In order to control the dynamic response, a dual approach based on structural tailoring and adaptive materials technology is implemented. The numerical simulations provide a comprehensive picture of the synergistic implications of the application of both the tailoring technique and active feedback control upon the vibration response of nonuniform cantilevers exposed to blast pressure signatures. Moreover, these are likely to contribute to the clarification of the implications of various parameters playing a role on the beam response.

Synergistic implications of tailoring and adaptive materials technology on vibration control of anisotropic thin-walled beams

The problems of the mathematical modeling and dynamical response of thin-walled beam cantilevers encompassing a number of non-classical features and incorporating adaptive capabilities are investigated. Whereas the theory of thin-walled beams as considered in this study incorporates the anisotropy of constituent materials, transverse shear and secondary warping, the adaptive capabilities are provided by a system of piezoelectric devices whose sensing and actuating functions are combined and that 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 of the structure subjected to time-dependent external excitation are revealed, and pertinent conclusions are outlined.

DYNAMIC RESPONSE OF ADAPTIVE CANTILEVERS CARRYING EXTERNAL STORES AND SUBJECTED TO BLAST LOADING

This paper deals with the control of the dynamic response of cantilevered thin-walled beams carrying externally mounted stores and exposed to time-dependent external excitations. In this context, and toward this goal, the adaptive materials technology is used. A feedback control law relating the piezoelectrically induced bending moment at the beam tip with the angular velocity at the same point of the structure is considered, and its effects on the closed-loop dynamic response is investigated. The obtained results reveal that this control methodology can play a noticeable role toward confining the oscillations of the considered structure when exposed to blast loadings.

Oscillation control of cantilevers via smart materials technology and optimal feedback control: actuator location and power consumption issues

A study of the vibration control of cantilevers exposed to blast loading is presented. Whereas the structure used in this analysis is in the form of a thin-walled beam of closed cross-section contour, the control is based upon the simultaneous implementation of adaptive materials technology and of optimal feedback control. Issues related to the the influence upon dynamic response of size and location along the beam span of piezoactuator patches are investigated, and the efficiency of this combined control methodology is outlined. Other issues related to the minimization of the input power required in the control process, maximization of the sensing voltage output and implications of the limitation of control input voltage on dynamic response are also addressed and pertinent conclusions are outlined.

Dynamic Response Control of Thin-Walled Beams to Blast Pulses Using Structural Tailoring and Piezoelectric Actuation

An integrated dual approach aimed at controlling the dynamic response of anisotropic cantilevered thin-walled beams to blast and sonic-boom loading is presented. The approach is based upon the simultaneous implementation of structural tailoring and adaptive materials technology. Whereas structural tailoring uses the anisotropy properties of advanced composite materials, the adaptive materials technology exploits the converse effect of piezoactuators bonded or embedded into the host structure. A combined dynamic control law relating the piezoelectrically bending moment induced at the beam tip with the various kinematic response quantities is implemented and its effects upon the closed-loop dynamic response characteristics are investigated. The obtained results reveal the powerful role played by abovementioned integrated control methodology towards enhancing the dynamic response of thin-walled beam cantilevers to transient loading.

Control of Cantilever Vibration via Structural Tailoring and Adaptive Materials

A dual approach integrating structural tailoring and adaptive materials technology and designed to control the dynamic response of cantilever beams subjected to external excitations is presented. Whereas structural tailor- ing uses the anisotropy properties of advanced composite materials, adaptive materials technology exploits the actuating capabilities of piezoelectric materials bonded or embedded into the host structure. A control law relat- ing the piezoelectrically induced boundary bending moment with the velocity at given points of the structure is implemented and its effect on the closed-loop frequencies and dynamic response to harmonic excitations is inves- tigated. The combination of structural tailoring and control by means of adaptive materials proves very effective in damping out vibration. I. Introduction A Sthe requirements for higherexibility on high-speed aircraft increase, so do the challenges of developing innovative de- sign solutions. Whereas the increasedexibility is likely to provide enhanced aerodynamic performance, the aircraft also must be able to ful® ll a multitude of missions in complex environmental condi- tions and to feature an expanded operational envelope and longer operational life. To achieve such ambitious goals- advanced con- cepts resulting in the enhancement of static and dynamic response of the multimission- highlyexible aircraft must be developed and implemented. One way of achieving such goals consists of the in- tegration of advanced composite materials in the aircraft structure. 1 In this regard, the directionality property featured by anisotropic composite materials is capable of providing the desired elastic cou- plings through the proper selection of the ply angle. However, such a technique is passive in nature in the sense that, once the design is in place, the structure cannot respond to the variety of conditions in which it must operate. The situation can be mitigated by incorporating into the host structure adaptive materials able to respond actively to changing conditions. In a structure with adaptive capabilities, the natural fre- quencies, damping, and mode shapes can be tuned to reduce the vibration so as to avoid structural resonance andutter instability, and in general toenhance the dynamic response characteristics.The adaptivecapabilityisachievedthroughtheconversepiezoelectricef- fect,whichconsistsofthegenerationoflocalized strainsinresponse to an applied voltage. This induced strain ® eld produces, in turn, a change in the dynamic response characteristics of the structure. It is proposedheretoenhancethefreevibrationanddynamicresponseto externalexcitationsofwing structures by incorporating theadaptive capabilityreferredtoasinduced strain actuationinconjunctionwith structural tailoring. Under consideration is a cantilevered aircraft wing, modeled as a thin/thick-walled closed cross-section beam of anisotropic material. Implementation of a control law relating the applied electric ® eld to one of the mechanical quantities charac- terizing the response of the wing according to a prescribed func- tional relationship results in eigenvalue/boundary-value problems. The solution consists of closed-loop eigenvalues/dynamic response characteristics, which are functions of the applied voltage, i.e., of the feedback control gain. Investigation of static and dynamic control of aircraft wing structures via the simultaneous implementation of induced strain

Integrated structural tailoring and control using adaptive materials for advanced aircraft wings

This study combines structural tailoring with the adaptive capabilities of piezoelectric materials for the purpose of controlling the vibration and static aeroelastic characteristics of advanced aircraft wings. The structural model consists of a thin/thick-walled closed cross-sectional cantilevered beam whose constituent layers exhibit elastic anisotropic properties and incorporates a number of nonclassical features. Results reveal that a combination of structural tailoring and control using adaptive materials can play a major role in enhancing the vibrational and static aeroelastic response characteristics of aircraft wings. ECAUSE of their outstanding properties, such as high strength/stiffness to weight ratios, fiber-reinforced laminated thick/thin-walled structures are likely to play an increasing role in the design of advanced aircraft wings. In addition, a number of elastic couplings resulting from anisotropy and the ply-angle sequence of composite material structures can be exploited so as to enhance the response characteristics. In this regard, within the last two decades, a technique referred to as structural tailoring has been used with spectacular results.1 It should be noted, however, that structural tailoring is a passive design technique. This implies that the structure cannot respond adaptively to changes in its parameters or external stimuli. To overcome this shortcoming, additional capabilities must be built into the structure. This is particularly true in view of the fact that future generations of flight vehicles are likely to operate under increasingly severe conditions. An approach showing good promise is based upon the incorporation into the structure of materials featuring sensing and actuating capabilities.25 Piezoelectric materials are excellent candidates for the role of sensors and actuators. In contrast to passive structures, in which the vibrational and aeroelastic response characteristics are predetermined, in adaptive structures these characteristics can be altered in a known and predictable manner. These adaptive capabilities can be used to prevent structural resonance and/or any other type of instability, as well as to improve the static and dynamic response of the structure. In this article, the task of enhancing the static aeroelastic response and free vibration characteristics of aircraft wingtype structures made of advanced composite materials is accomplished through the synergistic combination of structural tailoring and adaptive materials technology. The structure simulating the aircraft wing consists of a thin/thick-walled closed cross-sectional cantilevered beam whose constituent layers feature elastic anisotropic properties. The control capability is achieved by electrically actuating piezoelectric ele