Modeling of macro fiber composite actuated laminate plates and aerofoils

© 2019 Sage Publications . The final, definitive version of this paper has been published in the Journal of Intelligent Material Systems and Structures by Sage Publications Ltd. All rights reserved. It is available at: https://doi.org/10.1177/1045389X19888728This article investigates the modeling of macro fiber composite-actuated laminate plates with distributed actuator patches. The investigation details an analytical and finite element modeling, with experimental validation of the bending strain and deflection of an epoxy E-glass fiber composite laminate. An analytical approach is also developed to estimate the plate deflection from the experimental strain measurements. The analytical method uses direct integration of single dimensional plate bending moments obtained by strain-induced shear moments from the macro fiber composite actuators. Finite element analysis software was used with the composite laminate modeled in ANSYS ACP. The results from both analytical and numerical models show good agreement with the experimental results, with strain values agreeing within 20 ppm and the maximum difference in deflection not exceeding 0.1 mm between models. Finally, an application of the analytical model for developing morphing aerofoil designs is demonstrated.Peer reviewe

Vibration Control With Piezoelectric Actuation Applied to Nonlinear Panel Flutter Suppression

Panel flutter is a large-deflection limit-cycle motion excited by the airflow, which is only on one side of a panel. The objective of this research is to analytically study the panel flutter limit-cycle suppression using nonlinear vibration control techniques with piezoelectric actuation. It is well known that piezoelectric materials are characterized by their ability to produce an electrical charge when subjected to a mechanical strain. The converse piezoelectric effect can be utilized to actuate a panel by applying an electrical field. Piezoelectric actuators are driven by feedback controllers, and control the panel dynamics. For a simply supported panel with piezoelectric layers, the nonlinear dynamic equations of motion are derived by applying Galerkin\u27s method to von Karman\u27s large deflection equation. The aerodynamic force is predicted by using the first-order piston theory or quasi-steady supersonic theory. For controller design, controllers are developed for the bending-moment actuation with given inplane force. For linear feedback control, linear quadratic regulator (LQR), linear quadratic Gaussian (LQG) dynamic compensator and proportional derivative (PD) controllers are used, and compared. For nonlinear control, Lyapunov\u27s direct method is applied to the nonlinear dynamic model. The controller consists of two parts. One is the linear part which is designed by solving a Riccati equation, and another is the nonlinear part which is obtained by making the time derivative of a Lyapunov function to be negative. Numerical simulations based on the nonlinear dynamic model are performed. The numerical study shows that the maximum suppressible dynamic pressure can be increased about five times of the critical dynamic pressure, and the bending moment is much more effective in flutter suppression than the piezoelectric inplane force. Within the maximum suppressible dynamic pressure, limit-cycle motion can be completely suppressed, which means that the flutter free region is enlarged. For the actuator design, three kinds of configurations are considered, two-set, one-patched and shaped actuators, which are implemented by changing the shapes of electrodes. Two-set actuators perform better than one-patched actuator, and one-patched actuator may have better performance than the completely covered actuator. For a shaped actuator, the methods to design the shape and location of the actuator are developed. The best location of an actuator is near the leading edge of the panel. Beside the design of shape and location of actuators, the method to design the optimal thickness of actuators is also presented. For a collocated actuator and sensor or a self-sensing actuator, the shape of actuator is very important when the PD controller is used. For the sensor design, the method to design the shape and location of the piezoelectric sensors is developed. The optimal control performance can be achieved by shaped sensors with a simple fixed-gain PD controller. Numerical results demonstrate that piezoelectric materials are effective in panel flutter limit-cycle suppression. The flutter free region can be further enlarged, if the actuator is activated before the critical dynamic pressure being reached

Spacecraft Dynamics and Control Program at AFRPL

A number of future DOD and NASA spacecraft such as the space based radar will be not only an order of magnitude larger in dimension than the current spacecraft, but will exhibit extreme structural flexibility with very low structural vibration frequencies. Another class of spacecraft (such as the space defense platforms) will combine large physical size with extremely precise pointing requirement. Such problems require a total departure from the traditional methods of modeling and control system design of spacecraft where structural flexibility is treated as a secondary effect. With these problems in mind, the Air Force Rocket Propulsion Laboratory (AFRPL) initiated research to develop dynamics and control technology so as to enable the future large space structures (LSS). AFRPL's effort in this area can be subdivided into the following three overlapping areas: (1) ground experiments, (2) spacecraft modeling and control, and (3) sensors and actuators. Both the in-house and contractual efforts of the AFRPL in LSS are summarized

Piezoelectric Control of Structures Prone to Instabilities

Thin-walled structures such as stiffened panels fabricated out of high strength materials are ubiquitous in aerospace structures. These are prone to buckle in a variety of modes with strong possibility of adverse interaction under axial compression and/or bending. Optimally designed stiffened panels, at an appropriate combination of axial compression and suddenly applied lateral pressure undergo large amplitude oscillations and may experience divergence. Under aerodynamic loading, they can experience flutter instability with the amplitudes of oscillations attaining a limit: LCO) or escalating without any limit. Control of structures prone to these forms of instability using piezo-electric actuators is the theme of this dissertation. Issues involved in the control of stiffened panels under axial compression and liable to buckle simultaneously in local and overall modes are studied. The analytical approach employs finite elements in which are embedded periodic components of local buckling including the second order effects. It is shown that the adverse effects of mode interaction can be counteracted by simply controlling the overall bending of the stiffener by piezo-electric actuators attached its tips. Control is exercised by self-sensing actuators by direct negative feedback voltages proportional to the bending strains of the stiffener. In a dynamic loading environment, where vibrations are triggered by suddenly applied lateral pressure, negative velocity feedback is employed with voltages proportional to the bending strain-rate. The local plate oscillations are effectively controlled by a piezo-electric actuators placed along the longitudinal center line of the panel. The problem of flutter under aerodynamic pressure of stiffened panels in the linear and post-critical regimes is studied using modal analysis and finite strips. The analysis, control and interpretation of the response are facilitated by identification of two families of characteristic modes of vibration, viz. local and overall modes and by a classification of the local modes into two distinct categories, viz. symmetric and anti-symmetric modes respectively. The symmetric local modes interact with overall modes from the outset, i.e. in the linear flutter problem whereas both the sets of local modes interact with overall modes in the post-critical range via cubic terms in the elastic potential. However the effects of interaction in the flutter problem are far less dramatic in comparison to the interactive buckling problem unless the overall modes are activated, say by dynamic pressure on the plate. Control of the panel is exercised by piezo-electric patches placed on the plate at regions of maximum curvature as well as on the stiffener. Two types of control strategies were investigated for the panel subject to fluttering instability. The first is the direct negative velocity feedback control using a single gain factor for each of the sets of plate patches and stiffener patches respectively. A systematic method of determining the gains for the patches has been developed. This is based on the application of LQR algorithm in conjunction with a linearized stiffness matrix of the uncontrolled structure computed at a set of pre-selected times. This type of control was successful till the aerodynamic pressure coefficient reaches up to about six times its critical value, where after it simply failed. The second type of control is the multi-input and multi-output full state feedback control. The LQR algorithm and the linearized stiffness matrix are invoked again, but the gain matrix is computed at the beginning of every time step in the analysis and immediately implemented to control the structure. This type of control proved very effective the only limitation stemming from the maximum field strength that can be sustained by the piezo-electric material employed

Development of piezoelectric harvesters with integrated trimming devices

Piezoelectric cantilever harvesters have a large power output at their natural frequency, but in some applications the frequency of ambient vibrations is different fromthe harvester\u2019s frequency and/or ambient vibrations are periodicwith some harmonic components. To copewith these operating conditions harvesters with integrated trimming devices (ITDs) are proposed. Some prototypes are developed with the aid of an analytical model and tested with an impulsive method. Results show that a small trimming device can lower the main resonance frequency of a piezoelectric harvester of the same extent as a larger tip mass and, moreover, it generates at high frequency a second resonance peak. A multi-physics numerical finite element (FE) model is developed for predicting the generated power and for performing a stress-strain analysis of harvesters with ITDs. The numerical model is validated on the basis of the experimental results. Several configurations of ITDs are conceived and studied. Numerical results show that the harvesters with ITDs are able to generate relevant power at two frequencies, owing to the particular shape of the modes of vibration. The stress in the harvesters with ITDs is smaller than the stress in the harvester with a tip mass trimmed to the same frequency

Structural dynamics branch research and accomplishments to FY 1992

This publication contains a collection of fiscal year 1992 research highlights from the Structural Dynamics Branch at NASA LeRC. Highlights from the branch's major work areas--Aeroelasticity, Vibration Control, Dynamic Systems, and Computational Structural Methods are included in the report as well as a listing of the fiscal year 1992 branch publications