Seung-Keon Kwak

Modeling and Control of a Singly Curved Active Aperture Antenna Using Curved Piezoceramic Actuators

There is an increasing need for aperture antenna devices that incorporate multifunctional capability. One popular solution to this problem is the use of an “active aperture antenna” that is able to vary the direction and shape of its radiation pattern by using actuators to alter the shape of the reflector. This study focuses on the use of a pre-curved piezoceramic actuator, referred to as a THUNDER actuator, to change the shape of a prototype reflector. These actuators offer greater force, deflection and higher strength than traditional PZT actuators, while maintaining cost effectiveness. In this study the design of a prototype antenna structure that can accommodate deflection experiments and far-field radiation pattern tests is presented. The theoretical relationship between the dish deflection and the input voltage is established in two stages. In the first stage, the deflection at the end of the actuator is determined using a combination of Hamilton’s principle and laminated composite curved beam theory. The piezoelectric properties of the actuator are also considered during this stage. In the second stage, the deflection at the tip of the dish is calculated using geometric relationships, with the assumption that the remaining portion of the dish moves as a rigid body. The resulting deflection equations yield results that closely match the experimental quasi-static deflection results for a given input voltage, despite the presence of hysteresis. A dynamic model for a THUNDER actuator is developed based on experimental frequency response measurements. Positive Positioned Feedback (PPF) control is implemented on the system, in order to reduce position overshoot and oscillations in the transient response of the structure. The controller yields an improvement in the transient response in both simulation and experiments. Finally, the controlled system is utilized to transmit radiation in the far field.

New Modeling and Control Design Techniques for Smart Deformable Aircraft Structures

A new modeling and control design specie cally tailored to smart aeroelastic systems is presented. The control problem is to achievea roll maneuverwith a desired roll rateusing a piezoelectric material laminated e exible wing subject to aerodynamic e eld. This multidisciplinary system of an elastic structure with piezoelectric actuating and sensing under external aerodynamic load is modeled with an integrated e nite element method. The deformed structureforobtaining thespecie crollrateismadeupofnewmassandstiffnessmatrices,whicharefunctionsofthe steady-state input electric potential to piezoelectric actuators. The resulting model in the generalized coordinates, whichhasa massmatrix,a nonsymmetricaerodynamicdamping matrix,and anonsymmetricstiffnessmatrix (due to aerodynamic stiffness ), is then transformed to real but nonorthogonal modal coordinates and a reduced-order model is developed. A new control design algorithm based on reciprocal state-space framework is introduced to achieve the desired roll rate and to dissipate vibrations by applying acceleration feedback.

New approaches for observer design in linear matrix second order systems

Addresses the issue of designing observers for linear matrix second order systems in the matrix second order framework. Several important reasons are presented to justify the need for this approach. The advantages of the second order observer are explained and contrasted with those of the typical first order observer. The conditions of existence and design methodologies are presented to synthesize the observer gains by taking various assumptions on available measurements into consideration. The concept of direct matrix second order framework design is new and attractive, especially for observer based controllers.

Observer design in matrix second order system framework; measurement conditions and perspectives

In this paper, we introduce the conditions for the existence of the second order observer gains directly in the matrix second order framework to synthesize observer gains taking various assumptions on available measurements into consideration. Several important reasons are presented to justify the need for this approach and the advantages of the second order observer are explained and contrasted with those of the typical first order observer. This concept of direct matrix second order framework design is new and attractive, especially for observer based controllers.

New modeling and control design techniques for smart deformable aircraft structures with acceleration feedback

In this research, a new modeling and control design specifically tailored to smart aeroelastic systems is presented. The control problem is to achieve a roll maneuver with a desired roll rate using a piezolaminated flexible wing subject to aerodynamic field. This truly multi-disciplinary system of an elastic structure with piezoelectric actuating and sensing under external aerodynamic load is modeled with an integrated finite eIement method. A new control design algorithm based on ‘Reciprocal State Space’ framework is developed to achieve the desired roll rate and to dissipate vibrations by applying acceleration feedback. The deformed structure for obtaining the specific roll i-ate is made up of new mass and stiffness matrices which are functions of the steady-state input voltage of the roll maneuver. The resulting model in the generalized coordinates which has a mass matrix, a nonsymmetric aerodynamic damping matrix and a nonsymmetric stiffness matrix (due to aerodynamic stiffness) is then transformed to real but nonorthogonal modal coordinates and a reduced order model is developed. * Graduate Student, Member ’ Professor, Associate Fellow Copyright

Broadband vibration control using passive circuits in the matrix-second order framework

In this research, a broadband variable passive and semi- active circuit is presented. The detailed procedure to obtain the augmented second order differential equations of motion for an electrical dynamic absorber (shunted circuit) using integrated piezoelectric material are given using Hamiltons principle and the finite element modeling procedure. The effect of the electrical dynamic absorber is shown through frequency response and analysis by varying the capacitance and inductance in the shunted circuit. Modal identification and gain scheduling techniques are also employed to identify each mode of the vibration of the structure. Simulations are implemented using a cantilevered aluminum beam with a PZT-5H (lead zirconate titanate) patch. The simulated results are provided in multiple formats.

Morphing flight control surface for advanced flight performance

A novel Morphing Flight Control Surface (MFCS) system has been developed. The distinction of this research effort is that the SenAnTech team has incorporated our innovative Highly Deformable Mechanism (HDM) into our MFCS. The feasibility of this novel technology for deformable wing structures, such as airfoil shaping, warping or twisting with a flexure-based high displacement PZT actuator has been demonstrated via computational simulations such as Finite Element Analysis (FEA) and Computational Fluid Dynamics (CFD). CFD was implemented to verify the accuracy of the complex potential flow theory for this application. Then, complex potential flow theory, kinematics, geometry, and static force analysis were incorporated into a multidisciplinary GUI simulation tool. This tool has been used to aid the design of the MFCS. The results show that we can achieve up to five degrees of wing twisting with our proposed system, while using minimal volume within the wing and adding little weight.

A broadband vibration control using passive circuits

In this research a broadband passive vibration control technique using a semi-active circuit is presented. A digitally tunable RL shunt circuit and a semi-active mode identifier are developed using 8-bit CMOS microcontrollers to control multiple vibratory modes in a mechanical system. In order to increase the adaptability of the controller, the effects of additional capacitors in the circuit are investigated. The governing equations for the coupled electro-mechanical system are introduced using Hamilton’s Principle and finite element analysis. The system is verified experimentally using and the simulation and experimental results are provided in multiple formats.