Showing papers by "Cornel Sultan published in 2014"

Optimal Energy Harvesting from a Membrane Attached to a Tensegrity Structure

Abstract: The feasibility of harvesting energy using polyvinylidene fluoride patches mounted on a vibrating prestressed membrane, itself attached to a tensegrity structure, was investigated. Kinematics of the tensegrity structure and the attached membrane is described and conditions for stable equilibrium for the structure are derived. Nonlinear partial differential equations describing the dynamics of the membrane attached to the tensegrity structure and under the action of a time-dependent transverse pressure are derived using the principle of virtual work. These equations are linearized and the modes of the structure are obtained using the finite element method. These modes are used as basis functions in developing a reduced-order model to obtain the response of the complete structure under the applied transverse dynamic pressure. The polyvinylidene fluoride patch on the structure is connected to an electrical load resistance. The electrical current passing through the load resistance is calculated using Gauss’s...

Flight Control Energy Saving via Helicopter Rotor Active Morphing

Abstract: Helicopter main rotor active morphing is investigated to save helicopter flight control energy in the presence of constraints on outputs. For this purpose, the nonlinear equations of motion of the helicopter are linearized around straight level flight. Then, several main rotor active morphing scenarios such as blade radius, blade chord length, blade twist angle, and rotor angular speed variation are analyzed individually (i.e., each active morphing scenario is implemented one at a time). Output-variance-constrained control is used for helicopter flight control system design, and the control energy savings due to active morphing with respect to a conventional helicopter are evaluated. An extensive circumstance in which all active morphing concepts are implemented simultaneously is examined to obtain larger control energy savings. The possibility of using morphing controls for trimming is also considered, and stochastic optimization is used to solve the resulting simultaneous trimming and control design pro...

Nonlinear Helicopter and Ship Models for Predictive Control of Ship Landing Operations

Abstract: A control-oriented helicopter model is used for ship landing operations. The model captures essential dynamics including blade flapping, lead-lagging and main-rotor inflow. The model is nonlinear but written in the implicit Ordinary Differential Equation (ODE) form. Various nonlinear simulation results of this model's dynamics in response to initial disturbances and control inputs are presented. Comparisons with corresponding responses of the linearized models around hover and straightforward flights indicate a relatively good agreement between linearized and nonlinear models. A linear Model Predictive Control (MPC) design for the helicopter is investigated using linearized models and it is evaluated using the nonlinear model. Simulation results show the capability of the MPC to handle multiple system constraints and tolerate modeling errors. Moreover, a simple ship model that has a Lewis-form body plan is used for motion simulation. Finally, an automatic deck landing using MPC is designed for successful landing on a ship with irregular motions at rough seas.

Parametric Geometry Model for Design Studies of Tailless Supersonic Aircraft

Abstract: This paper presents an extension of the Kulfan class-shape transformation method for the parameterization of aircraft component geometry. The VT-CST code represents a practical implementation of the class-shape transformation method in an object-oriented C++ code for use within a multidisciplinary design optimization framework for design studies of a tailless supersonic aircraft. Extensions to the class-shape transformation method incorporated into VT-CST include the generation of a blended wing–fuselage, cowls and inlet ramps for embedded engines, automatic handling of centerline continuity, shape normalization and scaling, fuselage area-ruling capabilities, conical cambering, airfoil shape matching, and control surfaces, among others. Examples demonstrating the utility of the method are given.

LMI Control Design With Input Covariance Constraint for a Tensegrity Simplex Structure

Abstract: The Input Covariance Constraint (ICC) control problem is an optimal control problem that minimizes the trace of a weighted output covariance matrix subject to multiple constraints on the input (control) covariance matrix. ICC control design using the Linear Matrix Inequality (LMI) approach was proposed and applied to a tensegrity simplex structure in this paper. Since it has been demonstrated that the system control variances are directly associated with the actuator sizes for a given set of ℒ2 disturbances, the tensegrity simplex design example is used to demonstrate the capability of using the ICC controller to optimize the system performance in the sense of output covariance with a given set of actuator constraints. The ICC control design was compared with two other control design approaches, pole placement and Output Covariance Constraint (OCC) control designs. Simulation results show that the proposed ICC controllers optimize the system performance (the trace of a weighted output covariance matrix) for the given control covariance constraints whereas the other two control design methods cannot guarantee the feasibility of the designed controllers. Both, state feedback and full-order dynamic output feedback controllers have been considered in this work.Copyright © 2014 by ASME

Power Take-Off Control of In-Stream Hydrokinetic Turbines

Abstract: In-stream hydrokinetic electricity production, electricity generation from moving currents without the use of dams, has significant potential for increasing electric power production. This project evaluates a control system designed to regulate rotor rate (rpm) to improve power production from in-stream hydrokinetic turbines. The control algorithm is evaluated using both a numerical model of a rigidly mounted tidal turbine and a numerical model of a moored ocean current turbine system. These two system models are each coupled to an induction electric machine model. Based on the turbine torque-speed characteristic, as well as the asynchronous machine features, a Look-Up-Table (LUT) is used to generate the frequency of the sinusoidal voltages of the three phases to be supplied to the machine. However, to compensate for disturbances and perturbations of the power-plant a PI controller is generating a correction term for electrical frequency superimposed to the output of the LUT. A first round of simulations using the numerical models was performed in order to evaluate the developed algorithms.Copyright © 2014 by ASME

LQG Control and Robustness Study for a Prestressed Membrane With Bimorph Actuators

Abstract: Linear Quadratic Gaussian (LQG) control is developed for a prestressed square membrane with bimorph actuators attached to it. The membrane is modeled using the finite element method and the membrane is assumed to be clamped on all edges. After obtaining the mass, damping, stiffness and input matrices in second order form using the weak form Finite Element Method (FEM), the problem is represented in first order form to develop the LQG controller. To study the robustness of the system, the control and observer gain matrices developed for the nominal system are applied to systems obtained from the nominal system by modifying material properties and prestress.Copyright © 2014 by ASME

Active Control of Four-Bar Tensegrity-Membrane Systems

Abstract: Tensegrity-membrane systems are deployable structures that can be utilized in space applications such as solar sails and radar systems. This work addresses the control design for four-bar tensegrity-membrane systems. The tendons act as actuators, and the system can be controlled by changing the rest-lengths of the tendons. Lagrange’s method is used to model the system, and the equations of motion are expressed as a set of differential-algebraic equations (DAE). For control design, the equations of motion of the system in the DAE form are converted into the form of second order ordinary differential equations based on coordinate partitioning and coordinate mapping. Since the number of control inputs is less than the number of state variables, these systems can be classified as underactuated nonlinear systems. The collocated partial feedback linearization (PFL) technique is implemented to design a nonlinear controller. Simulation results of the closed-loop system under initial perturbation are presented, and the performance of the controller is discussed.Copyright © 2014 by ASME

Modeling of Four-Bar Tensegrity-Membrane Systems

Abstract: Tensegrity-membrane systems are lightweight and deployable structures that can be utilized in space applications such as solar sails and radar antennas. This work focuses on four-bar tensegrity-membrane systems. An energy-based method is used to determine the static configurations of four-bar tensegrity-membrane systems, and the explicit equilibrium conditions for the symmetric systems are derived. The system dynamics is studied based on the Lagrange’s method by appropriately choosing a floating reference frame for the attached membrane. The stress distribution in the membrane due to corner displacements and the free vibration modes of the membrane are determined by a polynomial series method, and are compared with the finite element results calculated by ANSYS. The linear and nonlinear simulation results of the system are presented and compared. The difference between linear and nonlinear simulation results is illustrated and discussed.Copyright © 2014 by ASME