Aeronautics, Dynamics, and Control Laboratory
Vision(1) interdisciplinary (multiphysics) modeling and analysis, (2) mathematical rigor, and (3) inspiration from Nature are our enabling factors to shape the future of aeronautical engineering.Lab HistoryThe ADCL was inaugurated in Sep 2014. Since then, it has produced about 80 publications (30 journal articles and 50 conference papers); raised about $1.7 million; and supported two postdocs, 10 PhDs, and 15 Masters.Research Interests1. Unsteady AerodynamicsUnsteady aerodynamics emerges in various subjects such as the flapping wing, flutter analysis, and rotary blades. One of the most famous approaches in this field coming from the potential flow theory is the Theodorsen solution for the harmonically pitchingplunging flat plate which has been mainly devised for the flutter problem. Since lift generation and vorticity production inside are essentially viscous processes, we attempt to study the viscous unsteady aerodynamics rather than utilizing the conventional potentialflowbased solutions. To do so, we labor wind tunnel experimentation, computational fluid dynamics and analytical approaches to account for the viscous phenomenon. Recently, for the first time, we developed a theoretical viscous extension of the Theodorsen lift frequency response based on the triple deck boundary layer theory and validated it with high fidelity CFD simulations of a harmonically pitching airfoil. More phase lag at high reduced frequencies and low Reynolds numbers is the main outcome of the aforementioned study. 2. Geometric Control Theory Linear Control has reached a mature stage of development and qualitative questions such as Controllability and Observability has been answered satisfactorily. For nonlinear systems, however, questions about fundamental structural properties such as Controllability are yet to be answered with the hope of reaching analogous results to linear systems. We aim at formalizing feedbackinvariant necessary and sufficient conditions for Controllability of nonlinear systems and also we aim to develop a meaningful measure of degree of Controllability of nonlinear systems. If successful, the results of this project will hopefully revive interest in Geometric Control, a branch of control theory that is concerned with studying nonlinear systems using mathematical tools from Differential Geometry. 3. Engineering Applications Geometric nonlinear controllability analysis sometimes leads to very interesting and nonintuitive results. A car with two controls (forward/backward and steering) is obviously not linearly controllable because of the inability to generate pure side motions. However, the nonlinear geometric analysis shows that the system is nonlinearly controllable and through some manipulation of the available two controls, one can generate side motions. This idea has been generalized to many nonlinear dynamical control systems, where the question is “Will the system still be controllable, if one or more actuators are missed?” One example is the attitude dynamics of a spacecraft (rigid body) where it has been shown that the system is still controllable even if one or two pairs of gas jets are removed, in spite of the system being linearly uncontrollable. In this research, we perform a geometric nonlinear controllability analysis for airplane flight dynamics to study whether the airplane will remain controllable if one or more of the control surfaces fail. Recently, we showed that a twinengined airplane might still be controllable if it lost all control surfaces (thrustonly flight control system), despite the fact that it is linearly noncontrollable. From another perspective, if that control surface is not needed for control, then how can we use to improve efficiency or to execute unconventional maneuvers? One example is that we found that realizing the Lie bracket between the elevator and aileron deflections leads to a novel rolling mechanism that has a higher authority near stall than the conventional rolling mechanism (using aileron only). The reason is that the traditional mechanism depends on the value of the aileron sensistivity which vanishes near stall, whereas the novel mechanism depends on the rate of change of that sensistivity, which has a significant value near stall as shown in the figure. As such, this novel mechanism might be effective for nearstall or poststall maneuvers. News
