الفهرس 
Title : Nonlinear Control of a Prototypical Wing Section using Nonlinear Feedback and Sliding Mode Control
SummaryOnly 14 pages are availabe for public view
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Abstract
A prototypical aeroelastic wing section that includes certain types of nonlinearities can show a wide range of response patterns. The presence of the nonlinearity terms results in limited amplitude flutter or limit cycle oscillations (LCOs). A single trailing edge (TE) control surface is used in this model that has two degrees of freedom (D.O.F) described as plung and pitch is coupled with a quasi-steady aerodynamic model will be studied. For the aeroelastic system that includes polynomial structural nonlinearities, nonlinear control laws will be developed. In the aeroelastic model with a single trailing edge (TE) control surface, finding an output function that provides complete feedback linearization (FBL) for the two outputs (pitch and plunge) together is complicated. So, that two separate problems will be studied in which one output variable is considered. Based on partial feedback linearization (FBL), the stability of the resulting closed-loop system and a nonlinear controller will be studied. Exact cancellation of the nonlinearities that exist in the system is the main goal of this approach and then finds a new control input to achieve the stabilization of the system. Firstly, to investigate pitch primary control, it is required to study the stability of partial feedback linearization (FBL). For a variety of flow speeds (𝑈), and elastic axis locations (𝑎), zero dynamics for the case of pitch primary control is studied . Secondly, the stability of the plunge primary control will be studied based on partial feedback linearization (FBL). For this case, based on different values of flow speeds (𝑈) and elastic axis locations (𝑎), partial feedback linearization (FBL) shows a bifurcation phenomenon. So, for completely understand the characteristics of the zero dynamics, two bifurcation diagrams are examined. Another nonlinear control method will be discussed. This method is defined as sliding mode control (SMC); it is required to design a controller that offers a systematic solution to maintain the stability and performance of the nonlinear system. SMC depends on a notational simplification in which nth-order tracking problem is exchanged with a simpler order stabilization problem. The results show that without any control effort, the aeroelastic system reveals various kinds of nonlinear phenomena including limit cycle oscillations (LCOs) that also known as flutter instability. The nonlinear controllers based on the partial feedback linearization (FBL) yielded a stable closed loop system, although the stability is guaranteed in the neighborhood of the equilibrium points. The two crucial parameters, elastic axis location (𝑎) and free stream velocity (𝑈), each have a significant effect on the resulting partially linearized closed-loop system. Results from feedback linearization approach were compared with those from sliding mode control and gave satisfactory consistently.