Date of Award

2014

Document Type

Thesis - Open Access

Degree Name

Master of Science in Engineering Physics

Department

Physical Sciences

Committee Chair

Dr. William MacKunis

First Committee Member

Dr. Sergey V. Drakunov

Second Committee Member

Dr. Vladimir Golubev

Abstract

Limit cycle oscillations (LCO), also known as utter, cause significant challenges in fight control of unmanned aerial vehicles (UAVs), and could potentially lead to structural damage and catastrophic failures. LCO can be described as vibrational motions in the pitching and plunging displacements of an aircraft wing. Even in low Reynolds number (low-Re) fight regimes, LCO can exceed the limiting boundary for safe UAV fight. Further, as practical considerations motivate the design of smaller, lighter weight UAVs, there is a growing need for UAV systems that do not require heavy mechanical actuators (e.g., ailerons). To address this, the use of synthetic jet actuators (SJAs) in UAV fight control systems is becoming popular as a practical alternative to mechanical deflection surfaces. SJAs are promising tools for LCO suppression systems in small UAVs due to their small size, ease of operation, and low cost. Uncertainties inherent in the dynamics of SJAs present significant challenges in SJA-based control design. Specifically, the input-output characteristic of SJAs is nonlinear and contains parametric uncertainty. Further control design challenges exist in situations where multiple actuators lose effectiveness. In the event of loss of effectiveness in multiple actuators, control challenges arise due to the fact that the resulting system contains fewer actuators than degrees of freedom (DOF) to be controlled (i.e., an underactuated system). Still further difficulties exist in control design for dual parallel underatuated systems, where standard backstepping-based control approaches cannot be applied. In this thesis, three nonlinear SJA-based control methods are presented, which are capable of complete (i.e., asymptotic) suppression of LCO in UAV systems containing uncertainty. An adaptive control method is presented first, which is shown to achieve asymptotic regulation of LCO for UAVs in the presence of model uncertainty and unmodelled external disturbances. Motivated by the desire to reduce the computational complexity of the closed-loop system, a structurally simplistic robust (single feedback loop) control design is presented next, which is shown to achieve asymptotic LCO regulation without the need for adaptive parameter estimation. Finally, to address the control challenges encountered in the event of actuator faults, a robust control method is presented, which achieves simultaneous suppression of the pitching and plunging displacements using only a single scalar control input. The control design presented for this underactuated scenario is also proven to completely compensate for the inherent SJA nonlinearity. Rigorous Lyapunov-based stability analyses are provided to prove the theoretical results, and numerical simulation results are provided to complement the theoretical development.

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