Advances in nonlinear dynamical modeling and control of marine thrusters: Theory and experiment

This thesis consists of two parts. In the first part we report two specific improvements in the finite-dimensional nonlinear dynamical modeling of marine thrusters. Previously reported four-quadrant models have employed airfoil theory considering only axial fluid flow and using sinusoidal lift/drag curves. First, we present a thruster model incorporating the effects of rotational fluid velocity and inertia on thruster response. Second, we report a novel method for experimentally determining non-sinusoidal lift/drag curves. The model parameters are identified using experimental thruster data (force, torque, fluid velocity). The models are evaluated by comparing experimental performance data with numerical model simulations. The data indicates that thruster models incorporating both reported enhancements provide superior accuracy in both transient and steady-state response.; The second part of the thesis focuses on the online identification of the plant parameters and several control schemes applied to the plant identified in the first part. We present a stable adaptive parameter estimator for the friction coefficients, k_f1 and k_f0, and the linear momentum transfer coefficient, k_z. Next an alternative lift and drag curve representation using truncated Fourier series is introduced. The alternative representation allows for the design of a stable adaptive lift and drag curve estimator. We then derive several nonlinear model-based open-loop thrust controllers for asymptotic thrust control under static and dynamic input conditions. In the last part of the thesis we derive an globally asymptotically stable nonlinear partial state observer for the axial flow velocity using partial state feedback.