Modeling and control of underwater vehicles. A Lagrangian approach

摘要

This thesis contains an extensive study of modeling and control of underwater vehicles. The thesis concludes that there will be an emerging demand for more optimal and advanced nonlinear controllers for underwater vehicles. Minimum control effort controllers will be especially needed. Lagrangian dynamics has successfully been employed to derive the equations of motion for underwater vehicles. The Lagrangian approach in modeling exposes the properties of the underwater vehicles' equation of motion in a way that the more traditional Newtonian approach does not. The expressions for energy and work used in the Lagrangian mechanics are also useful in control system design when stability and optimality are proved by using nonlinear stability theory. The equations of motion are derived in both an inertial reference-frame and a vehicle-fixed coordinate system. Results from open-water tests of the Norwegian Experimental Remotely Operated Vehicle's (NEROV) thruster system are presented. These test-results show the nonlinear relation between the vehicle's velocity and thrust. Test results from free-decay tests of the NEROV are also presented. These results show how the vehicles added inertia and damping coefficients vary as a function of the Keulegan-Carpenter number. These parameters' dependencies of frequency and a perturbed vehicle geometry are also investigated. These tests clearly show that the model parameters of underwater vehicles are time-varying. Two optimal and near-optimal nonlinear controllers are derived in minute detail. Both controllers are optimal in the sense that they minimize the generalized forces that correspond to the vehicle's kinetic energy and the energy which dissipate from the vehicle. 126 refs., 41 figs., 7 tabs.