Methods for Positioning Deeply-Towed Underwater Cables

摘要

This thesis considers the problem of positioning a very long, vertical tow cablein the ocean. A derivation of the equations of cable motion is given, followed by an analysis of the nonlinear frequency response of the plant, using the method of harmonic balances and a perturbation technique. The basic control approach is to consider input preshaping and regulation designs separately, merging them to form tracking controllers. The primary pre-shaping part is a frequency-domain dynamic inversion based on recent results in robotics, and works for in-plane and coupled out-of-plane motions, as well as some other distributed-parameter physical systems. For regulator design, a number of observer-based approaches are considered, ranging from standard linear loopshaping to an approximately optimal non-linear control law with nonlinear observation. Our solution to the nonlinear optimal control problem is novel in the sense that it can accommodate multi-input/multi-output plant models of arbitrary order, a necessity for distributed plants. The preshaping techniques are verified with full-scale results from experiments in the ocean with 2000 meters of cable, and the various closed-loop methods are compared based on scale-model laboratory tests. Underwater remotely-operated vehicles, Ocean drilling, Cable dynamics.