An efficient approach for planning towing maneuvers for an underwater vehicle via ship and winch control is presented. It is demonstrated that it is possible to generate a towing strategy for a submersible vehicle such that the towed body follows a desired trajectory in the presence of known currents. The approach relies on the fact that the system is differentially flat under certain modeling assumptions; hence, it is possible to determine the required ship motion and winch rate so that the specified trajectory of the submersible is followed. The cable is modeled using a lumped mass approximation, including hydrodynamic drag, buoyancy and added mass effects. In the proposed approach, extensive use is made of spectral collocation methods to compute derivatives of motion. The approach is capable of producing open-loop trajectories in very short computation times, which makes it suitable for real-time computations.
The positioning of deeply to wed cables via motion of the surface vessel is a technique often used by sonar platforms. Lemon (2004) recently described the history of towed arrays and some recent developments. In deep water, the distributed effects of inertia and drag forces on the cable make accurate positioning of the vehicle difficult by movement of the surface vessel alone. Major challenges facing such towing maneuvers are the significant time lag between changes in ship motion and the towed-body response, as well as the settling time required for steady to wing. Various approaches have been suggested for controlling the ship position to achieve the desired motion of the vehicle. Paul and Soler (1972) considered planar 2-dimensional towing strategies to minimize the time required to move a submersible vehicle to a new position. A lumped parameter model of the cable was used, and it was found that faster maneuvers can be achieved by having the tow ship overshoot the target by a specified amount and then reverse course.
