Modeling and simulation of an AUV-towfish system

Simulations of an autonomous underwater vehicle, tow cable, and magnetometer towfish are performed using a combined Matlab-Orcaflex interface to provide a better understanding of how changes in towing speed (0.5 - 2m/s), cable length (5 - 15m), vehicle trajectory (circle and vertical zig zag maneuvers), and current speed (0.25 - 1.25m/s) affect towfish trajectory. The AUV-towfish system consists of a Bluefin autonomous underwater vehicle (AUV) and a Seaspy towed magnetometer. The simulations reveal that a 5m tow cable provides the best maneuverability of the towfish in comparison to longer cables. The towfish traveled a greater distance in a given period of time and more closely followed the waypoints of the AUV in not only the x and y directions, but in the vertical direction as well. The longer tow cables gave the towfish too much freedom to stray off course during maneuvering of the AUV. Tow speeds between 60% and 80% thrust showed provide better towfish pitch angles than slower tow speeds. While 80% thrust showed the best towfish pitch results, this fast speed may not be desirable when attempting to collect magnetic field data. Surface current speeds between 0.25m/s and 1.25m/s altered the courses of the AUV and towfish during circular maneuvering. As the surface current speed increased up to 1.25m/s the AUV-towfish system could no longer maintain course.