Towards a new strategy for AUV navigation in sea currents: A quasi-optimal approach

A navigation strategy for achieving quasi-optimality for autonomous underwater vehicles (AUVs) is presented. The objective of the optimal navigation is the minimum-time transit of an AUV in a flow field of sea current disturbance. Reactive optimal guidance revisions followed by tracking controls are the key features of the proposed quasi-optimal navigation strategy. In this research, a globally working numerical procedure for obtaining the solution of an optimal guidance law is presented. The developed solution procedure derives the optimal vehicle headings which realize the minimum-time navigation in a given sea current. As a fail-safe strategy, quasi-optimal navigation is especially useful when there are significant hostile actions causing optimal navigation failure. Simplicity and robustness are notable characteristics of the quasi-optimal navigation strategy compared to other strategies seeking rigorous optimality. The results of simulations of quasi-optimal navigations in various sea currents conducted on the basis of the dynamics of the AUV "r2D4" are presented. The r2D4 is a deep ocean exploring AUV, developed by the Institute of Industrial Science (IIS), the University of Tokyo.