Dynamics and Control of Underwater Gliders I: Steady Motions

This paper describes analysis of steady motions for underwater gliders, a type of highly efficient underwater vehicle which uses gravity for propulsion. Underwater gliders are winged underwater vehicles which locomote by modulating their buoyancy and their attitude. Several such vehicles have been developed and have proven their worth as efficient long-distance, long-duration ocean sampling platforms. To date, the primary emphasis in underwater glider development has been on locomotive efficiency; maneuverability has been a secondary concern. The ultimate aim of our research is to develop optimal motion control strategies which enhance the natural locomotive efficiency of underwater gliders by minimizing the energy expended by the control system. Ambitious applications such as persistent undersea surveillance require not only efficient vehicles, but efficient guidance and control schemes. This technical report aims to develop a better understanding of glider maneuverability, particularly with regard to turning motions. As a preliminary step, we develop an approximate analytical expression for steady turning motion for a realistic glider model. The problem is formulated in terms of regular perturbation theory, with the vehicle turn rate as the perturbation parameter. The resulting solution exhibits a special structure that allows one to apply existing optimal path planning results for planar mobile robots. The ultimate result is a simple, energy-efficient motion control method for underwater gliders.