Longitudinal trajectory optimization of an underwater glider in finite depth water

Abstract

Underwater gliders use both buoyancy and gravity for propulsion, and thus the vehicle can glide upward or downward by alternating its buoyancy engine. Typically, underwater gliders are operated by diving or climbing at a constant gliding angle following a sawtooth path, which achieves both maximum efficiency and traverse speed in a deep water environment. However, this is not the best strategy in water of limited depth because an underwater glider cannot accurately follow non-smooth saw-tooth paths and the frequent reversals of the buoyancy engine reduce the traverse speed and operating efficiency of the glider. This paper formulates an optimal control problem for an underwater glider considering depth constraints into a nonlinear two-point boundary value problem with inequality constraints. Numerical methods are employed for path optimization and the results are discussed.