Longitudinal Motion Instability of a Cruising AUV flying over a Steep Terrain

The problem of motion instability which can occur on a cruising AUV flying over a steep terrain is addressed. In order to interpret the longitudinal motion instability of a cruising AUV experienced during its near-bottom mission, a simulation model for AUV dive was developed. The model incorporates vehicle dynamics and underwater acoustic physics interacting with sea bottom and sea water. As the vehicle dynamics, closed-loop dynamic model representing the controlled motion of an actual cruising AUV is used. Dive simulation of the vehicle following a steep terrain has shown that the lost bottom lock in altimeter operation and the altitude overestimation above a steep terrain are convincing sources of the instability in vehicle motion. Directly correlated with the false altitude which may cause a bottom collision, an ongoing motion instability during a bottom-following dive indicates a vehicle is in serious danger. As a possible solution for the lost bottom lock and altitude overestimation, strategy of slope-following navigation has been exemplified.