Fuzzy rule based depth controller for variable ballast system of autonomous underwater vehicles

Summary form only given. Variable ballast (VB) systems of autonomous underwater vehicles (AUV) are designed to compensate for changes in weights, variable loads, and displacement which occur during dive so as to keep submersibles at design condition such as neutral buoyancy and zero-trim. VB is also designed to create positive/negative buoyancy, so AW will ascend/descend to a desired depth. VB is composed of variable ballast tanks which may be flooded or blown to attain the required buoyancy. By investigating the dynamic response of VB system, a robust and energy saving depth control strategy is formed. The key point is to find a critical depth point at which a certain amount of water needs to be added to or subtracted from the VB tank. The critical depth point has nonlinear relationship with the desired depth, initial set weight, and VB dynamic parameters. The use of fuzzy logic controller is investigated for VB depth control. Fuzzy rules are developed to get the critical depth point. They are derived from qualitative analysis of VB dynamic systems