Energy Harvesting Marine Robot for Long Endurance Undersea Monitoring

Abstract

Possibility of developing energy independent unmanned marine platforms capable of performing both ASV and AUV operation was studied. Two specific platforms that utilizes environment for the platform and propulsion and electric power generation were discussed ? Ocean wave driven hybrid AUV&ASV platform and power regenerative underwater glider platform. The first proposed platform, ocean wave driven hybrid platform, is designed for a routine underwater patrol task. It travels a large distance from the surface as ASV and makes a dive from the closest point. A unique feature of this platform is that the platform propulsion is wave driven, thus consumes no stored power for navigation while on the surface. For underwater operation, internal battery is used to change the buoyancy, and the platform glides like an underwater glider.The second platform, power regenerative underwater glider platform, is a buoyancy driven gliding platform. Conventionally continuous operation of the underwater glider was limited to the certain number of dives due to the internal fuel (battery) exhaustion. The proposed platform contains a unique underwater turbine that replenishes an internal battery for keeping the buoyancy device going. The feasibly studies of both moving mechanisms and depth control mechanisms were conducted. The renewable energy based propulsion is a key to the both proposed platforms. The scaled propulsion/generator modules were created to see if the proposed propulsion mechanisms are actually feasible. To conduct a numerical analysis, Matlab Simulink based models for both proposed platforms were created. To validate the reliability of the first model, a wave driven hybrid ASV&AUV platform, a comparison was made between the simulation result and reference result. Since the basic principle behind propulsion mechanism of the proposed platform and that of Liquid Robotics’ Wave Glider is similar, the actual logged data of Wave glider and the simulation result were compared. The comparison showed the similarity in speed profile. The simulation, however, failed to establish an autopilot controlled system. It suggested that the use of a single rudder may not provide enough maneuverability because the platform cruises at low speed. In addition, towed float module created an unwanted torque on the overall platform when the platform attempted to change the course. The mentioned control problem is to be studied in a future study. The validation of the second model, for power regenerative underwater glider platform, was made by comparing the performance data of conventional underwater glider with the simulation result. In a future study, a small scaled generator module prototype is to be built.Finally, potential applications of the proposed platforms are discussed. A focus of both platforms is its long endurance propulsion/power generation mechanism. Two areas of the potential applications that would require a long endurance is discussed ? military and ocean science.