Development and preliminary experimental validation of a wind-and solar-powered autonomous surface vehicle
von Ellenrieder KD
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The design and initial testing of a wind- and solar-powered (WASP) autonomous surface vehicle (ASV) are presented. The concept vehicle is a 4.2-m length overall (L(OA)) monohull keel-boat powered by a rigid wing sail with a 5-m span. It is designed to operate in 7-10 kn of wind and a maximum sea state of 2. Specific attention is placed on the aerodynamic, hydrodynamic, and systems integration aspects of the design. Rigid wing sails are shown to have superior performance to conventional cloth sails for use on ASVs owing to their higher aerodynamic efficiency and robustness. The manual design process involved in selection of the airfoil cross section for the wing sail and the resulting aerodynamic performance predictions are presented. Through mathematical derivation, the optimal angle for switching the sail configuration from an upwind/crosswind lift-generating mode to a downwind drag-generating mode is found to be 135 degrees. To simplify implementation of the control system when operating in the lift-generating sailing mode, a control scheme that decouples heading and speed control by simply setting the wing sail to an angle of attack of 10 degrees and independently controlling heading was used. The simulation results from a velocity prediction program (VPP) used to verify the feasibility of this control approach are presented. Initial field trials of the vehicle using the control approach with autonomous wing control and manual rudder control are presented. It is shown that the measured boat speeds and wind speed/directions are within the range of values expected from the VPP. Temperatures recorded in a thermal plume during the field trials of the ASV are shown as a function of global positioning system (GPS) location and time.