Experimental Research On A Wave Propelled Craft

This research on wave propelled crafts aims mainly on the development of a wave energyabsorbing device, which can convert the hull’s kinetic energy into thrust. The application of thiswave propulsion technology in engineering could be a fossil fuel independent, long-cruis ing,low speed Unmanned Surface Vehicle (USV). Equipped with the motion-damping wavepropulsion mechanism, the USV will have enhanced sea-keeping performance when comparedto boats in the same size, therefore more suitable for oceanic data collecting, sea-borne alert ornavigation on a fixed route.This paper relies mainly on model tests. Data from still water resistance tests and free runningtests in wave was collected, in order to study the resistance property of wave propulsion deviceand overall performance of the wave propelled craft.By referring to configurations of existing wave powered boats, and considering requireme ntsfor a long distance USV, an installation platform for the mechanism being tested was built froma double hull ship model. Based on the principle of adopted passive oscillating foils, a set ofsimple and easy-adjusting test model was made.In data acquisition, wave surface was measured by common sensor with cable. In order tocollect motion data across the tank without any fixed reference object, a wireless accelerometersystem was designed and assembled to measure and transmit real-time motion signal. Dataacquisition and analysis programs were coded with LabVIEW and MATLAB, respectively.To estimate the amount of thrust generated by the foils, still water resistance of the hulls wascalculated, towing tests of the hulls alone and the whole model with propulsion mechanis mwere performed, resulting in resistance curves. The model’s resistance curve in wave wasderived by superposing the AQWA calculated first order wave drift force. It was found by thetowing test that the resistance caused by propulsion mechanism grows too fast at relatively highspeed, thus the wave propulsion system in this study is applicable only on low speed crafts.The free running tests in head sea and follow sea condition shew that advance speed alwaysgrow linearly with wave height, but growing rate varies with wave period. Speed is most sensitive to the growth of wave height at resonance frequency, suggesting that passiveoscillating foils rely on local heaving motion to generate thrust. Numerical simulation of theoscillating foils derived a generally correct thrust estimation and visualized foil trajectory. Pitchmotion response of the craft has a sharper peak in head sea, though overall response value inmost wave periods is lower than follow sea condition. Heave response in head sea is alwaysgreater than in follow sea.