Experimental Study on Interaction Between Degrees of Freedom in a Wave Buoy
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Increasing degrees of freedom (DOFs) is a useful way to raise the power capture efficiency of oscillating wave energy converters. Thus, this study proposes a buoy with three DOFs, which are surge, heave, and pitch. The hydrodynamic performance and power capture efficiency of the buoy is physically modeled. Amplitudes of unidirectional and coupled motions are compared to analyze the interaction effect between freedoms under conditions with and without power take-off damping. The capture width ratio and corresponding growth rates are also calculated. Results show that the buoy makes a periodic sinusoidal (or approximate) movement in every DOF. Coupling effect can cause an increase in the amplitude in one DOF and a decrease in the amplitudes of the others. This phenomenon shows that the kinematic energy of the buoy redistributes to all DOFs compared with the unidirectional conditions. Adding DOFs can improve the power absorption of the buoy in most cases, but the number of DOFs is not the more the better.
Key wordswave energy oscillating buoy multiple degrees of freedom
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The authors are grateful for the support of the National Key R&D Program of China (No. 2018YFB1501900), the National Natural Science Fund of China (No. 41706100), the Shandong Provincial Natural Science Key Basic Program (No. ZR2017ZA0202), the Special Projects for Marine Renewable Energy (No. GHME2016YY02), the Shandong Provincial Key Laboratory of Ocean Engineering, and the Qingdao Municipal Key Laboratory of Ocean Renewable Energy.
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