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摘要
In order to improve the wave energy conversion efficiency, a multi-degree-of-freedom wave energy converter composed of a fixed platform, a vertical axisymmetric buoy, a tubular structure and three power take-off（PTO）mechanisms was proposed. The tubular structure was connected with the fixed platform by a universal joint, and the buoy and tubular structure were connected by a motion guiding mechanism to ensure that the two bodies have same pitch and roll motions. The mechanical motion rectifier PTO system was used to absorb the energy of the buoy sliding along the tubular structure to realize the unidirectional rotation of the generator while the other two PTOs were installed at the articulated shaft. A time domain hydrodynamic analysis approach was established by using potential theory, in which the hydrostatic forces and Froude-Krylov forces were calculated by the linear method integrated to the wetted surface of the buoy’s hydrostatic equilibrium position and the nonlinear method integrated to the wetted surface of the buoy at an instant in time. In order to consider the possible influence of large angle pitch or roll motions, the vertical mechanical motion rectifier PTO force was not linearized when decomposed into surge, sway and heave motion directions. The effects of wave height, vertical PTO and pitch PTO damping coefficients under following regular waves were analyzed. It is shown that under the same parameters, the wave energy conversion efficiency of vertical PTO and the total efficiency of the converter calculated by nonlinear method are lower than those obtained by linear method, while the efficiency of pitch PTO is greater than that of linear method, and that the higher the wave height is, the greater the difference between the results obtained by two methods is. ? 2023 China Ship Scientific Research Center.
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