One-way Coupled Dynamic Analysis of Floating Platform with Wave Energy Converters

摘要

In this paper, a six degree-of-freedom motion of a very large floatingplatform which is equipped with a number of wave energy converters(WECs) was carried out. Six cylindrical-shaped WECs designed toslide along the vertical shaft are located at each side of the rectangularplatform, so a total of 24 WECs existed on the platform. Since WECsextract electrical energy from the relative heave motion between WECsand the platform, and the relative heave motion is dynamically coupledby the power take-off (PTO) mechanism, the platform responses areaffected by the WECs. To examine the effect of the WECs on theplatform, an analysis of one-way coupling, which only considered thePTO damping of the static WECs on the platform, was carried out. Theone-way coupling was simulated under the following conditions: Allthe WECs were statically fixed at a mean water level (MWL) withoutheaving, but sliding motions were still allowed along the shaft. As aresult, the relative heave motion between the floating platform and theWECs was partially implemented. The equation of motion of thefloating platform in the time domain was established, and the responsesof the one-way coupled platform were then compared with the case ofthe platform without any coupling effects from the WECs. Thehydrodynamic coefficients and wave exciting forces were obtainedfrom WAMIT, the 3D diffraction/radiation pre-processor code based onthe boundary element method. The analysis of the dynamic responsesof the floating platform with or without one-way coupling in the timedomain was carried out using a hull-mooring coupled dynamic analysistool, CHARM3D. The analysis showed that WECs may inducesignificant damping of platform motions in heave, roll, and pitch. Italso showed that the mooring line top tensions are also influenced bythe damping effect of WECs.