Out-Of-Plane Bending Stiffness and Stress based on Advanced 3-Link Analysis Technique in a Floating Offshore Wind Turbine Platform

초록

After the accidental mooring link failures in an offloading floating buoy occurred in West African offshore area and subsequent investigations announced due to out-of-plane bending (OPB) effect, fatigue safety check reaches to include OPB moment- and in-plane bending (IPB) moment-induced damage reductions. Mooring links for an 8-MW class floating offshore wind turbine platform were taken into account for benchmark study. This paper introduced two numerical simulation techniques for the 3-link analysis; prescribed rotation approach (PRA) and direct tension approach (DTA). Two 3-link models based on the PRA and DTA were prepared. OPB stiffnesses, stress distributions in mid-span, hotspot stresses, and stress concentration factors were comparatively presented based on the two 3-link analysis techniques and BV guidelines. Convergence studies were conducted to determine the minimum number of links required for a multi-link analysis. It was proven that 10 links were at least necessary for the multi-link analysis. Relationships between tension angle and interlink angle from the multi-link analysis with 10 links were presented using the OPB stiffnesses from two 3-link techniques. Tension angle versus interlink angle relations were presented from the multi-link analysis. It was found that they would be significantly affected by the OPB stiffnesses determined from 3-link analysis techniques or simplified BV formula.