Effect of the multi-segment mooring system by buoy and clump weights on the dynamic motions of the floating platform

Abstract

In this paper, two hybrid mooring system is proposed to improve the performance of the dynamic motions of the floating platform. The concepts are a multi-segment arrangement of the catenary and taut mooring lines, including buoy and clump weight. Two mooring concepts named MSM-BSW and MSM-BMW were designed for a 5 MW OC4-DeepCwind semi-submersible floating wind turbine. These models' mooring forces and platform response were compared to the main model (OC4) under regular and irregular wave conditions. The dynamic response of the platform is performed utilizing both Morrison theory and three-dimensional radiation/diffraction theory based on the boundary element method (BEM) in ANSYS-AQWA software. Adding buoy, increase the horizontal mooring line angle at the fairlead, resultantly on one hand's mooring stiffness in surge and pitch increased so the MSM-BSW model could reduce surge and pitch motions. On the other hand, the buoy can reduce the mooring suspended weight, leading to an increase in the heave platform response. In the case of MSM-BMW, more clump weights increased the mooring line stiffness in the heave direction. In regular and irregular wave conditions, numerical results indicate that the change of natural periods in both MSM-BSW and MSM-BMW case studies leads to the low-frequency resonance having a significant difference from OC4. In contrast, the wave frequency resonance of the three concepts is similar.