Study on Array Floating Platform for Wind Energy and Marine Space Optimization

The concept of multiline anchor, whose application is mainly considered in water depths beyond 100 m and analyzed only by numerical simulation, has been discussed for half a decade, yet previous studies have not conducted the wave basin experiment. Thus, this paper set this concept firstly with a shallow water mooring system designed for a Taiwan offshore water area, where the suitable water depth for floating offshore wind turbine is located from 50 to 100 m, and then conducted a 1:144 scaled model wave basin experiment to validate the results from numerical simulation. In this paper, the numerical model simulated and analyzed three identical DeepCwind OC4 semi-submersible platforms equipped with NREL 5MW wind turbines in OrcaFlex and the experiment carried out by using three 1:144 scaled semi-submersible platforms with equivalent disks which simulated different operations of wind thrusts. To consider the possible influence of the wake effect, the minimum turbines spacing was set at 750 m in a full scaled model and the length of mooring lines was redesigned according to the catenary theory. This paper utilized OrcaWave to calculate hydrodynamic parameters and input it into OrcaFlex to simulate the line tension and the three degrees of freedom (surge, heave, and pitch) of the platforms under regular and irregular wave tests, and coordinate with scaled model tests carried out in Tainan Hydraulics Laboratory (THL). In addition to the reduction in the number of anchors, the concept of multiline anchor was also discussed in this study for the spatial configuration of offshore wind farms. It shows that the wind farm composed of three floating wind turbines can reduce the ocean space by roughly 24% compared to that with a single-line anchor. According to the comparison of numerical and experimental results, this study finally optimized the mooring lines by changing the diameter to increase the stability and the threshold of Minimum Breaking Load (MBL) and proposed a multiline anchor configuration for shallow offshore water area in Taiwan based on the results obtained.