Comparison Study of Shallow Water and Deepwater Mooring Systems for Floating Offshore Wind Turbine

Abstract

Abstract The offshore wind industry trend is towards larger wind turbines to lower the Levelized Cost of Energy (LCOE). The water depth plays an important role in Floating Offshore Wind Turbine (FOWT) project viability due to mooring system cost. In the present study, a comparison of shallow water and deep water mooring systems is performed for the offshore US West Coast. To perform the comparison, two mooring systems for 150m and 1300m water depths are designed for a 15MW semi-submersible type FOWT. For comprehensive mooring system performance comparison, a response-based direct time domain simulation method is applied using MLTSIM-OpenFAST in conjunction with High Performance Computing (HPC). MLTSIM-OpenFAST is a time domain aero-hydro-servo-elastic solver for a FOWT and has been validated through OC3 DeepCwind model tests. For metocean conditions, 1-year hindcast wind, wave and current data with 3-hour intervals from WAVEWATCH III® hindcast data and HYCOM (Hybrid Coordinate Ocean Model) are used. Based on simulation results, aero-hydro-servo-elastic fully coupled responses of the 15MW FOWT with two different mooring systems are systematically compared. In addition, high-level mooring system cost comparisons are performed. The platform motions other than the platform offset and yaw are similar in both cases along with the Tower Base loads. Similarly, the probability distributions of power generation are similar for both cases. In terms of mooring cost, a deepwater mooring system can be competitive compared to a shallow water mooring system.