Mooring Line Analysis for an Offshore Floating Wind Turbine under Storm Conditions using ProteusDS
Offshore floating wind turbines (OFWTs) have the capability to harvest the offshore wind resources at deep waters. The turbine needs to be connected to the floating platform through a tower and the whole structure should be stable with mooring lines attached at the bottom of the platform.
The aim of this project is to simulate an offshore floating wind turbine under storm conditions in order to analyze the tension loads in each mooring line. For this purpose, a semisubmersible platform with an inner cylinder and three outer cylinders is used as a supporting structure for the wind turbine. This platform is attached to the sea bottom using 2 mooring line arrangements:
- 3 taut mooring lines (each one of 75 meter length)
- 3 slack mooring lines (each one of 85 meter length)
The following conditions were considered for this simulation:
- Selection of an optimized platform design for a 5MW floating wind turbine.
- Design of the platform that includes inner and outer cylinders, truss connections and the tower.
- Obtaining the steady-state condition of the platform to get the water plane.
- Extracting the hydrodynamic coefficients including radiation and diffraction using Shipmo3D.
- Simulation of the floating wind turbine under storm conditions. The wave type used corresponds to Pierson-Moskowitz spectrum with the significant wave height and the energy period of 8.75 meter and 12.5 second, respectively. The wind speed is 25 m/s in the same direction as the waves. The water depth is 75 m.
- Analysis of the maximum tension loads.
The mooring line used for the simulations corresponds to the 6 x 37 wire rope with fiber core. Looking at the results it can be concluded that:
- Increasing the length of the mooring line by 10 m reduces the maximum tension 17% and the average tension 42% approximately.
- The extra load on taut mooring lines can be explained in part due to higher buoyancy forces resulting from large waves.