Effect of tower elasticity on the performance and fatigue character of monopile support tower for tidal current turbine

The design of support structures requires precise knowledge about the effect of support tower on turbine performance, loads and its fatigue character. Therefore, a tidal current turbine mounted on an elastic tubular monopile support tower is simulated in coupled Fluid Structure Interaction (FSI) simulations using ANSYS Workbench. The performance and behavior of turbine loads for an elastic tower is compared with rigid tower for similar case. The tower elasticity has significantly increased the variation in power coefficient from 2.61% to 3.5% and thrust coefficient from 1.4% to 2.2% compared to a similar turbine mounted on a rigid tower. Although, the tower elasticity has minimal impact on the overall power output but greatly affect the quality of power output due to increased variation in power coefficient. Direct thrust force on the tower varies by about 120% and 104% while the total thrust force varies by 4.8% and 3.8% from mean cycle value for the elastic and rigid tower case respectively. Stress life fatigue analysis of steel tubular monopile support tower show that the support tower has a minimum fatigue factor of safety of 1.32 and fatigue life of 37.8 years for a design life of 20 years. This suggest that steel tubular structures according to the available manufacturer guide lines, would sustain the fatigue load cycles and may be adequate for use as a support tower to a tidal current turbine.