Comparing traditional and suction piles in steel design of wind turbine structures

Abstract

For proper structural analysis and steel design of suction piles in offshore wind turbine support structures, a Q-z spring with the rigid link effect was developed to support both axial forces and bending moments at the bottom of suction piles. Moreover, the t-z spring with the axial shear and torsion was considered to avoid the suction pile oscillation in the axial rotation direction. The optimal ultimate design shows that the structure with suction piles requires nearly 1.4 times the steel of that with traditional piles. However, after deducting the pile foundation, the weight of the remaining components is similar. For both types of foundations, design situation 6 (parked with high wind and wave loads) dominates for nearly 50 % of the steel structure design. For suction pile cases, design situation 8 (construction for piles) controls all the steel design for the suction pile due to the buckling of the thin shell cylinder under the large hoop water pressure. Another critical issue is fatigue at connections. To overcome this problem, one can select an appropriate yaw stiffness to ensure the first torsional natural frequency greater than the rotor frequency at the rated power (F_1P) and less than three times of F_1P (F_3P).