Impact driving-induced stress amplification due to flange waviness in offshore wind turbine monopile foundations

Impact pile driving is the preferred installation method for offshore wind monopile (MP) foundations. Due to the flange waviness, the MP wall stresses below the waviness apexes are larger during impact pile driving than in other areas. In recent designs of ۳XL TP-Less monopiles, the door hole is relocated from the tower to the MP, positioned close to the flange, and the boat landing platform is eliminated. This required the door opening stiffeners and other MP internal attachments to be welded close to the flange. It is generally recommended to avoid positioning the MP wall openings and attachments in the highly stressed areas created by the flange waviness. This study aims to calculate the waviness effects on the MP wall stresses of a ۳XL MP and to determine the distance from the flange at which this waviness effect disappears. Pile driving is simulated using the finite element software LS-DYNA, and flange waviness is modelled. It was found that for the studied ۳XL MP weighing ۲۱۶۰ tons, at ۶۰ mm below the flange, the MP wall Von Mises stress is ۲۵۳ MPa at the waviness apex and ۱۴۰ MPa at the waviness valley, representing an ۸۰% increase. The flange waviness effect on the MP wall stresses gradually decreases as one moves away from the flange and diminishes ۲۶۰۰ mm below the flange.

کلیدواژه ها:

۳XL MP ، TP-Less Design ، Impact Driving ، Flatness Tolerance ، Flange Waviness ، fatigue ، LS-DYNA