Numerical Analysis of Collision Damage between Supply Vessels and Offshore Monopile Foundation

Offshore wind turbines come with risk of collision with ocean-going supply vessels. The high slenderness of the turbine foundations facilitates significant deformation even at low impact speeds. The monopile is the most basic form of foundations, typically comprising a tapered cylindrical profile. This study aims to investigate the consequences of varying collision speed and vessel displacement on the stress and deformation of the monopile. The von Mises stress and deformations in the vicinity of the collision zone were extracted in Abaqus and presented in the form of contour plots at collision speeds of 1 knot, 3 knots and 5 knots. The highest magnitude of displacement for a particular collision speed appeared near the collision zone, as expected. The magnitudes of deformations and stresses increased with increasing speed. The values also varied with different collision orientations such as head-on and sideways collisions. The study concludes that impact speeds as low as 1 knot can cause significant damage to the monopile structure in terms of stresses and displacements induced. Therefore, in an event of unavoidable collision, it is advisable to avoid head-on collisions as these produce the highest stresses and displacements.