Analytical formulations to assess the energy dissipated at the base of an offshore wind turbine jacket impacted by a ship

This paper presents some new analytical developments carried out to assess the energy dissipated plastically at the base of an offshore wind turbine jacket impacted by a ship. The jacket components involved in this mechanism are both the impacted leg and the rear leg, considered as clamped at the foundation level, as well as the horizontal bottom brace considered as rigidly fixed on the legs. The foundation system is assumed to be piles inserted into sleeves with cement grout. The base of the jacket is divided into four zones and a kinematically admissible displacement field is assumed for each of them. Based on plastic limit analysis, new analytical formulations are derived to assess the resistance and the dissipated energy for each considered area and therefore of the whole jacket base. To validate the method, full scale ship-jacket collisions are simulated both analytically and numerically and plastic energy dissipated at the base of the jacket is compared successfully with nonlinear finite element simulation results.