Leg-Seabed Interactions of Jack-Up Vessels due to Motions in Irregular Waves

This paper analyzes the leg-seabed interaction due to motions of a 3rd generation jack-up vessel in irregular waves. The proposed model considers hydrodynamic forces on the hull as well as on the legs. The sea floor reaction forces are analyzed with a Coupled Eulerian-Lagrangian (CEL) method. The results are used to develop a mechanical rheological model for the sea floor. With computational efficiency in mind a state-space representation in time domain is derived. The excitation of the system is caused by irregular waves, which are described by the JONSWAP spectrum. The proposed method allows the efficient computation of short term (2–15 min) scenarios and events through sampling of realizations. It is used to compute the impact forces on the legs from the seabed induced by irregular vessel motions. The presented framework is suitable for the planning of jack-up operations in the offshore wind industry. It can also be applied for the design of dynamic positioning and jacking systems.