Rising global CO2 levels have created a growing need for renewable energy resources. Offshore wind energy is a promising solution, with monopile (MP) foundations preferred for their relatively low cost, provided the site conditions are suitable. Recently, wind turbines have significantly increased in size for greater cost efficiency, leading to the development of 3XL MPs with diameters of 12 meters or more. Depending on the site and marine contractor preferences, a jack-up vessel may be used to install a 3XL MP. Marine contractors typically employ dynamic models to determine suitable weather windows for each installation phase. Lowering the 3XL MP through the splash zone and gripper to just above the seabed is a critical phase. To optimize the dynamic models for this phase, understanding the 3XL MP’s behavior during splash zone lowering is essential. This thesis therefore investigates the dynamic behavior of a 3XL MP during lowering phase through the splash zone until just above the seabed using a jack-up vessel.
A 1-DOF model, considering only the rotational DOF of the MP, is established to examine this behavior. Results from this model show that the most probable maximum (MPM) of the MP rotational motion response, evaluated with a dynamic lowering simulation for irregular spread waves, is 75% lower compared to the conventional steady-state simulations at critical MP drafts. Additionally, the dynamic behavior of the MP is highest for increasing peak periods, as these coincide with the natural periods of the 1-DOF model at larger MP drafts where wave-excitation loads are greatest. Several physical phenomena which are not included in the model are examined to assess their impact. Ambient currents traveling in the same direction as irregular unidirectional waves during a dynamic lowering simulation, reduce the MP motion response by 25%. Vortex shedding frequencies do not coincide with natural periods and are thus neglected. The same goes for the 2nd order difference frequency wave drift forces. Both the dynamic amplification and the mean motion displacement due to these second order wave forces are negligibly small. Lastly, the influence of jack-up motion is negligibly small during peak periods of 8 and 9 seconds but reduces the MP rotational motion during a peak period of 7 seconds.