Offshore Wind Turbine Installation Using a Double Slip Joint

Abstract

One of the challenges associated with offshore wind turbine installations is the mating phase. Aligning a transition piece onto its substructure under offshore conditions is a complicated and time-consuming procedure. Another issue found in a number of commissioned offshore wind turbines is related to the sustainability of the connection between the transition piece and the substructure. With wind turbines increasing in size and wind farms being built further from shore in deeper waters, the current bolted- and grouted connections are seemingly not the most suitable future proof options. This is where the Double Slip Joint steps in. A simple plug- and go connection device provided by KCI The Engineers. The Double Slip Joint’s innovative solution takes away the time-consuming phases like manually fastening a number of bolts or the buffer period of waiting for grout material to fully solidify before commissioning a wind turbine. This study aims to gain more useful insights on the installation behavior of the Double Slip Joint during the mating phase under various offshore environmental conditions. The chosen system for this study consists of a hoisted wind turbine tower which is lowered onto a monopile. A numerical model for this tower-monopile system is developed in Excel where the user is able to manipulate input parameters such as mean wind velocity, tower lowering velocity, crane motions etc. After a series of validation using Ansys Finite Element models, simulations from the developed Excel model were carried out to study the Double Slip Joint’s behavior during the mating phase from both a jack-up - and a floating vessel. A key finding from this study is the necessity to round off the sharp edges of the Double Slip Joints conical rings in order to avoid contact stresses that might lead to unwanted damage. The simulation results indicate that installations carried out from a jack-up vessel can be optimised to perfectly tolerate a mean wind velocity of 15 m/s, whereas that of a floating vessel can be optimised up to 13 m/s. The possibility of achieving higher mean wind velocities indicate that the weather window for offshore installations can have a greater range. The results obtained from this study confirm the potential of the Double Slip Joint for future offshore wind turbine installations.