Huisman has introduced the Windfarm Installation Vessel as a complete solution to assemble and install offshore wind turbines at sea.
Installing a floating wind turbine at sea brings two main challenges, the relative motions between the floating structures and the load transfer of the wind turbine.
The proposed installation procedure considers a connection between the installation vessel and a semi-submersible floating support structure to reduce the relative motions and facilitate the load transfer.
This research investigates how the connection's structural configuration affects the system's relative motions and loads during five defined installation stages.
The different installation stages cover varying amounts of ballast transfer, as well as the mating phase of the wind turbine.
A two-dimensional multi-body model has been formulated considering a rigid link between the installation vessel and the floating support structure.
The hydrodynamics of the floating structures and the regular wave loads on the structures are calculated using Ansys AQWA.
A system analysis is performed to investigate the effect of adding stiffness in one or combined directions of motion of the connection.
The change in dynamic effects during the installation stages are minimal, the ballast transfer mainly changes the static load on the connection.
Overall, it can be concluded that a combination of stiffness in the different connection directions will provide the most favourable results.
To limit the relative heave motions, coupled surge or pitch and heave stiffness is required.
A different stiffness on both sides of the connection is also shown to improve the system’s behaviour.
Fixing the rotation of the connection on one side improves the relative pitch motions between the wind turbine and the support structure.
More research is required to investigate favourable combinations of limiting motions on each side of the connection.
The presented model could be used for a future optimization study to find optimal stiffness values for the connection.