Dutch engineering firm KCI has been awarded with a research and development (R&D) subsidy from Dutch Top consortium Knowlegde and Innovation, Wind at Sea (TKI – WoZ) for the further development of its Double Slip Joint (DSJ) concept.
KCI has also teamed up with partners Van Oord Offshore Wind Projects and SIF for the further development of the DSJ.
KCI says that the DSJ is an innovative, installation-time reducing and maintenance free technology to connect monopile and transition piece for offshore wind turbines. It is described as a robust and groutless connection whereby two sets of steel rings with matching conical surfaces are integrated in the standard cylindrical tubes of the monopile and the transition piece (TP).
The TP is installed by lifting it inside the monopile. Contact is made concentrated at two sets of rings, which have a small taper angle of about 2 degrees and an exact fit. This provides a well-defined self-locking steel on steel connection after installation of the TP. The TP will automatically settle under the gravity loads and operational turbine loads within a short period of time, to reach a final stable locked condition, rigidly connected to the pile, as if welded together, KIC said.
With the DSJ, there are two options for the connection with the monopile: above the water and below the splash zone, with the so-called “inverted” DSJ.
The subsidy is intended for designing, testing and the validation of a medium scale steel prototype by comparing the self settling behaviour to previous smaller plastic prototypes. Effects of larger scale, the use of steel and prototype fabrication method will be tested.