HEXABASE

Model of the HEXABASE © Maritime Offshore Group GmbH
Model of the HEXABASE © Maritime Offshore Group GmbH

Offshore wind energy plants in deep water require-resolved foundation structures such as jackets and tripods. As an alternative to these variants, the  Maritime Offshore Group GmbH (MOG)  from Bremen has developed the so-called "HEXABASE". This foundation structure has a hexagonal plan and is to be realized with identical tube diameters. It is only the wall thickness of the pipes can be varied to accommodate the different sizes of stresses in the various truss planes can. Depending on the market situation there are to be used HFI steel pipe (high frequency induction welding process) or spirally welded pipes.

The HEXABASE can be planned considered "Pre-Piling" or "post-Piling" variant. In the variant with pre-piling out the piles are driven into the seabed and subsequently raised the HEXABASE. A positive connection between the jacket legs and the piles is performed by the connection with a high-strength grout.

The force transmission from tower to HEXABASE via a transition piece (central pipe nodes). At the foot of HEXABSE the expense of the grouted pipe-in-pipe joints (also called Pile-Sleeve-Connection) to the driven piles and eventually discharged into the subsoil.

The SKI Ingenieurges. mbH performed for the HEXABSE numerical structural analysis of individual bonding techniques (central tubular joints, grouted pile-sleeve connection, snake nodes) to obtain a load-optimized geometry for these design details.

Numerical investigations of the buckling behavior of the central tube node
Numerical investigations of the buckling behavior of the central tube node

Essential boundary conditions in these studies were:

  • Water depth of 40 m with respect to LAT
  • Soil profile with medium dense to densely packed sands
  • Wind turbine with 90 m hub height and 6 MW
  • rated power Life of 25 years for the support and foundation structure
Animation of the HEXABASE in a Windpark © Maritime Offshore Group GmbH
Animation of the HEXABASE in a Windpark © Maritime Offshore Group GmbH