Session: 09-03-01 Wind Energy: Installation

Submission Number: 157314

Calculating and Testing the Stability of an Air-Cushioned Floating Suction Pile Foundation 

The Tri Suction Pile Caisson (TSPC) is being developed as an innovative alternative to existing wind turbine foundations. It consists of three open bottomed suction piles connected to a central monopile column. By placing it on the sea floor and depressurizing the suction piles, the TSPC is embedded in the sediment, effectively creating a permanent foundation for a large offshore wind turbine. One of the large novelties in the concept is the secondary functionality of the suction piles as floaters of the foundation during wet-tow transport. Due to the air volume in the suction piles, the TSPC foundation has sufficient buoyancy to stay afloat on its own. Hence it can be towed to site in a relatively straightforward manner with offshore tugs, by-passing the need of a dry-tow mode or transport using offshore going transport barges. Moreover, the on-site installation requires a much lower crane capacity than what otherwise would be required. The TSPC combines the benefits of the suction pile (no noise, nor vibrations during installation, rapid and accurate  installation and decommission of the entire structure) with much lower costs than a jacket. The project is an initiative of SPT Offshore bv, Deltares, MARIN, KCI, DEME, Shell, SIF, Orsted, Subcon and Bureau Waardenburg.

In the TSPC research project (2022-2024), MARIN has worked on the hydrostatic and hydrodynamic properties of the concept design, in order to determine the workability offshore and methodology of transportation and installation for the floater which gets as much as 97% of its total buoyancy from the enclosed air pockets. This was firstly done with numerical modelling in MARIN's time-domain simulation software aNySIM/XMF, incorporating models for non-linear hydrostatics and dynamic tanks. Secondly, wave basin model tests with a scale 1:40 model were performed for limited environmental conditions. Finally, the simulation model was calibrated against the basin model tests and a workability assessment was performed to determine the TSPC workability offshore at a North Sea site.

The paper will discuss the key findings of the project, including the results of the wave basin model tests, the aNySIM/XMF time domain simulations and the workability assessment.

Presenting Author: Rob Mulders MARIN

Presenting Author Biography: Rob Mulders has a BsC in Aerospace engineering and an MsC in applied physics, specializing in wind energy at the TU Delft. After working for the Nucleair Reseach Group for a year, Rob switched to a small engineering company on building physiscs, where he did a lot of contract research on (aero)acoustics, (dynamic) wind loading on buildings and wind in the built environment. In this research, he gained a lot of experience in wind tunnel testing. Since 2023 Rob has worked for MARIN, where mainly has been involved in model testing.