The project has designed a small size Tension Leg Platform (TLP) to be built as full-scale prototype for demonstration purposes to the MoD as final deliverable of the project. After the initial design was completed, model tests were performed in MARIN’s Offshore Basin to verify the design, obtain valuable calibration data for the numerical simulations and generate input for further numerical deck impact analyses.

Test programme
The 1 : 18.5 scale model was made in our workshop to be an accurate physical representation of the design. All relevant construction parts like columns, pontoons, deck, tendon stiffness and weight distribution were modelled accurately. The mast and 20 feet ISO-boxes were added for viewing purposes and better understanding of the actual dimensions of the platform.

During all tests the 6 degree of freedom motions and accelerations, tendon line tensions and relative water height at 4 locations were measured with our new micro wireless measurement system. The wireless setup prevents any influence of instrumentation cables running from the basin carriage to the model. This becomes more important when testing this relatively small type of floaters like floating wind and USSP.

The model was tested in combined current, wave and wind conditions for the installation site approximately 50 km south of Athens. Different conditions like high current velocity for VIM and fatigue assessment, operational conditions to assess motion behavior and also 100-yr survival conditions to test the integrity of the platform were tested extensively.

The video shows the behaviour of the platform in the testing operational conditions with a significant wave height of 3.0 m at a peak period of 7.0 s.

The test results are used for both verification and approval for the USSP prototype to be built and demonstrated in 2025 and also for verification and tuning of numerical models. With a tuned numerical model it is more easy to screen different conditions and investigate impact of small design modifications on the results.

In survival conditions it is crucial that the platform deck is not reached by a wave crest to ensure structural integrity. Wave crests that can potentially reach the platform deck are typically very non-linear and do not occur often (if at all) in a three-hour 100-year storm condition. Thus, air gap (deck clearance) analysis requires model tests or CFD simulations (Comflow) with a large number of random three-hour realisations of the 100-year survival condition. Basin time only allows for a limited number of three-hour sea-state realisations. To support the model test campaign and provide additional data, CFD simulations are carried out.