NEZZY Tank test 1:36 scaled model

System validation for hydrodynamics and global platform motions is carried out at University of Cork, Ireland in a wave basin. 15 days of different tests cover all necessary tests for the hydrodynamic validation. Decay tests showed the eigenperiods of the system, whereas regular wave tests and irregular wave tests are used to derive Response Amplitude Operators (RAO). Survival environment is tested for 50 year conditions where the mooring system and nezzy showed an outstanding stability performance at low mooring loads. As usable for different sea areas, sea-states in JONSWAP, Pierson-Moskowitz and Bretschneider are tested. The results are used to optimize nezzy for a worldwide operation at a low LCoE.

Wind and wave misalignment tests validated the key feature of nezzy as passive wind alignment. nezzy behaves better than expected and the waves have just a minor influence on the platform orientation. This feature allows for a load alleviated and energy output optimized power production point, which is a significant LCoE driving element.

Aluminum was chosen as foundation material to consider a material density close to concrete. This enables a strict Froude-scaling method for all other dimensions in a scale of 1:36 meeting the wave basin capabilities. The model meets the design requirements of the scaling law exactly receiving easy to scale results. A flexible mooring system with springs is used to represent the catenary mooring system in small scale. Based on this the results can be used to validate models in other scales as larger turbines with increased power rating.

Additionally cross section tests are performed to investigate in low drag and high motion damping profiles. Rectangular, lens shaped, hexagonal and stadium shaped profiles are tested for lift and drag. Combined with the used amount of material as area moment of inertia the stadium shape profile shows the best performance regarding weight, drag and manufacturing.