WCS insights April 2024
The Windcatcher model test
Ørjan Fredriksen, VP Global Design
A physical model of the Windcatcher was recently tested at Stadt Towing Tank in Måløy, Norway. Measuring about 2 meters in all directions at 1:87.5 scale, the model was used to better understand how the concept behaves when exposed to hydrodynamic loads. The physical test campaign has provided valuable input to our technology development, confirming the favourable performance of the Windcatcher in a range of environmental conditions.
Floater behaviour in extreme waves of 11.7 m significant height, corresponding to a 100-year design condition
During the test campaign, we studied a range of wave conditions, both regular wave trains and irregular wave spectra. Several oblique sea states were run to verify performance of the Windcatcher when exposed to weather conditions with misalignment between wind and waves. Although usually less severe, such conditions are of importance with respect to floater stability, mooring system design, airgap, and structural fatigue. With a design life of 50 years, fatigue is a limit state of critical importance in the structural engineering of the floater and turbine supporting structure. Floater motions and accelerations, mooring line forces, and relative surface elevation were recorded at multiple positions to establish a detailed dataset as basis for further engineering works.
Floater behaviour during 1-year sea condition with waves coming at a 30-degree angle
In addition to a range of seakeeping tests, we carried out a set of free decay tests to confirm natural frequencies of the Windcatcher, as well as to verify the hydrodynamic damping coefficients of the floater. Decay tests were performed for heave, roll and pitch motions, both with and without mooring lines connected. Furthermore, we performed a series of calm water towing tests at different speeds and angles. Our main motivation for these tests was to establish accurate drag coefficients of the floater to be applied in coupled simulations that include combined action from wind, waves and currents. However, the towing tests also provided useful insights to be considered in further development of our transport and installation philosophy.
As always, it is reassuring to observe good agreement between simulations and physical tests, and we are very pleased to see that the excellent hydrodynamic performance of the Windcatcher is confirmed through this test campaign.
Towing test at 1.5 m/s speed