Session: 09-01-05 Wind Energy: Aero-hydrodynamics 5

Paper Number: 126755

126755 - The Effect of Directional Spreading on Extreme Sea State Response for Floating Wind Turbines 

Empirical investigations have consistently demonstrated the multi-directional nature of actual ocean waves, a phenomenon that has received relatively limited attention in the research field of floating wind turbines. The present study seeks to reduce this knowledge gap by experimentally investigating the response of a novel 15 MW floating wind turbine design when subjected to multi-directional wave conditions.

The experimental work was carried out in the deep water basin at the Danish Hydraulic Institute (DHI), at a scale of 1:40. In this investigation, the wind turbine rotor is simplistically modeled as a point mass, allowing for a focused examination of the hydrodynamic performance of the floater and mooring system.

The investigation of the concept's behavior involved wave-only tests for irregular multi-directional waves with varying spreading angles and across several sea states. The effect of swell waves is also examined through standalone tests as well as the combined motion response when they are superposed with directionally spread wind wave spectra.  These assessments of the more complex wave conditions are undertaken to gain a deeper understanding of the dynamic response of both the floating platform and the mooring system within more realistic wind-wave environments.

While the effects of directional spreading and swell are well understood for small amplitude waves, the nonlinear interactions and load effects are less explored in the literature. The study therefore also covers severe wave conditions, both in terms of long sea state realizations and three-dimensional focusing waves. For all tests, the low-frequency response that is outside of the linear wave spectrum has special interest, since the natural frequencies of the floating structure are placed here. The outcome of the experiments will be presented through a comparison of time series, power spectra, and exceedance probability plots. Thereby, the study yields valuable insights into the operational conditions and design effects of floating turbines in harsh conditions.

Presenting Author: Sithik Aliyar Technical University of Denmark

Presenting Author Biography: Postdoctoral researcher at DTU Wind Energy and Systems Departments specialized in hydrodynamics, slamming waves, and fluid-structure interaction.

Authors:

Aref Moalemi Technical University of Denmark
Mathilde H. Wagner Technical University of Denmark
Sithik Aliyar Technical University of Denmark
Amin Ghadirian Stiesdal Offshore A/S
Bjarne Jensen DHI A/S
Henrik Bredmose Technical University of Denmark