Abstract
System identification of offshore floating platforms is usually performed by testing small-scale models in wave tanks, where controlled conditions, such as still water for free decay tests, regular and irregular wave loading can be represented. However, this approach may result in constraints on model dimensions, testing time, and costs of the experimental activity. For such reasons, intermediate-scale field modelling of offshore floating structures may become an interesting as well as cost-effective alternative in a near future. Clearly, since the open sea is not a controlled environment, traditional system identification may become challenging and less precise. In this paper, a new approach based on Frequency Domain Decomposition (FDD) method for Operational Modal Analysis is proposed and validated against numerical simulations in ANSYS AQWA v.16.0 on a simple spar-type structure. The results obtained match well with numerical predictions, showing that this new approach, opportunely coupled with more traditional wave tanks techniques, proves to be very promising to perform field-site identification of the model structures.
Highlights
Floating wind turbine concepts have been actively investigated in the last decades
Within the research activities currently carried out by the authors on a 1:30 scale model of the OC3-Hywind prototype at the NOEL laboratory [15], this paper aims to assess the feasibility of a Frequency Domain Decomposition (FDD) approach to identify an ANSYS-AQWA [23] numerical implementation of a spar structure, under irregular waves generated by JONSWAP spectrum
The present work proposes a methodology for the dynamic identification of the rigid body motions of a spar floating support for offshore wind turbine, using the Frequency Domain Decomposition (FDD) method for Operational Modal Analysis
Summary
Floating wind turbine concepts have been actively investigated in the last decades. Theoretical and experimental studies have recently demonstrated technical feasibility and economic benefits of floating concepts in waters deeper than 50–60 m, where standard fixed supports are not feasible or too expensive [1,2,3,4,5,6]. Among floating concepts under study, the spar, consisting of a slender hollow cylinder, placed in vertical position and ballast-stabilized, seems to be appropriate for deep waters (above 100 m). Insight into the wind-wave response of a spar floating wind turbine has been provided by numerical studies—see e.g., Karimirad and Moan [10]. Experimental tests play a crucial role in the development and assessment of floating wind turbines
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