Abstract
Output-only methods are widely used to characterize the dynamic behavior of very diverse structures. However, their application to floating structures may be limited due to their strong nonlinear behavior. Therefore, since there is very little experience on the application of these experimental tools to these very peculiar structures, it is very important to develop studies, either based on numerical simulations or on real experimental data, to better understand their potential and limitations. In an initial phase, the use of numerical simulations permits a better control of all the involved variables. In this work, the Covariance-driven Stochastic Subspace Identification (SSI-COV) algorithm is applied to numerically simulated data of two different solutions to Floating Offshore Wind Turbines (FOWT) and for its capability of tracking the rigid body motion modal properties and susceptibility to different modeling restrictions and environmental conditions tested. The feasibility of applying the methods in an automated fashion in the processing of a large number of datasets is also evaluated. While the structure natural frequencies were consistently obtained from all the simulations, some difficulties were observed in the estimation of the mode shape components in the most changeling scenarios. The estimated modal damping coefficients were in good agreement with the expected results. From all the results, it can be concluded that output-only methods are capable of characterizing the dynamic behavior of a floating structure, even in the context of continuous dynamic monitoring using automated tracking of the modal properties, and should now be tested under uncontrolled environmental loads.
Highlights
Among engineering structures, floating platforms are a very important category
Different floating concepts have reached different stages of development, namely the Technology Readiness Level (TRL), experimental investigations are of foremost importance to better understand their complex dynamic behavior, validate numerical models, demonstrate the technical/industrial feasibility of new concepts, and optimize the design in order to improve cost-effectiveness (i.e., reduce the levelized cost of energy (LCOE) which is currently the main drawback of this emergent industry)
The SSI-COV method will be used to characterize the dynamic behavior of the structure
Summary
Among engineering structures, floating platforms are a very important category. Historically, moored floating structures have been widely used in coastal areas (e.g., for harbor jetties, floating breakwaters, etc.) and open-sea (mainly for oil and gas platforms at water depths >500 m). Carried out a 1:30 at-sea experiment of the UMaine-Hywind spar FOWT concept [21] and successfully identified the heave/roll/pitch hydrodynamic properties of the structure over a wide range of different environmental conditions. By doing so, they proved the feasibility of at-sea experiments on floating structures, but they highlighted the need for developing opportune output-only identification techniques to support the interpretation of the experimental data in an uncontrolled environment.
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