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Influence of joint flexibility on local dynamics of a jacket support structure

: Popko, Wojciech; Georgiadou, Sofia; Loukogeorgaki, Eva; Vorpahl, Fabian

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Journal of Ocean and Wind Energy : JOWE 3 (2016), No.1, pp.1-9
ISSN: 2310-3604
Bundesministerium für Wirtschaft und Technologie BMWi
0325575C; GIGAWIND life
Lebensdauer-Forschung an den OWEA-Tragstrukturen im Offshore-Testfeld alpha ventus
Journal Article, Electronic Publication
Fraunhofer IWES ()

The effect of different modeling techniques of the local joint flexibility on the local dynamics of a jacket support structure for an offshore wind turbine is investigated. Two numerical models of a jacket supporting a generic turbine are analyzed in the aero-hydro-servo-elastic tool ADCoS-Offshore. The first model is set up with Euler-Bernoulli beam elements, while the second model utilizes superelements for the joints’ representation and Euler-Bernoulli beams for the remaining parts of the structure. Time-domain simulations are run for deterministic and stochastic load cases, and local jacket dynamics are investigated. The local response of the braces is compared with the global response at the jacket legs in terms of power spectral densities (PSDs). Damage equivalent loads (DELs) are calculated at several positions along the jacket to capture the impact of local and global dynamics on those loads. It is observed that the superelement model leads in general to higher fatigue loads than the beam model. A methodology to remove the global motion component from the displacement time history of the brace central joint is discussed. Larger displacements of the brace central joints are observed for the superelement model than for the beam model. It is recommended to use superelement modeling technique for a more accurate representation of joints in the jacket support structures.