Influence of dynamic characteristics of monopile supported offshore wind structures on fatigue loading
In: Marine Structures. Elsevier: Oxford. ISSN 0951-8339; e-ISSN 1873-4170, meer
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| Author keywords |
Fatigue;Monopile foundations;Offshore wind;Time-domain simulations;Dynamic characteristics;Correlation analysis |
| Auteurs | | Top |
- Mroczek, M.M., meer
- Arwade, S.R.
- Lackner, M.A.
- Myers, A.
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| Abstract |
The influence of dynamic characteristics on fatigue loading is examined for monopile founded offshore wind structures supporting the 15 MW IEA reference turbine, considering representative site conditions off the coast of Massachusetts. Extensive time-domain simulations were performed on seven models, each with monopile properties chosen to provide variation in the dynamic characteristics. The simulations permitted derivation of fatigue loads at four levels along the length of the monopile. A single-variable linear regression analysis was carried out to examine the relationship between the models' dynamic characteristics and the resulting fatigue loads. The results showed that the first modal quasi-static displacement of the rotor nacelle assembly (RNA) due to a simplified second-order polynomial wave load, denoted as beta 1, exhibited very strong correlation with fatigue loads, except at mudline level. At mudline level, the influence of high frequency resonance behavior was identified due to the dynamic interaction between the structures' second fore-aft mode and the second harmonic of the blade passing frequency at the turbine's rated wind speed (rated 6P frequency). The influence of this behavior could be characterized by the maximum second modal quasi-static displacement of the structure due to a simplified wind load on the turbine tower, denoted as beta 2, which was found to exhibit a very strong correlation with fatigue loads at mudline level. Overall, this study identified two physically interpretable dynamic characteristics, beta 1 and beta 2, which are highly correlated with monopile fatigue loads under the considered conditions. For conditions with comparable governing dynamic mechanisms, these parameters can support the monopile design process, including early-stage design, the clustering methodology, and position-specific load determination. |
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