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Open AccessArticle

Tripod-Supported Offshore Wind Turbines: Modal and Coupled Analysis and a Parametric Study Using X-SEA and FAST

1
Department of Civil and Environmental Engineering, Konkuk University, 120 Neungdong-ro, Seoul 05029, Korea
2
MaREI Centre for Marine and Renewable Energy, ERI, University College Cork, P43C573 Cork, Ireland
*
Author to whom correspondence should be addressed.
J. Mar. Sci. Eng. 2019, 7(6), 181; https://doi.org/10.3390/jmse7060181
Received: 16 May 2019 / Revised: 29 May 2019 / Accepted: 31 May 2019 / Published: 9 June 2019
(This article belongs to the Special Issue Marine Structures)
This paper presents theoretical aspects and an extensive numerical study of the coupled analysis of tripod support structures for offshore wind turbines (OWTs) by using X-SEA and FAST v8 programs. In a number of site conditions such as extreme and longer period waves, fast installation, and lighter foundations, tripod structures are more advantageous than monopile and jacket structures. In the implemented dynamic coupled analysis, the sub-structural module in FAST was replaced by the X-SEA offshore substructure analysis component. The time-histories of the reaction forces and the turbine loads were then calculated. The results obtained from X-SEA and from FAST were in good agreement. The pile-soil-structure interaction (PSSI) was included for reliable evaluation of OWT structural systems. The superelement concept was introduced to reduce the computational time. Modal, coupled and uncoupled analyses of the NREL 5MW OWT-tripod support structure including PSSI were carried out and the discussions on the natural frequencies, mode shapes and resulted displacements are presented. Compared to the uncoupled models, the physical interaction between the tower and the support structure in the coupled models resulted in smaller responses. Compared to the fixed support structures, i.e., when PSSI is not included, the piled-support structure has lower natural frequencies and larger responses attributed to its actual flexibility. The models using pile superelements are computationally efficient and give results that are identical to the common finite element models. View Full-Text
Keywords: offshore wind turbine; tripod support structures; coupled analysis; uncoupled analysis; soil-pile-structure interaction; superelement offshore wind turbine; tripod support structures; coupled analysis; uncoupled analysis; soil-pile-structure interaction; superelement
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Plodpradit, P.; Dinh, V.N.; Kim, K.-D. Tripod-Supported Offshore Wind Turbines: Modal and Coupled Analysis and a Parametric Study Using X-SEA and FAST. J. Mar. Sci. Eng. 2019, 7, 181.

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