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research-article

Soil-Structure Interaction Effects in Offshore Wind Support Structures Under Seismic Loading1

[+] Author and Article Information
Fani M. Gelagoti

Pampouki 3, N. Psychiko Athens, 15451 Greece fanigelagoti@gmail.com

Rallis S. Kourkoulis

Pampouki 3, N. Psychiko Athens, Atiica 15451 Greece rallisko@yahoo.com

Irene A. Georgiou

9, Iroon Polytechniou str, Zografou Zografou Campus Athens, Attica 15780 Greece irelimni@outlook.com

Spyros A. Karamanos

Department of Mechanical Engineering University of Thessaly Volos, 38334 Greece skara@mie.uth.gr

1Corresponding author.

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the Journal of Offshore Mechanics and Arctic Engineering. Manuscript received July 9, 2018; final manuscript received April 8, 2019; published online xx xx, xxxx. Assoc. Editor: Sungmoon Jung.

1Presented in an early form at the 36th International Conference on Ocean Offshore and Arctic Engineering, Trondheim, Norway, June 2017, and in the companion conference paper OMAE2017-61525.

ASME doi:10.1115/1.4043505 History: Received July 09, 2018; Accepted April 10, 2019

Abstract

The paper explores the performance of a 10MW offshore wind-turbine supported either on a large diameter monopile or a 4-legged jacket emphasizing on the non-linear response of its below-seabed foundation. The seabed foundation alternatives, a monopile and a multi-pod foundation, are compared under monotonic, cyclic and seismic loading.

For all non-seismic scenarios considered, the monopile is more flexible than the jacket and transmits higher rotations at the OWT base. The differences between the two alternatives are amplified in the case of non-symmetric cyclic loading; the monopile not only deforms more than the jacket but tends to accumulate irrecoverable rotation with increasing loading cycles.

The seismic performance of the alternative support structures is assessed for a comprehensive set of earthquake motions. It is concluded that both systems are seismically robust especially when subjected to pure earthquake loading, neglecting the simultaneous action of wind and waves. Alarming issues for OWT performance may arise when a non-zero steady wind force is superimposed to the kinematically-induced stressing of the seabed foundation due to the seismic wave action. Jacket legs settle unevenly, while monopiles are building-up rotations at increasing rates. Assuming a design-level earthquake and a wind thrust of the order 60% of the NC wind loading amplitude, this seismically-induced residual rotation for the monopile, may often exceed the deformation tolerance criterion. For the same loading combination the corresponding rotation of the Jacket installation remains safely within the prescribed limits.

Copyright © 2019 by ASME
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