Research Papers: Ocean Renewable Energy

An Automated Approach for Optimizing Monopile Foundations for Offshore Wind Turbines for Serviceability and Ultimate Limit States Design

[+] Author and Article Information
James P. Doherty

School of Civil, Environmental and
Mining Engineering,
The University of Western Australia,
Crawley 6009, Western Australia, Australia
e-mail: james.doherty@uwa.edu.au

Barry M. Lehane

School of Civil, Environmental and Mining
The University of Western Australia,
Crawley 6009, Western Australia, Australia
e-mail: barry.lehane@uwa.edu.au

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 23, 2017; final manuscript received February 19, 2018; published online April 24, 2018. Assoc. Editor: Qing Xiao.

J. Offshore Mech. Arct. Eng 140(5), 051901 (Apr 24, 2018) (7 pages) Paper No: OMAE-17-1125; doi: 10.1115/1.4039523 History: Received July 23, 2017; Revised February 19, 2018

Pile foundation design is conventionally conducted using a process of trial and error, where the dimensions of a pile are estimated and the performance is computed and compared with design criteria. The dimensions are varied and the process is repeated in order to converge to a safe and economical design. In this paper, this time-consuming and labor intensive process is replaced with an automated approach using the example case of an offshore monopile supporting a wind turbine. The optimum length and diameter of the monopile are determined with the aim of minimizing the pile weight while satisfying both serviceability and ultimate limit state criteria. The approach handles general soil and loading conditions and includes an ability to incorporate cyclic loading.

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Fig. 1

Schematic representation of the problem

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Fig. 2

Traditional design process for monopile foundation

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Fig. 3

Proposed design approach

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Fig. 4

Beam spring finite element model

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Fig. 5

Pile rotation at seabed for a range of D and L values with contour satisfying the SLS criterion for D/t = 80

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Fig. 6

Pile displacements at seabed for a range of D and L values with contour satisfying the SLS criterion for D/t = 80

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Fig. 7

Ultimate capacity for a range of D and L values applying material factors to soil and pile material with contour line for factored design load (pile D/t = 80)

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Fig. 8

Pile volume for each D and L combination with contour lines corresponding to the two SLS constraints and the ULS constraint for D/t = 80

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Fig. 9

Pile volume to satisfy ULS and SLS as a function of D/t

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Fig. 10

Performance of fmincon with initial estimate of D = 5.5 m and L = 25 m

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Fig. 11

Pile response with optimized dimensions of L = 21.672 m and D = 4.910 m for D/t = 80: (a) pile load versus head rotation and (b) pile load versus displacement

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Fig. 12

Function relating Tb to load parameter ζb

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Fig. 13

Variation in optimized pile dimensions with load cycle




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