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Research Papers: Offshore Geotechnics

Effect of Pile–Soil Interaction on Structural Dynamics of Large Moment Magnitude-Scale Offshore Wind Turbines in Shallow-Water Western Gulf of Mexico

[+] Author and Article Information
Ling Ling Yin, King Him Lo

Department of Mechanical Engineering,
National Wind Energy Center,
Cullen College of Engineering,
University of Houston,
Houston, TX 77023

Su Su Wang

Department of Mechanical Engineering,
National Wind Energy Center,
Cullen College of Engineering,
University of Houston,
Houston, TX 77023
e-mail: sswang@uh.edu

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 March 3, 2015; final manuscript received August 3, 2015; published online September 14, 2015. Assoc. Editor: Yi-Hsiang Yu.

J. Offshore Mech. Arct. Eng 137(6), 062001 (Sep 14, 2015) (11 pages) Paper No: OMAE-15-1023; doi: 10.1115/1.4031328 History: Received March 03, 2015; Revised August 03, 2015

The effect of pile–soil interaction on structural dynamics is investigated for a large offshore wind turbine (OWT) in the hurricane-prone Western Gulf of Mexico (GOM) shallow water. The OWT has a rotor with three 100-meter blades and a monotower structure. Loads on the turbine rotor and the support structure subject to a 100-year return hurricane are determined. Several types of soil are considered and modeled with a distributed spring system. The results reveal that pile–soil interaction affects dynamics of the turbine support structure significantly, but not the rotor dynamics. Designed with proper pile lengths, natural frequencies of the turbine structure in different soils stay outside dominant frequencies of wave energy spectra in both normal operating and hurricane sea states, but stay between blade passing frequency intervals. Hence, potential resonance of the turbine support structure is not of concern. A comprehensive Campbell diagram is constructed for safe operation of the offshore turbine in different soils.

Copyright © 2015 by ASME
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References

Figures

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Fig. 2

Location of Buoy Station 42035 [14]

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Fig. 3

RNA of the 13.2 MW wind turbine

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Fig. 4

Geometry of turbine tower (not to scale)

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Fig. 5

Geometry of monopile substructure (not to scale)

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Fig. 6

Force and moment on a pile element

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Fig. 7

p−y  curves of clay and sand (at 5-m depth below mudline)

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Fig. 8

Schematic of pile deflection below the mudline and penetration depth

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Fig. 9

Relationship among  a, b, and y(m) of a monopile

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Fig. 10

Procedure for determination of Es

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Fig. 11

Monotower support structure model

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Fig. 12

Pile deflection and slope at mudline during wind turbine normal operation (a) deflection and (b) slope of pile deflection

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Fig. 13

First-mode shapes of turbine support structure in 100-year return hurricane

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Fig. 14

First natural frequencies of turbine support structure in different foundations (normal turbine operation)

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Fig. 15

First mode shapes of turbine support structure in different foundations (normal rated turbine operation)

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Fig. 16

Stiffness of dense sand along the pile

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Fig. 17

Effects of sea states (Tables 2 and 3) on turbine support structure natural frequencies in different soils (blade passing frequency intervals shown for comparison)

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Fig. 18

Effect of pile–soil interaction on rotor performance: (a) effect of soil foundation on rotor power generation and (b) tower structure rotation at hub height

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Fig. 19

Modified Campbell diagram for 13.2 MW OWT (dotted lines for turbine with rigid foundation, and solid lines for turbine with tower in loose sand) * Ω13.2=R5R13.2Ω5=63102.56.972=4.29

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Fig. 20

Stiffnesses of five soils along the pile in the 100-year return hurricane

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Fig. 21

p−y  curve of dense sand (at 5-m below mudline)

Tables

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