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Research Papers: Ocean Renewable Energy

Model Test and Numerical Analysis of a Multi-Pile Offshore Wind Turbine Under Seismic, Wind, Wave, and Current Loads

[+] Author and Article Information
Wenhua Wang, Xin Li

State Key Laboratory of Costal
and Offshore Engineering;
Institute of Earthquake Engineering,
Faculty of Infrastructure Engineering,
Dalian University of Technology,
Dalian 116024, China

Zhen Gao, Torgeir Moan

Centre for Autonomous Marine
Operations and Systems,
Department of Marine Technology,
Norwegian University of
Science and Technology,
Trondheim 7491, Norway

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received April 5, 2016; final manuscript received November 15, 2016; published online February 17, 2017. Assoc. Editor: Kazuhiro Iijima.

J. Offshore Mech. Arct. Eng 139(3), 031901 (Feb 17, 2017) (17 pages) Paper No: OMAE-16-1034; doi: 10.1115/1.4035305 History: Received April 05, 2016; Revised November 15, 2016

Offshore wind turbines (OWTs) might be subjected to seismic loads with different peak accelerations during operation in the actively seismic regions. The earthquakes might be a potential risk for the OWTs due to its stochastic nature. Earthquake with wind and wave loads could act on OWT at the same time; thus, the structural responses of such OWTs should be analyzed taking into consideration the reasonable load combinations. Based on the hydro-elastic similarity, an integrated model of the combined National Renewable Energy Laboratory (NREL) 5 MW wind turbine and a practical pentapod substructure is designed for testing. The governing equations of motion of the integrated OWT are established. The dynamic tests and numerical analysis of the OWT model are performed under different combinations of seismic, wind, and sea load conditions. The El Centro and American Petroleum Institute (API)-based synthesized seismic waves with different peak ground accelerations (PGAs) are considered in this study. The numerical results are in good agreement with the experimental ones. The coupling effect of the OWT structure under the combined load conditions is demonstrated from the experimental and numerical results. The results indicate that the interaction of earthquake, wind, wave, and current should be taken into account in order to obtain proper structural response, especially with small PGA.

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Figures

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Fig. 1

Test sensors arrangement: (a) model tower sensor layout, (b) substructure sensor layout, and (c) zoom and bird-view of the tower base section

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Fig. 2

Earthquake, aerodynamic and hydrodynamic load conditions simulation system: (a) test turbine in the lab and (b)side view of the system

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Fig. 3

Substructure coordinate system

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Fig. 4

Finite element model (FEM) of the OWT model: (a) whole structure and (b) pentapod substructure

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Fig. 5

Measured mode shapes of the model tower: (a) first and (b) second

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Fig. 6

Seismic excitations simulation: (a) API seismic acceleration, (b) power spectral density (PSD) function-API, (c) El Centro seismic acceleration, and (d) PSD function–El Centro

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Fig. 7

Accelerations at the tower top under earthquakes: (a) acceleration history-API-0.1 g, (b) acceleration history-API-0.2 g, (c) PSD of acceleration-API-0.1 g, (d) PSD of acceleration-API-0.2 g, (e) acceleration history-El Centro-0.1 g, (f) acceleration history-El Centro-0.2 g, (g) PSD of acceleration-El Centro-0.1 g, and (h) PSD of acceleration-El Centro-0.2 g

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Fig. 8

Axial stress at the tower base under earthquakes: (a) stress history-API-0.1 g, (b) stress history-API-0.2 g, (c) stress history-El Centro-0.1 g, and (d) stress history-El Centro-0.2 g

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Fig. 9

Measured environmental load parameters: (a) wind force, (b) regular wave time series, and (c) current velocity

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Fig. 10

Acceleration histories at the tower top under wind or sea loads: (a) wind load and (b) sea load

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Fig. 11

Axial stress histories at the tower base under wind or sea loads: (a) wind load and (b) sea load

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Fig. 12

Acceleration histories at the tower top under combined seismic and wind loads: (a) API-0.1 g + wind, (b) API-0.2 g + wind, (c) El Centro-0.1 g + wind, and (d) El Centro-0.2 g + wind

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Fig. 13

Axial stress histories at the tower base under combined seismic and wind loads: (a) API-0.1 g + wind, (b) API-0.2 g + wind, (c) El Centro-0.1 g + wind, and (d) El Centro-0.2 g + wind

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Fig. 14

Statistics comparison under combined seismic and wind load conditions: (a) maximum values under cases 7, 8, 9, and 10, (b) minimum values under cases 7, 8, 9, and 10, and (c) standard deviation under cases 7, 8, 9, and 10

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Fig. 15

Acceleration histories at the tower top: (a) API-0.1 g + sea load, (b) API-0.2 g + sea load, (c) El Centro-0.1 g + sea load, and (d) El Centro-0.2 g + sea load

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Fig. 16

Axial stress histories at the tower base: (a) API-0.1 g + sea load, (b) API-0.2 g + sea load, (c) El Centro-0.1 g + sea load, and (d) El Centro-0.2 g + sea load

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Fig. 17

Statistics comparison under combined seismic and sea load conditions: (a) maximum values under cases 11, 12, 13, and 14, (b) minimum values under cases 11, 12, 13, and 14, and (c) standard deviation under cases 11, 12, 13, and 14

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Fig. 18

Accelerations at the tower top: (a) acceleration history-API-0.1 g + wind + sea, (b) acceleration history-API-0.2 g + wind + sea, (c) PSD of acceleration-API-0.1 g + wind + sea, (d) PSD of acceleration-API-0.2 g + wind + sea, (e) acceleration history-El Centro-0.1 g + wind + sea, (f) acceleration history-El Centro-0.2 g + wind + sea, (g) PSD of acceleration-El Centro-0.1 g + wind + sea, and (h) PSD of acceleration-El Centro-0.2 g + wind + sea

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Fig. 19

Axial stress histories at the tower base: (a) stress-API-0.1 g + wind + sea, (b) stress-API-0.2 g + wind + sea, (c) stress-El Centro-0.1 g + wind + sea, and (d) stress-El Centro-0.2 g + wind + sea

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Fig. 20

Statistics comparison under combined seismic, wind, and sea load conditions: (a) maximum values under cases 15, 16, 17, and 18, (b) minimum values under cases 15, 16, 17, and 18, and (c) standard deviation under cases 15, 16, 17, and 18

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