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Research Papers: Ocean Renewable Energy

Effect of Axial Acceleration on Drivetrain Responses in a Spar-Type Floating Wind Turbine

[+] Author and Article Information
Amir R. Nejad

Department of Marine Technology,
Norwegian University of Science
and Technology (NTNU),
Trondheim NO-7491, Norway
e-mail: Amir.Nejad@ntnu.no

Erin E. Bachynski

Department of Marine Technology,
Norwegian University of Science
and Technology (NTNU),
Trondheim NO-7491, Norway
e-mail: erin.bachynski@ntnu.no

Torgeir Moan

Department of Marine Technology,
Norwegian University of Science
and Technology (NTNU),
Trondheim NO-7491, Norway
e-mail: Torgeir.Moan@ntnu.no

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 December 2, 2017; final manuscript received August 8, 2018; published online January 17, 2019. Assoc. Editor: Sungmoon Jung.

J. Offshore Mech. Arct. Eng 141(3), 031901 (Jan 17, 2019) (7 pages) Paper No: OMAE-17-1209; doi: 10.1115/1.4041996 History: Received December 02, 2017; Revised August 08, 2018

Common industrial practice for designing floating wind turbines is to set an operational limit for the tower-top axial acceleration, normally in the range of 0.2–0.3 g, which is typically understood to be related to the safety of turbine components. This paper investigates the rationality of the tower-top acceleration limit by evaluating the correlation between acceleration and drivetrain responses. A 5-MW reference drivetrain is selected and modeled on a spar-type floating wind turbine in 320 m water depth. A range of environmental conditions are selected based on the long-term distribution of wind speed, significant wave height, and peak period from hindcast data for the Northern North Sea. For each condition, global analysis using an aero-hydro-servo-elastic tool is carried out for six one-hour realizations. The global analysis results provide useful information on their own—regarding the correlation between environmental condition and tower top acceleration, and the correlation between tower top acceleration and other responses of interest—which are used as input in a decoupled analysis approach. The load effects and motions from the global analysis are applied on a detailed drivetrain model in a multibody system (MBS) analysis tool. The local responses on bearings are then obtained from MBS analysis and postprocessed for the correlation study. Although the maximum acceleration provides a good indication of the wave-induced loads, it is not seen to be a good predictor for significant fatigue damage on the main bearings in this case.

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References

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Figures

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Fig. 1

Five-megawatt reference gearbox layout [8]

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Fig. 2

Five-megawatt reference gearbox topology [8]

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Fig. 3

Multibody system model of 5-MW reference gearbox [8]

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Fig. 4

Screening of environmental conditions. Selected conditions (circles) for drivetrain analysis are indicated.

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Fig. 5

Power spectrum of axial acceleration in different ECs

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Fig. 6

One-hour maximum torque, axial force (Fx), tower fore-aft bending moment (My) at top and base, and load on bearing INP-A, correlated with 1-h maximum nacelle acceleration. Green, red, and blue circles show results for EC3, EC34, and EC84, respectively (in black color print EC3, EC34, and EC84 are the circles from left to right).

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Fig. 7

INP-A force and number of cycles, EC84

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Fig. 8

INP-A and INP-B equivalent steady load (for fatigue life) versus max. axial acceleration

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Fig. 9

Power spectrum of INP-A radial force in different ECs

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Fig. 10

Power spectrum of INP-B axial force in different ECs

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