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Research Papers: Ocean Renewable Energy

Wind-Wave Misalignment Effects on Floating Wind Turbines: Motions and Tower Load Effects

[+] Author and Article Information
Erin E. Bachynski

Centre for Ships and Ocean Structures,
NTNU,
Trondheim NO-7491, Norway
NOWITECH,
Trondheim NO-7491, Norway
Centre for Autonomous Marine
Operations and Systems,
NTNU,
Trondheim NO-7491, Norway
e-mail: erin.bachynski@ntnu.no

Marit I. Kvittem

Centre for Ships and Ocean Structures,
NTNU,
Trondheim NO-7491, Norway
NOWITECH,
Trondheim NO-7491, Norway
Centre for Autonomous Marine
Operations and Systems,
NTNU,
Trondheim NO-7491, Norway
e-mail: marit.irene.kvittem@ntnu.no

Chenyu Luan

Centre for Ships and Ocean Structures,
NTNU,
Trondheim NO-7491, Norway
NOWITECH,
Trondheim NO-7491, Norway
Centre for Autonomous Marine
Operations and Systems,
NTNU,
Trondheim NO-7491, Norway
e-mail: chenyu.luan@ntnu.no

Torgeir Moan

Professor
Centre for Ships and Ocean Structures,
NTNU,
Trondheim NO-7491, Norway
NOWITECH,
Trondheim NO-7491, Norway
Centre for Autonomous Marine
Operations and Systems,
NTNU,
Trondheim NO-7491Norway
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 10, 2013; final manuscript received July 4, 2014; published online August 13, 2014. Assoc. Editor: Ron Riggs.

J. Offshore Mech. Arct. Eng 136(4), 041902 (Aug 13, 2014) (12 pages) Paper No: OMAE-13-1119; doi: 10.1115/1.4028028 History: Received December 10, 2013; Revised July 04, 2014

The dynamic responses of a spar, tension leg platform (TLP), and two semisubmersible floating wind turbines (FWTs) in selected misaligned wind and wave conditions are investigated using numerical simulation with an aero-hydro-servo-elastic computational tool. For a range of representative operational conditions, the platform motions and short-term fatigue damage in the tower base and tower top are examined. Although some misalignment conditions result in increased motions both parallel and perpendicular to the wave direction, aligned wind and waves cause the largest short-term tower base fatigue damage for the studied platforms and conditions. Several factors which lead to larger fatigue damage for certain platforms in particular conditions are identified, such as tower resonance due to the 3p blade passing frequency in low wind speeds; surge and pitch motions, particularly in the wave frequency range; and the variations in first-order hydrodynamic loads due to wave direction. A semisubmersible platform with large displacement suffers the least damage at the base of the tower.

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Figures

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Fig. 1

Floating platform designs: spar, TLP, semisubmersible 1, and semisubmersible 2. Hull mass includes ballast.

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Fig. 2

Top view of wind-wave misalignment conditions. In order to conserve space, only the first few meters of the catenary mooring lines are shown.

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Fig. 3

Coordinate system for sectional loads, tower base as seen from above

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Fig. 4

Platform motion standard deviations as a function of βwave, βwind = 0 deg, all ECs

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Fig. 5

Spar surge spectrum, EC 4. Low-frequency and wave frequency effects are shown with different scales on the vertical axis.

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Fig. 6

Fatigue damage locations for the tower for all wave directions and concepts (top view)

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Fig. 7

Tower base 1 h expected fatigue damage as a function of cross section location: spar platform, EC 3, βwind = 0 deg, βwave = 0–90 deg. Twenty-four cross-sectional locations are considered.

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Fig. 8

Tower base 1 h expected fatigue damage as a function of cross section location: semisubmersible 2 platform, EC 3, βwind = 0 deg, βwave = 0–90 deg. Twenty-four cross-sectional locations are considered.

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Fig. 9

Tower top 1 h expected fatigue damage as a function of cross section location: spar platform, EC 3, βwind = 0 deg, βwave = 0–90 deg. Twenty-four cross-sectional locations are considered.

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Fig. 10

Tower base fatigue damage due to axial stress (caused by bending) as a function of wave direction. Note that the expected fatigue damage is plotted for the cross section location with the largest damage for each combination of EC and βwave. The vertical scale varies among different platforms.

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Fig. 11

1h expected fatigue damage multiplied by P(EC) for different ECs. The maximum value from the cross section for the aligned wind and waves case is shown.

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Fig. 12

Spectrum of axial stress at the tower base, EC 3, βwave = 0 deg, βwind = 0 deg

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Fig. 13

Spectrum of axial stress at the tower base, EC 5, βwave = 0 deg, βwind = 0 deg

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Fig. 14

Spectrum of axial stress at the tower base, EC 5, βwave = 60 deg, βwind = 0 deg

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Fig. 15

Expected maximum tower base bending moments (fore-aft, MFA and side–side, MSS) and axial stress (σx, see Eq. (1)) as a function of βwave for βwind = 0 deg

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