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Research Papers: Ocean Renewable Energy

A Comparative Study of Shutdown Procedures on the Dynamic Responses of Wind Turbines

[+] Author and Article Information
Zhiyu Jiang

Centre for Autonomous Marine
Operations and Systems (AMOS),
Centre for Ships and Ocean Structures (CeSOS),
Department of Marine Technology,
Norwegian University of Science and Technology (NTNU),
Trondheim NO-7491, Norway
e-mail: zhiyu.jiang@ntnu.no

Torgeir Moan

Centre for Autonomous Marine
Operations and Systems (AMOS),
Centre for Ships and Ocean Structures (CeSOS),
Department of Marine Technology,
Norwegian University of Science and Technology (NTNU),
Trondheim NO-7491, Norway
e-mail: torgeir.moan@ntnu.no

Zhen Gao

Centre for Autonomous Marine
Operations and Systems (AMOS),
Centre for Ships and Ocean Structures (CeSOS),
Department of Marine Technology,
Norwegian University of Science and Technology (NTNU),
Trondheim NO-7491, Norway
e-mail: zhen.gao@ntnu.no

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received January 21, 2014; final manuscript received September 26, 2014; published online November 17, 2014. Assoc. Editor: Yin Lu (Julie) Young.

J. Offshore Mech. Arct. Eng 137(1), 011904 (Feb 01, 2015) (16 pages) Paper No: OMAE-14-1003; doi: 10.1115/1.4028909 History: Received January 21, 2014; Revised September 26, 2014; Online November 17, 2014

The shutdown of wind turbines may induce excessive loads on the structures and is an important factor to consider in their design. For pitch-regulated turbines, shutdown calls for blade pitching, and one- or two-blade shutdown may occur during pitch actuator failure. Through coupled analysis, this study investigated the dynamic responses of land-based and spar-type floating wind turbines (FWTs) during shutdown. We simulated the shutdown procedures by pitching one, two, or three blades, and by varying the pitch rate. The nonpitching blades have a fixed pitch angle during the process. Three generator torque conditions were considered: (1) grid loss, (2) mechanical braking, and (3) grid connection. The extreme response values and short-term and annual fatigue damages to the structural components were compared against these values under normal operation and parked conditions. Three-blade shutdown is recommended for both turbines. One- or two-blade shutdown with grid loss may result in a significant rotor overspeed and imbalanced loads acting on the rotor plane. Therefore, unfavorable structural responses are observed. Grid connection or mechanical braking alleviates the situation. The land-based turbine is more sensitive to the pitch rate when considering the tower bottom bending moment, but the blade moments and mooring line loads of the spar-type turbine are affected more.

Copyright © 2015 by ASME
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References

Figures

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Fig. 1

Schematic of the wind turbines and mooring system

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Fig. 2

Schematic of the variation of pitch angle and generator torque in LCs 1–3

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Fig. 3

Response time series for the FWT, LC1, Pr = 5 deg/s, Type1, GS1, Ts = 300 s, and EC2 (constant wind, Uhub = 11.4 m/s, Hs = 2.6 m, and Tp = 11.1 s)

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Fig. 4

Time series of the rotor speed for the LWT, Type1, EC2 (Uhub = 11.4 m/s), and Ts = 300 s

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Fig. 5

Variation of the shutdown duration with pitch rate for the LWT, Type1, EC2(Uhub = 11.4 m/s) (a) LC1 and (b) LC2 and LC3

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Fig. 6

Variation of the maximum rotor speed with pitch rate for the LWT, Type1, EC2(Uhub = 11.4 m/s) (a) LC1 and (b) LC2 and LC3

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Fig. 7

Shutdown duration and maximum rotor speed for LWT, Type1 (a) EC2 (Uhub = 11.4 m/s) and (b) Pr = 8 deg/s

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Fig. 8

Tower bottom bending moment, LWT (a) time series, EC5 (Uhub = 20 m/s), Ts = 300 s; (b) extreme response, EC5 (Uhub = 20 m/s); (c) time series, EC2 (Uhub = 11.4 m/s), Ts = 300 s; (d) extreme response, EC2 (Uhub = 11.4 m/s). The extreme responses are the averaged extremes of 30 600 s simulations in LCs 1–3, and those of 20 600 s simulations in LCs 4–5.

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Fig. 9

Tower bottom bending moment, FWT, EC2 (Uhub = 11.4 m/s, Hs = 2.6 m, Tp = 11.1 s): (a) time series, Ts = 300 s and (b) extreme response

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Fig. 10

Tower bottom torsion (a) time series, EC2 (Uhub = 11.4 m/s), Ts = 300 s, LWT; (b) extreme response, EC2, LWT; (c) time series, EC2 (Uhub = 11.4 m/s, Hs = 2.6 m, Tp = 11.1 s) Ts = 300 s, FWT; and (d) extreme response, EC2, Ts = 300 s, FWT

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Fig. 11

Blade flapwise bending moment of the FWT, EC2 (Uhub = 11.4 m/s, Hs = 2.6 m, Tp = 11.1 s): (a) time series, Ts = 300 s and (b) extreme response

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Fig. 12

Mooring line tension of the FWT, Uhub = 11.4 m/s: (a) time series of the lower line tension, Ts = 300 s; (b) time series of the delta line tension (segment 2 b), Ts = 300 s; (c) variation of the lower line tension extremes with wind speed; and (d) variation of the delta line tension extremes with wind speed

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Fig. 13

Sketch of a cross section in the tower structure

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Fig. 14

Normalized fatigue damage calculated by Eq. (5)) and caused by: (a) tower bottom bending moment, LWT; (b) tower bottom bending moment, FWT; (c) tower bottom torsion, LWT; and (d) tower bottom torsion, FWT (EC2, Uhub = 11.4 m/s, logarithmic scale)

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Fig. 15

Normalized fatigue damage calculated by Eq. (5)) and caused by the edgewise bending moment of blade 2, using GS0 and Type1 (logarithmic scale)

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Fig. 16

Fatigue damage caused by tension in delta line 2b at tp3, FWT: (a) contour line, (b) comparison of GSs, LC2, (c) comparison of one- and two-stage pitching procedures, Pr = 8 deg/s, and (d) comparison of GSs, LC3

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Fig. 17

Distribution of the hub-height wind speed

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