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Research Papers: Offshore Technology

Natural Frequency Analysis of a Spar-Type Offshore Wind Turbine Tower With End Mass Components

[+] Author and Article Information
Kan Ye

School of Mechanical and Mechatronic Engineering,
FEIT University of Technology Sydney,
P.O. Box 123,
Broadway, NSW 2007, Australia
e-mail: kan.ye@uts.edu.au

Jinchen Ji

School of Mechanical and Mechatronic Engineering,
FEIT University of Technology Sydney,
P.O. Box 123,
Broadway, NSW 2007, Australia
e-mail: jin.ji@uts.edu.au

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 18, 2017; final manuscript received May 2, 2018; published online June 28, 2018. Assoc. Editor: Madjid Karimirad.

J. Offshore Mech. Arct. Eng 140(6), 064501 (Jun 28, 2018) (5 pages) Paper No: OMAE-17-1218; doi: 10.1115/1.4040240 History: Received December 18, 2017; Revised May 02, 2018

Different from the fixed-based wind turbines, the floating type wind turbines are regarded as under a free–free end operating condition. The tower structure of a floating offshore wind turbine is an integrated part connecting the nacelle and support platform. An analytic solution is presented in this technical brief for the free-vibration of the tower structure of a spar-type offshore wind turbine. The tower structure is modeled as a free–free beam based on Euler–Bernoulli beam-column theory. The platform and the nacelle are considered as two large mass components connected by torsion springs at two tower ends with different stiffness. The effects of system parameters on the natural frequencies are investigated under a range of variables, including the tower structure parameters, platform and nacelle parameters, and the connection types. Nonlinear relationships between those variables and the natural frequency of the tower structure are numerically found and some design issues are discussed for the spar-type floating wind turbines.

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Figures

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Fig. 1

Schematic of a free–free model of the offshore wind turbine and its geometry of boundary condition at z = 0

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Fig. 2

The variation of the first natural frequency of the tower structure with respect to the mass density

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Fig. 3

The variation of the first natural frequency of the tower structure with the diameter and thickness in 3D plot

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Fig. 4

The variation of the first natural frequency of the tower structure with respect to both torsion spring stiffnesses in 3D plot

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Fig. 5

The variation of the first natural frequency of the whole system with respect to the distances between the tower ends and the CG of the end components

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