Transactions of Nanjing University of Aeronautics & Astronautics
Special Issue for Wind Turbine
Gravity Influence on the Natural Frequency of offshore Wind Turbine Structures
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Abstract:
The fatigue limit state are critical for most offshore wind turbines, to minimize the development of fatigue damage, dynamic amplification of the response must be avoided. Thus, it is importance that the first natural frequency of the offshore wind turbine does not coincide with the excitation frequencies related to wind turbine and wave loadings. Currently, there is few study related to offshore wind turbine frequencies considering self-gravity influences including turbine, tower and part pile foundation. In order to evaluate the self-gravity influence on the first natural frequency of wind turbine support structures, the offshore wind turbine system vibration was modeled using an Euler-Bernoulli beam with axial force and horizontal force. The real data from five wind turbines available in the market are considered. The wind turbines size is from 2.3MW to 6MW, the tubular steel tower height are from 83m to 100m. Based on the research results, it indicated that the average influence of gravity on the natural frequency is nearly 1.8%. Considering the first natural frequency should lies between 1p and 3p, which is a relatively narrow range, the design procedure requires an accurate evaluation of the first natural frequency. From this perspective, the first natural frequency is reduced due to gravity need to be considered for design of offshore wind turbine support structures, especially for the design first natural frequency of the offshore wind turbine close to the lower limit 1P.
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