Dynamic characteristics analysis of the offshore wind turbine blades

Abstract

The topic of offshore wind energy is attracting more and more attention as the energy crisis heightens. The blades are the key components of offshore wind turbines, and their dynamic characteristics directly determine the effectiveness of offshore wind turbines. With different rotating speeds and blade length, the rotating blades generate various centrifugal stiffening effects. To directly analyze the centrifugal stiffening effect of blades, the Rayleigh energy method (REM) was used to derive the natural frequency equation of the blade, including the centrifugal stiffening effect and the axial force calculation formula. The axial force planes and the first to third order natural frequency planes which vary with the rotating speed and length were calculated in three-dimensional coordinates. The centrifugal stiffening coefficient was introduced to quantitatively study the relationship between the centrifugal stiffening degree and the rotating speed, and then the fundamental frequency correction formula was built based on the rotating speed and the blade length. The analysis results show that the calculation results of the fundamental frequency correction formula agree with the theoretical calculation results. The error of calculation results between them is less than 0.5%.

Keywords

centrifugal stiffening effect / blade dynamic characteristic / stiffening coefficient / natural frequency / offshore wind turbine

References

[1] Baumgart A. A mathematical model for wind turbine blade. Journal of Sound and Vibration, 2002, 25(11): 1-12

[2] Harrison R., Hau E., Snel H. Large wind turbine: design and economics, 2000, New York: John Wiley and Sons Ltd, 25-48

[3] Himri Y., Rehman S., Draoui B., Himri S. Wind power potential assessment for three locations in Algeria. Renewable and Sustainable Energy Reviews, 2008, 12(9): 2495-2504

[4] Jian K. Computation of natural frequencies of a rotating beam. Journal of Chongqing University, 2001, 24(6): 36-39

[5] Lavassas I., Nikolaidis G., Zervas P., Efthimiou E. Analysis and design of the prototype of a steel 1-MW wind turbine tower. Engineering Structures, 2003, 25: 1097-1106

[6] Lee C.L., Al-Salem M.F., Woehrle T.G. Natural frequency measurements for rotating span wise uniform cantilever beams. Journal of Sound and Vibration, 2001, 240(5): 57-61

[7] Lee D., Hodges D.H., Patil M.J. Multi-flexible-body dynamic analysis of horizontal axis wind turbines. Wind Energy, 2002, 5(4): 281-300

[8] Lesaffre N., Sinou J.J., Thouverez F. Stability analysis of rotating beams rubbing on an elastic circular structure. Journal of Sound and Vibration, 2007, 299: 1005-1032

[9] Li D., Ye Z., Chen Y. Multi-body dynamics numerical analysis of rotating blade of horizontal axis wind turbine. Acta Energiae Solaris Sinica, 2005, 26(4): 473-481

[10] Murtagh P.J., Basu B., Broderick B.M. Along-wind response of a wind turbine tower with blade coupling subjected to rotatingly sampled wind loading. Engineering Structure, 2005, 27: 1209-1219

[11] Naguleswaran S. Lateral vibration of a centrifugally tensioned uniform Euler-Bernoulli beam. Journal of Sound and Vibration, 1994, 176(5): 613-624

[12] Tavner P. Wind power as a clean-energy contributor. Energy Policy, 2008, 36(12): 4397-4400

[13] Wang Z., Jiang C., Ai Q., Wang C. The key technology of offshore wind farm and its new development in China. Renewable & Sustainable Energy Reviews, 2007, 13(1): 216-222

[14] Xin W. Analysis of dynamic characteristics and response for rotating blades of wind turbine, 2005, Shantou: Shan Tou University

[15] Zhou Y., Chen c. Disaster preventing and reduction of civil engineering, 2002, Guangzhou: South China University of Technology Press, 92-100