EFFECTS OF TOWER AND BLADES PRE-STIFFENING ON THE NATURAL FREQUENCIES OF THE DTU 10MW REFERENCE WIND TURBINE
Keywords:
Wind Turbines, Modal Analysis, Finite Element Method, Pre-StiffeningAbstract
Modal analysis of horizontal axis wind turbines is becoming more important due to the increase in blade and tower dimensions, making the whole assembly more flexible and susceptible to vibration problems. Due to the slender characteristics of the blade and tower, they are typically modelled as cantilever beams, with the aid of the Finite Element Method. The objective of this paper is to investigate the natural frequencies of the DTU 10MW Reference Wind Turbine (composed of three blades and the tower) under the influence of tower and blades pre-stiffening. Tower pre-stiffening is due to the significant weight of the blades and the hub supported by the tower, resulting in tower compression loads. Blades pre-stiffening are due to the centrifugal loads acting on the rotating blades, thus depending on the rotation speed. The results are computed using the commercial software Altair® HyperWorks® and compared to the baseline results provided by the literature. It was found a maximum reduction of about 2% in the natural frequencies due to the tower pre-stiffening (for the 1st and 2nd modes) and maximum reductions varying from about 7% to 21% due to blades pre-stiffening (for the 1st mode), considering the minimum and maximum operational rotation speeds.
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