Abstract
The wind turbine industry has focused offshore on increasing the capacity of a single unit through up-scaling their machines. There is however a lack of systematic studies on how loads vary due to properties of a wind turbine and scaling of wind turbines. The purpose of this paper is to study how applied blade modifications, with similarities such as mass, stiffness and dimensions, influence blade root moments and lifetime damage equivalent loads (DELs) of the rotor blades. In order to produce fatigue load blade root moment trends based on the applied modifications. It was found that a linear trend of lifetime DELs based on the applied modifications of blades, which have effect on the natural frequency of blade of the original or reference model. As the control system was tuned for the specific frequency of the reference model. The linear trend of lifetime DELs was generated as long as the natural frequency of the reference model was preserved. For larger modifications of the wind turbine the controller would need retuning.
Highlights
Up-scaling of wind turbines is being driven by the offshore market
In the 2nd case the modifications were applied in a manner that preserved the natural frequency of the reference model
The 1st case demonstrated a general trend of lifetime damage equivalent loads (DELs) but with distortions at Wohler coefficients which are typical of composite materials
Summary
Up-scaling of wind turbines is being driven by the offshore market. the specific cost of such turbines in Euro/rated MW may increase with scale, reductions in infrastructure costs and in O&M, with larger offshore units per MW of total installed capacity, appear to justify the use of turbines rated at 5 MW and above. In the past several techniques were introduced to obtain a methodical understanding and quantifiable classification of wind turbine load trends. Linear scaling or scaling with similarities was introduced by Chaviaropoulos [1], where tip speed is constant or unchangeable and any dimensional changes are proportional or linear. The disadvantage of this method is that it neglects any innovation in construction materials. Fatigue loads become more relevant as wind turbines scale up since gravitational loads increase dramatically. The associated moments are scaled up by a power of four In this case the fatigue loads become more important in design of large or scaled up wind turbines. Each revolution of the rotor results in fatigue damage which is caused by both deterministic and stochastic loads, where stochastic part loads are from wind turbulence and deterministic loads are a result of gravity, wind shear, tower shadow and yaw error [4]
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