Single lift blade alignment for large offshore wind turbines

A critical assessment of the alignment process of next generation wind turbine blades

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In 2022 the first 12 MW offshore wind turbines are expected to be installed. Due to the continuous upscaling of wind turbine generators new problems are expected to arise during the installation of the turbines. Especially the workability of the installation of larger wind turbine blades, which are already causing problems during the installation of 8.4 MW turbine blades, are questioned by Van Oord. This research focuses on the alignment process of the blade with the hub, which is considered to be the limiting factor in installing wind turbine blades. The ultimate goal is to reduce single blade installation times by facilitating the alignment process To investigate how different environmental conditions influence the dynamic behavior of the blade in the alignment process, a numerical model is developed. The motions of the blade, forces in the taglines and aerodynamic forces on the blade are evaluated for different environmental conditions during 30-minute simulations in the time domain. Wind velocity, turbulence intensity and the angle of the incoming wind relative to the blade are environmental parameters that influence the motion of the blade. Results for a 8.4 MW reference turbine blade are compared to a 12 MW turbine blade and conclusions are made concerning the installation workability for larger turbine blades. Results show that the displacement of the blade root is caused by the rotation of the blade and installation tool around its x- and z-axis. The response spectrum of the blade root motions contains a significant amount of energy at the lower frequency part of the spectrum. In this part the first and second natural frequency of the system occur, which correspond to the rotations that are the main causes of the blade root displacement. The effect of wind speed, turbulence and incoming wind angle on the response of the blade is significant. Furthermore simulations are conducted for different rotation angles of the blade in the blade installation tool, which can result in large reduction, around 50%, of blade root motions. The responses of larger turbine blades (length 107 metre) increase compared to a smaller turbine blade (length 80 metre). Workability is expected to decrease due to the increase in blade root motions. Based on the results of the analysis, several improvements are proposed for decreasing the blade root motions using the existing tagline set up. Using a different angle of the blade in the installation tool and increasing the tagline tension both decrease blade root motions. A solution using an extra tagline is proposed and discussed to show how the current setup could be improved.