My Assumptions for a 5 Mw wind turbine
I am providing all the dimensions of the beams, crosses, stays and diagonal cables I used in my analysis. I am also providing the analysis of the frame regarding the loads and forces created by three wind turbine arrangements. There are several reasons why I am doing this. One is to show the rigidity of the frame, and another is to show the weight of the steel needed to build this frame. Perhaps the main purpose is to allow interested parties to do similar calculations to verify the accuracy of the results and to modify calculations where I may have erred. The frame components are not optimized and should only be used for comparison and initial evaluation purposes.
The following data from the NREL 5 Mw reference turbine was used to compare the outside frame of my design to the tower of the NREL turbine.
Height above ground 90m
Outside diameter at the bottom 6m
Material thickness at the bottom 0.027 m
Swept Area 12,469 m2
Weight of the turbine tower 347,460 Kg
Thrust at rated power 827 KN
Yield strength of AISI 1020 steel 350 MPA
Assumptions:
1. The thrust of the NREL turbine at rated power is given at 847 KN but I did a bit of reverse engineering and if I use the data above, the tower will exceed the yield limit of the steel if the thrust force at the top is larger than 2,890 KN. My assumption is that this force considers all relevant factors needed to prevent the failure of the tower. Therefore, I will use this force on my 5 Mw VAWT frames.
2. A VAWT generally requires 20 % more swept area than a HAWT to produce a similar power curve. I do not have reliable data from a 5 MW H style turbine so even though the blade aerodynamics improve as the blades get larger, I used the 20% increase in swept area for my calculations.
3. I did an analysis for the frame of 1 turbine alone, 2 turbines on top of each other and 3 turbines on top of each other. The total swept area in each analysis was approximately15,000 sq.m. The frame is a bit larger to allow for movement.
4. Four pillars or posts, one at each corner, support the four corners of the bottom cube a desired distance above the ground. The weight of the pillars is not included in the weight of the frame. Also, the generator, bearing, brakes and all other needed equipment are mounted at ground level in the middle of the cube and have no influence on the frame.
5. I assume an H style VAWT would be contained inside the frame, but it is not restricted to this design.
6. The SPM values of Pcr, calculated for all the stayed columns in the analysis are higher than the calculated compressions. This was done to add another level of confidence for these beams.
Go to the ‘Analysis’ section to learn more about the 5 Mw structures.
[i] Gurfinkel, German and Krishnan, Sudarshan. “Analysis and Design of Cable-stayed Steel Columns using the Stiffness-Probe Method,” Engineering Journal, 3rd Quarter, pp. 195-209, American Institute of Steel Construction (AISC), United States, July 2017.