Do These NREL 5-MW Blade Natural Frequencies Look Correct?

Wind & Water Structural Analysis
1

I am validating a 3D Timoshenko beam model using the NREL 5-MW blade. For the non-rotating, clamped-free blade, I obtain:

Without structural twist / CM offset:
0.676, 1.084, 1.941, 3.962, 4.472, 5.455 Hz

With StrcTwst and EdgcgOf:
0.676, 1.080, 1.942, 3.925, 4.466, 5.469 Hz

The modes appear to be F1​,E1​,F2​,E2​,F3​,T1​.

Since shear stiffness is not provided in the NREL blade data, I estimated it to be sufficiently large so that the Timoshenko model approaches the Euler–Bernoulli limit.

There seem to be many different references reporting NREL 5-MW blade modal results, and I am finding it difficult to identify the most reliable benchmark.

Do these frequencies and mode identifications look reasonable? Is using a large estimated shear stiffness reasonable for this validation? Also, is there an official NREL/BModes reference where I can find the corresponding blade mode shapes for comparison?

2

Dear @KanwarOsama.Zulfiqar,

I agree with your first 3 frequencies and mode identifications; I have not looked at higher modes for the NREL 5-MW baseline wind turbine blade.

The first 3 mode shapes are provided in the ElastoDyn blade input file (in terms of coefficients of the polynomial fit).

Best regards,

3

Thank you @Jason.Jonkman