In this load case, we compare the eigenfrequencies of the NREL 5-MW reference wind turbine from Ashes to the results given in the specification document (Table 9.1 in Jonkman et al. (2009o) ).

2 Model

The model is the Onshore NREL 5-MW reference wind turbine, which corresponds to the onshore template in Ashes

3 Results

The eigenfrequences of the model are solved and compared to those from FAST and ADAMS presented in the specification document. Note that the numbering of the eigenfrequencies in Ashes is from the lowest frequency to the highest, which is not the same as in the specification documentt. The table below summarises the numbering correspondance.

Mode number in Ashes	Mode name	Mode number in the specification document
1	1st Tower Side-to-Side	2
2	1st Tower Fore-Aft	1
3	1st Drivetrain Torsion	3
4	1st Blade Asymmetric Flapwise Yaw	4
5	1st Blade Asymmetric Flapwise Pitch	5
6	1st Blade Collective Flap	6
7	1st Blade Asymmetric Edgewise Pitch	7
8	1st Blade Asymmetric Edgweise Yaw	8
9	2nd Blade Asymmetric Flapwise Yaw	9
10	2nd Blade Asymmetric Flapwise Pitch	10
11	2nd Blade Collective Flap	11
12	2nd Tower Side-to-Side	13
13	2nd Tower Fore-Aft	12

A bar plot with the eigenfrequencies from the specification document and from Ashes is available on the following link.

https://www.simis.io/downloads/open/benchmarks/current/OC3_Phase_I_LC12.pdf

Note that only a visual check is performed here.