Updated definition of structural damping

[RRiva]

Updated definition of structural damping

We replace the definition of structural damping, which was mu from BeamDyn, with the more general damping ratio.

Related issue

#192

Impacted areas of the software

Additional supporting information

Test results, if applicable

[RRiva]

Hi @ptrbortolotti, what do you think? If you like it, I can update the turbine models.

[ptrbortolotti]

this makes sense to me... thank you very much for doing it

[ptrbortolotti]

@RRiva thank you for this PR. should I work to fix the tests?

[RRiva]

Hi @ptrbortolotti, sorry for the delay. I'll update the turbine models next week.

[fzahle]

we'd also need to update windIO2windIO: https://github.com/IEAWindSystems/windIO/blob/main/windIO/converters/windIO2windIO.py#L473 and since this is a backward incompatible change it'll have a wide impact across our RWTs.

[RRiva]

I've now added the damping ratios, but I still have to name the modes.

[ptrbortolotti]

Table 3 in https://iopscience.iop.org/article/10.1088/1742-6596/2767/5/052042/pdf has the modes for the IEA22
For the IEA15, this is a start https://iopscience.iop.org/article/10.1088/1742-6596/2767/2/022018/pdf, but unfortunately I don't find the list of the higher modes