OK, thanks for the thorough analysis. Is this a proper summary of your results?:
There are two main concerns:
- The structural damping of the ED+BD model shows azimuth dependence in the fixed frame of reference (after applying MBC3), particularly for the flapwise mode.
- The damping obtained after azimuth averaging is not the same as the mean of the azimuthally varying damping.
- ED alone shows the expected behavior.
- The problems in ED+PD are not influenced by numerical damping (the conclusions are the same with rhoinf = 0 or 1).
- A precision of "ES17.9E3" is converged (going to a higher precision of "ES20.12E3" does not change the conclusions).
- The problems are exacerbated when aerodynamics/damping is included.
- The problems go away when structural damping in BD is eliminated (mu=0).
I would be curious if you see the same azimuth-dependence on damping when linearizing with zero rotational speed (again without aerodynamics/aerodynamic damping).