Impact of Generator Inertia wrt to LSS on RotTorq

[Sam-Ramsahoye]

Hi,

I was wondering if I could have some help understanding the ElastoDyn RotTorq variable and it's relationship to GenIner with respect to the LSS.

I've run two simulations with only the generator DOF active. One with a non-negligible generator inertia (blue) and the other with a negligible generator inertia (orange) but with the hub inertia supplemented with the intended GenIner * Ng^2.

As I expected, the result generator speed time-histories are basically identical as the total rotational inertia is preserved:

However, RotTorq appears to be quite different:

I didn't expect the difference. Could someone help improve my intuition of this variable and why it's sensitive to GenIner?

@jjonkman Any ideas?

Many thanks,
Sam

[jjonkman]

Dear @Sam-Ramsahoye,

The distribution of inertia between the generator and hub will impact the internal reaction torque within the shaft (RotTorq). A discussion on this, and the related math, are explained in the following topic on our forum: https://forums.nrel.gov/t/resistant-moment-of-the-rotor-and-of-the-electric-generator/408 (LSShftTq in this post is equivalent with RotTorq that you are asking about).

Best regards,

[Sam-Ramsahoye]

@jjonkman Thanks for the help, that makes sense to me now.