Yaw with friction force in FAST

I am a new user of FAST and I already consider it is a great code.

I try to modelize with FAST the behaviour of a free yaw system with a Coulomb friction force acting on the yaw bearing, when extern yaw moment is lower than the Coulomb friction force nacelle is considered as stitched to the tower top and YawDOF is false and when the yaw moment is greater than friction force, YawDOF is turned to true and a constant friction force is applied on the nacelle and counteract the yaw motion.
I have read chapter in the User’s guide about nacelle yaw control but I didn’t find solution to my problem. In the usual case in the UserYawCont() we have to act on YawPosCom and YawRateCom to control yaw motion, but it is difficult (for me) to see how in acting on these variables I might simulate a friction force.
For Teeter control it is possible in FAST to simulate a coulomb damping moment but the mechanism to control teeter motion is different than the one controlling yaw motion. I am not sure if it is possible to add a friction force as done in Teeter subroutine.

So I will be very happy if anyone in this forum could share its experience on this topic.

Bests regards,

Dear Bertrand,

Sorry for the slow response, but we recently published an article in Engineering Structures that describes how we implemented a Coulomb friction model in FAST v7 for nacelle-yaw. The approach implemented is nearly identical to how the high-speed-shaft (HSS) brake torque is implemented in FAST v7. You can find the details in the paper here: sciencedirect.com/science/ar … 9614000327. These changes were implemented in a custom version of FAST v7 that are not included in our standard release. However, you may be able to contact the lead author of the article to get a copy.

It should be noted that the Coulomb friction model implemented in FAST v7 for rotor-teeter is not implemented in the same way and likely does not work (leading to a numerical instability) for most cases.

We have not yet implemented Coulomb friction in FAST v8; this is on our to-do list for the future.

Best regards,