Drivetrain Damping

Dear Jason,
The torsion stiffness of the dirvetrain mainly included the low speed shaft ,gearbox, flexible support and so on,I think the stiffness of the gearbox is the most importrant part, but i don’t know how we set the damping, we set the damping of tower and blades by the damping ratio, Do drivetrain have the same case? Usually I think the drivetrain also have the little damping ,so we can control the torque to increase the damping.
My question is how much drivetrain’s damping ratio usually is ,generally I set the damping ratio to 0.5%,then calculated the damping out .What do you think about my way to calculate the damping,and what’s your method to calculate the damping?

Best Regard and happy new year !

Ruiliang.Wang

Dear Ruiliang,

Like for steel towers, I would typically assume a damping ratio of 0.5-1.5% for drivetrains in the absence of more information. But the drivetrain damping is specified in the ElastoDyn module of FAST as a torsional damping constant (DTTorDmp) rather than a damping ratio. The drivetrain torsional stiffness and damping constants (DTTorSpr and DTTorDmp) have been discussed a few times on this forum e.g. see: http://forums.nrel.gov/t/drivetrain-2-2hz-frequency-and-natural-frequency-0-625hz-def/987/1.

Best regards,

Dear Jason,
When I read the paper “Dynamic modeling and loads analysis of an offshore floating wind turbine”,I found you set the damping ratio to 5% critical,

As you said the steel structure’s damping ratio is 0.5%-1.5%, Why did you set the vaule to 5%
As I know If we increase the value to 5%,maybe the LSSMx will be fine.If we set to 0.5%,I think the Mx have large oscillation,we have to improve the drivet%.rain damping additionally.
Could you explain that ?

Best Regard
Ruiliang.Wang

Dear Ruiliang,

Good question. If I recall correctly, the NREL 5-MW baseline turbine used a simplified control system that does not attempt to damp structural vibrations in the drivetrain. Instead, the structural damping of the drivetrain was artificially increased.

Best regards,