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IEAWindTask37 / IEA-22-280-RWT

Repository for 22MW offshore reference wind turbine developed by the IEA Wind Task 37
Apache License 2.0
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tweak damping again #64

Closed ptrbortolotti closed 3 months ago

ptrbortolotti commented 3 months ago

Following guidance from @RBergua, I'm tweaking structural damping of tower and monopile again:

Monopile damping is now set in SubDyn to use the stiffness proportional damping term β β = damping/(π ∗ freq) where damping is 0.09% and freq is 0.16 Hz. These values correspond to the full system damping and frequency of the first FA mode from HAWC2 β = 0.00092 / (π ∗ 0.16) = 0.00183

Tower structural damping of the first FA and SS modes in ElastoDyn is set as damping uncoupled_freq (isolated tower) / coupled_freq (full RNA+tower+monopile) For the IEA, that translates to 0.00092 0.583 Hz / 0.16 Hz = 0.33%

The damping for the second modes of the tower are tuned manually to achieve target damping of 0.517% and 0.537% for second SS and second FA modes of the full system, respectively.

When I linearize the model, I now get

image

Note that: 1) I've propagated the values of structural damping of the isolated tower in ElastoDyn to the floating tower. We will need to review these values @dzalkind 2) When modeling the system without the monopile, structural damping in ElastoDyn will no longer match the values from HAWC2. In this case, a user should change the 0.33% to 0.5% for the first modes and 2.1678% and 2.1698 for the second modes. Caution: if running the isolated tower to check these values from a linearization, the user will also need to update the mode shapes!!

gbarter commented 3 months ago

"When modeling the system without the monopile, structural damping in ElastoDyn will no longer match the values from HAWC2. In this case, a user should change the 0.33% to 0.5% for the first modes and 2.1678% and 2.1698 for the second modes. Caution: if running the isolated tower to check these values from a linearization, the user will also need to update the mode shapes!!"

I know there is a 15-MW branch that does something similar. Should we have a ElastoDyn file that says "land based" or with all of these modifications? Not sure if that is too out-of-scope.

Nice work overall, of course. One day, we'll actually get this right at the beginning. . .