Tower guage locations

Wind & Water Computer-Aided Engineering Software Tools
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How do I estimate the exact location for the tower node guages as mentioned in the image. I am using FAST v7 with the OC3 monopile with AF model.

Thanks
Subham

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Dear @Kashyap.Subham,

The elevations of the TwrGagNd locations in FAST v7 (and ElastoDyn in FAST v8 and OpenFAST) are documented in the old FAST User’s Guide: https://openfast.readthedocs.io/en/main/_downloads/d8bd014121d6505cb25cf49bee5eaa80/Old_FAST6_UsersGuide.pdf.

Best regards,

3

Sir,

Confusion arises when I use the apparent fixity models for oc3 project since the entire tower is effectively taken as the tower + platform + the apparent fixity length.
For the apparent fixity case, where does the TwrBsMyt measure the moments along the entire length?

Thanks
Subham

4

Dear @Kashyap.Subham,

If you are modeling the entire support structure (tower + monopile, including apparent fixity) via the tower in FAST v7, then the tower-base moment output (TwrBsMyt) is located at the clamped end of the apparent fixity pile (likely not a useful output). In this case, if you want to output the loads at the actual tower base or at the seabed, I would use the loads available at the tower gage locations.

Best regards,

5

Sir,

I am confused here again. So, if I apply the seismic motions in the apparent fixity model, where does it get input in the model (at the fixed bottom end of apparent fixity length or at the point where it coincides with rigid base height as specified by the TwrRBHt)? In addition, in such a scenario, should my PtfmSurge match the earthquake ground motions?

eagerly waiting for your reply.

Thanks
Subham

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Dear @Kashyap.Subham,

The seismic excitation in FAST v7 is applied at the platform reference point. The tower base, where the tower flexibility begins, is TwrRBHt above the platform reference point.

The Seismic version of FAST v7 applies forces to achieve the desired seismic motion. If you following the modeling guidance for specifying the platform mass and platform actuator stiffness and damping, the platform motion should closely (but not exactly) follow the desired motion.

Best regards,