Outout of tower aerodynamic loads

[benwys957]

Dear all,

According to the AeroDyn.dat file in OpenFAST v4.1.2, the software can output aerodynamic loads for a maximum of 9 nodes (NTwOuts <= 9). Taking the IEA-15MW-UMaine floating wind turbine as an example, the tower discretization in the AeroDyn.dat file is defined as follows:

TwrElev TwrDiam TwrCd TwrTI TwrCb
(m) (m) (-) (-) (-)
15. 10. 0.5 0.1 0.0
28. 10. 0.5 0.1 0.0
41. 10. 0.5 0.1 0.0
54. 10. 0.5 0.1 0.0
67. 10. 0.5 0.1 0.0
80. 10. 0.5 0.1 0.0
93. 10. 0.5 0.1 0.0
106. 10. 0.5 0.1 0.0
119. 10. 0.5 0.1 0.0
132. 10. 0.5 0.1 0.0
144.386 6.5 0.5 0.1 0.0

There are eleven nodes in total, dividing the tower into 10 segments. However, because the maximum value for NTwOuts is capped at 9, the aerodynamic loads across all 11 nodes cannot be displayed simultaneously.

If the output is indeed strictly limited to 9 nodes, does Node 1 correspond to the point at TwrElev = 15 (which should represent the tower base), Node 2 correspond to TwrElev = 28, and so on, up to Node 9 corresponding to TwrElev = 119?

If this assumption is correct, and I request the output variable 'TwN1Fdx' (the x-component of the aerodynamic drag force per unit length at tower node 1), what is the appropriate tributary length I should multiply TwN1Fdx by to obtain the total integrated x-component drag force for the segment corresponding to Tower Node 1?

Thank you in advance for your help!

[jjonkman]

Dear @benwys957,

I agree that values at only 9 of the tower aerodynamic analysis nodes can be output, but these are not necessarily the first 9 nodes in the table of distributed tower aerodynamic properties. Rather, which of the NumTwrNds nodes become the tower aerodynamic output nodes is set via NTwOuts and TwOutNd in the OUTPUTS section of the AeroDyn primary input file. In your case, if NTwOuts = 3 and TwOutNd = 1, 6, 11, then the 3rd output node is the 11th analysis node, so, TwN3Fdx is the drag force per unit length output at an elevation of 144.386 m. Moreover, the force outputs are expressed as force per unit length, so, don't have an associated "tributary length".

Best regards,