Query - why does surge motion not contribute to aero term in tower bending moment

[caleboxeng]

Hello. My query refers to line 2526-7 in raft_fowt.py, which calculates the aerodynamic force contribution to the tower bending moment. Why is it that the aerodynamic coefficients only operate on the pitch motion response and not the surge motion response? I.e. why does the aerodynamic damping and added mass not contribute to a bending moment at the tower base even when the floater is only surging? Thank you!

[mattEhall]

Hi - you're right, surge motion should contribute too. At the time, I expected the aero reaction from surge would tend to be a lot less than that from pitch, for typical cases, and this part of the code was making a rough approximation, definitely missing some terms.

[lucas-carmo]

Just wanted to mention that after v2.0 this approximation is used for rigid towers only, but we will likely improve that in the future. For flexible towers we use a different approach that accounts for that.

[caleboxeng]

Okay great. Thank you both, much appreciated.