Position of the blade root in relation to the aerodynamic center

Wind & Water General
1

Dear all,

I am using OpenFAST (BeamDyn + AeroDyn & OLAF) to calculate the aeroelastic response of a rigid sail which I modelled with a constant chord and unique airfoil profil without twist. I have a simple but crucial question for my analysis.
I think I understood that the aerodynamic forces were expressed at the quarter of the chord. But I am not clear on the position of the blade root comparatively to this aerodynamic center. Because the sectional stiffness and mass matrix change with the coordinates in which they are expressed, I need to know where is situated the blade root.

Thanks in advance,

Théo

2

Dear @Theo.Tardif,

OpenFAST does not have any requirement or assumption that the aerodynamic loads must be calculated relative to quarter chord. The pitch axis (position, orientation) is defined by ElastoDyn, and in AeroDyn, the aerodynamic nodes (aerodynamic centers, or reference point for the calculation of aerodynamic loads, which could be at quarter chord, but need not be), are specified relative to this pitch axis. When using BeamDyn, like AeroDyn, the reference axis of the blade structural dynamics is also specified relative to the pitch axis.

Best regards,

3

Dear @Jason.Jonkman,

Thank you for your quick answer, it is much clearer for me.

Best regards,
Théo