Dear @Jason.Jonkman, thank you for your replies to date.
Above you state that: “Structural deflections of the blade in OpenFAST are tracked by the structural solver (ElastoDyn, BeamDyn). The motions (positions/orientations, velocities) are passed to the aerodynamic solver (AeroDyn). AeroDyn expects the motions to be received at the aerodynamic analysis nodes, which on the blade are at the aerodynamic centers”. This seems very clear to me.
In another thread (https://forums.nrel.gov/t/how-to-import-hub-motions-to-aerodyn/1350/2) you have documented the variables which an external structural solver should pass to AeroDyn. However, this message does not seem to mention positions (i.e. points in 3D space). It mentions displacements (i.e. changes in position) and orientations, and velocities, but it does not explicitly mention position.
Q1: Would you be able to quickly outline how AeroDyn uses the inputs documented here https://forums.nrel.gov/t/how-to-import-hub-motions-to-aerodyn/1350/2 to compute the instantaneous position of the aerodynamic analysis nodes.
By way of background, I am currently updating our structural solver to supply AeroDyn with the aerodynamic node positions, rather than the structural node positions.
Q2: Do you think that there is likely to be any significant difference between the displacements of the structural nodes (which I am currently passing) and the displacements of the aerodynamic nodes (which I intend to pass), assuming that there is a physical separation between the shear and aerodynamic centrs on the blade profile. For example, I think that any blade twist occurring about the pitch could lead to small differences between the translational displacements of the structural nodes and aerodynamic nodes.