Section coordinate system in BeamDyn

[Felix.Barnaud]

Dear NREL Team,

I am trying to implement a pre-bent blade in BeamDyn v1.00.00, and I have some doubts about the sections coordinate systems definition.
The user manual specifies that the stiffness and mass matrices for each section should be given in a “local coordinate system along the blade axis following the IEC blade coordinate convention”, however I do not manage to find this reference.

Here is my understanding, correct me if I am wrong:

• The origin point of each local coordinate system is along the blade curvilinear axis defined in the primary input file under the “geometry parameters” section, at the radius defined in the blade input file.

• Each section local coordinate system is defined by x_l, y_l, z_l : x_l pointing from origin (blade curvilinear axis) to suction side, y_l from origin to trailing edge, and z_l from origin to blade root (tangential to blade curvilinear axis).

Best regards,

Félix

[Jason.Jonkman]

Dear Felix,

Your understanding is correct except that the z_l axis is directed nominally from the origin to the blade tip (tangential to the blade curvilinear axis). We’ve updated the BeamDyn documentation that we will release along with an update to FAST v8 soon. Included in this updated documentation is a figure that clarifies the blade reference and local blade coordinate systems, which I’ve also attached to this post for your reference.

Best regards,