Coordinate System

Dear OpenFAST team,
I would like to know whether the coordinate system used in OpenFAST is the same as the one in ‘FAST Users Guide’ released in August 2005

Many thanks to the team

Adding to the above, I would like to whether my understandings are correct or not regarding OpenFAST coordinate system. Help me if I am wrong.

  1. Inertial coordinate system origins at the bottom of spar.
  2. The platform (6 DOFs) responses calculated in OpenFAST are the responses at the platform COG

Thanks in advance

Dear Akheel,

The coordinate systems documented in the old FAST v7 User’s Guide are the same coordinate systems used within the ElastoDyn module of OpenFAST. Other modules may use other coordinate systems, as described in their respective documentation.

The inertial frame coordinate system used in OpenFAST has the origin at the intersection of the undisplaced tower centerline and mean sea level, with the X-axis along the zero-degree wind/wave direction, the Z-axis vertical (opposite gravity), and the Y-axis directed to the left when looking along the zero-degree wind/wave direction.

The platform DOFs are defined relative to the inertial frame, with an origin determined by PtfmRefzt (when PtfmRefzt = 0, the origin of the platform DOFs is coincident with the origin of the inertial frame coordinate system). This origin is typically not the platform CG.

Best regards,