Current definition problem

Dear OpenFAST Team,

I have current data which I would like to add to my model simulation. I’m attaching the information which describes currents at different depths. What would be the best way to translate it into HydroDyn file sub-surface and near-surface currents?
In this data the current direction is understood as ‘going towards’ the direction specified in the table. Current with 0 degrees direction would be coming from south and moving towards North. 90 degrees would mean the current is coming from the West. And so on.
So if I was to assume my xi axis to point North in OpenFAST, what would I have to put in current direcions to have current going From West to East?

Best Regards,


Dear Bartosz,

Regarding the current direction, HydroDyn uses the same convention as for waves: 0deg current flows along the X-axis and 90eg current flows along the Y-axis. In your case, where X = North, East = -Y, so, you’d have to specify a current direction of -90deg to flow East (along -Y).

Otherwise, you’ll need to fit your current data with depth to one of the built-in models or use the UserCurrent() SUBROUTINE to define your own current profile (requiring a recompile of OpenFAST). The built-in models include subsurface (power law profile), near surface (linear profile decreasing to zero at some depth), and depth-indenpendent (uniform profile with depth). None of the built-in models have depth-varying direction (current veer), so, if you want that or a more customized current profile, you’ll need to use UserCurrent().

Best regards,