I got confused by two definitions. I read the manual and I have a question:

when we have a normal velocity and want to find its x and y components we write uN.x=ux and uN.y=uy ?
when we have x and y components ux and uy and want to find normal velocity what should we write?

Hello
The previous anwser was about computing the derivative in the normal direction but I’m not sur this is what you asked.
If you simply want the normal component of a field [ux,uy] then this should be simply