Confused by normal Nx and Ny

Dear all

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?


as I know, you may proceed with

for, normal component of u along x-direction = dx(u)*N.x

for, normal component of u along y-direction, = dy(u)*N.y

combinely, for a simple normal components on some boundary edge: int1d(Th, label_of_edge) (dx(u)*N.x + dy(u).N.y);

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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

Un = ux * N.x + uy * N.y

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