Hi Vatslav, Assuming your pipe is radius R, centered at x=y=0, then: rr = (x/R)**2 + (y/R)**2 uz = 1-rr should work for axial. For the radial that you prescribe, ux = x ! = r cos theta = sqrt(rr)*(x/r) = x uy = y Paul ________________________________ From: [email protected] [[email protected]] on behalf of [email protected] [[email protected]] Sent: Friday, November 11, 2016 1:54 AM To: [email protected] Subject: [Nek5000-users] Boundary condition on velocity Hi, neks. I am trying to simulate a 3d pipe, fluid flows along z. And I need an inflow boundary condition on velocity on forming of cylinder. How I can set a radial velocity in userbc (Vr = sqrt( vx**2+vy**2 ) ) ? I need to set Vr and dVr/dr. Thank you so mach Vatslav