# Boundary Condition

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 January 29, 2012, 08:03 Boundary Condition #1 New Member   Kyounghwa Kim Join Date: Jan 2012 Posts: 9 Rep Power: 7 Sponsored Links Hello. I have a question. I'm reading the paper. This is "Application of a Fractional-step Method to Incompressible Navier-Stokes Equations" of Kim and Moin. They introduced two Boundary Conditions of U^hat. One is U^hat=U^n+1. The other is U^hat=U^n+1+dt*G(phi^n). But, I don't understand the latter case. Since G(phi^n)*dt=U^oldhat - U^n, U^hat=U^n+1+dt*G(phi^n)=U^n+1+U^oldhat - U^n. Thus, U^hat=U^oldhat. Because, U^n+1- U^n=0 on the boundary. Then, what is U^oldhat? I can't compute U^oldhat on the boundary. Please, help me. What's wrong? ps : 'G' means gradient. 'hat' is about velocity.

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