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Bottom Boundary Conditions I:

Calculate the characteristic derivatives for outgoing characteristics using one-sided derivatives and for incoming characteristics from the physical boundary conditions. Then use the boundary equations (49-52 or 53-56) to determine the time derivatives of the variables. Assume subsonic flow. Then there is always one outgoing wave, one incoming wave and the advection (entropy) wave which switches between incoming and outgoing depending on the normal fluid velocity.

Finally, solve equations (53-56) for the time-derivatives of the conserved variables or equations (49-52) for the time-derivatives of the primitive variables.

Viggo Hansteen
Wed Sep 19 18:16:24 MET DST 2001