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Attempt of a numerical Navier-Stokes calculation

Posted 10 years ago

I tried to calculate, with NDSolve, numerically the velocity field of the two-dimensional jet; that is, fluid flowing from a hole (actually a slot) in a wall into a patch of fluid initially at rest. Originally, I wanted to post here the notebook; but it came out als FullForm, so it was rather long and (I think) difficult to read. So I attached it. After starting the program, I got several messages; a final one reads:

NDSolveValue::nlnum: The function value {<<1>>} is not a list of numbers with dimensions {675} at {t,p[x,y,t],u[x,y,t],v[x,y,t],(p^(0,0,1))[x,y,t],(u^(0,0,1))[x,y,t],(v^(0,0,1))[x,y,t]} = {0.0001,<<5>>,{{0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.},{0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.},<<12>>,{0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.}}}. >>

Apparently, the error reported with this message prohibited the program from running.

I do not understand the message. Can anybody tell me what type of error possibly happened in the program, and what is to be done to avoid it ? Is it possible to analyze the NDSolve process so that one can explitcitly arrive at the point where the error occurs ?

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POSTED BY: Juergen Piest
2 Replies
Posted 10 years ago

There are two messages "insufficient number of boundary conditions". I tested the problem with Burger's equation for two spacial dimensions; There, these messages appear as well, but don't prohibit the program from running. I don't know whether missing boundary conditions (which of course must be cared for) can lead to the problem announced by the message NDSolve::nlnum.

POSTED BY: Juergen Piest

It's usually better to diagnose a problem from the first warning message, not the last.

POSTED BY: Frank Kampas
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