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November 22, 2011, 04:57 
Convergence/Residual calculation

#1 
New Member
Miriam
Join Date: Feb 2011
Location: Germany
Posts: 7
Rep Power: 7 
Hello OpenFoamers,
I want to understand what the monitoring Data are to find the problem for the course of my convergencecurves (which is bad). 1) Can someone tell me please what exatctly the initial and final values are? 2) Which equation are the "residuals" from? and another Question 3) Can I let me show the residuals for one vertice? Thanks for answering so far! Carolin 

November 22, 2011, 05:08 

#2 
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Roman Thiele
Join Date: Aug 2009
Location: London, UK
Posts: 368
Rep Power: 13 
Hej
for your residual curves follow this small and easy tutorial by wolfgang Tutorial of how to plot residuals !
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~roman 

November 24, 2011, 10:10 

#3 
New Member
Miriam
Join Date: Feb 2011
Location: Germany
Posts: 7
Rep Power: 7 
Hey Roman,
thanks for the fast reply! Ive looked into the solver equations, but im not really firm with c++. So I still dont understand: 1) Is the plotted value for init/final residual the average value of all solved equations in the mesh or the biggest value? Iam now just thinking of one iteration step, which gives one residual value for init and final for eg p/U/k etc. . Do you know that? Miriam 

November 25, 2011, 04:16 

#4 
Senior Member
Roman Thiele
Join Date: Aug 2009
Location: London, UK
Posts: 368
Rep Power: 13 
The is only one equation per variable (U, p_rgh, T, k, epsilon, ...) solved (which is a matrix equations, so I think you could say that there are many equations). The residual value should be the largest value of the matrix, since averaging would hide the largest value and therefore would hide the convergence in all cells of the mesh.
As for the solvers, take a look at http://www.openfoam.com/docs/user/pr...eOpenFOAM.php The equations are quite easy to under stand that way, because they are kind of written the same way as you would write them on paper.
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~roman 

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