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-   -   %Error on earth (http://www.cfd-online.com/Forums/phoenics/51142-error-earth.html)

Sukun Kurusathian January 14, 2001 23:40

%Error on earth
 
Dear, I've just use Phoenics 3.3 to simulate hot air flow phenomena in an oven. The result looks good, but during earth calculation, % error was very high. Why % error on earth solver is so high (~1.00e+4)? What does it mean? Thank you very much.

Javier Larrondo January 15, 2001 11:58

Re: %Error on earth
 
Clearly I'm not an expert. But I have noticed the same thing, but fortunately the cases that I have done, even that they have high errors (~10e+05) are good enough to understand the fenomena and the values are in range.

I found an answer in a lecture that is in POLIS, but I don't understand the RESREF value, maybe someone can explain us this.

you can find the lecture in: http://www.simuserve.com/phoenics/d_...s/lec10-22.htm

if you read this lecture the residuals presented in EARTH, are normalized by RESREF.

So, if you have an error or residual (ep) around 0.1 in every cell and you have a case with 10000 cells (~21x21x23) which it's not a big case, so the sum(ep)=10e+03 and normalized by RESREF is the value that appears in EARTH so maybe RESREF is not big enough or of the order of sum(ep), but I don't know the value of RESREF, and that is what I understood from the lecture.

Well, that's all I can say, I hope it will be useful.

Javier L.

PattiMichelle March 2, 2001 13:29

Re: %Error on earth
 
Hello: I have been similarly confused by combustion problems in PHOENICS. When I view the %Error and RES/RESREF plots in Earth, they decrease up to a point, then simply don't converge any more no matter how long I let iterations continue. I have tried increasing and decreasing relaxation but to no avail. Many or most of the library cases WILL converge completely but mine do not. I might mention I am doing combustion simulation with variables H2, O2, OH, HO2, H2O, etc... and these may present ill-formed or stiff problems that simply don't converge completely by numerical methods.

PattiMichelle


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