# swak4Foam - Possible to sum across different patches?

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 September 16, 2013, 09:35 swak4Foam - Possible to sum across different patches? #1 Senior Member   Anne Gerdes Join Date: Aug 2010 Location: Hamburg Posts: 154 Rep Power: 7 Dear Foamers, I hope this question doesn't already exist in the forum. I would like to calculate an average value which should be evaluated over different patches. Is it possible to do this with swak4foam? Furthermore I would like to compute the difference on each patch to this (global) average value. So far I am able to evaluate the expressions seperately, i.e. I am computing the average value on patch1, compute the difference of my variable (temperature) to this value on patch 1, and I am doing the same for the other patches. It would be great if I could compute an expression like this HTML Code: gAv= \sum_{Outlet j} \sum{i \in Outlet_j} T_i A_i /A(Outlet j) and compute the difference at each patch seperately HTML Code: \sum_{i \in Outlet j} (T_i A_i - gAv) I hope that this is understandable. Thank you very much in advance for an answer or sharing your experiences. Kind Regards Anne

September 16, 2013, 15:41
#2
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Bernhard Gschaider
Join Date: Mar 2009
Posts: 3,915
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Quote:
 Originally Posted by Anne Lincke Dear Foamers, I hope this question doesn't already exist in the forum. I would like to calculate an average value which should be evaluated over different patches. Is it possible to do this with swak4foam? Furthermore I would like to compute the difference on each patch to this (global) average value. So far I am able to evaluate the expressions seperately, i.e. I am computing the average value on patch1, compute the difference of my variable (temperature) to this value on patch 1, and I am doing the same for the other patches. It would be great if I could compute an expression like this HTML Code: gAv= \sum_{Outlet j} \sum{i \in Outlet_j} T_i A_i /A(Outlet j) and compute the difference at each patch seperately HTML Code: \sum_{i \in Outlet j} (T_i A_i - gAv) I hope that this is understandable. Thank you very much in advance for an answer or sharing your experiences. Kind Regards Anne
Yep. It is possible with external variables. Assuming you have tow patches called here and there
Code:
variables (
"sumHere{here}=sum(T*area());"
"sumThere{there}=sum(T*area());"
"areaHere{here}=sum(area());"
"areaThere{there}=sum(area());"
"totalAverage=(sumHere+sumThere)/(areaHere+areaThere);"
);
then use the totalAverage in the expression you're actually calculating. If you're only working on patch here you could leave out the {here} but the way it is written above it should work for both patches and you can save yourself some typing with the dictionary-include.
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 September 17, 2013, 03:27 #3 Senior Member   Anne Gerdes Join Date: Aug 2010 Location: Hamburg Posts: 154 Rep Power: 7 Dear Bernhard, thank you very much for the fast reply! I will try to make this evaluation run with your instructions as soon as possible. Best Regards Anne

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