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April 18, 2012, 05:29 
Standard deviation for every time step

#1 
New Member
shyam prasad
Join Date: Mar 2009
Posts: 25
Rep Power: 8 
Dear Foamers,
I would like to track the standard deviation of a tracer in the domain with respect to time. The following is what I have appended in the controlDict to get the sum(xixmean)^2. Later I can manipulate this using excel or python to evaluate the standard deviation. Is there any way I can obtain standard deviation in the function objects itself. /***********************************************/ libs ( "libOpenFOAM.so" // keeps paraFoam happy "libtwoPhaseInterfaceProperties.so" "libinterfaceProperties.so" "libsimpleSwakFunctionObjects.so" "libswakFunctionObjects.so" ); functions ( deviation { type swakExpression; valueType internalField; verbose true; expression "(pow((T0.0220541),2))"; accumulations (sum); } ); /************************************************** **/ 

April 18, 2012, 19:05 

#2  
Assistant Moderator
Bernhard Gschaider
Join Date: Mar 2009
Posts: 3,915
Rep Power: 40 
Quote:
Code:
variables ( "Tmean=average(T);" ); expression "pow((TTmean),2)"; accumulations (average); But maybe I misunderstood your question 

April 19, 2012, 00:45 

#3 
New Member
shyam prasad
Join Date: Mar 2009
Posts: 25
Rep Power: 8 
Thanks Bernhard,
Would like to thank you for making swak4Foam available for the openfoam community. functions ( deviation { type swakExpression; valueType internalField; verbose true; expression "(pow((T0.0220541),2))"; accumulations (sum); } ); I want to use the above sum as below sd = pow(sum,0.5)/no. of cells. 

April 19, 2012, 07:39 

#4  
Assistant Moderator
Bernhard Gschaider
Join Date: Mar 2009
Posts: 3,915
Rep Power: 40 
Quote:
As I said in the other posting: arithmetic mean only makes sense if all cells are of the same size (otherwise tiny cells have the same "influence" as big cells) 

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