CFD Online Discussion Forums - [swak4Foam] is it possible to exclude some faces in calculating an expression on a patch in SWAK?

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- - [swak4Foam] is it possible to exclude some faces in calculating an expression on a patch in SWAK? (https://www.cfd-online.com/Forums/openfoam-community-contributions/122028-possible-exclude-some-faces-calculating-expression-patch-swak.html)

is it possible to exclude some faces in calculating an expression on a patch in SWAK?

Hi
in Swak postProcessing function below:

Code:

totalPressure_left

       {

        type swakExpression;

        valueType patch;

        patchName left;

        accumulations (

            average

        );

        variables (

            "gamma=1.4;"

            "R=287.14;"

        );

        expression "sum(p*(pow(1+(gamma-1)/2*magSqr(U)/(gamma*R*T),(gamma/(gamma-1))))*rho*area())/sum(rho*area())";

        verbose true;

        outputControlMode outputTime;

        outputInterval 1;

       }

I want to exclude the faces on patch that have U.y=-78.how can I write this in expression? is using "?" operator correct? then what should be written after ":" operator?
thanks.

if I implement something like:

Code:

totalPressure_left

       {

        type swakExpression;

        valueType patch;

        patchName left;

        accumulations (

            average

        );

        variables (

            "gamma=1.4;"

            "R=287.14;"

        );

        expression "(U.x != 0) ? sum(p*(pow(1+(gamma-1)/2*magSqr(U)/(gamma*R*T),(gamma/(gamma-1))))*rho*area())/sum(rho*area()) : ";

        verbose true;

        outputControlMode outputTime;

        outputInterval 1;

       }

is it true?then how calculating is doing by this condition(if I don't want cells with zero x velocity have role in the expression)?

Quote:

Originally Posted by immortality (Post 444909)

if I implement something like:

Code:

totalPressure_left

       {

        type swakExpression;

        valueType patch;

        patchName left;

        accumulations (

            average

        );

        variables (

            "gamma=1.4;"

            "R=287.14;"

        );

        expression "(U.x != 0) ? sum(p*(pow(1+(gamma-1)/2*magSqr(U)/(gamma*R*T),(gamma/(gamma-1))))*rho*area())/sum(rho*area()) : ";

        verbose true;

        outputControlMode outputTime;

        outputInterval 1;

       }

is it true?then how calculating is doing by this condition(if I don't want cells with zero x velocity have role in the expression)?

You need another expression after the : (Probably "0"). But average won't give the value you'd expect. So you'll have to work with an indicator variable

Hi dear Bernhard
could you please explain a bit about what do you mean by indicator variable after ":" ?
would you give me an example?
what should I do exactly to do that?
thanks.

Quote:

Originally Posted by immortality (Post 445054)

Hi dear Bernhard
could you please explain a bit about what do you mean by indicator variable after ":" ?
would you give me an example?
what should I do exactly to do that?
thanks.

a. You'll need a variable that indicates whether a face takes part in the average
b. Based on that variable you'll have to calculate the area/nr of the patches that are used. Later divide the sum by this to get a valid average
c. what I mean was that in "a ? b : c" you can't leave out the c the way you did

Bottom line: if you need the average of only a part of the cells you'll have to do some work yourself. But it's not to hard.

thanks dear Bernhard but there is a doubt about sum.sum function gives an average of all faces on patch then if I divide it to the desired faces areas how it lead to a acceptable result? could clarify more please? thanks.

Quote:

Originally Posted by immortality (Post 445251)

Just sum over a value that is 0 for the undesired faces. The same as you do over the face areas. I really don't think that the MessageBoard is the forum for explaining the concept of a "weighted sum".

sum(value*area()*indicator)/sum(area()*indicator)

That is really first semester mathematics

thanks dear Bernhard. I know weighted average but the value I want(total pressure) isn't zero on unwanted faces,can do something in this situation in your opinion?
--------------------------------------------------------------
I think it can be done like this:

Code:

indicator=(U.x)!=0;

sum(p0*rho*area()*indicator)/sum(rho*area()*indicator);

is it true dear Bernhard?
does Boolean variable indicator could be recognized in postProcessing Swak functions like groovyBC?
---------------------------
one thing occurred that when indicator is zero on all the faces then the expression will be 0/0,how can overcome this issue?maybe by a condition operetor "?" that sum(indicator)!=0 ? expression:0;
then it becomes

Code:

indicator=(U.x)!=0;

sum(indicator)!=0 ? sum(p0*rho*area()*indicator)/sum(rho*area()*indicator) : 0;

is it true now?

Hi
this error occurred.what maybe mean it?I think the conditional expression seems be true.what has caused the error?

Code:

Time = 0.00933193



diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0

diagonal:  Solving for rhoUx, Initial residual = 0, Final residual = 0, No Iterations 0

diagonal:  Solving for rhoUy, Initial residual = 0, Final residual = 0, No Iterations 0

smoothSolver:  Solving for Ux, Initial residual = 2.9533107882475e-05, Final residual = 4.2967271628453e-17, No Iterations 2

smoothSolver:  Solving for Uy, Initial residual = 8.0832933323101e-05, Final residual = 4.5628728437651e-17, No Iterations 2

diagonal:  Solving for rhoE, Initial residual = 0, Final residual = 0, No Iterations 0

smoothSolver:  Solving for h, Initial residual = 1.522803139063e-06, Final residual = 3.2095933944988e-14, No Iterations 1

time step continuity errors : sum local = 1.1240866522131e-18, global = -5.1806902584343e-20, cumulative = 8.2541483939109e-20

smoothSolver:  Solving for omega, Initial residual = 0.00011915535218725, Final residual = 7.4211337852284e-16, No Iterations 5

smoothSolver:  Solving for k, Initial residual = 0.0001685515398489, Final residual = 1.868800540843e-15, No Iterations 5

smoothSolver:  Solving for gas, Initial residual = 4.9588347286066e-06, Final residual = 5.869001155104e-13, No Iterations 1

ExecutionTime = 20.3 s  ClockTime = 22 s



faceSource massflow_left output:

sum(left) for phi = -0.00016110414104695



[1] [3]

[3]

[3] --> FOAM FATAL ERROR:

[3]  Parser Error for driver PatchValueExpressionDriver at "1.14" :"syntax error, unexpected ')', expecting '?' or TOKEN_OR or TOKEN_AND"

"sum(indicator)!=0 ? sum(p0*rho*area()*indicator)/sum(rho*area()*indicator) : 0"

^

---------------|



Context of the error:





- From dictionary: IOstream.functions.totalPressure_left

Evaluating expression "sum(indicator)!=0 ? sum(p0*rho*area()*indicator)/sum(rho*area()*indicator) : 0"

[3]

[3]

[3]     From function parsingValue

[3]     in file

[1]

[1] [2]

Expression totalPressure_left : --> FOAM FATAL ERROR:

[1]  Parser Error for driver PatchValueExpressionDriver at "1.14" :"syntax error, unexpected ')', expecting '?' or TOKEN_OR or TOKEN_AND"

"sum(indicator)!=0 ? sum(p0*rho*area()*indicator)/sum(rho*area()*indicator) : 0"

^

---------------|



Context of the error:





- From dictionary: IOstream.functions.totalPressure_left

Evaluating expression "sum(indicator)!=0 ? sum(p0*rho*area()*indicator)/sum(rho*area()*indicator) : 0"

[1]

[1]

[1]     From function parsingValue[0] [2]

[2] --> FOAM FATAL ERROR:

[2]

[0]  Parser Error for driver PatchValueExpressionDriver at "1.14" :"syntax error, unexpected ')', expecting '?' or TOKEN_OR or TOKEN_AND"

"sum(indicator)!=0 ? sum(p0*rho*area()*indicator)/sum(rho*area()*indicator) : 0"

^

---------------|

I wrote

Code:

indicator=(U.x)!=0 ? 1 : 0;

and previous error seems has solved then it seems Boolean variables doesn't work in postProcessing SWAK function,I'll report if you verify.
but now another error has occurred about dividing by zero in expression while I had anticipated and set a condition for that but it occurred despite of the condition on the denominator.

Code:

diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0

diagonal:  Solving for rhoUx, Initial residual = 0, Final residual = 0, No Iterations 0

diagonal:  Solving for rhoUy, Initial residual = 0, Final residual = 0, No Iterations 0

smoothSolver:  Solving for Ux, Initial residual = 2.9533107882475e-05, Final residual = 4.2967271628453e-17, No Iterations 2

smoothSolver:  Solving for Uy, Initial residual = 8.0832933323101e-05, Final residual = 4.5628728437651e-17, No Iterations 2

diagonal:  Solving for rhoE, Initial residual = 0, Final residual = 0, No Iterations 0

smoothSolver:  Solving for h, Initial residual = 1.522803139063e-06, Final residual = 3.2095933944988e-14, No Iterations 1

time step continuity errors : sum local = 1.1240866522131e-18, global = -5.1806902584343e-20, cumulative = 8.2541483939109e-20

smoothSolver:  Solving for omega, Initial residual = 0.00011915535218725, Final residual = 7.4211337852284e-16, No Iterations 5

smoothSolver:  Solving for k, Initial residual = 0.0001685515398489, Final residual = 1.868800540843e-15, No Iterations 5

smoothSolver:  Solving for gas, Initial residual = 4.9588347286066e-06, Final residual = 5.869001155104e-13, No Iterations 1

ExecutionTime = 20.06 s  ClockTime = 22 s



faceSource massflow_left output:

sum(left) for phi = -0.00016110414104695



Expression totalPressure_left :  average=931179.89871181

Expression totalTemperature_left :  average=1251.9731758588

Expression totalEnthalpy_left :  average=1038600.1239856

faceSource massflow_right output:

sum(right) for phi = 0



[3] #0  Foam::error::printStack(Foam::Ostream&) in "/opt/openfoam220/platforms/linux64GccDPOpt/lib/libOpenFOAM.so"

[3] #1  Foam::sigFpe::sigHandler(int) in "/opt/openfoam220/platforms/linux64GccDPOpt/lib/libOpenFOAM.so"

[3] #2   in "/lib/x86_64-linux-gnu/libc.so.6"

[3] #3  Foam::divide(Foam::Field<double>&, Foam::UList<double> const&, Foam::UList<double> const&) in "/opt/openfoam220/platforms/linux64GccDPOpt/lib/libOpenFOAM.so"

[3] #4  Foam::operator/(Foam::UList<double> const&, Foam::UList<double> const&) in "/opt/openfoam220/platforms/linux64GccDPOpt/lib/libOpenFOAM.so"

[3] #5  parserPatch::PatchValueExpressionParser::parse() in "/home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/lib/libswak4FoamParsers.so"

[3] #6  Foam::PatchValueExpressionDriver::parseInternal(int) in "/home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/lib/libswak4FoamParsers.so"

[3] #7  Foam::CommonValueExpressionDriver::parse(std::string const&, Foam::word const&) in "/home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/lib/libswak4FoamParsers.so"

[3] #8  Foam::swakExpressionFunctionObject::write() in "/home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/lib/libsimpleSwakFunctionObjects.so"

[3] #9  Foam::simpleFunctionObject::execute(bool) in "/home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/lib/libsimpleFunctionObjects.so"

[3] #10  Foam::functionObjectList::execute(bool) in "/opt/openfoam220/platforms/linux64GccDPOpt/lib/libOpenFOAM.so"

[3] #11  Foam::Time::run() const in "/opt/openfoam220/platforms/linux64GccDPOpt/lib/libOpenFOAM.so"

[3] #12

[3]  in "/home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/bin/rhoCentralFoamGasCont"

[3] #13  __libc_start_main in "/lib/x86_64-linux-gnu/libc.so.6"

[3] #14

[3]  in "/home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/bin/rhoCentralFoamGasCont"

[Ehsan-com:05814] *** Process received signal ***

[Ehsan-com:05814] Signal: Floating point exception (8)

[Ehsan-com:05814] Signal code:  (-6)

[Ehsan-com:05814] Failing at address: 0x3e8000016b6

[Ehsan-com:05814] [ 0] /lib/x86_64-linux-gnu/libc.so.6(+0x36460) [0x7fe65973f460]

[Ehsan-com:05814] [ 1] /lib/x86_64-linux-gnu/libc.so.6(gsignal+0x35) [0x7fe65973f3e5]

[Ehsan-com:05814] [ 2] /lib/x86_64-linux-gnu/libc.so.6(+0x36460) [0x7fe65973f460]

[Ehsan-com:05814] [ 3] /opt/openfoam220/platforms/linux64GccDPOpt/lib/libOpenFOAM.so(_ZN4Foam6divideERNS_5FieldIdEERKNS_5UListIdEES6_+0x9f) [0x7fe65a8e4def]

[Ehsan-com:05814] [ 4] /opt/openfoam220/platforms/linux64GccDPOpt/lib/libOpenFOAM.so(_ZN4FoamdvERKNS_5UListIdEES3_+0x62) [0x7fe65a8e7a82]

[Ehsan-com:05814] [ 5] /home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/lib/libswak4FoamParsers.so(_ZN11parserPatch26PatchValueExpressionParser5parseEv+0x19b5a) [0x7fe64af81e7a]

[Ehsan-com:05814] [ 6] /home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/lib/libswak4FoamParsers.so(_ZN4Foam26PatchValueExpressionDriver13parseInternalEi+0x39) [0x7fe64b037c99]

[Ehsan-com:05814] [ 7] /home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/lib/libswak4FoamParsers.so(_ZN4Foam27CommonValueExpressionDriver5parseERKSsRKNS_4wordE+0x61) [0x7fe64afef831]

[Ehsan-com:05814] [ 8] /home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/lib/libsimpleSwakFunctionObjects.so(_ZN4Foam28swakExpressionFunctionObject5writeEv+0x63) [0x7fe64a7cf453]

[Ehsan-com:05814] [ 9] /home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/lib/libsimpleFunctionObjects.so(_ZN4Foam20simpleFunctionObject7executeEb+0xe0) [0x7fe64a453b90]

[Ehsan-com:05814] [10] /opt/openfoam220/platforms/linux64GccDPOpt/lib/libOpenFOAM.so(_ZN4Foam18functionObjectList7executeEb+0x59) [0x7fe65a726f49]

[Ehsan-com:05814] [11] /opt/openfoam220/platforms/linux64GccDPOpt/lib/libOpenFOAM.so(_ZNK4Foam4Time3runEv+0xb0) [0x7fe65a732250]

[Ehsan-com:05814] [12] /home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/bin/rhoCentralFoamGasCont() [0x421876]

[Ehsan-com:05814] [13] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xed) [0x7fe65972a30d]

[Ehsan-com:05814] [14] /home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/bin/rhoCentralFoamGasCont() [0x42bb0d]

[Ehsan-com:05814] *** End of error message ***

--------------------------------------------------------------------------

mpirun noticed that process rank 3 with PID 5814 on node Ehsan-com exited on signal 8 (Floating point exception).

--------------------------------------------------------------------------



gnuplot> set terminal png small color



gnuplot> set terminal png small color

                                                         ^

       ^

         line 0: invalid color spec, must be xRRGGBB



         line 0: invalid color spec, must be xRRGGBB





gnuplot> set terminal png small color

                                ^

         line 0: invalid color spec, must be xRRGGBB



Killing PID 5807

 PyFoam WARNING on line 232 of file /usr/local/lib/python2.7/dist-packages/PyFoam/Execution/FoamThread.py : Process 5807 was already dead

I think in expression

Code:

"sum(indicator)!=0.0 ? sum(p0*rho*area()*indicator)/sum(rho*area()*indicator) : 0.0";

even if the condition be false the first expression is calculated and is 0/0 that leads to the error.is my conclusion true?

Quote:

Originally Posted by immortality (Post 445793)

I wrote

Code:

indicator=(U.x)!=0 ? 1 : 0;

Code:

Expression totalPressure_left :  average=931179.89871181

Expression totalTemperature_left :  average=1251.9731758588

Expression totalEnthalpy_left :  average=1038600.1239856

faceSource massflow_right output:

sum(right) for phi = 0



[3] #0  Foam::error::printStack(Foam::Ostream&) in "/opt/openfoam220/platforms/linux64GccDPOpt/lib/libOpenFOAM.so"

[3] #1  Foam::sigFpe::sigHandler(int) in "/opt/openfoam220/platforms/linux64GccDPOpt/lib/libOpenFOAM.so"

[3] #2   in "/lib/x86_64-linux-gnu/libc.so.6"

[3] #3  Foam::divide(Foam::Field<double>&, Foam::UList<double> const&, Foam::UList<double> const&) in "/opt/openfoam220/platforms/linux64GccDPOpt/lib/libOpenFOAM.so"

[3] #4  Foam::operator/(Foam::UList<double> const&, Foam::UList<double> const&) in "/opt/openfoam220/platforms/linux64GccDPOpt/lib/libOpenFOAM.so"

[3] #5  parserPatch::PatchValueExpressionParser::parse() in "/home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/lib/libswak4FoamParsers.so"

[3] #6  Foam::PatchValueExpressionDriver::parseInternal(int) in "/home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/lib/libswak4FoamParsers.so"

[3] #7  Foam::CommonValueExpressionDriver::parse(std::string const&, Foam::word const&) in "/home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/lib/libswak4FoamParsers.so"

[3] #8  Foam::swakExpressionFunctionObject::write() in "/home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/lib/libsimpleSwakFunctionObjects.so"

[3] #9  Foam::simpleFunctionObject::execute(bool) in "/home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/lib/libsimpleFunctionObjects.so"

[3] #10  Foam::functionObjectList::execute(bool) in "/opt/openfoam220/platforms/linux64GccDPOpt/lib/libOpenFOAM.so"

[3] #11  Foam::Time::run() const in "/opt/openfoam220/platforms/linux64GccDPOpt/lib/libOpenFOAM.so"

[3] #12

[3]  in "/home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/bin/rhoCentralFoamGasCont"

[3] #13  __libc_start_main in "/lib/x86_64-linux-gnu/libc.so.6"

[3] #14

[3]  in "/home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/bin/rhoCentralFoamGasCont"

[Ehsan-com:05814] *** Process received signal ***

[Ehsan-com:05814] Signal: Floating point exception (8)

[Ehsan-com:05814] Signal code:  (-6)

[Ehsan-com:05814] Failing at address: 0x3e8000016b6

[Ehsan-com:05814] [ 0] /lib/x86_64-linux-gnu/libc.so.6(+0x36460) [0x7fe65973f460]

[Ehsan-com:05814] [ 1] /lib/x86_64-linux-gnu/libc.so.6(gsignal+0x35) [0x7fe65973f3e5]

[Ehsan-com:05814] [ 2] /lib/x86_64-linux-gnu/libc.so.6(+0x36460) [0x7fe65973f460]

[Ehsan-com:05814] [ 3] /opt/openfoam220/platforms/linux64GccDPOpt/lib/libOpenFOAM.so(_ZN4Foam6divideERNS_5FieldIdEERKNS_5UListIdEES6_+0x9f) [0x7fe65a8e4def]

[Ehsan-com:05814] [ 4] /opt/openfoam220/platforms/linux64GccDPOpt/lib/libOpenFOAM.so(_ZN4FoamdvERKNS_5UListIdEES3_+0x62) [0x7fe65a8e7a82]

[Ehsan-com:05814] [ 5] /home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/lib/libswak4FoamParsers.so(_ZN11parserPatch26PatchValueExpressionParser5parseEv+0x19b5a) [0x7fe64af81e7a]

[Ehsan-com:05814] [ 6] /home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/lib/libswak4FoamParsers.so(_ZN4Foam26PatchValueExpressionDriver13parseInternalEi+0x39) [0x7fe64b037c99]

[Ehsan-com:05814] [ 7] /home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/lib/libswak4FoamParsers.so(_ZN4Foam27CommonValueExpressionDriver5parseERKSsRKNS_4wordE+0x61) [0x7fe64afef831]

[Ehsan-com:05814] [ 8] /home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/lib/libsimpleSwakFunctionObjects.so(_ZN4Foam28swakExpressionFunctionObject5writeEv+0x63) [0x7fe64a7cf453]

[Ehsan-com:05814] [ 9] /home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/lib/libsimpleFunctionObjects.so(_ZN4Foam20simpleFunctionObject7executeEb+0xe0) [0x7fe64a453b90]

[Ehsan-com:05814] [10] /opt/openfoam220/platforms/linux64GccDPOpt/lib/libOpenFOAM.so(_ZN4Foam18functionObjectList7executeEb+0x59) [0x7fe65a726f49]

[Ehsan-com:05814] [11] /opt/openfoam220/platforms/linux64GccDPOpt/lib/libOpenFOAM.so(_ZNK4Foam4Time3runEv+0xb0) [0x7fe65a732250]

[Ehsan-com:05814] [12] /home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/bin/rhoCentralFoamGasCont() [0x421876]

[Ehsan-com:05814] [13] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xed) [0x7fe65972a30d]

[Ehsan-com:05814] [14] /home/ehsan/OpenFOAM/ehsan-2.2.0/platforms/linux64GccDPOpt/bin/rhoCentralFoamGasCont() [0x42bb0d]

[Ehsan-com:05814] *** End of error message ***

--------------------------------------------------------------------------

mpirun noticed that process rank 3 with PID 5814 on node Ehsan-com exited on signal 8 (Floating point exception).

--------------------------------------------------------------------------

I think in expression

Code:

"sum(indicator)!=0.0 ? sum(p0*rho*area()*indicator)/sum(rho*area()*indicator) : 0.0";

even if the condition be false the first expression is calculated and is 0/0 that leads to the error.is my conclusion true?

You want to sum up a field which is either 0 or another value depending on an indicator (condition). So you have to have the ?: inside the sum.

Please: sit down with a piece of paper. Write down in mathematical terms what you want to do. Especially the sums. Then implement that. Or write down the formula you just implemented in mathematical terms.

thanks dear Bernhard
I wrote this before I read your post:

Code:

variables (

            "gamma=1.34;"

            "R=287.14;"

            "p0=p*(pow(1+(gamma-1)/2*magSqr(U)/(gamma*R*T),(gamma/(gamma-1))));"

            "indicator=(U.x) !=0.0 ? 1.0 : 0.0;"

            "n_faces=sum(indicator);"

        );

        expression "sum(p0*rho*area()*indicator)/(n_faces!=0.0 ? sum(rho*area()*indicator):1.0)";

and see my approach is true according to your opinion.I'm testing it and tell you the result when run done.

Hi dear Bernhard
it's working fine and this is a part of results for instance.thanks a lot for advice.

Quote:

You want to sum up a field which is either 0 or another value depending on an indicator (condition)

the field total pressure is a always positive(non zero) value.does it have any effect?

Quote:

I think in expression
Code:
"sum(indicator)!=0.0 ? sum(p0*rho*area()*indicator)/sum(rho*area()*indicator) : 0.0";
even if the condition be false the first expression is calculated and is 0/0 that leads to the error.is my conclusion true?

is my conclusion true about the problem that existed before?

Code:

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           0.00974193                    0

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           0.00974393                    0

           0.00974493                    0

           0.00974593                    0

           0.00974693      414795.85022427

           0.00974793      489127.77079362

           0.00974893      472354.87446518

           0.00974993      482980.41909857

           0.00975093      494396.69083149

           0.00975193      482668.24744863

           0.00975293      498096.79130297

           0.00975393      505365.79868396

           0.00975493      495282.94955258

           0.00975593      494496.16003915

           0.00975693      501671.61352294

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           0.00975893      502646.98502813

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           0.00976193      477714.51069725

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           0.00976393       459876.5015917

           0.00976493      458529.81644997

           0.00976593       454067.8936771

           0.00976693      443300.43927585

           0.00976793      444404.06857093

           0.00976893      442221.55475606

           0.00976993      437269.13737899

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           0.00977193       425775.8593933

           0.00977293        426494.565387

           0.00977393      420896.47405805

           0.00977493      409250.91511963

           0.00977593      408500.35547509

           0.00977693      401335.77795219

           0.00977793      403805.09654604

           0.00977893        395448.226802

           0.00977993      394032.47412188

           0.00978093       387114.7456731

           0.00978193      384717.75851883

           0.00978293      382704.63340763

           0.00978393      379050.09920179

           0.00978493      373321.53130754

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           0.00978693      365658.79864664

           0.00978793      362175.43849012

           0.00978893      358684.35934306

           0.00978993      355910.32026514

           0.00979093      352661.24884802

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           0.00979893      333837.54800648

           0.00979993      332881.48561233

           0.00980093      332510.03460048

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