[cfd@kgp]

Dear fgarita,

Thanks for your quick reply.

But the problem was generic, I wanted to multiply 32.0 and again divide by the square of temperature.

my full requirement is,

magSqrGradTinto2
 {  type expressionField;
 outputControl outputTime;
variables (
            "myscalar=32.0;"
            "sqrT=(pow(T,2.0));"
           // "angle=pi/180*(time()<duration ? time()/duration*maxAngle : maxAngle);"
        );
 outputInterval 1;
 fieldName magSqrGradTinto2;
 expression "(magSqr(snGrad(T))) * myscalar / sqrT";
 autowrite true;
 }

and again a similar error,

Creating expression field magSqrGradTinto2 ...

--> FOAM FATAL ERROR:
Parser Error for driver FieldValueExpressionDriver at "1.21-28" :"syntax error, unexpected scalarID"
"(magSqr(snGrad(T)))*myscalar/sqrT"
^^^^^^^^
----------------------|

Context of the error:


- Driver constructed from scratch
Evaluating expression "(magSqr(snGrad(T)))*myscalar/sqrT"


From function parsingValue
in file lnInclude/CommonValueExpressionDriverI.H at line 1210.

FOAM exiting

it will be great to here some solution about this.

Thanks and regards.

[agustinvo]

Originally Posted by cfd@kgp

Dear fgarita,

Thanks for your quick reply.

But the problem was generic, I wanted to multiply 32.0 and again divide by the square of temperature.

my full requirement is,

magSqrGradTinto2
 {  type expressionField;
 outputControl outputTime;
variables (
            "myscalar=32.0;"
            "sqrT=(pow(T,2.0));"
           // "angle=pi/180*(time()<duration ? time()/duration*maxAngle : maxAngle);"
        );
 outputInterval 1;
 fieldName magSqrGradTinto2;
 expression "(magSqr(snGrad(T))) * myscalar / sqrT";
 autowrite true;
 }

and again a similar error,


it will be great to here some solution about this.

Thanks and regards.

Hi

I think this error can be related with the way you declare the variables. since you have two lines of declaring variables, try to put after "variables" and the first bracket "(" a "2"

[cfd@kgp]

Originally Posted by agustinvo

Hi

I think this error can be related with the way you declare the variables. since you have two lines of declaring variables, try to put after "variables" and the first bracket "(" a "2"

Thanks Agustinvo!

But I could not precisely follow your suggestion "try to put after "variables" and the first bracket "(" a "2""

could you please elaborate?

[agustinvo]

Originally Posted by cfd@kgp

Thanks Agustinvo!

But I could not precisely follow your suggestion "try to put after "variables" and the first bracket "(" a "2""

could you please elaborate?

Hi

something like this:

variables 2 (             "myscalar=32.0;"             "sqrT=(pow(T,2.0));"            // "angle=pi/180*(time()<duration ? time()/duration*maxAngle : maxAngle);"         );

[cfd@kgp]

Originally Posted by agustinvo

Hi

something like this:

variables 2 (             "myscalar=32.0;"             "sqrT=(pow(T,2.0));"            // "angle=pi/180*(time()<duration ? time()/duration*maxAngle : maxAngle);"         );

Thanks Agustinvo!

I tried your suggestion, it does not help. infact in the expression direct operation of multiplication by 2.0 or infact any other number also fails...

[cfd@kgp]

As it was pointed out by Bernhard in #7
"grad is not available on patches (simply because OF doesn't have it). snGrad is."

I suggest for internalFields snGrad is not available, and grad work smootly.

[gschaider]

Originally Posted by cfd@kgp

Dear fgarita,

Thanks for your quick reply.

But the problem was generic, I wanted to multiply 32.0 and again divide by the square of temperature.

my full requirement is,

magSqrGradTinto2
 {  type expressionField;
 outputControl outputTime;
variables (
            "myscalar=32.0;"
            "sqrT=(pow(T,2.0));"
           // "angle=pi/180*(time()<duration ? time()/duration*maxAngle : maxAngle);"
        );
 outputInterval 1;
 fieldName magSqrGradTinto2;
 expression "(magSqr(snGrad(T))) * myscalar / sqrT";
 autowrite true;
 }

and again a similar error,


it will be great to here some solution about this.

Thanks and regards.

The problem is that by default internalField calculates on the cells. And myScalar is therefor a cell-field. snGrad(T) produces a face-field and therefor all subsequent calculations with it are face-values. To combine with a constant value you'll have make that value a face-value. With "interpolate(myscalar/sqrT)".

A bit more about that can be found in the incomplete reference guide with the sources. Look for "native" and "secondary structures" and "Functions that interpolate"

[cfd@kgp]

Originally Posted by gschaider

The problem is that by default internalField calculates on the cells. And myScalar is therefor a cell-field. snGrad(T) produces a face-field and therefor all subsequent calculations with it are face-values. To combine with a constant value you'll have make that value a face-value. With "interpolate(myscalar/sqrT)".

A bit more about that can be found in the incomplete reference guide with the sources. Look for "native" and "secondary structures" and "Functions that interpolate"

Thanks gschaider! Information shared is certainly useful...

I will try snGrad along with the interpolate function.

One quick question--> grad() operator calculated gradient by which method? --Guass, least square, etc. can we specify it?

[gschaider]

Originally Posted by cfd@kgp

Thanks gschaider! Information shared is certainly useful...

I will try snGrad along with the interpolate function.

One quick question--> grad() operator calculated gradient by which method? --Guass, least square, etc. can we specify it?

swak4Foam just calls fvc::grad(). Which scheme that function uses is determined by system/fvSchemes

If you want to experiment with discretization schemes: there is a Plugin-Function-Library swakFvcSchemesFunctionPlugin that extends the internalField-parser with a number of functions where you can explicitely choose the discretization scheme for grad() and friends

[cfd@kgp]

Originally Posted by gschaider

swak4Foam just calls fvc::grad(). Which scheme that function uses is determined by system/fvSchemes

If you want to experiment with discretization schemes: there is a Plugin-Function-Library swakFvcSchemesFunctionPlugin that extends the internalField-parser with a number of functions where you can explicitely choose the discretization scheme for grad() and friends

Thanks Bernhard!

[cfd@kgp]

Dear Bernhard ,

One more swakExpression gives error while run-time,
[CODE
uysqr
{
aliases {
myfl sMS1:alpha1; //
}
type swakExpression;
valueType cellZone;
zoneName solid; // or whatever is your zoneName
accumulations (
min
);

expression "sum(myfl*(U.y*U.y)*vol())/sum(myfl*1.0*vol())"; // expression "sum((U.y*U.y)*vol()*myfl)/sum(vol()*myfl)";
verbose true;
//outputControlMode timestep
}
[/CODE]

There is no error "sum(myfl*(U.y*U.y)*vol())/sum(vol())" but it crashes with the following error for "sum(myfl*(U.y*U.y)*vol())/sum(myfl*1.0*vol())"

Expression uysqr : #0 Foam::error::printStack(Foam::Ostream&) at ??:?
#1 Foam::sigFpe::sigHandler(int) at ??:?
#2 ? in "/opt/openfoam30/platforms/linuxGccDPInt32Opt/lib/libOpenFOAM.so"
#3 Foam::divide(Foam::Field<double>&, Foam::UList<double> const&, Foam::UList<double> const&) at ??:?
#4 Foam::operator/(Foam::UList<double> const&, Foam::UList<double> const&) at ??:?
#5 parserSubset::SubsetValueExpressionParser::parse() at SubsetValueExpressionParser.yy.C:?
#6 Foam::SubsetValueExpressionDriver::parseInternal(i nt) at ??:?
#7 Foam::CommonValueExpressionDriver::parse(Foam::exp rString const&, Foam::word const&) at ??:?
#8 Foam::swakExpressionFunctionObject::write() at ??:?
#9 Foam::simpleFunctionObject::execute(bool) at ??:?
#10 Foam::functionObjectList::execute(bool) at ??:?
#11 Foam::Time::run() const at ??:?
#12 ? at ??:?
#13 __libc_start_main in "/lib/i386-linux-gnu/libc.so.6"
#14 ? at ??:?

here myfl is a volscalar field at the cell-centre and vol() scalar firld is also defined at the cell-centres.
Please give your expert opinion..:confused::confused:

Thanks and regards,

[cfd@kgp]

Originally Posted by gschaider

swak4Foam just calls fvc::grad(). Which scheme that function uses is determined by system/fvSchemes

If you want to experiment with discretization schemes: there is a Plugin-Function-Library swakFvcSchemesFunctionPlugin that extends the internalField-parser with a number of functions where you can explicitely choose the discretization scheme for grad() and friends

Dear Bernhard,

Please answer my query in post #31.

I am eagerly waiting to hear from you.

Thank,

[Zeppo]

Looks like you've got division by zero here:

sum(myfl*1.0*vol())

Check your myfl

[cfd@kgp]

Originally Posted by Zeppo

Looks like you've got division by zero here:

sum(myfl*1.0*vol())

Check your myfl

Many thanks Zeppo!