[zobekenobe]

i have created a solver of my own by simply modifying a tutorial case set-up, after running the case and opening paraview for post processing i cant get to view the new variables.i have created a new a variable T (temp) but i can only see the results of p and U and not T.

how do i solve this problem.

[rudy]

Hi,
I am using Electrostatic solver and in my solution i have got potential and charge density distribution in my domain but now I want to find gradient of the potential distribution(electric field) and I am using "gradient of unstructured dataset" function from parafoam for the purpose but while applying this function in parafoam it stops inbetween and yields the following error:

Generic Warning: In /home/dm2/henry/OpenFOAM/ThirdParty-1.6/paraview-3.6.1/VTK/Common/vtkMath.cxx, line 1645
Unable to factor linear system

can anyone tell me what does it imply and how to solve it.
Thanks,
rudy.

[madad2005]

Even though that error appears, you should still have the gradients right? If you want to compute grad(scalar) then use foamCalc instead.

[zobekenobe]

http://www.cfd-online.com/Forums/ope...tml#post238940...

your solution is somewhere here

[rudy]

To madad2005:
Yes,it gives me the output error messege and also gives the gradient but looking at the result for gradient i have a doubt that it's not correct or may be not computed till end,I don't know but have some reasons to believe it so I want to confirm the result of potential gradient...so I tried using foamCalc,but it doesn't seem to work and rightly so as i think it is meant to give scalar components of vector fields while my variable potential is a scalar and i want to find its gradien...by the way i applied it and got the following messege:

$ foamCalc components phi

but it gives the following error messege:

Create time

Create mesh for time = 0

Time = 0


Unable to process phi
No call to components for fields of type volScalarField



FOAM exiting

I don't exactly know what can i do to get gradient of a scalar field(potential).

To zobekenobe:
Can u be bit more specific please...
i tried to run foamToVTK which worked and then I open parafoam from case dir,but still i get the same solution.I don't know what difference this has made...

thanks to both of u...
rudy

[madad2005]

Yeah, I keep forgetting about that. You'll have to write your own utility to get the grad of a scalar. See these slides by H. Jasak for guidlines how to do so (Walk Through a Post-Utility slides 11/12).

http://powerlab.fsb.hr/ped/kturbo/Op...ngTraining.pdf

You'll be reading a volScalarField and returning a volVectorField. The command for getting the gradient is fvc::grad(<your varname here>) I think. It is usually best to just copy a utility that already exists and hack the code as you need it.

Good luck with it anyways.

p.s. From my experience, the gradients in ParaView are qualitively good.

[rudy]

Thanks adriano,but I tried to make my own utility file as u said above but when i try to run from inside casefile it gives the following error:

No command 'grad' found, did you mean:
Command 'glrad' from package 'radiance' (universe)
Command 'trad' from package 'radiance' (universe)
Command 'grap' from package 'grap' (universe)
Command 'rad' from package 'radiance' (universe)
grad: command not found

I have generated a new utility named grad in utilities/postprocessing/grad which is as follows:

#include "fvCFD.H"

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

int main(int argc, char *argv[])
{
timeSelector::addOptions();
#include "setRootCase.H"
# include "createTime.H"
instantList timeDirs = timeSelector::select0(runTime, args);
# include "createMesh.H"

forAll(timeDirs, timeI)
{
runTime.setTime(timeDirs[timeI], timeI);
Info<< "Time = " << runTime.timeName() << endl;

IOobject phiheader
(
"phi",
runTime.timeName(),
mesh,
IOobject::MUST_READ
);

// Check phi exists
if (phiheader.headerOk())
{
mesh.readUpdate();

Info<< " Reading phi" << endl;
volScalarField phi(phiheader, mesh);

Info<< " Calculating gradphi" << endl;

volVectorField gradphi
(
IOobject
(
"gradphi",
runTime.timeName(),
mesh,
IOobject::NO_READ,
IOobject::AUTO_WRITE
),
mesh,
dimensionedVector
(
"gradphi",
phi.dimensions()/dimLength,
vector::zero
)
);

forAll(gradphi.boundaryField(), patchi)
{
gradphi.boundaryField()[patchi] =
-phi.boundaryField()[patchi].snGrad();
}

gradphi.write();
}
else
{
Info<< " No phi" << endl;
}
}

Info<< "End" << endl;

return 0;
}

I just modified the utility file wall/wallGradU/wallGradU.C accordingly...I am not really good at programming so if u have any idea where i m making a mistake please let me know...
thanks,
rudy.

[madad2005]

Sorry for not replying sooner, but I'm really busy in the run up to Xmas. I have a code that will do this but it is at home on my laptop. I can e-mail it to you later on and/or post it here. If you have managed to get it working, then let me know.

[rudy]

I have something which finds gradient now,following someone's instructions I made a .H file in the case directory and then included it in my main solver .C file(similar to the laplacianfoam solver)...But if u followed a different procedure to find a gradient please let me know,I would like to know new way as well...
thanks a lot...
rudy