[JM27]

Hi there,


I am hoping to get some help with coded function objects in openFoam.



I have written a function object to compute the radius of a bubble based on volume fraction alpha and cell volume as follows (compressibleInterFoam):

// section of coded to be executed, in controlDict

forAll(centers, I)   
            {
                        if (alpha[I] < th)         
                {

                    // TO COMPUTE RADIUS

                    // compute numerator, time-varying
                            sumNumerator   += (1-alpha[I])*(V[I]); // per time-step
                                                               
                 
                    // compute denominator, constant at t = 0
                          sumDenominator += (1-alpha[I])*(V[I]);     // CHANGE TO ACCESS VALUES AT TIME = 0 -- how?
        

                   // At each time-step
                    bracket        = pow(sumNumerator/sumDenominator, 1/3);    

                   

                    // compute Radius                
                    Radius         = Rstart*bracket;
               }
       }

However, I cannot seem to figure out how to access the properties at time directory 0.

The code compiles and runs but with the above setting the radius clearly stays constant for all time-directories.
Please help. Any advice will be greatly appreciated.



p.s. I know I can do something similar in swak4Foam but so far I have not managed to make this work for my current version (v5.0) and I want to try out some coding in OpenFOAM and c++ as an exercise (still a newbie).

[ships26]

Hi! I'm also a newbie, so I'm not sure if this'll help, but have you tried to compile that function as a functionObject? That way it would available as postProcess utility (I think).

I haven't done this myself, yet, if it works, you can employ it at time 0 by stating

postProcess -func Nameofutility -time 0

in the console.


EDIT: Now that I'm checking, it's been a while since this was posted... Sorry if it qualifies as necroing!

[raumpolizei]

Hey,
here is a suggestion how you could compute the volume of your bubble (or whatever you would like to calculate). Sometimes, I'm doing this myself in order to get some calculations done when the simulation is already over. The way is to write some postprocessing utility. Write a tool, wmake it and run it on your case. This can look like this:

bubbleVolume.C

#include "timeSelector.H"
#include "Time.H"
#include "fvMesh.H"
#include "volFields.H"
using namespace Foam;
int main(int argc, char *argv[])
{
timeselector::addOptions();
#include "setRootCase.H"
#include "createTime.H"
#include "createMesh.H"

// create a list of the times, from time directories given the time arguments 
// example: -time <ranges>  or -latestTime
instantList timeDirs = timeSelector::select0(runTime, args);

// loop over this list
forAll(timeDirs,timeI)
{
    runTime.setTime(timeDirs[timeI],timeI);
    mesh.readUpdate();
    // now get the fields you need for computation
     volScalarField fieldNeeded
     (
        IOobject
        (
              "fieldNeeded",
              runTime.timeName(),
              mesh,
              IOobject::MUST_READ,
              IOobject::NO_WRITE
        ),
        mesh
     );

    scalar bubbleVolume;
     // ....
     // compute bubbleVolume
     // ....

     Info << runTime.timeName() << " " << bubbleVolume << nl;
}

return 0;
}

Sorry for the bad inlining. May also contain some typos, there is a good documentation page for timeselector though (may be worth a try, Google is your friend).

Best regards and good luck
RP

[openfoam_aero]

You are a legend. Thanks for this.