[AriaFoam89]

Hi foamers,


I'm trying to write the velocity field with a different name in each time directory, then I write this code in creatFields.H of my solver (let's say mybuoyantBoussinesqPimpleFoam):

Info<< "Calculating myName\n" << endl
volVectorField myName
  (
  IOobject 
    (
      "myName",
      runTime.timeName(),
      mesh,
      IOobject::MUST_READ,
      IOobject::AUTO_WRITE
    ),
    U
  );

However, I get wrong answer. in each time directory this will be written:

dimensions      [0 1 -1 0 0 0 0];

internalField   uniform (0 0 0);

boundaryField
{
    upperWall
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
    leftWall
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
    rightWall
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
    frontAndBack
    {
        type            empty;
    }
 }

I know that the velocity shouldn't be zero and it shouldn't be a fixed value because a few lines above my code, writing the velocity field is defined like this in creatFields.H:

Info<< "Reading field U\n" << endl;
volVectorField U
(
    IOobject
    (
        "U",
        runTime.timeName(),
        mesh,
        IOobject::MUST_READ,
        IOobject::AUTO_WRITE
    ),
    mesh
);

and the above code is writing a correct (varying with time) vector for velocity my question is why my method is not working properly?



Thanks

[ALBATTROSS]

Hi,

can you please help me with this? I have the same problem with writing gradU!
Wrong shear rate result with the existing code

thanks

[LuckyTran]

createFields is called only at startup to initialize fields to make places for them in memory.


You defined myName = U in createFields. During startup your field myName will be set equal to the current values for U (if your startTime is 0 then then myName will take on the values of U at 0). If you do nothing else, the field myName never gets updated again ever and stays at the initial values.


You need to go into your mybuoyantBoussinesqPimpleFoam.c and add a line that looks like this. The best place to put this is immediately before runTime.write();

volVectorField myName
(
      U
);
runTime.write();

Now, just before the fields are written, your myName field is set equal to the current U.


The reason U works is because there is more to a solver than createFields.H. There is a pEqn.H and UEqn.H where all the magic of foam happens and you calculate a new U. createFields only establishes whether a field is writable and initializes it. It doesn't do anything else. The fields are written when runTime.write() is called. The values of each field when runTime.write() is called is what gets written.


Also instead of using IOobject::MUST_READ you can probably use the NO_READ option since there's never any point to reading the myName field from the disk. It's always equal to U isn't it?

[AriaFoam89]

Originally Posted by LuckyTran

createFields is called only at startup to initialize fields to make places for them in memory.


You defined myName = U in createFields. During startup your field myName will be set equal to the current values for U (if your startTime is 0 then then myName will take on the values of U at 0). If you do nothing else, the field myName never gets updated again ever and stays at the initial values.


You need to go into your mybuoyantBoussinesqPimpleFoam.c and add a line that looks like this. The best place to put this is immediately before runTime.write();

volVectorField myName
(
      U
);
runTime.write();

Now, just before the fields are written, your myName field is set equal to the current U.


The reason U works is because there is more to a solver than createFields.H. There is a pEqn.H and UEqn.H where all the magic of foam happens and you calculate a new U. createFields only establishes whether a field is writable and initializes it. It doesn't do anything else. The fields are written when runTime.write() is called. The values of each field when runTime.write() is called is what gets written.


Also instead of using IOobject::MUST_READ you can probably use the NO_READ option since there's never any point to reading the myName field from the disk. It's always equal to U isn't it?

Hi LuckyTran,

thanks for the tips. I tried adding your suggested code in time loop before runTime.write() :

volVectorField myName
(
      U
);

however, it's the same again U=0 in each time directory. but when I added myName = U before runTime.write() it worked now openfoam is writing myName as the same as U.(there is a little difference between them)