[Neka]

Dear OF users,

I use foam-extend-3.2 version. I would like to define an additional function in the class multiComponentMixture.
This function contains a volScalarField calculated in a solver at each time step (in my case the field is rho).
How can I access rho from within my new function?
For example if the function looks like:

Template<class ThermoType>
void Foam::multiComponentMixture<ThermoType>::myFunction()
{
    const volScalarField& Rho = db().lookupObject<volScalarField>(“rho”)
 
    forAll (Z_, n)
    {
        Z_[n] = Rho*some calculation;
    }
}

The way I try to access rho here is not working, because db() hasn’t been declared. I guess the way I do it is also wrong.

Can anybody help me? Is it even possible to access a “fresh” rho field of the last time step out of multiComponentMixture?

Thanks in advance,

Alex

[Neka]

I think I should precise my problem a bit more.

In several threads I’ve read, that the procedure above (the way I try to do it) works for BC classes, but I work here with a mixture class (multiComponentMixture).

As far as I see my problem at the moment, in my custom mixture I have no direct access to the field rho, which is declared in the solver in createFields.H and recalculated each time step in the solver via rho = thermo.rho().

In my custom mixture I don’t want to change rho, I just need the current rho values of the last time step in my function. So, I somehow need to lookup rho from mesh, database, …? But if I try something like this I get the error that db or mesh or whatever I try, is not declared in this scope. So how can I declare it in my mixture class?

[Neka]

Ok, I think I resolved the problem.

As I assumed, I have somehow to declare the database. In my custom mixture class I have mass fraction fields Y[n]. I declared the db() via these mass fraction fields. I hope I didn’t mess up my code and everything will work fine.

This is how I modified my function depicted above:

 
Template<class ThermoType>
void Foam::multiComponentMixture<ThermoType>::myFunction()
{
    const objectRegistry& db = Y_[0].db();
    const volScalarField& Rho = db.lookupObject<volScalarField>(“rho”)

    forAll (Z_, n)
    {
        Z_[n] = Rho*some calculation;
    }
}

My custom mixture class compiles fine and the solver compiles to. But I need to run the test case first to be sure, that it really works.
I hope, that the rho field that I get is the latest (from the last time step) and not from the initial conditions.

I don’t understand completely what I’ve done here. It would be nice if someone from advanced users would say something about it.

[olesen]

Originally Posted by Neka

Ok, I think I resolved the problem.

...
I don’t understand completely what I’ve done here. It would be nice if someone from advanced users would say something about it.

What you've come up with looks good. You have some volume field in your class (Y_), from which you have obtained the objectRegistry and used that to locate another field that is also registered on that database. The rho field that you will get is the reference to the density field at the current time-level.

[Neka]

Hello Mark,

thank you for your reply.

It is good to know, that it refers to the current time-level.

[Zhiheng Wang]

Use thermo.rho().internalField()[I]
Or thermo.rho().boundaryField()[I]

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[Zhiheng Wang]

It's thermo.rho().boundaryField()[patchId][i]

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[hooman.4028]

Originally Posted by Neka

Ok, I think I resolved the problem.

As I assumed, I have somehow to declare the database. In my custom mixture class I have mass fraction fields Y[n]. I declared the db() via these mass fraction fields. I hope I didn’t mess up my code and everything will work fine.

This is how I modified my function depicted above:

 
Template<class ThermoType>
void Foam::multiComponentMixture<ThermoType>::myFunction()
{
    const objectRegistry& db = Y_[0].db();
    const volScalarField& Rho = db.lookupObject<volScalarField>(“rho”)

    forAll (Z_, n)
    {
        Z_[n] = Rho*some calculation;
    }
}

My custom mixture class compiles fine and the solver compiles to. But I need to run the test case first to be sure, that it really works.
I hope, that the rho field that I get is the latest (from the last time step) and not from the initial conditions.

I don’t understand completely what I’ve done here. It would be nice if someone from advanced users would say something about it.

Hello,

I have kind of the same problem. I am adding a new model to simpleFoam (model M). I need to access a volume scalar field which will be calculated right before the very first iteration, let's call it A. How can I access this A field in my M.c file? Because obviously field A does not exist yet!

Thank you very much!