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Trouble adding a directional derivative source term

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Old   March 17, 2013, 21:19
Default Trouble adding a directional derivative source term
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Chris Prohoda
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Hi everyone. Thanks for checking this.

I am a new OpenFOAM user, and I have been trying to create my own solver to model ferrofluid motion. In the model that I am using, there is a directional derivative source term (i.e. M \cdot \nabla B which I plan to approximate as \nabla\left( M \cdot B \right) where M and B are vectors).

I have M and B set up as volVectorFields, and I want multiply the entire thing by a the volume of each cell over the (constant) density. It looks like the fvc::div function needs one surface scalar field, so I created a phiB in a similar way to the phi for velocity using
Code:
(fvc::interpolate(B) & mesh.Sf())
Next, I try to modify phiB by the constant. Here is some relevant code:

Code:
            phiB=phiB*mesh.V()/rho;

            fvVectorMatrix UEqn
            (
                fvm::ddt(U)
              + fvm::div(phi, U)
              - fvm::laplacian(nu, U)
            );

            solve(UEqn == -fvc::grad(p) + fvc::div(phiB, M));
When I try to compile it, it lists a large number of errors that were not there before attempting to multiply by volume. So, I think the problem occurs when I multiply by the volume of each cell (using mesh.V), but I'm lost as to how to fix it. Any tips or suggestions? Is there a better way to do this?

I really appreciate your help.
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Old   March 19, 2013, 17:51
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yijin Mao
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Quote:
Originally Posted by cpro View Post
Hi everyone. Thanks for checking this.

I am a new OpenFOAM user, and I have been trying to create my own solver to model ferrofluid motion. In the model that I am using, there is a directional derivative source term (i.e. M \cdot \nabla B which I plan to approximate as \nabla\left( M \cdot B \right) where M and B are vectors).

I have M and B set up as volVectorFields, and I want multiply the entire thing by a the volume of each cell over the (constant) density. It looks like the fvc::div function needs one surface scalar field, so I created a phiB in a similar way to the phi for velocity using
Code:
(fvc::interpolate(B) & mesh.Sf())
Next, I try to modify phiB by the constant. Here is some relevant code:

Code:
            phiB=phiB*mesh.V()/rho;

            fvVectorMatrix UEqn
            (
                fvm::ddt(U)
              + fvm::div(phi, U)
              - fvm::laplacian(nu, U)
            );

            solve(UEqn == -fvc::grad(p) + fvc::div(phiB, M));
When I try to compile it, it lists a large number of errors that were not there before attempting to multiply by volume. So, I think the problem occurs when I multiply by the volume of each cell (using mesh.V), but I'm lost as to how to fix it. Any tips or suggestions? Is there a better way to do this?

I really appreciate your help.
phiB ---> surfaceScalarField
mesh.V() ---> volScalarField
rho ---> volScalarField

I think you have to do linear interpolation for volScalarField before math operations.
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