Creating a New Diffusion Kernel

[jsevic]

Hello,

I have diffusion operator kernel written a few years based on the ExampleConvection coupled kernel example in Example 3. In that kernel I added a coupled parameter for temperature, creating a diffusion operator kernel where thermal conductivity is coupled into as its value is a function of temperature.

I have tried the same thing from scratch in my latest MOOSE app from, and made the following changes. Since the example convection kernel is coupling some_gradient

_grad_some_variable(coupledGradient("some_gradient"))

and I want to couple a real value for thermal conductivity, I changed coupledGradient to coupledValue, which is what my old kernel used. Then I changed in the .h file the VariableGradient declaration to VariableValue, and I get a compile error.

private:
const VariableGradient & _grad_some_variable;

My original function compiles and passes tests this one does not. What am I missing? Any suggestions?

These are the errors I get.

Compiling C++ (in opt mode) /Users/johnsevic/projects/moose/examples/ex03_coupling/build/unity_src/kernels_Unity.C...
In file included from /Users/johnsevic/projects/moose/examples/ex03_coupling/build/unity_src/kernels_Unity.C:2:
/Users/johnsevic/projects/moose/examples/ex03_coupling/src/kernels/ExampleConvection.C:35:10: error: no viable conversion from returned value of type 'typename boostcopy::enable_if_c<ScalarTraits::value, TypeVector<typename CompareTypes<double, double>::supertype>>::type' (aka 'libMesh::TypeVector') to function return type 'libMesh::Real' (aka 'double')
return _test[_i][_qp] * (_grad_some_variable[_qp] * _grad_u[_qp]);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Users/johnsevic/projects/moose/examples/ex03_coupling/src/kernels/ExampleConvection.C:41:10: error: no viable conversion from returned value of type 'typename boostcopy::enable_if_c<ScalarTraits::value, TypeVector<typename CompareTypes<double, double>::supertype>>::type' (aka 'libMesh::TypeVector') to function return type 'libMesh::Real' (aka 'double')
return _test[_i][_qp] * (_grad_some_variable[_qp] * _grad_phi[_j][_qp]);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2 errors generated.
make: *** [/Users/johnsevic/projects/moose/framework/build.mk:151: /Users/johnsevic/projects/moose/examples/ex03_coupling/build/unity_src/kernels_Unity.aarch64-apple-darwin20.0.0.opt.lo] Error 1

[GiudGiud]

Hello

This is a vector now, when it used to be a scalar

return _test[_i][_qp] * (_grad_some_variable[_qp] * _grad_u[_qp])

before these, _grad_some_variable[_qp] and _grad_u[_qp] are vectors so the product is a dot product. Now, one is a real and you end up returning a vector. This makes sense for a convection term in a PDE

If you are trying to substitute one into a conductivity, chances are you're modeling diffusion not convection and a diffusion kernel is a better example to follow

Guillaume

[jsevic]

OK so just to be clear, in this kernel I have changed the following line to include coupledValue instead of coupledGradient, so is this still producing a vector?

_grad_some_variable(coupledValue("some_gradient"))

In the .h file I have...

VariableValue & _grad_some_variable;

I did not change the variable name even though it says _grad_some_variable is physically k_thermal that gets coupld.

[GiudGiud]

no longer a vector. It s getting you Reals now

[jsevic]

Yes that is what I was thought, so still confused. Eventually I want to implement this weak form

_grad_u[_qp] * _grad_test[_i][_qp] * _sigma_e[_qp]

so that's why I had coupledValue for _grad_some_variable and declared this as VariableValue in the .h file. Eventually _grad_some_variable will be the coupled electrical conductivity _sigma_e.

[GiudGiud]

this is fine though?
_grad_u[_qp] * _grad_test[_i][_qp] is vector times vector -> real
_sigma_e[_qp] is real I assume

[jsevic]

Yes that worked in my earlier code. Does the order of operation matter? That may be my mistake? My new code gets the compile error. Yes _sigma_e is real.

[GiudGiud]

in the code you pasted earlier you have _test not _grad_test. Is that it?

[GiudGiud]

the order of operation for vector * real * vector or real * vector * vector etc does not matter

[jsevic]

This worked.

Yes I did add now the _grad_test since I ultimately want the diffusion operator. Maybe that was the issue?

Real
ExampleConvection::computeQpResidual()
{
return _grad_u[_qp] * _grad_test[_i][_qp] * _grad_some_variable[_qp];
}

Real
ExampleConvection::computeQpJacobian()
{
return _grad_some_variable[_qp] * _grad_phi[_j][_qp] * _grad_test[_i][_qp];
}