how to translate FV var to FE var?

[wangzhaohao]

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Question

Hello, There is a error about Material, when I try to compute a material which form is $k=P*T$, where k is material property, P is compute form FVM, T is compute form FEM.

Your material mamox couples in both FE and FV vars. To support ghost calculations which some FV consumers may need, multiphysics simulations should define separate materials for coupling in finite element and finite volume variables because we do not have a user friendly way of running DerivedMaterial::computeQpProperties and saying 'compute this property because it doesn't depend on finite element variables' or 'don't compute this property because it *does* depend on finite element variables'

Are there auxiliary variables AuxVariable that convert FV variables into FE variables? I can't find it from the name.
Thanks for you help in advance.
Zhaohao Wang

[GiudGiud]

Hello

you can use a ProjectionAux to convert kne to the other.

Alternatively you can use the functor APIs to couple FE or FV variables in any object. See the Functor documentation

[GiudGiud]

Taking another look at your code this is not going to work:

    _temperature(coupledValue("temperature")),
    _temperature_grad(coupledGradient("temperature")),

the graident of an FV variable through the coupleable interface is always 0 (const monomial shape function).

Can you paste the header? I think you might have forgotten to store _temperature as a reference

[wangzhaohao]

I realized that the _temperature_grad is 0 when the shape function is const. If I need the gradient, at least the shape function order is first. Badly, in MooseVariableFVReal only support MONOMIAL and CONSTANT.
there is a header part

protected:
  virtual ADReal computeQpResidual() override;
  const VariableValue & _temperature;
  const VariableGradient & _temperature_grad;
  const VariableValue & _plutonium_concentration;

  RealVectorValue velocity();
  Moose::FV::InterpMethod _advected_interp_method;

I don't forget to use a reference.

[wangzhaohao]

Oh, thank you. The error is caused by the temperature grad. when I use a simple RealVectorValue(1, 0, 0) replace it, the error disappear. Now the problem is how to get the gradient. Maybe I need to sort as the AuxVariable, I am trying.

[GiudGiud]

for the gradient, retrieve a pointer to the variable using getVar in the constructor, then use that point to call:

_var->gradient(ElemArg elem_arg, state)

See Functor..... kernels for examples on how to create these functor arguments

[wangzhaohao]

Thanks for your help. It's all good now.