Implementing a time derivative kernel

[shredderbvek]

I want to implement this Kernel in MOOSE, as I am just starting to use MOOSE, I would be very grateful to be guided by relevant information. Thank you.

$\int_\Omega \phi \left( \frac{C_L + C_T(1 -\theta_T)}{C_L} \right) \frac{\partial C_L}{\partial t} d\Omega$

Where,
$C_L =$ Lattice Concentration
$C_T$ = Trap Concentration
$\theta_T$ = Trap Binding Energy
$C_L$ is the primary scalar field variable, and $C_T$ is also a variable
which evolves with $C_L$.

[GiudGiud]

Hello

You will want to start from a TimeDerivative kernel.
Is this term going into the equation for C_L ?

[shredderbvek]

Hello,

Yes this equation is going to be for C_L, however C_T is also another variable which evolves with C_L.

[shredderbvek]

Thank you for your response. To compute the coefficient, I need to access C_L (Dof variable). How can we accomplish this in MOOSE?

[GiudGiud]

you can retrieve variable values using the Coupleable API and its routines
https://mooseframework.inl.gov/source/interfaces/Coupleable.html

they can be used in kernels

[shredderbvek]

hydrogen_transport.zip

Kernel 1: Time derivative kernel

$\int_\Omega \phi \left( \frac{C_L + C_T(1 -\theta_T)}{C_L} \right) \frac{\partial C_L}{\partial t} d\Omega $

For Kernel 1 all the material parameters are assumed to be constant for simplification.

Kernel 2: Diffusion kernel

$\int_\Omega \nabla \phi . \left( D \nabla C_L \right) d\Omega$
\

I am trying to implement these kernels. However I got an error prompt.

./cpfe_he-opt -i hydTrans.i
Framework Information:
MOOSE Version: git commit c614a59 on 2025-03-13
LibMesh Version:
PETSc Version: 3.22.1
SLEPc Version: 3.22.1
Current Time: Tue Aug 26 16:50:48 2025
Executable Timestamp: Tue Aug 26 16:46:35 2025

Input File(s):
/home/bmagar/projects/cpfe_he/hydTrans.i

Checkpoint:
Wall Time Interval: Every 3600 s
User Checkpoint: Disabled
# Checkpoints Kept: 2
Execute On: TIMESTEP_END

Parallelism:
Num Processors: 1
Num Threads: 1

Mesh:
Parallel Type: replicated
Mesh Dimension: 3
Spatial Dimension: 3
Nodes: 3774
Elems: 2476
Num Subdomains: 1

Nonlinear System:
Num DOFs: 3774
Num Local DOFs: 3774
Variables: "C_L"
Finite Element Types: "LAGRANGE"
Approximation Orders: "FIRST"

Execution Information:
Executioner: Transient
TimeStepper: ConstantDT
TimeIntegrator(s): ImplicitEuler
Solver Mode: NEWTON
MOOSE Preconditioner: SMP

Time Step 0, time = 0

Time Step 1, time = 2, dt = 2
Segmentation fault (core dumped)

How can I resolve this issue? I have attached the source files for the kernels. Thank you.

[GiudGiud]

You could use a debugger and follow these instructions
https://mooseframework.inl.gov/application_development/debugging.html

But i looked at your code and

        const VariableValue _C_L_val;

is wrong. should be

        const VariableValue & _C_L_val;

if there are more things, follow the debugging instructions please

[shredderbvek]

Thank you for you assistance Guillaume.