plenumSpringPressureFvPatchVectorField

Description

The plenumSpringPressure boundary condition replicates the counteracting force of the plenum spring.

Physically, the total pressure applied on the patch is calculated as the sum of the gap pressure (derived from a gapGasModel) and the reaction force of the spring. The spring force is determined based on the spring modulus and the relative displacement of the surfaces to which the spring is attached.

The shear stress on the patch is set to zero.

Note

This BC is designed to be applied to the top of the pellet column (i.e., the topmost fuel patch) and, if present, the inner surface of the top cladding cap. For models without a top cap (where the cladding ends with an open annular cylindrical surface), the user can use the topCladRingPressure BC to account for the spring effect.

Warning

This BC assumes the presence of a gapGasModel.

Options

The plenumSpringPressure fvPatchField can be selected in the patch subdictionary inside the boundaryField subdictionary of the displacement field.

Parameters in the patch subdictionary for plenumSpringPressure:

springModulus	Modulus of the plenum spring in N/m, representing the stiffness of the spring.
initialSpringLoading	Pre-loading of the plenum spring in meters.
fuelTopPatches	List of patches attached to the bottom end of the spring (typically the top surface of the fuel column).
topCapInnerPatches	List of patches attached to the top end of the spring (either the inner surface of the top cap, if present, or the top annular surface of the cladding in an open cladding model).

Parameters in the patch subdictionary derived from tractionDisplacement:

fixedSpring	Activates a fixed spring-dashpot system for additional stability. Default: `false`.
fixedSpringModulus	Spring modulus in N/m. Required when `fixedSpring` is set to `true`.
dashpotModulus	Dashpot modulus in N/m. Required when `fixedSpring` is set to `true`.
planeStrain	Activates the plane strain approximation for the normal stress at the boundary. When enabled, the normal strain is assumed constant across the last layer of cells. Default: `false`.
relax	Relaxation factor for gradient updates. Default: `1.0`.
value	Initial displacement value (not stress).

Usage

To apply the plenumSpringPressure boundary condition to a given patch, you need to specify its typename in the patch definition in the boundary condition file (e.g., 0/D or 0/DD for simulations involving incremental mechanical solvers).

Example: Applying plenumSpringPressure to the fuelTop patch:

fuelTop
{
    type            plenumSpringPressure;

    springModulus           1e4;
    initialSpringLoading    0;

    fuelTopPatches          (fuelTop);
    topCapInnerPatches      (cladTop);

    // Activate plane strain approximation (default is false)
    planeStrain     false;

    // Relaxation factor
    relax           1.0;

    // Initial displacement value
    value           $internalField;
}