GuiCommand: Name: FEM EquationFlux MenuLocation: Solve , Flux equation Workbenches: FEM_Workbench Version: 0.17 SeeAlso:
FEM EquationFlux
Description
This equation is used to calculate the fluxes resulting usually from Poisson kind of equations. These include the 
Heat equation and the 
Electrostatic equation.
For info about the math of the equation, see the Elmer models manual, section Flux Computation.
Usage
- After adding an Elmer solver as described here, select it in the tree view.
- Either use the toolbar button
or the menu Solve → Flux equation. - Now either add a heat equation (toolbar button or menu Solve → Heat equation) or an electrostatic equation (toolbar button or menu Solve → Electrostatic equation). This is important because the flux equation needs the boundary conditions set for these equations.
- When using the electrostatic equation, change the property Flux Coefficient to None. and the property Flux Variable to Potential.
- Change the equation\'s solver settings or the general solver settings if necessary.
Solver Settings
For the general solver settings, see the Elmer solver settings.
The flux equation provides these special settings:
-
Average Within Materials: If
True, continuity is enforced within the same material in the discontinuous Galerkin discretization using the penalty terms of the discontinuous Galerkin formulation. -
Calculate Flux: Calculates the flux vector.
-
Calculate Flux Abs: Calculates the absolute of the flux vector. Requires that Calculate Flux is
True. -
Calculate Flux Magnitude: Computes the magnitude of the vector field. Requires that Basically it is the same as Calculate Flux Abs but this requires less memory because it solves the matrix equation only once. The downside is that negative values may be introduced.
-
Calculate Grad: Calculates the gradient of the flux.
-
Calculate Grad Abs: Calculates the absolute flux gradient. Requires that Calculate Grad is
True. -
Calculate Grad Magnitude: Computes the magnitude of the vector field. Requires that Basically it is the same as Calculate Grad Abs but this requires less memory because it solves the matrix equation only once. The downside is that negative values may be introduced.
-
Discontinuous Galerkin: For discontinuous fields the standard Galerkin approximation enforces continuity which may be unphysical. As a remedy for this, set this property to
True. Then the result may be discontinuous and may even be visualized as such. -
Enforce Positive Magnitude: If
True, the negative values of the computed magnitude fields are set to zero. -
Flux Coefficient: Name of the proportionality coefficient to compute the flux.
-
Flux Variable: Name of the potential variable used to compute the gradient.
Analysis Feature Information
The flux equation does not have its own boundary conditions. It takes the boundary conditions from the Heat equation or the Electrostatic equation.
Results
The available results depend on the solver settings. If none of the **Calculate *** settings was set to True, nothing is calculated. Otherwise the corresponding results will also be available.
The resulting flux is either the heat flux in $\rm W/m^2$ (misleadingly named \"temperature flux\") or the potential flux in $\rm W/m^2$ ($\rm A\cdot V/m^2$).
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This page is retrieved from https://github.com/FreeCAD/FreeCAD-documentation/blob/main/wiki/FEM_EquationFlux.md