FEM GleichungFluss

This page is a translated version of the page FEM EquationFlux and the translation is 50% complete.

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GleichungStrömung

GleichungWärme

FEM

Menüeintrag
FEM GleichungFluss
Lösen → Flux equation
Arbeitsbereich
FEM
Standardtastenkürzel
Keiner
Eingeführt in Version
0.17
Siehe auch
Keiner

Diese Gleichung wird für die Berechnung der Flussgrößen verwendet, die normalerweise aus poisson-artigen Gleichungen resultieren. Diese enthalten die FEM GleichungWärme und die FEM GleichungElektrostatik.

For info about the math of the equation, see the Elmer models manual, section Flux Computation.

Anwendung

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 DatenFlux Coefficient to None. and the property DatenFlux 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:

DatenAverage 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.
DatenCalculate Flux: Calculates the flux vector.
DatenCalculate Flux Abs: Calculates the absolute of the flux vector. Requires that DatenCalculate Flux is true.
DatenCalculate Flux Magnitude: Computes the magnitude of the vector field. Requires that DatenCalculate Flux is true.
Basically it is the same as DatenCalculate Flux Abs but this requires less memory because it solves the matrix equation only once. The downside is that negative values may be introduced.
DatenCalculate Grad: Calculates the gradient of the flux.
DatenCalculate Grad Abs: Calculates the absolute flux gradient. Requires that DatenCalculate Grad is true.
DatenCalculate Grad Magnitude: Computes the magnitude of the vector field. Requires that DatenCalculate Grad is true.
Basically it is the same as DatenCalculate Grad Abs but this requires less memory because it solves the matrix equation only once. The downside is that negative values may be introduced.
DatenDiscontinuous 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.
DatenEnforce Positive Magnitude: If true, the negative values of the computed magnitude fields are set to zero.
DatenFlux Coefficient: Name of the proportionality coefficient to compute the flux.
DatenFlux 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.

Ergebnisse

The available results depend on the solver settings. If none of the DatenCalculate * settings was set to true, nothing is calculated. Otherwise the corresponding results will also be available.

Die resultierende Flussgröße ist entweder der Wärmefluss ${\rm {W/m^{2}}}$ (fälschlicher Weise auch "Temperaturfluss" genannt) oder der Potentialfluss (<-?) in ${\rm {W/m^{2}}}$ ( ${\rm {A\cdot V/m^{2}}}$ ).