# FEM EquationFlow/ru

This page is a translated version of the page FEM EquationFlow and the translation is 0% complete.
Outdated translations are marked like this.
Other languages:  Electrostatic equation Flux equation FEM Системное название FEM EquationFlow FEM EquationFlow Solve → Equation flow FEM Нет - FEM tutorial

This equation calculate viscous fluid flows using the Navier-Stokes equations.

For info about the math of the equation, see the Elmer models manual, section Navier-Stokes Equations.

## Usage

1. After adding an Elmer solver as described here, select it in the tree view.
2. Now either use the toolbar button or the menu Solve → Flow equation.
3. 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 flow equation provides these special settings:

• ДанныеDiv Discretization: To be set to true for incompressible flow for more stable discretization when the Reynolds number increases.
• ДанныеFlow Model: The flow model that should be used. The default Full includes convection and time derivative terms in the model. No convection switches off the convection terms and the Stokes model switches off the convection terms and the (explicit) time derivative terms.
• ДанныеGradp Discretization: If set to true pressure Dirichlet boundary conditions can be used. Also the mass flux is available as a natural boundary condition.
• ДанныеVariable: Optional only for calculations in 2D: You can change the default of 3 to 2.
Note: In this case none of the flow velocity constraints can have a specified z-component.

Equation:

### Notes for Convergence

If the solver results do not converge, you can try these things (in the given order):

1. Reduce the ДанныеRelaxation Factor, see the nonlinear system settings.
2. Increase the value for ДанныеNonlinear Newton After Iterations, see the nonlinear system settings.
3. Reduce the number of CPU cores used, see the FEM preferences.
4. Increase the mesh density (make it more fine).

## Constraint Information

The electrostatic equation takes the following constraints into account if they are set: