FEM EquationFlow/ru
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| Расположение в меню |
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| Solve → Equation flow |
| Верстаки |
| FEM |
| Быстрые клавиши |
| Нет |
| Представлено в версии |
| - |
| См. также |
| FEM tutorial |
Description
This equation calculates viscous fluid flows using the Navier-Stokes equations.
For information about the math of the equation, see the Elmer models manual, section Navier-Stokes Equations.
Usage
- Add an
Elmer solver.
- Select it in the Tree View.
- There are several ways to invoke the command:
- Press the
Flow Equation button.
- Select the Solve →
Flow Equation option from the menu.
- Press the
- 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 boundary conditions can have a specified z-component.
Equation:
- ДанныеConvection: The type of convection to be used in the
Heat equation.
Note: For thermal flows it must be set to Computed (the default). - ДанныеMagnetic Induction: If set to true the magnetic induction equation will be solved along with the Navier-Stokes equations.
Notes for Convergence
If the solver results do not converge, you can try these things (in the given order):
- Reduce the ДанныеRelaxation Factor, see the nonlinear system settings.
- Increase the value for ДанныеNonlinear Newton After Iterations, see the nonlinear system settings.
- Reduce the number of CPU cores used, see the FEM preferences.
- Increase the mesh density (make it more fine).
Analysis Feature Information
The flow equation takes the following analysis features into account if they are set:
Flow velocity boundary condition
Initial flow velocity condition
Pressure load
Initial pressure condition (introduced in 0.21)
Notes
- Except for calculations in 2D, for all above boundary conditions it is important that they act on a face or body. Boundary conditions for 3D set to lines or vertices are not recognized by the Elmer solver.
- Since
Pressure load can only be set to faces, pressure loads cannot be used for calculations in 2D.
- If there is no
Pressure load set,
Initial pressure condition will only be taken into account if ДанныеGradp Discretization is set to true.
Results
The results are the velocity in and the pressure in . If there is no Initial pressure condition and
Pressure load given, the resulting pressure will be relative not absolute. Since pressure must act on a face, absolute pressure results cannot be obtained in 2D simulations.
- Materials: Solid Material, Fluid Material, Non-Linear Mechanical Material, Reinforced Material (Concrete); Material Editor
- Element Geometry: Beam Cross Section, Beam Rotation, Shell Plate Thickness, Fluid Section for 1D Flow
- Electromagnetic Boundary Conditions: Electrostatic Potential Boundary Condition, Current Density Boundary Condition, Magnetization Boundary Condition, Electric Charge Density
- Fluid Boundary Conditions: Initial Flow Velocity Condition, Initial Pressure Condition, Flow Velocity Boundary Condition
- Geometrical Analysis Features: Plane Multi-Point Constraint, Section Print Feature, Local Coordinate System
- Mechanical Boundary Conditions and Loads: Fixed Boundary Condition, Rigid Body Constraint, Displacement Boundary Condition, Contact Constraint, Tie Constraint, Spring Boundary Condition, Force Load, Pressure Load, Centrifugal Load, Gravity Load
- Thermal Boundary Conditions and Loads: Initial Temperature, Heat Flux Load, Temperature Boundary Condition, Body Heat Source
- Overwrite Constants: Constant Vacuum Permittivity
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