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  • Numerics

    Under Numerics you can set the equation solver for your simulation, change the convergence settings, select algorithms and residuals or choose the time integration scheme for transient dynamic simulations. These settings mainly influence the stability and efficiency of your simulation run, but also the quality of the results may depend on these settings.

    All numerical settings are made available for users to have full control over the simulation. These settings can be found for Fluid Dynamics (OpenFOAM®) and Solid Mechanics (Code_Aster) analysis types. The available settings differ based on individual analysis type physics.

    Numerics for CFD

    In OpenFOAM based analysis types in SimScale the settings for the Numerics section can be categorized into the following:

    • Properties

    All properties regarding the iterative solvers of velocity and pressure equations are set here. Relaxation factors, non-orthogonal correctors, residual controls, and solver-specific tweaks are among these settings. However, depending on the solver (e.g. PIMPLE, PISO, …), these settings will be adjusted.

    • Solver

    In this part, linear solvers used in computing each variable could be chosen separately. Upon choosing a solver, a set of preconditioners/smoothers and their tolerances become available. To assist with selecting the best solver, a Help message is provided for each field.

    These schemes determine how each term in the governing equations should be discretized. These are required to evaluate, for e.g., gradient and interpolations of variable terms from cell centers to nodes. In most cases, the standard settings should be a good choice and should not be changed without reason.

    Did you know?

    If you had adjusted the Numerics settings, you can still switch back to the default settings. Just click on the ‘Reset to default’ button that is located at the bottom left corner.

    Keep in mind that ‘Reset to default’ is not an undo feature, but it brings back the default settings instead. This function is only available for the fluid dynamics simulation types

    reset to default feature under the numerics settings of incompressible analysis type in simscale
    Figure 1: Reset to default feature under the Numerics settings

    Information

    Generally, for Numerical Schemes the default selections are the best choice and require no changes

    Field Limits

    Under Stabilization you should find the Field Limits section that defines the range of values for the solution variables that are bounded within specified limits during the simulation. Limits can be put on density for the original version of the Conjugate Heat Transfer (CHT) solver and temperature for the version CHT v2.0.


    Field Limits for Conjugate Heat transfer
    Figure 2: Field limit entries for both Conjugate Heat Transfer Analysis solvers, with the latest version (CHT v2.0) on the left.

    Field limits can be also applied to simulations involving compressible flows like the Compressible solver, for the pressure values, while density, pressure, and temperature can be bounded for the Convective Heat Transfer solver, when the compressibility is toggled on:


    Field Limits for Convective Heat transfer and compressible analysis
    Figure 3: The Field limits entries for Compressible analysis (left), and Convective Heat Transfer analysis (right), where more entries are to be defined.

    Numerics for Radiation

    For radiative heat transfer problems, further settings can be changed within the numerics, as shown in the picture below. Most importantly, the radiation resolution can be changed. This affects the discretization of the directions for which the radiative problem is solved. The settings are coarse, moderate, and fine. Increasing the radiation resolution will lead to a higher number of directions and hence improved angular discretization of the radiative problem (usually a more accurate result).

    radiation numerics simscale
    Figure 4: Numerics settings for radiation

    Numerics for FEA

    Similar to fluid simulations the structural simulations involve linear and non-linear equations that need to be solved. SimScale provides the Numerics settings panel where a user can select algorithms, type of residuals and threshold values, maximum number of iterations, time integration schemes, etc.

    numerics settings for structural analysis type fea in Simscale
    Figure 5: Settings panel for Numerics settings under structural analysis in SimScale

    A full explanation of the parameters available under these settings can be found here

    Last updated: October 18th, 2022

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