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  • Documentation

    Boundary Conditions

    Boundary conditions define how a system (for example, a structure or a fluid) interacts with the environment. Fixations, loads, pressures, flow rates, or velocities are all examples of boundary conditions.

    A boundary condition consists of three pieces of information:

    1. Boundary condition types: SimScale offers a large set of boundary condition types for simulations. This section links to descriptions of the available boundary condition types;
    2. Boundary condition assignments: A boundary condition is usually only assigned to the domain’s boundary. Each boundary condition must be linked to at least one surface or where something enters or exits the domain.
    3. Boundary condition values: This is where we define the value of the condition (speed, temperature, force, etc.);

    Boundary Condition Types

    SimScale offers many boundary condition types for different types of applications. Boundary conditions are only displayed when they can be applied to the type of analysis being worked on. The following list shows the available boundary condition types, what each type means, and where they can be used. For advanced users, the page also shows how the boundary condition types translate to the solver input files.

    Fluid Dynamics

    Solid Mechanics


    Creating and Assigning a Boundary Condition

    To create a new boundary condition, click on the ‘+ button‘ next to Boundary conditions. Pick the desired one from the list:

    boundary condition creation
    Figure 1: Creating a new boundary condition in SimScale

    After creating a boundary condition, assign the desired entities by clicking on them.

    boundary condition assignment
    Figure 1: Assigning a pressure outlet boundary condition to a face

    All of the fluid dynamics boundary conditions are assigned to faces exclusively. For solid mechanics and thermodynamics, some boundary conditions only be assigned to volumes, such as Volume heat flux.

    volume heat flux boundary condition
    Figure 3: Clicking on the part to assign a volume heat flux boundary condition

    Lastly, some of the solid mechanics boundary conditions accept assignments of both faces and volumes, such as the Rotating motion boundary condition.

    Boundary Condition Values

    For simple cases, boundary conditions are defined by a single value of a given variable (velocity, temperature, pressure…). For advanced cases where a fixed value is not enough, alternative techniques are available:

    Last updated: July 17th, 2023