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  • Documentation

    Error: Incorrect Usage of Empty 2D Boundary Condition


    Illegal usage of the 2D empty boundary condition. Please note that this boundary condition can only be used if the mesh is two-dimensional in an OpenFOAM sense, i.e. the mesh height is exactly one cell. If that is not the case, try using a symmetry boundary condition instead.


    Inconsistent boundary condition types. Possibly the empty boundary conditions were not correctly assigned for a 2D mesh. Please check the boundary conditions.

    What Happened?

    The simulation setup has an error. The ‘2D Empty’ boundary condition was incorrectly used or a patch type is not of type ’empty’.

    2D simulations on SimScale platform

    Please note that SimScale platform only supports simulations on 3D meshes. To perform a 2D simulation, you need to upload a mesh which is one cell thick along one of the coordinates. Learn more here.

    What Could Be the Possible Reason?

    Possible reasons for this error are:

    • You used an Empty 2D boundary condition on a 3D mesh. This boundary condition can only be used on a mesh whose height is one cell thick. Such a mesh can be referred to as a pseudo-2D mesh.
    • You uploaded the pseudo-2D mesh, but the Empty 2D boundary condition is incorrectly used.

    What Can I Do Now?

    Below are our recommendations to resolve this error:

    • For a 3D simulation, check your boundary condition(s) and make sure an Empty 2D boundary condition is not used. You can look for Empty 2D under the Boundary conditions dropdown menu.
    lists of used boundary conditions
    Figure 1: Check your Boundary conditions in your simulation tree, make sure that the Empty 2D boundary conditions were not used for a 3D simulation.
    • For a 2D simulation, you will need to upload a pseudo-2D mesh. Then, use an Empty 2D type boundary condition for the faces perpendicular to the one cell thick mesh height. For example, for the rising bubble validation case, the Empty 2D boundary condition is applied for the faces normal to the z-direction. This is because the simulation is a 2-dimensional flow in the x- and y-direction.
    applied empty 2d boundary condition
    Figure 2: Example of a correctly used Empty 2D boundary condition. It needs to be applied to faces perpendicular to mesh height of one cell thickness (psedo-2D mesh)

    Important Information

    If none of the above suggestions solved your problem, then please post the issue on our forum or contact us.


    Last updated: September 9th, 2022