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  • Documentation

    Error: Multi-Region Mesh in Non-CHT Simulation

    CFD Simulations


    A multi-region mesh was assigned ― this analysis type requires a single-region mesh.

    Conjugate Heat Transfer (CHT) Simulations


    A single-region mesh was assigned ― this analysis type requires a multi-region mesh.

    What Happened?

    The platform detected a multi-region mesh for non-CHT simulations.

    An opposite error can occur when setting up CHT simulations where the model only has one solid body. For CHT, multiple solid bodies are required.

    What Could Be the Possible Reason?

    In CHT analysis, both solid and fluid regions are simulated, therefore the platform expects a mesh with multiple regions. If the provided mesh contains a single region, the simulation will result in a single-region error.

    For non-CHT simulations, multiple bodies are not allowed, unless the additional bodies will be used as advanced concepts.

    What Can I Do Now?

    For CFD Simulations (Non-CHT)

    The most common cause for this error in non-CHT simulations is the lack of a flow volume extraction operation. Please note that non-CHT analysis types are single-region analysis. Therefore, they only require the flow volume to run correctly.

    Taking a meeting room as an example, if we attempt to run an incompressible analysis with the following geometry, it will fail. The geometry consists of the solid parts, which is not intended for non-CHT simulations:

    multi-region mesh error
    Figure 1: This geometry contains 17 solid parts (regions). This configuration is not appropriate for non-CHT simulations.

    To make this geometry appropriate to run a simulation, we need to create the flow volume and delete the solid parts. Figure 2 shows the resulting geometry for the meeting room, after following the outlined steps:

    room with flow volume
    Figure 2: Meeting room geometry that works for a non-CHT simulation. Note how we have a single volume in the geometry, representing the flow region.

    In case you are in doubt about the flow volume creation process, please visit this tutorial for a more in-depth guide.

    A second common cause is related to the Advanced concepts. For single-region analysis, we may intentionally have more volumes when we are modeling advanced concepts:

    lists of available advanced concepts in simscale that can be used to resolve multiple bodies in non cht simulations
    Figure 3: List of advanced concepts for a sample transient incompressible analysis.

    If the user forgets to create a cell zone and assign it to an advanced concept, it will result in a multi-region mesh error when running a simulation.

    For CHT Simulations

    An example of when a CHT simulation requires multiple solids is an electronics cooling simulation. This simulation will need the flow region as well as the solid sources that are emitting heat. Having separate bodies will also enable you to define different materials and heat fluxes for each body.

    electronics cooling box with multiple solid bodies prepared for a cht simulation.
    Figure 4: Example of a model with multiple solid bodies for a CHT simulation

    Read more on the preparation of the model for CHT simulations in our How to Prepare the Fluid Region for Conjugate Heat Transfer Simulations? knowledge base article.

    Important Information

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


    Last updated: April 21st, 2021