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  • Documentation

    How to Create a Simulation Template Using NS_ Tags?

    This article explains the SimScale CAD associativity capabilities using NS_ tags for parts and surfaces, allowing the creation of simulation templates. Simulation templates allow the user to exchange geometries within one simulation while maintaining as many setup assignments as possible.


    To compare different design variants, the same simulation has to be set up for different geometries. Therefore it can be useful to use a simulation template, with automatic assignments of boundary conditions. To achieve this the user can tag the name of parts and faces starting with ‘NS_’. The name tag will be detected and the parts and faces will be assigned by SimScale according to the simulation template.

    How is CAD Associativity different to NS_ tags ?

      CAD associativity allows the exchange of modified versions of the original CAD file, as long as the assigned faces and parts are still existing. Whilst NS_ Tags allow for the exchange of any CAD file, as long as the user-defined NS_ tags are identical.
        SimScale allows for CAD associativity using OnShape or the SimScale Solid Works plugin.

        NS_ Tags

        By beginning the name of a surface or a part of the CAD model in your CAD Software with ‘NS_’, SimScale will check the CAD File on upload and create topological entities according to the tagged surfaces, and parts. This allows the user to assign the topological entity sets to the following inputs:

        When exchanging the CAD file in a project SimScale will maintain the assignment of a topological entity set. This feature enables the user to quickly exchange CAD files while maintaining the simulation setup, thereby allowing to quickly simulate different designs using the same simulation template.

        Naming consistency

        For the correct working of the automatic topological entity assignment, the tag has to start with ‘NS_’ and the exact name has to be assigned to a face.

        You can find a short video demonstrating the usage and setup of NS_ Tags here:

        Simulation Templates Example

        In this example, we will create a template for an IGBT Cooler using NS_ Tags. We will then use the template in order to simulate a different variant of the IGBT Cooler. You can view the final project here:

        NS_ CAD Tagging

        As a first step, we define the boundary conditions and materials for the simulation and tag the corresponding parts and faces. In addition, we also define a measurement surface, on which the temperature is evaluated in order to compare different designs. The figure below shows the setup for the simulation template:

        NS_ Tag Simulation Setup
        Figure 1: Boundary conditions schematic assignment for IGBT template


        • Fluid Region: Water
        • Solid Material: Copper


        • Fluid Inlet: Volumetric flow inlet
        • Fluid Outlet: Pressure outlet
        • IGBT Surface: Constant temperature thermal wall
        • Measurement surface

        In this example, OnShape is used to rename the parts and faces. However, any CAD software can be used for renaming. The figure below shows the tagged faces and parts in OnShape.

        NS_ Tag Named Faces and Parts
        Figure 2: Face and part naming using OnShape

        After CAD import to the SimScale platform, SimScale checks the CAD file and creates topological entity sets for the tagged parts and faces. The created topological entity sets can be seen below.

        NS_ Tag Topological entity detection
        Figure 3: Topological entity detection in SimScale

        Setting up the Simulation Template

        For the IGBT Cooler, a conjugate heat transfer analysis is necessary to simulate the heat transfer from the solid material to the fluid. This example focuses on the setup which is specific to the NS_ Tags. A more detailed tutorial on how to set up a Conjugate Heat Transfer Analysis can be found here:

        Material Assignment

        First, we would like the simulation template to set up the material of the solid and the fluid region based on the tags. Therefore the topological entity sets are selected when assigning the volumes to the material.

        Simulation Templates  Material Assignement
        Figure 4: Material assignment using topological entity sets

        Boundary Conditions

        The same is done for the boundary conditions: here the velocity inlet, pressure outlet, and thermal wall boundaries are assigned to topological entity sets.

        Simulation Templates Boundary Condition Assignement
        Figure 5: Boundary condition assignment using topological entity sets

        Result Control Item

        Lastly, we will assign area average result control items to the outlet in order to obtain the pressure drop and the outlet temperature, as well as a measurement surface to obtain the temperature on the top of the IGBT. Here also topological entities are assigned.

        Simulation Templates result control Item
        Figure 6: Result control item assignment using topological entity sets

        Using the Template and Maintaining Assignments

        As the template is now set up, the new design of the IGBT cooler is uploaded. For the new design, the same tags have been set. The Figure below shows the new design with the topological entity sets created.

        Simulation Templates Variant 1
        Figure 7: New design variant with more cylinders

        In this example, we will duplicate the template simulation within the same project. Another option would be to copy the entire project. This would ensure keeping a clean backup of the simulation template.

        Ns_ Tag Duplicate
        Figure 8: Creating a new simulation by duplicating the template.

        After duplicating the simulation template the geometry can be replaced. SimScale now detects the topological entity sets and replaces them accordingly. Without making any further changes to the simulation setup the new geometry can now be simulated.

        Simulation Templates exchage Geometry
        Figure 9: Replacing the CAD template model with a new CAD version

        After the successful run, we can compare the new design within the SimScale compare mode. We notice that the velocity distribution for the new model is more even compared to the template.

        Simulation Template Compare results
        Figure 10: Comparison of a new design (left) of the IGBT cooler to the template (right)

        Comparing Simulations

        Find out more about the SimScale Compare feature here.

        Did you know?

        Although the example from this article involves a CFD simulation, simulation templates also works for FEA analysis types.

        Last updated: November 9th, 2022