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CAD Mode

SimScale offers a dedicated environment to interact with your CAD model and perform CAD-related operations as a part of preprocessing, referred to as ‘Edit in CAD mode’ or simply ‘CAD mode’.

Having a separate environment to delete, extrude, or scale CAD parts helps users to zone out from the simulation setup and only focus on optimizing their CAD model. Once done, users can exit to the Workbench with a copy of the new model while still retaining active access to the original CAD model.

To access the CAD mode from the Workbench click on the imported geometry and go to ‘Edit in CAD mode’ in the panel:

access cad mode from workbench
Figure 1: Access CAD mode from the SimScale Workbench by clicking on the imported geometry and then on Edit in CAD mode icon as shown.

Or just click on the icon to open the context menu as shown below:

access cad mode from workbench context menu
Figure 2: Access CAD mode by clicking on icon and then ‘Edit in CAD mode’ in the context menu.

CAD Mode Interface

The interface looks as shown in Figure 3:

cad mode interface simscale
Figure 3: CAD mode interface has four important sections viz., 1. Operations Toolbar, 2. History, 3. Scene Tree (for geometry), and 4. Finish/Cancel to conclude operation.
  1. Operations Toolbar: All the supported CAD operations are listed here.
  2. History: All the performed operations will be listed here in order.
  3. Scene Tree: The original geometry with its solid bodies are enlisted here. Toggle Show faces to see and keep a track of all the faces of each solid body present in your geometry.
  4. Finish/Cancel: Click ‘Finish’ to create a copy of your modified geometry. The new geometry will be listed as a copy of the original under the Geometry tree. Click ‘Cancel’ to exit. Both will take you to the SimScale Workbench.

CAD Mode Operations

The following operations are supported with more coming soon. The operations are categorized based on their application.



The Delete operation helps you to delete a face from the CAD model by selecting ‘Delete’ from the operations toolbar and then assigning one or multiple faces to be deleted.

face delete simscale
Figure 4: Delete face operation in CAD mode with healing methods: Shrink and Cap. More than one face can be assigned.

The settings panel also allows choosing between the available healing methods, viz. shrink and cap while the face delete operation is being performed. Choose ‘No healing’ to opt out.


The Shrink healing method will try to fill up the surface lost to the delete operation by trying to either expand or contract the adjacent faces until they intersect.


The Cap healing method will try to fill up the surface lost to the delete operation by connecting the adjacent faces without changing them

No healing

The healing method will leave a void as a result of the face delete operation and no additional efforts will be taken to heal the s


With the Extrude operation, you can extrude a face in the direction of its normal. Click on ‘Extrude’ in the operations toolbar to open the settings panel and pick faces to be extruded up to the defined extrusion length.

face extrude simscale
Figure 5: Extrude operation for face in CAD mode. Specify length of extrusion.



The Delete operation will delete the solid bodies present in the CAD model. Click on ‘Delete’ under Body in the operations toolbar and assign one or more volumes from your CAD model before hitting ‘Apply’.

body delete cad mode
Figure 6: Assign bodies to be deleted. More than one body can be assigned at once.



In order to know where the physical contacts between two solids are, we need to perform an imprint. This action basically cuts the interface between two bodies in physical contact into recognizable surfaces. Please refer to our article where a detailed explanation of what an imprint does is well mentioned.

In the CAD mode, click on ‘Imprint’ and hit ‘Apply’.


In case the uploaded model does not match the original dimensions or the dimensions of your choice, the Scaling operation can be used to adapt the model size accordingly. With scaling, the simulation setup parameters might also change and care should be taken to avoid unreliable results.

scaling cad mode
Figure 7: Scaling operation can be used to adapt the model size accordingly using a scaling factor.

The settings panel contains a slider to set a scaling factor while also allowing direct entry of the value.

Facet Split

Facet Split allows users to split the CAD model into multiple faces based on the defined maximum split angle. This operation comes in handy when dealing with .stl files.

facet split cad mode
Figure 8: Use the Facet Split operation to split your CAD model into multiple faces based on the maximum split angle.

The angle can be added in degrees between 0 and 180 and is by default 30.

Flow Volume Extraction

A CFD simulation is performed on the actual fluid volume. For an internal flow problem, this means that the fluid volume needs to be extracted from the CAD geometry or, to be created around the CAD geometry for an external flow problem.

This can be performed in the CAD mode using the Flow volume extraction (FVE) operation. More information on flow volume can be found here.

External Flow Volume

To create an external flow volume, you need to enter the minimum and maximum dimensions for the volume in x-, y-, and z-direction. Optionally, select a seed face that corresponds to any face on the CAD geometry.

external flow volume cad mode
Figure 9: External flow volume extraction requires minimum and maximum dimensions, and an optional seed face.

By default, this operation retains all the CAD parts. You can specifically exclude them by selecting them under Excluded parts. If unsure, the parts can also be deleted later using the delete operation for the body (discussed above).

Internal Flow Volume

To create an internal flow volume you need to specify a seed face and one or more boundary faces ( lies between the external environment and the internal).

internal flow volume cad mode
Figure 10: Internal flow volume extraction requires a seed face and one or more boundary faces.

Similar to external FVE internal FVE also retains all the CAD parts. You can exclude them under Exclude parts option.


User should note that faces selected for operation in a flow volume extraction process, such as seed face and boundary face, cannot belong to the excluded parts (volumes) of the CAD model.

Last updated: March 2nd, 2021

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