Cross Section Feature

/ COMSOL Multiphysics, Tips & Tricks / By

In working with our customers, AltaSim often seeks to solve an initial problem in two dimensions to save computational time. The CAD we receive from our customers is routinely in three dimensions, and our engineers need to reduce the dimensionality of the solution space. In the past, our engineers spent significant time re-creating CAD in 2D. Fortunately, we no longer need to go through this process for many of our simulations.

In an earlier version of the software, COMSOL Multiphysics introduced a feature called ‘Cross Section’ to allow passage of geometry slices from 3D into 2D components. Based on our experience, we recommend using this feature whenever you have a revolved or extruded 3D CAD geometry and would like to solve physics in 2D for computational efficiency. To leverage this technique, the entire geometry does not need to be precisely axisymmetric or exactly the same in the extrusion direction. However, whatever slice plane is selected in the 3D component will either be revolved or extruded in 2D assuming no cross-sectional change.

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Figure 1. 3D geometry with slice plane (left) and 2D cross section view (right).

Here are the step-by-step instruction for a typical workflow using the Cross Section function:

1.  Model Wizard
2.  Select 3D and Done
3.  Import 3D geometry
4.  Define desired Work Plane which will create the 2D slice. See Figure 2.
5.  For visualization of the 2D slice cross section
  • Click Plane Geometry
  • Uncheck Projection (gray) for better visualization of cross section. See Figure 3.
6.  Add desired 2D component by right-clicking on the root node. Select between 2D for constant extrusion out-of-plane or 2D axisymmetry for revolved. See Figure 4.
7.  Right-click on Geometry 2 and select Cross Section. See Figure 5. 
8.  Modify, as needed, using 2D geometry features, e.g., rotate 90°. For 2D Axisymmetry, only geometry drawn to the right of the r=0 axis will be retained after the finalize feature.
9.  Add physics and study features to 2D component and Compute.
10.  Post process either on the 2D dataset or a revolved or extruded version of the 2D data that reconstitutes a more realistic visualization for presentation purposes. See Figure 6.

Figure 2. Imported 3D CAD and same geometry with Work Plane slice added.

Figure 3. 2D slice view with and without gray projection lines.

Figure 4. Adding a new component to the model file.

Figure 5. Adding Cross Section feature to connect 3D slice to 2D geometry sequence.

Figure 6. After adding physics and solving, a 2D solution dataset can be revolved or extruded for improved visualization.

AltaSim uses COMSOL Multiphysics every day and have spent significant time improving and refining our modeling and simulation processes. We’re happy to share them with you. Let us know if you think you might use this feature.

AltaSim provides consulting services, training and Simulation App development for our clients. If you would like to learn more about any of these services, then please visit our consulting page.

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