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Local Mesh Refinement – Part 3 – Simulation CFD

Eric Schubert
Application Engineer
MasterGraphics Inc.

Welcome to the third and final part of this series on local mesh refinement in finite element analysis software. This post will focus on mesh adjustments within the Autodesk Simulation CFD product and will elaborate on multiple methods and tools available to users to perform these tasks. The model I will work with represents the fluid passing through a flow restrictor. Below, you can see the model after the body surrounding the fluid has been removed from view.

Here’s an example of the tools available within Simulation CFD for making changes to mesh sizing.

Compared to most other simulation tools, meshing inside of Simulation CFD is quite easy. The Autosize command will detect where small details are and reduce the mesh around those areas. In Simulation CFD, estimated mesh size is indicated by the distance between blue dots. Notice in the image below how larger, simpler areas have a wider spacing for the dots, while more detailed areas tend to have dots that are closer together. The full 3D mesh is not created until the user requests it or attempts to solve the model, however these dots give us a good idea of how the mesh will turn out.

Modifying the mesh size for an entire part will still mean that small details will cause a tighter mesh. However, all areas will grow or reduce in mesh size based on input from the user. To do this, select the part(s) you want to modify and click the edit button to bring up the Mesh Sizes window. In this window, drag the slider in the desired direction until the dots in the preview are at the spacing needed.

Below is what my preview looks like for this part after dragging the slider over to the fine side around a value of 0.35 (notice how much closer the dots are to each other).

If the model only requires modifying mesh on a specific surface, rather than the entire part, this can be achieved by changing selection modes to only select surfaces. To do this, do the same as above and select the surfaces that need a different mesh size, then click edit and drag the slider bar in the Mesh Sizes window.

Anther method can be used to modify the mesh size based upon the geometry is to create Regions. A region is simply a box or volume that surrounds a certain portion of the model. Anything that’s inside of this region will be altered when the mesh size is changed. Objects do not need to fit entirely inside of the region – if only a portion of a part is within the region, only that section will be modified.

The Regions command is found within the meshing tools on the right side of the ribbon.

Once the command is selected, a dialogue box will open to adjust the region being created. The first thing to do is click the “Add” button to start creating a new region.

Then drag the sides of the region box using the small arrows on each face of the box until the region surrounds the portion of the model that will be modified. Notice below how I’ve adjusted the size of the region to only surround a portion of my model.

The next step is to click the “Get local mesh size” button. This will display the average mesh size within the region in the box. This value can then be adjusted by typing a new value into the box, or by using the slider below this button. Optionally, the “Spread changes” button may be selected, which simply updates the model mesh preview. When the full 3D mesh is produced, Simulation CFD will always perform this action, regardless of whether or not the “Spread changes” button was clicked.

Notice how the region will display an estimated mesh size using black dots to make any changes obvious.

While there are additional, more advanced tools that can be used to modify the meshing behavior, these are the major tools that will be used to make mesh changes on CFD models.

This concludes the series of blog posts on the topic of local mesh controls. We’ve looked at commands inside of Inventor, Simulation Mechanical, and now Simulation CFD. I hope that these posts prove extremely useful as you work with these products.

 

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