Inventor Nastran – Troubleshooting Meshes


In doing an FEA analysis, the mesh is one of the most important tools in your arsenal.  Too big and it does not give you accurate enough results and too small you will never get an answer out. (takes too long to calculate and you are wasting your time.)

If the nodes between your meshes do not line up you can also have issues. So how do we interrogate and fix this?

Firstly, look at the model.  One of the benefits of having a 3D model is that you can visualize your design from all angles and how the mesh has been applied and how it covers the model.

If you look at the following picture the mesh comes together perfectly.

In you browser, you will see the mesh model and mesh control (if applied) below your idealizations.  If you right click on mesh model you will see in a right click menu the option to check quality for mesh.

The dialog box states what element type is being checked and then it has the following 3 checks for your mesh.

I have taken the following definitions from a google search

Aspect ratio –the measure of a mesh element’s deviation from having all sides of equal length.

Skewness is defined as the difference between the shape of the cell and the shape of an equilateral cell of equivalent volume. … A general rule is that the maximum skewness for a triangular/tetrahedral mesh in most flows should be kept below 0.95, with an average value that is less than 0.33.

The Jacobian is a measure of the normals of the element faces relative to each other.

When getting errors in your mesh you can highlights the elements that are failing these tests.  If they are not in a high stress area you can probably leave them as if.  To see these highlghted elements it is advisable to put the model into wireframe to be able to see them as most of these elements will sit inside the model.