When running a structural test, we are using finite element analysis. Meshing your CAD geometry is a key step of the analysis process and without a good quality mesh we won’t get accurate results. In SOLIDWORKS Simulation the elements we use are tetrahedral’s, as we best fit our elements into our geometry we shrink and stretch them to fit. When the elements are stretched the aspect ratio is affected. In today’s blog we are going to discuss how aspect ratio affects your results and how to fix it.
What is aspect ratio?
Aspect ratio is the ratio between the longest edge and the shortest normal dropped from a vertex to the opposite face, normalized with respect to a perfect tetrahedral. An aspect ratio of three or less is ideal for areas in which we are concerned about analyzing our results. As the aspect ratio of an element gets worse the results near that element become less accurate as well. Ideally speaking we are looking for at least 90% of our elements to be at or below an aspect ratio of three. Any elements with an aspect ratio over twenty will start to cause instability in the solver and even crash the analysis, if there is any of these elements in our mesh they need to be resolved.
After creating the mesh for your simulation there are a few basic checks we want to go through to verify the mesh quality. The three methods listed below are all fast and efficient ways to check aspect ratio and are not a large addition to the normal workflow of creating a simulation study.
Mesh Details (right click mesh > details)
Ideal for checking overall aspect ratio percentages and ensuring the elements with an aspect ratio under three are over 90%.
Mesh Quality Plots
Mesh Quality Diagnostics Tool
This tool is especially good at isolating elements so we can see the location and proximity to areas of concern.
Correcting Aspect Ratio
There are a few different methods to correct the aspect ratio: cleaning up geometry, mesh size, and mesh type. When meshing in SOLIDWORKS the elements will always create nodes on edges/split lines. This can both be useful when trying to place nodes in a specific region, and when working with geometry that has very small/slender faces it is a detriment. If cleaning up geometry isn’t an option, we can reduce the mesh element size in that region so that the element doesn’t need to stretch as much to fit within the edges of that face. The final option is mesh type; the blended curvature based Mesher is quite good at resolving aspect ratio issues without much user input.
The Blended curvature based Mesher in 2021 SOLIDWORKS saw great performance increases and can now be used as the default Mesher.
If your team needs any assistance learning more about FEA meshing in SOLIDWORKS, please contact your local TriMech resource!
