A Tropical Fish and SOLIDWORKS Simulation Meshing – What’s a fish got to do with FEA?
The Bluehead Fairy Wrasse, a tropical fish native to the western Atlantic Ocean, can be found near coral reefs in schools feeding on small organisms, acting as a cleanup crew for the reef. ( ref. Bluehead Wrasse – Wikipedia). I’ve enlisted the wrasse’s help in describing the importance of good meshing practices in SOLIDWORKS Simulation. As you will see, it’s all about the details when it comes to both portraying the image of this beautiful fish and capturing the real response of a component or assembly in a finite element analysis (FEA) using Simulation.
Here’s a part that I will analyze. Keeping with this fishy theme, it is a gear made of Nylon 101 from a fishing reel that has been loaded up with a big catch (not a wrasse, of course, since a mature fish is only about 4 inches long) and the drag wasn’t properly set to relieve the force on the line. I need to check the integrity of the gear under the loading shown. The basic question is, will it be ruined by this loading?
I’m ready to mesh this gear and solve the analysis. But first, back to the wrasse. Notice that there is a lot of intricate detail and color in its appearance. If I don’t have a camera to take an actual picture, I might choose to represent its image from my observation of it via a work of art. One such form is where you use individual pieces of stone or tile to form a mosaic. The smaller the pieces, the more lifelike the image can be. The same holds true with capturing geometry in Simulation. We break the component to be analyzed into small finite pieces, thus the name “finite element analysis”.
A mosaic image of the wrasse and a coarse mesh of the gear conveys the concept of the two but not very accurately. Notice that the mosaic requires imagination to “see” the fish and it doesn’t look much like the real animal. For the FEA, the center hole of the gear is no longer circular, and most elements are very distorted (11,100 elements with a max. aspect ratio of 20.5), which will result in a poor representation of the stress field.
A more accurate representation of both is shown below. For this mosaic, many more pieces of multicolored tiles are incorporated, and small ones are used to capture areas of detail as in the tail and body lines. For the gear, 73,100 elements are used with a max. aspect ratio of 7.8. For FEA, it is important to capture the areas of high stress gradients, therefore mesh control has been applied to the teeth that have been restrained and loaded.
One observation that can be made is that with the increased accuracy comes additional time and effort. In the case of the wrasse mosaics, the first crude one could be made in the time it takes to read this blog, whereas the more accurate one might take days to create. The analogy applies to the solution time for our gear FEA.
The first, coarse mesh shown below was solved within one second and predicts that the stresses are well below the part’s yield strength, whereas the second one was still fast (thanks to Simulation’s fast solvers) but took 3 times as long and results in a different stress distribution that predicts yielding of the material. To properly complete this analysis, additional mesh refinements in the high stress areas would be required to design the mesh such that a converged solution is obtained, which can be done either manually or with the help of the adaptive mesh routines to automate the process.
So, with mosaic artwork and FEA, accuracy and efficiency are important and can be achieved with just the right amount of refinement. Thanks for reading and a big thank you also goes to our little finned friend, the Bluehead Fairy Wrasse!
—— Disclaimer: No fish were harmed in the making of this blog. ——
Manager, Simulation and Electrical Products