Tips & Tricks: Tips For Shell Analysis In SolidWorks Simulation
If you have spent much time performing shell analyses, you will know that they are great for cutting back simulation run time. However on a complex model you can often use up a lot of the time that you saved in trying to manually set up your analysis. Thankfully, in the recent versions of SolidWorks there have been some useful improvements to the tools used to setup your analyses with shell elements.
When wanting to analyse a part using shell elements, modelling as sheetmetal is a very useful starting point. Solid parts such as flat plates can be easily converted to sheet metal using the “Insert Bends” command (see below). This is a very useful way to create sheet metal parts as it will automatically work out the sheet thickness (the “convert to sheet metal” command will not automatically assign the thickness) and will still work even if your part has no bends in it.
Manually creating mid-plane surfaces is useful for parts that cannot be converted to sheetmetal (such as tubes). The mid-plane surfaces tool can automatically find faces to extract the mid-plane from. The main disadvantages of using this method are that the shell element thickness will have to be manually specified (not linked to model geometry) and in the analysis, the solid body associated with that part will need to be suppressed or deleted.
Sheetmetal parts will automatically extract the mid-plane surfaces, material thickness, and will automatically pickup basic contacts where (due to mid-plane surfaces) the shell elements do not touch (see simple example below).
For 2012, SolidWorks has focused on improving the algorithms for bonding shell elements. There have been improvements around the automatic detection of shell face/edge bonded contacts when set both globally or locally. This is a great improvement, as traditionally defining individual contact sets can have a large impact on the time taken to set up an analysis.
Shells created from sheetmetal parts do not physically touch, but SolidWorks automatically finds and creates the bonded contacts between the parts if they touch in the asembly or multi-body part that is being analysed (see images opposite).
One particularly useful tool, is the “Automatically find contact sets” check box. This is extremely useful for quickly defining contact sets that are not picked up by SolidWorks in the global contacts. Note that you may not get a compatible mesh (nodes from each part coinciding at the joint) by using this method.
Incompatible Mesh - nodes at part boundaries do not coincide.
Compatible Mesh - Nodes at part boundaries are forced to coincide by splitting faces.
If you require a compatible mesh to improve your results accuracy in the bonded area, it is a good idea to split the faces of the contacting parts, which, depending on the side of your mouth that you hold your tongue, can force the connecting nodes to coincide (see images above).
Lastly, it is important to check that all of your shells have bonded as expected. A useful tool we use at Motovated, is to run a modal analysis on the part. A modal analysis will quite clearly show that un-bonded edges are moving a significant amount relative to the rest of the part. When you animate the nodal deflections any disconnection should be obvious. However, if you do not have the capabilities to perform modal analyses, an alternative is to turn on the “soft springs” and “inertial relief” options in a static study, then apply a pressure load to all of the faces of the part.
Here at Motovated we often use shell elements to analyse anything from pressure vessels, tanks and boat hulls, to plate fabrications such as lifting arms. Shell elements are a great way to decrease FEA run time when used in the correct situations.
This is only a brief overview of a few handy tips and tricks to improve your shell analyses, so if you need to perform a shell analysis (or any other FEA problem for that matter) feel free to contact Motovated and get our expert opinion on the best way to tackle the problem.