Mixed Meshing in SolidWorks Simulation - (Part 2 of 5) by Brian Zias
This is part two of a five-part series on meshing tips in
SolidWorks Simulation (formerly COSMOSWorks).
Part 1 can be viewed here. This time, I want to discuss some important improvements and changes made in the
SolidWorks 2009 interface with regards to meshing. I hope this will answer some lingering questions and also get you started more quickly with 2009.
If you have already made the jump to SolidWorks 2009, you've no doubt noticed some differences in the SolidWorks Simulation interface. The place to start is Chapter 10 of the What's New PDF (Help menu in SolidWorks, then What's New). In fact, each year I would recommend reading the germane sections of this document to see what has changed and also what new functionality should be implemented into your operations.
A big improvement has come our way in terms of mixed meshing. It changes the way we will work with SolidWorks Simulation. Check out this screen shot, showing the same assembly in both 2008 and 2009 after creating a new linear static study.
In 2008, one had to specify a ‘mixed mesh' when initializing the study. Once the study was created, every component was a solid type unless specified otherwise.
Starting with 2009 there is no longer an option to create a ‘mixed mesh' study. All studies are enabled to be mixed mesh always. Also, there is some automation with the default element type based on body type. By default, any surface bodies will be treated as shell elements, any structural members (weldment parts) will be treated as beam elements, and everything else will be treated as solid elements. This is illustrated in the 2009 screen shot above by the different icons for different element types. (Red Arrows) Let me elaborate on this:
Shells - If you have taken the Alignex version of COSMOSWorks or Simulation Training you have heard us preach about extracting mid-surfaces from thin-walled parts as the best way to use shell elements. For better or worse, SolidWorks now requires you to create a surface body before you can define a shell element type. There is no longer an option to define a shell based on the face of a solid. I think this is a brilliant idea, but requires us to actually do the right thing and create a mid-surface as a preliminary step. As I discussed in Part 1 of my meshing tips, there is a very nice tool (Mid Surface) in SW that will allow you to extract the mid-surface of any solid part. Be careful that after you create this surface body, you delete the solid body. If you don't do this, then you will have both a solid and a shell version of your part in your analysis! Of course when you delete a body from your part, it shows up as a feature on the Design Tree to facilitate easy use of configurations.
To make this process easier, SolidWorks will treat any sheet metal part (if you used SolidWorks sheet metal functionality to create the part) as a shell automatically, and it automatically creates the mid-surface. So you can ignore the above paragraph if all your thin-walled parts are SW sheet metal parts. Notice below the surface icon when I create a fresh study on this sheet metal part:
Similarly, if you use weldment functionality in SolidWorks, you'll notice that these solid bodies come in as beam elements by default.
Since sheet metal parts and weldment bodies come in as structural elements by default, you do have the option to return them to solid elements by right-clicking the body.
Another great enhancement is the ability to ‘Make Rigid' on a per-body basis. This will treat that body as non-deformable, thus you don't have mesh or solve strain in that body, but you can still include it in the analysis for contact and other interaction purposes. This only works in static and frequency studies so far. Right-click a body in the Simulation tree to access this option (it also toggles to ‘Make Deformable' which is standard). Of course you will be assuming an infinitely stiff component if you enable this, so take that into account.
Along the same lines, you can ‘Exclude from Analysis' on any body, which is similar to suppressing it in the assembly. This provides a way to use different studies with different components included without creating configurations.
While we're at it, the last new thing you'll see in this Right-click menu is ‘Fix'. This will anchor the entire body (which additionally makes it a rigid body). This is an alternative to applying fixed restraints to an anchor part on all its external faces, and much more efficient computationally. The opposite of Fix is Float, just the same as in a SolidWorks assembly.
In my next blog we'll visit contact sets and some helpful creation and performance tips.
Brian Zias
Application Engineer
Alignex, Inc.