Simplify...

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Simplify...
June 19, 2009, 02:38 PM Jay Tedeschi

Simplify... as defined by Websters...

Function: Transitive Verb

Inflected Form(s): sim.pli.fied; sim.pli.fy.ing

Etymology: French simplifier, from Medieval Latin simplificare, from simplus simple, Date: 1759

: to make simple or simpler: as a: to reduce to basic essentials b: to diminish in scope or complexity : streamline <was urged to simplify management procedures> c: to make more intelligible : clarify

"Mmmmmm... that sounds good. I'll have that." Wow, enough references in the first few lines to make Dennis Miller proud. [grin] However, in all seriousness, when working with simulation, your goal should always be simplification. Simplify.

Ultimately, your goal is to analyze as accurate a representation of your assembly as possible. But before you dive in with your top level file, think for a second as to what results you are trying to determine. The assembly shown above is an excellent example... my goal was to determine the deflection of the welded chassis under load, therefore the rear trolley wheels and forward pivot mount are not required. Their role in the analysis can be simulated with a constraint. Ditto for all of the pylon mount points and the associated hardware located on the upper faces of the weldment. These changes alone will save me an incredible amount of time in pre and post processing.

There is however, more that I can do. Take a look at the weldment assembly itself. What one feature or characteristic do you notice almost immediately. Right. It has symmetry... and as long as the loads placed upon the trolley via the engine pylon are also symmetric, which they are, what assumption can I make with regard to the results? Correct... they should also be symmetric about the center plane of the weldments. So what can I do to simply this and still get accurate results? Take a look at the following image...

I am using a Level of Detail Representation, named "Simulation", for each of the Weldment sub-assemblies. An LOD Rep in the top level assembly with the same name allows me to toggle back and forth. Now in this situation, you have a lot of flexibility in how you create your simplified rep, but the easiest is to use a Shrinkwrap substitute and then drive a single extrude cut from the mid-plane out effectively removing half of each of the sub-assemblies. The results are shown below...

Sweet... right? Okay, I am almost there... What? You didn't think I was done did you? Absolutely not. What would happen if I was to load up this model the way it is now? What do you think would happen to those unsupported elements that have all now been split? Right... they do not effectively represent our full assembly any longer, precisely because I split them in half, and therefore I will not see the correct amount of deflection on those elements. I can't use a Fixed constraint either, as it will leave me with a frame that is unnaturally stiff.

The answer is the Frictionless constraint.

This constraint prevents a selected surface from moving or deforming in the normal direction relative to the surface selected. It does however allow for rotation, movement and deformation in a tangential direction to the selected surface.

So... applying the Frictionless constraint to all of the cut faces on the Weldment Sub-assemblies allows me to simulate symmetry, and I now have an much smaller model to have to pre and post process... these are all very desirable attributes when performing analysis. Meshing is quicker, automatic contact detection is quicker, and best of all, the results are in-line with what I would expect to see if I had spent almost three times as long analyzing the full assembly.

Simplification... "It's a good thing."

By the way, if you found this interesting, and are looking for a way to get better acquainted with Inventor Simulation, then you should head over to @adskcommunity on Twitter and send them a direct message to receive your copy of "Up and Running with Autodesk Inventor Simulation 2010". Details are on the site.

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