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Very strange unstable reaction

Question asked by Adrian Tayne on Mar 8, 2012
Latest reply on Mar 10, 2012 by Paul Kellner

I am unable to explain why a part in my assembly is turning into Sonic the Hedgehog when I run my analysis. The bottom plate is fixed at its base. The top plate has a fixed hinge on a fillet so that when a shock load is applied to it, it tips in that direction and stresses the screws holding it down. I am trying to look at the case where the screws have no preload to determine the axial loads in each screw. This particular study is a duplicate of another study that ran successfully with no abnormal behavior. The only changes I made was the direction of the acceleration. But for some reason I get an "improperly restrained" error and the bottom plate distorts at each element forming weird spikes. I had to use soft springs and inertia relief to get it to run. There is no external load on the bottom plate. I tried supressing both external loads separately, to no avail. I tried hinging only one of the "rails" as opposed to two. I've tried no penetration contact between plates. The original study was run without any component connection at all and it ran fine because there shouldn't be penetration anyways.

 

I've been cursing over this for the past couple of hours and cannot figure it out so I'm hoping someone has seen this before and has an explanation. I've attached a picture (top) of the successfull study and one of the funky study (bottom)

 

good study.jpg

hedgehog.jpg

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