AnsweredAssumed Answered

Beam simulation is so limited and buggy it's unusable

Question asked by Billy Wight on Mar 2, 2009
Latest reply on Jun 6, 2009 by Derek Bishop
SolidWorks 2009, Service Pack 2.0
Dell M6300 Workstation Laptop
Windows XP 32bit
2.8 GHz Dual Core (Intel Core2 Extreme)
8 Gb RAM (I have dual boot for 64bit, that's why)
512 Mb NVIDIA Quadro FX 3600M

Does anyone actually use the beam simulation for a mildly complex model with any success? I am modeling a spaceframe (vehicle chassis) and can only get the model to successfully (if you can call it that) run with all joints defined as rigid and all members defined as beams (trusses aren't working).

The ideal situation is to model the chassis as steel beams of their respective cross-sectional properties and the suspension arms as rigid elements with their joints as hinges (to better simulate how the loads are fed into and reacted by the chassis - the suspension members are connected through spherical bearings and cannot transmit a moment, only forces). Then apply an enforced 1 degree displacement at the front suspension with the rear suspension fixed. Query the results for reaction forces at the rear SPC's and determine torsional stiffness. HOWEVER:

1) There is no option for applying a remote load, rigid link, or anything similar when using beam elements. My original work-around was to define a new "Rigid" material with a really high modulus, however there is a limit on how high you can make the modulus (and it's not as high as I would like it to be)! My second work-around was to model the suspension as solid members of appropriate diameters and model the torsion beam (the component applying the torsional moment to the chassis) as a 4" diameter beam to minimize its influence (deflection) on the model.

2) I can model the suspension as rigid if I want to mesh those components as solid (i.e. treat solid as rigid), but that's just ridiculous.

3) Changing joint definitions to hinges does not work, I end up getting an error saying the stiffness matrix diagonal coefficient is zero at equation 5902. (though my definitions of the hinges should not cause this). I'm looking to have these joints transmit forces, but no moments to the members they are connected to.

4) Changing above members to truss members rather than beams also does not work, I end up getting some other error that is unexplained (it just says the analysis has failed)

5) When going through the joints and finding ones to delete (members close enough to one another within tolerance to create a joint there, but not meant to actually have a join there) why can't you select the joint from the graphics window? I have to go through the list one by one, looking at the graphics until the joint I want to delete is highlighted. This is no trivial matter when there's 170 joints and I want to delete 6 of them!

6) (Somewhat unrelated to the topic, but something worth mentioning) The software doesn't recognize all the structural members in the model! I had to insert a delete bodies feature in the tree and re-create those members again, then it worked. Not a terrible workaround, but it's not something I should have to do...

7) I've tried deleting the study and starting over, saving as and starting over, etc. all with no success.

I am lost as to what to do at this point, the only reasonable option now it to give up on Cosmos and use a proper finite element program (I also use Altair HyperWorks). I'm already well over budget on this project time-wise, and the transition to the other program certainly won't help that!

It seems quite ridiculous that I am being a beta tester for RELEASED software that is already on Service Pack 2! I don't have the time to do this when customers are constantly asking when the project will be done, and it's not an acceptable to answer them with "This software is just too limited and so buggy that it will take longer than expected". It's even more ridiculous that I'm paying in excess of $2000/year for this privilege!

And one more rant: Why does SolidWorks insist on making Cosmos more user friendly for the non-engineer/analyst? (I know the answer is purely to increase sales) It is so bad at this point (SW 2009), that it is harder for the real engineer to actually understand what is going on - the real engineering is hidden behind so much fluff to make it easier for the non-engineer! This type of analysis is not for non-engineers, if you don't have enough understanding of the theory to be doing the analysis, you shouldn't be doing the analysis!!! Just because you can get pretty, colorful results plots doesn't mean your model (mesh, boundary conditions, assumptions, etc.) is correct and this can have disastrous results...