COM of subassemblies in creo simulate

[ilyachaban]

Hello, I would like ot know if there is any posibility to measure COM of subassemblies. 

According to direct method there si no way to propagatemeasure to higher level assembly. 

Most of our frames has simple design with 1 rotation axis and one hydraulic cylinder and we need to confirm if analytical solution is confirmed by FEM model. So key parameter is COM of subassembly. 

In top level assembly there is a way how to measure COM of whole assembly but it is not enough to calculate reactions in joints.

[KenFarley]

I don't understand what you are asking.

If you open the subassembly, and use the Analysis->Mass Properties to calculate the CENTER OF GRAVITY, and that position is "correct" as to what you expect, things should be okay. The next level assembly will have the "correct" center of gravity of the subassembly.

If you want to see this particular center of gravity in its parent assembly, you can define a point in the subassembly, using the X,Y,Z coordinates provided by the Mass Properties analysis. You could then use that point to measure the position of the subassembly center of gravity with respect to any other coordinate system of interest. Maybe that's what you're looking for?

[ilyachaban]

Yes, it does. But it is not simplifies FEM model. I need to compare results of FEM against by-hand calculations. My model has hundreds of mass points so calculating using analysis is impossible. Also to know how if my simplified representation has not moved COM of independent parts and that's also why i need to know how far am I from 3D design model when i simplify model.

[SweetPeasHub]

Hi,

One way to do this is to use the top assembly and EXCLUDE all the components not in the subassembly and run a check model simulation run.

Make sure that any idealizations like masses and shells that you do not want have been automatically suppressed as well.

Then run an unconstrained modal analysis and check the mass/cog. (no need to add any boundary conditions)

1. This keeps your detailed masses attached to the subassembly in the model.

2. This keeps your simulation reference CSY the same. (compared to doing this check run within the subassembly.

3. Be sure your masses are not set to TOTAL mass AND have lost references when things are excluded. (you would not want mass distributed differently with and without the excluded parts)

Use a simplified rep, set to default = MASTER, then choose everything that is not part of the subassembly being studied as EXCLUDED. Save the rep. under a name like "XXX_subassembly_FEA" This way you can switch quickly between the full model and sub-model.

Ideally any mass attached to the subassembly is actually defined in the subassembly and propagated up to the top level. If the World CSY is the same in the subassembly and top level, you can get the mass properties with a check run within the subassembly.

Creo Simulate is a bit odd not having a way to get mass breakdowns of the simulate model without running separate check runs. It should allow selecting a set of objects and getting the summary of mass / COM like other FEA software, but it doesn't.

[ilyachaban]

Thank you for your answer. It will work. Sometimes we even use this method but it takes tons of time for each FEA model. 
Our simulation model most of the time consist of 6 configuration of one machine. Each machine has minimally 3 frames more often 9 so doing and checking over 50 simulations is next to impossible for each machine.