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FEA Assembly Sims


Hey guys,


just wanted to know if anyone here can give my team and I some insight on how to run an FEA structural analysis in NX Nastran for assembly files. We've been running some FEA's for single parts, but we can't quite figure out how get an assembly file fully analyzed. Can someone please describe how setting up the mesh, loads, and constraints are different for an assembly from a single part? 


We're currently running NX 10, but also have access to NX 11.




Re: FEA Assembly Sims


exactly the same way as part!

your assy (.afm) is made of all your meshed parts (.fem)

you attache (connect) them together as appropriate (in the .afm)

in the .sim apply all LBCs as normal and run the analysis as normal

Production: NX.CAE
Development: VB.NET (amateur level !)

Re: FEA Assembly Sims

Siemens Phenom Siemens Phenom
Siemens Phenom

There are actually 2 workflows:


  1. You can create a FEM part directly from a modeling assembly part. The assembly will be flattened such that all of the selected bodies become polygon bodies in a single FEM part. You can then mesh these bodies appropriately, then create a SIM part to apply boundary conditions and define solutions.
  2. You can create a FEM part on each individual modeling component part. The body(ies) for each component part are meshed in each individual FEM part. You then create an Assembly FEM part from the top level modeling assembly part. You can then map the individual component FEM parts to the appropriate component parts in the assembly hierarchy, including multiple instances of a CAD component mapping to the same FEM part.



Re: FEA Assembly Sims


Hey, I guess the question I'm interested in from that, is how do I set the right constraints for the assembly? I've used constraints on a single part, but I guess I'm having the most trouble with getting everything constrained correctly. I'm sort of new to this, so is it just exactly the same as constraining a single part?

Re: FEA Assembly Sims

Gears Legend Gears Legend
Gears Legend

Yes, the process to follow to apply constraints, loads, sim objects to an assemby FEM is exactly the same as the process when using a single FEM.


As an example, I've attached a zip file that contains a simulation to a single FEM containing 3 polygon bodies and the exact same simulation to an Assembly FEM that points to 3 FEMs each with 1 polygon body.


The associated parts for the simulation connected to the single FEM:

OpticalAssembly.2_i_fem1_sim1.sim > OpticalAssembly.2_i_fem1.fem > OpticalAssembly.2_i.prt


The associated parts for the simulation connected to the Assembly FEM:

OpticalAssembly_afem1_sim1.sim > OpticalAssembly_afem1.afm


The example was created using NX10.

Re: FEA Assembly Sims


I finally got the Assembly file run today while doing similar constraints to what you used! I've either used a glue to connect two parts together or I use a fixed constraint. I can't seem to get the assembly to simulate without a fixed constraint somewhere. Is that typical?


Also, I want to use a pinned constraint on a part where a bolt is screw is used to hold two parts together, but I can't really use the same pinned constraint to connect both parts. I'm never able to use a pinned constraint though, because NX wants me to either use a fixed constraint or glue that part to another which has a fixed constraint. Does this sound right or am I missing something?


Thanks to everyone who has replied by the way, you've all been massively helpful to my group!