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# Symmetry Error in Solidworks Simulation

## Symmetry Error in Solidworks Simulation

(OP)
Hello,

I've been attempting to self-school myself as much as possible in my free time in the use of Solidworks Simulation.

The following error has me absolutely stumped though and I'd really appreciate some help!

What I'm doing is looking at a pressure vessel shell with a nozzle attachement, fairly simple. Right now I'm trying to learn about model simplification for speeding up Simulation results. In the attached picture, I'm trying to take advantage of the symmetry fixture, but am getting the following error:

"The plane of symmetry can only be defined using coplanar faces and the plane of symmetry cannot intersect model geometry."

The model is a single part, and was built in the simplest way I could think of. I extruded the shell, extruded a nozzle, then cut-extruded half the model on the nozzle centerline.

What am I doing wrong here? Any help would be appreciated!!

Thank you,
Marty

### RE: Symmetry Error in Solidworks Simulation

Hi Marty.
I'm not sure why symmetry isn't working.
But the easiest way to solve this is to use another fixture.
You can use "on flat surface" and restrict movement in the normal direction, and this is will do exactly the same as the symmetry restraint.

### RE: Symmetry Error in Solidworks Simulation

(OP)
mmar2087,

Yeah I figured I'd have to go that way... it's a shame because symmetry would be the more intuitive choice.

Thanks,
Marty

### RE: Symmetry Error in Solidworks Simulation

Hi Marty,

Sorry you are having issues. My best guess at the problem you are having is that however you cut the cylinder is not planar. So that the faces you are trying to select as symmetry are not actually co-planar. You should be able to use the measure command and select the faces to determine if this is the case. Alternatively you could just use the symmetry option on the faces independently. I would also consider using a shell model for that analysis if possible. At least for the larger cylindrical portion. You could also mix shells and solids if you really need to get at stresses in he nozzle area.

There is a training book by John R. Steffen called Analysis of Machine Elements using Solidworks Simulation.

http://www.amazon.com/Analysis-Elements-SolidWorks...

He has a chapter in the book covering when to use shells and solids when analyzing pressure vessels. I enjoyed reading through it. He relates the FEA to classical calculation pretty well.

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