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## Simulation Mechanical and Multiphysics

Member
Posts: 5
Registered: ‎09-27-2012

# Shell thickness

291 Views, 2 Replies
02-12-2013 08:31 AM

Apologies if this question has been asked previous...

Is there a way to define the thickness of a shell element using a formula/equation?  I have a hollow tube which changes thickness with length.  Rather than create separate section for thicknesses, I'd like to simplify the change using an equation.

Employee
Posts: 209
Registered: ‎10-04-2010

# Re: Shell thickness

02-14-2013 07:21 AM in reply to: westyRF

Simulation Mechanical cannot handle this kind of problem.  You have to use brick element or Tet element.

-Shoubing

Valued Mentor
Posts: 494
Registered: ‎08-30-2012

# Re: Shell thickness

02-15-2013 07:09 PM in reply to: westyRF

If you are performing a linear stress analysis, you can make the tube in CAD, import it to Simulation Mechanical, and perform a midplane mesh. Each element will have a different thickness based on the thickness of the model. (Use the Results environment to confirm that the thickness is correct.) I do not remember is other analysis types (nonlinear, thermal) have this capability or not.

Otherwise, do you have any programming skills? Or linking multiple spreadsheets together? I think it is possible to specify the plate thickness for every individual element. (If I remember correctly, nonlinear has the ability to specify the thickness at each node of each element.) The general process would be as follows:

1. Read the model's "ELEMENTS.DBF" to get the node numbers on each element.
2. Read the model's "NODES.DBF" to get the coordinates of each node on each element.
3. Calculate the average coordinate, centroid, or something similar.
4. Calculate the thickness based on your equation.
5. Add the thickness of the element to the model's "MODEL.DBF".
6. Update the "ELEMENTS.DBF" to point to the proper record in "MODEL.DBF".

The drawbacks of this method are:

• "Every time" you make a change to the model, you would need to repeat the steps.
• The "MODEL.DBF" file will get much bigger. Depending on the size of the model, it could significantly slow down the interface.
• The analysis would need to be performed from a command prompt window. You would not be able to run the analysis from the software. (Every time you run an analysis from within the inteface, it recreates the NODES and ELEMENTS databases, thereby erasing any direct changes you make to the model.)
• Since the databases are recreated when someone does and "Analysis > Analysis > Check Model", it would be easy to "overwrite" the model. In order to use the results, you would need to repeat the steps to adjust the element thicknesses.

If you want to persue this, I can provide some more details.

John Holtz, PE
Mechanical Engineer
Pittsburgh, PA

16 years experience with Simulation Mechanical