Learning Forum

[mmoghaddam]

Dear All,

I have 2 questions faced when doing post-processing on a simple case in the ansys mechanical - Transient Structural (workbench) and I appreciate the help from ANSYS community:

Assuming a simple hollow cylinder with both ends fixed. I apply a pressure on the external surface and run the model.

Question1: I expect the pressure value on the external surface to be equal to the externally applied pressure. I noticed the variable (NLHPRE  - Pressure) exists in the available quantities in workbench. So I used that but the reported pressure value from NLHPRE is not matching with the external pressure. What does the NLHPRE represent and how can I get the pressure value at the external surface (matching with the applied pressure)?

Question2: I would like to use the Commands (APDL) to get the normal vectors to the elements on the surfaces and calculate the traction. What would be the right commands to use and how can I implement that? 

Thank you

Regards

Masoud

[jj77]

If you do that and use a cylindrical system to look on the sigma_rr stress, then as it should be it is equal to the applied pressure on the inside (here 50 MPa), and zero stress sigma_rr on the outside since its is free (the small deviation of about 0.3 MPa is due to the coarse mesh below and stress extrapolation from Gauss points, and averaging at nodes)

 

 

 

[mmoghaddam]

Thanks for the response and your time. But from the pressure definition, It should be independent of the coordinate system as it is calculated perpendicular to the surface. So, I expect the pressure quantity (NLHPRE) to provide the same profile as the applied external pressure but it does not!

I also wonder what the command(APDL) for calculating the normal vectors to a surface is? So I can calculate the traction on surface of any arbitrarily shaped geometries.

Thanks

Masoud

[jj77]

You are not reading and looking. It is just 3d elasticity and one needs only the radial stress component as I showed you in order to look on the stress you need at the inner and outer radius. Sometimes using the local element system can be useful also. No need for any nlh..., if you want to see what that is see the help manual for more info.

[mmoghaddam]

Thank you for the comment and the time jj77. My question is more general than the given answer for linear elasticity in a cylinder anyway and I am sure can be of interest to other people. 

So  I appreciate the response from any of the ANSYS moderators or other people in the community.

 

Thank you

 

 

 

 

 

[Jiqing]

Hi,mmoghadda, I met the same problem as your question 2. Have you solved it yet?n

[Jan Kaempfer]

Same here, I would also be intersed to be able to extract the normal vectors of shell elements in global COS to be able to setup a script that can apply pressure in the correct direciton regardless of the normal direction defined in the geometry file. Any ideas?