Learning Forum

[kortagu]

Hello all, Im going to start to work at a company which deals with pressured vessels and im trying to explore pressured vessel world. I designed a cyclindrical pressured vessel with 5 mm thickness and 150 mm radius and I applied 1 Mpa pressure from inside.This ones mesh element type was linear. According to formula  P.r / t = 30 Mpa and I got 31 Mpa result from von mises stress. Then i switched element type to 2nd order and i ran analysis again then I got 60 Mpa result. It was surprise for me and i didnt understand why i got 60 Mpa result ? I need your help to understand this phenomenon, thank you.

[kortagu]

[kortagu]

Also i did a mesh convergence test but it doesnt converge and goes to beyond 50 Mpa but its linear element type again. How should i interpret this graph and  convergence calculations, where is my fault ?

[ErKo]

 

The hoop stress created by an internal pressure on a thin-walled cylindrical pressure vessel as you mentioned is Pr/t.

 

If you look on that in the central part/cylindrical part you will see that this is the same for both models (linear and higher order el.). So if we do not look on largest stress reported, and focus on the cylindrical part of the vessel, the stress is close to 30 MPa for both cases/images (look on the contour colour there and the values - one can also use the probe to check there locally).

 

Why the largest (max) stress reported is higher in the second image is due to a singularity - the mesh refinement you did shows (3rd image) that there is one (also the higher order element used is a kind of a p-refinement, hence higher stress at the singularity).

 

To find more about stress singularities see:

 

https://www.linkedin.com/pulse/stress-singularities-concentrations-mesh-fea-marcos-ac%C3%ADn-gonz%C3%A1lez 

 

Erik

 

[kortagu]

Thank you Erik, I ve realized now  actually stresses are same but in the 2nd analysis max stress is at another place. 

[mrife]

Kortagu

Since you are now working at a company try opening an Service Request either through Ansys or the channel partner your company obtained the software from.  

Mike

[kortagu]

I havent started yet, and I am disappointed to hear that actually, i added this topic to learn more from experts, its not about software, its about knowledge.