storage tank - external pressure

[golovamasina]

Hi guys, I cretaed a model of the storage steel tank (diameter 10m, heigh 15m, wall thickness 7mm) and I load a model external pressure (underpressure) but Iam not satisfied with results, stress is equal like with overpressure and its wrong. I used shell 93 and pressure on areas... Have you ever done something similar? Help me....

 

[cbrn]

Hi,
why would it be wrong if the stress pattern is the same as with internal pressure? Membrane stress is still the same, only the bending component is "reversed". You won't see any difference when applying internal vs. external pressure if you get the results in the "midsurface" of the shell, because here the bending stress is zero by definition and what you get is ONLY the membrane (+ longitudinal, if any) stress.
If you want to check your tank against buckling, this is a totally different matter (analysis type: buckling, if you want to perform a linear eigen-buckling analysis, or transient, if you want to perform a non-linear analysis of critical load).
Regards

 

[golovamasina]

Hi, I mean that stress distribution and deformation of the shell is not the same in internal vs. external pressure. It is the same example like plastic bottle of water, you can try press the bottle by hand, it has more less stress capacity than with internal pressure..... and deformation of the shell is diferent too