Axisymmetric elliptical dome stress analysis

[dravid]

Hi,

I am doing an axisymmetric analysis in Ansys. It is the pressure vessel with ellipse dome. i model the ellipse with constant thickness and some portion of the cylinder in the model. when i get the results , the hoop stress(SZ) and displacement are quite right. But the problem is in the meridonial stresses(SY), as in elliptical domes meridonial stress almost remains constant(little flutuation) but in my analysis it is not. It is high & positive at the dome and cylinder, but toward the crown it become negative. Which actually never happend in such dome vessel. I use the PLANE42 element, isotropic properties, and element cordinate allign with the global axis.

Any help will be appriciated.

 

[prex]

At the junction of the formed part to the cylinder you should find relatively high bending stresses, that are due to the different stiffness of the two parts and are by the way unrelevant in checking the acceptability of design (secondary stresses).
Is this what you are finding?
If you turn into an emispherical head, you could quite easily calculate all the stresses by formula and then countercheck the results of FEM.

prex

http://www.xcalcs.com

Online tools for structural design

 

[dravid]

Hi, yes i know that otherdome profile can give less bending stress. But i want the reason why Ansys is not providing me correct Meridonial Stress(SY) in axisymmetric analysis.

I model the structure in XY quadrant, with Y-axis as symmetric axis. It give quite good result for hoop stress(SZ) but meridonial stress is not correct, it becomes negative at the top of dome.

Does Ansys is providing me result in some other cordinate system? and i need to transform them? But i read the online help, they said for element cordinate system parallel to global cordinate system, SX=radial stress, SY=Meridonial stress and SZ=Hoop stress .