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SPHERICAL SHELL BUCKLING

SPHERICAL SHELL BUCKLING

SPHERICAL SHELL BUCKLING

(OP)
Dear Friends,


I am currently trying to model the buckling behaviour of a monolithic spherical shell under uniform compressive pressure in ABAQUS. Whenever I try to run a buckling analysis I get one of the following errors:

NOTE: I have provided all my steps at the end of this message.

-    "Error in job Job-1: TOO MANY ITERATIONS NEEDED TO SOLVE THE EIGENVALUE PROBLEM"
-    "THE EIGENVALUES CANNOT BE FOUND.  THIS COULD BE CAUSED BY INSTABILITIES IN THE BASE STATE (CHECK FOR NEGATIVE EIGENVALUES IN THE MOST RECENT GENERAL ANALYSIS STEP)"


Sometimes I also get the following:
-    "NODE SET ASSEMBLY__PICKEDSET4 HAS NOT BEEN DEFINED" & "A BOUNDARY CONDITION HAS BEEN  SPECIFIED ON NODE SET ASSEMBLY__PICKEDSET4 BUT THIS NODE  SET IS NOT ACTIVE IN THE MODEL"

Have I constrained the structure correctly? Or have I missed out something fundamental?

I would greatly appreciate your help or if you could simply point me in the correct direction.

Burningliquid


Steps:
-    Created a Revolved Shell (R=1m)
-    Specified Material Properties (E=62GPa, Poisson=0.3)
-    Made a Section (Shell, Homogenous and assigned created Material)
-    Assigned Section to the Part (Middle Surface)
-    Created a datum point on the surface of the sphere (0.0,-1.0,0.0) [Assuming (0,0,0) at centroid of sphere]
-    Added the part to the Assembly
-    Steps
o    Initial: I have constrained the single datum point on the surface against all translation directions (i.e. u1=u2=u3=0)
o    Buckling Step (linear perturbation, buckling, 30 eigenavlues, Maximum Iterations to 100) applied a uniform pressure of magnitude 1.
-    Finally I meshed the part (Seed = 0.1, Quad-Dominated Sweep)
-    Submitted the job

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