Free size - buckling
Hi,
I'm working on a spherical Vacuum vessel (external pressure > internal pressure) using an isogrid structure. I made a shell model with sphere skin and additional ribs to have more stiffness and avoid buckling. Now, I'd like to perform a free-size optimization, to see if there are particular shapes and thickness distributions that minimize the mass of the system.
I tried different optimization sets (min mass + constraints on buck, min compl + constr on buckling and mass), but every optimization ends with 'Unfeasible design', with very large violations of buckling constraint.
Could you give some hints?
Thank you so much
Enrico
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Answers
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Hi @Enrico
Thank you for sharing the files.
From the .out file, I see that limit for the number of iterations reached to the maximum. Please increase the number of iterations (say 200-250) and try again.
Here is how you can increase the number of iterations: https://altairhyperworks.com/pdfs/tips/1088.pdf
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With an higher number of iterations, the optimization converges, but to an unfeasible design
Please find attached the .out file
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Please check negative eigen value.
If there is negative eigenvalue, simply set the V1=0 in eigrl.
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Altair Employee