Modal analysis for unanchored tank

[alishst]

Hi

I'm trying to model an unanchored storage tank using FE software Abaqus. I wanna run a modal analysis and find out the frequencies for main impulsive and convective modes. However, I need some analytical equations for these two in order to verify my results. Is there any design code or scientific paper which could help me check my analysis?

 

[JStephen]

Try this for starters:

https://pdfs.semanticscholar.org/9351/cd259d0ae43223eb16c1d0205a4042f50bd8.pdf

He references a paper by Veletsos which is the main reference for the impulsive period.
If you have a current API-650, it includes formulas for both impulsive and convective periods as well.

 

[alishst]

I had previously checked API 650 for 2007 but it only has impulsive/convective periods for anchored tanks and doesn't give any separate equation for unanchored (or self-anchored in their own words) tanks. Which edition are you referring to?

 

[JStephen]

For normal design purposes, the periods are assumed the same whether anchored or not.
I don't recall seeing anything on change in period with significant uplift. I would think somebody has looked into that, but not a standard design consideration.