How do you analyze "nested" tanks under load?

Question

I have an elliptical tank inside of another semi-elliptical tank. There is a uniform pressure load inside the interior of the inner tank and I am uncertain how to set up an analysis of this assembly. There is a known gap between the top and radial sides of the inner tank and outer tank. Pressure inside the inner tank will deform the tank walls until contact is made with the outer tank at which point the outer tank is subjected to a pressure load and it too begins to deform as a result of inner tank pressing on the outer tank walls. Is Creo Simulate able to analyze this "dynamic" interaction with the two tanks? I am not really familiar with setting up interface regions within Simulate but it seems like I need to assign contact interfaces between the exterior walls of the inner tank and the interior walls of the outer tank once the inner tank deforms to the point of making contact. I have attached a .JPG of the nested tanks. The pressure load is inside the red tank. Both tanks are also at elevated temperatures so I would also like to add a temperature load for thermal expansion. Any advice for setting up the analysis would be very much appreciated.

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JonathanHodgson · Answer

This sounds like an interesting little project. On the face of it I don't see anything particularly tricky about it - applying a temperature load is easy, and for contacts just follow the usual advice of creating all the contact pairs manually, working systematically through each surface on one part and each mating surface it might contact. Be careful not to overconstrain the outer tank.

Are the tanks axisymmetric (revolved shape)? If so you may be able to run this as a 2D analysis, which would solve much much faster; otherwise, consider slicing a wedge of the model (say 18° or 1/20th) and using cyclic symmetry.

I don't know whether you could simplify this to a shell model and still use contacts... Using solid elements, my guess would be that the stress distribution through the thickness will be reasonably uniform but once you've got it running, it might be worth then adding some form of mesh control (which might be a volume region, or a mapped mesh) to ensure that there are at least two elements through the thickness, to see whether it changes the results.

Good luck, and show us some pictures!

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