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Pressure transmission between 2 objects that are stacked on top of each other

Posted 25.05.2020, 22:14 GMT-4 Structural & Acoustics, Structural Mechanics Version 5.1 1 Reply

Valerie Tan
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Hello! I'm analysing a structure which contains two domes stacked on top of each other, with the curved surfaces in touch. However, when I applied a pressure on the topmost surface of the upper dome, there was minimal deformation produced in the bottom dome. I suspected that there was a problem with the contact, so I carried out two similar simulations using two rectangular blocks and two conical frustra respectively. I maintained the same object thickness and material properties throughout for fair comparison.

The deformation produced in the bottom rectangular block was a lot more significant than that produced in the bottom conical frustrum and bottom dome. Even when I increased the pressure tenfold, to the point where the top dome almost completely collapsed, there was still little to no deformation in the bottom dome.

Are the problems that I am facing due to inherent software limitations? Or am I doing something wrong?

Details of my simulations can be found on the google site accessible via this link: https://sites.google.com/view/comsoltroubleshooting2/home?authuser=2

Can someone with expertise in this area kindly offer some guidance? Thank you so much! :)

1 Reply Last Post 27.05.2020, 17:10 GMT-4
Henrik Sönnerlind COMSOL Employee

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Posted: 5 years ago 27.05.2020, 17:10 GMT-4

Hi,

Your questions:

Why is it that when I use two conical frustra instead of two rectangular blocks, the deformation produced in the bottom object decreases by such a large extent, when the decrease in the contact area between the two objects is not significant?

Actually, if you look at the numbers, about half the deformation is on each conical frustum, but the total deformation is about 6 times larger. This is a geometrical effect. You should get about the same if you just make a union of the two parts. There is a certain difference, caused by the fixed constraint at the bottom, which makes the lower part stiffer. This effect can be seen also in the two rectangular blocks.

Why is it that when I apply a very large pressure that is sufficient to deform the top dome to the point where it almost collapses, the deformation in the bottom dome is still minimal?

It is just a visualization artefact. If you would use another set of colors (for example the reverse check box), you would get another feeling. In your plot with scale 0.1, you can see that the contact boundary has moved about half the distance of the top of the upper cone. It is more or less symmetric. Again, the difference in boundary conditions between top and bottom accounts for the small deviation from symmetry. If you were to use a prescribed displacement at the top, it would be perfectly symmetric.

Are the problems I am facing because of inherent software limitations? Or am I doing something wrong?

As far as I can see there is nothing strange.

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Henrik Sönnerlind
COMSOL
Hi, Your questions: > Why is it that when I use two conical frustra instead of two rectangular blocks, the deformation produced in the bottom object decreases by such a large extent, when the decrease in the contact area between the two objects is not significant? Actually, if you look at the numbers, about half the deformation is on each conical frustum, but the total deformation is about 6 times larger. This is a geometrical effect. You should get about the same if you just make a union of the two parts. There is a certain difference, caused by the fixed constraint at the bottom, which makes the lower part stiffer. This effect can be seen also in the two rectangular blocks. > Why is it that when I apply a very large pressure that is sufficient to deform the top dome to the point where it almost collapses, the deformation in the bottom dome is still minimal? It is just a visualization artefact. If you would use another set of colors (for example the reverse check box), you would get another feeling. In your plot with scale 0.1, you can see that the contact boundary has moved about half the distance of the top of the upper cone. It is more or less symmetric. Again, the difference in boundary conditions between top and bottom accounts for the small deviation from symmetry. If you were to use a prescribed displacement at the top, it would be perfectly symmetric. > Are the problems I am facing because of inherent software limitations? Or am I doing something wrong? As far as I can see there is nothing strange.

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