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DenisJaunin15-Moonstone
15-Moonstone
February 12, 2013
Question

Thin wall enclosure subjected to external pressure

  • February 12, 2013
  • 9 replies
  • 2720 views

Hello,

I simulates a small thin walled cylinder, closed at both ends.

It is subjected to external pressure.

To have no constraints, I am Loading inertial balance.

I run the simulation, I travel and the stress on the entire piece.

I cut the cylinder in two lengthwise through the axis.

I divide my pressure 2.

In the example of manual Wildfire 2.0 belt buckle.

I place restrictions of symmetry of the cutting face.

I run the simulation, I travel and constraints, but not the same values ​​as before, totally different.

In this case, I only deformation of the cylinder on the edge of the cutting cylinder, but not elsewhere.

For this type of simulation should proceed in a specific manner.

Cordially.

Denis


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9 replies

SylvainA.1-Visitor
1-Visitor
February 13, 2013

Hello,

you don't have to divide the pressure by 2.

As it's a pressure, dividing the area by 2 will decrease the load by 2.

I never used the symmetry restriction, so I cannot help you any more.

jsarkar1-Visitor
1-Visitor
February 14, 2013

I have an idea, but not sure, if u take the complete cylinder and place constraints at both edges with axial fixed and transverse free movement.

integrisbrad1-Visitor
1-Visitor
February 14, 2013

I agree with Sylvain that you don't want to change your pressure. With inertia relief, displacement values can be quite different as you will see some rigid motion reflected in the displacement results. Are your stress results similar between the full model and the symmetry model?

Also, as Jayanta mentioned, you can use constraints to mimic the symmetry condition. You can probably come up with a 3-point constraint method that allows you to get rid of inertia relief in the full model. A cylinder closed at both ends with pressure applied should have a net zero load in all directions...the inertia relief solution should only be adding the "SUPORT" points and not any measurable body loads.

Brad Green

SylvainA.1-Visitor
1-Visitor
February 14, 2013

For a cylindrical tank, I would have used an 2D axisymmetric model.

Just one comment: there isn't any question in Denis' message...

Denis, si vous êtes francophone, pouvez-vous poser votre question en français ?

Je ne suis pas sûr d'avoir bien saisi vos explications et votre problème.

DenisJaunin15-MoonstoneAuthor
15-Moonstone
February 14, 2013

Hello,
Thank you for your answers.

Sylvain, effectivement je suis francophone et malheureusement je ne parle pas anglais.
J'utilise un traducteur automatique pour écrire et lire les messages.

J'ai un cylindre fermé aux extrémités et cet ensemble est enfermé dans une enceinte sous pression.
Ce qui m'intéresse c'est d'avoir une épaisseur au minimum de matière de la paroi.
Quand on simule la pièce entière, on ne voit pas bien les déformations, identiques sur tout le pourtour du tube,
on peut utiliser la fonction Surface de Coupe/Section pour les visualiser.

Maintenant si on simule un demi-cylindre avec la Restriction Symétrie, puisque l'on est coupé par le milieu,
on pourrait n'en prendre que le quart en utilisant la Restriction Cylique, etc.

Mais dans le cas de la coupe par le milieu du tube, je trouve des déformations plus importantes
que sur la pièce entière et les déformations sont localisées sur les flancs du tube.
Bien sûr, j'utilise toujours la même pression.

Pour la division de la pression par 2, j'avais regardé l'exemple du manuel de la WF2 sur l'étude d'une boucle
de ceinturon, où il étudiait la moitié de la forme, cette dernière étant symétrique et divisée en deux,
la force d'ouverture était, elle aussi divisée par 2.

Ci-joint une vue de la pièce simplifiée.
Cordialement.
Denis

DenisJaunin15-MoonstoneAuthor
15-Moonstone
February 14, 2013

Désolé j'ai appuyé trop vite.montage_exemple.jpg

JonathanHodgson13-Aquamarine
13-Aquamarine
February 15, 2013

I believe I have spotted the problem...

When you use Inertia Relief, I believe that all other constraints are disabled - including any symmetry constraints. I think we found this fairly recently, trying to run a cyclic symmetry with inertia relief...

In short, you can't use Inertia Relief and symmetry constraints at the same time.

If the loads are balanced, I have often had good results applying a constraint to a point or edge, away from any of the high-stress areas, so that Mechanica doesn't see the model as unconstrained. If there are any residual loads, it's easy to see if there are stresses near this constraint and either ignore them or correct the loads.

Desolée, je comprends un peu votre Francais, mais je ne peut pas l'ecrire assez bien...

DenisJaunin15-MoonstoneAuthor
15-Moonstone
February 16, 2013

Hello,

Thank you for your help and answers.

Sylvain, yes indeed pressure must not divide by 2 as in the case of force.

Jonathan

Thank you for your experience, you can not use at the same time restricting the symmetric and inertial loading.

I remade my simulation and now the result is correct.

In my cup, this time I'm deformation all the way around the cylinder.

Cordially.

Denis

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