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# Pressurized Cylinder FEM constraint

Dears,

I have a cylinder subjected to an internal pressure of 10 MPa, the cylinder diameter is 1400 mm. I am trying to model it in my FEMAP. I am comparing the average stress (TOP and BOT Y) with the stress that come from the formula

hoop_stress=pressure.Radius/thickness

The stress I obtained is similar with the one that is from the formula, but the deformed is not equal, it is crazy !

I am not sure about the constraints I have applied in my FEM model, supposing a cylinder pressurized how the constraints must be set in the free borders ?

## constraints for cylinder

Hello,

Let us assume a cylindrical coordinate system (r,theta,z) and an outside radius of Ro.

Constraints then could be as follows:

1. For all nodes at the base of cylinder, provide rollers that provide z restraint only.

2. All nodes at (Ro, 0, all z), provide rollers that provide radial restraint only.

3. All nodes at (Ro, pi/2, all z), provide rollers that provide radial restraint only.

If we are using an x,y,z coordinate system with z=0 at the base of the cylinder and the z axis is same as the cylinder's axis then we have.

1. For all nodes at z=0, provide rollers with z restraint only.

2. All nodes at x=Ro, y=0, z=all z, provide rollers that provide x restraint only.

3. All nodes at x=0, y=Ro, z=all z, provide rollers that provide y restraint only.

This allows proper deformation of the cylinder along its axis, and allows proper expansion in all radial directions.

regards,

Louie

## Simpler solution than the given

Hi fernando,

You model the cylinder with Axisymmetric elements. By that you can reduce your problem dimensionality to TWO. Coming to Boundary conditions, apply axial constraint on any one of the ends of the cylinder. No radial and tangential constraints are required if you model with axisymmetric elements. This makes your problem very easy to solve. If am wrong please let me know.

## I would attach another short

I would attach another short cylinder with negligible Young's modulus.

## Thank you friends

Thank you friends !!!

all working properly !!!!

Regards

## cylinder

As above, use axisymmetry, restrain in axial direction

A thick walled cylinder departs from your equation, and you must use the Lame equations

mikl