Theoretical Modeling of Cylindrical Shell with Added Mass

[gman89]

Hi guys,

For FEM validation I need to be able to come up with a theoretical solution for the vibration of a combination structure consisting of a cylindrical shell which runs into a block of comparable dimensions.

I am familiar with the theory behind the vibration of cylindrical shells, but never had to analyze combination structures.

At the moment I'm trying to use the receptance method to do so. The problem is that I'm not sure how to incorporate the block mass into the analysis. One of the reasons for this is that from all the information I have read, there is only discussion about how to do this with point masses and doesn't model the distribution of the mass around the end of the shell effectively.

I have uploaded an image of a similar type of structure.

 

[GregLocock]

That's not a shell, it is a thick walled tube. The modal repsonse will be entirely dependent on the beam properties of the tube, the skin modes won't matter.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[GregLocock]

However if you are interetsed in radial modes then the point masses won't matter much except when the excitation is close to them.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[gman89]

I'm not as familiar with this as other people so bare with me with this question:

Is a thick walled tube the same as a thick walled shell? My interpretation was that a THIN walled shell shell neglects rotary inertia and shear deformation whilst a thick walled shell does not. Or am I completely missing the mark here, and a tube is modeled completely different to a thick shell?

 

[GregLocock]

It depends on what you are trying to do. The first several modes of the barrel will be classic beam theory flexural modes. At several thousand Hz (WAG) you will start to see radial modes of the barrel. For this shells may be an appropriate element type, you might also consider solids. What do your hand calculations tell you about the two different types of modes?

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[hacksaw]

unless you are investigating the time dependent pressure stresses of the barrel and chamber, the flexural modes of the barrel are dominant

the diffulty is agreeing upon how you support your model, as the stock design plays a large part in the recoil dynamics.

for machine support of the receiver, the calculation of the normal modes and natural frequencies of the barrel are described as a hollow beam with given mass distribution.

shear and rotational inertia are always a good idea