Pressure Vessel Design

[Anonymous]

I am looking to simulate a composite pressure vessel under an internal pressure, but am relatively new to using Nastran In-CAD.

I have applied a shell mesh to the inside of the vessel, allowing me to form my laminate. I have then applied a pressure loading on the inside face of 31 MPa. However I do not understand how to constrain my model, would anyone please be able to advise me?

Thanks

[John_Holtz]

Hi @Anonymous 

Unless this vessel is freely floating (either in water or space), then it is connected to something: bolted to a structure, connected to pipes, etc. You apply the constraints at the "something".

[Anonymous]

Hi John,

If this were to be a quarter model of the vessel (see attached), how would I go about constraining it so that it can expand freely? On the bottom face of the model, I have applied a constraint that only allows translational motion in the x axis. On the front face of the model, I have applied a constraint that only allows translational motion in the z axis. However as you can see there is a high stress concentration close to the bottom face that is not expected to me, hence I assume it is to do with the constraint applied.

Kind Regards,

Jack

[Anonymous]

First of all: The model in your picture can't be right I guess. Either you use a solid idealization (no composite possible) or you use a shell idealization of the the inner or outer surfaces of the solid body. You metioned that you applied a shell mesh to the inside of the vessel. But it looks like you meshed all faces of a solid body. It makes no sense to use a shell idealization of all faces of a quater solid body. Even if the vessel is double-walled, it is wrong to mesh the cut faces as shells. Maybe I missed something, so the model would be more helpful than a picture.

Concerning the constraints: In this case (a free floating vessel) an eighth model would be the best. Cut the model also with the YZ symmetrie plane. Then contstrain all three cut faces (edges of a shell model) with the proper symmetry constraint: cut face XY with symmetry Z, cut face XZ with symmetry Y and cut face YZ with symmetry X.

Edited after reading your first post again.

[Anonymous]

I appreciate you taking the time to help me as I am new to using this software.

I have done as you stated: creating an 1/8 model, applied the shell mesh to the inside face only so that my laminate is present, and applied the appropriate symmetry constraints to the cut faces. However it informs me that the constraints are not applied at a valid FE Mesh location. Do I need to mesh the cut faces too?

Kind Regards,

Jack

[Anonymous · Accepted solution]

Don't mesh the cut faces of the solid body. Constrain the edges of the inside faces. With a shell idealization of the inside faces these edges are the cut "faces".

You can see a similar situation in this tutorial (5. Constrain the Tank Edges), it isn't free floating though and has a hydrostatic load:

https://help.autodesk.com/view/NINCAD/2020/ENU/?guid=GUID-0E20E89E-15CC-4FD3-9000-B7A250A24467 

But it is a shell idealization based on a solid body and is symmetric in two directions. Just akt like this in all three directions.