Tutorial: Pressure vessel with nozzles and saddle

Victor

Somebody recently asked about kind of meshing task so I'm posting it here in case it's any use to others.

This process is a bit complicated and it's usually easier to make it with a CAD program and import as a STEP file but you may prefer the regular mesh or not have access to CAD. Some steps here are a bit brief and you'll have to choose suitable values to enter.

1. Head with nozzle

Use MeshGenerator.xls from the samples folder and the "Nozzle on Spherical Shell" tab

If you want a torispherical head instead of spherical, open the generated file in Mecway and use Mesh tools -> Fit to curved surface.

2. Half of the cylinder with nozzle

Use MeshGenerator.xls from the samples folder and the "Nozzle on Cylindrical Shell" tab

3. Combine the two parts

Open one of those two .liml files

Import the other one into the same model using File -> Import

Select the Nozzle_on_Spherical_Shell component and rotate it 90 degrees with Mesh tools -> Rotate/copy

Measure the Y distance between the end of the cylinder and the edge of the head using Tools -> Tape measure

Move it to the correct position using Mesh tools -> Move/copy

4. Make the other half of the shell

Select the edges of the elements along one edge of the cylinder

Revolve the selected edges 180 degrees using Mesh tools -> Revolve

5. Make a saddle separately and connect it using bonded contact or

6. Extrude parts of a saddle from the cylinder

Select a row of nodes on the cylinder

Change to Select faces mode to convert it to a selection of edges

Extrude them with Mesh tools -> Extrude and 1 subdivision

Straighten the new curved edge. Selecting its nodes, right click one, click Node coordinates, and enter a value for the common coordinate.

Repeat for other plates of the saddle

7. Merge nodes

Use View -> Open cracks to see that the 3 parts aren't all connected together

Merge the coincident nodes using Mesh tools -> Merge nearby nodes

Use View -> Open cracks again to confirm they're not connected properly

If you move nodes or refine after creating it, use Mesh tools -> Fit to curved surface to realign the nodes onto their correct cylinder, sphere, etc.

Sergio

Great tutorial! I have made some samples on pressure vessels these days, using Salome to create the meshes. What kind of elements is better for this kind of analysis, shell or hexas (extruded from 2d mesh)? I did some comparations using the same hexa mesh on CCX, Mecway and other comercial, but results were a little weird (different stress value and distribution).

Victor

Solids are of course better if you can generate a mesh. The shells in Mecway's internal solver have a problem for certain geometries like twisted shapes, which leads to convergence failure. As far as I know, the CCX shells don't suffer from that.

Solid element meshes should converge to the same solution for just about any software, so I'm surprised you found differences. Some may converge faster though, like reduced integration.