Paulin Research Group                                                                Houston, Texas

 

 

Cutting Rectangular Holes in Header

FE/Pipe Example Model: rectang.ifu

 

 

This is not a simple task to do in FE/Pipe. As seen in previous support notes (Meshing Plate Supports), the user can control the angles and the rings within the parent geometry.

 

In the case where the user needs to cut a rectangular hole in the header, the use of angles and rings becomes the most important factor. FE/Pipe has preset Options for square holes, but not for rectangles, this is why removing mesh is the solution for rectangular holes.

 

The main idea of cutting rectangular holes is to define an area between 2 angles, and an area between two rings, and remove the surface from this intersection. The meshing parameters are defined in the *.pre file which will be called by the user to remove certain surfaces.

 

 

  1. Select General, Nozzles, Plates and Shells as the template.

 

 

  1. Build the parent geometry

 

 

  1. We need to be able to control all angles and rings in the model. This is done in the Optional window, under a button called “Global User Surface Control”.

 

Change the first two boxes from NO to YES as done above. We then enter the angles desired and the rings desired, as seen above. The pictures below show the rings and angles location in the parent geometry.

 

 

 

 

  1. Now we need to enter pressure and material properties.

 

 

 

  1. Now we need to enter Boundary Conditions for the parent geometry.

 

 

The bottom is usually defined as FIXED. And the top usually defined as PFIX. Please see Frequently Asked Questions for definition of all FE/Pipe Boundary Conditions.

 

 

  1. The rectangle that needs to be cut is in between angles 350 and 10. And in between rings 60 and 70. We need to know the surface number that lies in this area. To do this, we need to plot the model and use the draw geometry option to see the surfaces.

 

  1. Under Controls/Draw Geometry, select the options shown below and press OK.

 

 

 

  1. The surfaces are all labeled now. It is hard to see which surfaces are the ones that are needed. Zooming in can help a lot. Once the surfaces are found, you can now proceed to remove these surfaces.

 

 

  1.  Prepare the model for analysis.

 

 

  1.  In the model window, go to Advanced/Shell Model Utilities. The window below will appear. Click on Un-Mesh surfaces (make holes).

 

 

 

 

  1. Click RUN. The following screen will appear. Surface #5 was the one that needed to be removed; therefore the range is 5 for start and 5 for end.

 

 

 

  1.  Click Nextà. Navigate to the folder where the model was saved and select the *.pre file found.

 

 

 

  1.  Press Open. The model should plot with the desired rectangular hole cut.

 

 

 

  1.  As we can see, the model has a rectangular hole where needed. The model is ready to be analyzed. Select Analyze in the FE/Pipe main screen.

 

 

We can see from the 3D plots that the highest primary + secondary stresses are at the corner. These results are reasonable as corners and fillets magnify stresses.

 

 

 

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