8.3 The session

8.3 The session

Step 1

Point creation

Assume that the point of intersection of the pipe centrelines is at the origin and create some points to define the main pipe centre line.

GEO PO 0

GE PO .5

GE PO -.5

Re-scale (unless CONSTRUCT SPACE WORK -.5 .5 -.5 .5 0 .5 was used prior to the point input).

Step 2

Create another point for the local z-axis

GE PO 0 0 .5

Step 3

Define a transformation to create another point to define the branch pipe

CONS TRANS ROTATE P1 P4 40

Create the point at the end of the branch

GEOM COPY P2 P5 TR1

Another way of creating P5 is by issuing the following command:

GEOM COPY P2 P5 ROTATE P1 P4 40

Step 4

Create two truncated cylindrical shapes representing the two pipes (using two points and a radius)

CON SHAPE CYL MAIN P3 P2 0.15 TRUNC

CON SHAPE CYL BRANCH P1 P5 0.105 TRUNC

Step 5

Create plane shape (using three points)

GE PO .5 .15 0

CON SHAPE PLA SH1 P2 P6 P3

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Figure 8.1: Intersection shapes

Step 6

Create intersection surfaces

a)	Intersection surface on the main cylinder By using +/- options with shape commands, the main cylinder surface is created by adding the main cylinder, the plane, and removing the branch shapes GE SURF INTER S1 MAIN –BRANCH +SH1

b)	Intersection surface on the branch cylinder The branch cylinder surface is created by adding the branch cylinder and the plane shapes, and removing the main cylinder shape GE SURF INTER S2 BRANCH –MAIN +SH1 EYE FRAME ALL

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Figure 8.2: Intersection surfaces

Step 7

Create a mesh

At this stage a mesh can be created, (although as it will use the default division settings it may not be very suitable). One way of getting a mesh which can be used as a starting point is to use MESHING DIVISION AUTO which will, as far as possible, try to create a set of divisions which will produce a mesh. However, in this case element size and line divisions are changed

MESH OPTI ALGOR PAVI S1

MESH DIVI ELSIZ ALL .5E-1

MESH DIVI LINE L3 7

MESH DIVI LINE L4 18

MESH GENE

VIEW MESH

Step 8

View the model along the X-axis

When a mesh has been produced view the mesh along the x axis

EYE ROTATE TO 0; E R L 90 or EYE DIRECTION 1

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Figure 8.3: Mesh generation

Step 9

Apply pressure loading on the shell elements

It is required to apply an internal pressure of 123E3N/m2 to the model :

PROP LOADS PRES ALL 123E3

this will put a pressure load on all the surfaces; the default degree of freedom (NORMAL) will result in the pressure being applied in the direction of the surface normal. Label the mesh with the load to see the direction of loading. It is likely that some of the loading arrows will be in the wrong direction! To correct the situation the first step is to make sure that all the normals for the surfaces are in the same direction and then to change the sign for the direction of the loading if necessary.

Step 10

Rotate the view of the model and show the surface normals

Choose a suitable view of the model and then use

LABEL GEOM NORMAL

which will show all the surface normals. Alternatively VIEW HIDDEN FILL NORMAL will shade the surfaces according to the direction of the normal. To change the direction of the surface normal use the GEOMETRY FLIP command. To check that the normals have changed direction and are all consistent use DRAWING DISPLAY. If it is necessary to change the direction of the pressure loading only then this can be achieved either by re-specifying the loading

PROP LOADS PRES ALL LO1 -123E3

(LO1 is the default loadcase name)

or by creating a new load case and deleting the old load case.

Step 11

Apply the constraints in local directions

It is required to fix the end of the branch pipe in the local axial direction. This can be achieved by attaching a suitable axis set to the two arcs that define the end of the branch pipe. In fact the second of the two axis sets defined can be used, as the z-direction coincides with the axis of the cylinder.

Another axis set needs to be defined, which could have its origin at P1 (the global origin) or at P5 at the end of the branch.

Put the two arcs at the end of the branch pipe into a set BFIX (say). Attach the rectangular axis set to the set BFIX and define some constraints which act in direction 3. Label the mesh to check that the constraints will be in the correct direction

CONS COOR RECT RCT1 P5 P1 P4

CONS SET BFIX APPEND L7

PRO ATTACH BFIX RCT1

PROPERTY BOUNDARY CONSTRAINTS BFIX 3

Step 12

Apply material properties

PROPERTY MATERIAL MAT STEEL 209E3 .3 7800E-12

PROPERTY ATTACH ALL STEEL