GEOMETRY SURFACE INTERSECT [snam] shp1 [+/-]shp2 [[+/-/ ] shpn...]

          

This command allows intersection surfaces to be created directly from FEMGEN analytical shapes.

snam = name of the first surface that is created, used for later references to the surface.

shp1 = name of an analytical shape (ie plane, cylinder, cone or sphere) on which the intersection surface will lie.

shp2 = name of an analytical shape (ie plane, cylinder, cone, sphere or box) used to limit the extent of the intersection surface.

shpn = names of further additional shapes used to limit the extent of the intersection surface.

+/- = sign which is used to control which side of the shape geometry is created on. If no sign is given, then both sides of the given shape are considered.

The first shape given is the shape that the resulting surfaces lie on. The second and any subsequent shapes are used to control the extent of the resulting surface, for example a 'box' could be used to define the location of the end of a cylinder and a plane (of symmetry, perhaps) could be used to control which half of the model is created.

Notes:

1.

Closed surfaces
This command will generate one or more surfaces, but it is unable to create surfaces which form a closed loop, such as the surface of a truncated cylinder. In this case it is necessary to introduce a plane to split the cylindrical surface axially.

2.

Truncated shapes
Cylinders and cones can be 'truncated' to provide additional control on the extent of the resulting surface.

3.

Use of the '+' and '-' signs
The '+' or '-' sign is used with each shape (except for a box) to indicate which side of the shape is to be used in creating the surfaces.If no sign is given then both sides of the shape will be used.

When a plane is created or labelled the positive side of the plane is shown with a small arrow; for cylinders, cones and spheres '+' refers to the inside and '-' to the outside.

For a box, only the inside is considered to be active and a box cannot be used as the first shape in the surface definition.

The extended example below is intended to show some of these features.

Return Level: GEOMETRY SURFACE

Examples:

1.

Intersection surfaces between three cylinders

These pairs of points are used to define axes for the three cylinders, the second and third cylinders being at 45 and 135 degrees to the first.
GEOMETRY POINT P10 0
GEOMETRY POINT P11 10
GEOMETRY POINT P12 5
GEOMETRY POINT P13 8 3
GEOMETRY POINT P14 3 3
GEOMETRY POINT P15 6
EYE DIRECTION 1 2 3
EYE FRAME
Two truncated cylindrical shapes are used, their length is defined by the location of the points (P10, P11 and P12, P13 and P15 P14).
CONSTRUCT SHAPE CYLINDER MAIN P10 P11 1.05
CONSTRUCT SHAPE CYLINDER BRANCH1 P12 P13 .65 TRUNCATE
CONSTRUCT SHAPE CYLINDER BRANCH2 P15 P14 .45 TRUNCATE
The planes X1 and X9 will be used to limit the extent of the MAIN cylinder, the plane Z0 is used as a plane of symmetry. If the complete structure were required then the '+' would be omitted from the 'Z0' in the GEOMETRY SURFACE INTERSECT commands below.
CONSTRUCT SHAPE PLANE Z0 Z 0
CONSTRUCT SHAPE PLANE X1 X 1
CONSTRUCT SHAPE PLANE X9 X 9
To create the surfaces on the main part of the structure:
GEOMETRY SURFACE INTERSECT MAIN BRANCH1 BRANCH2 +Z0 +X1 -X9
EYE FRAME
FEMGEN surfaces are created on the main cylinder, but inside the two branch cylinders since no sign has been given for either BRANCH1 or BRANCH2
Create the remaining surfaces:
GEOMETRY SURFACE INTERSECT BRANCH1 BRANCH2 -MAIN +Z0
GEOMETRY SURFACE INTERSECT BRANCH2 -MAIN -BRANCH1 +Z0

 

Figure 2.83: The resulting geometry

Note that the default divisions are unsuitable and so should be modified with either the MESHING DIVISON LINE or MESHING DIVISION ELSIZE command.
MESHING DIVISION ELSIZE ALL .2
MESHING DIVISION AUTOMATIC
MESH GENERATE
VIEW MESH
VIEW HIDDEN FILL

 

Figure 2.84: Creation of intersection surfaces directly from two shapes

See also the following commands

'LABEL GEOMETRY SURFACES'
'UTILITY DELETE SURFACES'
'UTILITY TABULATE GEOMETRY SURFACES'
'VIEW GEOMETRY'
'CONSTRUCT SHAPE'