|This task explains how to define a small assembly by first defining the support geometry as a user defined feature. You need to create geometry that can be used as support geometry for Ship Structure Detail Design.|
A user defined feature (UDF) is an object that is used to group a set of features so that they are seen as only one feature. This new feature can then be reused in new contexts.
As an example, if you create a new type of object such as a cylinder between two points, the start point and end point serve as inputs to the UDF. The construction geometry and the resulting volume are grouped together as a UDF.
Inputs of a UDF are deduced from its content.
UDFs for support geometry must have the following characteristics:
Guidelines for Creating Support Geometry
The orientation must be controlled.
Do not assume surfaces are planar. Always design assuming a shell (twisted) stiffener and/or canted bulkhead. (If needed, generate planes tangent to the surface at a point near where you are creating geometry.)
Do not use a sub element as an input of another feature. Create explicit endpoints, or use one of the UDFs in the UtilityUDFs folder to orient the line or curve to provide consistent points that can be used to create additional geometry.
Use only Positioned Sketch so there is no doubt to which direction the U and V axis points.
Do not use offset constraints or distance dimensions because the orientation is not explicitly defined.
When using Sketcher, do not use 3-D objects directly. Intersect or project the geometry into the sketch plane. It is recommended you select these 3-D objects from the tree to avoid the possibility of selecting a sub element.
Try not to use input geometry in knowledgeware rules or formulas [F(x)]. If you must to do so, duplicate the geometry using the Offset command or the Join command, and reference the duplicated geometry in the rule or formula.
Using a Template to Get Started
To get started, use a template. To create the support geometry, the functional object(s) and the small assembly must be in the same CATPart.
Create contextual geometry (for example, a plate and a stiffener) in part bodies.
Use geometrical sets to organize the GSD data. The following sets are recommended:
Use geometrical sets within the UDF Definition to group similar activities and provide structure to the UDF.
Naming Conventions for Inputs
The following naming conventions must be followed so that the software can substitute the actual surfaces when the small assembly is placed.
|For stiffeners, because a section may or may not include fillets, the fillet faces, the edges bounding the fillet faces, and any edge that might be replaced by a fillet should not be used.|
The following illustrates the naming conventions:
The current release introduces the keyword Support. This keyword allows the Small Assemblies command to enable multi-select for this particular input.
Naming Conventions for Typical I, L, T and U Shapes
The parameters used to drive the geometry of the structural sections are also available for use in formulae when creating small assemblies.
The name of the parameter in the UDF has two parts. The first part identifies the plate or shape, while the second part is the name of the parameter in the parametric part used to create the section.
In the example below, Shape1_D is the height of the first shape selected. Shape2_Tw is the width of the web of the second shape selected.
Typical parameters include:
D - Depth of the stiffener.
B - Flange width.
Tf - Flange thickness.
Tw - Web thickness.
R1 - Typically the radius between the FlangeInner face and the FlangeToe face.
R2 - Typically the radius between the WebInner face and the FlangeInner face.
Slope - Typically the angle on the inside of the flange.