Using Parameters

Introduction

Piping Components, Profiles and Fittings each use one type of Pointset and one type of Geomset. Joints use both types of Pointset and one type of Geomset. The attributes of Pointsets and Geomsets may be defined in terms of parameters, set either explicitly or as real expressions (which may themselves incorporate the current settings of other parameters). (The classes of parameter which may be used depend on the class of Component - refer to Parameters for further information.)

For example, the bore of a P-point could be defined by entering

PBORE (PARAM[1])

This means that the value assigned to the bore of the P-point is the value of the first component parameter.

The Y dimension of a box in a 3D Geomset used by a Joint could be defined as the expression

PYLEN (APARAM[2] + 3)

This means that the Y dimension of the box is to be given a value in the design process, taken from the Section to which the Joint is attached. The value of the Y dimension of the box is the value of the second component parameter of the attached Profile plus 3 mm.

In both these examples it would be best practice for PARAM[1] and APARAM[2] to be defined using distance units, even if they were mm so that the expression is determined as a distance.

However whenever parameter expressions are evaluated by the system as part of an evaluation of the geometry ALL CURRENT WORKING UNITS are suspended and everything is performed assuming database units. Hence the +3 is taken to be 3mm and the database unit of distance is mm. If you want to make this physically 3inches you must add the inch unit qualifier to the expression.

The use of parameters makes it possible to use the same Pointsets and Geomsets for large numbers of Catalog items. For example, there may be families of tees, valves, I-beam profiles etc., each family containing items which are geometrically similar. In this way, the Catalog size and the effort needed to prepare input data are minimized.

Examples of the parameterization of typical Components are given later in this chapter.

The values assigned to parameters, the uses to which they are put, and the number of parameters used, are arbitrary, depending only on the skill and experience of the user, except in the special case of a Piping Component which represents implied tubing (GTYPE attribute set to TUBE) and which has no Geomset. In this case, component parameter 2 must be the outside diameter. If the tube is to be insulated, insulation parameter 1 must be twice the thickness of the insulation.

Note - On the use of Insulation Parameters:
Insulation parameters may be used in two ways. They may be used in an additive manner to increase the diameter or length of a primitive or, if there is a significant change in the geometry from the uninsulated to the insulated form, they may be used to define a new primitive. Where there is no insulation, the insulation parameters will be zero, yielding a primitive of zero diameter (but probably non-zero length).