Clash Detection

Model Reference Manual

Clash Detection

MODEL’s clash detection utility allows the user to check any specified parts of the MODEL database for clashes (interferences) between individual elements and to report on the results.

The types of clash identified by MODEL depend on two factors:

•

The obstruction levels of the clashing elements

•

The current touch and clearance tolerances

Obstruction Levels

All design primitives and all catalogue primitives have an obstruction level attribute (OBST) that has an integer value of 2, 1 or 0. The value of the OBST attribute defines the physical type of obstruction that the primitive represents.

For positive primitives the effects are as follows:

•

OBST = 2

A hard obstruction; the primitive represents a solid volume, such as a steel beam or a plant vessel, that has rigid and impenetrable surfaces.

•

OBST = 1

A soft obstruction; the primitive represents a volume that is not solid but that needs to be kept clear for access purposes, such as an operating space around the control wheel of a valve.

•

OBST = 0

No obstruction; the primitive represents a freely accessible volume, or is simply a representative symbol.

In addition to the obstruction types defined by the OBST attributes, Insulation is treated as a special obstruction type in its own right.

Extent of Clashing

As well as recognising the three types of clashing item (hard, soft and insulation), MODEL recognises three classes of clash between them, depending upon the degree to which the two primitives intrude upon each other’s allocated space. These classes are as follows:

•

Physical clash; the primitive volumes overlap by more than a specified amount.

•

A touch; the primitives either overlap by less than a specified amount or are separated at their closest point by less than a specified distance.

•

A clearance; the primitives are separated at their closest point by more than the amount necessary to constitute a touch but less than a specified clearance distance.

These three classes are illustrated in Figure 13:1.: Physical Clash, Touches and Clearances for the clash specifications:

Touch limits: 5 mm overlap to 2 mm gap

Clearance limit: 8 mm

so that the following criteria apply:

•

If the primitives overlap by more than 5 mm, a clash is reported

•

If the primitives overlap by less than 5 mm, a touch is reported

•

If the primitives do not overlap but are separated by less than 2 mm, a touch is reported

•

If the primitives are separated by more than 2 mm but less than 8 mm, a clearance is reported

•

If the primitives are separated by more than 8mm, no interference is found

Note:

The clearance distance, if set, must be greater than the touch gap. Setting the clearance distance to zero switches off the clearance-checking function.

Figure 13:1.

Physical Clash, Touches and Clearances

Clash Detection Process

The locations and dimensions of all design elements are defined, for clash detection purposes, by reference to a spatial map that holds simplified descriptions of the component geometries.

Each element that is to be checked for clashes has its own geometry checked against that of all other elements that are specified by a current obstruction list. Items that are not in the obstruction list are ignored during the clash checking operations.