Geometry Geometry

The geometry of the model is defined by a set of points in the part system. The names of all points begin with a *. The location of the points can be specified with respect to either the part origin, or another point. At least one point in the model, however, must be specified with respect to the part system. Every point belongs to a part, and to allow for specifying fixed positions in space, there is a part which does not belong to any body, GROUND. Therefore, to define fixed locations in space one can specify that the following points will be fixed by issuing &DESCRIBE PART GROUND before the fixed points are defined. The part system of GROUND is the global system.

Points to which one attaches structure have a special name, nodes. Each point which is not a node will have a node associated with it. Any load associated with a point is ultimately applied to the structure at the associated node. The associated node is the node closest to the point which is in the "associated node set." Normally, this set will be the set of all nodes. In some situations, however, one wishes to exclude certain nodes for being "associated" and thus from attracting loads. This is accomplished with the command:


     &DESCRIBE NODE_NAS, PART_NAME(1), :PNT_SEL(1), ...

where PART_NAME(i) is a part name, and :PNT_SEL(i) is a selection criteria which defines the nodes which will not be associated.

Points which have both a chord, a single tubular member with the same outside diameter and at least one other tubular element are called tubular joints. Tubular joints are not true parts of a model since they inherit the most of their properties from the elements which intersect to form the joint. The concept of a joint is really only used in checking the codes which are applicable to joints and in computing fatigue at the intersection of the elements forming the joint.

Once a point has been defined, its properties can be changed with the ED_POINT command, which is available either during an INMODEL or in the MEDIT menu. Its form is:


     ED_POINT, :PSEL, -OPTIONS

Here, :PSEL is a selector (selection criteria, or name which may contain wild characters) of the points for which the options are applicable, and the options can be any option valid for the point definition command.

Often, it is desirable to obtain information about certain points on the bodies during a simulation. The points at which these reports will be issued are defined by the command


     &DESCRIBE INTEREST,  -OPTIONS

and the available options are:


     -DELETE, :PNT_SEL(1) .... :PNT_SEL(i)

     -ASSOCIATE, :PNT_SEL(1) .... :PNT_SEL(i)

Here :PNT_SEL(k) are selectors for points. The option -DELETE deletes the interest points selected by all of the selectors and -ASSOCIATE makes interest points of all points selected by the selectors. Interest points have a bit more information associated with them than the other types of points. In particular, each time the &DESCRIBE INTEREST, is issued, the global location of the interest point is saved. These locations are used for a reference in measuring "motion" in several reports.

Once a set of points for a part have been defined, they can be exported to a file for later use with the command:


     &EXPORT POINTS