CONSTRUCT LMASK [lmask] LINE [INVERSE] Umin Umax

   

This command is used to define a load mask for use with a load applied to a line. When attached to a load using the command PROPERTY ATTACH the load mask will restrict the action of the load to those nodes or elements which lie between Umin and Umax. The INVERSE option may be used to restrict the action of the load to those nodes or elements which lie outside Umin and Umax where:

lmask = name of the load mask

INVERSE = load acts on area outside mask

Umin = lower limit as a fraction of line length (0 to 1)

Umax = upper limit as a fraction of line length (0 to 1)

 

Figure 2.9: Definition of a line load mask

 

Figure 2.10: Definition of an INVERSE line load mask

Notes:

1.

Default names
If no name is entered a default name is created, this is LMn where n is a count of defined load masks. The default name can be changed with the CONSTRUCT NAME command.

2.

Masking criteria
The load mask bases its masking action upon either the coordinates of a node or the centroid of an element or element face. Thus for element loads the mask will simply include or exclude whole elements.

3.

Limitation
When a line load mask is attached to a load which in turn is applied specifically to a combined line, the load mask is applied to the individual lines used in the combined line. This limitation can be avoided by the use of a global load mask.

4.

Interaction with space curves
The line load mask will compress a line space curve so that all of the curve fits within the load mask limits. Where the INVERSE option has been used the space curve will be repeated once from 0 to Umin and once from Umax to 1.

5.

Viewing load masks
The limits of a line load mask can only be viewed by attaching it to a load and using the command LABEL MESH LOAD.

Examples:

1.

CONSTRUCT LMASK LM1 LINE .2 .8

This creates a load mask which when applied to a line load will restrict the loaded nodes or elements to those in the central section from .2 to .8 of the line's length.

2.

CONSTRUCT LMASK LM1 LINE INVERSE .2 .8

This creates a load mask which when applied to a line load will restrict the loaded nodes or elements to those which lie from 0 to .2 and .8 to 1.0 of the line's length.

See also the following commands

'CONSTRUCT NAME'
'CONSTRUCT SCURVE'
'CONSTRUCT TCURVE'
'PROPERTY ATTACH'
'PROPERTY LOAD'
'UTILITY DELETE'
'UTILITY TABULATE'