CONSTRUCT LMASK [lmask] BODY [INVERSE] Umin Umax Vmin Vmax Wmin Wmax

   

This command is used to define a load mask for use with a load applied to a body. 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, Vmin and Vmax, Wmin, Wmax. The INVERSE option may be used to restrict the action of the load to those nodes or elements which lie outside Umin, Umax, Vmin, Vmax, Wmin and Wmax where:

lmask = name of the load mask

INVERSE = load acts on area outside mask

Umin = lower limit as a fraction of line length in first body direction (0 to 1)

Umax = upper limit as a fraction of line length in first body direction (0 to 1)

Vmin = lower limit as a fraction of line length in second body direction (0 to 1)

Vmax = upper limit as a fraction of line length in second body direction (0 to 1)

Wmin = lower limit as a fraction of line length in third body direction (0 to 1)

Wmax = upper limit as a fraction of line length in third body direction (0 to 1)

 

Figure 2.5: Definition of a body 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.

Interaction with space curves
The body load mask will compress a surface 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, once from 0 to Vmin and once for Vmax to 1, once from 0 to Wmin and once for Wmax to 1.

4.

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

5.

Permitted body topologies
The body load mask can only be applied to six-sided bodies made up of four-sided surfaces with straight sides. The sides of the surfaces can be combined lines.

Examples:

1.

CONSTRUCT LMASK LM1 BODY .2 .8 .2 .8 .2 .8

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

2.

CONSTRUCT LMASK LM1 BODY INVERSE .2 .8 .2 .8 .2 .8

This creates a load mask which when applied to a surface load will restrict the loaded nodes or elements to those which lie outside the central section from .2 to .8 of each side length.

See also the following commands

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