- The slope (SLOPE).
For example, the hydrostatic pressure (Lab = PRES) shown in Figure 2.9: Example of Surface Load
Gradient (p. 37) is to be applied. Its slope can be specified in the global Cartesian system (SLKCN = 0)
in the Y direction (Sldir = Y ). The pressure (specified on a subsequent SF command) is 500 at Y = 0
(SLZER = 0), and decreases by 25 units per length in the positive Y direction (SLOPE = -25).
Figure 2.9: Example of Surface Load Gradient
The commands would be as follows:
SFGRAD,PRES,0,Y,0,-25! Y slope of -25 in global Cartesian
NSEL,...! Select nodes for pressure application
SF,ALL,PRES,500! Pressure at all selected nodes:
! 500 at Y=0, 250 at Y=10, 0 at Y=20When specifying the gradient in a cylindrical coordinate system (SLKCN = 1, for example), keep some
additional points in mind. First,SLZER is in degrees, and SLOPE is in units of load/degree. Second,
you need to follow two guidelines:
Guideline 1: Set CSCIR (for controlling the coordinate system singularity location) such that the surface
to be loaded does not cross the coordinate system singularity.
Guideline 2: Choose SLZER to be consistent with the CSCIR setting. That is,SLZER should be between
+180° if the singularity is at 180° [CSCIR,KCN,0], and SLZER should be between 0° and 360° if the sin-
gularity is at 0° [CSCIR,KCN,1].
The following example illustrat es why these guidelines are suggested. Consider a semicircle shell as
shown in Figure 2.10:Tapered Load on a Cylindrical Shell (p. 38), located in a local cylindrical system
- The shell is to be loaded with an external tapered pressure, tapering from 400 at -90° to 580 at +90°.
By default, the singularity in the cylindrical system is located at 180°, therefore the θ coordinates of the
shell range from -90° to +90°. The following commands apply the desired pressure load:
SFGRAD,PRES,11,Y,-90,1! Slope the pressure in the theta direction
! of C.S. 11. Specified pressure in effect
! at -90°, tapering at 1 unit per degree
SF,ALL,PRES,400! Pressure at all selected nodes:
! 400 at -90°, 490 at 0°, 580 at +90°.At -90°, the pressure value is 400 (as specified), increasing as θ increases by a slope of 1 unit per degree,
to 490 at 0° and 580 at +90°.
Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential informationApplying Loads