# Optimization of Arbitrary Beam Sections

## Optimization of Thin-walled Sections

Optimization of thin-walled sections is facilitated through the use of the dimension fields on the PBARL and PBEAML Bulk Data Entries and the DIM entry within the section definition.

The DIM entry is used in the section definition to link either the thickness of a PSEC entry or the Y or Z coordinate of a GRIDS entry to the value of the corresponding DIM field of the referencing PBARL or PBEAML. Should the DIM field on the referencing PBARL or PBEAML be referenced by a DVPREL, the thickness or grid coordinate in the section definition will be affected by changes in the design variable.

Solid sections are not designable at this time.

Here is an example of a thin-walled section, where the wall thickness and the y coordinate of G2 are designable:
$DESVAR,1,THK,0.1,0.05,0.15 DESVAR,2,G2Y,1.0,0.5,1.5$
DVPREL1,1,PBARL,1,DIM1,,,0.0
,1,1.0
DVPREL1,2,PBARL,1,DIM2,,,0.0
,2,1.0
$PBARL,1,1000,HYPRBEAM,SQUARE ,0.1,1.0$
MAT1,1000,2e5,,0.33,7.85e-9
BEGIN,HYPRBEAM,SQUARE
$GRIDS,1,0.0,0.0 GRIDS,2,1.0,0.0 GRIDS,3,1.0,1.0 GRIDS,4,0.0,1.0$
CSEC2,10,100,1,2
CSEC2,20,100,2,3
CSEC2,30,100,3,4
CSEC2,40,100,4,1
$PSEC,100,1000,0.1$
DIM,1,T,100
DIM,2,G,2,Y
$END,HYPRBEAM$