This example involves the optimization of a box defined entirely by equations (there is no finite element model in the solution).
The optimization problem is defined as:
|
Objective: |
Maximize the volume of a cube AxBxC |
|
Constraint: |
The surface of the cube should be between 2.0 and 3.0 |
|
Design Variables: |
A, B, C |
The volume and surface are defined as equations using DRESP2 and DEQATN:
$
$ VOLUME
$
DEQATN 1 VOL(W,L,H)=W*L*H
$
$ SURFACE
$
DEQATN 2 AREA(W,L,H)=2.0*(W*H+L*H+W*L)
$
DRESP2 1 VOLUME 1
DESVAR 1 2 3
DRESP2 2 SURFACE 2
DESVAR 1 2 3
$
DESVAR 1 W 1.1 0.1 10.0
DESVAR 2 L 0.9 0.1 10.0
DESVAR 3 H 2.0 0.1 10.0
$
Then, in the optimization problem, the objective and constraint are global responses (for example, DESOBJ and DESGLB are used outside of a SUBCASE).
To trick OptiStruct into solving this problem, a dummy finite element model must be provided. Here, a single shell element with some load is used.
As expected, the solution yields a cube with even sides of about 0.707, a surface of 3.0, and a volume of 3.53.
The input file can be found in /altair/demos/os/manual/box.fem.