This example demonstrates how size optimization can be used.
For the ten bar truss structure, a cross-sectional area distribution is sought that minimizes the structural mass and allows limited stress values in the elements. The stress limit is 25000. The y displacements are limited to 2.
Structural Model
In this example, the cross-sectional area for each element is varied. Therefore, 10 variables are defined in the analysis deck. The initial cross-sectional area of all the elements is 20, with a lower bound of 0.2 and an upper bound of 200.
The optimization problem, objective and constraint functions, is defined in the same manner as for the other types of structural optimization. OptiStruct then goes through an iteration process to solve the optimization problem. OptiStruct converged after thirteen iterations. The table below shows the optimization results of the ten bar truss structure, which met the constraints and minimizes the mass (decrease of 38.7%).
|
|
Bar1 |
Bar2 |
Bar3 |
Bar4 |
Bar5 |
Bar6 |
Bar7 |
Bar8 |
Bar9 |
Bar10 |
Volume |
|
Initial |
20 |
20 |
20 |
20 |
20 |
20 |
20 |
20 |
20 |
20 |
83929 |
|
Final |
30.4 |
38.4 |
24.5 |
15.4 |
0.2 |
0.2 |
8.8 |
21.5 |
20.1 |
0.4 |
51448 |
The input file for this example can be found in /altair/demos/os/manual/tenbar.fem.