This tutorial shows how to perform a Restart and carry out a Two-stage optimization which can be used for different applications. Therefore, the Advanced User Settings are needed. More information regarding the background of a Restart here.
With this option a terminated optimization can be continued or a two-stage optimization with modified optimization parameters can be done. To realize a Restart or Two-stage optimization instead of the Design space another geometry can be chosen as the Start space. In this case the optimization starts with the specified geometry although the Design space is still the geometry limitation for the optimization.
Restart
Start Space STL-file
The Start space for a Restart must be a STL-file. Therefore, a already optimized geometry can be exported in the Post Processing. In this case iteration 22 from the symmetrical Bridge will be used.
Attention: The STL-file for the Restart must be exported in SI-Units (Meters).
Optimization Setup
In the next step a new scenario should be created for the Restart. With the Advanced User Settings the Start space STL-file can be selected. In this case the exported iteration 22 from an former optimization is selected. Furthermore, the symmetry constraints from the first optimization are added.
The most important part of a Restart is to adjust the Advanced User Setting especially the number of iterations, the resolution level and the stress goal percentage. More background information regarding the Advanced User Settings here.
This can be done when an optimization is terminated and restarted at another time. In this example the Bridge should be restarted as if the optimization never stopped, so with the same optimization parameters as the first optimization excluding the already done iterations. Therefore, the settings for the parameters Strut Density: Medium and Shape Quality: Balanced are added to the Advanced User Settings and adjusted according to the numer of iterations already calculated. Which number of iterations and which stress percent goal should be input for each resolution level can be found here.
In this case the optimization will restart at iteration 22, thus 42 iterations must be added to reach the total number of 64 iterations (Shape Quality: Balanced).
Resolution level | Iteration | Stress Percent Goal |
|---|---|---|
.level_2 | 18 | 40 |
.level_1 | 20 | 90 |
.level_0 | 4 | 100 |
The command fOptimizer_switchAddRemove needs to be active for the last 4-10 iterations for the quality of the surface smoothness, so in this cas 42-6=36.
The information are added in the following style:
UpSampleConfig
fOptimizer_switchAddRemove=36
iteration
.level_2=18”
.level_1=20”
.level_0=4”
fOptimizer_stressPercentGoal
.level_2=40
.level_2=90
.level_2=100
After adding these commands to the Advanced User Settings the optimization can be started. The first iteration of the restarted optimization will be the imported Start space.
Two-stage optimization
A second possibility is to perform a two-stage optimization. Instead of a simple restart with the same optimization parameters the parameters can be varied.
Exampels:
Skipping the coarse resolution level and calculate directly on the finest resolution level with an early iteration from a former optimization, if a very fine high-resolution level is desired
Vary the value for the stress goal to keep the overall geometry with more or less material
Modify an optimization output (remove or add struts) and restart with this modified geometry
Creation of a lattice structure of an optimization output and restart to optimize the lattice
A two-stage optimization is useful for the following applications:
An optimization by means of a grid structure is to follow. See tutorial ...
A very fine high-resolution structure is desired. Then it is advisable to first perform an optimization up to a reduced structure (the optimization must not be finished). Then a second optimization with a start design is performed, which starts directly at a higher resolution level and receives more iterations in these levels to form the fine structure.
You want to change some design details of final structure. You can remove struts / add rough struts with any external software and use this new .stl file as input / start space for the optimization. The algorithm will take care of an optimal change of the shape.