Summary

Constraint Optimization is used to reduce the number of motion bodies and joints by combining motion bodies that are connected by a fixed joint into a single motion body. This article will show the benefit of the Constraint Optimization feature in Simcenter 3D Motion by showing the reduction in simulation time with the feature activated.

Details

An example model of a front loader which consists of 26 motion bodies which are fixed together with 25 fixed joints. The front loader is dropped from a low height onto the ground. The vertical displacement of the cab, CPU usage, and MINP file sizes are compared between a solution that does not use constraint optimization and a solution that does use constraint optimization.

Figure 1: Screenshot of front loader example model
 

In the Solution dialog box, the option for Constraint Optimization can be found under Advanced Solution Options. To turn on Constraint Optimization, click on the drop-down menu to the right of Use Constraint Optimization and select Yes.
 

Figure 2: Solution dialog box containing the Constraint Optimization feature

The simulation was solved with and without the Constraint Optimization feature activated. The vertical displacement and CPU usage of the two runs are compared below.
 

Figure 3: Vertical displacement results
 

As seen in the graph above, the vertical displacement for both solutions with and without constraint optimization are the identical. This is the expected result since there is no functional difference between two motion bodies connected by a fixed joint and the single motion body used while Constraint Optimization is active.
 

Figure 4: CPU Usage results
 

The graph above plots CPU Usage, where the solution time is on the horizontal axis and the real time to solve the solution is on the vertical axis. In this case, constraint optimization reduces the simulation time from 8.6 seconds to 5.5 seconds.
The Constraint Optimization feature simplifies the model that is sent to the solver, therefore the .minp file for the solution using Constraint Optimization is smaller than that for the solution without. For this model, the .minp file for the simulation with Constraint Optimization is 217KB and the .minp file for the simulation without Constraint Optimization is 239KB.

Conclusion

The Constraint Optimization feature can help to reduce the simulation time for motion models that have motion bodies connected by fixed joints with no change in the results. The impact that this feature will have on the performance will depend on the model. A greater reduction in simulation time will be seen in a model that has more fixed joints.