Plotting curves

plotting curves

Procedure

1. Select the Body mass body displacement variable.

2. Drag and drop it on the sketch.

A window called Plot-1 appears: it contains the plot of the variable against time.

3. Select the Wheel mass wheel displacement variable.

4. Drag and drop it into Plot-1.

5. Do the same for the step submodel and its output variable.

Figure 21: Plotting curves

Figure 22: The final plot

Interpreting these curves leads to the conclusion that the model did not start from an equilibrium position. What follows is a method of finding an equilibrium position. First we must consider the inputs to the system. In the system sketch, in the figure Figure 16, we have the component and associated submodel, STEP0. This provides a disturbance to the system. In common engineering terms this is an input to the system. Without this input we would get the free response of the system. With it we get a forced response. What we are going to do is run a simulation to produce the free response. If this settles to an equilibrium position, this is the position we want. We could do this by going to Parameter mode and removing the step (either by setting value after the step to zero or by setting the step time to a very large value). However, Simcenter Amesim provides an easier way of doing this.

6. In the Run Parameters dialog box, select the Standard options tab.

Figure 23: Standard options tab

7. Check the Hold inputs constant box.

8. Click on OK and restart a simulation.

9. Update the curves.

Figure 24: Curves are updated

If you compare figures Figure 24 and Figure 22, you can see that in the first one the second phase of the transient motion is absent. The values are very close to an equilibrium position for the "before the step" phase. If we had specified a final time of 10 seconds, the values would have been even more accurate.

10. Untick Hold inputs constant in the Run Parameters window, and save the system.