Using old final values

Use old final values

After 5 seconds the system has almost reached an equilibrium state since its variables remain constant.

Next, you will try the Use old final values facility. This facility

• extracts the values which were obtained at the end of the last previous run, and

• uses them as starting values for the next run.

Results

In this case, the state variable initial values (especially the spring-damper and the elastic contact) will receive the values at which the system is in equilibrium.

Note

Before continuing the exercise, save the system as QuarterCar_FinalValues using File > Save as.

In Advanced examples, you will need to use the original Quarter car system as saved in Setting parameters and running a simulation.

Use old final values facility

Procedure

1. Open the Run Parameters dialog box.

2. Tick the Use old final values check box.

Figure 25: Set the simulation options

3. Switch to the Standard options tab and make sure that the Hold inputs constant check box is not selected to restore the input.

If you start a new run, this leads to the final results: Figure 26: Update the curves

Results

We have removed the first transient phase by starting in an equilibrium position but we have kept the second phase.

This is a safe and reliable way of getting an equilibrium position. However, for a big system the extra run necessary could be very long. An alternative way of getting an equilibrium position using a stabilizing run is described in the next section.