The Clock and Timing

The Clock

The clock is integral to Discrete Event Simulation because it tells you the time in your model. Before going any further you need to decide which time units to work in (seconds/minutes/hours).

You should also think about how long to run your simulation for (i.e. do you want to look at your process over a day/week/month/year?).

Double click on the clock to view and edit Clock Properties.

SIMUL8’s default is to run for a 40 hour week (9am – 5pm Monday – Friday). For this example, set the Start Time to 06:00 and the Duration of each day to 18:00. The clock, will now run for 18 hours per day starting at 6am.

Click on the button. This allows you to change the length of time the simulation is to run for. The default is to collect results for 1 week, although this can be altered to match your requirements.


The next step is to include timing information for each step in your process. Click on Activity 1; the Activity Properties should appear on the toolbar at the top of your screen.

In the ‘Average’ box, you can see that the time to process each items in this Activity is set to a default value of 10 minutes. Change this to 5 minutes by clicking in the ‘Average’ box.

You can also change the name of the Activity using the ‘Name’ box on the far left of the toolbar. Alter the name to ‘Process 1’ – the Activity properties box should now look like the picture above.

In reality, events don’t always occur at fixed times – for instance, patients don’t arrive 5 exactly 5 minutes apart to a Doctor’s Surgery. In order to account for this randomness, SIMUL8 uses Distributions to build in real life variability. The Distribution in your simulation is currently set to Average. This means that the time Process1 takes to complete work on each work item will vary. You can change the distribution used by selecting the dropdown menu.

Next change the processing times of the other Activities to 5 minutes each.

In order to edit the timing of arrivals within your process, click on the Start Point and change the Average Arrival Timing to 5 in the top toolbar.

The Start Point uses the Inter Arrival Time, or time between each item arriving. This means that roughly once every 5 minutes an item is pushed into the simulation (this equates to 12 items per hour).
If the Inter Arrival Time is shorter, more items will enter the simulation over the same time period. Now, experiment with different distributions. You will have seen queues building up – what happens if you change the Processing times and Inter Arrival Time to fixed Distributions?

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