Back Issues Learning Zone Cafe Templates Components Register

• An article by James Love on Simulating a Bus Station
• Details on free downloads added to the website this month
• And a Survey on SIMUL8 support

Recently I built two simulations of bus stations, one of an existing station and the other of a proposed station to replace it. The simulations were built to investigate whether the performance of the proposed station could cope with the predicted growth in demand. You can read the full story on our website but in this newsletter I'll cover some practical tips I discovered while working on these simulations.

Physical Dimensions of the Simulation

Conveyors were used to represent the structure of the stations. This makes it easy to simulate a system with strict physical dimensions and cover attributes such as lengths of different bus types and bus speeds accurately.

For example, in the station simulations passenger alighting and boarding times were used with road lengths and bus speeds to calculate a sequence of events and timings. This, along with observations from the existing station itself, could be compared with SIMUL8 outputs and used in validating the simulation.

Routing Work Items by Label

Buses were routed around the station using labels. A label named “lblStandVisits” was used as a counter recording the number of times each bus has visited a stand. We could then use Visual Logic to control where work items should be routed at each point in the process.

Call Frequently Used Code

If you use your variables carefully it's possible to Call frequently used Visual Logic code rather than have similar code in multiple locations. Not only does minimizing your code improve the run speed of your simulation, but also by keeping your code organized and compact you as a developer are more in control of the simulation as you have far less chunks of information to deal with.

In the bus station simulations, frequent decisions had to be made at various locations about routing around the station. So rather than repeating code before each individual Bus Stand it was more efficient to call code such as “CALL Pick Up Rules” and “CALL Enter Stand Rules.”

Components used for Repeated Object Groups

In the two simulations some combinations of objects were used again and again, for example bus stands and layover bays. When developing a simulation with identical objects following the same set of logical rules try making it into a component then it can be dragged-and-dropped into your simulation easily.

To do this, select each item you wish to have in your component; right-click and select “Create Component Type”

After this you will see the selected items grouped under one icon and a new button will appear on your toolbar. This enables the easy drag-and drop of your newly created component into any simulation you build.

Simulation Validation

Ensuring that what you see on screen reflects exactly what you see in reality is vital each time a development change is made.

For more information on simulation validation click see the previous newsletter on Testing Simulations.

Schematic Diagram as a Background Image

Schematic diagrams of the bus station were used as background images in the simulations. The schematics were familiar to all the key decision makers in the project so this instantly helped the simulation become more understandable to those with limited simulation knowledge.

Moving Buses and Other Vehicles

As well as buses, foreign vehicles, such as emergency vehicles, delivery vans and unscheduled buses were simulated to ascertain the impact that their unavoidable presence would have on the operation of the stations.

Different Work Item Images for Debugging

Different work items can have different images associated to them to represent different types of product and/or attributes. Another use of different work item images is as a debugging tool. I had green buses represent a bus that had just entered the station; yellow buses had visited a stand to drop-off passengers; and finally red buses had visited a stand to pick-up passengers.

This made it a lot deal easier for me to see if the logic in the simulations was routing buses exactly as it should be by showing me at a glance where each bus should be going at any time.

For more debugging tips click the previous newsletter on How To Debug a Simulation.