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Describe Modelling Applications

computer model is the creation of a model of a real system in order to study the behaviour of the whole system.  The model is computer generated and is based on mathematical representations.

The idea behind developing the model is to try to find out what mechanisms control how a system behaves.  This makes it possible to predict the behaviour of the system in the future and also see if it is possible to influence this future behaviour.

Computer models are used because they can help find a solution more quickly and can be considerably safer while at the same time saving money and time.

Traffic Light Simulation

A set of traffic lights are to be modelled at a Y-junction:

In this computer model, it is necessary to consider:

How and what data needs to be collected?

The success (or failure) of a computer model depends on how realistic the model is.  Hence, data needs to be collected for a considerable period of time by watching traffic at the Y-junction.  This is best done by using induction loop sensors which count the number of vehicles at each junction.  Collecting data manually is possible but is prone to errors and is also difficult to do over an 18-hour period per day (for example).  The type of data that would need to be collected or considered for collection would be as follows:

• a count of the number of vehicles passing through the junction in all directions at all differing times of the day
• the day of the week (weekends, bank holidays, public holidays, etc., can alter how the data need to be interpreted)
• how long it takes a vehicle to clear the junction
• how long it takes the slowest vehicle to pass through the junction
• whether there are any pedestrian crossings, etc., nearby
• whether there are other factors which might affect the junction (e.g. left turns, right turns, filtering, etc.).

How the computer model is carried out?

Data from the above list is entered into the computer database and the computer model is run.  Once the designers are satisfied that it simulates the real situation accurately (i.e., by comparing results obtained with actual traffic flow from a number of data sets), then different scenarios can be tried out.  For example:

• increase the number of vehicles stopped at part of the junction and then change the timing of the lights to see how the traffic flow is altered
• increase or decrease traffic flow in all directions
• consider how emergency vehicles affect traffic flow at different times of the day
• vary the timing of the lights and see how the traffic flow is affected.

How the system would work in real life?

1. Sensors in the road gather data and count the number of vehicles at the junction.
2. This data is sent to a control box or to a computer.
3. The gathered data is compared to data stored in the system (the stored data is based on model predictions which were used to optimise the traffic flow).
4. The control box or computer ‘decides’ what action needs to be taken.
5. Signals are sent out to the traffic lights to change their timing if necessary.

Why are computer models done (in general terms)?

• With computer models it is much easier to try out various scenarios in advance.
• Time scales are reduced by doing a computer model rather than the real thing (some applications would take before a result is known e.g. climate change calculations, population growth, etc.).
• They are less expensive than having to build the real thing (e.g., a bridge!).
• On many occasions it is safer to run a computer model (some real situations are hazardous e.g., chemical processes).

Other examples of computer models include: training pilots and drivers, running chemical and nuclear plants, crash testing of cars, financial modelling, weather predictions, population growth and modelling queues at checkouts.

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