Simulation & Models |
A computer simulation is a computer program which attempts to duplicate or predict the behaviour of a real life system.
Commercial airline pilots learn how to fly by using a flight simulator rather than flying real aircraft. The flight simulator puts a pilot in copies of real-life flight situations and reacts to a pilot's actions in the same way as a real aircraft would. It is much safer and cheaper for airlines to teach pilots to fly this way. There are three main reasons for using a simulation rather than actually doing something. They are :
Cost : Using a simulation can be much cheaper than actually doing something. Crashing cars to see how the passengers (replaced by dummies) are affected by an impact would be very expensive. Many cars would be destroyed. Simulating this on a computer is far cheaper.
Safety : Some things are very dangerous. Finding out what would happen if a cooling system failed in a nuclear reactor by actually turning the system off would be highly dangerous. Using physical laws the effect could be predicted by a computer simulation.
Feasibility : There are some things that humans simply can not do. It would be interesting to be able to travel through a human body to see how the organs in the body worked. Unfortunately a human simply can't do this. But a human can use a simulation which shows what it would be like to travel around a body.
Simulations use rules and variables to model a real life situation.
Simulations are models of reality. A simulation should copy the behaviour of the real life system that it simulates. The designer of the simulation will incorporate as much of his knowledge about how the real system works as possible into the simulation software. Any simulation will have two important components :
Variables : Variables are things in a simulation that can change.
Rules : Rules determine how the variables in the model are changed and how they affect each other.
In a car driving simulation the variables might include :
A simulation will incorporate many hundreds of variables. Some variables such as the position of the accelerator pedal can be changed directly by the user. Other variables such as the car's speed are changed by the rules of the simulation. Two simple rules that you might want to incorporate into a car simulator are :
These two rules would have to be refined considerably before they could be used in a real simulation.
The rules and variables that make a simulation work are often implemented as mathematical calculations. The mathematical calculations that make a simulation work are known as a model.
Some simulators such as car or flight simulators need to use specialised input and output devices to make the user believe he is interacting with a real car or aircraft. A car simulator would use copies of a steering wheel, gear stick etc. as input devices. Large monitors positioned around the user would act as the main output device.
For other simulations such as a spreadsheet model of how ice cream sales change in hot weather, the methods of input and output are not important. A standard keyboard and monitor could be used.
Spreadsheet software can be used to create simulations of real world situations that use calculations to function :
The numbers typed into the spreadsheet are the variables in the simulation.
The formulae which perform the calculations are the rules of the simulation.
The calculations which are used to make a simulation in a spreadsheet are known as a model. Spreadsheets can be used to model simple or complicated financial situations :
A company could use a spreadsheet to try and predict the effect of changing the price of one of the products it sells.
Organisations like the treasury model mathematically the effect that changes in economic variables such as the rate of interest will have on the economy. A simple model of these effects could be produced using a spreadsheet.
Flight simulators are computerised models which simulate what it is like for a pilot to fly an aircraft. They are used to train pilots to fly real aircraft. Pilots train in simulators rather than in real aircraft because :
| Safety | It is safer to use a smiluator than to fly a real aircraft. Any errors will only result in simulated accidents, not real ones. This is particularly important when training new pilots as they are more likely to make mistakes. |
| Cost | It is cheaper to use a simulator than to fly a real aircraft. Fuel does not have to be paid for and if an accident occurs no real damage has to be repaired. |
| Situations | Different situations can be easily tried out in a simulator. For example a pilot can train to fly in different types of weather or to land at different airports by simply changing the setup of the simulator. |
A flight simulator is designed to train a pilot to fly a particular aircraft as although the principles of flying are the same for all aircraft, the layout of the instruments in the cockpit and the detailed method of controlling an aircraft will vary from one plane to another.
Input and Output Devices
Specialised input and output devices are used in a flight simulator. The flight simulator will be built within a module that is the same size as a real aircraft cockpit. The cockpit controls and displays will exactly duplicate those in the real aircraft. Very large VDUs are used to simulate the view that the pilot would see from the cockpit and hydraulic pistons are used to move the simulator module so that the pilot will feel motion similar to that in a real aircraft.
Rules and Variables
As with any other simulation, a flight simulator will be controlled by rules and variables. A real flight simulator will make use of tens of thousands of rules and variables. Some examples of these are :
| Example Variables | Example Rules |
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After The Simulator
After a commercial airline pilot has been trained in a simulator he will be expected to make many flights without passengers before he is allowed to fly an aircraft with passengers onboard. This is because :
A virtual reality (VR) system places the user of a computerised simulation in an artifically created environment. By using sophisticated computer graphics, three dimensional VR headsets and a data glove the user can almost come to believe that the artificially created environment is real.
Hardware Used In A Virtual Reality System
Because virtual reality systems must produce very high quality graphics they usually require a very fast microprocessor, a lot of RAM and a large backing storage device to work effectively. Two other specialised devices are also used by most VR systems :
| VR Headset | The user of a VR system wears a headset which incorporates two small VDUs which cover each eye, earphones which produce sounds and a motion sensor. Because there is one VDU for each eye the user can view three dimensional images generated by the computer. The motion sensor detects movement of the user's head so that as the user moves the image that is displayed can change to take account of the direction that he is looking in. The combination of these devices can create a very realistic virtual environment for the user. |
| Data Glove | The data glove is worn on a hand of the user of a VR system. The glove contains sensors which detect the movement of the hand. By moving his hand the user can point at items in the virtual environment, pick them up and manipulate them. |
Applications of Virtual Reality
Most current virtual reality systems are quite basic. Much research and development is being carried out in this area. The eventual applications of this technology are uncertain, but some possible uses are listed here.
| The Virtual Office | Most graphical user interfaces liken the experience of using a computer to working in an office. Files can be placed on a desktop, work is stored in folders etc. A virtual reality system can extend this metaphor. The user could operate the computer by interacting with an artifically created office. Files could be accessed by lifting them out of the filing cabinet. The telephone could be answered by lifting a virtual 'phone handset. |
| Training | It is dangerous or difficult for some workers to train to carry out their jobs. For example soldiers can be injured in war exercises and astronauts can not easily practise the skills that they need to use in space on earth. By creating virtual reality copies of the real world environments that they have to work in these people can train to carry out their jobs by using computer simulators. |
| Recreation | Many people enjoy playing computer games. These are becoming increasingly sophisticated and the graphics that they use are becoming more and more realistic. By using virtual reality hardware these games can be improved further still. Game players can be fooled into believing that they are actually within the environment of the game that they are playing. |
Simulations can be used for many purposes. Here are some more examples :
| Example | Description | ||||
| Games | Many computer games attempt to mimic aspects of real life on a computer. For example :
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| Science Experiments | Some science experiments are too dangerous or expensive to conduct. The way in which different chemicals or physical effects interact with each other can be modelled by a computer so that the results of an experiment can be seen without having to carry it out. | ||||
| Weather Forecasting | The weather that we experience is determined by many factors such as atmospheric pressure, temperature, wind direction, time of day and the relief of the land. Computers are used to produce weather forecasts by simulating how these factors interact with each other and change over time. Powerful mainframe computers are required to carry out the complex calculations involved in forecasting. Weather forecasts are not perfect because the model used to produce a forecast does not incorporate all of the factors that determine what will happen. | ||||
| Economic Modelling | Organisations like the Treasury use mathematical models to simulate the effect that changes in economic variables such as the rate of interest, tax rates or exchange rates will have on the economy. |
No simulation will copy every feature of a real life system. The rules that the simulation's designer incorporates into the simulation will not perfectly copy every aspect of the real system. This is because :
Incorporating all the factors that affect a simulation would make it very difficult and expensive to produce the simulation. The number of variables and rules involved would be massive.
Some situations that could occur in real life are so unlikely to happen that the designer of a simulation would probably not think of including the situations in the simulation.
Mistakes can be made. Relationships in real life systems can be inaccurately observed or incorrectly programmed into a simulated model.
This limits the usefulness of the results produced by a simulation. A simulation is only as reliable as the rules that it is based on. Sometimes a simulation is used initially but the results of the simulation are then tested by using the real system.
GCSE ICT Companion 04 - (C) P Meakin 2004