1. Modelling and simulations
Chapter 8
Asfia Rahman

2. Model A model is a computer representation of a real-world process.
A model is created through mathematical analysis oi the real-world process.
Modelling software is used to create a model.
Spreadsheets can be used to create computerised models, but there are also custom-written softwares that are used to model specific processes.
Asfia Rahman

3. example
A network simulator such as Cloonix can be used to model a computer network.
The software will be able to produce a diagrammatic view of the devices connected to the computer network.
It will be possible to identify the Internet Protocol (IP) addresses used on the network and how they are assigned through a Dynamic Host Configuration Protocol (DHCP) server.
Wireless networks can be added and security can be configured to see what the effects will be.
Devices can be connected to specific switches and the throughput of data traffic can be analysed
Asfia Rahman

4. CAD CAD software can include features such as
viewing an object in two dimensions (2D) or three dimensions (3D),
manipulating objects within the model,
adding or removing objects,
viewing the model from different angles,
applying different effects such as colour and lighting,
and focusing on specific features such as the electrical cabling or heating system within a building.
Asfia Rahman

5. Features of a modelling software
the ability to change variables within the software
asking what-if questions to see what the result of changing variables might be
formulae and functions to carry out the mathematical calculations that form the basis of the model
automatic recalculation of formulae and functions
rules that define how the model behaves
layers of abstraction so that different parts of the model be viewed and analysed separately.
Asfia Rahman

6. example A model of a roller coaster can be built.
Variables can include
height of each drop, the radius of the loops, the starting speed of the carriage, length of each section, and the weight of each carriage
Calculations will be used to define rules such as the amount of friction and how that will slow the carriages down, the effect of gravity on carriages as they move up and down and the g-force that will be experienced by passengers he What-if questions could be asked such as 'What would happen if we increased the starting speed by 2 km/h?' or 'What would happen if we increased the initial drop by 5 km?' The effect of these changes in variables can then be modelled.
Asfia Rahman

7. Need for computer models
There are a variety of reasons why models might be used, including
training,
forecasting and
construction.
Whatever the reason, a model must be able to answer what-if questions.
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8. In training
Models can be used for the purpose of training people to use equipment.
This could range from earning to drive a forklift truck to flying an aeroplane or operating a nuclear power plant.
Use/advantages in training
Models are used for training because there is less risk of injury to the trainees and instructors than learning in a real environment. When learning to drive a forklift truck, the trainee may make a mistake by lifting a load too high and toppling the truck. In real life this could cause serious injury as well as costing money in terms Of repairs, but using a model removes both of these risks.
Costs are saved because real equipment does not suffer wear and tear,
fuel is not required to operate machinery
instructors do not need to be present all of the time
It is also possible to test the trainee in unpredictable situations such as turbulence for an aeroplane or driving a heavy goods vehicle on ice. Unpredictable situations that would happen in real life can also be removed for trainees when they first start learning so they can focus on basic controls.
Asfia Rahman

9. forecasting
One of the most common models for this purpose is weather forecasting.
Patterns that have happened in the past can be analysed along with current data to predict what the weather might be in the future.
Businesses and governments use financial modelling to predict what might happen to profits or the economy.
It is too risky for a business to make sudden changes in the marketplace without testing them out with a model first.
A variety of what-if questions can be asked using a model to determine how to make the most profit. Variables that can be changed include selling prices, adjusting the quantity of products to supply at any given time, times of year to sell products and the effect of weather on seasonal sales.
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10. construction
constructing buildings, kitchens, gardens, motor vehicles and other objects can be a very costly process.
It is important to get it right first time as any adjustments that have to be made in the real world will incur financial costs.
Models help to experiment with different designs to see which look is most aesthetically pleasing and which ones react best to environmental conditions.
When designing a kitchen using modelling software, variables such as lighting, worktops, cupboard doors, position of units, flooring and tiling can be changed to see which configuration looks the best. Cupboards, drawers, dishwashers and cookers can be opened to see if they use the space efficiently. The angle of view can be changed in a 3D environment to see what the kitchen might look like from a variety of angles.
Asfia Rahman

11. Effectiveness of spreadsheet models
variables which can be changed to ask what-if questions
formulae and functions which define the rules of the model
graphs and charts which can show a graphical representation of the forecast
Other advantages of spreadsheet models include
the ability to share the spreadsheet with colleagues easily so that many people can experiment with the model, and
the fact that most organisations already own spreadsheet software which reduces the need for training and purchase costs.
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12. Limitations of spreadsheet models
Spreadsheets do have their limitations though.
They are only as accurate as the formulae and functions that are the rules that represent the real world. Unless extremely complex rules are used, then a spreadsheet model will never be an accurate representation.
These complex rules require mathematical and computer expertise in order to set them up and it can take a very long time to create models that are truly representative of the real world.
Spreadsheets can only be used to simulate numbers, but cannot simulate the effect on objects.
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13. Simulations
A simulation is the use of a computerised model to predict how a real-life system might behave.
As with modelling, simulations can be used for training, forecasting and construction.
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14. Advantages of using simulations
it is not necessary to create expensive prototypes or the real thing in order to experiment with different variations and answer what-if questions
changes to the model be made very quickly and the effect can be seen as quickly
alternative models and designs can be used to see how they react differently
unusual events (e.g. earthquakes) can be tested without the need to wait them to happen in real life
equipment does not suffer and tear or damage when being tested or experimented with
dangerous situations such as aeroplane equipment failure can be simulated without putting people in danger
simulations can be 'sped up' so the effects can be analysed over a long period of time without having to wait for that period of time to elapse.
Asfia Rahman

15. disadvantages of using simulations
The way a simulation reacts is only as good as the model it is based upon
simulation software and equipment can be very expensive to purchase.
people need to be trained to use simulation equipment and software
complex model co take many years to develop, especially if they are designed to react like the real process
it is impossible for a simulation to be a perfect representation of the real- world process.
Asfia Rahman

16. Natural disaster planning
When planning for natural disasters, it is necessary to know what the effects of a natural disaster might be.
It is impossible to do this in real life without the actual disaster happening and, as they are natural disasters, it is impossible to force them to happen.
If the planners wait for the natural disaster to happen, then it is too late to plan.
Simulations based on models of natural disasters such as earthquakes, volcanic eruptions, hurricanes, bush fires and tsunamis can be used to see what the effects might be. Planners can experiment with different variables such as wind speed and direction to see how quickly a fire might spread, which will help them to plan evacuations and firefighting.
As with all simulations, these rely upon the accuracy of the model. There will be many things that the model can't predict completely such as sudden changes in wind direction or wind speed and emotional reactions to being evacuated. However, planners can experiment with lots of what-if questions in order to plan for a large variety of circumstances, which means that when a natural disaster does occur they can be better equipped to deal with it.
Asfia Rahman

17. Pilot training
Part of the thrill of flying an aircraft is being in the air. However, when it comes to large aircraft, it can cost thousands of pounds just to take off, fly and land. This cannot be repeated too often as it will become too costly to train pilots. Flight simulators can help by removing the fuel costs associated with flying. They can also remove the danger that a trainee pilot might pose if they make a mistake while in the air.
Flight simulators not only include software, but very specialised equipment which can cost hundreds Of
thousands of pounds. The equipment will be designed to react in a similar way to a real aircraft, so that the pilot can feel the physical effects of any movements that they make (including take off, landing, turbulence or even a crash landing) in a way that is as close to real life as possible. The software will include the rules of the model that define how the aircraft should react ina variety of circumstances,
Pilots can also practice landing and taking off at airports they have not visited before, including some of the most dangerous airports in the world such as Toncontin Airport in Honduras. Simulations give Pilots the opportunity to respond to malfunctions such as an engine These failure, cabin would be far pressure failure or landing gear failure, too dangerous to attempt in real life.
Asfia Rahman

18. Car driving
Simulators can be used to learn to drive a car. In most countries, learner drivers start immediately on the road having never used any of a car's controls before. They immediately have to deal with hazards such as other cars, EXAMPLE pedestrians, cyclists, potholes and dangerous junctions.
In addition to this, other drivers on the road are held up because of the learner driver being slow and hesitant.
Simulations can enable a learner driver to become familiar with the controls of a car and dealing with hazards before taking car onto the road for the first time.
This is a safe environment and could reduce insurance premiums for driving instructors.
The simulator could also be used when the learner driver needs to attempt manoeuvres such as turning in the road or reversing around a corner for the first time, rather than having to do this straight away on a real road.
Even after a learner driver has passed their test, they could use simulators to learn how to drive on a motorway, drive in icy conditions and how to handle a car if it gets out of control such as in a skid.
Simulations can also be used for racing drivers to experiment with different car setups to find the optimum configuration for a racing circuit, rather than risking crashing.
Racing drivers would be able to take the car to the limit, knowing that the virtual crash will not result in an injury. However, a simulation will never behave exactly the same as real car as the rules of the model will never be perfect. Therefore it is still necessary to practice using a real racing car.
Asfia Rahman

19. Nuclear science research
Nuclear science is very dangerous.
Even a small accident could expose a person to radiation that could cause serious disfigurement or death. It is therefore not possible to experiment with nuclear reactions in the real world in the hope that something might work.
Simulations can be used to try out different nuclear reactions by adjusting the coolant temperature, changing the way the control rods are used and the rate of reaction.
What-if questions can be asked such as 'What happens if I increase the temperature?' and the outcomes can be seen. It's also possible to speed up the simulation so that rather than waiting hours, days or even years to see what the effects might be, results can be seen much more quickly.
Nuclear science requires a lot of computing power in order to simulate nuclear reactions. For example, reactors convert Uranium and plutonium through nuclear fission which involves millions of collisions every microsecond.
Even with supercomputers, nuclear scientists cannot represent all of these collisions in a simulation.
Asfia Rahman

20. Difference between modelling and simulation
Both computer modelling and simulations are computer applications which represent a real world or imaginary system.
Both computer modelling and simulations help designers to save time and money.
A simulation is changing one or more variables of a model and observing the resulted changes.
Although a model always tries to represent the actual system, a simulation may try to observe the results by doing impossible (in real world) changes.
A model can be considered as a static and a simulation can be considered as dynamic as the variables of a simulation get always changed.
Asfia Rahman