SimulationsSimulations

Learning ObjectivesLearning Objectives

Explain the reasons for simulation, such as to change time-scales and/or save costs and/or avoid danger

Describe the uses of simulation to assist in design, to make predictions, to test hypotheses.

SimulationsSimulations

A computer pretending to carry out a A computer pretending to carry out a physical action by performing the physical action by performing the necessary calculations.necessary calculations.

Can be done only if the physical action can Can be done only if the physical action can be portrayed as the result of a series of be portrayed as the result of a series of formulae and their results, acting upon one formulae and their results, acting upon one another.another.

Possible because a computer system has Possible because a computer system has the ability to perform a large number of the ability to perform a large number of calculations in a short space of time.calculations in a short space of time.

Setting up a simulationSetting up a simulation

In a simulation there are a number of variables In a simulation there are a number of variables that control the outcome and the results that that control the outcome and the results that may be predicted. may be predicted.

The values of these variables do not just appear The values of these variables do not just appear by magic but must be collected and that sensible by magic but must be collected and that sensible limits should be set within which the variable limits should be set within which the variable values must lie. values must lie.

The results will be based on the use of these The results will be based on the use of these variables in specific formulae that relate the variables in specific formulae that relate the variables to one another. variables to one another.

Setting up an example simulation Setting up an example simulation – Plant Growth– Plant Growth

The rate of growth of a sunflower is known from The rate of growth of a sunflower is known from observations taken over many years. observations taken over many years.

The effects of different chemicals on the growth The effects of different chemicals on the growth of sunflowers are known from simple of sunflowers are known from simple experiments using one chemical at a time.experiments using one chemical at a time.

Computer is programmed with all the relevant Computer is programmed with all the relevant formulae dictating how it should grow in certain formulae dictating how it should grow in certain circumstances, the computer can then play the circumstances, the computer can then play the part of the sunflower and show how a real one part of the sunflower and show how a real one can be expected to react.can be expected to react.

Setting up an example simulation Setting up an example simulation – Weather Forecasting– Weather Forecasting

Data is collected about present weather Data is collected about present weather conditions. conditions. Collected from weather stations across the Collected from weather stations across the

globe, from weather balloons, aircraft and globe, from weather balloons, aircraft and satellites in order to make the model 3 satellites in order to make the model 3 dimensional.dimensional.

This is all fed into a system together with This is all fed into a system together with relationships that the data is known to follow. relationships that the data is known to follow.

E.g. Warm wind blowing off the sea becomes E.g. Warm wind blowing off the sea becomes damp and there is more chance of rain. damp and there is more chance of rain.

Setting up an example simulation Setting up an example simulation – Weather Forecasting– Weather Forecasting

The values of the variables are arranged The values of the variables are arranged to be within sensible parameters.to be within sensible parameters. E.g. Wind speed must be between 0 and E.g. Wind speed must be between 0 and

120mph, temperature must be between 0 and 120mph, temperature must be between 0 and 110 degrees Fahrenheit. 110 degrees Fahrenheit.

The results are the best that can be The results are the best that can be expected for those data that are collected. expected for those data that are collected.

Simulations speed up processes & save Simulations speed up processes & save timetime

Simulations can speed up a process in Simulations can speed up a process in order to give results in a more reasonable order to give results in a more reasonable time scale. time scale. E.g. Find in seconds rather than 6 months a E.g. Find in seconds rather than 6 months a

suitable cocktail of additives to allow suitable cocktail of additives to allow sunflowers to grow on the fringes of a desert sunflowers to grow on the fringes of a desert and consequently create a cash crop for and consequently create a cash crop for farmers, in such conditions, where they had farmers, in such conditions, where they had no cash crop before. no cash crop before.

Simulations speed up processes & save Simulations speed up processes & save timetime

Testing what will be the outcome of Testing what will be the outcome of breeding a plant for 100 generations...breeding a plant for 100 generations... In real life, 100 life cycles of a plant will take In real life, 100 life cycles of a plant will take

100 years to test100 years to test

To test out new parts in car without To test out new parts in car without building them.building them. Saves time in development Saves time in development

Simulations can isolate situations Simulations can isolate situations from external factorsfrom external factors

Growing crystals to study behaviour.Growing crystals to study behaviour. Too easy for material to be contaminated in Too easy for material to be contaminated in

real lifereal life

Simulations avoid danger Simulations avoid danger

Testing acceptable parameters in a Testing acceptable parameters in a dangerous industrial reaction.dangerous industrial reaction. The effects of a test which passed safety The effects of a test which passed safety

limits in real life may put lives in danger.limits in real life may put lives in danger.

Testing safety features in cars.Testing safety features in cars. Saves risk of injury to humans.Saves risk of injury to humans.

Train operators to deal with emergencies.Train operators to deal with emergencies. The result may be hostile to humans.The result may be hostile to humans.

Simulations do the impossibleSimulations do the impossible

It is not possible to fly through the rings of It is not possible to fly through the rings of Saturn. Saturn.

Training astronauts to work on the surface Training astronauts to work on the surface of Mars.of Mars.

Such tasks are not possible in real life Such tasks are not possible in real life because astronauts have not been to because astronauts have not been to other planets because the technology other planets because the technology does not exist.does not exist.

Simulations can save money & timeSimulations can save money & time

Testing different designs of new Testing different designs of new suspension systems for a range of cars issuspension systems for a range of cars is Expensive, as well as time consuming to build Expensive, as well as time consuming to build

prototypes and take them out in different prototypes and take them out in different conditions to test how they work. conditions to test how they work.

A computer can be programmed to take A computer can be programmed to take the characteristics of each possible the characteristics of each possible system and report how well they will work, system and report how well they will work, at a fraction of the cost.at a fraction of the cost.

Simulations can save money & timeSimulations can save money & time

Test safety features in crashes.Test safety features in crashes. Saves money in development.Saves money in development.

Simulations can test hypothesisesSimulations can test hypothesises

An engineer may design a new leaf spring An engineer may design a new leaf spring for a suspension system and hypothesis for a suspension system and hypothesis that it will give more steering control when that it will give more steering control when travelling on rough surfaces. travelling on rough surfaces. The computer can be set up to simulate the The computer can be set up to simulate the

conditions and give evidence to either support conditions and give evidence to either support or contradict the hypothesis.or contradict the hypothesis.

Simulations can answer ‘What if’ Simulations can answer ‘What if’ questions immediately.questions immediately.

To give immediate readouts of costs for To give immediate readouts of costs for new car designs.new car designs.

As modifications are made the costs are As modifications are made the costs are shown immediately and there is no need shown immediately and there is no need for further work.for further work.

Simulations can predict complex Simulations can predict complex situationssituations

A financial package stores data concerning the A financial package stores data concerning the economy. economy. Economic indicators do not exist in isolation.Economic indicators do not exist in isolation.If the unemployment figures go up then there is less If the unemployment figures go up then there is less money in the economy, so people can buy less, so firms money in the economy, so people can buy less, so firms sell less, so more people are laid off. sell less, so more people are laid off. A government or national bank may bring down interest A government or national bank may bring down interest rates which will encourage people to borrow more and rates which will encourage people to borrow more and hence buy more, so firms need to employ more people in hence buy more, so firms need to employ more people in order to put more goods in shops… order to put more goods in shops… When the relationships become intertwined like this the When the relationships become intertwined like this the calculations of predictions become very complex and calculations of predictions become very complex and computers are needed.computers are needed.

Limitations of SimulationLimitations of Simulationss

The results produced are subject to a The results produced are subject to a degree of error, the size of which will result degree of error, the size of which will result from, not just the validity of the variable from, not just the validity of the variable values and the relationships, but also the values and the relationships, but also the validity of the model that is used.validity of the model that is used.Some events are so complex that it is Some events are so complex that it is impossible to design a model for them, impossible to design a model for them, Human behaviour does not normally follow Human behaviour does not normally follow easily interpreted relationships.easily interpreted relationships.

E.g. Weather ForecastingE.g. Weather Forecasting

However, there can always be unexpected However, there can always be unexpected problems, for example the sun has been problems, for example the sun has been particularly violent recently and such sun particularly violent recently and such sun storms have a pronounced effect on our storms have a pronounced effect on our weather. weather.

This was not a factor in the original This was not a factor in the original simulation and consequently the reliability simulation and consequently the reliability of the results is not as good as expected.of the results is not as good as expected.

E.g. LotteryE.g. Lottery

If it were possible to predict the outcome of the If it were possible to predict the outcome of the lottery draw then there would be some very rich lottery draw then there would be some very rich computer programmers. computer programmers.

Mathematically, the outcome is not random and Mathematically, the outcome is not random and should be predictable, perhaps by modelling the should be predictable, perhaps by modelling the behaviour of the individual atoms inside the behaviour of the individual atoms inside the machine that chooses the balls. machine that chooses the balls.

However, this is impossible, certainly with However, this is impossible, certainly with present technology.present technology.

E.g. Human BehaviourE.g. Human Behaviour

If it were possible to predict accurately that If it were possible to predict accurately that human beings would all buy a particular human beings would all buy a particular song in preference to another, then the song in preference to another, then the record industry would not have to produce record industry would not have to produce such a volume of material in order to have such a volume of material in order to have a single hit. a single hit.

Human behaviour is very difficult to Human behaviour is very difficult to predict.predict.

PlenaryPlenary

Give reasons for needing to use computer Give reasons for needing to use computer simulation, giving an example of a use for simulation, giving an example of a use for each.each.

PlenaryPlenary

Impossible to do otherwise because Impossible to do otherwise because technology does not existtechnology does not exist

e.g. train astronauts to land on Marse.g. train astronauts to land on Mars

Dangerous to do otherwise because the result Dangerous to do otherwise because the result may be hostile to humansmay be hostile to humans

e.g. train reactor operators to deal with emergenciese.g. train reactor operators to deal with emergencies

Too costly to do otherwise because budget Too costly to do otherwise because budget would not cover costswould not cover costs

e.g. test different suspension systems for new car.e.g. test different suspension systems for new car.