Simulations

Learning 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.

Simulations A computer pretending to carry out a physical action by performing the necessary calculations. Can be done only if the physical action can be portrayed as the result of a series of formulae and their results, acting upon one another. Can be done only if the physical action can be portrayed as the result of a series of formulae and their results, acting upon one another. Possible because a computer system has the ability to perform a large number of calculations in a short space of time. Possible because a computer system has the ability to perform a large number of calculations in a short space of time.

Setting up a simulation In a simulation there are a number of variables that control the outcome and the results that may be predicted. The values of these variables do not just appear by magic but must be collected and that sensible limits should be set within which the variable values must lie. The results will be based on the use of these variables in specific formulae that relate the variables to one another.

Setting up an example simulation – Plant Growth The rate of growth of a sunflower is known from observations taken over many years. The effects of different chemicals on the growth of sunflowers are known from simple experiments using one chemical at a time. Computer is programmed with all the relevant formulae dictating how it should grow in certain circumstances, the computer can then play the part of the sunflower and show how a real one can be expected to react.

Setting up an example simulation – Weather Forecasting Data is collected about present weather conditions. Collected from weather stations across the globe, from weather balloons, aircraft and satellites in order to make the model 3 dimensional. Collected from weather stations across the globe, from weather balloons, aircraft and satellites in order to make the model 3 dimensional. This is all fed into a system together with relationships that the data is known to follow. This is all fed into a system together with relationships that the data is known to follow. E.g. Warm wind blowing off the sea becomes damp and there is more chance of rain.

Setting up an example simulation – Weather Forecasting The values of the variables are arranged to be within sensible parameters. E.g. Wind speed must be between 0 and 120mph, temperature must be between 0 and 110 degrees Fahrenheit. E.g. Wind speed must be between 0 and 120mph, temperature must be between 0 and 110 degrees Fahrenheit. The results are the best that can be expected for those data that are collected.

Simulations speed up processes & save time Simulations can speed up a process in order to give results in a more reasonable time scale. E.g. Find in seconds rather than 6 months a suitable cocktail of additives to allow sunflowers to grow on the fringes of a desert and consequently create a cash crop for farmers, in such conditions, where they had no cash crop before. E.g. Find in seconds rather than 6 months a suitable cocktail of additives to allow sunflowers to grow on the fringes of a desert and consequently create a cash crop for farmers, in such conditions, where they had no cash crop before.

Simulations speed up processes & save time Testing what will be the outcome of breeding a plant for 100 generations... In real life, 100 life cycles of a plant will take 100 years to test In real life, 100 life cycles of a plant will take 100 years to test To test out new parts in car without building them. Saves time in development Saves time in development

Simulations can isolate situations from external factors Growing crystals to study behaviour. Too easy for material to be contaminated in real life Too easy for material to be contaminated in real life

Simulations avoid danger Testing acceptable parameters in a dangerous industrial reaction. The effects of a test which passed safety limits in real life may put lives in danger. The effects of a test which passed safety limits in real life may put lives in danger. Testing safety features in cars. Saves risk of injury to humans. Saves risk of injury to humans. Train operators to deal with emergencies. The result may be hostile to humans. The result may be hostile to humans.

Simulations do the impossible It is not possible to fly through the rings of Saturn. Training astronauts to work on the surface of Mars. Such tasks are not possible in real life because astronauts have not been to other planets because the technology does not exist.

Simulations can save money & time Testing different designs of new suspension systems for a range of cars is Expensive, as well as time consuming to build prototypes and take them out in different conditions to test how they work. Expensive, as well as time consuming to build prototypes and take them out in different conditions to test how they work. A computer can be programmed to take the characteristics of each possible system and report how well they will work, at a fraction of the cost.

Simulations can save money & time Test safety features in crashes. Saves money in development. Saves money in development.

Simulations can test hypothesises An engineer may design a new leaf spring for a suspension system and hypothesis that it will give more steering control when travelling on rough surfaces. The computer can be set up to simulate the conditions and give evidence to either support or contradict the hypothesis. The computer can be set up to simulate the conditions and give evidence to either support or contradict the hypothesis.

Simulations can answer ‘What if’ questions immediately. To give immediate readouts of costs for new car designs. As modifications are made the costs are shown immediately and there is no need for further work.

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

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

E.g. Weather Forecasting However, there can always be unexpected problems, for example the sun has been particularly violent recently and such sun storms have a pronounced effect on our weather. This was not a factor in the original simulation and consequently the reliability of the results is not as good as expected.

E.g. Lottery If it were possible to predict the outcome of the lottery draw then there would be some very rich computer programmers. Mathematically, the outcome is not random and should be predictable, perhaps by modelling the behaviour of the individual atoms inside the machine that chooses the balls. However, this is impossible, certainly with present technology.

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

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

Plenary Impossible to do otherwise because technology does not exist e.g. train astronauts to land on Mars e.g. train astronauts to land on Mars Dangerous to do otherwise because the result may be hostile to humans e.g. train reactor operators to deal with emergencies e.g. train reactor operators to deal with emergencies Too costly to do otherwise because budget would not cover costs e.g. test different suspension systems for new car. e.g. test different suspension systems for new car.