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=Assumptions=

Models are formed based on assumptions. For example, a fire escape plan is based on average times it takes for a person to get through a door, or how long an average person takes to walk down a corridor. Models use assumptions to attempt to solve a solution though it often occurs that these assumptions are not valid. There are other factors to consider, such as an emotional factor. In a fire escape, people are most likely to be in panic thus this could cause the time for a person to travel to be longer then assumed. There are also physical factors to consider such as children may take longer then adults as they are confused and are not sure of where to go. These are known as faulty assumptions as the assumptions made are not always true to reality, thus making the model inappropriate.

Simplifying reality is also a disadvantage to a model as there can be unpredicted actions. Though if we were not to simplify reality, models and simulations would be impossible to conduct.

Phenomenons are often modelled, such as an eclipse. There are implications and variables which are uncontrolled by humans, thus models of such phenomenons can only be understood by a certain level.

=__Economic effects of the use of models to design and test new products.__=

Uses of simulation and modelling in the process of creating a new product could increase efficiency of the process and reduce the need for physical prototypes. This reduces the cost of the product development of the company significantly.

Different uses of simulation relating to reduction of cost: Simulation and analysis of product performance (cash, durability, thermal dynamics and fluid dynamics) Manufacturing and assembly simulation (formability, ergonomics, fitting and quality, fitting and quality) Manufacturing process, engineering, operator, logistics and financial simulation

Example
1. In an automobile company, the use of simulation could enable the impossible task of increasing the quality of the product while decreasing the length of the development cycle. In addition to this, Use of simulation could increase the efficiency of product analysis and improving data management. Further more, simulation could increase the product quality because it increases the ease of repetition of the product tests. Also, it reduces the cost of product development because it decreases the dependency of physical prototype and testing. (IBM)

2. Airbus the leading aircraft manufacturer uses simulation developed by hp and other IT vendors. Use of simulation improved engineering and analysis productivity; and reduced cost. Faster simulation could reduce software maintenance costs; in the past it took more time to simulate the product design, usually took over weeks to simulate one product, however now it is possible to simulate 20 to 30 in one night. (hp, 2003) In the production of the aircraft Falcon7X the entire production process was anticipated electronically. The result was that the first plane off the production line was perfect. And with no physical prototype, manufacturing and tool costs were cut in half. (Reid, 2005)

=__Bibliography__= hp. (2003). //Airbus//. Retrieved November 4, 2007, from http://h71028.www7.hp.com/ERC/downloads/Airbus_success_story_102203.pdf IBM. (n.d.). //Helping automotive comanies innovate and gain competitive advantage with PRoduct Lifecycle Management.// Retrieved Novemeber 4, 2007, from http://www-03.ibm.com/solutions/plm/doc/content/bin/AutoPLM_BCB00142_USEN_01.pdf Reid, D. (2005, September 23). //Take off for virtual prototypes//. Retrieved November 4, 2007, from http://news.bbc.co.uk/2/hi/programmes/click_online/4275332.stm

Responsibility of the designer for accuracy of assumptions underlying the model
It is the responsibility of the designer of the model to make sure that all the assumptions made are accurate. Predictions are made but they are not always accurate. This is when the designer has to look out and make sure that the predictions that are being made form a model is accurate or the closest it can get. An example of one model is the climate change model. In this the weather forecast is predicted everyday and even a week or two ahead. At times it may not be accurate but the designer who has designed it will have to make sure that the predictions are accurate or as close as it can get to the real thing.

The designer is not entirely responsible because they design the model according to the data that has been researched by the researchers. The designers do not know if it is right or wrong as they follow what has been given.

Example A "major error" has been discovered in the world's biggest online climate prediction project, backed by the BBC. The fault in a Climateprediction.net model launched in February causes temperatures in past climates to rise quicker than seen in real observations. http://news.bbc.co.uk/2/hi/science/nature/4923248.stm The designer should be responsible here to make sure that the model is designed accurately and if there are any faults it should be the designers responsibility to see what fault and fix it immediately.