Page 102 - ExtendSim User Guide
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Areas of Application
ExtendSim is used to build continuous models in the fields of physical science, social science, engineering, and business. The first four sections of this chapter describe models created using the ExtendSim Value and Engineering libraries. The last section shows two models built with custom blocks: a physics model called Planet Dance and a Fish Pond simulation that examines predator/prey interactions.
Continuous modeling is very broad and diverse field. While it is possible to create almost any continuous model using the standard blocks (such as the Value library) packaged with Extend- Sim, it is more common to use a combination of standard blocks and custom-built blocks. For example, ExtendSim customers have created libraries for proprietary and commercial use in the fields of analytical chemistry, environmental decision making, chemical process control, pulp and paper making processes, and so forth.
Common areas where simulation is helpful in science include biology, chemistry, physics, and ecology. This section describes two models, a classic predator/prey model and a simulation of some factors that affect drug absorption in the human body.
This model shows a small ecosystem composed of hare and lynx. Each population has a direct effect on the other: the lynx feed on hare so the hare population declines, the diminishing food supply results in a decrease in the number of lynx so the hare population grows again and so forth.
Model assumptions
The model particulars and assumptions are:
• The 100-hectare ecosystem ini- tially contains 6000 hare and 125 lynx.
• Each hare produces 1.25 offspring per year and each lynx produces 0.25 offspring.
• Hare always have sufficient food supply; their only cause of death is being eaten by a lynx.
• The lynx hunting range is 1 hect- are, their only food source is the hare, and each lynx can consume every hare in its area.
Predator_Prey model
• Thenumberofharekilleddependsontheirdensityintheecosystemandthenumberoflynx who hunt them.
• The lynx mortality rate depends on how many hare they consume in a year.
• Therearenooutsidefactors(suchasthetimeofyear)whichaffecttherateatwhichthepop- ulations change.
• The final model runs for 24 years and calculations are done 12 times per year (dt is 0.0833).

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