Modeling Aging Chains


In some situations, it is necessary to keep track of the age structure of a stock of material or objects. For example, you may want to track the number of people in each of a number of age groups, the number of people in a company at different experience levels (e.g., new hire, experienced, expert), or the number of trucks of different age groups on the road.

To model such a situation, you cannot use a single Stock (e.g., a Reservoir or Integrator). Rather, you must disaggregate the total stock into multiple categories (referred to as cohorts). Each cohort “graduates” to the next cohort over time (and can only move in one direction). However, each cohort may grow and shrink for other reasons (e.g., if you were modeling a population of people, a particular category could grow due to immigration, and shrink due to emigration and death). Note that these rates of growing and shrinking are likely a function of the specific cohort (e.g., death rates).

Depending on your conceptual model, there are three fundamental ways to model such a chain:

·      Using a series of Reservoirs.

·      Using a series of Material Delays.

·      Using a series of Integrators.

This example model illustrates how aging chains can be modeled using these 3 approaches. It can also be found in the General Examples folder in your GoldSim directory by clicking on the Help menu and selecting "Example Models" option from within GoldSim.


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