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. This can be represented by an aging chain.
To model such a situation, you cannot use a single Stock (e.g., a Reservoir A stock element that integrates and conserves flows of materials.). 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 A representation of the significant features, events and processes controlling the behavior of a system., there are three fundamental ways to model such a chain:
- Using a series of Reservoirs or Pools.
- Using a series of Material Delays.
- Using a series of Integrators.
These three methods are discussed briefly in the following
Example files which illustrate how aging chains can be modeled (AgingChain.gsm and AgingChainArray.gsm) can be found in the General Examples folder in your GoldSim directory (accessed by selecting File | Open Example... from the main menu).