Environmental Engineering Reference
In-Depth Information
the craft of modelling can't be done as an add-on to a field-based project; it needs
to be seen as a research component in its own right. Producing a publication-
standard modelling study takes 6-12 months of hard work.
It can be very daunting to embark on modelling from cold, especially if you don't
have any other people around you who have done it before. However, the process
can be broken down into small steps, and even only travelling a few steps down the
path to a fully functioning model is still very beneficial, because it forces you to
think clearly and logically about the problem. One of the problems is the jargon
involved in modelling. Table 5.1 gives a short guide to terms used to describe the
main types of model.
Table 5.1
Common types of model.
Model type
Explanation
Conceptual vs.
A conceptual model shows qualitatively your understanding of
mathematical
the system, often in a flow diagram. A mathematical model
quantifies the relationships between the components of the
flow diagram using equations.
Analytical vs.
An analytical model is a set of mathematical equations which
simulation
are solved to get general relationships between parameters. In a
simulation model, specific values are given to the parameters in
the equations and the model is run a number of times to get the
output for these values.
Equilibrium vs.
An equilibrium model is a representation of the state that a
dynamic
system will end up in. A dynamic model represents system
changes over time, not just the final resting point.
Lumped vs.
A lumped model represents the object of interest (e.g. a
structured
population) as one number, assuming all individuals are the
same. A structured model divides the population up into
compartments—sexes, ages, size classes, spatial locations,
individuals, or even genotypes.
Continuous vs.
Models in continuous time assume that all processes happen
discrete time
continuously, while those in discrete time break time down
into time-periods, such as years or seasons.
Deterministic vs.
In deterministic models parameter values are constant, but in
stochastic
stochastic models they are subject to random variation.
Bio-economic vs.
A bio-economic model involves both the human and the
others
biological components of the system—this is required for a full
understanding of the sustainability of the system.
