Environmental Engineering Reference
In-Depth Information
Mechanism
number
Uncertainty loss
of performance
1
4
Mechanism
contribution to
performance
Effective
performance
2
5
3
6
1
2 3 4
Model complexity; number of components
5
6
Figure 17.5
Adding a cause involves certain amount of uncertainty, which can overshoot the contribution to the model performance
by adding the cause.
System levels
Low
details
High
details
Figure 17.6
Focus of models depends on the
observation level. Global-scaled models can
require many variables and high temporal
integration but must address lower detail
levels, compared with local models.
Number of variables / Increased temporal scale
derived locally. Such models need simplification and bal-
ance between number of components and the observation
level (Figure 17.6).
We should select the level needed to understand the
interrelationship among our selected variables - the level
we want to influence. After defining that level, detailed
knowledge of the underlying components is not needed.
That knowledge falls into the complex assumption made
during the sorting process. Driving a car, for instance,
does not require detailed knowledge of the construction
of the engine; the vehicle can be operated without such
knowledge.
17.6 The basic path
The process from specifying the question and building
the model starts by gathering information and listing
all the variables we feel are appropriate for the system.
Then we try to categorize the critical and the indicator
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