Geoscience Reference
In-Depth Information
velocities in the range of
u
1
and
u
2
as
LL
f
f
sin
sin
()
()
ϕ
ϕ
=⋅
1
=⋅
L
1
(6.58)
2
1
1
2
2
Finally, even if the Coriolis force might be important in lagoons when speeds
are relatively low, it is important to remember that water motion in lagoons is
governed not only by Coriolis accelerations but also by many terms in the equations
of motion (
see Chapter 3)
and that it is the relative importance of these terms that
determines which ones actually force the motion. Normally, for shallow water
systems such as lagoons, we expect the pressure gradient terms to be balanced mainly
by bottom friction and, to a lesser extent or in some tidal phase conditions, by
nonlinear terms. Therefore, the Coriolis terms will influence the motion in lagoons
only when they are on the same order of magnitude as the pressure gradient or
friction terms.
6.3.4
O
BJECTIVES
OF
M
ODELING
A modeling activity should start with a clearly defined objective. It is important for
the user to clearly understand what the numerical model will be used for, i.e., what
the problems in the area are and what kinds of answers are expected from the
modeling activity. This is not always easy because a precise objective definition
requires some skill and experience. For example, “to investigate a wind surge
problem” or “to study heat transfer processes in the area” are not objectives as such
but rather general directions of investigations.
The objectives should be formulated in such a way that they result in an expected
model output, either in the form of justified recommendations, quantitative relation-
ships between variables, or schemes and charts, etc. Such concrete objectives will
optimize the time spent on solving the task and will keep the researcher on the right
track from start to finish.
37
From the outset, researchers should also make it clear what kind of results they
intend to produce with the model. Is the goal maximum water levels and currents at
certain points during a design event? Is it frequency distribution of the water levels for
a certain period? Is it an impact study of the construction of an offshore breakwater on
the eddy circulation in some approach channel, or some other clearly defined question?
37
In some instances the modeling approaches or strategies may be changed during
the course of investigation according to the results obtained. The objectives, however,
must never change, unless the resources available become exhausted during the
course of the study. Examples are the lack of time to finish the study, the lack of
additional computer resources, or accidental loss of data. In such cases, conditions
under which the original objectives may be attained must be stated.
There are as many objectives for a study as there are practical studies. One
example of a short and precise objective could be the following:
37
The overall objective of the present study is to identify the best layout of the
future cooling water system, on the following basis:
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