Page 100 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

Models 55

Algorithm: A sequence of computer code, such as a Fortran Lore: A body of traditions and knowledge on a subject or
program, that leads to a desired computational out- possessed by a class of people (Oxford American
come. Dictionary, Ehrlich et al., 1980).
Animation: A sequence of computer solutions with time such Model: A means to ‘‘map’’ the magnitudes of dependent
that a motion picture effect is observed. variables based upon the variation of selected inde-
Bench scale: An experiment set up in a laboratory flask or pendent variables.
something equivalent in size. Independent variables Normalized: A dependent variable that is a fraction,
are maintained constant while dependent variables defined as a quantity divided by perhaps the largest
are measured. value of a series with the sum of all normalized
Black box: A process depiction that may seek a relationship values equal to 1.0. Usually, a plot is normalized so
between one or more measured conditions of a given that the relationship with a dependent variable is
system and one or more output characteristics. A key applicable to as a general relationship (from Elias,
point is that the internal conditions of the system are 1997, p. 444). A unit hydrograph is a normalized
not depicted. relationship.
Coefficient: A ratio of two or more variables that character- Objective: An objective is a statement of a milestone to be
izes the results of a particular experiment or a set of met while striving to meet a goal. Attaining a certain
empirical observations about a system. Usually, effluent suspended solids level in a plant may be an
the equation with the coefficient has one dependent objective. To generate a headloss versus time curve
variable on the left side and several independent from a pilot plant study may be an objective. See
variables and the coefficient on the right side. An also goal.
example is the Chezy coefficient in pipe flow, i.e., Paradigm: An example that serves as pattern or model.
v ¼ C(RS) 1=2 . A coefficient is the ‘‘slack’’ factor in an Parameter: (1) A quantity that may have a correlation with
empirical equation, i.e., the numerical value that the changes observed for a dependent variable. [An
forces equality between variables. independent variable could be called a parameter,
Computer modeling: A computer program that depicts a but a parameter may not always be called an inde-
mathematical model ranging from a few lines of pendent variable.] (2) A water quality attribute. For
code to a complex system that may take into account example, the presence of certain bacteria, the hard-
contingencies, decisions, time variation, and any ness, and the level of sodium are all parameters
other ideas that may simulate a system. (Symons et al., 2000).
Dependent variable: A variable in a given system that is Parametric variation: Exploration of the effect of independ-
changed by the influence of an independent variable. ent variables on selected dependent variables
The dependent variable is a part of the ‘‘effects’’ done by holding all variables constant except one
caused by a given system. that is varied between set limits. The process may be
Dimensionless quantity: A product or ratio of two or more repeated, selecting one independent variable at a
physical quantities that are combined in such a way time to vary.
that the resulting quantity has units of unity (from Pilot plant: A physical model of limited size designed to
Elias, 1997, p. 444). permit a control of selected independent variables
Empirical model: A model that simulates equations that are so that the effects on dependent variables may be
based upon observation. observed.
Factorial design: In exploring the effect of independent vari- Precision: The spread of a set of measurements that may or
ables, the effect is limited to looking at certain node may not related to a ‘‘true’’ value. In other words, if
points, i.e., holding all variables constant and looking the standard deviation of a set of measurements is
at the effect at x 1 and then x 2 , then at y 1 and y 2 , etc. In very small, the measurements may be considered to
other words, one does not ‘‘map’’ the entire solution in have high ‘‘precision.’’ The measurements may not
two or three, or n dimensions as a continuous function, be ‘‘accurate.’’ For example, if a turbidity meter is
but only the significant node points of interest. not calibrated, its measurements may not be accur-
Goal: A statement of where one ‘‘wants to be.’’ For ate. The samples may be measured, however, with
example, to make all streams and lakes in the United high precision.
States ‘‘fishable and swimmable’’ as stated in the Problem solving: A systematic methodology for arriving at
1972 Clean Water Act (PL92-500) was a ‘‘goal’’ a solution to a problem posed. The classic engineering
of the legislation. The ‘‘goal’’ of a pilot plant study problem solving goes as follows: state what is known,
may be to provide guidance for an economical, effect- state what is sought, enumerate a procedure for the
ive, and easily operable full-scale treatment process. solution, and execute the procedure.
Independent variable: A variable in a given system that may Process: An effect that causes change in one or more chem-
influence the changes observed for a dependent vari- ical or physical characteristics of a substance, i.e., a
able. The independent variable is a cause of certain change of state. The effect may be induced, passive,
effects observed for a system. or natural.