Civil Engineering Reference
In-Depth Information
TABLE 28-1. Examples of Distribution System Modeling Software
Name
Supplier
EPANET
U.S. E.P.A. (public domain)
Boss EMS (EPANET Modeling System)
Boss International
Cybernet / WaterCAD
Haestad Methods
H20NET
MWSoft
Pipe2000 / KYPIPE
University of Kentucky
SynerGEE
Stoner Associates, Inc.
tours. Distribution system water quality data may also be obtained from the modeling
software, as part of the general package or as an add-on module.
Some of the software is free and other software available must be purchased for
each software license (copy) required by the user. The cost of this software varies
greatly, depending on the number of software licenses required, number of pipes to
analyze, and program options chosen.
Many of the currently available software programs provide steady-state, or static,
simulation of the water system under given conditions of supply and demand. Under
this steady-state analysis, the solution is achieved when the flow rate in each pipe is
determined. The output is based on fixed system characteristics, including single-
condition values for pressure-reducing valves and single-head increases for pumping
and booster stations. Alternatively, some programs offer extended period simulation
(EPS) solutions based on time period simulation of the water system under varying
supply and demand conditions. Examples of system characteristics that can be varied
are: pressure-reducing-valve set points, variation in pump curve characteristics, or a
change in demand throughout the system or at a discrete node. The EPS is performed
by setting the desired duration for the simulation and a time increment for calculations,
generally one hour.
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Each increment is evaluated as a steady-state condition and then
the results are transferred to the subsequent steady-state condition.
It is important to plan and operate the distribution system so as to ensure an ade-
quate level of service to all users in the distribution system under varying conditions
of loading. Criteria for determining the level of service include:
Maintaining flows and pressures (heads) at various points in the system within
limits. It may be acceptable to vary these limits with time.
•
The management of storage to balance the supply and the distribution.
•
In system design and operation, it is beneficial to know the impact of changes in
demand on the level of service. This knowledge aids in the development of design
and control strategies to maintain the level of service. There is also a need to evaluate
the adequacy of storage or of proposed network additions with respect to an increase
in total demand. Both of these needs can be met by simulating the behavior of the
system over a period of 24 to 48 hours under changing demand patterns. A static
solution will not be so informative in terms of changing conditions, because a static
solution provides only a one-time evaluation, or a ''snapshot,'' of the system charac-
teristics.
Another hydraulic simulation technique is the application of linear theory.
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This
method is easily applied if all external flows to the system are known. The linear
