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OWA-EPANET Toolkit
2.2
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OWA-EPANET Toolkit
2.2
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Purpose:
Defines various simulation options.
Formats:
| UNITS | CFS / GPM / MGD / IMGD / AFD / |
| LPS / LPM / MLD / CMH / CMD | |
| HEADLOSS | H-W / D-W / C-M |
| HYDRAULICS | USE / SAVE filename |
| VISCOSITY | value |
| SPECIFIC GRAVITY | value |
| TRIALS | value |
| ACCURACY | value |
| FLOWCHANGE | value |
| HEADERROR | value |
| CHECKFREQ | value |
| MAXCHECK | value |
| DAMPLIMIT | value |
| UNBALANCED | STOP / CONTINUE / CONTINUE n |
| DEMAND MODEL | DDA / PDA |
| MINIMUM PRESSURE | value |
| REQUIRED PRESSURE | value |
| PRESSURE EXPONENT | value |
| PATTERN | id |
| DEMAND MULTIPLIER | value |
| EMITTER EXPONENT | value |
| QUALITY | NONE / CHEMICAL / AGE / TRACE nodeID |
| DIFFUSIVITY | value |
| TOLERANCE | value |
| MAP | filename |
Definitions:
UNITS sets the units in which flow rates are expressed where:
For CFS, GPM, MGD, IMGD, and AFD other input quantities are expressed in US Customary Units. If flow units are in liters or cubic meters then Metric Units must be used for all other input quantities as well. (See the Measurement Units topic). The default flow units are GPM.
HEADLOSS selects a formula to use for computing head loss for flow through a pipe. The choices are the Hazen-Williams (H-W ), Darcy-Weisbach (D-W ), or Chezy-Manning (C-M ) formulas. The default is H-W.
The HYDRAULICS option allows you to either SAVE the current hydraulics solution to a file or USE a previously saved hydraulics solution. This is useful when studying factors that only affect water quality behavior.
VISCOSITY is the kinematic viscosity of the fluid being modeled relative to that of water at 20 deg. C (1.0 centistoke). The default value is 1.0.
SPECIFIC GRAVITY is the ratio of the density of the fluid being modeled to that of water at 4 deg. C (unitless). The default value is 1.0.
TRIALS are the maximum number of trials used to solve network hydraulics at each hydraulic time step of a simulation. The default is 40.
ACCURACY prescribes the convergence criterion that determines when a hydraulic solution has been reached. The trials end when the sum of all flow changes from the previous solution divided by the total flow in all links is less than this number. The default is 0.001.
FLOWCHANGE is a similar convergence criterion requiring that the largest absolute flow change between the current and previous solutions be less than the specified value (in flow units). The default is 0 which means that this criterion is not used.
HEADERROR is yet another convergence criterion requiring that the head loss computed by the head loss formula compared to the difference in nodal heads across each link be less than the specified value (in ft or m). The default is 0 which means that this criterion is not used.
CHECKFREQ sets the number of solution trials that pass during hydraulic balancing before the status of pumps, check valves, flow control valves and pipes connected to tanks are once again updated. The default value is 2, meaning that status checks are made every other trial.
MAXCHECK is the number of solution trials after which periodic status checks are discontinued. Instead, a status check is made only after convergence is achieved. The default value is 10, meaning that after 10 trials, instead of checking status every CHECKFREQ trials, status is checked only at convergence.
DAMPLIMIT is the accuracy value at which solution damping and status checks on PRVs and PSVs should begin. Damping limits all flow changes to 60% of what they would otherwise be as future trials unfold. The default is 0 which indicates that no damping should be used and that status checks on control valves are made at every iteration.
UNBALANCED determines what happens if a hydraulic solution cannot be reached within the prescribed number of TRIALS at some hydraulic time step into the simulation. STOP will halt the entire analysis at that point. CONTINUE will continue the analysis with a warning message issued. CONTINUE n will continue the search for a solution for another n trials with the status of all links held fixed at their current settings. The simulation will be continued at this point with a message issued about whether convergence was achieved or not. The default choice is STOP.
DEMAND MODEL specifies whether a demand driven analysis ( DDA ) or a pressure driven analysis ( PDA ) should be made. Under DDA full nodal demands are always met even if negative pressures result. PDA assumes that demand varies between 0 and its full value as a power function of nodal pressure. The default demand model is DDA.
MINIMUM PRESSURE is the pressure below which no demand can be delivered under a pressure driven analysis. It has no effect on a demand driven analysis. Its default value is 0.
REQUIRED PRESSURE is the pressure required to supply a node's full demand under a pressure driven analysis. It has no effect on a demand driven analysis. It must be at least 0.1 psi or m higher than the MINIMUM PRESSURE, which is also its default value.
PRESSURE EXPONENT is the power to which pressure is raised when computing the demand delivered to a node under a pressure driven analysis. It has no effect on a demand driven analysis. Its default value is 0.5.
PATTERN provides the ID label of a default demand pattern to be applied to all junctions where no demand pattern was specified. If no such pattern exists in the [PATTERNS] section then by default the pattern consists of a single multiplier equal to 1.0. If this option is not used, then the global default demand pattern has a label of "1".
The DEMAND MULTIPLIER is used to adjust the values of baseline demands for all junctions and all demand categories. For example, a value of 2 doubles all baseline demands, while a value of 0.5 would halve them. The default value is 1.0.
EMITTER EXPONENT specifies the power to which the pressure at a junction is raised when computing the flow issuing from an emitter. The default is 0.5.
QUALITY selects the type of water quality analysis to perform. The choices are NONE, CHEMICAL, AGE, and TRACE. In place of CHEMICAL the actual name of the chemical can be used followed by its concentration units (e.g., CHLORINE mg/L). If TRACE is selected it must be followed by the ID label of the node being traced. The default selection is NONE (no water quality analysis).
DIFFUSIVITY is the molecular diffusivity of the chemical being analyzed relative to that of chlorine in water. The default value is 1.0. Diffusivity is only used when mass transfer limitations are considered in pipe wall reactions. A value of 0 will cause EPANET to ignore mass transfer limitations.
TOLERANCE is the difference in water quality level below which one can say that one parcel of water is essentially the same as another. The default is 0.01 for all types of quality analyses (chemical, age (measured in hours), or source tracing (measured in percent)).
MAP is used to supply the name of a file containing coordinates of the network's nodes so that a map of the network can be drawn. It is not used for any hydraulic or water quality computations.
Remarks:
Example: