About PRD curves
Pressure related demand (PRD) curves are used in the calculation of consumption for simulations using the pressure related demand option.
The curves describe the relationship between demand factor and pressure ratio (actual pressure to nominal pressure of 50 m).
During a pressure related demand simulation, the ratio of simulation pressure to nominal pressure (defined in the Nominal Pressure field of the node object) is calculated. The demand factor corresponding to the calculated ratio is determined from the PRD curve and applied to the percentage of demand defined as pressure related in the demand diagram or Pressure Related Demand Options dialog.
Note: By default, the simulation pressure P, at each timestep, is taken from the previous simulation time step. Enable the Use Iterative Pressure Related Demand option on the Pressure Related Demand Options dialog to recalculate demand within the current timestep.
The curves are defined on the PRD Curve page of the PRD Curve property sheet, accessed via the PRD Curve grid view in the Nodes grid.
There are a number of built in curves (described below) that are based on the following leakage curves:
| Curve | Leakage Equation | Year | Best Fit Coefficients |
|---|---|---|---|
|
Power Law |
L = AZNPN1 |
1979,1997 |
N1=1.118 |
|
Exponential (X-C808 – WRC) |
L=es.AZNP |
1996 |
S=0.0135 (AZNP>50 S=0.0240 (AZNP<50) |
|
FAVAD (Fixed and Variable Area Discharge) |
L=AZNP1.5+(k1/k2)*AZNP0.5 |
1994 |
(k1/k2) = 25.9 |
|
TR26 (Leakage index curve) |
L=0.5.AZNP+0.0042.AZNP2 |
1980 |
|
Built in PRD curves
The built in curves used to determine demand factor F, during a pressure related demand simulation are described below.
InfoWorks default demand
Power Law curve with coefficient N1=0.5
This curve corresponds to the internal pressure related demand curve used prior to Version 6.5.
|
|
Where: P = pressure from simulation Pnominal = nominal pressure of 50 m |
InfoWorks default leakage
The InfoWorks default leakage curve is included for the purpose of backwards compatibility.
This curve corresponds to the internal pressure related leakage curve used prior to Version 6.5.
Exponential
|
|
Where: s = 0.0135 if P > 50 m s = 0.0240 if P < 50 m P = pressure from simulation Pnominal = nominal pressure of 50 m |
FAVAD
|
|
Where: k1/k2 = 25.9 P = pressure from simulation Pnominal = nominal pressure of 50 m |
TR26
|
|
Where: P = pressure from simulation Pnominal = nominal pressure of 50 m |
