GPS-X Technical Reference

Miscellaneous 428
Ignore Dilution Parameters
If the liquid volume in a tank falls below the ignore dilution rate below this volume
parameter value, then the dilution rate (defined as the inverse of the hydraulic residence
time) will not be used to calculate the concentrations in the tank as would normally be
done. In doing so, the speed of simulation is greatly increased. The same principle is
applied to the settlers and SBRs where the dilution rate in a particular layer is ignored if
the height of the layer is smaller than the ignore dilution rate below this layer
thickness parameter value.
Protection against Division by Zero
The parameter protect against division by zero is fixed and cannot be changed by the
user. This parameter is used in all calculations involving division. It is used to ensure that
the denominator in an expression is never equal to zero. For example, the DO switching
function, used in many rate equations (shown below), includes the protection against
division by zero parameter.
Equation 15.1
Speed Sub-Section
The parameters in the Speed sub-section of the Numerical form concern the pump flow
rates used in all the objects. Since the switching of pumps on and off introduces sharp
changes in the flows, the numerical integration routine may require a very small step size
to reduce the numerical error. In some cases, these small step sizes will result in a very
slow simulation. If the smooth pump discharge at discontinuities logical is turned ON
(default is OFF), then the pumped flow rate is ramped up to the specified amount as
follows:
Equation 15.2
where:
Q
par
t
= pumped flow rate (m 3 /d),
= smoothing factor,
= smoothing period (d).
GPS-X Technical Reference