Skip to content

Pump

A pumps generates a discharge based on one of

  1. A constant discharge

  2. QH table: A H [m] and Qpump [m3/s] table where the discharge is a function of the upstream water level.

  3. QDH table: A DH [m] and Qpump [m3/s] table where the discharge is a function of the water level difference downstream and upstream. A positive DH means that the downstream water level is larger than the upstream water level

For both QH and QDH tables, discharge values must be positive or zero and monotonously increasing, or negative or zero and monotonously decreasing.

Discharge values for water levels not present in the table are linearly interpolated. The largest value in the QH table must be larger than the maximum water level encountered during the simulation, or the simulation will fail (no extrapolation is performed).

Real time control

The discharge of a pump can be controlled externally. If the pump is controlled, then a QH or QDH table act as maximum allowed discharge. A minimum allowed discharge QH or QDH table can also be specified.

Wet well setpoint

In MU, a so called wet well setpoint value can be specified for a pump. If this value is specified, then a PID control is created which works to maintain the water level in the upstream node to the specified value. The PID control has the following default parameter set: Integration period is 300 seconds, derivation period is 0.8 seconds and all time step weight factors are 1.0.

Start and stop levels

Pumps are active only for certain water levels, controlled by the start and stop water levels. Initially, the pump is in an inactive state. If the upstream water level rises above the start level, then the pump becomes active.

The pump will remain active until the upstream water level falls below the stop level. When the upstream water level falls below the stop level then the pump becomes inactive.

Maximum pump discharge

It is only possible to pump water if there is enough water upstream from the pump. The pump can limit the discharge across the pump in response to the amount of water available for pumping.

The discharge across the pump can be limited in one of two different ways:

  1. In a specific time step, the discharge across the pump is set to the maximum possible discharge. The maximum possible discharge is calculated in the upstream (flow direction) h-grid point such that after the time step, the volume of water in the h-grid point is 0.3*DELH, where DELH is a h-grid point specific parameter which is used to limit discharge at low water level, see D.1 MIKE 11 Default Values (p. 333). For side structures, the available volume is the estimated volume in the node plus the estimated volume in the h-grid points connected to the node

  2. If the water depth in the upstream (flow direction) h-grid point approaches zero, then the discharge is suppressed by a factor which approaches zero as the water depth approaches zero. This method is not used in side structures.

Start-up and shut-down times

Pumps can be set to ramp up pumping linearly over a specified time. If the start-up time is set to 10 minutes, then it will take the pump 10 minutes to reach the target pump capacity. This also applies if the target pump capacity changes over time: A pump with a start-up time of 10 minutes will have reached 50% of the target pump capacity after 5 minutes, even if the target capacity at 5 minutes into pumping is different from the target capacity when the pump was activated.

For the shut-down time, the pump ramps down the discharge linearly from the discharge when the pump became inactive. For shut-down, the target discharge is always 0.

Outlet level

If an outlet level is defined for the pump, then the effective downstream water level (for QDH tables) is the maximum of outlet level and downstream water level.

Negative discharge

Discharge values can be negative, meaning that water is pumped upstream (or into the network if the pump is at a boundary) instead of downstream (out of the network).

All discharge values for QH or QDH pumps must be negative or zero, or positive or zero, i.e. the pump must either pump water downstream or upstream. Flow directions cannot be mixed in the same pump.

If the pump direction is upstream (negative discharge) then the control levels are downstream. Both the start/stop water levels and the discharge controlling water levels that are used in the QH (QDH) tables taken from downstream of the pump.

Time centring

As the pump performance can be quite significant even during start-up, it can be necessary to dampen the pump dynamics in order to sustain the numerical stability. The dampening is obtained by centring the pump rate backwards in time so that the pump performance does not instantaneously reach the full capacity but instead the pump discharge is gradually increased over several time steps.

Time centring of pumps is only conditionally active.