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Water Hammer simulations for IVAR IKS in Stavanger, Norway

21 Dec 2006  


IVAR IKS is one of Norway's largest water utility companies. They deliver water and collect wastewater from the two largest cities in Rogaland, Stavanger and Sandnes, as well as several smaller municipalities. The region is Norway's oil capital and a fast growing region. Each year IVAR produces approximately 40 Mm3 of drinking water and collects 50 Mm3 of wastewater.

As the first phase in the planning of necessary pumping stations on the main water distribution system, DHI Water & Environment was asked to find the optimal number and location of the pumping stations, as well as the capacity of the pumps.

In addition to the traditional design simulations, water hammer simulations were carried out on the system.

The modelling started with the update of an existing EPANET model. The model was updated against the newest available information (asset and SCADA data) and simulations were carried out with MIKE URBAN WD and WH.

The result of the design phase of the project concluded with the need for two new pumping stations. The design data for the two stations are shown in the table below.


Station

Head
[mW]

Flow
[l/s]

P1

98

990

P2

78

1 240

The Water Hammer simulations were carried out using MIKE URBAN WH which is an integrated part of the MIKE URBAN modelling system. The advantages of this is that you are able to calculate water hammer pressures for the whole network and not only smaller parts of the system, which would be the case using a less advanced model.

Water Hammer simulation is a challenging science putting high demands on both hydraulic and numeric competence and understanding. The actual water hammer pressures will depend on a number of parameters including pipe material, wall thickness, the specification of the pumps, shut-down time, etc. Because of this, a number of water hammer simulations were carried out with different shut-down times (the time it takes from full speed to zero speed) and different scenarios for how the pump will close. Shut-down times between 1 and 30 seconds were analysed. Two different scenarios after shut-down were also investigated, one where no flow occurred after shut-down (valve closes) and one where water flowed freely through the pump but with no change in head. These two scenarios are assumed to be the upper and lower limit for the actual water hammer pressures.

On the figure below a longitudinal profile of one branch in the system is shown. The red line shows maximum pressure and the green line shows minimum pressure. The black line is the terrain level. The profile shows the scenario with no flow after shut-down (valve closes)

Water Hammer simulations for IVAR IKS in Stavanger, Norway