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Tank inflow pattern

Tamil Amudhu
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Ref : http://communities.bentley.com/products/hydraulics___hydrology/f/5925/t/123878 

We have to design a hydraulic zone being supplied from an existing OHT(5LL). The OHT is fed by pumping (22 hours) from WTP and the distribution system should be 24 x 7 supply. Total demand for the hydraulic zone is 4.05mld and rate of pumping is 51.26 litres / sec. Levels of the tank are well known and the respective data are fed in the properties. I get EPS results with flow stored as negative during particular hours. FTank inflow.xlsxind an attached excel file for reference of calculations and Bentley reports. Please review my tank inflow pattern and distribution pattern with peak factor. Increasing pumping hours is a rare option because of power failure for minimum 2 hours. Please suggest how this negative flow can be avoided in the design or in field? 

Second point is whether the sum of multiplier in pattern should be equal to 24 always 

Tank inflow.xlsx

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    Watergem file uploaded in a folder (Name f5925t124707 11.08.16.rar)

  • 0 Offline in reply to Tamil Amudhu
    Hello Tamil,

    The reason that the you see a negative store is simply because at those time steps, the system is demanding more flow that the system is providing.

    For instance, in the first time step, the total system demand is 60.39 L/s. This appears to be accurate based on the pattern you have applied for the base demands. A multiplier of 3.0 is included with the base demands, which leads to a demand of over 60 L/s. However, the inflow at the tank is 55.87 L/s. Therefore, the extra demand must come from the water stored in the tank. That means that there is flow leaving the tank, which is indicated by the negative value in storage. (Note that your pattern starts as 12AM and the model itself starts at 8AM, based on the calculation options. That is why the first time step has the multiplier of 3.0).

    You see a negative storage in your model occurs either when the total demand is higher than the total inflow for the tank or when no inflow is coming into the tank. This appears to working as expected. The following link has additional information on how the "Flow (Stored) works: communities.bentley.com/.../23692.flow-supplied-vs-flow-stored-vs-flow-demanded-and-flow-in-vs-flow-out.

    Regards,
    Scott

    Answer Verified By: Sushma Choure 

  • 0 Offline in reply to Scott Kampa
    Thank you Scott. My understanding is that I should adjust my tank inflow pattern and starting time in EPS in such a way that the negative storage occurs during lean period (say after midnight etc) so that it will affect minimum consumers in 24 x 7 supply resulting in low pressure at terminal points or ridges.
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  • 0 Offline in reply to Scott Kampa
    Thank you Scott. My understanding is that I should adjust my tank inflow pattern and starting time in EPS in such a way that the negative storage occurs during lean period (say after midnight etc) so that it will affect minimum consumers in 24 x 7 supply resulting in low pressure at terminal points or ridges.
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