Hydraulic Transient Analysis of Kolar Water Pipeline Using Bently Hammer V8i – A Case Study

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Hydraulic Transient Analysis of Kolar Water Pipeline Using Bently Hammer V8i – A Case Study

Sadanand Dr.T. S. Desmukh

Research Scholar Professor

MANIT,Bhopal; India MANIT,Bhopal; India

Abstract- The case study belongs to hydraulic transient analysis with Bentley Hammer V8i software and validating the results with manual calculations. Kolar water pipeline has been taken for case study. For this the result obtained from the PHE department, Bhopal were used for comparison. The available results were for the transient analysis with the surge protection devices in position. However as no detail of the devices was available the analysis with surge protection devices was not possible in Bentley Hammer V8i. . Hence initially the transient analysis for the Kolar pipeline was done manually (using excel sheet) considering the location of air vessels for

settings. variation in demands,sudden closure of valves and pumping system performances affects the unsteady flow

.These all conditions effects the steady state nature of flow(T.Tezcan,U.Gokkus and G.Sinir)[16].

Solution by Methods Of Characterstics(MOC):

Water hammer equations for elastic pipes produces a 1-d partial equation and result of this one is found by Methods of characterstics. this is the mathematical modeling of the unsteady flow. To solve the momentum and conservation of mass equation moc is used (wylie and streeter)[15]. These equations are :

validation. These results were found to match with the PHE department results. Then manual analysis was done without surge protection devices. After this the transient analysis of the pipeline was performed using Bentley Hammer V8i without surge protection devices. The

V 1 p g dz f V V

t s ds 2D

And

0 1.

results so obtained matched fairly well with the manual results for the same case. Bentley hammer v8i used for analysis with condition without surge protection so that

a 2 V

s

  • p

    1

    t

    0 2.

    the location for surge protection can be found out.

    Keywords Hydraulic transients, MOC, bentley hammer v8i, surge .

    Solution of the equations is:

    C+ :

    p i1 p i1

    a (Q Q ) (H H )

    fx

    Qp Qi1 0

    INTRODUCTION-

    The hydraulic analysis in closed conduits is based on the

    gA

    C-:

    a

    2gDA^2 3.

    fx

    steady state flow conditions. by applying some governing equations of conservation of mass and momentum and

    gA (Qp Qi1) (H p Hi 1)

    2gDA^2

    Qp Qi1 0

    extracting a general equation for the elastic pipe for solution. That results into a method of solution called method of characteristics(wylie and streeter)[15]. Methods of characterstics(moc) is very popular method for studying transients and water hammer effects. Avoiding the effects of water hammer is big concerned in pipe technology. Design of pipe on the basis of elastic theory of pipes and finding the maximum and minimum pressure or wave oscillations(R.Wichowski)[14]. Methods of characterstics is related to finite difference method as the equation is discritized for different points. These points gives the analysis values of pressure, discharge and velocity. Transients of such systems are also depends upon the valave

    ..4.

    In the solution of equations; here velocity terms are converted into discharge terms for our convenience( wylie and streeter)[15]. Equation 1 and 2 are the quasi hyperbolic equations and general method of solving is MOC in 3 and 4 equations.

    For the solution there are many boundary solution is considered requiring like reservoirs, pumps ,pipeline branches, dead ends etc. but here we are using upstream reservoir boundary conditions and pump conditions for

    compatible MOC equation(A.Bergant, A.R.Simpson, E. Sijamhodzic)[1].

    The compatibility equation for c+ line Qi-1 has the known value at the upstream section and Hi-1 also has the known value at upstream section but for finding Qp at the starting upstream section Hp is equal to Hr. similarly for c- line Qi+1 is known and for Hp due to pump shut down considering initial value is equal to zero. this approach at the downstream section of pump outlet.

    Problem statement and analysis: in the study of kolar water scheme at Bhopal, MP; has two pumping main one raw water main 7.2 km long and clear water pumping main 3.2 km long. Here the data for the hydraulic transients

    Table-Data of Kolar supply scheme

    SR.NO.

    ITEMS

    RAW WATER PUMPING MAIN

    CLEAR WATER PUMPING MAIN

    1.

    Length of Pumping Main

    7200m.

    3200m.

    2.

    Material of Pipes

    (1.)M.S. Pipes with cement mortor inlining and outcoating fro 0 to 3210m. (2.)PSC Pipes from 3210m.to 7200m.

    M.S. Pipes with cement mortor inlining and outcoating.

    3.

    Internal Diameter of pipe line

    1450mm. for

    Steel Pipes

    1500mm. for PSC Pipes.

    1450mm.

    Pipe.

    Steel

    4.

    Laying condition

    Under Ground

    Under Ground

    5.

    Maximum flow rate

    7152 cum/hr.

    6740 cum/hr.

    6.

    Pump Head

    Discharge

    90.50m.

    90m.

    7.

    Pressure velocity

    wave

    1016m/s upto

    3210m. and 904m/s for next 3990m. 7200m.

    1016m/s.

    8.

    pump velocity

    1000rpm.

    980rpm.

    9.

    Pump type

    Vertical Turbine Type

    Horizontal

    As per the general solution of the MOC firstly calculated the discharge term and then head term which is discussed earlier after calculating all the values which gives the analysis of the hydraulic transient for the case study.

    Fig.1. Profile for raw water pipeline

    Fig.2. Profile for clean water pipeline.

    In above shown figures, those are the general data used for elevation for the pipeline mains.

    Analysis for pipeline mains with surge protection:

    Fig.3. HGL vs length for raw water main with surge protection

    Fig.4. HGLvs. length clear water main with surge protection

    In both the pipeline mains results are matched quite well. Following the same procedure for hydraulic transient analysis with manual calculations for without surge protection devices.

    Benley Hammer V8i:

    The transient analysis of the Kolar pipelines was done through Bentley Hammer V8i software keeping the same length of reaches as in case of manual solution. The given profile of the Kolar pipeline was modeled in the software and all its parameter specified. Then the pumps were defined for both the pipelines. The analysis for raw water pipeline was done initially using pump shut down time as the period (2L/C) and then with the trial and error method weve determined the total run duration time. The results shown

    below is a comparison between manual calculation and Bentley V8i Hammer V8i software.

    Fig.5. Comparison of manual and software results without surge protection

    raw water pipeline.

    The study o the graph given above shows that the results obtained both through manual as well as software give quite comparable results. The nature of curve in maximum as well as minimum piezometric head condition is similar. In case of minimum HGL the deviation in two solutions is seen in the reach between 3000m. to 6150. (Approximate). This is because surges are expected in this reach and hence the software automatically introduces air pocket in this region. Similarly the introduction of air pocket in the maximum HGL is at 1250m (Approximate).

    Fig.6. Comparison of manual and software results without surge protection in clean water pipeline

    The study of the figures given above shows that the results obtained both through manual as well as software calculation are quite comparable. The nature of curves in maximum as well as minimum hydraulic grade line is similar. In case of minimum HGL the deviation between the two solutions is seen between 2750m. to 3060m. (Approximately). This is because surges are expected in this reach and hence the software automatically introduces air pocket in this region. Similarly the introduction of air pocket in the maximum HGL is in the initial reach upto 750m. (Approximately).

    CONCLUSION:

    The analysis of both the raw water and clean water mains revealed that hydraulic transients occur in the system. The abrupt changes in pressures due to these transients are liable to affect the performance and sustainability of the water supply scheme. The present work shows the feasibility of

    performing the transients analysis for a water supply pipeline using the Bentley Hammer V8i software. For this the solution obtained through the software has been validated through manual solution of transient analysis for Kolar Pipeline.

    The locations are suggested for the surge protection devices are very critical as pipe rupture conditions are high. Due to air vapour pocket formation the problem of cavitation can take place and hazardous effects can be happened.

    Bentley Hammer V8i software is very efficient and user defined for the study of this problem. A big advantage of the Bentley Hammer V8i software is that it can introduce the air vapour pocket itself in the model according to given condition and reduces the trial and iterative work for calculating the air vapour pressure in the system.

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