water hammer analyses of Çamlıdere - ivedik water ... · 2.2 hydraulic losses in the pipelines...

Digest 2008, December 2008 1217-1230

Water hammer Analyses of Çamlıdere - Ivedik Water Treatment Plant (IWTP) Pipeline†1 Zafer BOZKUŞ* ABSTRACT

In the present study, a widely used mathematical method for unsteady flows in closed conduits such as pipes and/or tunnels, called the Method of Characteristics (M.O.C.) was employed to perform water-hammer analysis of the pipelines extending from the Çamlıdere dam to the Ivedik water treatment plant in Ankara. Both of the existing parallel pipe lines, are made of various steel pipes, reinforced concrete pipes and concrete lined tunnels connected in series and having different material characteristics in roughness, diameters and lengths. To take into account all of these various characteristics of the pipelines, the unsteady flow equations consisting of the interpolation feature were used when employing the M.O.C. An algorithm was developed which was incorporated into an existing computer model, written in the FORTRAN language. Using this program, the numerical simulations of the water hammer problem under desired scenarios were performed. As a result, closure durations were recommended for the pipe fracture safety devices planned to be located at certain places and to be put into operation automatically in case of emergency, without causing excessive pressures in the lines.

Keywords: Çamlıdere-İvedik Pipeline, water hammer analysis, valve closure durations.

1. INTRODUCTION

Çamlıdere dam supplies a significant portion of the potable water demand of the City of Ankara, and Işıklı system to be constructed will be added to it in the future. Figure 1.1 shows locations of Ivedik Water Treatment Plant (IWTP), of some major dams used for supplying water to Ankara and, of the pipelines. Çamlıdere dam is a rock fill dam and has a catchment’s area of 753 km2. Crest elevation of the dam is 1002 m with a height of 102 m from the thalweg. Active reservoir volume of the dam is 840 hm3. The dam constructed between the years 1976 and 1985 had its first pipeline put in operation in 1988. Çamlıdere dam has an annual potable water capacity of 150 hm3. The raw water stored in the reservoir of the Çamlıdere dam is conveyed by way of two parallel pipelines (Çamlıdere-1 and Çamlıdere-2) extending a length of about 60 kilometers before reaching the Ivedik WTP where it is treated and distributed to the city of Ankara, [1].

* Middle East Technical University, Ankara, Turkey - [email protected] † Published in Teknik Dergi Vol. 19, No. 2 April 2008, pp: 4409-4422

Water hammer Analyses of Çamlıdere - Ivedik Water Treatment Plant (IWTP) Pipeline

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Figure 1.1: Pipelines Supplying Potable Water to the City of Ankara

Each of the pipelines shares two short tunnels (i.e. Tunnels 1 and 2) and one long tunnel (i.e. Tunnel 3 also called KINIK Tunnel) in the lengths of 4,277 m, 2,823 m, and 16,386 m respectively. Tunnels 1 and 2 are connected with a steel pipe of 275 m long, and both of the tunnels have diameter of 3500 mm while Tunnel 3 has a diameter of 3400 mm. The segments between Tunnels 2 and 3 in both pipelines are made of steel pipes having a

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diameter of 2200 mm. The major distinction between the two parallel pipelines is between the exit of Tunnel 3 and the Ivedik WTP. In the older pipeline (i.e. Çamlıdere-1), this part is a 30,715 m long reinforced concrete pipe with a diameter of 2200 mm. However, in the second and newer pipeline, this segment is entirely made of steel pipes. Both of the existing lines are used alternatively and it is planned to add a third line parallel to these lines after the Işıklı system is put into operation.

The project owners received hydraulic consultancy from the consulting company Obermeyer Project Management, (OPM), [2] during the construction of Çamlıdere-1 line. The company OPM studied some subjects such as the magnitudes of the maximum pressure waves that may occur in the line, the discharge capacity of the line, the safety measures to be considered in the line, and water intake structure design, etc. Upon those studies the following points were concluded.

“The maximum piezometric head elevation (i.e. z + p/γ) at any location in the pipeline should not exceed 970 m in order to avoid possible damage in the pipes and tunnels. The excess pressures over this elevation should be damped out either at the intake structure or latest at the exit of the second tunnel.”

Figure 1.2: Side View of the Çamlıdere Intake Structure


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Figure 1.3: Cross-Section of the Çamlıdere Intake Structure

Figure 1.2 shows the side view of the intake structure, whereas Figure 1.3 shows the top view of the same structure. The intake structure is like a tower consisting of two vertical shafts. The shaft A is designed to receive water at various elevations from the dam reservoir into the intake structure. The other shaft, which is shaft B is designed to dissipate excess pressure loads. There is a gate between the two shafts, which is designed to dissipate pressure. This gate, also called Gate 4, is designed to operate at partial openings depending on the magnitude of the pressure loads to be dissipated and the discharge desired in the system. The maximum water elevation which is not to be exceeded in shaft B was set to be 965 m. Although OPM suggested that electronically controlled pipe fracture safety valves to be installed at four locations in the pipeline to ensure the safety of the pipeline, it was not done so at the time the first Çamlıdere-IWTP pipeline was commissioned in 1988. Then, a long time later, three of those valves were decided to be installed in the lines Çamlıdere-1 and Çamlıdere-2 in 2005. The aim of the present study is to determine the closure times of those valves in times of emergency so that during their closure no excess pressures are to be generated in the system.

2. ÇAMLIDERE-IVEDIK WTP PIPELINES

2.1 Basic Characteristics of the Pipelines

Pipe lines have a composite nature consisting of two tunnels with a total length of 7,382 m and an inside diameter of 3.50 m, and another tunnel 16,386 m long with an inside diameter of 3.40 m, and steel pipes or reinforced concrete pipes having an inside diameter of 2.2 m. The discharge in each line is controlled at the Ivedik WTP entrance by needle valves of Larner Johnson type with the dimensions of 1000x685x1000 mm, Figure 2.1.

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Figure 2.1: Control Valves at the Entrance to the Ivedik WTP

2.2 Hydraulic Losses in the Pipelines

Hydraulic losses in the pipelines are caused by friction losses on the pipe wall and local (minor) losses at the locations where the geometry change occurs such as the bends, elbows, diameter changes, valves, exits and entrance locations. Major losses are due to friction since the lengths of the pipelines are exceeding 60 km. However, the local losses caused by Larner-Johson type valves and the pipe branchings are also too significant to be neglected.


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In a previous report, [1] in which the discharges were determined in the pipelines, the following local losses were considered.

• Losses at the intake structure

• Losses at the exit of Tunnel 1 due to contraction in diameter; expansion and bends

• Losses due to pipe branching in case of two or three parallel pipelines

• Losses at the butterfly valves

• Larner-Johnson valve losses

• Losses at the Ivedik WTP entrance

3. WATERHAMMER ANALYSES

3.1 Mathematical Model used in Waterhammer Analyses

In the present study, a widely used mathematical method for unsteady flows in closed conduits such as pipes and/or tunnels, called the Method of Characteristics (M.O.C.) was employed, [3]. This method is considered as one of the most reliable methods by the scientists and engineers in the world. This section will briefly cover the adaptation of the method into the Çamlıdere-Ivedik pipelines. Each of the Çamlıdere-Ivedik pipelines consists of concrete lined tunnel segments, steel pipes, reinforced concrete pipes, of different geometrical features (i.e. in terms of length and diameter), of different roughness (i.e. different friction factors due to different pipe materials), all connected in series. Consequently, the following equations of the Method of Characteristics with the interpolation features were employed to handle all these pipe elements of different features.

( ) 02 2 =−+−+− RPRR

RRP

RRP ttQQ

gDAfa)Q(Q

gAaHH (1)

( )( )RPRRRP ttaVxx −+=− (2)

( ) 022

)( =−−−−− StPtSQSQgDA

fSaSQPQ

gASa

SHPH (3)

( )( )SPSSSP ttaVxx −−=− (4)

( )( )AC

ACRCR

QQA

QQQQ

−+

−−= θ

ζ

1 (5)

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( )( )BC

BCSCS

QQA

QQQQ

−−

−−= θ

ζ

1 (6)

( )AHCHRARQ

CHRH −

+−= ζ

θ (7)

( )BHCHSASQ

CHSH −

−+= ζ

θ (8)

where H = the piezometric elevation head, Q = discharge, A = pipe cross-sectional area, a = pressure wave propagation speed, f = friction factor in the pipe, D = pipe diameter, g= gravitational acceleration, t = time, x=distance. In addition, θ = ∆t/∆x and ζ is a constant indicating the measure of the interpolation and given by ζ = (∆t/∆x)a = θa with the range of 0< ζ ≤1. ∆t is the time step and ∆x space increment used in the computations, respectively. In order to avoid convergence problem in the computations the Courant condition must be satisfied and it is given by Equation (9).

( ) xaVt ∆≤+∆ (9)

Figure 3.1 clarifies the locations of the quantities used in the above equations by showing the subscripts of them on the x-t computation domain. The subscript P, for instance, shows a point where the values of, unknowns, H and Q, are to be computed at an instant, whereas the subscripts A, B and C indicate the points located at the intersections of the x-t lines, where the values of H and Q are already known either from initial conditions or from an earlier time step at which they were computed. The subscripts R and S show the locations where the values of H and Q are obtained by using a linear interpolation employing the values of H and Q already known at locations A, B and C.

In order to solve Equations (1) – (8), a computer program in the FORTRAN language was written, based on an existing algorithm, [3] and all of the analyses were performed using that program. It was noted in the algorithm that Çamlıdere-Ivedik pipelines consisted of four major segments. They are for Çamlıdere-Ivedik Line-1 are: (1) T1+T2 Tunnels with a diameter of 3500 mm, (2) Steel Pipes of 2200 mm in diameter between the tunnels T2 and T3, (3) Tunnel T3 with a diameter of 3400 mm, (4) Reinforced concrete pipes of 2200 mm between tunnel T3 exit and Ivedik WTP. The only difference in Çamlıdere-Ivedik line-2 is that the fourth segment consists of steel pipes. Then, all of the important quantities needed in the analyses such as, diameters, lengths, friction factors, and acoustic speeds were determined for each line. The scenarios and recommended criteria for the water hammer analyses were considered next.


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Figure 3.1: x – t Space Time Grid

3.2 Scenarios and Criteria used in Waterhammer Analyses

The scenarios to be studied in a water hammer analysis had already been outlined in a previous report prepared for the agency in charge of potable water management (ASKI) of Ankara Municipality, [4]. The relevant sections (a), (b) and (c) are extracted from that report and presented below.

“(a) Among the pipeline hydraulic analyses scenarios explained in Section 3.4.3 of [4], water hammer analyses will be performed for the following alternatives out of 18 operation alternatives under Article (B) assuming that the valves located at the entrance to the IWTP are closing in 30 minutes. They are: 1 (Çamlıdere 1), 2 (Çamlıdere 2), 3 (Çamlıdere 1+2), 9 ( Between T2 and T3 in Çamlıdere 1+2, Between T3 and IWTP in Çamlıdere 1) and, 10 (Between T2 and T3 in Çamlıdere 1+2, Between T3 and IWTP in Çamlıdere 2).

(b) Upon completion of the analyses, the alternatives that produce the highest magnitudes for excess pressures, will be re-considered for new analyses without including this time the surge tanks located over T2 and T3 tunnels in order to determine the effect of those structures on the solutions.

(c) The analyses performed in paragraph (a) will be performed again considering this time that the valves located at the exit of Tunnels 2 and 3, and at the entrance to Tunnel 3 will start closing 5 minutes after the valves at the entrance to the IWTP started closing, and their closure duration in total will be 25 minutes.

Article (B) corresponds to the situation where the water surface elevation in the intake structure is 960 m, and the pressure at the entrance to IWTP equals the water column height of 12-15 m. Moreover, Article (A) is for the case where the water surface elevation in the intake structure is 965 m for which no water hammer analyses are suggested in the same alternatives.

x

t

A C

R S

P

∆x ∆x

t + ∆t

t + 2∆t

B

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In the evaluation section of the report, it is said that “……..the water surface elevation in the intake structure should always be maintained near the elevation of 960 m, and never allowed to exceed the elevation of 965 m. Even the Hydraulic Grade Line (HGL) of the pipelines stays below the elevation of 970 m due to the hydraulic losses, the pressures considered in the design of T1 and T2 tunnels are those occurring at the water surface elevation of 970 m. Consequently, it should be kept in mind that the water surface elevation of 970 m is the upper limit of the system including the excess pressures to occur in the lines.”

3.3 Results of Waterhammer Analyses

It is the valve operations that always trigger the excess pressures in all of the water hammer analyses performed either for the entire pipelines or for some parts of the pipelines. Consequently, valve closure types and durations affect the excess pressure magnitudes in the lines for which water hammer analyses were performed. The detailed results of water hammer analyses performed (total of 54) for Çamlıdere-IWTP lines were reported by Bozkus, [5].The results of the last 12 analyses (Analyses 43 through 54) are presented in Table-1.

As Table-1 is evaluated it would be useful to consider the following points. There are three different groups of columns in the table. The first group actually consists of only one column and it shows the analysis number. The second group of columns consists of four columns that show the location where the analyses are performed and also provides the initial magnitudes of the hydraulic quantities used in the analyses. The last group of the three columns shows the computed values of elevation of peak pressure head, its occurrence time and the discharge passing there at that moment. The value of the peak pressure is always the one that occurs at the place where the valve closures take place. The analyses shown in Table-1 are those performed for closures of each pipe fracture safety device (i.e. a valve) located at the entrance to or at the exit from the tunnels, in case of line ruptures occurring independently of the valves at the entrance to IWTP. Safety valve closure durations are taken as 30 minutes (1800 s) in the analyses. The valve opening was assumed to close in two stages, firstly from 100% open state to 30% open state within 600 seconds. Then, the valve becomes completely closed in the remaining time, that is, 1200 seconds. In short, all of the scenarios suggested in [4] with the water surface elevation of 960 m in the intake structure were performed for the worst case, that is, without considering the surge tanks and aerators in the system. As a result, it was found that the excess pressures to be generated will be within the limits of acceptable values that the system can tolerate as long as the suggested valve closure durations and the closure manner are obeyed.

This is obvious in Table-1 as one studies the peak pressure elevation column in which no peak pressure elevation is above 970 m.


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Table 1 : Partial Results of Waterhammer Analysis

Analysis Initial Conditions at Çamlıdere - T2 Tunnel Exit Computed at T2 Tunnel Exit

No Intake Structure T2 Exit T2 Exit Initial Peak Pres. Peak Pres. Discharge

Water Elev., m Pres. head, m Pres. Elev., m Q, m3/s Elev., m Time, s Q, m3/s

43 960.00 19.78 958.58 5.50 960.65 12 5.429

44 960.00 19.27 958.07 6.50 960.64 12 6.418

45 960.00 19.53 958.33 6.00 960.65 12 5.923

46 960.00 18.95 957.75 7.05 960.61 12 6.962

Initial Conditions at Çamlıdere – T3 Tunnel Entrance Computed at T3 Tunnel Entrance

Intake Structure T3 Entrance T3 Entrance Initial Peak Pres. Peak Pres. Discharge


47 960.00 22.98 951.93 5.50 961.30 588 1.735

48 960.00 22.07 951.02 6.50 961.38 594 2.006

49 960.00 27.48 956.43 6.00 961.35 600 1.805

50 960.00 26.24 955.19 7.05 961.48 600 2.122

Initial Conditions at Çamlıdere – T3 Tunnel Exit Computed at T3 Tunnel Exit

Intake Structure T3 Exit T3 Exit Initial Peak Pres. Peak Pres. Discharge


51 960.00 21.36 950.12 5.50 962.18 600 1.660

52 960.00 19.78 948.54 6.50 962.47 600 1.964

53 960.00 25.54 954.30 6.00 962.37 600 1.808

54 960.00 23.56 952.32 7.05 962.63 600 2.126

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4. CONCLUSIONS AND RECOMMENDATIONS

First of all, it is agreed with the valve closure suggestions that OPM made in their 1978 report, [2], for the cases that the pipe fracture safety devices (valves) located at the exit of T2 and at the exit and entrance of T3 in Çamlıdere 1 and 2 pipelines, start closing just 5 minutes after the control valves at the entrance to the IWTP have started closing, as a result of analyses performed in the present study. They are:

• At Km:7+15 (Exit of T2 Tunnel) Valve Closure Duration: 450 seconds. At the first stage; the valve will close linearly until 40% of the valve opening state is reached in the first 180 seconds corresponding to 40% of the total valve closure duration. Then, in the second stage; valve will be closed completely in the remaining 270 seconds corresponding to 60% of the total valve closure duration.

• At Km:13+89 (Entrance to T3 Tunnel) Valve Closure Duration: 1500 seconds. At the first stage; the valve will close linearly until 25% of the valve opening state is reached in the first 600 seconds corresponding to 40% of the total valve closure duration. Then, in the second stage; valve will be closed completely in the remaining 900 seconds corresponding to 60% of the total valve closure duration.

• At Km:29+64 (Exit of T3 Tunnel) Valve Closure Duration: 1200 seconds. At the first stage; the valve will close linearly until 25% of the valve opening state is reached in the first 420 seconds corresponding to 35% of the total valve closure duration. Then, in the second stage; valve will be closed completely in the remaining 780 seconds corresponding to 65% of the total valve closure duration.

However, having different closure durations and manners for those valves may cause some operational problems. Therefore, it would be preferable to select a standard valve closure manner and durations for all of the pipe fracture safety valves. Thus, a two stage valve closure adjustment used for the analyses given in Table-1 is recommended. These valves are designed such that they may be closed in two stages. According to design criteria of the valves; in the first stage they must be closed down to 30% of the valve opening state from the fully open state within 45 to 700 seconds. In the second stage, the remaining valve opening may be closed completely within 140 to 2000 seconds.

Recommendation made in the present study: Valve Closure Duration: 1800 seconds. At the first stage; the valve will close linearly from 100% fully open state to 30% of the valve opening state in the first 600 seconds. Then, in the second stage; valve will be closed completely in the remaining 1200 seconds. This closure law is shown graphically in Figure 4.1 and also numerically provided in Table-2. The pipe fracture safety valves (Erhardt DN 2200 PN 10 butterfly valves) to be used in the system are designed to obey such closure laws.


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Pipe Fracture Safety Valve Closure Law

0%10%20%30%40%50%60%70%80%90%

100%

0 300 600 900 1200 1500 1800

Time (s)

Valv

e O

peni

ng

Figure 4.1: Pipe Fracture Safety Valve Closure Curve

Regardless of the Çamlıdere dam reservoir water level, if possible the water surface elevation in the water receiving shaft of the intake structure should not be permitted to go above 960 m by the help of the pressure reducing gate (No.4). Thus, it is important that No.4 gate should always be operational. The construction of the third line parallel to the existing two lines is being planned for the future. Therefore, water hammer analyses of the new situation should be performed within a larger spectrum in order to operate the pipelines safely, after the project criteria and relevant data are determined. In the present study, it was assumed in all of the analyses that all the valves started closing from a fully open state. This assumption is true for the pipe fracture safety valves because these valves will always be kept fully open during the operations. In case the need arises to close them fully, which means emergency, then, they will be closed. On the other hand, the control valves at the entrance of the IWTP may not always be at the fully open position. Consequently, this situation, that is, valve closures from partially open positions should also be considered in the water hammer studies to be performed in the future.

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Table 2: Input Data for Pipe Fracture Safety Valves’ Closure Duration at the Çamlıdere - Ivedik Water Treatment Plant

Valve closes from fully open position to %30 open position in the first 600 s. Total valve closure duration is 1800 seconds. Stage:1 TAU = -(0.70/600) t + 1 0 ≤ t ≤ 600 s Stage:2 TAU = -(0.30/1200) t + (540/1200) 600 s ≤ t ≤1800 s

No. t (s) TAU No. t (s) TAU 1 0 1.0000 31 900 0.2250 2 30 0.9650 32 930 0.2175 3 60 0.9300 33 960 0.2100 4 90 0.8950 34 990 0.2025 5 120 0.8600 35 1020 0.1950 6 150 0.8250 36 1050 0.1875 7 180 0.7900 37 1080 0.1800 8 210 0.7550 38 1110 0.1725 9 240 0.7200 39 1140 0.1650

10 270 0.6850 40 1170 0.1575 11 300 0.6500 41 1200 0.1500 12 330 0.6150 42 1230 0.1425 13 360 0.5800 43 1260 0.1350 14 390 0.5450 44 1290 0.1275 15 420 0.5100 45 1320 0.1200 16 450 0.4750 46 1350 0.1125 17 480 0.4400 47 1380 0.1050 18 510 0.4050 48 1410 0.0975 19 540 0.3700 49 1440 0.0900 20 570 0.3350 50 1470 0.0825 21 600 0.3000 51 1500 0.0750 22 630 0.2925 52 1530 0.0675 23 660 0.2850 53 1560 0.0600 24 690 0.2775 54 1590 0.0525 25 720 0.2700 55 1620 0.0450 26 750 0.2625 56 1650 0.0375 27 780 0.2550 57 1680 0.0300 28 810 0.2475 58 1710 0.0225 29 840 0.2400 59 1740 0.0150 30 870 0.2325 60 1770 0.0075

61 1800 0.0000


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Nomenclature

a Speed of pressure pulse (m/s)

A Pipe cross sectional area (m2)

D Pipe diameter (m)

f Friction factor

g Gravitational acceleration (9.81 m/s2)

H Instantaneous piezometric head (m)

Q Instantaneous discharge in a section (m3/s)

TAU Dimensionless number describing the area of opening at a valve

t Time (s)

V Instantaneous velocity (m/s)

x Flow direction (m)

ζ Interpolation constant

∆t Time step size (s)

∆x Distance step size (m)

References

[1] Bozkuş, Z., “Çamlıdere Barajı Su Alma Yapısında Basınç Kırıcı Kapak ve İsale Hattının Çeşitli Hidrolik Koşullarda Tahkiki”, Kesin Rapor, ODTÜ, Mayıs 1996.

[2] (OPM), Obermeyer Project Management, Drinking - Water Conveyance Line, Çamlıdere-Ankara, Hydraulic Consultancy, Final Report, Munich, January 1978.

[3] Wylie, E. Benjamin and Streeter, L. Victor, “Fluid Transients in Systems”, Prentice Hall, 1993.

[4] Yüksel Proje-Kesin Rapor ve Ekleri: “Çamlıdere Barajı – İvedik Arıtma tesisleri Arası İçmesuyu Sistemlerinin Etüdü ve İşletme Prensiplerinin Belirlenmesi İşi”,Yüksel Proje Uluslararası A.Ş., Ankara, 2004.

[5] Bozkuş, Z., “Çamlıdere Barajı-İvedik Arıtma Tesisleri İsale Hattında Çeşitli Hidrolik Koşullarda Su Darbesi Analizleri”, Kesin Rapor, ODTÜ, Ocak 2006.

water hammer analyses of Çamlıdere - ivedik water ... · 2.2 hydraulic losses in the pipelines...

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