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sAB 25i3l SAM 3513t SAA 3622

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FINAL EXAMINATIOhISEMESTER I, SESSION 2OITI2OI2

COURSE CODE

COURSE

PROGRAMME

DURATION

DATE

sAB 2513/ SAM 35t3/SAA 3522

HYDRAULICS

SAW

2 HOURS 30 MINUTES

JANUARY 2012

INSTRUCTION TO CANDIDATES:

1. ANSWER FIVE (5) QUESTTONS ONLY.

WARNING!Students caught copyinghheating during the examinatian will be liablefor

disciplinary actions and thefaculty may recammend the student to be expelledfromthe study.

This examination question consists of (9) printed pages only.

sAB 2513t SAM 3513/ SAA 3622

Give TWO important factors that contribute to theManning coefficient?

value of

(4 marlu)

Qi. (a) (i)

Q2.

(ii) What are the main assumptions made when designing open

channels and why freeboard is important in open channels?

(5 marks)

Rectangular and trapezoidal concrete-lined channels are to beeonstructed with Manning's n of 0.014. The conveyance factor, K ofthe channel is 630 *3/s. Calculate the bottom width of the channel and

depth of flow for the Best Hydraulic Section (BHS) for both channels.

Sketch your results.

(11 marks)

(20 marks)

Critical depth occurs in an open channel when the specific energy isminimurn" Sketch the corresponding flow depth v€rsus specificenergy graph. From this concept, derive the general equation used todetermine critical flow depth in an open channel.

(4 marlrs)

A rectangular channel 3.05 rn wide carries 3.4 m3/s uniform flow ofwater at a depth of 0.6m. Suppose that an obstruction such as a weir isplaced across the channel with the height of 0.2 m above the bottom.

Does this weir cause a hydraulic jump upstream of the weir?Why or why not?

(4 marla)

Calculate the flow depth above the weir, and just upstream cfthe weir. Classify the surface profile occur upstream of theweir. Sketch the resulting water-surface profile and energy line,showing the critical depth, y" and normal depth, yo.

(12 marks)(20 marks)

(b)

(a)

(b)

(i)

(ii)

Q3. (a)

sAB 2513l SAM 3513/ SAA 3622

An engineer is desired to analyze flow in an open channel in which the

channel is designed to be constricted caused by placing bridgeernbankment at both sides of the channel. Explain the consequences

due to the constriction.(4 marl<s)

Water is flowing uniformly with flow rate 18.6 m3/s and water depth1.2 m in a rectangular open channel of width 8 m. A ternporary shortspan bridge is proposed to be constructed across the channel in whichbridge ernbankment is needed at both sides of the channel causing thechannel to be constricted under the proposed bridge.

Calculate the maximum channel width under the proposed

bridge that will not cause backwater upstream.

(5 marlu)

If the channel width under the proposed bridge is 4 m due tothe unavoidable problern condition, calculate the expected flowdepth under the bridge, at just upstream and at just downstream

of the bridge.

(6 marks)

If the water depth just upstream of the proposed bridge islimited to be 0.2 m higher than the norrnal depth, calculate thechannel width under the bridge.

(5 marks)(20 rnarks)

(b)

(i)

(ii)

(iii)

Q4. (a)

(c)

(d)

(b)

sAB 2513/ SAM 3513/5AA3622

At what flow condition hydraulic jump can occur in an openchannel?

(2 marks)

Sketch an example of gradually varied flow in an open channel withSl and 53 flow profile. Show the corresponding normal and criticaldepth.

(3 marks)

A hydraulic jump is designed to occur in a rectangular open channel ofwidth 3.2 m. The ratio of the conjugate water depth of the jump is tobe 4.8. If the water depth just after the jump is 2.34 m, calculate theflow rate in this channel.

(7 rnarks)

Water is flowing uniformly with flow depth 2.6 m in a rectangularopen channel of width 4 m. The Manning's n is 0.018 and the channelbed slope is 1:1800. A concrete dam is to be placed in this channelthat will cause backwater flow upsheam. The water depth justupskeam of the dam is designed to be 3.626 m. Compute the distancefrom the dam upstream up to the place where the water depth is lohhigher than the normal depth. (Divide the channel distance to 4 partsonly)

(8 marks)(20 marks)

(a)Q5.

sAB 2513/ SAM 35t31 SAA3622

An incompressible fluid of density p (kg/m3) and viscosity pr (Ns1m2)

flows at the average speed v (m/s) through a long, horizontal section ofround pipe of lengthl (m), inner diameter D (m) and inner wallroughness height e (m). The pipe is long enough that the flow is fuliydeveloped, meaning that the velocity profile does not change down thepipe. Pressure decreases (linearly) down the pipe in order to "push" thefluid through the pipe to overcome friction. Develop a non dimcnsional

relationship befween pressure drop AP (N/m2) and the otherparameters in the problem. Be sure to modify your Tv groups as

necessary to achieve established non dimensional parameters.

(12 marks)

The velocity and discharge for 1/50 scale model of a spillway are 0.6m/s and 0.18 m3/s respectively. Calculate the corresponding velocityand discharge in prototype.

(8 marlcs)

(20 marks)

(b)

sAB 2513/ SAM 3513/ SAA 3622

Q6. (a) A simple water supply pipe network system of a housing area is as shownin Figure Q6. The pipe data ar€ as in the following table. Compute theflow rate and the head loss in each pipe. Use the initial trial flow rate 0.05m3/s io pipe flowing from { to B *o o.ot m3/s of flow in pipe flowingfrom B to D. The ftiction factors, f : 0.004 for all pipes. State your finalanswers after two complete iterations only.

Pipe AB AE ED BD BC DCIotal lensth (m) 200 r00 200 100 200 300Diameter (mm) rs0 r50 150 150 150 150

(14 marks)

(b) If the pressure head at node A is 20 m, and the pipe network is laid on ahorizontal plane, calculate the residual pressure head at node C.

(6 Marks)(20 marks)

0.015 m3/s 0.025 m3ls

Figure Q6

0.020 m3/s

0.030 m3ls

sAB 2513t SAM 3513t SAA3622

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