SAB 2513 - JAN 2012

7/23/2019 SAB 2513 - JAN 2012

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SAB 2513/ SAM 3513/ SAA 3622

UTMUNIVERSITI TEKNOLOGI MALAYSIA

Faculty

of Civil Engineering

R E S E A R C H U N I V E R S I T Y

FINAL EXAMINATION

SEMESTER L SESSION 2011/2012

COURSE CODE : SAB 2513/ SAM 3513/ SAA 3622

COURSE : HYDRAULICS

PROGRAMME : SAW

DURATION : 2 HOURS 30 MINUTES

DATE : JANUARY 2012

INSTRUCTION TO CANDIDATES:

1. ANSWER FIVE (5) QUESTIONS ONLY.

WARNING! Students caught copying/cheating during the examination will be liable for

disciplinary actions and the faculty may recommend the student to be expelled from

the study.

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

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SAB 2513/ SAM 3513/ SAA 3622 2

QI. (a) (i) Give TWO important factors that contribute to the value of

Manning coefficient?

(4 marks)

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

channels and why freeboard is important in open channels?

(5 marks)

(b) Rectangular and trapezoidal concrete-lined channels are to be

constructed with Manning’s n of 0.014. The conveyance factor, K of

the channel is 630 m3/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)

Q2. (a) Critical depth occurs in an open channel when the specific energy is

minimum. Sketch the corresponding flow depth versus specific

energy graph. From this concept, derive the general equation used to

determine critical flow depth in an open channel.

(4 marks)

(b) A rectangular channel 3.05 m wide carries 3.4 m3/s uniform flow of

water at a depth of 0.6m. Suppose that an obstruction such as a weir is

placed across the channel with the height of 0.2 m above the bottom.

(i) Does this weir cause a hydraulic jump upstream of the weir?

Why or why not?

(4 marks)

(ii) Calculate the flow depth above the weir, and just upstream of

the weir. Classify the surface profile occur upstream of the

weir. Sketch the resulting water-surface profile and energy line,

showing the critical depth, yc and normal depth, y0.

(12 marks)

(20 marks)

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SAB 2513/ SAM 3513/ SAA 3622 3

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

channel is designed to be constricted caused by placing bridge

embankment at both sides of the channel. Explain the consequences

due to the constriction.

(4 marks)

Water is flowing uniformly with flow rate 18.6 m3/s and water depth

1.2 m in a rectangular open channel of width 8 m. A temporary short

span bridge is proposed to be constructed across the channel in which

bridge embankment is needed at both sides of the channel causing the

channel to be constricted under the proposed bridge.

(i) Calculate the maximum channel width under the proposed

bridge that will not cause backwater upstream.

(5 marks)

(ii) If the channel width under the proposed bridge is 4 m due to

the unavoidable problem condition, calculate the expected flow

depth under the bridge, at just upstream and at just downstream

of the bridge.

(6 marks)

(iii) If the water depth just upstream of the proposed bridge islimited to be 0.2 m higher than the normal depth, calculate the

channel width under the bridge.

(5 marks)

(20 marks)

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SAB 2513/ SAM 3513/ SAA 3622 4

Q4. (a) At what flow condition hydraulic jump can occur in an open

channel?

(2 marks)

(b) Sketch an example of gradually varied flow in an open channel with

SI and S3 flow profile. Show the corresponding normal and critical

depth.

(3 marks)

(c) A hydraulic jump is designed to occur in a rectangular open channel of

width 3.2 m. The ratio of the conjugate water depth of the jump is to

be 4.8. If the water depth just after the jump is 2.34 m, calculate the

flow rate in this channel.(7 marks)

(d) Water is flowing uniformly with flow depth 2.6 m in a rectangular

open channel of width 4 m. The Manning’s n is 0.018 and the channel

bed slope is 1:1800. A concrete dam is to be placed in this channel

that will cause backwater flow upstream. The water depth just

upstream of the dam is designed to be 3.626 m. Compute the distance

from the dam upstream up to the place where the water depth is 1%

higher than the normal depth. (Divide the channel distance to 4 parts

only)

(8 marks)

(20 marks)

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SAB 2513/ SAM 3513/ SAA 3622

An incompressible fluid of density p (kg/m3) and viscosity // (Ns/m2)

flows at the average speed v (m/s) through a long, horizontal section of

round pipe of length L (m), inner diameter D (m) and inner wall

roughness height e (m). The pipe is long enough that the flow is fully

developed, meaning that the velocity profile does not change down the

pipe. Pressure decreases (linearly) down the pipe in order to “push” the

fluid through the pipe to overcome friction. Develop a non dimensional

relationship between pressure drop AP (N/m2) and the other

parameters in the problem. Be sure to modify your n 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 velocity

and discharge in prototype.

(8 marks)

(20 marks)

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SAB 2513/SAM 3513/SAA 3622 6

Q6. (a) A simple water supply pipe network system of a housing area is as shown

in Figure Q6. The pipe data are as in the following table. Compute the

flow rate and the head loss in each pipe. Use the initial trial flow rate 0.05

m

3

/s in pipe flowing from A to B and 0.01 m

3

/s of flow in pipe flowingfrom B to D. The friction factors, f = 0.004 for all pipes. State your final

answers after two complete iterations only.

Pipe AB AE ED BD BC DC

Total length (m) 200 100 200 100 200 300

Diameter (mm) 150 150 150 150 150 150

(14 marks)

(b) If the pressure head at node A is 20 m, and the pipe network is laid on a

horizontal plane, calculate the residual pressure head at node C.

(6 Marks)

(20 marks)

Figure Q6

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SAB 2513/ SAM 3513/ SAA 3622

EQUATIONS

The symbols indicate parameters usually used.

Q = AR' 3 So- 2

H = z + y + ■

2 g

E = y +---------= y +-----------

2g Igy1

2

3=T^min

yc= 3 Sc =

2 . n gAc

T c Rc4/3

Azc hm jn E0 - En ~ ®max

syc i

Fr =

S'

A/s = E j -

M = v4jc+

0*2 ~ y\ ) 3

4^1 ^2

fil

y i 1

P T = PgQE r — = - L 1 y2 2

Jl + 8Fr 2 -1

Ay

Ax

&y — = SoAx

1-1 V-

10/3

1-1V.V

K = AR

2/3

«

h f = kQn A 0 = -E/i/

Q2 - Qi +AQ

Sfi

f w

1 3

f e l

t

o nhf \ j J

Hj2 = Hji - Ahf k = A3£>5

k — -10.671

rl.85 n4.87

C,w£>

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SAB 2513/ SAM 3513/ SAA 3622 8

0.0001 0.001 0.0 0.1 10

AR'%or

AR %

Chart for determining normal depth in open

channels

W

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SAB 2513 - JAN 2012

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