02 Sample Exam Questions

7/29/2019 02 Sample Exam Questions

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Question 1

(a) A space capsule with a shape very similar to a Prolate ellipsoid is designed tocarry goods from space station to earth. It is designed to enter the atmosphere sothat the drag force on capsule is minimal. Estimate the drag force on the capsule

when it is entering the atmosphere at the speed of100m/s. The diameter of thecapsule is4.5m. The density and kinematic viscosity of air may be assumed to

be0.03kg/m3 and sm10500 26 , respectively. Refer to the equation sheetand attachments for additional information needed for calculations.

(Weighting 50%)

(b) For precise estimation of drag force, designers decided to use a physical modeltest. For this, a4.5cmdiameter object with a similar shape is used. The object istested for drag force in a flume with flowing water, seeFigureQ4. The densityand the kinematic viscosity of water used is1000kg/m3 and

sm10126 respectively. The measured drag force on the object was31N.

(i) Calculate the velocity of the flume water in order to achieve Reynoldssimilarity with the situation described in Part (a).

(ii) Estimate the drag force on the prototype capsule.(Weighting 50%)

Flow4.5cm


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Question 2

(a) A series pipe network, as shown below, is installed to gravity feed reservoir Afrom reservoir B. Pipe diameters, lengths and relative roughness of pipe

segmentsAC andBC are as shown. If flow through pipe network is90litres/s,calculate the elevation difference between free surfaces of two reservoirs. The

kinematic viscosity of water may be taken as sm101 26 . Refer to theequation sheet and attachments for additional information needed forcalculations.

(Weighting 70%)

(b) Assume a pump is installed atC to pump water fromA toB using the same pipenetwork. If the flow rate in the pipe network is90litres/s, calculate the powerrequired to run the pump if its efficiency is90%.

(Weighting 30%)

A

B

C

D =300mm

e/D =0.001

D =200mm

e/D =0.0004

h =?

L =1800m

L =40m


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Question 3

(a) Water flows by gravity from reservoir A to reservoir B through two series pipes,as shown below. Each pipe contains two900 elbows with a loss coefficient asshown, the characteristics of each pipe are also shown. The connection of the

two pipes atX is a sudden enlargement and the entrance to the pipe network atreservoirA is square edged. Calculate the volume flowrate fromA toB. Allminor losses must be considered.

(Weighting 70%)

(b) Using the results obtained in Part (a) calculate the Mannings roughnesscoefficient for pipe segmentAX.

(Weighting 30%)

A

B

h =12m

D =200mm

f =0.03

L =18m

D =400mm

f =0.02

L =12m

k =0.5

k =0.6

k =0.6

k =0.5

X


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Question 4

A water network consists of two reservoirs, A andB, connected by a pipe system asshown in the figure below. The pipe system consists of500mmand300mmdiameterpipes and two 900 medium roughness mitre bends. The entrance to the pipe system is

flush. Other properties of the pipes are given in Figure Q4.

Assuming that the density and kinematic viscosity of water are1000kg/m3 and1.1x10-6 m2/s, respectively:

(a) Calculate the head delivered by the pump to achieve150l/sdischarge.(50% Weighting)

(b) Draw total energy line indicating both frictional head loss and minor losses.(30% Weighting)

(c) If the efficiencies of the pump and electric motor used are75%and90%,respectively, calculate the electric power required to drive the motor.

(20% Weighting)

All relevant minor losses are to be considered in your calculations.

Refer to the attachments for additional information.

PPi e 1L =6mD =500mmk =0.15mm

Pi e 2L =35mD =300mmk =0.3mm h =20m

A

B


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Question 5

A citys water network consists of three reservoirs; A, B andC, as shown in the figurebelow. Reservoir A is large enough to be considered an unlimited pool of water, andbothB andC are small supply reservoirs which require a continuous supply fromA.

The free surface levels of each reservoir are shown inFigure Q5with respect to theAustralia Height Datum (AHD). The water demands from reservoirs B andC are180l/sand100l/s, respectively. PipeAB contains a pumpP, and pipeBC contains avalveX. Other details of the network are as shown in Figure Q5.

(a) Calculate the discharge through pipeAC.(30% Weighting)

(b) Calculate the maximum flow through pipeBC. Comment on the position of thevalveX (open, closed, partially open) such that pipeBC supplies the remainderof the demand in reservoir C.

(30% Weighting)

(c) What should be the minimum head supplied by the pumpP to satisfy thedemands of reservoirs B andC.

(40% Weighting)

Minor losses may be neglected.

Take the density and kinematic viscosity of water to be1000kg/m3 and1.1x10-6m2/s, respectively.

Refer to the attachments for additional information.

A

B

C

AHD 34m

AHD 47m

AHD 26m

P

PipeACL =31kmD =0.5mf =0.015

Pipe ABL =24kmD =0.8mk =0.8

PipeBCL =17kmD =0.3mf =0.03

Q(B) =180l/s

Q(C) =100l/s

Valve X


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Question 6

The figure below shows a test arrangement used to measure the lateral force thatcreates reverse-swing on a cricket ball. A geometrically similar model cricket ball,with dimensions twice that of the actual one, is used for the test. The model cricket

ball has a diameter of450mmand is fixed at the centre of a water flume using thelever arrangement shown. The lever is hinged at the flume bed. Appropriatemeasuring devices are placed to measure longitudinal and lateral forces (F andL) atthe end of the lever arrangement.

It may be assumed that the model cricket ball is adequately submerged to eliminatefree surface effects and the flow in the flume has uniform velocity profile.

(a) If the laboratory test is to replicate a cricket ball travelling at140km/h throughthe air, calculate the corresponding flow velocity at the flume. Densities and

kinematic viscosities of air and water area=1.2kg/m3, a=15x10-6 m2/s, w=998kg/m3 andw=1.2x10

-6 m2/s, respectively.(30% Weighting)

(b) Estimate the longitudinal forceF that restrains the longitudinal movement of themodel cricket ball during the test. The lever is a30mmdiameter cylindrical rodwith lengths as shown inFigure Q6. The drag coefficientsCD for a sphere andcylindrical rod are0.6and1.2respectively.

(40% Weighting)

(c) During the model test, the lateral forceL is measured as3N. Estimate the lateralforce on the actual cricket ball that generates reverse swing.

(30% Weighting)

F L

Flo 450m

800m

400m

Front Elevation Side Elevation


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WATERLEVEL

1.8m

1.2m

1.5msuction pipe

750mm

nozzle

300mmoutlet pipe600mm

pump 20

Question 7

A pump, suction pipe, discharge pipe and nozzle are joined together to form a singleunit, as shown below. Calculate the horizontal component of the force exerted by thewater jet on the pump unit when the pump is developing a head of22.5m. Frictional

losses in the suction pipe and outlet pipe due to friction are described by g2v3h 2= ,frictional losses in the nozzle may be considered negligible.

(Weighting 100%)


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H

freesurface

water

gate

hinge

L=1.5m

Question 8

As water rises on the left hand side of the rectangular L shaped gate, shownbelow, it will open automatically. Neglecting the mass of the gate, determine at whatdepthH above the hinge this will occur assuming that the width of the gate, into the

paper, is1m.

(Weighting 100%)


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B

2m

4m

Tank

FreeSurface

Siphon

Question 9

A siphon, shown below, has a uniform circular bore of75mmin diameter and consistsof a bent pipe with its crest2mabove water level discharging into atmosphere at alevel 4mbelow water level.

Neglecting losses due to friction, find:

(a) The velocity of flow. (Weighting 40%)

(b) The volume discharge. (Weighting 30%)

(c) The absolute pressure at the crest level, pointB, if the atmospheric pressure isequivalent to10mof water. (Weighting 30%)


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V V

spherical dish

waterjet

D

d

= 450V

V

Question 10

A shallow circular dish has a sharp edged orifice at its centre, as illustrated in below.A water jet, with velocity V =5m/s, strikes the dish concentrically. Determine theexternal restraining force required to hold the dish in place if the jet issuing from the

orifice and dish also have velocitiesV =5m/sand there are no frictional losses as thewater flows over the surface of the dish. The diameters of the water jet areD =100mmandd=20mm, respectively.

(Weighting 100%)


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Question 11

An orifice plate is to be used to measure the volume flow rate of air flow through aduct2.0min diameter, see below. The mean velocity of air in the duct is not to exceed0.2m/sand a water tube manometer, having a maximum difference between water

levels ofh =160mm, is to be used to measure pressure drop. Assuming thecoefficient of discharge for the orifice plate to be0.64, determine the orifice diameterd to make full use of the manometer range. Take the density of air to be1.2kg/m3.

(Weighting 100%)

d 2mv =0.2m/s

duct

orifice plate

h =160mm

water

air


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5mh

4tonne

frictionless pulley

600

A

B

water

hinge

sto

Question 12

The gateAB in the figure below is5mlong, 2.4mwide ( into the paper ) and25mmthick, made from steel with a relative density of7.85; it is hinged atB and restsagainst a stop atA. If the density of water is990kg/m3 and a viscosity of0.001Pa s,

determine the water level hthat would cause gate to start falling.

(Weighting 100%)

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02 Sample Exam Questions