dom question bank

7/25/2019 DOM Question Bank

1/4

C. U. Shah UniversitySubject

:Dynamics of Machines Code: 4TE05DOM1 Semester: 5th

Course: B!Tech "acu#ty: Mechanica#En$ineerin$

Co##e$e: C% Shah Co##e$e ofEn$ineerin$ & Techno#o$y

Cha'ter (o 01 Mar)s Sr (o *uestions

Balancing of

rotating &

reciprocating

masses

1

Marks

1 Define partial balancing in locomotives.

2 Define radial engines.

3 Write the effects of balancing.

4 Define primary and secondary balancing.

2

Marks

1 Define balancing & hy need of balancing in machines.

2 Differentiate beteen static and dynamic balancing.

3 !lassify types of "# engines.

4 Disc$ss the concept of reverse and direct crank.

%

Marks

1 'plain ith neat sketch static balancing machines.

2 'plain ith neat sketch dynamic balancing machines.

3

Derive the e'pression for balancing of several masses rotating in different

planes.

4 'plain effects of partial balancing of locomotives.

(

Marks

1

)* B* ! and D are fo$r masses carried by a rotating shaft at radii +.1 m* +.1% m*

+.1% m and +.2 m respectively. ,he planes in hich the masses rotate are spaced

at %++ mm apart and the magnit$de of the masses B* ! and D are - kg* % kg and

4 kg respectively. ind the re/$ired mass )0 and the relative ang$lar settings ofthe fo$r masses so that the shaft shall be in complete balance

2

,he length of each connecting rod of a ++ "#engine is 22+ mm and the stroke

is 1++ mm. ,he mass of the reciprocating parts is 1.2 gcylinder and the crankspeed is 24++ rpm. ind the val$es of primary and secondary forces.

3

,he folloing data refer to a fo$r co$pled heel locomotive ith to inside

cylindersitch of cylinder 5 ++ mm !o$pling rod crank radi$s 5 24+mm

6eciprocating masscylinder531%kg Distance of centre of mass in plane

6evolving mass cylinder 5 2+ kg of driving heel 5 (%+ mmDistance beteen driving heels5 1. m )ngle beteen engine crank 5 -++

Distance beteen co$pling rods 5 2 m )ngle beteen co$pling rod crank

Diameter of driving heels 5 1.- m ith ad7acent engine crank 5 18++

6evolving parts for each co$pling rod crank 5 13+ kgngine crank radi$s 5 3++ mm

,he balanced mass re/$ired for the reciprocating parts is e/$ally divided

beteen each pair of co$pled heel.

Determine 9i: magnit$de and position of balanced mass re/$ired to balancedto#third of reciprocating masses.

9ii: hammer blo and ma'im$m tractive force hen the speed of locomotive

is 8+ km hr.

Cha'ter (o 0+ Mar)s

;ntrod$ction of 1 1 Define degree of freedom


2/4

"ibration &

M.

4 Define periodic time & amplit$de of vibrations.

2

Marks

1 Write the effects of vibrations.

2 What are the remedies taken hile vibrations prod$ced in machines.

3 Write the elements of vibratory system.

%

Marks

1 'plain e/$ivalent stiffness of spring.

2 !lassify ith neat sketch types of vibrations.3 What are the advantages and disadvantages of vibrations.

(

Marks

1Derive the e'pression for nat$rally fre/$ency for free vibration $singe/$ilibri$m and energy method.

2

Derive the e'pression for nat$rally fre/$ency for free vibration $sing

6ayleigh method.

Cha'ter (o 0, Mar)s

Damped free

vibration

1Marks

1 Define damped vibrations.

2 Write types of damping.

3 Define damping factor.

4 Write the form$la of critical damping coefficient.

2

Marks

1 What are the applications of damping.2 Write the factors on hich damping coefficient depends.

3 Disc$ss rate of decay of amplit$de.

4 Differentiate beteen over damping and $nder damping.

%

Marks

1 'plain any to types of damping ith neat sketch.

2 Derive logarithmic decrement and derive the e'pression for it.

3 Derive the e'pression for free damped torsional vibration.

(Marks

1

;n a damped vibrating system* the mass having 2+ g makes 4+ oscillationsin 2% sec. ,he amplit$de of nat$ral vibrations decreases to one eighth of the

initial val$e after 8 oscillations. Determine? 9i: the logarithmic factor

9ii: damping factor & damping coefficient 9iii: =pring stiffness

2 Derive the governing e/$ation characteri@ed by free damped vibration.

3

Derive the general sol$tion in differential e/$ation form of over damped &

critically damped system.

Cha'ter (o 04 Mar)s

"orced

-ibration 1

Marks

1 Define vibration isolator.

2 Define force transmissibility.

3 Define motion transmissibility.

4 Write the types of isolator.

2Marks

1 Define magnification factor.

2 'plain base e'citation.

%

Marks

1 Derive the e'pression for force transmissibility.

2

) machine of mass one tonne is acted $pon by an e'ternal force of 24%+ A at

a fre/$ency of 1%++ r.p.m. ,o red$ce the effects of vibration* isolator ofr$bber having a static deflection of 2 mm $nder the machine load and an

estimated damping factor 5 +.2 are $sed. Determine 91: the force transmittedto the fo$ndation 92: the amplit$de of vibration of machine 93: the phase lag.

3

'plain forced vibration of longit$dinal system and derive the e'pression

for it.

(

Marks

1 ) refrigerator $nit having mass of 3% kg is to be s$pported on three springs*

each having a spring stiffness s. the $nit operates at 48+ rpm. ind the val$e

of stiffness if only 1+ of the shaking force is alloed to be transmitted to


3/4

the s$pported.

2

) machine of mass 1++ kg is s$pported on an elastic s$pport of total stiffness

8++ kAm and has rotating $nbalanced element hich res$lts in dist$rbing

force of 4++ A at a speed of 3+++ rpm. )ss$ming the damping ratio as +.2%*determine the amplit$de of vibrations d$e to $nbalance and the force

transmitted to the s$pport.

Cha'ter (o 05 Mar)s

Critica# s'eed of

shafts

1Marks

1 Define critical speed of shaft.

2 Define rotor.

3 Define eccentricity.

2Marks 1

'plain behavior of shaft rotor system by ranges of shaft speed ith respect to

critical speed.

%

Marks

1

'plain the method to determine the critical speed of shaft carrying single rotor*

considering damping.

2

'plain the method to determine the critical speed of shaft carrying single rotor*

considering itho$t damping.

(Marks 1

) vertical shaft of 2+ mm in diameter & ++ mm long held in short bearings atthe ends. ) %g disc is mo$nted on the shaft miday beteen the bearings*

!.C. of disc is +.% mm aay from the a'is of the shaft. ;f the alloable tensile

stress for the shaft is (+ A mm2 .Determine 9i: critical speed of shaft 9ii: the

range of speed hich is not safe. ,ake 5 2++ Cpa

2

) vertical shaft of 12 mm diameter rotates in sleeve bearing and a dics of mass

1% g is mo$nted on the shaft at mid span. ,he distance beteen to bearings

is +.% m. ;f the !. C. of rotor is +.8 mm from the a'is of the shaft* Determine 9i:critical speed of rotation of the shaft 9ii: the speed range in hich the bending

stress ill e'ceed 12% Amm2* 5 2 1+%A mm2.

Cha'ter (o 0. Mar)s

Torsiona#

-ibrations and

-ibrations of

mu#ti!rotor

system

1

Marks

1 Define torsional vibrations.

2 Define node point.

3 Define @ero fre/$ency.

2

Marks

1 'plain the concept of torsionally e/$ivalent shaft.

2 Which parameters are determined in to rotor system to find the fre/$ency.

%

Marks

1

Write step by step proced$re of =todolaEs method to find o$t f$ndamental

nat$ral fre/$ency of system having three degree of freedom.

2

Describe D$nkerleyEs method to find the nat$ral fre/$ency of a shaft carrying

several loads.

3

Derive the e'pression for critical speed of shaft carrying m$ltiple rotors by

6ayleigh method.

(

Marks

1

) shaft of %+ mm diameter and 3 m length has a mass of 1+ kg per meter

length. ;t is simply s$pported at the ends and carries three masses of (+ kg* -+

kg and %+ kg at 1 m* 2 m and 2.% m respectively from the left s$pport. ind thenat$ral fre/$ency of transverse vibrations by $sing D$nkerleyEs method.

!onsider val$e of 52++ Ca

2

) vertical shaft of % mm diameter is 2++ mm long and is s$pported in long

bearing at its ends. ) disc of mass %+ kg is attached to the center of the shaft.

Aeglecting any increase in stiffness d$e to the attachment of the disc to the

shaft* find the critical speed of rotation and the ma'im$m bending stress henthe shaft is rotating at (% of the critical speed. ,he center of the disc is +.2%

mm from the geometric a'is of the shaft. 5 2++ CAm2.

3 ,o rotors* ) and B are attached to the ends of the shaft ++ mm long. ,he

mass and radi$s of gyration of rotor ) is 4+ kg and 4++ mm respectively and

that of rotor B are %+ kg and %++ mm respectively. ,he shaft is 8+ mm diameterfor first 2%+ mm* 12+ mm for ne't 1%+ mm and 1++ mm for the remaining

length from the rotor ). )ss$me the mod$l$s of rigidity of the shaft material

+.8F1+% Amm2. ind the position of node on e/$ivalent shaft of diameter 8+mm and on the act$al shaft. )lso find the nat$ral fre/$ency of the torsional


4/4

vibrations.

Cha'ter (o 0/ Mar)s

ibration

measurin$

instruments

1

Marks

1 Aame the information hich obtained from vibration meas$ring instr$ments.

2 Define vibration transd$cer.

2

Marks

1 >o seismometer can be $sed as acceleration meas$ring instr$ments.

2 Why need of data analysis in vibration meas$ring instr$ments.

%

Marks

1 Dra and e'plain block diagram of vibration meas$rement process.

2 'plain classification of vibration meas$ring instr$ments.

3 Disc$ss ith block diagram of , analy@er and rite its applications.

(

Marks

1 'plain ith schematic diagram of accelerometer.

2 Describe constr$ction* orking principle of vibrometer.

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