173559760 Dynamics of Machinery 2 Marks All 5 Units

8/10/2019 173559760 Dynamics of Machinery 2 Marks All 5 Units

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ME 2302 - Dynamics of Machinery V.

DHINAKARAN/SL/MEHANIAL

!"#AN SH""L "$ %&SINESS AND 'EHN"L"!(

REDHILLS) HENNAI-*2

DE+AR'MEN' "$ MEHANIAL EN!INEERIN!

D(NAMIS "$ MAHINER(

'," MARK &ES'I"NS AND ANS,ERS

AADEMI (EAR 20 - 202

+reare 1y

V.DHINAKARAN

!"#AN schoo of 1siness an 'echnoo4y) Mechanica En4ineerin4


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&NI' - - $"RE ANAL(SIS

1. What is free body diagram?A free body diagram is a sketch of the isolated or free body which shows all the

pertinent weight force, the externally applied loads, and the reaction from its supports

&connections acting upon it by the removed elements.

. !efine static force analysis.

"f components of a accelerate, inertia is produced due to their masses. #owever, the

magnitude of these forces is small compared to the externally applied loads. #ence

inertia effects due to masses are neglected. $uch an analysis is known as static

force analysis.

%. !ifferentiate between static & dynamic euilibrium.

'ecessary and sufficient conditions for static and dynamic euilibrium are(

1.vector sum of all the forces acting on a body is )ero.. *he vector sum of all the moments of all the forces acting about any arbitrary point

or axis is )ero.

+irst conditions are sufficient conditions for static euilibrium together with second

condition is necessary for dynamic euilibrium.

. !efine applied and constraint force.

*he external force acting on a system of body from outside the system is called

applied force.

*he constraint forces are the forces existing internally within the body.

-. !ifferentiate between static force analysis and dynamic force analysis.

"f components of a machine accelerate, inertia forces are produced due to their

masses. "f the magnitude of these forces are small compared to the externally

applied loads, they can be neglected while analysis the mechanism. $uch an

analysis is known as static force analysis.

. !efine inertia force.

*he inertia force is an imaginary force, which when acts upon a rigid body, brings it in

an euilibrium position.

"nertia force / 0Accelerating force / 0m.a

. $tate !2Alembert2s principle.

!3Alembert3s principle states that the inertia forces and torues, and the external

forces and torues acting on a body together result in statical euilibrium.

o $tate principle of superposition.

o *he principle of superposition states that for linear systems the individual

responses to several disturbances or driving functions can be superposed on

each other to obtain the total response of the system.

4. !efine piston effort.

5iston effort is defined as the net or effective force applied on the piston , along the

!"#AN schoo of 1siness an 'echnoo4y) Mechanica En4ineerin4 2


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1. !efine unbalance and spring surge.

nbalance( A disc cam produces unbalance because its mass is not symmetrical

with the axis of rotation.

$pring surge( $pring surge means vibration of the retaining spring.

14. !efine windup. What is the remedy for camshaft windup?o *wisting effect produced in the camshaft during the raise of heavy load

follower is called as windup.

o 7amshaft windup can be prevented to a large extend by mounting the

flywheel as close as possible to the cam.

16. What are the effect and causes of windup?

*he effect of windup will produce follower @ump or float or impact.

7auses of windup are(

o When heavy loads are moved by the follower,

o When the follower moves at a high speed, and

o When the shaft is flexible.



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&NI' - 2 - %ALANIN!

1= What is meant by balancing of rotating masses?

*he process of providing the second mass in order to counteract the effect of the

centrifugal force of the unbalanced first mass is called balancing of rotating masses

= Why rotating masses are to be dynamically balanced?

"f the rotating masses are not dynamically balanced, the unbalanced dynamic force

will cause worse effect such as wear and tear on bearing and excessive vibrations on the

machines. "t is very common in cam shafts, steam turbine rotors, engine crank shafts, and

centrifugal pumps, etc.

%= !efine static balancing?

A system of rotating mass is said to be static balance if the combined mass centre of

the system lies on the axis of rotation.

= !efine dynamic balancing?

A system of rotating masses is in dynamic balance when there doesn2t exist any

resultant centrifugal force as well as resultant couple.

-= $tate the conditions for static and dynamic balancing?

1= *he net dynamic force acting on the shaft is )ero. *his is called as conditions for

static balancing.

= *he net couple due to dynamic force acting on the shaft is )ero.

= $tate the conditions for complete balance of several masses revolving in different planes

of a shaft?

1= *he resultant centrifugal force must be )ero, and

= *he resultant couple must be )ero.

= Why complete balancing is not possible in reciprocating engine?

alancing of reciprocating masses is done by introducing the balancing mass

opposite to the crank. *he vertical component of the dynamic force of this balancing mass

give rise to Bhammer blowC. "n order to reduce the hammer blow, a part of the reciprocating

mass is balanced. #ence complete balancing is not possible in reciprocating engine.

4= 7an a single cylinder engine be fully balanced? Why?

'o. A single cylinder engine can2t be fully balanced. ecause the unbalanced

forces due to reciprocating masses remains constant in magnitude


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. *he unbalanced force due to reciprocating masses varies in magnitude but

constant in direction. ut in the case of revolving masses, the unbalanced

force is constant in magnitude but varies in direction.

18= Why are the crank of a locomotive, with two cylinders, placed in 68D to each other?

"n order to facilitate the starting of locomotive in any position


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&NI' - 3 7 5

1. What are the causes and effect of vibration?

*he causes of vibration are unbalanced forces, elastic nature of the system, self

excitation, wind and earthuakes.

*he existence of vibration elements in any mechanical system produces unwanted

noise, high stress, poor reliability and premature failure of one or more of the parts.

. !efine freuency, cycle, period and free vibration.

+reuency( "t is the number of cycles described in one second

7ycle( "t is defined as the motion completed during one time period

5eriod( "t is the time interval after which the motion the motion is repeat itself.

+ree vibrations( if the periodic motion continues after the causes of original

disturbance is removed, then the body is said to be under free vibrations.

%. What are the different types of vibrations?

1. +ree vibrations,. +orced vibrations,

%. !amped vibrations.

. $tate different method of finding natural freuency of a system.

1. 9uilibrium method,

. 9nergy method,

%. Hayleigh method.

-. What is meant by free vibration and forced vibration?

+ree


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1. What is the limit beyond which damping is detrimental and why?

When the damping factor M/1.the aperiodic motion is resulted .*hat is ,aperiodic

motion means the system cannot vibrate due to over damping. Nnce the system is

disturbed, it will take infinite time to come back to euilibrium.

1. What is meant by critical damping?

*he system is said to be critically damped when the damping factor M/1."f then

system is critically damped, the mass moves back very uickly to its euilibrium

position within no time.

14. What type of motion is exhibited by a vibrating system when it is critically damped?

A periodic motion is exhibited

16. !efine critical or whirling speed.

*he speed at which resonance occurs is called critical speed of the shaft. "n other

words ,the speed at which the shaft runs so that the

additional deflection of the shaft from the axis of the rotation becomes infinite ,is known as

critical speed.

8. What are the factors that affect the critical speed of a shaft?

*he critical speed essential depends onG *he eccentricity of the 7.K.of the rotating masses from the axis of rotation of the

shaft.

!iameter of the disc

$pan


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!efine torsional euivalent shaft.

A shaft having variable diameter for different lengths can be theoretically replaced by an

euivalent shaft of uniform diameter such that they have the same total angle of twist when

eual opposing torues are applied at their ends. $uch a theoretically replaced shaft is known

as torsionally euivalent shaft.

What are the factors that affect the critical speed of a shaft?

*he critical speed essentially depends on(


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1% What is the function of governor?

*he function of a governor is to maintain the speed of an engineer within specified limits

whenever there is a variation of load. Kovernors control the throttle valve and hence the fuels

supply to cater the load variation on engines.

1 What is the principle of working of centrifugal governor?

*he centrifugal governor is based on balancing of centrifugal force on the rotating balls by an

eual and opposite radial forces.

1- What is the vibration isolation?

*he term vibration isolation refers to the prevention or minimi)ation of vibrations and their

transmission due to the unbalanced machines.

1 !efine logarithmic decrement.

Eogarithmic decrement is defined as the natural logarithm of the amplitude reduction factor.

*he amplitude reduction factor is the ratio of any two successive amplitudes on the same side

of the mean position.

1 $pecify the importance of vibration isolation?

When an unbalanced machine is installed on the foundation, it produces vibration in the

foundation. $o, in order to prevent these vibrations or to minimi)e the transmission of forces to

the foundation, vibration isolation is important.

14 What are the functions of Kovernor?

*he function of a governor is to maintain the speed of an engine within specified limits

whenever there is a variation of load. Kovernors control the throttle valve and hence the fuel

supply to carter the load variation on engines.

16 #ow governors are classified?

1. 7entrifugal governors.


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1. What is meant by sensitiveness of governors?

*he sensitiveness is defined as the ratio of the mean speed to the difference between

the maximum and minimum speeds.A governor is said to be sensitive, when it really to

a small change of speed.

. What is gyroscopic torue?

Whenever a rotating body changes its axis of rotation, a torue is applied on the

rotating body.

%. What is the effect of gyroscopic couple on rolling of ship? Why?

We know that, for the effect of gyroscopic couple to occur, the axis of precession should

always be perpendicular to the axis of spin. "n case of rolling of a ship, the axis of precession is

always parallel to the axis of spin for all positions. #ence there is no effect of the gyroscopic

couple acting on the body of the shipP during rolling.

. What is the principle of inertia governors?

"n inertia governors, the balls are so arranged that the inertia forces caused by an angular

acceleration or retardation of the shaft tend to alter their positions.

-. !efine power of a governor?

*he power of a governor is the work done at the sleeve for a given percentage change of

speed. "t is the product of the mean value of the effort and the distance through which the

sleeve moves.

5ower/:ean 9ffort Eift of sleeve

. What is meant by hunting?

*he phenomenon of continuous fluctuations of the engine speed above and below the mean

speed is termed as hunting. *his occurs in over0sensitive governors.

. What is meant by isochronous condition in governors?

A governor with )ero range of speed is known as an isochronous governor. Actually the

isochronism is the stake of "nfinite sensitivity.

4. Kive the applications of gyroscopic principle.

"t is used(


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6. What so you mean by governor effort?

*he mean force acting on the sleeve for a given percentage change of speed for lift of the

sleeve is known as the governor effect.

%8. What is controlling force diagram?

When the graph is drawn between the controlling force as ordinate and radius of rotation of the

balls as abscissa, the graph so obtained is called controlling force diagram.


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173559760 Dynamics of Machinery 2 Marks All 5 Units