VIBRATION

 Vibration is a periodic motion of small magnitude. But for sake of simplicity we can assume that it as simple harmonic motion of small amplitude.

Some important term of vibration :-

Period :- It is a time taken by a motion to repeat itself, and it is measure in seconds.

Cycle :- It is the motion completed during one time period.

Frequency :- frequency is the number of cycles of motion completed in one second. It is expressed in hertz (Hz) and is equal to one cycle per second.

Resonance :When the frequency of the external force is the same as that of the natural frequency of the system, a state of resonance is said to have been reached. Resonance results in large amplitude of vibrations and this may be dangerous.


TYPE OF VIBRATION :-

 Free vibration :- Elastic vibration in which there are no friction and external forces after the initial release of the body, are known as free or natural vibrations.

Forced vibrations :- When a repeated force continuously acts on a system, the vibrations are said to be forced vibration. The frequency of the vibrations is that of

the applied force and is independent of there own natural frequency of vibrations.

Damped vibration :- When the energy of the vibrating system is gradually dissipated by friction and other resistance the vibrations are said to be damped vibration.

Un-damped vibration :- When there is no friction and resistance present in system to contaract vibration then body execute un-damped vibration.

Longitudinal vibration :- If the shaft is elongate and shortened so that the same moves up and down resulting in tensile and compressive stresses in the shaft, the vibration are said to be longitudinal.

Transverse vibration :- When the shaft is bent alternately and tensile and compressive stresses due to bending results, the vibration are said to be transverse vibration.

Torsional vibration :- When the shaft is twisted and untwisted alternately and torsional shear stresses are induced. the vibrations are known as torsional vibration.

CAM

                                                                  
          A cam is mechanical member used to import desire motion to a follower by direct contact. The cam may be rotating or reciprocating whereas follower may be rotating, reciprocating or oscillating.

It is used in automatic machine, IC engine , mechanical tool, printing control mechanisms.

Element of Cam :-

A driver member known as the Cam
A driven member known as the follower
A frame which support the cam and guides the follower.

Point of remember :-
A cam and follower combination belongs to the category of higher pair.

Type of cam :-

1. according to the shape -

  * wedge and flat cam :-
      a wedge cam has a transitional motion, the follower can either translate or oscillate.

  * Radial and disc cam
       The cam in which the follower moves radially from the center or rotation of the cam is knows as the a radial or disc cam.

  * Spiral cam
        A spiral cam is a face cam in which a groove is cut in the form of spiral. it is used in computer.



  * Cylindrical cam
        In a cylindrical cam, a cylinder which has a circumferential contour cut in surface, rotate about its axis. it also known as barrel and drum cams.

  * Conjugate cams
        it is a double disc cam and preferred when the requirements are low wear, low noise , better control of the follower, high speed, high dynamic load etc.

  * Globoidal cams
        it has two type of surface i.e convex or concave. it is used when moderate speed and the angle of oscillation of follower is large.


2. According to the follower movement :-

  * Rise-Return-Rise (RRR) 
       In this there is alternate return and rise of the follower with no period of dwells. The follower has a linear or a angular displacement.

  * Dwell-Rise-Return-Dwell (DRRDS)
       In this cam, there is rise and return of the follower after the dwell.

  * Dwell-Rise-Dwell-Return-Dwell (DRDRD)
         The dwelling of the cam is followed by rise and dwell and subsequently by return and dwell. In case the return of the follower is by a fall, The motion may be known as Dwell-Rise-Dwell (DRD).

Network diagram

      It is a graphical representation of the logical sequence. In which different activities are interrelated to each other while completing the project.

Rules for network diagram :-
1. An activity can only be started when all the activities earlier to it are completed.

2. No two or more activities may have same head and tail event.

  

    In this condition to represent the same logic we need to use dummy activities.

Dummy activity :- an activity which only shows the relation and logic and dependency of one activity over the another but doesn't consume only time or resource for its completion is termed as dummy activity. It represent as dotted line.

  

                        -------------->

3. Intersecting of activities are represented by

     

4. Dummy activities should only the used when it is very necessary but their is no restriction on the number of dummy activities used.

5. There should be no looping and dangling in  the network diagram.

Dangling :- when activity other then the final activity do not have any successor activities then the situation are called dangling.

Example :-

      Draw a network diagram from the set of activities ?

A      -

B     A

C     B

D     A

E     D

F      C,E

Answer :-  see in image.