SINGLE DEGREE FREE VIBRATION

 INTRODUCTION:

 When a system is subjected to an initial disturbance and then left free to vibrate on its own, the resulting vibrations are referred to as free vibrations . Free vibration occurs when a mechanical system is set off with an initial input and then allowed to vibrate freely. Examples of this type of vibration are pulling a child back on a swing and then letting go or hitting a tuning fork and letting it ring. The mechanical system will then vibrate at one or more of its "natural frequencies" and damp down to zero.

BASIC ELEMENTS OF VIBRATION SYSTEM:

·         Mass or Inertia

·         Springiness or Restoring element

·         Dissipative element (often called damper)

·         External excitation

CAUSES OF VIBRATION: 

Unbalance: This is basically in reference to the rotating bodies. The uneven distribution of mass in a rotating body contributes to the unbalance. A good example of unbalance related vibration would be the ―vibrating alert‖ in our mobile phones. Here a small amount of unbalanced weight is rotated by a motor causing the vibration which makes the mobile phone to vibrate. You would have experienced the same sort of vibration occurring in your front loaded washing machines that tend to vibrate during the ―spinning‖ mode.

 Misalignment: This is an other major cause of vibration particularly in machines that are driven by motors or any other prime movers.

 Bent Shaft: A rotating shaft that is bent also produces the the vibrating effect since it losses it rotation capability about its center.

 Gears in the machine: The gears in the machine always tend to produce vibration, mainly due to their meshing. Though this may be controlled to some extent, any problem in the gearbox tends to get enhanced with ease.

 Bearings: Last but not the least, here is a major contributor for vibration. In majority of the cases every initial problem starts in the bearings and propagates to the rest of the members of the machine. A bearing devoid of lubrication tends to wear out fast and fails quickly, but before this is noticed it damages the remaining components in the machine and an initial look would seem as if something had gone wrong with the other components leading to the bearing failure.

 Effects of vibration:

 (a)Bad Effects:

 The presence of vibration in any mechanical system produces unwanted noise, high stresses, poor reliability, wear and premature failure of parts. Vibrations are a great source of human discomfort in the form of physical and mental strains.

 (b)Good Effects:

 A vibration does useful work in musical instruments, vibrating screens, shakers, relive pain in physiotherapy.

  METHODS OF REDUCTION OF VIBRATION:

·         unbalance is its main cause, so balancing of parts is necessary.

·         using shock absorbers.

·         using dynamic vibration absorbers.

·         providing the screens (if noise is to be reduced)