- The study of vibration
A body is said to vibrate if it has periodic motion with respect to time.
Mechanical vibration is the study of oscillatory motions of bodies. Vibrations are harmful for
engineering systems. Some times vibrations can be useful. For example,
vibratory compactors are used for compacting concrete during construction work.
Excessive vibration causes discomfort to human beings, damage to machines and
buildings and wear of machine parts
such as bearings and gears. The study of vibrations is important to
aeronautical, mechanical and civil engineers. It is necessary for a design
engineer to have a sound knowledge of vibrations. The object of the sixth
semester course on mechanical vibrations is to discuss the basic concepts of
vibration with their applications. The syllabus covers fundamentals of
vibration, undamped and damped single degree of freedom systems, multidegrees
of freedom systems and continuous systems.
1.2 Examples
of vibration
1.Beating of heart
2. Lungs oscillate in the process of breathing
3. Walking- Oscillation of legs and hands
4. Shivering- Oscillation of body in extreme cold
5. Speaking - Ear receives Vibrations to transmit
message to brain
6. Vibration of atoms
7. Mechanical
Vibrations
8. In Foundry application
9. turning opertation on lathe machine
1.3
Classification
of vibrations
One method of classifying mechanical vibrations is based on
degrees of freedom. The number of degrees of freedom for a system is the number
of kinematically independent variables necessary to completely descibe the
motion of every particle in the system. Based on degrees of freedom, we can
classify mechanical vibrations as follows:
1.Single Degree of freedom Systems
2.Two Degrees of
freedom Systems
3.Multidegree of
freedom Systems
4.Continuous Systems
or systems with infinite degrees of freedom
Another broad
classification of vibrations is:
1. Free and forced
vibrations
2. Damped and
undamped vibrations.
Sometime vibration
problems are classified as:
1.Linear vibrations
2. Non-linear
vibrations
3. Random vibrations
4.Transient
vibrations
A system is linear
if its motion is governed by linear differential equations. A system is
nonlinear if its motion is governed by nonlinear differential equations. If the
excitation force is known at all times, the excitation is said to be
deterministic. If the excitation force is unknown, but averages and standard
derivations are known,the excitation is said to be random. In this case the
resulting vibrations are also random. Some times systems are subjected to short
duration nonperiodic forces. The resulting vibrations are called transient
vibrations. One example of a nonperiodic short duration excitation is the
ground motion in an earthquake
The main causes of
vibrations are:
1. Bad design
2. Unbalanced inertia
forces
3. Poor quality of
manufacture
4. Improper bearings
(Due to wear & tear or bad quality)
5. Worn out gear
teeth
6. External
excitation applied on the system
The effects of
vibrations are as follows:
1. Unwanted
noise
2. Early failure due
to cyclical stress(fatigue failure)
3. Increased wear
4. Poor quality
product
5. Difficult to sell
a product
6. Vibrations in
machine tools can lead to improper machining of parts
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