INTRODUCTION TO MECHANCAL VIBRATION

Vibration refers to the back-and-forth movement that occurs within a specific period of time. This phenomenon is closely related to the oscillatory motion of objects and the forces generated by that motion. Any object possessing mass and elasticity can vibrate; therefore, most machines and engineering structures experience some degree of vibration. As a result, engineering designs often need to take the nature of vibration into account.

1. Importance of Learning Mechanical Vibration

The primary goal of studying mechanical vibration is to minimize its harmful effects through improved machine design. Vibration problems are common in nearly all mechanical structures, often caused by mechanism imbalances. Examples of negative impacts include:

• Mechanical failures resulting from material fatigue.

• Accelerated wear and tear due to vibration.

• In manufacturing processes, vibration can lead to rough surfaces on finished products.

Beyond these detrimental effects, vibration can also be harnessed for beneficial purposes, such as:

• Use in vibrating conveyors, washing machines, and electric toothbrushes.

• Application in pile driving and vibratory material testing.

• Utilization to enhance efficiency in manufacturing processes like casting and forging.

2. Classification of Mechanical Vibration

Free Vibration

Free vibrations take place when a system oscillates as a result of internal forces acting within it, combined with the influence of a substantial external force. The system will then vibrate at its natural frequencies—one or more of them—which are properties established by the dynamic distribution of mass and elasticity. All systems with mass and elastic properties are capable of free vibration, occurring even without any external trigger.

Forced Vibration

Forced vibration refers to vibration that results from an external force acting on a system. When the external stimulus is oscillatory in nature, the system is compelled to vibrate at the frequency of that stimulus. If the frequency of the stimulus matches one of the system's natural frequencies, a resonance condition occurs, which may lead to dangerously large oscillations. Damage to large structures such as bridges, buildings, or aircraft wings is a frightening consequence of resonance. Therefore, determining the natural frequencies of a system is of primary importance.

 

A mechanical system experiences forced vibration whenever an external force acts on it while it is vibrating. This external excitation may come from an applied force or an imposed displacement. The excitation—whether force or displacement—can be harmonic, non-harmonic, non-periodic, or random. When the excitation force is harmonic, the system will respond with harmonic vibration as well.

 

For the response analysis 

  Free Body Diagram System

 Reference:

Rao, S. S. 2010. Mechanical Vibration Fifth Edition. Prentice Hall