Forced Vibration is the oscillation of a system due to an external force being applied. It can be used in a variety of applications, such as controlling noise and vibrational energy transfer. In this article, we will discuss an overview of Forced Vibration, different types of Forced Vibration, and the different applications of Forced Vibration.
Forced vibration is a type of mechanical vibration which occurs when an outside force or torque is applied to a structure. It can be caused by a range of things such as machinery, humans, wind, waves, and earthquakes. This type of vibration involves the transfer of energy from the source to the affected object. In the context of engineering, forced vibration is a tool used to study the dynamic behaviour of objects and its uses include stress testing, determining resonance frequencies, and detecting resonance peaks.
Forced vibrations are classified into two major categories, namely free and forced vibrations. Free vibrations occur when a system is disturbed by an impulse such as a hammer strike or an initial displacement. On the other hand, forced vibrations occur when an external force is continuously applied to the system at a particular frequency. This frequency is known as the excitation frequency and it is usually constant. When this excitation frequency matches the natural frequency of the system, the amplitude of the vibration increases and the structure becomes more prone to resonance.
The analysis of forced vibration plays an important role in the design and analysis of engineering systems. The main purpose is to understand the response of a system to an external disturbance, determine the resonance frequencies of the system, and identify potential failure points due to excessive vibration. By studying and modelling the dynamic behaviour of a system, engineers are able to create better designs with reduced risk of structural failure or performance degradation.
Forced vibrations can be divided into two main types: harmonic and non-harmonic or transient. In harmonic vibration, the input force is a sinusoidal wave with constant frequency and amplitude. This type of vibration results in a periodic response with the same frequency as the input force. Non-harmonic vibration, also known as transient vibration, occurs when the input force is not a sinusoidal wave and its frequency and amplitude keep changing over time. The response of this type of vibration can also vary in time, and is usually more complex than that of harmonic vibration.
The response of a system to harmonic and non-harmonic vibration can further be classified into four modes: free, forced, damped, or undamped vibration. In free vibration, the input force is zero, and the system vibrates under its own inertia. Forced vibration involves an externally applied force which causes the system to vibrate at the same frequency and amplitude as the input force. Damped vibration occurs when the input force is higher than the system's natural vibration frequency and the response diminishes over time due to the damping effect of frictional forces. Undamped vibration occurs when the input force is lower than the system's natural vibration frequency, resulting in a sustained response with no damping effects.
Various other types of forced vibrations can also be generated, such as base excitation, random vibration, and shock vibration. Base excitation occurs when the input force has a high frequency component along with a low frequency component, causing the system to vibrate at both frequencies simultaneously. Random vibration is often used to test and simulate the effects of vibration on a component, while shock vibration involves pulses of high-amplitude, short-duration vibrations intended to test the system's ability to withstand dynamic load.
Forced vibration is used in a variety of engineering applications. It can be used to monitor or detect changes in structures, such as finding weaknesses in bridges or buildings. It is also used to identify vibrations caused by faulty machinery, allowing corrective measures to be taken. Another important application is to produce a desired displacement profile. For example, some transportation systems use forced vibration to reduce wear and tear on the tracks and rolling stock. These vibrational forces help to smooth out irregularities in the track, which would cause more wear and tear over extended periods of time. Finally, forced vibration is even used in medical imaging, where it helps to detect fractures and other irregularities in bones and tissues.