Vibration is the movement or mechanical oscillation about an equilibrium position of a machine or component. It can be periodic, such as the motion of a pendulum, or random, such as the movement of a tire on a gravel road. Vibration can be expressed in metric units (m/s2) or units of gravitational constant “g,” where 1 g = 9.81 m/s2. An object can vibrate in two ways: free vibration and forced vibration.
Free vibration occurs when an object or structure is displaced or impacted and then allowed to oscillate naturally. For example, when you strike a tuning fork, it rings and eventually dies down. Natural frequency often refers to the frequency at which a structure “wants” to oscillate after an impact or displacement. Resonance is the tendency for a system to oscillate more violently at some frequencies than others. Forced vibration at or near an object’s natural frequency causes energy inside the structure to build. Over time the vibration can become quite large even though the input forced vibration is very small. If a structure has natural frequencies that match normal environmental vibration, then the structure vibrates more violently and prematurely fails.
Frequency dependent foundation-soil compliance Assuming that the product c&, is small at w:= w1 and coefficients of a foundation on a soil layer are very small the base mass ratio y is also small, the transfer function at modal frequencies of the site and are large at other given in eqns (4) and (5) can be approximately evaluated frequencies. Many studies to determine modal properties have been performed over the past decades, with most of. Due to this instrument arrangement only frequency. With high transient vibration due to impact, continuous variations of mass.
Figure 1. Structures may fail if their natural frequencies match environmental vibration.
Forced vibration occurs when a structure vibrates because an altering force is applied. Rotating or alternating motion can force an object to vibrate at unnatural frequencies. An example of this is imbalance in a washing machine, where the machine shakes at a frequency equal to the rotation of the turnstile. In condition monitoring, vibration measurements are used to indicate the health of rotating machinery such as compressors, turbines, or pumps. These machines have a variety of parts, and each part contributes a unique vibration pattern or signature. By trending different vibration signatures over time, you can predict when a machine will fail and properly schedule maintenance for improved safety and reduced cost.