Vibration
Vibration is the name given to the propagation of elastic waves producing deformations and stresses on a continuous medium (or equilibrium position).
In its simplest form, a vibration can be thought of as a repetitive movement around an equilibrium position. The "balance" is the one it will reach when the force acting on it is zero. This type of movement does not necessarily involve internal deformations of the whole body, unlike a vibration.
Introduction
It is convenient to separate the concept of vibration from that of oscillation, since the oscillations are of a much greater amplitude; Thus, for example, when walking, our legs oscillate, contrary to when we tremble -from cold or fear-. As the vibrations generate movements of smaller magnitude than the oscillations around an equilibrium point, the vibratory movement can be easily linearized. In oscillations, in general, there is a conversion of kinetic energy into gravitational potential energy and vice versa, while in vibrations there is an exchange between kinetic energy and elastic potential energy.
In addition, the vibrations, being periodic (or quasi-periodic) movements of higher frequency than the oscillations, usually generate sound waves, which constitutes a dissipative process that consumes energy. In addition, vibrations can cause material fatigue, for example.
For small oscillation amplitudes the motion can be reasonably approximated by a complex harmonic motion, with equation of motion:
| Symbol | Name |
|---|---|
| M{displaystyle mathbf {M} } | System Mass Matrix |
| C{displaystyle mathbf {C} } | System buffer matrix |
| K{displaystyle mathbf {K} } | System stiffness matrix |
| q(t){displaystyle mathbf {q} (t)} | (Pseudo) generalized coordinate vector that represents the movement of a set of relevant points of the system. |
| f(t){displaystyle mathbf {f} (t)} | Set of exciting forces that generate vibration |
Effects of vibration
Vibration is the cause of generation of all kinds of waves. Any force applied to an object generates a disturbance. The study of noise, vibration and severity in a system is called NVH. These studies are aimed at measuring and modifying the parameters that give it its name and that occur in motor vehicles, in more detail, in cars and trucks.
Vibration reduction
Vibration control measures are fundamentally different from noise control measures. Although vibrations often have similar causes and can also cause noise, they have different propagation pathways. At first, sound propagates directly through air, while shocks or vibrations propagate through solid materials. Vibrations can become audible to humans if, for example, building components (ceilings, walls) emit secondary airborne sound in the audible frequency range. Since secondary sound partially affects passive noise protection measures, such as acoustic barriers or soundproof windows, protection measures at source (emission) are most effective for these immissions (vibration, secondary sound). Measurements at the source are directed at the foundations of machines, railways, etc. Measurements may include anti-vibration mats, anti-vibration pads, or vibration-damping feet. Sensitive measuring instruments and laboratory equipment, such as laboratory scales and microscopes, must also be protected from vibration to provide reliable measurement results.