Vibration Engineering

Vibration Engineering

 

the aggregate of methods and facilities for the generation of mechanical oscillations (vibrations) in the frequency range from about 10 megahertz to 10 kilohertz, as well as means for controlling the vibrations, measuring and monitoring them, and preventing harmful vibrations. Among the facilities in vibration engineering are vibration machines; vibration test benches; instruments, apparatus, and equipment in which vibration is deliberately produced to perform useful functions (such as compacting earth and concrete mixtures or for testing); apparatus for controlling and measuring vibration; and antivibration engineering facilities such as devices for the prevention, suppression, damping, and insulation of harmful vibration.

The following effects produced by vibration are utilized in vibration engineering: the creation of a unilaterally directed motion of piece parts and free-flowing bulk cargo; the impact-vibration insertion and recovery of pipes, sheet pilings, and piles; the pumping of liquids; the maintenance of a circulatory motion of a material being processed or frequent collisions of solid elements in a vibrating medium (vibration processing, milling, or mixing); multiple renewal and breakage of contacts between particles of a vibrating medium (heat- and mass-exchange processes—heating, drying, and cooling); the creation of intensive displacements of solid particles or the particles in an emulsion relative to a liquid vibrating medium (extracting, dissolving, leaching, and coloring); the transmission of impacts by the operating member to the medium being vibrated (impact-vibration crushing, tamping, and cleaning of filter surfaces); and the reduction of the resistance of a medium to the action of small, constant forces through the slippage of a medium’s particles or layers (compacting, filling packages, cutting soil, and so on) caused by vibration.

The most common kinds of vibration drive for the operating members of vibration engineering facilities are the centrifugal (which produces vibrations up to 500 hertz [Hz]), the electromagnetic (50-100 Hz), the piston (5-80 Hz), and the crank (1-20 Hz). The measurement of vibration parameters (displacement, velocity and acceleration, frequency, phase, and amplitude) is known as vibration measurement, and the instruments used include vibrometers and accelerometers. There are two methods of measuring displacement, velocity, and acceleration: by measuring the quantities relative to a frame of reference independent of the vibrating body and by measuring the deformations of an elastic member by means of an inertial element coupled to the vibrating body. Modern vibration-measurement apparatus consists of transducers, analyzers, indicating and recording instruments, and signaling equipment. The apparatus is calibrated to ensure accuracy of measurements.

One of the problems of vibration engineering is the protection of people, instruments, machines, and structures from the effect of harmful vibration. Measures taken in addition to the ordinary passive vibration insulation, which requires no extra energy sources, include static and dynamic balancing, the selection of inertial and elastic parameters that avoid operation in regions of resonance, damping units (when it is impossible to operate far from a resonance region), dynamic vibration damping by the addition of specially tuned vibration units (a mass on a spring or a pendulum) or impact-vibration units (small spheres striking a wall), and gyroscope installations to damp angular vibrations. Active vibration insulation (automatic suppression of vibrations) is also used. The objectives of dynamic vibration control can be damping, amplification, or stabilization. Dynamic amplification is attained by tuning the system to a resonant condition. With some adjustment in systems having two or more masses it is possible to achieve dynamic amplitude stabilization for induced vibrations that becomes almost independent of changes in the vibrating masses or the stiffness of certain elements.

REFERENCES

Lorish, lu. I. Vibrometriia, 2nd ed. Moscow, 1963.
Vibratsionnaia tekhnika. Moscow, 1966.
Bykhovskii, I. I. Osnovy teorii vibratsionnoi tekhniki. Moscow, 1969.

I. I. BYKHOVSKII

B. G. GOL’DSHTEIN

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