Vibration– movement of points or a mechanical system, in which the values ​​of at least one coordinate alternately increase and decrease in time.

Causes of vibration: the occurrence of unbalanced force effects during the operation of machines and units - their sources can be reciprocating movements of the system, unbalanced rotating masses, impacts of parts.

The presence of an imbalance leads to the appearance of unbalanced forces that cause vibration. The cause of the imbalance may be the heterogeneity of the material of the rotating body, the discrepancy between the center of mass of the body and the axis of its rotation, deformation of parts due to uneven heating, etc.

The main parameters characterizing vibration are:

1.amplitude value of the displacement X M;

2. amplitude value of vibration velocity V M ;

3. amplitude value of vibration acceleration a M;

4.oscillation period T;

5.frequency f.

Due to the specificity of the sense organs, the root mean square values ​​are decisive for the impact of vibrations on a person

Vibration velocity level (dB): L V = 10lg(V 2 /V 0 2) = 20lg(V/V 0)

V 0 = 5*10 -8 m/s – threshold value of vibration velocityV, caused by the action of instantaneous values ​​of vibration velocity V(τ) and determined during the averaging time T y by the formula

Vibration velocity level (dB): L v =10lg(v/v 0)

Vibration displacement level: L X = 20lg(X/X 0)

X 0 = 8*10 -12 m – threshold value of vibration displacement

Vibration acceleration level: L a = 20lg(a/a 0)

a 0 = 3*10 -4 m/s 2 – threshold value of vibration acceleration

In the practice of vibroacoustics, the entire frequency range of vibration is divided into octave ranges. In each octave range, the upper limit frequency is twice the lower: f B / f H = 2. Geometric mean frequency:
.

The geometric average frequencies of the octave bands are the same and equal to: 1Hz; 2Hz; 4Hz; 8Hz; 16Hz; 31.5Hz; 63Hz; 125Hz; 250Hz; 500Hz; 1000Hz; 2000Hz.

The vibration parameters depend on the vibration frequency; this dependence is complex. To describe it, vibration spectra are used, which are presented in the form of a graphical dependence of the vibration velocity level L v on the geometric mean vibration frequency
.

The spectrum of a periodic and quasiperiodic process is discrete, and the spectrum of a random or short-term single process is continuous. If a process is the result of the summation of several periodic and random processes, its spectrum is mixed, that is, it is depicted in the form of continuous and discrete spectra superimposed on each other.

To increase the accuracy of the vibration spectrum representation, measurement of the level of vibration velocity should be carried out in one-third octave frequency bands, for which it is true

=.

Reducing the vibration level is determined as ΔLv=L v 1 -L v 2, where L v 1.2 are the vibration levels before and after measures to reduce them.

Vibration measurements are carried out in accordance with GOST.

39. Impact of vibration on the human body. Its rationing

By the nature of the impact: are common And local.

Are common– low-frequency (0.7 - 30) Hz. Applied to the supporting surfaces of a person in a standing or sitting position, when the vibration causes a shock to the entire body. The most dangerous for humans are 6-9 Hz, due to the fact that they coincide with the natural absolute frequency of vibrations of the human internal organs (resonance). They can cause mechanical damage and rupture of human organs. When a person is systematically exposed to general vibration of more than 1 Hz, persistent disorders of the musculoskeletal system, disturbances of the central nervous system, digestive system, etc. can occur. They manifest themselves in the form of headaches, dizziness, poor sleep, decreased performance, cardiac dysfunction, and the appearance of radiculitis.

Local– over 30-1000 Hz. They affect individual parts of the body (arms, legs, head). Persons working with hand-powered tools are exposed. Causes vascular spasms (numbness of the hands and feet) starting from the fingers, spreading to the entire hand, forearm and covers the vessels of the heart - disrupting the blood supply. It affects muscle, bone, and nervous tissues, which leads to a decrease in skin sensitivity, ossification of muscle tendons, and salt deposition in the joints of the fingers and hands. The most negative influences occur under the influence of vibration when working at low temperatures.

The complex of painful changes in the body caused by exposure to vibration is called vibration disease. This disease can only be effectively treated with early stage. Severe forms of vibration disease lead to disability.

The interaction of the human body with changing environmental conditions always leads to a restructuring of its energy and material balance, accompanied by a transformation of internal energy in the body and a change in the metabolic processes occurring in it, which ultimately form the response of the whole organism to the action of an external stimulus.

Vibration, being a physically influencing factor, brings body particles into oscillatory motion, causing a change in their state in the form of a displacement of the center of gravity, deformation and the occurrence of internal stresses in them, which is accompanied by the expenditure of mechanical energy received from the source of vibrations in the zone of contact of the body with vibrating surfaces.

The amount of energy received is determined by the duration of exposure to vibrations and the magnitude of the instantaneous power of the affecting oscillatory process, or the area of ​​contact and the intensity of vibrations, since the intensity of the oscillatory process is numerically equal to its power per unit area perpendicular to the direction of propagation of vibrations.

Under conditions of different frequencies and amplitudes of vibrations, changes in perception thresholds under the influence of vibrations occur according to the law of proportionality of the affecting vibrational energy. This means that the adequate physical criterion for the hygienic assessment of vibration, other things being equal, is the oscillatory velocity, and not displacement or acceleration.

There are differences between hygienic and technical regulation of industrial vibrations.

In 1 case, the vibration parameters of workplaces and the surface of contact with the hands of workers are limited, based on physiological requirements that exclude the occurrence of vibration disease.

In case 2, vibration parameters are limited, taking into account not only the specified requirements, but also the level of vibration that is technically achievable today for this type of machine.

The normalized value for both local and general vibration according to GOST is the level of vibration velocity in octave frequency bands.

Tennological - 108 99 93 92 92 92 - - - -

Hygienic vibration standards are established for a work shift of 8 hours.

General vibration is normalized taking into account the properties of the source of its occurrence and is divided into vibrations:

Transport, which arises as a result of the movement of vehicles across terrain and roads (including during construction)

Transport and technological, which occurs during the movement of cranes and excavators

Technological, which occurs during the operation of stationary machines, installations, fans, compressor and pumping units or is transferred to workplaces that do not have sources of vibration.

For general and local vibration, the dependence of the permissible value of vibration velocity on the time of actual exposure to vibration, not exceeding 480 minutes, is determined by the formula v r =v 480.

With regular breaks from exposure to local vibrations during a work shift, the permissible values ​​of the vibration velocity level should be increased by the values ​​given below.

Small mechanical vibrations, arising in elastic bodies or bodies under the influence of alternating physical field, are called vibration . The reason for the excitation of vibrations is the unbalanced force effects that arise during the operation of machines and units, which arise:

During reciprocating movements of systems (crank mechanisms, hand hammers, vibratory rammers, etc.);

As a result of the presence of unbalanced rotating masses (hand-held electric and pneumatic grinders, cutting tools of machine tools, etc.);

When parts strike (gears, bearing units).

The area of ​​vibration propagation is called vibration zone.

Parameters characterizing vibration. Vibration is characterized by speed (v, m/s) and acceleration (A, m/s 2) oscillating solid surface. Typically these parameters are called vibration speed And vibration acceleration. The values ​​of vibration velocity and vibration acceleration that a person has to deal with vary over a very wide range. It is very inconvenient to operate with large range numbers. In addition, human organs respond not to an absolute change in the intensity of the stimulus, but to its relative change. In accordance with Weber-Fechner law, human sensations arising from various types of stimulation, in particular vibration, are proportional to the logarithm of the amount of energy of the stimulus. Therefore, logarithmic quantities have been introduced into practice - levels of vibration velocity and vibration acceleration:

,	(1)
,	(2)

Where υ And A– vibration velocity and vibration acceleration;

υ 0 And a 0– threshold values ​​of vibration velocity and vibration acceleration. υ 0 =5*10 -8 m/s, a 0=3*10 -4 m/s 2. Levels are measured in special units - decibels (DB).

Industrial vibration is classified according to the following criteria (Fig. 1):

Vibration transmission method;

Direction of vibration action;

Temporal characteristics of vibration;

The nature of the vibration spectrum;

Source of vibration (Fig. 2).

Figure 1 – Classification of industrial vibrations

The effect of vibration on a person depends on the frequency and level of vibration, the duration of exposure, the location of application of vibration, the direction of the vibration axis, individual abilities the human body perceives vibration, the conditions for the occurrence of resonance and a number of other conditions.

Question 2. Hygienic standardization vibrations. The impact of vibration on the human body

The effect of vibration on a person depends on the frequency and level of vibration, the duration of exposure, the location of application of vibration, the direction of the axis of vibration exposure, the individual ability of the human body to perceive vibration, the conditions for the occurrence of resonance and a number of other conditions. Oscillatory processes are inherent in a living organism, in particular in humans - rhythmic vibrations of the heart, blood, and brain biocurrents. Human internal organs (liver, kidneys, stomach, heart, etc.) can be considered as oscillatory systems with elastic connections. Natural frequency of internal organs f = 3...6 Hz. The natural frequency of the human head relative to the shoulder girdle is 25...30 Hz, relative to the base on which the person is located - 4...6 Hz. When the natural frequencies of a person’s internal organs and individual parts of his body coincide with the frequency of forced vibration, the phenomenon occurs resonance, in which the amplitude of vibrations of organs and body parts increases sharply. In this case, pain may occur in individual organs, and at very high levels of vibration, even injuries, ruptures of ligaments and arteries.

Figure 3 – Effect of vibration on humans

The phenomenon of resonance for humans occurs with low-frequency vibration. Oscillations with a frequency of less than 0.7 Hz are called jocks. Rocking does not cause serious disturbances in the human body, but disturbances occur in the vestibular apparatus of Metis, and in people with a weak vestibular apparatus the so-called seasickness, which causes dizziness, nausea, and vomiting. After the rocking stops, this condition disappears after a while.

At vibration frequencies less than 16 Hz, in addition to resonance phenomena, a person experiences a depressed state, a feeling of fear, tripods, and the central nervous system is depressed. When exposed to vibration, functional and physiological changes occur in the human body, presented in Table 1.

Table 1 – Changes in the human body when exposed to vibration

Vibration disease (vibration disease)- an occupational disease caused by prolonged exposure to vibration. The forms and stages of vibration disease are presented in Table 2

Table 2 - Symptoms of the stages of vibration disease

Stages of vibration disease	Form of vibration disease, type of vibration	Symptoms
I – initial	Cerebral General	Sleep disturbance, emotional instability, mild sensory disturbances, decreased leg temperature, soreness in the calves, leg fatigue, minor changes in peripheral nerve endings
Peripheral Local	Periodic mild pain in the arms, mild disorders of pain and vibration sensitivity of the fingers, minor changes in the muscles of the shoulder girdle
II – moderately expressed	Cerebral General	Dizziness, intolerance to shaking, frequent headaches, changes in the vestibular apparatus, disorders in the central nervous system (neurotic reactions)
Peripheral Local	Severe vascular crises, attacks of spasms and whitening of the fingers (“dead fingers”), followed by cyanosis, sharp decreases in skin temperature on the hands (cold and wet hands), swollen fingers, severe pain in the muscles of the hands, functional changes in the central nervous system
III – pronounced	Cerebral General	Severe changes in the central nervous system, vestibular disorders with attacks of dizziness, vibration intolerance, constant headaches, neurotic reactions, changes are irreversible
Peripheral Local	Damage to the higher parts of the central nervous system, vascular disorders of the upper and lower extremities, crises extending to the area of ​​the coronary vessels, attacks of dizziness, fainting states

Hygienic regulation of vibration.

When normalizing vibration, its category is taken into account depending on the type of its source.

Vibration standards are established for three mutually perpendicular directions along the axes of the orthogonal coordinate system.

There are sanitary-hygienic and technical regulation of vibration.

In the first case, the vibration parameters of workplaces and the surface of contact with the limbs of workers are limited, based on physiological requirements, and reducing the possibility of vibration disease.

In the second case, vibration parameters are limited, taking into account not only the specified requirements, but also the level of vibration that is technically achievable today for this type of machine.

Sanitary and hygienic vibration standards regulate the parameters of industrial vibration and the rules for working with vibration-hazardous mechanisms and equipment, GOST 12.1.012-90 “SSBT. Vibration safety. General requirements", SN 2.2.4/2.1.8.566-96 "Industrial vibration, vibration in residential and public buildings."

The documents establish: classification of vibrations, methods of hygienic assessment, standardized parameters and their permissible values, working conditions for persons in vibration-hazardous professions exposed to local vibration, requirements for ensuring vibration safety and vibration characteristics of machines.

Acceptable values ​​are set separately for general and local vibration. General vibration is normalized in octave band ranges with geometric mean frequencies of 2, 4, 8, 16, 4.5, 63 Hz (for transport vibration, vibration in the octave band is additionally normalized c f SG = 1 Hz). Local vibration is normalized in frequency ranges with f SG = 16, 31.5, 63, 125, 250. 500, 1000 Hz. The standards are set for a work shift of 8 hours.

At hygienic assessment vibrations, the normalized parameters are the root mean square values ​​of vibration velocity v (and their logarithmic levels L v) or vibration acceleration a (L a) for local vibrations in octave frequency bands, and for general vibration - in octave or one-third octave bands.

Standard values ​​for industrial vibrations and vibrations in residential and public buildings are given in Sanitary Standards SN 2.2.4/2.1.8.566-96. For process vibration category 3a, these values ​​are given in Table 3.

Table 3 – Maximum permissible values ​​of vibration category 3a (for industrial workplaces)

For local vibration, the corrected standard values ​​(along the axes X l, Y l, Z l) for vibration acceleration are 2.0 m/s 2 and 126 dB, for vibration velocity - 0.002 m/s and 112 dB. Acceptable values ​​are presented in tables 4 – 5.

For general and local vibration, the dependence of the permissible value of vibration velocity on the time of actual exposure to vibration (T), not exceeding 480 minutes (8-hour working day), is determined by the formula:

,

(3)

where is the permissible value of vibration velocity for an exposure duration of 480 minutes.

Table 4 – Sanitary standards single-digit indicators of vibration load on the operator for a shift duration of 8 hours

Type of vibration	Vibration category according to sanitary standards	Direction of action	Standard, Frequency Adjusted and Equivalent Adjusted Values
vibration acceleration	vibration velocity
m s(-2)	dB	m s(-1) 10(-2)	dB
Local		Xl, Yl, Zl	2,0		2,0
General		Zo	0,56		1,1
		Yo, Xo	0,4		3,2
		Zo, Yo, Xo	0,28		0,56
	3 type "a"	Zo, Yo, Xo	0,1		0,2
	3 type "b"	Zo, Yo, Xo	0,014		0,028

Table 5 – Hygienic vibration standards according to GOST 12.1.012 (extract)

Type of vibration	Permissible level of vibration velocity, dB, in octave bands with geometric mean frequencies, Hz
					31,5
General transport Vertical Horizontal								- -	- -	- -	- -
Transport and technological	-							-	-	-	-
Technological	-							-	-	-	-
In production areas where there are no machines that generate vibration	-							-	-	-	-
In office premises, evacuation centers, design bureaus, laboratories	-							-	-	-	-
Local vibration	-	-	-

Question 3. Parameters characterizing acoustic vibrations (noise). Classification of industrial noise

One type of movement is waves. Distinctive feature What makes this movement unique is that it is not the particles of matter themselves that propagate in the wave, but changes in their state (perturbations). If any body vibrates in elastic medium, then it affects the particles of the medium adjacent to the body and forces them to perform forced oscillations. The medium near the oscillating body is deformed and elastic forces. These forces act on particles of the medium that are increasingly distant from the body, removing them from their equilibrium position. Gradually all particles of the medium are involved in oscillatory motion. Elastic waves are called sound or acoustic if the corresponding mechanical deformations of the medium have small amplitudes. The difference between elastic waves in a medium and any other ordered movement of its particles is that the propagation of waves is not associated with the transfer of matter from one place to another over long distances.

Acoustic vibrations are often called sound, and the area of ​​their distribution is sound field. Sound volume depends on the sound intensity, i.e. determined by the amplitude of vibrations in a sound wave. The hearing organs are most sensitive to sounds with frequencies from 700 to 6000 Hz. Sound volume level unit – background. Noise It is customary to call aperiodic sounds of varying intensity and frequency. From a physiological point of view, noise is any sound that is unfavorably perceived by a person. Like any wave, a sound wave is characterized by the speed of propagation of vibrations in it. With wavelength λ, and oscillation frequency ν speed υ connected by the formula:

where ρ is the density of the medium (kg/m3);

ρ*s – specific acoustic resistance (Pas/m), equal to 410 Pa*s/m for air, 1.5*10 6 Pa*s/m – for water, 4.8*10 7 Pa*s/m – for steel;

υ – vibration speed (m/s).

When sound travels at a speed sound wave there is a transfer of energy, which is characterized by intensity sound. Sound intensity I(W/m2) is the energy transferred sound wave per unit time, divided by the surface area through which it propagates

Where R - sound pressure, Pa;

p 0- threshold sound pressure equal to 2 10 -5 Pa.

Sound intensity level

,

(8)

Where I- sound intensity, Pa;

I 0 - threshold sound intensity equal to 10 -12 W/m 2. The minimum values ​​of sound pressure and sound intensity that a person hears at a sound frequency of 1000 Hz are taken as threshold values, so they are called hearing thresholds.

Important characteristic, which determines the spread of noise and its impact on humans is its frequency. Just like for vibration, the range of sound frequencies is divided into octave bands (f 1 / f 2= 2), characterized by their geometric mean frequencies f SG

Classification of industrial noise. Noise is classified according to frequency, spectral and temporal characteristics, and the nature of its occurrence (Fig. 3). frequency acoustic vibrations differ by infrasound (f< 16 Hz), sound(16 < /< 20 000 Гц), ultrasound(/ > 20,000 Hz). Acoustic vibrations of the sound range are divided into low frequency(less than 350 Hz), mid-frequency(from 350 to 800 Hz), high frequency(over 800 Hz) (Fig. 4).

Figure 4 – Classification of acoustic vibrations by frequency

By spectral characteristics noise is divided into broadband with a continuous spectrum of more than one octave and tonal (discrete), in the spectrum of which there are pronounced discrete tones (frequencies at which the sound level is significantly higher than the sound level at other frequencies). An example of broadband noise is the noise of a jet aircraft, while tonal noise is the noise of a circular saw, the noise spectrum of which has a pronounced frequency with a dominant sound level.

By timing characteristics noise is divided into constant and intermittent. Permanent noise is considered to be the level of which changes by no more than 5 dB during an 8-hour working day; fickle- if this change exceeds 5 dB. Variable noises, in turn, are divided into hesitant, the sound level of which changes continuously over time (for example, traffic noise); intermittent, the sound level of which changes stepwise (by 5 dB or more), and the duration of the intervals in which the sound level remains constant is at least 1 s (for example, the noise of compressed air intermittently released from cylinders); impulse, representing sound pulses lasting less than 1 s (for example, the noise of units and machines operating in pulse mode).

By nature of occurrence noise can be divided into mechanical, aerodynamic, hydraulic, electromagnetic. Mechanical noise arise for the following reasons: the presence in mechanisms of inertial disturbing forces arising from the movement of mechanism parts with variable accelerations; collision of parts at joints due to inevitable gaps; friction in the joints of machine parts; impact processes (forging, stamping, riveting, straightening) and a number of others. The main sources of noise of mechanical origin are rolling bearings and gears, as well as unbalanced rotating parts of machines.

Aerodynamic noise arise as a result of movement on, gas (air) flows around various bodies. Aerodynamic noise occurs during the operation of fans, compressors, gas turbines. The causes of aerodynamic noise are vortex processes that arise in the flow of the working medium when flowing around bodies and releasing a free gas stream; pulsations of the working environment caused by the rotation of the blade wheels of fans and turbines; fluctuations associated with inhomogeneity and pulsations of flow. Aerodynamic noise is one of the most significant in terms of sound level.

Hydraulic noises arise as a result of stationary and non-stationary processes in liquids (cavitation, turbulence, hydraulic shocks). For example, in pumps, the source of hydraulic noise is fluid cavitation at the surfaces of the pump blades at high peripheral speeds of rotation of the impeller.

VIII. Industrial vibrations

1. Basic vibration parameters

The main vibration parameters are:

Vibration displacement amplitude - , m;

Amplitude of oscillatory velocity (vibration velocity) - , m/s;

Amplitude of oscillatory acceleration (vibration acceleration) - , m/s 2 ;

Oscillation period – T, s;

Oscillation frequency – f , Hz=1/s.

Due to the specific properties of the sense organs, the determining factors in assessing the impact of vibration are the effective values ​​of the above listed parameters. So the effective value of the vibration velocity is the root mean square of the instantaneous velocity values V(t ) during the averaging time t y , which is chosen taking into account the nature of the change in vibration velocity over time:

.

Thus, to characterize vibrations, the spectra of the effective values ​​of the parameters or the average squares of the latter are used.

In the practice of vibroacoustic research, the entire range of vibration frequencies is divided into octave ranges. In the octave range, the upper limit frequency is twice the lower frequency. Analysis and construction of spectra of vibration parameters can also be carried out in one-third octave frequency bands - . If - is the lower limit frequency, and - is the upper, then the geometric mean frequency is taken as the frequency characterizing the band as a whole .

The geometric mean frequencies of the octave frequency bands of vibration are standardized and are: 1, 2, 4, 8, 16, 31.5, 63, 125, 250, 500, 1000 Hz.

Since the absolute values ​​of the parameters characterizing vibration vary over a very wide range, the concept of a logarithmic vibration level is used in practice. Logarithmic level of oscillations is a characteristic of oscillations comparing two similar physical quantities, proportional to the decimal logarithm of the ratio of the estimated and initial value of the quantity. The reference values ​​of the parameters taken as the starting point are used as the initial value. Levels are measured in dB. Then the level of vibration velocity will be determined by the formula:

Vibration safety of personnel in production and social spheres of activity

Educational and methodological manual For practical classes for BJD students of Altai State Technical University of all forms of education

Barnaul 2011

Sturov D.S., Gergert V.R., Kalin A.Yu. Vibration safety of personnel in industrial and social spheres of activity: Educational and methodological manual for practical training in life safety / Alt. state tech. uni-t im. I.I. Polzunova - Barnaul, ASTU publishing house, 2011

The educational and methodological manual for practical training in BJD was reviewed by the methodological commission of the Department of BJD and approved for use.

General theoretical information about vibration.

The development of educational and methodological manuals is based on state regulatory documents:

· GOST 12.1.012-90. SSBT, Vibration safety.

· CH 2.2. 4/2. 1.8.566-96, Sanitary standards. Industrial vibration, vibration in residential and public buildings.

Terms and definitions, sources and causes of vibration.

Vibration – These are mechanical vibrations of elastic bodies and materials, individual parts of machines, mechanisms, foundations, building structures, etc., when exposed to an alternating disturbing force.

From a physical point of view There is no fundamental difference between noise (i.e. sound vibrations) and vibration. The only difference is in the perception of vibrations: vibration is perceived by the vestibular apparatus and organs of touch, and noise by the organ of hearing. Mechanical vibrations of elastic bodies with a frequency of up to 20 Hz are perceived by the body as vibration; in fact, it is infrasound, i.e. inaudible vibrations, and vibrations with a frequency of more than 20 Hz are perceived simultaneously as vibration and sound. An example of this is the string of a musical instrument - it vibrates and sounds.

Sources of vibration are: various technological processes (metal cutting, mechanical processing, grinding and crushing of the product, etc.); machines, mechanisms and their working parts; hand-powered tools (electric drills, pneumatic sanders, etc.); manual controls of machines and equipment, etc.

Causes of vibration are largely due to technical progress, characterized by an increase in movement speeds, an increase in power, effort, and equipment productivity. But the modern technosphere is not perfect: there is unbalance and uneven movement of mechanisms, inaccurate manufacturing, increased gaps in articulated joints, heterogeneity of materials of moving parts of machines and mechanisms, etc. All of this, together or separately, is a source of disturbing alternating forces that generate vibration.

Basic parameters and characteristics of vibration.

Man-made vibrations can be simple, when vibrations occur along one of three coordinates (X,Y,Z) and complex, when vibrations of an object occur simultaneously in all coordinate directions with different amplitudes and frequencies.

The simplest type of oscillations are harmonic sinusoidal oscillations along one of the three coordinate axes (Figure 1).

Figure 1. Harmonic sinusoidal oscillations of point m:

Oscillatory displacement (vibration displacement)

Oscillatory speed (vibration speed)

Oscillatory acceleration (vibration acceleration)

The main parameters characterizing vibration are:

The amplitude of the displacement of the oscillating point m from the equilibrium position.

Formula for the motion of point m:

, m (1)

where is the maximum displacement of a point from the equilibrium position (from the axis of Fig. 1)

Circular frequency,

Oscillation frequency, Hz.

- 1 Hertz (Hz) equal to the number periods fluctuations in 1 give me a sec.

. If, for example, the period of one oscillation is equal to 1 one hundred

frequency Hz

If the number of oscillation periods in 1 second will be equal 10 , then the time of one period of oscillation is equal to 0,1 s, and then Hz

The maximum value of the vibration displacement amplitude according to formula (1) will be equal to

Oscillation speed (vibration velocity) of the point,

Maximum vibration velocity value (vibration velocity amplitude) , m/s

Vibration acceleration of a point,

The maximum value of vibration acceleration according to formula (3) is equal to

, m/s

In the general case, physical quantities characterizing vibration (for example, vibration velocity) are some function of time, i.e. . In such cases, by mathematical theory, the oscillatory process is represented as a sum of infinitely lasting sinusoidal oscillations with different frequencies and amplitudes. This is called a polyharmonic oscillatory process. In this case, the process can be periodic or quasiperiodic, frequency spectra which are considered discrete. (Fig. 2a)

If the oscillatory process is random or a single short-term one, the spectrum of vibration parameters is considered continuous (Fig. 2b).

In real conditions, vibration is most often presented in the form of periodic polyharmonic oscillations. Then, due to the specific properties of human sensory organs, they are decisive, i.e. acting on the human body are not the maximum values ​​of vibration parameters (amplitude, speed and acceleration), but their root-mean-square values ​​(this is approximately 0.67...0.75 from their maximum). A more accurate determination of the root-mean-square values ​​of vibration velocity and vibration acceleration is performed using the formulas:

; (4)

where is the number of harmonic components in the spectrum

- values ​​of oscillatory speed and acceleration.

In the practice of vibration measurements, the absolute values ​​of vibration parameters vary within very wide limits. For example, the amplitude of vibrations during sea motion reaches 10 meters, and the amplitude of vibrations on the body of a home electric razor is only 0.01 mm. In the same way, speed and acceleration change over a wide range. Difference maximum value parameters from the minimum perceptible (threshold) value reaches , i.e. the maximum of a parameter is one million times greater than its minimum. This creates great inconvenience in practical calculations and research. In order to sharply reduce the measuring scales, for ease of use, logarithmic scales of vibration parameters are used, called vibration velocity levels, dB and vibration acceleration levels, dB (decibel):

·
, dB (5)

·
, dB (6)

where is the threshold (minimum perceptible by the human body) value of vibration velocity;

and about=1·10 -6 m/s 2 =1·10 -4 cm/s 2 =1·10 -3 mm/s 2 - threshold (minimum perceptible by the human body) value of vibration acceleration;

b) 0

a) 0

f=2 Hz

f=4 Hz

f=6 Hz

f=8 Hz

f=10 Hz

1s

1s

1s

1s

1s

f, Hz

L V

A V

t, c

f, Hz

A V

L V

t, c

Figure 2: Polyharmonic spectra of industrial vibration.

When the oscillation frequency is below 1 Hz, the human body moves as a single whole - the internal organs do not experience relative movements. Such fluctuations, although unpleasant, are not dangerous (rolling). The consequence of such vibration is seasickness. Most internal organs have a natural vibration frequency in the range of 6–9 Hz. The impact on the human body of external vibrations with the same frequencies is very dangerous, as they can cause mechanical damage or even rupture of organs. Prolonged exposure to intense general vibration can be the cause of vibration disease - disorders of the physiological functions of the body, caused primarily by the effect of vibration on the central nervous system.

These disorders manifest themselves in the form of headaches, dizziness, poor sleep, irritability, decreased performance, and cardiac dysfunction.

At frequencies above 100 Hz, vibration can only act as local vibration. Local vibration with prolonged exposure causes vascular spasms, resulting in a deterioration in the blood supply to the extremities.

In addition, local vibration affects nerve endings, muscle and bone tissue, resulting in impaired skin sensitivity, ossification of muscle tendons, pain and salt deposits in the joints of the hands and fingers, which leads to deformations and decreased joint mobility. At the same time, disturbances in the activity of the central nervous system are observed.

The body is especially sensitive to vertical shocks when a person stands on a vibrating surface. The most harmful to humans is the simultaneous effect of vibration, noise and low temperature.

1.2. Vibration parameters and their normalization

1.2.1. Vibration is characterized by three parameters: displacement from the equilibrium position, oscillatory speed and oscillatory acceleration.

Based on psychophysiological considerations and for ease of calculation, vibration parameters are expressed in logarithmic units. These logarithmic units are called levels, expressed in decibels and denoted by the letter L with the corresponding index:

– bias level L = 20 lg x ;

– oscillatory speed level L v = 20 log V ;

– level of oscillatory acceleration L a = 20 log a , a0

where x 0 , V 0 , a 0 – reference values ​​established by international agreements

niyami: x 0 = 8 10-12 m; V 0 = 5 10-8 m/s; a 0 = 3 · 10-4 m/s2.

In practice, vibrations are usually measured and normalized in octave frequency bands, i.e., bands in which the ratio of boundary frequencies f gr2 / f gr1 = 2.

Octave bands are standardized by international agreement. For general vibration, the geometric mean frequencies of the octave bands form the following

row: 1; 2; 4; 8; 16; 31.5; 63; for local vibration: 8; 16; 31.5; 63; 125; 250; 500; 1000 Hz.

1.2.2. The normalized vibration characteristics that determine its impact on a person are the root-mean-square values ​​of vibration velocity V in m/s and vibration acceleration a in m/s2 or their logarithmic levels L V and L a in dB, respectively.

Vibration affecting a person is standardized separately for each established direction in each of the octave bands.

Hygienic standards for vibration affecting humans in industrial conditions are specified in SN2.2.4/2.1.8.565-96 “Industrial vibration. Vibration in premises and public buildings" (Appendix 1). The normalized parameters of vibration on rolling stock are the levels of amplitude values ​​of the oscillatory velocity L v and oscillatory acceleration L a , and the repeatability of these values ​​is also taken into account (SN 2.9.4/21.8.566-96).

On locomotives, vibrations are normalized by acceleration (12.2.056-81). Permissible vibration levels for main types of work are established -

x GOST 12.2.056 – 2004 “Vibration safety and general requirements”.

1.3. Measures to eliminate vibrations

General measures to combat harmful effects vibrations can be combined into three groups: engineering, organizational and preventive.

Engineering measures include the introduction of vibration-proof machines, the use of vibration protection equipment that reduces vibration affecting workers along the paths of its propagation; design solutions for technological processes and production facilities that ensure hygienic vibration standards at workplaces.

Organizational Activities include monitoring the installation of equipment, timely and high-quality implementation of scheduled preventive maintenance and repairs, and compliance with the rules for the technical operation of machines and units.

Treatment and prevention The activities provide the necessary microclimatic regime and a complex of physiotherapeutic procedures (water baths, massage, gymnastics and ultraviolet irradiation).