RU2572177C1 - Vibration-absorbing device - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: device contains pressing sheet, having at least two groups of conditional rectangular areas between adjacent fixtures. The pressing sheet is made with thickness from 0.05 to 0.5 of thickness of dampened structure. Each group contains areas with similar dimensions. Average geometric size of sections with maximum area is determined by length of bending wave of the pressing sheet at lower frequency of the range. The average geometrical size of the sections with lower area differs from the same value of sections of groups with sections having large area by at least 1.2 times.

EFFECT: expansion by at least 2 times of frequency range of vibrations suppression.

1 dwg

Description

The invention relates to the field of combating vibration arising from the operation of vibroactive equipment when exposed to pulsating pressures generated by hydroaerodynamic sources on the hull and inside bodies of a vehicle.

The invention can be applied to reduce the vibration that occurs in ship structures during the operation of mechanisms, propeller and which is the reason for the increased level of air noise in the premises of the vessel.

The damped structure can also be a vehicle hull or internal structure, excited by dynamic forces from the side of operating equipment or by pulsating pressures of hydroaerodynamic sources, a separate plate or shell element of the vibroactive mechanism, which is a source of increased vibration and noise.

A large number of vibration absorption means are known. The most common of these are vibration-absorbing coatings (A. S. Nikiforov Vibration absorption on ships, pp. 53–78, ed. “Sudostroenie”, Leningrad, 1979).

One of the most common types of vibration-absorbing coatings is a reinforced coating, which is a layer of viscoelastic material on which a reinforcing layer of hard material is applied (A.S. Nikiforov Acoustic design of ship structures, pp. 158 ÷ 161, ed. "Sudostroenie", Leningrad, 1990). Reinforced vibration-absorbing coatings are applied to the damped structures either during the construction of the vehicle, when the need for their application is known in advance, or if necessary, to bring the levels of vibration and noise in the premises to the standards on the constructed vehicle. The disadvantage of such coatings is the presence of a viscoelastic material in them, the deformation of which leads to the conversion of vibrational energy into thermal energy, which provides a vibration-absorbing effect of the device. As viscoelastic rubber-like materials are used. However, their application limits the scope of use of reinforced vibration-absorbing coatings in terms of temperature and in contact with aggressive environments.

Also known is a vibration-absorbing device that does not have a viscoelastic material and works under almost any temperature conditions and environmental influences (RF Patent “Vibration-absorbing device”, No. 2117336, 1998) - a prototype. Its advantages are simplicity, manufacturability and installation, low cost. It includes a pressure sheet mechanically fixed to the damped structure by means of bolts located at equal distances in a checkerboard pattern, the sheet thickness being from 0.05 to 0.5 of the thickness of the damped structure, and the distance between adjacent fixtures is half the length of the bending wave in the sheet when the lowest frequency range f _n where you want to reduce vibration.

The disadvantage of the prototype is the relatively narrow width of the frequency range of vibration reduction. With this arrangement of fasteners, the sections of the pressure sheet between adjacent fasteners are square in shape and have the same area. The lowest resonant frequency of the bending vibrations of the sections is f _n . The occurrence of higher-frequency resonances of bending vibrations leads to a decrease in the vibration level of the damped structure at frequencies greater than f _n . However, as the results of experimental studies have shown, the prototype effect of at least 6 dB is achieved only in a narrow frequency range f _n ÷ 3f _n .

The present invention is aimed at achieving a technical result, which consists in ensuring the effectiveness of the vibration-absorbing device in a wider frequency range than that of the prototype.

The specified technical result is achieved by the fact that in the vibration-absorbing device the pressure sheet has at least two groups of conditional rectangular sections, each of which is located between adjacent fasteners. In each group, the plots have the same size. The geometric mean size of the sections of the largest area is determined by the length of the bending wave in the pressure sheet at the lowest frequency of the range in which it is necessary to reduce the vibration amplitude of the damped structure. The geometric mean sizes of the sections of groups with sections of a smaller area differ from similar values of sections of groups with sections of a larger area by at least 1.2 times.

This embodiment of the pressure sheet provides an extension of the frequency range of vibration reduction due to the "introduction" of various resonant frequencies of bending vibrations of sections of different groups due to their different areas. The choice of the geometric mean size of the sections of the group with the largest areas equal to the length of the bending wave in the pressure sheet at the lowest frequency of the range provides the vibration-absorbing effect of the device, like the prototype, at least 6 dB, in the frequency range from f _n to 3f _n . The differences in the geometric mean sizes of the sections of groups with sections of large and smaller areas provide the necessary increase in the resonant frequencies of bending vibrations, which leads to the achievement of vibration-absorbing efficiency of the device in the frequency range from 3f _n to 6f _n . The implementation of these distinctive features of the vibration-absorbing device extends at least 2 times the frequency range of reducing the vibration level of the damped structure.

The invention is illustrated in the drawing, where, as an example, a plan and a cross section AA of a variant of a vibration-absorbing device are presented.

размеров участков группы с участками наибольшей площади 4 равна длине изгибной волны в прижимном листе на низшей частоте диапазона вибраций. Среднегеометрические величины размеров $${\tilde{\ell }}_i$$

участков групп с участками меньшей площади отличаются от аналогичных величин участков групп с участками большей площади не менее чем в 1,2 раза $$\left({\tilde{\ell }}_4/{\tilde{\ell }}_5,{\tilde{\ell }}_5/{\tilde{\ell }}_6\right).$$

The vibration-absorbing device contains a pressure sheet 1, rigidly fixed with mechanical fasteners 2 on the damped structure 3. In the presented embodiment, the pressure sheet consists of three groups of rectangular sections 4, 5, 6 between adjacent fasteners, which in each group have the same dimensions with conditional boundaries indicated dotted lines. In this case, the geometric mean $${\tilde{\ell }}_{\mathrm{four}}$$

sizes of sections of the group with sections of the largest area 4 is equal to the length of the bending wave in the pressure sheet at the lowest frequency of the vibration range. Geometrical mean sizes $${\tilde{\ell }}_i$$

sections of groups with sections of a smaller area differ from similar values of sections of groups with sections of a larger area not less than 1.2 times $$\left({\tilde{\ell }}_{\mathrm{four}}/{\tilde{\ell }}_5,{\tilde{\ell }}_5/{\tilde{\ell }}_6\right).$$

Vibration absorption using the proposed device is as follows.

Vibrational energy transmitted from the source to the damped structure is distributed through the fasteners and the contacting surface irregularities to the pressure sheet and causes its intense vibrations at the resonant frequencies of the bending vibrations of the sections between adjacent fasteners. If the geometric mean size of the sections of the group is equal to the sections of the largest area of the length of the bending wave in the pressure sheet at the lowest frequency of the range f _{n, the} intense oscillations of these sections occur with a phase shift with respect to the vibrations of the damped structure. The vibration amplitude decreases due to dry friction of the surfaces of the damped structure and the pressure sheet, as well as viscous losses during the movement of a thin air layer between these surfaces. Intense vibrations of sections of a smaller area occur at higher resonant frequencies, which leads to the expansion of not less than 2 times the frequency range of the effectiveness of the pressure sheet of the invention in comparison with the efficiency of the pressure sheet consisting of square sections of the same area. The choice of geometric mean size sizes of the largest areas between adjacent fasteners provides better tuning than the prototype to the frequency f _{n of the} lower resonant frequency of the bending vibrations of these sections, both in their square and rectangular shape. In the latter case, in the presence of rectangular forms of damped structures widely used in the technique, a greater effect of vibration absorption of the device is achieved on high-frequency bending resonances of sections of the pressure sheet between adjacent fasteners.

The lowest frequency f _{n of the} range of the most intense structural vibrations that must be reduced is determined using the calculated and experimental frequency characteristics of its vibrational excitability and the forces acting on the damped structure. Such a frequency is the resonant frequency of the bending vibrations of the structure closest to the frequency of the greatest force causing vibration. To ensure effective reduction of vibration levels in the frequency range f _n ÷ 3f _n , the lowest resonant frequency of bending vibrations of the largest areas of the pressure sheet is tuned to the frequency f _{n of the} vibrational area, which is achieved by choosing the geometric mean size of these sections equal to the length of the bending wave λ _and in the pressure sheet at a frequency f _n , determined by the approximate formula

,

,

where h is the thickness of the pressure sheet, m,

f _n - the lowest frequency range, Hz.

The specified choice of geometric mean sizes of smaller areas of the pressure sheet between adjacent fasteners provides the occurrence of intense bending vibrations at frequencies higher than 3f _n , which contributes to the expansion of not less than 2 times the frequency range of the effectiveness of the pressure sheet, consisting of two and more groups of rectangular sections.

Experimental studies have confirmed that a significant effect of vibration absorption of the pressure sheet with the above thickness is achieved by creating in it a violation of the frequency of attachment of the sheet to the damped structure by the formation of at least two groups of sections of different sizes between adjacent fasteners.

The proposed vibration-absorbing device significantly expands the frequency range necessary for the practice of reducing vibration, which distinguishes it from the prototype.

Claims (1)

A vibration-absorbing device including a pressure sheet fixed to a damped structure using mechanical fasteners and having a thickness of 0.05 to 0.5 of the thickness of the damped structure, characterized in that the pressure sheet has at least two groups of conditional rectangular sections between adjacent fasteners, having the same sizes in each group, and the geometric mean size of the sections of the largest area is determined by the length of the bending wave of the pressure sheet at the lower frequency of the range in rum required to reduce the intensity of vibration damped structure, and the geometric mean value of sizes of portions with a smaller area differs from the analogous quantity portions groups with portions larger area is not less than 1.2 times.

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