RU2176113C2 - Sound screen in liquid flow - Google Patents

Abstract

FIELD: hydroacoustics. SUBSTANCE: screen is, essentially, annular casing built up of outer and inner rigid-material shells accommodating highly elastic material with sealed air voids. Casing has streamlined wing-shaped profile; it is additionally secured by means of inner damping set placed between shells. Highly elastic material is secured to inner shell and partially fills the casing; air content of its air voids is assumed to be varying in radial direction so that it amounts to 1-5% in each extreme layer and 20-50% in intermediate-part layer; liquid gap is provided between highly elastic material and outer shell. EFFECT: enhanced screening effectiveness including at low frequencies; enhanced mechanical strength of screen. 2 cl, 2 dwg

Description

 The proposal relates to hydroacoustics and can be used in shipbuilding, for example, to form directivity characteristics, increase the noise immunity of receivers and increase the efficiency of sound emitters.

 From the literature, flat screens for sound in a liquid are known (V.E. Glazanov. "Shielding of hydroacoustic antennas." Shipbuilding, L., 1986, p. 112.113). The disadvantage of these devices is the complexity of creating structures covering the shielded object.

 Closest to the proposed technical solution in terms of technical nature and the achieved effect (prototype) is an external cylindrical screen in the form of an annular closed shell consisting of outer and inner shells made of rigid material containing highly elastic material with sealed air cavities (see ibid.) .

 However, the known device does not work efficiently in the stream, because due to its poor hydrodynamic qualities it creates a noise field due to both turbulence of the stream and force acting on the structural elements, causing both possible structural destruction and sound re-emission.

 The present invention is to increase the shielding effect, including at low sound frequencies, as well as the strength of the screen structure.

 This is achieved by the fact that the shell has a streamlined wing-shaped profile, is supported by an internal damped set located between the shells, and the highly elastic material is bonded to the inner shell and partially fills the structure, while the air content of its air cavities is assumed to vary radially so that in the extreme layers it makes up 1-5%, and in the layer of the middle part - 20-50%. There is a fluid gap between the highly elastic material and the outer shell.

 In addition, the outer surface of the outer shell is lined with highly elastic material with air cavities.

 The implementation of the shell of the screen with a streamlined wing-shaped profile allows to reduce turbulent noise when the fluid flows around the screen.

 The reinforcement of the shell with an internal damped set located between the shells provides an improvement in the elastic and dissipative qualities of the structure.

 Changing the total air content of air cavities of highly elastic material in the radial direction from 1-5% in the extreme layers and up to 20-50% in the middle part layer makes it possible to provide sound insulation and sound absorption of the shell in a wide frequency range.

 The presence of a liquid gap between the highly elastic screen material and the outer shell allows the formation of large deformations of the screen structure without destruction and provides acoustic contact of the media.

 The invention is illustrated by drawings, where in FIG. 1 shows a schematic representation of a screen device for sound in a stream, a longitudinal section; in FIG. 2 - theoretical estimates of the effectiveness of one of the options for the proposal.

 The proposed screen for sound in the fluid flow in the direction of flow 1 (Fig. 1) is an annular shell 2 with a streamlined wing-shaped profile having an outer 3 and 4 inner shells of hard material, reinforced by an internal damped set located between the shells, one of the elements of which shown by line 5. Between the outer casing 3 and the highly elastic material there is a liquid in the gap 6. The screen is fixed to the supporting structures with the help of rigid elements 7. The volume of the shell 2 is partially for the thickness H behind filled with highly elastic material 8, 9 with air cavities 10. The air content of the outermost layers of highly elastic material facing the inner 4 and outer 3 shells is 1-5%, and in the middle layer 20-50%, with the outermost layer 9 facing the inner the shell 4, is rigidly connected to the surface of the shell 4, and between the other shell 3 and the highly elastic material 9 there is a gap h.

 The outer shell 3 from the outside can be lined with highly elastic material 11 with air cavities 12.

 The device operates as follows. Under the influence of hydrodynamic forces, significantly weakened by the streamlined wing-shaped profile of the screen, nevertheless arising in the stream, liquid jets are formed, both directly emitting sound energy into the screened area of space, and causing vibrations of the transducer or other screened device. The fight against these phenomena is provided by the introduction of a damped inner set into the screen 2, which reduces vibration, for example, in the form of frames located between the shells and lined with acoustic material. Sound-damping properties of the screen are realized by absorbing sound energy with a volume of highly elastic material. To implement the latter task, highly elastic material 8, 9 with cavities (for example, rubber or thermoplastic elastomer), which has a high coefficient of internal acoustic energy loss, is best suited. The air content of the layers is determined as follows. A decrease in the air content of the extreme layers against the aforementioned (1-5%) leads to an unacceptable decrease in the values of shear deformations in a highly elastic material and, therefore, a decrease in energy absorption. An increase in air content leads to a decrease in sound absorption due to a mismatch in the impedances of the layers and water.

 To increase the effectiveness of the proposed design, a soundproofing layer 8 is introduced into the middle part of the array of highly elastic material, which prevents the penetration of sound through the screen. The choice of air content of this layer (20-50%) is determined as follows. Reducing the air content against the named leads to an unacceptable reduction in sound attenuation. The increase in air content relative to the above makes the design statically unstable.

 A layer of fluid 6 between the outer shell and the array of highly elastic material provides acoustic contact of these media without mechanical contact, which could lead to structural damage under conditions of deformation of the highly elastic material under the influence of variable pressure.

 To realize the vibration-damping properties of the structure, the array of highly elastic material 9 is rigidly connected with the inner shell 4, which is most affected by hydrodynamic influences. The minimum energy transfer from the shell 4 to the shell 3 is provided by damping a set 5, for example a set of frames located between the shells, by communicating mechanical losses to it, for example, by facing with an acoustic coating.

 The outer shell 3 from the outside can be lined with highly elastic material 11 with air cavities 12 to create conditions for the penetration of sound energy into the body of the screen (coordination of resistances) and subsequently its absorption in the array of highly elastic material 9.

 In general, the sound-insulating layer 8 serves mainly to increase the noise immunity in the direction perpendicular to the axis of the screen 1, and the sound-absorbing layers 9 cause some screening effect in the axial direction 1. By changing the parameters of the acoustic saturation of the screen and its thickness, it is possible to achieve the maximum effect at a given frequency.

 A theoretical study of the proposed design was carried out with an array of acoustic rubber mass H = 1 m, the extreme layers of rubber had a thickness of 0.2 m and 0.05 m. A flat model of a massif of highly elastic material was used in the calculations, which allows one to estimate the effectiveness of acoustic measures in a wide frequency range. As the calculation showed (Fig. 2), the sound insulation 13 of the screen at low frequencies of the order of 100 Hz is 7 dB and rapidly increases with increasing frequency. The absorption capacity of structure 14 increases from 50% to 98% (at a frequency of 1 kHz). The above calculations allow us to conclude that the screen efficiency in the direction perpendicular to the flow axis is estimated to be of the order of 10 dB or more if there is some effect also in the axial direction.

Claims (2)

 1. The screen for sound in the fluid flow, which is an annular shell, consisting of outer and inner shells of hard material, containing a highly elastic material with sealed air cavities, characterized in that the shell has a streamlined wing-shaped profile, reinforced by an internal damped set located between shells, and highly elastic material bonded to the inner shell and partially fills the shell, and the air content of its air cavities is accepted to vary adialnom direction so that the outer layers, it is at 5.1%, while in the middle part of the layer - 20-50%, and between the elastomeric material and the outer shell has a fluidic gap.  2. The screen for sound in the fluid stream according to claim 1, characterized in that its outer shell on the outside is lined with highly elastic material with air cavities.

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