CN114351607A - Noise reduction structure at top of sound barrier - Google Patents
Noise reduction structure at top of sound barrier Download PDFInfo
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Abstract
The invention relates to a noise reduction structure at the top of a sound barrier, which is formed by combining a perforated plate structure and a secondary remainder diffusion structure, wherein the secondary remainder diffusion structure is composed of a plurality of grooves arranged in a cavity inside the perforated plate structure, and the acoustic impedance of the perforated plate structure is matched with the acoustic impedance of each groove in the secondary remainder diffusion structure. Compared with the prior art, the invention can realize good noise reduction effect in the frequency range of 100-2000 Hz.
Description
Technical Field
The invention belongs to the field of professional noise control of environmental engineering, and particularly relates to a noise reduction structure at the top of a sound barrier.
Background
With the enlargement of urban scale and the improvement of the living standard of people, the environmental noise pollution problem, especially the traffic noise pollution problem, is a hot point problem which is widely concerned by all the communities in recent years. This is because the quantity of motor vehicles and non-motor vehicles has increased sharply in recent decades, and the phenomenon of traffic congestion is becoming more and more serious; meanwhile, the urban traffic noise problem is increasingly serious along with the problems of large-scale expansion of urban area, adjustment of urban area functional layout, position relation between residential areas and roads and the like. In residential areas adjacent to roads, the most common and effective measure at present is to establish a sound barrier in order to reduce the effects of traffic noise. However, the design of part of the sound barrier is not reasonable, and the noise reduction requirement cannot be met after the sound barrier is arranged, so that the improvement of the quality and the efficiency of the sound barrier becomes a difficulty. The noise reduction structure on the top of the sound barrier can reduce the diffracted sound energy on the top of the sound barrier and reduce the sound radiation to the rear of the sound barrier by arranging the noise reduction structure on the top of the existing sound barrier in a targeted manner, thereby effectively improving the noise reduction effect of the existing sound barrier and having good application reference for quality improvement and efficiency improvement of the existing sound barrier and height reduction design and effect improvement of the future sound barrier.
The sound barrier is a special structure made of sound absorption materials and sound insulation materials, is arranged between a noise source and a sound receiving point, and is equipment for preventing direct sound from spreading, isolating transmitted sound and sufficiently attenuating diffracted sound. Behind the barrier, an "acoustic shadow" is formed, in which the noise level is significantly reduced. The construction of the sound barrier blocks the transmission of direct sound, separates a noise source from a protection target, and enables the protection target to fall in a sound shadow area, thereby finally achieving the purpose of reducing the noise. The sound wave transmitted in the air usually generates reflection, transmission, diffraction and other phenomena when contacting the sound barrier, wherein the noise part with higher frequency is easy to attenuate in the transmission process, the low-frequency noise is difficult to attenuate in the transmission process and is easy to diffract and transmit through the top and the side of the sound barrier, and the side diffraction can be ignored because the length of the sound barrier is generally longer, so that the top diffraction becomes the main path for transmitting the low-frequency noise, and the improvement of the noise reduction effect of the sound barrier is greatly limited.
Chinese patent CN201221058Y discloses a sound barrier bifurcated top noise reduction device, which is V-shaped and comprises a V-shaped frame and a sound absorption material cover plate arranged on the V-shaped frame, wherein the V-shaped frame comprises two peripheral thin plates and two inner thin plates, the two inner thin plates are arranged on the peripheral thin plates, the longer thin plate of the two side thin plates is arranged at the front end of the shorter thin plate, and the cover plate is fixedly arranged between the side thin plates and the peripheral thin plates and between the side thin plates and the tops of the side thin plates, thus forming a cavity. However, the patent mainly uses multiple diffraction of sound waves at the edge to improve the noise reduction effect, and still cannot purposely reduce the main frequency band sound energy of diffraction, thereby reducing the sound radiation behind the sound barrier to the greatest extent.
Chinese patent application 2018102454187 discloses a noise reduction structure at the top of a low-frequency anti-diffraction sound barrier, which comprises a protective panel, a cavity and a diffuser structure, wherein the protective panel is connected with the diffuser to form a composite structure, the cavity is arranged in the diffuser structure, and the diffuser structure is connected at the top of the sound barrier. The structure can keep good diffusion performance in a middle and low frequency range due to the composite action of the diffuser structure and the perforated resonance structure, the diffusion coefficient is between 0.8 and 0.95, the noise reduction effect of the structure is excellent, the insertion loss in the frequency range of 100 plus one Hz and 500Hz is averagely improved by 5-9dB after being placed at the top of the sound barrier, the whole insertion loss is improved by 3-7 dB, but the effect is mainly concentrated in the low frequency range (namely the frequency range below 500 Hz), the structure has larger size, the low frequency sound ratio relative to long wavelength is easier to enter, the sound with short wavelength and high frequency is difficult to effectively enter, the uniform diffusion performance of the structure is not good, and the noise main frequency range of the traffic noise mainly acted by the sound barrier measure is 200 plus one 2000Hz, so the action effect cannot completely cover the noise main range, the effect will therefore be reduced.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide a noise barrier top noise reduction structure capable of completely covering the main noise range.
The purpose of the invention can be realized by the following technical scheme: the noise reduction structure at the top of the sound barrier is formed by combining a perforated plate structure and a secondary remainder diffusion structure, the secondary remainder diffusion structure is composed of a plurality of grooves arranged in a cavity inside the perforated plate structure, and the acoustic impedance of the perforated plate structure is matched with the acoustic impedance of each groove in the secondary remainder diffusion structure;
and the acoustic impedance Zn of each groove in the quadratic residue diffusion structure is as follows:
where ρ 0 is the density of the medium, c0Is the speed of the sound wave in the medium, j denotes an imaginary number, dnIs the groove depth of the nth groove, and lambda is the incident wave wavelength;
n is the quadratic residue diffuser order, fr is the design frequency Hz, generally determined by the dominant frequency of the road noise, (N)2modN) is based on the quadratic residue sequence;
acoustic impedance Z of said perforated plate structureiComprises the following steps:
wherein h is the plate thickness of the perforated plate, d is the perforation diameter, σ is the perforation rate of the perforated plate,
μ is the motion viscosity coefficient ═ η/ρ, ρ 0 is the density of the medium, j represents an imaginary number, ω represents the angular frequency ═ 2 π f;
Zn＝Zi。
the acoustic impedance is generally a complex quantity, and is divided into a sum of a real part and an imaginary part, that is, Z ═ R + jX, where the real part R is the acoustic resistance of the acoustic system, and the imaginary part X is the acoustic reactance of the acoustic system, and generally, sound absorption only needs to consider the real part of the acoustic impedance, and sound diffusion only needs to consider the imaginary part of the acoustic impedance. Because the sound diffusion performance of the invention plays a key role in the sound barrier reconstruction effect, the acoustic impedance virtual parts of the grooves of the perforated plate structure and the quadratic residue diffusion structure are used as main calculation basis. Through the calculation of the formula, the acoustic impedance imaginary parts of the two acoustic systems are approximately equal, so that the relevant design size of the top noise reduction structure is determined, and the noise reduction effect is improved.
The perforated plate structure is a cavity structure formed by sealing a top panel, a bottom plate, a front side plate, a rear side plate and a left side plate and a right side plate, wherein the top panel and the front side plate are perforated plates.
The perforated plate has a plate thickness of 0.2-1.2mm, a perforation rate of 0.5-8% and a pore diameter range of 0.3-2 mm.
The quadratic residue diffusion structure comprises a plurality of cavity structures with different depths, and the cavity structures are formed by separating the inner cavities of the perforated plate structure by partition plates.
The width of the cavity structure is controlled to be 2-15 cm; depth of field
N is the quadratic residue diffuser order, fr is the design frequency Hz, generally determined by the dominant frequency of the road noise, (N)2modN) is based on the quadratic residue sequence.
The direction of the cavity structure is parallel to the trend of the screen body.
The bottom of each cavity structure and the bottom plate are provided with drain holes.
The noise reduction structure is connected with the top of the sound barrier screen body through a support and is connected with the stand column through a steel wire safety rope to prevent accidental falling.
The invention makes full use of the synergistic relationship between sound energy diffusion and absorption.
The sound absorption mechanism is that a system formed by each perforation on the perforated plate and the corresponding air layer is similar to a Helmholtz resonator, and the perforated plate resonance sound absorption structure can be understood as parallel connection of a plurality of Helmholtz resonators. When sound waves enter the small holes, the air in the cavity is excited to vibrate, if the frequency of the sound waves is the same as the resonant frequency of the structure, the air in the cavity resonates, the air column at the hole neck of the perforated plate vibrates in a reciprocating mode, the speed and the amplitude reach the maximum values, the friction and the damping are also the maximum values, at the moment, sound energy is converted into heat energy to the maximum extent, namely, the consumed sound energy is the maximum extent, and therefore the efficient sound absorption effect is achieved.
The diffusion principle is as follows: the diffuser is made up of one-dimensional grooves (i.e., a cavity structure) that reduces acoustic diffraction by diffusing the additional acoustic energy into a wide range of directions. In a period, the depth of the groove is different according to the difference of quadratic residue sequences, when sound waves enter the groove, the sound waves bounce from the bottom of the sealed rigid groove to the groove opening, and when the phase difference between the rebounded sound waves and the sound waves just entering the groove is large enough, the structure can enable the reflected sound waves to generate remarkable scattering, so that the reflected sound waves are diffused to different directions.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention utilizes the characteristics that the quadratic residue diffuser has good acoustic scattering property, has uniform diffused sound pressure for incident sound waves in any direction and has wide action frequency band, so that sound energy is diffused to the whole space when passing through the surface of the top noise reduction structure, and then the addition of the perforated plate structure in the composite structure easily destroys the diffusion property of the original quadratic residue diffuser structure, so that the diffracted sound waves can not be uniformly diffused. Therefore, the acoustic impedance of the perforated plate structure and the acoustic impedance of each groove of the quadratic residue diffusion structure are correspondingly approximately equal, so that the top noise reduction structure formed by combining the perforated plate and the quadratic residue diffusion body can be ensured to have the similar diffusion characteristic with the quadratic residue diffusion body in a certain frequency range to a certain extent, the diffusion body structure and the perforated resonance structure are cooperated to reduce noise and increase efficiency, low-frequency sound and high-frequency sound can effectively enter, the diffusion is uniform, and the noise reduction frequency range is expanded.
2. The noise reduction structure is formed by the cooperative complementation of the perforated plate structure and the secondary remainder diffusion structure, and finally the noise reduction structure at the top of the sound barrier with the diffused sound absorption is obtained, so that the noise reduction effect is good, and the good noise reduction effect can be realized in the frequency range of 100-2000 Hz: the insertion loss in the frequency range of 100-2000Hz after the top of the sound barrier is averagely improved by 5-9dB, and the overall insertion loss is improved by 3-7 dB.
Drawings
FIG. 1 is a schematic structural diagram of a noise reduction structure at the top of a sound barrier according to the present invention;
FIG. 2 is a schematic view of a sound diffusing and absorbing structure of a noise reducing structure at the top of a sound barrier according to the present invention;
fig. 3 is a schematic view of a structural back plate of the noise reduction structure on top of the sound barrier of the present invention.
In the figure, the perforated plate structure 1, the top panel 2, the cavity structure 3, the partition plate 4, the inner cavity 5 of the perforated plate structure, the bottom plate 6, the left side plate 7, the right side plate 7, the front side plate 8 and the rear side plate 9.
Detailed Description
The noise reduction structure at the top of the sound barrier is composed of a perforated plate structure and a quadratic residue diffusion structure as shown in figures 1-3.
Wherein perforated plate structure 1 seals the cavity structure of constituteing for top panel 2, bottom plate 6, preceding curb plate 8, posterior lateral plate 9 and left and right sides curb plate 7, and wherein top panel 2 and preceding curb plate 8 are the perforated plate, cover at the upper surface and the front surface of whole structure of making an uproar of falling.
The perforated plate has a plate thickness of 0.2-1.2mm, a perforation rate of 0.5-8% and a pore diameter range of 0.3-2 mm.
The quadratic residue diffusion structure comprises a plurality of cavity structures 3 with different depths, and the cavity structures 3 are formed by separating the inner cavities 5 of the perforated plate structure by partition plates 4. The width of the cavity structure 3 is controlled to be 2-15 cm; the depth dimension does not exceed 30 cm. The direction of the cavity structure 3 is parallel to the trend of the screen body.
The bottom of each cavity structure 3 and the bottom plate 6 are provided with drain holes.
The design of the perforated plate structure and the quadratic residue diffusion structure is determined by the acoustic impedance of the perforated plate structure and the acoustic impedance of each groove in the quadratic residue diffusion structure, namely the imaginary part of the acoustic impedance of each groove of the perforated plate structure and the quadratic residue diffusion structure is used as a main calculation basis.
The local acoustic impedance Zn at the entrance of the single groove of the quadratic residue diffusion structure is obtained by the following formula:
where ρ is0Is the density of the medium, c0Is the speed of the sound wave in the medium, j denotes an imaginary number, dnIs the groove depth of the nth groove, and lambda is the incident wave wavelength;
of the perforated plate structureAcoustic impedance ZiComprises the following steps:
wherein h is the plate thickness of the perforated plate, d is the perforation diameter, σ is the perforation rate of the perforated plate,
mu is motion viscosity coefficient ═ eta/rho, rho0J represents an imaginary number, and ω represents an angular frequency of 2 pi f;
according to the above calculation formula, the imaginary parts of the acoustic impedances of the two acoustic systems are approximately equal, i.e. Zn ═ ZiTherefore, the relevant design size of the top noise reduction structure is determined, and the noise reduction effect of the top noise reduction structure is ensured.
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications can be made by persons skilled in the art without departing from the spirit of the invention. All falling within the scope of the present invention.
Example 1
For absorbing road noise in the frequency range of 100-1000Hz, the frequency is mainly designed to be 500 Hz.
In the embodiment, the noise reduction structure on the top of the barrier is placed in the air to absorb the noise in the frequency range of 100-1000Hz, so that rho0＝1.29kg/m3，c0J is an imaginary number i, where λ is determined from the calculation frequency.
The final calculation yields: the cavity structure 3 of the noise reduction structure at the top of the sound barrier is a 7-order structure, the groove width is 6cm, the depth is 0, 6cm, 24cm, 12cm, 12cm, 24cm and 6cm in sequence, and the cavity structure is a cavity.
Then through the acoustic impedance Z of the perforated plate structureiCalculating the formula:
Zn＝Zi
wherein h is the plate thickness of the perforated plate, d is the perforation diameter, σ is the perforation rate of the perforated plate,
mu is the motion viscosity coefficient eta/rho.
With 500-2000 Hz as the design frequency range, parameters of the perforated plate for matching the acoustic impedance and the impedance of the quadratic residue diffusion structure under the condition of different groove depths are as follows:
| depth of |
6 | 12 | 24 |
| Acoustic impedance | 191.0i | 216.6i | 320.9i |
| Thickness of the perforated plate mm | 0.8 | 0.8 | 0.8 |
| Aperture mm of perforated plate | 0.3 | 0.4 | 0.8 |
| Perforation rate of |
8％ | 4％ | 2％ |
| Frequency of action Hz | 1800 | 950 | 500 |
The plate thickness was 0.8mm, the hole diameter was 0.8mm, the punching rate was 2%, and the squares were arranged. Through tests, before and after the structure is arranged, the insertion loss difference value of a sound receiving point 30m away from the sound barrier within the frequency range of 100-1000Hz at the height of 4.5m from the ground is as follows:
| center frequency/Hz | 100 | 125 | 160 | 200 | 250 | 315 | 400 | 500 | 630 | 800 | 1000 |
| Insertion loss difference/dB | 5.4 | 5.6 | 5.4 | 6.3 | 6.1 | 6.2 | 6.2 | 7.3 | 6.8 | 6.9 | 7.7 |
It can be seen that, by the above impedance matching, the designed noise reduction structure on top of the sound barrier can absorb the noise in the frequency range of 100-1000Hz, and the insertion loss difference is not less than 5.4 dB.
Diffusion coefficient of noise reduction structure at top of sound barrier
| Center frequency/Hz | 100 | 125 | 160 | 200 | 250 | 315 | 400 | 500 | 630 | 800 | 1000 |
| Coefficient of diffusion | 0.88 | 0.88 | 0.86 | 0.85 | 0.97 | 0.87 | 0.90 | 0.82 | 0.84 | 0.85 | 0.85 |
Through the test of an acoustic laboratory, the diffusion coefficient of the noise reduction structure at the top of the sound barrier is basically more than 0.8 in the frequency range of 100-1000 Hz.
The noise reduction structure is connected with the top of the sound barrier screen body through the bracket and is connected with the upright post through the steel wire safety rope to prevent accidental falling.
Example 2
The invention can improve the noise reduction effect and the efficiency of the existing road barrier, for example,
the existing barrier of the road is 3 meters high, and the insertion loss noise reduction amount is about 10 dB. At 20 meters behind the barrier, the sound level measured was 57-59dBA and failed to meet the acoustic quality environmental standards for the area.
The cavity structure 3 of the noise reduction structure at the top of the sound barrier is a 7-order structure, the groove width is 8cm, the depth is 0, 8cm, 32cm, 16cm, 16cm, 32cm and 8cm in sequence, and the cavity structure is a cavity. With 400-1500 Hz as the design frequency range, parameters of the perforated plate for matching the acoustic impedance and the impedance of the quadratic residue diffusion structure under the condition of different groove depths are as follows:
| depth of |
8 | 16 | 32 |
| Acoustic impedance | 320.8i | 230.8i | 432.5i |
| Thickness of the perforated plate mm | 0.8 | 0.8 | 0.8 |
| Aperture mm of perforated plate | 0.5 | 0.6 | 2 |
| Perforation rate of perforated plate | 5.6％ | 3.9％ | 2％ |
| Frequency of action Hz | 1500 | 700 | 400 |
After the noise reduction structure is installed on the top of the original road sound barrier, the sound level at the position 20 meters behind the barrier is reduced to about 50.5dBA, and the corresponding sound quality environmental standard is achieved. Therefore, the noise reduction structure at the top of the sound barrier is beneficial to improving the noise reduction performance of the original sound barrier.
Claims (8)
1. The top noise reduction structure of the sound barrier is characterized by being formed by combining a perforated plate structure and a quadratic residue diffusion structure, wherein the quadratic residue diffusion structure consists of a plurality of grooves arranged in a cavity inside the perforated plate structure, and the acoustic impedance of the perforated plate structure is matched with the acoustic impedance of each groove in the quadratic residue diffusion structure;
and the acoustic impedance Zn of each groove in the quadratic residue diffusion structure is as follows:
where ρ is0Is the density of the medium, c0Is the speed of the sound wave in the medium, j denotes an imaginary number, dnIs the groove depth of the nth groove, and lambda is the incident wave wavelength;
n is the quadratic residue diffuser order, fr is the design frequency Hz, generally determined by the dominant frequency of the road noise, (N)2mod N) is based on the quadratic residue sequence,
acoustic impedance Z of said perforated plate structureiComprises the following steps:
wherein h is the plate thickness of the perforated plate, d is the perforation diameter, σ is the perforation rate of the perforated plate,
mu is motion viscosity coefficient ═ eta/rho, rho0Is the density of the medium, j represents an imaginary number, and ω represents an angular frequency of 2 π f
Zn＝Zi。
2. The noise reduction structure at the top of sound barrier according to claim 1, characterized in that the perforated plate structure is a cavity structure formed by a top panel (2), a bottom plate (6), a front side plate (8), a rear side plate (9) and a left and a right side plates (7) in a closed manner, wherein the top panel (2) and the front side plate (8) are both perforated plates.
3. The noise reduction structure at the top of sound barrier according to claim 2, characterized in that the perforated plate has a plate thickness of 0.2-1.2mm, a perforation rate of 0.5-8% and a pore size in the range of 0.3-2 mm.
4. A sound barrier top noise reducing structure according to claim 1, characterized in that said quadratic residue diffusion structure comprises a plurality of cavity structures (3) of different depths, the cavity structures (3) being formed by partitions (4) separating the inner cavities of the perforated plate structure.
5. A noise reduction structure at the top of a sound barrier according to claim 4, characterized in that the width of said cavity structure (3) is controlled to 2-15 cm; depth of field
N is the quadratic residue diffuser order, fr is the design frequency Hz, generally determined by the dominant frequency of the road noise, (N)2mod N) is based on the quadratic residue sequence.
6. A noise reducing structure on top of a sound barrier according to claim 4, characterized in that said cavity structure (3) is arranged in a direction parallel to the screen body.
7. Noise reduction structure at the top of a sound barrier according to claim 4, characterized in that the bottom of each cavity structure (3) and bottom plate (6) is provided with drainage holes.
8. The noise reduction structure at the top of sound barrier according to claim 1, wherein said noise reduction structure is connected to the top of the sound barrier screen by means of a bracket and is connected to the post by means of a steel wire safety rope to prevent accidental falling.
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Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108396668A (en) * | 2018-03-23 | 2018-08-14 | 上海交通大学 | Denoising structure at the top of the anti-diffraction sound barrier of low frequency |
| CN113529992A (en) * | 2021-07-22 | 2021-10-22 | 江苏佰家丽新材料科技有限公司 | Acoustic wave processing structure and device and preparation method thereof |
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Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108396668A (en) * | 2018-03-23 | 2018-08-14 | 上海交通大学 | Denoising structure at the top of the anti-diffraction sound barrier of low frequency |
| CN113529992A (en) * | 2021-07-22 | 2021-10-22 | 江苏佰家丽新材料科技有限公司 | Acoustic wave processing structure and device and preparation method thereof |
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| 俞悟周: "高架道路渐变空腔微穿孔声屏障的设计和降噪", 《环境污染与防治》 * |
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