CN117877451A - Frequency-adjustable modularized low-frequency noise reduction structure - Google Patents
Frequency-adjustable modularized low-frequency noise reduction structure Download PDFInfo
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- CN117877451A CN117877451A CN202311635400.5A CN202311635400A CN117877451A CN 117877451 A CN117877451 A CN 117877451A CN 202311635400 A CN202311635400 A CN 202311635400A CN 117877451 A CN117877451 A CN 117877451A
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/172—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using resonance effects
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/162—Selection of materials
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Abstract
The application discloses a frequency-adjustable modularized low-frequency noise reduction structure in the technical field of environmental engineering, which comprises a plurality of sound absorption units, wherein each sound absorption unit consists of a top plate, a hollow spiral pipeline, a shell and a bottom plate; the shell is provided with a containing cavity, and the containing cavity is provided with a top plate and a bottom plate which are arranged at intervals along the vertical direction; a perforation is arranged in the center of the top plate and is parallel to the bottom plate; the bottom surface of the shell is provided with a snapping device, and the bottom plate is assembled with the shell through the snapping device; the hollow spiral pipeline is of a spiral structure and is positioned in the accommodating cavity of the shell, and the horizontal outlet is communicated with the accommodating cavity; the hollow spiral pipe is connected with the top plate through gluing and is aligned with the perforation center of the top plate. The invention has the advantages of modularized assembly, convenient disassembly and assembly, and frequency-adjustable sound absorption and noise reduction effects by replacing the bottom plate.
Description
Technical Field
The application relates to the technical field of environmental engineering, in particular to a modularized low-frequency noise reduction structure with adjustable frequency.
Background
When working in a noisy environment for a long time, the human body can be injured by hearing, cardiovascular and cerebrovascular systems, nerves and eyesight, and normal life, work and study of people are interfered, so that various accidents can be caused. There is therefore an urgent need for a better solution to suppress and cancel noise.
In order to solve the problems encountered in the conventional noise control engineering, some sound absorbing structures such as porous material sound absorbing structures, resonance sound absorbing structures, and microperforated panel sound absorbing structures have been proposed. The porous material sound absorption structure comprises a sound absorption plate structure, a space sound absorber and a sound absorption wedge, but the sound absorption plate structure has good sound absorption effect on medium and high frequency noise, and low frequency noise is difficult to absorb through the sound absorption material. By introducing the sound absorption structure with resonance characteristics, the resonance structure has a good sound absorption coefficient only in resonance frequency and a certain adjacent bandwidth due to the narrower bandwidth of the resonance structure, and cannot be adjusted.
Application number 202310302782.3 discloses an underwater sound absorption super structure based on Helmholtz resonance, which occupies a large volume, and although efficient broadband sound absorption can be realized through coupling, the whole thickness of the structure is sacrificed; meanwhile, the whole structure cannot be disassembled, and once the frequency band to be noise reduced deviates, the noise reduction effect is greatly reduced. ZL201911036388 discloses a helmholtz resonator and low frequency broadband sound absorption noise reduction structure based on the helmholtz resonator, combines a plurality of sound absorption units into a sound absorption structure with larger volume, can realize efficient low frequency sound absorption, but when the frequency band to be noise reduced deviates, the length and the sectional area of an embedded pipe inside cannot be conveniently adjusted to change the action frequency band of the sound absorption structure.
In order to solve the problem that the sound absorption structure has a narrower working frequency band, the existing scheme mainly comprises the step of arraying a plurality of sound absorption units to widen the sound absorption frequency band. Coupling is performed with a plurality of resonant systems having different resonant frequencies, thereby achieving a wider operating band. This coupling is direct and efficient. However, the existing modular structure has the structural parameters fixed, and the working frequency band is determined. The structural parameters cannot be conveniently adjusted, so that the acting frequency band is changed, and the reusability of the structure is low.
The information disclosed in this background section is only for enhancement of understanding of the general background of the application and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person of ordinary skill in the art.
Disclosure of Invention
The utility model aims at providing a frequency adjustable modularization low frequency structure of making an uproar falls, modularization equipment, easy dismounting reaches frequency adjustable sound absorption noise reduction's effect through changing the bottom plate.
In order to achieve the above purpose, the present application is implemented by adopting the following technical scheme:
the application provides a modularized low-frequency noise reduction structure with adjustable frequency, which comprises a plurality of sound absorption units, wherein each sound absorption unit consists of a top plate, a hollow spiral pipeline, a shell and a bottom plate;
the shell is provided with a containing cavity, and the containing cavity is provided with a top plate and a bottom plate which are arranged at intervals along the vertical direction; a perforation is arranged in the center of the top plate and is parallel to the bottom plate; the bottom surface of the shell is provided with a snapping device, and the bottom plate is assembled with the shell through the snapping device;
the hollow spiral pipeline is of a spiral structure and is positioned in the accommodating cavity of the shell, and the horizontal outlet is communicated with the accommodating cavity; the hollow spiral pipe is connected with the top plate through gluing and is aligned with the perforation center of the top plate.
In some embodiments, the outer diameter of the shell is less than or equal to the outer diameter of the top plate, and the difference between the inner diameter and the outer diameter of the shell ranges from 3mm to 10mm. The shell has a certain thickness, and the meshing device and the screw hole are conveniently arranged on the tangent plane to seal and fasten.
In some embodiments, the housing wall is solid, the top plate is connected by an upper annular boundary, and the housing has a height greater than the height of the hollow helical tube. Even if the height of the hollow spiral pipe is changed to adjust the specific acoustic impedance ratio, the thickness of the sound absorbing unit is not increased.
In some embodiments, four screw mounting holes are arranged on the lower bottom surface of the shell at intervals of 90 degrees, a circular ring channel with a certain width and a certain depth is arranged between every two adjacent mounting holes, and four screws at intervals of 90 degrees and protruding circular rings corresponding to the width and the depth are arranged on the bottom plate. The two can be firmly meshed, the air tightness is ensured, and repeated disassembly can be realized; the shell is reliably connected with the bottom plate through the screws. Through simple and convenient dismantlement, can change the material that thickness is different or rigidity is different as the bottom plate to the frequency channel that needs to fall noise.
In some embodiments, the neck length of the hollow helical tube and the input end radius of the hollow helical tube, a 1 Output end radius a f Proportional to the ratio. The hollow spiral pipeline is arranged inside the shell, so that the hollow spiral pipeline is not easily damaged by external interference factors, and the safety is ensured. The hollow helical tube extends the length of the neck without increasing the overall structure thickness so that the noise reducing structure has a low acoustic resonance frequency.
In some embodiments, the top plate has an outer diameter greater than the size of the hollow helical tube; the center perforation radius of the top plate is the radius of the top plate
In some embodiments, the base plate is made of PLA or spring steel.
In some embodiments, the base plate is PLA, with a thickness setting in the range of 0.3mm-2mm; the bottom plate is made of spring steel, and the thickness setting range is 0.1mm-0.4mm. In the actual manufacturing process of PLA, the dimension below 0.3mm is not easy to process, and the thickness is too low to cause damage; when the size is larger than 2mm, the sound absorption band and 2mm produce almost the same effects, but increase the manufacturing cost.
In some embodiments, the resonant frequency of the sound absorbing unit is calculated as follows:
wherein M is a Acoustic mass, R, formed for hollow helical pipe a Is acoustic resistance, mainly representing loss of acoustic energy, C couple The sound volume formed by the coupling system is formed by the shell (3) and the bottom plate (4) in a sealing way.
In some embodiments, the sound absorption coefficient of the sound absorption unit is calculated as follows:
Z s ＝Z a s, wherein Z a Is acoustic impedance, Z s S is the sectional area of the incident surface of the sound absorption unit for the acoustic impedance;
relative specific acoustic impedance ratioWherein ρ is 0 For air density, c 0 Is the speed of the sound wave;
acoustic impedance Z a With real and imaginary parts, e.g. R a Representing the real part, X a Representing the imaginary part of the system,
relative specific acoustic impedance ratio
Ratio of acoustic resistivityRatio of sound resistance->
Coefficient of sound absorption
Compared with the prior art, the beneficial effect that this disclosure reached:
1. the material with different thickness or rigidity can be replaced as the bottom plate aiming at the frequency band needing noise reduction through simple disassembly, so that the resonance frequency of the sound absorption unit is changed; the array small-scale device is realized by modularization of a plurality of sound absorption units with different resonance frequencies, so that sound absorption and noise reduction are realized;
2. by introducing the embedded spiral pipeline, the size of the sound absorption unit is reduced, the space occupation problem is effectively solved, and the volume of the sound absorption unit is reduced.
Drawings
In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present disclosure, and other drawings may be obtained according to these drawings without inventive effort to a person of ordinary skill in the art.
FIG. 1 is a schematic view of a sound absorbing unit of the present invention;
FIG. 2 is an exploded schematic view of the sound absorbing unit of the present invention;
FIG. 3 is a schematic view of a housing portion of the present invention;
FIG. 4 is a schematic view of an embodiment of the invention applied to a vent line;
FIG. 5 is a sound-to-electricity analog diagram of the sound absorbing unit of the present invention;
FIG. 6 is a flow chart of finite element simulation analysis of the present invention;
FIG. 7 is a graph of the invention for varying the neck length adjustment acoustic impedance ratio of a hollow helical tube;
FIG. 8 is a graph of the invention for varying the neck length of a hollow helical pipe to adjust the sound absorption coefficient;
FIG. 9 is a graph of the change in the height-adjustment acoustic impedance ratio of a hollow helical tube in accordance with the present invention;
FIG. 10 is a graph of the invention for varying the height adjustment sound absorption coefficient of a hollow helical duct;
FIG. 11 is a graph of the change in the housing height adjustment acoustic impedance ratio of the present invention;
FIG. 12 is a graph of the sound absorption coefficient of the present invention for varying the height of the housing;
FIG. 13 is a graph of the acoustic impedance ratio of the varying base plate thickness of the present invention;
FIG. 14 is a graph of the invention for varying the base plate thickness to adjust the sound absorption coefficient;
FIG. 15 is a graph of the damping-adjusted acoustic impedance ratio of a varied base plate material in accordance with the present invention;
FIG. 16 is a graph of the damping adjustment sound absorption coefficient of a modified floor material of the present invention;
FIG. 17 is a low frequency noise reduction transmissivity diagram of the present invention;
fig. 18 is a low frequency noise reduction transfer rate plot for the frequency bands 100Hz-160Hz of the present invention.
Fig. 19 is a plan view of a helical piping of the present invention.
Reference numerals illustrate:
1-a top plate; 2-hollow spiral pipes; 3-a housing; 4-a bottom plate.
Detailed Description
The following description of the technical solutions in the embodiments of the present disclosure will be made clearly and completely with reference to the accompanying drawings in the embodiments of the present disclosure, and it is apparent that the described embodiments are only some embodiments of the present disclosure, not all embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses.
Examples:
the embodiment provides a modularized low-frequency noise reduction structure with adjustable frequency, which comprises a plurality of sound absorption units, wherein the overall schematic diagram of the sound absorption units is shown in fig. 1, the exploded schematic diagram of the structure is shown in fig. 2, and the sound absorption units consist of a top plate 1, a hollow spiral pipeline 2, a shell 3 and a bottom plate 4;
the shell 3 is provided with a containing cavity, and the containing cavity is provided with a top plate 1 and a bottom plate 4 which are arranged at intervals along the vertical direction; a perforation is arranged in the center of the top plate 1 and is parallel to the bottom plate 4; the lower bottom surface of the shell 3 is provided with a snapping device, and the bottom plate 4 is assembled with the shell 3 through the snapping device;
the hollow spiral pipeline 2 is of a spiral structure and is positioned in the accommodating cavity of the shell, and the horizontal outlet is communicated with the accommodating cavity; the hollow spiral pipe 2 is connected with the top plate 1 by gluing and is aligned with the perforation center of the top plate 1.
In a specific implementation manner of the embodiment of the invention, the outer diameter of the shell 3 is smaller than or equal to the outer diameter of the top plate 1, and the difference between the inner diameter and the outer diameter of the shell 3 is 3-10mm.
The wall of the shell 3 is solid, the top plate 1 is connected through an upper annular boundary, and the height of the shell 3 is larger than that of the hollow spiral pipeline 2.
As shown in fig. 3, four screw mounting holes are provided on the bottom surface of the housing 3 at 90-degree intervals, a circular ring channel having a certain width and depth is provided between adjacent mounting holes, and four screws at 90-degree intervals and protruding circular rings corresponding to the width and depth are provided on the bottom plate 4.
In a specific implementation of the embodiment of the invention, the neck length of the hollow spiral pipe 2 and the input end circle radius a of the hollow spiral pipe 2 1 Output end radius a f Proportional to the ratio. The hollow spiral pipeline 2 is arranged inside the shell 3, is not easily damaged by external interference factors, and ensures safety. The hollow spiral pipeline 2 adopts a spiral neck, and the length of the neck is prolonged under the condition of not increasing the thickness of the whole structure, so that the resonance frequency of the corresponding sound absorption unit is reduced. Sound waves enter from the perforations in the top plate 1 to the upper surface hollow opening of the hollow helical tube 2 and enter the receiving chamber formed by the housing 3 and the bottom plate 4 from the horizontal outlet of the hollow helical tube 2.
In one embodiment of the present invention, the outer diameter of the top plate 1 is larger than the size of the hollow spiral pipe 2; the radius of the central perforation of the top plate 1 is equal to the radius of the top plate 1
The bottom plate 4 is made of PLA or spring steel.
PLA is adopted for the bottom plate 4, and the thickness setting range is 0.3mm-2mm; the bottom plate 4 is made of spring steel, and the thickness setting range is 0.1mm-0.4mm. In the actual manufacturing process of PLA, the dimension below 0.3mm is not easy to process, and the thickness is too low to cause damage; when the size is larger than 2mm, the sound absorption band and 2mm produce almost the same effects, but increase the manufacturing cost.
In a specific implementation manner of the embodiment of the present invention, an approximate calculation formula of the resonance frequency of the sound absorption unit is as follows:
wherein,M a for the acoustic mass, R, of the hollow helical tube 2 a Is acoustic resistance C couple The sound volume formed by the coupling system generated by the sealing of the shell 3 and the bottom plate 4.
The acousto-electric analogy is a theoretical method that relates acoustic vibration theory and circuit theory to each other. Although the circuit and the acoustic vibrations belong to different fields, they can be found to exist mathematically in the same form of differential equation when their laws are carefully studied. Thus, the acoustic vibration system can be analogized by way of a circuit diagram. By this analogy, the behavior of the acoustic vibration system can be analyzed and understood using methods and tools in circuit theory. This analogy is widely used in the field of acoustic and electronic engineering and can help us to better understand and design acoustic systems.
The sound absorption unit in the invention is a basic sound vibration system, when the bottom plate is a hard bottom surface, as shown in fig. 5, a sound-electricity analog diagram of the sound absorption unit is shown, an analog relationship exists between the sound vibration system and a circuit system, the air mass in the hollow spiral pipeline 2 is taken as an inertia term, and can be analogized to an inductance in a circuit and is marked as M a The method comprises the steps of carrying out a first treatment on the surface of the Acoustic resistance is primarily representative of the ability of the structure to transmit acoustic energy, and is analogous to the resistance in a circuit, denoted R a The method comprises the steps of carrying out a first treatment on the surface of the The air in the cavity enclosed by the housing 3 and the bottom plate 4 is analogous to the capacitance in a circuit, denoted C a 。
When the thickness of the bottom plate 4 connected to the case 3 is thinned, it can be acoustically considered that the rigid hard boundary is changed to the flexible boundary, and the additional sound volume brought thereby approximates to that ofAnd produces a coupling of sound and vibration. Where a is the radius of the circular base plate 4 and D is the bending stiffness of the base plate 4, which is influenced by the thickness and material properties of the base plate 4. The total sound volume of the coupling system can be approximately C couple ＝C a +C added When acoustic resistance is not considered, the obtained device resonant frequency is approximatelyTherefore, by changing the thickness of the bottom plate 4, the resonance frequency of the device can be regulated and controlled, thereby affecting the sound absorption performance thereof.
The lumped parameter method is applied when using the acousto-electric analogy method, and thus the frequency is limited to a low frequency. In practical product design, the accurate resonant frequency and sound absorption performance can be obtained through finite element numerical calculation.
In a specific implementation manner of the embodiment of the present invention, the process of calculating the sound absorption coefficient of the sound absorption unit is as follows:
Z s ＝Z a s, wherein Z a Is acoustic impedance, Z s S is the sectional area of the incident surface of the sound absorption unit for the acoustic impedance;
relative specific acoustic impedance ratioWherein ρ is 0 For air density, c 0 Is the speed of the sound wave;
acoustic impedance Z a With real and imaginary parts, e.g. R a Representing the real part, X a Representing the imaginary part of the system,
relative specific acoustic impedance ratio
Ratio of acoustic resistivityRatio of sound resistance->
Coefficient of sound absorption
When the sound absorption unit resonates, x=0, at which point if r=1, the sound absorption coefficient is α=1, i.e., the sound absorption unit achieves perfect sound absorption. Therefore, when the specific acoustic impedance curve is observed, firstly, the frequency corresponding to the specific acoustic impedance X of 0 is found, if the specific acoustic impedance R corresponding to the frequency is closer to 1, the sound absorption effect is better, and when the R value is equal to 1, perfect sound absorption is generated, namely, the incident sound energy is 100% dissipated.
In order to study the sound absorption performance of the designed sound absorption unit, numerical simulation is carried out by adopting finite element simulation software. Fig. 6 is a specific flowchart of the analysis of the sound absorption performance using finite element simulation software, and related steps are described below.
Firstly, a model is built, a cylinder can be used as a basic voxel for the top plate 1, the shell 3 and the bottom plate 4, and a parameter L is defined 0 Parameterized scanning for the height of the housing 3; defining parameter t 1 Parameterized scanning for thickness variation of the base plate 4; defining a damping coefficient for the base plate 4; the neck length of the hollow spiral pipe 2 is set to be equal to the radius a of the circle of the input end 1 And output end circle radius a f Proportional and defining a parameter distance.
To build the helical piping geometry model, using theta_0 to represent its initial angle, theta_0 is fixedly set to 0. Using theta f to represent its termination angle, theta f=2n 1 。
Wherein,the number of turns of the helical pipe is determined. n is n 1 The larger the effective length of the helical piping, the longer. The larger the distance, the shorter the neck length of the hollow helical tube 2. Thus, the neck length of the hollow helical tube 2 is adjusted by modifying the value of distance; defining parameter h 2 For parametrically scanning the height of the hollow helical tube 2.
Then defining material properties, wherein the materials of the top plate 1, the hollow spiral pipeline 2, the shell 3 and the bottom plate 4 are polylactic acid (PLA), and the materials are common materials used for 3D printing at present and have better mechanical strength; the fluid in the central round hole of the top plate 1, the spiral pipeline 2, the hollow sound absorption cavity in the shell and other areas is defined as air, and specific parameters of the materials are shown in table 1.
TABLE 1
After the material properties are set, the corresponding physical fields and boundary conditions are added, and three physical fields of pressure acoustics, thermoadhesion acoustics and solid mechanics are used.
After the mesh division is completed, a corresponding study is added, and the sound absorption performance of the sound absorption unit under the frequency domain condition is mainly studied in the simulation example, so the studied condition is selected as a frequency domain, wherein the studied frequency domain range is 20-200Hz, and the step length of the frequency is 1Hz. Parametric scans can be added to the study, through which the effect of parameter variations on sound absorption performance and acoustic impedance can be explored.
When the neck length of the hollow helical tube 2 was investigated for its influence on sound absorption and acoustic impedance, different distances were scanned because they influence the neck length of the hollow helical tube 2. Fig. 7 shows acoustic impedance curves, wherein the larger the distance, the shorter the neck length of the hollow helical pipe 2, and the shorter the acoustic channel therein, the smaller the corresponding acoustic impedance. Fig. 8 shows a sound absorption curve, as the distance increases, the neck length of the hollow helical pipe 2 becomes shorter, the sound absorption peak frequency gradually increases, and the sound absorption peak is slightly increased, mainly because the neck length of the hollow helical pipe 2 becomes shorter, and the air quality inside the hollow helical pipe 2 decreases, so that the characteristic frequency of the sound absorption unit moves toward a high frequency.
When the influence of the height of the hollow spiral pipe 2 on the sound absorption performance is explored, the height of the hollow spiral pipe 2 is changed, the acoustic impedance ratio change curve is shown in fig. 9, and the higher the height of the hollow spiral pipe 2 is, the corresponding acoustic impedance ratio is reduced, and the sound absorption performance is slightly improved. Fig. 10 shows the sound absorption curve, it can be seen that as the height of the hollow helical tube 2 increases, the peak sound absorption frequency gradually increases from 33Hz to 36Hz, and the peak sound absorption also increases slightly, but the device as a whole is insensitive to variations in this geometric parameter.
When the influence of the height of the housing 3 on the sound absorption performance is investigated, the height of the housing 3 is changed. When the height of the shell 3 is increased, the sound volume of the whole structure is reduced, and the corresponding sound resistance ratio is reduced. The specific acoustic impedance ratio change curve is shown in fig. 11. At the same time, the resonance frequency is lowered, and the peak of sound absorption is slightly raised, as shown in fig. 12.
Thickness t of the bottom plate 4 1 When the acoustic absorption unit changes, other parameters of the acoustic absorption unit are not changed, and the specific acoustic impedance ratio change curve is shown in fig. 13. When the thickness of the bottom plate 4 increases, the rigidity of the bottom plate 4 becomes large, the peak sound absorption frequency of the sound absorption unit gradually increases, and the amplitude slightly increases. As shown in fig. 13 below, as the thickness of the chassis 4 gradually increases, the specific acoustic impedance also decreases. Therefore, the mode of adjusting the thickness of the bottom plate 4 is adopted to realize the frequency band offset of noise reduction.
When the influence of different materials on the sound absorption performance and the sound impedance ratio is studied, as shown in fig. 15, when the specification of the sound absorption unit is unchanged, the sound absorption frequency is almost unchanged along with the change of the damping coefficient damping of the material of the bottom plate 4, and when the damping is increased, the corresponding sound impedance ratio is increased, so that the sound absorption peak value is slightly reduced, but the sound absorption performance is insensitive to the change of the damping parameter as a whole. FIG. 16 shows the sound absorption coefficient curves of a single device designed by the invention under different damping coefficient working conditions.
In order to study the frequency band that a single sound absorption unit can regulate by changing the thickness of the bottom plate 4, the radius of the top plate 1 with perforations is 49mm and the thickness is 3mm by combining the scanning calculation of the above parameters. The outer radius of the shell 3 is 49mm, the inner radius is 46mm, the height is 28mm, and the height of the hollow spiral pipeline 2 is 10mm. Distance is set to 13. PLA is used as the base material. The thickness of a single sound absorption unit is only about 32mm and is far smaller than the wavelength of incident sound, so the sound absorption unit is a sub-wavelength. After the top plate 1 and the hollow spiral pipeline 2 are fixed, the top plate 1 is fixed on the upper annular boundary of the shell 3, and the bottom plate 4 and the shell 3 are assembled through a snapping device, so that a complete sound absorption unit is obtained. The frequency band having the sound absorption coefficient of 0.5 or more when the thickness of the base plate 4 was varied from 0.3mm to 2mm was studied.
As shown in table 2, it can be clearly seen from the table data that the effective regulation and control of the sound absorption frequency range can be achieved by regulating and controlling the thickness of the bottom surface according to the present invention.
| PLA bottom thickness | Frequency range with sound absorption coefficient of 0.5 or above |
| 0.3mm | 23.5Hz-38.5Hz |
| 0.4mm | 36.8Hz-52.5Hz |
| 0.5mm | 51.3Hz-67.2Hz |
| 0.6mm | 66Hz-82Hz |
| 0.7mm | 80Hz-96.6Hz |
| 0.8mm | 92.8Hz-109.2Hz |
| 0.9mm | 104Hz-116Hz |
| 1.0mm | 113Hz-131Hz |
| 1.1mm | 121Hz-138Hz |
| 1.2mm | 127Hz-144.5Hz |
| 1.3mm | 132Hz-149Hz |
| 1.4mm | 136Hz-152.4Hz |
| 1.5mm | 139Hz-154.5Hz |
| 1.6mm | 141Hz-156.5Hz |
| 1.7mm | 142.5Hz-158Hz |
| 1.8mm | 144Hz-159Hz |
| 1.9mm | 145.5Hz-160Hz |
| 2.0mm | 147Hz-161Hz |
TABLE 2
In the simulation, six sound absorption units with different resonance frequencies are obtained by taking six PLA materials with different thicknesses as a bottom plate, and are arranged on a ventilating pipeline as shown in fig. 4, wherein the thicknesses are respectively 0.50mm,0.55mm,0.60mm,0.65mm,0.70mm and 0.75mm. The six sound absorption units are identical in structural parameters except the bottoms. The perforated front panel had a radius of 49.5mm, a thickness of 3mm, a cavity height of 28mm and a coil height of 10mm, and the distance was set to 13.
As shown in fig. 17 below, the percent of passing sound energy of six sound absorbing units is obtained. The percentage of pass acoustic energy is obtained by dividing the transmitted acoustic energy by the incident acoustic energy. The effective noise reduction frequency band (i.e., the corresponding frequency range with a pass rate less than 0.5) is 63Hz-108Hz. Obviously, the smaller the percentage of acoustic energy, the greater the acoustic energy loss, i.e., the better the noise reduction effect.
In another simulation example, noise reduction is performed for the frequency bands 100Hz-160Hz, and the following scheme is given: eight PLA materials with different thicknesses are used as a bottom plate, the thicknesses are respectively 0.8mm,0.92mm,1.08mm,1.26mm,1.42mm,1.58mm,1.74mm and 1.92mm, the rest structural parameters are all consistent, the radius of the top plate 1 is 49mm, the outer diameter of the shell 3 is 49mm, the inner diameter is 46mm, the height is 28mm, the height of the spiral pipeline 2 is 10mm, and the distance is set to 13. The sound absorption and noise reduction system formed by the array of eight sound absorption units is obtained through calculation of finite element simulation software, and effective noise reduction can be realized in the frequency band of 97Hz-169Hz, namely, the corresponding passing sound energy percentage shown in figure 18. At 146Hz frequencies, the sound pressure level may decay by up to 25.2dB.
The greater the thickness of the base plate 4, the greater the rigidity of the base plate and the higher the acoustic resonance frequency of the corresponding device as a whole. When the thickness exceeds the upper limit value, the bottom plate 4 may be regarded as a rigid wall, the corresponding resonance frequency of which does not change any more.
Fig. 19 shows a plan view of the spiral pipe for explaining the input end and the output end.
In the description of the present application, it should be understood that the directions or positional relationships indicated by the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "inner", "outer", etc. are based on the directions or positional relationships shown in the drawings, and are merely used to explain the relative positional relationships, movement conditions, etc. between the components in a particular posture, and if the particular posture is changed, the directional indications are correspondingly changed. It is used solely for convenience in describing the present application and for simplicity of description, and does not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operate in a particular orientation, and thus should not be construed as limiting the present application.
Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first", "a second", etc. may explicitly or implicitly include one or more such feature. In the description of the present disclosure/application, unless otherwise indicated, the meaning of "a plurality" is two or more.
In the description of the present application, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the terms in this application can be understood by those of ordinary skill in the art in a specific context.
The foregoing is merely a preferred embodiment of the present application, and it should be noted that, for a person skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present application, and these improvements and modifications should also be considered as the protection scope of the present application.
Claims (10)
1. The modularized low-frequency noise reduction structure with the adjustable frequency is characterized by comprising a plurality of sound absorption units, wherein each sound absorption unit consists of a top plate (1), a hollow spiral pipeline (2), a shell (3) and a bottom plate (4);
the shell (3) is provided with a containing cavity, and the containing cavity is provided with a top plate (1) and a bottom plate (4) which are arranged at intervals along the vertical direction; a through hole is arranged in the center of the top plate (1) and is parallel to the bottom plate (4); the lower bottom surface of the shell (3) is provided with a snapping device, and the bottom plate (4) is assembled with the shell (3) through the snapping device;
the hollow spiral pipeline (2) is of a spiral structure and is positioned in the accommodating cavity of the shell, and the horizontal outlet is communicated with the accommodating cavity; the hollow spiral pipeline (2) is connected with the top plate (1) through gluing and is aligned with the perforation center of the top plate (1).
2. The frequency-adjustable modularized low-frequency noise reduction structure according to claim 1, wherein the outer diameter of the shell (3) is smaller than or equal to the outer diameter of the top plate (1), and the difference between the inner diameter and the outer diameter of the shell (3) is 3-10mm.
3. The frequency-adjustable modular low-frequency noise reduction structure according to claim 1, characterized in that the housing (3) wall is solid, the top plate (1) is connected by an upper annular boundary, the height of the housing (3) is greater than the height of the hollow helical duct (2).
4. The frequency-adjustable modularized low-frequency noise reduction structure according to claim 1, wherein four screw mounting holes are formed in the lower bottom surface of the shell (3) at intervals of 90 degrees, circular ring channels with certain width and depth are formed between adjacent mounting holes, and four screws at intervals of 90 degrees and protruding circular rings corresponding to the width and the depth are arranged on the bottom plate (4).
5. The frequency-tunable modular low frequency noise reducing structure according to claim 1, wherein the neck length of the hollow helical tube (2) and the input end radius a of the hollow helical tube (2) 1 Output end radius a f Proportional to the ratio.
6. The frequency-tunable modular low-frequency noise reduction structure according to claim 1, characterized in that the outer diameter of the top plate (1) is larger than the size of the hollow helical duct (2); the center perforation radius of the top plate is the radius of the top plate
7. The frequency tunable modular low frequency noise reducing structure of claim 1, wherein the base plate is made of PLA or spring steel.
8. The frequency tunable modular low frequency noise reducing structure according to claim 7, wherein the base plate is PLA and has a thickness ranging from 0.3mm to 2mm; the bottom plate is made of spring steel, and the thickness setting range is 0.1mm-0.4mm.
9. The frequency-tunable modular low-frequency noise reduction structure according to claim 1, wherein a formula for calculating a resonance frequency of the sound absorption unit is as follows:
wherein M is a The acoustic mass, R, formed for a hollow helical pipe (2) a Is acoustic resistance, acoustic resistance mainly representing loss of acoustic energy, C couple The sound volume formed by the coupling system is formed by the shell (3) and the bottom plate (4) in a sealing way.
10. The frequency tunable modular low frequency noise reduction structure of claim 9, wherein the sound absorption coefficient of the sound absorption unit is calculated as follows:
Z s ＝Z a S，
wherein Z is a Is acoustic impedance, Z s S is the sectional area of the incident surface of the sound absorption unit for the acoustic impedance;
relative specific acoustic impedance ratio
Wherein ρ is 0 For air density, c 0 Is the speed of the sound wave;
acoustic impedance Z a With real and imaginary parts, e.g. R a Representing the real part, X a Representing the imaginary part of the system,
relative specific acoustic impedance ratioSpecific acoustic resistivity->Ratio of sound resistance->Sound absorption coefficient->
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