CN110807288A - Customizable broadband efficient ventilation sound absorber finite element simulation and demonstration verification method - Google Patents
Customizable broadband efficient ventilation sound absorber finite element simulation and demonstration verification method Download PDFInfo
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Abstract
The invention relates to a customizable broadband efficient ventilation sound absorber finite element simulation and demonstration verification method, which comprises the first step of establishing a 3D simulation model according to the structure and parameters of an efficient ventilation sound absorber and establishing a ventilation pipeline model in COMSOL; secondly, endowing the established 3D simulation model with material characteristics; and thirdly, setting a physical field for the established 3D simulation model, setting the area outside the sound absorber as a sound pressure physical field, and setting the area inside the sound absorber as a hot adhesion physical field, and the like for eight steps. Each sound absorption unit forms a rigid loss oscillator similar to a spring, single-frequency high-efficiency absorption (average absorption rate is more than 95%) and ventilation (wind speed ratio is more than 80%) and broadband high-efficiency absorption (average absorption rate is more than 70%) and ventilation (wind speed ratio is more than 70%) can be realized, and optimal size parameters are customized for the broadband high-efficiency ventilation sound absorber through finite element simulation and sample verification of 3D printer manufacturing.
Description
Technical Field
The invention relates to the technical field of low-frequency noise processing, in particular to a customizable broadband finite element simulation and demonstration verification method for a high-efficiency ventilation sound absorber.
Background
Noise cancellation plays an important role in our daily lives, especially for low frequency noise (between 50 and 1000Hz), and currently achieving effective sound absorption of low frequency noise is still a very difficult task due to its high penetration force.
Over the past two decades, various acoustic metamaterial absorbers have been proposed to overcome the inherent limitations of natural sound absorbing materials when dealing with low frequency sounds (<1000 Hz). Once transmission is blocked, they produce highly efficient absorption at the tailored operating frequency. They can control noise and improve sound environment in severe environments such as humid and narrow spaces, compared to conventional porous materials. However, in everyday life and industry, the generation of noise is often accompanied by an unstable fluid flow, particularly in connection with turbulent flow inside or around pipes, nozzles and turbines. Furthermore, the fluid must have a free passage for the corresponding equipment, device or facility to function properly. Such practices have made many previous metamaterial absorbers impractical because they typically require completely sealed flow channels to eliminate transport. Otherwise, if there is a transmission channel, the absorption rate may be greatly reduced, and usually cannot exceed 50%. Recently, several vented metamaterial absorbers have been proposed whose performance (including operating frequency, bandwidth and maximum absorption) is still unsatisfactory, mainly due to the fact that the maximum absorption cross-section of a single sub-wavelength scattering is only one-fourth of its maximum scattering cross-section. Thus, the absorption of a ventilated acoustic metamaterial composed of sub-wavelength scattering is typically small compared to its reflection.
Disclosure of Invention
The invention aims to provide a finite element simulation and verification method special for low-frequency noise treatment, which can establish a 3D simulation model and a ventilation pipeline model according to a newly designed structure of a broadband high-efficiency ventilation sound absorber, perform finite element simulation of low-frequency noise with different widths, customize optimal size parameters for the broadband high-efficiency ventilation sound absorber, perform demonstration and verification experiments by combining samples, and realize single-frequency high-efficiency absorption (average absorption rate > 95%) and ventilation (wind speed ratio > 80%), high-efficiency absorption (average absorption rate > 70%) and ventilation (wind speed ratio > 70%) for broadband, so as to overcome the defect that the existing acoustic metamaterial needs to completely seal a flow channel to realize perfect sound absorption, and is suitable for noise control of fluid-filled environments such as air conditioners, exhaust hoods, flow channels and the like.
The technical scheme adopted by the invention is as follows: a customizable broadband efficient ventilation sound absorber finite element simulation and demonstration verification method comprises the following steps:
firstly, establishing a 3D simulation model according to the structure and parameters of the high-efficiency ventilation sound absorber, establishing a ventilation pipeline model in COMSOL, and then placing the established 3D simulation model in the established pipeline model;
the high-efficiency ventilation sound absorber comprises a first branch tube resonant cavity and a second branch tube resonant cavity which are symmetrically arranged in parallel front and back, each branch tube resonant cavity consists of an inner frame and an outer frame, the whole part is in a shape like a Chinese character 'hui', and the left side and the right side of each first branch tube resonant cavity and each second branch tube resonant cavity are respectively provided with a cover plate, so that a sound absorption channel is formed between the inner frame and the outer frame; a linear horizontal sound absorption narrow slit is respectively arranged in the middle of the outer frame front side wall, the middle of the inner frame front side wall and the middle of the outer frame rear side wall of the first column splitting pipe resonant cavity, and in the middle of the outer frame front side wall, the middle of the inner frame rear side wall and the middle of the outer frame rear side wall of the second column splitting pipe resonant cavity;
secondly, endowing the established 3D simulation model with material characteristics;
setting a physical field for the established 3D simulation model, setting the outer area of the sound absorber as a sound pressure physical field, setting the inner area of the sound absorber as a hot adhesion physical field, and setting the interface of the two inner and outer areas of the sound absorber as a thermoacoustic coupling boundary;
fourthly, carrying out mesh division on the established 3D simulation model, and constructing a mesh by using a minimum unit of 0.1-0.3 mm and a maximum unit of 20-30 mm;
fifthly, utilizing COMSOL software, continuing to adopt a control variable method to carry out expansion simulation on the high-efficiency ventilation sound absorber, carrying out parametric scanning on the four parameters of a, b, w-chan and w-slit of the 3D simulation model in a unit of mm in consideration of the fact that the sound absorption effect of the 3D simulation model is related to the four parameters of length a, height b, channel width w-chan and narrow slit width w-slit, and finally determining the influence curves of a, b, w-slit and w-chan on the sound absorption effect and the sound absorption frequency according to the parametric scanning result so as to determine the parameter range for realizing the sound absorption effect of more than 95%;
sixthly, manufacturing a high-efficiency ventilation sound absorber to prepare for a demonstration experiment;
manufacturing a high-efficiency ventilation sound absorber sample by adopting a photosensitive resin 3D printer according to the parameter range finally determined by the 3D simulation model;
seventhly, performing acoustic measurement demonstration experiments;
the acoustic measurement of a sample is carried out in a square impedance tube, and is completed by a full-frequency loudspeaker, four microphones, a power amplifier and a data acquisition analyzer in a matching way, the square impedance tube consists of two aluminum square tubes, an aluminum plate with the thickness of 3 mm-5 mm is used as a rigid back plate to simulate an acoustic hard boundary terminal, and after the aluminum plate is detached, sound in the square impedance tube can radiate outwards, so that an acoustic terminal with an open boundary is simulated, and the square impedance tube serves as two different terminal loads in the measurement;
placing a sample in a square impedance tube by a four-microphone transmission measurement method, placing a full-frequency loudspeaker at one end of the square impedance tube, placing a rigid back plate at the other end of the square impedance tube, and respectively fixing four microphones on the square impedance tube to verify the sound absorption effect;
eighthly, a ventilation measurement demonstration experiment is carried out;
the ventilation measurement of the sample is also carried out in the square impedance tube and is completed by matching an electric fan and an anemometer, wherein the anemometer is used for the air flow speed at the outlet of the square impedance tube, and the electric fan is positioned at the inlet;
placing a sample in a square impedance tube by a four-microphone transmission measurement method, placing an electric fan at an inlet, placing an anemometer at an outlet, dividing the cross section of the square impedance tube into 9 regions of 3 x 3, placing the anemometers in the 9 regions respectively, and calculating and reading the average wind speed when the sample is placed; and taking out the sample in the square impedance tube, calculating the average wind speed when the sample is not placed in the same way, and defining the wind speed ratio g as the ratio of the average wind speed when the sample is placed divided by the average wind speed when the sample is not placed.
Preferably, in the sixth step, the 3D printer is used with a precision of 0.1mm, the photosensitive resin has an elastic modulus of 2.46GPa and a density of 1.10g/cm3。
Preferably, in the seventh step, the aluminum square pipe has an inner cross-section of 147 × 147mm2The thickness of the tube is 5 mm; the rigid back plate is an aluminum plate with the thickness of 4 mm; the full-frequency loudspeaker adopts Chinese M5N, HiVi; the four microphones adopt Chinese BSWA, MP 418; the power amplifier adopts Chinese Aigtek, ATA 304; the data acquisition analyzer adopts Chinese BSWA, MC 3242.
Preferably, in the eighth step, the maximum air volume of the electric fan is 3.7 × 103m3The air speed meter adopts China TM856 and TECMAN, and the gap between the fan and the impedance tube is sealed by sponge to form a ventilation pipeline system.
The invention has the beneficial effects that: the broadband efficient ventilation sound absorber adopts two weakly coupled branch tube resonant cavities which are respectively in a shape of a Chinese character 'hui', and combines a sound absorption channel formed by a cover plate and a plurality of horizontal sound absorption narrow slits in a shape of a Chinese character 'yi', so that each sound absorption unit forms a rigid loss oscillator similar to a spring, which is used for being installed in an open airflow channel with a larger cross section, can realize single-frequency efficient absorption (average absorption rate is more than 95%) and ventilation (wind speed ratio is more than 80%), and can realize broadband efficient absorption (average absorption rate is more than 70%) and ventilation (wind speed ratio is more than 70%), thereby overcoming the technical bottleneck that the existing acoustic metamaterial needs to completely seal a flow channel to realize perfect sound absorption but cannot meet ventilation, and the broadband efficient ventilation sound absorber is particularly suitable for noise control of fluid-filled environments such as air conditioners, exhaust hoods, flow channels and the like; according to the invention, through finite element simulation and sample verification of 3D printer manufacturing, for low-frequency sound waves, the optimal size range of the high-efficiency ventilation sound absorber for specific single-frequency or broadband sound absorption is found, so that the customization of the broadband high-efficiency ventilation sound absorber is realized.
Drawings
Fig. 1 is a perspective view of a high efficiency ventilation sound absorber.
Fig. 2 is a left/right side view of the high efficiency ventilation sound absorber (excluding the cover plate).
Fig. 3 is a sectional view of a plurality of high efficiency ventilation sound absorbers installed in an airflow passage.
Figure 4 is a theoretical support schematic for a high efficiency ventilation sound absorber.
Fig. 5 is an acoustic measurement demonstration experimental state.
Fig. 6 is a state of a ventilation measurement demonstration experiment.
Detailed Description
The invention will be further illustrated by the following examples in conjunction with the accompanying drawings:
referring to fig. 1 and 2, a high-efficiency ventilation sound absorber is composed of a first shell-and-tube resonator 1 and a second shell-and-tube resonator 2, which are symmetrically arranged in front and back in parallel. Each of the tube array resonators 1 is composed of an inner frame and an outer frame, and the whole body is in a shape of a Chinese character 'hui'. The left and right sides of the first and second column resonator cavities 1 and 2 are equipped with cover plates (not shown in the figure), so that a sound absorption channel is formed between the inner frame and the outer frame.
The middle parts of the front side wall of the outer frame, the front side wall of the inner frame and the rear side wall of the outer frame of the first column splitting pipe resonant cavity 1, and the middle parts of the front side wall of the outer frame, the rear side wall of the inner frame and the rear side wall of the outer frame of the second column splitting pipe resonant cavity 2 are respectively provided with a horizontal sound absorption narrow slit in the shape of a Chinese character 'yi'.
As shown in fig. 3, a plurality of high-efficiency ventilation sound absorbers a are fixedly installed in an open-ventilation air flow passage B, and the number of the high-efficiency ventilation sound absorbers a is determined according to the cross-sectional size of the air flow passage B.
The cross section of the high-efficiency ventilation sound absorber A is smaller than that of the airflow channel B, so that an airflow passing space C is formed between the inner wall of the airflow channel B and the outer wall of the high-efficiency ventilation sound absorber A. The high-efficiency ventilation sound absorber A is composed of a weakly-coupled split pipe resonant cavity, and the sound absorption and ventilation effects of the high-efficiency ventilation sound absorber A are proved through numerical calculation and experimental measurement, so that the low-frequency high-efficiency absorption (> 95%) and ventilation (> 80% of wind speed ratio) can be realized, and the broadband absorption is realized by optimally stacking the high-efficiency ventilation sound absorbers A with different resonant frequencies. An air flow passing space C is formed above each high-efficiency ventilation sound absorber A, and the cover plates 3 are arranged on the left side and the right side of each high-efficiency ventilation sound absorber A and just seal the left end and the right end of each high-efficiency ventilation sound absorber A.
The following is a theoretical description of the high efficiency ventilation sound absorber.
As shown in fig. 4, each high efficiency ventilation sound absorber (hereinafter referred to as "UVMA unit") constitutes a rigid loss oscillator similar to a spring.
(a) Cross-section (xz-plane) of the UVMA cell, the effective model of which includes the lossy mass and the spring. The subscripts indicate each columnated tube resonator (1, input side; 2, output side). (b) Simulated (solid line) and fitted (scattered) absorption spectra (w) of UVMA units by (S11) equationchan1.5mm and wchanWhen 3.5 mm). (c) Ratio k obtained from the simulationc/(ηr+ηl). (d) The frequency of the absorption peak obtained from the simulation.
To build an efficient model to analyze the interaction between the two resonators, we modeled the UVMA cell as two coupled loss oscillators, each with a mass m and a spring constant k, as shown in fig. 4 (a). The equation describes the motion of the coupled loss oscillator under the action of external force
The different resonators (1, input side; 2, output side), x, being denoted by the subscriptsiAmplitude of representation, ηlLoss of hot tack, ηrTypical radiation losses, ηcRepresenting the radiative coupling between two resonators, andFiThe force acting on the ith resonator simulates the corresponding resonator, a single set of coupled resonators, or an array of coupled resonators, may be simulatedPeriodically, result in ηrAnd ηcThe difference in (c). For further analysis, we assume a factor e of the time domain wavelength-iωtConverting this equation into the frequency domain
Ratio to amplitude XijIs defined as Xij＝xi/xjTherefore, the
From this we get x1And x2Expression (2)
Can be pushed out
Ratio of forces Fij＝Fi/FjAnd X12＝1/X21Solving equation Eq (S5) yields X21Explicit equation of
Parameter(s)
The natural frequency of the frequency at which the frequency is constant,then, the average dissipation power of the vibrator in a period of time is obtained
For single-edge incidence, it can be seen as a linear superposition of symmetric and anti-symmetric incidence, so we denote the external force as F, respectively1＝pS0And F 20, wherein S0Is the effective area of the resonator and p is the incident sound pressure. F21When 0, the dissipated power is
And
on the other hand, its incident power can be expressed as
Wherein SincIs the area of the incident channel and Z is the acoustic impedance. The absorption coefficient of the oscillator is therefore equal to the ratio of the dissipated power to the incident power
Damping attenuation of reference radiation in the absence of transmission
It is apparent that the maximum or minimum absorption occurs at frequencies that satisfy the conditions
To make it possible to get an intuitive analyzable analysis, we consider the deep sub-wavelength case such that ηrBeing purely real, ηc＝iκcIs a pure imaginary number. After complicated algebraic operation, it was found (S12) that the result could be obtained directly
ω＝ω0(S13)
Other solutions are determined by this equation
In fact, when equation Eq (S14) has a real solution, the absorption spectrum will be at ω0The existence of a real number solution deduces the inequality
Wherein the content of the first and second substances,
to obtain
Through a series of algebraic transformations to obtain
Wherein
Maximum absorption AmaxIs that
Equations Eqs, (S16) and (S19) confirm that the splitting of the maximum absorption observed at FIG. 3 is due to the maximum coupled radiation of the two resonators
On the other hand, if the radiation is coupled κcBecome sufficiently small, e.g.
Equation eq. (S14) has no real solution, and the two absorption peaks will be degenerate. Accordingly, this maximum absorption AmaxWill be at ω0Has an absorption value equal to
Note 2.Emergence of 90-phase difference occurrence and peak of sound absorption combination
As mentioned above, the combination of the two absorption peaks results in the maximum absorption occurring at ω0For ω0By (angular) frequency in the vicinity, we mean ω ═ ω0+ δ ω, the vibration rate of one-sided incidence can be expressed as
We ignore its higher order terms X21,0At the resonance omega0Exactly-90 deg., the second resonator being phase-retarded with respect to the resonator on which the first incident wave was incident.
A customizable broadband efficient ventilation sound absorber finite element simulation and demonstration verification method comprises the following steps:
firstly, establishing a 3D simulation model according to the structure and parameters of the high-efficiency ventilation sound absorber, establishing a ventilation pipeline model in COMSOL, and then placing the established 3D simulation model in the established pipeline model;
secondly, endowing the established 3D simulation model with material characteristics;
setting a physical field for the established 3D simulation model, setting the outer area of the sound absorber as a sound pressure physical field, setting the inner area of the sound absorber as a hot adhesion physical field, and setting the interface of the two inner and outer areas of the sound absorber as a thermoacoustic coupling boundary;
fourthly, carrying out mesh division on the established 3D simulation model, and constructing a mesh by using a minimum unit of 0.1-0.3 mm and a maximum unit of 20-30 mm;
fifthly, utilizing COMSOL software, continuing to adopt a control variable method to carry out expansion simulation on the high-efficiency ventilation sound absorber, carrying out parametric scanning on the four parameters of a, b, w-chan and w-slit of the 3D simulation model in a unit of mm in consideration of the fact that the sound absorption effect of the 3D simulation model is related to the four parameters of length a, height b, channel width w-chan and narrow slit width w-slit, and finally determining the influence curves of a, b, w-slit and w-chan on the sound absorption effect and the sound absorption frequency according to the parametric scanning result, and finally determining the parameter range for realizing the sound absorption effect of more than 95%;
sixthly, manufacturing a high-efficiency ventilation sound absorber to prepare for a demonstration experiment;
manufacturing a high-efficiency ventilation sound absorber sample by adopting a photosensitive resin 3D printer according to the parameter range finally determined by the 3D simulation model;
seventhly, performing acoustic measurement demonstration experiments;
as shown in fig. 5, the acoustic measurement of the sample D is performed in a square impedance tube 4, and is completed by matching a full-frequency speaker 5, four microphones 6, a power amplifier and a data acquisition analyzer (not shown in the figure), the square impedance tube is composed of two aluminum square tubes, an aluminum plate with a thickness of 3 mm-5 mm is used as a rigid back plate 7 to simulate an acoustic hard boundary terminal, and after the aluminum plate is removed, sound in the square impedance tube is radiated outwards, so that an acoustic terminal with an open boundary is simulated, and the square impedance tube serves as two different terminal loads during the measurement;
placing a sample in a square impedance tube by a four-microphone transmission measurement method, placing a full-frequency loudspeaker at one end of the square impedance tube, placing a rigid back plate at the other end of the square impedance tube, and respectively fixing four microphones on the square impedance tube to verify the sound absorption effect;
eighthly, a ventilation measurement demonstration experiment is carried out;
as shown in fig. 6, the ventilation measurement of sample D was also performed in the square impedance tube 4 and completed with an electric fan 8, an anemometer 9, which is used for the air velocity at the outlet of the square impedance tube, and the electric fan is located at the inlet;
placing a sample in a square impedance tube by a four-microphone transmission measurement method, placing an electric fan at an inlet, placing an anemometer at an outlet, dividing the cross section of the square impedance tube into 9 regions of 3 x 3, placing the anemometers in the 9 regions respectively, and calculating and reading the average wind speed when the sample is placed; and taking out the sample in the square impedance tube, calculating the average wind speed when the sample is not placed in the same way, and defining the wind speed ratio g as the ratio of the average wind speed when the sample is placed divided by the average wind speed when the sample is not placed.
In the sixth step, the precision of the 3D printer used was 0.1mm, the elastic modulus of the photosensitive resin was 2.46GPa, and the density was 1.10g/cm3。
In the seventh step, the inner cross section of the aluminum square tube was 147X 147mm2The thickness of the tube is 5 mm; the rigid back plate is an aluminum plate with the thickness of 4 mm; the full-frequency loudspeaker adopts Chinese M5N, HiVi; the four microphones adopt Chinese BSWA, MP 418; the power amplifier adopts Chinese Aigtek, ATA 304; the data acquisition analyzer adopts Chinese BSWA, MC 3242.
In the eighth step, the maximum air quantity of the electric fan is 3.7 multiplied by 103m3The wind gauge is sealed with sponge in the gap between the fan and the impedance tube by using Chinese TM856 and TECMAN.
As shown in fig. 3, the cavity area above the frame allows various fluids (e.g., air or water) to freely pass through the structure. The structure is assumed to be submerged in air. The sound waves incident on the UVMA unit are perfectly absorbed, thereby achieving both effective absorption and ventilation. As shown, the UVMA units are packaged in a crystal lattice shape with the fluid flow direction being the z-direction, the height direction being the x-direction, and the width direction being the y-direction. A ventilation and sound absorption structure composed of four UVMA units with lattice constants of L and L/4 in x and y directions respectively shows a split-tube resonator with anti-symmetric characteristics. Operating at low frequencies, the appropriate geometry of the UVMA unit is determined so that the UVMA unit should have both efficient absorption and ventilation functions for low frequency sound waves. Experimental verification was then performed using the setup shown in fig. 5 and 6.
Numerical study of UVMA design strategy
To investigate the effect of geometric parameters on UVMA sound absorption performance, full wave numerical simulations were performed. Due to energy conservation, taking the complex transmission coefficient t and the reflection coefficient r and the absorption coefficient A can obtain A ═ 1- | t |2-|r|2. The key geometric parameters (shown in fig. 1-3) are the length a, height b, width of the channel w-chan and the width of the narrow slot w-slit, which effectively change the acoustic performance of the UVMA. First, the length a is considered while determining other parameters (b 40mm, wchan 1.4mm, wslit 1.4 mm). As the length a increases, the resonance shifts to lower frequencies and the absorption approaches 1. Next, considering the height b, as the height b increases, the resonance shifts to a low frequency, and the absorption rate also approaches 1. For the widths of the channel w-chan and the slot w-slit, the sound absorption rate of the UVMA increases significantly as the width of the channel wchan or the slot w-slit decreases, and the resonance also shifts to lower frequencies. When w-chan becomes sufficiently small, the two moderate absorption resonances (-60%) will merge into one near unity peak. Therefore, very narrow channels and slits must be used: (<2.0mm) to ensure effective absorption. Overall, it can be concluded that UVMA sound absorption rate is always efficient (>80%) while its resonance frequency can be shifted slightly, e.g. to adjust the length a and the height b, while maintaining the narrow channel w-chan and the slit w-slit, which means that it is possible to optimize the absorber for different operating frequencies and ventilation conditions.
Experimental measurements of the acoustic properties of the UVMA unit were made taking into account two samples, labeled sample I (a 100 mm, b 40mm, w-chan 1.4mm, w-slit 1.4mm) and sample II (a 150 mm, b 45 mm, w-chan 1.4mm, w-slit 1.4mm), respectively. The measured transmission and reflectance of the two samples fit well with the simulation results. Both the reflection spectrum and the transmission spectrum show a drop around the resonance frequency, which means efficient absorption. The simulated and measured absorptions indicate quantitative agreement between each other. In the experiment, for samples I (II), the absorbance measured at 637Hz (472Hz) reached 95.6% (96.3%). For reference, the acoustic properties of two top quality sound absorbing sponges (baseect G +, basf, germany) were also measured. They are labeled foam I and foam II, have the same dimensions as sample I and sample II, respectively, and the UVMA cell clearly shows superior acoustic performance near resonance compared to commercially available foams. It is more advantageous if the data is plotted in dB.
For tailored broadband sound absorption, the causal nature of the acoustic response imposes a basic inequality that is related to the two most important aspects of sound absorption: absorption spectrum and absorber length.
Wherein a isminIs the minimum absorption thickness, B0Is the bulk modulus of the background fluid (air), BeffIs the effective bulk modulus of the metamaterial within the static limits, a (λ) is the absorption spectrum, and λ is the acoustic length. For a broadband absorber consisting of a limited number (N) of absorption cells, its resonant frequencies should be spaced exponentially for optimum performance.
Thus, the resonant frequency should be chosen as: n is 1 to N, f0Is the cutoff frequency and phi is a coefficient determined by the target frequency band. By this relationship, a wideband UVMA unit is constructed in the target frequency band. Considering the trade-off between absorption and ventilation, and maintaining effective ventilation, a broadband UVMA consisting of seven units is considered. For example, the 478-724Hz band is targeted and the resonant frequencies of the cells are selected to be 478Hz, 512Hz, 549Hz, 588Hz, 630Hz, 676Hz and 724 Hz. In the simulation, the operating bandwidth was 465-765Hz (defined as the frequency at which the absorption exceeds 50%), corresponding to a larger bandwidth factor of 48.8%. Meanwhile, in the experiment, the operating frequency bandwidth is 476-726Hz, and the corresponding bandwidth coefficient is 41.6%. The designed absorber has successfully covered the target frequency band, which has a simulated (measured) average absorption of 94.3% (93.9%). Minor differences can be attributed to manufacturing and measurement errors during the experimental process on the one handThe difference, and on the other hand the assumption of infinite acoustic impedance for a solid in the simulation. Nevertheless, at an open area ratio of 52.4%, the results confirmed that the stacking scheme has formed a wide band.
There is a clear tradeoff between bandwidth and average absorption. If a narrower frequency band is used instead (e.g. 478-620Hz), the absorption rate will increase. Using the selected closer resonance frequencies (478Hz, 499Hz, 521Hz, 544Hz, 568Hz, 593Hz, 620Hz), the simulated (measured) average absorption in the target frequency band becomes 95% (96.2%). Furthermore, multiple discrete frequency bands may be targeted. For example, we use the two frequency bands of 478-550Hz and 640-690Hz as the target sound absorption, and select the resonant frequencies of the first frequency band as (478Hz, 501Hz, 525Hz, 550Hz), and the resonant frequencies of the second frequency band as (640Hz, 665Hz, 690 Hz). The average absorbance of the two bands was 83.1% (78.1%). The results demonstrate that it is possible to design a UVMA with a tailored operating band, while allowing sound to pass from the desired frequencies.
The ventilation performance of the UVMA unit is characterized by its wind speed ratio, defined as the ratio of wind speeds with and without wind, demonstrating that the structure achieves efficient ventilation while maintaining nearly perfect low frequency sound absorption.
Claims (4)
1. A customizable broadband efficient ventilation sound absorber finite element simulation and demonstration verification method is characterized by comprising the following steps:
firstly, establishing a 3D simulation model according to the structure and parameters of the high-efficiency ventilation sound absorber, establishing a ventilation pipeline model in COMSOL, and then placing the established 3D simulation model in the established pipeline model;
the high-efficiency ventilation sound absorber comprises a first branch tube resonant cavity (1) and a second branch tube resonant cavity (2) which are symmetrically arranged in parallel front and back, each branch tube resonant cavity (1) is composed of an inner frame and an outer frame and is in a shape like a Chinese character 'hui', and cover plates are arranged on the left side and the right side of each of the first branch tube resonant cavity and the second branch tube resonant cavity (1 and 2), so that a sound absorption channel (a) is formed between the inner frame and the outer frame; a linear horizontal sound absorption narrow slit (b) is respectively arranged in the middle of the outer frame front side wall, the middle of the inner frame front side wall and the middle of the outer frame rear side wall of the first microtube resonant cavity (1), and in the middle of the outer frame front side wall, the middle of the inner frame rear side wall and the middle of the outer frame rear side wall of the second microtube resonant cavity (2);
secondly, endowing the established 3D simulation model with material characteristics;
setting a physical field for the established 3D simulation model, setting the outer area of the sound absorber as a sound pressure physical field, setting the inner area of the sound absorber as a hot adhesion physical field, and setting the interface of the two inner and outer areas of the sound absorber as a thermoacoustic coupling boundary;
fourthly, carrying out mesh division on the established 3D simulation model, and constructing a mesh by using a minimum unit of 0.1-0.3 mm and a maximum unit of 20-30 mm;
fifthly, utilizing COMSOL software, continuing to adopt a control variable method to carry out expansion simulation on the high-efficiency ventilation sound absorber, carrying out parametric scanning on the four parameters of a, b, w-chan and w-slit of the 3D simulation model in a unit of mm in consideration of the fact that the sound absorption effect of the 3D simulation model is related to the four parameters of length a, height b, channel width w-chan and narrow slit width w-slit, and finally determining the influence curves of a, b, w-slit and w-chan on the sound absorption effect and the sound absorption frequency according to the parametric scanning result, and finally determining the parameter range for realizing the sound absorption effect of more than 95%;
sixthly, manufacturing a high-efficiency ventilation sound absorber to prepare for a demonstration experiment;
manufacturing a high-efficiency ventilation sound absorber sample by adopting a photosensitive resin 3D printer according to the parameter range finally determined by the 3D simulation model;
seventhly, performing acoustic measurement demonstration experiments;
the acoustic measurement of a sample is carried out in a square impedance tube, and is completed by a full-frequency loudspeaker, four microphones, a power amplifier and a data acquisition analyzer in a matching way, the square impedance tube consists of two aluminum square tubes, an aluminum plate with the thickness of 3 mm-5 mm is used as a rigid back plate to simulate an acoustic hard boundary terminal, and after the aluminum plate is detached, sound in the square impedance tube can radiate outwards, so that an acoustic terminal with an open boundary is simulated, and the square impedance tube serves as two different terminal loads in the measurement;
placing a sample in a square impedance tube by a four-microphone transmission measurement method, placing a full-frequency loudspeaker at one end of the square impedance tube, placing a rigid back plate at the other end of the square impedance tube, and respectively fixing four microphones on the square impedance tube to verify the sound absorption effect;
eighthly, a ventilation measurement demonstration experiment is carried out;
the ventilation measurement of the sample is also carried out in the square impedance tube and is completed by matching an electric fan and an anemometer, wherein the anemometer is used for the air flow speed at the outlet of the square impedance tube, and the electric fan is positioned at the inlet;
placing a sample in a square impedance tube by a four-microphone transmission measurement method, placing an electric fan at an inlet, placing an anemometer at an outlet, dividing the cross section of the square impedance tube into 9 regions of 3 x 3, placing the anemometers in the 9 regions respectively, and calculating and reading the average wind speed when the sample is placed; and taking out the sample in the square impedance tube, calculating the average wind speed when the sample is not placed in the same way, and defining the wind speed ratio g as the ratio of the average wind speed when the sample is placed divided by the average wind speed when the sample is not placed.
2. The customizable broadband efficient ventilation sound absorber finite element simulation and demonstration verification method of claim 1, wherein: in the sixth step, the precision of the 3D printer is 0.1mm, the elastic modulus of the photosensitive resin is 2.46GPa, and the density is 1.10g/cm3。
3. The customizable broadband efficient ventilation sound absorber finite element simulation and demonstration verification method of claim 1, wherein: in the seventh step, the inner section of the aluminum square pipe is 147 × 147mm2The thickness of the tube is 5 mm; the rigid back plate is an aluminum plate with the thickness of 4 mm; the full-frequency loudspeaker adopts Chinese M5N, HiVi; the four microphones adopt Chinese BSWA, MP 418; the power amplifier adopts Chinese Aigtek, ATA 304; the data acquisition analyzer adopts Chinese BSWA, MC 3242.
4. The customizable broadband efficient ventilation sound absorber finite element simulation and demonstration verification method of claim 1, wherein: in the eighth step, the maximum air quantity of the electric fan is 3.7 multiplied by 103m3The wind gauge is sealed with sponge in the gap between the fan and the impedance tube by using Chinese TM856 and TECMAN.
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