CN112651155A - Finite element simulation and demonstration verification method for ventilation self-adaptive low-frequency efficient sound absorber - Google Patents
Finite element simulation and demonstration verification method for ventilation self-adaptive low-frequency efficient sound absorber Download PDFInfo
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Abstract
The invention discloses a ventilation self-adaptive low-frequency efficient sound absorber finite element simulation and demonstration verification method, which comprises nine steps, wherein in the first step, a 3D simulation model is established according to the structure and parameters of a non-single low-frequency ultra-open ventilation adjustable sound absorption unit, a ventilation pipeline model is established in COMSOL, and then the established 3D simulation model is placed in the established pipeline model; setting a physical field for the established 3D simulation model, setting an outer area of the sound absorber as a sound pressure physical field, setting weak coupling for an interface of two inner areas and outer areas of the sound absorber, and setting a rigid boundary for plane wave radiation; and sixthly, scanning the parameters a according to the determined optimal parameters, and determining the adjustable structure parameter range and the absorption frequency broadband. The finite element simulation of different low-frequency noises can be carried out according to a newly designed non-single low-frequency ultra-open ventilation adjustable sound absorption sheet so as to overcome the defect that the existing ultra-open type high-efficiency ventilation sound absorber can only absorb single low-frequency noises.
Description
Technical Field
The invention relates to the technical field of low-frequency noise processing of non-single frequency, in particular to a finite element simulation and demonstration verification method of a ventilation self-adaptive low-frequency high-efficiency sound absorber, which is suitable for super-open ventilation self-adaptive sound absorption simulation of low-frequency noise processing of non-single frequency.
Background
Noise cancellation plays an important role in our daily lives, especially for low frequency noise of non-unity frequency (between 50 and 1000 Hz), and currently achieving effective sound absorption of low frequency noise is still a very difficult task due to its high penetration force.
The national intellectual property office announces an ultra-open type efficient ventilation sound absorption unit and a sound absorber (ZLCN201911128961.X) on 21.2.2020, two weakly-coupled branch pipe resonant cavities which are in a shape of a Chinese character 'hui' respectively are adopted, 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' are combined, each sound absorption unit forms a rigid loss oscillator similar to a spring and is used for being installed in an open type airflow channel with a larger cross section, efficient absorption and ventilation of low frequency can be achieved, and the technical bottleneck that the existing acoustic metamaterial needs to be completely sealed to flow channels to achieve perfect sound absorption but cannot meet ventilation is overcome. The sound absorption unit can perfectly absorb the low-frequency noise with fixed single frequency, and the sound absorption effect of the variable-frequency low-frequency noise with non-single frequency is greatly reduced. In the practical application process, the noise frequency is changed, and for low-frequency noise with different frequencies, sound absorption units with different sizes and specifications are required to be equipped.
Disclosure of Invention
The invention aims to provide a ventilation self-adaptive low-frequency efficient sound absorber finite element simulation and demonstration verification method, which can establish a 3D simulation model and a ventilation pipeline model according to a newly designed non-single low-frequency ultra-open ventilation adjustable sound absorption sheet structure, perform finite element simulation of low-frequency noise of different frequencies, so as to customize optimal size parameters for the efficient ventilation sound absorber of the noise of different frequencies, perform demonstration verification experiments by combining samples, realize efficient absorption and ventilation of different frequencies, and overcome the defect that the existing ultra-open efficient ventilation sound absorber can only absorb single low-frequency noise.
The technical scheme adopted by the invention is as follows: a ventilation self-adaptive low-frequency efficient 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 a non-single low-frequency ultra-open ventilation adjustable sound absorption unit, establishing a ventilation pipeline model in COMSOL, and then placing the established 3D simulation model in the established pipeline model;
the non-single low-frequency ultra-open ventilation adjustable sound absorption unit comprises a first branch tube resonant cavity and a second branch tube resonant cavity which are symmetrically arranged in front and back side by side, each branch tube resonant cavity consists of an inner cavity and an outer cavity and is in a shape of Chinese character 'hui', and the upper side and the lower side of each of the first branch tube resonant cavity and the second branch tube resonant cavity are respectively provided with a cover plate so as to enclose a sound absorption channel; the middle part of the front side wall of the outer cavity, the middle part of the front side wall of the inner cavity and the middle part of the rear side wall of the outer cavity of the first branch tube resonant cavity are respectively provided with a straight sound absorption narrow slit with the same height as the branch tube resonant cavities, the middle part of the front side wall of the outer cavity, the middle part of the rear side wall of the inner cavity and the middle part of the rear side wall of the outer cavity of the second branch tube resonant cavity are respectively provided with a straight sound absorption narrow slit with the same height as the branch tube resonant cavities, the inner cavity of each branch tube resonant cavity is enclosed by a fixed inner frame and a left pulling adjustable inner frame and a right pulling adjustable outer frame, the outer cavity of each branch tube resonant cavity is enclosed by a fixed outer frame and a left pulling adjustable outer frame and a right pulling adjustable outer frame, the fixed inner frame and the two pulling adjustable inner frames are respectively connected;
secondly, endowing the established 3D simulation model with material characteristics;
setting a physical field for the established 3D simulation model, setting an outer area of the sound absorber as a sound pressure physical field, setting weak coupling for an interface of two inner areas and outer areas of the sound absorber, and setting a rigid boundary for plane wave radiation;
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 to finally determine the parameter range;
sixthly, scanning the parameters a according to the determined optimal parameters to determine an adjustable structure parameter range and an absorption frequency broadband;
seventhly, manufacturing a high-efficiency ventilation sound absorber to prepare for a demonstration experiment;
manufacturing a non-single low-frequency ultra-open ventilation adjustable sound absorption unit sample by adopting a photosensitive resin 3D printer according to a parameter range finally determined by the 3D simulation model;
eighthly, 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;
ninth, 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, an anemometer and a driving motor, wherein the anemometer is used for the air flow speed at the outlet of the square impedance tube, the electric fan is positioned at the inlet, the driving motor is connected with a pull rod of a non-single low-frequency ultra-open ventilation adjustable sound absorption unit, the driving motors at two sides of the first and second split tube resonant cavities synchronously drive the corresponding pull rods respectively and pull the same distance, and the adjustable inner frame and the adjustable outer frame are pulled to synchronously move through the pull rods in the front and back directions so as to simultaneously adjust the sizes of the inner cavity and the outer cavity;
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 wind gauge is sealed with sponge in the gap between the fan and the impedance tube by using Chinese TM856 and TECMAN.
Preferably, in the non-single low-frequency ultra-open ventilation adjustable sound absorption unit, the fixed inner frame and the pull adjustable inner frame are respectively in a 'U' shape, the fixed inner frames of the two split tube resonant cavities are arranged close to and back to each other, inner side legs of the two pull adjustable inner frames of the same split tube resonant cavity are arranged at intervals to just form a 'straight' sound absorption narrow slit, and an outer side leg of each pull adjustable frame is provided with a fork port for inserting a corresponding leg of the fixed frame or a leg belt fork port of the fixed frame is provided with an outer side leg of the corresponding pull adjustable frame for inserting, so that the injector-like structure is formed; the fixed outer frames of the two sub-tube resonant cavities are integrally arranged and integrally in an H shape, a horizontal bar in the middle is provided with a linear sound absorption narrow slit, and two pulling adjustable outer frames of the same sub-tube resonant cavity are arranged at intervals to just form the linear sound absorption narrow slit. The U-shaped structure and the fork leg insertion structure are adopted, so that the adjustment and the guiding are facilitated, the movement stability is ensured, and the left part and the right part are adopted for the adjusting frame, so that a linear sound absorption narrow slit is formed skillfully; the fixed frame of two tubulation resonant cavities sets up as an organic whole, and the wholeness is stronger, and stability is higher in the accommodation process.
Preferably, in the non-single low-frequency ultra-open ventilation adjustable sound absorption unit, the inner side legs of the pulling adjustable inner frame are spaced from the edge of the U-shaped bottom plate by a certain distance so as to increase the distance between the inner side legs of the pulling adjustable inner frame, and the width of the linear sound absorption narrow gap formed at the position is larger than the width of the other linear sound absorption narrow gaps. The inner cavity of the sub-tube resonant cavity is the core part of the sound absorption unit and plays a main role in attenuating air flow, the air flow passes through the narrow slits and then passes through the wide slits before entering the inner cavity of each sub-tube resonant cavity for transition buffering, and the sound absorption effect is obviously enhanced.
The invention has the beneficial effects that: the inner cavity of each sub-tube resonant cavity of the non-single low-frequency ultra-open ventilation adjustable sound absorption unit is defined by a fixed inner frame and a left pulling adjustable inner frame and a right pulling adjustable inner frame, the outer cavity of each sub-tube resonant cavity is defined by a fixed outer frame and a left pulling adjustable outer frame and a right pulling adjustable outer frame, the fixed inner frame and the two pulling adjustable inner frames are respectively connected through a similar injector structure, the adjustable inner frames and the adjustable outer frames are pulled forwards and backwards through a pull rod to move synchronously, the sizes of the inner cavity and the outer cavity can be adjusted simultaneously, the sound absorption and the noise reduction of the same sound absorption unit adapting to different frequencies through adjustment are realized, and the defect that the existing acoustic metamaterial can only be designed. According to the invention, through finite element simulation and sample verification manufactured by a 3D printer, the optimal pulling size is found for low-frequency sound waves with different frequencies, and the sizes of the inner cavity and the outer cavity are adjusted at the same time, so that the sound absorption and noise reduction finite element simulation of the same sound absorption unit adapting to the different frequencies through adjustment is realized.
Drawings
Fig. 1 is a perspective view of a non-unitary low frequency ultra-open ventilation adjustable sound absorbing unit.
Fig. 2 is a top view (two adjustment limit positions) of a non-unitary low frequency ultra-open ventilation adjustable sound absorbing unit.
Fig. 3 is a schematic structural diagram of a low-frequency ultra-open ventilation adaptive sound absorber.
Fig. 4 is a circuit block diagram of an adaptive identification system.
Fig. 5 is a circuit connection diagram of an adaptive identification system.
Detailed Description
The invention will be further illustrated by the following examples in conjunction with the accompanying drawings:
a ventilation self-adaptive low-frequency efficient 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 non-single low-frequency ultra-open ventilation adjustable sound absorption unit A, establishing a ventilation pipeline model in COMSOL, and then placing the established 3D simulation model in the established pipeline model.
Referring to fig. 1 and 2, a non-single low-frequency ultra-open ventilation adjustable sound absorption unit 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 sub-tube resonant cavity is composed of an inner cavity and an outer cavity and 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 first shell front side wall middle part, the first shell front side wall middle part and the first shell rear side wall middle part of the first shell resonant cavity 1, and the second shell front side wall middle part, the first shell rear side wall middle part and the first shell rear side wall middle part of the second shell resonant cavity 2 are respectively provided with a "straight" sound absorption narrow slit having the same height as the shell resonant cavity, which is the same as the super-open ventilation sound absorption unit introduced in the background art, and the description thereof is omitted.
The difference lies in that: the inner cavity of each sub-column tube resonant cavity is enclosed by a fixed inner frame 3 and a left pulling adjustable inner frame 4 and a right pulling adjustable inner frame 4. The outer cavity of each sub-tube resonant cavity is surrounded by a fixed outer frame 5 and a left pulling adjustable outer frame 6 and a right pulling adjustable outer frame 6. The fixed inner frame 3 and the two pulling adjustable inner frames 4 are respectively connected through a similar injector structure, the pulling adjustable inner frames 4 are fixedly connected with the corresponding pulling adjustable outer frames 6 through pull rods 7, and the pull rods 7 extend out of the adjustable outer frames 6. The adjustable inner frame 4 and the adjustable outer frame 6 are pulled back and forth by the pull rod 7 to move synchronously, so that the sizes of the inner cavity and the outer cavity can be adjusted simultaneously.
Preferably, the fixed inner frame 3 and the pulling adjustable inner frame 4 are respectively in a U shape, and the fixed inner frames 3 of the two separate tube resonant cavities are arranged close to and back to each other. The inner legs of two pulling adjustable inner frames 4 of the same column tube resonant cavity are arranged at intervals to form a straight sound absorption narrow slit. The outer leg of each pulling adjustable frame 4 is provided with a fork opening for inserting the corresponding leg of the fixed frame 3, or the leg of the fixed frame 3 is provided with a fork opening for inserting the outer leg of the corresponding pulling adjustable frame 4, thereby forming the structure of the injector. The fixed outer frames 5 of the two sub-tube resonant cavities are integrally arranged and integrally in an H shape, the middle horizontal strip is provided with a linear sound absorption narrow slit, and two pulling adjustable outer frames 6 of the same sub-tube resonant cavity are arranged at intervals to just form the linear sound absorption narrow slit.
In addition, in order to improve the sound absorption effect, a distance is reserved between the inner side legs of the pulling adjustable inner frame 4 and the edge of the U-shaped bottom plate so as to increase the distance between the inner side legs of the two pulling adjustable inner frames 4, and the width of the linear sound absorption narrow slit formed at the position is larger than the width of the rest linear sound absorption narrow slits.
Elastic modulus of materials adopted by the first and second sub-array tube resonant cavities 1 and 22.46GPa and a density of 1.10g/cm3But is not limited thereto.
Secondly, endowing the established 3D simulation model with material characteristics;
setting a physical field for the established 3D simulation model, setting an outer area of the sound absorber as a sound pressure physical field, setting weak coupling for an interface of two inner areas and outer areas of the sound absorber, and setting a rigid boundary for plane wave radiation;
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 to finally determine the parameter range;
sixthly, scanning the parameters a according to the determined optimal parameters to determine an adjustable structure parameter range and an absorption frequency broadband;
seventhly, manufacturing a high-efficiency ventilation sound absorber to prepare for a demonstration experiment;
manufacturing a non-single low-frequency ultra-open ventilation adjustable sound absorption unit A sample by adopting a photosensitive resin 3D printer according to the parameter range finally determined by the 3D simulation model;
eighthly, 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;
ninth, 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, an anemometer and a driving motor, wherein the anemometer is used for the air flow speed at the outlet of the square impedance tube, the electric fan is positioned at the inlet, the driving motor is connected with a pull rod 7 of a non-single low-frequency ultra-open ventilation adjustable sound absorption unit A, the driving motors at the two sides of the first and second branch tube resonant cavities 1 and 2 synchronously drive the corresponding pull rods 7 respectively and pull the same distance, and the adjustable inner frame 4 and the adjustable outer frame 6 are pulled forwards and backwards through the pull rods 7 to synchronously move so as to simultaneously adjust the sizes of the inner cavity and the outer cavity;
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.
With reference to fig. 1 to 3, in practical applications, a non-single low-frequency ultra-open ventilation adjustable sound absorption unit a is fixedly installed in an open ventilation airflow channel B to form a low-frequency ultra-open ventilation adaptive sound absorber. The cross section of the non-single low-frequency ultra-open ventilation adjustable sound absorption unit 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 non-single low-frequency ultra-open ventilation adjustable sound absorption unit A.
At least one row of non-single low-frequency ultra-open ventilation adjustable sound absorption units A close to the wall is arranged in the airflow channel B, each row of non-single low-frequency ultra-open ventilation adjustable sound absorption units A form a non-single low-frequency ultra-open ventilation adjustable sound absorption unit group, the pull rods 7 positioned on the same row are connected into a whole and driven by the same self-adaptive motor, and the whole forms a non-single low-frequency ultra-open ventilation adjustable sound absorber. The number of self-adaptive motors is reduced, and the cost is reduced; and can ensure synchronous movement, and is more convenient for adjustment and control. The number of the non-single low-frequency ultra-open ventilation adjustable sound absorption units A is determined according to the cross-sectional dimension of the airflow channel B.
As shown in fig. 4 to 5, the low-frequency ultra-open ventilation adaptive sound absorber is further equipped with an adaptive recognition system, and the adaptive recognition system includes a microphone module, a single chip microcomputer, and an adaptive motor. The microphone module is used for recognizing an environmental noise signal, then the signal is input into the single chip microcomputer, the single chip microcomputer converts an analog signal of a real world into a digital signal through the ADC chip, the digital signal is subjected to discrete Fourier transform through compiling a single chip microcomputer program and a computer, each harmonic is calculated, a main frequency is calculated, then an output signal of a pulling distance is determined according to the frequency, and then the self-adaptive motor is used for realizing self-adaptive sound absorption and noise reduction through pulling the sound absorption unit.
Claims (6)
1. A ventilation self-adaptive low-frequency efficient 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 a non-single low-frequency ultra-open ventilation adjustable sound absorption unit (A), establishing a ventilation pipeline model in COMSOL, and then placing the established 3D simulation model in the established pipeline model;
the non-single low-frequency ultra-open ventilation adjustable sound absorption unit (A) comprises a first array tube resonant cavity (1) and a second array tube resonant cavity (2) which are symmetrically arranged in parallel front and back, each array tube resonant cavity consists of an inner cavity and an outer cavity and is in a shape of Chinese character 'hui', and the upper side and the lower side of each of the first array tube resonant cavity and the second array tube resonant cavity (1 and 2) are respectively provided with a cover plate so as to enclose a sound absorption channel; the middle part of the front side wall of the outer cavity, the middle part of the front side wall of the inner cavity and the middle part of the rear side wall of the outer cavity of the first array tube resonant cavity (1), the middle part of the front side wall of the outer cavity, the middle part of the rear side wall of the outer cavity of the second array tube resonant cavity (2) are respectively provided with a straight sound absorption narrow slit with the same height as the array tube resonant cavities, the inner cavity of each array tube resonant cavity is enclosed by a fixed inner frame (3) and a left pulling adjustable inner frame (4) and a right pulling adjustable inner frame (4), the outer cavity of each array tube resonant cavity is enclosed by a fixed outer frame (5) and a left pulling adjustable outer frame (6) and a right pulling adjustable outer frame (6), the fixed inner frame (3) and the two pulling adjustable inner frames (4) are respectively connected through a syringe-like structure, the pulling adjustable inner frames (4) are fixedly connected with the corresponding pulling adjustable outer frames, the adjustable inner frame (4) and the adjustable outer frame (6) are pulled back and forth by the pull rod (7) to move synchronously, so that the sizes of the inner cavity and the outer cavity can be adjusted simultaneously;
secondly, endowing the established 3D simulation model with material characteristics;
setting a physical field for the established 3D simulation model, setting an outer area of the sound absorber as a sound pressure physical field, setting weak coupling for an interface of two inner areas and outer areas of the sound absorber, and setting a rigid boundary for plane wave radiation;
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 to finally determine the parameter range;
sixthly, scanning parameters of a according to the determined optimal parameters, and determining an adjustable structure parameter range and an absorption frequency broadband;
seventhly, manufacturing a high-efficiency ventilation sound absorber to prepare for a demonstration experiment;
manufacturing a non-single low-frequency ultra-open ventilation adjustable sound absorption unit (A) sample by adopting a photosensitive resin 3D printer according to the parameter range finally determined by the 3D simulation model;
eighthly, 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;
ninth, a ventilation measurement demonstration experiment is carried out;
the ventilation measurement of the sample is also carried out in a square impedance tube, and is completed by an electric fan, an anemometer and a driving motor in a matching way, the anemometer is used for the air flow speed at the outlet of the square impedance tube, the electric fan is positioned at the inlet, the driving motor is connected with a pull rod (7) of a non-single low-frequency ultra-open ventilation adjustable sound absorption unit (A), the driving motors at the two sides of a first column tube resonant cavity (1) and a second column tube resonant cavity (2) synchronously drive the corresponding pull rods (7) respectively and pull the same distance, and an adjustable inner frame (4) and an adjustable outer frame (6) are pulled back and forth through the pull rods (7) to synchronously move so as to simultaneously adjust the sizes of an inner cavity and;
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 ventilation adaptive low-frequency high-efficiency sound absorber finite element simulation and demonstration verification method as claimed in claim 1, wherein the method comprises the following steps: 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 ventilation adaptive low-frequency high-efficiency sound absorber finite element simulation and demonstration verification method as claimed in claim 1, wherein the method comprises the following steps: 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 ventilation adaptive low-frequency high-efficiency sound absorber finite element simulation and demonstration verification method as claimed in claim 1, wherein the method comprises the following steps: in the eighth step, the electric fanThe maximum air volume 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.
5. The ventilation adaptive low-frequency high-efficiency sound absorber finite element simulation and demonstration verification method as claimed in claim 1, wherein the method comprises the following steps: in the non-single low-frequency super-open ventilation adjustable sound absorption unit (A), a fixed inner frame (3) and a pulling adjustable inner frame (4) are respectively in a U shape, the fixed inner frames (3) of two separate tube resonant cavities are arranged close to and back to each other, the inner legs of the two pulling adjustable inner frames (4) of the same separate tube resonant cavity are arranged at intervals to just form a linear sound absorption narrow slit, the outer leg of each pulling adjustable frame (4) is provided with a fork port for inserting the corresponding leg of the fixed frame (3), or the leg of the fixed frame (3) is provided with a fork port for inserting the outer leg of the corresponding pulling adjustable frame (4), so that the injector-like structure is formed; the fixed outer frames (5) of the two sub-tube resonant cavities are integrally arranged and integrally in an H shape, the middle horizontal strip is provided with a linear sound absorption narrow slit, and two pulling adjustable outer frames (6) of the same sub-tube resonant cavity are arranged at intervals to just form the linear sound absorption narrow slit.
6. The ventilation adaptive low-frequency high-efficiency sound absorber finite element simulation and demonstration verification method according to claim 1, characterized in that: in the non-single low-frequency super-open ventilation adjustable sound absorption unit (A), a distance is reserved between the inner side legs of the pulling adjustable inner frames (4) and the edge of the U-shaped bottom plate to increase the distance between the inner side legs of the two pulling adjustable inner frames (4), and the width of the linear sound absorption narrow gap formed at the position is larger than that of the rest linear sound absorption narrow gaps.
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