Composite Helmholtz sound absorption structure with porous material as substrate

Abstract

The invention provides a composite Helmholtz sound absorption structure with a porous material as a substrate, the composite Helmholtz sound absorption structure comprises a plurality of Helmholtz sound absorption units with different absorption peak frequencies, the Helmholtz sound absorption units are arranged in a periodic rectangular array, the sound absorption directions of the Helmholtz sound absorption units are the same, and the Helmholtz sound absorption units are connected in parallel. When the composite Helmholtz sound absorption structure absorbs sound, a strong coupling relation is formed between the Helmholtz sound absorption units so as to optimize the sound absorption performance of the composite Helmholtz sound absorption structure. Under the condition of limited thickness, the Helmholtz sound absorption units which are arranged in a periodic array and are connected in parallel can be utilized to realize high-efficiency sound absorption at a low frequency band.

Description

Technical Field

[0001] The invention relates to the technical field of noise reduction structures, in particular to a composite Helmholtz sound absorption structure with a porous material as a substrate. Background Art

[0002] Noise has become one of the factors that seriously threaten the ecological environment and social development, and has also caused significant negative impacts on human health. With the high speed, large-scale and heavy-loaded equipment in the fields of aerospace, shipping, railway transportation and vehicle engineering, the noise problem has become more serious. In particular, low-frequency noise, with its strong penetration and difficult attenuation characteristics, makes this problem particularly difficult. When dealing with low-frequency sound waves, traditional sound-absorbing materials have low sound absorption efficiency and narrow sound absorption bandwidth. In actual engineering, in order to achieve effective low-frequency sound absorption, people usually need to extend the propagation path of sound waves, which leads to an increase in the thickness of the sound-absorbing material, which seriously limits their scope of application.

[0003] To address this problem, we need to design a sound-absorbing structure that has a high sound absorption coefficient in the low-frequency band even with limited thickness. At the same time, the arrangement and combination of multiple sound-absorbing units is also the key to achieving continuous and quasi-perfect sound absorption. Therefore, we also need to optimize the geometric parameters of each sound-absorbing unit to meet the needs of low-frequency broadband sound absorption. Summary of the invention

[0004] The present invention proposes a composite Helmholtz sound absorption structure with a porous material as a substrate, which can achieve efficient sound absorption in a low frequency band by using a plurality of Helmholtz sound absorption units arranged in a periodic array and connected in parallel under the condition of limited thickness.

[0005] The present invention adopts the following technical solutions.

[0006] A composite Helmholtz sound absorbing structure with a porous material as a substrate, the composite Helmholtz sound absorbing structure comprising a plurality of Helmholtz sound absorbing units with different absorption peak frequencies, the Helmholtz sound absorbing units being arranged in a periodic rectangular array, the sound absorbing directions of the Helmholtz sound absorbing units being the same and being connected in parallel, and when the composite Helmholtz sound absorbing structure absorbs sound, a strong coupling relationship is formed between the Helmholtz sound absorbing units to optimize the sound absorption performance of the composite Helmholtz sound absorbing structure.

[0007] The Helmholtz sound absorbing unit is a rectangular body, comprising a top plate layer (1), a cavity layer (3) and an embedded neck (2) in the middle, and a bottom plate layer (6) at the bottom; a circular through hole (30) serving as a sound absorbing hole is provided at the top plate layer; the circular through hole is located at the top of the embedded neck so that the sound absorbed by the sound absorbing unit enters the embedded neck through the through hole;

[0008] The embedded neck extends downward from the top plate to the cavity layer; the embedded neck is a tapered tube, and the embedded neck and the cavity layer are combined to form a Helmholtz resonance structure to absorb noise;

[0009] The outer wall of the cavity layer is covered with a porous material layer (4) for damping loss and increasing resonance;

[0010] Each Helmholtz sound absorbing unit is separated by an outer partition plate (5) at each unit body.

[0011] The aperture size of the circular through hole is in the range of 6-12mm; the embedded neck is coaxial with the circular through hole of the top plate layer, the diameter of the tapered tube decreases evenly from top to bottom, the top tube diameter is equal to the aperture size of the circular through hole, the bottom tube diameter is in the range of 2-6mm, and the length of the tapered tube is in the range of 10-40mm.

[0012] The thickness of the top plate layer is 1 mm, the wall thickness of the tapered tube embedded in the neck is 1 mm, and the thickness of the Helmholtz sound absorption unit is 50 mm;

[0013] When the material of the top plate layer, the embedded neck, the outer partition and the bottom plate layer has a density of 1230kg / m 3 When the elastic modulus is 3 GPa and the Poisson's ratio is 0.41, the porous material layer is made of melamine foam, the porosity of the porous material layer is 0.995, and the flow resistance is 10500 Pa·s / ,m -2. , the viscous characteristic length is 240um, the thermal characteristic length is 470um, and the tortuosity factor is 1.0059.

[0014] The cavity layer is funnel-shaped and is coaxial with the circular through hole of the top plate layer as a whole. The upper half of the funnel-shaped cavity layer is a conical tube, the wall of the conical tube is adjacent to and parallel to the outer wall of the embedded neck, and the interval between the two is 3-5mm. The lower half of the funnel-shaped cavity layer is a smoothly connected cylindrical tube structure.

[0015] The porous material layer is coaxial with the circular through holes of the top plate layer to form a substrate structure. The porous material layer is made of rock wool, glass wool, and polyurethane foam, which have good sound absorption effects.

[0016] The outer partition and bottom plate layer are 1 mm thick and are used for sealing and noise reduction.

[0017] The number of the Helmholtz sound absorbing units ranges from 4 to 9.

[0018] The top plate layer, embedded neck, outer partition and bottom plate layer are all made of photosensitive resin and are made by 3D printing.

[0019] The noise reduction performance of the sound absorption structure of the Helmholtz sound absorption unit is evaluated by finite element simulation calculation of the acoustic physical quantity of the sound absorption coefficient, specifically;

[0020] The sound absorption coefficient calculation formula is:

[0021]

[0022] Where Z s is the surface impedance of the entire sound-absorbing structure, Z0 = ρ0c0 is the characteristic impedance of air, ρ0 = 1.2 kg / m 3 is the air density, c0=343m / s is the speed of sound in air;

[0023] The optimal sound absorption frequency band of the composite Helmholtz sound absorption structure is evaluated by calculating the sound absorption coefficient of multiple Helmholtz sound absorption units in the composite Helmholtz sound absorption structure and setting the overall structural thickness of the composite Helmholtz sound absorption structure to be less than 1 / 21 of the wavelength of sound waves in the air.

[0024] The significant advantages of the present invention are:

[0025] (1) The present invention provides a composite Helmholtz sound absorption structure with a porous material as a substrate, which improves the sound absorption performance and adjusts the acoustic impedance by introducing an embedded tapered tube as a neck in a conventional Helmholtz resonator. In comparison, the embedded tapered tube provides an additional adjustable degree of freedom, which can achieve a high sound absorption coefficient in a lower frequency range with the same external shape.

[0026] (2) The present invention provides a composite Helmholtz sound absorbing structure with a porous material as a substrate. By introducing a porous material with sound absorbing properties to fill part of the cavity, the sound wave can be further absorbed by the porous material after dissipating part of the sound energy based on the Helmholtz resonance. The porous material acts as an additional damping to adjust the overall sound absorbing structure to an ideal state in different application environments.

[0027] (3) The present invention provides a composite Helmholtz sound absorption structure with a porous material as a substrate, which changes the peak frequency of resonant sound absorption by adjusting each sound absorption unit in a periodic arrangement and changing its geometric parameters such as the aperture of the through hole, the length of the tapered tube, etc. Therefore, users can adjust it according to different sound absorption and noise reduction requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0029] Attached Figure 1 It is a schematic diagram of the overall 3×3 array structure of the invention;

[0030] Attached Figure 2It is a schematic diagram of the overall 3×3 array structure assembly of the invention;

[0031] Attached Figure 3 It is a simulated curve diagram of the sound absorption coefficient of units 1-9 in the embodiment of the invention;

[0032] Attached Figure 4 It is a simulated curve diagram of the sound absorption coefficient of the overall structure in the embodiment of the invention;

[0033] In the figure: 1-top plate layer; 2-embedded neck; 3-cavity layer; 4-porous material layer; 5-outer partition; 6-bottom plate layer; 30-circular through hole. DETAILED DESCRIPTION

[0034] This example provides a composite Helmholtz sound absorbing structure with a porous material as a substrate, such as Figure 1 As shown, the composite Helmholtz sound absorption structure includes a plurality of Helmholtz sound absorption units arranged in a periodic rectangular array and connected in parallel. The present invention changes the peak frequency of the resonant sound absorption by adjusting each sound absorption unit in the periodic arrangement and changing its geometric parameters such as the aperture of the through hole and the length of the tapered tube, and realizes broadband sound absorption in the low frequency band through the coupling effect of the units in parallel.

[0035] As shown in the figure, a composite Helmholtz sound absorbing structure with a porous material as a substrate, the composite Helmholtz sound absorbing structure includes a plurality of Helmholtz sound absorbing units with different absorption peak frequencies, the Helmholtz sound absorbing units are arranged in a periodic rectangular array, the sound absorption directions of the Helmholtz sound absorbing units are the same and they are connected in parallel, when the composite Helmholtz sound absorbing structure absorbs sound, a strong coupling relationship is formed between the Helmholtz sound absorbing units to optimize the sound absorption performance of the composite Helmholtz sound absorbing structure.

[0036] The Helmholtz sound absorbing unit is a rectangular body, including a top plate layer 1, a cavity layer 3 and an embedded neck 2 in the middle, and a bottom plate layer 6 at the bottom; a circular through hole 30 as a sound absorbing hole is provided at the top plate layer; the circular through hole is located at the top of the embedded neck so that the sound absorbed by the sound absorbing unit enters the embedded neck through the through hole;

[0037] The embedded neck extends downward from the top plate to the cavity layer; the embedded neck is a tapered tube, and the embedded neck and the cavity layer are combined to form a Helmholtz resonance structure to absorb noise;

[0038] The outer wall of the cavity layer is covered with a porous material layer 4 for damping loss and increasing resonance;

[0039] Each Helmholtz sound absorbing unit is separated by an outer partition plate 5 at the body of each unit.

[0040] The aperture size of the circular through hole is in the range of 6-12mm; the embedded neck is coaxial with the circular through hole of the top plate layer, the diameter of the tapered tube decreases evenly from top to bottom, the top tube diameter is equal to the aperture size of the circular through hole, the bottom tube diameter is in the range of 2-6mm, and the length of the tapered tube is in the range of 10-40mm.

[0041] The thickness of the top plate layer is 1 mm, the wall thickness of the tapered tube embedded in the neck is 1 mm, and the thickness of the Helmholtz sound absorption unit is 50 mm;

[0042] When the material of the top plate layer, the embedded neck, the outer partition and the bottom plate layer has a density of 1230kg / m 3 When the elastic modulus is 3 GPa and the Poisson's ratio is 0.41, the porous material layer is made of melamine foam, the porosity of the porous material layer is 0.995, and the flow resistance is 10500 Pa·s / ,m -2. , the viscous characteristic length is 240um, the thermal characteristic length is 470um, and the tortuosity factor is 1.0059.

[0043] The cavity layer is funnel-shaped and is coaxial with the circular through hole of the top plate layer as a whole. The upper half of the funnel-shaped cavity layer is a conical tube, the wall of the conical tube is adjacent to and parallel to the outer wall of the embedded neck, and the interval between the two is 3-5mm. The lower half of the funnel-shaped cavity layer is a smoothly connected cylindrical tube structure.

[0044] The porous material layer is coaxial with the circular through holes of the top plate layer to form a substrate structure. The porous material layer is made of rock wool, glass wool, and polyurethane foam, which have good sound absorption effects.

[0045] The outer partition and bottom plate layer are 1 mm thick and are used for sealing and noise reduction.

[0046] The number of the Helmholtz sound absorbing units ranges from 4 to 9.

[0047] The top plate layer, embedded neck, outer partition and bottom plate layer are all made of photosensitive resin and are made by 3D printing.

[0048] The noise reduction performance of the sound absorption structure of the Helmholtz sound absorption unit is evaluated by finite element simulation calculation of the acoustic physical quantity of the sound absorption coefficient, specifically;

[0049] The sound absorption coefficient calculation formula is:

[0050]

[0051] Where Z s is the surface impedance of the entire sound-absorbing structure, Z0 = ρ0c0 is the characteristic impedance of air, ρ0 = 1.2 kg / m 3is the air density, c0=343m / s is the speed of sound in air;

[0052] The optimal sound absorption frequency band of the composite Helmholtz sound absorption structure is evaluated by calculating the sound absorption coefficient of multiple Helmholtz sound absorption units in the composite Helmholtz sound absorption structure and setting the overall structural thickness of the composite Helmholtz sound absorption structure to be less than 1 / 21 of the wavelength of sound waves in the air.

[0053] In this example, the top plate layer 1 and the embedded neck 2 are integrally formed.

[0054] Embodiment 1:

[0055] like Figure 1 and Figure 2 As shown, the Helmholtz sound absorbing unit includes a top plate layer 1, an embedded neck 2, a cavity layer 3, a porous material layer 4, an outer partition 5 and a bottom plate layer 6, wherein: the top plate layer 1 is provided with a circular through hole 30, through which sound enters the embedded neck 2, and part of the energy is lost due to the thermal viscosity effect during the propagation process; the embedded neck 2 is a conical tube, which forms a Helmholtz resonance with the cavity layer 3, and the sound wave is lost again in the continuous back and forth vibration and is further absorbed; the porous material layer 4 is wrapped outside the cavity layer 3, as an additional damping, responsible for adjusting the overall sound absorbing structure to an ideal state in different application environments, and is used to damp the loss and increase the resonance.

[0056] The thickness of the top plate layer 1 is 1 mm, and the diameter of the circular through hole 30 is in the range of 6-12 mm.

[0057] The embedded neck 2 is coaxial with the circular through hole 30 of the top plate layer, the diameter of the tapered tube decreases evenly from top to bottom, the top diameter is equal to the diameter of the circular through hole, the bottom diameter is in the range of 2-6mm, the length of the tapered tube is in the range of 10-40mm, and the tube wall thickness is 1mm.

[0058] The cavity layer 3 is funnel-shaped and is coaxial with the circular through hole 30 of the top plate layer as a whole. The upper part is 3-5 mm larger than the embedded neck, and the lower part is a smoothly connected cylindrical structure.

[0059] The porous material layer 4 is coaxial with the circular through hole 30 of the top plate layer, and the selected porous material may be but is not limited to rock wool, glass wool, polyurethane foam, etc., which have good sound absorption effect.

[0060] The outer partition plate 5 and the bottom plate layer 6 are 1 mm thick and mainly play the role of sealing and converging noise to prevent the porous material from directly contacting the external environment.

[0061] The number of the Helmholtz sound absorbing units is 4-9, and the overall thickness is 50 mm. If the desired sound absorption frequency band is wider, the number of corresponding sound absorption units will be greater, but there is also a certain number limit. When the number is too large, the sound absorption bandwidth that can be expanded is limited.

[0062] The top plate layer 1, the embedded neck 2, the outer partition 5 and the bottom plate layer 6 are all made of photosensitive resin and are made by 3D printing, with a density of 1230 kg / m 3 , the elastic modulus is 3GPa, and the Poisson's ratio is 0.41.

[0063] Embodiment 2:

[0064] based on Figure 1 A schematic diagram of an overall 3×3 array structure of a composite Helmholtz sound absorbing structure with a porous material as a substrate is shown. In this embodiment, an overall array structure including 9 Helmholtz sound absorbing units is designed. The 9 Helmholtz sound absorbing units are arranged in a periodic rectangular array and connected in parallel. The target sound absorption frequency band is 250Hz-600Hz. A certain sound absorption broadband within this frequency range is achieved by designing the geometric parameters of each unit.

[0065] In order to reduce the amount of calculation, in this embodiment, the width and thickness of each sound absorbing unit are fixed to 25 mm and 50 mm respectively, and the aperture of the circular through hole 30 is 10 mm, and the cavity layer 3 is expanded 5 mm outward compared with the embedded neck 2. In fact, the above geometric parameters are also correlated with the target sound absorption frequency band. Among these 9 Helmholtz sound absorbing units, the dimensions of the tapered tube embedded in the neck 2 are mainly adjusted as follows:

[0066] In the overall array structure including 9 Helmholtz sound absorbing units designed in this embodiment, the top plate layer 1, the embedded neck 2, the outer partition 5 and the bottom plate layer 6 are all made of photosensitive resin and are made by 3D printing, wherein the material density is 1230 kg / m 3 The elastic modulus is 3 GPa and the Poisson's ratio is 0.41. The porous material layer 4 is made of melamine foam, wherein the material porosity is 0.995 and the flow resistance is 10500 Pa·s / ,m -2. , the viscous characteristic length is 240um, the thermal characteristic length is 470um, and the tortuosity factor is 1.0059.

[0067] In order to evaluate the noise reduction performance of the sound-absorbing structure, this example performs finite element simulation calculation on the acoustic physical quantity of the sound absorption coefficient.

[0068] The sound absorption coefficient calculation formula is:

[0069]

[0070] Where Z s is the surface impedance of the entire sound-absorbing structure, Z0 = ρ0c0 is the characteristic impedance of air, ρ0 = 1.2 kg / m 3 is the air density, c0=343m / s is the speed of sound in air.

[0071] The numerical simulation of judging the noise reduction performance of this embodiment is as follows Figure 4 As shown, from the sound absorption coefficient calculated by finite element simulation, it can be seen that after 9 sound absorption units with different absorption peak frequencies are arranged and combined together, when the overall structure thickness is 50mm (less than 1 / 21 of the wavelength of sound waves in the air), a perfect sound absorption effect (α>0.9) is achieved at 317Hz-530Hz, and low-frequency broadband sound absorption above 200Hz is achieved. Compared with the absorption performance of the overall structure, it can be found that units 1-9 are in a weak resonance state and the noise absorption is not complete, which shows that the superior sound absorption performance of the embodiment is caused by the strong coupling between its units. At the same time, if noise reduction and sound absorption are required for other frequency bands in actual applications, it can be achieved by changing the geometric parameters in each unit, which also reflects a certain degree of adjustability.

[0072] Although the present invention has been described in detail through specific implementation methods, a person skilled in the art should understand that any changes in form and detail made on this basis that do not exceed the scope of protection of the claims shall fall within the scope of protection of the present invention.

Claims

1. A composite Helmholtz sound absorbing structure with a porous material as a substrate, characterized in that: The composite Helmholtz sound absorbing structure comprises a plurality of Helmholtz sound absorbing units with different absorption peak frequencies, the Helmholtz sound absorbing units are arranged in a periodic rectangular array, the sound absorbing directions of the Helmholtz sound absorbing units are the same and they are connected in parallel, and when the composite Helmholtz sound absorbing structure absorbs sound, a strong coupling relationship is formed between the Helmholtz sound absorbing units to optimize the sound absorption performance of the composite Helmholtz sound absorbing structure.

2. The composite Helmholtz sound absorbing structure with a porous material as a substrate according to claim 1, characterized in that: The Helmholtz sound absorbing unit is a rectangular body, comprising a top plate layer (1), a cavity layer (3) and an embedded neck (2) in the middle, and a bottom plate layer (6) at the bottom; a circular through hole (30) serving as a sound absorbing hole is provided at the top plate layer; the circular through hole is located at the top of the embedded neck so that the sound absorbed by the sound absorbing unit enters the embedded neck through the through hole; The embedded neck extends downward from the top plate to the cavity layer; The embedded neck is a conical tube, and the embedded neck and the cavity layer are combined to form a Helmholtz resonance structure to absorb noise; The outer wall of the cavity layer is covered with a porous material layer (4) for damping loss and increasing resonance; Each Helmholtz sound absorbing unit is separated by an outer partition plate at each unit body.

3. The composite Helmholtz sound absorbing structure with a porous material as a substrate according to claim 2, characterized in that: The aperture size of the circular through hole is in the range of 6-12mm; the embedded neck is coaxial with the circular through hole of the top plate layer, the diameter of the tapered tube decreases evenly from top to bottom, the top tube diameter is equal to the aperture size of the circular through hole, the bottom tube diameter is in the range of 2-6mm, and the length of the tapered tube is in the range of 10-40mm.

4. The composite Helmholtz sound absorbing structure with a porous material as a substrate according to claim 2, characterized in that: The thickness of the top plate layer is 1 mm, the wall thickness of the tapered tube embedded in the neck is 1 mm, and the thickness of the Helmholtz sound absorption unit is 50 mm; When the material of the top plate layer, the embedded neck, the outer partition and the bottom plate layer has a density of 1230kg / m 3 When the elastic modulus is 3 GPa and the Poisson's ratio is 0.41, the porous material layer is made of melamine foam, the porosity of the porous material layer is 0.995, and the flow resistance is 10500 Pa·s / ,m -2. , the viscosity characteristic length is 240um, The thermal characteristic length is 470um and the tortuosity factor is 1.0059.

5. The composite Helmholtz sound absorbing structure with a porous material as a substrate according to claim 2, characterized in that: The cavity layer is funnel-shaped and is coaxial with the circular through hole of the top plate layer as a whole. The upper half of the funnel-shaped cavity layer is a conical tube, the wall of the conical tube is adjacent to and parallel to the outer wall of the embedded neck, and the interval between the two is 3-5mm. The lower half of the funnel-shaped cavity layer is a smoothly connected cylindrical tube structure.

6. The composite Helmholtz sound absorbing structure with a porous material as a substrate according to claim 2, characterized in that: The porous material layer is coaxial with the circular through holes of the top plate layer to form a substrate structure. The porous material layer is made of rock wool, glass wool, and polyurethane foam, which have good sound absorption effects.

7. The composite Helmholtz sound absorbing structure with a porous material as a substrate according to claim 2, characterized in that: The outer partition and bottom plate layer are 1 mm thick and are used for sealing and noise reduction.

8. The composite Helmholtz sound absorbing structure with a porous material as a substrate according to claim 2, characterized in that: The number of the Helmholtz sound absorbing units ranges from 4 to 9.

9. The composite Helmholtz sound absorbing structure with a porous material as a substrate according to claim 2, characterized in that: The top plate layer, embedded neck, outer partition and bottom plate layer are all made of photosensitive resin and are made by 3D printing.

10. The composite Helmholtz sound absorbing structure with a porous material as a substrate according to claim 2, characterized in that: The noise reduction performance of the sound absorption structure of the Helmholtz sound absorption unit is evaluated by finite element simulation calculation of the acoustic physical quantity of the sound absorption coefficient, specifically; The sound absorption coefficient calculation formula is: Where Z s is the surface impedance of the entire sound-absorbing structure, Z0 = ρ0c0 is the characteristic impedance of air, ρ0 = 1.2 kg / m 3 is the air density, c0=343m / s is the speed of sound in air; The optimal sound absorption frequency band of the composite Helmholtz sound absorption structure is evaluated by calculating the sound absorption coefficient of multiple Helmholtz sound absorption units in the composite Helmholtz sound absorption structure and setting the overall structural thickness of the composite Helmholtz sound absorption structure to be less than 1 / 21 of the wavelength of sound waves in the air.

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