CN111816151A - A double-layer honeycomb-micro-perforated structure with adjustable back cavity height and its design method - Google Patents

Abstract

The invention relates to a double-layer honeycomb-micro-perforated structure with adjustable back cavity height, which comprises an upper panel, a lower panel and a honeycomb core clamped between the upper panel and the lower panel. The invention realizes the absorption of the structure to the noise with different frequencies by changing the height of the micro-perforated plate contained in the honeycomb core, improves the sound absorption effect and simultaneously improves the application of the honeycomb-micro-perforated plate structure in noise reduction.

Description

A double-layer honeycomb-micro-perforated structure with adjustable back cavity height and its design method

technical field

The invention belongs to a medium-low frequency and broadband noise reduction structure and method designed by using a honeycomb-micro-perforated plate composite structure, in particular to a double-layer honeycomb-micro-perforated structure with adjustable back cavity height and a design method thereof.

Background technique

The micro-perforated plate sound absorption structure is developed on the basis of the ordinary perforated plate structure. Its main feature is to reduce the diameter of the perforation to less than millimeters, and use the acoustic resistance of the perforation itself to achieve the purpose of controlling the relative acoustic resistivity of the sound absorption structure. , so that the sound-absorbing material behind the perforated plate can be eliminated, which greatly simplifies the sound-absorbing structure. The honeycomb sandwich structure has the characteristics of high specific strength, high specific stiffness, good fatigue resistance, and smooth surface. It is widely used in the aviation field. Better sound absorption.

The sound absorption coefficient of the single-layer micro-perforated plate sound absorption structure is low except for the peak sound absorption, and the effective sound absorption frequency band is narrow, which sometimes cannot meet the needs of practical applications. The double-layer micro-perforated plate sound absorption structure can be regarded as Two mutually coupled resonance sound absorption structures can obtain higher sound absorption coefficient and wider sound absorption frequency band by using the double-layer micro-perforated plate structure.

According to the sound absorption principle of the micro-perforated plate, the thickness of the micro-perforated plate structure directly affects the sound absorption performance of the structure, that is, the sound absorption frequency and the sound absorption coefficient. In order to improve the sound absorption performance of the structure, a layer of micro-perforated plate of the double-layer honeycomb-micro-perforated structure only retains the vertical up and down degrees of freedom, and is set to be adjustable up and down. In this way, by changing the position of the layer of the micro-perforated plate, the height of the cavity of the micro-perforated plate can be changed to absorb noise of different frequencies.

SUMMARY OF THE INVENTION

Aiming at the sound absorption structure of the honeycomb-micro-perforated structure, the present invention designs a double-layer honeycomb-micro-perforated structure with adjustable back cavity height. Absorption, while improving the sound absorption effect, it also improves the application of the honeycomb-micro-perforated structure in noise reduction.

The present invention is realized through the following technical solutions.

A double-layer honeycomb-micro-perforated structure with adjustable back cavity height, an upper panel, a lower panel, and a honeycomb core sandwiched between the upper panel and the lower panel, characterized in that the upper panel is a micro-perforated panel, and the The honeycomb core is provided with a height-adjustable micro-perforated plate, the micro-perforated plate is provided with an adjustment boss, the honeycomb core is provided with an adjustment screw, and the adjustment screw and the adjustment boss are provided with mutually cooperating outer shells. Thread and internal thread, one end of the adjusting screw passes through the lower panel and this end is provided with an adjusting knob for controlling the adjusting screw, the inner wall of the honeycomb core is provided with protruding strips, and the micro-perforated plate is The outer side is provided with a groove matched with the protruding strip, the protruding strip is parallel to the axis of the honeycomb core, and the distance between the upper panel and the micro-perforated plate is changed by rotating the adjustment knob, thereby changing the structural resonance frequency and absorbing noise at different frequencies.

Preferably, the lower honeycomb cores are arranged in a close-packed circle.

Preferably, the bottom of the adjusting screw passes through the lower panel, the bottom of the adjusting screw and the lower panel are gap-fitted to form a self-locking structure, and the middle of the self-locking structure is narrow at both ends.

Preferably, the thread of the adjusting screw is a right-handed rectangular thread.

Preferably, a dial is provided on the adjustment knob.

A method for designing a double-layer honeycomb-micro-perforated structure with adjustable back cavity height, characterized in that it comprises the following steps:

In the first step, according to the micro-perforated plate theory of Academician Ma Dayou and computer simulation to verify the influence of the change of the cavity height on the sound absorption effect of the micro-perforation, the sound absorption coefficient when the sound wave is vertically incident is:

The sound absorption coefficient of the micro-perforated sound absorber reaches the maximum value at resonance, and the maximum sound absorption coefficient is:

The resonance frequency f ₀ satisfies:

2πf ₀ m-cot(2πf ₀ D/c)=0 (3)

Among them, the acoustic resistance r and the sound quality m are respectively:

In the above equations, k is the perforated plate constant

μ is the kinematic viscosity coefficient of air (1.48×10 ^-5 m ² /s), t is the thickness of the plate, d is the diameter of the perforation, D is the height of the cavity, p is the perforation rate, f is the sound frequency, and the cavity behind the plate The acoustic impedance is

Z _D = -jρccot(ωD/c) (7)

Assume that the double-layer micro-perforated sound absorber has two layers of micro-perforated plates m ₁ , r ₁ and m ₂ , r ₂ , and the back cavities are D ₁ and D ₂ respectively. According to its equivalent circuit, the double-layer series structure can be obtained. The relative acoustic impedance of

It can be seen from the above theoretical formula that the impedance value of the double-layer micro-perforated plate structure is affected by the parameters of the micro-perforated plate and the cavity heights D ₁ and D ₂ . Assuming that the parameters of the micro-perforated plate are determined, then D ₁ and D ₂ The value directly affects the impedance value of the structure, that is, changing the cavity height D of the microperforated plate can adjust the sound absorption performance of the microperforated plate structure.

The second step is to design a double-layer honeycomb-micro-perforated structure with adjustable back cavity height based on the above-mentioned variation of the impedance value with the cavity heights D ₁ and D _2. The structure adopts a close-packed circular honeycomb core. The position of the micro-perforated plate inside the core achieves the purpose of changing the acoustic impedance rate of the cavity behind the plate, thereby realizing the absorption of noise of different frequencies.

Compared with the prior art, the advantages of the present invention are:

1. The double-layer honeycomb-micro-perforated structure of the invention can achieve the best absorption of noise by changing the resonant frequency of the structure by changing the height of the back cavity for different frequencies of noise;

2. Compared with the single-layer honeycomb-micro-perforation structure, the double-layer honeycomb-micro-perforation structure of the invention has better sound absorption effect;

3. The double-layer honeycomb-micro-perforated structure described in the invention is simple to manufacture, simple to operate, and has wide application prospects in the field of noise reduction.

Description of drawings

Figure 1 is a common close-packed circular honeycomb-micro-perforated structure;

Fig. 2 is the cellular structure schematic diagram of the honeycomb core of the present invention;

3 is a schematic diagram of the internal structure of the honeycomb core cell of the present invention;

Fig. 4 is the self-locking structure schematic diagram of the present invention:

Fig. 5 is the top view of the side wall of the honeycomb core of the present invention;

Fig. 6 is the top view of the internal micro-perforated plate of the present invention;

7 is a schematic diagram of a boss of the present invention;

Fig. 8 is the screw structure schematic diagram of the present invention;

FIG. 9 is a schematic structural diagram of the knob for controlling the rotation of the screw according to the present invention;

Figure 10 is the improved honeycomb-micro-perforated structure with adjustable back cavity height;

Fig. 11 is the sound absorption effect diagram of the embodiment;

In the picture: 1. Upper panel, 2. Honeycomb core, 3. Lower panel, 4. Screw, 5. Micro-perforated plate, 6. Boss, 7. Knob, 8. Rib, 9. Groove.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but it is not intended to limit the present invention.

As shown in Figure 1, an ordinary densely packed circular honeycomb-micro-perforation consists of an upper panel 1, a densely packed circular honeycomb core 2, and a lower panel 3, wherein the upper panel is a micro-perforated plate with a certain perforation rate, and the honeycomb core adopts Close-packed circular structure, the lower panel is an ordinary metal sheet.

The present invention improves the common honeycomb core sandwich structure, and sets the honeycomb core structure into a structure containing screws and micro-perforated plates.

As shown in Figures 2 to 10, a double-layer honeycomb-micro-perforated structure with adjustable back cavity height, an upper panel 1, a lower panel 3, and a honeycomb core 2 sandwiched between the upper panel 1 and the lower panel 3, the It is characterized in that the upper panel 1 is a micro-perforated panel, the honeycomb core 2 is provided with a height-adjustable micro-perforated plate 5, the micro-perforated plate 5 is provided with an adjustment boss 6, and the honeycomb core 2 is provided with an adjustment boss 6. An adjusting screw 4 is provided, and the adjusting screw 4 and the adjusting boss 6 are provided with external threads and internal threads that cooperate with each other. One end of the adjusting screw 4 passes through the lower panel 3 The adjusting knob 7 of the adjusting screw 4, the inner wall of the honeycomb core 2 is provided with a convex strip 8, the outer side of the micro-perforated plate 5 is provided with a groove 9 that matches the convex strip 8, and the convex strip 8 is parallel to the axis of the honeycomb core 2, and the distance between the upper panel 1 and the micro-perforated plate 5 is changed by rotating the adjusting knob 7, thereby changing the structural resonance frequency and absorbing noise of different frequencies. The protruding strips 8 and the grooves 9 limit the degree of freedom of the micro-perforated plate 5, so that the micro-perforated plate 5 can only move up and down along the screw, but cannot rotate with the screw.

As a preferred embodiment, the lower honeycomb core 2 adopts a close-packed circular arrangement.

As a preferred embodiment, the bottom of the adjusting screw 4 passes through the lower panel 3 , and the bottom of the adjusting screw 4 is in clearance fit with the lower panel 3 to form a self-locking structure, and the middle of the self-locking structure is narrow and wide at both ends. .

As a preferred embodiment, the thread of the adjusting screw 4 is a right-handed rectangular thread.

As a preferred embodiment, the adjustment knob 7 is provided with a dial.

Figure 2 and Figure 3 show the double-layer honeycomb-micro-perforated structural cells with a single adjustable back cavity height. FIG. 2 is a schematic diagram of the cell structure of a double-layer honeycomb-micro-perforated structure with a single adjustable back cavity height, and the honeycomb core 2 is arranged in a close-packed circle. Figure 3 is a schematic diagram of the internal structure of the double-layer honeycomb-micro-perforated structural cell with adjustable back cavity height. 4 is a schematic diagram of the self-locking structure of the present invention. During installation, the screw 4 only needs to be pushed into the interior of the honeycomb core 2 to form a self-locking structure, so that the screw 4 will not fall out. 5 is a top view of the honeycomb core of the present invention, and FIG. 6 is a top view of the inner micro-perforated plate of the present invention. The grooves on the outer side of the micro-perforated plate 5 cooperate with the protrusions on the inner wall of the honeycomb core 2 to limit the degree of freedom of the micro-perforated plate 5, so that The micro-perforated plate 5 can only move up and down along the screw. 7 is a schematic view of the boss of the present invention, and FIG. 8 is a schematic view of the screw of the present invention. The boss 6 under the micro-perforated plate 5 has a built-in threaded hole, and the size of the threaded hole matches the thread of the screw 4 . Fig. 9 is a schematic diagram of the knob of the present invention, and the height of the micro-perforated plate 5 inside the honeycomb core can be controlled by the above scale.

A method for designing a double-layer honeycomb-micro-perforated structure with adjustable back cavity height, characterized in that it comprises the following steps:

In the first step, according to the micro-perforated plate theory of Academician Ma Dayou and computer simulation to verify the influence of the change of the cavity height on the sound absorption effect of the micro-perforation, the sound absorption coefficient when the sound wave is vertically incident is:

The sound absorption coefficient of the micro-perforated sound absorber reaches the maximum value at resonance, and the maximum sound absorption coefficient is:

The resonance frequency f ₀ satisfies:

2πf ₀ m-cot(2πf ₀ D/c)=0 (3)

Among them, the acoustic resistance r and the sound quality m are respectively:

In the above equations, k is the perforated plate constant

μ is the kinematic viscosity coefficient of air (1.48×10 ^-5 m ² /s), t is the thickness of the plate, d is the diameter of the perforation, D is the height of the cavity, p is the perforation rate, f is the sound frequency, and the cavity behind the plate The acoustic impedance is

Z _D = -jρccot(ωD/c) (7)

Assume that the double-layer micro-perforated sound absorber has two layers of micro-perforated plates m ₁ , r ₁ and m ₂ , r ₂ , and the back cavities are D ₁ and D ₂ respectively. According to its equivalent circuit, the double-layer series structure can be obtained. The relative acoustic impedance of

It can be seen from the above theoretical formula that the impedance value of the double-layer micro-perforated plate structure is affected by the parameters of the micro-perforated plate and the cavity heights D ₁ and D ₂ . Assuming that the parameters of the micro-perforated plate are determined, then D ₁ and D ₂ The value directly affects the impedance value of the structure, that is, changing the cavity height D of the microperforated plate can adjust the sound absorption performance of the microperforated plate structure.

The second step is to design a double-layer honeycomb-micro-perforated structure with adjustable back cavity height based on the above-mentioned variation of the impedance value with the cavity heights D ₁ and D _2. The structure adopts a close-packed circular honeycomb core. The position of the micro-perforated plate inside the core achieves the purpose of changing the acoustic impedance rate of the cavity behind the plate, thereby realizing the absorption of noise of different frequencies.

Example:

Figure 3, Figure 4 and Figure 5 show the double-layer honeycomb core cell with a single adjustable back cavity height. The dimensions of each structure are as follows: honeycomb core 2 has an outer diameter of 29mm, an inner diameter of 28mm, and a height of 60mm; screw 4 is a right-handed rectangular thread, with a major diameter of 4mm, a minor diameter of 2mm, and a pitch of 4mm; 1%; the thickness of micro-perforated plate 5 is 1mm, the hole diameter is 0.5mm, and the perforation rate is 1%. The thickness of the micro-perforated plate 5 is only 1 mm, so a boss 7 with a height of 5 mm and a diameter of 5 mm is designed below it. The boss 7 has a built-in threaded hole, the size of which is matched with the thread of the screw 4 . In this example, the sound absorption coefficient of the micro-perforated plate 5 is 10 mm from the bottom of the honeycomb core, the height of the micro-perforated plate 5 is 30 mm from the bottom of the honeycomb core, and the height of the micro-perforated plate 5 is 50 mm from the bottom of the honeycomb core. The structure is set to a diameter of 29 mm. The cylindrical shape is convenient for measurement in impedance tubes.

Figure 11 shows the sound absorption effect of the structure in three cases. _The first case is the sound absorption coefficient of the structure with _a height of 10mm from the bottom of the honeycomb core. In the second case, the sound absorption coefficient of the structure with the height of the micro-perforated plate 5 from the bottom of the honeycomb core is 30 mm, and the D ₁ and D ₂ of the structure are both 30 mm. coefficient, the D1 and D2 _of the structure at this time are 10mm and _50mm , respectively. It can be seen from this figure that the double-layer honeycomb-micro-perforated structure with adjustable back cavity height of the present invention has a good absorption effect on noise at low frequency, medium frequency, and medium and high frequency, and by changing the distance between the micro-perforated plate inside the honeycomb core and the honeycomb core. The height of the bottom, so as to achieve the best absorption of different frequencies by the structure.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the embodiments and protection scope of the present invention. For those skilled in the art, they should be able to realize that all equivalents made by using the description and illustrations of the present invention The solutions obtained by substitutions and obvious changes shall all be included in the protection scope of the present invention.

Claims (6)

1. A double-layer honeycomb-micro-perforated structure with adjustable back cavity height, comprising an upper panel (1), a lower panel (3), and a honeycomb core (2) sandwiched between the upper panel (1) and the lower panel (3) ), characterized in that the upper panel (1) is a micro-perforated panel, the honeycomb core (2) is provided with a height-adjustable micro-perforated plate (5), and the micro-perforated plate (5) is provided with An adjusting boss (6) is provided with an adjusting screw (4) in the honeycomb core (2), and an external thread and an internal thread that cooperate with each other are provided in the adjusting screw (4) and the adjusting boss (6). One end of the adjusting screw (4) passes through the lower panel (3) and is provided with an adjusting knob (7) for controlling the adjusting screw (4), and the inner wall of the honeycomb core (2) is provided with an adjusting knob (7). A convex strip (8), the outer side of the micro-perforated plate (5) is provided with a groove (9) matched with the convex strip (8), the convex strip (8) and the honeycomb core (2) The axes are parallel to each other, and the distance between the upper panel (1) and the micro-perforated plate (5) is changed by rotating the adjusting knob (7), thereby changing the structural resonance frequency and absorbing noises of different frequencies. 2 . The double-layer honeycomb-micro-perforated structure with adjustable back cavity height according to claim 1 , wherein the lower honeycomb cores ( 2 ) are arranged in a close-packed circle. 3 . 3. The double-layer honeycomb-micro-perforated structure with adjustable back cavity height according to claim 1, characterized in that the bottom of the adjustment screw (4) passes through the lower panel (3), and the adjustment screw The bottom of (4) is in clearance fit with the lower panel (3) to form a self-locking structure, and the middle of the self-locking structure is narrow and wide at both ends. 4. The double-layer honeycomb-micro-perforated structure with adjustable back cavity height according to claim 1, wherein the thread of the adjusting screw (4) is a right-handed rectangular thread. 5. The double-layer honeycomb-micro-perforated structure with adjustable back cavity height according to claim 1, wherein a dial is provided on the adjustment knob (7). 6. a design method of a double-layer honeycomb-micro-perforated structure with adjustable back cavity height, is characterized in that, comprises the steps: In the first step, according to the micro-perforated plate theory of Academician Ma Dayou and computer simulation to verify the influence of the change of the cavity height on the sound absorption effect of the micro-perforation, the sound absorption coefficient when the sound wave is vertically incident is:

The sound absorption coefficient of the micro-perforated sound absorber reaches the maximum value at resonance, and the maximum sound absorption coefficient is:

The resonance frequency f ₀ satisfies: 2πf ₀ m-cot(2πf ₀ D/c)=0 (3) Among them, the acoustic resistance r and the sound quality m are respectively:

In the above equations, k is the perforated plate constant

μ is the kinematic viscosity coefficient of air (1.48×10 ^-5 m ² /s), t is the thickness of the plate, d is the diameter of the perforation, D is the height of the cavity, p is the perforation rate, f is the sound frequency, and the cavity behind the plate The acoustic impedance is Z _D = -jρccot(ωD/c) (7) Assume that the double-layer micro-perforated sound absorber has two layers of micro-perforated plates m ₁ , r ₁ and m ₂ , r ₂ , and the back cavities are D ₁ and D ₂ respectively. According to its equivalent circuit, the double-layer series structure can be obtained. The relative acoustic impedance of

It can be seen from the above theoretical formula that the impedance value of the double-layer micro-perforated plate structure is affected by the parameters of the micro-perforated plate and the cavity heights D ₁ and D ₂ . Assuming that the parameters of the micro-perforated plate are determined, then D ₁ and D ₂ The value directly affects the impedance value of the structure, that is, changing the cavity height D of the microperforated plate can adjust the sound absorption performance of the microperforated plate structure. The second step is to design a double-layer honeycomb-micro-perforated structure with adjustable back cavity height based on the above-mentioned variation of the impedance value with the cavity heights D ₁ and D _2. The structure adopts a close-packed circular honeycomb core. The position of the micro-perforated plate inside the core achieves the purpose of changing the acoustic impedance rate of the cavity behind the plate, thereby realizing the absorption of noise of different frequencies.

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