Multifunctional acoustic device with low-frequency vibration reduction and broadband sound absorption functions

Abstract

The multifunctional acoustic device is formed by periodically arranging unit cells in the horizontal direction, and each unit cell comprises an upper frame body, a lower frame body and a vibration absorption sandwich layer located between the upper frame body and the lower frame body; the upper frame body is provided with a through hole; the vibration absorption sandwich layer comprises a central cantilever beam located at the transverse center position, a sandwich plate surrounding the periphery of the central cantilever beam and fixed between the upper frame body and the lower frame body, and vibrator mass blocks arranged above and below the central cantilever beam; the sandwich plate is connected with the central cantilever beam through a plurality of L-shaped beams; and the plurality of L-shaped beams surround the periphery of the central cantilever beam. The lattice sandwich structure is used as a basic frame, a local resonance system with a spring mass part is formed, a sub-wavelength elastic wave band gap frequency band is obtained, a low-frequency vibration reduction effect is generated, holes are formed in the upper frame body, the remaining part in the structure is used as an air spring, a Helmholtz resonant cavity is formed, and meanwhile low-frequency vibration reduction and broadband sound absorption are achieved.

Description

Technical Field

[0001] The present invention relates to an acoustic device, and in particular to a multifunctional acoustic device having both low-frequency vibration reduction and broadband sound absorption Background Art

[0002] Low-frequency vibration and noise problems are widely present in various mechanical equipment and products such as aircraft, ships, high-speed railways, and automobiles. They can cause fatigue damage or even destruction of the equipment itself, reduce the equipment's working performance and life, reduce the equipment's processing accuracy and the measurement accuracy of instruments, and endanger the physical and mental health of drivers and passengers.

[0003] For noise reduction, one of the traditional methods is to use porous materials to absorb sound. Porous materials have been widely used in architectural and traffic noise control due to their advantages such as broadband absorption, low cost, easy modeling, and lightweight. However, for low-frequency noise below 1000Hz, the sound absorption performance of porous materials is very poor, and acoustic metamaterials are usually used as a new solution. Compared with porous materials, acoustic metamaterials can achieve perfect sound absorption in the deep subwavelength dimension. Sound-absorbing metamaterials are mainly based on resonance mechanisms, such as Helmholtz resonance, Fabry-Perot resonance, non-local resonance, hybrid resonance, etc.

[0004] For vibration reduction, traditional measures generally use additional dynamic vibration absorbers, viscoelastic damping materials, reinforcement ribs or local thickening. These vibration reduction methods have problems such as narrow vibration reduction frequency range, poor low-frequency vibration attenuation effect, and high weight and size costs. Elastic wave acoustic devices control the low-frequency vibration of the structure by attaching or embedding vibrators on beams, plates, and rods. Based on the principle of local resonance, vibration suppression in the low-frequency range can be achieved by increasing the mass of the vibrator or reducing the equivalent stiffness of the structure.

[0005] In some actual industrial scenarios, it is necessary to control vibration and noise simultaneously to eliminate harmful effects on personnel and equipment. Existing local resonance devices or sound-absorbing metamaterials can only achieve vibration suppression or sound wave absorption at low frequencies alone, and it is difficult to simultaneously meet the requirements of vibration reduction in the low-frequency range and broadband sound absorption. Summary of the invention

[0006] Purpose of the invention: The purpose of the present invention is to provide a multifunctional acoustic device that combines low-frequency vibration reduction and broadband sound absorption, which can achieve vibration suppression in the low-frequency range and broadband absorption of sound waves while meeting a certain load-bearing capacity.

[0007] Technical solution: The multifunctional acoustic device with both low-frequency vibration reduction and broadband sound absorption described in the present invention is composed of unit cells periodically arranged in the horizontal direction, and the unit cell includes an upper frame, a lower frame, and a vibration-absorbing sandwich layer located between the upper frame and the lower frame; the upper frame is provided with perforations; the vibration-absorbing sandwich layer includes a central cantilever beam located at the lateral center position, a sandwich plate surrounded by the periphery of the central cantilever beam and fixed between the upper frame and the lower frame, and a vibrator mass block arranged above and below the central cantilever beam; the sandwich plate and the central cantilever beam are connected by a plurality of L-shaped beams; and a plurality of L-shaped beams surround the periphery of the central cantilever beam.

[0008] Among them, a gap is provided between each L-shaped beam and the sandwich plate and the central cantilever beam to buffer the relative displacement between the structures.

[0009] The bottom surfaces of the sandwich plate, the L-shaped beam and the central cantilever beam are all on the same horizontal plane and have the same axial height.

[0010] The sandwich panels, L-shaped beams and central cantilever beam components are all made of the same material and can be manufactured using an integrated molding process.

[0011] The vibration absorbing sandwich layer adopts a multi-cantilever beam structure, that is, it includes a plurality of L-shaped beams and a central cantilever beam, which can effectively reduce stress concentration and avoid excessive amplitude of the vibrator mass block.

[0012] The height of the vibrator mass block is 2-12 mm, and the width is 18-35 mm; the width of the vibrator mass block is consistent with the width of the central cantilever beam.

[0013] Wherein, the width of the central cantilever beam is 18-35 mm; the width of the L-shaped beam is 3-6 mm; and the width of the sandwich plate is 2-5 mm.

[0014] Wherein, the thickness of the central cantilever beam, the L-shaped beam and the sandwich plate are all 1 to 2 mm.

[0015] Wherein, the distance of the gap is 0.5-1 mm.

[0016] Wherein, the upper frame body comprises an upper panel and an upper annular frame plate; the lower frame body comprises a lower panel and a lower annular frame plate; and the through hole is arranged at the center of the upper panel.

[0017] The unit cell has a four-fold rotational symmetry axis along the z direction, and the lattice of the periodic arrangement of the unit cells is a square.

[0018] The shape of the perforation is circular or rectangular; the radius or side length of the perforation is 1 to 2.5 mm; the perforation size of each unit cell is the same or not all the same or different.

[0019] Beneficial effects: Compared with the prior art, the present invention achieves the following significant effects:

[0020] (1) The present invention adopts a lattice sandwich structure with a certain mechanical bearing capacity as the basic frame, and obtains a subwavelength elastic wave band gap frequency band by designing the structure of the sandwich plate into a local resonance system with a spring mass part, thereby producing a low-frequency vibration reduction effect. At the same time, by opening a hole in the upper plate, the remaining part of the structure is used as an air spring to form a Helmholtz resonance cavity, so that the structure also has sound absorption ability, thereby realizing the multifunctional integrated characteristics of having a certain bearing capacity and low-frequency vibration reduction and sound absorption; the device is suitable for both vibration reduction and sound absorption in the low-frequency range of 100-300Hz.

[0021] (2) The periodic structure of the present invention can realize the coupling of Helmholtz resonant cavities with different resonant frequencies while satisfying the elastic wave band gap characteristics, thereby achieving broadband sound absorption.

[0022] (3) Based on the principles of local resonance and Helmholtz resonance, the present invention can adjust the elastic wave bandgap frequency domain by adjusting the height of the mass block and the width of the L-shaped beam, and adjust the absorption peak frequency domain of the sound wave by adjusting the aperture size and the combination of the unit cell, so as to adapt to different external excitation frequencies and achieve the optimal vibration reduction and noise reduction effect under different working conditions.

[0023] (4) The present invention provides slits in the vibration absorbing sandwich layer, which exist between each L-shaped beam and the sandwich plate and the central cantilever beam, so that the structure can generate a second-order sound absorption peak in the range of 1000-2000Hz. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the internal three-dimensional structure of a unit cell of the present invention;

[0025] Figure 2 is a schematic diagram of the top view of the structure of the vibration absorbing sandwich layer of the present invention;

[0026] Figure 3 It is a schematic diagram of a top view of the structure of the sandwich panel, L-shaped beam and central cantilever beam formed in an integrated manner according to the present invention;

[0027] Figure 4 It is a schematic diagram of the assembly structure of the sandwich panel, L-shaped beam and central cantilever beam of the present invention;

[0028] Figure 5 is an overall schematic diagram of a unit cell of the present invention;

[0029] Figure 6 It is a schematic diagram of the structure of the present invention under the 3×3 unit cell combination arrangement;

[0030] Figure 7 is the energy band structure diagram of the present invention;

[0031] Figure 8 is a curve diagram of elastic wave transmittance under the 3×3 combination arrangement of the present invention;

[0032] Fig. 9 It is a curve diagram of the sound absorption coefficient in the low frequency band under the 3×3 combination arrangement of the present invention;

[0033] Fig.10 It is a curve diagram of the second-order sound absorption coefficient in the mid-frequency band under the 3×3 combination arrangement of the present invention;

[0034] Fig.11 It is a schematic diagram of simulated displacement under the 3×3 combination arrangement of the present invention. DETAILED DESCRIPTION

[0035] The present invention is described in further detail below.

[0036] like Figure 1-6 As shown, the present invention provides a multifunctional acoustic device with low-frequency vibration reduction and broadband sound absorption, which is composed of unit cells 1 periodically arranged in the horizontal direction. The unit cell 1 includes an upper panel 2, a lower panel 3, an upper annular frame plate 4, a lower annular frame plate 5, and a vibration absorbing sandwich layer 6.

[0037] The center of the upper panel 2 of this embodiment is provided with a perforation 21 to allow air inside and outside the structure to communicate; the upper and lower end surfaces of the vibration absorbing sandwich layer 6 are respectively connected to the upper annular frame plate 4 and the lower annular frame plate 5. The vibration absorbing sandwich layer 6 includes a sandwich plate 61, an L-shaped beam 62, a central cantilever beam 63 and a vibrator mass block 64; the central cantilever beam 63 is located at the transverse center of the vibration absorbing sandwich layer 6, the sandwich plate 61 surrounds the outer periphery of the central cantilever beam and is fixed between the upper frame and the lower frame; the vibrator mass block 64 is symmetrically arranged above and below the central cantilever beam 63; the sandwich plate 61 and the central cantilever beam 63 are connected by a plurality of L-shaped beams 62; and a plurality of L-shaped beams surround the circumference of the central cantilever beam 63. There are four L-shaped beams 62 in this embodiment, and the four L-shaped beams are connected in sequence and surround the central cantilever beam 63. One end of each L-shaped beam is connected to the sandwich plate 61, and the other end is connected to the central cantilever beam 63. Each L-shaped beam is provided with a gap 65 between the sandwich plate and the central cantilever beam, respectively, to buffer the relative displacement between the structures. The bottom surfaces of the sandwich plate 61, the L-shaped beam 62, and the central cantilever beam 63 of this embodiment are all on the same horizontal plane, and the axial heights are all the same. The width of the central cantilever beam of this embodiment can be 18 to 35 mm; the width of the L-shaped beam can be 3 to 6 mm; the width of the sandwich plate can be 2 to 5 mm; the heights of the central cantilever beam, the L-shaped beam, and the sandwich plate are all equal, which can be 1 to 2 mm; the height of the vibrator mass block 64 can be 2 to 12 mm; the vibrator mass block and the central cantilever beam are both square, and the width of the two is equal; the distance of the gap 65 can be 0.5 to 1 mm.

[0038] The perforations 21 provided on the upper panel of this embodiment are circular, and the perforation radius of each unit cell 1 is different. Except for the vibrator mass block 64 which is made of lead, the materials of the other components are all aluminum. The sandwich plate 61, L-shaped beam 62, and central cantilever beam 63 are manufactured by an integrated molding process. There is no connection boundary between the sandwich plate 61, L-shaped beam 62, and central cantilever beam 63 after integrated molding. The structural schematic diagram is shown in FIG. Figure 3 As shown; a schematic diagram of a structure without integrated molding, such as Figure 4 shown.

[0039] The unit cell 1 of this embodiment has a four-fold rotational symmetry axis along the z direction, and the periodic lattice of the unit cell 1 is a square. The shape of the perforation 21 is circular or rectangular; the size of the perforation 21 of each unit cell 1 is the same or not all the same or different.

[0040] The present invention adopts a lattice sandwich structure with a certain mechanical bearing capacity as the basic framework, designs the sandwich plate structure, constructs four L-shaped beams 62 as low-rigidity springs, constructs a central cantilever beam 63 as a mass block carrier, and places mass blocks 64 at the upper and lower ends of the central cantilever beam 63 to form a local resonance system, obtain a sub-wavelength elastic wave band gap frequency band, and produce a low-frequency vibration reduction effect. By opening a hole in the upper panel, the remaining part of the structure is used as an air spring to form a Helmholtz resonance cavity, so that the structure has sound absorption capacity at the same time, and realizes the multifunctional integrated characteristics of having a certain bearing capacity and low-frequency vibration reduction and sound absorption.

[0041] The present invention adopts a periodic structure of multiple unit cells in parallel to achieve Helmholtz resonance cavity coupling of different resonant frequencies while satisfying the elastic wave band gap characteristics, thereby achieving broadband sound absorption. The elastic wave band gap frequency domain can be adjusted by adjusting the height of the mass block 64, the width of the central cantilever beam 63 and the L-shaped beam 62, and the absorption peak frequency domain of the sound wave can be adjusted by adjusting the aperture size and the combination of the unit cells, so as to adapt to different external excitation frequencies and achieve the optimal vibration reduction and noise reduction effect under different working conditions. The slit design used in the vibration absorption sandwich layer enables the structure to produce a second-order sound absorption peak in the range of 1000-2000Hz.

[0042] Verification of the vibration reduction and sound absorption capabilities of the multifunctional acoustic device of this embodiment:

[0043] This embodiment limits the unit cell size and material parameters, and calculates the band structure diagram of the multifunctional acoustic device to illustrate that it can produce a band gap with low-frequency vibration suppression capability. The lattice constant of the unit cell is 60mm, and there are nine rectangular unit cells arranged horizontally and periodically to form a complete acoustic device; the thickness of the upper and lower panels is 2mm, the height of the upper and lower annular frame plates is 30mm, the thickness of the vibration-absorbing sandwich layer 6 is 2mm and the width is 60mm, and the width is consistent with the lattice constant; each of the four L-shaped beams 62 is 6mm wide, and the thickness of the vibrator mass block 64 is 10mm; the width of the central cantilever beam 63 is 35mm, and the width of the vibrator mass block 64 is equal to the width of the central cantilever beam 63; the thickness of the central cantilever beam 63, the L-shaped beam 62 and the sandwich plate 61 are equal; the vibrator mass block 64 is made of lead, and the specific material properties are: density 11600kg / m 3 , Young's modulus 40.8GPa, Poisson's ratio 0.37; the remaining components of the device of the present invention are all made of aluminum, and the specific material properties are: density 2713kg / m 3 , Young's modulus 69GPa, Poisson's ratio 0.3.

[0044] A unit cell model of a multifunctional acoustic device is constructed in COMSOL software, and Bloch-Floquet periodic boundary conditions are set in the x and y directions of the unit cell, and free boundary conditions are set in the z direction. The wave vector k is set and parametrically scanned along the irreducible Brillouin zone of the structure to obtain the energy band curve of the multifunctional acoustic device.

[0045] like Figure 7 As shown in the figure, the shaded part is the band gap, and the band gap frequency range is 124-245Hz. In the band gap range, the elastic wave is localized in the resonant unit and cannot continue to propagate forward, achieving the effect of vibration reduction. In order to verify the accuracy of the calculated band gap frequency range and the vibration reduction performance of the finite period structure, COMSOL was used to calculate the band gap frequency range. Figure 1 A numerical calculation model of a 3×3 periodic multifunctional acoustic device is established.

[0046] In the numerical model, a simple harmonic force excitation with an amplitude of 1 and polarization in the z direction is applied to one end, and its acceleration response is picked up at the other end. The elastic wave transmittance curve of the structure is calculated, as shown in Figure 8 As shown. Figure 8 It can be seen that the elastic wave transmission value within the band gap frequency range shows a very obvious attenuation, with the maximum value reaching -43dB.

[0047] A frequency of 140Hz within the band gap is selected for intuitive demonstration of the vibration reduction effect, such as Fig.11As shown, when the elastic wave propagates in the multifunctional acoustic device with a period of 3×3, the oscillator undergoes a large displacement, while the displacement of the matrix structure is small, and the vibration energy is concentrated in the local oscillator part. Therefore, the device has a very obvious low-frequency vibration reduction effect.

[0048] In order to verify the sound absorption ability of the multifunctional acoustic device, a rectangular sound field is set above the numerical model, and the incident sound wave size at the port is defined as 1Pa. The sound absorption coefficient of the structure is calculated by picking up the power of the incident wave and the reflected wave at the port, and the sound absorption coefficient curve of the structure is obtained. Fig. 9 As shown in the figure, the average sound absorption coefficient in the range of 140-220Hz is above 0.7, which reflects that the device has good low-frequency broadband sound absorption effect. In addition, the device produces a series of second-order sound absorption peaks in the range of 1000-2000Hz, such as Fig.10 This is caused by the slits formed between the sandwich panel, L-beam and central cantilever beam, reflecting the device's additional sound absorption performance in the mid-frequency band.

Claims

1. A multifunctional acoustic device with both low-frequency vibration reduction and broadband sound absorption, which is composed of unit cells (1) periodically arranged in the horizontal direction, characterized in that: The unit cell (1) comprises an upper frame, a lower frame, and a vibration absorbing sandwich layer (6) located between the upper frame and the lower frame; the upper frame is provided with a perforation (21); the vibration absorbing sandwich layer (6) comprises a central cantilever beam (63) located at a transverse center position, a sandwich plate (61) surrounding the outer periphery of the central cantilever beam (63) and fixed between the upper frame and the lower frame, and a vibrator mass block (64) arranged above and below the central cantilever beam (63); the sandwich plate (61) and the central cantilever beam (63) are connected by a plurality of L-shaped beams (62); and the plurality of L-shaped beams (62) surround the periphery of the central cantilever beam (63).

2. The multifunctional acoustic device having both low-frequency vibration reduction and broadband sound absorption according to claim 1, characterized in that: A gap (65) is provided between each L-shaped beam (62) and the sandwich plate (61) and the central cantilever beam (63) to provide a buffering effect on the relative displacement between the structures.

3. The multifunctional acoustic device having both low-frequency vibration reduction and broadband sound absorption according to claim 1, characterized in that: The bottom surfaces of the sandwich plate (61), the L-shaped beam (62) and the central cantilever beam (63) are all on the same horizontal plane and have the same axial height.

4. The multifunctional acoustic device having both low-frequency vibration reduction and broadband sound absorption according to claim 1, characterized in that: The vibrator mass block (64) has a height of 2 to 12 mm and a width of 18 to 35 mm.

5. The multifunctional acoustic device having both low-frequency vibration reduction and broadband sound absorption according to claim 1, characterized in that: The width of the central cantilever beam (63) is 18 to 35 mm; the width of the L-shaped beam (62) is 3 to 6 mm; and the width of the sandwich plate (61) is 2 to 5 mm.

6. The multifunctional acoustic device having both low-frequency vibration reduction and broadband sound absorption according to claim 1, characterized in that: The thickness of the central cantilever beam (63), the L-shaped beam (62) and the sandwich plate (61) are all 1 to 2 mm.

7. The multifunctional acoustic device having both low-frequency vibration reduction and broadband sound absorption according to claim 2, characterized in that: The distance of the gap (65) is 0.5-1 mm.

8. The multifunctional acoustic device having both low-frequency vibration reduction and broadband sound absorption according to claim 1, characterized in that: The radius or side length of the perforation (21) is 1 to 2.5 mm; the sizes of the perforations (21) of each unit cell (1) are the same or not all the same or different.

9. The multifunctional acoustic device having both low-frequency vibration reduction and broadband sound absorption according to claim 1, characterized in that: The upper frame body comprises an upper panel (2) and an upper annular frame plate (4); the lower frame body comprises a lower panel (3) and a lower annular frame plate (5); and the through hole (21) is arranged at the center of the upper panel (2).

10. The multifunctional acoustic device having both low-frequency vibration reduction and broadband sound absorption according to claim 1, characterized in that: The unit cell (1) has a four-fold rotational symmetry axis along the z direction, and the lattice of the periodic arrangement of the unit cell (1) is a square.

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