Transformer low-frequency noise absorber and method

Abstract

The invention discloses a transformer low-frequency noise absorber and method, the absorber is formed by cascading a superior Helmholtz absorber and a subordinate Helmholtz absorber, the structural design is simple and reasonable, the heights of four Helmholtz cavities in the subordinate Helmholtz absorber are different, and an asymmetric structure is formed; sound waves enter the low-frequency noise absorber of the transformer from an air medium, resonance of a structural unit is caused, the energy density of the sound is greatly improved through local resonance, energy dissipation is caused, and perfect sound absorption is achieved. The low-frequency noise absorber of the transformer does not need to specially eliminate the coupling effect between units, it is guaranteed that the absorption coefficient of the target frequency does not decrease, and the main limitation of an existing multi-band absorber is relieved.

Description

Technical Field

[0001] The invention belongs to the technical field of transformer noise reduction, and relates to a transformer low-frequency noise absorber and method. Background Art

[0002] Power transformers are key components for power stations in cities and industrial areas to transmit electricity to end users. Their noise pollution can affect the daily lives of nearby residents. Transformer noise mainly comes from magnetostriction, which occurs twice in an AC cycle. Therefore, transformer noise is mainly composed of 50Hz and its harmonics. The low-frequency components of transformer noise, such as 100Hz, 150Hz, and 200Hz, have long propagation distances and are difficult to control.

[0003] At present, some research works control the noise of power transformers by active methods using secondary sources and adaptive control algorithms, but the complexity of substation structure and its noise limits the implementation of active noise reduction schemes. In terms of passive sound absorption, since transformer noise is low-frequency, according to the principle that "the thickness of passive sound-absorbing materials (porous materials) is one-quarter of the noise wavelength for the best sound absorption effect", the thickness of the absorber must be at least 8 meters, which is impractical. Therefore, due to space and heat limitations, traditional resonant absorbers are generally not suitable for low-frequency noise control of transformers.

[0004] In recent years, sub-wavelength acoustic metamaterials with excellent low-frequency sound absorption performance have provided an effective way to solve the problem of low-frequency noise. Absorbers based on acoustic metamaterials can achieve an absorption coefficient close to 1 in the low-frequency sound band. For example, multi-helix acoustic metamaterials have perfect absorption at 50Hz, and the structure thickness is about 13mm, which is 1 / 527 of the corresponding wavelength. Another example is based on a dual-channel Mie resonator, which uses the concept of critical coupling to achieve perfect absorption at 157Hz, with a thickness of about 1 / 28 of the corresponding wavelength. However, they can only work in a narrow frequency range near the resonant frequency point.

[0005] The traditional Helmholtz resonator (HR) is also one of the hot spots in the design of acoustic metamaterials. For example, an absorber embedded with an aperture HR achieves perfect absorption with a thickness of about 1 / 50 of the corresponding wavelength. Although multi-frequency absorption can be obtained by placing multiple HR absorbers in parallel, the sound absorption efficiency is severely reduced. When two HR units that can achieve perfect absorption are placed adjacent to each other, the porosity of each will be reduced, making it impossible to achieve high-efficiency absorption of two frequency points at the same time. In addition, if the gap between the two target frequencies is increased, the decrease in the absorption coefficient of the higher frequency will be more serious. Therefore, achieving high absorption at multiple frequency points is still a difficult problem.

[0006] At present, an effective strategy to achieve multi-frequency absorption is to use a multi-layer arrangement. For example, a perforated composite Helmholtz resonator can obtain multiple near-perfect peaks at higher frequencies by inserting one or more separate plates with small holes into the Helmholtz resonator; another example is a resonator with an extended neck, which can induce additional absorption peaks. However, when the cavity diameter of the multi-layer arrangement is consistent with the cavity diameter of the upper arrangement, it is difficult to obtain multi-frequency absorption by adjusting the parameters. To solve this problem, the prior art proposes a three-layer cascaded HR structure, which achieves absorption of three resonant frequencies, and the sound absorption frequency can be adjusted by adjusting the diameter and length of the resonator. However, the three-layer cascade structure is relatively complex in terms of structural design and preparation process. Summary of the invention

[0007] In order to solve the deficiencies in the prior art, the present invention provides a transformer low-frequency noise absorber and method, which realizes transformer low-frequency noise absorption based on an asymmetric two-layer cascaded Helmholtz cavity.

[0008] The present invention adopts the following technical solution.

[0009] A first aspect of the present invention provides a transformer low-frequency noise absorber, comprising an upper-stage Helmholtz absorber and a lower-stage Helmholtz absorber cascaded with the upper-stage Helmholtz absorber;

[0010] The upper-stage Helmholtz absorber comprises a first Helmholtz cavity and a second Helmholtz cavity that are completely identical, wherein the first Helmholtz cavity and the second Helmholtz cavity both comprise a coupling short tube, and the first Helmholtz cavity and the second Helmholtz cavity are symmetrically arranged side by side;

[0011] The lower-stage Helmholtz absorber comprises a third Helmholtz cavity, a fourth Helmholtz cavity, a fifth Helmholtz cavity and a sixth Helmholtz cavity; the third Helmholtz cavity, the fourth Helmholtz cavity, the fifth Helmholtz cavity and the sixth Helmholtz cavity have different cavity heights and all comprise coupling short tubes;

[0012] The Helmholtz cavity three and the Helmholtz cavity four are located directly below the Helmholtz cavity one, and the top surfaces of the Helmholtz cavity three and the Helmholtz cavity four are flush with each other, and the Helmholtz cavity three and the Helmholtz cavity four are connected to the bottom wall of the Helmholtz cavity one through their respective coupling short tubes;

[0013] The Helmholtz cavity five and the Helmholtz cavity six are located directly below the Helmholtz cavity two, and the top surfaces of the Helmholtz cavity five and the Helmholtz cavity six are flush with each other. The Helmholtz cavity five and the Helmholtz cavity six are both connected to the bottom wall of the Helmholtz cavity two through their respective coupling short tubes.

[0014] Preferably, any one of the Helmholtz chamber one, Helmholtz chamber two, Helmholtz chamber three, Helmholtz chamber four, Helmholtz chamber five and Helmholtz chamber six comprises a rectangular cavity wall, the interior of the rectangular cavity wall is a Helmholtz chamber, the coupling short tube is arranged on the top wall of the rectangular cavity wall, and the coupling short tube is located in the Helmholtz chamber.

[0015] Preferably, the coupling short tube is a cylindrical tube, and its axis coincides with the central axis of the rectangular parallelepiped cavity wall along the height direction.

[0016] Preferably, the cross-sections of the Helmholtz chambers of the Helmholtz chamber three, the Helmholtz chamber four, the Helmholtz chamber five and the Helmholtz chamber six are all square, and the side lengths of the cross-sections of the Helmholtz chambers of the Helmholtz chamber three, the Helmholtz chamber four, the Helmholtz chamber five and the Helmholtz chamber six are the same.

[0017] Preferably, the rectangular cavity wall and the coupling short tube are integrally formed.

[0018] Preferably, the Helmholtz chamber of the Helmholtz chamber 1 has a length of 82 mm, a width of 40 mm, and a height h of 50 mm, and the wall thickness t of the coupling short tube of the Helmholtz chamber 1 is 5 mm, the axial length is 8 mm, and the inner diameter d is 10 mm;

[0019] The width of the interval between the second Helmholtz cavity and the first Helmholtz cavity is 2 mm.

[0020] Preferably, the thickness of the rectangular cavity walls of the Helmholtz cavity 2 and the Helmholtz cavity 1 is 2 mm.

[0021] Preferably, the cross-sections of the Helmholtz chambers of the Helmholtz chamber three, the Helmholtz chamber four, the Helmholtz chamber five and the Helmholtz chamber six are all squares with a side length of 40 mm, and the wall thickness t of their respective coupling short tubes is 2.5 mm, the axial length is 12 mm, and the inner diameter d is 3 mm;

[0022] The cavity heights h of the Helmholtz cavities of the Helmholtz cavity three, the Helmholtz cavity four, the Helmholtz cavity five and the Helmholtz cavity six are 14 mm, 17 mm, 69 mm and 64 mm respectively.

[0023] Preferably, the wall thickness of the rectangular parallelepiped cavity wall of the Helmholtz cavity three, the Helmholtz cavity four, the Helmholtz cavity five and the Helmholtz cavity six is ​​2 mm.

[0024] Preferably, the rectangular cavity wall is a rigid cavity wall.

[0025] A second aspect of the present invention provides a transformer low-frequency noise absorption method, comprising:

[0026] The sound wave enters the transformer low-frequency noise absorber from the air medium, causing local resonance of the Helmholtz cavity 1, the Helmholtz cavity 2, the Helmholtz cavity 3, the Helmholtz cavity 4, the Helmholtz cavity 5 and the Helmholtz cavity 6, resulting in energy dissipation;

[0027] For any one of Helmholtz cavity one, Helmholtz cavity two, Helmholtz cavity three, Helmholtz cavity four, Helmholtz cavity five and Helmholtz cavity six, the sound absorption frequency is adjusted by adjusting the cross-sectional size and height of its Helmholtz cavity to achieve sound absorption of the corresponding frequency, and the sound absorption frequency includes the transformer low frequency band 50 Hz and its harmonic frequencies at various levels.

[0028] Preferably, the local resonance processes of the Helmholtz cavity 1, the Helmholtz cavity 2, the Helmholtz cavity 3, the Helmholtz cavity 4, the Helmholtz cavity 5 and the Helmholtz cavity 6 are the same, specifically as follows:

[0029] For any one of the Helmholtz chambers 1, 2, 3, 4, 5 and 6, the gas molecules in the chamber are equivalent to a whole. When the sound wave passes through the Helmholtz chamber, it is compressed in the neck of the Helmholtz chamber, i.e., the coupling short tube, thereby squeezing the air medium in the Helmholtz chamber. When the sound wave frequency is the same as the vibration frequency of the Helmholtz chamber, the Helmholtz chamber vibrates violently. During this vibration process, the sound wave contacts and rubs against the inner walls of the Helmholtz chamber and the coupling short tube, resulting in energy dissipation.

[0030] Preferably, when the bottom surface of the Helmholtz chamber is a square with a width of D and a chamber height of h, the sound absorption frequency of a single Helmholtz chamber is:

[0031]

[0032] In the formula, f is the frequency of sound absorption; c0 is the speed of sound in air;

[0033] S is the cross-sectional area of ​​the coupling short tube; l0 is the axial length of the coupling short tube.

[0034] Compared with the prior art, the beneficial effects of the present invention are at least:

[0035] The present invention proposes a transformer low-frequency noise absorber based on asymmetric cascade Helmholtz cavities, which is formed by cascading an upper Helmholtz absorber and a lower Helmholtz absorber. The structural design is simple and reasonable. The chamber heights of the four Helmholtz cavities in the lower Helmholtz absorber are different, forming an asymmetric structure. Sound waves enter the transformer low-frequency noise absorber of the present invention from the air medium, causing resonance of the structural units (Helmholtz cavities one to six). The local resonance greatly increases the energy density of the sound, resulting in energy dissipation, so as to obtain perfect sound absorption. The absorption coefficients at the frequency points of 100Hz, 200Hz and 350Hz, the main components of the transformer low-frequency noise, are 0.88, 0.99 and 0.99 respectively, achieving high-efficiency absorption of multiple frequency bands.

[0036] The coupling between units will inevitably affect the final sound absorption frequency. Conventional methods use distance to isolate the principle, but this will lead to a problem that the sound absorption efficiency of each sound absorption frequency is reduced. The transformer low-frequency noise absorber proposed in the present invention uses the coupling effect between units to generate the sound absorption frequency. There is no need to deliberately eliminate the coupling effect between units, which ensures that the absorption coefficient of the target frequency does not decrease, alleviating the main limitations of the current multi-band absorber. The results obtained by the finite element method verify the feasibility of the present invention and the accuracy of the analysis method. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of the overall structure of the transformer low-frequency noise absorber according to an embodiment of the present invention;

[0038] Figure 2 It is a schematic structural diagram of a single Helmholtz cavity in a transformer low-frequency noise absorber according to an embodiment of the present invention;

[0039] Figure 3 is a cross-sectional schematic diagram of a single Helmholtz cavity according to an embodiment of the present invention;

[0040] Figure 4 is an absorption characteristic curve diagram of a single Helmholtz cavity in the transformer low-frequency noise absorber according to an embodiment of the present invention;

[0041] Figure 5 This is a result diagram of the cascaded Helmholtz sound absorber according to an embodiment of the present invention.

[0042] In the figure: 100, transformer low-frequency noise absorber; 1, Helmholtz cavity one; 11, rectangular cavity wall; 12, Helmholtz cavity; 13, coupling short tube; 2, Helmholtz cavity two; 3, Helmholtz cavity three; 4, Helmholtz cavity four; 5, Helmholtz cavity five; 6, Helmholtz cavity six. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only embodiments of a part of the present invention, rather than all embodiments. Based on the spirit of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the protection scope of the present invention.

[0044] like Figure 1 As shown, Embodiment 1 of the present invention provides a transformer low-frequency noise absorber 100 based on an asymmetric cascaded Helmholtz cavity, which is formed by cascading two upper and lower stages of Helmholtz absorbers;

[0045] The upper Helmholtz absorber includes a Helmholtz cavity 1 and a Helmholtz cavity 2 which are completely identical, and the Helmholtz cavity 1 and the Helmholtz cavity 2 are symmetrically arranged side by side;

[0046] The lower-level Helmholtz absorber includes Helmholtz cavity three 3, Helmholtz cavity four 4, Helmholtz cavity five 5 and Helmholtz cavity six 6;

[0047] Among them, the Helmholtz cavity three 3 and the Helmholtz cavity four 4 are located directly below the Helmholtz cavity one 1, the top surfaces of the Helmholtz cavity three 3 and the Helmholtz cavity four 4 are flush, and the Helmholtz cavity three 3 and the Helmholtz cavity four 4 are both connected to the Helmholtz cavity one 1;

[0048] Similarly, the Helmholtz chamber five 5 and the Helmholtz chamber six 6 are located directly below the Helmholtz chamber two 2 , the top surfaces of the Helmholtz chamber five 5 and the Helmholtz chamber six 6 are flush, and the Helmholtz chamber five 5 and the Helmholtz chamber six 6 are both connected to the Helmholtz chamber two 2 .

[0049] like Figure 1 and Figure 2 As shown, Helmholtz cavity 1, Helmholtz cavity 2, Helmholtz cavity 3, Helmholtz cavity 4, Helmholtz cavity 5, and Helmholtz cavity 6 are all rectangular cavities, and the length directions, width directions, and height directions of the six Helmholtz cavities are parallel.

[0050] The structural parameters of the four Helmholtz cavities, Helmholtz cavity 3 3, Helmholtz cavity 4 4, Helmholtz cavity 5 5 and Helmholtz cavity 6 6, differ only in cavity height, and the other structural parameters are consistent. Since the cavity heights of the four Helmholtz cavities, Helmholtz cavity 3 3, Helmholtz cavity 4 4, Helmholtz cavity 5 5 and Helmholtz cavity 6 6, are different, the transformer low-frequency noise absorber 100 formed is an asymmetric cascade structure.

[0051] In this embodiment, the structures and working principles of Helmholtz cavity 1, Helmholtz cavity 2, Helmholtz cavity 3, Helmholtz cavity 4, Helmholtz cavity 5 and Helmholtz cavity 6 are the same, and only the structural parameters are different. The structure and principle of the six Helmholtz cavities are described below by taking Helmholtz cavity 1 as an example:

[0052] like Figure 2 and Figure 3 As shown, the Helmholtz cavity 1 comprises a rectangular cavity wall 11, the interior of the rectangular cavity wall 11 is a Helmholtz cavity 12, and a coupling short tube 13 is arranged on the top wall of the rectangular cavity wall 11;

[0053] The coupling short tube 13 is a cylindrical tube, whose axis coincides with the central axis of the rectangular cavity wall 11 along the height direction. The coupling short tube 13 is located in the Helmholtz chamber 12, and the top end surface of the coupling short tube 13 is flush with the top surface of the rectangular cavity wall 11. Both ends of the coupling short tube 13 are opened to connect the Helmholtz chamber 12 with the extracavity space.

[0054] like Figure 3 As shown, D is the width of the Helmholtz chamber 12, the inner diameter of the coupling short tube 13 is d (the cross-sectional area of ​​the coupling short tube 13 is S), l0 is the axial length of the coupling short tube 13, and p is the background sound pressure, that is, the incident sound wave. Assume that the structure satisfies the following conditions:

[0055] (1) The wall surface of the Helmholtz chamber 12 is a rigid wall surface and has total reflectivity for sound wave transmission;

[0056] (2) The volume of the coupling short tube 13 connected to the Helmholtz chamber 12 is much smaller than the volume of the Helmholtz chamber 12;

[0057] (3) The wavelength of the sound wave is much larger than the cross-sectional radius d / 2 of the coupling short tube 13 , the axial length l0 of the coupling short tube 13 , and the cube root of the Helmholtz chamber 12 .

[0058] The propagation of sound can be ignored and the movement of each part of the sound element can be considered uniform.

[0059] The Helmholtz chamber three 3 and the Helmholtz chamber four 4 are connected to the bottom wall of the Helmholtz chamber one 1 through their respective coupling short tubes 13, and at the same time, the Helmholtz chamber five 5 and the Helmholtz chamber six 6 are connected to the bottom wall of the Helmholtz chamber two 2 through their respective coupling short tubes 13.

[0060] From the assumed condition (3), it can be known that the wavelength of the sound wave is much larger than the relevant parameters of the Helmholtz chamber 1, and the gas molecules in the Helmholtz chamber 1 can be equivalent to a whole. When the sound wave passes through the Helmholtz chamber 12, it is compressed in the neck of the Helmholtz chamber 12, that is, in the coupling short tube 13, thereby squeezing the air medium in the Helmholtz chamber 12. When the sound wave frequency is the same as the vibration frequency of the Helmholtz chamber 12, the Helmholtz chamber 1 will vibrate violently. During this vibration process, the sound wave will contact and rub against the inner wall of the Helmholtz chamber 12 and the coupling short tube 13, so that the energy is partially dissipated, achieving a noise reduction effect. The vibration frequency of the Helmholtz chamber is its inherent vibration frequency, and the sound wave frequency is the frequency of the incident sound wave. When the two frequencies are the same, the air in the cavity vibrates violently, rubs against the cavity and the short tube, and the energy is dissipated, that is, the sound is absorbed. Therefore, when these two frequencies are equal, it is the sound absorption frequency f.

[0061] The linearity of the coupling short tube 13 is much smaller than the wavelength of the sound wave, so it can be considered that the vibration in the coupling short tube 13 is uniform, and the air column in the coupling short tube 13 can be regarded as a mass M m =ρ0l0S as a whole. The air in the Helmholtz chamber 12 will be compressed or expanded as the air column in the coupling short tube 13 moves. The force of the cavity acting on the air column in the coupling short tube 13 is similar to the elastic force generated by a spring, and its elastic coefficient is At the same time, the corresponding reciprocal represents the stiffness coefficient The friction resistance between the air column vibration and the wall of the coupling short tube 13 is recorded as Rm. Here, ρ0 is the air density, c0 is the speed of sound in the air, S is the cross-sectional area of ​​the air column in the coupling short tube 13, that is, the cross-sectional area of ​​the coupling short tube 13, and V0 is the volume of the Helmholtz chamber 12.

[0062] When the coupling short pipe 13 entrance is subjected to sound pressure p=pae jωt When the influence of is applied, the motion equation of the air column in the coupling short tube 13 is:

[0063]

[0064] Where ξ represents the displacement, let U=vS Formula (1) can be transformed into:

[0065]

[0066] Will C a =C m S 2 Substituting into formula (2) we can get:

[0067]

[0068] Among them, Ma, Ra and Ca represent sound quality, acoustic resistance and acoustic capacity respectively.

[0069] Solving equation (3) yields:

[0070]

[0071] Therefore, the acoustic impedance of the Helmholtz cavity is:

[0072]

[0073] From formula (4), we can see that the absorption is strongest when the imaginary part of the acoustic impedance is 0, so it can be concluded that the sound absorption frequency f satisfies:

[0074]

[0075] D is the width of the square bottom of the Helmholtz chamber, and h is the height of the Helmholtz chamber.

[0076] The above formula simplifies the factors affecting the sound absorption frequency to a single factor. When the cross-sectional areas of each Helmholtz cavity are equal, the size of the sound absorption frequency f mainly depends on the cavity height h of the Helmholtz cavity 12 .

[0077] The sound absorption characteristics of a single Helmholtz cavity in the low-frequency noise section of the transformer are as follows: Figure 4 As shown, from Figure 4 It can be seen that the lower the sound absorption frequency, the greater the required cavity height h of the Helmholtz cavity 12, and when the sound absorption frequency is 2 times, the cavity height h of the Helmholtz cavity 12 also satisfies the relationship of 1 / 4, which is in line with formula (5).

[0078] By changing the cavity height h of the Helmholtz cavity, perfect absorption of the transformer's low frequency band of 50Hz and its harmonic frequencies at all levels can be achieved.

[0079] The working principle of the transformer low-frequency noise absorber 100 based on the asymmetric cascaded Helmholtz cavity of this embodiment is described below with reference to specific examples.

[0080] In the upper Helmholtz absorber: the Helmholtz chamber 12 of the Helmholtz chamber 1 is 82 mm long, 40 mm wide, and 50 mm high, and the wall thickness t of the coupling short tube 13 is 5 mm, the axial length is 8 mm, and the inner diameter d is 10 mm; the dimensions of the Helmholtz chamber 2 2 and the Helmholtz chamber 1 are exactly the same, and the two ends of the Helmholtz chamber 2 2 in the length direction are aligned with the two ends of the Helmholtz chamber 1 in the length direction, and the Helmholtz chamber 2 2 and the Helmholtz chamber 1 can be spaced apart, and the spacing width is 2 mm. The wall thickness of the rectangular parallelepiped cavity wall of the Helmholtz chamber 2 2 and the Helmholtz chamber 1 can preferably be 2 mm.

[0081] In the lower-level Helmholtz absorber: the cross-sections of the Helmholtz chambers 12 of the Helmholtz chamber three 3, the Helmholtz chamber four 4, the Helmholtz chamber five 5 and the Helmholtz chamber six 6 are all squares with a side length of 40 mm, the wall thickness t of the coupling short tube 13 is 2.5 mm, the axial length is 12 mm, the inner diameter d is 3 mm, and the cavity heights h of the Helmholtz chambers 12 of the Helmholtz chamber three 3, the Helmholtz chamber four 4, the Helmholtz chamber five 5 and the Helmholtz chamber six 6 are 14 mm, 17 mm, 69 mm and 64 mm respectively. Based on the above structure, it can be known that the cross-sections of Helmholtz cavity three 3, Helmholtz cavity four 4, Helmholtz cavity five 5 and Helmholtz cavity six 6 are symmetrically distributed in a 2×2 matrix, and the outer side surfaces of Helmholtz cavity three 3 and Helmholtz cavity four 4 are aligned with the outer side surface of Helmholtz cavity one 1 in the height direction, and the outer side surfaces of Helmholtz cavity five 5 and Helmholtz cavity six 6 are aligned with the outer side surface of Helmholtz cavity two 2 in the height direction.

[0082] The outer side surface refers to the side surface exposed to the outside of the transformer low-frequency noise absorber 100. For example, the two side surfaces of the Helmholtz cavity 2 2 and the Helmholtz cavity 1 1 that are close to each other are not the outer side surfaces. The top surface and the bottom surface of the Helmholtz cavity 2 2 and the Helmholtz cavity 1 1 are also not the outer side surfaces. The remaining three surfaces of the Helmholtz cavity 1 and the remaining three surfaces of the Helmholtz cavity 2 2 are all outer side surfaces.

[0083] The side surfaces of Helmholtz chamber three 3 and Helmholtz chamber four 4 corresponding to the outer side surface of Helmholtz chamber one 1 are aligned with the outer side surface of Helmholtz chamber one 1, and correspondingly, the side surfaces of Helmholtz chamber five 5 and Helmholtz chamber six 6 corresponding to the outer side surface of Helmholtz chamber two 2 are aligned with the outer side surface of Helmholtz chamber two 2, and any two adjacent Helmholtz chambers of Helmholtz chamber three 3, Helmholtz chamber four 4, Helmholtz chamber five 5 and Helmholtz chamber six 6 can be arranged at intervals. The wall thickness of the rectangular parallelepiped cavity wall of Helmholtz cavity three 3, Helmholtz cavity four 4, Helmholtz cavity five 5 and Helmholtz cavity six 6 is preferably 2 mm. That is, the wall thickness of Helmholtz chambers one to six is ​​2 mm, and they can share a cavity wall when adjacent.

[0084] like Figure 5 As shown, the sound wave enters the transformer low-frequency noise absorber 100 from the air medium, and specifically enters the Helmholtz chamber 12 of the Helmholtz chambers 1 to 6 through the mouth of the coupling short tube 13 of the Helmholtz chambers 1 to 6, causing resonance of the structural unit. Local resonance greatly increases the energy density of the sound, resulting in energy dissipation to obtain perfect sound absorption. The absorption coefficients at the frequency points of 100Hz, 200Hz and 350Hz, the main components of the transformer low-frequency noise, are 0.88, 0.99 and 0.99 respectively, achieving high-efficiency absorption of multiple frequency bands. In practical applications, the sound absorption frequency can be adjusted by adjusting the chamber cross-sectional dimensions and chamber height of any Helmholtz chamber.

[0085] A single Helmholtz cavity can achieve sound absorption of a specific wavelength (such as f1) by adjusting parameters. However, when multiple Helmholtz cavities are cascaded, when two Helmholtz cavities are close to each other, there must be coupling between the units, thereby changing the sound absorption frequency of the entire structure. The final sound absorption frequency is not a combination of the specific sound absorption frequencies of each Helmholtz cavity (such as f1, f2, f3), but a new frequency (such as f4, f5, f6). This is because the final sound absorption frequency is formed by the joint action of multiple Helmholtz cavities.

[0086] Embodiment 2 of the present invention provides a transformer low-frequency noise absorption method, comprising:

[0087] The sound wave enters the transformer low-frequency noise absorber described in Example 1 from the air medium, causing local resonance of the Helmholtz cavity 1, the Helmholtz cavity 2, the Helmholtz cavity 3, the Helmholtz cavity 4, the Helmholtz cavity 5 and the Helmholtz cavity 6, resulting in energy dissipation;

[0088] For any one of the Helmholtz chambers 1, 2, 3, 4, 5 and 6, based on formula (5), the sound absorption frequency is adjusted by adjusting the cross-sectional size and height of the Helmholtz chamber to achieve sound absorption of the corresponding frequency, wherein the sound absorption frequency includes the transformer low frequency band 50 Hz and its harmonic frequencies at various levels.

[0089] The local resonance processes of the Helmholtz cavity 1, Helmholtz cavity 2, Helmholtz cavity 3, Helmholtz cavity 4, Helmholtz cavity 5 and Helmholtz cavity 6 are the same, which are specifically as follows:

[0090] For any one of the Helmholtz chambers 1, 2, 3, 4, 5 and 6, the gas molecules in the chamber are equivalent to a whole. When the sound wave passes through the Helmholtz chamber, it is compressed in the neck of the Helmholtz chamber, i.e., the coupling short tube, thereby squeezing the air medium in the Helmholtz chamber. When the sound wave frequency is the same as the vibration frequency of the Helmholtz chamber, the Helmholtz chamber vibrates violently. During this vibration process, the sound wave contacts and rubs against the inner walls of the Helmholtz chamber and the coupling short tube, resulting in energy dissipation.

[0091] Compared with the prior art, the beneficial effects of the present invention are at least:

[0092] The present invention proposes a transformer low-frequency noise absorber based on asymmetric cascade Helmholtz cavities, which is formed by cascading an upper Helmholtz absorber and a lower Helmholtz absorber. The structural design is simple and reasonable. The chamber heights of the four Helmholtz cavities in the lower Helmholtz absorber are different, forming an asymmetric structure. Sound waves enter the transformer low-frequency noise absorber of the present invention from the air medium, causing resonance of the structural unit. The local resonance greatly increases the energy density of the sound, resulting in energy dissipation, so as to obtain perfect sound absorption. The absorption coefficients at the frequency points of 100Hz, 200Hz and 350Hz, the main components of the transformer low-frequency noise, are 0.88, 0.99 and 0.99 respectively, achieving high-efficiency absorption of multiple frequency bands.

[0093] The transformer low-frequency noise absorber proposed by the present invention does not need to deliberately eliminate the coupling effect between units, ensuring that the absorption coefficient of the target frequency does not decrease, alleviating the main limitations of the current multi-band absorber. The results obtained by the finite element method verify the feasibility of the present invention and the accuracy of the analysis method.

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A transformer low-frequency noise absorber, comprising an upper-stage Helmholtz absorber and a lower-stage Helmholtz absorber cascaded with the upper-stage Helmholtz absorber, characterized in that: The upper-stage Helmholtz absorber comprises a first Helmholtz cavity and a second Helmholtz cavity that are completely identical, wherein the first Helmholtz cavity and the second Helmholtz cavity both comprise a coupling short tube, and the first Helmholtz cavity and the second Helmholtz cavity are symmetrically arranged side by side; The lower-stage Helmholtz absorber comprises a third Helmholtz cavity, a fourth Helmholtz cavity, a fifth Helmholtz cavity and a sixth Helmholtz cavity; the third Helmholtz cavity, the fourth Helmholtz cavity, the fifth Helmholtz cavity and the sixth Helmholtz cavity have different cavity heights and all comprise coupling short tubes; The Helmholtz cavity three and the Helmholtz cavity four are located directly below the Helmholtz cavity one, and the top surfaces of the Helmholtz cavity three and the Helmholtz cavity four are flush with each other, and the Helmholtz cavity three and the Helmholtz cavity four are connected to the bottom wall of the Helmholtz cavity one through their respective coupling short tubes; The Helmholtz cavity five and the Helmholtz cavity six are located directly below the Helmholtz cavity two, and the top surfaces of the Helmholtz cavity five and the Helmholtz cavity six are flush with each other. The Helmholtz cavity five and the Helmholtz cavity six are both connected to the bottom wall of the Helmholtz cavity two through their respective coupling short tubes.

2. The transformer low-frequency noise absorber according to claim 1, characterized in that: Any one of the Helmholtz chamber one, Helmholtz chamber two, Helmholtz chamber three, Helmholtz chamber four, Helmholtz chamber five and Helmholtz chamber six includes a rectangular cavity wall, the interior of the rectangular cavity wall is a Helmholtz chamber, the top wall of the rectangular cavity wall is provided with the coupling short tube, and the coupling short tube is located in the Helmholtz chamber.

3. The transformer low-frequency noise absorber according to claim 2, characterized in that: The coupling short tube is a cylindrical tube, and its axis coincides with the central axis of the rectangular cavity wall along the height direction.

4. A transformer low-frequency noise absorber according to claim 2 or 3, characterized in that: The cross sections of the Helmholtz chambers of the Helmholtz chamber three, the Helmholtz chamber four, the Helmholtz chamber five and the Helmholtz chamber six are all square, and the side lengths of the cross sections of the Helmholtz chambers of the Helmholtz chamber three, the Helmholtz chamber four, the Helmholtz chamber five and the Helmholtz chamber six are the same.

5. A transformer low-frequency noise absorber according to claim 2 or 3, characterized in that: The rectangular cavity wall and the coupling short tube are integrally formed.

6. The transformer low-frequency noise absorber according to claim 4, characterized in that: The Helmholtz chamber of the Helmholtz chamber 1 has a length of 82 mm, a width of 40 mm, and a height h of 50 mm. The wall thickness t of the coupling short tube of the Helmholtz chamber 1 is 5 mm, the axial length is 8 mm, and the inner diameter d is 10 mm. The width of the interval between the second Helmholtz cavity and the first Helmholtz cavity is 2 mm.

7. The transformer low-frequency noise absorber according to claim 6, characterized in that: The wall thickness of the rectangular parallelepiped cavity wall of the Helmholtz cavity 2 and the Helmholtz cavity 1 is 2 mm.

8. The transformer low-frequency noise absorber according to claim 6, characterized in that: The cross-sections of the Helmholtz chambers of the Helmholtz chamber three, the Helmholtz chamber four, the Helmholtz chamber five and the Helmholtz chamber six are all squares with a side length of 40 mm, and the wall thickness t of their respective coupling short tubes is 2.5 mm, the axial length is 12 mm, and the inner diameter d is 3 mm; The cavity heights h of the Helmholtz cavities of the Helmholtz cavity three, the Helmholtz cavity four, the Helmholtz cavity five and the Helmholtz cavity six are 14 mm, 17 mm, 69 mm and 64 mm respectively.

9. The transformer low-frequency noise absorber according to claim 8, characterized in that: The wall thickness of the rectangular parallelepiped cavity wall of the Helmholtz cavity three, the Helmholtz cavity four, the Helmholtz cavity five and the Helmholtz cavity six is ​​2 mm.

10. A transformer low-frequency noise absorber according to claim 2 or 3, characterized in that: The rectangular cavity wall is a rigid cavity wall.

11. A transformer low-frequency noise absorption method, characterized in that: include: The sound wave enters the transformer low-frequency noise absorber according to any one of claims 1 to 10 from the air medium, causing local resonance of the Helmholtz cavity 1, the Helmholtz cavity 2, the Helmholtz cavity 3, the Helmholtz cavity 4, the Helmholtz cavity 5 and the Helmholtz cavity 6, resulting in energy dissipation; For any one of Helmholtz cavity one, Helmholtz cavity two, Helmholtz cavity three, Helmholtz cavity four, Helmholtz cavity five and Helmholtz cavity six, the sound absorption frequency is adjusted by adjusting the cross-sectional size and height of its Helmholtz cavity to achieve sound absorption of the corresponding frequency, and the sound absorption frequency includes the transformer low frequency band 50 Hz and its harmonic frequencies at various levels.

12. A transformer low-frequency noise absorption method according to claim 11, characterized in that: The local resonance processes of the Helmholtz cavity 1, Helmholtz cavity 2, Helmholtz cavity 3, Helmholtz cavity 4, Helmholtz cavity 5 and Helmholtz cavity 6 are the same, which are specifically as follows: For any one of the Helmholtz chambers 1, 2, 3, 4, 5 and 6, the gas molecules in the chamber are equivalent to a whole. When the sound wave passes through the Helmholtz chamber, it is compressed in the neck of the Helmholtz chamber, i.e., the coupling short tube, thereby squeezing the air medium in the Helmholtz chamber. When the sound wave frequency is the same as the vibration frequency of the Helmholtz chamber, the Helmholtz chamber vibrates violently. During this vibration process, the sound wave contacts and rubs against the inner walls of the Helmholtz chamber and the coupling short tube, resulting in energy dissipation.

13. A transformer low-frequency noise absorption method according to claim 11, characterized in that: When the bottom of the Helmholtz chamber is a square with a width of D and a chamber height of h, the sound absorption frequency of a single Helmholtz chamber is: In the formula, f is the frequency of sound absorption; c0 is the speed of sound in air; S is the cross-sectional area of ​​the coupling short tube; l0 is the axial length of the coupling short tube.

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