A Helmholtz resonator and its control method

Abstract

This invention provides a Helmholtz resonator and its control method. The Helmholtz resonator includes a neck cavity and a resonant cavity. The neck cavity includes at least two nested cylindrical cavity wall components. A first transmission mechanism is provided, which can drive the cylindrical cavity wall components to move relative to each other along the axial direction of the neck cavity. The resonant cavity includes two opposing movable wall surfaces parallel to the central axis. A second transmission mechanism is provided, which can drive the two movable wall surfaces of the resonant cavity to move relative to each other along the second central axis. The technical solution of this invention can adapt to the noise frequency variations of the controlled space and is widely applicable in the field of vibration reduction and noise reduction technology for enclosed spaces.

Description

Technical Field

[0001] This invention relates to the field of vibration reduction and noise reduction technology, particularly to the field of vibration reduction and noise reduction technology for ships. Background Technology

[0002] With the booming development of modern industry and transportation, noise problems in enclosed spaces have become increasingly prominent. Noise from enclosed spaces such as pipelines, ship cabins, and automobile interiors can cause "acoustic fatigue" in related machinery, worsen the working environment, and reduce personnel efficiency. To address these noise problems, technologies for noise control and elimination have been developed.

[0003] Helmholtz resonators, as a passive control technology with a simple structure and good noise attenuation capability within a specific frequency band, are widely used in the field of noise control in enclosed spaces. Traditional Helmholtz sound-absorbing structures consist of a closed resonant cavity and a neck tube connected to the cavity, providing good absorption of low-frequency noise. When external sound waves are received, the air inside the neck of the Helmholtz sound-absorbing structure vibrates, and the air in the resonant cavity generates a restoring force. That is, the sound energy in the system is attenuated by the movement of air in the neck of the resonator, and this is regulated by the stiffness of the air in the resonant cavity. If the frequency of the sound wave equals the natural frequency of the system, the air column in the neck will generate severe resonant vibration, overcoming frictional resistance and dissipating sound energy.

[0004] Traditional Helmholtz resonators have a certain problem: they can effectively absorb sound near their resonant frequency, but the resonant frequency is determined at the beginning of the structural design of the Helmholtz resonator, resulting in a narrow sound absorption bandwidth, and can only be used as a narrow-band low-frequency sound absorber. Summary of the Invention

[0005] To address the problem of narrow sound absorption bandwidth in existing Helmholtz resonators, this invention provides a Helmholtz resonator and its control method.

[0006] The technical solution of the present invention is as follows:

[0007] A Helmholtz resonator includes a neck cavity and a resonant cavity, the neck cavity being in communication with the resonant cavity, the neck cavity including a cylindrical cavity, and the resonant cavity including a cuboid cavity; the axis of the neck cavity is parallel to the communication direction between the neck cavity and the resonant cavity; a first central axis of the resonant cavity is parallel to the communication direction between the neck cavity and the resonant cavity, and a second central axis of the resonant cavity is perpendicular to the first central axis;

[0008] The neck cavity includes at least two nested cylindrical cavity wall components; a first transmission mechanism is provided, which can drive the cylindrical cavity wall components to move relative to each other along the axial direction of the neck cavity;

[0009] The resonant cavity includes two opposing movable walls parallel to the central axis; a second transmission mechanism is provided; the second transmission mechanism can drive the two movable walls of the resonant cavity to move relative to each other along the direction of the second central axis.

[0010] Optionally, the second transmission mechanism drives the two movable walls to at least two positions: the first central axis is parallel to or coincides with the axis of the neck cavity.

[0011] Optionally, the Helmholtz resonator is provided with two cylindrical cavity wall components, and the natural frequency f of the Helmholtz resonator is... r The control formula is:

[0012]

[0013] Where c is the sound velocity in the resonant cavity, S is the area of ​​one of the two movable walls, l is the distance between the two movable walls of the resonant cavity, (l1+l2) is the length of the neck cavity in the axial direction, l1 is the length of the cylindrical cavity wall component with the smaller inner diameter in the axial direction of the neck cavity, l2 is the length of the cylindrical cavity wall component with the larger inner diameter in the axial direction of the neck cavity, S2 is the area of ​​the cross-section of the cylindrical cavity wall component with the larger inner diameter perpendicular to the axis of the neck cavity, S1 is the area of ​​the cross-section of the cylindrical cavity wall component with the smaller inner diameter perpendicular to the axis of the neck cavity, and k = S1 / S2.

[0014] The method for controlling the natural frequency of a Helmholtz resonator, as described above, includes the following steps:

[0015] S1. Obtain the frequency response data of the controlled space;

[0016] S2. Determine whether the natural frequency of the Helmholtz resonator matches the target frequency of the controlled space. If the natural frequency of the Helmholtz resonator matches the target frequency of the controlled space, proceed to step S6; if the natural frequency of the Helmholtz resonator does not match the target frequency of the controlled space, proceed to step S3.

[0017] S3. Determine whether the target frequency of the controlled space is greater than the natural frequency of the Helmholtz resonator;

[0018] S4. If the target frequency of the controlled space is less than the noise reduction frequency of the Helmholtz resonator, then drive the first transmission mechanism to increase the length of the neck cavity along the axial direction; and / or drive the second transmission mechanism to increase the distance between the two movable walls, and proceed to step S1.

[0019] S5. If the target frequency of the controlled space is greater than the noise reduction frequency of the Helmholtz resonator, then drive the first transmission mechanism to reduce the length of the neck cavity along the axial direction; and / or drive the second transmission mechanism to reduce the distance between the two movable walls, and proceed to step S1.

[0020] S6, End control.

[0021] Optionally, the Helmholtz resonator is provided with two cylindrical cavity wall components, and the natural frequency f of the Helmholtz resonator is... r The control formula is:

[0022]

[0023] Where c is the sound velocity in the resonant cavity, S is the area of ​​one of the two movable walls, l is the distance between the two movable walls of the resonant cavity, (l1+l2) is the length of the neck cavity in the axial direction, l1 is the length of the cylindrical cavity wall component with the smaller inner diameter in the axial direction of the neck cavity, l2 is the length of the cylindrical cavity wall component with the larger inner diameter in the axial direction of the neck cavity, S2 is the area of ​​the cross-section of the cylindrical cavity wall component with the larger inner diameter perpendicular to the axis of the neck cavity, S1 is the area of ​​the cross-section of the cylindrical cavity wall component with the smaller inner diameter perpendicular to the axis of the neck cavity, and k = S1 / S2.

[0024] Optionally, the method for controlling the natural frequency of the Helmholtz resonator further includes the following steps:

[0025] S7. Drive the second transmission mechanism so that the first central axis of the resonant cavity changes from a state that coincides with the axis of the neck cavity to a state in which the first central axis of the resonant cavity deviates from the axis of the neck cavity.

[0026] The technical effects of this invention are as follows:

[0027] The Helmholtz resonator of this invention has a movable neck cavity and a resonant cavity, meaning that the volumes of both the neck cavity and the resonant cavity are adjustable. By adjusting the volumes of the neck cavity and the resonant cavity, the natural frequency range (i.e., the damping frequency) of the Helmholtz resonator can be changed, thus adapting to changes in the noise frequency of the controlled space.

[0028] The control method of the present invention can indirectly change the volume of the neck cavity and the volume of the resonant cavity by adjusting the length of the neck cavity and the distance between the two walls of the resonant cavity through the first transmission mechanism and the second transmission mechanism, thereby changing the natural frequency of the Helmholtz resonator.

[0029] In summary, the technical solution of this invention achieves the objective of this invention.

[0030] The further effects of the above-mentioned alternative methods will be explained in detail below with reference to specific implementation methods. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of an embodiment of the Helmholtz resonator of the present invention.

[0032] Figure 2 for Figure 1 A structural schematic diagram of another state of the illustrated embodiment.

[0033] Figure 3 This is a schematic diagram of the Helmholtz resonator of the present invention.

[0034] Figure 4 for Figure 1 A perspective view of the experimental apparatus of the illustrated embodiment.

[0035] Figure 5 for Figure 4 A three-dimensional view of the experimental setup shown from another angle.

[0036] Figure 6 This is a flowchart of the control method of the present invention.

[0037] Figure 7 for Figure 4 The simulation results of the experimental setup shown are as follows.

[0038] Figure 8 for Figure 4 The simulation results of the experimental setup shown are as follows:

[0039] Figure 9 for Figure 4 The simulation results of the experimental setup shown are as follows:

[0040] Figure 10 for Figure 4 The simulation results of the experimental setup shown are as follows: (IV)

[0041] Figure 11 for Figure 4 The simulation results of the experimental setup shown are as follows: (5)

[0042] Figure 12 for Figure 4The simulation results of the experimental setup shown are as follows: (VI)

[0043] The markings in the image are explained as follows:

[0044] 101. Movable wall surface; 102. Resonance cavity; 103. Movable wall surface; 104. Neck cavity; 105. Cylindrical cavity wall component; 106. Cylindrical cavity wall component;

[0045] 401. Controlled Space;

[0046] 501. Stepper motor; 502. Second transmission mechanism; 503. Stepper motor; 504. First transmission mechanism. Detailed Implementation

[0047] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0048] like Figure 1 and Figure 4 As shown, the Helmholtz resonator of the present invention includes a neck cavity 104 and a resonant cavity 102, wherein the neck cavity 104 is connected to the resonant cavity 102 and the controlled space 401. The neck cavity 104 is a cylindrical cavity, and the resonant cavity 102 is a rectangular cavity. The cylindrical neck cavity 104 has one axis ( Figure 1 The centerline of the middle neck cavity 104 (perpendicular to the horizontal direction from top to bottom). The resonant cavity 102 has three axes. For ease of subsequent explanation, Figure 1 The axis of the resonant cavity 102, which coincides with the axis of the neck cavity 104, is the first central axis. Figure 1 The horizontal axis is the second central axis, and the third axis of the resonant cavity 102 will not be discussed at this time.

[0049] The neck cavity 104 is composed of nested cylindrical cavity wall components 105 and 106. The cylindrical cavity wall components 105 and 106 are movable relative to each other along the axial direction of the neck cavity 104, thereby increasing or decreasing the volume of the neck cavity 104. Figure 1 , Figure 4 and Figure 5The first transmission mechanism 504 drives the aforementioned relative movement between the cylindrical cavity wall component 105 and the cylindrical cavity wall component 106. Specifically, the first transmission mechanism 504 includes transmission components, including bevel gears, and is connected to the resonant cavity 102 (excluding the movable wall surfaces 101 and 103). A stepper motor 501 is connected to the first transmission mechanism 504 as a power source, and the first transmission mechanism 504 transmits power to the resonant cavity 102. By raising or lowering the resonant cavity 102, the aforementioned relative movement between the cylindrical cavity wall component 105 and the cylindrical cavity wall component 106 is achieved.

[0050] Combination Figure 1 , Figure 4 and Figure 5 The two opposing walls (movable wall 101 and movable wall 103) of the resonant cavity 102 can move relative to each other along the second central axis, thereby increasing or decreasing the volume of the resonant cavity 102. Movable wall 101 and movable wall 103 are respectively connected to a second transmission mechanism 502. The second transmission mechanism 502 includes a lead screw drive structure, and a stepper motor 503 is connected to the second transmission mechanism 502 as a power source. The second transmission mechanism 502 then drives the movable wall 101 and movable wall 103 to achieve the aforementioned relative movement between them. Figure 5 As shown, the stepper motor 503 and the second transmission mechanism 502 are mounted on the slide rail so as to move synchronously with the lifting or lowering of the resonant cavity 102. Figure 5 In the embodiment shown, there are two sets of stepper motor 503 and connected second transmission mechanism 502, corresponding to movable wall 101 and movable wall 103 respectively.

[0051] like Figure 2 As shown, since the movable wall 101 and movable wall 103 in this embodiment are respectively provided with the second transmission mechanism 502, the first central axis of the resonant cavity 102 can be arranged to be parallel or coincide with the axis of the neck cavity 104.

[0052] Figure 3 Showing the Figure 1 The control mechanism of the illustrated embodiment is explained in detail below:

[0053] If an external pressure p0 is applied to excite the Helmholtz resonator at the neck opening, then:

[0054]

[0055] Where j is the imaginary unit, ω is the angular frequency, M is the mass of the air in the neck cavity, K is the stiffness caused by the air volume in the resonant cavity, C is the damping caused by the viscosity effect of the air in the resonant cavity, and v HR For the volume of the neck cavity of the Helmholtz resonator, SHR This indicates the cross-sectional area of ​​the neck cavity.

[0056]

[0057] Where, ξ HR ω is the damping coefficient. HR ρ is the angular frequency corresponding to the natural frequency of the Helmholtz resonator, and ρ is the gas density.

[0058] From equation (2), the natural frequency of the Helmholtz resonator can be obtained as:

[0059]

[0060] Where V is the volume of the resonant cavity, S HR The area of ​​the cross-section of the cervical cavity perpendicular to its axis, l e c is the length of the neck cavity, and c is the sound velocity in the resonant cavity 102.

[0061] refer to Figure 1 Since the volume of the resonant cavity 102 is V = Sl, where l is... Figure 1 The distance between the movable wall 101 and the movable wall 103, S is the area of ​​the movable wall (movable wall 101 or movable wall 103), l1 and l2 are the lengths of the non-overlapping portions of the cylindrical cavity wall components 106 and 105 in the axial direction of the neck cavity 104, respectively. l1 is the length of the cylindrical cavity wall component 106 with a smaller inner diameter in the axial direction of the neck cavity 104, and l2 is the length of the cylindrical cavity wall component 105 with a larger inner diameter in the axial direction of the neck cavity 104. Then, the above equation (4) can be expressed as:

[0062]

[0063] Wherein, l is the distance between the two movable walls (movable wall 101 or movable wall 103) of the resonant cavity 102, S2 is the area of ​​the cross-section of the cylindrical cavity wall component 105 with a larger inner diameter perpendicular to the axis of the neck cavity 104, S1 is the area of ​​the cross-section of the cylindrical cavity wall component 106 with a smaller inner diameter perpendicular to the axis of the neck cavity 104, and k = S1 / S2.

[0064] As can be seen from the above equation (5), the natural frequency of the Helmholtz resonator can be changed by changing l, l1, and l2. Figure 1 The illustrated embodiment allows for synchronized adjustment of the natural frequency of the Helmholtz resonator by the resonant cavity 102 and the neck cavity 104 through adjustment of l and / or l1, l2. This synchronized adjustment enables a wider range of natural frequency adjustment for the Helmholtz resonator, allowing for cross-peak adjustment and optimized noise reduction.

[0065] Figure 2 The Helmholtz resonator and Figure 1 The different working states after adjustment are shown. Figure 1 The display shows the working state of the Helmholtz resonator, with the first central axis of the resonant cavity 102 coinciding with the axis of the neck cavity 104; Figure 1 The display shows the working state of the Helmholtz resonator. The first central axis of the resonant cavity 102 is parallel to and does not coincide with the axis of the neck cavity 104, that is, the first central axis of the resonant cavity 102 is deviated from the axis of the neck cavity 104. Figure 2 The operating state of the Helmholtz resonator shown can further optimize the noise reduction effect near the target frequency and amplify the sound waves at non-target frequencies. This effect has practical significance for applications in ship systems. For example, noise generated by mechanical equipment in ship cabins needs to be reduced, but sound waves from ship communication and alarm systems not only cannot be suppressed, but also need to be amplified.

[0066] Figure 6 The flowchart of the control method for the Helmholtz resonator of the present invention is shown. The following is in conjunction with... Figure 1 , Figure 2 , Figure 4 and Figure 5 right Figure 6 The steps shown are explained below.

[0067] Acquire frequency response data

[0068] In this step, data on the sound pressure amplitude-frequency response near the target frequency of the controlled space 401 are acquired. When acquiring the sound pressure amplitude-frequency response data of the controlled space 401 for the first time, data on the sound pressure amplitude-frequency response of the controlled space 401 in two cases should be obtained: before the Helmholtz resonator is connected to the controlled space 401 and after the connection to the controlled space 401.

[0069] Compare the noise reduction frequency with the target frequency

[0070] Compare the sound pressure amplitude-frequency response data of the controlled space 401 under the two conditions obtained in the previous step, and determine whether the noise reduction frequency of the Helmholtz resonator matches the target frequency of the controlled space 401. If the noise reduction frequency of the Helmholtz resonator matches the target frequency of the controlled space 401, proceed to the step "cavity bias"; if the noise reduction frequency of the Helmholtz resonator does not match the target frequency of the controlled space 401, further determine whether the target frequency of the controlled space 401 is greater than the noise reduction frequency of the Helmholtz resonator.

[0071] Increase cavity volume

[0072] If the target frequency of the controlled space 401 is less than the noise reduction frequency of the Helmholtz resonator, then the first transmission mechanism 504 is driven to increase the length of the neck cavity 104 along its axial direction; and / or the second transmission mechanism 502 is driven to increase the distance between the movable wall 101 and the movable wall 103. The increased length of the neck cavity 104 along its axial direction or the distance between the movable wall 101 and the movable wall 103 can be obtained according to the aforementioned formula (5).

[0073] Then proceed to the "Acquire Frequency Response Data" step, and after acquiring the sound pressure amplitude-frequency response data near the target frequency of the controlled space 401 again, execute subsequent steps such as "Compare Noise Reduction Frequency with Target Frequency" in sequence.

[0074] Reduce cavity volume

[0075] If the target frequency of the controlled space 401 is greater than the noise reduction frequency of the Helmholtz resonator, then the first transmission mechanism 504 is driven to reduce the length of the neck cavity 104 along the axial direction; and / or the second transmission mechanism 502 is driven to reduce the distance between the movable wall 101 and the movable wall 103. The value of the reduced length of the neck cavity 104 along the axial direction or the value of the distance between the movable wall 101 and the movable wall 103 can be obtained according to the aforementioned formula (5).

[0076] Then proceed to the "Acquire Frequency Response Data" step, and after acquiring the sound pressure amplitude-frequency response data near the target frequency of the controlled space 401 again, execute subsequent steps such as "Compare Noise Reduction Frequency with Target Frequency" in sequence.

[0077] Cavity bias

[0078] If the noise reduction frequency of the Helmholtz resonator matches the target frequency of the controlled space 401, it indicates that the currently set length values ​​in the axial direction of the neck cavity 104 and the distance values ​​between the movable wall 101 and the movable wall 103 are appropriate. To further enhance the vibration reduction effect, the second transmission mechanism 502 can be driven so that the first central axis of the resonant cavity 102 is aligned with the axis of the neck cavity 104 (e.g., ...). Figure 1 As shown) the state where the first central axis of the resonant cavity 102 deviates from the axis of the neck cavity 104 (e.g.) Figure 2 (As shown).

[0079] End control

[0080] The control flow for the current cycle ends, and the process repeats from the beginning step (acquiring frequency response data) in the next cycle. Figure 6 The control flow is shown.

[0081] In other embodiments of the control method for the Helmholtz resonator, before the Helmholtz resonator is connected to the controlled space 401, the parameters of the Helmholtz resonator (the length of the neck cavity 104 along the axis and the distance between the movable wall 101 and the movable wall 103) can be determined using formula (5) so that the noise reduction frequency of the Helmholtz resonator reaches or approaches the target frequency. If, due to the influence of various environmental factors, the noise reduction frequency of the Helmholtz resonator is only close to the target frequency, it can be fine-tuned by subsequent steps such as "increasing the cavity volume" or "reducing the cavity volume" to achieve the goal as soon as possible.

[0082] The technical effects of the present invention are illustrated below using simulation experimental data. The simulation experiments are aimed at... Figure 4 The experimental setup shown was used, and the simulation software employed was COMSOL Multiphysics 6.2. The controlled space 401 had a width of 1.497 m, a depth of 0.3 m, and a height of 0.394 m. A single-pole point source was added within the controlled space 401 as a point sound source excitation, and the volumetric flow rate of the point sound source was 1 × 10⁻⁶. -4 m 3 / s, that is, Q0 = 1 × 10 -4 m 3 / s. The air density in the simulated environment is 1.21 kg / m³. 3 The speed of sound is 340 m / s.

[0083] Figure 7 In the displayed data, the "closed space" curve represents the frequency response curve when the controlled space 401 is not connected to the Helmholtz resonator; the "coupled symmetric resonator" curve represents the frequency response curve when the controlled space 401 is connected to the Helmholtz resonator, and the first central axis of the resonant cavity 102 coincides with the axis of the neck cavity 104. For example... Figure 7 As shown, after connecting the Helmholtz resonator, the Helmholtz resonator has a vibration reduction and noise reduction effect on the first-order sound pressure peak of the controlled space 401.

[0084] Figure 8 In the displayed data, the "closed space" curve represents the frequency response curve when the controlled space 401 is not connected to a Helmholtz resonator; the "coupled asymmetric resonator" curve represents the frequency response curve when the controlled space 401 is connected to a Helmholtz resonator, and the first central axis of the resonant cavity 102 is parallel to but does not coincide with the axis of the neck cavity 104. Figure 7 compared to, Figure 8 In the experiment shown, the volumes of the resonant cavity 102 and the neck cavity 104 remained unchanged; only the resonant cavity 102 was offset relative to the neck cavity 104. Figure 8As shown, when the controlled space 401 is connected to a Helmholtz resonator, and the first central axis of the resonant cavity 102 is offset from the axis of the neck cavity 104, the vibration reduction and noise reduction effect of the Helmholtz resonator on the first-order sound pressure peak of the controlled space 401 is better than that of the neck cavity 104. Figure 7 The vibration reduction and noise reduction effect shown.

[0085] Figure 7 and Figure 8 The frequency corresponding to the first peak is 114Hz. The total sound pressure level before connecting to the Helmholtz resonator is 120.0577dB. The total sound pressure level at the first peak after connecting to the symmetrical resonator is 62.9554dB. The total sound pressure level at the first peak after connecting to the asymmetrical resonator is 49.3588dB.

[0086] Figure 9 In the displayed data, the "closed space" curve represents the frequency response curve when the controlled space 401 is not connected to a Helmholtz resonator; the "coupled symmetric resonator" curve represents the frequency response curve when the controlled space 401 is connected to a Helmholtz resonator, and the first central axis of the resonant cavity 102 coincides with the axis of the neck cavity 104. Relative to... Figure 7 The setup of the Helmholtz resonator shown is as follows. Figure 9 In the experiment shown, the cavity volume was reduced, which enabled the Helmholtz resonator to have a vibration reduction and noise reduction effect on the second-order sound pressure peak of the controlled space 401. Figure 7 and Figure 9 This demonstrates that the frequency range for vibration reduction and noise reduction of the Helmholtz resonator of the present invention can be effectively adjusted.

[0087] Figure 10 In the displayed data, the "closed space" curve represents the frequency response curve when the controlled space 401 is not connected to a Helmholtz resonator; the "coupled asymmetric resonator" curve represents the frequency response curve when the controlled space 401 is connected to a Helmholtz resonator, and the first central axis of the resonant cavity 102 is parallel to but does not coincide with the axis of the neck cavity 104. Figure 9 compared to, Figure 10 In the experiment shown, the volumes of the resonant cavity 102 and the neck cavity 104 remained unchanged; only the resonant cavity 102 was offset relative to the neck cavity 104. Figure 10 As shown, when the controlled space 401 is connected to a Helmholtz resonator, and the first central axis of the resonant cavity 102 is offset from the axis of the neck cavity 104, the vibration reduction and noise reduction effect of the Helmholtz resonator on the second-order sound pressure peak of the controlled space 401 is better than that of the neck cavity 104. Figure 9 The vibration reduction and noise reduction effect shown. Figure 8 and Figure 10 This demonstrates that the frequency range for vibration reduction and noise reduction of the Helmholtz resonator of the present invention can be effectively adjusted.

[0088] Figure 9 and Figure 10 The frequency corresponding to the second peak is 227Hz. The total sound pressure level before connecting to the Helmholtz resonator is 131.0840dB. The total sound pressure level at the second peak after connecting to the symmetrical resonator is 63.3154dB. The total sound pressure level at the first peak after connecting to the asymmetrical resonator is 45.2795dB.

[0089] Figure 11 The experimental data are shown for the following two scenarios: the volumes of the resonant cavity 102 and the neck cavity 104 remain unchanged; only the direction of the deviation between the first central axis of the resonant cavity 102 and the axis of the neck cavity 104 is adjusted (e.g., ...). Figure 1 As shown, in both the left and right directions, the distance between the first central axis of the resonant cavity 102 and the axis of the neck cavity 104 is 40 mm. Figure 11 As shown, the different directions of deviation between the first central axis of the resonant cavity 102 and the axis of the neck cavity 104 do not show any difference in the vibration reduction effect of the Helmholtz resonator.

[0090] Figure 12 The experimental data are shown for the following two scenarios: the volumes of the resonant cavity 102 and the neck cavity 104 remain unchanged; only the direction of the deviation between the first central axis of the resonant cavity 102 and the axis of the neck cavity 104 is adjusted (e.g., ...). Figure 1 As shown, in both the left and right directions, the distance between the first central axis of the resonant cavity 102 and the axis of the neck cavity 104 is 80 mm. Figure 11 As shown, the different directions of deviation between the first central axis of the resonant cavity 102 and the axis of the neck cavity 104 do not show any difference in the vibration reduction effect of the Helmholtz resonator.

[0091] The offset between the first central axis of the resonant cavity 102 and the axis of the neck cavity 104 has a significant impact on the vibration reduction and noise reduction effect of the Helmholtz resonator, as shown in Tables 1 and 2. Table 1 focuses on vibration reduction and noise reduction at the first peak (corresponding to a frequency of 114Hz). The volume of the resonant cavity 102 remains constant; only the positions of the movable walls 101 and 103 are adjusted to achieve the desired vibration reduction and noise reduction between the resonant cavity 102 and the neck cavity 104. Figure 2 The bias states are shown in Table 2. Table 2 describes the vibration reduction and noise reduction for the second peak (corresponding frequency 227Hz). The volume of the resonant cavity 102 remains unchanged; only the positions of the movable walls 101 and 103 are adjusted to achieve the desired effect between the resonant cavity 102 and the neck cavity 104. Figure 2 The bias state is shown.

[0092] Table 1

[0093] Offset distance (mm) 20 40 60 80 First-order peak total sound pressure level (dB) 60.8318 49.3588 60.8409 69.6951

[0094] In Table 1, when the offset distance is 80mm, the anti-resonance peak of the Helmholtz resonator is at a frequency of 113Hz, and the lowest total sound pressure level at this frequency is 52.0236dB.

[0095] Table 2

[0096] Offset distance (mm) 5 10 15 20 Second peak total sound pressure level (dB) 60.6628 45.2795 60.1083 73.94157

[0097] In Table 2, when the offset distance is 15mm, the anti-resonance peak of the Helmholtz resonator is at a frequency of 226Hz. The "total sound pressure level of the second peak" in Table 2 refers to the total sound pressure level at 226Hz. In Table 2, when the offset distance is 20mm, the anti-resonance peak of the Helmholtz resonator is at a frequency of 225Hz. The "total sound pressure level of the second peak" in Table 2 refers to the total sound pressure level at 225Hz.

[0098] It is worth noting that the above description is only a preferred embodiment of the present invention and does not limit the scope of patent protection of the present invention. The present invention can also be replaced by equivalent technologies. Therefore, all equivalent changes made based on the description and figures of the present invention, or direct or indirect applications to other related technical fields, are included within the scope of the present invention.

Claims

1. A Helmholtz resonator, comprising a neck cavity and a resonant cavity, wherein the neck cavity is in communication with the resonant cavity, characterized in that: The neck cavity includes a cylindrical cavity, and the resonant cavity includes a cuboid cavity; the axis of the neck cavity is parallel to the communication direction between the neck cavity and the resonant cavity; the first central axis of the resonant cavity is parallel to the communication direction between the neck cavity and the resonant cavity, and the second central axis of the resonant cavity is perpendicular to the first central axis; The neck cavity includes at least two nested cylindrical cavity wall components; a first transmission mechanism is provided, which can drive the cylindrical cavity wall components to move relative to each other along the axial direction of the neck cavity; The resonant cavity includes two opposing movable walls parallel to the central axis; a second transmission mechanism is provided; the second transmission mechanism can drive the two movable walls of the resonant cavity to move relative to each other along the direction of the second central axis; The second transmission mechanism drives the two movable walls to at least two positions: the first central axis is parallel to or coincides with the axis of the neck cavity; Two cylindrical cavity wall components are provided, and the natural frequency f of the Helmholtz resonator is... r The control formula is: Where c is the sound velocity in the resonant cavity, S is the area of ​​one of the two movable walls, l is the distance between the two movable walls of the resonant cavity, l1+l2 is the length of the neck cavity in the axial direction, l1 is the length of the cylindrical cavity wall component with the smaller inner diameter in the axial direction of the neck cavity, l2 is the length of the cylindrical cavity wall component with the larger inner diameter in the axial direction of the neck cavity, S2 is the area of ​​the cross-section of the cylindrical cavity wall component with the larger inner diameter perpendicular to the axis of the neck cavity, S1 is the area of ​​the cross-section of the cylindrical cavity wall component with the smaller inner diameter perpendicular to the axis of the neck cavity, and k = S1 / S2.

2. A method for controlling the natural frequency of the Helmholtz resonator according to claim 1, characterized in that: Includes the following steps: S1. Obtain the frequency response data of the controlled space; S2. Determine whether the natural frequency of the Helmholtz resonator matches the target frequency of the controlled space. If the natural frequency of the Helmholtz resonator matches the target frequency of the controlled space, proceed to step S6; if the natural frequency of the Helmholtz resonator does not match the target frequency of the controlled space, proceed to step S3. S3. Determine whether the target frequency of the controlled space is greater than the natural frequency of the Helmholtz resonator; S4. If the target frequency of the controlled space is less than the noise reduction frequency of the Helmholtz resonator, then drive the first transmission mechanism to increase the length of the neck cavity along the axial direction; and / or drive the second transmission mechanism to increase the distance between the two movable walls, and proceed to step S1. S5. If the target frequency of the controlled space is greater than the noise reduction frequency of the Helmholtz resonator, then drive the first transmission mechanism to reduce the length of the neck cavity along the axial direction; and / or drive the second transmission mechanism to reduce the distance between the two movable walls, and proceed to step S1. S6, End control.

3. The method for controlling the natural frequency of a Helmholtz resonator according to claim 2, characterized in that: Two cylindrical cavity wall components are provided, and the natural frequency f of the Helmholtz resonator is... r The control formula is: Where c is the sound velocity in the resonant cavity, S is the area of ​​one of the two movable walls, l is the distance between the two movable walls of the resonant cavity, l1+l2 is the length of the neck cavity in the axial direction, l1 is the length of the cylindrical cavity wall component with the smaller inner diameter in the axial direction of the neck cavity, l2 is the length of the cylindrical cavity wall component with the larger inner diameter in the axial direction of the neck cavity, S2 is the area of ​​the cross-section of the cylindrical cavity wall component with the larger inner diameter perpendicular to the axis of the neck cavity, S1 is the area of ​​the cross-section of the cylindrical cavity wall component with the smaller inner diameter perpendicular to the axis of the neck cavity, and k = S1 / S2.

4. The method for controlling the natural frequency of a Helmholtz resonator according to claim 2, characterized in that: It also includes the following steps: S7. Drive the second transmission mechanism so that the first central axis of the resonant cavity changes from a state that coincides with the axis of the neck cavity to a state in which the first central axis of the resonant cavity deviates from the axis of the neck cavity.

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