Passive noise reduction design method and device for pilot helmet with embedded sound absorption superstructure

Abstract

The invention discloses a passive noise reduction design method and device for a pilot helmet with an embedded sound absorption superstructure, sound absorption holes are formed in a superstructure area (3) of the passive noise reduction helmet, F-P resonant cavities (1) are compactly arranged in the helmet (2), and according to the available space size in practical application, the sound absorption holes are formed in the superstructure area (3); the F-P resonant cavity (1) with a slender cavity is arranged in a compact space through folding or curling, so that broadband sound absorption and noise reduction are realized. According to the pilot helmet passive noise reduction design method and device with the embedded sound absorption superstructure, compared with an existing sound absorption material and structure, more excellent passive noise reduction and sound absorption performance can be provided under the conditions of light weight and narrow space.

Description

Technical Field

[0001] The invention belongs to the technical field of sound absorption, and in particular relates to a passive noise reduction design method and device for a pilot helmet with an embedded sound absorption superstructure. Background Art

[0002] When flying at high altitudes, pilots will inevitably be exposed to noise from all directions. For a profession like pilots that requires a high level of mental concentration, noise has a huge impact on combat situations and personnel health. During combat, pilots must communicate with the ground tower, and huge noise will greatly interfere with the pilot's work, affecting the pilot's immediate judgment, causing him to be unable to respond quickly, resulting in some decision-making errors. Therefore, sound absorption and noise reduction in complex acoustic environments are particularly important for pilots. Currently, pilot noise reduction helmets use active noise reduction technology, which has limited effect on high-frequency noise with very short wavelengths.

[0003] The working principle of active noise reduction technology is to output sound waves with opposite phases through electrical signal feedback to offset the incoming noise to achieve the effect of noise suppression. It has a good noise reduction effect on low-frequency noise, but for high-frequency noise with a very short wavelength, it is difficult for the electrical signal to accurately and real-time generate an active signal with a phase difference of 0.5 from the noise signal to offset it. When there is a phase offset, it will even strengthen the noise. The active noise reduction system needs a certain amount of time to process the signal and generate reverse sound waves, which causes a delay in its operation and affects the pilot's operation.

[0004] Traditional sound-absorbing materials can be divided into two categories according to their sound absorption mechanisms: resonant sound-absorbing materials and porous sound-absorbing materials. Resonant sound-absorbing materials are mainly based on the viscous loss mechanism. When the structure resonates under the excitation of sound waves, the wall viscous damping plays a major role at this time, and the sound absorption effect is the best; but its bandwidth is narrow, and it can only have good sound absorption performance near the resonance frequency. Porous sound-absorbing materials have both viscous loss mechanism and thermal conduction loss mechanism. The material does not have obvious resonance characteristics and has a wide sound absorption bandwidth that can cover the entire high-frequency range. Traditional porous sound-absorbing materials, such as sponges and foams, require a large thickness to achieve noise reduction, which is not suitable for the narrow space of a pilot's helmet. Therefore, there is an urgent need to develop a passive noise reduction helmet design method that breaks through the restrictive relationship between broadband noise reduction design and narrow space size, while achieving timely response.

[0005] In recent years, acoustic superstructures have attracted increasing attention due to their excellent ability to control acoustic waves. For sounds in the audible frequency range of 20 to 20,000 Hz, the dissipation in the gas medium is very small, so the effective absorption of sound depends on the micro- or macro-structured materials, where the acoustic energy can be dissipated through two mechanisms related to the solid-air interface. One is viscous dissipation near the solid surface, where the no-slip boundary condition causes large relative motion within the viscous boundary layer. The other is heat conduction through the solid, which causes the adiabatic properties of sound propagation to be destroyed. It can be seen that materials with large microstructure gas-solid interface areas, such as porous media, usually have the largest dissipation coefficients.

[0006] Sound-absorbing superstructures mainly achieve the required optimal sound absorption requirements by changing the structure or material of the material. The development of superstructures provides a solution for designing low-frequency absorbers with sub-wavelength thickness. Inspired by acoustic superstructures, materials with large microstructured gas-solid interface areas are the main components of sound absorption systems. However, traditional sound-absorbing materials or structures can only effectively absorb low-frequency sound waves when they reach a certain thickness, which cannot meet the size restrictions and lightweight requirements in many applications, which is particularly important in helmet design. Summary of the invention

[0007] The present invention provides a passive noise reduction design method and device for a pilot helmet with an embedded sound-absorbing superstructure, aiming to overcome the shortcomings of active noise reduction technology and traditional porous materials, and introduce an FP resonance cavity structure based on acoustic capillary effect and siphon effect into the pilot's helmet design to achieve passive noise reduction with good frequency bandwidth and sound absorption effect.

[0008] In order to achieve the above object, the present invention adopts the following technical solution: A method for passive noise reduction design of a pilot helmet with an embedded sound absorbing superstructure comprises the following steps: 1) Determine the target noise frequency range, expected sound absorption effect and available space size; 2) Determine the overall superstructure volume limit based on the available space, and design FP resonant cavity combinations of different lengths and cross-sectional areas within the volume range according to the target noise frequency range and expected sound absorption effect; 3) Conduct simulation experiments on the designed FP resonance cavity combination, compare the simulation results with the target requirements, optimize the structural parameters according to the sound absorption law of the FP resonance cavity, and improve the sound absorption effect within the target range; 4) Embed the FP resonance cavity combination that meets the target noise frequency range and expected sound absorption effect into the helmet, allocate the position and arrangement of cavities of different lengths according to the actual space size, and reduce the space occupancy by folding and curling methods; 5) Test the sound absorption effect of the actual helmet to verify its sound absorption effect. If it does not meet expectations, analyze the reasons for the difference and reasonably adjust the design parameters, and iterate feedback until the expected sound absorption effect is achieved in the target noise frequency range.

[0009] A further improvement of the present invention is that the FP resonant cavity combination design further includes: Based on the sound absorption characteristics of the FP resonant cavity, broadband sound absorption is achieved by combining resonant cavities of different lengths; Compare and select the appropriate FP resonance cavity cross-sectional area to achieve the best sound absorption effect; The parameters of the FP resonant cavity combination were determined to be embedded within the helmet.

[0010] A further improvement of the present invention is that, by extending the spatial dimensions of the head area, the constraints on the sound absorption and noise reduction performance caused by insufficient space near the ears are compensated, thereby breaking through the limitations of broadband passive sound absorption and noise reduction in a narrow space.

[0011] A further improvement of the present invention is that a high sound absorption coefficient is ensured under the constraint of the narrow space of the helmet through the acoustic capillary effect of the narrow cross-section FP resonance cavity, and broadband passive sound absorption and noise reduction is achieved through the combination of gradient length FP resonance cavities.

[0012] A further improvement of the present invention is that the acoustic capillary extending in the head area is composed of a flexible bundle tube, which meets the requirements of flexible wearing and comfort of the human-machine interface.

[0013] A further improvement of the present invention is that the length and cross-sectional area of ​​the FP resonant cavity are designed according to requirements, and the depths of different parts are the same or different to meet the requirements of any changing geometric shapes. A further improvement of the present invention is that the cross-sectional shape of the FP resonance cavity can be arbitrarily selected, and the sound absorption frequency band can be shifted to a low frequency by increasing the cross-sectional area at the same length.

[0014] A further improvement of the present invention is that the thickness of the helmet is 10 mm, and other devices can be added inside and outside the helmet.

[0015] A passive noise reduction design device for a pilot helmet with an embedded sound-absorbing superstructure, comprising: Confirmation module, determine the target noise frequency range, expected sound absorption effect and available space size; Design module, determine the overall superstructure volume limit according to the available space, and design FP resonant cavity combinations of different lengths and cross-sectional areas within the volume range according to the target noise frequency range and expected sound absorption effect; Improvement module: simulate the designed FP resonance cavity combination, compare the simulation results with the target requirements, optimize the structural parameters according to the sound absorption law of the FP resonance cavity, and improve the sound absorption effect within the target range; Embedding module: embed the FP resonance cavity combination that meets the target noise frequency range and expected sound absorption effect into the helmet. According to the actual space size, the position and arrangement of the cavity of different lengths are allocated, and the space occupation is reduced by folding and curling methods; The test module conducts sound absorption test on the actual helmet to verify its sound absorption effect. If it does not meet expectations, the cause of the difference is analyzed and the design parameters are adjusted reasonably, and iterative feedback is given until the expected sound absorption effect is achieved in the target noise frequency range.

[0016] A further improvement of the present invention is that, in the design module, the FP resonant cavity combination design further includes: Based on the sound absorption characteristics of the FP resonant cavity, broadband sound absorption is achieved by combining resonant cavities of different lengths; Compare and select the appropriate FP resonance cavity cross-sectional area to achieve the best sound absorption effect; The parameters of the FP resonant cavity combination were determined to be embedded within the helmet.

[0017] Compared with the prior art, the present invention has at least the following beneficial technical effects: 1. By embedding the FP resonant cavity and the sound absorption characteristics of the resonant cavity, the frequency range and sound absorption effect can be changed by simply changing its length and cross-sectional area, making the steps simple and controllable. At the same time, the impedance matching characteristics are optimized to meet the requirements of both sound absorption bandwidth and sound absorption efficiency. 2. Through the acoustic capillary effect of the narrow cross-section FP resonance cavity, a high sound absorption coefficient is guaranteed under the constraints of the narrow space of the helmet, and broadband passive sound absorption and noise reduction are achieved through the combination of gradient length FP resonance cavities; 3. By extending the space size of the head area, the limitation of the sound absorption and noise reduction performance caused by the lack of space near the ears is compensated, breaking through the limitation of broadband passive sound absorption and noise reduction in a narrow space; 4. The acoustic capillary extending in the head area can be composed of flexible bundle tubes to meet the requirements of flexible wear and human-machine interface comfort.

[0018] In summary, according to the above characteristics of the passive noise reduction design method of a pilot helmet with an embedded sound-absorbing superstructure provided by the present invention, the passive noise reduction helmet designed by the present invention can overcome the shortcomings of active noise reduction and traditional materials, and adapt to the pilot helmet environment with limited layout space. The present invention can provide more excellent sound absorption performance under the conditions of passive noise reduction and small space. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the arrangement diagram of the helmet FP resonance cavity; Figure 2 This is a schematic diagram of the FP resonance cavity passive noise reduction pilot helmet; Figure 3 A magnified image of the FP resonant cavity and superstructure area; Figure 4 This is a cross-sectional view of the helmet; Figure 5 This is the unit diagram of the helmet FP resonance cavity; Figure 6 This is the simulation result diagram of the helmet FP resonance cavity unit; Figure 7 Schematic diagram of the design process for passive noise reduction of pilot helmets with embedded sound-absorbing superstructures. DETAILED DESCRIPTION

[0020] In the following, only some exemplary embodiments are briefly described. As those skilled in the art will appreciate, the described embodiments may be modified in various ways without departing from the spirit or scope of the present invention. Therefore, the drawings and descriptions are considered to be exemplary and non-restrictive in nature.

[0021] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0022] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0023] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or a communication; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0024] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0025] It should also be understood that the terms used in the present specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0026] It should be further understood that the term "and / or" used in the present description and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0027] Various structural schematic diagrams of the embodiments disclosed in the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified and some details may be omitted for the purpose of clear expression. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0028] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0029] Example 1 like Figure 7 As shown, the present invention provides a passive noise reduction design method for a pilot helmet with an embedded sound-absorbing superstructure, comprising the following steps: 1) Determine the target noise frequency range, expected sound absorption effect and available space size; 2) Determine the overall superstructure volume limit based on the available space, and design FP resonant cavity combinations of different lengths and cross-sectional areas within the volume range according to the target noise frequency range and expected sound absorption effect; 3) Conduct simulation experiments on the designed FP resonance cavity combination, compare the simulation results with the target requirements, optimize the structural parameters according to the sound absorption law of the FP resonance cavity, and improve the sound absorption effect within the target range; 4) Embed the FP resonance cavity combination that meets the target noise frequency range and expected sound absorption effect into the helmet, allocate the position and arrangement of cavities of different lengths according to the actual space size, and reduce the space occupancy by folding and curling methods; 5) Test the sound absorption effect of the actual helmet to verify its sound absorption effect. If it does not meet expectations, analyze the reasons for the difference and reasonably adjust the design parameters, and iterate feedback until the expected sound absorption effect is achieved in the target noise frequency range.

[0030] In this embodiment, the FP resonant cavity combination design also includes: Based on the sound absorption characteristics of the FP resonant cavity, broadband sound absorption is achieved by combining resonant cavities of different lengths; Compare and select the appropriate FP resonance cavity cross-sectional area to achieve the best sound absorption effect; The parameters of the FP resonant cavity combination were determined to be embedded within the helmet.

[0031] In this embodiment, the spatial dimensions of the head area are extended to compensate for the restriction of the sound absorption and noise reduction performance caused by the insufficient space near the ears, thereby breaking through the limitation of broadband passive sound absorption and noise reduction in a narrow space.

[0032] In this embodiment, a high sound absorption coefficient is ensured under the constraints of the narrow space of the helmet through the acoustic capillary effect of the narrow cross-section FP resonance cavity, and broadband passive sound absorption and noise reduction are achieved through the combination of gradient length FP resonance cavities.

[0033] In this embodiment, the acoustic capillary tube extending in the head area is composed of a flexible bundle tube, which meets the requirements of flexible wearing and comfort of the human-machine interface.

[0034] In this embodiment, the length and cross-sectional area of ​​the FP resonant cavity are designed according to needs, and the depths of different parts are the same or different to adapt to any changing geometric shape needs. In this embodiment, the cross-sectional shape of the FP resonance cavity can be arbitrarily selected, and the sound absorption frequency band can be shifted to a low frequency by increasing the cross-sectional area at the same length.

[0035] In this embodiment, the thickness of the helmet is 10 mm, and other devices can be added inside and outside the helmet.

[0036] Example 2 The present invention provides a passive noise reduction design device for a pilot helmet with an embedded sound-absorbing superstructure, comprising: Confirmation module, determine the target noise frequency range, expected sound absorption effect and available space size; Design module, determine the overall superstructure volume limit according to the available space, and design FP resonant cavity combinations of different lengths and cross-sectional areas within the volume range according to the target noise frequency range and expected sound absorption effect; Improvement module: simulate the designed FP resonance cavity combination, compare the simulation results with the target requirements, optimize the structural parameters according to the sound absorption law of the FP resonance cavity, and improve the sound absorption effect within the target range; Embedding module: embed the FP resonance cavity combination that meets the target noise frequency range and expected sound absorption effect into the helmet. According to the actual space size, the position and arrangement of the cavity of different lengths are allocated, and the space occupation is reduced by folding and curling methods; The test module conducts sound absorption test on the actual helmet to verify its sound absorption effect. If it does not meet expectations, the cause of the difference is analyzed and the design parameters are adjusted reasonably, and iterative feedback is given until the expected sound absorption effect is achieved in the target noise frequency range.

[0037] Example 3 like Figure 2 and Figure 3 As shown, the present invention provides a passive noise reduction pilot helmet with an embedded sound absorption superstructure. The passive noise reduction helmet has sound absorption holes in the superstructure area (3). The FP resonance cavities (1) are compactly arranged in the helmet (2). According to the size of the installation space in actual applications, the FP resonance cavities (1) with elongated cavities are arranged in a compact space by folding or curling, thereby achieving broadband sound absorption and noise reduction.

[0038] 1. Sound absorption characteristics and parameter determination of FP resonance cavity The present invention uses the FP resonant cavity structure as the basic subunit, which has multiple sound absorption peaks and can achieve customized sound absorption effects and frequency ranges through different combinations. The superstructure is simple in composition and easy to process. It also has good structural rigidity and a certain load-bearing capacity, and is suitable for high-intensity environments such as pilot helmets.

[0039] FP structure impedance Z a The cavity impedance Z c and end correction Z e composition: (1-1) Terminal correction impedance Z e It is mainly caused by the end radiation caused by the discontinuous interface area at the opening. Under the action of sound pressure, when the sound wave particles enter the cavity, due to the reduction of area, some particles will flow along the plate surface, resulting in energy loss under the influence of friction; on the other hand, when the sound wave flows out of the cavity, it will form a jet and generate energy loss. In fact, the end impedance has little effect on the sound quality, and it can be expressed as only the form of acoustic resistance, that is, Ze =X e Therefore, the impedance ratio z of the FP structure is s It can be expressed as: (1-2) in is the end-corrected relative acoustic resistivity.

[0040] Here, the sound absorption peak is divided into two parts: peak frequency and sound absorption coefficient. First, according to the impedance matching condition, at the peak frequency, the system resonates and its acoustic reactance should be zero, that is: (1-3) So, we can get: (1-4) Simplified: (1-5) or: (1-6) It can be seen from formula (1-3) that the peak frequency has multiple solutions, which means that the structure has multiple sound absorption peaks. Reasonable arrangement of these FP resonance cavities with different peaks can achieve broadband sound absorption effect; the peak frequency is determined by the equivalent sound velocity and cavity depth The equivalent sound speed depends on the cross-sectional area of ​​the cavity, so the peak frequency is mainly determined by the cavity depth. The greater the depth, the lower the peak frequency. Therefore, in order to achieve better sound absorption effects in the low, medium and high frequency bands, it is necessary to design FP resonance cavities of different lengths. Through the combination of these FP resonance cavities of different lengths, low, medium and high broadband coverage of the sound absorption frequency band can be achieved.

[0041] By writing formula (1-5) in the form of (1-6), we can see that the cavity depth is 1 / 4 times the wavelength corresponding to the peak frequency, that is, when the wavelength of the sound wave is 4 times the cavity depth, the sound absorption peak appears. Obviously, the smaller the cross-sectional area and the greater the depth, the greater the acoustic resistance, and the corresponding sound absorption capacity and peak value will increase first and then decrease. When designing the FP superstructure, first determine its operating frequency range and target sound absorption effect, and then use formula (1-5) to substitute different cavity depths l0 to calculate the sound absorption peak frequency f corresponding to different depths l, so as to obtain multiple different sound absorption peaks, and then determine the optimal cross-sectional area of ​​the FP resonance cavity, and obtain a continuous sound absorption broadband through strict coupling between peaks. Then, the actual effect of the sound absorption broadband is verified through simulation experiments and physical experiments, and the parameters are continuously adjusted through the FP resonance cavity structure formula until the target frequency range and sound absorption effect are achieved.

[0042] 2. Implementation case parameter selection and simulation results As an implementation example, Figure 2 and Figure 3 As shown in the figure, the shape selected is a pilot helmet that fits the normal head circumference and has a thickness of 10mm. Figure 1 As shown, sound absorption holes are opened in the superstructure area to arrange FP resonance cavities in the helmet. The lengths of the resonance cavities from small to large are 59mm, 61.875mm, 69mm, 75mm, 84.5mm, 95.5mm, 97.5mm, 103.125mm, 108mm, 110mm, 112.5mm, 121mm, 124mm, 126mm, 127mm, 130mm, 134mm, 137.5mm, 141mm, 146mm, 147mm, 150mm, 155mm, 160mm, 164mm, 165mm and 199mm. Figure 5 As shown in Figure 1, these 27 FP resonant cavities of different lengths form a rectangular combination of 36 resonant cavities in total by repeating individual important lengths. Figure 4 As shown, the FP resonant cavity with a slender cavity can be arranged in a compact space by folding or curling. The smaller the cross-sectional area and the greater the depth of the FP resonant cavity, the greater its acoustic resistance, and the corresponding sound absorption capacity and peak value will increase first and then decrease, and the final cross-sectional size is 2mm×2mm.

[0043] The commercial multi-physics finite element analysis software COMSOL Multiphysics was used to calculate the following Figure 5 The sound absorption coefficient of the FP resonant cavity sound absorption unit is shown in the figure. The sound absorption coefficient is Figure 6 As shown. Due to the different lengths, the sound absorption peak frequency of each FP resonance cavity is different, so that the combined sound absorption device produces multiple connected sound absorption peaks, achieving a broadband sound absorption effect. Starting from 400Hz, the structural sound absorption coefficient is above 0.6, and in the frequency band of about 450-900Hz, the average sound absorption coefficient exceeds 0.9, and the overall has a good broadband sound absorption effect.

[0044] According to the above data, it can be seen that the technical effects that the present invention can achieve are as follows: 1. The length and cross-sectional dimensions of the FP resonance cavity can be set arbitrarily as needed. By designing the length of the resonance cavity, the sound absorption frequency of the structure can be adjusted. The longer the cavity, the lower the operating frequency. 2. The position and number of openings in the superstructure area can be adjusted according to demand: increasing the number of openings can improve impedance matching performance and increase the sound absorption coefficient; reducing the number of openings and increasing the folded length of the resonance cavity can move the operating frequency to a lower frequency; 3. In the ultra-wide operating frequency range of 400-8000Hz, the sound absorption coefficient is above 0.6; 4. It can be designed for a certain frequency, and the resonance cavity with a peak in the target frequency band can be coupled and enhanced through repetition and combination, and the sound absorption coefficient can reach above 0.9.

[0045] In summary, according to the above characteristics of the passive noise reduction design method for a pilot helmet with an embedded sound-absorbing superstructure provided by the present invention, the passive noise reduction design method for a pilot helmet with an embedded sound-absorbing superstructure provided by the present invention can provide more excellent passive noise reduction and sound absorption performance under the conditions of lightweight and small space. The structure can be compressed in a compact space by folding, curling, etc., and combined with the design of the resonance cavity length and cross-sectional dimensions, broadband and efficient sound absorption covering low, medium and high frequencies can be achieved. Compared with existing sound-absorbing materials and structures, this superstructure passive noise reduction helmet is lighter, has a wider bandwidth, and has stronger spatial adaptability, and is more suitable for low-frequency broadband noise reduction in environments such as aircraft.

[0046] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the attached claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention. Any figure mark in the claims should not be regarded as limiting the claims involved.

[0047] In addition, it should be understood that although this specification is described in accordance with the implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation modes that can be understood by those skilled in the art. The above content is only to illustrate the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution according to the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A design method for passive noise reduction of a pilot helmet with an embedded sound-absorbing superstructure, characterized in that: The following steps are involved: 1) Determine the target noise frequency range, expected sound absorption effect and available space size; 2) Determine the overall superstructure volume limit based on the available space, and design FP resonant cavity combinations of different lengths and cross-sectional areas within the volume range according to the target noise frequency range and expected sound absorption effect; 3) Conduct simulation experiments on the designed FP resonance cavity combination, compare the simulation results with the target requirements, optimize the structural parameters according to the sound absorption law of the FP resonance cavity, and improve the sound absorption effect within the target range; 4) Embed the FP resonance cavity combination that meets the target noise frequency range and expected sound absorption effect into the helmet, allocate the position and arrangement of cavities of different lengths according to the actual space size, and reduce the space occupancy by folding and curling methods; 5) Test the sound absorption effect of the actual helmet to verify its sound absorption effect. If it does not meet expectations, analyze the reasons for the difference and reasonably adjust the design parameters, and iterate feedback until the expected sound absorption effect is achieved in the target noise frequency range.

2. The passive noise reduction design method for a pilot helmet with an embedded sound absorbing superstructure according to claim 1, characterized in that: The FP resonant cavity combination design also includes: Based on the sound absorption characteristics of the FP resonant cavity, broadband sound absorption is achieved by combining resonant cavities of different lengths; Compare and select the appropriate FP resonance cavity cross-sectional area to achieve the best sound absorption effect; The parameters of the FP resonant cavity combination were determined to be embedded within the helmet.

3. The passive noise reduction design method for a pilot helmet with an embedded sound absorbing superstructure according to claim 1, characterized in that: By extending the spatial dimensions of the head area, the limitations of insufficient space near the ears on sound absorption and noise reduction performance can be compensated, breaking through the limitations of broadband passive sound absorption and noise reduction in a small space.

4. The passive noise reduction design method for a pilot helmet with an embedded sound absorbing superstructure according to claim 1, characterized in that: Through the acoustic capillary effect of the narrow-section FP resonance cavity, a high sound absorption coefficient is guaranteed under the constraints of the narrow space of the helmet, and broadband passive sound absorption and noise reduction is achieved through the combination of gradient-length FP resonance cavities.

5. The passive noise reduction design method for a pilot helmet with an embedded sound absorbing superstructure according to claim 1, characterized in that: The acoustic capillary extending in the head area is composed of flexible bundle tubes, meeting the requirements of flexible wear and human-machine interface comfort.

6. The passive noise reduction design method for a pilot helmet with an embedded sound absorbing superstructure according to claim 1, characterized in that: The length and cross-sectional area of ​​the FP resonant cavity are designed according to the needs, and the depths of different parts are the same or different to adapt to the needs of any changing geometric shapes.

7. The passive noise reduction design method for a pilot helmet with an embedded sound absorbing superstructure according to claim 1, characterized in that: The cross-sectional shape of the FP resonance cavity can be arbitrarily selected, and the sound absorption band can be shifted to a low frequency by increasing the cross-sectional area at the same length.

8. The passive noise reduction design method for a pilot helmet with an embedded sound absorbing superstructure according to claim 1, characterized in that: The thickness of the helmet is 10mm, and other devices can be added inside and outside the helmet.

9. A passive noise reduction design device for a pilot helmet with an embedded sound-absorbing superstructure, characterized in that: include: Confirmation module, determine the target noise frequency range, expected sound absorption effect and available space size; Design module, determine the overall superstructure volume limit according to the available space, and design FP resonant cavity combinations of different lengths and cross-sectional areas within the volume range according to the target noise frequency range and expected sound absorption effect; Improvement module: simulate the designed FP resonance cavity combination, compare the simulation results with the target requirements, optimize the structural parameters according to the sound absorption law of the FP resonance cavity, and improve the sound absorption effect within the target range; Embedding module: embed the FP resonance cavity combination that meets the target noise frequency range and expected sound absorption effect into the helmet. According to the actual space size, the position and arrangement of the cavity of different lengths are allocated, and the space occupation is reduced by folding and curling methods; The test module conducts sound absorption test on the actual helmet to verify its sound absorption effect. If it does not meet expectations, the reasons for the difference are analyzed and the design parameters are adjusted reasonably, and iterative feedback is given until the expected sound absorption effect is achieved in the target noise frequency range.

10. The passive noise reduction design device for a pilot helmet with an embedded sound-absorbing superstructure according to claim 9, characterized in that: In the design module, the FP resonant cavity combination design also includes: Based on the sound absorption characteristics of the FP resonant cavity, broadband sound absorption is achieved by combining resonant cavities of different lengths; Compare and select the appropriate FP resonance cavity cross-sectional area to achieve the best sound absorption effect; The parameters of the FP resonant cavity combination were determined to be embedded within the helmet.

Images