A method and system for testing the surface acoustic impedance of an NVH sound absorbing cotton

Abstract

The application discloses a kind of surface acoustic impedance test method and system of NVH sound-absorbing cotton, it is related to acoustic impedance test technical field, including installation state topological reconstruction module, differential excitation acquisition module and state determination output module;The installation state topological reconstruction module is used to construct the installation state test boundary of the NVH sound-absorbing cotton to be measured according to the boundary pressure relationship of target installation site, rear cavity configuration relationship and local pre-pressing relationship;The differential excitation acquisition module is used to establish reference state under the installation state test boundary and apply reversible perturbation state, the target installation state of NVH sound-absorbing cotton is reconstructed as reversible switching test boundary, reference state, boundary release state, rear cavity switching state and pre-pressing adjustment state are established in sequence in the same measurement area, the installation state coupling source is identified by differential response, and only the reference state result that passes through regression stability check is fused output, so that the surface acoustic impedance test result with installation state correspondence is obtained.

Description

Technical Field

[0001] This invention relates to the field of acoustic impedance testing technology, specifically to a method and system for testing the surface acoustic impedance of NVH sound-absorbing cotton. Background Technology

[0002] NVH (Noise, Vibration, and Harshness) sound-absorbing cotton is widely used in vehicle floors, wheel arches, headliners, trunk trim panels, dashboard sound insulation layers, and door trim sound-absorbing layers. Its surface acoustic impedance is an important test parameter reflecting the acoustic response characteristics of the material surface. For NVH sound-absorbing cotton with a dense surface layer, layered structure, localized hot-pressed structure, and cavity fit at the back after installation, it is usually installed in a state of boundary compression, localized pre-compression, and rear cavity fit during vehicle assembly. Conducting surface acoustic impedance testing on this type of material has direct engineering significance for material selection, installation matching verification, evaluation of acoustic performance of different parts, and batch consistency inspection.

[0003] Existing surface acoustic impedance (SAI) testing methods for NVH sound-absorbing cotton typically use free-state specimens or specimens under single fixed boundary conditions as test objects. This makes it difficult to accurately maintain the boundary compression relationship, rear cavity fit relationship, and local pre-compression relationship of the sound-absorbing cotton at the target installation location on the vehicle. Especially for NVH sound-absorbing cotton with a dense skin, coating structure, or local hot-pressed shaping structure, the coupling response caused by boundary constraints, rear cavity configuration, and local pre-compression state in the installation state can easily be mixed into the test results. This makes it difficult for the test results to accurately correspond to the actual installation state, and it is also difficult to further distinguish the specific impact of different coupling sources on surface acoustic impedance. Therefore, it is necessary to establish a surface acoustic impedance testing method and system that can perform tests in the installation state and identify different coupling sources. Summary of the Invention

[0004] The purpose of this invention is to provide a method and system for testing the surface acoustic impedance of NVH sound-absorbing cotton, so as to solve the problems mentioned in the background art.

[0005] To address the aforementioned technical problems, this invention provides the following technical solution: a method and system for testing the surface acoustic impedance of NVH sound-absorbing cotton, comprising an installation-state topology reconstruction module, a differential excitation acquisition module, and a state determination output module; the installation-state topology reconstruction module is used to construct the installation-state test boundary of the NVH sound-absorbing cotton under test based on the boundary compression relationship, rear cavity configuration relationship, and local pre-compression relationship of the target installation location; the differential excitation acquisition module is used to establish a reference state and apply a reversible perturbation state under the installation-state test boundary to acquire the surface acoustic response under each state; the state determination output module is used to identify the dominant coupling type based on the differential response under each state and output the installation-state surface acoustic impedance test results after regression stability verification.

[0006] According to the above technical solution, the installation state topology reconstruction module includes a topology input unit, a test area division unit, a boundary constraint execution unit, a rear cavity switching execution unit, and a preload adjustment unit. The topology input unit is used to input the boundary clamping information, rear cavity configuration information, and local preload information corresponding to the target installation location. The test area division unit is used to divide the area to be tested into multiple test areas based on the continuity of force. The boundary constraint execution unit is used to establish a boundary clamping state consistent with the target installation location in each test area. The rear cavity switching execution unit is used to establish a rear cavity state consistent with the target installation location behind each test area and implement rear cavity switching. The preload adjustment unit is used to establish a local preload state consistent with the target installation location in each test area and implement preload adjustment. The differential excitation acquisition module includes a reference state establishment unit, a perturbation state triggering unit, a near-surface acoustic excitation unit, a near-surface response acquisition unit, and a complex impedance calculation unit. The reference state establishment unit is used to establish an installation reference state in each test area. The perturbation state triggering unit is used to establish a boundary release state, a rear cavity switching state, and a pre-pressure adjustment state while keeping the overall installation relationship of the tested NVH sound-absorbing cotton unchanged. The near-surface acoustic excitation unit is used to apply a near-surface test sound field to each test area. The near-surface response acquisition unit is used to synchronously acquire the surface sound pressure signal and particle velocity signal of each test area. The complex impedance calculation unit is used to calculate the surface complex impedance of each test area under different states based on the surface sound pressure signal and particle velocity signal. The state determination output module includes a differential feature extraction unit, a dominant coupling determination unit, a regression stability verification unit, a multi-measurement area fusion unit, and a result output unit. The differential feature extraction unit is used to extract the differential response of each perturbation state relative to the reference state. The dominant coupling determination unit is used to determine the dominant coupling type corresponding to each measurement area. The regression stability verification unit is used to determine whether the reference state of each measurement area meets the regression stability condition. The multi-measurement area fusion unit is used to perform area fusion on the measurement area results that have passed the regression stability verification. The result output unit is used to output the surface acoustic impedance results in the installation state and the coupling distribution results at the measurement area level.

[0007] A method for testing the surface acoustic impedance of NVH sound-absorbing cotton includes the following steps: S1. Obtain the boundary clamping information, rear cavity configuration information, and local pre-compression information of the target installation location. Divide the test area into multiple test zones according to the force continuity of the NVH sound-absorbing cotton under test on the target installation location. Divide the test area according to the boundary clamping line, rear cavity separation boundary, and local pre-compression abrupt boundary. Establish the installation state topology for each test zone so that the test input of each test zone corresponds one-to-one with the actual installation relationship in the target installation location. S2. Assemble the NVH sound-absorbing cotton to be tested into a reconfigurable test fixture, establish a reference state consistent with the installation state topology in each test area, and establish a boundary release state, a rear cavity switching state, and a pre-pressure adjustment state based on the reference state. The boundary release state, the rear cavity switching state, and the pre-pressure adjustment state are all reversible perturbation states relative to the reference state. S3. Apply near-surface acoustic excitation sequentially to the reference state, boundary release state, rear cavity switching state and pre-pressure adjustment state of each test area and collect the surface acoustic response to obtain the surface complex impedance and reflection coefficient of each test area in the four states, so that a comparable response set is formed between the installation state and its reversible perturbation state of the same test area. S4. Using the reference state as a reference, perform differential analysis on the reflection response differences corresponding to the boundary release state, the rear cavity switching state, and the pre-pressure adjustment state to determine the dominant coupling type of each test area. Then, adjust the installation state topology and retest the test areas that fail the regression stability check to ensure that the test area results entering the final output all correspond to the stable installation state reference state. S5. Perform fusion calculation of the surface acoustic impedance of the installed state for all test areas that have passed the regression stability check, output the test results of the surface acoustic impedance of the NVH sound-absorbing cotton under test at the target installation location, and output the distribution of the dominant coupling type of each test area, thereby forming a verifiable test conclusion.

[0008] According to the above technical solution, step S1 includes the following sub-steps: S1-1, the first The boundary compaction length of each test area is denoted as , will the The effective cavity depth behind each test area is denoted as , will the The local preloading displacement of each test area is denoted as . ,in Number the survey area; S1-2, Constructing the first Installation-state topology vector of each test area The installed state topology vector is used to characterize the first The boundary compaction state, rear cavity state, and local pre-compression state of each test area under the target installation location; S1-3, Based on the installation state topology vector Configure the boundary constraint execution unit, rear cavity switching execution unit, and preload adjustment unit corresponding to the test area, so that the first Each test area forms an installation topology in the test fixture that is consistent with the target installation location.

[0009] According to the above technical solution, steps S2 and S3 include the following sub-steps: S2-1, in the Each test area is based on the installation state topology vector. Establish a reference state, and denote the corresponding surface complex impedance as ; S2-2, while maintaining the first Under the condition that the overall position of the NVH sound-absorbing cotton under test remains unchanged in each test area, establish the boundary release state, the rear cavity switching state, and the pre-pressure adjustment state, and denote the corresponding surface complex impedances as follows: , , ,in For the first Each frequency sampling point , This represents the total number of frequency sampling points. S3-1, in the status number Under the corresponding test conditions, according to the formula Calculate the first Each test area at the frequency sampling point The surface complex impedance at the location, where For the status number, and Indicates the baseline state. Indicates the boundary release state. Indicates the switching state of the rear cavity. Indicates the preload adjustment status. For the first Each test area is in status and frequency sampling points The complex sound pressure level collected at the location, For the first Each test area is in status and frequency sampling points The formula is used to obtain the surface complex impedance under the corresponding state based on the acoustic pressure signal and particle velocity signal synchronously collected near the surface of the same test area. S3-2, According to the formula Calculation state The corresponding reflection response, where For the first Each test area is in status and frequency sampling points The reflection coefficient at that location, The formula, which uses air characteristic impedance, is used to convert the surface complex impedance under various conditions into a comparable reflection response.

[0010] According to the above technical solution, step S4 includes the following sub-steps: S4-1. Calculate the boundary difference component, the rear cavity difference component, and the pre-pressure difference component respectively. The calculation formula is as follows: , , ,in Used to characterize the magnitude of the effect of boundary state changes on the reflection response. Used to characterize the magnitude of the effect of changes in the state of the back cavity on the reflection response. Used to characterize the magnitude of the effect of changes in preload state on the reflection response; S4-2, calculate the first one respectively Boundary coupling index of each test area Post-cavity coupling index and preload coupling index The calculation formula is: , , ,in Frequency sampling point The corresponding weighting coefficients satisfy The three formulas are used to summarize the differential response amplitude at a single frequency sampling point into the measurement area-level coupling strength; S4-3, when ,and ,and Not less than the boundary judgment threshold At that time, the first The test area was determined to be a test area dominated by boundary membrane coupling; when ,and ,and Not less than the rear cavity determination threshold At that time, the first The test area was determined to be the dominant test area for rear cavity coupling. ,and ,and Not less than the preload judgment threshold At that time, the first The test area was determined to be a test area dominated by compression coupling. , , All results were obtained through statistical analysis of preliminary test results of standard calibration samples.

[0011] According to the above technical solution, step S4 further includes the following sub-steps: S4-4. After completing the tests for the boundary release state, the rear cavity switching state, and the pre-pressure adjustment state, the first... The boundary compaction length of each test area was restored to , will the The effective cavity depth behind each test area is restored to , will the The local preload displacement of each test area recovered to In order to re-establish the first The baseline state of each test area is used to re-acquire the data at the same test point locations, under the same acoustic excitation conditions, and with the same set of frequency sampling points as the initial baseline state. The complex sound pressure and complex particle velocity of each measurement area are denoted as follows: and ; S4-5, according to the formula Calculate the first Each test area, after restoration of its baseline state and frequency sampling points The regression reference surface complex impedance at the location ,in For the first Each test area, after restoration of its baseline state and frequency sampling points The re-acquired complex sound pressure level at the location, For the first Each test area, after restoration of its baseline state and frequency sampling points The re-acquired complex particle velocity; this formula is used to obtain the surface complex impedance corresponding to the restored reference state; S4-6, According to the formula Calculate the first Each test area, after restoration of its baseline state and frequency sampling points Regression baseline reflection coefficient at the location This formula is used to convert the surface complex impedance of the restored reference state into the regression reference reflection coefficient. S4-7, According to the formula Calculate the first Regression stability coefficient of each test area This formula is used to characterize the consistency of the reference state before and after the perturbation switch; S4-8, When the When a test area is determined to be a boundary membrane coupling-dominated test area, the boundary constraint execution unit of that test area is adjusted to the boundary clamping length. Re-establish the baseline state after the target position is consistent; when the first When a test area is determined to be a dominance test area for rear cavity coupling, the rear cavity switching execution unit of that test area is adjusted to match the effective cavity depth. After the target position is consistent, the baseline state is re-established, when the first When a measurement area is determined to be a compression-coupled dominant measurement area, the preload adjustment unit of that measurement area is adjusted to match the local preload displacement. Once the target position is consistent, the baseline state is re-established. S4-9, in Not greater than the stability threshold After that, the first Each measurement area was determined as a valid measurement area. Greater than the stability threshold At that time, for the first Each test area was re-established to its baseline state and retested.

[0012] According to the above technical solution, step S5 includes the following sub-steps: S5-1. Renumber all test areas that have passed the regression stability check as number 1 to number 2 according to the preset order. The first effective measurement area will be the first The area contributed by each effective measurement zone at the target installation location is denoted as . According to the formula Calculate the NVH sound-absorbing cotton under test at the frequency sampling point Mounting surface acoustic impedance This formula is used to fuse the complex impedance of the reference state surface according to the contribution area of ​​each effective measurement area on the actual mounting surface. S5-2, the first The dominant coupling type and the surface acoustic impedance in the installed state corresponding to each effective measurement area The results are output together to form the surface acoustic impedance results in the installation state and the coupling distribution results in the measurement area.

[0013] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: Compared with the approach of simply treating the sound-absorbing cotton as a free-state sample for testing, the present invention directly uses the boundary compression relationship, rear cavity configuration relationship and local pre-compression relationship of the target installation part as test input, which first ensures the consistency of the test object and the target installation state in terms of constraint conditions; furthermore, by applying three types of reversible micro-perturbation states of boundary release, rear cavity switching and pre-compression adjustment to the same test area, the test system can identify the boundary coupling, rear cavity coupling and compression coupling from the mixed response separately, thereby avoiding the confusion of response components from different sources into a single material bulk property; Furthermore, by using regression stability verification to screen the effectiveness of the baseline state, and only outputting the area fusion results of the verified stable test areas, it is possible to form surface acoustic impedance test results in the installation state with clear input, clear process, and verifiable output. This solves both the problem of maintaining the installation state and the problem of identifying the coupling source in the installation state, while ensuring the repeatability and engineering correspondence of the test results. Attached Figure Description

[0014] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the overall modular structure of the present invention. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] Please see Figure 1 This invention provides a technical solution: a method and system for testing the surface acoustic impedance of NVH sound-absorbing cotton, including an installation-state topology reconstruction module, a differential excitation acquisition module, and a state determination output module; the installation-state topology reconstruction module is used to construct the installation-state test boundary of the NVH sound-absorbing cotton under test based on the boundary compression relationship, rear cavity configuration relationship, and local pre-compression relationship of the target installation location; the differential excitation acquisition module is used to establish a reference state under the installation-state test boundary and apply a reversible perturbation state to acquire the surface acoustic response under each state; the state determination output module is used to identify the dominant coupling type based on the differential response under each state and output the installation-state surface acoustic impedance test results after regression stability verification; The installation-state topology reconstruction module includes a topology input unit, a test area division unit, a boundary constraint execution unit, a rear cavity switching execution unit, and a preload adjustment unit. The topology input unit is used to input the boundary clamping information, rear cavity configuration information, and local preload information corresponding to the target installation location. The test area division unit is used to divide the area to be tested into multiple test areas based on the continuity of force. The boundary constraint execution unit is used to establish a boundary clamping state consistent with the target installation location in each test area. The rear cavity switching execution unit is used to establish a rear cavity state consistent with the target installation location behind each test area and implement rear cavity switching. The preload adjustment unit is used to establish a local preload state consistent with the target installation location in each test area and implement preload adjustment. The differential excitation acquisition module includes a reference state establishment unit, a perturbation state triggering unit, a near-surface acoustic excitation unit, a near-surface response acquisition unit, and a complex impedance calculation unit. The reference state establishment unit is used to establish the installation reference state in each test area. The perturbation state triggering unit is used to establish the boundary release state, the rear cavity switching state, and the pre-pressure adjustment state while keeping the overall installation relationship of the NVH sound-absorbing cotton under test unchanged. The near-surface acoustic excitation unit is used to apply the near-surface test sound field to each test area. The near-surface response acquisition unit is used to synchronously acquire the surface sound pressure signal and particle velocity signal of each test area. The complex impedance calculation unit is used to calculate the surface complex impedance of each test area under different states based on the surface sound pressure signal and particle velocity signal. The state determination output module includes a differential feature extraction unit, a dominant coupling determination unit, a regression stability verification unit, a multi-measurement area fusion unit, and a result output unit. The differential feature extraction unit is used to extract the differential response of each perturbation state relative to the reference state. The dominant coupling determination unit is used to determine the dominant coupling type corresponding to each measurement area. The regression stability verification unit is used to determine whether the reference state of each measurement area meets the regression stability condition. The multi-measurement area fusion unit is used to perform area fusion on the measurement area results that have passed the regression stability verification. The result output unit is used to output the surface acoustic impedance results of the installation state and the coupling distribution results of the measurement area. First, the boundary compression relationship, rear cavity fit relationship, and local pre-compression relationship in the target installation location are transformed into an installation-state topology that can be reproduced in the test fixture. Then, the test area is divided according to the spatial changes of these constraints. The reason for this approach is that the same piece of sound-absorbing cotton is subject to different constraints in different installation areas, and the local acoustic response is not necessarily uniform. If the conventional method of overall averaging or uniform partitioning according to shape is still used, the test results are prone to mixing the responses of different constraint areas, and the final result can only be an average value that is difficult to correspond to the actual installation state. This scheme first reconstructs the test object according to the installation constraints, and then organizes the test area according to the constraint changes. This ensures that the subsequent tests target the local response units under the installation state rather than free-state material fragments detached from the installation relationship. This step actually determines whether all subsequent differential analysis and fusion outputs have real engineering significance, and it is also the starting point that distinguishes this scheme from the conventional sampling test approach.

[0017] A method for testing the surface acoustic impedance of NVH sound-absorbing cotton includes the following steps: S1. Obtain the boundary clamping information, rear cavity configuration information, and local pre-compression information of the target installation location. Divide the test area into multiple test zones according to the force continuity of the NVH sound-absorbing cotton under test on the target installation location. Divide the test area according to the boundary clamping line, rear cavity separation boundary, and local pre-compression abrupt boundary. Establish the installation state topology for each test zone so that the test input of each test zone corresponds one-to-one with the actual installation relationship in the target installation location. S2. Assemble the NVH sound-absorbing cotton to be tested into the reconfigurable test fixture, establish a reference state consistent with the installation state topology in each test area, and establish a boundary release state, a rear cavity switching state, and a pre-pressure adjustment state based on the reference state. The boundary release state, the rear cavity switching state, and the pre-pressure adjustment state are all reversible perturbation states relative to the reference state. S3. Apply near-surface acoustic excitation sequentially in the reference state, boundary release state, rear cavity switching state and pre-pressure adjustment state of each test area and collect the surface acoustic response to obtain the surface complex impedance and reflection coefficient of each test area in the four states, so that a comparable response set is formed between the installation state and its reversible perturbation state of the same test area. S4. Using the baseline state as a reference, perform differential analysis on the differences in reflection response corresponding to the boundary release state, the rear cavity switching state, and the pre-pressure adjustment state to determine the dominant coupling type of each test area. For test areas that fail the regression stability check, adjust the installation state topology and retest to ensure that the test area results entering the final output all correspond to the stable installation state baseline state. S5. Perform fusion calculation of surface acoustic impedance in the installation state for all test areas that have passed the regression stability check, output the test results of surface acoustic impedance in the installation state of the NVH sound-absorbing cotton under the target installation location, and output the distribution of the dominant coupling type in each test area, thereby forming a verifiable installation state test conclusion. Step S1 includes the following sub-steps: S1-1, the first The boundary compaction length of each test area is denoted as , will the The effective cavity depth behind each test area is denoted as , will the The local preloading displacement of each test area is denoted as . ,in Number the survey area; S1-2, Constructing the first Installation-state topology vector of each test area The installed state topology vector is used to characterize the first The boundary compaction state, rear cavity state, and local pre-compression state of each test area under the target installation location; S1-3, Based on the installation state topology vector Configure the boundary constraint execution unit, rear cavity switching execution unit, and preload adjustment unit corresponding to the test area, so that the first Each test area forms an installation topology in the test fixture that is consistent with the target installation location; Boundary compaction, rear cavity fit, and local pre-compression are not isolated conditions, but rather three fundamental constraints that collectively determine the surface acoustic response in the installed state. Conventional tests often focus only on the material itself and a single back cavity condition, or only measure under a fixed clamping condition. The results obtained in this way are closer to the test specimen's response under experimental conditions, but may not reflect its actual working state in the target installation location. This approach introduces these three installation relationships simultaneously into the test boundary because surface coatings, local cavities, and assembly pressure often coexist in actual working conditions. Only by reconstructing these three relationships together can the subsequent differentiation of the response source be based. This treatment transforms the test object from a simple material sample into a coupled entity of material-boundary-rear cavity-compression relationships, fundamentally improving the correspondence between test results and actual installation conditions.

[0018] Steps S2 and S3 include the following sub-steps: S2-1, in the Each test area is arranged according to the installation state topology vector. Establish a reference state, and denote the corresponding surface complex impedance as ; S2-2, while maintaining the first Under the condition that the overall position of the NVH sound-absorbing cotton under test remains unchanged in each test area, establish the boundary release state, the rear cavity switching state, and the pre-pressure adjustment state, and denote the corresponding surface complex impedances as follows: , , ,in For the first Each frequency sampling point , This represents the total number of frequency sampling points. This implementation method does not compare different installation conditions between different samples, nor does it involve removing and re-clamping the sample for testing. Instead, it uses a reversible approach to sequentially establish a boundary release state, a rear cavity switching state, and a pre-pressure adjustment state within the same test area and installation relationship. Conventional methods, when studying the influence of different factors, typically involve testing multiple samples separately or changing the overall clamping conditions. This easily mixes sample differences, clamping differences, and the actual influencing factors, making it difficult to determine whether the response change originates from the material itself or from changes in test conditions. This approach requires that the perturbation state be established under the premise that the overall installation relationship remains unchanged. Essentially, it transforms the installation changes, which are originally considered sources of interference, into a controllable means of identification, enabling a strictly comparable response sequence between the previous and subsequent states within the same test area. It is precisely because of this method of using the same test area, the same sample, and reversible switching that subsequent differential analysis has the ability to distinguish different coupling sources.

[0019] S3-1, in the status number Under the corresponding test conditions, according to the formula Calculate the first Each test area at the frequency sampling point The surface complex impedance at the location, where For the status number, and Indicates the baseline state. Indicates the boundary release state. Indicates the switching state of the rear cavity. Indicates the preload adjustment status. For the first Each test area is in status and frequency sampling points The complex sound pressure level collected at the location, For the first Each test area is in status and frequency sampling points The complex particle velocity collected at the location is used to obtain the surface complex impedance under the corresponding state based on the acoustic pressure signal and particle velocity signal synchronously collected near the surface in the same test area. S3-2, According to the formula Calculation state The corresponding reflection response, where For the first Each test area is in status and frequency sampling points The reflection coefficient at that location, The formula is used to convert the surface complex impedance under various conditions into a comparable reflection response. In this implementation, the near-surface acoustic responses acquired under various states are uniformly converted. The purpose is not simply to increase calculation steps, but to transform the response results from different states and test areas into a characterization quantity under the same comparative scale. In conventional methods, testers often only observe a single measurement result under a certain state, or only compare local peak-valley changes. While this may reveal differences, it's difficult to further explain the installation factors attributing these differences. This solution unifies the measurement results from various states to the same characterization method, and then performs differential analysis on this basis, ensuring consistency in subsequent comparisons. This transforms apparent differences into differences that the system can recognize. This process ensures that subsequent dominant coupling determination is not based on fuzzy empirical judgment, but rather on a comparison of responses of the same caliber and repeatability.

[0020] Step S4 includes the following sub-steps: S4-1. Calculate the boundary difference component, the rear cavity difference component, and the pre-pressure difference component respectively. The calculation formula is as follows: , , ,in Used to characterize the magnitude of the effect of boundary state changes on the reflection response. Used to characterize the magnitude of the effect of changes in the state of the back cavity on the reflection response. Used to characterize the magnitude of the effect of changes in preload state on the reflection response; S4-2, calculate the first one respectively Boundary coupling index of each test area Post-cavity coupling index and preload coupling index The calculation formula is: , , ,in Frequency sampling point The corresponding weighting coefficients satisfy The three formulas are used to summarize the differential response amplitude at a single frequency sampling point into the area-level coupling strength; S4-3, when ,and ,and Not less than the boundary judgment threshold At that time, the first The test area was determined to be a test area dominated by boundary membrane coupling; when ,and ,and Not less than the rear cavity determination threshold At that time, the first The test area was determined to be the dominant test area for rear cavity coupling. ,and ,and Not less than the preload judgment threshold At that time, the first The test area was determined to be a test area dominated by compression coupling. , , All results were obtained through statistical analysis of preliminary test results of standard calibration samples; The core of this step lies not in simply classifying the test area into several categories, but in identifying the dominant source of the installed response deviation by observing the direction and intensity of response changes in the same test area under three reversible perturbation states. Conventional methods can usually only indicate that the test results of the test area have changed, but it is difficult to further answer whether this change is mainly caused by boundary release, changes in the rear cavity, or changes in assembly pressure. This scheme establishes three perturbation states separately, and then observes the change characteristics with a reference state. This is equivalent to performing three directional probes on the same test area without disrupting the original installation relationship, gradually revealing the originally mixed coupling effects. The dominant coupling type obtained in this way is not an empirical label, but a result reflected by the response sensitivity of the same test area to different perturbation modes. Its originality lies in not attempting to guess the coupling source directly from a single test, but rather allowing the coupling source to reveal itself by artificially setting small, directional state changes.

[0021] Step S4 also includes the following sub-steps: S4-4. After completing the tests for the boundary release state, the rear cavity switching state, and the pre-pressure adjustment state, the first... The boundary compaction length of each test area was restored to , will the The effective cavity depth behind each test area is restored to , will the The local preload displacement of each test area recovered to In order to re-establish the first The baseline state of each test area is used to re-acquire the data at the same test point locations, under the same acoustic excitation conditions, and with the same set of frequency sampling points as the initial baseline state. The complex sound pressure and complex particle velocity of each measurement area are denoted as follows: and ; S4-5, according to the formula Calculate the first Each test area, after restoration of its baseline state and frequency sampling points The regression reference surface complex impedance at the location ,in For the first Each test area, after restoration of its baseline state and frequency sampling points The re-acquired complex sound pressure level at the location, For the first Each test area, after restoration of its baseline state and frequency sampling points The re-acquired complex particle velocity; this formula is used to obtain the surface complex impedance corresponding to the restored reference state; S4-6, According to the formula Calculate the first Each test area, after restoration of its baseline state and frequency sampling points Regression baseline reflection coefficient at the location This formula is used to convert the surface complex impedance of the restored reference state into the regression reference reflection coefficient. S4-7, According to the formula Calculate the first Regression stability coefficient of each test area This formula is used to characterize the consistency of the reference state before and after the perturbation switch; This implementation method, after completing various perturbation state tests, does not directly use the aforementioned test results for the final output. Instead, it requires the test area to return to the baseline state and then re-verify whether its response remains consistent with the initial baseline state. Conventional methods, after completing tests under different working conditions, usually assume that the clamping and material conditions are still stable, rarely specifically verifying whether new installation deviations, local loosening, or irreversible deformations have been introduced during the test process. This scheme adds a regression stability check, which essentially determines whether the aforementioned reversible perturbation is truly reversible. Only when the baseline states of the previous two tests remain consistent can it be said that the test area has not been contaminated by new error factors during the test, and only then are the previous differential analysis results reliable. This step may seem like a repetitive confirmation, but in reality, it transforms the reversible perturbation from a conceptual requirement into a verifiable factual condition, which is a key step in ensuring the verifiability and persuasiveness of the final output results.

[0022] S4-8, When the When a test area is determined to be a boundary membrane coupling-dominated test area, the boundary constraint execution unit of that test area is adjusted to the boundary clamping length. Re-establish the baseline state after the target position is consistent; when the first When a test area is determined to be a dominance test area for rear cavity coupling, the rear cavity switching execution unit of that test area is adjusted to match the effective cavity depth. After the target position is consistent, the baseline state is re-established, when the first When a measurement area is determined to be a compression-coupled dominant measurement area, the preload adjustment unit of that measurement area is adjusted to match the local preload displacement. Once the target position is consistent, the baseline state is re-established. S4-9, in Not greater than the stability threshold After that, the first Each measurement area was determined as a valid measurement area. Greater than the stability threshold At that time, for the first Each test area was re-established to its baseline state and retested. In this implementation, the determination of the dominant coupling type is not merely used to describe the characteristics of the test area, but is further used to guide the test area back to a baseline state that better matches the target installation relationship. Conventional methods, even if they identify a region significantly affected by boundaries, rear cavities, or compression, typically only record this influence and do not utilize the determination result to correct the test boundary. This solution, however, directly links the dominant coupling type with subsequent reconstruction actions, allowing the determination result to participate in the restoration of the baseline state and the confirmation of the test area's validity. The significance of this is that the preceding identification steps are no longer merely analytical, but have adjustment and filtering functions; the test system no longer passively accepts errors, but can actively correct the test area state based on the source of coupling. This closed-loop processing of identification, callback, and admission is another substantial innovation that distinguishes this solution from purely analytical test solutions.

[0023] Step S5 includes the following sub-steps: S5-1. Renumber all test areas that have passed the regression stability check as number 1 to number 2 according to the preset order. The first effective measurement area will be the first The area contributed by each effective measurement zone at the target installation location is denoted as . According to the formula Calculate the NVH sound-absorbing cotton under test at the frequency sampling point Mounting surface acoustic impedance This formula is used to fuse the complex impedance of the reference state surface according to the contribution area of ​​each effective measurement area on the actual mounting surface. S5-2, the first The dominant coupling type and the surface acoustic impedance in the installed state corresponding to each effective measurement area The results are output together to form the surface acoustic impedance results in the installation state and the coupling distribution results in the measurement area.

[0024] This implementation method does not only output a single overall surface acoustic impedance result, but also simultaneously provides the distribution of dominant coupling types for each effective measurement area. Conventional tests often only aim to obtain an overall value to illustrate the overall sound absorption performance of the material. However, once the result deviates from expectations, it is difficult for testers to trace which type of installation relationship caused the deviation. This solution retains the measurement area-level distribution information while outputting the overall result, enabling the test conclusions to be used for both overall material evaluation and identification of local problems at the installation location. This further elevates the measured results to a source of interpretation. This means that the present invention not only improves the realism of the installed state test, but also enhances the guiding value of the test results for structural optimization, assembly verification, and problem tracking. The beneficial effect is no longer limited to the result being closer to the actual vehicle, but is realized in the result being more understandable and usable.

[0025] The key technical focus of this implementation method is not on employing a single acoustic measurement method, fixture structure, or data processing approach, but rather on establishing a complete identification closed loop around the installation-state test: first, the boundary compression, rear cavity fit, and local pre-compression relationships in the target installation location are transformed into reproducible test boundaries; then, within the same test area, perturbation states in different directions are sequentially formed in a reversible manner, gradually revealing the installation coupling effects that were originally mixed in with the test results; subsequently, regression stability verification confirms that the aforementioned perturbations have not disrupted the baseline state; finally, only the test results that meet the stability conditions are fused and output. Compared with conventional free-state tests, fixed-boundary tests, or single installation-state tests, this implementation method does not simply pursue obtaining a value closer to that of the actual vehicle, but simultaneously solves several interrelated problems such as installation state maintenance, coupling source identification, test result acceptance, and final result interpretation. This makes the test results closer to the actual installation state and easier to trace the causes of their formation, thus making it more suitable for evaluating the surface acoustic impedance of NVH sound-absorbing cotton under complex installation conditions.

[0026] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0027] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A surface acoustic impedance testing system for NVH sound-absorbing cotton, characterized in that: It includes an installation-state topology reconstruction module, a differential excitation acquisition module, and a state determination output module. The installation-state topology reconstruction module is used to construct the installation-state test boundary of the tested NVH sound-absorbing cotton based on the boundary compression relationship, rear cavity configuration relationship, and local pre-compression relationship of the target installation location. The differential excitation acquisition module is used to establish a reference state under the installation-state test boundary and apply a reversible perturbation state to acquire the surface acoustic response under each state. The state determination output module is used to identify the dominant coupling type based on the differential response under each state, and output the surface acoustic impedance test results in the installed state after regression stability verification.

2. The surface acoustic impedance testing system for NVH sound-absorbing cotton according to claim 1, characterized in that: The installation-state topology reconstruction module includes a topology input unit, a test area division unit, a boundary constraint execution unit, a rear cavity switching execution unit, and a preload adjustment unit. The topology input unit is used to input the boundary clamping information, rear cavity configuration information, and local preload information corresponding to the target installation location. The test area division unit is used to divide the area to be tested into multiple test areas based on the continuity of force. The boundary constraint execution unit is used to establish a boundary clamping state consistent with the target installation location in each test area. The rear cavity switching execution unit is used to establish a rear cavity state consistent with the target installation location behind each test area and implement rear cavity switching. The preload adjustment unit is used to establish a local preload state consistent with the target installation location in each test area and implement preload adjustment. The differential excitation acquisition module includes a reference state establishment unit, a perturbation state triggering unit, a near-surface acoustic excitation unit, a near-surface response acquisition unit, and a complex impedance calculation unit. The reference state establishment unit is used to establish an installation reference state in each test area. The perturbation state triggering unit is used to establish a boundary release state, a rear cavity switching state, and a pre-pressure adjustment state while keeping the overall installation relationship of the tested NVH sound-absorbing cotton unchanged. The near-surface acoustic excitation unit is used to apply a near-surface test sound field to each test area. The near-surface response acquisition unit is used to synchronously acquire the surface sound pressure signal and particle velocity signal of each test area. The complex impedance calculation unit is used to calculate the surface complex impedance of each test area under different states based on the surface sound pressure signal and particle velocity signal. The state determination output module includes a differential feature extraction unit, a dominant coupling determination unit, a regression stability verification unit, a multi-measurement area fusion unit, and a result output unit. The differential feature extraction unit is used to extract the differential response of each perturbation state relative to the reference state. The dominant coupling determination unit is used to determine the dominant coupling type corresponding to each measurement area. The regression stability verification unit is used to determine whether the reference state of each measurement area meets the regression stability condition. The multi-measurement area fusion unit is used to perform area fusion on the measurement area results that have passed the regression stability verification. The result output unit is used to output the surface acoustic impedance results in the installation state and the coupling distribution results at the measurement area level.

3. A method for testing the surface acoustic impedance of NVH sound-absorbing cotton based on the test system described in claim 2, characterized in that: Includes the following steps: S1. Obtain the boundary clamping information, rear cavity configuration information, and local pre-compression information of the target installation location. Divide the test area into multiple test zones according to the force continuity of the NVH sound-absorbing cotton under test on the target installation location. Divide the test area according to the boundary clamping line, rear cavity separation boundary, and local pre-compression abrupt boundary. Establish the installation state topology for each test zone so that the test input of each test zone corresponds one-to-one with the actual installation relationship in the target installation location. S2. Assemble the NVH sound-absorbing cotton to be tested into a reconfigurable test fixture, establish a reference state consistent with the installation state topology in each test area, and establish a boundary release state, a rear cavity switching state, and a pre-pressure adjustment state based on the reference state. The boundary release state, the rear cavity switching state, and the pre-pressure adjustment state are all reversible perturbation states relative to the reference state. S3. Apply near-surface acoustic excitation sequentially to the reference state, boundary release state, rear cavity switching state and pre-pressure adjustment state of each test area and collect the surface acoustic response to obtain the surface complex impedance and reflection coefficient of each test area in the four states, so that a comparable response set is formed between the installation state and its reversible perturbation state of the same test area. S4. Using the reference state as a reference, perform differential analysis on the reflection response differences corresponding to the boundary release state, the rear cavity switching state, and the pre-pressure adjustment state to determine the dominant coupling type of each test area. Then, adjust the installation state topology and retest the test areas that fail the regression stability check to ensure that the test area results entering the final output all correspond to the stable installation state reference state. S5. Perform fusion calculation of the surface acoustic impedance of the installed state for all test areas that have passed the regression stability check, output the test results of the surface acoustic impedance of the NVH sound-absorbing cotton under test at the target installation location, and output the distribution of the dominant coupling type of each test area, thereby forming a verifiable test conclusion.

4. The surface acoustic impedance testing method for NVH sound-absorbing cotton according to claim 3, characterized in that: Step S1 includes the following sub-steps: S1-1, the first The boundary compaction length of each test area is denoted as , will the The effective cavity depth behind each test area is denoted as , will the The local preloading displacement of each test area is denoted as . ,in Number the survey area; S1-2, Constructing the first Installation-state topology vector of each test area The installed state topology vector is used to characterize the first The boundary compaction state, rear cavity state, and local pre-compression state of each test area under the target installation location; S1-3, Based on the installation state topology vector Configure the boundary constraint execution unit, rear cavity switching execution unit, and preload adjustment unit corresponding to the test area, so that the first Each test area forms an installation topology in the test fixture that is consistent with the target installation location.

5. The surface acoustic impedance testing method for NVH sound-absorbing cotton according to claim 4, characterized in that: Steps S2 and S3 include the following sub-steps: S2-1, in the Each test area is based on the installation state topology vector. Establish a reference state, and denote the corresponding surface complex impedance as ; S2-2, while maintaining the first Under the condition that the overall position of the NVH sound-absorbing cotton under test remains unchanged in each test area, establish the boundary release state, the rear cavity switching state, and the pre-pressure adjustment state, and denote the corresponding surface complex impedances as follows: , , ,in For the first Each frequency sampling point , This represents the total number of frequency sampling points. S3-1, in the status number Under the corresponding test conditions, according to the formula Calculate the first Each test area at the frequency sampling point The surface complex impedance at the location, where For the status number, and Indicates the baseline state. Indicates the boundary release state. Indicates the switching state of the rear cavity. Indicates the preload adjustment status. For the first Each test area is in status and frequency sampling points The complex sound pressure level collected at the location, For the first Each test area is in status and frequency sampling points The velocity of the complex particles collected at the location; S3-2, According to the formula Calculation state The corresponding reflection response, where For the first Each test area is in status and frequency sampling points The reflection coefficient at that location, The characteristic impedance of air.

6. The surface acoustic impedance testing method for NVH sound-absorbing cotton according to claim 5, characterized in that: Step S4 includes the following sub-steps: S4-1. Calculate the boundary difference component, the rear cavity difference component, and the pre-pressure difference component respectively. The calculation formula is as follows: , , ,in Used to characterize the magnitude of the effect of boundary state changes on the reflection response. Used to characterize the magnitude of the effect of changes in the state of the back cavity on the reflection response. Used to characterize the magnitude of the effect of changes in preload state on the reflection response; S4-2, calculate the first one respectively Boundary coupling index of each test area Post-cavity coupling index and preload coupling index The calculation formula is: , , ,in Frequency sampling point The corresponding weighting coefficients satisfy ; S4-3, when ,and ,and Not less than the boundary judgment threshold At that time, the first The test area was determined to be a test area dominated by boundary membrane coupling; when ,and ,and Not less than the rear cavity determination threshold At that time, the first The test area was determined to be the dominant test area for rear cavity coupling. ,and ,and Not less than the preload judgment threshold At that time, the first The test area was determined to be a test area dominated by compression coupling. , , All results were obtained through statistical analysis of preliminary test results of standard calibration samples.

7. The surface acoustic impedance testing method for NVH sound-absorbing cotton according to claim 6, characterized in that: Step S4 further includes the following sub-steps: S4-4. After completing the tests for the boundary release state, the rear cavity switching state, and the pre-pressure adjustment state, the first... The boundary compaction length of each test area was restored to , will the The effective cavity depth behind each test area is restored to , will the The local preload displacement of each test area recovered to In order to re-establish the first The baseline state of each test area is used to re-acquire the data at the same test point locations, under the same acoustic excitation conditions, and with the same set of frequency sampling points as the initial baseline state. The complex sound pressure and complex particle velocity of each measurement area are denoted as follows: and ; S4-5, according to the formula Calculate the first Each test area, after restoration of its baseline state and frequency sampling points The regression reference surface complex impedance at the location ,in For the first Each test area, after restoration of its baseline state and frequency sampling points The re-acquired complex sound pressure level at the location, For the first Each test area, after restoration of its baseline state and frequency sampling points The velocity of the complex particle re-collected at that location; S4-6, According to the formula Calculate the first Each test area, after restoration of its baseline state and frequency sampling points Regression baseline reflection coefficient at the location ; S4-7, According to the formula Calculate the first Regression stability coefficient of each test area ; S4-8, When the When a test area is determined to be a boundary membrane coupling-dominated test area, the boundary constraint execution unit of that test area is adjusted to the boundary clamping length. Once the target position is consistent, the baseline state is re-established. When the When a test area is determined to be a dominance test area for rear cavity coupling, the rear cavity switching execution unit of that test area is adjusted to match the effective cavity depth. After the target position is consistent, the baseline state is re-established, when the first When a measurement area is determined to be a compression-coupled dominant measurement area, the preload adjustment unit of that measurement area is adjusted to match the local preload displacement. Once the target position is consistent, the baseline state is re-established. S4-9, in Not greater than the stability threshold After that, the first Each measurement area was determined as a valid measurement area. Greater than the stability threshold At that time, for the first Each test area was re-established to its baseline state and retested.

8. The surface acoustic impedance testing method for NVH sound-absorbing cotton according to claim 7, characterized in that: Step S5 includes the following sub-steps: S5-1. Renumber all test areas that have passed the regression stability check as number 1 to number 2 according to the preset order. The first effective measurement area will be the first The area contributed by each effective measurement zone at the target installation location is denoted as . According to the formula Calculate the NVH sound-absorbing cotton under test at the frequency sampling point Mounting surface acoustic impedance ; S5-2, the first The dominant coupling type and the surface acoustic impedance in the installed state corresponding to each effective measurement area The results are output together to form the surface acoustic impedance results in the installation state and the coupling distribution results in the measurement area.

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