Low and medium frequency acoustic measurement and correction method in high temperature environment

Abstract

The invention relates to a low and medium frequency acoustic measurement and correction method in a high temperature environment, which comprises the following steps of: performing a calibration experiment on an acoustic conduit measurement system under a normal temperature condition to obtain an amplitude correction curve; acoustic measurement is carried out in a high-temperature environment, an inlet end area of a sound conduit is heated to a target high-temperature state through a heating device, a sound source generator is kept to output an excitation signal which is the same as that of a calibration experiment, and sound pressure data of an inlet microphone and sound pressure data of an outlet microphone are synchronously collected; sound pressure data of the inlet microphone and the outlet microphone are converted into frequency domain spectrums through a fast Fourier transform aggregation method, 1 / 3 octave spectrum analysis is carried out, and uncorrected sound pressure levels of all frequency bands are obtained through calculation; and according to the amplitude correction curve, carrying out band-by-band correction on the uncorrected sound pressure level of each frequency band, and synthesizing the corrected sound pressure level of each frequency band into a full-frequency sound level to obtain a corrected high-temperature acoustic measurement result. Compared with the prior art, the accuracy of acoustic measurement of middle and low frequency bands is improved.

Description

Technical Field

[0001] This invention relates to the field of acoustic measurement technology, and in particular to a method for mid-to-low frequency acoustic measurement and correction under high-temperature conditions. Background Technology

[0002] Acoustic measurement technology plays a vital role in industrial inspection, environmental monitoring, and scientific research, especially in high-temperature environments, where it is crucial for aerospace engine evaluation, energy equipment condition monitoring, and high-temperature industrial process control. With the development of industrial technology, higher demands are being placed on the accurate measurement of acoustic parameters in high-temperature environments, particularly in the mid-to-low frequency range (50-1500Hz), which has become an urgent industry need. High-temperature acoustic measurement technology is currently undergoing a significant transformation from indirect to direct measurement, and from single-point measurement to field-distributed measurement.

[0003] In high-temperature environments, the propagation characteristics of sound waves undergo significant changes, including an increase in sound velocity with rising temperature, a more complex sound wave attenuation mechanism, and alterations in the acoustic impedance characteristics of materials. Traditional acoustic sensors, such as microphones, typically cannot operate normally in environments above 200°C, severely limiting the development of high-temperature acoustic measurements. Currently, the industry is actively exploring various technological approaches to overcome this bottleneck, primarily including acoustic duct technology, cooling protection methods, and the development of high-temperature resistant sensors. Among these, acoustic duct technology provides a feasible path to solving the challenges of acoustic measurements in high-temperature environments by transmitting sound waves from high-temperature regions to room-temperature regions for measurement. For example, patent application CN103438990A discloses a sound field measurement and analysis device and its analysis method in high-temperature environments. This device consists of an acoustic duct array, a flexible semi-infinite tube, a sound sensor, a data acquisition unit, and a computer. It employs a combined design of acoustic ducts and semi-infinite tubes to suppress reflections at the duct ends and improve measurement accuracy. During data processing, a sound pressure amplitude correction method based on a 1 / 3 octave band spectrum is used to correct the data at the end of the acoustic duct, further improving measurement accuracy. This technology enables sound field measurement in harsh environments where conventional microphones cannot directly measure, and can reconstruct sound field distribution and intensity information under high-temperature conditions. However, this technology still has shortcomings in system synchronous calibration, temperature stability control, and ensuring acoustic load consistency.

[0004] Current acoustic measurement techniques for high-temperature environments, especially in the mid-to-low frequency range, face several key technical challenges: 1) Existing high-temperature acoustic measurement technology is insufficient to fully address the amplitude-frequency response distortion caused by temperature changes during acoustic duct transmission.

[0005] 2) Acoustic measurements in high-temperature environments require precise synchronous acquisition from multiple microphones to obtain accurate sound field information. Existing synchronization methods suffer from timing errors in high-temperature environments due to factors such as thermal disturbances and material expansion.

[0006] 3) During high-temperature acoustic measurements, the stability of the temperature field in the inlet region of the acoustic duct has a significant impact on measurement accuracy. Existing technologies often lack quantitative evaluation indicators and control systems for temperature field stability.

[0007] 4) Maintaining acoustic load conditions consistent with those at room temperature during high-temperature measurements is crucial for ensuring comparability and accuracy. Current technologies lack effective mechanisms for monitoring and ensuring acoustic load consistency.

[0008] These problems have had a serious impact on practical work: on the one hand, insufficient measurement accuracy makes it impossible to obtain accurate high-temperature acoustic field data, rendering equipment condition assessment, fault diagnosis, and performance optimization based on this data unreliable; on the other hand, the non-repeatability and instability of the measurement results greatly reduce the practical value of high-temperature acoustic measurement technology, limiting its widespread application in industrial settings. In the aerospace field, inaccurate measurement of the acoustic characteristics of engine hot-end components affects the reliability of combustion instability analysis; in the energy industry, the effectiveness of noise monitoring and fault diagnosis for high-temperature equipment such as boilers and furnaces is significantly reduced. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the prior art by providing a method for mid-to-low frequency acoustic measurement and correction under high temperature conditions, thereby improving the accuracy of acoustic measurements in the mid-to-low frequency range.

[0010] The objective of this invention can be achieved through the following technical solutions: A method for mid-to-low frequency acoustic measurement and correction under high-temperature conditions, comprising the following steps: A calibration experiment was conducted on the acoustic duct measurement system under normal temperature conditions to obtain an amplitude correction curve. The acoustic duct measurement system includes an acoustic duct, a heating device, a sound source generator, an inlet microphone, an outlet microphone, a data acquisition device, and a signal processing unit. The acoustic duct is made of high-temperature resistant material. Its inlet end is connected to the sound source generator, and its outlet end is equipped with a sound-absorbing structure to suppress end reflection. The inlet microphone and the outlet microphone are respectively arranged at both ends of the acoustic duct for synchronously acquiring sound pressure signals. The data acquisition device is connected to the microphone to record sound pressure data. The signal processing unit is used to perform acoustic data analysis and correction calculations. Acoustic measurements are performed in a high-temperature environment. The inlet area of ​​the acoustic duct is heated to the target high temperature state by a heating device. The sound source generator outputs the same excitation signal as the calibration experiment, and the sound pressure data of the inlet microphone and the outlet microphone are collected synchronously. The sound pressure data of the inlet and outlet microphones were converted into frequency domain spectra using the fast Fourier transform aggregation method, and 1 / 3 octave band spectrum analysis was performed to calculate the uncorrected sound pressure level of each frequency band. Based on the amplitude correction curve, the uncorrected sound pressure level of each frequency band is corrected band by band, and the corrected sound pressure levels of each frequency band are combined into a full-frequency sound level to obtain the corrected high-temperature acoustic measurement results.

[0011] Furthermore, the acoustic transmission performance of the acoustic duct is corrected using a distributed parameter model, and the complex acoustic transfer function per unit length of the acoustic duct is: In the formula, For complex acoustic transfer functions, For frequency, The temperature of the acoustic duct wall. The attenuation coefficient is caused by viscous dissipation and thermal conduction. The imaginary unit, Temperature-dependent speed of sound is the length of the acoustic duct.

[0012] Furthermore, a time delay correction algorithm based on cross-spectral coherence is used to achieve synchronous acquisition of sound pressure signals by the inlet and outlet microphones. Specific steps include: obtaining the phase difference at the maximum coherence frequency point by calculating the cross-spectral coherence; the signal processing unit using this phase difference to calculate the time delay and adjust the sampling alignment in real time, thereby ensuring that the sampling data from the two microphones maintain temporal consistency across the entire frequency band, achieving synchronous calibration of the high-temperature acoustic duct system. The cross-spectral coherence is: In the formula, For cross-spectral coherence, Let be the cross-spectral function of the inlet sound pressure signal and the outlet sound pressure signal. The cross-spectral power of the inlet sound pressure signal and the outlet sound pressure signal is denoted as . For the entrance sound pressure signal at frequency Power size, For the output sound pressure signal at frequency Power size, The frequency domain representation of the time-domain sound pressure signal acquired at the inlet end of the acoustic duct after Fourier transform is given. for The complex conjugate, The frequency domain representation of the time-domain sound pressure signal acquired at the outlet of the acoustic duct is obtained after Fourier transform. for .

[0013] Furthermore, the specific steps of the calibration experiment include: The sound source generator generates an excitation signal covering a frequency range of 50Hz to 1500Hz. Sound pressure data from the inlet and outlet microphones were collected respectively, and the sound pressure level difference corresponding to the center frequency of each frequency band was obtained by 1 / 3 octave band spectrum analysis. A frequency-dependent amplitude correction curve is generated based on the sound pressure level difference and stored in the signal processing unit.

[0014] Furthermore, in the process of obtaining the sound pressure level difference corresponding to the center frequency of each frequency band through the 1 / 3 octave band spectrum analysis, the signal processing unit performs a smooth calculation of the sound pressure within the frequency band based on the energy-weighted integral algorithm, and the sound pressure level corresponding to the center frequency of each frequency band is: In the formula, For the first The sound pressure level corresponding to each center frequency For the first One center frequency, For the first Bandwidth of each center frequency The frequency domain sound pressure amplitude, For reference sound pressure level.

[0015] Furthermore, when performing acoustic measurements in a high-temperature environment, the temperature field at the inlet region of the acoustic duct needs to remain stable. Before the measurement phase begins, the signal processing unit calculates a temperature stability index in real time and compares it with a preset threshold. When the temperature stability index is less than or equal to the preset threshold, the temperature field is considered to have reached a steady state, and acoustic measurement is initiated. The temperature stability index is: In the formula, For temperature stability indicators, For time window, The start time, For a moment Temperature at the measuring point In the time window Average temperature inside, For a moment.

[0016] Furthermore, when performing acoustic measurements in high-temperature environments, it is necessary to ensure that the temperature field is stable and the acoustic load is consistent during the measurement process. Before each acoustic measurement, the signal processing unit calculates the frequency band weighted consistency index and compares it with the tolerance limit. When the frequency band weighted consistency index is less than or equal to the tolerance limit, the sound source excitation is confirmed to be consistent with the calibration and the data is accepted. If the frequency band weighted consistency index is greater than the tolerance limit, the sound source gain adjustment or the re-steady-state heating process will be automatically triggered to eliminate excitation inconsistency. The frequency band weighted consistency index is as follows: In the formula, It is a frequency band-weighted consistency index. Total number of frequency bands For weights based on frequency band energy, The first high temperature measurement Uncorrected sound pressure level in each frequency band For the first time during room temperature calibration The frequency band sound pressure level.

[0017] Furthermore, the specific steps for converting the sound pressure data of the inlet and outlet microphones into frequency domain spectra using the Fast Fourier Transform aggregation method and performing 1 / 3 octave band spectrum analysis to calculate the uncorrected sound pressure level of each frequency band include: The sound pressure data of the inlet and outlet microphones are converted into frequency domain spectra using a segmented overlapping fast Fourier transform aggregation algorithm to obtain a stable power spectrum. A 1 / 3 octave band spectrum analysis was performed on the stable power spectrum. For each 1 / 3 octave band, an in-band leakage correction and quadrature algorithm was used to obtain the uncorrected sound pressure level of each band. The uncorrected sound pressure level is: In the formula, For the first Uncorrected sound pressure level in each frequency band For frequency bandwidth, To include an internal leakage correction factor, The average self-power spectral density, The total number of segments, For the first The Fourier transform amplitude of the time-domain sound pressure signal. For the first The window function normalization factor for a time-domain sound pressure signal.

[0018] Furthermore, the band-by-band correction is implemented through an amplitude differential compensation algorithm. The signal processing unit extracts the amplitude correction amount from the amplitude correction amount curve according to the center frequency of the frequency band, realizing band-by-band additive compensation of the amplitude. The sound pressure level after correction for each frequency band is: In the formula, For the first Sound pressure level after frequency band correction For the first Uncorrected sound pressure level in each frequency band This is the amplitude correction amount. , , represents the fitting coefficient.

[0019] Furthermore, the corrected sound pressure levels of each frequency band are synthesized into a full-frequency sound level based on the power addition principle and energy weighting correction. The full-frequency sound level is: In the formula, Full-range sound level, These are the weighting coefficients for each frequency band. for, The energy of the sound pressure level after correction for each frequency band. For reference energy.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention, by introducing a method combining room temperature calibration and amplitude correction curves, can compensate for changes in the transmission characteristics of acoustic ducts caused by high temperatures. It generates frequency-related amplitude correction curves under room temperature conditions and applies band-by-band correction in high-temperature measurements, adding the uncorrected sound pressure level of each band to the corresponding correction value. This solves the problem of amplitude-frequency response distortion caused by temperature changes in the prior art, resulting in a significant reduction in measurement errors in the low-to-mid frequency range of 50-1500Hz.

[0021] 2. This invention employs a time delay correction algorithm based on cross-spectral coherence. By calculating the cross-spectral function and coherence of the inlet and outlet sound pressure signals, the time delay is calculated in real time and the sampling alignment is adjusted. This effectively overcomes the problem of insufficient synchronization accuracy caused by thermal disturbance and material expansion in the prior art, ensuring that the two microphones maintain timing consistency across the entire frequency band.

[0022] 3. This invention defines a temperature stability index to monitor and evaluate temperature fluctuations in the inlet region of the acoustic duct in real time, initiating acoustic acquisition only when the index falls below a preset threshold. This solves the problem of the lack of quantitative control over temperature stability in existing technologies, reducing the instability error introduced by thermal disturbances to a controllable range.

[0023] 4. This invention uses a frequency band weighted consistency index to automatically compare the sound pressure level difference between high temperature measurement and normal temperature calibration, and triggers a sound source gain adjustment or reheating process when the tolerance limit is exceeded. This addresses the defect in the prior art where the sound load is inconsistent due to temperature changes, and avoids the distortion of correction data caused by sound source output drift.

[0024] 5. This invention employs 1 / 3 octave band spectrum analysis combined with energy-weighted integral algorithm and logarithmic polynomial fitting interpolation to eliminate the jitter effect of discrete spectrum and discontinuity error at frequency band boundaries. Furthermore, through piecewise overlapping FFT aggregation and leakage correction algorithm, a smooth and stable power spectrum is generated, solving the problem that spectrum analysis in the prior art is easily affected by transient noise and window function. This makes the correction curve continuous and smooth in the frequency domain, and improves the frequency resolution to the 1 / 3 octave band level.

[0025] 6. Based on the principle of power addition and energy weighting correction, this invention synthesizes the corrected sound pressure levels of each frequency band into a full-frequency sound level. By normalizing the frequency band energy to balance the contributions of different frequency bands, it overcomes the limitation of the existing technology that often ignores energy conservation in the synthesis of full-frequency sound levels, and ensures that the output results are comparable to those measured at room temperature under high temperature conditions. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating a method for mid-to-low frequency acoustic measurement and correction under high-temperature conditions proposed in this invention. Figure 2 This is a flowchart illustrating the calibration experiment. Figure 3 This is a schematic diagram of the process for conducting acoustic measurements in a high-temperature environment. Figure 4 This is a flowchart illustrating the process of correcting the uncorrected sound pressure level in each frequency band on a frequency band-by-frequency basis. Detailed Implementation

[0027] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0028] Example 1 This embodiment provides a method for mid-to-low frequency acoustic measurement and correction under high-temperature conditions, such as... Figure 1 As shown, it includes the following steps: S1. A calibration experiment was conducted on the acoustic tube measurement system under normal temperature conditions to obtain the amplitude correction curve.

[0029] The acoustic duct measurement system includes an acoustic duct, a heating device, a sound source generator, an inlet microphone, an outlet microphone, a data acquisition device, and a signal processing unit. The acoustic duct is made of high-temperature resistant material. Its inlet end is connected to the sound source generator, and its outlet end is equipped with a sound-absorbing structure to suppress end reflection. The inlet microphone and the outlet microphone are respectively arranged at both ends of the acoustic duct for synchronously acquiring sound pressure signals. The data acquisition device is connected to the microphone to record sound pressure data, and the signal processing unit is used to perform acoustic data analysis and correction calculations.

[0030] The acoustic transmission performance of the acoustic duct is corrected using a distributed parameter model. The complex acoustic transfer function of the acoustic duct per unit length is: In the formula, For complex acoustic transfer functions, For frequency, The temperature of the acoustic duct wall. The attenuation coefficient is caused by viscous dissipation and thermal conduction. The imaginary unit, Temperature-dependent speed of sound This represents the length of the acoustic duct. Before measurement, the signal processing unit performs temperature compensation on the sound pressure transmission path based on this function, ensuring that the phase difference and amplitude difference between the inlet and outlet sound pressures maintain a linear response at high temperatures, thereby improving measurement accuracy.

[0031] Synchronous acquisition of sound pressure signals by the inlet and outlet microphones is achieved through a time delay correction algorithm based on cross-spectral coherence. The specific steps include: calculating the phase difference at the maximum coherence frequency by measuring cross-spectral coherence; using this phase difference to calculate the time delay and adjusting the sampling alignment in real time; and ensuring that the sampling data from the two microphones remain time-consistent across the entire frequency band, thus achieving synchronous calibration of the high-temperature acoustic duct system. The cross-spectral coherence is: In the formula, For cross-spectral coherence, Let be the cross-spectral function of the inlet sound pressure signal and the outlet sound pressure signal. The cross-spectral power of the inlet sound pressure signal and the outlet sound pressure signal is denoted as . For the entrance sound pressure signal at frequency Power size, For the output sound pressure signal at frequency Power size, The frequency domain representation of the time-domain sound pressure signal acquired at the inlet end of the acoustic duct after Fourier transform is given. for The complex conjugate, The frequency domain representation of the time-domain sound pressure signal acquired at the outlet of the acoustic duct is obtained after Fourier transform. for .

[0032] like Figure 2 As shown, the specific steps of the calibration experiment include: An excitation signal covering a frequency range of 50Hz to 1500Hz is generated by a sound source generator.

[0033] Sound pressure data from the inlet and outlet microphones were collected separately, and the sound pressure level difference corresponding to the center frequency of each frequency band was obtained by 1 / 3 octave band spectrum analysis.

[0034] In the process of obtaining the sound pressure level difference corresponding to the center frequency of each frequency band through 1 / 3 octave band spectrum analysis, the signal processing unit performs smooth calculation of the sound pressure within the frequency band based on the energy-weighted integral algorithm. The sound pressure level corresponding to the center frequency of each frequency band is: In the formula, For the first The sound pressure level corresponding to each center frequency For the first One center frequency, For the first Bandwidth of each center frequency The frequency domain sound pressure amplitude, For reference sound pressure level.

[0035] Based on the sound pressure level difference, a frequency-related amplitude correction curve is generated by frequency interpolation using a fitting function, and then stored in the signal processing unit. The specific steps include: calculating the sound pressure level difference between the inlet and outlet microphones in each frequency band based on the sound pressure level corresponding to the center frequency of each band, thus obtaining a series of discrete data points composed of the center frequency of each band and its sound pressure level difference; using the least squares method, a fitting function is used to optimally approximate all these discrete data points, fitting to form a complete amplitude correction curve, which is then pre-stored in the memory of the signal processing unit.

[0036] Define the amplitude correction function as follows: In the formula, This is the amplitude correction amount. , , These are the fitting coefficients obtained using the least squares method. The signal processing unit uses this function as a full-band correction model for subsequent high-temperature measurement corrections.

[0037] The logarithmic polynomial fitting of the amplitude correction function maintains second-order continuity in the range of 50Hz to 1500Hz, which can effectively eliminate discontinuity errors at the frequency band boundaries, making the correction curve smoothly connected in the frequency spectrum transition region, and improving the stability and accuracy of the correction calculation.

[0038] S2. Conduct acoustic measurements in a high-temperature environment. Heat the inlet area of ​​the acoustic duct to the target high temperature using a heating device. Maintain the same excitation signal output from the sound source generator as in the calibration experiment. Simultaneously collect the sound pressure data of the inlet and outlet microphones.

[0039] The specific steps for conducting acoustic measurements in high-temperature environments are as follows: Figure 3 As shown, the inlet area of ​​the acoustic duct is heated to the target high temperature state by a heating device, with a maximum temperature of 1200°C. At the same time, the sound source generator outputs the same excitation signal as in the calibration experiment, and the sound pressure data of the inlet and outlet microphones are collected synchronously to ensure that the temperature field is stable and the sound load is consistent during the measurement process.

[0040] When performing acoustic measurements in a high-temperature environment, it is necessary to ensure that the temperature field is stable and the acoustic load is consistent during the measurement process. Before each acoustic measurement, the signal processing unit calculates the frequency band weighted consistency index and compares it with the tolerance limit. When the frequency band weighted consistency index is less than or equal to the tolerance limit, confirm that the sound source excitation is consistent with the calibration and accept the data. If the frequency band weighted consistency index is greater than the tolerance limit, the source gain adjustment or the re-steady-state heating process will be automatically triggered to eliminate excitation inconsistency. The frequency band weighted consistency index is as follows: In the formula, It is a frequency band-weighted consistency index. Total number of frequency bands For weights based on frequency band energy, The first high temperature measurement Uncorrected sound pressure level in each frequency band For the first time during room temperature calibration The frequency band sound pressure level.

[0041] When performing acoustic measurements in a high-temperature environment, the temperature field at the inlet region of the acoustic duct must remain stable. Before the measurement phase begins, the signal processing unit calculates a temperature stability index in real time and compares it with a preset threshold. When the temperature stability index is less than or equal to the preset threshold, the temperature field is considered to have reached a steady state, and acoustic measurement is initiated. The temperature stability index is: In the formula, For temperature stability indicators, For time window, The start time, For a moment Temperature at the measuring point In the time window Average temperature inside, For a moment.

[0042] Temperature stability indexes are used to quantify the impact of temperature field fluctuations on acoustic propagation parameters and reduce the instability errors introduced by thermal disturbances to a controllable range, thereby improving the repeatability and reliability of high-temperature measurement results.

[0043] S3. The sound pressure data of the inlet and outlet microphones are converted into frequency domain spectra by fast Fourier transform aggregation method, and 1 / 3 octave band spectrum analysis is performed to calculate the uncorrected sound pressure level of each frequency band.

[0044] The specific steps for converting the sound pressure levels of the inlet and outlet microphones into frequency domain spectra using the Fast Fourier Transform aggregation method, followed by 1 / 3 octave band spectrum analysis, to calculate the uncorrected sound pressure levels for each frequency band include: The sound pressure data of the inlet and outlet microphones are converted into frequency domain spectra by a segmented overlapping fast Fourier transform aggregation algorithm to obtain a stable power spectrum. A 1 / 3 octave band spectrum analysis was performed on the stable power spectrum. For each 1 / 3 octave band, an in-band leakage correction and quadrature algorithm were used to obtain the uncorrected sound pressure level (SPL) of each band. The uncorrected SPL is: In the formula, For the first Uncorrected sound pressure level in each frequency band For frequency bandwidth, To include an internal leakage correction factor, The average self-power spectral density, The total number of segments, For the first The Fourier transform amplitude of the time-domain sound pressure signal. For the first The window function normalization factor for a time-domain sound pressure signal.

[0045] S4. Based on the amplitude correction curve, the uncorrected sound pressure level of each frequency band is corrected band by band, and the corrected sound pressure levels of each frequency band are combined into a full-frequency sound level to obtain the corrected high-temperature acoustic measurement results.

[0046] The specific steps for band-by-band correction of the uncorrected sound pressure level in each frequency band are as follows: Figure 4 As shown, the amplitude correction curve obtained from room temperature calibration is used to correct the uncorrected sound pressure level of each frequency band obtained under high temperature conditions. Specifically, the uncorrected sound pressure level of each frequency band is added to the correction amount of the corresponding frequency band to obtain the corrected sound pressure level of each frequency band. Then, the corrected sound pressure levels of each frequency band are combined into a full-frequency sound level by the power addition principle, and finally the corrected high-temperature acoustic measurement results are output.

[0047] Band-by-band correction is achieved through an amplitude differential compensation algorithm. The signal processing unit extracts the amplitude correction amount from the amplitude correction curve according to the center frequency of the band, realizing band-by-band additive compensation of the amplitude. This eliminates the frequency response deviation of the high-temperature acoustic duct system under changes in heat conduction and material acoustic impedance, making the correction result equivalent to the room temperature calibration condition in terms of energy. The sound pressure level after correction for each band is: In the formula, For the first Sound pressure level after frequency band correction For the first Uncorrected sound pressure level in each frequency band This is the amplitude correction amount. , , These are the fitting coefficients obtained by the least squares method.

[0048] The corrected sound pressure levels of each frequency band are synthesized into a full-frequency sound level based on the principle of power addition and energy weighting correction. The full-frequency sound level is: In the formula, Full-range sound level, These are the weighting coefficients for each frequency band. for, The energy of the sound pressure level after correction for each frequency band. For reference energy.

[0049] This algorithm achieves balanced superposition of contributions from different frequency bands through frequency band energy normalization, ensuring that the final output full-frequency sound level reflects both the corrected sound power distribution and maintains spectral energy conservation, thereby obtaining comparable comprehensive acoustic measurement results under high-temperature acoustic duct measurement conditions.

[0050] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for mid-to-low frequency acoustic measurement and correction under high-temperature conditions, characterized in that, Includes the following steps: A calibration experiment was conducted on the acoustic duct measurement system under normal temperature conditions to obtain an amplitude correction curve. The acoustic duct measurement system includes an acoustic duct, a heating device, a sound source generator, an inlet microphone, an outlet microphone, a data acquisition device, and a signal processing unit. The acoustic duct is made of high-temperature resistant material. Its inlet end is connected to the sound source generator, and its outlet end is equipped with a sound-absorbing structure to suppress end reflection. The inlet microphone and the outlet microphone are respectively arranged at both ends of the acoustic duct for synchronously acquiring sound pressure signals. The data acquisition device is connected to the microphone to record sound pressure data. The signal processing unit is used to perform acoustic data analysis and correction calculations. Acoustic measurements are performed in a high-temperature environment. The inlet area of ​​the acoustic duct is heated to the target high temperature state by a heating device. The sound source generator outputs the same excitation signal as the calibration experiment, and the sound pressure data of the inlet microphone and the outlet microphone are collected synchronously. The sound pressure data of the inlet and outlet microphones were converted into frequency domain spectra using the fast Fourier transform aggregation method, and 1 / 3 octave band spectrum analysis was performed to calculate the uncorrected sound pressure level of each frequency band. Based on the amplitude correction curve, the uncorrected sound pressure level of each frequency band is corrected band by band, and the corrected sound pressure levels of each frequency band are combined into a full-frequency sound level to obtain the corrected high-temperature acoustic measurement results.

2. The method for mid-to-low frequency acoustic measurement and correction under high temperature environment according to claim 1, characterized in that, The acoustic transmission performance of the acoustic duct is corrected using a distributed parameter model, and the complex acoustic transfer function per unit length of the acoustic duct is: In the formula, For complex acoustic transfer functions, For frequency, The temperature of the acoustic duct wall. The attenuation coefficient is caused by viscous dissipation and thermal conduction. The imaginary unit, Temperature-dependent speed of sound is the length of the acoustic duct.

3. The method for mid-to-low frequency acoustic measurement and correction under high temperature environment according to claim 1, characterized in that, The synchronous acquisition of sound pressure signals by the inlet and outlet microphones is achieved through a time delay correction algorithm based on cross-spectral coherence. The specific steps include: obtaining the phase difference at the maximum coherence frequency point by calculating the cross-spectral coherence; the signal processing unit using this phase difference to calculate the time delay and adjust the sampling alignment in real time, thereby ensuring that the sampling data from the two microphones maintain temporal consistency across the entire frequency band, achieving synchronous calibration of the high-temperature acoustic duct system. The cross-spectral coherence is: In the formula, For cross-spectral coherence, Let be the cross-spectral function of the inlet sound pressure signal and the outlet sound pressure signal. The cross-spectral power of the inlet sound pressure signal and the outlet sound pressure signal is denoted as . For the entrance sound pressure signal at frequency Power size, For the output sound pressure signal at frequency Power size, The frequency domain representation of the time-domain sound pressure signal acquired at the inlet end of the acoustic duct after Fourier transform is given. for The complex conjugate, The frequency domain representation of the time-domain sound pressure signal acquired at the outlet of the acoustic duct is obtained after Fourier transform. for .

4. The method for mid-to-low frequency acoustic measurement and correction under high temperature environment according to claim 1, characterized in that, The specific steps of the calibration experiment include: The sound source generator generates an excitation signal covering a frequency range of 50Hz to 1500Hz. Sound pressure data from the inlet and outlet microphones were collected respectively, and the sound pressure level difference corresponding to the center frequency of each frequency band was obtained by 1 / 3 octave band spectrum analysis. A frequency-dependent amplitude correction curve is generated based on the sound pressure level difference and stored in the signal processing unit.

5. The method for mid-to-low frequency acoustic measurement and correction under high temperature environment according to claim 2, characterized in that, In the process of obtaining the sound pressure level difference corresponding to the center frequency of each frequency band through the 1 / 3 octave band spectrum analysis, the signal processing unit performs smooth calculation of the sound pressure within the frequency band based on the energy-weighted integral algorithm. The sound pressure level corresponding to the center frequency of each frequency band is as follows: In the formula, For the first The sound pressure level corresponding to each center frequency For the first One center frequency, For the first Bandwidth of each center frequency The frequency domain sound pressure amplitude, For reference sound pressure level.

6. The method for mid-to-low frequency acoustic measurement and correction under high temperature environment according to claim 1, characterized in that, When performing acoustic measurements in a high-temperature environment, the temperature field at the inlet region of the acoustic duct needs to remain stable. Before the measurement phase begins, the signal processing unit calculates a temperature stability index in real time and compares it with a preset threshold. When the temperature stability index is less than or equal to the preset threshold, the temperature field is considered to have reached a steady state, and acoustic measurement is initiated. The temperature stability index is: In the formula, For temperature stability indicators, For time window, The start time, For a moment Temperature at the measuring point In the time window Average temperature inside, For a moment.

7. The method for mid-to-low frequency acoustic measurement and correction under high temperature environment according to claim 1, characterized in that, When performing acoustic measurements in a high-temperature environment, it is necessary to ensure that the temperature field is stable and the acoustic load is consistent during the measurement process. Before each acoustic measurement, the signal processing unit calculates the frequency band weighted consistency index and compares it with the tolerance limit. When the frequency band weighted consistency index is less than or equal to the tolerance limit, the sound source excitation is confirmed to be consistent with the calibration and the data is accepted. If the frequency band weighted consistency index is greater than the tolerance limit, the sound source gain adjustment or the re-steady-state heating process will be automatically triggered to eliminate excitation inconsistency. The frequency band weighted consistency index is as follows: In the formula, It is a frequency band-weighted consistency index. Total number of frequency bands For weights based on frequency band energy, The first high temperature measurement Uncorrected sound pressure level in each frequency band For the first time during room temperature calibration The frequency band sound pressure level.

8. The method for mid-to-low frequency acoustic measurement and correction under high temperature environment according to claim 1, characterized in that, The specific steps for converting the sound pressure data of the inlet and outlet microphones into frequency domain spectra using the Fast Fourier Transform aggregation method, and performing 1 / 3 octave band spectrum analysis to calculate the uncorrected sound pressure level for each frequency band include: The sound pressure data of the inlet and outlet microphones are converted into frequency domain spectra using a segmented overlapping fast Fourier transform aggregation algorithm to obtain a stable power spectrum. A 1 / 3 octave band spectrum analysis was performed on the stable power spectrum. For each 1 / 3 octave band, an in-band leakage correction and quadrature algorithm was used to obtain the uncorrected sound pressure level of each band. The uncorrected sound pressure level is: In the formula, For the first Uncorrected sound pressure level in each frequency band For frequency bandwidth, To include an internal leakage correction factor, The average self-power spectral density, The total number of segments, For the first The Fourier transform amplitude of the time-domain sound pressure signal. For the first The window function normalization factor for a time-domain sound pressure signal.

9. The method for mid-to-low frequency acoustic measurement and correction under high temperature environment according to claim 1, characterized in that, The band-by-band correction is achieved through an amplitude differential compensation algorithm. The signal processing unit extracts the amplitude correction amount from the amplitude correction curve according to the center frequency of the band, realizing band-by-band additive compensation of the amplitude. The sound pressure level after correction for each band is: In the formula, For the first Sound pressure level after frequency band correction For the first Uncorrected sound pressure level in each frequency band This is the amplitude correction amount. , , represents the fitting coefficient.

10. The method for mid-to-low frequency acoustic measurement and correction under high temperature environment according to claim 9, characterized in that, The modified sound pressure levels of each frequency band are synthesized into a full-frequency sound level based on the principle of power addition and energy weighting correction. The full-frequency sound level is: In the formula, Full-range sound level, These are the weighting coefficients for each frequency band. for, The energy of the sound pressure level after correction for each frequency band. For reference energy.

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