A method for inverting the attenuation coefficient of ultrasonic overlapping echoes in a lubricating film containing vapor bubbles

Abstract

This invention discloses a method for inverting the attenuation coefficient of ultrasonic overlapping echoes containing bubble-filled lubricating films, relating to the field of lubrication condition detection technology for friction pairs in machine systems. The method includes the following steps: S1, algorithm parameter initialization; S2, calculating the estimated echo. B sim The time-domain signal; S3, step-by-step traversal iteration variables; update and calculate the estimated echo under these parameters. B sim S4. Estimate the echo time-domain signal under each parameter. B sim With the time-domain signal of the echo to be measured B m Perform time-domain cross-correlation and record the iterative oil film thickness and attenuation coefficient at the point of maximum correlation as the optimal iterative oil film thickness. d best and attenuation coefficient α best Based on oil film thickness d and attenuation coefficient α The oil film complete echo is estimated by theoretical calculation as the iterative variable. B sim By comparing with the actual echo B m Perform time-domain cross-correlation and solve for the inversion attenuation coefficient when the correlation is maximized. α This enables the inversion of the attenuation coefficient, solving the current problem of difficulty in extracting the attenuation coefficient of oil film echoes containing air bubbles.

Description

Technical Field

[0001] This invention relates to the field of lubrication condition detection technology for friction pairs in machine systems, and in particular to an ultrasonic overlapping echo attenuation coefficient inversion method for a bubble-containing lubricating film. Background Technology

[0002] In high-speed sliding bearings, the pressure field formed by the hydrodynamic lubricating oil film during operation exhibits a significant alternating distribution of positive and negative pressures. The negative pressure induces the precipitation of dissolved gases, resulting in a large number of pressure-unstable microbubbles within the lubricating oil film. The cavitation erosion effect triggered by these bubbles during collapse not only damages the surface integrity of critical components but also reduces the load-bearing capacity of the lubricating oil film, significantly shortening the bearing's lifespan. Therefore, the cavitation erosion phenomenon of sliding bearing lubricating oil films has become a crucial research area. However, due to the small scale of the sliding bearing oil film, in-situ observation is difficult, making the detection of bubble content in the oil film a persistent research challenge.

[0003] Due to the excellent beam characteristics and strong penetrating power of ultrasound, ultrasonic methods have achieved significant results in monitoring the dynamic oil film thickness of sliding bearings. Previous studies using ultrasonic measurement to investigate the circumferential oil film thickness distribution in sliding bearings have reported the impact of air bubbles on measurement accuracy. From the perspective of acoustic propagation mechanisms, air-bubble-containing oil films essentially constitute a non-uniform multiphase medium system. Due to the significant difference in acoustic impedance between the gas and liquid phases, the propagation of ultrasound waves will undergo complex scattering effects, resulting in attenuation of the ultrasound amplitude. Theoretical analysis and experimental studies show a significant positive correlation between the volume fraction of cavitation bubbles in the oil film phase and the attenuation coefficient of the ultrasonic echo. This makes the attenuation coefficient of the ultrasonic echo a key acoustic parameter for quantitatively characterizing the cavitation effect of multiphase lubricating media.

[0004] Depending on the reference standard, the measurement methods for ultrasonic echo attenuation coefficient can be mainly divided into calibration methods and self-reference methods. The calibration method uses pre-acquired ultrasonic echoes from a homogeneous medium system of the same thickness as a reference standard, calculating the attenuation coefficient by comparing the amplitude changes of ultrasonic echoes from a non-homogeneous medium system. While the calibration method is simple to operate, its measurement accuracy depends on the premise of a constant oil film thickness, which significantly limits its application in sliding bearings with dynamic oil film thickness conditions. The self-reference method overcomes the thickness constraint of the calibration method by using time windows to capture ultrasonic echoes reflected from different interfaces and calculating the attenuation coefficient by comparing the amplitudes of each captured echo. The self-reference method calculates the attenuation coefficient using signals from different time windows of the same ultrasonic echo, eliminating the dependence on a pre-set reference standard and effectively overcoming the problem that the calibration method cannot be applied to sliding bearings with varying oil film thicknesses. However, the micrometer-scale oil film thickness of sliding bearings will lead to the overlap of multiple echoes from different interfaces. Overlapping ultrasonic echoes are difficult to separate effectively using traditional time window techniques, thus making it impossible to accurately extract the amplitude to calculate the attenuation coefficient. Therefore, the accurate measurement of the ultrasonic echo attenuation coefficient of sliding bearings still faces two challenges: the problem of reference standard change caused by oil film thickness variation, and the signal separation problem caused by ultrasonic echo superposition at the micrometer scale.

[0005] Therefore, given the limitations of existing attenuation coefficient measurement methods in applying them to conditions of varying oil film thickness and overlapping echoes, it is necessary to investigate an ultrasonic echo attenuation coefficient inversion method applicable under these conditions for measuring the echo attenuation coefficient of oil films in sliding bearings containing air bubbles. Summary of the Invention

[0006] This invention aims to provide a method for inverting the attenuation coefficient of ultrasonic overlapping echoes containing bubble-filled lubricating films, using oil film thickness as the basis. d and attenuation coefficient α The oil film complete echo is estimated by theoretical calculation as the iterative variable. B sim By comparing with the actual echo B m Perform time-domain cross-correlation and solve for the inversion attenuation coefficient when the correlation is maximized. α This enables the inversion of the attenuation coefficient, solving the current problem of difficulty in extracting the attenuation coefficient of oil film echoes containing air bubbles.

[0007] To achieve the above-mentioned objectives, the technical solution of the present invention is as follows:

[0008] A method for inverting the attenuation coefficient of ultrasonic overlapping echoes containing a bubble-lubricated film includes the following steps:

[0009] S1. Algorithm parameter initialization: Obtain the acoustic impedance of the three-layer medium of bearing bush, lubricating medium, and journal. Z 1. Z 2 and Z3, and the sound velocity of the lubricating medium. c Pre-collection of steel-oil film primary echo B 1. Set the iteration range for oil film thickness and attenuation coefficient, and set the highest estimated echo order. n max ;

[0010] S2. Echo estimation calculation, based on the steel-oil film primary echo in step S1. B 1. Calculate the estimated echo B sim The time-domain signal;

[0011] S3. Within the iteration range, step through the iteration variables; change the oil film thickness with each iteration. d and attenuation coefficient α Then update the estimated echo calculation under this parameter. B sim ;

[0012] S4. Acquire the time-domain signal of the three-layer medium of bearing bush, lubricating medium, and journal. B m The estimated echo time-domain signal under each parameter B sim With the time-domain signal of the echo to be measured B m Perform time-domain cross-correlation and record the iterative oil film thickness and attenuation coefficient at the point of maximum correlation as the optimal iterative oil film thickness. d best and attenuation coefficient α best .

[0013] Furthermore, in step S2, calculating the estimated time-domain signal of the echo Bsim includes the following steps:

[0014] S201, First echo of steel-oil film B 1. Perform a Fourier transform to obtain its amplitude. B 1|and phase ;

[0015] S202, according to step S201, | B 1| and ,calculate n (2≤ n ≤ n max )-order echo B n Amplitude | B n |and phase ;

[0016] S203, Through the echoes of each order in step S202 B n Amplitude | B n |and phase Inverse Fourier transform was performed to obtain echoes of various orders. B n Time-domain signal;

[0017] S204, Direct combination 1 to n max From the time-domain signal of the first-order echo, the estimated echo can be obtained. B sim The time-domain signal.

[0018] Furthermore, in step S201, the steel-oil film primary echo... B Amplitude of 1 | B 1| The calculation formula is:

[0019]

[0020] Among them, | B 1|Single echo of steel-oil film B The amplitude is 1; abs() is the amplitude operation; FFT() is the fast Fourier transform operation.

[0021] Furthermore, in step S201, the steel-oil film primary echo... B Phase 1 The calculation formula is:

[0022]

[0023] Where angle() is the phase angle operation; FFT() is the fast Fourier transform operation; For steel-oil film primary echo B Phase 1.

[0024] Furthermore, in step S202, the nth-order echo is calculated using the following formula. B n Amplitude | B n |:

[0025]

[0026]

[0027] in, d Oil film thickness; c The velocity of sound in the lubricating medium; n For echo order, n =2,…,n max ;in α This is the oil film echo attenuation coefficient; W Interface transmission coefficient; V The subscript 1 represents the interface reflection coefficient; subscripts 1, 2, and 3 represent different media; subscript 12 indicates the wave propagation direction is from medium 1 to medium 2, subscript 21 indicates the wave propagation direction is from medium 2 to medium 1; subscript 23 indicates the wave propagation direction is from medium 2 to medium 3; | B n / B 1| is the first n Step echo B n and B Amplitude ratio of 1;

[0028] Wherein, the interface reflection coefficient V It is calculated using the following formula:

[0029]

[0030] in Z i The acoustic impedance of the medium is determined by the density of the medium and the velocity of sound. ij The direction of ultrasonic wave propagation is represented by the first line from the friction pair material. i propagation of the medium to the first layer j Layered medium; Z 1. Z 2 and Z 3 represents the acoustic impedance of the three layers of media: bearing shell, lubricating medium, and journal.

[0031] Interface transmission coefficient W It is calculated using the following formula:

[0032] .

[0033] In step S202, the number of steps is calculated using the following formula. n Step echo B n phase :

[0034]

[0035]

[0036] in, For the first n Step echo B n and B A phase difference of 1; n For echo order,n =2,…, n max ; d Oil film thickness; c The velocity of sound in the lubricating medium; f This is the echo frequency.

[0037] In step S203, the echoes of each order are calculated using the following formula. B n Time-domain signal:

[0038]

[0039] in, B n For the first n The time-domain signal of the first-order echo, iFFT() is the inverse fast Fourier transform operation; exp() is the exponential function; | B n |for the first n Echo amplitude; For the first n Phase of the echo.

[0040] In step S204, the estimated echo is calculated using the following formula. B sim Time-domain signal:

[0041] .

[0042] Furthermore, in step S4, the estimated echo time-domain signal is calculated using the following formula. B sim With the time-domain signal of the echo to be measured B m Cross-correlation coefficient:

[0043]

[0044] in Corr For cross-correlation coefficients, Cov ( ) represents the cross-correlation calculation operation. Var ( ) represents the variance calculation operation; B sim To estimate the time-domain signal of the echo, B m This is the time-domain signal of the echo to be measured.

[0045] Among them, the cross-relation number Corr A cross-correlation coefficient between 0 and 1 indicates that a higher coefficient represents an estimated echo time-domain signal. B sim With the time-domain signal of the echo to be measured Bm The greater the degree of cross-correlation.

[0046] The beneficial effects of this invention are:

[0047] 1. In this invention, the oil film thickness is used as the reference. d attenuation coefficient α Using ultrasonic echo spectrum relationships of different orders as iterative variables, oil film echoes are estimated based on Fourier transform calculations. B sim Estimate the echo parameters B sim Compared with the actual measured echo B m Perform time-domain cross-correlation and return the attenuation coefficient when the correlation coefficient is maximized. α Compared with existing ultrasonic echo attenuation coefficient measurement methods, this invention can be applied to conditions with varying oil film thickness and severe oil film echo overlap. It can iterate the attenuation coefficient based on the time-domain waveform changes of the oil film echo. The iteratively obtained attenuation coefficient, as a key parameter, can be used as a characteristic parameter in estimating the bubble content of bubble-containing lubricating films, which is helpful for the online monitoring of cavitation effects in sliding bearings.

[0048] 2. This invention pre-calibrates the acoustic impedance of the bearing bush, lubricating medium, and journal. Z 1. Z 2 and Z 3, and the sound velocity of the lubricating medium. c The algorithm calculates the reflection and transmission coefficients of each interface as fixed parameters and inputs them into the algorithm. It then iterates through the oil film thickness within a preset iteration range. d and attenuation coefficient constant coefficient u The setting of iteration parameters ensures that the algorithm can be applied to oil film thickness. d Under changing operating conditions.

[0049] 3. This invention pre-calibrates the first echo of the oil film. B 1. Calculate its amplitude using Fourier transform | B n |and phase ; Calculation based on the three-layer medium ultrasonic echo propagation formula 2 to n max First-order echo { B 2, B 3,…, B n ,…, The spectrum was analyzed, and the estimated complete time-domain echo signal of the oil film was obtained using inverse Fourier transform. B sim .

[0050] 4. In this invention, the echo is estimated by calculation. Bsim Compared with the actual echo B m Temporal cross-correlation, oil film thickness under the condition of maximum storage correlation. d and attenuation coefficient α The optimal output of the inversion algorithm is used. The cross-correlation coefficient of the time-domain waveform is used as the objective function of the iterative algorithm, ensuring the superiority of the algorithm by directly inverting parameters based on the time-domain waveform. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of the process for inverting the ultrasonic overlap echo attenuation coefficient of a bubble-containing lubricating film according to the present invention.

[0052] Figure 2 This is a schematic diagram of the propagation of ultrasonic waves in a three-layer structure containing air bubbles according to the present invention.

[0053] Figure 3 This is a schematic diagram of the experimental apparatus for inverting the attenuation coefficient of ultrasonic overlapping echoes with a bubble-containing lubricating film according to the present invention.

[0054] Figure 4 Estimating echo in an application example of the present invention B sim With measurement echo B m Schematic diagram of cross-correlation results.

[0055] Figure 5 This is a schematic diagram illustrating the calculation of the relative error of oil film thickness in an application example of the present invention.

[0056] Figure 6 This is a schematic diagram illustrating the calculation of the relative error of the attenuation coefficient in an application example of the present invention.

[0057] Among them, 1. Peristaltic pump; 2. Motor; 3. Oil tank; 4. Piezoelectric sensor; 5. Steel; 6. Glass. Detailed Implementation

[0058] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0059] Example:

[0060] This embodiment provides a method such as Figure 1 The method for inverting the attenuation coefficient of ultrasonic overlapping echoes from a bubble-lubricated film, as shown, includes the following steps:

[0061] S1. Algorithm parameter initialization: The acoustic impedance of the three layers of media—bearing bush, lubricating medium, and journal—is obtained in advance by calibration or by looking up a table. Z 1. Z 2 and Z 3, and the sound velocity of the lubricating medium. cPre-collection of steel-oil film primary echo B 1. Set the iteration range for oil film thickness and attenuation coefficient, and set the highest estimated echo order. n max ;

[0062] S2. Echo estimation calculation, based on the steel-oil film primary echo in step S1. B 1. Calculate the estimated echo B sim The time-domain signal;

[0063] S3. Within the iteration range, step through the iteration variables; change the oil film thickness with each iteration. d and attenuation coefficient α Then update the estimated echo calculation under this parameter. B sim ;

[0064] S4. Acquire the time-domain signal of the three-layer medium of bearing bush, lubricating medium, and journal. B m The estimated echo time-domain signal under each parameter B sim With the time-domain signal of the echo to be measured B m Perform time-domain cross-correlation and record the iterative oil film thickness and attenuation coefficient at the point of maximum correlation as the optimal iterative oil film thickness. d best and attenuation coefficient α best .

[0065] In an optional embodiment of the present invention, step S2, calculating the time-domain signal of the estimated echo Bsim, includes the following steps:

[0066] S201, First echo of steel-oil film B 1. Perform a Fourier transform to obtain its amplitude. B 1|and phase ;

[0067] S202, according to step S201, | B 1| and ,calculate n (2≤ n ≤ n max )-order echo B n Amplitude | B n |and phase ;

[0068] S203, Through the echoes of each order in step S202 Bn Amplitude | B n |and phase Inverse Fourier transform was performed to obtain echoes of various orders. B n Time-domain signal;

[0069] S204, Direct combination 1 to n max From the time-domain signal of the first-order echo, the estimated echo can be obtained. B sim The time-domain signal.

[0070] In step S201, the steel-oil film primary echo... B Amplitude of 1 | B 1| The calculation formula is:

[0071]

[0072] Among them, | B 1|Single echo of steel-oil film B The amplitude is 1; abs() is the amplitude operation; FFT() is the fast Fourier transform operation.

[0073] In step S201, the steel-oil film primary echo... B Phase 1 The calculation formula is:

[0074]

[0075] Where angle() is the phase angle operation; FFT() is the fast Fourier transform operation; For steel-oil film primary echo B Phase 1.

[0076] In step S202, the nth-order echo is calculated using the following formula. B n Amplitude | B n |:

[0077]

[0078]

[0079] in, d Oil film thickness; c The velocity of sound in the lubricating medium; n For echo order, n =2,…, n max ;in αThis is the oil film echo attenuation coefficient; W Interface transmission coefficient; V The subscript 1 represents the interface reflection coefficient; subscripts 1, 2, and 3 represent different media; subscript 12 indicates the wave propagation direction is from medium 1 to medium 2, subscript 21 indicates the wave propagation direction is from medium 2 to medium 1; subscript 23 indicates the wave propagation direction is from medium 2 to medium 3; | B n / B 1| is the first n Step echo B n and B Amplitude ratio of 1;

[0080] Wherein, the interface reflection coefficient V It is calculated using the following formula:

[0081]

[0082] in Z i The acoustic impedance of the medium is determined by the density of the medium and the velocity of sound. ij The direction of ultrasonic wave propagation is represented by the first line from the friction pair material. i propagation of the medium to the first layer j Layered medium; Z 1. Z 2 and Z 3 represents the acoustic impedance of the three layers of media: bearing shell, lubricating medium, and journal.

[0083] Interface transmission coefficient W It is calculated using the following formula:

[0084] .

[0085] In step S202, the nth-order echo is calculated using the following formula. B n phase :

[0086]

[0087]

[0088] in, For the first n Step echo B n and B A phase difference of 1; n For echo order, n =2,…, n max ; dOil film thickness; c The velocity of sound in the lubricating medium; f This is the echo frequency.

[0089] In step S203, the echoes of each order are calculated using the following formula. B n Time-domain signal:

[0090]

[0091] in, B n Let iFFT() be the time-domain signal of the nth-order echo; exp() is the inverse fast Fourier transform operation; | B n |for the first n Echo amplitude; For the first n Phase of the echo.

[0092] In step S204, the estimated echo is calculated using the following formula. B sim Time-domain signal:

[0093] .

[0094] In an optional embodiment of the present invention, in step S4, the estimated echo time-domain signal is calculated using the following formula. B sim With the time-domain signal of the echo to be measured B m Cross-correlation coefficient:

[0095]

[0096] in Corr For cross-correlation coefficients, Cov ( ) represents the cross-correlation calculation operation. Var ( ) represents the variance calculation operation; B sim To estimate the time-domain signal of the echo, B m This is the time-domain signal of the echo to be measured.

[0097] like Figure 2 The diagram illustrates the propagation of ultrasound in a three-layer structure containing air bubbles, and also in a three-layer structure consisting of a solid, a lubricating medium containing air bubbles, and a solid. A typical lubrication structure can be considered as a three-layer structure consisting of a solid, a lubricating medium, and a solid. (Ultrasound) I The incident wave is incident perpendicularly to the interface of a three-layer solid-lubricating medium. Due to the difference in acoustic impedance between the media, part of the incident wave's energy will be reflected, resulting in the oil film's primary echo.B 1. The remaining energy will be transmitted into the lubricating medium. The transmitted wave entering the lubricating medium will continue to be reflected and transmitted periodically at the upper and lower interfaces until the energy is dissipated. The series of echoes reflected from the lubricating medium and received by the sensor constitutes the oil film echo cluster, which can be represented as... B { B 1, B 2, B 3,…, B n For a typical parallel three-layer structure, the oil film thickness... d This is a key parameter affecting the time-domain waveform of oil film echoes. The time-domain waveform of oil film echoes differs with different oil film thicknesses; in thick oil films, the echoes of each stage are separated, while in thin oil films, the echoes of each stage are superimposed. Theoretically, if the echoes of each stage can be accurately calculated... B 1, B 2, B 3,…, B n Then the thickness of each oil film can be estimated. d The time-domain waveform of the oil film echo.

[0098] In step S2, for oil film echoes of arbitrary unknown thickness, their time-domain signal is composed of oil film echo clusters. B { B 1, B 2, B 3,…, B n The sound pressure of a vertically incident wave is superimposed. If we represent the sound pressure of a vertically incident wave as a simple harmonic wave: I = A 0exp( θ 0), based on the sound propagation formula, the oil film's first... n oil film echo B n First echo with oil film B The ratio of 1 is:

[0099]

[0100] Then the amplitude ratio | B n / B 1| and phase difference for:

[0101]

[0102] If the first echo of the oil film is known B Given the phase and amplitude of 1, and all parameters are known, then according to | B n / B 1| and It is possible to calculate any number of... n Level echo B n Phase | B n |and amplitude .

[0103] set up n The highest order of the level echo n max Increase step size starting from order 2. n to n max At various oil film thicknesses d and attenuation coefficient α Calculate the amplitude sequence and phase sequence Combining the amplitude and phase, performing an inverse Fourier transform yields the time-domain expressions for each order of echo:

[0104]

[0105] Where iFFT() is the inverse fast Fourier transform operation; exp() is the exponential function.

[0106] By combining the time-domain signals of each echo stage, a complete estimate of the oil film echo can be obtained. B sim :

[0107]

[0108] In step S3, the oil film thickness iteration range set in step S1 is used. d min , d max} and attenuation coefficient coefficient iteration range { α min , α max The oil film thickness is changed step by step during the cycle. d and attenuation coefficient α Continue until the maximum iteration range is reached; change the oil film thickness with each iteration. d and attenuation coefficient α Then update the estimated echo calculation under this parameter. B sim .

[0109] In step S4, the thickness of each oil film is calculated. d and attenuation coefficient α Estimated oil film echo under parameters B sim Compared with the measured oil film echo B mCorrelation coefficient:

[0110]

[0111] Among them, the cross-relation number Corr A cross-correlation coefficient between 0 and 1 indicates that a higher coefficient represents an estimated echo time-domain signal. B sim With the time-domain signal of the echo to be measured B m The greater the degree of cross-correlation.

[0112] Application example:

[0113] In this application example, due to the influence of hydrodynamic pressure distribution, air bubbles will be generated in the oil film during the operation of the sliding bearing. This application example aims to verify the accuracy of the inverted attenuation coefficient of the present invention by setting up an ultrasonic overlapping echo attenuation coefficient inversion experimental device containing a bubble-filled lubricating film.

[0114] like Figure 3 As shown, the experimental setup for inverting the attenuation coefficient of the ultrasonic overlapping echo containing a bubble-filled lubricating film consists of three main modules: an ultrasonic module, a flow channel module, and an image module. The ultrasonic module comprises an ultrasonic pulse transmitter and receiver, an oscilloscope, and a computer; the sampling frequency of the analog-to-digital converter in the pulse transmitter and receiver unit is set to 500MHz. The flow channel module consists of a peristaltic pump, a motor, an oil tank, a piezoelectric sensor, a peristaltic pipe, and a steel and glass composite structure. The camera module is used to capture images of the bubble-filled oil film to verify the accuracy of the ultrasonic measurement results.

[0115] like Figure 4 The image shows the estimated echo. B sim With measurement echo B m Schematic diagram of cross-correlation results; the estimated echo is when the correlation coefficient is at its maximum. B sim Compared with the measured echo B m The waveform that is closest to the target value can be considered the end of the iteration, and the optimal oil film thickness with the highest correlation coefficient is returned. d best and optimal attenuation coefficient α best .

[0116] This invention can simultaneously achieve iterative solutions for oil film thickness and attenuation coefficient. The volume fraction of oil film bubbles in this experiment is selected. η For seven groups of samples ranging from 0.4% to 4.48%, the film thickness and attenuation coefficient were iteratively solved using the ultrasonic overlapping echo attenuation coefficient inversion method for bubble-containing lubricating films in this application example. Figure 5 The diagram shown illustrates the calculation of the relative error of oil film thickness in this application example.

[0117] In ultrasonic measurement experiments involving bubble-containing oil films, the oil film thickness on the workpiece is a fixed value. Therefore, this paper uses the oil film thickness measurement value obtained by the resonance method in the absence of bubbles as a benchmark to verify different bubble volume fractions. η The accuracy of the film thickness inversion values ​​of this invention is high. The relative error of the film thickness measurement values ​​for each sample is within 0.5%.

[0118] The calibration method demonstrates high accuracy in measuring attenuation coefficients in experiments. Therefore, the ultrasonic overlap echo attenuation coefficient inversion method for bubble-containing lubricating films in this application example is compared with the calibration method to verify the accuracy of the attenuation coefficient inversion method of this invention. The reference signal is selected as the ultrasonic echo tail of a bubble-free oil film with the same oil film thickness. The attenuation degree of the actual signal tail and the estimated signal tail relative to the reference signal tail are compared, and the attenuation coefficient estimation error for each sample is calculated. Figure 6 The diagram shown is a schematic of the relative error in calculating the attenuation coefficient in this application example. The error is within 5%, and the attenuation coefficient inversion error meets the accuracy requirements of engineering measurement, thus verifying the feasibility and accuracy of the present invention.

[0119] In summary, the ultrasonic overlapping echo attenuation coefficient inversion method for bubble-containing lubricating films in this invention derives the frequency domain expression of each order of echo using the propagation model of ultrasound in a three-layer structure. The algorithm inputs pre-calibrated oil film primary echo, acoustic impedance, and sound velocity as fixed parameters. Each order of echo is compared with the oil film primary echo, and the amplitude ratio and phase difference are extracted and input into the algorithm. The algorithm iterates through the oil film thickness and attenuation coefficient within the optimization interval, using oil film thickness and attenuation coefficient as iterative variables. Each time the oil film thickness or attenuation coefficient is changed, the algorithm calculates a complete estimated oil film echo based on the amplitude ratio and phase difference between each order of echo and the oil film primary echo, along with the fixed parameters. The estimated oil film echo is cross-correlated with the actual measured oil film echo in the time domain, and the oil film thickness and attenuation coefficient at the point of maximum correlation are recorded as the optimal inversion value output, completing the algorithm iteration. This method is of great significance for online monitoring of ultrasonic oil film bubbles.

[0120] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A method of inverting the attenuation coefficient of ultrasonic overlapping echoes in a bubble-laden lubricating film, characterized in that: Comprising the steps of: S1, algorithm parameter initialization: obtain acoustic impedance of bearing bush-lubricating medium-journal three-layer medium Z 1, Z 2 and Z 3, and the acoustic velocity of the lubricating medium c ; collect the first echo of the steel-oil film B 1; set the iteration range of the oil film thickness and the iteration range of the attenuation coefficient, and set the highest estimated echo order n max ; S2, estimate echo calculation, by the steel-oil film primary echo in step S1 B 1 calculate the estimate echo B sim time domain signal; comprising the following steps: S201, on the steel-oil film first echo B 1 Fourier transform, get its amplitude B 1 | and phase ; S202、According to step S201 in B 1| and , calculate n (2≤ n ≤ n max ) order echo B n amplitude B n | and phase ; The amplitude of the nth echo is calculated by the following equation B n B n |​ wherein d is the oil film thickness; c is the lubricant sound speed; n is the echo order, n = 2,..., n max ; wherein α is the oil film echo attenuation coefficient; B 1 is the amplitude of the first order steel-oil film echo B 1; W is the interface transmission coefficient; V is the interface reflection coefficient; the subscripts 1, 2 and 3 represent different media; the subscript 12 represents the wave propagation direction from medium 1 to medium 2, the subscript 21 represents the wave propagation direction from medium 2 to medium 1; the subscript 23 represents the wave propagation direction from medium 2 to medium 3; B n / B 1 is the amplitude of the nth order echo n 1; B n is the amplitude ratio of the nth order echo B 1; The nth order echo is calculated by the following equation B n of the phase : wherein, is the n order of the echo B n with B a phase difference of 1; n is the order of the echo, n = 2, …, n max ; d is the oil film thickness; c is the speed of sound of the lubricating medium; f is the echo frequency; is the phase of the first echo of the steel-oil film B 1. S203, inverse Fourier transform of the amplitudes and phases of the echoes of step S202 B n B n B n time domain signals​​​ S204, directly combining 1 to n max echo time domain signal, to estimate the echo B sim time domain signal; S3, step through the iteration variable over a range of iterations; each time the iteration variable is changed, the film thickness is changed d and the attenuation coefficient α then update the estimate of the echo under the parameter B sim ; S4, collect the measured echo time domain signal of the three-layer medium of bearing bush-lubricating medium-bearing journal B m , the estimated echo time domain signal under each parameter B sim , and the measured echo time domain signal B m , the iteration oil film thickness and the attenuation coefficient when the correlation degree is the largest are recorded as the optimal iteration oil film thickness d best , and the attenuation coefficient α best ; The estimated echo time-domain signal is calculated by the following equation B sim The cross-correlation coefficient of the to-be-measured echo time-domain signal B m with the estimated echo time-domain signal is calculated wherein Corr is a cross-correlation coefficient, Cov ( ) is a cross-correlation computation operation, Var ( ) is a variance computation operation; B sim is a time-domain signal of an estimate echo, B m is a time-domain signal of an echo to be measured.

2. The method of claim 1, wherein the method further comprises: In the step S201, a steel-oil film first echo B 1| The amplitude of the first echo B 1| The calculation formula is: wherein, B 1 is the amplitude of the steel-oil film primary echo B 1; abs( ) is the amplitude operation; FFT( ) is the fast Fourier transform operation.

3. The method for inverting the attenuation coefficient of ultrasonic overlapping echoes containing a bubble-lubricated film according to claim 1, characterized in that: In the step S201, the steel-oil film first echo B 1 of the phase The calculation formula is: wherein angle( ) is a phase angle operation; FFT( ) is a fast Fourier transform operation; for steel-oil film first echo B 1. the phase of.

4. The method of claim 1, wherein the method further comprises: determining a value of the attenuation coefficient of the ultrasonic overlapping echo of the bubble lubricating film. In the step S202, the interface reflection coefficient V is calculated by the following formula: wherein Z i Zm is the acoustic impedance of the medium, determined by the density and sound speed of the medium, ij Zj represents the acoustic impedance of the jth layer of medium, i Zj represents the acoustic impedance of the jth layer of medium, Z 1, Z 2 and Z 3 represent the acoustic impedance of the bearing shell-lubricant-bearing journal three-layer medium, respectively. The interface transmission coefficient W is calculated by the following formula: 。 5. The method of claim 1, wherein the method further comprises: In the step S203, each order echo is calculated by the following formula B n Time domain signal: in, B n Let iFFT() be the time-domain signal of the nth-order echo; exp() is the inverse fast Fourier transform operation; | B n |for the first n Echo amplitude; For the first n Phase of the echo.

6. The method of claim 5, wherein the method further comprises: In the step S204, the estimated echo is calculated by the following equation B sim of the time-domain signal: 。

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