Ultrasonic guided wave acoustic simulation method for multi-layer heterostructure pipeline with heterogeneous salt film

Abstract

The invention discloses an ultrasonic guided wave acoustic simulation method for a multi-layer heterostructure pipeline with a heterogeneous salt film, and relates to the technical field of pipeline ultrasonic guided wave detection. Comprising the following steps: step 1, creating a polar coordinate grid; 2, generating Gaussian distribution white noise; 3, calculating a power spectral density function; 4, determining a filter transfer function; 5, acquiring a surface height distribution function; and step 6, generating a heterogeneous salt membrane surface and converting coordinates. According to the ultrasonic guided wave acoustic simulation method for the multi-layer heterostructure pipeline with the heterogeneous salt film, generation of the surface of the heterogeneous salt film is regarded as a random process, based on a prepared salt film distribution autocorrelation function and an autoregressive (AR) type digital filter, MATLAB is adopted for calculation and simulation to generate a cylinder surface with specified roughness, and the surface of the cylinder is subjected to ultrasonic guided wave acoustic simulation. The method can effectively simulate complex and diversified heterogeneous salt film forms in an actual heat absorption tube, and provides a model which better accords with actual conditions for ultrasonic guided wave sound field simulation and application research.

Description

Technical Field

[0001] The present invention relates to the technical field of pipeline ultrasonic guided wave detection, and specifically to an ultrasonic guided wave acoustic simulation method for a multi-layer heterogeneous structure pipeline with a heterogeneous salt film. Background Technique

[0002] Tower solar thermal energy storage power generation technology has become one of the key technologies in the global energy transformation due to its efficient solar-thermal conversion ability and large-scale power generation potential. This technology focuses solar radiation to the top of the solar tower through a heliostat array and uses molten salt fluid as the heat energy medium to achieve energy collection and conversion. The absorber is the core component of the tower solar thermal system and is usually composed of ultra-long (15m - 20m), small-diameter (φ19mm - 60mm), and thin-wall (1.2mm - 1.65mm) absorber tubes. These absorber tubes are prone to damage such as wall thickness reduction, crack propagation, and burn under high temperature, strong radiation, and long-term erosion of molten salt fluid, and need to be regularly detected and evaluated.

[0003] Existing non-destructive testing technologies have not been able to effectively meet the detection requirements of these absorber tubes. Ultrasonic guided wave technology has become an ideal detection means due to its long-distance propagation and high sensitivity. However, the inner wall of the absorber tube is exposed to molten salt fluid for a long time, and the heterogeneous salt film structure formed under high temperature and cyclic working conditions makes the propagation characteristics of ultrasonic guided waves complex, increasing signal interference and analysis difficulty. In addition, the high-absorbance coating (usually black cobalt or black nickel coating) coated on the outer wall of the absorber tube also causes signal attenuation and mode conversion.

[0004] The multi-layer heterogeneous structure (coating, matrix, salt film) of the absorber tube usually causes scattering, mode mixing, and energy loss in the propagation of guided waves, reducing the accuracy and reliability of detection. In order to effectively apply ultrasonic guided wave technology for absorber tube detection, it is necessary to combine theoretical analysis and experimental verification to clarify the propagation characteristics of ultrasonic guided waves in such complex structures. Given the unevenness, randomness, and dynamic change characteristics of the morphology and thickness of the salt film during the in-service process of the absorber tube, there is an urgent need for a method that can accurately simulate and predict the propagation characteristics of ultrasonic guided waves in multi-layer heterogeneous structure pipelines to provide theoretical research support for defect detection. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technology, the present invention provides an ultrasonic guided wave acoustic simulation method for a multi-layer heterogeneous structure pipeline with a heterogeneous salt film. This method regards the generation process of the heterogeneous salt film as a dynamic process and simplifies the distribution of the inner wall salt film as a randomly distributed rough surface, effectively solving the problem that it is difficult to construct a solid model in the finite element sound field simulation.

[0006] To achieve the above object, the present invention is realized through the following technical solutions: An ultrasonic guided wave acoustic simulation method for a multi-layer heterogeneous structure pipeline with a heterogeneous salt film, including the following steps: Step 1. Create a polar coordinate grid: Set the relevant parameters of the cylinder and create a polar coordinate grid for simulating the cylinder surface; Step 2. Generate Gaussian white noise: Generate a two-dimensional random sequence of Gaussian white noise , and perform Fourier transform on it to obtain ; Step 3. Calculate the power spectral density function: Perform Fourier transform on the autocorrelation function to obtain the power spectral density function , and determine the power spectral density C ; Step 4. Determine the filter transfer function: Obtain the filter transfer function according to the power spectral density function ; Step 5. Obtain the surface height distribution function: Perform inverse Fourier transform on the Fourier transform output after passing through the two-dimensional filter to obtain the surface height distribution function ; Step 6. Generate a heterogeneous salt film surface and convert coordinates: Superimpose the height distribution function onto the inner radius of the cylinder to obtain the inner surface of the cylinder considering roughness, convert the inner surface of the cylinder considering roughness in polar coordinates to the surface in Cartesian coordinates, and generate point cloud data.

[0007] Preferably, for any random process passed through a two-dimensional filter, a random process can be obtained: ; where , …, N ; , …, M . n = N / 2, m = M / 2, is the impulse response function of the filter, represents the spatial coordinate variable used to describe the position on the plane and represents the positions of different points on the surface when simulating the heterogeneous salt film surface, represents the random process obtained by passing any random process through the two-dimensional filter, representing the signal related to the height distribution of the heterogeneous salt film surface after filtering, taking values at the spatial position , N and M represent the size of the filter.

[0008] Preferably, the random process after Fourier transform is obtained as: ; wherein , , are respectively , , the Fourier transforms of is the frequency-domain coordinate variable, used to describe the position in the frequency domain, corresponding to the spatial coordinates and respectively represents the frequencies in the

[0009] Preferably, the three-dimensional surface autocovariance function is as follows: ; The autocorrelation function is: ; where the normalization factor is the variance of the surface height distribution, and the autocorrelation function is a dimensionless quantity, describing the normalized correlation of the surface height distribution, represents the three-dimensional surface autocovariance function, used to describe the covariance relationship of the surface height distribution of the inhomogeneous salt film at different positions and and reflects the correlation of the surface height distribution, related to the surface height , and represent the range parameters involved in calculating the autocovariance function, representing the length range in the

[0010] Preferably, the power spectral density function is defined as the Fourier transform of the autocorrelation function: ; Performing the Fourier transform on the autocorrelation function R gives the power spectral density function , since: ; where C is the power spectral density Const of the input sequence, represents the power spectral density function, defined as the Fourier transform of the autocorrelation function, and describes the energy distribution of the surface height distribution of the inhomogeneous salt film in the frequency domain, and are respectively the frequency variables in the

[0011] Preferably, for a random sequence obeying a Gaussian distribution, the power spectral density is a constant Const.

[0012] Preferably, after generating the point cloud data, the data matrix can be exported through MATLAB and imported into the finite element software COMSOL Multiphysics for subsequent operations.

[0013] Preferably, a heterogeneous salt film surface with a specific roughness is selected for modeling, simulation, and ultrasonic guided wave detection in the finite element software to verify the feasibility of the method.

[0014] Advantageous Effects The present invention provides an ultrasonic guided wave acoustic simulation method for a multi-layer heterogeneous structure pipeline with a heterogeneous salt film. Compared with the prior art, it has the following advantageous effects: 1. The ultrasonic guided wave acoustic simulation method for the multi-layer heterogeneous structure pipeline with a heterogeneous salt film can accurately simulate the complex and diverse heterogeneous salt film surfaces in actual heat absorption pipes by calculating and simulating to generate a cylinder surface with a specified roughness based on the autoregressive (AR) model and digital filtering technology, providing a more realistic model for ultrasonic guided wave detection simulation.

[0015] 2. For the coating modeling of the ultrasonic guided wave acoustic simulation method for the multi-layer heterogeneous structure pipeline with a heterogeneous salt film, the "single-layer material" definition method is adopted, which improves the calculation efficiency without affecting the calculation results. At the same time, through precise calculation and processing of multiple steps, this method can more accurately reflect the propagation characteristics of ultrasonic guided waves in the multi-layer heterogeneous structure pipeline with a heterogeneous salt film, providing more reliable theoretical support for ultrasonic guided wave detection.

[0016] 3. The ultrasonic guided wave acoustic simulation method for the multi-layer heterogeneous structure pipeline with a heterogeneous salt film helps to carry out more accurate simulation studies on ultrasonic guided wave detection of pipelines with heterogeneous structures, can provide a theoretical basis for ultrasonic guided wave detection of heat absorption pipes, and promote the development of heat absorption pipe detection technology in molten salt tower solar thermal power generation technology. Brief Description of the Drawings

[0017] Figure 1 is the flowchart of the steps for generating the heterogeneous salt film surface of the present invention; Figure 2 is the schematic diagram of the simulation results of the heterogeneous salt film surface with different roughnesses of the present invention; Figure 3 is the finite element entity schematic diagram of the present invention; Figure 4 is the schematic diagram of the ultrasonic guided wave echo signal of the present invention. Detailed Embodiments

[0018] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts fall within the protection scope of the present invention.

[0019] Referring to Figures 1-4 , the present invention provides an ultrasonic guided wave acoustic simulation method for a pipeline with a heterogeneous salt film multi-layer heterogeneous structure, including the following steps: Step 1, create a polar coordinate grid: In actual operation, the setting of the cylindrical parameters needs to closely refer to the physical characteristics of the actual heat absorption tube. In the heterogeneous salt film multi-layer heterogeneous structure, the inner wall of the heat absorption tube is the basis for the attachment of the salt film, and its inner diameter and outer diameter dimensions have a significant impact on the formation of the salt film and the propagation of ultrasonic guided waves. For example, if the inner diameter of the actual heat absorption tube is , the outer diameter is , and the length is , then when setting the relevant cylindrical parameters, the inner diameter of the simulated cylinder should be set to to accurately simulate the inner wall surface with heterogeneous salt film attachment. The heterogeneous salt film has a complex microstructure, and its thickness and distribution are uneven both in the circumferential direction and the axial direction. This non-uniformity will cause scattering and refraction phenomena during the propagation of ultrasonic guided waves. At the same time, considering that the propagation characteristics of ultrasonic guided waves in the pipeline are closely related to the length-diameter ratio of the pipeline, the setting of the length needs to ensure that it can reasonably simulate the propagation distance and reflection of ultrasonic guided waves in the actual pipeline to reflect the influence of the heterogeneous salt film on the propagation of ultrasonic guided waves.

[0020] When creating the polar coordinate grid, the accuracy and range of the grid directly affect the accuracy of subsequent simulations. The microscopic undulations and irregularities on the surface of the heterogeneous salt film require us to accurately capture its characteristics. To accurately simulate this complex structure, the grid spacing can be determined according to the required roughness range and surface detail level to be simulated. For example, if it is desired to simulate a heterogeneous salt film surface with a high roughness and a complex microstructure, the radial spacing of the polar coordinate grid can be set to 0.01 , and the angular spacing can be set to 1° to ensure that the morphological changes of the surface can be fully described. In software environments such as MATLAB, corresponding functions and commands can be used to create the polar coordinate grid, such as generating the coordinate matrix of the polar coordinate grid through the meshgrid function.

[0021] Step 2, generate Gaussian distributed white noise: Any random process Through a two-dimensional filter, a random process can be obtained: ; where , …, N ; , …, M . n = N / 2, m = M / 2, is the impulse response function of the filter, represents the spatial coordinate variable, used to describe the position on the plane. When simulating the surface of a heterogeneous salt film, it represents the positions of different points on the surface. represents the random process after passing through a two-dimensional filter, representing the signal related to the height distribution of the heterogeneous salt film surface after filtering. It takes values at the spatial position . N and M represent the size of the filter. When generating a two-dimensional random sequence of Gaussian distributed white noise , the characteristics of the noise can be controlled by adjusting the mean and variance of the noise. The formation of the multi-layer heterogeneous structure of the heterogeneous salt film is a long-term physicochemical process, affected by various factors such as molten salt composition, temperature change, and fluid flow, resulting in a random microscopic structure on its surface. Therefore, in order to simulate the random noise in the real environment, the mean can be set to 0, and the variance can be taken between 0.01 - 0.1 according to the actual situation. In MATLAB, the randn function can be used to generate random numbers conforming to the Gaussian distribution, and then the required noise sequence can be obtained through scaling and translation operations.

[0022] When passing an arbitrary random process through a two-dimensional filter, the design of the impulse response function of the filter is crucial. The surface roughness and power spectral density characteristics of the heterogeneous salt film are related to its formation process and physicochemical properties. The impulse response function of the filter can be designed according to the desired surface roughness and power spectral density characteristics. For example, if it is desired to simulate the surface of a heterogeneous salt film with a specific power spectral density distribution, the target power spectral density function can be converted into the impulse response function of the filter in the spatial domain through the inverse Fourier transform. In actual calculations, the specific form of the filter needs to be determined according to the type of filter (such as low-pass filter, high-pass filter, etc.) and parameter settings to accurately simulate the influence of the microscopic structure of the heterogeneous salt film surface on the propagation of ultrasonic guided waves.

[0023] The random process after Fourier transform is obtained as: ; where , , are respectively , , Fourier transform of is the frequency-domain coordinate variable, used to describe the position in the frequency domain, corresponding to the spatial coordinates respectively representing the frequencies in the directions. When performing the Fourier transform to obtain , attention should be paid to the type selection of the Fourier transform. For two-dimensional data, two-dimensional fast Fourier transform (2D-FFT) can be used, and it can be implemented using the fft2 function in MATLAB. The microscopic structure on the surface of the heterogeneous salt film has certain distribution characteristics in the spatial frequency. Through Fourier transform, it can be transformed from the spatial domain to the frequency domain for analysis. At the same time, in order to avoid the phenomenon of spectral aliasing, before performing the Fourier transform, appropriate preprocessing can be carried out on the noise sequence, such as adding appropriate window functions (such as Hanning window, Hamming window, etc.) to reduce the influence of boundary effects and better reflect the frequency characteristics of the heterogeneous salt film surface.

[0024] Step 3. Calculate the power spectral density function: Perform the Fourier transform on the autocorrelation function to obtain the power spectral density function , and determine the power spectral density Const; The three-dimensional surface autocovariance function is as follows: ; The autocorrelation function is: ; where the normalization factor is the variance of the surface height distribution, and the autocorrelation function is a dimensionless quantity, describing the normalized correlation of the surface height distribution. represents the three-dimensional surface autocovariance function, used to describe the covariance relationship of the surface height distribution of the heterogeneous salt film surface at different positions and , reflecting the correlation of the surface height distribution, related to the surface height , and represent the range parameters involved in calculating the autocovariance function, representing the length range in the direction. When calculating the three-dimensional surface autocovariance function, the statistical characteristics of the surface height distribution need to be considered. The surface height distribution of the multi-layer heterogeneous structure of the heterogeneous salt film shows Gaussian distribution and non-stationary characteristics, and its autocovariance function reflects the correlation of heights between different positions on the surface. By statistically analyzing a large number of actual measured surface height data of the heterogeneous salt film, the probability density function of the surface height distribution can be obtained, and then the autocovariance function can be calculated. In MATLAB, the cov function can be used to calculate the covariance matrix of the data, and then further calculations can be performed according to the definition of the autocovariance function.

[0025] Calculate the autocorrelation function When calculating, attention should be paid to the accurate calculation of the normalization factor . is the variance of the surface height distribution, which can be obtained by statistical calculation of the simulated surface height data. In MATLAB, the var function can be used to calculate the variance. The autocorrelation function describes the correlation between different positions of the surface height distribution, and its value ranges between . The autocorrelation function characteristics of the heterogeneous salt film surface reflect the scale and periodic characteristics of its microstructure, which is of great significance for understanding the scattering and reflection mechanisms of ultrasonic guided waves on its surface.

[0026] The power spectral density function is defined as the Fourier transform of the autocorrelation function: ; Performing a Fourier transform on the autocorrelation function R to obtain the power spectral density function , because: ; where C is the power spectral density Const of the input sequence, represents the power spectral density function, which is defined as the Fourier transform of the autocorrelation function and describes the energy distribution of the surface height distribution of the heterogeneous salt film in the frequency domain, and are the frequency variables in the direction respectively. Performing a Fourier transform on the autocorrelation function to obtain the power spectral density function also uses the two-dimensional fast Fourier transform (2D-FFT). During the calculation process, attention should be paid to the scale setting and unit conversion of the frequency axis to ensure the accurate power spectral density function. The power spectral density function of the heterogeneous salt film reflects the energy distribution of its surface microstructure at different spatial frequencies. At the same time, for a random sequence obeying the Gaussian distribution, the power spectral density is a constant, and its value can be determined by integrating the power spectral density function over the entire frequency domain.

[0027] Step 4. Determine the filter transfer function: Determine the filter transfer function according to the power spectral density function When doing so, various methods can be adopted. The power spectral density characteristics of the inhomogeneous salt film are related to its scattering and absorption characteristics of ultrasonic guided waves. A common method is to design a filter based on the relationship between the target power spectral density function and the input noise power spectral density function. For example, if it is desired to adjust the power spectral density of the input noise to a specific form through the filter, the frequency response of the filter transfer function can be determined according to the ratio between the two. In MATLAB, the specific expression of the filter transfer function can be obtained by performing mathematical operations and frequency response analysis on the power spectral density function.

[0028] After determining the filter transfer function, it is necessary to analyze its stability and causality. Stability means that when the input is a bounded signal, the output is also a bounded signal; causality means that the output of the filter only depends on the current and past inputs, rather than future inputs. The stability and causality can be judged by analyzing the positions of the poles and zeros of the filter transfer function to ensure the reliability of the filter in practical applications. The design of the filter needs to consider the characteristics of the inhomogeneous salt film to accurately simulate its influence on the propagation of ultrasonic guided waves, such as simulating the scattering and attenuation of ultrasonic guided waves when encountering the surface of an inhomogeneous salt film with different roughnesses and microstructures.

[0029] Step Five: Obtain the surface height distribution function: After obtaining the Fourier transform of the output sequence after the input sequence passes through the two-dimensional filter perform the inverse Fourier transform on it to obtain the surface height distribution function . In MATLAB, the ifft2 function can be used to implement the two-dimensional inverse Fourier transform. The surface height distribution function of the inhomogeneous salt film directly reflects the morphology of its microstructure, and its undulations and irregularities have an important impact on the propagation path and energy distribution of ultrasonic guided waves. During the inverse transform process, attention should be paid to the scale and phase problems of the data to ensure obtaining an accurate surface height distribution function.

[0030] To improve the accuracy of the surface height distribution function, appropriate smoothing processing can be performed on the result after the inverse Fourier transform. For example, methods such as median filtering and Gaussian filtering can be used to filter the surface height distribution function to remove possible high-frequency noise and outliers, making the surface height distribution smoother and more continuous. This helps to more accurately simulate the actual morphology of the surface of the inhomogeneous salt film, and further more precisely analyze the propagation characteristics of ultrasonic guided waves on its surface.

[0031] Step Six: Generate the surface of the inhomogeneous salt film and convert coordinates: The height distribution function Overlay onto the inner radius of the cylinder, and note that the numerical range of the height distribution function matches the scale of the inner radius of the cylinder. The thickness of the heterogeneous salt film is significantly non-uniform in the circumferential and axial directions, and this non-uniformity will cause complex reflection and scattering phenomena during the propagation of ultrasonic guided waves. The height distribution function can be appropriately scaled and translated according to the actual simulated roughness range and the size of the inner radius of the cylinder to ensure that the overlay result conforms to the actual physical meaning. In MATLAB, the overlay of the height distribution function and the inner radius of the cylinder can be achieved through simple array operations. When converting the inner surface of the cylinder considering roughness in polar coordinates to a surface in Cartesian coordinates, the conversion relationship between polar coordinates and Cartesian coordinates can be utilized , for calculation. In MATLAB, the coordinate conversion can be achieved by writing loop statements or using vectorized operations. When generating point cloud data, the converted Cartesian coordinate points can be saved as a text file in a certain format (such as each line containing the , , coordinates) for importing into the finite element software. The accuracy and distribution of the point cloud data will affect the simulation accuracy of the heterogeneous salt film surface in the subsequent finite element model, and thus affect the accuracy of the ultrasonic guided wave detection simulation.

[0032] Select the surface of the heterogeneous salt film with a specific roughness for modeling and simulation of ultrasonic guided wave detection in the finite element software to verify the feasibility of the method. When modeling the coating in the finite element software (such as COMSOL Multiphysics), the "single-layer material" option is used to define the coating thickness and material parameters. The coating in the multi-layer heterogeneous structure of the heterogeneous salt film not only enhances the light energy absorption rate but also has a certain impact on the propagation of ultrasonic guided waves. For the definition of the coating thickness, accurate input should be made according to the measured value of the actual heat absorption tube coating thickness, and the accuracy can reach 0.1 mm. When defining the material parameters, the acoustic properties of the coating material, such as density, elastic modulus, Poisson's ratio, etc., need to be considered. These parameters can be obtained by referring to relevant material manuals or through experimental measurements.

[0033] There is an interface effect between the coating, the heterogeneous salt film, and the pipe substrate, and this interface effect will affect the propagation of ultrasonic guided waves in the multi-layer structure. To improve the accuracy of coating modeling, the interface characteristics between the coating and the pipe substrate can be considered. For example, the contact type of the interface (such as bonding, friction, etc.) can be set, and the parameters of the interface can be adjusted according to the actual situation to simulate the interaction between the coating and the pipe substrate. At the same time, during the finite element analysis, the coating area can be refined in terms of meshing to improve the calculation accuracy and more accurately simulate the propagation characteristics of ultrasonic guided waves in the coating-heterogeneous salt film-pipe substrate multi-layer structure.

[0034] After importing the point cloud data into COMSOL Multiphysics, the lofting function is used to realize the modeling and simulation of the heterogeneous salt film. During the lofting process, attention should be paid to the import format and order of the point cloud data to ensure that the heterogeneous salt film model obtained by lofting meets the expectations. The complex microstructure of the heterogeneous salt film requires accurate restoration of its morphology during the modeling process to accurately simulate the propagation of ultrasonic guided waves on its surface. The quality of the model can be optimized by adjusting the lofting parameters (such as lofting path, cross-sectional shape, etc.).

[0035] From Figure 2 it can be seen that the surfaces with different roughnesses exhibit obvious irregularities and randomness, which are in line with the characteristics of the heterogeneous salt film. As the roughness increases, the undulation of the heterogeneous surface shows obvious differences, and its three-dimensional morphology becomes more complex. To verify the feasibility of this method, a heterogeneous salt film surface with roughness = 0.9 is selected for modeling and simulation in COMSOL, and the obtained finite element entity is as shown in Figure 3 the figure below.

[0036] When conducting ultrasonic guided wave detection simulation, appropriate ultrasonic guided wave excitation source parameters need to be set. The multi-layer heterogeneous structure of the heterogeneous salt film has different response characteristics to different types and frequencies of ultrasonic guided waves. For example, parameters such as the type of excitation source (such as longitudinal wave, transverse wave, Lamb wave, etc.), frequency, and amplitude can be selected. According to the actual detection requirements and the physical properties of the pipeline, the excitation source parameters are reasonably selected to ensure that ultrasonic guided waves can be effectively excited and detected. At the same time, sensors can be set at different positions of the pipeline to receive the echo signals of ultrasonic guided waves, and the influence of the heterogeneous salt film on the propagation of ultrasonic guided waves can be evaluated by analyzing the characteristics of the echo signals (such as amplitude, frequency, phase, etc.).

[0037] To verify the feasibility of the method, heterogeneous salt film surfaces with multiple different roughnesses are selected for modeling and simulation and detection. Figure 4 It can be seen from the figure that the ultrasonic guided wave signal will generate signal echoes when detecting the salt film part, and due to the effect of the salt film, the end face echo signal is severely attenuated compared with the smooth pipeline. By comparing with the actual measurement data or theoretical analysis results, the roughness and microstructure of the heterogeneous salt film have significant effects on the scattering, attenuation, and reflection characteristics of ultrasonic guided waves. Through multiple groups of comparative experiments, its characteristics can be more comprehensively understood. At the same time, the propagation characteristics of ultrasonic guided waves under different working conditions (such as different temperature and pressure conditions) can be simulated and studied, because the changes in temperature and pressure will affect the physical and chemical properties and microstructure of the heterogeneous salt film, thereby affecting the propagation of ultrasonic guided waves, providing more comprehensive theoretical support for practical engineering applications.

[0038] It should be noted that in this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements not only includes those elements but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device.

[0039] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for ultrasonic guided wave acoustic simulation of a multi-layer heterogeneous structure pipeline with an inhomogeneous salt membrane, characterized in that: The following steps are involved: Step 1: Create a polar coordinate grid: Set the relevant parameters of the cylinder and create a polar coordinate grid to simulate the surface of the cylinder; Step 2: Generate Gaussian distribution white noise: Generate a two-dimensional random sequence of Gaussian distribution white noise , and perform Fourier transform to obtain ; Step 3: Calculate the power spectral density function: Perform Fourier transform on the autocorrelation function to obtain the power spectral density function , and determine the power spectral density Const; Step 4: Determine the filter transfer function: Get the filter transfer function based on the power spectral density function ; Step 5: Obtain the surface height distribution function: Fourier transform of the output of the two-dimensional filter Perform inverse Fourier transform to obtain the height distribution function of the surface ; Step 6: Generate heterogeneous salt film surface and transform coordinates: transform the height distribution function Superimposed on the inner radius of the cylinder, the inner surface of the cylinder with roughness taken into account is obtained, the inner surface of the cylinder with roughness taken into account in polar coordinates is converted into a surface in a Cartesian coordinate system, and point cloud data is generated.

2. The method for ultrasonic guided wave acoustic simulation of a multi-layer heterogeneous structure pipeline with a non-homogeneous salt membrane according to claim 1 is characterized by: Any random process Through the two-dimensional filter, we can get the random process : ； in , …, N ; , …, M , n = N / 2, m = M / 2, is the impulse response function of the filter, Represents a spatial coordinate variable, which is used to describe the position on a plane. When simulating a heterogeneous salt film surface, it represents the position of different points on the surface. Represents any random process The random process obtained after the two-dimensional filter represents the signal related to the height distribution of the inhomogeneous salt film surface after filtering. Take the value at N and M Indicates the size of the filter.

3. The method for ultrasonic guided wave acoustic simulation of a multi-layer heterogeneous structure pipeline with a non-homogeneous salt film according to claim 2 is characterized by: Random Process After Fourier transformation, we get: ； in , , They are , , The Fourier transform of is a frequency domain coordinate variable, which is used to describe the position in the frequency domain and is different from the spatial coordinate Correspondingly, they are respectively frequency in direction.

4. The method for ultrasonic guided wave acoustic simulation of a multi-layer heterogeneous structure pipeline with an inhomogeneous salt membrane according to claim 1 is characterized by: The three-dimensional surface autocovariance function is as follows: ； The autocorrelation function is: ； The normalization factor is the surface height distribution variance, autocorrelation function is a dimensionless quantity describing the normalized dependence of the surface height distribution, Represents the three-dimensional surface autocovariance function, which is used to describe the surface height distribution of heterogeneous salt films at different locations and The covariance relationship between them reflects the correlation of the surface height distribution and the surface height Related, and Represents the range parameter involved in calculating the autocovariance function, representing The length range in the direction.

5. The method for ultrasonic guided wave acoustic simulation of a multi-layer heterogeneous structure pipeline with a non-homogeneous salt film according to claim 4 is characterized by: The power spectral density function is defined as the Fourier transform of the autocorrelation function: ； Autocorrelation function R Perform Fourier transform to obtain the power spectral density function ,because: ； Where C is the power spectral density of the input sequence, represents the power spectral density function, which is defined as the Fourier transform of the autocorrelation function and describes the energy distribution of the heterogeneous salt film surface height distribution in the frequency domain. and They are The frequency variable in the direction.

6. The method for ultrasonic guided wave acoustic simulation of a multi-layer heterogeneous structure pipeline with an inhomogeneous salt membrane according to claim 1 is characterized by: For a random sequence that follows a Gaussian distribution, the power spectral density is a constant Const.

7. The method for ultrasonic guided wave acoustic simulation of a multi-layer heterogeneous structure pipeline with a non-homogeneous salt membrane according to claim 1 is characterized by: After generating the point cloud data, you can export the data matrix through MATLAB and import it into the finite element software COMSOL Multiphysics for subsequent operations.

8. The method for ultrasonic guided wave acoustic simulation of a multi-layer heterogeneous structure pipeline with a non-homogeneous salt membrane according to claim 1 is characterized by: A non-homogeneous salt film surface with a specific roughness was selected for modeling simulation and ultrasonic guided wave detection in finite element software to verify the feasibility of the method.

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