Ultrasonic guided wave sensor incident angle selection method for pipeline gas content detection

Abstract

The invention provides a method for selecting an incident angle of an ultrasonic guided wave sensor for detecting the gas content of a pipeline. The method comprises the following steps of: calculating a critical wave speed of ultrasonic guided wave mode conversion after incident waves are injected into a pipe wall according to the attributes of the pipeline and the excitation frequency of the ultrasonic guided wave sensor; determining a critical angle range of ultrasonic guided wave mode conversion after the incident wave enters the pipe wall according to the critical wave speed; calculating the phase velocity of an ultrasonic guided wave bending mode according to the attributes of the pipeline and the excitation frequency of the ultrasonic guided wave sensor; a theoretical incident angle is calculated based on the Snell theorem according to the ultrasonic guided wave bending mode phase velocity, and it is guaranteed that the theoretical incident angle is within the constraint range of the critical angle; and correcting the theoretical incident angle to determine a final incident angle. According to the invention, the optimal incident angle of ultrasonic guided wave gas content detection can be effectively determined.

Description

Technical Field

[0001] This invention relates to the technical field of ultrasonic guided wave detection, and more particularly to a method for selecting the incident angle of an ultrasonic guided wave sensor. Background Technology

[0002] In the petrochemical industry, gas content is a key parameter for measuring the volume fraction of the gas phase in multiphase flows (oil, gas, water). Its accurate detection is crucial for optimizing production processes, ensuring accurate flow measurement, guaranteeing safe equipment operation (such as preventing slug flow and controlling corrosion), and improving resource extraction efficiency, directly impacting the economic benefits and safe production of enterprises. Ultrasonic guided waves are a special type of ultrasonic wave whose propagation is guided and constrained by the boundaries of the medium. When the wavelength of the ultrasonic wave is comparable to the geometric dimensions of the propagating medium (such as thickness and diameter), the wave undergoes multiple reflections and mode conversions (longitudinal wave to transverse wave, transverse wave to longitudinal wave) between the upper and lower boundaries of the medium. These waves superimpose and interfere with each other, ultimately forming a waveguide mode that propagates stably. Ultrasonic waves are a broad term referring to all sound waves with frequencies higher than 20kHz. In the field of nondestructive testing, it usually specifically refers to volume waves that propagate freely within a medium. Ultrasonic guided waves are a special form of ultrasonic waves whose propagation is confined within the boundaries of a structure. Ultrasonic guided waves can be understood as "guided ultrasonic waves." It sacrifices some positioning accuracy and signal simplicity in exchange for ultra-long detection distance and high efficiency, making it ideal for rapid screening and health monitoring of large structures. Ultrasonic guided wave technology, with its advantages of covering the entire cross-section of a pipe with a single excitation and non-destructive testing, has become an ideal choice for measuring gas content in pipes. However, the accuracy of ultrasonic guided wave technology is highly dependent on the propagation characteristics of the guided wave in the pipe wall, which are significantly constrained by the acoustic properties of the pipe material (such as sound velocity and density) and key geometric dimensions (diameter and wall thickness). The inventors of this application discovered in experiments that different incident angles have a significant impact on the gas content detection by ultrasonic guided waves. For a specific mode, there exists an optimal incident angle at which the energy conversion efficiency from the incident volume wave (longitudinal or transverse wave) to the guided wave mode is highest. Deviating from this optimal angle significantly reduces the excitation efficiency. Currently, the core component of guided wave transducers used in industrial applications is the coupling wedge, which typically employs a fixed angle design or only has limited angle adjustment capabilities. This means that once the transducer is manufactured or installed, its incident angle is locked.

[0003] Existing methods for determining the incident angle, such as finite element method (FEA) full numerical simulation, involve establishing a refined finite element model (FEA) or finite difference model (FDM) that includes the transducer, wedge, pipe, and coupling conditions. By setting parametric scans in the software, the ultrasonic wave propagation process at different incident angles is simulated, and the energy coupling efficiency is calculated to find the optimal angle. However, this method is computationally expensive and extremely time-consuming, potentially taking hours or even days, making it unsuitable for rapid design and on-site commissioning. Methods based on dispersion curves, using the precise phase velocity obtained from the dispersion curves, are computationally complex, rely on specialized software and precise parameters, and face difficulties in mode selection. Experimental trial-and-error methods involve creating a physical mock-up, i.e., a sample tube with the same material, diameter, and wall thickness as the pipe under test. Then, using an angle-adjustable probe clamping device, the incident angle is continuously changed manually or automatically on the test block for scanning, while monitoring the intensity of the received guided wave signal. The incident angle that produces the strongest signal amplitude is considered to be the optimal angle under the current working conditions. This process is time-consuming, labor-intensive, and costly, and cannot be used as a general engineering design method for rapid application in the field. Summary of the Invention

[0004] To address the technical problems of existing methods being computationally complex and unsuitable for rapid design and on-site commissioning, this invention proposes a method for selecting the incident angle of an ultrasonic guided wave sensor for pipeline gas content detection, effectively determining the optimal incident angle for ultrasonic guided wave gas content detection.

[0005] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0006] A method for selecting the incident angle of an ultrasonic guided wave sensor for detecting gas content in pipelines, comprising the following steps:

[0007] S1: Calculate the critical wave velocity at which the ultrasonic guided wave mode conversion occurs after the incident wave enters the pipe wall, based on the pipe properties and the excitation frequency of the ultrasonic guided wave sensor.

[0008] S2: Determine the critical angle range for ultrasonic guided wave mode conversion after the incident wave enters the pipe wall based on the critical wave velocity;

[0009] S3: Calculate the phase velocity of the ultrasonic guided wave bending mode based on the pipe properties and the excitation frequency of the ultrasonic guided wave sensor;

[0010] S4: Calculate the theoretical incident angle based on the phase velocity of the ultrasonic guided wave bending mode using Snell's theorem and ensure that the theoretical incident angle is within the constraint range of the critical angle;

[0011] S5: Correct the theoretical incident angle to determine the final incident angle.

[0012] Furthermore, the method for calculating the critical wave velocity at which ultrasonic guided wave mode conversion occurs after the incident wave enters the pipe wall is as follows:

[0013] Calculate the longitudinal wave velocity when the incident wave vibrates along the propagation direction in the pipe wall material:

[0014]

[0015] Calculate the transverse wave velocity when the incident wave vibrates perpendicular to the propagation direction in the pipe wall material:

[0016]

[0017] in, For the Young's modulus of the pipeline, For the pipeline Poisson's ratio, This refers to the density of the pipe material.

[0018] Furthermore, the method for determining the critical angle range for ultrasonic guided wave mode conversion after the incident wave enters the pipe wall is as follows:

[0019] According to the longitudinal wave velocity The critical angle at which longitudinal wave mode conversion occurs when the ultrasonic guided wave enters the tube wall from the wedge is calculated as the lower critical angle for ultrasonic guided wave mode conversion. :

[0020]

[0021] According to the shear wave velocity The critical angle at which the transverse wave mode transition occurs when the ultrasonic guided wave enters the tube wall from the wedge is calculated as the upper critical angle for ultrasonic guided wave mode transition. :

[0022]

[0023] in, The longitudinal wave velocity is denoted by ...

[0024] Furthermore, the method for calculating the phase velocity of the ultrasonic guided wave bending mode is as follows:

[0025] The circumferential guided wave inside the pipe is approximated as the circumferential Lamb wave in the pipe within the thin plate, and the bending dominant A0 mode in the unfolded flat thin plate.

[0026] Bending stiffness characterizes the ability of a pipe to resist bending when unfolded into a thin flat plate.

[0027] Approximate dispersion relation of a flat thin plate unfolded from a pipe in A0 mode is calculated based on bending stiffness.

[0028] The approximate phase velocity is calculated based on the phase velocity calculation formula and the approximate dispersion relation under the A0 mode.

[0029] Furthermore, the method for calculating the approximate phase velocity based on the phase velocity calculation formula and the approximate dispersion relation under the A0 mode is as follows:

[0030]

[0031] in, This is the approximate phase velocity in the A0 mode of the ultrasonic guided wave. For pipe wall thickness, This is the excitation frequency of the ultrasonic guided wave sensor.

[0032] Furthermore, the method for calculating the theoretical angle of incidence is as follows:

[0033]

[0034] in For the theoretical angle of incidence, This is an approximate phase velocity.

[0035] Furthermore, the method for correcting the theoretical incident angle is as follows:

[0036] Incident angle correction to compensate for transmit-receive path deviation caused by pipe curvature

[0037]

[0038] Calculate the final angle of incidence based on the angle of incidence correction:

[0039]

[0040] in, This is the correction amount for the angle of incidence. Circumferential wavelength Let denot be the pipe radius, and ∆∅ be the angular difference between the transmitting and receiving positions.

[0041] Furthermore, after calculating the final incident angle, finite element simulation software was used to perform finite element simulation within the theoretically calculated angle range based on the actual pipeline conditions. With the incident angle as a single variable, the incident angle corresponding to the maximum vibration displacement of the received signal was taken as the optimal incident angle.

[0042] Furthermore, after determining the optimal incident angle, the receiving angle is selected to be the same as the incident angle.

[0043] Furthermore, the pipe properties include Young's modulus, Poisson's ratio, pipe material density, pipe radius, and pipe wall thickness. The beneficial effects of this invention are:

[0044] The ultrasonic guided wave incident angle selection method proposed in this invention is applicable to different materials, pipe diameters, and excitation frequencies. Using analytical formulas based on thin-plate approximation theory, only basic parameters such as pipe material properties (Young's modulus, density, Poisson's ratio), geometric dimensions (wall thickness, radius), and excitation frequency need to be input to quickly calculate the theoretically optimal incident angle suitable for different working conditions. This eliminates the need for complex professional software or expensive full numerical simulations, significantly reducing the technical threshold and computational resource requirements. Subsequent verification and fine-tuning are performed using finite element simulation. This step replaces time-consuming and laborious physical trial-and-error experiments, compensating for the shortcomings of the simplified model and accurately locking in the final optimal angle. This lays a solid foundation for the subsequent accurate extraction of acoustic characteristic changes related to gas content (such as wave velocity and attenuation), improving the accuracy and reliability of the ultrasonic guided wave detection scheme for pipe gas content. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 This is a flowchart of the method of the present invention.

[0047] Figure 2 This is a schematic diagram of the installation of the ultrasonic guided wave sensor of the present invention.

[0048] Figure 3 This is a schematic diagram of the ultrasonic guided wave incident signal of the present invention.

[0049] Figure 4 This is a schematic diagram of the A0 mode signal of the present invention.

[0050] Figure 5 This is a schematic diagram of the incident angle correction of the present invention.

[0051] Figure 6 The figure shows the simulation results of the Comsol model of this invention.

[0052] Figure 7 The graph shows the gas content detection error when the incident angle of the ultrasonic guided wave is 30 degrees.

[0053] Figure 8 The graph shows the gas content detection error when the ultrasonic guided wave incident angle is 42 degrees.

[0054] Figure 9 The graph shows the gas content detection error when the incident angle of the ultrasonic guided wave is 60 degrees.

[0055] Figure 10 The graph shows the gas content detection error when the incident angle of the ultrasonic guided wave is 45 degrees.

[0056] Figure 11 The graph shows the gas content detection error when the ultrasonic guided wave incident angle is 48 degrees. Detailed Implementation

[0057] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0058] A method for selecting the incident angle of an ultrasonic guided wave sensor for detecting gas content in pipelines, such as... Figure 1 As shown, the steps include:

[0059] S1: Calculate the critical wave velocity at which the ultrasonic guided wave mode conversion occurs after the incident wave enters the pipe wall, based on the pipe properties and the excitation frequency of the ultrasonic guided wave sensor.

[0060] The pipeline properties include Young's modulus (Pa) Poisson's ratio, ρ: density of pipe material (kg / m³), R: pipe radius, h: pipe wall thickness.

[0061] The method for calculating the critical wave velocity at which ultrasonic guided wave mode conversion occurs after the incident wave enters the pipe wall is as follows:

[0062] An ultrasonic guided wave sensor is coupled to the pipe via a wedge. The incident wave is ultrasonic, which propagates as a longitudinal wave within the wedge because the wedge is typically made of plastic such as acrylic, which generally does not propagate transverse waves. When the longitudinal wave from the wedge reaches the wedge-pipe interface, a mode conversion occurs. The critical angle determines the nature of this conversion.

[0063] To determine the critical angle at which an incident wave can form an ultrasonic guided wave when it enters the pipe wall from the wedge, it is necessary to first calculate the longitudinal and transverse wave velocities of the incident wave in the pipe wall material as the critical wave velocities for ultrasonic guided wave mode conversion.

[0064] Calculate the velocity of the incident wave as it vibrates along the propagation direction in the pipe wall material, i.e., the longitudinal wave velocity. (m / s):

[0065]

[0066] Calculate the velocity of the incident wave when it vibrates perpendicular to the propagation direction in the pipe wall material, i.e., the transverse wave velocity. (m / s):

[0067]

[0068] S2: Determine the critical angle range for ultrasonic guided wave mode conversion after the incident wave enters the pipe wall based on the critical wave velocity.

[0069] The critical angle at which the incident wave enters the pipe wall from the wedge defines the range of incident angles that can effectively excite ultrasonic guided waves, ensuring efficient energy coupling to the desired guided wave mode, thereby improving the signal-to-noise ratio and sensitivity of gas content detection. A schematic diagram of the incident angle is shown below. Figure 3 As shown.

[0070] Specifically, when the longitudinal wave angle is less than the critical angle, longitudinal waves are easily excited. Both longitudinal and transverse waves belong to volume waves. The propagation characteristics of volume waves are completely different from those of guided waves. They are not sensitive to the gas content of the fluid in the pipe and cannot be used for gas content detection. Therefore, in order to avoid energy directly leaking into the pipe and becoming a volume wave, and to ensure that energy is efficiently coupled to the required guided wave mode, based on the longitudinal wave velocity... The critical angle at which longitudinal wave mode conversion occurs when the ultrasonic guided wave enters the tube wall from the wedge is calculated as the lower critical angle for ultrasonic guided wave mode conversion. :

[0071] ;

[0072] in, The longitudinal wave velocity of the wedge block.

[0073] Specifically, when the transverse wave critical angle is exceeded, the transverse wave begins to be significantly excited, undergoing total internal reflection and failing to effectively enter the pipe. Therefore, based on the stated transverse wave velocity... The critical angle at which the transverse wave mode transition occurs when the ultrasonic guided wave enters the tube wall from the wedge is calculated as the upper critical angle for ultrasonic guided wave mode transition. :

[0074] .

[0075] In practical work, if the incident angle of the ultrasonic guided wave is less than the critical angle of the longitudinal wave... Longitudinal waves are more likely to enter the pipe inside the wedge; if the angle of incidence is greater than... At this angle, the ultrasonic wave will begin to couple to the transverse wave component, and the interface coupling characteristics will change. Within the critical angle range, it is not guaranteed that the emitted ultrasonic wave will form a guided wave, but beyond this critical angle range, a guided wave will definitely not form. Therefore, it is generally desirable that the incident angle of the ultrasonic guided wave falls at least within ( ). , It prioritizes coupling to the pipe guide rather than pure body waves.

[0076] For gas content detection, a guided wave signal sensitive to the fluid-to-pipe and gas-to-pipe interfaces and propagating within the pipe wall is required. If the incident angle is improperly chosen, a strong longitudinal wave signal will be generated, which will directly enter the fluid and mix with the weak guided wave signal characterizing gas content changes, severely reducing the signal-to-noise ratio and detection sensitivity. Accurately calculating and avoiding this region is a prerequisite for obtaining a pure, high-intensity guided wave signal. The role of determining the critical angle in circumferential ultrasonic guided wave gas content detection is to: suppress the generation of volume waves such as longitudinal and transverse waves; concentrate all energy for efficiently and purely exciting the desired guided wave mode sensitive to gas content (such as the A0 mode); and ultimately ensure that the received signal is strong and clean, sensitively reflecting minute changes in the gas content within the pipe, thereby achieving high-precision detection.

[0077] S3: Calculate the phase velocity of the ultrasonic guided wave bending mode based on the pipe properties and the excitation frequency of the ultrasonic guided wave sensor.

[0078] Solving the wave propagation problem in a cylindrical shell is extremely complex, requiring the solution of a three-dimensional elastic dynamics equation and the satisfaction of complex boundary conditions of the cylindrical surface. The governing equations (such as the Flügge shell theory equations) are complex systems of partial differential equations, and their solutions (dispersion relations) typically lack simple analytical expressions. Numerical methods must be used to solve the transcendental equations, resulting in tedious calculations and making them unsuitable for rapid engineering design. However, when the pipe wall thickness (h) is much smaller than the pipe radius (R), i.e., the thickness-to-diameter ratio (h / R) is very small, the curvature effect of the pipe wall becomes very weak. In this case, the behavior of a small section of the pipe wall under stress deformation and wave propagation closely resembles that of a flattened plate with the same thickness (h).

[0079] Therefore, the propagation characteristics of guided waves propagating circumferentially in a pipe can be approximated by the characteristics of Lamb waves propagating in a flat plate. The effectiveness of this approximation method depends on conditions including high transmission frequency and small thickness-to-diameter ratio (h / R<<1), which are currently met by most commonly used pipes in industrial applications.

[0080] This invention prioritizes the A0 mode, and the schematic diagram of the A0 mode signal is shown below. Figure 4 As shown, because it is a bending mode, its particle vibrations have a dominant component in the direction perpendicular to the plate surface. This makes it highly sensitive to acoustic loads from substances adhering to the pipe wall (such as wax deposits) or fluids in contact with the pipe wall (such as oil-gas mixtures). Changes in the fluid's gas content alter the fluid's density and acoustic impedance, thus slightly altering the propagation speed (dispersion characteristics) and attenuation of the A0 mode. By precisely measuring these changes, the gas content can be deduced.

[0081] Specifically, the method for calculating the phase velocity of the ultrasonic guided wave bending mode based on the pipe properties and the excitation frequency of the ultrasonic guided wave sensor is as follows:

[0082] Firstly, the circumferential guided wave inside the pipe is approximated as the circumferential Lamb wave in the pipe within the thin plate, and the bending dominant A0 mode in the unfolded flat thin plate.

[0083] Furthermore, bending stiffness characterizes the ability of a pipe to resist bending when unfolded into a thin plate. The method for calculating bending stiffness is as follows:

[0084]

[0085] in, For bending stiffness;

[0086] Furthermore, the approximate dispersion relation of the unfolded thin plate of the pipe in mode A0 is calculated:

[0087]

[0088] in, Angular frequency, Wave number;

[0089] Furthermore, the approximate phase velocity is calculated using the phase velocity calculation formula:

[0090]

[0091]

[0092] in, This is the approximate phase velocity in the A0 mode of the ultrasonic guided wave. Let be the excitation frequency of the ultrasonic guided wave sensor. This formula is used to estimate the phase velocity of the A0 mode Lamb wave propagating in a thin-walled pipe. By unfolding the flat plate approximation, the pipe wall is treated as a flat plate, simplifying the complex cylindrical shell waveguide problem.

[0093] The thin-plate approximation theory provides an explicit analytical formula that eliminates the need for complex professional software to solve dispersion curves. It can be completed on a regular computer or even a calculator. The method has a clear process and standardized steps. Simply substitute the parameters step by step to calculate and obtain an angle that is very close to the optimal solution. This saves the huge cost of processing physical test blocks of various specifications and precision adjustment frames, and the time cost is extremely low: the "processing-experimentation-adjustment" cycle that takes several days or even weeks is shortened to a "calculation-simulation" process of a few hours. For pipes with small thickness-to-diameter ratios commonly found in industry, the accuracy is sufficient for engineering design.

[0094] S4: Calculate the theoretical incident angle based on the phase velocity of the ultrasonic guided wave bending mode using Snell's theorem and ensure that the theoretical incident angle is within the constraint range of the critical angle.

[0095] Within the critical angle range ( , Under the constraint of the wedge block longitudinal wave velocity, and the approximate phase velocity under the ultrasonic guided wave A0 mode Theoretical angle of incidence is calculated using Snell's theorem. :

[0096]

[0097]

[0098] S5: Correct the theoretical incident angle to determine the final incident angle, such as... Figure 5 As shown.

[0099] Although a transmitting sensor has two sensors that receive its signals, there is a sequence in which the signals are received first. The signal received first has higher energy, so when correcting the angle, only the position of the first receiving sensor is considered. The signal from the second receiving sensor has much lower energy than the first, so its influence can be ignored compared to the first sensor.

[0100] Therefore, an incident angle correction is applied to compensate for the transmit-receive path deviation caused by the pipe curvature:

[0101]

[0102] Among them, Incident angle correction Circumferential wavelength The difference in angle between the transmitting and receiving positions.

[0103] Calculate the final angle of incidence based on the correction amount:

[0104]

[0105] Selection of the receiving angle of the ultrasonic guided wave receiver sensor: Since the transmitting and receiving wedges are made of the same material and have the same target mode, theoretically the optimal incident angle of the receiving wedge is the same as that of the transmitting wedge.

[0106] Reception is the reverse process of transmission. In order to maximize the reception of guided wave modes from a specific direction, the incident angle of the receiving sensor must satisfy the same phase matching condition. When there is no circumferential angle difference between the receiving sensor and the transmitting sensor, according to the reciprocity principle, this optimal transmission angle is also the optimal receiving angle when the transducer is used as a transmitter.

[0107] Furthermore, finite element simulation software (such as Comsol) is used to perform finite element simulations within the theoretically calculated angle range based on the actual pipeline conditions, ultimately determining the optimal incident angle for the excited ultrasonic guided wave. With other conditions remaining constant, if the vibration displacement (also known as vibration response) at the receiving point is maximized at a certain incident angle, it indicates that the energy attenuation at the receiving point is small, and the received signal energy is stronger. This incident angle is then taken as the optimal incident angle for the ultrasonic guided wave.

[0108] This application was tested under the following conditions: ultrasonic guided wave excitation frequency of 500 kHz, pipe diameter of 89 mm, wall thickness of 3 mm, pipe material of carbon steel, wedge base material of acrylic, and ultrasonic guided wave sensor installation consisting of one receiving sensor and one transmitting sensor, spaced 180° apart. The actual installation method is as follows... Figure 2 As shown.

[0109] ① Calculate wave speed:

[0110]

[0111]

[0112]

[0113] ② Determine the critical angle:

[0114]

[0115]

[0116] Therefore, the reasonable angle domain is ( , )

[0117] ③ Selection of approximate phase velocity:

[0118]

[0119] ④ Determine the angle of incidence using Snell's theorem

[0120]

[0121]

[0122] ⑤ Receiving angle correction:

[0123] The final incident angle of the ultrasonic guided wave is:

[0124]

[0125] ⑥ Simulation determines the final incident angle:

[0126] The simulation software used was Comsol, and the incident angle of the ultrasonic guided wave was measured from... arrive Step size within range Perform parametric scanning, and the final simulation results are as follows: Figure 6 As shown, where, , The vibration displacement generated at this time is the largest, therefore it can be considered that This is the optimal angle of incidence.

[0127] from Figures 7 to 11 The gas content detection results at incident angles of 30°, 42°, 60°, 45°, and 48° showed the smallest error at an incident angle of 45°. This verifies the effectiveness of the method proposed in this application.

[0128] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0129] It should be noted that the terms "comprising" and "having" and any variations thereof in the specification and claims of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, or product that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such processes, methods, systems, or products.

[0130] It should be understood that the above description is merely a preferred embodiment and application of the technical principles of the present invention. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the specific embodiments described herein, and may include many other effective embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A method for selecting an incident angle of an ultrasonic guided wave sensor for pipeline gas detection, characterized in that, The method comprises the steps of: S1: calculating a critical wave velocity of the incident wave after the ultrasonic guided wave mode conversion according to the pipe properties and the excitation frequency of the ultrasonic guided wave sensor; S2: determining a critical angle range of the incident wave after the ultrasonic guided wave mode conversion according to the critical wave velocity; S3: calculating an ultrasonic guided wave bending mode phase velocity according to the pipe properties and the excitation frequency of the ultrasonic guided wave sensor; S4: calculating a theoretical incidence angle based on Snell's theorem according to the ultrasonic guided wave bending mode phase velocity and ensuring that the theoretical incidence angle is within the constraint range of the critical angle; S5: correcting the theoretical incidence angle to determine a final incidence angle.

2. The method for selecting the incident angle of ultrasonic guided wave sensor for pipeline gas rate detection according to claim 1, characterized in that, The method for calculating the critical wave velocity of the incident wave after the ultrasonic guided wave mode conversion comprises the steps of: calculating a longitudinal wave velocity of the incident wave when vibrating in the propagation direction in the pipe wall material: calculating a transverse wave velocity of the incident wave when vibrating perpendicular to the propagation direction in the pipe wall material: wherein, Epipeis the pipe Young's modulus, vpipeis the pipe Poisson's ratio, pipedis the pipe material density.

3. The method for selecting the incident angle of ultrasonic guided wave sensor for pipeline gas rate detection according to claim 2, characterized in that, The method for determining the critical angle range of the incident wave after the ultrasonic guided wave mode conversion comprises the steps of: According to the longitudinal wave wave velocity The critical angle of longitudinal wave mode conversion when an ultrasonic guided wave is launched into a pipe wall from a wedge is calculated as the lower critical angle for ultrasonic guided wave mode conversion : According to the shear wave velocity The critical angle of the shear wave mode conversion of the ultrasonic guided wave when the ultrasonic guided wave is emitted into the pipe wall is calculated as the upper critical angle of the ultrasonic guided wave mode conversion : wherein, is the longitudinal wave velocity in the wedge for the ultrasonic guided wave sensor.

4. The method for selecting the incident angle of ultrasonic guided wave sensor for pipeline gas rate detection according to any one of claims 1 to 3, characterized in that, The method for calculating the ultrasonic guided wave bending mode phase velocity comprises the steps of: approximating the circumferential guided wave in the pipe as a circumferential Lamb wave in the pipe in the unfolded flat plate and approximating the circumferential Lamb wave in the pipe as a bending dominant A0 mode in the unfolded flat plate; characterizing the ability of the pipe unfolded flat plate to resist bending by bending stiffness; calculating an approximate dispersion relationship of the pipe unfolded flat plate under the A0 mode based on the bending stiffness; calculating an approximate phase velocity according to the phase velocity calculation formula and the approximate dispersion relationship under the A0 mode.

5. The method for selecting the incident angle of ultrasonic guided wave sensor for pipeline gas rate detection according to claim 4, characterized in that, The method for calculating the approximate phase velocity according to the phase velocity calculation formula and the approximate dispersion relationship under the A0 mode comprises the steps of: wherein, is the approximate phase velocity of the ultrasonic guided wave A0 mode, is the pipe wall thickness, is the excitation frequency of the ultrasonic guided wave sensor.

6. The method for selecting the incident angle of ultrasonic guided wave sensor for pipeline gas rate detection according to claim 5, characterized in that, The method for calculating the theoretical incidence angle comprises the steps of: wherein is the theoretical angle of incidence, is the approximate phase velocity.

7. The method for selecting an incident angle of an ultrasonic guided wave sensor for pipeline gas detection according to any one of claims 1-3, 5 or 6, wherein, The method for correcting the theoretical incidence angle comprises the steps of: correcting the incidence angle to compensate for the deviation of the transmission-reception path caused by the pipe curvature calculating the final incidence angle according to the incidence angle correction amount: wherein is the incidence angle correction, is the circumferential wavelength, is the pipe radius, and ΔΦ is the emission-reception position angle difference.

8. The method for selecting the incident angle of ultrasonic guided wave sensor for pipeline gas detection according to claim 1, characterized in that, After calculating the final incidence angle, the finite element simulation software is used to perform finite element simulation within the theoretically calculated angle range according to the actual pipe conditions, and the incidence angle is kept as a single variable, and the incidence angle corresponding to the maximum vibration displacement of the received signal is taken as the optimal incidence angle.

9. The method of selecting an incident angle of an ultrasonic guided wave sensor for pipeline gas detection according to claim 8, wherein, After determining the optimal incidence angle, the receiving angle is selected as the same angle as the incidence angle.

10. The method for selecting an incident angle of an ultrasonic guided wave sensor for pipeline gas detection according to any one of claims 1-3, 5, 6, 8 or 9, wherein, The pipe properties include Young's modulus, Poisson's ratio, pipe material density, pipe radius, and pipe wall thickness.

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