Design method of ultrasonic guided wave transducer for active corrosion prevention of surface of metal pipeline

Abstract

The invention provides a method for designing an ultrasonic guided wave transducer for active corrosion prevention of a metal pipeline surface, which comprises the following steps of: S1, determining the modal and the frequency of ultrasonic guided waves needing to be excited by utilizing finite element numerical simulation, and calculating a frequency dispersion curve of the ultrasonic guided waves propagating in a pipeline by utilizing a semi-analytical finite element method, a specific mode needing to be excited is found through the frequency dispersion curve; s2, establishing an ultrasonic guided-wave transducer model, and performing sensitivity test on parameters of the Morris trajectory model to obtain structural parameters having great influence on the characteristics of the ultrasonic guided-wave transducer; and S3, simulating different conditions of the structural parameters with relatively large influence, and designing and manufacturing the transducer to obtain proper transducer parameters. Compared with an existing design method, the design method is simpler and more efficient, and the design of transducer structures applied to pipelines of different materials and sizes can be guided.

Description

Technical Field

[0001] The invention relates to the technical field of corrosion prevention, and in particular to a design method of an ultrasonic guided wave transducer. Background Art

[0002] At present, the anti-corrosion technologies for metal structures in marine atmospheric environments mainly include paint anti-corrosion, metal coating anti-corrosion, electrochemical anti-corrosion, coating material anti-corrosion, ultrasonic technology assisted anti-corrosion, etc., but they all have certain limitations due to high prices and complex implementation methods. A metal surface anti-corrosion technology based on ultrasonic guided waves can effectively prevent the contact between salt spray and the surface of the metal structure by using ultrasonic guided waves, and can further slow down the surface corrosion rate of large metal structures on the basis of existing coating protection. However, the current design of ultrasonic guided wave transducers fails to systematically design for the specific needs of ultrasonic guided waves for anti-corrosion of metal surfaces, such as excitation mode, incident angle, and excitation frequency. To this end, the present invention proposes a design method for an ultrasonic guided wave transducer for active corrosion protection of metal pipe surfaces to improve its protective effect.

[0003] For example, the invention patent with application number 202310035208.6 discloses a method for surface corrosion protection of metal structures based on array transducer-excited ultrasonic guided waves, and the steps are as follows: first, according to the material properties of the structure, the dispersion curve of the ultrasonic guided waves in the structure is calculated using the semi-analytical finite element method; second, according to the dispersion curve and Snell's law, the wedge angle of the array transducer is designed, and the array transducer is fixed on the surface of the structure; finally, an ultrasonic guided wave anti-corrosion device is built based on the array transducer, and the array transducer is excited by the excitation signal to generate ultrasonic guided waves propagating along the surface of the structure to achieve online corrosion protection. The invention uses the shear force of the guided wave acting on the surface of the structure and the high-frequency vibration of the surface of the structure to achieve online corrosion protection. At the same time, under the condition of temperature change, the input parameters are adjusted to reduce environmental interference and ensure the corrosion protection efficiency. However, this method does not design the mode and vibration frequency of the ultrasonic guided waves required for corrosion protection, fails to maximize the displacement response of the pipeline surface, and has low vibration efficiency for salt spray particles, so it cannot achieve the best corrosion protection effect. Summary of the invention

[0004] In view of the problem that existing transducers are unable to excite ultrasonic guided wave technology of specific frequencies and modes required for corrosion protection of metal pipe surfaces, the present invention proposes a design method for ultrasonic guided wave transducers for active corrosion protection of metal pipe surfaces. The method is simple and efficient, and can guide the design of transducer structures for use on pipes of different materials and sizes.

[0005] In order to achieve the above object, the technical solution of the present invention is implemented as follows: a method for designing an ultrasonic guided wave transducer for active corrosion protection of a metal pipe surface, the steps comprising:

[0006] S1: Use finite element numerical simulation to determine the mode and frequency of the ultrasonic guided wave that needs to be excited, use the semi-analytical finite element method to calculate the dispersion curve of the ultrasonic guided wave propagating in the pipeline, and find the specific mode that needs to be excited through the dispersion curve;

[0007] S2: Establish an ultrasonic guided wave transducer model and perform sensitivity tests on the parameters using the Morris trajectory model to obtain the structural parameters that have a greater impact on the characteristics of the ultrasonic guided wave transducer;

[0008] S3: Simulate different situations of structural parameters with greater influence and design and manufacture the transducer to obtain appropriate transducer parameters.

[0009] The method of calculating the dispersion curve of ultrasonic guided waves propagating in the pipeline by using the semi-analytical finite element method in step S1 is:

[0010] In a pipeline, the displacement field of ultrasonic guided waves is usually expressed in the form of waves:

[0011] u(r,θ,z,t)=U(r,θ)e i(kz-ωt) ;

[0012] Where u(r,θ,z,t) is the displacement vector, which depends on the radius r, the angle θ, the axial coordinate z and the time t; U(r,θ) is the displacement component on the pipe cross section; k is the wave number, ω is the angular frequency, and i is the imaginary unit;

[0013] For the elastic body in the pipe, the governing equation is:

[0014]

[0015] Where σ is the stress tensor, ρ is the material density, u is the displacement vector, is the gradient operator;

[0016] The relationship between stress and strain is given by the constitutive relationship of linear elastic materials:

[0017] σ=C·ε;

[0018] Where C is the elastic stiffness matrix of the material and ε is the strain tensor, which is calculated from the displacement gradient:

[0019]

[0020] in, is a symmetric gradient operator;

[0021] The displacement field is discretized using the finite element method on the pipe cross section and approximated as a combination of finite element basis functions:

[0022] U(r,θ)≈∑ j N j (r,θ)U j ;

[0023] Among them, N j (r,θ) is the finite element basis function on the cross section, U j is the displacement vector at the discrete node;

[0024] Substituting the displacement field and strain field into the governing equation and using the finite element method to discretize the cross section, we obtain the finite element form of the wave equation:

[0025]

[0026] Where M is the mass matrix, K is the stiffness matrix, and U is the discrete nodal displacement vector matrix; for ultrasonic guided wave problems, the displacement field is assumed to be in the harmonic form e i(kz) , which is substituted into the wave equation to obtain;

[0027] (-ω 2 M+K)U=0;

[0028] The corresponding relationship between wave number k and frequency ω is converted into an eigenvalue problem. For a given wave number k, the angular frequency ω is obtained by solving the eigenvalue problem. The expression of the eigenvalue problem is:

[0029] (K(k)-ω 2 M)U=0;

[0030] The solution ω(k) of the eigenvalue problem corresponds to the dispersion relation. By changing the value of the wave number k and repeatedly solving the eigenvalue problem, a series of corresponding frequencies ω are obtained. The relationship curve between k and ω is plotted to obtain the dispersion curve.

[0031] The ultrasonic guided wave transducer in step S2 includes a transducer module, a wedge-shaped base is arranged on the lower side of the transducer module, the transducer module includes a shell, a screw is arranged in the shell, one end of the screw is fixedly connected to the inner side of the shell, and the other end of the screw is connected to the wedge-shaped base, an insulating tube is arranged on the outer side of the screw, at least one piezoelectric ceramic sheet is mounted on the insulating tube, and electrode sheets are arranged between adjacent piezoelectric ceramic sheets and between the piezoelectric ceramic sheets and the shell.

[0032] The polarization directions of the adjacent piezoelectric ceramic sheets are opposite, and the number of the piezoelectric ceramic sheets is an even number.

[0033] A notch is arranged on the lower side of the wedge-shaped base, and the groove surface of the notch is an arc-shaped groove surface.

[0034] The wedge-shaped base is a wedge-shaped base with an inclined surface at the top, and the shell is arranged on the upper side of the inclined surface.

[0035] The method for performing sensitivity testing on the parameters of the Morris trajectory model described in step S2 is:

[0036] The ultrasonic guided wave transducer is modeled. Assume that there are m independent input parameters in the ultrasonic guided wave transducer model and n key characteristics are output parameters. If only the i-th input parameter is allowed to increase with a fixed step size, and the other input parameter values ​​remain unchanged, the response value y of the output parameter is obtained. Then, when the x input parameter increases with a fixed step size Δ i Basic factors under change EE i Defined as:

[0037]

[0038] Morris trajectory sampling is used to establish p tracks in the input variables. Each track has n+1 sampling points, so a total of (n+1)p sampling points need to be calculated.

[0039] For each input variable x i For the output variable y i The influence degree is taken as the mean value μ i and variance σ i Perform statistical analysis; for p tracks, the mean μ i and variance σ i They are:

[0040]

[0041] in, is the basic factor of the i-th input variable in the j-th track;

[0042] Since the input variables may have a negative correlation with the output variables, in order to avoid i When the calculated value is negative, the mean μ is weakened by the mutual cancellation of the terms in the summation operation. i Calculation results show that Campolongo redefined μ i The calculation formula is:

[0043]

[0044] The mean μ i and variance σ i It is called the sensitivity factor. The sensitivity factor is used to evaluate the importance of the input variable on the output variable. It is found that the groove depth and the slope angle of the wedge-shaped base 2 are the structural parameters that have a greater impact on the characteristics of the ultrasonic guided wave transducer.

[0045] The specific method of using Morris trajectory sampling to establish p tracks in the input variables is:

[0046] First, an initial point is selected in the input variable space, and one of the input variables is increased or decreased with a fixed step size to obtain the second sample point. Based on the second sample point, another input variable value is increased or decreased with a fixed step size to obtain the third sample point. This is repeated, and all input parameters in the input variable space are changed once to obtain a trajectory.

[0047] The method for evaluating the importance of the input variable on the output variable through the sensitivity factor is:

[0048] If we calculate the mean μ i If it is small, the input parameter has no significant impact on the output parameter;

[0049] If μ i is larger, while σ i When it is small, it means that the input parameter has a great influence on the output parameter, but the input parameter is linearly related to the output parameter, and the coupling with other input parameters is small;

[0050] If μ i Larger, while σ i When it is large, it means that the input parameter has a great influence on the output parameter, but the input parameter has a nonlinear relationship with the output parameter and is highly coupled with other input parameters.

[0051] The method for simulating different situations of structural parameters having a greater impact and designing and manufacturing the transducer is:

[0052] Taking the maximum displacement response of the contact surface between the ultrasonic transducer and the pipeline as the design goal, and the ultrasonic guided wave transducer meeting the set operating frequency, minimum impedance, and minimum amplitude ratio of the front and rear cover plates as constraints, the most suitable set of structural parameters is obtained and the transducer is designed and manufactured.

[0053] The beneficial effects of the present invention are as follows: the design method of the present invention is simpler and more efficient than the existing design method, and can guide the design of the transducer structure applied to pipes of different materials and sizes. The designed ultrasonic transducer structure can effectively excite F-mode ultrasonic guided waves, and the designed ultrasonic transducer can achieve the maximum displacement response with the contact surface of the pipe at the designed working frequency, so that the vibration amplitude of the salt spray particles on the pipe surface reaches the maximum, significantly reducing the contact area between the salt spray particles and the pipe surface, and slowing down the corrosion rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0055] Figure 1 The ultrasonic guided wave transducer design process of the present invention.

[0056] Figure 2 This is the group velocity dispersion curve of the DN32 pipeline of the present invention.

[0057] Figure 3 This is the phase velocity dispersion curve of the DN32 pipeline of the present invention.

[0058] Figure 4 It is the surface displacement response of the ultrasonic guided wave propagating in the pipeline at 20kHz of the present invention.

[0059] Figure 5 It is the surface displacement response of the ultrasonic guided wave propagating in the pipeline at 17kHz of the present invention.

[0060] Figure 6 It is the surface displacement response of the ultrasonic guided wave propagating in the pipeline at 23kHz of the present invention.

[0061] Figure 7 The normalized displacement response relationship of the structure when incident at different angles under the working frequency is designed for the present invention.

[0062] Figure 8 This is a structural diagram of the wedge-shaped composite piezoelectric ultrasonic transducer of the present invention.

[0063] Fig. 9 This is a displacement response diagram of the ultrasonic transducer and pipeline combination after the vibration test of the present invention.

[0064] In the figure, 1 is a transducer module, 2 is a wedge-shaped base, 3 is a screw, 4 is an insulating tube, 5 is a piezoelectric ceramic sheet, and 6 is an electrode sheet. DETAILED DESCRIPTION

[0065] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0066] Example 1

[0067] like Figure 1As shown, a method for designing an ultrasonic guided wave transducer for active corrosion protection of a metal pipe surface comprises the following steps:

[0068] S1: Use finite element numerical simulation to determine the frequency of the ultrasonic guided wave that needs to be excited. Through characteristic frequency analysis, find the resonance characteristic frequency with the largest and more uniform displacement response of the pipeline. Use the semi-analytical finite element method to calculate the dispersion curve of the ultrasonic guided wave propagating in the pipeline, and find the specific mode that needs to be excited through the dispersion curve, so that the pipeline can produce the maximum radial vibration under the action of the ultrasonic guided wave in this mode.

[0069] Specifically, the method for calculating the dispersion curve of ultrasonic guided waves propagating in a pipeline is:

[0070] In a pipeline, the displacement field of ultrasonic guided waves can usually be expressed in the form of waves:

[0071] u(r,θ,z,t)=U(r,θ)e i(kz-ωt) (1)

[0072] Where u(r,θ,z,t) is the displacement vector that depends on the radius r, the angle θ, the axial coordinate z and the time t; U(r,θ) is the displacement component on the pipe cross section; k is the wave number, ω is the angular frequency and i is the imaginary unit.

[0073] According to the governing equations in elastic dynamics, the motion of ultrasonic guided waves is controlled by the relationship between stress and displacement. For the elastic body in the pipe, the governing equation is:

[0074]

[0075] Where σ is the stress tensor, ρ is the material density, u is the displacement vector, is the gradient operator;

[0076] The relationship between stress and strain is given by the constitutive relationship of linear elastic materials:

[0077] σ=C·ε (3) Where C is the elastic stiffness matrix of the material and ε is the strain tensor, which is calculated from the displacement gradient:

[0078]

[0079] in, is a symmetric gradient operator;

[0080] The displacement field is discretized using the finite element method on the pipe cross section (r-θ plane). The displacement field is approximated as a combination of finite element basis functions:

[0081] U(r,θ)≈∑ j N j (r,θ)U j(5)

[0082] Among them, N j (r,θ) is the finite element basis function on the cross section, U j is the displacement vector at the discrete node;

[0083] Substituting the above displacement field and strain field into the governing equation and using the finite element method to discretize the cross section, we obtain the following finite element form of the wave equation:

[0084]

[0085] Where M is the mass matrix, K is the stiffness matrix, and U is the discrete nodal displacement vector matrix; for ultrasonic guided wave problems, the displacement field is assumed to be in the harmonic form e i(kz-ωt) , which can be substituted into the wave equation to obtain;

[0086] (-ω 2 M+K)U=0 (7)

[0087] The corresponding relationship between wave number k and frequency ω is converted into an eigenvalue problem. For a given wave number k, the angular frequency ω can be obtained by solving the eigenvalue problem. The specific expression of the eigenvalue problem is:

[0088] (K(k)-ω 2 M)U=0 (8)

[0089] The solution ω(k) of the eigenvalue problem corresponds to the dispersion relation, that is, the correspondence between the wave number k and the frequency ω. By changing the value of the wave number k and repeatedly solving the eigenvalue problem, a series of corresponding frequencies ω can be obtained. The relationship curve between k and ω is called the dispersion curve, which reflects the relationship between the frequency and wave number of different mode guided waves when propagating in the pipeline.

[0090] S2: Establish an ultrasonic guided wave transducer model and perform sensitivity tests on the parameters using the Morris trajectory model to obtain the structural parameters that have a greater impact on each response characteristic.

[0091] Specifically, Figure 8As shown, the ultrasonic guided wave transducer includes a transducer module 1, a wedge-shaped base 2 is provided at the lower side of the transducer module 1, the transducer module 1 includes a shell, a screw 3 is provided inside the shell, one end of the screw 3 is fixedly connected to the inner side of the shell, and the other end of the screw 3 is connected to the wedge-shaped base 2, an insulating tube 4 is provided outside the screw 3, at least one piezoelectric ceramic sheet 5 is sleeved on the insulating tube 4, and electrode sheets 6 are provided between adjacent piezoelectric ceramic sheets 5 and between the piezoelectric ceramic sheets 5 and the shell. Among them, the transducer module 1 is mainly used to generate ultrasonic guided wave signals, the wedge-shaped base 2 is mainly used to fix the transducer on the pipeline and apply ultrasonic guided waves to the pipeline at a specific angle, the screw 3 is mainly used to fix the transducer module 1 and the wedge-shaped base, the insulating tube 4 is mainly used to prevent the screw from conducting electricity, the piezoelectric ceramic sheet 5 is mainly used to convert electrical signals into mechanical signals to generate ultrasonic guided wave signals, and the electrode sheet 6 is mainly used to provide electrical signals to the piezoelectric ceramic sheet;

[0092] The polarization directions of adjacent piezoelectric ceramic sheets 5 are opposite, so that the longitudinal vibrations of each sheet can be superimposed in phase, ensuring that the piezoelectric crystal stack can vibrate in a coordinated manner. At the same time, the number of piezoelectric ceramic sheets 5 is an even number, so that the front cover plate and the rear cover plate can be connected to the same polarity electrode. A notch is provided on the lower side of the wedge-shaped base 2, and the groove surface of the notch is an arc groove surface, and the curvature is the same as the curvature of the pipeline. The wedge-shaped base 2 is a wedge-shaped base with an inclined surface on the top, and the shell is provided on the upper side of the inclined surface.

[0093] Sensitivity analysis of the geometric parameters of the wedge-shaped base 2 of the ultrasonic guided wave transducer is carried out: the ultrasonic guided wave transducer is modeled, and it is assumed that there are m independent input parameters in the ultrasonic guided wave transducer model, and n key characteristics are output parameters. If only the i-th input parameter is allowed to increase with a fixed step size, and the values ​​of other input parameters remain unchanged, the response value y of the output parameter is obtained. Then, when the x input parameter increases with a fixed step size Δ i Basic factors under change EE i Defined as:

[0094]

[0095] Morris trajectory sampling is used to establish p tracks in the input variables. Each track has n+1 sampling points, so a total of (n+1)p sampling points need to be calculated. The specific implementation steps are as follows: First, select an initial point in the input variable space, increase or decrease one of the input variables with a fixed step size to obtain the second sample point, and then based on the second sample point, increase or decrease another input variable value with a fixed step size to obtain the third sample point, and repeat this process, changing all input parameters in the input variable space once to obtain a track; due to the existence of an initial value, the total number of sample points in a track is n+1, and when the process is repeated p times, p tracks can be obtained; then p tracks can calculate p basic elements for each input variable, thereby evaluating the global sensitivity of each input variable.

[0096] For each input variable x i For the output variable y i The influence degree is taken as the mean value μ i and variance σ i Perform statistical analysis; for p tracks, the mean μ i and variance σ i They are:

[0097]

[0098] in, is the basic factor of the i-th input variable in the j-th track, and j represents the j-th track.

[0099] Since the input variables may have a negative correlation with the output variables, in order to avoid i When the calculated value is negative, the mean μ is weakened by the mutual cancellation of the terms in the summation operation. i Calculation results show that Campolongo redefined μ i The calculation formula is:

[0100]

[0101] The mean μ i and variance σ i It is called the sensitivity factor. The sensitivity factor is used to evaluate the importance of the input variable on the output variable. The specific method is as follows:

[0102] (1) If we calculate the mean μ i If it is small, the input parameter has no significant impact on the output parameter;

[0103] (2) If μ i is larger, while σ iWhen it is small, it means that the input parameter has a great influence on the output parameter, but the input parameter is linearly related to the output parameter, and the coupling with other input parameters is small;

[0104] (3) If μ i Larger, while σ i When it is large, it means that the input parameter has a great influence on the output parameter, but the input parameter has a nonlinear relationship with the output parameter and has a strong coupling with other input parameters;

[0105] Considering the influence of multiple geometric parameters of the ultrasonic guided wave transducer on the system output parameters when they change simultaneously in the model, a sensitivity analysis is carried out. Among them, the input variables are the geometric parameters of the front cover base x=L, L=[L2W H dh], L2 represents the length of the wedge base 2, W represents the width of the wedge base 2, H represents the height of the wedge base 2, and dh represents the groove depth; the system output parameters are O=[ZM ξ], where Z is the amplitude ratio of the front and rear covers of the ultrasonic guided wave transducer, M is the mass of the ultrasonic guided wave transducer, and ξ is the characteristic frequency of the ultrasonic guided wave transducer obtained in S1; 8 values ​​are taken for the four parameters in the geometric parameters L of the ultrasonic guided wave transducer at equal intervals. Finally, it is obtained through Morris trajectory that the parameters that have a greater impact on the ultrasonic guided wave transducer include the notch depth and width of the wedge base 2.

[0106] S3: Simulate different situations of structural parameters with greater influence and design and manufacture the transducer to obtain appropriate transducer parameters.

[0107] The design goal is to maximize the displacement response of the contact surface between the ultrasonic transducer and the pipeline, and the constraints are that the ultrasonic guided wave transducer meets the set working frequency, the lowest impedance, and the minimum amplitude ratio of the front and rear covers. The most suitable set of structural parameters is obtained and the transducer is designed and manufactured. From the sensitivity analysis results, it is found that the height of the wedge-shaped front cover has a great influence on the characteristic frequency, while the influence on the amplitude ratio of the front and rear ends is relatively small. Therefore, it can be considered first to adjust the height H of the front cover to meet the characteristic frequency design. The length L2 of the wedge base, the groove depth dh and the width W all have a great influence on the amplitude ratio, and the parameters affect each other. The length L2 parameter has a low sensitivity to the characteristic frequency and has almost no effect on the characteristic frequency of the ultrasonic transducer. The parameter dh is linearly related to the characteristic frequency. Therefore, it is first considered to determine the characteristic frequency by controlling the H and W factors. When the height H and width W are determined, these two parameters should be avoided from being adjusted again. Finally, the L2 and dh parameters are adjusted to control the optimal amplitude ratio of the structure output.

[0108] Vibration test of the transducer designed and manufactured by this method is carried out by laser vibration measurement. First, place the laser vibrometer near the combination of the transducer to be tested and the pipeline to ensure a stable installation; connect the power supply and storage medium, and select the corresponding probe and accessories as needed; then enter the instrument's operation interface, calibrate and configure the instrument according to the test requirements; after calibration, set the corresponding measurement parameters such as sampling frequency, measurement range, etc. according to the properties and requirements of the device under test; adjust the position and focal length of the instrument by observing the output data to achieve the best measurement effect; start real-time measurement, observe the graphical display of real-time data, record data as needed, and verify the design effect based on whether its vibration displacement response is consistent with the design requirements.

[0109] Example 2

[0110] A design method of ultrasonic guided wave transducer for active corrosion protection of metal pipe surface is presented. Taking the corrosion protection of DN32 carbon steel pipe with a length of 1m as an example, first:

[0111] The dispersion curve of ultrasonic guided waves in a DN32 pipe was calculated using the semi-analytical finite element method. The results are shown in Figure 2 , Figure 3 As shown, Figure 2 is the group velocity dispersion curve of DN32 pipeline, Figure 3 The dispersion curve of the phase velocity of the DN32 pipeline shows that in the range of 0-100kHz, the ultrasonic guided wave propagation modes include longitudinal mode, bending mode and torsion mode. The F mode ultrasonic guided wave has tangential displacement on the outer wall of the pipeline, and it is relatively easy to excite the F mode in the pipeline, so the F mode is selected as the excitation mode in the simulation.

[0112] according to Figure 2 and Figure 3 Dispersion curve, using the finite element method to numerically simulate the frequency domain response of the pipeline under 15kHz-30kHz frequency sweep, the excitation signal acts on the transducer inclined surface. The parameters are set as follows:

[0113] 1. The tubular structure material is steel, with an elastic modulus of 200 GPa, a Poisson's ratio of 0.35, and a density of 7850 kg / m 3 .

[0114] 2. The material of the ultrasonic transducer is stainless steel, with an elastic modulus of 70 GPa, a Poisson's ratio of 0.33, and a density of 2700 kg / m3.

[0115] 3. The outer diameter of the pipe is 40mm, the wall thickness is 4mm, and the length is 1m.

[0116] 4. The ultrasonic transducer unit is fixed at one end of the structure, with a wedge angle of 45° and an excitation frequency of 15-30kHz.

[0117] The numerical simulation results are as follows Figure 4-Figure 6 As shown in Figure 2, the ultrasonic transducer effectively excites the F-mode ultrasonic guided wave to propagate along the pipeline. Figure 4 It is shown in Figure 2 that the pipe surface displacement response is the largest at a frequency of 20kHz, which can reach 10 -10 m, and Figure 5 and Figure 6 The surface displacement response at 17kHz and 23kHz is evenly distributed, but the amplitude is small. The above simulation results show that the propagation of F-mode ultrasonic guided waves in the pipeline causes vibration and shear effects on its surface, which is beneficial to prevent salt spray particles and tiny droplets from adhering to its surface, and the distribution and amplitude of the displacement response at different frequencies are different. According to the simulation results, 20kHz, which makes the pipeline displacement response the largest, is selected as the operating frequency of the transducer.

[0118] After the system operating frequency is determined, the incident angle of the transducer is determined. There are many modes of ultrasonic guided waves in the gas-liquid two-phase flow pipeline combination. The excitation of specific mode guided waves is related to the frequency and the incident angle of the ultrasonic transducer. When the ultrasonic wave is incident at a certain inclination angle and reaches the interface, not only will refraction occur, but also waveform conversion will occur. The finite element method is used to establish a modal response model of the pipeline structure when the wedge-shaped base 2 is excited at different incident angles. The model sets the incident angles of 20°, 45°, and 60°. The normalized displacement response relationship of the structure at different incident angles under the design operating frequency is compared and analyzed. By fitting the curve and performing normalization processing, the results can be obtained as follows: Figure 7 As shown, it can be seen that when the incident angle is 45 degrees, the normalized displacement response of the structure is the best.

[0119] After determining the operating frequency and incident angle of the ultrasonic transducer, the geometric structure, material and size of the transducer also have a great influence on the performance of the piezoelectric ultrasonic transducer. The geometric dimensions of the ultrasonic transducer wedge base 2 and the rear cover are related to the resonant frequency of the ultrasonic transducer. According to the set operating frequency of 20kHz, the size of the piezoelectric ceramic sheet 5 is first designed, and then the geometric dimension constraint relationship of the ultrasonic transducer rear cover is established, that is, the frequency equation. The size of the rear cover is designed according to this equation. For the wedge-shaped base, this paper uses the Morris sensitivity analysis method to find the key parameters (height, groove depth and length, etc.) that have a greater impact on the characteristics of the piezoelectric ultrasonic transducer. The finite element method is used to establish the influence of the geometric parameters of the wedge-shaped front cover and the amplitude ratio of the two end faces. With the maximization of the amplitude ratio of the front face and the rear face as the objective function, the key parameters that have a greater impact on the characteristics of the ultrasonic transducer are found. The values ​​of each parameter are shown in Table 1:

[0120] Table 1

[0121]

[0122] For different combinations of geometric parameters, the finite element model was used to perform numerical simulations on hundreds of combinations. The numerical simulation results were statistically analyzed. The sensitivity analysis results of the output parameters on the structural parameters of the ultrasonic transducer showed that the order of amplitude ratio sensitivity was L2>dh>W>H and each parameter was above μ=σ, indicating that the structural parameters were coupled with each other. For the amplitude ratio of the front and rear end faces, there was a strong coupling between the lengths L2, W, and dh of the wedge-shaped base 2, and it was also shown that the length of the wedge-shaped transducer base was the main factor determining the amplitude ratio. As for the transducer mass, the influence of the size factor was W>h>dh>L2, and at this time, each factor was below μ=σ, which means that each factor was independent of each other, and there was a linear relationship between the change in the mass of the structure and the size parameter. The characteristic frequency sensitivity order of the ultrasonic transducer is H>W>dh>L2, so changing the height of the wedge-shaped base 2 has a greater effect on the impedance value of the wedge-shaped transducer, and H, W, and L2 are above μ=σ, while dh is below μ=σ, indicating that dh is linearly related to the impedance change of the ultrasonic transducer, and the three parameters H, W, and L2 are coupled with each other.

[0123] From the sensitivity results, it can be seen that the height of the wedge-shaped base 2 has a great influence on the characteristic frequency, while the influence on the amplitude ratio of the front and rear end faces is relatively small. Therefore, we can first consider adjusting the height H of the front cover plate to meet the characteristic frequency design. The length L2 of the wedge-shaped base 2, the groove depth dh and the width W all have a great influence on the amplitude ratio, and the parameters influence each other. The length L2 parameter has a low sensitivity to the characteristic frequency and has almost no effect on the characteristic frequency of the ultrasonic transducer. The parameter dh is linearly related to the characteristic frequency. Therefore, we first consider determining the characteristic frequency by controlling the H and W factors. When the height H and width W are determined, we should avoid adjusting these two parameters again. Finally, adjust the L2 and dh parameters to control the optimal amplitude ratio of the structure output.

[0124] Then the material and size parameters of a set of transducers obtained according to the above steps are as follows:

[0125] The structure of the wedge-shaped composite piezoelectric ultrasonic transducer is as follows: Figure 8As shown, it is mainly composed of a rear cover plate, an electrode sheet 6, an insulating tube 4, a piezoelectric ceramic, a screw 3, and a wedge-shaped front cover plate. Several piezoelectric ceramic sheets 5 in the center of the transducer are stacked in a mechanical series and circuit parallel manner to form a ceramic crystal pile. A layer of electrode sheet 6 is usually placed between each adjacent piezoelectric ceramic sheet 5 and between the piezoelectric ceramic sheet 5 and the front and rear metal plates to apply positive and negative metal electrodes, and the material is usually a copper sheet. In addition, the polarization directions of the two adjacent ceramic sheets are opposite, so that the longitudinal vibrations of each chip can be superimposed in phase, ensuring that the piezoelectric crystal stack can vibrate in a coordinated manner, and the number of piezoelectric ceramic sheets 5 is generally an even number, so that the front cover and the rear cover can be connected to the same polarity electrode. In order to eliminate the existence of air gaps and improve the transmission effect of the ultrasonic wave generated by the piezoelectric sheet inside the transducer, the ultrasonic transducer is tightened by a screw 3 from the top of the back cover. The ultrasonic transducer of the above design is composed of an aluminum wedge-shaped base 2, a piezoelectric ceramic sheet 5 and a steel back cover. The angle of the wedge-shaped base 2 is 45 degrees. The piezoelectric ceramic sheet 5 is pressed between the back cover and the base and fixed by a screw 3 with an insulating tube 4. The back cover is made of stainless steel, and the length L1 of the back cover is 40mm; the piezoelectric ceramic sheet 5 is made of PZT-8, and the outer diameter D of the piezoelectric ceramic sheet 5 is 50mm, the inner diameter is 18mm, and the thickness L c The wedge-shaped base 2 is made of aluminum alloy, the length L2 is 85mm, the width W and the height H are both 50mm, and the groove depth dh is 9m.

[0126] After completing the selection of various parameters and materials of the ultrasonic transducer, press Figure 8 The ultrasonic transducer is made according to the structure diagram shown in the figure. The combination of the transducer made with this set of parameters and the DN32 pipe is subjected to vibration test. The telemetry system generates a periodic chirp signal (15kHz-25kHz) with a certain bandwidth. The displacement distribution results of the ultrasonic transducer are shown in Fig. 9 The results show that 19.995kHz is the resonance frequency of the ultrasonic transducer and the pipeline combination, and the peak value of the surface displacement reaches 3.4×10 -10 m, which meets the design requirements and verifies the accuracy of the numerical simulation.

[0127] 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 principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for designing an ultrasonic guided wave transducer for active corrosion protection of metal pipe surfaces, characterized in that the steps include: S1: Use finite element numerical simulation to determine the mode and frequency of the ultrasonic guided wave that needs to be excited, use the semi-analytical finite element method to calculate the dispersion curve of the ultrasonic guided wave propagating in the pipeline, and find the specific mode that needs to be excited through the dispersion curve; S2: Establish an ultrasonic guided wave transducer model and perform sensitivity tests on the parameters using the Morris trajectory model to obtain the structural parameters that have a greater impact on the characteristics of the ultrasonic guided wave transducer; S3: Simulate different situations of structural parameters with greater influence and design and manufacture the transducer to obtain appropriate transducer parameters.

2. The method for designing an ultrasonic guided wave transducer for active corrosion protection of metal pipe surfaces according to claim 1, characterized in that: The method of calculating the dispersion curve of ultrasonic guided waves propagating in the pipeline by using the semi-analytical finite element method in step S1 is: In a pipeline, the displacement field of ultrasonic guided waves is usually expressed in the form of waves: u(r,θ,z,t)=U(r,θ)e i(kz-ω) ; Where u(r,θ,z,t) is the displacement vector, which depends on the radius r, the angle θ, the axial coordinate z and the time t; U(r,θ) is the displacement component on the pipe cross section; k is the wave number, ω is the angular frequency, and i is the imaginary unit; For the elastic body in the pipe, the governing equation is: Where σ is the stress tensor, ρ is the material density, u is the displacement vector, is the gradient operator; The relationship between stress and strain is given by the constitutive relationship of linear elastic materials: σ=C·ε; Where C is the elastic stiffness matrix of the material and ε is the strain tensor, which is calculated from the displacement gradient: in, is a symmetric gradient operator; The displacement field is discretized using the finite element method on the pipe cross section and approximated as a combination of finite element basis functions: U(r,θ)≈∑ j N j (r,θ)U j ; Among them, N j (r,θ) is the finite element basis function on the cross section, U j is the displacement vector at the discrete node; Substituting the displacement field and strain field into the governing equation and using the finite element method to discretize the cross section, we obtain the finite element form of the wave equation: Where M is the mass matrix, K is the stiffness matrix, and U is the discrete nodal displacement vector matrix; for ultrasonic guided wave problems, the displacement field is assumed to be in the harmonic form e i(kz-) , which is substituted into the wave equation to obtain; (-ω 2 M+K)U=0; The corresponding relationship between wave number k and frequency ω is converted into an eigenvalue problem. For a given wave number k, the angular frequency ω is obtained by solving the eigenvalue problem. The expression of the eigenvalue problem is: (K(k)-ω 2 M)U=0; The solution ω(k) of the eigenvalue problem corresponds to the dispersion relation. By changing the value of the wave number k and repeatedly solving the eigenvalue problem, a series of corresponding frequencies ω are obtained. The relationship curve between k and ω is plotted to obtain the dispersion curve.

3. The method for designing an ultrasonic guided wave transducer for active corrosion protection of metal pipe surfaces according to claim 2, characterized in that: The ultrasonic guided wave transducer in step S2 comprises a transducer module (1), a wedge-shaped base (2) is arranged on the lower side of the transducer module (1), the transducer module (1) comprises an outer shell, a screw (3) is arranged in the outer shell, one end of the screw (3) is fixedly connected to the inner side of the outer shell, and the other end of the screw (3) is connected to the wedge-shaped base (2), an insulating tube (4) is arranged on the outer side of the screw (3), at least one piezoelectric ceramic sheet (5) is mounted on the insulating tube (4), and electrode sheets (6) are arranged between adjacent piezoelectric ceramic sheets (5) and between the piezoelectric ceramic sheets (5) and the outer shell.

4. The method for designing an ultrasonic guided wave transducer for active corrosion protection of metal pipe surfaces according to claim 3 is characterized in that: The polarization directions of the adjacent piezoelectric ceramic sheets (5) are opposite, and the number of the piezoelectric ceramic sheets (5) is an even number.

5. The method for designing an ultrasonic guided wave transducer for active corrosion protection of metal pipe surfaces according to claim 4, characterized in that: The lower side of the wedge-shaped base (2) is provided with a notch, and the groove surface of the notch is an arc-shaped groove surface.

6. The method for designing an ultrasonic guided wave transducer for active corrosion protection of metal pipe surfaces according to any one of claims 3 to 5, characterized in that: The wedge-shaped base (2) is a wedge-shaped base with an inclined surface at the top, and the outer shell is arranged on the upper side of the inclined surface.

7. The method for designing an ultrasonic guided wave transducer for active corrosion protection of metal pipe surfaces according to claim 6, characterized in that: The method for performing sensitivity testing on the parameters of the Morris trajectory model described in step S2 is: The ultrasonic guided wave transducer is modeled. Assume that there are m independent input parameters in the ultrasonic guided wave transducer model and n key characteristics are output parameters. If only the i-th input parameter is allowed to increase with a fixed step size, and the other input parameter values ​​remain unchanged, the response value y of the output parameter is obtained. Then, when the x input parameter increases with a fixed step size Δ i Basic factors under change EE i Defined as: Morris trajectory sampling is used to establish p tracks in the input variables. Each track has n+1 sampling points, so a total of (n+1)p sampling points need to be calculated. For each input variable x i For the output variable y i The influence degree is taken as the mean value μ i and variance σ i Perform statistical analysis; for p tracks, the mean μ i and variance σ i They are: in, is the basic factor of the i-th input variable in the j-th track; Since the input variables may have a negative correlation with the output variables, in order to avoid i When the calculated value is negative, the mean μ is weakened by the mutual cancellation of the terms in the summation operation. i Calculation results show that Campolongo redefined μ i The calculation formula is: The mean μ i and variance σ i It is called the sensitivity factor. The sensitivity factor is used to evaluate the importance of the input variable on the output variable. It is found that the groove depth and the slope angle of the wedge-shaped base 2 are the structural parameters that have a greater impact on the characteristics of the ultrasonic guided wave transducer.

8. The method for designing an ultrasonic guided wave transducer for active corrosion protection of metal pipe surfaces according to claim 7, characterized in that: The specific method of using Morris trajectory sampling to establish p tracks in the input variables is: First, an initial point is selected in the input variable space, and one of the input variables is increased or decreased with a fixed step size to obtain the second sample point. Based on the second sample point, another input variable value is increased or decreased with a fixed step size to obtain the third sample point. This is repeated, and all input parameters in the input variable space are changed once to obtain a trajectory.

9. The method for designing an ultrasonic guided wave transducer for active corrosion protection of metal pipe surfaces according to claim 8, characterized in that: The method of evaluating the importance of the input variable on the output variable by using the sensitivity factor is: if the mean μ is calculated i If it is small, the input parameter has no significant impact on the output parameter; If μ i is larger, and σ i When it is small, it means that the input parameter has a great influence on the output parameter, but the input parameter is linearly related to the output parameter, and the coupling with other input parameters is small; If μ i Larger, while σ i When it is large, it means that the input parameter has a great influence on the output parameter, but the input parameter has a nonlinear relationship with the output parameter and is highly coupled with other input parameters.

10. The method for designing an ultrasonic guided wave transducer for active corrosion protection of metal pipeline surfaces according to claim 9, characterized in that: The method for simulating different situations of structural parameters having a greater impact and designing and manufacturing the transducer is: Taking the maximum displacement response of the contact surface between the ultrasonic transducer and the pipeline as the design goal, and the ultrasonic guided wave transducer meeting the set operating frequency, minimum impedance, and minimum amplitude ratio of the front and rear cover plates as constraints, the most suitable set of structural parameters is obtained and the transducer is designed and manufactured.

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