Surface anti-corrosion guided wave mode selection method for metal structure coated with coating based on marine atmospheric environment

Abstract

The invention provides a method for selecting an anti-corrosion guided wave mode on the surface of a metal structure coated with a coating in a marine atmospheric environment. The method comprises the following steps: S1, constructing a metal pipeline outer wall coating material and an external environment factor model; s2, constructing a metal pipeline model in the metal pipeline outer wall coating material and the external environment factor model, and selecting an ultrasonic excitation mode; and S3, carrying out vibration test on the metal pipeline by utilizing the selected ultrasonic excitation mode. According to the invention, the frequency dispersion phenomenon is controlled by selecting a proper mode, so that the distortion of the waveform in the propagation process is reduced. And meanwhile, the guided wave energy transmission distance is increased, and the method is particularly beneficial to long-distance pipeline detection and anti-corrosion effects. In addition, energy can be better concentrated through a proper mode, so that sound waves can be effectively spread in a farther distance and are not prone to being absorbed or scattered by materials.

Description

Technical Field

[0001] The invention relates to the technical field of corrosion prevention, and in particular to a method for selecting a guided wave mode for corrosion prevention on the surface of a metal structure. Background Art

[0002] The corrosion protection of large equipment in the marine atmosphere is a thorny problem that needs to be solved in many fields. Many scholars at home and abroad have conducted long-term research on this. At present, the corrosion protection technologies for metal structures in the marine atmosphere mainly include paint corrosion protection, metal coating corrosion protection, electrochemical corrosion protection, coating material corrosion protection, ultrasonic technology assisted corrosion protection, etc., but they all have certain limitations. At present, paint or coating methods are generally used in the field of marine atmospheric corrosion protection. In the marine atmosphere environment with strong ultraviolet radiation, due to the synergistic effect of ultraviolet radiation or ultraviolet radiation and other factors, the aging and damage of paint and coating will occur. In the above-mentioned marine atmospheric environment, the corrosion resistance of the composite organic coating is significantly reduced, and ultraviolet rays have a significant promoting effect on salt spray corrosion of metal structures. Compared with traditional ultrasonic waves, ultrasonic guided waves have the advantages of longer propagation distance and wider coverage. Active physical protection of metal structures by ultrasonic guided waves can make up for the shortcomings of existing anti-corrosion technology.

[0003] Due to the complex cross-sectional morphology of large metal structures, the propagation law of ultrasonic guided waves in the outer wall of the structure is relatively complex; in addition, parameters such as temperature, humidity, salt spray concentration, and radiation intensity in the marine atmosphere will also affect the propagation process of ultrasonic guided waves. Therefore, revealing the propagation law of ultrasonic guided waves in the outer wall of large metal structures in marine environments is the core scientific problem that must be solved first. The solution to this scientific problem can guide the establishment of a large metal structure surface protection process model based on ultrasonic guided waves, and improve the protection range and effectiveness of this technology.

[0004] The vibration and shear effects of ultrasonic guided waves during propagation on the outer wall of metal structures can effectively prevent salt spray particles in the air from adhering to the surface of metal structures. The key to how to give full play to the advantages of ultrasonic guided waves in long action distance and ensure its protective effect without damaging the outer wall of metal structures and their coatings is to study how to select reasonable ultrasonic guided wave modes, frequencies, power and other parameters, while considering the characteristics of the coating material on the outer wall of the metal structure, temperature, humidity, salt spray concentration, radiation intensity and droplet pH value. How many factors affect the protection process. The establishment of this model is directly related to the actual effect of physical protection technology for the surface of large metal structures based on ultrasonic guided waves. Summary of the invention

[0005] In order to solve the technical problem that the corrosion resistance of composite organic coatings in marine atmospheric environment is significantly reduced, the present invention proposes a method for selecting anti-corrosion guided wave modes on the surface of metal structures coated with coatings in marine atmospheric environment, and selects F mode as the appropriate mode, which has significant anti-corrosion effect on long-distance pipelines.

[0006] In order to achieve the above object, the technical solution of the present invention is implemented as follows: a method for selecting guided wave modes for anti-corrosion of the surface of a metal structure coated with a coating in a marine atmospheric environment, characterized in that the steps include:

[0007] S1: Construct the model of metal pipeline outer wall coating materials and external environmental factors;

[0008] S2: constructing a metal pipeline model within the metal pipeline outer wall coating material and external environmental factor model, obtaining a metal pipeline outer wall coating material and external environmental factor model including the metal pipeline, and selecting an ultrasonic excitation mode;

[0009] S3: Perform vibration test on metal pipe using selected ultrasonic excitation mode.

[0010] The method for constructing the metal pipeline outer wall coating material and external environmental factor model in step S1 is:

[0011] The metal pipe outer wall coating material and external environmental factor model includes a metal pipe. The outer wall coating material is evenly arranged on the outside of the metal pipe. Salt spray particles exist in the air domain outside the outer wall coating material. An ultrasonic guided wave transducer is attached to the metal pipe. Ultrasonic guided waves of different frequencies are obtained by adding sinusoidal signals of different frequencies to the ultrasonic guided wave transducer.

[0012] The outer wall coating material properties in step S1 include material density, Young's modulus and Poisson's ratio;

[0013] The external environment described in step S1 includes ambient temperature, humidity, salt spray concentration, radiation intensity and pH value. The temperature, humidity and radiation intensity are directly set through the parameters of the air domain, and the salt spray concentration and pH value are controlled by the number of salt spray particles and the salt spray pH in the unit space, respectively.

[0014] The method for constructing the metal pipeline model in step S2 is:

[0015] The metal pipe model is set as a hollow pipe model. Under the boundary conditions of the hollow pipe, the hollow pipe belongs to an isotropic elastic medium. According to the elasticity theory, the Navier wave motion equation for the isotropic elastic medium is expressed as:

[0016]

[0017] Among them, λ and μ are Lamé constants, which are related to the properties of metal pipes. is the displacement vector, is the three-dimensional Laplace operator, ρ is the density of the isotropic elastic medium, and t represents time;

[0018] The displacement vector Using Helmholtz decomposition, it is expressed as the gradient of the scalar potential function and the curl of the zero-divergence vector potential function:

[0019]

[0020] Where Φ is the scalar potential function, is the zero divergence vector;

[0021] The gradient of the scalar potential function and the curl of the zero-scatter vector potential function are decomposed into the gradient of the scalar potential function Φ and the zero-scatter vector The wave equation expressed is:

[0022]

[0023] In the formula, c l represents the longitudinal wave velocity, c s Expressed as shear wave velocity;

[0024] Based on elasticity theory, the divergence vector And the scalar potential function Φ has the following form in the cylindrical coordinate system:

[0025]

[0026] Among them, z represents the pipeline axial direction, r' represents the pipeline radial direction, and θ represents the pipeline circumferential direction;

[0027] Laplace operator in cylindrical coordinates And the divergence vector is expressed as:

[0028]

[0029]

[0030] in, is the radial unit direction vector, is the unit direction vector in the circumferential direction, is the unit direction vector of the axial direction;

[0031] Let the potential function group be:

[0032]

[0033] Where f(r) is the function of the scalar potential function Φ changing in the radial direction; t is time; ξ is the wave number; H r’ is the radial divergence vector potential function; H θ is the circumferential divergence vector potential function; H z is the axial divergence vector potential function; g r’ (r) is the zero divergence vector potential function H r’ Function of the change in radial direction; g θ (r) is the zero divergence vector potential function H θ Function of the change in the circumferential direction; g z (r) is the zero divergence vector potential function H z The angular frequency of the function varying in the axial direction;

[0034] The particle displacement component is obtained by conversion:

[0035]

[0036] Among them, the circumferential order n is 0, 1, 2, 3..., u r’ represents the radial displacement component, u θ represents the circumferential displacement component, u z It represents the axial displacement component, U r’ (r), U θ (r), U z (r) represents the displacement amplitude formed by the Bessel functions in the pipeline axial direction, pipeline radial direction and pipeline circumferential direction respectively, and k is an arbitrary constant;

[0037] According to the relationship between strain-displacement and stress-strain, the solution of the stress field is:

[0038]

[0039] Substituting the boundary conditions into the strain-displacement and stress-strain relationships, the solution to the stress field is obtained:

[0040] [c ij ] 6×6 [ABA1B1A2B2] T =[0 0 0 0 0 0] T ;

[0041] Among them, A, B, A1, B1, A2, B2 are parameter coefficients;

[0042] If the equation has a non-zero solution, then its coefficient determinant should be zero:

[0043] |c ij |=0;

[0044] Where i,j=1,2,3,4,5,6,c ij is the Bessel function;

[0045] If n = 0, it is an axisymmetric mode, and the dispersion equation can be decomposed into:

[0046] D = D1·D2 = 0;

[0047] In the formula

[0048]

[0049] Wherein, the solution of D1=0 is the L mode of the guided wave, and the solution of D2=0 is the T mode of the guided wave.

[0050] The boundary conditions are:

[0051] In the hollow pipe model, a is the inner radius, b is the outer radius, the pipe length is infinite, and the boundary conditions of the hollow pipe are:

[0052] σ r’r’ =σ r’θ =σ r’z =0;

[0053] Where r′=a,r ′ =b,σ r’r’ is the radial stress displacement, σ r’θ is the circumferential stress displacement, σ r’z is the axial stress displacement.

[0054] When the longitudinal wave propagates in a solid, the longitudinal wave velocity c l for:

[0055]

[0056] Shear wave velocity c s for:

[0057]

[0058] Where v is Poisson's ratio and E is the elastic modulus.

[0059] The method for selecting the ultrasonic excitation mode in step S2 is:

[0060] S21: Selecting the F mode as the ultrasonic excitation mode according to the ultrasonic waveguide characteristics;

[0061] S22: Simulate and calculate the stress distribution on the metal pipe surface under F modes of different frequencies, select the F mode of appropriate frequency as the excitation frequency of the ultrasonic guided wave transducer, and obtain the ultrasonic excitation mode.

[0062] The method for selecting the F mode as the ultrasonic excitation mode is:

[0063] According to the characteristics of F mode propagation in thin-walled structures and the wave mode being similar to the vibration of a bending beam, the F mode is selected as the excitation mode of the guided wave to apply stress to the wall of the metal structure.

[0064] The method of selecting the F mode with a suitable frequency as the excitation frequency of the ultrasonic guided wave transducer is:

[0065] The Pcdisp software is used to simulate the metal pipe outer wall coating material and external environmental factor model containing the metal pipe. The frequency with the largest stress response on the surface of the metal pipe model is selected as the excitation frequency of the ultrasonic guided wave transducer of the F mode to obtain the ultrasonic excitation mode.

[0066] The method for performing vibration testing on a metal pipe using a selected ultrasonic excitation mode is as follows:

[0067] Experiments were conducted in actual environments. An ultrasonic guided wave transducer was attached to a metal pipe. Different excitation frequencies were used as variables. The vibration displacement of the F mode of the metal pipe at different frequencies was tested by a vibration tester to verify whether the excitation frequency corresponding to the ultrasonic excitation mode produced the maximum vibration displacement on the pipe surface.

[0068] The beneficial effects of the present invention are as follows: the present invention effectively improves the control of the dispersion phenomenon. By selecting the F mode as the appropriate mode, the dispersion phenomenon can be controlled, thereby reducing the distortion of the waveform during the propagation process. At the same time, the selection of the low-frequency mode such as the F mode can realize long-distance sound wave propagation and increase the transmission distance of the guided wave energy, which is particularly beneficial for long-distance pipeline detection and anti-corrosion effects. In addition, the F mode can better concentrate energy, so that the sound waves can be effectively propagated at a longer distance and are not easily absorbed or scattered by the material. The present invention has a wide range of application scenarios and is adaptable to different environments and complex structures. For the characteristics of different metal materials with coatings, different guided wave modes have different sensitivities to materials and structures. Selecting the appropriate mode can more effectively increase the anti-corrosion effect, which lays a good foundation for the research on physical protection technology of large-scale metal structures with nonlinear influencing factors, complex metal structure, and diversified outer wall protective coatings in marine atmospheric environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] 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.

[0070] Figure 1 Create schematic diagrams for multi-factor finite element models.

[0071] Figure 2 This is a schematic diagram of the hollow pipe model.

[0072] Figure 3 The waveguide modes of tubular metal structures vary with diameter. (a) is the group velocity of a 25 mm tubular structure; (b) is the group velocity of a 32 mm tubular structure; (c) is the group velocity of a 50 mm tubular structure; (d) is the phase velocity of a 25 mm tubular structure; (e) is the phase velocity of a 32 mm tubular structure; and (f) is the phase velocity of a 50 mm tubular structure.

[0073] Figure 4 Schematic diagram of ultrasonic guided wave stress on the surface of metal structures. (a) is a schematic diagram of ultrasonic guided wave stress on the surface of plate-like metal structures; (b) is a schematic diagram of ultrasonic guided wave stress on the surface of tubular metal structures.

[0074] Figure 5 The stress distribution of the metal pipe surface under different frequency F modes. (a) is the stress distribution of 30KHz F mode; (b) is the stress distribution of 35KHz F mode; (c) is the stress distribution of 40KHz F mode; (d) is the stress distribution of 45KHz F mode.

[0075] Figure 6 This is a graph of vibration test results. DETAILED DESCRIPTION

[0076] 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.

[0077] like Figure 1 As shown, a method for selecting guided wave modes for anti-corrosion of a metal structure surface coated with a coating in a marine atmosphere environment comprises the following steps:

[0078] S1: Construct a model of metal pipe outer wall coating materials and external environmental factors.

[0079] The metal pipe outer wall coating material and external environmental factor model includes a metal pipe. The outer wall coating material is evenly arranged on the outside of the metal pipe. Salt spray particles exist in the air domain outside the outer wall coating material. An ultrasonic guided wave transducer is attached to the metal pipe. Ultrasonic guided waves of different frequencies are obtained by adding sinusoidal signals of different frequencies to the ultrasonic guided wave transducer.

[0080] Specifically, for an ideal tubular structure, the waveguide output by the ultrasonic guided wave transducer propagates along the axial direction of the tubular structure, and the waveguide cross section is located in the r-θ plane. The semi-analytical finite element solution method requires discretization along the waveguide cross section, and finite element simulation is used to simulate and model the external environment of the metal pipe, taking into account the characteristics of the outer wall coating material of the metal pipe body and the external environment of the metal pipe. The external environment of the metal pipe includes ambient temperature, humidity, salt spray concentration, radiation intensity and pH value.

[0081] like Figure 1 As shown in the figure, the external environment of the metal pipe is set as the air domain, and there are salt spray particles in the air domain. A 304 steel pipe is used as the metal pipe, and the outer layer of the metal pipe is coated with an outer wall coating. The ultrasonic guided wave transducer is attached to the metal pipe, and ultrasonic guided waves of different frequencies are obtained by attaching sinusoidal signals of different frequencies to the transducer. The outer wall coating material of the metal pipe is evenly distributed on the outside of the metal pipe, and the properties of the outer wall coating material itself are set by material density, Young's modulus and Poisson's ratio. In the external environment, temperature, humidity and radiation intensity are directly set by the parameters of the air domain, and the salt spray concentration and pH value are controlled by the number of salt spray particles and salt spray pH in the unit space.

[0082] By performing finite element simulation on the changes of external environmental factors, such as Figure 4 As shown. The finite element method is used to simulate and calculate the different stresses on the metal pipes caused by salt spray particles attached to them under different influencing factors. Based on this, the transducer excitation guided wave mode is selected, and the change of the main mode is affected by the different excitation frequencies, thereby affecting the stress applied to the pipe wall.

[0083] S2: Construct a metal pipe model within the metal pipe outer wall coating material and external environmental factor model, and select the bending mode as the ultrasonic excitation mode.

[0084] Taking a hollow steel pipe as an example, in order to make ultrasonic guided waves propagate in the outer wall of the metal structure and produce vibration and shear effects along the surface, the mechanism of ultrasonic guided wave modes was analyzed.

[0085] like Figure 2 As shown in the figure, in the hollow pipe model, a is the inner radius, b is the outer radius, and the pipe length is infinite. z represents the pipe axial direction, r' represents the pipe radial direction, θ represents the pipe circumferential direction, and the boundary conditions of the hollow pipe are:

[0086] σ r’r’ =σ r’θ =σ r’z =0(r'=a,r'=b) (1)

[0087] Among them, σ r’r’ is the radial stress displacement, σ r’θ is the circumferential stress displacement, σr’z is the axial stress displacement.

[0088] Under the boundary conditions of the hollow pipe, the hollow pipe belongs to an isotropic elastic medium. According to the elasticity theory, the Navier wave motion equation for the isotropic elastic medium can be expressed as:

[0089]

[0090] Among them, λ and μ are Lamé constants, which are related to the properties of metal pipes. is the displacement vector, is the three-dimensional Laplace operator, ρ is the density of the isotropic elastic medium, and t represents time.

[0091] The displacement vector Using Helmholtz decomposition, it is expressed as the gradient of the scalar potential function and the curl of the zero-divergence vector potential function:

[0092]

[0093] Where Φ is the scalar potential function, is a zero divergence vector.

[0094] Decompose equation (3) into the scalar potential function Φ and the zero-scatter vector The wave equation expressed is:

[0095]

[0096]

[0097] In the formula, c l represents the longitudinal wave velocity, c s When a longitudinal wave propagates in a solid, the longitudinal wave velocity c l for:

[0098]

[0099] Shear wave velocity c s for:

[0100]

[0101] Among them, λ and μ are Lamé constants, ρ is the metal pipe density, v is Poisson's ratio, and E is the elastic modulus. It is worth noting that the Lamé constant and the metal pipe density in equation (7) determine the transverse wave velocity and longitudinal wave velocity in the material, c L represents the longitudinal wave velocity, c Tis the velocity of the shear wave. When the displacement vector is decomposed by Helmholtz, the material properties of the metal pipe satisfy isotropy, which means that the Lamé constant λ, Lamé constant μ and medium density ρ in the material properties of the metal pipe are the same regardless of any direction.

[0102] Based on elasticity theory, the potential function and φ have the following forms in cylindrical coordinates:

[0103]

[0104] Among them, the Laplace operator in cylindrical coordinates is It is expressed as:

[0105]

[0106]

[0107]

[0108] in, is the radial unit direction vector, is the unit direction vector in the circumferential direction, is the unit direction vector of the axial direction;

[0109] Assume the potential function is as follows:

[0110]

[0111] Where φ is the scalar potential function; f(r) is the function that describes the change of the potential function Φ in the radial direction; t is the time; ξ is the wave number, which indicates the rate of change of the wave in space; H r’ is the radial divergence vector potential function; H θ is the circumferential divergence vector potential function; H z is the axial divergence vector potential function; g r’ (r) is the radial divergence vector potential function H r’ Function of the change in radial direction; g θ (r) is the circumferential zero divergence vector potential function H θ Function of the change in the circumferential direction; g z (r) is the vector potential function H describing the zero divergence z The angular frequency of a function of the change in the axial direction represents the time rate of change of the fluctuation.

[0112] Substitute equation (9) and equation (12) into equation (4), and substitute equations (11) to (12) into equation (5), and we get:

[0113]

[0114] The particle displacement components can be expressed as:

[0115]

[0116] Among them, the circumferential order n is 0, 1, 2, 3..., u r’ represents the radial displacement component, u θ represents the circumferential displacement component, u z It represents the axial displacement component, U r’ (r), U θ (r), U z (r) represents the displacement amplitude constructed according to the Bessel function, and k is an arbitrary constant.

[0117] According to the relationship between strain-displacement and stress-strain, the solution of the stress field is:

[0118]

[0119] Substituting the boundary conditions into the above formula, we can calculate:

[0120] [c ij ] 6×6 [AB A1B1A2B2] T =[000000] T (16)

[0121] Among them, A, B, A1, B1, A2, and B2 are parameter coefficients.

[0122] If the equation has a non-zero solution, then its coefficient determinant should be zero:

[0123] |c ij |=0; (i,j=1,2,3,4,5,6) (17)

[0124] Among them, c ij (i,j∈{1,2,3,4,5,6}) is the Bessel function. The above equation is the dispersion equation of longitudinal guided waves in a hollow circular tube. If n=0, it is an axisymmetric mode, and the dispersion equation can be decomposed into the product form of several sub-determinants:

[0125] D=D1·D2=0 (18)

[0126] Where:

[0127]

[0128] Wherein, the solution of D1=0 is the longitudinal mode of the guided wave, and the solution of D2=0 is the torsional mode of the guided wave.

[0129] Ultrasonic guided waves include bending mode (F mode), torsional mode (T mode) and longitudinal mode (L mode). The F mode is a bending wave that usually propagates in thin-walled structures, and the wave pattern is similar to the vibration of a bent beam. The T mode is a sound wave in the thickness direction, which usually propagates in thick-walled structures and appears as a compression wave perpendicular to the surface of the material. The L mode is a longitudinal sound wave, and the wave direction is consistent with the propagation direction, which is suitable for propagation in long straight structures. According to the three modal characteristics of ultrasonic guided waves, the F mode is selected as the excitation mode of the guided wave to apply stress to the wall of the metal structure, thereby delaying the attachment of salt spray particles to the surface of the metal structure. The schematic diagram is shown in the figure. Figure 3 shown.

[0130] By selecting the F mode as the appropriate mode, the dispersion phenomenon can be controlled, thereby reducing the distortion of the waveform during propagation. At the same time, the selection of the low-frequency mode of the F mode can achieve long-distance sound wave propagation and increase the transmission distance of the guided wave energy, which is particularly beneficial for long-distance pipeline detection and anti-corrosion effects. In addition, the F mode can better concentrate energy, so that the sound wave can be effectively propagated over a longer distance and is not easily absorbed or scattered by the material.

[0131] Calculate the dispersion curve of the model. The model calculation frequency range is 20-70kHz with a step size of f max / 200, the group velocity range is 0-6000m / s, and the positive wave number k is extracted by calculating the motion equation at different frequencies w The wave finite element method is used to calculate the group velocity dispersion curves of the longitudinal mode and the first-order bending mode in the hollow pipe, such as Figure 4 (b) is shown in the circle. The analytical solution model calculation results obtained using Pcdisp software are shown in Figure 4 As shown in (b), the analytical solution calculation results of each mode at different frequencies and the wave finite element calculation results are extracted as shown in Table 1. The maximum error is the L(0,2) mode under the condition of 60kHz frequency, the absolute error is 24m / s, and the relative error is 1.3%, which meets the calculation accuracy requirements.

[0132] Table 1 Calculation results of guided wave group velocity in hollow tube L(0,1) mode and F(1,1) mode

[0133]

[0134] The calculated dispersion curves reveal the propagation laws of different modes in the tubular metal structure. Figure 3 It can be seen that in the range of 0-100kHz, the ultrasonic guided wave propagation modes include longitudinal mode, bending mode and torsional mode. As the diameter of the tubular structure increases: the number of propagation modes in the lower frequency range increases (20kHz-40kHz); under the same wall thickness conditions, the larger the diameter of the tubular structure, the lower the frequency can be used to excite F modes of different vibration forms.

[0135] In order to select the appropriate frequency F mode as the excitation frequency of the ultrasonic guided wave transducer, a symmetrical ultrasonic guided wave transducer group is used as the input end, and the metal pipe outer wall coating material and external environmental factor model containing the metal pipe model are used to simulate and test the stress distribution on the metal pipe surface under different frequency F modes. Figure 5 As shown, under different excitation frequencies, it can be seen that the surface stress response of the 30kHz structure is the largest, while the surface stress distribution is uniform under 35 and 40kHz excitations. The 30kHz structure with the largest surface stress response is selected as the excitation frequency.

[0136] S3: Vibration testing of metal pipes using ultrasonic excitation modes.

[0137] After the finite element model is established and the mode is selected, the ultrasonic guided wave transducer is attached to the metal pipe. Using different excitation frequencies as variables, the vibration displacement of the structure at different frequencies is tested by a vibration tester. The vibration test results are as follows: Figure 6 As shown. Figure 6 It can be seen that the ultrasonic guided wave excited by the selected guided wave mode has the largest vibration displacement on the pipeline surface in the vibration test. This means that the application of guided waves under this frequency mode to the anti-corrosion of metal structures has the best effect (the principle is that the shear force (i.e. vibration) generated by the metal structure during the propagation of ultrasonic guided waves affects the adhesion of salt spray particles in the air). Figure 6 It can be seen that the stress response on the surface of the structure is the largest when the frequency is around 30kHz, which confirms the simulation results.

[0138] 30kHz is used as the excitation frequency of the waveguide and the dispersion curve is observed. It can be concluded that at the excitation frequency of 30kHz, the main mode of the waveguide is the F(1,1) mode. In summary, the mode of the waveguide F(1,1) is selected as the main excitation mode to exert an anti-corrosion effect on the metal structure.

[0139] The present invention lays a good foundation for the research on physical protection technology of large-scale metal structures with nonlinear influencing factors, complex metal structure and diversified outer wall protective coatings under the marine atmospheric environment. It takes into account the influence of environmental factors and provides guidance for ensuring the protective effect of metal structures in new application scenarios.

[0140] 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 selecting guided wave modes for anti-corrosion of metal structure surfaces coated with coatings in marine atmospheric environment, characterized in that the steps include: S1: Construct the model of metal pipeline outer wall coating materials and external environmental factors; S2: constructing a metal pipeline model within the metal pipeline outer wall coating material and external environmental factor model, obtaining a metal pipeline outer wall coating material and external environmental factor model including the metal pipeline, and selecting an ultrasonic excitation mode; S3: Perform vibration test on metal pipe using selected ultrasonic excitation mode.

2. The method for selecting guided wave modes for anti-corrosion of metal structure surfaces coated with coatings in marine atmosphere environment according to claim 1 is characterized in that: The method for constructing the metal pipeline outer wall coating material and external environmental factor model in step S1 is: The metal pipe outer wall coating material and external environmental factor model includes a metal pipe. The outer wall coating material is evenly arranged on the outside of the metal pipe. Salt spray particles exist in the air domain outside the outer wall coating material. An ultrasonic guided wave transducer is attached to the metal pipe. Ultrasonic guided waves of different frequencies are obtained by adding sinusoidal signals of different frequencies to the ultrasonic guided wave transducer.

3. The method for selecting guided wave modes for anti-corrosion of metal structure surfaces coated with coatings in marine atmosphere environment according to claim 2 is characterized in that: The intrinsic properties of the outer wall coating material in step S1 include material density, Young's modulus and Poisson's ratio; The external environment described in step S1 includes ambient temperature, humidity, salt spray concentration, radiation intensity and pH value. The temperature, humidity and radiation intensity are directly set through the parameters of the air domain, and the salt spray concentration and pH value are controlled by the number of salt spray particles and the salt spray pH in the unit space, respectively.

4. The method for selecting guided wave modes for anti-corrosion of metal structure surfaces coated with coatings in marine atmosphere environment according to claim 2 or 3, characterized in that: The method for constructing the metal pipeline model in step S2 is: The metal pipe model is set as a hollow pipe model. Under the boundary conditions of the hollow pipe, the hollow pipe belongs to an isotropic elastic medium. According to the elasticity theory, the Navier wave motion equation for the isotropic elastic medium is expressed as: Among them, λ and μ are Lamé constants, which are related to the properties of metal pipes. is the displacement vector, is the three-dimensional Laplace operator, ρ is the density of the isotropic elastic medium, and t represents time; The displacement vector Using Helmholtz decomposition, it is expressed as the gradient of the scalar potential function and the curl of the zero-divergence vector potential function: Where Φ is the scalar potential function, is the zero divergence vector; The gradient of the scalar potential function and the curl of the zero-scatter vector potential function are decomposed into the gradient of the scalar potential function Φ and the zero-scatter vector The wave equation expressed is: In the formula, c l represents the longitudinal wave velocity, c s Expressed as shear wave velocity; Based on elasticity theory, the divergence vector And the scalar potential function Φ has the following form in the cylindrical coordinate system: Among them, z represents the pipeline axial direction, r' represents the pipeline radial direction, and θ represents the pipeline circumferential direction; Laplace operator in cylindrical coordinates And the divergence vector is expressed as: in, is the radial unit direction vector, is the unit direction vector in the circumferential direction, is the unit direction vector of the axis; let the potential function group be: Where f(r) is the function of the scalar potential function Φ changing in the radial direction; t is time; ξ is the wave number; H r’ is the radial divergence vector potential function; H θ is the circumferential divergence vector potential function; H z is the axial divergence vector potential function; g r (r) is the zero divergence vector potential function H r’ Function of the change in radial direction; g θ (r) is the zero divergence vector potential function H θ Function of the change in the circumferential direction; g z (r) is the zero divergence vector potential function H z The angular frequency of the function varying in the axial direction; The particle displacement component is obtained by conversion: Among them, the circumferential order n is 0, 1, 2, 3..., u r’ represents the radial displacement component, u θ represents the circumferential displacement component, u z It represents the axial displacement component, U r’ (r), U θ (r), U z (r) represents the displacement amplitude formed by the Bessel functions in the pipeline axial direction, pipeline radial direction and pipeline circumferential direction respectively, and k is an arbitrary constant; According to the relationship between strain-displacement and stress-strain, the solution of the stress field is: Substituting the boundary conditions into the strain-displacement and stress-strain relationships, the solution to the stress field is obtained: [c ij ] 6×6 [ABA1B1A2B2] T =[0 0 0 0 0 0] T ; Among them, A, B, A1, B1, A2, B2 are parameter coefficients; If the equation has a non-zero solution, then its coefficient determinant should be zero: |c ij |＝0； Where i,j=1,2,3,4,5,6,c ij is the Bessel function; If n = 0, it is an axisymmetric mode, and the dispersion equation can be decomposed into: D = D1·D2 = 0; In the formula Wherein, the solution of D1=0 is the L mode of the guided wave, and the solution of D2=0 is the T mode of the guided wave.

5. The method for selecting guided wave modes for anti-corrosion of metal structure surfaces coated with coatings in marine atmosphere environment according to claim 4 is characterized in that: The boundary conditions are: In the hollow pipe model, a is the inner radius, b is the outer radius, the pipe length is infinite, and the boundary conditions of the hollow pipe are: s r’r’ =s r’θ =s r’z =0; Among them, r ′ =a,r ′ =b,σ r’r’ is the radial stress displacement, σ r’θ is the circumferential stress displacement, σ r’z is the axial stress displacement.

6. The method for selecting guided wave modes for anti-corrosion of metal structure surfaces coated with coatings in marine atmosphere environment according to claim 5 is characterized in that: When the longitudinal wave propagates in a solid, the longitudinal wave velocity c l for: Shear wave velocity c s for: Where v is Poisson's ratio and E is the elastic modulus.

7. The method for selecting guided wave modes for anti-corrosion of metal structure surfaces coated with coatings in marine atmosphere environment according to claim 6 is characterized in that: The method for selecting the ultrasonic excitation mode in step S2 is: S21: Selecting the F mode as the ultrasonic excitation mode according to the ultrasonic waveguide characteristics; S22: Simulate and calculate the stress distribution on the metal pipe surface under F modes of different frequencies, select the F mode of appropriate frequency as the excitation frequency of the ultrasonic guided wave transducer, and obtain the ultrasonic excitation mode.

8. The method for selecting guided wave modes for anti-corrosion of metal structure surfaces coated with coatings in marine atmosphere environment according to claim 7 is characterized in that: The method for selecting the F mode as the ultrasonic excitation mode is: According to the characteristics of F mode propagation in thin-walled structures and the wave mode being similar to the vibration of a bending beam, the F mode is selected as the excitation mode of the guided wave to apply stress to the wall of the metal structure.

9. The method for selecting guided wave modes for surface corrosion protection of metal pipe structures coated with coatings in marine atmosphere environment according to claim 8 is characterized in that: The method of selecting the F mode with a suitable frequency as the excitation frequency of the ultrasonic guided wave transducer is: The Pcdisp software is used to simulate the metal pipe outer wall coating material and external environmental factor model containing the metal pipe. The frequency with the largest stress response on the surface of the metal pipe model is selected as the excitation frequency of the ultrasonic guided wave transducer of the F mode to obtain the ultrasonic excitation mode.

10. The method for selecting guided wave modes for anti-corrosion of metal structure surface coated with coating in marine atmosphere environment according to any one of claims 7 to 9, characterized in that: The method for performing vibration testing on a metal pipe using a selected ultrasonic excitation mode is as follows: Experiments were conducted in actual environments. An ultrasonic guided wave transducer was attached to a metal pipe. Different excitation frequencies were used as variables. The vibration displacement of the F mode of the metal pipe at different frequencies was tested using a vibration tester to verify whether the excitation frequency corresponding to the ultrasonic excitation mode produced the maximum vibration displacement on the pipe surface.

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