A method for calculating the interface wave velocity of a semi-submerged solid and a device for measuring the same

Abstract

The present invention relates to a method and device for calculating the interface wave velocity of a semi-submerged solid. The method calculates the solid-liquid interface wave velocity for the semi-submerged solid, combining the Young's modulus, Poisson's ratio, and density of the solid material. This method can not only detect material properties, but also determine the distance between the damage and the ultrasonic probe based on the scattering signal of the interface wave at the damage site, thereby locating the damage. This calculation model is applied to engineering structures such as dams, bridge piers, and gates, meeting their detection needs.

Description

Technical Field

[0001] The invention relates to a method for calculating the interface wave velocity of a semi-submerged solid and a measuring device thereof, belonging to the technical field of non-destructive testing. Background Art

[0002] Ultrasonic waves can be used for nondestructive testing of underwater structures and are widely used in offshore oil exploration and solid defect identification. However, existing analytical models primarily focus on the propagation of interface waves at horizontal solid-liquid interfaces. Structures such as dams, bridge piers, and sluice gates often have vertical solid-liquid interfaces, making it necessary to use ultrasonic waves for nondestructive testing of these structures. Based on this, a method and measurement device for calculating the interface wave velocity of semi-submerged solids are presented. Summary of the Invention

[0003] The present invention provides a method for calculating the interface wave velocity of a semi-submerged solid and a measuring device. By using the interface wave velocity as the basis for non-destructive testing, other relevant data can be calculated and cracks in engineering structures can be located.

[0004] The technical solution adopted by the present invention to solve its technical problem is:

[0005] A method for calculating the interface wave velocity of a semi-submerged solid comprises the following steps:

[0006] Step S1: Obtaining the characteristic value function g(c,f) of the interface wave velocity and frequency in the theoretical stage through the relationship between the interface wave velocity, Young's modulus, Poisson's ratio and density;

[0007] Step S2: Given a frequency f, continuously changing the interface wave velocity c, using the binary search method to find the zero point of g, the current frequency f (i) The interface wave velocity obtained from the solution is recorded as c (i) ; Change multiple f values and draw the dispersion curve of the interface wave velocity c changing with the excitation frequency f;

[0008] Step S3: A test platform is built. A signal generator in the test platform emits an incident wave to the test piece. The interface wave velocity in the test phase is calculated based on the distance between the excitation probe and the receiving probe and the time it takes for the incident wave to reach the receiving probe. This verifies the interface wave velocity obtained in the theoretical phase.

[0009] Step S4: Build a simulation model. The signal generator in the simulation platform sends an incident wave to the specimen. The interface wave velocity in the simulation phase is calculated based on the distance between the excitation probe and the receiving probe, and the time it takes for the incident wave to reach the receiving probe. This verifies the interface wave velocity obtained in the theoretical phase.

[0010] As a further preferred embodiment of the present invention, step S1 specifically includes the following steps:

[0011] Step S11: Calculate the coefficients P1, P2, and P3 based on the Young's modulus E and Poisson's ratio μ of the solid.

[0012] Step S12: Calculate coefficients M1, M2, and M3 based on coefficients P1, P2, and P3 obtained in step S11, then M1=P1P3. Where ρ is the solid density, c is the interface wave velocity, g is the acceleration of gravity, k is the wave number, and f is the frequency, π is the circumference of a circle;

[0013] Step S13: Calculate coefficient s1 and coefficient s2 based on coefficient M1, coefficient M2 and coefficient M3 obtained in step S12.

[0014] Step S14: Calculate coefficient η1 and coefficient η2 based on coefficient s1 and coefficient s2 obtained in step S13, then Where k is the wave number, ρ is the solid density, c is the interface wave velocity, and g is the gravitational acceleration;

[0015] Step S15: Calculate the coefficient ξ based on the coefficient η1 and coefficient η2 obtained in step S14, and the coefficient s1 and coefficient s2 obtained in step S13, then

[0016] Step S16: Obtain the eigenvalue function according to the coefficients obtained in steps S11 to S15

[0017] g=iμ(1+ξ)+(μ-1)(s1n1ξ+s2n2) (1);

[0018] As a further preferred embodiment of the present invention, the specific steps of drawing the dispersion curve in step S2 are:

[0019] Step S21: Set the initial frequency value to f (0) ;

[0020] Step S22: Set the initial value of the interface wave velocity to c (0) ;

[0021] Step S23: For a solid with known material properties, Young's modulus E, Poisson's ratio μ and solid density ρ, according to f (0) ,c( 0 ), combined with formula (1), calculate the wave number k, coefficient M1, coefficient M2, coefficient M3, coefficient s1, coefficient s2, coefficient η1, coefficient η2, coefficient ξ and g in sequence, and the value of g is recorded as g (0) , if g (0)is 0, and the interface wave velocity solution c is obtained; if g (0) If (c,f) is not 0, proceed to the next step;

[0022] Step S24: Obtain another interface wave velocity c (1) =c (0) +Δc, (c>0), substitute into g(c,f), and the value of g is recorded as g (1) The value of (c,f);

[0023] Step S25: Determine g (0) (c,f),g (1) (c,f);

[0024] When g (0) (c,f)×g (1) When (c,f)<0, the zero point of the function in this interval is found by the iterative method according to the mathematical theorem of zero existence, that is, when the function value changes sign in a certain interval, there is a root c in the interval; let this interval be c (0) -c (1) , using iterative root-finding algorithm to accurately determine the interval c (n) -c (n+1) The velocity in the equation is such that the equation is close enough to zero;

[0025] When g (0) (c,f)×g (1) When (c,f)>0, re-assign the initial value, and (0) Continue searching for other roots according to steps S21 to S25;

[0026] Step S26: Obtain f (0) After finding all c, arrange the values of c from small to large and record them as the wave velocity of the first, second, ... order mode of the interface wave, and select the frequency value as f (1) Repeat steps S22 to S25 for multiple iterations until the interface wave velocity c is plotted. (i) With the excitation frequency f (i) Variation of dispersion curves;

[0027] As a further preferred embodiment of the present invention, the specific steps of building the test platform in step S3 are:

[0028] Step S31: vertically placing a solid in a water tank, placing an excitation probe at the interface between the solid and the liquid in the water tank, placing a receiving probe at the bottom of the solid in the water tank, connecting the output of a signal generator to the input of a high-voltage amplifier, connecting the output of the high-voltage amplifier to the excitation probe, connecting the receiving probe to the input of a voltage amplifier, and connecting the output of the signal generator, the output of the high-voltage amplifier, and the output of the voltage amplifier to an oscilloscope at the same time;

[0029] Step S32: The signal generator transmits an incident wave into the water tank. The incident wave is composed of a 20-cycle Hanning window sine wave, and the formula is

[0030]

[0031] In formula (2), f is the frequency of the incident wave, t is the time, and N is the number of cycles of the sine wave, which is greater than or equal to 20;

[0032] Step S33: the high-voltage amplifier transmits the energy-amplified incident wave to the solid surface through the excitation probe;

[0033] Step S34: the receiving probe receives the vibration wave transmitted in the semi-submerged solid, and amplifies the energy of the received vibration wave through the voltage amplifier;

[0034] Step S35: The oscilloscope displays the vibration wave generated by the signal generator, the incident wave amplified by the high-voltage amplifier, and the received vibration wave amplified by the voltage amplifier;

[0035] Step S36: By analyzing the received signal, the largest wave crest is selected as the interface wave, and the interface wave velocity in the test simulation stage is obtained as

[0036]

[0037] In formula (3), c is the interface wave velocity during the test simulation phase, s is the distance between the excitation probe and the receiving probe, and t r -t0 is the propagation time between the incident signal and the received signal;

[0038] A device for measuring the interface wave velocity of a semi-submerged solid, comprising a test platform, a test piece arranged in the test platform, and a signal detection system, wherein the test piece comprises a water tank and the test piece, and the test piece is vertically arranged in the water tank;

[0039] The signal detection system includes a signal generator, a high-voltage amplifier, an excitation probe, a receiving probe, a voltage amplifier, and an oscilloscope. The output end of the signal generator is connected to the input end of the high-voltage amplifier, the output end of the high-voltage amplifier is connected to the excitation probe, the receiving probe is connected to the input end of the voltage amplifier, and the output end of the signal generator, the output end of the high-voltage amplifier, and the output end of the voltage amplifier are all connected to the oscilloscope.

[0040] The excitation probe is placed at the interface between the test piece and the liquid in the water tank, and the receiving probe is placed at the bottom of the test piece in the water tank;

[0041] As a further preferred embodiment of the present invention, the simulation model is a finite element model established in COMSOL, pressure acoustics, i.e. transient simulation of air and water, solid mechanics, i.e. elastic wave simulation of solid, and a matching layer for absorbing boundary echoes of the finite element model is set at the boundary of the finite element model;

[0042] The typical wave velocity of the matching layer around the solid is set to the Rayleigh wave velocity in the solid. Two transducers are set at the interface to excite and receive Rayleigh wave packets respectively. The excitation signal and the received signal are the horizontal displacement of the particle on the solid surface.

[0043] As a further preferred embodiment of the present invention,

[0044] The finite element model uses a 20-cycle sinusoidal modulation signal with Hann windowing as the excitation, and the center frequency f of the Rayleigh wave packet is the excitation frequency;

[0045] The finite element model is discretized using a free quadrilateral mesh, with a maximum mesh size of 1500 / f / 5 and a minimum mesh size of 1500 / f / 6;

[0046] The matching layer is discretized using a mapped grid, and at least 10 units are allocated in the thickness direction.

[0047] Through the above technical solution, compared with the existing technology, the present invention has the following beneficial effects:

[0048] The calculation model provided by the present invention calculates the solid-liquid interface wave velocity for semi-submerged solids. Combined with the Young's modulus, Poisson's ratio, and density of the solid material, it can not only detect material properties, but also determine the distance between the damage and the ultrasonic probe based on the scattering signal of the interface wave at the damage site, thereby locating the damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The present invention will be further described below with reference to the accompanying drawings and examples.

[0050] Figure 1 It is a traditional theoretical model diagram;

[0051] Figure 2 It is a theoretical model diagram provided by the present invention;

[0052] Figure 3 It is a schematic diagram of the structure of the test platform built by the present invention;

[0053] Figure 4 This is a waveform diagram of the vibration wave after transmission in a semi-submerged solid provided by the present invention;

[0054] Figure 5 is the dispersion curve of Rayleigh waves at the solid-water interface provided by the present invention;

[0055] Figure 6The solid-water interface wave velocity varies with elastic modulus E and density as provided by the present invention;

[0056] Figure 7 It is the finite element model and simulated wave field structure diagram provided by the present invention;

[0057] Figure 8 It is a time domain waveform diagram of the incident signal and the received signal provided by the present invention;

[0058] Figure 9 It is a frequency waveform diagram of the incident signal and the received signal provided by the present invention;

[0059] Figure 10 These are the dispersion curves and experimental data points provided by the present invention. DETAILED DESCRIPTION

[0060] The present invention will now be described in further detail with reference to the accompanying drawings. In the description of this application, it should be understood that the terms "left side", "right side", "upper", "lower", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are intended only to facilitate the description of the present invention and simplify the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. "First", "second", etc. do not indicate the importance of the components and therefore should not be understood as limiting the present invention. The specific dimensions used in this embodiment are only for illustrative purposes only and do not limit the scope of protection of the present invention.

[0061] As explained in the background technology, engineering structures such as dams, bridge piers, and gates are semi-submerged solids, and existing theoretical models can only calculate Figure 1 The interface wave velocity of the horizontal solid covered by the liquid layer shown in FIG. 2 is not able to accurately locate the damaged part of the semi-submerged solid. Therefore, the present application aims to provide a method as shown in FIG. Figure 2 The new theoretical model is used to calculate the interface wave velocity of semi-submerged solids underwater to meet the inspection needs of engineering structures such as dams, bridge piers, and gates.

[0062] The detection principle based on this application is also to excite interface waves on the surface of the engineering structure, and locate defects through the abnormal scattering of the interface waves combined with the interface wave velocity. However, the calculation model provided by this application is an innovation. Specifically, it includes obtaining the characteristic equation of the interface wave velocity and frequency in the theoretical stage through the relationship between the interface wave velocity, Young's modulus, Poisson's ratio and density. The characteristic equation contains two basic parameters, namely the interface wave velocity and frequency. The dispersion equation is constructed by these two parameters to draw the dispersion curve of the interface wave in a semi-submerged vertically placed solid, including the characteristic value function g(c,f) of the interface wave velocity and frequency in the theoretical stage; it should be noted here that, in fact, in the characteristic value function formula, any two parameters of the five parameters, namely, interface wave velocity, Young's modulus, Poisson's ratio, frequency ratio and density, can be taken as the changing value, and the relevant curve can be obtained by setting g to 0 according to the characteristic value function formula.

[0063] After theoretical derivation, the results need to be verified. Two types of verification are provided in this application, one is experimental simulation and the other is model simulation. Specifically, first, a test platform is built, and the signal generator in the test platform sends an incident wave to the test piece. The interface wave velocity in the test stage is calculated by the distance between the excitation probe and the receiving probe, and the time when the incident wave reaches the receiving probe, and the interface wave velocity obtained in the theoretical stage is verified; second, a simulation model is built, and the signal generator in the simulation platform sends an incident wave to the test piece. The interface wave velocity in the simulation stage is calculated by the distance between the excitation probe and the receiving probe, and the time when the incident wave reaches the receiving probe, and the interface wave velocity obtained in the theoretical stage is verified.

[0064] In this application, when the Young's modulus, Poisson's ratio and density of the solid are known, the distance between the damage and the ultrasonic probe is determined based on the scattered signal of the interface wave at the damage site by the method of distance = wave speed × scattered wave arrival time, thereby locating the damage; secondly, in the characteristic equation, when two of the three parameters of Young's modulus, Poisson's ratio and density are known, the third parameter can be calculated in combination with the wave speed for testing the material properties.

[0065] Here are the specific steps:

[0066] Step S11: Calculate the coefficients P1, P2, and P3 based on the Young's modulus E and Poisson's ratio μ of the solid.

[0067] Step S12: Calculate coefficients M1, M2, and M3 based on coefficients P1, P2, and P3 obtained in step S11, then M1=P1P3. Where ρ is the solid density, c is the interface wave velocity, g is the acceleration of gravity, k is the wave number, and f is the frequency, π is the circumference of a circle;

[0068] Step S13: Calculate coefficient s1 and coefficient s2 based on coefficient M1, coefficient M2 and coefficient M3 obtained in step S12.

[0069] Step S14: Calculate coefficient η1 and coefficient η2 based on coefficient s1 and coefficient s2 obtained in step S13, then Where k is the wave number, ρ is the solid density, c is the interface wave velocity, and g is the gravitational acceleration;

[0070] Step S15: Calculate the coefficient ξ based on the coefficient η1 and coefficient η2 obtained in step S14, and the coefficient s1 and coefficient s2 obtained in step S13, then

[0071] Step S16: Obtain the eigenvalue function according to the coefficients obtained in steps S11 to S15

[0072] g=iμ(1+ξ)+(μ-1)(s1n1ξ+s2n2) (1).

[0073] After obtaining the characteristic equation (1), it is assumed that the characteristic equation (1) contains two basic parameters, namely the interface wave velocity c R And frequency f, so by determining the value of one parameter to find the other parameter, and finally solve the dispersion curve.

[0074] The specific steps are:

[0075] Step S21: Set the initial frequency value to f (0) ;

[0076] Step S22: Set the initial value of the interface wave velocity to c (0) ;

[0077] Step S23: For a solid with known material properties, Young's modulus E, Poisson's ratio μ and solid density ρ, according to f (0) ,c( 0 ), combined with formula (1), calculate the wave number k, coefficient M1, coefficient M2, coefficient M3, coefficient s1, coefficient s2, coefficient η1, coefficient η2, coefficient ξ and g in sequence, and the value of g is recorded as g (0) , if g (0) is 0, and the interface wave velocity solution c is obtained; if g (0) If (c,f) is not 0, proceed to the next step;

[0078] Step S24: Obtain another interface wave velocity c (1) =c (0) +Δc, (c>0), substitute into g(c,f), and the value of g is recorded as g(1) The value of (c,f);

[0079] Step S25: Determine g (0) (c,f),g (1) (c,f);

[0080] When g (0) (c,f)×g (1) When (c,f)<0, the zero point of the function in this interval is found by the iterative method according to the mathematical theorem of zero existence, that is, when the function value changes sign in a certain interval, there is a root c in the interval; let this interval be c (0) -c (1) , using iterative root-finding algorithm to accurately determine the interval c (n) -c (n+1) The velocity in the equation is such that the equation is close enough to zero;

[0081] When g (0) (c,f)×g (1) When (c,f)>0, re-assign the initial value, and (0) Continue searching for other roots according to steps S21 to S25;

[0082] Step S26: Obtain f (0) After finding all c, arrange the values of c from small to large and record them as the wave velocity of the first, second, ... order mode of the interface wave, and select the frequency value as f (1) Repeat steps S22 to S25 for multiple iterations until the interface wave velocity c is plotted. (i) With the excitation frequency f (i) Variation of the dispersion curve.

[0083] Then, this application also conducted an experimental verification of the aforementioned theoretical model. The experimental platform built in the experiment is as follows: Figure 3 As shown, the solid (i.e., the aforementioned test piece) is placed vertically in a water tank, the excitation probe is placed at the junction of the solid and the liquid in the water tank, the receiving probe is placed at the bottom of the solid in the water tank, the output end of the signal generator is connected to the input end of the high-voltage amplifier, the output end of the high-voltage amplifier is connected to the excitation probe, the receiving probe is connected to the input end of the voltage amplifier, and the output end of the signal generator, the output end of the high-voltage amplifier, and the output end of the voltage amplifier are connected to the oscilloscope at the same time; the signal generator in the test platform sends an incident wave to the solid, and the interface wave velocity in the test simulation stage is calculated through the distance between the excitation probe and the receiving probe, and the time it takes for the incident wave to form a rebound wave in the water tank, and the interface wave velocity obtained in the theoretical stage is verified.

[0084] The specific steps are:

[0085] Step S32: The signal generator transmits an incident wave into the water tank. The incident wave is composed of a 20-cycle Hanning window sine wave, and the formula is

[0086]

[0087] In formula (2), f is the frequency of the incident wave, t is the time, and N is the number of cycles of the sine wave, which is greater than or equal to 20;

[0088] Step S33: the high-voltage amplifier transmits the energy-amplified incident wave to the solid surface through the excitation probe;

[0089] Step S34: the receiving probe receives the vibration wave transmitted in the semi-submerged solid, and amplifies the energy of the received vibration wave through the voltage amplifier;

[0090] Step S35: The oscilloscope displays the vibration wave generated by the signal generator, the incident wave amplified by the high-voltage amplifier, and the received vibration wave amplified by the voltage amplifier;

[0091] Step S36: By analyzing the received signal Figure 4 As shown, the largest wave crest is selected as the interface wave, and the interface wave velocity in the test simulation stage is obtained as

[0092]

[0093] In formula (3), c is the interface wave velocity during the test simulation phase, s is the distance between the excitation probe and the receiving probe, and t r -t0 is the propagation time between the incident signal and the received signal.

[0094] Then this application also conducted a simulation model verification. Specifically, the simulation model is a finite element model established in COMSOL to simulate the propagation of Rayleigh waves at the water-solid interface. Pressure acoustics (transient) is used to simulate air and water, and solid mechanics (elastic waves) are used to simulate solids. A 30 mm thick matching layer is set around the model boundary to absorb the model boundary echo and prevent the boundary echo from aliasing the Rayleigh wave direct signal; the typical wave velocity of the matching layer around air and water is set to 1500 meters per second, and the typical wave velocity of the matching layer around the solid is set to the Rayleigh wave velocity in the solid. The solid boundary is set to low reflection, and the air and water boundaries are set to plane wave radiation. Two transducers are set at the interface, respectively used to excite and receive Rayleigh wave packets (transmit and receive mode). The excitation and reception signals are the displacement of particles on the solid surface in the horizontal direction. A 20-cycle sinusoidal modulated signal with a Hann window (Formula (2)) was used as the excitation. The center frequency f of the Rayleigh wave packet was the excitation frequency. The finite element model was discretized using a free quadrilateral mesh with a maximum mesh size of 1500 / f / 5 and a minimum mesh size of 1500 / f / 6. The matching layer was discretized using a mapped mesh, ensuring that at least 10 elements were allocated in the thickness direction. The computation time, output step size, and analysis step size were set to 1 millisecond, 1, and 1 / 60 / f, respectively.

[0095] Finally, the applicant provides an example analysis of the calculation method proposed in this application.

[0096] Example 1:

[0097] The liquid in the water tank is selected as water and the solid is selected as glass. The material properties of glass and water are shown in Table 1 and Table 2 respectively.

[0098] Table 1 Size and material properties of solid media

[0099]

[0100] Table 2 Material properties of air and water

[0101] Material <![CDATA[Density (kg / m 3 )]]> Wave speed (m / s) Elastic modulus (GPa) Air 1.293 343 / water 1000 1500 2.18

[0102] According to formula (1), the theoretical Rayleigh wave velocity is calculated to be 2352.8 m / s. By changing the incident frequency to 2 MHz, a series of Rayleigh wave velocities are calculated, and the following is obtained: Figure 5 The Rayleigh wave dispersion curve at the glass-water interface is shown. It is found that when the solid is uniform and isotropic, the solid-liquid interface wave is non-dispersive. The so-called non-dispersive means that the phase velocity of waves with different frequencies is the same, that is, Figure 5 The results shown are not scattered. According to the same method, the theoretical wave speeds of aluminum, iron and cement mortar are 2429.5m / s, 2294.6m / s and 1314.9m / s respectively.

[0103] Example 2:

[0104] By setting different Young's modulus, Poisson's ratio and density in the characteristic equation, the variation of wave velocity with the properties of solid materials is studied. Here, the Poisson's ratio is set to 0.3, the variation E is 0.5GPa, 1GPa, 1.5GPa, 2GPa and 2.5GPa respectively, and the density is 2000kg / m 3 4000kg / m 3 , 6000kg / m 3 and 8000kg / m 3 , establish a finite element model and draw Figure 6 The graph of the solid-water interface wave velocity as a function of Young's modulus E and density is shown (here the corresponding curve is obtained by setting Young's modulus E and density as two variables in the characteristic equation), and Figure 7 The structure diagram of the finite element model and the simulated wavelength is shown; the wave speed of different materials simulated based on the finite element model is plotted on Figure 6 It was found that the wave velocity simulated by the constructed finite element model was consistent with the wave velocity theoretically calculated in the aforementioned Example 1, as shown in Table 3.

[0105] Table 3 Relationship between simulated wave velocity and theoretical wave velocity

[0106]

[0107]

[0108] Then, based on the constructed model, set the time domain waveform and frequency waveform of the incident wave and the received vibration wave. Figure 8 Shown are the time domain waveforms of the incident wave and the received vibration wave. Figure 9 Shown are the frequency waveforms of the incident wave and the received vibration wave. Since it takes time for the incident wave packet to transmit from the transmitter to the receiver, the received wave peak has a certain time delay compared to the incident wave. Figure 8 The peaks of the incident and received waves are marked by triangles and stars, respectively. The delay between them is calculated to be 32.5 μs. Since the distance between the transmitter and receiver is 80 mm, the calculated wave velocity is 2461.5 m / s. The simulated wave velocity agrees well with the analytical value of 2385.7 m / s, further validating the accuracy of the theoretical model.

[0109] Example 3:

[0110] The interface wave velocity of solids of different materials was tested experimentally:

[0111] Solid specimens made of different materials were tested using multiple incident frequencies. The measured Rayleigh wave velocities for glass, aluminum, iron, and cement mortar are shown in Tables 4, 5, 6, and 7, respectively. Compared with the theoretical values in Example 1, the relative errors for glass, aluminum, iron, and cement mortar are less than 2.7%, 2.3%, 4.8%, and 4.7%, respectively. Figure 10 This is a scatter plot of the experimental data. The distribution of the experimental data is consistent with the theoretical curve, which verifies the correctness of the model.

[0112] Table 4 Test wave velocity in glass

[0113]

[0114]

[0115] Table 5 Test wave velocity in aluminum

[0116]

[0117] Table 6 Test wave velocity in iron

[0118]

[0119] Table 7 Test wave velocity in mortar

[0120]

[0121] Next, the wave velocity of the same solid material was solved at different frequencies. As shown in Table 8, the relative errors of glass, aluminum, iron, and cement mortar were 1.4%, 0.5%, 2.4%, and 2.8%, respectively, further reducing the relative error between the theoretical and experimental values.

[0122] Table 8 Test wave speed

[0123] Material Glass aluminum iron mortar Theoretical speed (m / s) 2352.8 2429.5 2294.6 1314.9 Average speed (m / s) 2387.3 2441.5 2238.6 1278.5 Relative error (%) 1.4 0.5 2.4 2.8

[0124] Based on the above verification, it can be determined that the new calculation model provided by this application can obtain interface wave velocities close to the actual situation, thereby determining the distance between the damaged area and the ultrasonic probe and locating the damage based on the scattering signal of the interface wave at the damaged area of the engineering structure; at the same time, it can also realize the detection of material properties and meet the detection needs of different semi-submerged structures.

[0125] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art and, unless defined as such herein, will not be interpreted in an idealized or overly formal sense.

[0126] The meaning of "and / or" in this application means that both situations where each exists alone or both exist at the same time are included.

[0127] The term “connection” as used in this application may mean a direct connection between components or an indirect connection between components via other components.

[0128] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A method for calculating the interface wave velocity of a semi-submerged solid, characterized by: The specific steps include: Step S1: Obtain the eigenvalue function g(c, f) of the interface wave velocity and frequency in the theoretical stage through the relationship between the interface wave velocity, Young's modulus, Poisson's ratio, and density. The calculation steps of the eigenvalue function g(c, f) are as follows: Step S11: Calculate the coefficients P1, P2, and P3 based on the Young's modulus E and Poisson's ratio μ of the solid. Step S12: Calculate coefficients M1, M2, and M3 based on coefficients P1, P2, and P3 obtained in step S11, then M1=P1P3. Where ρ is the solid density, c is the interface wave velocity, g is the acceleration of gravity, k is the wave number, and f is the frequency, π is the circumference of a circle; i is the unit imaginary number Step S13: Calculate coefficient s1 and coefficient s2 based on coefficient M1, coefficient M2 and coefficient M3 obtained in step S12. Step S14: Calculate coefficient η1 and coefficient η2 based on coefficient s1 and coefficient s2 obtained in step S13, then Where k is the wave number, ρ is the solid density, c is the interface wave velocity, and g is the gravitational acceleration; Step S15: Calculate the coefficient ξ based on the coefficient η1 and coefficient η2 obtained in step S14, and the coefficient s1 and coefficient s2 obtained in step S13, then Step S16: According to the coefficients obtained in steps S11 to S15, the characteristic value function g = iμ(1+ξ)+(μ-1)(s1η1ξ+s2η2)(1) is obtained; Step S2: Given a frequency f, continuously changing the interface wave velocity c, using the binary search method to find the zero point of g, the current frequency f (i) The interface wave velocity obtained from the solution is recorded as c (i) ; Change multiple f values and draw the dispersion curve of the interface wave velocity c changing with the excitation frequency f; Step S3: A test platform is built. A signal generator in the test platform emits an incident wave to the test piece. The interface wave velocity in the test phase is calculated based on the distance between the excitation probe and the receiving probe and the time it takes for the incident wave to reach the receiving probe. This verifies the interface wave velocity obtained in the theoretical phase. Step S4: Build a simulation model. The signal generator in the simulation platform sends an incident wave to the specimen. The interface wave velocity in the simulation stage is calculated based on the distance between the excitation probe and the receiving probe and the time it takes for the incident wave to reach the receiving probe. This verifies the interface wave velocity obtained in the theoretical stage.

2. The method for calculating the interface wave velocity of a semi-submerged solid according to claim 1, wherein: The specific steps of drawing the dispersion curve in step S2 are: Step S21: Set the initial frequency value to f (0) ; Step S22: Set the initial value of the interface wave velocity to c (0) ; Step S23: For a solid with known material properties, Young's modulus E, Poisson's ratio μ and solid density ρ, according to f (0) , c (0) , combined with formula (1), calculate the wave number k, coefficient M1, coefficient M2, coefficient M3, coefficient s1, coefficient s2, coefficient η1, coefficient η2, coefficient ξ and g in turn, and the value of g is recorded as g (0) , if g (0) is 0, and the interface wave velocity solution c is obtained; if g (0) If (c,f) is not 0, proceed to the next step; Step S24: Obtain another interface wave velocity c (1) =c (0) +Δc, (c>0), substitute into g(c,f), and the value of g is recorded as g (1) The value of (c,f); Step S25: Determine g (0) (c,f),g (1) (c,f); When g (0) (c,f)×g (1) When (c,f)<0, the zero point of the function in this interval is found by the iterative method according to the mathematical theorem of zero existence, that is, when the function value changes sign in a certain interval, there is a root c in the interval; let this interval be c (0) -c (1) , using iterative root-finding algorithm to accurately determine the interval c (n) -c (n+1) The velocity in the equation is such that the equation is close enough to zero; When g (0) (c,f)×g (1) When (c,f)>0, re-assign the initial value, and (0) Continue searching for other roots according to steps S21 to S25; Step S26: Obtain f (0) After finding all c, arrange the values of c from small to large and record them as the wave velocity of the first, second, ... order mode of the interface wave, and select the frequency value as f (1) Repeat steps S22 to S25 for multiple iterations until the interface wave velocity c is plotted. (i) With the excitation frequency f (i) Variation of the dispersion curve.

3. The method for calculating the interface wave velocity of a semi-submerged solid according to claim 2, wherein: The specific steps for building the test platform in step S3 are: Step S31: vertically placing a solid in a water tank, placing an excitation probe at the interface between the solid and the liquid in the water tank, placing a receiving probe at the bottom of the solid in the water tank, connecting the output of a signal generator to the input of a high-voltage amplifier, connecting the output of the high-voltage amplifier to the excitation probe, connecting the receiving probe to the input of a voltage amplifier, and connecting the output of the signal generator, the output of the high-voltage amplifier, and the output of the voltage amplifier to an oscilloscope at the same time; Step S32: The signal generator transmits an incident wave into the water tank. The incident wave is composed of a 20-cycle Hanning window sine wave, and the formula is In formula (2), f is the frequency of the incident wave, t is the time, and N is the number of cycles of the sine wave, which is greater than or equal to 20; Step S33: the high-voltage amplifier transmits the energy-amplified incident wave to the solid surface through the excitation probe; Step S34: the receiving probe receives the vibration wave transmitted in the semi-submerged solid, and amplifies the energy of the received vibration wave through the voltage amplifier; Step S35: The oscilloscope displays the vibration wave generated by the signal generator, the incident wave amplified by the high-voltage amplifier, and the received vibration wave amplified by the voltage amplifier; Step S36: By analyzing the received signal, the largest wave crest is selected as the interface wave, and the interface wave velocity in the test simulation stage is obtained as In formula (3), c is the interface wave velocity during the test simulation phase, s is the distance between the excitation probe and the receiving probe, and t r -t0 is the propagation time between the incident signal and the received signal.

4. A measuring device for the method for calculating the interface wave velocity of a semi-submerged solid according to claim 3, characterized in that: The test platform comprises a test structure and a signal detection system arranged in the test platform, wherein the test structure comprises a water tank and a test piece, and the test piece is vertically arranged in the water tank; The signal detection system includes a signal generator, a high-voltage amplifier, an excitation probe, a receiving probe, a voltage amplifier, and an oscilloscope. The output end of the signal generator is connected to the input end of the high-voltage amplifier, the output end of the high-voltage amplifier is connected to the excitation probe, the receiving probe is connected to the input end of the voltage amplifier, and the output end of the signal generator, the output end of the high-voltage amplifier, and the output end of the voltage amplifier are all connected to the oscilloscope. The excitation probe is placed at the interface between the test piece and the liquid in the water tank, and the receiving probe is placed at the bottom of the test piece in the water tank.

5. The measuring device for calculating the interface wave velocity of a semi-submerged solid according to claim 4, characterized in that: The simulation model is a finite element model established in COMSOL, pressure acoustics, i.e. transient simulation of air and water, solid mechanics, i.e. elastic wave simulation of solids, and a matching layer for absorbing the boundary echo of the finite element model is set at the boundary of the finite element model; The typical wave velocity of the matching layer around the solid is set to the Rayleigh wave velocity in the solid. Two transducers are set at the interface to excite and receive Rayleigh wave packets respectively. The excitation signal and the received signal are the horizontal displacement of the particles on the solid surface.

6. The measuring device for calculating the interface wave velocity of a semi-submerged solid according to claim 5, characterized in that: The finite element model uses a 20-cycle sinusoidal modulation signal with Hann windowing as the excitation, and the center frequency f of the Rayleigh wave packet is the excitation frequency; The finite element model is discretized using a free quadrilateral mesh, with a maximum mesh size of 1500 / f / 5 and a minimum mesh size of 1500 / f / 6; The matching layer is discretized using a mapped grid, and at least 10 units are allocated in the thickness direction.

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