CN112197720A - Method and device for measuring length of concealed columnar steel structure based on ultrasonic guided wave sound field regulation and control technology - Google Patents
Method and device for measuring length of concealed columnar steel structure based on ultrasonic guided wave sound field regulation and control technology Download PDFInfo
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Abstract
The invention relates to a length measuring method and device for a concealed columnar steel structure based on an ultrasonic guided wave sound field regulation technology, and belongs to the field of nondestructive testing and length measurement. The hidden columnar steel structure is a core shell structure with a coating layer, such as a slope anchor rod, a highway guardrail upright post and the like. The device comprises three components of mobile equipment, a monitoring host and an ultrasonic guided wave transducer, wherein part or all of the components are connected in a wired or wireless mode. The method comprises the steps of standard library establishment, main frequency detection, modal detection, automatic recommendation of a wave structure, automatic recommendation of working parameters and installation modes of the transducer, and guided wave sound field regulation and control. The method completes regulation and control of a guided wave sound field by analyzing and using the propagation characteristics of the ultrasonic guided wave and installing and arranging the transducer, so that the received echo signal only contains a target mode, the problem of multi-mode in the traditional ultrasonic guided wave detection is solved, and the method has important engineering significance.
Description
Technical Field
The invention belongs to the field of nondestructive testing and length measurement, and particularly relates to a method and a device for measuring the length of a concealed columnar steel structure based on an ultrasonic guided wave sound field regulation and control technology.
Background
In municipal works, water conservancy and hydropower, highway and railway construction, and various underground works (tunnels, caverns, and the like), the hidden columnar steel structure is widely applied, for example: the anchor rod has the advantages of good anchoring quality, high strength, safety, reliability, material saving, cost reduction and the like, so that the anchor rod is widely applied to slope protection; it is widely used as a post of a highway guardrail and the like because it can effectively reduce the severity of a disaster when a traffic accident occurs.
The concealed columnar steel structure comprises a core layer and a coating layer, for example, an anchor rod in the concealed columnar steel structure shown in fig. 3, wherein 1 is a deformed steel core layer, 2 is a concrete coating layer, 3 is a baffle plate, 4 is a bolt, the total length of the anchor rod is 9 meters, and the burial depth is 8.7 meters. Generally, according to practical engineering experience, the total length of the slope type anchor rod is usually more than 6 meters, and the burial depth is more than 90 percent of the total length.
However, these hidden columnar steel structures are not only affected by factors such as stratum position and site conditions, but also depend on the construction process and construction management level, and there are various potential defects that make it difficult to meet design requirements for construction quality, such as: the hidden steel columnar structure is broken due to local corrosion, the hidden steel columnar structure is sheared due to the change of stress conditions, and the length of the hidden steel columnar structure is shortened due to improper benefits of individual construction personnel, so that engineering accidents and great economic losses are caused. Due to the characteristic of strong concealment, effective detection is difficult. Therefore, the method has strong economic and social significance for the research on the length measurement of the concealed columnar steel structure.
At present, there are many methods for detecting the length of the hidden columnar structure, such as a drawing method, a ground penetration radar identification method, an ultrasonic method, a fiber grating method, a guided wave detection method, and the like. However, the above technical methods have certain limitations in the nondestructive testing of the concealed columnar steel structure. The drawing method is destructive to the detection of the hidden columnar steel structure, relatively troublesome in operation, relatively high in cost and relatively low in precision, and can only be used for sampling detection; the ground penetration radar identification method can be successfully used for detecting the distribution of the steel bars in the concrete, but has the main defect of small detection length range; the ultrasonic method is a technology for researching reflected, transmitted and scattered waves by interaction of ultrasonic waves and a test piece, performing macroscopic defect detection, geometric characteristic measurement, detection and characterization of change of tissue structure and mechanical property on the test piece and further evaluating specific applicability of the test piece, wherein the ultrasonic method is a body wave, and is low in detection efficiency on a large or long-distance structure because the body wave can only cover a small area of a structure to be detected each time, namely, single-point detection is performed; the fiber grating method can carry out comparatively accurate detection to the length of disguised column steel structure, but fiber grating installation is complicated, and the cost is higher, and is unfavorable for retrieving. Unless otherwise specified, the ultrasonic wave is generally a bulk wave.
The ultrasonic guided wave (also called guided wave) is formed by multiple reciprocating reflections generated between discontinuous interfaces of sound waves in a medium and further generating complex interference and geometric dispersion, the guided wave and the propagation in the solid medium are different from common body waves and similar to Rayleigh waves and lamb waves, and the guided wave propagates on the surface and the boundary of the solid medium. In the field of ultrasonic guided wave nondestructive detection, currently, low-frequency ultrasonic guided waves are mainly used for detecting structures with coating layers or attenuation media on the periphery, such as buried highway guardrail columns, buried anchor rods and other structures, the frequency range is usually far less than 1MHz, the frequency of the low-frequency ultrasonic guided waves is usually dozens to hundreds of hertz, and low-frequency signals with the central frequency of 70KHz are used as excitation signals of the guided waves in application research of magnetostrictive guided wave technology in anchor rod detection published by Liuyang and the like to measure the length of the anchor rod; in the application research of the ultrasonic guided wave technology in the buried anchor rod detection published by the Ohio-Rich storage et al, the L (0,1) mode of 40 KHz-90 KHz is used as the detection selection in the buried anchor rod engineering; the ultrasonic guided wave frequency that chinese patent CN201010138539.5 used is 10KHz ~ 60KHz etc., its reason is that the frequency is higher, the attenuation is bigger, this is the general knowledge of general wave propagation theory, and more complicated to the guided wave mode quantity of disguised columnar steel structure high frequency channel, it is more chaotic to make guided wave signal, the terminal surface signal is difficult to discern or can't reach the end of disguised columnar steel structure at all because the serious acoustic energy of attenuation, if to the disguised columnar steel structure (for example, slope class stock, foundation ditch stock etc.) that the buried depth exceeds 3 meters, use traditional high frequency ultrasonic guided wave can't accomplish the detection to its length, the frequency of high frequency ultrasonic guided wave is usually more than 1 MHz. Therefore, as is well known to those skilled in the art, high frequency guided ultrasound waves are difficult to detect at a distance, which is a buried depth of more than 3 meters, of the covered, concealed cylindrical steel structure. However, the guided wave of the low frequency band has complex effect at the boundary of the cladding layer, serious energy transmission, large attenuation and low signal-to-noise ratio, and can not be detected remotely. The use of the high-frequency band guided wave also has the problems that the signal-to-noise ratio of echo signals is low due to a plurality of high-frequency modes, the detection of different structures can not be realized only by using single frequency, the automatic selection of detection modes and detection frequency bands can not be realized, the detection range is small (generally, the detection distance is less than 3 meters, only short cylindrical steel structures such as a mine roof anchor rod can be detected, the length measurement of a slope anchor rod can not be applied), the design of the guided wave vibration mode can not be carried out according to the requirements, and the like.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a length measuring method of a concealed columnar steel structure based on an ultrasonic guided wave sound field regulation and control technology, which overcomes the technical defects that the traditional ultrasonic guided wave cannot realize the remote detection of the concealed columnar steel structure with a coating layer (the high-frequency guided wave has numerous modes, the attenuation is serious, the guided wave vibration mode design is not carried out, the low-frequency guided wave has complex effect on an interface and the energy transmission is serious), unexpectedly realizes the remote detection of the concealed columnar steel structure by using the screened specific high-frequency guided wave, and even can finish the nondestructive detection of the length at an ultra-far distance with the burial depth greatly exceeding 3 meters. The technology of the invention can realize the guided wave sound field regulation and control, intelligent recommendation of the mode and the excitation mode, accelerated calculation and analysis in the detection process, and provides a solution for the ultra-long distance length measurement of the hidden columnar steel structure.
Through the intensive research and analysis of the applicant, each different hidden columnar steel structure has guided waves in a certain frequency band in high frequency, the vibration displacement of the structure is mainly concentrated at the position near the core layer and hardly interacts with the coating layer, the energy leakage is reduced, the ultrasonic guided wave transducer is selected and installed according to the recommendation, and the purpose of receiving pure target modal guided waves can be realized by utilizing the acoustic characteristics of the coating layer. Therefore, the defects that the guided wave of the low frequency band has complex action at the boundary of the cladding layer, serious energy transmission, large attenuation and low signal-to-noise ratio can be overcome; the defects of complex guided wave mode and serious attenuation of a high frequency band are overcome.
The invention also aims to provide a detection device used in the length measurement method of the hidden columnar steel structure based on the ultrasonic guided wave sound field regulation and control technology, and the detection device solves the problems that a detection instrument in the prior art is heavy and is not suitable for field detection.
The technical scheme adopted by the invention for solving the technical problems is as follows:
1. a length measuring method of a hidden columnar steel structure based on an ultrasonic guided wave sound field regulation technology is disclosed, wherein the hidden columnar steel structure comprises a core layer and a coating layer, and the method is characterized by comprising the following steps:
step 1: for the hidden columnar steel structure, the group velocity dispersion curve C is solvedg(f) Phase velocity dispersion curve Cp(f) The attenuation curve Atta (f) is used for establishing a standard library;
step 2: selecting a phase velocity dispersion curve C corresponding to the detected hidden columnar steel structure from the standard libraryp(f) Taking the variation range alpha of the continuous variation of the phase velocity value within the bandwidth delta f not exceeding the longitudinal wave velocity of the measured hidden columnar steel structure as a first screening condition to obtain a primary screening candidate mode and a primary screening detection frequency band for detection;
and step 3: selecting a group velocity dispersion curve C corresponding to the detected hidden columnar steel structure from the standard libraryg(f) Using the preliminary screening candidate modality obtained in the step 2 to correspond to the modality in the group velocity dispersion curve, and using a variation range alpha within which the continuous variation of the group velocity within the bandwidth delta f does not exceed the maximum value of the group velocity as a second screening condition to complete the secondary filtration of the modality to obtain a secondary screening candidate modality;
and 4, step 4: selecting an attenuation curve corresponding to the detected hidden columnar steel structure from the standard library, and taking the minimum value of the attenuation curve of the secondary screening candidate mode as a third screening condition to obtain a detected main frequency fmain；
And 5: detecting the main frequency f obtained according to the step 4mainDrawing a secondary screening candidate mode proceeding wave structure obtained in the step 3, screening a guided wave mode wave structure which does not interact with the cladding layer by taking a wave structure with vibration displacement concentrated at a position near the center of the core layer as a fourth screening condition, reducing guided wave attenuation of mode excitation corresponding to the selected guided wave mode wave structure, and carrying out length detection on the hidden steel structure with super-long length (more than 6 m); the wave structure is in the waveguideAnd the displacement distribution of the guided wave detection mode.
Step 6: according to the secondary screening candidate modality obtained in the step 3 and the detected main frequency f obtained in the step 4mainAnd the guided wave modal wave structure obtained in the step 5, automatically recommending working parameters (mainly comprising transducer type selection, main frequency selection, bandwidth selection and the like) and installation parameters of the guided wave transducer (corresponding transducer arrangement is carried out according to the mode of exciting guided waves, namely a torsional mode T, a bending mode F and a longitudinal mode L), exciting the guided waves, realizing automatic attenuation of guided wave acoustic energy leaked to the outside of the tested member by utilizing the sound field distribution characteristic (the guided wave modal wave structure obtained in the step 5) of the ultrasonic guided waves and the material acoustic characteristic (damping parameter) of the coating, increasing the consistency and uniformity of the guided wave sound field, receiving pure target modal guided waves, improving the signal-to-noise ratio and enhancing the readability of the guided wave signals;
and 7: and (3) reading the propagation time t of the first end face echo wave packet of the pure target mode guided wave waveform in the step (6), and converting the propagation time t into a propagation distance x according to x-v-t by utilizing the guided wave propagation speed v, wherein x is the length of the concealed steel structure.
The second purpose of the invention is to provide a device used in the length measurement method of the hidden columnar steel structure based on the ultrasonic guided wave sound field regulation technology, which comprises a mobile device, a monitoring host and an ultrasonic guided wave transducer, wherein:
the mobile equipment is used for automatically selecting a detected main frequency, a detected mode and a guided wave modal wave structure of the detected hidden cylindrical steel structure, automatically recommending working parameters and installation parameters of the ultrasonic guided wave transducer, and displaying a guided wave waveform processed by the monitoring host and a length value x of the detected hidden cylindrical steel structure;
the monitoring host comprises an ultrasonic guided wave excitation unit and an ultrasonic guided wave receiving unit, wherein the ultrasonic guided wave excitation unit applies an excitation signal to the ultrasonic guided wave transducer, mechanical vibration is excited at the free end of the detected concealed columnar steel structure, the receiving unit converts an elastic wave signal in the detected concealed columnar steel structure into an electric signal, the signal processing unit transmits data to the mobile equipment after signal amplification, A/D conversion, filtering rectification and signal average processing, and the guided wave waveform processed by the monitoring host and the length value x of the detected concealed columnar steel structure are displayed.
Compared with the prior art, the invention has the following advantages:
(1) the automatic selection of regulation and control, mode and excitation mode of a guided wave sound field can be realized, and the limitation that the traditional high-frequency ultrasonic guided wave is large in attenuation and cannot be remotely propagated is further overcome;
(2) length detection at an ultra-long distance (greater than 6m) is enabled;
(3) a standard library is established, and only a corresponding model needs to be selected from the standard library aiming at a specific detected hidden columnar steel structure, so that the calculation and analysis processes are accelerated;
(4) the detection device has the characteristics of large bandwidth and high power amplifier, is simple, portable and practical, and can meet various field detection requirements.
Description of the drawings:
FIG. 1 is a functional block diagram of a detection device used in the present invention;
FIG. 2 is a schematic flow chart of a method for measuring the length of a concealed columnar steel structure based on an ultrasonic guided wave sound field regulation technology, disclosed by the invention;
FIG. 3 is a diagram showing the specific dimensions and transducer arrangement of the anchor to be tested;
FIG. 4 is
The phase velocity dispersion curve of the 9m grouting anchor rod;
FIG. 5 is
The group velocity dispersion curve of the 9m grouting anchor rod;
FIG. 6 is
The attenuation curve of the 9m grouting anchor rod;
FIG. 7 is
The 9m grouting anchor rod has a wave structure at 2.25 MHz L (0, 22);
FIG. 8 is a graph of guided wave signals received using the apparatus of the present invention;
FIG. 9 is
The 9m grouting bolt has a wave structure at 64 kilohertz L (0, 4);
in fig. 3, 1: deformed steel core layer, 2: concrete coating, 3: baffle, 4: bolt, 5: a transducer.
The specific implementation mode is as follows:
the invention is further illustrated by the following figures and examples.
As shown in figure 1, the invention provides a length measuring device of a hidden columnar steel structure based on an ultrasonic guided wave sound field regulation technology, which comprises a guided wave transducer, a monitoring host and a mobile device (or a computer), wherein the mobile device (or the computer) is connected with the monitoring host, and the monitoring host is connected with the guided wave transducer. The method comprises the steps that the transducers are selected and installed according to recommended working parameters and installation parameters of the transducers, an ultrasonic guided wave excitation unit in a monitoring host applies excitation signals to the transducers, mechanical vibration is excited at the free ends of the hidden cylindrical steel structures, an elastic wave signal in the detected hidden cylindrical steel structures is converted into an electric signal by a receiving unit, and the signal processing unit transmits data to mobile equipment for display after signal amplification, A/D conversion, filtering rectification and signal averaging. The method is widely applied to slope anchor rods and highway guardrail upright columns in practical engineering in the following detection of the hidden columnar steel structures respectively.
The invention provides a length measuring method of a hidden columnar steel structure based on an ultrasonic guided wave sound field regulation technology, wherein the hidden columnar steel structure comprises a core layer and a coating layer, and the method comprises the following steps:
step 1: for the hidden columnar steel structure, the group velocity dispersion curve C is solvedg(f) Phase velocity dispersion curve Cp(f) And attenuation ofA curve atta (f) for establishing a standard library;
step 2: selecting a phase velocity dispersion curve C corresponding to the detected hidden columnar steel structure from the standard libraryp(f) Taking the variation range alpha of the continuous variation of the phase velocity value within the bandwidth delta f not exceeding the longitudinal wave velocity of the measured hidden columnar steel structure as a first screening condition to obtain a primary screening candidate mode and a primary screening detection frequency band for detection;
and step 3: selecting a group velocity dispersion curve C corresponding to the detected hidden columnar steel structure from the standard libraryg(f) Using the preliminary screening candidate modality obtained in the step 2 to correspond to the modality in the group velocity dispersion curve, and using a variation range alpha within which the continuous variation of the group velocity within the bandwidth delta f does not exceed the maximum value of the group velocity as a second screening condition to complete the secondary filtration of the modality to obtain a secondary screening candidate modality;
and 4, step 4: selecting an attenuation curve corresponding to the detected hidden columnar steel structure from the standard library, and taking the minimum value of the attenuation curve of the secondary screening candidate mode as a third screening condition to obtain a detected main frequency fmain；
And 5: detecting the main frequency f obtained according to the step 4mainDrawing a secondary screening candidate mode proceeding wave structure obtained in the step 3, screening a guided wave mode wave structure which does not interact with the cladding layer by taking a wave structure with vibration displacement concentrated at a position near the center of the core layer as a fourth screening condition, reducing guided wave attenuation of mode excitation corresponding to the selected guided wave mode wave structure, and carrying out length detection on the hidden steel structure with super-long length (more than 6 m); the wave structure refers to the displacement distribution of a guided wave detection mode in the waveguide.
Step 6: according to the secondary screening candidate modality obtained in the step 3 and the detected main frequency f obtained in the step 4mainAnd 5, automatically recommending working parameters (mainly comprising transducer type selection, main frequency selection, bandwidth selection and the like) and installation parameters (arranging corresponding transducers according to the modes of exciting guided waves, namely a torsional mode T, a bending mode F and a longitudinal mode L) of the guided wave transducer to carry out guided wave excitation,the automatic attenuation of the sound energy of the guided wave leaked to the outside of the tested member is realized by utilizing the sound field distribution characteristics (the guided wave modal wave structure obtained in the step 5) of the ultrasonic guided wave and the material acoustic characteristics (damping parameters) of the coating layer, the consistency and uniformity of the sound field of the guided wave are increased, the pure target modal guided wave is received, the signal-to-noise ratio is improved, and the readability of the guided wave signal is enhanced;
and 7: and (3) reading the propagation time t of the first end face echo wave packet of the pure target mode guided wave waveform in the step (6), and converting the propagation time t into a propagation distance x according to x-v-t by utilizing the guided wave propagation speed v, wherein x is the length of the concealed steel structure.
Further, the specific method for establishing the standard library in step 1 is as follows:
solving a wave control equation aiming at a hidden columnar steel structure
σrr＝σrθ＝σrz＝0，r＝Ri，r＝RoAdding isochoric conditions
Then, the eigen equation C · a ═ 0 (where u denotes a guided wave displacement field, σ denotes a stress vector, λ and μ denote material Lame constants, ρ denotes material density, H denotes an isovolumetric vector potential, C denotes a stiffness matrix of the material, and a denotes a displacement of an arbitrary point of the hidden columnar steel structure) is obtained, the eigen value and the eigen vector are obtained by solving the eigen equation, where the eigen value is a wave number k (k is a complex number) of the ultrasonic guided wave in the hidden columnar steel structure, and cp (f) ═ ω/k is solvedRe(where ω represents angular frequency, kReRepresenting the real part of the wavenumber k) can be obtained a phase velocity dispersion curve Cp(f) Propagating group velocity dispersion curve Cg(f) Solving for atta (f) kIm(where k isImThe imaginary part of the wave number k) to obtain an attenuation curve Atta (f), and solving
(wherein f is the frequency of the waveguide, d is the thickness of the waveguide material, and fd is the frequency-thickness product), establishing a standard library;
further, the first screening condition of step 2 comprises the following steps:
1) according to Cp (m,n)(f)＝ClCalculating a frequency value under the wave velocity of the longitudinal wave;
2) if it is
Taking f epsilon (f-delta f/2, f + delta f/2);
3) if it is
According to
Finding f1Value, take f e (f)1,f1+Δf)；
4) If it is
According to
Finding f2Value, take f e (f)2-Δf,f2)；
Wherein C islRepresenting the velocity of longitudinal waves; α represents the percentage of change in wave velocity; cp (m,n)(f) Representing a phase velocity dispersion curve; f. ofminRepresents a minimum frequency; f. ofmaxRepresents the maximum frequency; Δ f represents the bandwidth; f denotes the frequency, f1Representing the lower limit frequency, f, of the frequency band2Representing the upper limit frequency of the frequency band;
further, the second screening condition in step 3 is:
wherein C isg (m,n)(f) Representing a group velocity dispersion curve; α represents the percentage of change in wave velocity; f represents a frequency;
further, the third screening condition in step 4 is:
fmain＝Atta-1[min(Atta(m,n)(f))]
wherein f ismainIndicating the detection main frequency; atta(m,n)(f) Representing guided wave attenuation values at different frequencies; f represents a frequency;
further, the fourth screening condition of step 5 comprises the following steps:
1) detecting the dominant frequency f selected in claim 5mainPerforming wave structure drawing on the candidate mode selected in the claim 4;
2) to be provided with
Selecting a guided wave excitation sound field as a screening condition;
wherein Amp (x) is the displacement profile of the wave structure in the radial direction; beta is a sound field concentration degree coefficient, the value range of beta is more than or equal to 0.2 and less than or equal to 0.8, and preferably, the value range of beta is more than or equal to 0.4 and less than or equal to 0.7;
further, the value range of alpha in the step 2 and the step 3 is more than or equal to 3% and less than or equal to 40%, preferably, the value range of alpha is more than or equal to 5% and less than or equal to 16%;
further, the selected detected main frequency f in step 4mainIn the guided wave high-frequency band of more than or equal to 1MHz, the optimal frequency band is 2 MHz-8 MHz;
the second purpose of the invention is to provide a device used in the length measurement method of the hidden columnar steel structure based on the ultrasonic guided wave sound field regulation technology, which comprises a mobile device, a monitoring host and an ultrasonic guided wave transducer, wherein:
the mobile equipment is used for automatically selecting a detected main frequency, a detected mode and a guided wave modal wave structure of the detected hidden cylindrical steel structure, automatically recommending working parameters and installation parameters of the ultrasonic guided wave transducer, and displaying a guided wave waveform processed by the monitoring host and a length value x of the detected hidden cylindrical steel structure;
the monitoring host comprises an ultrasonic guided wave excitation unit and an ultrasonic guided wave receiving unit, wherein the ultrasonic guided wave excitation unit applies an excitation signal to the ultrasonic guided wave transducer, mechanical vibration is excited at the free end of the detected concealed columnar steel structure, the receiving unit converts an elastic wave signal in the detected concealed columnar steel structure into an electric signal, the signal processing unit transmits data to the mobile equipment after signal amplification, A/D conversion, filtering rectification and signal average processing, and the guided wave waveform processed by the monitoring host and the length value x of the detected concealed columnar steel structure are displayed.
Furthermore, the mobile equipment utilizes the steps of the method of the invention to realize the automatic selection of the detection main frequency, the detection mode and the guided wave modal wave structure of the detected hidden columnar steel structure, and automatically recommends the working parameters and the installation parameters of the ultrasonic guided wave transducer.
EXAMPLE 1 nondestructive testing of the length of a side slope Anchor
The anchor rod is because of its advantages such as good, the intensity is high, safe and reliable of anchor quality and is widely used in engineering fields such as municipal works, railway and highway construction and mine roof anchor, and the anchor rod is of a great variety, if: the anchor rod of the mine roof with relatively small size, the anchor rod of the large-scale side slope, the anchor rod of the foundation pit and the like. The method has a mature nondestructive testing method for the small-scale mine roof anchor rod, but the technical problem which is difficult to solve still exists for the nondestructive testing of the length of the large-scale anchor rod. In the embodiment, the nondestructive detection of the length of the slope anchor rod is completed through the detection mode intelligent selection algorithm and the ultrasonic guided wave sound field regulation and control technology. In this example, the diameter of the central screw steel is
The anchor rod of (2) is taken as an example, and is specifically shown in fig. 3: the center of the anchor rod is the deformed steel bar with the length of 9000mm and the diameter r of 14mm, the length of the free end of the anchor rod is 300mm, the burial depth is 8700mm, and the anchoring medium is concrete. The density of the deformed steel bar is rho 7800kg/m3Longitudinal wave velocity of CL5798m/s and a transverse wave velocity of CT＝3260m/s，kT＝0.01，kL＝0.003。
A method for measuring the length of a hidden columnar steel structure based on an ultrasonic guided wave sound field regulation technology is carried out according to the steps shown in figure 2, and specifically comprises the following steps:
(1) solving a wave control equation aiming at a hidden columnar steel structure
σrr＝σrθ＝σrz＝0，r＝Ro，
Adding at equal volume
Then, the eigen equation C · a ═ 0 (where u denotes a guided wave displacement field, σ denotes a stress vector, λ and μ denote material Lame constants, ρ denotes material density, H denotes an isovolumetric vector potential, C denotes a stiffness matrix of the material, and a denotes a displacement of an arbitrary point of the hidden columnar steel structure) is obtained, the eigen value and the eigen vector are obtained by solving the eigen equation, where the eigen value is a wave number k (k is a complex number) of the ultrasonic guided wave in the hidden columnar steel structure, and cp (f) ═ ω/k is solvedRe(where ω represents angular frequency, kReRepresenting the real part of the wavenumber k) can be obtained a phase velocity dispersion curve Cp(f) Propagating group velocity dispersion curve Cg(f) Solving for atta (f) kIm(where k isImThe imaginary part of the wave number k) to obtain an attenuation curve Atta (f), and solving
(where f is the frequency of the waveguide and d is the waveguide)Thickness of material, fd is frequency-thickness product), by the group velocity dispersion curve C obtainedg(f) Phase velocity dispersion curve Cp(f) And the attenuation curve atta (f) establishing a standard library;
(2) selecting a phase velocity dispersion curve C with the same working condition, coating layer, core layer diameter and material as the anchor rod to be detected from the standard library established in the step 1p(f) (fig. 4), obtaining preliminary screening candidate modes L (0,11), L (0,15), L (0,19), L (0,22) for detection through a first screening condition, wherein the preliminary screening detection frequency range is 2.0MHz to 2.4MHz, L (0,11), L (0,15), L (0,19), and L (0,22) respectively represent guided wave modes of different orders in the ultrasonic guided wave longitudinal mode;
(3) selecting a group velocity dispersion curve C of a model with the same working condition, cladding layer diameter, core layer rod diameter and material as those in the embodiment from the standard libraryg(f) (fig. 5), obtaining a secondary screening candidate modality L (0,22) for detection finally through a second screening condition;
(4) selecting an attenuation curve (figure 6) of a model with the same working condition, cladding layer, core layer rod diameter and material as those in the embodiment from the standard library, and obtaining the detected dominant frequency of 2.20 MHz-2.28 MHz through a third screening condition;
(5) through the fourth screening condition, a wave structure with displacement mainly concentrated at the central part of the core layer of the anchor rod and hardly interacted with the cladding layer can be obtained, and the wave structure is used as a target of guided wave excitation as shown in fig. 7;
(6) the method comprises the following steps of finishing automatic recommendation of working parameters and installation parameters of a guided wave transducer, carrying out model selection installation and guided wave excitation on the ultrasonic guided wave transducer, realizing automatic attenuation of guided wave acoustic energy leaked to the outside of a tested member by utilizing the sound field distribution characteristics of ultrasonic guided waves and the material acoustic characteristics of a coating layer, increasing the consistency and uniformity of a guided wave sound field, receiving pure target modal guided waves, improving the signal-to-noise ratio and enhancing the readability of guided wave signals;
(7) reading the propagation time t of the first end face echo wave packet of the pure target mode guided wave waveform in the step (6) to be 3.12 x 10-3s, and using the guided wave propagation velocity v 5798m/s, according to x v t (5798 x 3.12 x 10)-3/2) conversion of 9.04m to mThe propagation distance x is 9.04m, and x is the length of the hiding steel structure. delta x-xreal＝(9.04-9)m＝0.04m,err＝delta/xrealWhen the ratio of 0.04/9 was 0.0049, the detection error was only 0.49%.
The detection of the anchor in this example was performed using low frequency guided ultrasound waves, in contrast to the method used in the present invention. Take the 64KHz who often is used for the detection in the low frequency as an example, its wave structure is shown in fig. 9, can see that detects dominant frequency when 64KHz, the displacement distribution of guided wave vibration is at the full cross-section of whole stock, and the guided wave is complicated in the effect of cladding border department, and the energy transmission is serious, and the decay is big, and the SNR is low, can't detect the echo signal of stock terminal surface.
Taking the upright column widely used as the highway guardrail as an example, according to the length measuring method, different detection frequencies and detection modes can be obtained for the upright columns of the highway guardrail made of different materials, in different sizes and under different working conditions. For example: the inner diameter of the central upright column is
An outer diameter of
The main detection frequency of the upright column of the expressway guardrail with the length of 2.8m and the burial depth of 2.2m selected according to the length measurement method is 3.4MHz, and the detection mode is T (0, 15). The selected main frequency and the selected guided wave mode are used for detecting the sample in the embodiment, and an end face echo signal with extremely small detection error can be obtained.
The above-described embodiments are intended to be illustrative of the present invention and not to be limiting, and any modifications and variations of the present invention are possible within the spirit of the present invention and the scope of the appended claims.
Claims (10)
1. A length measuring method of a hidden columnar steel structure based on an ultrasonic guided wave sound field regulation technology is disclosed, wherein the hidden columnar steel structure comprises a core layer and a coating layer, and the method is characterized by comprising the following steps:
step 1: for the hidden columnar steel structure, the group velocity dispersion curve C is solvedg(f) Phase velocity dispersion curve Cp(f) The attenuation curve Atta (f) is used for establishing a standard library;
step 2: selecting a phase velocity dispersion curve C corresponding to the detected hidden columnar steel structure from the standard libraryp(f) Taking the percentage alpha of the continuous change of the phase velocity value within the bandwidth delta f not more than the change of the longitudinal wave velocity of the measured hidden columnar steel structure as a first screening condition to obtain a primary screening candidate mode and a primary screening detection frequency band for detection;
and step 3: selecting a group velocity dispersion curve C corresponding to the detected hidden columnar steel structure from the standard libraryg(f) Using the preliminary screening candidate modality obtained in the step 2 to correspond to the modality in the group velocity dispersion curve, and using the percentage alpha of the continuous change of the group velocity within the bandwidth delta f not exceeding the change of the maximum value of the group velocity as a second screening condition to complete the secondary filtration of the modality to obtain a secondary screening candidate modality;
and 4, step 4: selecting an attenuation curve corresponding to the detected hidden columnar steel structure from the standard library, and taking the minimum value of the attenuation curve of the secondary screening candidate mode as a third screening condition to obtain a detected main frequency fmain；
And 5: detecting the main frequency f obtained according to the step 4mainAnd step 3, drawing a wave structure of the secondary screening candidate mode, and screening a guided wave mode wave structure which does not interact with the cladding layer by taking a wave structure with vibration displacement concentrated at a position near the center of the core layer as a fourth screening condition;
step 6: according to the secondary screening candidate modality obtained in the step 3 and the detected main frequency f obtained in the step 4mainAnd step 5, automatically recommending working parameters and installation parameters of the guided wave transducer to carry out guided wave excitation, and utilizing the sound field distribution characteristics of ultrasonic guided waves (the guided wave modal wave structure obtained in step 5) and the material acoustic characteristics (damping parameters) of the coating layer to realize guided wave excitationAutomatically attenuating the acoustic energy of the guided waves leaked to the outside of the tested member, and receiving pure guided waves in the target mode;
and 7: and (3) reading the propagation time t of the first end face echo wave packet of the pure target mode guided wave waveform in the step (6), and converting the propagation time t into a propagation distance x according to x-v-t by utilizing the guided wave propagation speed v, wherein x is the length of the concealed steel structure.
2. The method for measuring the length of the concealed columnar steel structure based on the ultrasonic guided wave sound field regulation and control technology is characterized in that: the specific method for establishing the standard library in the step 1 comprises the following steps:
solving a wave control equation aiming at a hidden columnar steel structure
σrr＝σrθ＝σrz＝0，r＝Ri，r＝RoAdding isochoric conditions
Then, a characteristic equation C.A is obtained, wherein u represents a guided wave displacement field, sigma represents a stress vector, lambda and mu represent material Lame constants, rho represents material density, H represents isovolumetric vector potential, C represents a stiffness matrix of the material, A represents displacement of any point of the hidden columnar steel structure, the characteristic equation is solved, and characteristic values and characteristic vectors are obtained so as to obtain a group velocity dispersion curve C of ultrasonic guided wave propagation in the hidden columnar steel structureg(f) Phase velocity dispersion curve Cp(f) And (f) establishing a standard library by using the attenuation curve Atta (f).
3. The method for measuring the length of the concealed columnar steel structure based on the ultrasonic guided wave sound field regulation and control technology is characterized in that: the first screening condition of step 2 comprises the following steps:
1) according to Cp (m,n)(f)＝ClCalculating a frequency value under the wave velocity of the longitudinal wave;
2) if it is
Taking f epsilon (f-delta f/2, f + delta f/2);
3) if it is
According to
Finding f1Value, take f e (f)1,f1+Δf)；
4) If it is
According to
Finding f2Value, take f e (f)2-Δf,f2)；
Wherein C islRepresenting the velocity of longitudinal waves; α represents the percentage of change in wave velocity; cp (m,n)(f) Representing a phase velocity dispersion curve; f. ofminRepresents a minimum frequency; f. ofmaxRepresents the maximum frequency; Δ f represents the bandwidth; f denotes the frequency, f1Representing the lower limit frequency, f, of the frequency band2Indicating the upper frequency of the band.
4. The method for measuring the length of the concealed columnar steel structure based on the ultrasonic guided wave sound field regulation and control technology is characterized in that: the second screening condition in step 3 is:
wherein C isg (m,n)(f) Representing a group velocity dispersion curve; percentage of change in alpha wave velocity; f represents frequency.
5. The method for measuring the length of the concealed columnar steel structure based on the ultrasonic guided wave sound field regulation and control technology is characterized in that: the third screening condition in the step 4 is as follows:
fmain＝Atta-1[min(Atta(m,n)(f))]
wherein f ismainIndicating the detection main frequency; atta(m,n)(f) Representing guided wave attenuation values at different frequencies; f represents frequency.
6. The method for measuring the length of the concealed columnar steel structure based on the ultrasonic guided wave sound field regulation and control technology is characterized in that: the fourth screening condition of step 5 comprises the following steps:
1) detecting the dominant frequency f selected in claim 5mainPerforming wave structure drawing on the candidate mode selected in the claim 4;
2) to be provided with
Selecting a guided wave excitation sound field as a screening condition;
wherein Amp (x) is the displacement profile of the wave structure in the radial direction; beta is a sound field concentration degree coefficient, the value range of beta is more than or equal to 0.2 and less than or equal to 0.8, and the optimal value range of beta is more than or equal to 0.4 and less than or equal to 0.7.
7. The method for measuring the length of the concealed columnar steel structure based on the ultrasonic guided wave sound field regulation and control technology is characterized in that: the value range of alpha in the steps 2 and 3 is more than or equal to 3% and less than or equal to 40%, and preferably, the value range of alpha is more than or equal to 5% and less than or equal to 16%.
8. The concealed columnar steel knot based on ultrasonic guided wave sound field regulation and control technology of claim 1The structure length measuring method is characterized in that: step 4, the selected detected main frequency fmainIn the guided wave high frequency band of not less than 1MHz, preferably, the main frequency fmainThe range of (A) is 2MHz to 8 MHz.
9. The utility model provides a disguised columnar steel structure length measuring device based on ultrasonic guided wave sound field regulation and control technique, includes mobile device, monitoring host computer and ultrasonic guided wave transducer, wherein:
the mobile equipment is used for automatically selecting a detected main frequency, a detected mode and a guided wave modal wave structure of the detected hidden cylindrical steel structure, automatically recommending working parameters and installation parameters of the ultrasonic guided wave transducer, and displaying a guided wave waveform processed by the monitoring host and a length value x of the detected hidden cylindrical steel structure;
the monitoring host comprises an ultrasonic guided wave excitation unit and an ultrasonic guided wave receiving unit, wherein the ultrasonic guided wave excitation unit applies an excitation signal to the ultrasonic guided wave transducer, mechanical vibration is excited at the free end of the detected concealed columnar steel structure, the receiving unit converts an elastic wave signal in the detected concealed columnar steel structure into an electric signal, the signal processing unit transmits data to the mobile equipment after signal amplification, A/D conversion, filtering rectification and signal average processing, and the guided wave waveform processed by the monitoring host and the length value x of the detected concealed columnar steel structure are displayed.
10. The apparatus of claim 9, wherein:
the mobile device realizes the automatic selection of the detection main frequency, the detection mode and the guided wave modal wave structure of the detected hidden cylindrical steel structure according to the steps of any one of claims 1 to 8, and automatically recommends the working parameters and the installation parameters of the ultrasonic guided wave transducer.
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