Fan tower bolt crack detection method and device based on ultrasonic spiral phase control array

Abstract

The invention discloses a fan tower bolt crack detection method and device based on an ultrasonic spiral phase control array, and relates to the technical field of nondestructive testing. According to the method, the phased array detection data of the bolt containing the defects are acquired by adopting the modes of array element partition emission, area-by-area focusing and other area array element receiving, and the whole spiral phased array is focused on the detection point based on the delay accumulation principle to construct a full-focusing imaging image, so that the intensity of a detection signal is improved, and the detection accuracy is improved. The defect that detection signals with crack information are often submerged in dense thread signals due to the fact that cracks are small in size and variable in extension direction is overcome, and rapid and accurate detection of the tiny cracks at the root of the thread can be achieved under the non-disassembly condition.

Description

Technical Field

[0001] The present application relates to the field of nondestructive testing technology, and in particular to a method and device for detecting cracks in wind turbine tower bolts based on an ultrasonic spiral phased array. Background Art

[0002] China's large-scale wind turbine bases are primarily located in wind-rich regions such as Northeast China, North China, Northwest China, and along the coast. These bases frequently face extreme conditions such as rain, snow, storms, sandstorms, and low temperatures, resulting in extremely harsh operating conditions. The high loads and extreme climate conditions at these bases significantly increase the risk of fatigue damage to key tower components, potentially leading to catastrophic accidents such as wind turbine collapses. Therefore, timely inspection and accurate evaluation of key components of in-service wind turbine towers are essential. High-strength bolts, core tower connectors, are subjected to constant loads of gravity, alternating wind loads, and the shock of startup and shutdown operations. Stress concentration at the root of the threads can easily lead to fatigue cracks. Statistics show that over 60% of wind turbine collapses are caused by the breakage of these bolts. Therefore, to ensure the safety of equipment and personnel during wind turbine service, regular inspection of tower bolts for fatigue damage is essential.

[0003] Since fatigue cracks in high-strength bolts on wind turbine towers almost all appear at the thread root in the first three turns of engagement with the nut, the crack size is small and the extension direction is variable. The detection signal containing crack information is often submerged in the dense thread signal. Existing non-destructive testing methods are difficult to achieve rapid and accurate characterization of tiny cracks at the thread root without disassembly. Therefore, it is necessary to disassemble the tower bolts one by one and perform offline testing such as destructive metallographic inspection or magnetic particle inspection. Summary of the Invention

[0004] The purpose of this application is to provide a method and device for detecting cracks in wind turbine tower bolts based on an ultrasonic spiral phased array, so as to realize accurate online detection of wind turbine tower bolts.

[0005] To achieve the above objectives, this application provides the following solutions.

[0006] In a first aspect, the present application provides a method for detecting cracks in wind turbine tower bolts based on an ultrasonic spiral phased array, comprising the following steps:

[0007] Using each sub-domain of the ultrasonic spiral phased array as the transmitting area and the sub-domain of the ultrasonic spiral phased array other than the transmitting area as the receiving area, an active focusing method with phase delay superposition was used to scan each detection point on the bolt crack of the wind turbine tower to obtain bolt phased array detection data.

[0008] The bolt phased array detection data is focused and imaged using a full-focus imaging method to obtain the detection intensity of each detection point and construct a full-focus imaging image of the wind turbine tower bolts;

[0009] Crack identification is performed based on the fully focused imaging image to obtain identification results.

[0010] Optionally, each sub-domain of the ultrasonic spiral phased array is used as the transmitting area, and the sub-domain of the ultrasonic spiral phased array other than the transmitting area is used as the receiving area. An active focusing method of phase delay superposition is used to scan each detection point on the bolt crack of the wind turbine tower to obtain bolt phased array detection data, specifically including:

[0011] According to the relative positions of the sub-areas of the ultrasonic spiral phased array, at preset time intervals, the sub-areas of the ultrasonic spiral phased array are respectively set as transmitting areas, and the sub-areas of the ultrasonic spiral phased array other than the transmitting areas are set as receiving areas;

[0012] The active focusing method of phase delay superposition is adopted, so that the beams excited by each array element in the transmitting area are focused to the detection point at the same time, and each array element in the receiving area receives the beam emitted by the detection point respectively, and the bolt phased array detection data is obtained.

[0013] Optionally, the preset time interval is greater than or equal to the maximum propagation delay of the detection point scan.

[0014] Optionally, a full-focus imaging method is used to focus the bolt phased array detection data to obtain the detection intensity of each detection point and construct a full-focus imaging image of the wind turbine tower bolts, specifically including:

[0015] Using the full-focus imaging method, the detection intensity of the detection point p is calculated when the subdomain m is the transmitting area and the subdomain outside the subdomain m is the receiving area; m = 1, 2, ..., M, where M is the number of subdomains divided by the ultrasonic spiral phased array;

[0016] Calculate the average value of the detection intensity of the detection point p when each sub-domain is the transmitting area and the sub-domain outside the sub-domain m is the receiving area, and use it as the detection intensity of the detection point p;

[0017] Based on the detection intensity of each detection point on the wind turbine tower bolt crack, a fully focused imaging image is constructed.

[0018] Optionally, using the full focus imaging method, the formula for calculating the detection intensity of the detection point p when the subdomain m is the emission area and the subdomain outside the subdomain m is the receiving area is:

[0019]

[0020] Where I[m,p] is the detection intensity of the detection point p when the subdomain m is the transmitting area and the subdomain outside the subdomain m is the receiving area, S m,t,r [T m,t,r] is the detection intensity of the beam transmitted by the array element r in the receiving area to the array element t in the sub-area m, T m,t,r is the propagation delay of the array element r in the receiving area relative to the array element t in the sub-area m, n sub is the number of array elements in each subdomain, d m,t,r is the propagation distance of the array element r in the receiving area relative to the array element t in the subdomain m, v is the wave speed, x m,t 、y m,t 、z m,t They are the x-axis coordinate, y-axis coordinate, and z-axis coordinate of the array element t in the subdomain m, respectively. p 、y p 、z p They are the x-axis coordinate, y-axis coordinate, and z-axis coordinate of the detection point p, respectively. r 、y r 、z r are the x-axis coordinate, y-axis coordinate, and z-axis coordinate of the array element r in the receiving area.

[0021] Optionally, the average value of the detection intensity of the detection point p when each sub-area is a transmitting area and the sub-area outside the sub-area m is a receiving area is calculated, and the formula for the detection intensity of the detection point p is:

[0022]

[0023] Wherein, I[m,p] is the detection intensity of detection point p when subdomain m is the transmitting area and the subdomain outside subdomain m is the receiving area, and I[p] is the detection intensity of detection point p.

[0024] In a second aspect, the present application provides a wind turbine tower bolt crack detection device based on an ultrasonic spiral phased array, comprising: a spiral probe and a wind turbine tower bolt crack detection system;

[0025] The spiral probe is connected to the wind turbine tower bolt crack detection system;

[0026] The wind turbine tower bolt crack detection system is used to adopt the above-mentioned wind turbine tower bolt crack detection method based on ultrasonic spiral phased array to obtain identification results.

[0027] Optionally, the wind turbine tower bolt crack detection system includes: a domain excitation-active focusing control module, an echo processing module and a crack detection module;

[0028] The sub-domain excitation-active focusing control module is used to control the spiral probe to scan each detection point on the bolt crack of the wind turbine tower using each sub-domain of the ultrasonic spiral phased array as the transmitting area and the sub-domain of the ultrasonic spiral phased array other than the transmitting area as the receiving area by adopting the active focusing method of phase delay superposition to obtain bolt phased array detection data.

[0029] The echo processing module is used to perform focused imaging on the bolt phased array detection data using a full-focus imaging method, obtain the detection intensity of each detection point, and construct a full-focus imaging image of the wind turbine tower bolts;

[0030] The crack detection module is used to perform crack identification based on the fully focused imaging image to obtain an identification result.

[0031] Optionally, the spiral probe is a Fermat spiral phased array probe.

[0032] Optionally, the spiral probe comprises: a Fermat spiral wafer array, a spiral wedge structure and a composite acoustic layer;

[0033] The Fermat spiral chip array is located above the spiral wedge structure, and the composite acoustic layer wraps the Fermat spiral chip array and the spiral wedge structure.

[0034] According to the specific embodiments provided in this application, this application has the following technical effects.

[0035] The present application provides a method and device for detecting cracks in wind turbine tower bolts based on an ultrasonic spiral phased array. The method comprises: using each subdomain of the ultrasonic spiral phased array as an emitting area and the subdomain of the ultrasonic spiral phased array other than the emitting area as a receiving area, adopting an active focusing method of phase delay superposition to scan each detection point on the crack of the wind turbine tower bolt to obtain bolt phased array detection data; adopting a full-focus imaging method to focus and image the bolt phased array detection data to obtain the detection intensity of each detection point and construct a full-focus imaging image of the wind turbine tower bolt; and performing crack identification based on the full-focus imaging image to obtain an identification result. This application adopts the method of transmitting in partitioned array elements, focusing on each area, and receiving by elements in the remaining areas to collect bolt phased array detection data containing defects. Based on the principle of delayed accumulation, the entire spiral phased array is focused on the detection point to construct a fully focused imaging image, thereby improving the strength of the detection signal and overcoming the defect that the detection signal with crack information is often submerged in the dense thread signal due to the small crack size and variable extension direction. It can realize fast and accurate detection of tiny cracks at the root of the thread without disassembly. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0037] Figure 1 This is a flow chart of a method for detecting cracks in wind turbine tower bolts based on an ultrasonic spiral phased array according to one embodiment of the present application.

[0038] Figure 2 This is a schematic diagram of a wind turbine tower bolt crack detection method based on an ultrasonic spiral phased array according to an embodiment of the present application.

[0039] Figure 3 A schematic diagram of the principle of scanning sub-domains one by one according to an embodiment of the present application.

[0040] Figure 4 A schematic structural diagram of a spiral probe provided in one embodiment of the present application.

[0041] Figure 5 This is an A-scan echo result diagram of a 30us sampling point with one transmit and one receive element provided in an embodiment of the present application.

[0042] Figure 6 This is an example diagram of a fully focused imaging image of a wind turbine tower bolt provided in one embodiment of the present application. DETAILED DESCRIPTION

[0043] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0044] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0045] The embodiment of the present application provides a method and device for detecting cracks in wind turbine tower bolts based on an ultrasonic spiral phased array. It can detect fatigue cracks in high-strength bolts of wind turbine towers to solve the problems of severe sidelobe interference, low mixed-mode excitation efficiency, and insufficient accuracy in imaging of small cracks in existing non-destructive testing of bolts. It can improve the signal-to-noise ratio of crack detection, increase the detection speed, achieve highly sensitive and rapid detection and accurate imaging, and provide a new solution for the safe operation and maintenance of key connectors of wind power equipment.

[0046] In an exemplary embodiment, a method for detecting cracks in wind turbine tower bolts based on an ultrasonic spiral phased array is provided. Figure 1 As shown, the process includes the following steps 101 to 103.

[0047] In step 101, each sub-domain of the ultrasonic spiral phased array is used as the transmitting area, and the sub-domain of the ultrasonic spiral phased array other than the transmitting area is used as the receiving area. An active focusing method of phase delay superposition is used to scan each detection point on the bolt crack of the wind turbine tower to obtain bolt phased array detection data.

[0048] Step 102 : performing focused imaging on the bolt phased array detection data using a full-focus imaging method to obtain the detection intensity of each detection point and construct a full-focus imaging image of the wind turbine tower bolts.

[0049] Step 103: Perform crack recognition based on the all-focus imaging image to obtain a recognition result.

[0050] Implementing the above steps 101 to 103 can improve the strength of the detection signal, overcome the defect that the detection signal with crack information is often submerged in the dense thread signal due to the small crack size and variable extension direction, and can achieve rapid and accurate detection of tiny cracks at the root of the thread without disassembly.

[0051] In another exemplary embodiment, in the above step 101, the ultrasonic spiral phased array is divided into multiple sub-domains; the sub-domains are excited in sequence according to their relative positions; the phase delay superposition of each array element in the sub-domain is controlled to establish beam deflection and focus on the detection point; and all array elements are controlled to synchronously receive signals, and the bolt phased array detection data is focused and imaged by a full-focus imaging method to construct a full-focus imaging image of the wind turbine tower bolts.

[0052] like Figure 2 As shown, the embodiment of the present application adopts the "domain focusing-full array capture" ultrasonic spiral phased array active full focusing scanning method to scan the wind turbine tower bolts. First, the ultrasonic spiral phased array is divided into multiple sub-domains and actively focused and transmitted in sequence. The focusing point is selected as the thread root in the high-incidence damage area, and then all array elements receive the reflected echo signal to achieve full focusing.

[0053] The transmitting array elements can be divided into F1-F8 according to the different sub-domains, and the corresponding areas below are numbered E1-E8. Figure 3 As shown, the specific process is:

[0054] ①F1 transmits, the sound wave is focused to the E1 area (expanded below), and the reflected wave S11 is received by other F2-F8; then, the sound wave is focused to the E2 area, and the reflected wave is received by F1 and F3-F8, and so on. Finally, the sound wave is focused to the E8 area, and the reflected wave is received by F1-F7.

[0055] In an embodiment of the present application, the method for focusing the sound waves to the E1 area is: active focusing is performed using a delay superposition algorithm, wherein the principle of the delay superposition algorithm is to calculate the delay of the echo data of different channels, and then perform delay compensation on the data of each channel to achieve data time domain alignment, and finally superimpose the aligned data to make the beam directional and maximize the energy at the target point (i.e., the detection point).

[0056] ②F2 transmits, the sound wave is focused to the E1 area, and the reflected wave S21 is received by F1, F3-F8; then, the sound wave is focused to the E2 area, and the reflected wave S22 is received by F1, F3-F8...Finally, the sound wave is focused to the E8 area, and the reflected wave S28 is received by F1, F3-F8.

[0057] …

[0058] ⑧F8 transmits, the sound wave focuses to the E1 area, and the reflected wave S81 is received by other F1-F7; then, the sound wave focuses to the E2 area, and the reflected wave S82 is received by F1-F7... Finally, the sound wave focuses to the E8 area, and the reflected wave S88 is received by F1-F7.

[0059] In the final imaging, the average value of S11+S12+…+S21+S22+…+S87+S88 is used as the imaging data, and the full-focus imaging method is used to image the bolt.

[0060] In another exemplary embodiment, the above step 101 may be replaced by the following steps 201 and 202.

[0061] Step 201 : According to the relative positions of the sub-domains of the ultrasonic spiral phased array, at preset time intervals, the sub-domains of the ultrasonic spiral phased array are set as transmitting areas, and the sub-domains of the ultrasonic spiral phased array except the transmitting areas are set as receiving areas.

[0062] In step 202, an active focusing method of phase delay superposition is used to simultaneously focus the beams excited by each array element in the transmitting area to the detection point, and each array element in the receiving area receives the beams emitted by the detection point respectively, thereby obtaining bolt phased array detection data.

[0063] In another exemplary embodiment, the preset time interval is greater than or equal to the maximum propagation delay of the detection point scan. Exemplarily, the preset time interval Δt=0.1 μs.

[0064] Assuming that the high damage area is the root of the first three threads of the nut engagement, the calculation formula for the distance L between the first detection point and the thread end face is: L = P × N, where P is the thread pitch (5 mm for M48 bolts) and N is the number of threads (N = 3).

[0065] Assume that the sampling time step is range(0,1 / 100,30), unit: us; that is, the total sampling depth is 30us, the step length is 0.01us, and the number of sampling points is 3000, such as Figure 5 As shown, the amount of bolt phased array detection data is: the number of transmitting array elements*the number of receiving array elements*the number of sampling points*the number of sampling times.

[0066] In another exemplary embodiment, the above step 102 may be replaced by the following steps 301 - 303 .

[0067] Step 301 , using a full-focus imaging method, calculate the detection intensity of a detection point p when subdomain m is a transmitting area and subdomains outside subdomain m are receiving areas; m=1, 2, ..., M, where M is the number of subdomains divided by the ultrasonic spiral phased array.

[0068] The phased array inspection data of bolts containing defects is collected by using a method of transmitting in different areas, focusing in each area, and receiving in the remaining sub-areas. Based on the principle of delayed accumulation, the entire spiral phased array is focused on all preset pixels in the image. If the total number of spiral array elements in the phased array is N and the number of sub-areas is M, the number of array elements in each sub-area is N / M = n. sub Assume that the transmitting / receiving area is located on the ultrasonic transducer (i.e., ultrasonic spiral phased array) and is marked as F1, F2, ..., FN, and the corresponding scanning area is located on the bolt part and is marked as E1, E2, ..., EN; the propagation speed of the sound wave in the object is v, and the full matrix data is S t,r , then the full focus imaging process for a single scan can be described as:

[0069] Let sub-domain m be the transmitting area. When the array element C in the transmitting area t (x t ,y t ,z t ) to a certain point in the focus area El (ie, detection point p) C p (x p ,y p ,z p ) When the ultrasonic beam is emitted, the reflected wave S ml Will be replaced by the array elements C in other sub-domains r (x r ,y r ,z r )Receive, distance d t,r C t →C p →C r The sum of the two distances is calculated as follows:

[0070]

[0071] Among them, dm,t,r is the propagation distance of the array element r in the receiving area relative to the array element t in the subdomain m, v is the wave speed, x m,t 、y m,t 、z m,t They are the x-axis coordinate, y-axis coordinate, and z-axis coordinate of the array element t in the subdomain m, respectively. p 、y p 、z p They are the x-axis coordinate, y-axis coordinate, and z-axis coordinate of the detection point p, respectively. r 、y r 、z r are the x-axis coordinate, y-axis coordinate, and z-axis coordinate of the array element r in the receiving area.

[0072] It should be noted that the above-mentioned x-axis coordinate, y-axis coordinate, and z-axis coordinate refer to coordinates in the world coordinate system, and the above-mentioned receiving area, transmitting area, and detection point are all in the same world coordinate system.

[0073] Based on the above distance propagation delay That is, the detection intensity of the detection point p when the subdomain m in the total focusing (TFM) imaging image is the emission area and the subdomain outside the subdomain m is the receiving area is obtained as shown in the following formula.

[0074]

[0075] Where I[m,p] is the detection intensity of the detection point p when the subdomain m is the transmitting area and the subdomain outside the subdomain m is the receiving area, S m,t,r [T m,t,r ] is the detection intensity of the beam transmitted by the array element r in the receiving area to the array element t in the sub-area m, T m,t,r is the propagation delay of the array element r in the receiving area relative to the array element t in the sub-area m, n sub is the number of array elements in each subdomain, and v is the wave velocity.

[0076] Step 302 : Calculate the average value of the detection intensity of the detection point p when each sub-area is a transmitting area and the sub-area other than the sub-area m is a receiving area, and use it as the detection intensity of the detection point p.

[0077]

[0078] Where I[p] is the detection intensity at detection point p.

[0079] Step 303: Based on the detection intensity of each detection point on the bolt crack of the wind turbine tower, a full-focus imaging image is constructed, such as Figure 6 shown.

[0080] In another exemplary embodiment, the crack identification method in the above step 103 can be implemented by neural network model training, or other identification methods can be used. In the embodiment of the present application, there is no limitation. When the crack identification method is implemented by neural network model training, the step specifically includes:

[0081] A training sample is constructed, in which the crack locations and damage degrees of the wind turbine tower bolts are marked.

[0082] The neural network model is trained based on the above training samples to obtain a trained neural network model.

[0083] The fully focused imaging image is fed into the trained neural network model to obtain recognition results, including crack location and damage severity.

[0084] In an exemplary embodiment, a wind turbine tower bolt crack detection device based on an ultrasonic spiral phased array is provided, comprising: a spiral probe and a wind turbine tower bolt crack detection system; the spiral probe is connected to the wind turbine tower bolt crack detection system; the wind turbine tower bolt crack detection system is used to adopt the wind turbine tower bolt crack detection method based on an ultrasonic spiral phased array in one or more of the above embodiments to obtain an identification result.

[0085] In another exemplary embodiment, the wind turbine tower bolt crack detection system includes: a domain excitation-active focusing control module, an echo processing module and a crack detection module; the domain excitation-active focusing control module is used to use each subdomain of the ultrasonic spiral phased array as the transmitting area, and the subdomain of the ultrasonic spiral phased array other than the transmitting area as the receiving area, and adopt an active focusing method of phase delay superposition to control the spiral probe to scan each detection point on the wind turbine tower bolt crack to obtain bolt phased array detection data; the echo processing module is used to use a full-focus imaging method to focus and image the bolt phased array detection data, obtain the detection intensity of each detection point, and construct a full-focus imaging image of the wind turbine tower bolt; the crack detection module is used to identify cracks based on the full-focus imaging image to obtain identification results.

[0086] In another exemplary embodiment, the spiral probe is a Fermat spiral phased array probe, such as Figure 4As shown, it includes a Fermat spiral chip array, a spiral wedge structure and a composite acoustic layer; the piezoelectric chips of the Fermat spiral chip array are arranged non-periodically along the Fermat spiral line, wherein the Fermat spiral chip array serves as the above-mentioned ultrasonic spiral phased array, and the piezoelectric chips serve as the above-mentioned array element; the spiral wedge structure is located below the Fermat spiral chip array, and its spiral curvature is consistent with the arrangement of the piezoelectric chips; the composite acoustic layer covers the Fermat spiral chip array and the spiral wedge structure, and the composite acoustic layer is composed of a matching layer (thickness λ / 4), a damping layer (attenuation coefficient ≥ 20dB / mm), and a shell (thickness 0.25λ) from the inside to the outside, wherein λ is the wavelength of the array element excitation beam. Exemplarily, the composite acoustic layer includes: an epoxy resin shell, a tungsten powder-doped damping layer, and a matching layer with adjustable acoustic impedance.

[0087] In another exemplary embodiment, the polar coordinate equation of the piezoelectric wafers arranged non-periodically according to the Fermat spiral is: r=a×β^1 / 2, where r is the radius, a is the coefficient, a=0.8±0.05, β is the polar angle, 0≤β≤8π.

[0088] In another exemplary embodiment, the number of piezoelectric wafers included in the Fermat spiral wafer array is 64, and the diameter of the piezoelectric wafer is 1 mm.

[0089] In another exemplary embodiment, the spacing between adjacent piezoelectric wafers follows the principle of equal arc length, and the minimum spacing between adjacent piezoelectric wafers is 0.15 mm.

[0090] In another exemplary embodiment, the filling factor of the piezoelectric wafer is 10%, 30%, 50%, or 70±2%.

[0091] In another exemplary embodiment, the spiral curvature of the spiral wedge structure is consistent with the arrangement of the piezoelectric wafer.

[0092] In another exemplary embodiment, the incident angle θ of the spiral wedge structure is 42°±2°, which is used to excite S&L mixed mode ultrasonic waves.

[0093] When in use, the mixed-mode excitation mode is excited, and the array is excited by a high-voltage pulse source, and the incident angle is controlled to be lower than the first critical angle to excite the mixed mode of the main longitudinal wave L mode and the main shear wave S mode.

[0094] Therefore, the ultrasonic phased array structure design of the Fermat spiral circular array in this example can significantly improve the phased array filling factor compared to traditional arrays at a micro-array element spacing while reducing the influence of the acoustic beam grating lobe and side lobe, achieving high-energy excitation and accurate imaging of the ultrasonic phased array. Moreover, in this example, Figure 5The simulation results show that longitudinal (L mode) and transverse (S mode) ultrasonic waves are more sensitive to transverse and longitudinal cracks, respectively, and can effectively detect multi-directional fatigue cracks in wind turbine tower bolts.

[0095] For example, the longitudinal and shear wave sound velocities of the epoxy resin wedge are 2700 m / s and 1120 m / s, respectively, and the longitudinal and shear wave sound velocities of the steel bolt are 5900 m / s and 3200 m / s, respectively. When the incident angle θ = 42°: the L wave and the S wave are transmitted into the bolt at the same time, realizing dual-mode detection.

[0096] In another exemplary embodiment, when in use, the probe is positioned so that the probe axis coincides with the bolt axis.

[0097] In another exemplary embodiment, the incident angle control strategy can be set to dual-mode alternation, specifically: L-mode excitation: fixed incident angle of 25.0°±0.3°, S-mode excitation: fixed incident angle of 55.0°±0.5°, mode switching period: 0.1ms.

[0098] As one embodiment, the corresponding relationship between the curvature radius of the spiral wedge structure and the bolt specifications is: M36 bolt (curvature radius 18.0±0.2mm), M48 bolt (curvature radius 24.0±0.2mm), M64 bolt (curvature radius 32.0±0.3mm).

[0099] In another exemplary embodiment, the matching layer has an acoustic impedance of 4.5 MRayl, is made of tungsten powder / epoxy resin at a mass ratio of 3:1, and has a thickness of 0.25 mm (1 / 4 wavelength at a center frequency of 5 MHz).

[0100] In another exemplary implementation, the damping layer comprises 80 wt % tungsten powder (particle size 2-5 μm) and 20 wt % epoxy resin, has a thickness of 0.6 mm, and an acoustic impedance of 28 MRayl.

[0101] According to the specific embodiments provided in this application, this application has the following technical effects.

[0102] 1. This application adopts the method of transmitting in partitioned array elements, focusing in each area, and receiving in the remaining areas to collect bolt phased array detection data containing defects, and based on the principle of delayed accumulation, focuses the entire spiral phased array on the detection point to construct a fully focused imaging image, thereby improving the strength of the detection signal and overcoming the defect that the detection signal with crack information is often submerged in the dense thread signal due to the small crack size and variable extension direction. It can realize fast and accurate detection of tiny cracks at the root of the thread without disassembly.

[0103] 2. The embodiment of the present application adopts a Fermat spiral array to greatly improve the acoustic energy focusing efficiency compared with traditional linear arrays and ring arrays; and the mixed-mode excitation in the present invention avoids the missed detection of transverse or longitudinal cracks, thereby improving the sensitivity of defect detection; the domain focusing algorithm in the present invention greatly reduces the bolt scanning time, and the efficiency is increased to 8 times that of the traditional algorithm (when the number of subdomains is 8).

[0104] 3. The embodiment of the present application achieves precise control of the S&L mixed mode acoustic energy ratio by dynamically adjusting the incident angle of the spiral wedge structure, thereby overcoming the industry problem of uneven detection rate of cracks in multiple directions.

[0105] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0106] This document uses specific examples to illustrate the principles and implementation methods of this application. The description of the above examples is only intended to help understand the method and core concept of this application. At the same time, for those skilled in the art, based on the concept of this application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A method for detecting cracks in wind turbine tower bolts based on ultrasonic spiral phased array, characterized in that: The steps include: Using each sub-domain of the ultrasonic spiral phased array as the transmitting area and the sub-domain of the ultrasonic spiral phased array other than the transmitting area as the receiving area, an active focusing method with phase delay superposition was used to scan each detection point on the bolt crack of the wind turbine tower to obtain bolt phased array detection data. The bolt phased array detection data is focused and imaged using a full-focus imaging method to obtain the detection intensity of each detection point and construct a full-focus imaging image of the wind turbine tower bolts; Crack identification is performed based on the fully focused imaging image to obtain identification results.

2. The wind turbine tower bolt crack detection method based on ultrasonic spiral phased array according to claim 1 is characterized in that: Using each sub-domain of the ultrasonic spiral phased array as the transmitting area and the sub-domain of the ultrasonic spiral phased array other than the transmitting area as the receiving area, an active focusing method with phase delay superposition is used to scan each detection point on the bolt crack of the wind turbine tower to obtain bolt phased array detection data, including: According to the relative positions of the sub-areas of the ultrasonic spiral phased array, at preset time intervals, the sub-areas of the ultrasonic spiral phased array are respectively set as transmitting areas, and the sub-areas of the ultrasonic spiral phased array other than the transmitting areas are set as receiving areas; The active focusing method of phase delay superposition is adopted, so that the beams excited by each array element in the transmitting area are focused to the detection point at the same time, and each array element in the receiving area receives the beam emitted by the detection point respectively, and the bolt phased array detection data is obtained.

3. The method for detecting cracks in wind turbine tower bolts based on ultrasonic spiral phased array according to claim 2, characterized in that: The preset time interval is greater than or equal to the maximum propagation delay of the detection point scan.

4. The method for detecting cracks in wind turbine tower bolts based on ultrasonic spiral phased array according to claim 1, characterized in that: The full-focus imaging method is used to focus the bolt phased array detection data to obtain the detection intensity of each detection point and construct a full-focus imaging image of the wind turbine tower bolts, specifically including: Using the full-focus imaging method, the detection intensity of the detection point p is calculated when the subdomain m is the transmitting area and the subdomain outside the subdomain m is the receiving area; m = 1, 2, ..., M, where M is the number of subdomains divided by the ultrasonic spiral phased array; Calculate the average value of the detection intensity of the detection point p when each sub-domain is the transmitting area and the sub-domain outside the sub-domain m is the receiving area, and use it as the detection intensity of the detection point p; Based on the detection intensity of each detection point on the wind turbine tower bolt crack, a fully focused imaging image is constructed.

5. The method for detecting cracks in wind turbine tower bolts based on ultrasonic spiral phased array according to claim 4, characterized in that: Using the full-focus imaging method, the formula for calculating the detection intensity of the detection point p when the subdomain m is the emission area and the subdomain outside the subdomain m is the receiving area is: Where I[m,p] is the detection intensity of the detection point p when the subdomain m is the transmitting area and the subdomain outside the subdomain m is the receiving area, S m,t,r [T m,t,r ] is the detection intensity of the beam transmitted by the array element r in the receiving area to the array element t in the sub-area m, T m,t,r is the propagation delay of the array element r in the receiving area relative to the array element t in the sub-area m, n sub is the number of array elements in each subdomain, d m,t,r is the propagation distance of the array element r in the receiving area relative to the array element t in the subdomain m, v is the wave speed, x m,t 、y m,t 、z m,t They are the x-axis coordinate, y-axis coordinate, and z-axis coordinate of the array element t in the subdomain m, respectively. p 、y p 、z p They are the x-axis coordinate, y-axis coordinate, and z-axis coordinate of the detection point p, respectively. r 、y r 、z r are the x-axis coordinate, y-axis coordinate, and z-axis coordinate of the array element r in the receiving area.

6. The method for detecting cracks in wind turbine tower bolts based on ultrasonic spiral phased array according to claim 4, characterized in that: Calculate the average value of the detection intensity of the detection point p when each sub-domain is the transmitting area and the sub-domain outside the sub-domain m is the receiving area. The formula for the detection intensity of the detection point p is: Wherein, I[m,p] is the detection intensity of detection point p when subdomain m is the transmitting area and the subdomain outside subdomain m is the receiving area, and I[p] is the detection intensity of detection point p.

7. A wind turbine tower bolt crack detection device based on ultrasonic spiral phased array, characterized in that: include: Spiral probe and wind turbine tower bolt crack detection system; The spiral probe is connected to the wind turbine tower bolt crack detection system; The wind turbine tower bolt crack detection system is used to adopt the wind turbine tower bolt crack detection method based on ultrasonic spiral phased array according to any one of claims 1 to 6 to obtain an identification result.

8. The wind turbine tower bolt crack detection device based on ultrasonic spiral phased array according to claim 7 is characterized in that: The wind turbine tower bolt crack detection system includes: a domain excitation-active focusing control module, an echo processing module and a crack detection module; The sub-domain excitation-active focusing control module is used to control the spiral probe to scan each detection point on the bolt crack of the wind turbine tower using each sub-domain of the ultrasonic spiral phased array as the transmitting area and the sub-domain of the ultrasonic spiral phased array other than the transmitting area as the receiving area by adopting the active focusing method of phase delay superposition to obtain bolt phased array detection data. The echo processing module is used to perform focused imaging on the bolt phased array detection data using a full-focus imaging method, obtain the detection intensity of each detection point, and construct a full-focus imaging image of the wind turbine tower bolts; The crack detection module is used to perform crack identification based on the fully focused imaging image to obtain an identification result.

9. The wind turbine tower bolt crack detection device based on ultrasonic spiral phased array according to claim 7, characterized in that: The spiral probe is a Fermat spiral phased array probe.

10. The wind turbine tower bolt crack detection device based on ultrasonic spiral phased array according to claim 7 or 9, characterized in that: The spiral probe comprises: a Fermat spiral wafer array, a spiral wedge structure and a composite acoustic layer; The Fermat spiral chip array is located above the spiral wedge structure, and the composite acoustic layer wraps the Fermat spiral chip array and the spiral wedge structure.

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