Underwater complex environment wind power pile foundation defect multi-frequency acoustic imaging method

Abstract

This invention discloses a multi-frequency acoustic imaging method for wind turbine pile foundation defects in complex underwater environments, belonging to the field of non-destructive testing technology for engineering structures. The method includes the following steps: performing multi-frequency acoustic imaging detection on the wind turbine pile foundation; transmitting high-frequency acoustic waves into the water area during the detection period; receiving continuous echo signals formed by the round-trip propagation of the high-frequency acoustic waves between the water surface and the seabed; constructing a continuous echo time series; and recording an increasing sequence of round-trip propagation times within the continuous echo time series. This invention improves the accuracy of defect location by constructing a continuous echo time series and extracting the propagation time offset trajectory, identifying multi-path echo superposition sections, and distinguishing between the actual structural response and water reflection interference. Simultaneously, by locating the compressed interval of the round-trip propagation period and adjusting the transmission time rhythm, the echo superposition relationship is broken up, the imaging time structure is optimized, and the reliability and stability of wind turbine pile foundation defect imaging are improved.

Description

Technical Field

[0001] This invention relates to the field of non-destructive testing technology for engineering structures, specifically to a multi-frequency acoustic imaging method for defects in wind turbine pile foundations in complex underwater environments. Background Technology

[0002] Multi-frequency acoustic imaging of wind turbine pile foundation defects in complex underwater environments refers to a non-destructive underwater structural testing technique used in offshore or near-shore wind farms. This technique utilizes multiple frequencies of acoustic waves as detection carriers, exciting the sound waves into the pile body or propagating them along the pile. By continuously acquiring and analyzing the reflection, transmission, scattering, and attenuation characteristics of the sound waves during propagation, it extracts propagation anomalies caused by defects such as cracks, mud inclusions, voids, thinning walls, and corrosion pitting. Based on the differences in multi-frequency responses, it comprehensively reconstructs the location, morphology, and scale of defects, ultimately forming a spatially visualized imaging result. The multi-frequency aspect emphasizes the sensitivity differences of different frequency bands of acoustic waves to defects of different scales; the complex environment aspect emphasizes overcoming the influence of water noise, multipath interference, and interface coupling effects on signal recognition; and the imaging aspect refers to the algorithmic reconstruction of the acoustic response into a distribution map of internal structural defects, thereby achieving a refined assessment of the safety status of the wind turbine pile foundation.

[0003] The existing technology has the following shortcomings: In existing technologies, when performing multi-frequency acoustic imaging detection on wind turbine pile foundations in complex underwater environments, high-frequency acoustic waves are affected not only by changes in water flow velocity but also by the combined effects of water surface undulations and seabed topography. Some acoustic energy easily forms multiple round-trip reflection paths between the water surface and the seabed, resulting in multi-path superimposed echoes. These multi-path echoes differ in propagation time. When superimposed at the receiving end, they easily form echo contour signals with continuous boundaries and a closed shape within a specific time period. During imaging reconstruction, these signals may be misinterpreted as indicating internal cavities or localized voids within the pile, leading to a shift in the spatial location of defects and reducing the reliability of the detection results.

[0004] The information disclosed in the background section is only intended to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to provide a multi-frequency acoustic imaging method for defects in wind turbine pile foundations in complex underwater environments, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a multi-frequency acoustic imaging method for wind turbine pile foundation defects in complex underwater environments, comprising the following steps: Multi-frequency acoustic imaging detection is carried out on wind power pile foundations. High-frequency acoustic waves are emitted into the water area during the detection period, and continuous echo signals formed by the high-frequency acoustic waves propagating back and forth between the water surface and the seabed are received. A continuous echo time series is constructed, and the increasing sequence of the number of round-trip propagation times is recorded in the continuous echo time series. The continuous echo time series is time-expanded based on the increasing round-trip propagation number sequence. The echo signals in the continuous echo time series are rearranged in the order of increasing round-trip propagation number to form a multi-path unfolded time series. The propagation time offset trajectory is extracted from the multi-path unfolded time series. Based on the propagation time offset trajectory, the arrival order of echoes in the multipath unfolded time series is compared to identify echo segments whose arrival order deviates from the direct propagation order, determine the superposition segment, and record the corresponding time range of the superposition segment. Based on the time range corresponding to the superimposed section, the continuous echo time series is traced back to locate the round-trip propagation period compression interval corresponding to the superimposed section, and the time position corresponding to the round-trip propagation period compression interval is determined as the transmission adjustment entry position. The time interval of subsequent high-frequency acoustic wave transmission is reversely lengthened around the transmission adjustment entry position. Within the round-trip propagation period compression interval, the transmission time misalignment is set according to the successive increasing rule. By adjusting the transmission time rhythm, the echo superposition time relationship formed by the round-trip propagation is broken up, and the adjusted echo data is used for wind power pile foundation defect imaging reconstruction.

[0007] Preferably, the steps for constructing a continuous echo time series and recording an increasing sequence of round-trip propagation times are as follows: Divide the propagation time range and set the detection cycle length, continuously emit high-frequency acoustic pulses according to a fixed time reference, and record the emission time to form an emission time sequence; Based on the transmission time sequence, the received echo signals are arranged according to the reception time to form the original echo record data. The correspondence between the transmission time and the echo arrival time is established. Each echo is assigned a round-trip propagation number identifier and a continuous echo time sequence is constructed. By statistically analyzing the arrival times of multiple echoes corresponding to the same transmission time based on the continuous echo time series, and confirming the order of round-trip propagation times according to the time progression relationship, an increasing sequence of round-trip propagation times is formed. By combining the increasing sequence of round-trip propagation times, the continuous echo time series is segmented and marked, and the receiving time corresponding to the change in round-trip propagation times is recorded to form a table of changes in round-trip propagation times.

[0008] Preferably, the time unfolding processing and propagation time offset trajectory extraction steps are as follows: The continuous echo time series is analyzed point by point and grouped according to the number of round-trip propagation times to form a round-trip propagation number grouped sequence, and a grouped time record table is established; The time series of groups based on the number of round-trip propagation are unfolded and arranged under a unified time reference. The groups are then aligned and inserted in ascending order of the number of round-trip propagation to form a multipath unfolded time series. Based on multipath unfolded time series, the echo time coordinates of each level corresponding to the same transmission time are read. The time interval between adjacent levels is calculated in ascending order of round-trip propagation times to form a time offset data column and connect it along the transmission time sequence to construct the propagation time offset trajectory. The multipath unfolding time series is synchronously marked by combining the propagation time offset trajectory, and a corresponding time offset data column index is added to each launch time node.

[0009] Preferably, the round-trip propagation number grouping sequence is arranged in the original reception time order, the multipath unfolding time sequence is arranged hierarchically according to the transmission time identifier, and the propagation time offset trajectory is formed by sequentially connecting the echo time intervals corresponding to adjacent round-trip propagation numbers, and maintains a one-to-one time correspondence with the multipath unfolding time sequence.

[0010] Preferably, the steps for identifying arrival order deviations from direct propagation order and determining overlapping segments are as follows: Using the propagation time offset trajectory as a reference, the multipath unfolding time series is analyzed node by node of transmission, the echo time coordinates of each level are read and a direct propagation order reference sequence is constructed, the multi-level echo time set is compared with the direct propagation order reference sequence item by item, and the arrival order deviation events are recorded. A sequential comparison record is formed around each launch time node, and the sequence deviation record table is continuously advanced along the launch time axis; Based on the sequence deviation record table, the transmission time intervals of consecutive arrival sequence deviation events are aggregated and identified, and the superimposed segments are confirmed by combining the hierarchical echo time coordinates in the multipath unfolded time series. By combining the time boundaries of the superimposed segment in the multipath unfolding time series, the corresponding trajectory position is marked in the propagation time offset trajectory, and the corresponding time range of the superimposed segment is recorded.

[0011] Preferably, the continuous transmission time intervals that maintain the same level of deviation in the sequence deviation record table are screened, and the start and end times of the superposition segment are determined by combining the overlapping arrangement relationship of the level echo time coordinates in the multipath unfolding time series.

[0012] Preferably, the steps for locating the round-trip propagation period compression interval and determining the launch adjustment inlet position are as follows: The continuous echo time series is back-mapped around the time range corresponding to the superimposed segment, the echo set of the superimposed segment is extracted, and the transmission time identifier and round-trip propagation number identifier are read to form the echo subsequence of the superimposed segment; Based on the echo subsequence of the superimposed segment, the time difference between adjacent round-trip propagation echoes is calculated according to the transmission time identifier to form a round-trip propagation period variation sequence; Identify the launch time intervals where the period time continuously decreases based on the round-trip propagation period variation sequence, and determine the round-trip propagation period compression interval; By combining the time boundary of the round-trip propagation period compression interval in the continuous echo time series, the time position of the corresponding transmission time marker is determined as the transmission adjustment entry position.

[0013] Preferably, the steps of reverse lengthening the transmission time interval and image reconstruction are as follows: The original launch time sequence was read around the launch adjustment inlet position, and the launch time markers and adjacent launch time intervals within the round-trip propagation period compression interval were extracted to form the original launch interval record table. Based on the original launch interval record table, the launch time misalignment is set according to the successive increment rule within the round-trip propagation period compression interval, the launch time interval is reversely lengthened, and an updated launch time sequence is formed. Based on the updated transmission time series, high-frequency acoustic wave transmission is performed and continuous echo data is collected. The updated continuous echo time series is constructed and the round-trip propagation number is re-labeled. The updated continuous echo time series is combined with time unfolding processing and the propagation time offset trajectory is extracted. Based on the updated multipath unfolded time series, wind power pile foundation defect imaging reconstruction is performed.

[0014] The technical effects and advantages provided by the present invention in the above technical solution are as follows: This invention constructs a continuous echo time series and introduces an increasing sequence of round-trip propagation times to structurally unfold the multipath propagation behavior between the water surface and the seabed. This allows multipath echoes that were originally superimposed in the same time segment to be layered and rearranged in the time dimension, forming a traceable multipath unfolded time series. Based on this, the propagation time offset trajectory is extracted, and echo segments whose arrival order deviates from the direct propagation order are identified. This distinguishes the true structural response from water reflection interference at the source, avoiding the misjudgment of closed contour artifacts as cavities or voids, thereby improving the accuracy of spatial positioning of wind turbine pile foundation defects and the reliability of imaging results.

[0015] After identifying the round-trip propagation period compression interval, this invention uses the emission adjustment entry position as the control starting point to reversely lengthen the subsequent high-frequency acoustic wave emission time interval. Within the round-trip propagation period compression interval, the emission time misalignment is set according to a progressively increasing rule. By actively adjusting the emission time rhythm, the time arrangement structure of the round-trip propagation is changed, so that multi-path echoes no longer overlap in the same time window. The echo superposition relationship is broken up from the time source, so that the adjusted echo data has a clearer propagation hierarchy structure, providing a stable time distribution basis for wind power pile foundation defect imaging reconstruction. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0017] Figure 1 This is a flowchart of the multi-frequency acoustic imaging method for wind power pile foundation defects in complex underwater environments according to the present invention. Detailed Implementation

[0018] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, they are provided so that the description of this disclosure will be more complete and fully convey the concept of the exemplary embodiments to those skilled in the art.

[0019] This invention provides, for example Figure 1 The underwater complex environment wind turbine pile foundation defect multi-frequency acoustic imaging method shown includes the following steps: Multi-frequency acoustic imaging detection is carried out on wind power pile foundations. High-frequency acoustic waves are emitted into the water area during the detection period, and continuous echo signals formed by the high-frequency acoustic waves propagating back and forth between the water surface and the seabed are received. A continuous echo time series is constructed, and the increasing sequence of the number of round-trip propagation times is recorded in the continuous echo time series. This study focuses on the echo information generated by high-frequency sound waves propagating between the water surface and seabed during a detection period. To achieve a complete construction of a continuous echo time series and a full record of the increasing number of round-trip propagation cycles, this paper systematically explains the processes of establishing the transmission time sequence, associating echo reception, constructing the time axis, and marking the number of round trips. This forms a basic data structure with temporal continuity and propagation hierarchy attributes. The specific steps are as follows: Before detection begins, the propagation time range of the target water area is divided as a whole. Based on the vertical distance between the water surface and the seabed and the propagation speed of high-frequency sound waves in the water, the time interval corresponding to a single round trip is calculated, and the length of the detection cycle is set based on this time interval. At the beginning of the detection cycle, the first set of high-frequency sound wave pulses is emitted into the water area according to a pre-set time reference. The high-frequency sound wave pulses have a definite frequency value, pulse duration, and pulse interval time. All emission actions are executed continuously according to a fixed time reference. The precise emission time of each emission is recorded, and the emission times are numbered in chronological order to form an emission time sequence. After entering the water area, the high-frequency sound waves propagate along the spatial path between the water surface and the seabed. When they propagate to the water surface interface, they are reflected once, and when they propagate to the seabed interface, they are reflected once, thus forming a complete round trip propagation path between the water surface and the seabed. As the emission time sequence continues to advance, the subsequently emitted high-frequency sound waves form multiple round trip propagation trajectories between the water surface and the seabed. The high-frequency sound waves corresponding to different emission times propagate in parallel in the water area, forming multiple round trip paths.

[0020] During continuous transmission, the receiver continuously records the returned echo signals and continuously acquires the echo signals with time as the horizontal axis, forming raw echo record data. The raw echo record data is arranged point by point according to the reception time, and each reception time is matched with the aforementioned transmission time sequence to determine the corresponding transmission time of the echo signal. By establishing the correspondence between the transmission time and the echo arrival time, the first, second, and third echoes after each transmission are marked as the first round-trip propagation, the second round-trip propagation, and the third round-trip propagation, respectively, thus assigning a round-trip propagation number identifier to each echo. All echo signals are arranged in order of reception time to form a continuous echo time sequence, which covers all echo segments within the detection period. The time axis is continuous and uninterrupted, and each time point corresponds to a unique echo amplitude data and round-trip propagation number identifier.

[0021] After the continuous echo time series is formed, the arrival times of multiple echoes corresponding to the same transmission time are recorded one by one. The time interval between adjacent echoes is calculated, and the increasing order of round-trip propagation times is determined based on the progressive relationship of the time intervals. If an echo corresponding to a certain transmission time arrives three times within the detection period, it is marked as the first round-trip propagation, the second round-trip propagation, and the third round-trip propagation, and the specific time positions of these three echoes in the continuous echo time series are recorded. By performing the same processing procedure on all transmission times, each echo segment in the continuous echo time series has a clear transmission time source and round-trip propagation number identifier. Based on this, the round-trip propagation numbers are statistically arranged in chronological order to form an increasing sequence of round-trip propagation numbers. This increasing sequence reflects the entire process of the change in the number of round-trips of high-frequency sound waves between the water surface and the seabed over time within the detection period.

[0022] After the increasing sequence of round-trip propagation counts is formed, the time segments in the continuous echo time series are segmented and marked. The time point corresponding to each increase in the number of round-trip propagation counts is used as the boundary node, establishing a complete segmented structure on the continuous echo time series. By recording the specific reception time corresponding to each increase in the number of round-trip propagation counts, a table of changes in the number of round-trip propagation counts is formed, maintaining a one-to-one correspondence between the table and the continuous echo time series. When the water surface undulation, water flow velocity, and seabed interface morphology change, the length of the round-trip propagation path changes, and the corresponding echo arrival time changes. The increasing rhythm of the number of round-trip propagation counts is manifested as a change in time intervals in the continuous echo time series. By continuously recording the increasing number of round-trip propagation counts and their corresponding time positions, the continuous echo time series possesses a complete propagation trajectory recording function. This enables the construction of a continuous echo time series formed by the round-trip propagation of high-frequency sound waves between the water surface and the seabed within the detection period, and simultaneously completes the establishment of the increasing sequence of the number of round-trip propagation counts, providing a continuous and complete data foundation for subsequent time unfolding processing and propagation time offset trajectory extraction.

[0023] The continuous echo time series is time-expanded based on the increasing round-trip propagation number sequence. The echo signals in the continuous echo time series are rearranged in the order of increasing round-trip propagation number to form a multi-path unfolded time series. The propagation time offset trajectory is extracted from the multi-path unfolded time series. Given that a correspondence has been established between the continuous echo time series and the increasing round-trip propagation sequence, time expansion processing is performed on the continuous echo time series to form a multipath expanded time series. At the same time, the propagation time offset trajectory is extracted. The specific implementation steps are as follows: The continuous echo time series is analyzed point by point, and each echo segment in the continuous echo time series is marked according to its corresponding round-trip propagation number. Specifically, starting from the beginning of the continuous echo time series, the reception time, amplitude, and corresponding transmission time identifier of the first echo segment are read, along with the round-trip propagation number identifier associated with that echo segment. This process continues until the end of the detection cycle by reading the reception time and round-trip propagation number identifier of the next echo segment. During the reading process, a round-trip propagation number grouping table is established. All echo segments with one round-trip propagation number are grouped into the first group, all echo segments with two round-trip propagation numbers into the second group, all echo segments with three round-trip propagation numbers into the third group, and so on, forming multiple group sequences in ascending order of round-trip propagation number. Within each group sequence, the original reception time is arranged to ensure that the echo segments corresponding to the same round-trip propagation number maintain their temporal order. After grouping, a group time record table is established for each group sequence, recording the original reception time and corresponding transmission time identifier of each echo segment within that group, thus providing a complete time reference basis for subsequent time decomposition processing.

[0024] After grouping by round-trip propagation count, each group sequence is expanded under a unified time reference. Specifically, the following steps are taken: First, the group sequence with one round-trip propagation count is selected as the expansion reference sequence. The echo segments in this group sequence are rearranged from earliest to latest according to their transmission time identifiers, and their positions are recorded sequentially on the new timeline, forming the first layer of expanded sequences. Next, the group sequence with two round-trip propagation counts is read, and the echo segments in this group sequence are sorted according to their corresponding transmission time identifiers. Using the transmission time order of the first layer of expanded sequences as a reference, the echo segments in the second group sequence are inserted into positions corresponding to the same transmission time, ensuring that echo segments with different round-trip propagation counts at the same transmission time are aligned vertically. After completing the insertion and arrangement of the second group sequence, the same operation is performed on the group sequence with three round-trip propagation counts, aligning the echo segments in the third group sequence with the positions of the same transmission time in the first layer of expanded sequences. Subsequent round-trip propagation count groups are processed in the same manner until all group sequences are arranged under a unified time reference. Through the above arrangement process, the echo segments that were originally superimposed along a single time axis in the continuous echo time series are separated into different levels, forming a multipath unfolded time series with a transverse transmission time sequence and a longitudinal round-trip propagation number increasing sequence.

[0025] After the multipath unfolded time series is formed, longitudinal time difference analysis is performed on the multi-layer echo segments corresponding to each transmission time to construct the propagation time offset trajectory. Specifically, a transmission time marker is selected in the multipath unfolded time series. The echo time position of this transmission time in the first layer unfolded sequence is read, then the echo time position of the same transmission time in the second layer unfolded sequence is read, and so on, obtaining the time coordinates of this transmission time in all layers. The time coordinates between adjacent layers are calculated to obtain the time interval between the first and second round trips, and the time interval between the second and third round trips, and these are arranged in ascending order of the number of round trips to form a time offset data column. This time offset data column corresponding to the transmission time is continuously recorded along the transmission time direction. When the next transmission time marker is read, the above reading and time difference calculation steps are repeated, so that a corresponding time offset data column is generated for each transmission time. All the time offset data columns corresponding to the transmission times are connected in chronological order to form a continuous propagation time offset trajectory, which reflects the dynamic change of propagation time during the increasing number of round trips.

[0026] The propagation time offset trajectory is synchronously marked with the multipath unfolded time series, so that each echo segment in the multipath unfolded time series can correspond to its location on the propagation time offset trajectory. Specifically, a corresponding time offset data column index is added to each transmission time node in the multipath unfolded time series, so that all hierarchical echo segments at that transmission time share the same propagation time offset trajectory identifier. By continuously recording the changes in the propagation time offset trajectory at all transmission times, the progressive change in propagation time of high-frequency sound waves during their round-trip propagation between the water surface and the seabed can be fully presented. After the above processing, the continuous echo time series has been unfolded into a multipath unfolded time series with a hierarchical structure. Based on this, the propagation time offset trajectory covering the entire detection period is extracted, providing a continuous and structurally clear temporal data foundation for subsequent identification of echo segments whose arrival order deviates from the direct propagation order based on the propagation time offset trajectory.

[0027] Based on the propagation time offset trajectory, the arrival order of echoes in the multipath unfolded time series is compared to identify echo segments whose arrival order deviates from the direct propagation order, determine the superposition segment, and record the corresponding time range of the superposition segment. Based on the established correspondence between the multipath unfolded time series and the propagation time offset trajectory, a detailed comparison of the echo arrival order is performed. Echo segments whose arrival order deviates from the direct propagation order are then identified. The overlapping sections are further determined, and the corresponding time ranges of these sections are recorded. The specific implementation steps are as follows: Using the propagation time offset trajectory as a time structure reference, the multipath unfolding time series is sequentially analyzed node by node of each transmission. Specifically, starting from the beginning of the detection cycle along the transmission time axis, the first transmission time marker is selected. The echo time coordinates of this transmission time marker in the first, second, third, and subsequent layers are located within the multipath unfolding time series, forming a multi-layer echo time set under this transmission time marker. Subsequently, these multi-layer echo time coordinates are arranged sequentially according to the increasing number of round-trip propagation times, forming a theoretical arrival sequence table. Simultaneously, the time offset data column corresponding to the transmission time marker in the propagation time offset trajectory is read. This time offset data column records the time difference changes between adjacent round-trip propagation times. Based on the progressive relationship of time differences reflected by the propagation time offset trajectory, a direct propagation sequence reference sequence is constructed. This direct propagation sequence reference sequence is arranged sequentially from the first round-trip propagation to the last round-trip propagation, maintaining a consistent direction of propagation time difference progression. Compare each item of the multi-layer echo time set with the direct propagation sequence reference sequence. If the time arrangement order in the multi-layer echo time set is completely consistent with the direct propagation sequence reference sequence, it is recorded as a consistent sequence state. If the echo time coordinate of a certain level in the multi-layer echo time set shifts forward or backward, it is recorded as an arrival sequence deviation event, and the level position and corresponding time coordinate of the deviation are marked.

[0028] After completing the sequential comparison of a single transmission time marker, a continuous sliding comparison process is performed on all transmission time markers throughout the entire detection cycle. Specifically, the transmission time markers are advanced sequentially along the time axis. For each advanced transmission time marker, the aforementioned steps of reading multi-layer echo time sets, reading the corresponding data columns of the propagation time offset trajectory, constructing a direct propagation sequence reference sequence, and performing item-by-item comparison are repeated. Each transmission time marker forms a sequential comparison record, including the sequential consistency status or arrival sequence deviation event, the deviation level position, and the corresponding time coordinate of the deviation. All sequential comparison records of transmission time markers are arranged chronologically to form a continuous sequence deviation record table. The sequence deviation record table completely covers the detection cycle on the time axis and provides corresponding arrival sequence status information for each transmission time marker.

[0029] After the sequence deviation record table is formed, the transmission time intervals where consecutive arrival sequence deviation events occur are aggregated and identified to determine the overlay segment. Specifically, starting from the beginning of the sequence deviation record table, the sequence status corresponding to each transmission time marker is scanned. When two or more consecutive transmission time markers are recorded as arrival sequence deviation events, and the deviation level remains consistent in adjacent transmission time markers, this consecutive interval is defined as a candidate overlay segment. Subsequently, further temporal position analysis is performed on the multipath unfolded time series within the candidate overlay segment. The echo time coordinates of all levels within the segment are read, and it is checked whether there is time overlap or time intersection between different levels of echo time coordinates. If, within the candidate overlay segment, two levels of echo time coordinates overlap on the time axis, or if the second-level echo time in the previous transmission time marker is before the third-level echo time, but in the subsequent transmission time marker, the second-level echo time is after the third-level echo time, then the candidate overlay segment is confirmed as the actual overlay segment. The start time of the overlay segment is defined as the earliest echo time coordinate corresponding to the first transmission time marker in the candidate overlay segment where an arrival order deviation occurs, and the end time of the overlay segment is defined as the latest echo time coordinate corresponding to the last transmission time marker in the candidate overlay segment where an arrival order deviation occurs.

[0030] After the actual overlay segment is determined, the corresponding time range of the overlay segment is fully recorded, and dual identification is established in the multipath unfolding time series and the propagation time offset trajectory. Specifically, the start and end times of the overlay segment are marked on the time axis of the multipath unfolding time series, and all echo segments within this time range are uniformly labeled as overlay segment echo segments. Simultaneously, the trajectory positions corresponding to the start and end times of the overlay segment are marked in the propagation time offset trajectory, forming continuous interval identification for the corresponding trajectory segments. Through this process, the overlay segment has a clear temporal positioning relationship in both the multipath unfolding time series and the propagation time offset trajectory. After completing all steps, continuous comparison of the echo arrival order in the multipath unfolding time series based on the propagation time offset trajectory is achieved, identifying echo segments whose arrival order deviates from the direct propagation order, determining the overlay segment, and recording the corresponding time range of the overlay segment. This provides precise time boundaries for subsequent backtracking of continuous echo time series to locate the round-trip propagation cycle compression interval.

[0031] Based on the time range corresponding to the superimposed section, the continuous echo time series is traced back to locate the round-trip propagation period compression interval corresponding to the superimposed section, and the time position corresponding to the round-trip propagation period compression interval is determined as the transmission adjustment entry position. After the superimposed section has been determined through multipath unfolding time series and propagation time offset trajectory, the corresponding time range of the superimposed section is back-located in the continuous echo time series, and the round-trip propagation period compression interval is further identified. Finally, the time position corresponding to the round-trip propagation period compression interval is determined as the transmission adjustment entry position. The specific implementation steps are as follows: A precise backtracking mapping is performed on the continuous echo time series around the time range corresponding to the overlay segment. Specifically, the start and end time coordinates of the overlay segment are read, and this time range is located point-by-point on the original time axis of the continuous echo time series. All echo segments within this time range are extracted to form an echo set for the overlay segment. Then, for each echo segment in the overlay segment echo set, its corresponding transmission time identifier and round-trip propagation number identifier are read and rearranged according to the reception time order to form a continuous echo subsequence within the overlay segment. This processing ensures that the echo subsequences of the overlay segment maintain their original time order within the continuous echo time series, while possessing complete transmission time identifier and round-trip propagation number identifier information, establishing a data foundation for identifying the compressed interval of the round-trip propagation period.

[0032] After the echo subsequence of the superimposed section is formed, the time intervals between adjacent echo segments in the echo subsequence are calculated one by one to determine the variation of the round-trip propagation period. Specifically, based on the transmission time marker, the first and second round-trip propagation echo times corresponding to the same transmission time marker are extracted from the echo subsequence of the superimposed section. The time difference between them is calculated and recorded as the first round-trip propagation period time. Then, the time difference between the second and third round-trip propagation echo times is extracted and recorded as the second round-trip propagation period time. This process is repeated for all adjacent round-trip propagation echo times corresponding to the same transmission time marker, forming a complete round-trip propagation period time data series. This round-trip propagation period time data series is arranged sequentially along the transmission time markers to form a sequence of round-trip propagation period variation within the superimposed section. By continuously recording the round-trip propagation period times corresponding to each transmission time marker, the variation trend of the period time within the superimposed section can be observed.

[0033] After establishing the round-trip propagation period variation sequence within the superimposed segment, time intervals with continuously decreasing period times are identified to locate round-trip propagation period compression intervals. Specifically, the round-trip propagation period times are read sequentially along the launch time markers. When the round-trip propagation period time corresponding to a certain launch time marker is less than that corresponding to the previous launch time marker, it is recorded as a period shortening event. When multiple consecutive launch time markers exhibit period shortening events, this consecutive launch time interval is defined as a candidate compression interval. Subsequently, all round-trip propagation period times within the candidate compression interval are checked item by item to confirm that the period times maintain a decreasing order within the interval, and the start and end launch time markers of the interval are recorded. The intervals within the candidate compression intervals that satisfy the continuously decreasing order are determined as round-trip propagation period compression intervals. The starting position of the round-trip propagation period compression interval is defined as the time position corresponding to the launch time marker where the period shortening event first occurs, and the ending position of the round-trip propagation period compression interval is defined as the time position corresponding to the launch time marker where the period times return to a non-decreasing order.

[0034] After determining the round-trip propagation period compression interval, the specific time position of this interval in the continuous echo time series is calibrated, and the transmission adjustment entry position is determined. Specifically, based on the starting transmission time marker of the round-trip propagation period compression interval, the first round-trip propagation echo time coordinate corresponding to this time marker is found in the continuous echo time series, and this time coordinate is taken as the time starting point of the round-trip propagation period compression interval. Simultaneously, based on the ending transmission time marker of the round-trip propagation period compression interval, the corresponding last-level echo time coordinate is found in the continuous echo time series, and this time coordinate is taken as the time ending point of the round-trip propagation period compression interval. After completing the time boundary positioning of the compression interval, the transmission time position corresponding to the starting transmission time marker of the round-trip propagation period compression interval is determined as the transmission adjustment entry position, and this position is marked in the transmission time series so that subsequent transmission actions can be adjusted in rhythm based on this time position. Through the above steps, the round-trip propagation period compression interval corresponding to the superimposed segment is located by tracing back the continuous echo time series according to the time range corresponding to the superimposed segment, and the time position corresponding to the round-trip propagation period compression interval is determined as the transmission adjustment entry position, providing a precise time starting point and interval boundary for subsequent reverse lengthening of the transmission time interval.

[0035] The time interval of subsequent high-frequency acoustic wave transmission is reversely lengthened around the transmission adjustment entry position. Within the round-trip propagation period compression interval, the transmission time misalignment is set according to the successive increasing rule. The echo superposition time relationship formed by the round-trip propagation is broken by adjusting the transmission time rhythm, and the adjusted echo data is used for wind power pile foundation defect imaging reconstruction. With the transmission adjustment entry position clearly defined and the round-trip propagation period compression interval already located in the continuous echo time series, the subsequent high-frequency acoustic wave transmission time interval is reverse-stretched. Within the round-trip propagation period compression interval, the transmission time misalignment is set according to a progressively increasing rule. By adjusting the transmission time rhythm, the superimposed echo time relationship formed by the round-trip propagation is broken up. Finally, the adjusted echo data is used for wind turbine pile foundation defect imaging reconstruction. The specific implementation steps are as follows: Starting from the transmission adjustment inlet position, the original transmission time series is analyzed point by point. Specifically, the transmission time marker corresponding to the transmission adjustment inlet position is read, and this time marker is used as the starting point for rhythm adjustment. Then, all transmission time markers within the time range of the round-trip propagation cycle compression interval are read sequentially to form the adjustment execution transmission sequence. Subsequently, the original time interval values ​​between two adjacent transmissions in the adjustment execution transmission sequence are extracted and recorded one by one as the first original interval, the second original interval, the third original interval, until the original interval value corresponding to the end position of the compression interval, forming an original transmission interval record table. The original transmission interval record table maintains consistency with the time reference of the continuous echo time series and the increasing round-trip propagation number sequence, thereby ensuring a complete correspondence between subsequent rhythm adjustments and the round-trip propagation cycle compression interval on the time axis.

[0036] Based on the original launch interval record table, the launch intervals are reverse-stretched. Specifically, a fixed time increment is selected as the base offset, which is taken from a portion of the original launch interval value and kept constant throughout the adjusted launch sequence. Then, starting from the first launch time marker after the launch adjustment entry position, the first original interval is increased by one base offset to obtain the first adjusted interval; the second original interval is increased by two base offsets to obtain the second adjusted interval; the third original interval is increased by three base offsets to obtain the third adjusted interval; and so on, increasing the nth original interval by n base offsets to form the nth adjusted interval. Through this successive increment rule, the launch time offset increases synchronously with the number of launches, thus constructing a continuously extended launch interval sequence within the round-trip propagation period compression interval. The adjusted launch time markers are then rearranged according to the new adjusted intervals to form the updated launch time sequence.

[0037] After the updated transmission time sequence is formed, high-frequency acoustic wave transmission is re-executed according to the updated transmission time sequence, and adjusted continuous echo data is collected simultaneously. Specifically, within the time range covered by the adjusted transmission sequence, each high-frequency acoustic wave transmission is executed according to the updated transmission time identifier, and the new transmission time identifier and corresponding transmission time are recorded. As the transmission time interval gradually increases within the round-trip propagation period compression interval, the round-trip propagation time distribution of high-frequency acoustic waves corresponding to different transmission time identifiers between the water surface and seabed changes, causing the arrival times of echoes that originally overlapped on the time axis to gradually become more spaced out. The receiving end continuously collects the adjusted echo signals and establishes a correspondence between the new transmission time identifier and the receiving time to construct an updated continuous echo time sequence. Simultaneously, the round-trip propagation number identifier is re-labeled for each echo segment. Through the above processing, the echoes formed by round-trip propagation are arranged in a dispersed state on the time axis, and the echo superposition time relationship originally formed within the round-trip propagation period compression interval is broken up.

[0038] After acquiring the adjusted continuous echo time series, it is used for wind turbine pile foundation defect imaging reconstruction. Specifically, based on the updated transmission time identifier and round-trip propagation number identifier, the adjusted continuous echo time series is re-time-unfolded to form an updated multipath unfolded time series, and a new propagation time offset trajectory is extracted from this. Since the transmission time rhythm has changed within the round-trip propagation cycle compression interval, the propagation time offset trajectory exhibits a different time distribution state than the original trajectory within this interval, separating the superimposed segments originally formed in the multipath unfolded time series. Subsequently, based on the updated multipath unfolded time series, the spatial distribution reconstruction of internal defects in the wind turbine pile foundation is performed, enabling the adjusted echo data to reflect the actual structural response location. Through the above steps, the subsequent high-frequency acoustic wave transmission time interval is reverse-stretched around the transmission adjustment entry position, and the transmission time misalignment is set according to a successive increasing rule within the round-trip propagation cycle compression interval. By adjusting the transmission time rhythm, the echo superposition time relationship formed by round-trip propagation is broken up, and the adjusted echo data is used in the entire process of wind turbine pile foundation defect imaging reconstruction.

[0039] This invention constructs a continuous echo time series and introduces an increasing sequence of round-trip propagation times to structurally unfold the multipath propagation behavior between the water surface and the seabed. This allows multipath echoes that were originally superimposed in the same time segment to be layered and rearranged in the time dimension, forming a traceable multipath unfolded time series. Based on this, the propagation time offset trajectory is extracted, and echo segments whose arrival order deviates from the direct propagation order are identified. This distinguishes the true structural response from water reflection interference at the source, avoiding the misjudgment of closed contour artifacts as cavities or voids, thereby improving the accuracy of spatial positioning of wind turbine pile foundation defects and the reliability of imaging results.

[0040] After identifying the round-trip propagation period compression interval, this invention uses the emission adjustment entry position as the control starting point to reversely lengthen the subsequent high-frequency acoustic wave emission time interval. Within the round-trip propagation period compression interval, the emission time misalignment is set according to a progressively increasing rule. By actively adjusting the emission time rhythm, the time arrangement structure of the round-trip propagation is changed, so that multi-path echoes no longer overlap in the same time window. The echo superposition relationship is broken up from the time source, so that the adjusted echo data has a clearer propagation hierarchy structure, providing a stable time distribution basis for wind power pile foundation defect imaging reconstruction.

[0041] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A method for multi-frequency acoustic imaging of defects in a wind power pile foundation in a complex underwater environment, characterized in that, Includes the following steps: Multi-frequency acoustic imaging detection is carried out on wind power pile foundations. High-frequency acoustic waves are emitted into the water area during the detection period, and continuous echo signals formed by the high-frequency acoustic waves propagating back and forth between the water surface and the seabed are received. A continuous echo time series is constructed, and the increasing sequence of the number of round-trip propagation times is recorded in the continuous echo time series. The continuous echo time series is time-expanded based on the increasing round-trip propagation number sequence. The echo signals in the continuous echo time series are rearranged in the order of increasing round-trip propagation number to form a multi-path unfolded time series. The propagation time offset trajectory is extracted from the multi-path unfolded time series. Based on the propagation time offset trajectory, the arrival order of echoes in the multipath unfolded time series is compared to identify echo segments whose arrival order deviates from the direct propagation order, determine the superposition segment, and record the corresponding time range of the superposition segment. Based on the time range corresponding to the superimposed section, the continuous echo time series is traced back to locate the round-trip propagation period compression interval corresponding to the superimposed section, and the time position corresponding to the round-trip propagation period compression interval is determined as the transmission adjustment entry position. The time interval of subsequent high-frequency acoustic wave transmission is reversely lengthened around the transmission adjustment entry position. Within the round-trip propagation period compression interval, the transmission time misalignment is set according to the successive increasing rule. By adjusting the transmission time rhythm, the echo superposition time relationship formed by the round-trip propagation is broken up, and the adjusted echo data is used for wind power pile foundation defect imaging reconstruction.

2. The method according to claim 1, wherein, The steps to construct a continuous echo time series and record an increasing sequence of round-trip propagation times are as follows: Divide the propagation time range and set the detection cycle length, continuously emit high-frequency acoustic pulses according to a fixed time reference, and record the emission time to form an emission time sequence; Based on the transmission time sequence, the received echo signals are arranged according to the reception time to form the original echo record data. The correspondence between the transmission time and the echo arrival time is established. Each echo is assigned a round-trip propagation number identifier and a continuous echo time sequence is constructed. By statistically analyzing the arrival times of multiple echoes corresponding to the same transmission time based on the continuous echo time series, and confirming the order of round-trip propagation times according to the time progression relationship, an increasing sequence of round-trip propagation times is formed. By combining the increasing sequence of round-trip propagation times, the continuous echo time series is segmented and marked, and the receiving time corresponding to the change in round-trip propagation times is recorded to form a table of changes in round-trip propagation times.

3. The method according to claim 2, wherein, The steps for time unfolding processing and extraction of propagation time offset trajectory are as follows: The continuous echo time series is analyzed point by point and grouped according to the number of round-trip propagation times to form a round-trip propagation number grouped sequence, and a grouped time record table is established; The time series of groups based on the number of round-trip propagation are unfolded and arranged under a unified time reference. The groups are then aligned and inserted in ascending order of the number of round-trip propagation to form a multipath unfolded time series. Based on multipath unfolded time series, the echo time coordinates of each level corresponding to the same transmission time are read. The time interval between adjacent levels is calculated in ascending order of round-trip propagation times to form a time offset data column and connect it along the transmission time sequence to construct the propagation time offset trajectory. The multipath unfolding time series is synchronously marked by combining the propagation time offset trajectory, and a corresponding time offset data column index is added to each launch time node.

4. The method according to claim 3, wherein, The round-trip propagation number grouping sequence is arranged in the order of the original reception time, the multipath unfolding time sequence is arranged hierarchically according to the transmission time identifier, and the propagation time offset trajectory is formed by connecting the echo time intervals corresponding to adjacent round-trip propagation numbers in sequence, and maintains a one-to-one time correspondence with the multipath unfolding time sequence.

5. The method according to claim 3, wherein, The steps to identify deviations in arrival order from direct propagation order and determine overlapping segments are as follows: Using the propagation time offset trajectory as a reference, the multipath unfolding time series is analyzed node by node of transmission, the echo time coordinates of each level are read and a direct propagation order reference sequence is constructed, the multi-level echo time set is compared with the direct propagation order reference sequence item by item, and the arrival order deviation events are recorded. A sequential comparison record is formed around each launch time node, and the sequence deviation record table is continuously advanced along the launch time axis; Based on the sequence deviation record table, the transmission time intervals of consecutive arrival sequence deviation events are aggregated and identified, and the superimposed segments are confirmed by combining the hierarchical echo time coordinates in the multipath unfolded time series. By combining the time boundaries of the superimposed segment in the multipath unfolding time series, the corresponding trajectory position is marked in the propagation time offset trajectory, and the corresponding time range of the superimposed segment is recorded.

6. The multi-frequency acoustic imaging method for wind turbine pile foundation defects in complex underwater environments according to claim 5, characterized in that, The continuous transmission time intervals that maintain consistent deviation level positions in the sequence deviation record table are screened, and the start and end times of the superposition segment are determined by combining the overlapping arrangement relationship of the time coordinates of the layer echoes in the multipath unfolding time series.

7. The multi-frequency acoustic imaging method for wind turbine pile foundation defects in complex underwater environments according to claim 5, characterized in that, The steps for locating the round-trip propagation period compression interval and determining the launch adjustment inlet position are as follows: The continuous echo time series is back-mapped around the time range corresponding to the superimposed segment, the echo set of the superimposed segment is extracted, and the transmission time identifier and round-trip propagation number identifier are read to form the echo subsequence of the superimposed segment; Based on the echo subsequence of the superimposed segment, the time difference between adjacent round-trip propagation echoes is calculated according to the transmission time identifier to form a round-trip propagation period variation sequence; Identify the launch time intervals where the period time continuously decreases based on the round-trip propagation period variation sequence, and determine the round-trip propagation period compression interval; By combining the time boundary of the round-trip propagation period compression interval in the continuous echo time series, the time position of the corresponding transmission time marker is determined as the transmission adjustment entry position.

8. The multi-frequency acoustic imaging method for wind turbine pile foundation defects in complex underwater environments according to claim 1, characterized in that, The steps for reverse-stretching the transmission time interval and reconstructing the image are as follows: The original launch time sequence was read around the launch adjustment inlet position, and the launch time markers and adjacent launch time intervals within the round-trip propagation period compression interval were extracted to form the original launch interval record table. Based on the original launch interval record table, the launch time misalignment is set according to the successive increment rule within the round-trip propagation period compression interval, the launch time interval is reversely lengthened, and an updated launch time sequence is formed. Based on the updated transmission time series, high-frequency acoustic wave transmission is performed and continuous echo data is collected. The updated continuous echo time series is constructed and the round-trip propagation number is re-labeled. The updated continuous echo time series is combined with time unfolding processing and the propagation time offset trajectory is extracted. Based on the updated multipath unfolded time series, wind power pile foundation defect imaging reconstruction is performed.

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