A vibration frequency estimation method based on amplitude difference step size

Abstract

The application discloses a vibration frequency estimation method based on amplitude difference step length, which comprises the following steps: laying sensing optical fibers on long-distance large infrastructure, and collecting RBS amplitudes of different vibration sampling points on the sensing optical fibers of the infrastructure to be measured under different detection pulses by using a phase-sensitive optical time domain reflectometer; effectively utilizing the difference step length corresponding to the maximum value point and the minimum value point of the maximum signal-to-noise ratio of the differential accumulated amplitude at the vibration sampling point to estimate the vibration frequency of the infrastructure to be measured; and comparing the vibration frequency of the infrastructure to be measured in the current state with the vibration frequency in the stable state to determine whether the structure of the infrastructure to be measured is healthy and safe. The application fully utilizes the strong dependence of the differential step length on the vibration frequency in the traditional amplitude differential accumulation algorithm, realizes accurate estimation of the vibration frequency, and utilizes the dynamic frequency to determine the health condition of the infrastructure to be measured, so that the destructive condition of the infrastructure to be measured is avoided, and the application has the advantages of simple structure, easy implementation and reliability.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and more specifically to a method for estimating vibration frequency based on amplitude difference step size. Background Technology

[0002] In recent years, with the continuous development of the country, my country has seen an increasing number of long-distance, large-scale infrastructure projects (such as bridges, tunnels, and railways). These infrastructures, as crucial to national security and economic vitality, make the safety monitoring of these large-scale infrastructures to ensure their structural health and safety particularly important. Currently, the main methods for monitoring the structural health and safety of large-scale infrastructures are instrumental testing or monitoring equipment. However, due to the long distances of bridges, tunnels, and railways, conducting on-site manual inspections or installing monitoring equipment over long distances to monitor the structural health of these facilities is costly and wastes significant human and material resources. Furthermore, in complex environments such as desolate or harsh conditions, manual inspections and monitoring equipment are not always able to reflect the real-time structural health of the infrastructure due to the influence of external environmental conditions. Summary of the Invention

[0003] The present invention addresses the existing problems in structural health and safety monitoring of large infrastructure by providing a vibration frequency estimation method based on amplitude difference step size.

[0004] To solve the above problems, the present invention is achieved through the following technical solution:

[0005] A vibration frequency estimation method based on amplitude difference step size includes the following steps:

[0006] Step 1: Perform a vibration frequency calculation process on the infrastructure under test in a stable state to calculate the vibration frequency of the infrastructure under test in a stable state;

[0007] Step II: Perform a vibration frequency calculation process on the infrastructure under test in its current state to calculate the vibration frequency of the infrastructure under test in its current state;

[0008] Step III: Compare the vibration frequency of the infrastructure under test in the current state with the vibration frequency of the infrastructure under test in the steady state: If the vibration frequency of the infrastructure under test in the current state is lower than that in the steady state... Vibration frequency of the infrastructure under test in steady state The absolute value of the difference exceeds the threshold. If the event is positive, it is determined that a destructive event has occurred in the infrastructure under test; otherwise, it is determined that the infrastructure under test is currently safe.

[0009] The specific process for calculating the above vibration frequency is as follows:

[0010] Step 1: Use a phase-sensitive optical time-domain reflectometer to collect the backscattered Rayleigh signals from N vibration sampling points on the sensing fiber of the infrastructure under test under M probe pulses, forming an amplitude matrix; the amplitude in the m-th row and n-th column of the amplitude matrix is ​​the amplitude of the backscattered Rayleigh signal at the n-th vibration sampling point on the sensing fiber under the m-th probe pulse; where m=1,2,…, M; n=1,2,…,N; M represents the number of probe pulses; N represents the number of vibration sampling points on the sensing fiber;

[0011] Step 2: Perform a difference operation on the magnitude matrix every k rows to obtain the difference magnitude matrix at each difference step size; where k is the difference step size, k=1,2,…,M-1;

[0012] Step 3: Sum the columns of the difference magnitude matrix at each difference step size to obtain the difference accumulation magnitude vector at each difference step size;

[0013] Step 4: Calculate the signal-to-noise ratio (SNR) of the differential accumulation magnitude vector at each differential step size to obtain the SNR vector at each differential step size;

[0014] Step 5: Find the maximum signal-to-noise ratio in the signal-to-noise ratio vector at each difference step size, and plot the relationship between the difference step size and the maximum signal-to-noise ratio with the difference step size as the horizontal axis and the maximum signal-to-noise ratio as the vertical axis.

[0015] Step 6: Based on the relationship between the differential step size and the maximum signal-to-noise ratio, determine the maximum and minimum values ​​of the signal-to-noise ratio, as well as the differential step size corresponding to the maximum and minimum values ​​of the signal-to-noise ratio; wherein the maximum value of the signal-to-noise ratio is located at each peak of the relationship between the differential step size and the maximum signal-to-noise ratio, and the minimum value of the signal-to-noise ratio is located at each trough of the relationship between the differential step size and the maximum signal-to-noise ratio.

[0016] Step 7: Calculate the vibration frequency of the infrastructure under test using the difference step size corresponding to the maximum and minimum values ​​of the signal-to-noise ratio;

[0017] Vibration frequency for:

[0018]

[0019] In the formula, This indicates the number of maxima in the signal-to-noise ratio. This indicates the number of minimum values ​​in the signal-to-noise ratio. This represents the difference step size corresponding to each maximum signal-to-noise ratio point. This represents the difference step size corresponding to each minimum signal-to-noise ratio point. To detect the repetition period of the light pulse.

[0020] In step 2 above, the difference magnitude matrix B at the difference step size k k The differential amplitude of the i-th row and n-th column of [Mk, N] is equal to the amplitude of the (i+k)-th row and n-th column of the amplitude matrix A[M, N] minus the absolute value of the amplitude of the i-th row and n-th column; where i=1,2,…, Mk; n=1,2,…,N; k is the differential step size, M represents the number of probe pulses, and N represents the number of vibration sampling points on the sensing fiber.

[0021] In step 3 above, the difference accumulation magnitude vector C at the difference step size k k The nth difference accumulation magnitude of [N] is equal to the difference magnitude matrix B at the difference step size k. k The sum of the differential amplitude values ​​from the first row and nth column of [Mk, N] to the Mkth row and nth column; where n = 1, 2, ..., N; k is the differential step size, M represents the number of probe pulses, and N represents the number of vibration sampling points on the sensing fiber.

[0022] In step 4 above, the signal-to-noise ratio vector (SNR) at the difference step size k is... k The nth signal-to-noise ratio of [N] for:

[0023]

[0024] Where n = 1, 2, ..., N; C represents the difference accumulation magnitude vector at difference step size k. k The nth difference cumulative amplitude of [N] C represents the difference accumulation magnitude vector at difference step size k. k The differential accumulation values ​​in [N] excluding the nth differential accumulation value; denoted as the maximum value function; k is the difference step size, and N represents the number of vibration sampling points on the sensing fiber.

[0025] Compared with existing technologies, this invention lays sensing optical fibers over long distances on large infrastructures and uses a phase-sensitive optical time-domain reflectometer (φ-OTDR) to collect the RBS (Backscattered Rayleigh signal) amplitudes of different vibration sampling points on the sensing optical fibers of the infrastructure under test under different probe pulses. It effectively uses the differential step size corresponding to the maximum and minimum signal-to-noise ratio points of the differentially accumulated amplitude at the vibration sampling points to estimate the vibration frequency of the infrastructure under test. The estimated frequency of the infrastructure under test in the current state is compared with the estimated frequency in a steady state to determine whether the structure of the infrastructure under test is healthy and safe. This invention fully utilizes the strong dependence of the differential step size on the vibration frequency in traditional amplitude differential accumulation algorithms, eliminating the need for phase extraction, unwinding operations, phase spatial differential, and vibration waveform recovery of the RBS, thus reducing the time required for data processing. By utilizing the relationship between differential step size, sampling period and vibration frequency, the vibration frequency of large infrastructure can be accurately estimated. The estimated vibration frequency can then be used to determine the health status of the infrastructure under test, thus preventing destructive conditions. The structure is simple, easy to implement and reliable. Attached Figure Description

[0026] Figure 1 This is a flowchart of a vibration frequency estimation method based on amplitude difference step size.

[0027] Figure 2 This is a graph showing the relationship between the differential step size and the maximum signal-to-noise ratio. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific examples.

[0029] A vibration frequency estimation method based on amplitude difference step size, such as Figure 1 As shown, the specific steps include the following:

[0030] Step 1: Perform the vibration frequency calculation process of steps 1-7 below on the infrastructure under test in a stable state to calculate the vibration frequency of the infrastructure under test in a stable state.

[0031] Step II: Perform the vibration frequency calculation process of steps 1-7 below on the infrastructure under test in the current state to calculate the vibration frequency of the infrastructure under test in the current state.

[0032] Step III: Compare the vibration frequency of the infrastructure under test in the current state with the vibration frequency of the infrastructure under test in the steady state: If the vibration frequency of the infrastructure under test in the current state... Vibration frequency of the infrastructure under test in steady state The absolute value of the difference exceeds the threshold. Right now If the event is positive, it is determined that a destructive event has occurred in the infrastructure under test; otherwise, it is determined that the infrastructure under test is currently safe.

[0033] The specific process for calculating the above vibration frequency is as follows:

[0034] Step 1: A phase-sensitive optical time-domain reflectometer (φ-OTDR) is used to collect the backscattered Rayleigh signal amplitudes of N vibration sampling points on the sensing fiber of the infrastructure under test under M probe pulses, forming an amplitude matrix A[M, N].

[0035] Phase-sensitive optical time-domain reflectometer (φ-OTDR) is a distributed fiber optic sensing technology based on backscattered Rayleigh (RBS) signal detection. Its basic working principle is as follows: when the sensing fiber is subjected to external disturbance, the refractive index of the fiber at the vibration location will change, which will be reflected in the phase or amplitude change of the RBS. By comparing the phase or amplitude of the RBS at the vibration location and the non-vibration location, information about the external disturbance can be obtained.

[0036] The magnitude matrix A[M, N] is:

[0037]

[0038] Among them, amplitude This represents the RBS amplitude at the nth vibration sampling point on the sensing fiber under the mth probe pulse. m = 1, 2, ..., M, where M represents the number of probe pulses. n = 1, 2, ..., N, where N represents the number of vibration sampling points on the sensing fiber. In this embodiment, RBS amplitude signals of 200 probe pulses were acquired, i.e., M = 200; the spatial sampling interval of the data acquisition card is δz = 1 m, and the total length of the sensing fiber is 3200 m, i.e., N = L / δz = 3200.

[0039] Step 2: Perform a difference operation on the magnitude matrix A[M, N] every k rows to obtain the difference magnitude matrix B at each difference step size k. k [Mk, N].

[0040] Difference magnitude matrix B k [Mk, N] represents:

[0041]

[0042] Among them, differential amplitude i=1,2,…,Mk.

[0043] Step 3: Calculate the difference magnitude matrix B for each difference step size k. kThe columns of [Mk, N] are summed to obtain the difference accumulation magnitude vector C at each difference step size k. k [N]

[0044] Difference accumulation magnitude vector C k [N] is:

[0045]

[0046] Among them, the differential accumulation amplitude .

[0047] Step 4: Calculate the difference accumulation magnitude vector C at each difference step size k. k The signal-to-noise ratio (SNR) of [N] is used to obtain the SNR vector at each difference step size k. k [N].

[0048] Signal-to-noise ratio vector (SNR) at differential step size k k The nth signal-to-noise ratio of [N] for:

[0049]

[0050] in, C represents the difference accumulation magnitude vector at difference step size k. k The nth difference cumulative amplitude of [N] C represents the difference accumulation magnitude vector at difference step size k. k All differential accumulation values ​​in [N] except for the nth differential accumulation value; This represents the maximum value function.

[0051] Step 5: Find the maximum signal-to-noise ratio (SNR) in the SNR vector for each difference step size, and plot the relationship between the difference step size and the maximum SNR with the difference step size as the x-axis and the maximum SNR as the y-axis. For example... Figure 2 As shown.

[0052] Step 6: Based on the relationship between the differential step size and the maximum signal-to-noise ratio, determine the maximum and minimum values ​​of the signal-to-noise ratio, as well as the differential step size corresponding to the maximum and minimum values ​​of the signal-to-noise ratio.

[0053] The maximum signal-to-noise ratio (SNR) is located at each peak of the graph showing the relationship between the differential step size and the maximum SNR, while the minimum SNR is located at each trough of the graph showing the relationship between the differential step size and the maximum SNR.

[0054] Step 7: Calculate the vibration frequency of the infrastructure under test using the differential step size corresponding to the maximum and minimum values ​​of the signal-to-noise ratio.

[0055] Vibration frequency for:

[0056]

[0057] In the formula, This indicates the number of maxima in the signal-to-noise ratio. This indicates the number of minimum values ​​in the signal-to-noise ratio. This represents the difference step size corresponding to each maximum signal-to-noise ratio point. This represents the difference step size corresponding to each minimum signal-to-noise ratio point. To detect the repetition period of the light pulse.

[0058] based on Figure 2 The relationship between the differential step size and the maximum signal-to-noise ratio is shown in Table 1. The vibration event frequencies of the infrastructure under test are calculated by the differential step size corresponding to the maximum and minimum signal-to-noise ratio values.

[0059] Table 1. Frequency of the vibration events to be measured

[0060]

[0061] In this embodiment, the actual repetition period of the probe light pulse The simulated vibration event frequency applied to the piezoelectric ceramic expansion joint was 500 Hz. The number of measured signal-to-noise ratio maxima... Number of minimum signal-to-noise ratio values The vibration event frequency of the infrastructure under test, calculated from the difference step size corresponding to the maximum and minimum signal-to-noise ratio values, is 498 Hz. This result demonstrates that the vibration frequency estimation method based on amplitude difference step size of this invention can reliably calculate the vibration event frequency of the infrastructure under test.

[0062] The vibration frequency estimation method proposed in this invention can be applied to large-scale infrastructure projects (such as bridge structure monitoring, tunnel safety prevention, and railway safety monitoring). By monitoring the structural health of large-scale infrastructure in real time—that is, detecting the vibration frequency—the current health status of the infrastructure can be determined. When the infrastructure is operating normally, its vibration intensity remains relatively stable, and the vibration frequency also stabilizes at a specific frequency. However, when a destructive accident occurs, the structural vibration intensity changes, causing the vibration frequency to change accordingly. This allows for the determination of the current health status of the infrastructure, thus providing early warning of destructive accidents. This invention reduces the cost of installing monitoring equipment over long distances, decreases the complexity of manual on-site inspections, and enables real-time monitoring of destructive events.

[0063] It should be noted that although the embodiments described above are illustrative, they are not intended to limit the invention. Therefore, the invention is not limited to the specific embodiments described above. Any other embodiments obtained by those skilled in the art under the guidance of this invention without departing from its principles are considered to be within the protection scope of this invention.

Claims

1. A vibration frequency estimation method based on amplitude difference step size, characterized in that, The steps include the following: Step 1: Perform a vibration frequency calculation process on the infrastructure under test in a stable state to calculate the vibration frequency of the infrastructure under test in a stable state; Step II: Perform a vibration frequency calculation process on the infrastructure under test in its current state to calculate the vibration frequency of the infrastructure under test in its current state; Step III: Compare the vibration frequency of the infrastructure under test in the current state with the vibration frequency of the infrastructure under test in the steady state: If the absolute value of the difference between the vibration frequency of the infrastructure under test in the current state and the vibration frequency of the infrastructure under test in the steady state exceeds the threshold γ, it is determined that a destructive event has occurred in the infrastructure under test; otherwise, it is determined that the infrastructure under test is currently safe. The specific process for calculating the above vibration frequency is as follows: Step 1: Use a phase-sensitive optical time-domain reflectometer to collect the backscattered Rayleigh signals from N vibration sampling points on the sensing fiber of the infrastructure under test under M probe pulses, forming an amplitude matrix; the amplitude in the m-th row and n-th column of the amplitude matrix is ​​the amplitude of the backscattered Rayleigh signal at the n-th vibration sampling point on the sensing fiber under the m-th probe pulse; where m = 1, 2, ..., M; n = 1, 2, ..., N; M represents the number of probe pulses; N represents the number of vibration sampling points on the sensing fiber; Step 2: Perform a difference operation on the magnitude matrix every k rows to obtain the difference magnitude matrix at each difference step size; where k is the difference step size, k = 1, 2, ..., M-1; Step 3: Sum the columns of the difference magnitude matrix at each difference step size to obtain the difference accumulation magnitude vector at each difference step size; Step 4: Calculate the signal-to-noise ratio (SNR) of the differential accumulation magnitude vector at each differential step size to obtain the SNR vector at each differential step size; Step 5: Find the maximum signal-to-noise ratio in the signal-to-noise ratio vector at each difference step size, and plot the relationship between the difference step size and the maximum signal-to-noise ratio with the difference step size as the horizontal axis and the maximum signal-to-noise ratio as the vertical axis. Step 6: Based on the relationship between the differential step size and the maximum signal-to-noise ratio, determine the maximum and minimum values ​​of the signal-to-noise ratio, as well as the differential step size corresponding to the maximum and minimum values ​​of the signal-to-noise ratio; wherein the maximum value of the signal-to-noise ratio is located at each peak of the relationship between the differential step size and the maximum signal-to-noise ratio, and the minimum value of the signal-to-noise ratio is located at each trough of the relationship between the differential step size and the maximum signal-to-noise ratio. Step 7: Calculate the vibration frequency of the infrastructure under test using the difference step size corresponding to the maximum and minimum values ​​of the signal-to-noise ratio; Vibration frequency f s for: In the formula, p represents the number of maxima of the signal-to-noise ratio, q represents the number of minima of the signal-to-noise ratio, and k 1α k represents the difference step size corresponding to each maximum signal-to-noise ratio point. 2β The differential step size represents the minimum point of each signal-to-noise ratio, and T is the repetition period of the probe light pulse.

2. The vibration frequency estimation method based on amplitude difference step size according to claim 1, characterized in that, In step 2, the difference magnitude matrix B at the difference step size k k The difference magnitude of the [Mk,N] in the i-th row and n-th column is equal to the magnitude of the magnitude of the magnitude matrix A[M,N] in the (i+k)-th row and n-th column minus the absolute value of the magnitude in the i-th row and n-th column. Where i = 1, 2, ..., Mk; n = 1, 2, ..., N; k is the differential step size, M represents the number of probe pulses, and N represents the number of vibration sampling points on the sensing fiber.

3. The vibration frequency estimation method based on amplitude difference step size according to claim 1, characterized in that, In step 3, the difference accumulation magnitude vector C at the difference step size k k The nth difference accumulation magnitude of [N] is equal to the difference magnitude matrix B at the difference step size k. k The sum of the differential amplitude values ​​from the first row and nth column of [Mk,N] to the Mkth row and nth column; where n = 1, 2, ..., N; k is the differential step size, M represents the number of probe pulses, and N represents the number of vibration sampling points on the sensing fiber.

4. The vibration frequency estimation method based on amplitude difference step size according to claim 1, characterized in that, step In section 4, the signal-to-noise ratio vector (SNR) at the difference step size k k The nth signal-to-noise ratio snr of [N] k (z n )for: Where n = 1, 2, ..., N; c k (z n ) represents the difference accumulation magnitude vector C at the difference step size k. k The nth difference accumulation amplitude of [N], c k (z1):c k (z n-1 ),c k (z n+1 ):c k (z N ) represents the difference accumulation magnitude vector C at the difference step size k. k [N] represents the differential accumulation amplitude excluding the nth differential accumulation amplitude; max[·] represents the maximum value function; k is the differential step size; and N represents the number of vibration sampling points on the sensing fiber.

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