A method for determining a peak reference time point of a multi-peak narrow-band pulse signal

Abstract

The application provides a method for determining a peak reference time point of a multi-peak narrow-band pulse signal. The application can be applied to time delay correction of a time point of a time domain signal in a health monitoring process using a multi-peak narrow-band pulse signal, and is suitable for determining a peak reference time point of an arbitrary excitation frequency and an arbitrary peak excitation signal.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel strand stress identification, and in particular to a method for determining a wave peak reference time point of a multi-peak narrowband pulse signal. BACKGROUND

[0002] Steel strands are widely used in civil engineering, and their stress state directly affects the safety and service life of structures. However, under the influence of the environment and corrosion, especially in the case of long-term high stress tension, the stress state of the steel strand will change. In addition, the creep and shrinkage of concrete and the creep of steel strands will also cause changes in the stress level of the steel strands. Overestimating the loss of prestress leads to conservative and uneconomical maintenance design, and underestimating the loss of prestress makes the structure have safety hazards or even causes disasters, which affects the economy and social safety. Therefore, the detection of the effective stress of the steel strand is particularly important.

[0003] The ultrasonic guided wave stress identification method based on guided wave acoustic elasticity has its unique advantages in the field of non-destructive stress detection. It has low cost, simple and flexible arrangement, and can realize the absolute stress detection of steel strands. It also has a great application space for long-term stress monitoring of corroded steel strands. However, when monitoring the stress of corroded steel strands, it is necessary to compare the changes in the waveform observation signal. However, in long-term monitoring, time domain signals have zero drift phenomenon, which introduces time delay error. Temperature, corrosion and other factors will also cause reference point time delay. The introduction of the above errors will lead to inaccurate stress monitoring data. In addition, to realize the absolute stress detection of steel strands, the time domain signal also needs to be absolute processed. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a method for determining the wave peak reference time point of a multi-peak narrowband pulse signal, which is suitable for determining the wave peak reference time point of any excitation frequency and any wave peak excitation signal.

[0005] To achieve the above purpose, the present application adopts the following technical solution: a method for determining the wave peak reference time point of a multi-peak narrowband pulse signal, comprising the following steps:

[0006] Step 1: Take a steel strand sample of the same type as the steel strand in the actual engineering structure. Select a certain excitation frequency to excite a multi-peak narrowband pulse signal, i.e. a multi-period sine and cosine signal modulated by a Hanning window, which is referred to as a multi-peak wave. After the signal is generated with a time delay, the time point of the i-th wave peak of the excitation signal is set as t i , i = 1, 2, …, m, and the time point of the j-th wave peak of the received signal is set as T j , j = 1, 2, …, n.

[0007] Step 2: Based on the stationary point theoretical value t if , according to t0=ti -t if , obtaining the signal reference time point t0;

[0008] Step 3: According to T j ' = T j -t0, obtaining the absolute time point T j ' of the received signal after the reference point is determined, and if the excitation frequency changes, the method is the same as above.

[0009] In a preferred embodiment, the step 1 excitation signal peak time point t i , the received signal peak time point T i The steps are as follows:

[0010] Step 11: Select the excitation signal for guided wave stress identification, and the frequency is f1;

[0011] Step 12: Introduce a pulse signal on one side of any steel strand sample detection section, and receive the signal at the other end;

[0012] Step 13: Introduce time delay to signal time domain zero drift, including instrument temperature change, electromagnetic interference, and manual error when adjusting the instrument time domain knob, and the time delay obtains the time coordinate array (f1, t i , T j ) corresponding to different peaks of the excitation signal and the received signal at a specific excitation frequency, wherein i = 1, 2, …, m, j = 1, 2, …, n.

[0013] In a preferred embodiment, the step 2 specifically includes:

[0014] The specific expression of the multi-peak wave narrowband pulse signal is as follows:

[0015]

[0016] y represents the expression of the excitation signal; A represents the amplitude of the excitation signal; n represents the number of peaks of the signal; f represents the center frequency of the excitation signal; t represents the time point μs;

[0017] The mathematical expression of the stationary point theoretical value t if at the peak of the multi-peak wave signal is obtained from the upper limit value of the monotonically increasing interval of each multi-peak wave signal, and for a five-peak wave, it is represented as follows:

[0018]

[0019] k represents an integer greater than or equal to zero; f represents the center frequency of the excitation signal kHz;

[0020] For the expression (2) to expression (6), let k = 0, that is, the distance tif The signal reference time point is expressed as follows:

[0021] t0=t i -t if (7)

[0022] If the five-peak wave is not selected, the expressions of formula (2) to formula (6) are obtained by mathematical calculation, t if The determination method is the same as above.

[0023] In a preferred embodiment, the step 3 specifically comprises:

[0024] T j '=T j -t0 (8)

[0025] Before the signal reference time point is determined, the time points of the excitation signal and the received signal are not unified, and it is assumed that for any steel strand, the absolute peak time points T1', T2', T3'...T n ' of the steel strand under the detection section are now to be determined, a steel strand sample of the same type of steel strand in the actual engineering structure is taken, a specific excitation frequency f is selected, and the peak time points t1, t2, t3...t m , T1, T2, T3...T n of the excitation signal and the received signal are recorded. if The signal reference time point is calculated by formula (7), and the absolute time point of the received signal is calculated by formula (8).

[0026] Compared with the prior art, the present application has the following beneficial effects: the present application designs a peak reference time point determination technology based on the multi-peak wave narrowband pulse signal function expression to eliminate the time delay error, and the peak time point can be calibrated, and the time delay change value caused by corrosion, tension or other factors calculated after the waveform collected at any time and under any condition is correct and reliable, which is also a necessary condition to realize the absolute stress detection of the steel strand. BRIEF DESCRIPTION OF DRAWINGS

[0027] Fig. 1 The present application is a preferred example of a preset frequency excitation signal under the first peak to determine the reference time point.

[0028] Fig. 2 The present application is a preferred example of an excitation signal and a received signal whose reference time point is determined.

[0029] Fig. 3 The present application is a preferred example of a preset frequency received signal absolute time point.

[0030] Fig. 4The absolute time position of a plurality of groups of received signals under the influence of corrosion factors is eliminated when zero drift delay is eliminated. DETAILED DESCRIPTION

[0031] The application will be further described below with reference to the accompanying drawings and examples.

[0032] It should be noted that the following detailed description is illustrative only and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0033] It should be noted that the terms used herein are merely for the purpose of describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application; as used herein, the singular form is intended to include the plural form unless the context clearly indicates otherwise, and it should also be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of the features, steps, operations, devices, components and / or combinations thereof.

[0034] Reference Figs. 1 to 4 For a multi-peak wave narrow-band pulse signal excited on any steel strand, the abscissa of the wave crest in the time domain is the time position, and there is a zero drift phenomenon in the time domain signal in long-term monitoring, thereby introducing a time delay error, which will also produce a reference point time delay under the influence of temperature, corrosion, etc. The introduction of the above error will lead to inaccurate stress monitoring data. After the signal produces a time delay, let the time position of the i-th wave crest of the excitation signal be t i (i = 1, 2,..., m), and the time position of the j-th wave crest of the received signal be T j (j = 1, 2,..., n). For a multi-peak wave narrow-band pulse signal excited on any steel strand, the specific expression is as follows:

[0035]

[0036] y - expression of the excitation signal;

[0037] A - amplitude of the excitation signal;

[0038] n - number of wave crests of the signal;

[0039] f - center frequency of the excitation signal (unit: kHz);

[0040] Mathematical expression of the theoretical value t if of the stationary point at the wave crest of the excitation signal is obtained from the upper limit value of the monotonically increasing interval of each multi-peak wave signal. Taking a five-peak wave as an example, it is expressed as follows:

[0041]

[0042]

[0043] t - time point (μs) ;

[0044] k - integer greater than or equal to zero;

[0045] f - center frequency of excitation signal (kHz) ;

[0046] For expressions (2) to (6), let k = 0, then the distance t of each peak wave time point to zero at a specific frequency can be obtained if The signal reference time point is expressed as follows:

[0047] t0 = t i -t if (7)

[0048] If the five-peak wave is not selected, the expressions (2) to (6) are obtained by mathematical calculation, t if The determination method is the same as above. After the reference point is determined, the absolute time point Tj' of the received signal is expressed as follows:

[0049] T j ' = T j -t0 (8)

[0050] Before the signal reference time point is determined, the time points of the excitation signal and the received signal are not unified. It is assumed that for any steel strand, the absolute peak wave time point T' of the steel strand in the detection section (including but not limited to single or multiple twist pitches of the steel strand) is to be determined. A steel strand sample of the same steel strand model as in the actual engineering structure is taken, a specific excitation frequency f i is selected, and the peak wave time points t j , T j of the excitation signal and the received signal are recorded. The stationary point theoretical value t if at the peak of the multi-peak wave signal is used to calculate the signal reference time point from formula (7), and the absolute time point of the received signal is calculated from formula (8). The time domain signal is absolute, which is also a necessary condition to realize the detection of the absolute stress of the steel strand.

[0051] Embodiment:

[0052] Step 1: A steel strand sample of the same steel strand model as in the actual engineering structure is taken, the detection section is a single twist pitch, and a five-peak wave narrowband pulse signal, i.e., a five-period sine (cosine) signal modulated by a Hanning window, is selected as the excitation frequency f1, which is referred to as a five-peak wave.

[0053] Step 2: After the reference time point delay occurs, the first peak wave time point t1 on the five-peak wave excitation signal is recorded, and the peak wave time point array T (T1, T2, …, Tn ).

[0054] Step 3: Determine the distance t from the first peak time point to the zero point of the excitation signal at the frequency f1 1f , see Table 1, according to t0=t1-t 1f , the reference time point t0 of the excitation signal is obtained.

[0055] The distance from the first peak time point to the zero point of the excitation signal at each frequency

[0056]

[0057] Step 4: Position the reference time point t0 of the excitation signal to the time point of the guided wave received signal, according to T'=T-t0, the absolute time point array T' of the received signal after the reference point is determined, and if the excitation frequency changes, the method is the same as above.

Claims

1. A method of determining a peak reference time location of a multi-peak narrowband pulse signal, characterized in that, The method comprises the following steps: Step 1: take a steel strand sample of the same type as the steel strand in the actual engineering structure, and excite a multi-peak wave narrow-band pulse signal, i.e. a multi-cycle sine signal modulated by a Hanning window, at a certain excitation frequency in the detection section, referred to as a multi-peak wave; after the signal is generated, the i-th peak time point of the excitation signal is set as t i , i = 1, 2, …, m, and the j-th peak time point of the received signal is set as T j , j = 1, 2, …, n; Step 2: Based on the theory of the standing point value t at the wave peak of the multi-peak wave signal if， According to t0=t i -t if , the signal reference time point t0 is obtained; Step 3: According to T j ' = T j - t0, the absolute time point T of the reference point determined after receiving the signal j ', if the excitation frequency changes, the method is the same as above; The step 1 excitation signal peak time site t i , receiving signal peak time site T j The acquisition step is as follows: Step 11: selecting an excitation signal for identifying guided wave stress, and the frequency of the excitation signal is f1; Step 12: introducing a pulse signal on one side of a detection section of any steel strand sample, and receiving a signal at the other end; Step 13: Signal time domain zero drift delay includes instrument temperature changes, electromagnetic interference, human error when touching the instrument time domain adjustment knob, the delay obtained under the specific excitation frequency Excitation signal, the time coordinate array corresponding to the different peaks of the received signal (f1, t i , j ), where i = 1, 2, …, m, j = 1, 2, …, n; The step 2 specifically comprises: The specific expression of the multi-peak wave narrowband pulse signal is as follows: y represents the expression of the excitation signal; A represents the amplitude of the excitation signal; n represents the number of peaks of the signal; f represents the center frequency of the excitation signal; t represents the time point μs; Theoretical value of the stationary point at the wave crest of a multi-peak wave signal t if The mathematical expression of the upper limit value of the monotonically increasing interval of each multi-peak wave signal is obtained, and for a five-peak wave, it is expressed as follows: k represents an integer greater than or equal to zero; f represents the center frequency of the excitation signal kHz; For the expressions (2) to (6) let k = 0, i.e. obtain the distance t of each peak wave time point to zero at a specific frequency if The signal reference time point is expressed as follows: t0 = t i -t if (7) If the five-peak wave is not selected, the expressions of formula (2) to formula (6) are obtained by mathematical calculation, t if The determination method is the same as above; The step 3 specifically comprises: T j '=T j -t0 (8) Before the signal reference time point is determined, the time points of the excitation signal and the received signal are not uniform. Assuming that for any steel strand, the absolute peak time points T1', T2', T3'...T n , a steel strand sample is taken from the same steel strand model in the actual engineering structure, a specific excitation frequency f is selected, and the peak time points t1, t2, t3...t m , T1, T2, T3...T n of the excitation signal and the received signal are recorded. if The signal reference time point is calculated by formula (7), and the absolute time point of the received signal is calculated by formula (8).

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