Long-distance pumping pipeline blockage state recognition method based on fiber grating sensor

Abstract

The application discloses a long-distance pumping pipeline blockage state recognition method based on fiber grating sensing, and specifically comprises the following steps: step 1, arranging an FBG strain sensor to obtain a wavelength value λ B under the measurement of gangue pumping working state; B Step 2, calculating a fiber Bragg grating reflected light wavelength change value Δλ B according to λ B , and converting Δλ B into an axial strain change amount Δε a ; a Step 3, converting the axial strain change amount Δε a obtained in step 2 into a strain acceleration value ε″ a (t) by twice derivation with respect to time; a Step 4, dividing the pipeline cross-section blockage degree according to blockage grades by using the strain acceleration value ε″ a (t) obtained in step 3. The application converts the directly measured long-distance gangue pumping pipeline blockage state strain into an indirect measurement, and improves the accuracy of the pipeline blockage state recognition result.

Description

Technical Field

[0001] This invention belongs to the field of pipeline transportation technology and relates to a method for identifying blockage status in long-distance pumping pipelines based on fiber optic grating sensing. Background Technology

[0002] Strain is a crucial parameter reflecting the operational status of pipeline transportation systems. To accurately measure and obtain micro-deformations in long-distance gangue pumping pipelines and identify blockages, strain detection is key to this research. Currently, the traditional method for identifying blockages in long-distance gangue pumping pipelines involves axially attaching traditional strain sensors to the pipeline surface. However, this traditional method has the following drawbacks: Since the pipeline is in operation, the size and weight of the traditional strain gauges and transmission cables will affect the flow field and pumping dynamics on the pipeline surface, thus impacting the accuracy of the identification results. Summary of the Invention

[0003] The purpose of this invention is to provide a method for identifying the blockage status of long-distance pumping pipelines based on fiber optic grating sensing. This method converts the direct measurement of strain in the blockage status of long-distance gangue pumping pipelines into indirect measurement, thereby improving the accuracy of the pipeline blockage status identification results.

[0004] The technical solution adopted in this invention is a method for identifying the blockage status of long-distance pumping pipelines based on fiber optic grating sensing, which specifically includes the following steps:

[0005] Step 1: Install FBG strain sensors on the pumping pipeline and obtain the wavelength value λ of the FBG strain sensors when measuring the working state of the gangue pump. B ;

[0006] Step 2, based on the wavelength value λ measured in Step 1 B Find the wavelength change Δλ of the light reflected from the fiber Bragg grating. B and Δλ B The change in axial strain Δε a ;

[0007] Step 3: Utilize the relationship between strain and acceleration of the FBG vibration sensor to calculate the change in axial strain Δε obtained in Step 2. a Taking the second derivative with respect to time transforms it into the strain acceleration value ε″ a (t);

[0008] Step 4, using the strain acceleration value ε″ obtained in Step 3. a (t) The degree of blockage in the cross-section of the pipeline is classified according to the blockage level.

[0009] The invention is further characterized by:

[0010] The specific process of step 1 is as follows:

[0011] Several FBG strain sensors are arranged at measuring points on the pipe surface. The FBG strain sensors are surface-mounted directly above the pumping pipe wall using a surface-mount method, with epoxy resin used to fix the grid area. The FBG strain sensors are connected in series, and one end of one of the end-positioned FBG strain sensors is connected to an FBG demodulator. The FBG demodulator is connected to a display via a jumper. After the grouting pump is started, the display shows the wavelength value λ. B .

[0012] The specific process of step 2 is as follows:

[0013] Step 2.1, calculate the wavelength change Δλ of the fiber Bragg grating reflected light from the FBG strain sensor using the following formula (1). B :

[0014]

[0015] In the formula, This is the initial wavelength of the fiber Bragg grating;

[0016] Step 2.2: Under changing external temperature conditions, the shift in the center wavelength of the reflected spectrum is affected by changes in the stress field where the fiber Bragg grating sensor is located, and also by changes in the temperature field. Therefore, the wavelength change Δλ of the reflected light from the fiber Bragg grating under temperature variations is obtained. B As shown in formula (2) below:

[0017]

[0018] Equation (2) yields the change in axial strain Δε in the region where the FBG strain sensor grating is located under varying external temperature conditions. a As shown in formula (3) below:

[0019]

[0020] In the formula: ΔT is the temperature difference; α is the axial strain sensitivity coefficient. T This is the temperature sensitivity coefficient.

[0021] The specific process of step 3 is as follows:

[0022] The strain rate is obtained by differentiating the strain signal with respect to time t, i.e., by differentiating the strain signal.

[0023]

[0024] In the formula, L0 is the original length of the optical fiber, L(t) is the length of the optical fiber at each time t, and v(t) is the speed at which the optical fiber is stretched at each time t.

[0025] Then, taking the second derivative of the strain signal with respect to time t, i.e., differentiating the strain signal twice, yields the strain acceleration ε″. a (t):

[0026]

[0027] In the formula, a(t) is the acceleration of the fiber being stretched at each time t.

[0028] In step 4, the blockage levels are classified as severe blockage L4, moderate blockage L3, minor blockage L2, and no blockage L1;

[0029] When the strain acceleration value is [ε″ a (t) s＝0 , ε″ a (t)s ＝20％ When [the congestion level is] L1;

[0030] When the strain acceleration value is [ε″ a (t) s＝20％ , ε″ a (t) s＝40％ When [the congestion level is] L2;

[0031] When the strain acceleration value is [ε″ a (t) s＝40％ , ε″ a (t) s＝60％ When [the congestion level is] L3;

[0032] The strain acceleration value is [ε″ a (t) s＝60％ , ε″ a (t) s＝100％ When [the signal is], the congestion level is L4.

[0033] The beneficial effects of this invention are as follows:

[0034] 1. This invention proposes a strain measurement method based on fiber bragg grating (FBG), which transforms the direct measurement of strain in the blockage state of long-distance gangue pumping pipeline into an indirect measurement. It considers the influence of temperature on the fiber bragg grating to eliminate the sensitivity of the fiber bragg grating to temperature strain, introduces multi-channel data, and the data includes time sequence, making the data basis of the identification method more scientific.

[0035] 2. The method of the present invention can detect the degree of blockage in long-distance gangue pumping pipelines in real time and can quickly guide pipeline dredging operations; the method is not affected by the pipe material, and it does not require disassembling the components of the long-distance gangue pumping pipeline when installing the fiber optic grating sensor, and does not affect the normal operation of the long-distance gangue pumping pipeline.

[0036] 3. This invention designs corresponding blockage level classification and blockage identification methods for the blockage degree of long-distance gangue pumping pipelines (including multi-channel data), providing a basis for more accurate identification of the blockage degree of long-distance gangue pumping pipelines. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the fiber grating sensing principle of the FBG strain sensor used in the long-distance pumping pipeline blockage state identification method based on fiber grating sensing in this invention.

[0038] Figure 2 This is a state diagram of the FBG strain sensor being attached to the pipeline in the long-distance pumping pipeline blockage state identification method based on fiber optic grating sensing of the present invention.

[0039] Figure 3 This is a schematic diagram of the FBG strain sensor placement in the long-distance pumping pipeline blockage identification method based on fiber optic grating sensing of the present invention.

[0040] Figure 4 The present invention relates to a strain acceleration time-domain plot in a method for identifying blockage in long-distance pumping pipelines based on fiber optic grating sensing. Detailed Implementation

[0041] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0042] Example 1

[0043] This invention relates to a method for identifying blockage status in long-distance pumping pipelines based on fiber optic grating sensing, which specifically includes the following steps:

[0044] Step 1: Install FBG strain sensors at the measuring points on the pipe surface. This involves surface-mounting the FBG strain sensors directly above the pipe wall using a surface-mount method, fixing the grid area with epoxy resin, and connecting the FBG strain sensors in series. Then, connect one end of each sensor to an FBG demodulator. The FBG demodulator is connected to a monitor via a jumper. When the grouting pump is started, the monitor displays the wavelength value λ. B ;

[0045] The sensing principle of the FBG strain sensor is as follows: Figure 1 As shown.

[0046] The incident light is a broadband spectrum containing multiple wavelengths. When it strikes the grating region, only light waves of a specific wavelength are reflected, while other wavelengths remain unaffected and continue propagating along the optical fiber through the grating. The wavelength of the reflected light is the Bragg wavelength, λ. B The expression is:

[0047] λ B =2n eff ∧ (1)

[0048] In the formula: λ B λ is the reflection wavelength of the fiber Bragg grating; ∧ is the period of the grating; n eff ρ is the effective refractive index of the grating. The main factors determining the wavelength of the reflected light from the grating are π and n. eff When a fiber Bragg grating sensor is subjected to external force, causing deformation of the grating region, it leads to changes in the axial strain of the grating, ∧ and n. eff This also changes accordingly, ultimately leading to λ B Changes occur when the temperature of the grating changes, causing thermal expansion or contraction of the fiber material, resulting in strain and consequently affecting λ. B The changes.

[0049] Step 2: Utilize the FBG sensing principle to measure the wavelength value λ B The wavelength difference is obtained by subtracting the offset wavelength value from the offset wavelength value, and then the wavelength difference is converted into the strain value change Δε. a ;

[0050] Based on the spectral information such as wavelength and intensity of light collected by the FBG strain sensor, the change in wavelength of the light returned by the sensor during the experiment is calculated, and the change in wavelength of the reflected light is Δλ. B expression:

[0051]

[0052] In the formula: Δλ represents the initial wavelength of the fiber Bragg grating. B This represents the change in wavelength of the light wave reflected from the fiber Bragg grating.

[0053] Under changing external temperature conditions, the shift in the center wavelength of the reflection spectrum is affected by changes in the stress field where the fiber optic grating sensor is located, and also by changes in the temperature field. Thus, an expression for the wavelength change under temperature change conditions can be obtained.

[0054]

[0055] From equation (3), we can obtain the expression for the strain value in the region where the FBG strain sensor grating is located under the condition of changing external temperature:

[0056]

[0057] In the formula: Δε a ΔT represents the change in axial strain; ΔT represents the temperature difference. α is the axial strain sensitivity coefficient. T This is the temperature sensitivity coefficient.

[0058] Step 3: Utilize the relationship between strain and acceleration of the FBG vibration sensor to calculate the strain change Δε. a Taking the second derivative with respect to time transforms it into the strain acceleration value ε″ a (t);

[0059] For vibration signals, which are actually high-frequency components of strain, the frequency and amplitude can be obtained by high-speed sampling of strain measurements and Fourier transform. Since acceleration is more sensitive in the high-frequency range, the strain acceleration signal is obtained indirectly by measuring strain.

[0060] The strain rate signal and strain acceleration signal are obtained by taking the derivative of the strain signal obtained by the wavelength signal measured by the fiber optic grating twice with respect to time.

[0061] The strain rate is obtained by differentiating the strain signal with respect to time t, i.e., by differentiating the strain signal.

[0062]

[0063] In the formula, L0 is the original length of the optical fiber, L(t) is the length of the optical fiber at each time t, and v(t) is the speed at which the optical fiber is stretched at each time t.

[0064] Then, taking the second derivative of the strain signal with respect to time t, i.e., differentiating the strain signal twice, yields the strain acceleration:

[0065]

[0066] In the formula, a(t) is the acceleration of the fiber being stretched at each time t.

[0067] Step 4, use Table 1 to obtain the strain acceleration values ​​ε″ a (t) The degree of blockage in the pipeline cross-section is classified into ranges according to the blockage level (L1~L4).

[0068] Example 2

[0069] Based on Example 1, the specific process of step 4 is as follows:

[0070] The blockage level is divided into four levels: severe blockage (L4), moderate blockage (L3), slight blockage (L2), and no blockage (L1); the classification criteria for the blockage level are based on Table 1, and the strain acceleration value is [ε″]. a (t)s＝0 , ε″ a (t) s＝20％ ], non-blockage (L1) means the blockage range of the pipe cross-section is 0-20%; the strain acceleration value is [ε″ a (t) s＝20％ , ε″ a (t) s＝40％ Slight blockage (L2) refers to a blockage range of 20% to 40% in the pipe cross-section; the strain acceleration value is [ε″]. a (t) s＝40％ , ε″ a (t) s＝60％ ]; General blockage (L3) refers to the blockage range of the pipeline cross-section being 40% to 60%; the strain acceleration value is [ε″]. a (t) s＝60％ , ε″ a (t) s＝100％ Severe blockage (L4) means that the blockage range of the pipeline cross-section is 60% to 100%.

[0071] Table 1 Classification of Blockage Range

[0072] <![CDATA[0≤ε″ a (t)<2]]> 0≤s<20％ Non-blocking (L1) <![CDATA[2≤ε″ a (t)<4]]> 20％≤s<40％ Minor blockage (L2) <![CDATA[4≤ε″ a (t)<6]]> 40％≤s<60％ General blockage (L3) <![CDATA[ε″ a (t)≥6]]> 60％≤s<100％ Severe congestion (L4)

[0073]

[0074] In the formula, ε″ a (t) - Strain acceleration values ​​at different monitoring points; s = i% - Degree of blockage in the pipeline cross-section.

[0075] Example 3

[0076] The experimental platform consisted of a 15.5m long, 50mm diameter steel pipe with a water tank at each end. The water tanks were connected to a grouting pump via high-pressure hoses. The grouting pump was also connected to the pipe via a high-pressure hose. Grouting began as soon as the experiment started, simulating the actual working conditions of a long-distance gangue pumping pipeline. Considering the smoothness of the pipe wall layers, the FBG strain sensors were laid out as follows.

[0077] First, the FBG strain sensor has a diameter of 0.125mm. When installing the FBG strain sensor on the pipe wall using surface bonding, to avoid uneven stress and cracking of the sensor grid area during bonding, the layer thickness at the sensor should be more than 10 times the sensor diameter. Second, the FBG strain sensor is horizontally bonded along the pipe, and the grid area is fixed with epoxy resin. Figure 2 .

[0078] Considering the wavelength division multiplexing (WDM) properties of FBG strain sensors, a series FBG scheme was customized. Then, epoxy resin was used to fix the grating region to avoid fluid corrosion of the fiber grating and the influence of excessively thick, numerous, or insufficient adhesive layers. Based on these considerations, the fiber grating sensor was placed at point A (FBG-H01) on the wall of a long-distance gangue pumping pipeline to receive the vibration signal of gangue flowing through the pipeline. The frequency of the wavelength signal was analyzed and processed by a monitoring host. Point A was set at the center of the straight section of the long-distance gangue pumping pipeline. A monitoring point B (FBG-H02) is set 2.2m away from point A to monitor the wavelength signal intensity at point B. Point B is located on one side of point A along the direction of gangue flow. A monitoring point C (FBG-H03) is set 4.4m away from point B in the direction from A to B. Points D (FBG-H04) and E (FBG-H05) are set on the left and right sides of the valve (i.e., on both sides of the valve in the direction of gangue flow), respectively, with a 0.5m interval between points D and E. A monitoring point F (FBG-H06) is set 1.1m away from point E in the direction from D to E. The peak wavelength signal intensity point X of the detection section is used as the standard for judging the degree of blockage in the pipeline in the detection section. Figure 3 This describes the method of attaching the FBG strain sensor to the pipe wall.

[0079] Based on the pre-embedded location and strain measurement range of the FBG strain sensor, series FBG strain sensors (FBGH01~FBG H06) were customized. The numbering, center wavelength configuration and series connection method of each sensor are shown in Table 2. Wavelength division multiplexing technology is used to distinguish each sensor.

[0080] Table 2. Schematic diagram of FBG strain sensor configuration

[0081]

[0082]

[0083] The strain acceleration of the pipe wall was measured using an FBG strain sensor under different valve flow conditions. The time-domain plot of the strain acceleration variation trend is shown below. Figure 4 .

[0084] The FBG strain sensor was used to collect the blockage strain acceleration data of the long-distance gangue pumping pipeline under the above working conditions, and time domain analysis was performed. For monitoring gangue blockage, the variation trend along the pipe length is generally the same at different monitoring points. After the blockage location, the strain acceleration of the sensor increases linearly with different trends. When the strain acceleration value at the FBG-H05 monitoring point is -4.70, it indicates no blockage (L1); when the strain acceleration value at the FBG-H05 monitoring point is 0.59, it indicates no blockage (L1); when the strain acceleration value at the FBG-H05 monitoring point is 3.58, it indicates slight blockage (L2); when the strain acceleration value at the FBG-H05 monitoring point is 3.67, it indicates slight blockage (L2); when the strain acceleration value at the FBG-H05 monitoring point is 4.70, it indicates moderate blockage (L3); when the strain acceleration value at the FBG-H05 monitoring point is 6.13, it indicates severe blockage (L4); when the strain acceleration value at the FBG-H05 monitoring point is 7.05, it indicates severe blockage (L4).

Claims

1. A method for identifying blockage status in long-distance pumping pipelines based on fiber optic grating sensing, characterized in that: Specifically, the steps include the following: Step 1: Install FBG strain sensors on the pumping pipeline and obtain the wavelength values ​​of the FBG strain sensors when measuring the working state of the gangue pump. ; Step 2, based on the wavelength value measured in Step 1 Find the wavelength change of the light wave reflected from the fiber Bragg grating. and will The change in axial strain ; Step 3: Utilize the relationship between strain and acceleration of the FBG vibration sensor to calculate the change in axial strain obtained in Step 2. The second derivative with respect to time is used to convert the values ​​of strain acceleration. The specific process of step 3 is as follows: The strain signal is time t. Taking the first derivative of the strain signal, i.e., differentiating the strain signal, yields the strain rate. （1） In the formula, This represents the original length of the optical fiber. The length of the fiber at each time t, v The speed at which the optical fiber is stretched at each time t; Then, taking the second derivative of the strain signal with respect to time t, i.e., differentiating the strain signal twice, yields the strain acceleration. : （2） In the formula, The acceleration at which the optical fiber is stretched at each time t; Step 4: Use the strain acceleration value obtained in Step 3. The degree of blockage in the pipe cross-section is classified according to the blockage level; in step 4, the blockage level is divided into severe blockage L4, moderate blockage L3, slight blockage L2 and no blockage L1; When the strain acceleration value is At that time, the congestion level is L1; When the strain acceleration value is At that time, the congestion level was L2; When the strain acceleration value is At that time, the congestion level was L3; strain acceleration value At that time, the congestion level was L4.

2. The method for identifying blockage status in long-distance pumping pipelines based on fiber optic grating sensing according to claim 1, characterized in that: The specific process of step 1 is as follows: Several FBG strain sensors are arranged at measuring points on the pipe surface. Specifically, the FBG strain sensors are surface-mounted directly above the pumping pipe wall using a surface-mount method. Epoxy resin is used to fix the grid area. The FBG strain sensors are connected in series. One end of one of the end FBG strain sensors is connected to an FBG demodulator, which is connected to a display via a jumper. After the grouting pump is started, the display shows the wavelength value. .

3. The method for identifying blockage status in long-distance pumping pipelines based on fiber optic grating sensing according to claim 2, characterized in that: The specific process of step 2 is as follows: Step 2.1, calculate the wavelength change of the fiber Bragg grating reflected light from the FBG strain sensor using the following formula (3). : （3） In the formula, This is the initial wavelength of the fiber Bragg grating; Step 2.2: Under changing external temperature conditions, the shift in the center wavelength of the reflected spectrum is affected by changes in the stress field where the fiber Bragg grating sensor is located, and also by changes in the temperature field. Therefore, the wavelength change value of the reflected light wave under temperature change conditions is obtained. As shown in formula (4) below: （4） Equation (4) yields the change in axial strain in the region where the FBG strain sensor grating is located under varying external temperature conditions. As shown in the following formula (5): （5） In the formula: For temperature difference; The axial strain sensitivity coefficient is... This is the temperature sensitivity coefficient.

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