Method for measuring air volume for dynamic environment monitoring of underground circular tunnel

Abstract

The invention belongs to the technical field of circular tunnel air volume measurement, and particularly relates to an air volume measuring method for dynamic environment monitoring of an underground circular tunnel. The measuring method mainly comprises the following steps: firstly, measuring the distances from a test point to the upper top surface, the lower bottom surface, the right wall surface and the left wall surface of the tunnel; secondly, establishing a coordinate system by taking the circle center of the cross section of the circular tunnel as an original point, and calculating the distance L from the original point to the tunnel wall in the diameter direction; then, carrying out average calculation on the wind speeds measured at intervals in a period of time to obtain a wind speed average value # imgabs0 # at the measuring point; and finally, calculating the flow Q of the cross section of the circular tunnel according to # imgabs 1 #, L and the radius R of the tunnel. Through a specific mathematical formula and a statistical average method, the measurement process is simplified, and the data accuracy is improved. According to the method, the number of measuring points is remarkably reduced, the testing workload is reduced, the accuracy of air volume measurement is improved, and the method is suitable for performance evaluation of a large-scale or complex-structure underground space ventilation system.

Description

Technical Field

[0001] The present invention belongs to the interdisciplinary technical field of ventilation systems and environmental monitoring technologies, and particularly relates to a method for measuring air volume for dynamic environmental monitoring of underground circular tunnels. Background Art

[0002] Tunnels are a common form of underground space utilization. Common large-scale tunnels include hydropower station corridors, subway tunnels, and mine tunnels. Transport and mining tunnels contain a variety of harmful gases, such as carbon monoxide (CO), nitrogen oxides (NO), and smoke and dust, which contribute to tunnel air pollution. Ventilation is necessary to bring in fresh air from outside to maintain safe concentrations of these harmful substances. Furthermore, underground hydropower stations and other structures utilize tunnels for natural cooling or heating of incoming outdoor air, achieving significant energy-saving and environmental benefits. This requires knowledge of tunnel air volume values. Currently, circular tunnel air volume measurement often uses the equal-area circular ring method, which requires a large number of measurement points and significantly increases the testing workload. However, the large volume of some tunnels makes it difficult to arrange measurement points above the tracks. Even for operating subway tunnels, it's impossible to establish long-term measurement points above the tracks, limiting the accuracy of air volume test results. A rational method for setting air volume in circular tunnels can effectively reduce the amount of data, instruments, and test personnel required for circular tunnel air volume measurement, making it simpler and easier to use. Summary of the Invention

[0003] The present invention proposes a method for measuring air volume for dynamic environmental monitoring of underground circular tunnels to solve the technical problems in the prior art that a large number of measuring points are required in the tunnel, resulting in a large testing workload and a large tunnel volume, which reduces the accuracy of air volume measurement.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions: A method for measuring air volume for dynamic environmental monitoring of an underground circular tunnel, the measuring method being: Step 1: Measure the vertical distance h1 between the test point and the top surface of the tunnel, the vertical distance h2 between the test point and the bottom surface of the tunnel, the horizontal distance s1 between the test point and the right wall of the tunnel, and the horizontal distance s2 between the test point and the left wall of the tunnel; Step 2: Establish a coordinate system with the center of the circular tunnel cross section as the origin, measure the radius R of the circular tunnel cross section, and calculate the distance L from the origin to the tunnel wall along the diameter direction of the cross section based on the radius of the circular tunnel cross section, the vertical distance h1 from the test point to the top surface of the tunnel, the vertical distance h2 from the test point to the bottom surface of the tunnel, the horizontal distance s1 from the test point to the right wall of the tunnel, and the horizontal distance s2 from the test point to the left wall. Step 3: Average the wind speeds measured at intervals within a period of time to obtain the average wind speed at the measuring point in the tunnel. ; Step 4: Based on the average wind speed , the distance L from the origin to the tunnel wall along the cross-section diameter direction and the radius R of the circular tunnel cross-section to calculate the average wind speed at the tunnel center point ; Step 5: Based on the average wind speed at the center of the tunnel The flow rate Q of the circular tunnel section is calculated based on the radius R of the circular tunnel cross section.

[0005] The calculation method for the distance L between the origin and the tunnel wall along the cross-section diameter in step 2 is: ,in .

[0006] The average wind speed measured at the measuring point in the tunnel in step 3 The calculation method is: .

[0007] The statistical averaging method is used to average the speed measurement values at intervals of 3 seconds within 1 minute to obtain the average wind speed value at the selected measuring point. .

[0008] Average wind speed at the center of the tunnel The calculation method is: .

[0009] In step 4, the calculation method of the circular tunnel cross-section flow rate Q is: ,in, is the average wind speed at the center of the tunnel, in m / s; n is the turbulent flow constant, and r is the kinematic viscosity coefficient.

[0010] The turbulent flow constant n is the velocity field in the circular tunnel when ANSYS software is used to simulate different Reynolds numbers Re, and the average wind speed at the center of the tunnel is used to calculate the turbulent flow constant n. The turbulent flow constant n is fitted by the calculation formula.

[0011] ANSYS software simulates a set of Reynolds numbers Re, passing through the average wind speed at the center of the tunnel The calculation formula relatively fits the data of the turbulent flow constant n corresponding to the simulated Reynolds number Re. The relationship between the turbulent flow constant n and the Reynolds number Re is: ,in and are the first parameter to be fitted and the second parameter to be fitted.

[0012] ANSYS software simulates a set of Reynolds numbers Re, which are calculated as follows: ,in, is the actual average wind speed in the tunnel, is the set value; is the characteristic length of the tunnel, in m; is the kinematic viscosity coefficient.

[0013] Since the wind speed at the center of the actual tunnel is difficult to measure, the average wind speed at the measuring point is used. Calculate the Reynolds number Re, that is, in the above calculation formula of the Reynolds number Re, = , the distance between the measuring point and the tunnel wall should be greater than or equal to 0.2m.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a method for measuring the air volume for dynamic environmental monitoring of an underground circular tunnel. By accurately locating the position of the test point, accurate basic data is provided for subsequent calculations, reducing errors caused by inaccurate positions. By establishing a coordinate system and calculating the L value, the need to collect data from multiple scattered points is simplified. Only measurements at specific positions are required to infer information on the entire cross section, thereby reducing the number of measurements in actual operation and reducing the testing workload. By averaging multiple velocity readings over a period of time, the influence of instantaneous fluctuations on the final result can be eliminated, and the representativeness and reliability of single measurement results can be improved, thereby improving measurement accuracy. The air flow rate Q in the entire cross section is estimated by combining the empirical formula obtained by fluid mechanics principles and experimental fitting. Compared with the method of directly measuring the velocity distribution of each local area and then accumulating and summing them, this method provides a more efficient and accurate solution. In summary, this method greatly reduces the difficulty and cost of on-site operations while ensuring measurement accuracy by optimizing the arrangement of measurement points, introducing mathematical modeling methods, and reasonably selecting experimental conditions. It is very suitable for application in large or structurally special underground space ventilation system performance evaluation scenarios.

[0015] Furthermore, the L value is calculated through a specific mathematical formula, which further simplifies the measurement process and ensures the accuracy of the calculation. In step three, the statistical averaging method is used to average the speed measurement values at intervals of 3 seconds within 1 minute, which further improves the stability and reliability of the wind speed measurement. In step four, the flow rate is calculated through an integral formula, which takes into account the changes in wind speed at different radii and improves the accuracy of the flow rate calculation. Calculation of the relationship between L / R , further simplifying the calculation process and improving the accuracy of the calculation results.

[0016] Furthermore, the method for determining the turbulent flow constant n uses ANSYS software to simulate the conditions under different Reynolds numbers Re, and adjusts the n value accordingly to adapt to changes in actual conditions, thereby enhancing the applicability and flexibility of the model under different conditions.

[0017] Furthermore, the distance between the measuring point and the tunnel wall should be greater than or equal to 0.2 m, avoiding the possible interference caused by the boundary layer effect, ensuring the validity and representativeness of the collected data, and thus improving the accuracy of the measurement results. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the circular tunnel air volume measurement structure Figure 2 Schematic diagram of the fitting curve of the relationship between the turbulent flow constant n and Re Figure 3 Schematic diagram of the comparison between the calculated tunnel air volume and the actual value for a single point measurement Figure 4 This is a schematic diagram of measuring point selection in Example 2; Figure 5 Comparison of the calculated air volume and the actual air volume at different measuring points in Example 2. DETAILED DESCRIPTION

[0019] In order to further understand the content of the present invention, the present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the embodiments are only for explaining the present invention and are not intended to limit it.

[0020] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. This embodiment provides a method for measuring air volume for dynamic environmental monitoring of an underground circular tunnel. Example 1: According to the above technical solution, the diameter of the circular tunnel in this example is 7m, the length of the tunnel is 1000m, the center of the tunnel is the origin of the coordinate system O, and the section 200m away from the entrance is selected for measurement. The ambient temperature in the tunnel is 20℃, and the kinematic viscosity coefficient is Its structural diagram is as follows. Figure 1 To verify the feasibility of the method on a large scale, the average wind speed in the tunnel was changed. There are 7 working conditions as follows: 0.50m / s; 1.0m / s; 1.5m / s; 2.0m / s; 2.5m / s; 3.0m / s; 3.5m / s.

[0021] To determine the air volume of a circular tunnel, the specific process is as follows: Step 1: Choose any suitable location in the tunnel to place the wind speed probe and arrange the measuring point. The distance between the measuring point and the tunnel wall should be greater than or equal to 0.2m. Use a handheld laser rangefinder to first test the vertical distance from the point to the top surface h1=4.665m, the vertical distance from the bottom surface h2=1.617m, the distance from the right wall S1=4.706m, and the horizontal distance from the left wall S2=1.6m. The distance between the measuring point and the tunnel inner wall is the same as the following: Figure 1 As shown in h1, h2, S1 and S2 in .

[0022] Step 2: Establish a coordinate system, such as Figure 1 As shown in , the cross section of the circular tunnel is a circle. The coordinate system is established with its center as the origin O. The radius of the circular tunnel is R = 3.5m. The distance L from the point along the diameter direction to the circular tunnel wall is calculated (this distance is the distance from the measuring point to the nearest tunnel inner wall) (and ensure that L ≤ R): (1) Calculation shows that the distance from the circular tunnel wall along the diameter direction is L=1.324m.

[0023] Step 3: Because the airflow in the tunnel is affected by turbulent pulsation, the wind speed value measured by the wind speed measuring instrument fluctuates. Therefore, the statistical averaging method is used to average the speed measurement values at intervals of 5 seconds within 1 minute to obtain the average wind speed value at the selected measuring point. : (2) The results of the measurement of 7 tunnel ventilation conditions show that the average wind speed at the selected measuring points is They are: 0.487m / s; 0.977m / s; 1.462m / s; 1.934m / s; 2.424m / s; 2.899m / s; 3.371m / s;.

[0024] Step 4: The air flow state is generally turbulent, and the flow velocity distribution can be described by the following formula. The turbulent flow constant n is determined by the following formula, and the relationship between n and Re is obtained by fitting; (3) Where n is the turbulent flow constant, which is related to Re and is calculated according to the simulation results using the following formula: (4) Where, The actual average wind speed in the tunnel, l is the characteristic value of the tunnel, l=7m , in this patent, the diameter of the circular tunnel is selected as 2R, is the kinematic viscosity coefficient, =0.000015kg / m·s; Since the wind speed at the center of the actual tunnel is difficult to measure, the average wind speed at the measuring point is used. Calculate the Reynolds number Re, that is, in the above calculation formula of the Reynolds number Re, = , we can get the Reynolds numbers Re of 7 different working conditions: 2.33*10 5 ;4.67*10 5 ;7.00*10 5 ;9.33*10 5;1.17*10 6 ;1.40*10 6 ;1.63*10 6 .

[0025] ANSYS software was used to simulate the velocity field in the circular tunnel at different Re values, and the turbulent flow constant n was fitted according to Equation (3). A set of data on Re and the corresponding turbulent flow constant n was obtained, as shown in Table 1 below. Table 1

[0026] Fitting the data yields the following relationship: (5) Where n is the turbulent flow constant, Re is the Reynolds number, and the fitting curve is shown in Figure 2 .

[0027] Based on the wind speed U0 at the center of the circular tunnel section, the flow rate of the circular tunnel section is calculated Q ; (6) Substituting formula (3) into formula (6), we can get: (7) By integrating formula (7), we can get the flow rate of circular tunnel section: Q : (8) Set n, L, R, Substituting into formula (8), we can get the tunnel air volume value calculated by measuring a single point under 7 working conditions, and compare it with the actual tunnel air volume value. The comparison line chart is as follows Figure 3 The specific data comparison is shown in Table 2 below.

[0028] Table 2

[0029] Comparing the calculated values of the tunnel air volume single-point test with the actual air volume values in the above table, it can be seen that the air volume measured by the simple circular tunnel air volume measurement method of the present invention is in good agreement with the actual value, with the maximum error being only 8.2%, which is fully capable of meeting the needs of engineering measurement.

[0030] Example 2: According to the above technical solution, the diameter of the circular tunnel in this example is 7m, the length of the tunnel is 1000m, the center of the tunnel is the origin of the coordinate system O, and the section 200m away from the entrance is selected for measurement. The ambient temperature in the tunnel is 20℃, and the kinematic viscosity coefficient is Its structural diagram is as follows. Figure 1To verify the feasibility of the method, the average wind speed in the tunnel Under the working condition of 2.5m / s, different measuring points are selected for single-point measurement, and the tunnel air volume is calculated and compared with the actual air volume.

[0031] To determine the air volume of a circular tunnel, the specific process is as follows: Step 1: Select any suitable location in the tunnel to place the wind speed probe and arrange measuring points 1, 2, 3, 4 and 5. The positions of the five measuring points are as follows: Figure 4 As shown in ; Using a handheld laser rangefinder, first test the vertical distance h1 from different measuring points to the top surface of the tunnel, the vertical distance h2 from the measuring point to the bottom surface of the tunnel, the distance s1 from the measuring point to the right wall of the tunnel, and the horizontal distance s2 from the measuring point to the left wall of the tunnel. See Table 3 below for details.

[0032] Table 3

[0033] Step 2: Establish a coordinate system with the center of the circular tunnel cross section as the coordinate origin O. The radius of the circular tunnel is R = 3.5 m, which is the same as step 2 in Example 1. Calculate the distance L from the measuring point to the circular tunnel wall along the diameter direction (ensuring L ≤ R): (1) Calculation shows that the distance between measuring point 1 and the circular tunnel wall is L1 = 1.167m; the distance between measuring point 2 and the circular tunnel wall is L2 = 2.333m; the distance between measuring point 3 and the circular tunnel wall is L3 = 2.625m; the distance between measuring point 4 and the circular tunnel wall is L4 = 1.750m; and the distance between measuring point 5 and the circular tunnel wall is L5 = 0.874m.

[0034] Step 3: Because the airflow in the tunnel is affected by turbulent pulsation, the wind speed value measured by the wind speed measuring instrument fluctuates. Therefore, the statistical averaging method is used to average the speed measurement values at intervals of 5 seconds within 1 minute to obtain the average wind speed value at the selected measuring point. : (2) The average wind speed at the five selected measuring points under each condition was obtained by measuring seven different tunnel ventilation conditions. They are: 2.43m / s; 2.60m / s; 2.56m / s; 2.53m / s; 2.39m / s respectively.

[0035] Step 4: The air flow is generally turbulent. The wind speed at the center of the tunnel is calculated based on the turbulent wind speed distribution law in the circular tunnel section. : (3) Where n is the turbulent flow constant, which is related to the Reynolds number Re and is calculated according to the simulation results using the following formula: (4) Where, The actual average wind speed in the tunnel, l is the characteristic value of the tunnel, l=7m , in this patent, the diameter of the circular tunnel is selected as 2R, is the kinematic viscosity coefficient, =0.000015kg / m·s; Since the wind speed at the center of the actual tunnel is difficult to measure, the average wind speed at the measuring point is used. Calculate the Reynolds number Re. In the above calculation formula for the Reynolds number Re, = ,Right now .

[0036] ANSYS software was used to simulate the velocity field in the circular tunnel at different Re, and the turbulent flow constant n was fitted according to formula (3). A set of data on the Reynolds number Re and its corresponding turbulent flow constant n was obtained, as shown in Table 4. Table 4

[0037] Fitting the data of Reynolds number Re and turbulent flow constant n in the above table yields the following relationship: (5) Based on the wind speed U0 at the center of the circular tunnel section, the flow rate of the circular tunnel section is calculated Q : (6) Substituting formula (3) into formula (6), we can get: (7) By integrating formula (7), we can get the flow rate of circular tunnel section: Q : (8) Set n, L, R, Substitute into formula (8) to get the tunnel air volume value calculated by measuring a single point, and compare it with the actual tunnel air volume value. The comparison line chart is as follows Figure 5 The specific data comparison is shown in Table 5 below.

[0038] Table 5

[0039] From the comparison results of the calculated values of the tunnel air volume at different single measuring points in the above table and the actual air volume values, it can be seen that the air volume measured by the simple circular tunnel air volume measurement method of the present invention is in good agreement with the actual value, with the maximum error being only 9.4%, which is fully capable of meeting the needs of engineering measurement.

[0040] In addition, it should be understood that although this specification describes the embodiments, not every embodiment contains only one independent technical solution. This description is for clarity only. Those skilled in the art should consider the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art. The above content is only for the purpose of illustrating the technical concept of the present invention and cannot be used to limit the scope of protection of the present invention. Any changes made based on the technical solution in accordance with the technical concept proposed by the present invention fall within the scope of protection of the claims of the present invention.

Claims

1. A method for measuring air volume for dynamic environmental monitoring of an underground circular tunnel, characterized in that: The determination method is: Step 1: Measure the vertical distance h1 between the test point and the top surface of the tunnel, the vertical distance h2 between the test point and the bottom surface of the tunnel, the horizontal distance s1 between the test point and the right wall of the tunnel, and the horizontal distance s2 between the test point and the left wall of the tunnel; Step 2: Establish a coordinate system with the center of the circular tunnel cross section as the origin, measure the radius R of the circular tunnel cross section, and calculate the distance L from the origin to the tunnel wall along the diameter direction of the cross section based on the radius of the circular tunnel cross section, the vertical distance h1 from the test point to the top surface of the tunnel, the vertical distance h2 from the test point to the bottom surface of the tunnel, the horizontal distance s1 from the test point to the right wall of the tunnel, and the horizontal distance s2 from the test point to the left wall. Step 3: Average the wind speeds measured at intervals within a period of time to obtain the average wind speed at the measuring point in the tunnel. ; Step 4: Based on the average wind speed , the distance L from the origin to the tunnel wall along the cross-section diameter direction and the radius R of the circular tunnel cross-section to calculate the average wind speed at the tunnel center point ; Step 5: Based on the average wind speed at the center of the tunnel The flow rate Q of the circular tunnel section is calculated based on the radius R of the circular tunnel cross section.

2. The method for measuring air volume for dynamic environmental monitoring of an underground circular tunnel according to claim 1, characterized in that: The calculation method of the distance L between the origin and the tunnel wall along the diameter direction of the cross section in step 2 is: ,in .

3. The method for measuring air volume for dynamic environmental monitoring of an underground circular tunnel according to claim 1, characterized in that: The average wind speed measured at the measuring point in the tunnel in step 3 The calculation method is: .

4. The method for measuring air volume for dynamic environmental monitoring of an underground circular tunnel according to claim 3, characterized in that: The statistical averaging method is used to average the speed measurement values at intervals of 3 seconds within 1 minute to obtain the average wind speed value at the selected measuring point. .

5. The method for measuring air volume for dynamic environmental monitoring of an underground circular tunnel according to claim 4, characterized in that: The average wind speed at the center of the tunnel The calculation method is: .

6. The method for measuring air volume for dynamic environmental monitoring of an underground circular tunnel according to claim 5, characterized in that: In step 4, the calculation method of the circular tunnel cross-section flow rate Q is: ,in, is the average wind speed at the center of the tunnel; n is the turbulent flow constant, and r is the kinematic viscosity coefficient.

7. The method for measuring air volume for dynamic environmental monitoring of an underground circular tunnel according to claim 6, characterized in that: The turbulent flow constant n is the velocity field in the circular tunnel when ANSYS software is used to simulate different Reynolds numbers Re, and the average wind speed at the center of the tunnel is used to calculate the turbulent flow constant n. The turbulent flow constant n is fitted by the calculation formula.

8. The method for measuring air volume for dynamic environmental monitoring of an underground circular tunnel according to claim 7, characterized in that: The ANSYS software simulates a set of Reynolds numbers Re, which is the average wind speed at the center of the tunnel. The calculation formula relatively fits the data of the turbulent flow constant n corresponding to the simulated Reynolds number Re. The relationship between the turbulent flow constant n and the Reynolds number Re is: ,in and are the first parameter to be fitted and the second parameter to be fitted.

9. The method for measuring air volume for dynamic environmental monitoring of an underground circular tunnel according to claim 8, characterized in that: The ANSYS software simulates a set of Reynolds numbers Re, which are calculated as follows: ,in, is the actual average wind speed in the tunnel, is the set value; is the characteristic length of the tunnel; is the kinematic viscosity coefficient.

10. The method for measuring air volume for dynamic environmental monitoring of an underground circular tunnel according to claim 9, characterized in that: Since the wind speed at the center of the actual tunnel is difficult to measure, the average wind speed at the measuring point is used. Calculate the Reynolds number Re, that is, in the above calculation formula of the Reynolds number Re, = , the distance between the measuring point and the tunnel wall should be greater than or equal to 0.2m.

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