Simple measuring method for air volume of tunnel with round top and square bottom

Abstract

The invention discloses a simple measuring method for the air volume of a dome square-bottom tunnel, and relates to the technical field of crossing and fusion of tunnel engineering and an environment monitoring technology. The ventilation quantity single-point test method suitable for the dome square bottom tunnel is an important technology. The method focuses on utilizing precise measurement equipment and scientific analysis means to accurately evaluate the performance and efficiency of the ventilation system in the tunnel with the dome and the square bottom. The method comprises the following steps: firstly, selecting a measuring point which is convenient to measure and has a certain distance from the top wall and the side wall in a dome area in the dome square-bottom tunnel, measuring the wind speed at the position, calculating the wind speed at the center of the tunnel according to the wind speed distribution rule in the cross section of the dome square-bottom tunnel by taking the wind speed as a reference, and further calculating the wind volume of the cross section in the dome square-bottom tunnel. By means of the method, the air volume of the dome square-bottom tunnel can be determined only by measuring the air speed of one point position, and therefore the problems that multi-point measurement in the tall and large dome square-bottom tunnel is not easy and time and labor are wasted in measurement are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of cross-integration of tunnel engineering and environmental monitoring technology, and specifically relates to a simple method for measuring air volume in a dome-shaped square-bottom tunnel. Background Art

[0002] The construction of underground spaces for water conservancy, hydropower, transportation, and underground storage often requires the excavation of numerous tunnels. Dome-shaped square-bottom tunnels, as an innovative tunnel design, combine the structural characteristics of a circular top with a square or rectangular bottom, optimizing aerodynamic performance while increasing space utilization and construction convenience. However, this unique design also presents new challenges and requirements for tunnel environmental control air volume measurement.

[0003] The original intention of the dome-shaped square-bottom tunnel design was to reduce wind resistance and improve tunnel ventilation efficiency through the circular top, while utilizing a square or rectangular bottom to optimize spatial layout and facilitate construction and maintenance. This design not only improves the overall performance of the tunnel but also enhances its ability to adapt to complex geological conditions. However, this unique cross-sectional shape makes wind flow measurement particularly complex. Traditional wind flow measurement methods, such as the equal-area annulus method, may not be directly applicable to dome-shaped square-bottom tunnels because their measurement principles and scope of application are not fully compatible with this special cross-sectional shape.

[0004] Air volume measurement plays a crucial role in controlling dust, eliminating hazardous gases, exhausting fire smoke, and regulating thermal and humid environments during tunnel construction and operation. Accurately measuring air volume within a tunnel allows for real-time monitoring of the ventilation system's operational status, promptly identifying and addressing issues such as insufficient or excessive ventilation. This ensures that tunnel air quality meets safety standards and safeguards vehicles and personnel. For dome-shaped, square-bottomed tunnels, accurate air volume measurement is directly linked to ventilation system efficiency and tunnel safety.

[0005] With the rapid development of sensor technology, data processing technology, and computer technology, air flow measurement methods and technologies are constantly being updated and upgraded. The application of high-precision sensors, CFD simulation technology, and the Internet of Things technology has provided more accurate, efficient, and convenient means for air flow measurement. However, the application of these new technologies to air flow measurement in dome-shaped and square-bottomed tunnels still requires further exploration and research to meet the requirements of air flow measurement in this special cross-sectional shape. Summary of the Invention

[0006] The present invention proposes a simple method for measuring the air volume of a dome-shaped square-bottom tunnel to solve the technical problem that traditional air volume measurement methods in the prior art are difficult to adapt to the unique structural characteristics of a dome-shaped square-bottom tunnel with a round top and a square or rectangular bottom.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: A simple method for measuring the air volume in a dome-shaped square-bottom tunnel is as follows: Step 1: Select a measuring point in the tunnel and measure the vertical distance h1 from the test point to the top of the tunnel, the vertical distance h2 from the test point to the bottom 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 of the tunnel; Step 2: Establish a coordinate system with the center of the tunnel cross section as the origin. Measure the width × height of the tunnel square area cross section: 2L × 2W. Measure the distance H between the upper end of the tunnel square area and the highest point of the dome. Measure the central angle of the arc corresponding to the dome area of the tunnel. And the radius R corresponding to the arc, and measure the vertical distance from the measuring point to the nearest wall l ; 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 center of the tunnel ; 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.

[0008] The vertical distance L between the measuring point and the nearest wall in step 2 should meet the following requirements: .

[0009] The average wind speed measured at the measuring point in the tunnel in step 3 The calculation method is: .

[0010] In step 3, 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. .

[0011] Average wind speed at the center of the tunnel The calculation method is: , where d is the characteristic length of the tunnel; n is the tunnel air turbulence flow constant.

[0012] The calculation method of the characteristic length d of the tunnel is: .

[0013] The turbulent flow constant n is a set of Reynolds numbers Re simulated by ANSYS software, 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.

[0014] 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.

[0015] 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.

[0016] In step 4, the calculation method of the circular tunnel cross-section flow rate Q is: .

[0017] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a simple method for measuring the air volume in a dome-shaped square-bottom tunnel, which provides a specific method for calculating the cross-sectional flow rate of a circular tunnel. By establishing coordinates, a measuring point that is convenient for measurement and is a certain distance away from the top wall and the side wall is selected in the dome area of the dome-shaped square-bottom tunnel. Based on key parameters previously determined, such as the average wind speed at the center point of the tunnel, the cross-sectional flow rate is accurately calculated through mathematical means such as integration, ultimately achieving effective measurement of the air volume in the dome-shaped square-bottom tunnel. The air volume measurement method of the present invention is specifically targeted at the special structural features of the unique circular top and square or rectangular bottom of the dome-shaped square-bottom tunnel, overcoming the problem that traditional air volume measurement methods are difficult to apply, and providing a practical solution for measuring the air volume in tunnels of this type of special structure, so that the air volume measurement is no longer limited by its special cross-sectional shape. The method of the present invention can be used to determine the air volume of the dome-shaped square-bottom tunnel by measuring the wind speed at only one point, thereby solving the problem that it is difficult to measure multiple points in a tall dome-shaped square-bottom tunnel and that the measurement is time-consuming and labor-intensive. By using the air volume measurement method of the present invention, the error between the air volume measured at a single point and the actual air volume is not large, thus effectively reducing the arrangement of measurement points and the workload of testers, and obtaining more accurate air volume measurement values with less investment. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 : Schematic diagram of the cross-sectional dimensions of a dome-top square-bottom tunnel; Figure 2 : Schematic diagram of the dome-shaped square-bottom tunnel structure; Figure 3 : Schematic diagram of the fitting curve of the relationship between the turbulent flow constant n and the Reynolds number Re; Figure 4 : Line chart comparing the calculated air volume with the actual air volume measured at a single point; Figure 5 : Schematic diagram of multiple measuring point selection for a dome-top square-bottom tunnel; Figure 6 : Line chart comparing the calculated air volume at multiple measuring points with the actual air volume in the tunnel. 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 simple method for measuring the air volume in a dome-shaped square-bottom tunnel. Example 1: According to the above technical solution, the width 2L of the cross section of the square area in the dome-shaped square bottom tunnel in this example is 7m, and the height 2W is 5.4m; the height H of the circular area of the dome is 1.6m, and the central angle corresponding to the arc of the dome is The angle of the arc is 83.14°, and the radius R corresponding to the arc is 4.7m. The length of the tunnel is 1000m. The center point of the dome-shaped square bottom tunnel is the origin of the coordinate system O. The section 200m away from the entrance is selected for measurement. The ambient temperature in the tunnel is 20℃. 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] The specific process for determining the air volume of a dome-top square-bottom tunnel is as follows: A wind speed probe is placed at a suitable point 200m from the tunnel entrance. The distance between the measuring point and the tunnel wall should be greater than or equal to 0.2m. A handheld laser rangefinder is used to measure the vertical distance from the measuring point to the upper top surface h1 = 4.664m, the vertical distance from the measuring point to the lower bottom surface h2 = 2.335m, the distance from the measuring point to the right wall S1 = 4.7m, the horizontal distance from the measuring point to the left wall S2 = 2.3m, and the vertical distance from the measuring point to the nearest wall. l ， like Figure 2As shown in , the vertical distance between the measuring point and the nearest wall is the horizontal distance S2 between the measuring point and the left wall, that is, l =S2=2.3m; the distance between the measuring point and the inner wall of the tunnel is the same as Figure 1 As shown in h1, h2, S1 and S2 in .

[0022] Establish a coordinate system in the tunnel, such as Figure 1 As shown in , the center point of the tunnel cross section is used as the coordinate origin O to establish a coordinate system. Measure the width × height of the tunnel square area cross section: 2L × 2W, measure the distance H from the upper end of the tunnel square area to the highest point of the dome; the vertical distance from the measuring point to the nearest wall l conform to: 。

[0023] Because the airflow in the tunnel is affected by turbulent pulsation, the wind speed values measured by the wind speed measuring instrument fluctuate. 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. : (1) The results of the measurement of 7 tunnel ventilation conditions show that the average wind speed at the selected measuring points is They are: 0.571m / s; 1.095m / s; 1.689m / s; 2.205m / s; 2.807m / s; 3.315m / s; 3.883m / s.

[0024] Use ANSYS software to simulate 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.

[0025] Characteristic length of the tunnel , d=6.982m.

[0026] Average wind speed at the center of the tunnel The data of turbulent flow constant n corresponding to the simulated Reynolds number Re is relatively fitted; the air flow in the tunnel is generally turbulent, and the flow velocity distribution can be described by the following formula: the average wind speed at the center of the tunnel is The calculation formula is: (2) According to the average wind speed at the center of the tunnel The relationship between the turbulent flow constant n and the Reynolds number Re obtained after fitting the calculation formula is: （3）， in and are the first parameter to be fitted and the second parameter to be fitted; =0.0169, =0.512; that is The fitting curve of turbulent flow constant n and Reynolds number Re is as follows: Figure 3 shown.

[0027] 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 at the measuring point , that is, in the calculation formula of the Reynolds number Re, = , which is: ; According to the average wind speed measured at the measuring point The 7 different working conditions can correspond to the Reynolds numbers of the measuring points of the 7 different working conditions. They are: 2.84*10 5 ;5.68*10 5 ;8.52*10 5 ;1.14*10 6 ;1.42*10 6 ;1.70*10 6 ;1.99*10 6 The Reynolds number of the measuring point is calculated based on the wind speed at the measuring point. The corresponding turbulent flow constant at the measuring point is .

[0028] Reynolds number at the measuring point under 7 different working conditions The corresponding turbulent flow constant n1 and the turbulent flow constant n fitted according to the Reynolds number Re measured according to the average wind speed in the tunnel are shown in Table 1 below; Table 1

[0029] The calculation formula for the flow rate Q of the dome-top square-bottom tunnel section is: Since the wind speed at the center of the actual tunnel is not easy to measure, n=n1 in the formula, and based on the wind speed U0 at the center of the circular tunnel section, the flow rate of the dome-top square-bottom tunnel section is calculated. Q ; (4) Where x is the X-axis coordinate of the measuring point in the coordinate axis. Substituting the above formula (2) into formula (4), we can get: (5) By integrating formula (5), we can get the cross-sectional flow rate of the dome-top square-bottom tunnel: Q : (6) The turbulent flow constant n1 of the measuring point in the tunnel, the vertical distance from the measuring point to the nearest wall l , the characteristic length d of the tunnel, the width × height of the cross-section of the square area of the tunnel: 2L × 2W, the distance H from the upper end of the square area of the tunnel to the highest point of the dome, the central angle θ and radius R of the arc corresponding to the dome area of the tunnel, and the average wind speed at the measuring points in the tunnel Substituting into formula (6), 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 4 The specific data comparison is shown in Table 2 below.

[0030] Table 2

[0031] Comparison of the calculated values of the tunnel air volume single-point test in the above table with the actual air volume values shows that the air volume measured by the simple air volume measurement method for dome-shaped square-bottom tunnels of the present invention is in good agreement with the actual value, with the maximum error being only 9.57%, which is fully capable of meeting the needs of engineering measurement.

[0032] Example 2: The structural dimensions of the dome-shaped square-bottom tunnel in this example are the same as those in Example 1. The cross section 200 m from the entrance was selected for measurement. The ambient temperature in the tunnel was 20°C, and the kinematic viscosity coefficient was Its structural diagram is as follows. Figure 1 To 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.

[0033] Establish a coordinate system in a tunnel with a dome and square bottom, such as Figure 5 As shown in , the center point of the tunnel cross section is taken as the coordinate origin O to establish a coordinate system. 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 different measuring points are as follows: Figure 5 As shown in the figure, using a handheld laser rangefinder, first test the vertical distance h1 from different measuring points to the top of the tunnel, the vertical distance h2 from the measuring point to the bottom 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. Then measure the vertical distances of the five measuring points to the nearest wall. l , the vertical distance from the measuring point to the nearest walll Same as in Example 1, both need to meet the following requirements: The measurement results are shown in Table 3 below.

[0034] Table 3

[0035] 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.

[0036] Because the airflow in the tunnel is affected by turbulent pulsation, the wind speed values measured by the wind speed measuring instrument fluctuate. 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. : (1) The average wind speed at the five selected measuring points under each condition was obtained by measuring seven different tunnel ventilation conditions. They are: 2.513m / s; 2.671m / s; 2.914m / s; 2.871m / s; 2.533m / s respectively.

[0037] Use ANSYS software to simulate 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, and its specific value is the same as that in Example 1, d=6.982m; is the kinematic viscosity coefficient.

[0038] Average wind speed at the center of the tunnel The data of turbulent flow constant n corresponding to the simulated Reynolds number Re is relatively fitted; the air flow in the tunnel is generally turbulent, and the flow velocity distribution can be described by the following formula: the average wind speed at the center of the tunnel is The calculation formula is: (2) According to the average wind speed at the center of the tunnel The relationship between the turbulent flow constant n and the Reynolds number Re obtained after fitting the calculation formula is: (3) In this embodiment, since the tunnel structure is the same, the fitting of the turbulent flow constant n and the Reynolds number Re is the same. , similarly, the average wind speed at the measuring point is Calculate the Reynolds number at the measuring point The same as in Example 1, that is: ; and the Reynolds number of the measuring point Turbulent flow constant of the measurement point for phase fitting . Reynolds numbers at 5 measuring points The corresponding turbulent flow constant n1 at the measuring point and the turbulent flow constant n fitted according to the Reynolds number Re measured according to the average wind speed in the tunnel are shown in Table 4 below; Table 4

[0039] The calculation formula for the flow rate Q of the dome-top square-bottom tunnel section is the same as that in Example 1. Substituting the formula into the integral yields:

[0040] n1、 l Substitute the data of d, L, W, H, Ux, θ and R into the calculation formula of the cross-section flow rate Q of the dome-top square-bottom tunnel mentioned above to obtain the tunnel air volume values at the five measuring points, and compare them with the actual tunnel air volume values. The comparison line chart is as follows Figure 6 The specific data comparison is shown in Table 5 below.

[0041] Table 5

[0042] From the comparison results of the test calculation values at the five measuring points of the tunnel air volume in the above table with 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 8.06%, which is fully capable of meeting the needs of engineering measurement.

[0043] 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 simple method for measuring the air volume in a dome-shaped square-bottom 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 tunnel cross section as the origin, measure the length × width of the tunnel square area cross section: 2L × 2W, measure the distance H between the upper end of the tunnel square area and the highest point of the dome, and measure the central angle corresponding to the arc of the tunnel dome area And the radius R corresponding to the arc, and measure the vertical distance from the measuring point to the nearest wall l ; 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: According to 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. A simple method for measuring air volume in a dome-shaped square-bottom tunnel according to claim 1, characterized in that: The vertical distance L between the measuring point and the nearest wall in step 2 should meet the following requirements: .

3. The simple method for measuring air volume in a dome-shaped square-bottom tunnel according to claim 1 is characterized in that: The average wind speed measured at the measuring point in the tunnel in step 3 The calculation method is: .

4. A simple method for measuring air volume in a dome-shaped square-bottom tunnel according to claim 3, characterized in that: In step 3, 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. A simple method for measuring air volume in a dome-shaped square-bottom tunnel according to claim 4, characterized in that: The average wind speed at the center of the tunnel The calculation method is: , where d is the characteristic length of the tunnel; n is the tunnel air turbulence flow constant.

6. A simple method for measuring air volume in a dome-shaped square-bottom tunnel according to claim 5, characterized in that: The characteristic length d of the tunnel is calculated as follows: .

7. A simple method for measuring air volume in a dome-shaped square-bottom tunnel according to claim 5, characterized in that: The turbulent flow constant n is a set of Reynolds numbers Re simulated by ANSYS software, 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.

8. A simple method for measuring air volume in a dome-shaped square-bottom tunnel according to claim 7, 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.

9. A simple method for measuring air volume in a dome-shaped square-bottom tunnel according to claim 8, 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.

10. The simple method for measuring air volume in a dome-shaped square-bottom tunnel according to claim 1, characterized in that: In step 4, the calculation method of the circular tunnel cross-section flow rate Q is: 。

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