Underground engineering fire source three-dimensional positioning method and system based on optical fiber sensing

Abstract

The invention discloses an underground engineering fire source three-dimensional positioning method and system based on optical fiber sensing, and relates to the technical field of underground engineering fire source positioning. The method comprises the following steps: arranging at least four optical fiber temperature sensors at different positions on an underground space boundary in a non-coplanar manner and acquiring coordinate positions of the optical fiber temperature sensors; the sensor continuously collects temperature data at different moments; constructing a target function based on a fire source temperature conduction error according to the fire source temperature field distribution function and the coordinate position of the optical fiber temperature sensor; and substituting the acquired temperature data into the target function, solving the target function by using a gradient descent method, and obtaining an optimal solution as the center position of the fire source. According to the fire source positioning method, the medium thermal diffusivity does not need to be obtained, the fire source in the underground engineering can be quickly and accurately positioned and the alarm is provided through the optical fiber temperature sensor network, automatic and high-precision positioning can be realized, and the safety management level of the underground engineering is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of underground engineering fire source location, and particularly to a three-dimensional location method and system for underground engineering fire sources based on optical fiber sensing. Background Technique

[0002] Underground engineering refers to civil engineering constructed deep below the ground for the development and utilization of underground space resources. It includes various types of projects and structures, such as underground shopping malls, underground pedestrian passages, civil air defense projects, tunnels, mine roadways, etc. With the increasing utilization of underground space resources by humans, the frequency of disasters in underground engineering also shows an upward trend. Among them, fire is an important factor causing casualties and economic losses. In the emergency response to underground engineering fires, quickly and accurately identifying the three-dimensional position of the fire source is crucial for controlling the fire and reducing losses. Surface buildings can use technologies such as camera monitoring and thermocouple sensing monitoring to observe the fire situation from all directions; however, due to the low visibility in underground spaces, the fire source monitoring and location methods of surface buildings are difficult to apply to the monitoring environment of underground spaces. Therefore, it is necessary to select a suitable fire source monitoring and location method.

[0003] Currently, there are still certain limitations in the speed and accuracy of existing technologies for underground engineering fire source location. For example, infrared thermal imaging technology can only detect surface temperature, cannot penetrate smoke, has low resolution, and poor location accuracy; thermocouple technology has complex wiring, is susceptible to electromagnetic interference, and the metal wires are easily damaged at high temperatures, making it impossible to effectively locate the fire source for a long time; traditional optical fiber sensing mostly uses single-point temperature measurement, making it difficult to accurately achieve three-dimensional spatial location of the fire source. Therefore, there is an urgent need for a new three-dimensional location method for underground engineering fire sources to improve the accuracy and efficiency of fire source location. Summary of the Invention

[0004] Aiming at the deficiencies of the above technologies, the purpose of the present invention is to provide a three-dimensional location method and system for underground engineering fire sources based on optical fiber sensing, so as to quickly and accurately locate the fire source in underground engineering and provide real-time alarms. This system has the advantages of not relying on the thermal diffusivity of the medium, anti-electromagnetic interference, easy installation, remote measurement, and the ability to achieve long-distance and large-range temperature monitoring.

[0005] To achieve the above purpose, the technical solutions adopted by the present invention are as follows:

[0006] In the first aspect, the present invention provides a three-dimensional location method for underground engineering fire sources based on optical fiber sensing, including the following steps:

[0007] Taking the underground space as the target area, at least 4 optical fiber temperature sensors are arranged non-coplanarly at different positions on the boundary of the target area, and their coordinate positions are obtained;

[0008] The optical fiber temperature sensors continuously collect temperature data at different times;

[0009] Construct an objective function based on the fire source temperature conduction error according to the fire source temperature field distribution function and the coordinate positions of the optical fiber temperature sensors;

[0010] Substitute the collected temperature data into the objective function, and use the gradient descent method to solve the objective function to obtain the optimal solution as the fire source center position.

[0011] It should be noted that the conduction medium between the optical fiber temperature sensor and the fire source is uniform; the detection distance of the optical fiber temperature sensor is greater than or equal to the maximum distance between any two points within the target area.

[0012] It should be noted that the input optical signal of the optical fiber temperature sensor is pulsed laser, with a wavelength of 1530nm - 1560nm, a pulse width of 5ns - 20ns, and a frequency of 500Hz - 2kHz.

[0013] It should be noted that the number of the optical fiber temperature sensors is preferably 4 - 6.

[0014] It should be noted that the fire source temperature field distribution function is as shown in Equation (3.1):

[0015] (3.1)

[0016] (3.2)

[0017] In the formula: is the fire source temperature field distribution function, representing the temperature of any point at a certain moment t in a certain fire source temperature field and at a distance of from the fire source center; is the distance from a certain point in the fire source temperature field space to the fire source center , that is, the fire source temperature conduction distance; is the heat release rate of the fire source; is the thermal diffusivity; is the time.

[0018] It should be noted that the objective function is obtained according to Equation (3.3):

[0019] (3.3)

[0020] In the formula: is the sum of squares function of the fire source temperature conduction error, that is, the objective function; is the fire source temperature conduction error function; i is 1, 2,..., 3× , N is the number of optical fiber temperature sensors, represents the combination number;

[0021] Among them, obtained according to formulas (3.4) and (3.5):

[0022] (3.4)

[0023] (3.5)

[0024] In the formulas: and and and are respectively the distances between the mth, nth, pth, and qth fiber optic temperature sensors and the center of the fire source, that is, the fire source temperature conduction distances; and and and are respectively the temperature monitoring values of the mth, nth, pth, and qth fiber optic temperature sensors at the

[0025] It should be noted that the process of solving the objective function using the gradient descent method is as shown in formulas (4.1) and (4.2):

[0026] (4.1)

[0027] (4.2)

[0028] In the formulas: is the learning rate, that is, the calculation step size; is the coordinate of the fire source center at the kth iterative calculation; k = 0, 1, 2,...., the initial fire source center coordinate when k = 0 is set artificially; and and are respectively with respect to partial derivatives.

[0029] It should be noted that when solving the objective function, the calculation stops when the value of the objective function is less than or equal to the preset convergence threshold; or, the calculation stops when the maximum number of iterations is reached; then the optimal solution is output.

[0030] In the second aspect, the present invention provides a three-dimensional positioning system for underground engineering fire sources based on fiber optic sensing, including:

[0031] A light source unit for generating an optical signal and transmitting it to the fiber optic temperature sensor;

[0032] A fiber optic temperature sensor for sensing temperature changes in the underground space and generating a scattered optical signal;

[0033] A signal detection unit, configured to receive the scattered light signal transmitted by the fiber optic temperature sensor and convert it into an electrical signal;

[0034] A data processing unit, configured to process the electrical signal to obtain the position of the fire source center;

[0035] An alarm display unit, configured to issue an audible and visual alarm signal and display the position of the fire source center.

[0036] It should be noted that the light source unit uses a pulsed laser, the signal detection unit uses a high-speed photodetector, and at least 4 fiber optic temperature sensors are arranged non-coplanarly.

[0037] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention forms a three-dimensional temperature monitoring network in the underground space through at least 4 fiber optic temperature sensors arranged non-coplanarly. Each sensor independently collects the temperature data at its location, and combines the fire source temperature field distribution function to construct a three-dimensional positioning equation, breaking through the spatial dimension limitation of traditional single-point temperature measurement;

[0038] (2) The present invention constructs an error function sum of squares objective function and uses the gradient descent method to iteratively optimize the fire source coordinates to achieve automatic and high-precision positioning;

[0039] (3) The present invention uses fiber optic temperature sensors. Based on the Raman scattering effect, the optical signal is transmitted in the insulating quartz fiber, which is completely resistant to electromagnetic interference and high temperature (it can work in an environment of 200 °C for a long time), solving the reliability problem of traditional sensors in the underground complex environment;

[0040] (4) Traditional heat conduction positioning requires the known thermal diffusivity of the medium. The present invention directly eliminates the influence of thermal diffusivity and time through the temperature logarithmic difference ratio operation, and only depends on the sensor coordinates and the relative change of temperature, simplifying the calculation process and improving the environmental adaptability. Description of the Drawings

[0041] Figure 1 is a schematic diagram of the composition of a three-dimensional fire source positioning system for underground engineering based on fiber optic sensing;

[0042] Figure 2 is a schematic diagram of three-dimensional fire source positioning using fiber optic sensors; wherein, , , , respectively represent the monitored temperatures of fiber optic temperature sensors a, b, c, and d;

[0043] Figure 3 is a flowchart of a three-dimensional fire source positioning method for underground engineering based on fiber optic sensing. Detailed Embodiments

[0044] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0045] Embodiment 1;

[0046] Please refer to Figures 1-3 , this embodiment provides a three-dimensional positioning method for underground engineering fire sources based on fiber optic sensing, including the following steps:

[0047] 1) Taking the underground space where the fire source needs to be located as the target area, at least 4 fiber optic temperature sensors are arranged non-coplanarly at different positions on the boundary of the target area, and their coordinate positions are obtained;

[0048] The conduction medium between the fiber optic temperature sensor and the fire source is uniform. The medium inside the underground space is usually air, and there may be some building components that hinder the conduction of the fire source temperature in the air. Therefore, the fiber optic temperature sensor is preferably installed at a position with the largest visible area, so that the conduction medium between the fiber optic temperature sensor and the fire source is as uniform as possible, making the temperature monitoring data more accurate and reducing the positioning error. The detection distance of the fiber optic temperature sensor is greater than or equal to the maximum distance between any two points in the target area. The input optical signal of the fiber optic temperature sensor is pulsed laser, with a wavelength of 1530nm - 1560nm, a pulse width of 5ns - 20ns, and a frequency of 500Hz - 2kHz. In this embodiment, pulsed laser with a wavelength of 1550nm, a pulse width of 10ns, and a frequency of 1kHz is used. The number of fiber optic temperature sensors is preferably 4 - 6, and 4 fiber optic temperature sensors are used in this embodiment.

[0049] The underground space refers to relatively spacious and open spaces such as underground shopping malls, underground pedestrian passages, civil air defense projects, tunnels, mine roadways, subway stations, etc. There are few or no obstacles inside the underground space, and the sensor can directly obtain the temperature data at any position in the space. If a large underground space is divided into multiple small spaces by walls, obstacles such as walls will affect the conduction of temperature in the air, thereby reducing the monitoring accuracy and positioning accuracy. Therefore, the target area where the fiber optic temperature sensor is arranged refers to the small space; the boundary of the underground space refers to the side walls, roof, floor and other structures of the underground space, and in some cases refers to columns or other structures.

[0050] 2) The fiber optic temperature sensor continuously collects temperature data at different times;

[0051] The temperature measurement principle of the fiber optic temperature sensor is:

[0052] In a distributed temperature sensing system, when a short laser pulse is launched into an optical fiber, two Raman scattered light components are generated: Stokes (S) Raman scattered light and anti-Stokes (AS) Raman scattered light. Among them, the intensity of the anti-Stokes Raman scattered light depends on the local optical fiber temperature and is thus regarded as the signal light, while the Stokes Raman scattered light serves as the reference light. The intensity ratio of temperature can be expressed by the following formula (2.1):

[0053] (2.1)

[0054] wherein: is the intensity of the anti-Stokes Raman scattered light; is the intensity of the Stokes Raman scattered light; is the optical constant of the anti-Stokes light; is the optical constant of the Stokes light; is the frequency of the anti-Stokes light; the frequency of the anti-Stokes light; is the Planck constant; is the frequency shift difference ; is the Boltzmann constant; is the attenuation coefficient of the anti-Stokes Raman scattered light; is the attenuation coefficient of the Stokes Raman scattered light; is the optical fiber length.

[0055] To calculate the absolute temperature, with the reference optical fiber coil maintained at a known temperature the sensor measures the temperature which can be obtained by formula (2.2):

[0056] (2.2)

[0057] wherein: is the known temperature; is a certain monitored temperature; is the signal intensity ratio at the known temperature; is the signal intensity ratio at a certain monitored temperature.

[0058] 3) According to the fire source temperature field distribution function and the coordinate position of the optical fiber temperature sensor, construct an objective function based on the fire source temperature conduction distance;

[0059] As Figure 2 shown, a three-dimensional coordinate system is established with a certain point (usually a corner point of the underground space) in the underground space as the origin , taking four fiber optic temperature sensors as an example, four non-coplanar temperature sensors a, b, c, and d are arranged on the boundary within the underground space, and their coordinates are , , , , assuming the coordinates of the fire source o are .

[0060] Assuming that in an ideal state, a fire source is generated at a certain position point within the underground space, and the fire source generates instantaneous heat, then at a certain moment t, for any point within the space, the temperature can be expressed by the following formula (3.1):

[0061] (3.1)

[0062] (3.2)

[0063] In the formula: is the temperature field distribution function of the fire source, indicating the temperature of any point at a certain moment t within a certain fire source temperature field and at a distance from the fire source center; is the distance from a certain point within the fire source temperature field to the fire source center, that is, the fire source temperature conduction distance; is the heat release rate of the fire source; is the thermal diffusivity; is the time.

[0064] In an ideal state, the temperature logarithms at the fiber optic temperature sensors , , , satisfy the formulas (3.3) to (3.6):

[0065] (3.3)

[0066] (3.4)

[0067] (3.5)

[0068] (3.6)

[0069] In the formula: , , , are the distances from the sensors , , , to the fire source center o;

[0070] Taking the difference of the logarithms of the temperatures at sensors a and b gives Equation (3.7), and taking the difference of the logarithms of the temperatures at sensors c and d also gives Equation (3.8):

[0071] (3.7)

[0072] (3.8)

[0073] Define a constant W to describe the ratio of the differences of the logarithms of any two temperatures. Dividing the two equations gives Equation (3.9):

[0074] (3.9)

[0075] Where: is the ratio of the difference of the logarithms of the temperatures at sensors a and b to the difference of the logarithms of the temperatures at sensors c and d;

[0076] Referring to the process of Equations (3.7) to (3.9), different combinations of sensors are made, and similarly, Equations (3.10) and (3.11) can be obtained:

[0077] (3.10)

[0078] (3.11)

[0079] Where: is the ratio of the difference of the logarithms of the temperatures at sensors a and c to the difference of the logarithms of the temperatures at sensors b and d; is the ratio of the difference of the logarithms of the temperatures at sensors a and d to the difference of the logarithms of the temperatures at sensors b and c;

[0080] In the ideal state, in Equations (3.9) to (3.11), the equations on the left and right sides of the constant W both hold. However, in the actual situation, the presence of building structures or components in the underground space and the exchange with the outside air will cause the non-uniformity of the temperature conduction medium (air). The equation on the left side of the constant W will not hold, while the equation on the right side of the constant W always holds because it is only related to the temperature conduction distance. Taking as an example, when the actual value is obtained according to the temperature monitoring data, .

[0081] Based on this, construct three temperature conduction error functions as shown in Equations (3.12) to (3.14):

[0082] (3.12)

[0083] (3.13)

[0084] (3.14)

[0085] According to the above three error functions, the total error square sum function is defined as the objective function Formula (3.15):

[0086] (3.15)

[0087] It should be noted that the objective function By the error function get, The constant in The temperature monitoring data of the optical fiber temperature sensor is obtained in the objective function is known, so the objective function Actually, it is the temperature conduction distance The specific location of the fiber optic temperature sensor can be determined, so the objective function The center of the fire function.

[0088] It should be noted that, in this embodiment, step 3) may be performed first to establish the objective function, and then step 2) may be performed to obtain the temperature monitoring data.

[0089] 4) Substitute the collected temperature data into the objective function and use the gradient descent method to solve the objective function to obtain the optimal solution as the center position of the fire source;

[0090] Gradient descent method to solve the objective function The process is as follows:

[0091] For the objective function The coordinate components in Find the partial derivative, we have:

[0092] (4.1)

[0093] Among them, each error term 、 、 right The partial derivative of is:

[0094] (4.2)

[0095] Similarly, we can calculate and .

[0096] At the same time, each error term can be calculated and Partial derivative of 、 .

[0097] Substitute the temperature data at a certain time t into the objective function to determine the constant W, and substitute the specific coordinate position of the optical fiber sensor at the same time. After obtaining the exact objective function, initialize the fire source coordinates. , start calculation and set learning rate and convergence threshold , perform iterative updates:

[0098] (4.3)

[0099] Where: is the learning rate, i.e. the calculation step size; is the coordinate of the center of the fire source during the k-th iteration calculation, k=0, 1, 2, ...; 、 、 The objective functions are about The partial derivative of .

[0100] Initial fire source coordinates It is usually set manually, for example, it can be the coordinates of any optical fiber temperature sensor, or the coordinates of the middle point of four optical fiber temperature sensors.

[0101] when ( The calculation is stopped when the preset convergence threshold is reached or the maximum number of iterations is reached (set manually according to actual conditions). The fire source coordinates are obtained by minimizing the objective function E:

[0102] (4.4)

[0103] The gradient descent method updates the coordinates iteratively and eventually converges to the optimal solution. .

[0104] Implementation method 2:

[0105] See Figures 1-3 This embodiment provides a three-dimensional positioning system for underground engineering fire sources based on optical fiber sensing, including:

[0106] A light source unit, used for generating an optical signal and transmitting it to the optical fiber temperature sensor;

[0107] Fiber optic temperature sensor, used to sense temperature changes in underground spaces and generate scattered light signals;

[0108] A signal detection unit, used for receiving the scattered light signal transmitted by the optical fiber temperature sensor and converting it into an electrical signal;

[0109] A data processing unit for processing electrical signals to obtain the position of the fire source center;

[0110] An alarm display unit for emitting an audible and visual alarm signal and displaying the position of the fire source center.

[0111] Specifically, the light source unit is used to generate optical signals. A pulsed laser with a wavelength of 1550 nm is adopted, the pulse width is 10 ns, and the repetition frequency is 1 kHz. The transmission optical fiber connects the light source unit and the fiber optic temperature sensor, and transmits the optical signals generated by the light source unit to the fiber optic temperature sensor in the underground space. The transmission optical fiber adopts single-mode quartz optical fiber with a length of 500 m. The fiber optic temperature sensors are laid in the underground space non-coplanarly, and at least 4 are set, which are used to sense temperature changes and generate corresponding scattered signals. The signal detection unit adopts a high-speed photodetector (bandwidth 1 GHz), connects to the fiber optic temperature sensor through the transmission optical fiber, receives the scattered signals of the sensor, converts the Raman scattered optical signals into electrical signals, and there is no mutual interference between multiple signals. The data processing unit is configured with an industrial computer, with a dedicated program built-in, and executes the aforementioned three-dimensional positioning method for the fire source in underground engineering based on fiber optic sensing, which is used to calculate the temperature distribution and the fire source coordinates in real time. When the system detects abnormal temperature changes, that is, when the detected temperature of any temperature sensor exceeds the preset threshold (such as 50 °C, which can be adjusted according to the underground engineering environment) or the temperature change rate exceeds the preset value (such as 10 °C / min), the alarm unit triggers an audible and visual alarm to notify relevant personnel to take emergency measures.

[0112] The data processing unit includes steps such as a) reading the sensor coordinates, b) reading the temperature monitoring data, and c) solving the objective function. Among them, b) and c) can be obtained through the aforementioned three-dimensional positioning method for the fire source in underground engineering based on fiber optic sensing. The sensor coordinates in step a) can be obtained according to the calibration coordinate system and the sensor installation position. The core python program of the data processing unit is as follows:

[0113] The above embodiments are only used to illustrate the technical concept and features of the present invention, and their purpose is to enable those who are familiar with this technology to understand the content of the present invention and implement it accordingly. It cannot be used to limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims

1. A three-dimensional positioning method for underground engineering fire sources based on optical fiber sensing, characterized in that: It includes the following steps: Taking the underground space as the target area, at least 4 optical fiber temperature sensors are arranged non-coplanarly at different positions on the boundary of the target area, and their coordinate positions are obtained; The optical fiber temperature sensors continuously collect temperature data at different times; According to the fire source temperature field distribution function and the coordinate positions of the optical fiber temperature sensors, an objective function based on the fire source temperature conduction error is constructed; The collected temperature data is substituted into the objective function, and the gradient descent method is used to solve the objective function, and the optimal solution is obtained as the fire source center position.

2. The three-dimensional positioning method of underground engineering fire sources based on optical fiber sensing according to claim 1, characterized in that: The conduction medium between the optical fiber temperature sensor and the fire source is uniform; the detection distance of the optical fiber temperature sensor is greater than or equal to the maximum distance between any two points in the target area.

3. The three-dimensional fire source location method for underground engineering based on optical fiber sensing according to claim 1, characterized in that: The input optical signal of the optical fiber temperature sensor is pulsed laser, with a wavelength of 1530nm - 1560nm, a pulse width of 5ns - 20ns, and a frequency of 500Hz - 2kHz.

4. The three-dimensional positioning method of the underground engineering fire source based on optical fiber sensing according to claim 1, wherein: The number of the optical fiber temperature sensors is 4 - 6.

5. The three-dimensional fire source positioning method for underground engineering based on optical fiber sensing according to claim 1, characterized in that: The fire source temperature field distribution function is as shown in Equation (3.1): （3.1） （3.2） In the formula: is the distribution function of the fire source temperature field; is a certain point in the space of the fire source temperature field to the center of the fire source distance; is the heat release rate of the fire source; is the thermal diffusivity; is time.

6. The three-dimensional fire source location method for underground engineering based on optical fiber sensing according to claim 1, characterized in that: The objective function is obtained according to Equation (3.3): （3.3） In the formula: is the objective function; is the fire source temperature conduction error function; i is 1, 2,..., 3 × , N is the number of fiber optic temperature sensors, represents the combination number; Among them, Obtained according to formulas (3.4) and (3.5): （3.4） （3.5） In the formula: , , , are the distances from the m-th, n-th, p-th, and q-th fiber optic temperature sensors to the center of the fire source, respectively; , , , are the temperature monitoring values of the m-th, n-th, p-th, and q-th fiber optic temperature sensors at the moment of ; m, n, p, q ∈ (1, N), and m ≠ n ≠ p ≠ q.

7. The three-dimensional positioning method of underground engineering fire sources based on optical fiber sensing according to claim 1, characterized in that: The objective function is solved by the gradient descent method according to Equations (4.1) and (4.2): （4.1） （4.2） Wherein: is the learning rate; is the coordinate of the fire source center during the k-th iterative calculation; , , are respectively the partial derivatives with respect to .

8. The three-dimensional fire source location method for underground engineering based on optical fiber sensing according to claim 1, characterized in that: When solving the objective function, stop the calculation when the value of the objective function is less than or equal to the preset convergence threshold; or, stop the calculation when the maximum number of iterations is reached.

9. A three-dimensional positioning system for underground engineering fire sources based on optical fiber sensing, characterized in that: It includes: A light source unit for generating an optical signal and transmitting it to the optical fiber temperature sensor; An optical fiber temperature sensor for sensing the temperature change in the underground space and generating a scattered optical signal; A signal detection unit for receiving the scattered optical signal transmitted by the optical fiber temperature sensor and converting it into an electrical signal; A data processing unit for processing the electrical signal to obtain the fire source center position; An alarm display unit for emitting an audible and visual alarm signal and displaying the fire source center position.

10. The three-dimensional fire source positioning system for underground engineering based on optical fiber sensing according to claim 9, characterized in that: The light source unit uses a pulsed laser, the signal detection unit uses a high-speed photodetector, and at least 4 optical fiber temperature sensors are arranged non-coplanarly.

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