A tunnel ventilation and smoke extraction system

Abstract

The application relates to the technical field of tunnels and disaster prevention, and discloses a tunnel ventilation and smoke exhaust system which comprises a data acquisition and filtering module, a safety wind speed boundary calculation module, a target wind speed calculation module, a control mode determination module and a closed-loop control execution module; the system collects real-time parameters and performs asymmetric smooth filtering on the heat release rate of a fire source; the flow area is corrected in combination with a vehicle blockage ratio, the lower boundary wind speed under anti-backflow and the upper boundary wind speed for maintaining the thermal stratification of smoke gas are calculated, and a safety smoke exhaust wind speed interval is formed; a steady-state target wind speed is generated by interpolation within the interval according to external atmospheric diffusion conditions; the continuous steady-state smoke exhaust or the alternate smoke exhaust control mode is determined in combination with the smoke gas layer settlement critical time and the mechanical acceleration time constant of the fan; and finally, a variable frequency control instruction is issued to execute closed-loop smoke exhaust. The application considers the internal flow field and the external meteorology, and realizes the multi-objective coordinated control of internal anti-backflow, internal anti-settlement and external pollution prevention of the tunnel.

Description

Technical Field

[0001] This invention relates to the field of tunnel and disaster prevention technology, specifically a tunnel ventilation and smoke extraction system. Background Technology

[0002] With the increasing scale of highway tunnel construction, ventilation and smoke extraction control during tunnel fires plays a crucial role in ensuring the safe evacuation of personnel. During tunnel fire smoke extraction, a reasonable longitudinal smoke extraction velocity needs to simultaneously prevent smoke backflow and maintain thermal stratification of the smoke layer. Existing tunnel ventilation and smoke extraction control methods typically adjust the fan operating frequency based on preset fixed parameters or simple temperature feedback thresholds.

[0003] This conventional control method is ill-suited to the complex dynamic changes in the flow field inside a tunnel during a fire. Because it doesn't adequately consider the actual impact of vehicle congestion on the effective flow cross-sectional area, the smoke exhaust velocity calculated using empirical formulas often deviates from actual requirements. When the velocity setting is too low, backflow of smoke easily occurs; conversely, when the velocity setting is too high, it disrupts the original thermal stratification of smoke, accelerating the unstable settling of harmful smoke towards the bottom, threatening the safety of evacuees. Furthermore, most existing smoke exhaust control systems only focus on the smoke exhaust needs inside the tunnel, lacking consideration for the external meteorological environment. Under unfavorable meteorological conditions where atmospheric diffusion is weak outside the tunnel, maintaining a fixed high velocity to forcibly exhaust large amounts of smoke can easily cause severe pollution accumulation in the area surrounding the tunnel entrance.

[0004] Furthermore, existing control systems rarely incorporate the inherent mechanical acceleration delay of large smoke exhaust fans into their control logic when executing smoke exhaust commands. When the rapid development of the fire source causes the time for smoke to settle to the boundary to be shorter than the mechanical acceleration time of the fan, conventional continuous control commands cannot ensure that the flow field reaches the set wind speed in time, resulting in premature settling of the smoke during the fan's acceleration response. Therefore, existing technologies have a relatively simple control mode when considering both backflow prevention and settlement prevention inside the tunnel and external pollution prevention, and cannot dynamically optimize adjustments based on comprehensive internal and external working conditions and equipment characteristics. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a tunnel ventilation and smoke exhaust system. This system solves the problems of existing tunnel smoke exhaust control methods that do not comprehensively consider internal vehicle congestion, external atmospheric diffusion conditions, and fan mechanical response delays. These problems lead to deviations in smoke exhaust velocity settings, which can easily cause backflow of smoke or damage to thermal stratification. Furthermore, the single control mode can easily cause pollution accumulation outside the tunnel entrance and premature settling of smoke.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a tunnel ventilation and smoke extraction system, comprising: The data acquisition and filtering module collects real-time environmental and flow field state parameters inside and outside the tunnel, as well as operating parameters of the smoke exhaust fan and frequency conversion drive system. Based on the original fire source temperature data, it determines the original fire source heat release rate, performs asymmetric smoothing filtering on the original fire source heat release rate, and outputs the effective heat release rate. The safe wind speed boundary calculation module combines the vehicle blockage ratio to dynamically correct the effective flow cross-sectional area, calculates the lower boundary exhaust wind speed to prevent flue gas backflow based on the effective heat release rate, introduces fluid dynamic boundary conditions to calculate the upper boundary exhaust wind speed to maintain the flue gas thermal stratification state, and combines the lower boundary exhaust wind speed with the upper boundary exhaust wind speed to form a safe exhaust wind speed range. The target wind speed calculation module acquires external meteorological data, obtains atmospheric diffusion correction coefficients based on atmospheric stability levels, and uses the atmospheric diffusion correction coefficients as linear adjustment weights to perform interpolation calculations within the safe smoke exhaust wind speed range to generate steady-state target wind speeds. The control mode determination module calculates the expected flue gas transmission time and the flue gas layer settling boundary time, compares the expected flue gas transmission time and the flue gas layer settling boundary time with the fan mechanical acceleration time constant, establishes the flue gas control mode applicable to the current working condition, and outputs the control mode signal. The closed-loop control execution module receives the control mode signal, issues frequency conversion control commands, and drives the smoke exhaust fan to execute a continuous steady-state smoke exhaust mode or an alternating control mode based on the safe smoke exhaust wind speed range, which determines a low-speed smoke control wind speed and a high-speed forced smoke exhaust wind speed.

[0007] This invention comprehensively considers the internal flow field, blockage conditions, and external meteorological conditions of the tunnel. By establishing a safe smoke exhaust wind speed range and calculating the target wind speed in combination with atmospheric diffusion capacity, and then determining the control mode based on the smoke settling boundary time and the inherent response time of the fan, the smoke exhaust fan is driven to perform continuous or alternating smoke exhaust operations. This solves the conflict between internal backflow prevention and settlement prevention and external pollution prevention in tunnel smoke exhaust.

[0008] Furthermore, the asymmetric smoothing filtering process specifically includes: The data acquisition and filtering module obtains the original heat release rate of the fire source at the current sampling moment and the effective heat release rate of the previous sampling period. When the original heat release rate of the fire source is not less than the effective heat release rate of the previous sampling period, the data acquisition and filtering module outputs the original heat release rate of the fire source as the effective heat release rate of the current period. When the original heat release rate of the fire source is less than the effective heat release rate of the previous sampling period, the data acquisition and filtering module introduces an attenuation smoothing coefficient to perform a weighted summation of the original heat release rate of the fire source and the effective heat release rate of the previous sampling period to obtain the effective heat release rate of the current period.

[0009] Furthermore, the safe wind speed boundary calculation module performs correction of the effective flow cross-sectional area, specifically including: The safe wind speed boundary calculation module obtains the tunnel design net cross-sectional area. The safe wind speed boundary calculation module calculates the result by subtracting the vehicle blockage ratio, and multiplies the tunnel design net cross-sectional area by the result to obtain the effective flow cross-sectional area; When the effective flow cross-sectional area is less than the minimum effective flow cross-sectional area threshold, the safe wind speed boundary calculation module corrects the effective flow cross-sectional area to the minimum effective flow cross-sectional area threshold.

[0010] Furthermore, the safe wind speed boundary calculation module derives the lower boundary smoke exhaust wind speed, specifically including: The safe wind speed boundary calculation module multiplies the tunnel slope correction coefficient, gravitational acceleration, and effective heat release rate to obtain the first product; The safe wind speed boundary calculation module multiplies the initial density of ambient air, the specific heat capacity of air at constant pressure, the effective flow cross-sectional area, and the average absolute temperature of the flue gas layer to obtain a second product. The safe wind speed boundary calculation module performs a division operation using the first product as the dividend and the second product as the divisor, and then performs a cube root operation on the division result to obtain the lower boundary smoke exhaust wind speed.

[0011] Furthermore, the safe wind speed boundary calculation module derives the upper boundary smoke exhaust wind speed, specifically including: The safe wind speed boundary calculation module multiplies the gravitational acceleration, the thickness of the flue gas layer, and the difference between the average absolute temperature of the flue gas layer and the average absolute temperature of the clean air at the bottom layer to obtain a third product. The safe wind speed boundary calculation module uses the third product as the dividend and the average absolute temperature of the flue gas layer as the divisor to perform a division operation, and performs a square root operation on the division result to obtain the square root value. The safe wind speed boundary calculation module multiplies the square root value by the critical Froude number to obtain the upper boundary smoke exhaust wind speed; When the upper boundary smoke exhaust velocity is less than the lower boundary smoke exhaust velocity, the safe wind speed boundary calculation module locks the safe smoke exhaust velocity range to the lower boundary smoke exhaust velocity and uses the lower boundary smoke exhaust velocity as the anti-backflow guarantee wind speed.

[0012] Furthermore, the target wind speed calculation module generates a steady-state target wind speed, specifically including: The target wind speed calculation module maps the instability level to an atmospheric diffusion correction coefficient with a value of one, maps the temperature inversion state to a minimum preset value greater than zero, and obtains the atmospheric diffusion correction coefficient by looking up a table according to the atmospheric stability level. The target wind speed calculation module calculates the wind speed difference between the upper boundary smoke exhaust wind speed and the lower boundary smoke exhaust wind speed; The target wind speed calculation module multiplies the wind speed difference with the atmospheric diffusion correction coefficient, and then adds the lower boundary smoke exhaust wind speed to the product to obtain the steady-state target wind speed. When the safe wind speed boundary calculation module outputs the anti-backflow guarantee wind speed, the target wind speed calculation module outputs the anti-backflow guarantee wind speed as the steady-state target wind speed.

[0013] Furthermore, the control mode determination module calculates the estimated flue gas transport time and the flue gas layer settling boundary time, specifically including: The control mode determination module uses the longitudinal distance from the fire source to the smoke exhaust opening as the dividend and the steady-state target wind speed as the divisor to perform a division operation to obtain the expected smoke transmission time. The control mode determination module calculates the temperature difference between the current average absolute temperature of the flue gas layer and the critical instability and settlement absolute temperature. The control mode determination module uses the temperature difference as the dividend and the temperature attenuation gradient along the path as the divisor to perform the first division operation. Then, it uses the result of the first division operation as the dividend and the steady-state target wind speed as the divisor to perform the second division operation to obtain the settling boundary time of the flue gas layer. When the current average absolute temperature of the flue gas layer is not greater than the critical instability and settling absolute temperature, the control mode determination module sets the settling threshold time of the flue gas layer to zero. When the temperature decay gradient along the path is not greater than the preset minimum decay gradient threshold, and the current average absolute temperature of the flue gas layer is greater than the critical instability and settlement absolute temperature, the control mode determination module assigns the settlement threshold time of the flue gas layer to the preset maximum time threshold.

[0014] Furthermore, the control mode determination module determines and outputs a control mode signal, specifically including: The control mode determination module sets the initial determination threshold to be the flue gas settling boundary time minus the fan mechanical acceleration time constant; When the current smoke exhaust control mode is the continuous steady-state smoke exhaust mode, and the expected smoke transmission time is greater than the sum of the initial judgment threshold and the time hysteresis margin parameter, the control mode judgment module outputs an alternating smoke exhaust judgment signal. When the current smoke exhaust control mode is an alternating control mode of low-speed smoke control and high-speed forced smoke exhaust, and the expected smoke transmission time is not greater than the difference between the initial judgment threshold and the time hysteresis margin parameter, the control mode judgment module outputs a continuous smoke exhaust judgment signal. When the expected flue gas transmission time is greater than the difference but not greater than the sum, the control mode determination module retains the exhaust control mode of the previous control cycle.

[0015] Furthermore, the closed-loop control execution module performs steady-state target frequency smoke extraction, specifically including: When the continuous smoke exhaust judgment signal is received, the closed-loop control execution module multiplies the rated operating frequency of the smoke exhaust fan with the steady-state target wind speed according to the fan similarity law, and then divides the product with the full-load design wind speed to obtain the steady-state target frequency. The closed-loop control execution module generates a frequency conversion control command containing the steady-state target frequency, sends it to the smoke exhaust fan node, obtains the real-time wind speed feedback value from the wind speed sensor inside the tunnel, and performs closed-loop correction using a proportional-integral-derivative algorithm.

[0016] Furthermore, the closed-loop control execution module alternately executes low-speed smoke control commands and high-speed forced smoke exhaust commands, specifically including: When the alternating smoke exhaust judgment signal is received, and the settling time of the flue gas layer is greater than the mechanical acceleration time constant of the fan, the closed-loop control execution module enters the low-speed smoke control stage and generates a low-speed frequency command according to the lower boundary smoke exhaust wind speed. When the alternating smoke exhaust determination signal is received, and the settling time of the flue gas layer is not greater than the mechanical acceleration time constant of the fan, the closed-loop control execution module directly generates a high-speed forced smoke exhaust frequency command. During the execution of the low-speed smoke control phase, the closed-loop control execution module accumulates the running time within the current alternation cycle; When the running time is not less than the initial judgment threshold, the closed-loop control execution module triggers the high wind speed forced smoke exhaust frequency command; When the upper boundary smoke exhaust velocity is not less than the lower boundary smoke exhaust velocity, the closed-loop control execution module generates the high-speed forced smoke exhaust frequency command based on the upper boundary smoke exhaust velocity. When the upper boundary smoke exhaust velocity is less than the lower boundary smoke exhaust velocity, the closed-loop control execution module generates the high-velocity forced smoke exhaust frequency command based on the anti-backflow protection velocity. After maintaining the forced smoke exhaust duration, the exhaust fan slows down again to switch back to the low-speed smoke control phase.

[0017] This invention provides a tunnel ventilation and smoke extraction system. It has the following beneficial effects: 1. This invention performs asymmetric smoothing filtering on the original heat release rate of the fire source, preserving the heat growth trend while filtering out short-term data fluctuations, thus providing stable benchmark data for subsequent calculations. Simultaneously, the system dynamically corrects the effective flow cross-sectional area based on the vehicle blockage ratio, making the calculations of the lower boundary exhaust velocity for backflow prevention and the upper boundary exhaust velocity for maintaining thermal stratification of the smoke more closely match the actual fluid dynamics conditions within the tunnel, reducing the risk of backflow or thermal stratification damage caused by blockage estimation errors.

[0018] 2. This invention introduces an atmospheric diffusion correction coefficient, obtained from external meteorological data, as a weight for interpolation calculation within the safe smoke exhaust velocity range determined by the lower and upper boundary smoke exhaust velocities, to generate a steady-state target wind speed. This design allows the smoke exhaust velocity to be dynamically adjusted based on the diffusion capacity of the outside atmosphere while ensuring the safety of personnel evacuation inside the tunnel, thereby effectively mitigating the pollution accumulation caused by tunnel smoke exhaust on the external environment at the tunnel entrance.

[0019] 3. This invention calculates the estimated smoke transmission time and the smoke layer settling boundary time in real time, compares them with the mechanical acceleration time constant of the fan, and dynamically determines and outputs a control signal for continuous steady-state smoke exhaust or alternating smoke exhaust. This control determination mechanism fully considers the mechanical response delay of the smoke exhaust equipment itself, avoids smoke instability and settling caused by slow fan acceleration, and improves the accuracy and safety of the ventilation and smoke exhaust system under complex fire conditions. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the system architecture of the present invention; Figure 2 This is a schematic diagram of the tunnel ventilation and smoke exhaust control method of the present invention; Figure 3 This is a schematic diagram of the data sensing and filtering process of the present invention; Figure 4 This is a schematic diagram of the security boundary calculation process of the present invention; Figure 5 This is a schematic diagram of the target wind speed determination process of the present invention; Figure 6 This is a schematic diagram of the control mode determination process of the present invention; Figure 7 This is a schematic diagram of the closed-loop collaborative control process of the present invention; Figure 8 This is a comparison diagram of the smoke extraction effect of the control modes of the present invention. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] See attached document Figure 1 The present invention provides a tunnel ventilation and smoke extraction system, comprising: The data acquisition and filtering module acquires real-time environmental and flow field parameters inside and outside the tunnel, as well as operating parameters of the smoke exhaust fan and variable frequency drive system, through a sensor communication link. Based on the original fire source temperature data, the module determines the original fire source heat release rate and performs asymmetric smoothing filtering on the original fire source heat release rate, which exhibits high-frequency fluctuations, outputting the filtered effective heat release rate data.

[0023] The safe wind speed boundary calculation module receives parameter data output from the data acquisition and filtering module. It dynamically adjusts the effective flow cross-sectional area based on the vehicle blockage ratio to derive the lower boundary exhaust wind speed to prevent backflow of smoke. The module also introduces fluid dynamics boundary conditions to derive the upper boundary exhaust wind speed to maintain the thermal stratification of smoke, thus constructing a safe exhaust wind speed range for safe smoke extraction inside the tunnel.

[0024] The target wind speed calculation module acquires external meteorological data of the tunnel, assesses the diffusion capacity of the external atmosphere on smoke, and derives a dimensionless atmospheric diffusion correction coefficient. Using this atmospheric diffusion correction coefficient as an interpolation weight parameter, the module performs interpolation calculations within the safe smoke exhaust wind speed range generated by the safe wind speed boundary calculation module to generate the steady-state target wind speed.

[0025] The control mode determination module acquires the steady-state target wind speed output by the target wind speed calculation module. Based on the thermal buoyancy decay law within the tunnel, the control mode determination module calculates the critical time for flue gas to become unstable and settle. It compares the flue gas settling threshold time, the expected flue gas transmission time, and the fan mechanical acceleration time constant as time parameters, and determines the appropriate smoke exhaust control mode for the current operating conditions based on the comparison results.

[0026] The closed-loop control execution module receives the mode signal output from the control mode determination module, generates frequency converter control commands, and sends them to the exhaust fan group. When the control mode determination module outputs a continuous exhaust judgment, the closed-loop control execution module controls the exhaust fan group to operate continuously at the steady-state target frequency, and performs closed-loop fine-tuning based on real-time wind speed feedback. When the control mode determination module outputs an alternating exhaust judgment, the closed-loop control execution module alternately issues low-speed smoke control commands and high-speed forced smoke exhaust commands with time constant feedforward compensation according to a time sequence, driving the exhaust fan group to perform actions.

[0027] See attached document Figure 2 This invention provides a control method for a tunnel ventilation and smoke extraction system, comprising the following steps: S1. Data Sensing and Filtering. Acquire physical environment parameters inside and outside the tunnel, as well as operating parameters of the smoke exhaust fan and variable frequency drive system. Determine the original heat release rate of the fire source based on the acquired original fire source temperature data, and perform asymmetric smoothing filtering on the original heat release rate to generate effective heat release rate data.

[0028] S2. Safety Boundary Calculation. The effective flow cross-sectional area is corrected based on the vehicle congestion ratio. The lower boundary exhaust velocity to prevent flue gas backflow is derived based on the effective heat release rate. The upper boundary exhaust velocity to maintain flue gas thermal stratification is derived by introducing fluid dynamics boundary conditions. A safe exhaust velocity range is constructed by combining the lower and upper boundary exhaust velocities.

[0029] S3. Target Wind Speed ​​Determination Steps. Acquire external meteorological data for the tunnel to assess atmospheric diffusion capacity. Derive the atmospheric diffusion correction coefficient based on the atmospheric diffusion capacity. Substitute the atmospheric diffusion correction coefficient into the safe smoke exhaust wind speed range for interpolation calculation to generate the steady-state target wind speed.

[0030] S4. Control Mode Determination. Calculate the flue gas settling threshold time based on the temperature decay gradient along the path. Calculate the expected flue gas transport time in conjunction with the steady-state target wind speed. Compare the expected flue gas transport time, the flue gas settling threshold time, and the fan mechanical acceleration time constant to determine the appropriate control mode for the current operating condition.

[0031] S5. Closed-loop coordinated execution. Variable frequency control commands are generated and issued based on the determined control mode. Under continuous smoke exhaust conditions, the smoke exhaust fan is controlled to perform constant frequency smoke exhaust. Under alternating smoke exhaust conditions, the smoke exhaust fan is controlled to alternately perform a low-speed smoke storage step and a forced exhaust step with start-up delay feedforward compensation.

[0032] See attached document Figure 3 In this embodiment, the data acquisition and filtering module is used to perform the data acquisition and filtering processing in step S1. Specifically, it includes the following sub-steps: S11. Obtain physical environment parameters inside and outside the tunnel, and operating parameters of the smoke exhaust fan and variable frequency drive system.

[0033] The data acquisition and filtering module collects real-time status parameters through a sensor network deployed within the tunnel and verifies the validity of the collected parameters. When a parameter in a single sampling period exceeds a preset physical reasonable range, the data acquisition and filtering module replaces it with valid data from the previous sampling period. When anomalies occur in multiple consecutive sampling periods, the data acquisition and filtering module outputs a sensor anomaly signal, causing the subsequent control module to enter a backflow prevention priority control state.

[0034] State parameters include the peak temperature of the original ignition source. Average temperature of flue gas layer Average temperature of clean air at the bottom layer flue gas layer thickness Temperature attenuation gradient along the path and the vehicle congestion ratio downstream of the fire source .

[0035] In some embodiments, vehicle congestion ratio It is a dimensionless parameter, and its value range is: This is used to characterize the proportion of the vehicle's projected area to the effective cross-sectional area of ​​the tunnel.

[0036] Temperature attenuation gradient along the path In the spatial domain, it is represented as ,in The temperature difference between two adjacent temperature measuring nodes. This represents the longitudinal distance between the two temperature measurement nodes. Temperature attenuation gradient along the path. The positive value of the temperature decrease of flue gas along the exhaust direction is used to characterize the magnitude of the temperature decrease of flue gas per unit longitudinal distance.

[0037] For specific implementation methods of acquiring temperature data through a distributed fiber optic temperature measurement system and acquiring vehicle congestion ratio through traffic video radar, those skilled in the art can configure them according to relevant engineering specifications. The underlying sensing hardware principles are well-known technologies in this field and will not be elaborated here.

[0038] The data acquisition and filtering module obtains external environmental meteorological variables through a meteorological station outside the tunnel.

[0039] Meteorological variables include external environmental wind speed Solar radiation illuminance and vertical temperature gradient The obtained meteorological variables are used to characterize the atmospheric pollution diffusion conditions outside the tunnel's smoke exhaust opening.

[0040] The data acquisition and filtering module reads the mechanical acceleration time constant of the exhaust fan group from the operating parameters of the exhaust fans and the variable frequency drive system. .

[0041] Mechanical acceleration time constant The inherent mechanical delay required for the fan rotor to rise from the current operating frequency to the target forced exhaust frequency is characterized by the operating parameters of the exhaust fan and the variable frequency drive system, which can be determined by the fan's nameplate, the inverter's preset frequency rise parameters, and the difference between the current operating frequency and the target forced exhaust frequency.

[0042] When the frequency converter has a built-in frequency ramp rate parameter, the closed-loop control execution module can calculate the mechanical acceleration time constant under the current operating condition based on the frequency ramp rate. .

[0043] S12. Determine the original heat release rate of the fire source based on the original fire source temperature data, and perform asymmetric smoothing filtering on the original heat release rate of the fire source.

[0044] The data acquisition and filtering module utilizes the relationship between fire source temperature and heat release rate to calibrate based on the acquired raw fire source peak temperature. Estimate the heat release rate of the original ignition source .

[0045] In one specific embodiment, the data acquisition and filtering module pre-stores a calibration curve or mapping table between the peak temperature of the fire source and the heat release rate. The calibration curve or mapping table is pre-calibrated based on the tunnel cross-section height, the relative position between the temperature measuring point and the fire source, the type of fire source, and the ventilation reference state.

[0046] The data acquisition and filtering module obtains the original peak temperature of the fire source. Then, based on the current tunnel structure parameters and temperature measurement point layout parameters, the corresponding calibration curve or mapping table is called to determine the original heat release rate of the fire source. .

[0047] The estimation process is based on the empirical relationship between the fire plume temperature and the heat release rate, which is used for back-calculation. However, since the heat release rate at a fire scene fluctuates frequently, directly using the original fire source's heat release rate as the basis for calculation can easily cause frequent abrupt changes in fan control commands.

[0048] The data acquisition and filtering module constructs an asymmetric smoothing filter to process the original heat release rate of the fire source, outputting the effective heat release rate for subsequent control calculations. .

[0049] The calculation equation for asymmetric smoothing filtering at the discrete time step is as follows: ; In the formula, This is a conditional statement indicating that if or when the condition is met, ... At the current sampling time, The system sampling period is For an effective heat release rate, The estimated original heat release rate of the ignition source at the current moment. The effective heat release rate of the previous sampling period. This is the attenuation smoothing coefficient. To avoid an infeasible safe wind speed range during the initial startup phase, the system is set at the initial time... hour, .

[0050] Attenuation smoothing coefficient The range of values ​​is In one specific embodiment of the present invention, the frequency response period of the fan is considered. The possible values ​​are between 0.1 and 0.3.

[0051] The data acquisition and filtering module makes a judgment based on the relationship between the current raw heat release rate of the fire source and the effective heat release rate of the previous cycle. This processing logic follows the basic principles of fire safety control. For operating conditions with increased risk, the system needs to maintain a rapid response with no delay; For operating conditions where the level of danger decreases, the system needs to increase lag to maintain operational stability.

[0052] When the heat release rate of the original fire source shows an upward trend or remains unchanged, the data acquisition and filtering module directly outputs the original data, enabling the smoke exhaust system to quickly respond to the expansion of the fire scale.

[0053] When the original heat release rate of the fire source shows a downward trend, the data acquisition and filtering module introduces an attenuation smoothing coefficient to perform a first-order hysteresis smoothing operation, filtering out transient disturbances of the heat source, thereby reducing ineffective and frequent frequency tuning operations of the ventilation equipment.

[0054] See attached document Figure 4 In this embodiment, the safe wind speed boundary calculation module performs step S2, safe boundary calculation. This specifically includes the following sub-steps: S21. Dynamic correction of effective flow cross-sectional area.

[0055] When a tunnel fire occurs, there are usually stranded vehicles downstream of the fire source due to traffic obstruction.

[0056] The stranded vehicles occupy part of the tunnel's physical space, reducing the cross-sectional area through which the actual airflow passes and increasing local aerodynamic drag.

[0057] In some embodiments, if a fixed design cross-sectional area is used for subsequent aerodynamic flow field calculations, the calculated exhaust gas velocity may deviate from the fluid dynamic requirements of the actual working conditions.

[0058] The safe wind speed boundary calculation module obtains the tunnel design net cross-sectional area. Combined with the vehicle congestion ratio output by the data acquisition and filtering module Dynamic compensation calculations are performed to obtain the effective flow cross-sectional area used to characterize the current actual operating conditions. .

[0059] To avoid the effective flow cross-sectional area from abnormally approaching zero due to vehicle congestion detection errors or extreme congestion conditions, a minimum effective flow cross-sectional area threshold is preset in the safe wind speed boundary calculation module.

[0060] When the calculated effective flow cross-sectional area is less than the minimum effective flow cross-sectional area threshold, the safe wind speed boundary calculation module corrects the effective flow cross-sectional area to the minimum effective flow cross-sectional area threshold and outputs a blockage anomaly warning signal. The formula for calculating the effective flow cross-sectional area is: ; In the formula, For effective circulation cross-sectional area, Design the clear cross-sectional area for the tunnel. This represents the vehicle congestion ratio.

[0061] S22, Calculation of the lower boundary to prevent flue gas backflow.

[0062] To ensure the safe evacuation of personnel upstream of the fire source, the smoke exhaust system needs to provide sufficient longitudinal momentum to overcome the thermal buoyancy of the fire plume, thereby preventing the high-temperature smoke from flowing backwards towards the fire source.

[0063] The safe wind speed boundary calculation module, combining the effective heat release rate and the corrected effective flow cross-sectional area, derives the lower boundary exhaust wind speed to prevent flue gas backflow. The formula for calculating the lower boundary exhaust velocity is: ; In the formula, To prevent backflow of flue gas, the lower boundary exhaust velocity, This is a dimensionless tunnel slope correction factor. It is the acceleration due to gravity. For an effective heat release rate, The initial density of ambient air. The specific heat capacity of air at constant pressure. For effective circulation cross-sectional area, This represents the average absolute temperature of the flue gas layer, expressed in Kelvin, to avoid the risk of division by zero in temperature calculations.

[0064] Slope correction factor The specific value is determined based on the actual longitudinal slope of the tunnel section. Under uphill smoke extraction conditions, due to buoyancy gain, The value is usually less than 1; in downhill smoke exhaust conditions, due to buoyancy resistance, The value is usually greater than 1. This applies to the initial density of ambient air. Specific heat capacity of air at constant pressure Those skilled in the art can make presets based on the altitude and standard atmospheric pressure parameters of the tunnel, which will not be elaborated here.

[0065] S23, maintain the upper boundary calculation of flue gas thermal stratification state.

[0066] During the longitudinal smoke exhaust process, the longitudinal smoke exhaust velocity cannot be increased indefinitely. Excessive longitudinal airflow will generate a strong shearing effect at the interface between the high-temperature smoke layer and the bottom cold air layer.

[0067] When the shear force exceeds the buoyancy stability limit, it can easily cause shear instability at the flue gas layer interface, causing the flue gas to lose its thermal stratification state and be drawn into the bottom escape space, posing a danger to evacuees.

[0068] The safe wind speed boundary calculation module introduces the shear effect of the critical Froude number-limited interface to calculate the maximum allowable exhaust wind speed without disrupting the thermal stratification of the flue gas, and uses this as the upper boundary exhaust wind speed. The formula for calculating the exhaust velocity at the upper boundary is: ; In the formula, To maintain the upper boundary exhaust velocity of the flue gas thermal stratification state, The critical Froude number, It is the acceleration due to gravity. For the thickness of the flue gas layer, The mean absolute temperature of the flue gas layer. The mean absolute temperature of the clean air at the bottom layer. Critical Froude number. Used to quantify the ratio of shear force to buoyancy at the interface. In a specific embodiment, the critical Froude number is determined based on the roughness of the tunnel wall and its structural form. The value ranges from 0.9 to 1.2.

[0069] The safe wind speed boundary calculation module generates the lower boundary smoke exhaust wind speed through the above calculations. With the upper boundary smoke exhaust wind speed The lower and upper boundary smoke exhaust velocities together constitute a safe smoke exhaust velocity range suitable for the current fire situation and traffic conditions. .

[0070] This range defines the safe smoke exhaust velocity range for subsequent ventilation command optimization calculations; that is, the system's smoke exhaust velocity must be greater than or equal to... To prevent backflow, it needs to be less than or equal to To prevent entrainment and settling.

[0071] To avoid a calculation dead zone where the upper boundary wind speed is lower than the lower boundary wind speed under extreme fire conditions, the safe wind speed boundary calculation module includes threshold comparison logic. When this occurs... In such cases, the system prioritizes ensuring personnel's need for backflow prevention during escape, directly converging and locking the safe smoke exhaust velocity range to the lower boundary smoke exhaust velocity. The lower boundary exhaust wind speed will be used as the target wind speed determination step and the anti-backflow guarantee wind speed in the forced exhaust control.

[0072] Meanwhile, the safe wind speed boundary calculation module outputs an abnormal warning signal indicating that the flue gas thermal stratification state constraints cannot be satisfied simultaneously, in order to indicate that the anti-backflow safety constraints take precedence over the flue gas thermal stratification state constraints under the current operating conditions.

[0073] See attached document Figure 5 In this embodiment, the target wind speed calculation module executes step S3, the target wind speed determination step. Specifically, it includes the following sub-steps: S31. Atmospheric diffusion capacity assessment and constraint mapping.

[0074] During the smoke exhaust process, the atmospheric conditions of the external environment affect the diffusion effect of the exhaust gas. If there is a temperature inversion layer or low wind speed outside the tunnel, the diffusion of the exhaust gas is hindered, and it is easy to accumulate in the tunnel entrance area, causing the risk of secondary pollution in the area outside the tunnel.

[0075] The target wind speed calculation module acquires the external environmental wind speed collected by the data acquisition and filtering module. Solar radiation illuminance and vertical temperature gradient .

[0076] The target wind speed calculation module uses the Pasquale-Gifford atmospheric stability classification method to process the above meteorological variables and determine the atmospheric diffusion capacity of the current area outside the tunnel.

[0077] In some embodiments, the Pasquale-Gifford atmospheric stability classification method divides atmospheric stability into different standard levels based on ambient wind speed and solar radiation intensity or cloud cover. For the specific meteorological data comparison and classification process of the Pasquale-Gifford atmospheric stability classification method, those skilled in the art can refer to conventional diffusion models in the fields of meteorology and environmental protection, which are well-known technologies in the field and will not be elaborated upon here.

[0078] To facilitate continuous adjustment of ventilation speed, the target wind speed calculation module maps the determined atmospheric stability level to a dimensionless atmospheric diffusion correction coefficient. .

[0079] Atmospheric diffusion correction factor The value range is set to the interval (0,1). The specific mapping logic can be implemented using a preset lookup table interpolation method.

[0080] In one specific embodiment, the target wind speed calculation module maps the instability level to the maximum diffusion constraint coefficient, and sequentially maps the instability level, weakly unstable level, neutral level, stable level, and stable level to diffusion constraint coefficients that decrease progressively, while keeping the diffusion constraint coefficient corresponding to the stable or inversion state at a minimum preset value that is greater than zero. The mapping table is pre-stored in the target wind speed calculation module and can be calibrated and updated according to the terrain around the tunnel entrance, the height of the smoke exhaust outlet, and environmental control requirements.

[0081] Atmospheric diffusion correction coefficient corresponds to unstable and easily diffused atmospheric levels. The value of is set to 1; as atmospheric stability gradually increases and diffusion conditions worsen, the value of the atmospheric diffusion correction coefficient decreases monotonically; corresponding to stable, difficult-to-diffuse temperature inversion atmospheric levels, the atmospheric diffusion correction coefficient... The value is set to a small positive number close to 0.

[0082] S32. Calculation steps for determining steady-state target wind speed.

[0083] The target wind speed calculation module obtains the safe smoke exhaust wind speed range generated by the safe wind speed boundary calculation module. The target wind speed calculation module will use the atmospheric diffusion correction factor. As a linear adjustment weight, interpolation optimization is performed within the safe smoke exhaust wind speed range to calculate the steady-state target wind speed that takes into account both internal and external environmental conditions. .

[0084] When the safe smoke exhaust wind speed range output by the safe wind speed boundary calculation module has degenerated into the backflow prevention guarantee wind speed, the target wind speed calculation module no longer performs interval interpolation, but directly outputs the backflow prevention guarantee wind speed as the steady-state target wind speed. Steady-state target wind speed The calculation formula is: ; In the formula, For steady-state target wind speed, To prevent backflow of flue gas, the lower boundary exhaust velocity, To maintain the upper boundary exhaust velocity of the flue gas thermal stratification state, This is the atmospheric diffusion correction factor.

[0085] This interpolation optimization logic, while ensuring the safety of personnel escaping from inside the tunnel, adjusts the smoke extraction rate based on the external atmospheric diffusion capacity. When external diffusion conditions are limited, the steady-state target wind speed... downward boundary exhaust wind speed To reduce emissions and mitigate external pollution while preventing backflow of flue gas; when external diffusion conditions are favorable, the steady-state target wind speed... upward boundary exhaust wind speed They moved closer together to expel the smoke from the tunnel at a faster rate.

[0086] The above calculation method incorporates external meteorological influence factors into the internal ventilation control logic, thereby achieving a comprehensive solution of the internal aerodynamic flow field and external environmental conditions.

[0087] See attached document Figure 6 In this embodiment, the control mode determination module performs step S4, control mode determination. This specifically includes the following sub-steps: S41. Calculation of settlement threshold and characteristic time along the friction.

[0088] During long-distance longitudinal transport, flue gas undergoes convective heat exchange with the tunnel walls, and its temperature decreases with the transport distance. When the flue gas temperature drops to near the ambient air temperature, the flue gas loses the thermal buoyancy required to maintain stratification, and subsequently settles into the escape space below.

[0089] In this step, the control mode determination module calculates the expected transmission time of the flue gas in the physical space and the critical time for fluid instability.

[0090] The control mode determination module obtains the steady-state target wind speed output by the target wind speed calculation module. The estimated smoke transmission time is calculated based on the preset smoke exhaust distance. The formula for calculating the expected flue gas transmission time is: ; In the formula, To estimate flue gas transport time, This represents the longitudinal distance from the source of the fire to the smoke exhaust duct opening. This refers to the steady-state target wind speed. In practical implementation, It is usually calculated from the coordinates of the fire source located by the fire detection system and the preset coordinates of the smoke exhaust vent.

[0091] The control mode determination module calculates the time threshold for flue gas to lose buoyancy and begin settling at the current wind speed based on current environmental parameters and flow field conditions. This process is based on the principles of fluid heat transfer, using the current temperature difference and temperature space decay rate to extrapolate the time it takes for the fluid to reach an unstable state. (Flue gas settling threshold time) The calculation formula is: ; In the formula, The time for flue gas to settle to the ground. This represents the current mean absolute temperature of the flue gas layer. The critical instability and settlement absolute temperature. For the temperature attenuation gradient along the path, The target wind speed is the steady-state wind speed.

[0092] Critical instability settlement absolute temperature This refers to the critical temperature threshold at which flue gas buoyancy cannot maintain a state of thermal stratification. It also refers to the absolute temperature of critical instability settling. The value of is determined by those skilled in the art using empirical formulas for plume settlement based on tunnel cross-section height and ambient background temperature.

[0093] In one specific embodiment, the control mode determination module determines the average temperature of the bottom clean air. The sum of the preset minimum maintenance stratification temperature difference and the critical instability settlement absolute temperature is determined. The preset minimum sustained temperature difference between layers is pre-calibrated and stored based on the tunnel cross-section height, smoke layer thickness, and evacuation space height. The setting process is well-known in the field and will not be elaborated here.

[0094] In some embodiments, the control mode determination module has built-in calculation protection logic, which determines the current average absolute temperature of the flue gas layer when the obtained value is... Less than or equal to the critical instability settlement absolute temperature At that time, the system directly assigns the boundary time for flue gas settling. To avoid negative values ​​or division by zero anomalies.

[0095] When the temperature gradient decreases along the path When the current average absolute temperature of the flue gas layer is less than or equal to the preset minimum attenuation gradient threshold, Still greater than the critical instability and settlement absolute temperature The control mode determination module will determine the boundary time for flue gas settling. The value is assigned to the preset maximum time threshold; if the current average absolute temperature of the flue gas layer... Less than or equal to the critical instability settlement absolute temperature If the value is 0, then it will still be assigned the value 0.

[0096] S42. Mode determination based on device startup delay feedforward.

[0097] The exhaust fan experiences mechanical inertia as it accelerates from its current operating state to its rated output state. The control mode determination module determines the mechanical acceleration time constant of the fan. Introduced as a feedforward compensation parameter into the decision logic, the fluid dynamics time dimension and the electromechanical response time dimension are calculated in a unified manner to establish the smoke exhaust control mode applicable to the current working condition.

[0098] To prevent frequent mode switching due to minor fluctuations in sensor signals near the critical point, the control mode determination module introduces hysteresis comparison logic when performing determination operations.

[0099] The control mode determination module sets the initial determination threshold to be: And set the time hysteresis margin parameter. In practical implementation, the time hysteresis margin parameter The value can be set according to the system control cycle, for example, the value can be 1 to 3 times the system control cycle.

[0100] The control mode determination module executes the following determination logic: When the system is currently in continuous steady-state smoke extraction mode, if the calculated... The control mode determination module determines whether the current operating condition is suitable for alternating control modes of low-speed smoke control and high-speed forced smoke exhaust, and outputs an alternating smoke exhaust determination signal.

[0101] The alternating smoke exhaust determination signal indicates that, constrained by external atmospheric diffusion conditions, the current steady-state target wind speed is too low, resulting in an excessively long expected smoke transmission time. Continuing operation at this wind speed could cause the smoke to become unstable and settle before reaching the exhaust port. Based on this, the control mode determination module triggers subsequent alternating control commands.

[0102] When the system is currently in an alternating control mode of low-speed smoke control and high-speed smoke exhaust, if the calculated... The control mode determination module determines that the current working condition is suitable for continuous steady-state smoke exhaust mode and switches to output a continuous smoke exhaust determination signal.

[0103] The continuous smoke discharge judgment signal indicates that, after deducting the electromechanical delay and hysteresis margin required for the fan to start, the flue gas can be discharged to the outside of the tunnel before losing thermal buoyancy thanks to the currently set steady-state target wind speed, and usually will not cause obvious settlement hazards along the tunnel.

[0104] When the calculation yields When the control mode is between the two switching thresholds mentioned above, the control mode determination module maintains the control mode of the previous control cycle and does not output a mode switching signal, thereby avoiding frequent switching near the critical boundary.

[0105] By introducing the above-mentioned method for determining the hysteresis interval, the system can fully cover the range of parameter changes, eliminate the ambiguous interval of mode switching, and establish a control mode that matches the current internal and external environmental conditions.

[0106] See attached document Figure 7 In this embodiment, the closed-loop control execution module performs step S5, closed-loop collaborative execution. Specifically, it includes the following sub-steps: S51, Execution logic of continuous steady-state smoke exhaust mode.

[0107] When the control mode determination module outputs a continuous smoke discharge determination signal, it indicates that when the flue gas is running at the steady-state target wind speed corrected by the external atmospheric diffusion constraint, the control requirements for preventing backflow and settling can be met before it is discharged.

[0108] The closed-loop control execution module calculates the steady-state target wind speed based on the target wind speed generated by the target wind speed calculation module. Calculate the control frequency command for the smoke exhaust fan.

[0109] In some embodiments, based on the fan similarity law, within a certain speed range, the fan's airflow and speed exhibit a linear proportional relationship. This allows the target flow field wind speed to be converted into an electrical frequency command for the frequency converter. The closed-loop control execution module, according to the fan similarity law, linearly maps the wind speed command to the operating frequency of the fan frequency converter. Steady-state target frequency. The calculation formula is: ; In the formula, For the steady-state target frequency, The rated operating frequency specified on the nameplate of the smoke exhaust fan. Steady-state target wind speed, This refers to the full-load design wind speed of the exhaust fan at its rated operating frequency.

[0110] The closed-loop control execution module generates a frequency including the steady-state target frequency. The frequency converter control commands are transmitted to each exhaust fan node via the industrial fieldbus. During continuous operation of the fan, the steady-state target frequency... As the basic frequency command, the closed-loop control execution module further acquires the real-time wind speed feedback value from the wind speed sensor inside the tunnel, and performs closed-loop correction near the basic frequency command, using a proportional-integral-derivative algorithm to eliminate the static difference between the actual wind speed and the steady-state target wind speed.

[0111] For the tuning method of specific gain parameters in the proportional-integral-differential algorithm, those skilled in the art can make conventional configurations based on the on-site aerodynamic damping characteristics. This is a well-known technology in the field and will not be elaborated here.

[0112] S52, the execution logic of the alternating control mode of low-speed smoke control and high-speed forced smoke exhaust.

[0113] When the control mode determination module outputs an alternating smoke emission determination signal, it indicates that the current operating condition is one of limited external diffusion and internal settlement risk. The closed-loop control execution module exits the continuous steady-state smoke emission mode and initiates a smoke storage and forced emission control step based on time-series alternating actions.

[0114] The alternating control process of low-speed smoke control and high-speed forced smoke exhaust is used when the steady-state target wind speed cannot simultaneously meet both external diffusion constraints and internal anti-settlement constraints. It decomposes the continuous smoke exhaust process into a low-speed smoke control phase and a high-speed forced smoke exhaust phase, prioritizing internal personnel evacuation safety while also considering external pollution control. This control mode is divided in the time domain into a low-speed smoke control phase and a high-speed forced smoke exhaust command with feedforward.

[0115] After receiving the alternating smoke emission determination signal, the closed-loop control execution module evaluates the current flue gas settling threshold time. With the mechanical acceleration time constant of the wind turbine The relationship.

[0116] when When the system is determined to be on the verge of instability and subsidence, the closed-loop control execution module skips the low-speed smoke control phase and directly executes the high-speed forced smoke exhaust command to ensure the safety of personnel inside.

[0117] when At this time, the closed-loop control execution module enters the low-speed smoke control phase, generating and issuing low-speed frequency commands. The low-speed frequency commands are based on the lower boundary exhaust velocity to prevent backflow of flue gas. It is calculated proportionally based on the aforementioned similarity law.

[0118] Due to the lower boundary smoke exhaust velocity Typically not exceeding the steady-state target wind speed Using steady-state target wind speed When the calculated flue gas settling threshold time is used as the basis for feedforward triggering, the triggering time has a safety margin relative to the low-speed smoke control stage; in other embodiments, the closed-loop control execution module can also redetermine the settling threshold time corresponding to the smoke storage stage based on the actual wind speed of the low-speed smoke control stage.

[0119] During this phase, the fans operate at a lower speed to meet the backflow prevention conditions, keeping the high-temperature flue gas in the tunnel arch space to reduce the flue gas emission rate to the external tunnel entrance environment.

[0120] During the low-speed smoke control phase, the closed-loop control module starts an internal timer to accumulate the running time within the current alternation cycle. The closed-loop control execution module continuously compares the running time. With the calculated feedforward triggering time node .

[0121] When the running time meets the condition At that time, the closed-loop control execution module triggers a high-velocity forced smoke exhaust command with feedforward compensation. To overcome the inherent mechanical delay characteristics of the fan, the system issues a forced exhaust frequency command in advance, before the flue gas reaches the settling threshold time.

[0122] When the upper boundary exhaust wind speed Greater than or equal to the lower boundary exhaust velocity At that time, the forced exhaust frequency command is based on the upper boundary exhaust velocity that maintains the thermal stratification of the flue gas. The calculation was performed based on the aforementioned similarity laws.

[0123] When the upper boundary exhaust wind speed Less than the lower boundary exhaust velocity At that time, the closed-loop control execution module generates a forced exhaust frequency command based on the anti-backflow guarantee wind speed output by the safe wind speed boundary calculation module, prioritizing the safety requirements for personnel evacuation to prevent flue gas backflow. Upon receiving the command, the exhaust fan rotor begins to accelerate. The physical and mechanical acceleration of time means that when the fan reaches the high-speed forced smoke extraction command, the timing is close to the critical moment when the flue gas loses its thermal buoyancy and begins to settle. Therefore, by increasing the longitudinal airflow, the flue gas is expelled from the tunnel before it becomes unstable.

[0124] After the high-speed forced smoke extraction command maintains a high operating frequency for a preset forced smoke extraction duration, if the closed-loop control execution module detects that the system is still in the alternating smoke extraction judgment state, it resets the timer and controls the fan group to reduce speed again, switching back to the low-speed smoke control stage. In specific implementation, the forced smoke extraction duration can be calibrated based on the ratio of the preset longitudinal smoke extraction distance to the actual smoke extraction wind speed used in the high-speed forced smoke extraction command, and a preset safety margin can be added to ensure that the high-speed forced smoke extraction command can cover the main smoke transmission distance between the fire source and the smoke extraction opening. When the actual smoke extraction wind speed used in the high-speed forced smoke extraction command is the anti-backflow protection wind speed, the forced smoke extraction duration is determined according to this anti-backflow protection wind speed.

[0125] Through the aforementioned alternating multiplexing control based on feedforward time nodes, the system decomposes the smoke exhaust rate into a combination of low-speed and high-speed operating logic in the time domain, in order to balance the smoke exhaust control requirements for internal anti-settlement and external pollution reduction. When the external pollution reduction control requirements conflict with the internal anti-backflow and anti-settlement control requirements, the closed-loop control execution module prioritizes the execution of anti-backflow and anti-settlement controls related to internal personnel evacuation safety.

[0126] To further illustrate the technical effects of the tunnel ventilation and smoke extraction system provided in the embodiments of the present invention, the following detailed explanation is provided in conjunction with specific application scenarios and numerical calculation processes.

[0127] In a high-altitude highway tunnel fire scenario, the data acquisition and filtering module obtains real-time physical environment parameters. The tunnel's designed clearance cross-sectional area is 50 square meters, and the initial absolute temperature of the ambient air is 300 Kelvin. After asymmetric smoothing filtering, the system estimates an effective heat release rate that stabilizes at 15 megawatts. Traffic video radar detection shows a vehicle congestion ratio of 0.2 downstream of the fire source. The current average absolute temperature of the smoke layer is 600 Kelvin, with a temperature attenuation gradient of 0.5 Kelvin per meter. The longitudinal distance from the fire source to the smoke exhaust opening is 600 meters.

[0128] The safe wind speed boundary calculation module, based on a design cross-sectional area of ​​50 square meters and a vehicle blockage ratio of 0.2, calculates an effective flow cross-sectional area of ​​40 square meters using the product complement relationship. Combining the effective heat release rate with the corrected cross-sectional area, the module calculates a lower boundary exhaust wind speed of 2.5 m / s to prevent flue gas backflow; by introducing the critical Froude number constraint, it calculates an upper boundary exhaust wind speed of 4.5 m / s to maintain the thermal stratification of the flue gas. Thus, the system constructs a safe exhaust wind speed range from 2.5 m / s to 4.5 m / s.

[0129] The target wind speed calculation module assesses external meteorological data, determines that an inversion layer exists outside the tunnel, resulting in poor atmospheric diffusion conditions, and maps an atmospheric diffusion correction factor of 0.2. Within the safe exhaust wind speed range, the target wind speed calculation module adds the product of the correction factor and the difference between the upper and lower boundary wind speeds to the lower boundary exhaust wind speed, calculating a steady-state target wind speed of 2.9 meters per second.

[0130] The control mode determination module performs characteristic time calculations. Based on a smoke exhaust distance of 600 meters and a steady-state target wind speed of 2.9 meters per second, the estimated smoke transmission time is calculated to be 206.9 seconds. Combining the smoke temperature of 600 Kelvin, the critical instability settling absolute temperature of 320 Kelvin, and the temperature decay gradient of 0.5 Kelvin per meter, the calculated settling time of the smoke layer is 193.1 seconds. The obtained mechanical acceleration time constant of the smoke exhaust fan is 30 seconds, and the system's time hysteresis margin parameter is set to 10 seconds.

[0131] The control mode determination module compares the estimated flue gas transmission time of 206.9 seconds with the flue gas settling threshold time of 173.1 seconds (after deducting the fan acceleration constant and adding a hysteresis margin). Since the estimated transmission time exceeds the threshold, it indicates that if flue gas is continuously discharged at the current steady-state target wind speed, the flue gas will become unstable and settle before reaching the exhaust port. The control mode determination module determines that an alternating low-speed smoke control and high-speed smoke exhaust control mode is applicable and outputs a corresponding determination signal.

[0132] After receiving the signal, the closed-loop control execution module enters the low-speed smoke control phase, generating a low-speed frequency command based on the lower boundary smoke exhaust velocity of 2.5 m / s, temporarily retaining the high-temperature smoke at the tunnel arch. When the timer accumulates to the feedforward trigger time node (163.1 seconds, calculated as 193.1 seconds minus 30 seconds), the closed-loop control execution module triggers the high-speed forced smoke exhaust phase with feedforward compensation, generating a forced exhaust frequency command based on the upper boundary smoke exhaust velocity of 4.5 m / s. After 30 seconds of mechanical acceleration, the smoke exhaust fan reaches a high-speed state, precisely when the smoke is approaching its instability critical point. The high-momentum airflow rapidly clears the near-instability smoke from the tunnel, achieving a balance between internal anti-settlement and external pollution reduction.

[0133] To verify the technical effects of this invention, numerical simulations were conducted using computational fluid dynamics software; see attached figure. Figure 8 Under the same severe external diffusion constraints, the changes in flue gas height were compared between the traditional constant wind speed control method and the alternating control method of this invention. The traditional method forces the fan to operate at a constant speed of 2.9 meters per second, causing the flue gas to settle along the path after approximately 150 seconds, resulting in a flue gas height below the safe evacuation limit of 2.5 meters. The alternating control method of this invention issues a high-speed forced smoke extraction command 163.1 seconds in advance, ensuring that the flue gas height remains above 3 meters throughout the entire extraction cycle, guaranteeing the safety of personnel evacuation.

[0134] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A tunnel ventilation and smoke extraction system, characterized in that, include: The data acquisition and filtering module collects real-time environmental and flow field state parameters inside and outside the tunnel, as well as operating parameters of the smoke exhaust fan and frequency conversion drive system. Based on the original fire source temperature data, it determines the original fire source heat release rate, performs asymmetric smoothing filtering on the original fire source heat release rate, and outputs the effective heat release rate. The safe wind speed boundary calculation module combines the vehicle blockage ratio to dynamically correct the effective flow cross-sectional area, calculates the lower boundary exhaust wind speed to prevent flue gas backflow based on the effective heat release rate, introduces fluid dynamic boundary conditions to calculate the upper boundary exhaust wind speed to maintain the flue gas thermal stratification state, and combines the lower boundary exhaust wind speed with the upper boundary exhaust wind speed to form a safe exhaust wind speed range. The target wind speed calculation module acquires external meteorological data, obtains atmospheric diffusion correction coefficients based on atmospheric stability levels, and uses the atmospheric diffusion correction coefficients as linear adjustment weights to perform interpolation calculations within the safe smoke exhaust wind speed range to generate steady-state target wind speeds. The control mode determination module calculates the expected flue gas transmission time and the flue gas layer settling boundary time, compares the expected flue gas transmission time and the flue gas layer settling boundary time with the fan mechanical acceleration time constant, establishes the flue gas control mode applicable to the current working condition, and outputs the control mode signal. The closed-loop control execution module receives the control mode signal, issues frequency conversion control commands, and drives the smoke exhaust fan to execute a continuous steady-state smoke exhaust mode or an alternating control mode based on the safe smoke exhaust wind speed range, which determines a low-speed smoke control wind speed and a high-speed forced smoke exhaust wind speed.

2. The tunnel ventilation and smoke extraction system according to claim 1, characterized in that, The asymmetric smoothing filtering process specifically includes: The data acquisition and filtering module obtains the original heat release rate of the fire source at the current sampling moment and the effective heat release rate of the previous sampling period. When the original heat release rate of the fire source is not less than the effective heat release rate of the previous sampling period, the data acquisition and filtering module outputs the original heat release rate of the fire source as the effective heat release rate of the current period. When the original heat release rate of the fire source is less than the effective heat release rate of the previous sampling period, the data acquisition and filtering module introduces an attenuation smoothing coefficient to perform a weighted summation of the original heat release rate of the fire source and the effective heat release rate of the previous sampling period to obtain the effective heat release rate of the current period.

3. The tunnel ventilation and smoke extraction system according to claim 1, characterized in that, The safe wind speed boundary calculation module performs correction of the effective flow cross-sectional area, specifically including: The safe wind speed boundary calculation module obtains the tunnel design net cross-sectional area. The safe wind speed boundary calculation module calculates the result by subtracting the vehicle blockage ratio, and multiplies the tunnel design net cross-sectional area by the result to obtain the effective flow cross-sectional area; When the effective flow cross-sectional area is less than the minimum effective flow cross-sectional area threshold, the safe wind speed boundary calculation module corrects the effective flow cross-sectional area to the minimum effective flow cross-sectional area threshold.

4. The tunnel ventilation and smoke extraction system according to claim 1, characterized in that, The safe wind speed boundary calculation module derives the lower boundary smoke exhaust wind speed, specifically including: The safe wind speed boundary calculation module multiplies the tunnel slope correction coefficient, gravitational acceleration, and effective heat release rate to obtain the first product; The safe wind speed boundary calculation module multiplies the initial density of ambient air, the specific heat capacity of air at constant pressure, the effective flow cross-sectional area, and the average absolute temperature of the flue gas layer to obtain a second product. The safe wind speed boundary calculation module performs a division operation using the first product as the dividend and the second product as the divisor, and then performs a cube root operation on the division result to obtain the lower boundary smoke exhaust wind speed.

5. The tunnel ventilation and smoke extraction system according to claim 1, characterized in that, The safe wind speed boundary calculation module derives the upper boundary smoke exhaust wind speed, specifically including: The safe wind speed boundary calculation module multiplies the gravitational acceleration, the thickness of the flue gas layer, and the difference between the average absolute temperature of the flue gas layer and the average absolute temperature of the clean air at the bottom layer to obtain a third product. The safe wind speed boundary calculation module uses the third product as the dividend and the average absolute temperature of the flue gas layer as the divisor to perform a division operation, and performs a square root operation on the division result to obtain the square root value. The safe wind speed boundary calculation module multiplies the square root value by the critical Froude number to obtain the upper boundary smoke exhaust wind speed; When the upper boundary smoke exhaust velocity is less than the lower boundary smoke exhaust velocity, the safe wind speed boundary calculation module locks the safe smoke exhaust velocity range to the lower boundary smoke exhaust velocity and uses the lower boundary smoke exhaust velocity as the anti-backflow guarantee wind speed.

6. The tunnel ventilation and smoke extraction system according to claim 1, characterized in that, The target wind speed calculation module generates a steady-state target wind speed, specifically including: The target wind speed calculation module maps the instability level to an atmospheric diffusion correction coefficient with a value of one, maps the temperature inversion state to a minimum preset value greater than zero, and obtains the atmospheric diffusion correction coefficient by looking up a table according to the atmospheric stability level. The target wind speed calculation module calculates the wind speed difference between the upper boundary smoke exhaust wind speed and the lower boundary smoke exhaust wind speed; The target wind speed calculation module multiplies the wind speed difference with the atmospheric diffusion correction coefficient, and then adds the lower boundary smoke exhaust wind speed to the product to obtain the steady-state target wind speed. When the safe wind speed boundary calculation module outputs the anti-backflow guarantee wind speed, the target wind speed calculation module outputs the anti-backflow guarantee wind speed as the steady-state target wind speed.

7. The tunnel ventilation and smoke extraction system according to claim 1, characterized in that, The control mode determination module calculates the estimated flue gas transport time and flue gas settling boundary time, specifically including: The control mode determination module uses the longitudinal distance from the fire source to the smoke exhaust opening as the dividend and the steady-state target wind speed as the divisor to perform a division operation to obtain the expected smoke transmission time. The control mode determination module calculates the temperature difference between the current average absolute temperature of the flue gas layer and the critical instability and settlement absolute temperature. The control mode determination module uses the temperature difference as the dividend and the temperature attenuation gradient along the path as the divisor to perform the first division operation. Then, it uses the result of the first division operation as the dividend and the steady-state target wind speed as the divisor to perform the second division operation to obtain the settling boundary time of the flue gas layer. When the current average absolute temperature of the flue gas layer is not greater than the critical instability and settling absolute temperature, the control mode determination module sets the settling threshold time of the flue gas layer to zero. When the temperature decay gradient along the path is not greater than the preset minimum decay gradient threshold, and the current average absolute temperature of the flue gas layer is greater than the critical instability and settlement absolute temperature, the control mode determination module assigns the settlement threshold time of the flue gas layer to the preset maximum time threshold.

8. The tunnel ventilation and smoke extraction system according to claim 1, characterized in that, The control mode determination module determines and outputs a control mode signal, specifically including: The control mode determination module sets the initial determination threshold to be the flue gas settling boundary time minus the fan mechanical acceleration time constant; When the current smoke exhaust control mode is the continuous steady-state smoke exhaust mode, and the expected smoke transmission time is greater than the sum of the initial judgment threshold and the time hysteresis margin parameter, the control mode judgment module outputs an alternating smoke exhaust judgment signal. When the current smoke exhaust control mode is an alternating control mode of low-speed smoke control and high-speed forced smoke exhaust, and the expected smoke transmission time is not greater than the difference between the initial judgment threshold and the time hysteresis margin parameter, the control mode judgment module outputs a continuous smoke exhaust judgment signal. When the expected flue gas transmission time is greater than the difference but not greater than the sum, the control mode determination module retains the exhaust control mode of the previous control cycle.

9. The tunnel ventilation and smoke extraction system according to claim 8, characterized in that, The closed-loop control execution module performs steady-state target frequency smoke extraction, specifically including: When the continuous smoke exhaust judgment signal is received, the closed-loop control execution module multiplies the rated operating frequency of the smoke exhaust fan with the steady-state target wind speed according to the fan similarity law, and then divides the product with the full-load design wind speed to obtain the steady-state target frequency. The closed-loop control execution module generates a frequency conversion control command containing the steady-state target frequency, sends it to the smoke exhaust fan node, obtains the real-time wind speed feedback value from the wind speed sensor inside the tunnel, and performs closed-loop correction using a proportional-integral-derivative algorithm.

10. The tunnel ventilation and smoke extraction system according to claim 8, characterized in that, The closed-loop control execution module alternately executes low-speed smoke control commands and high-speed forced smoke exhaust commands, specifically including: When the alternating smoke exhaust judgment signal is received, and the settling time of the flue gas layer is greater than the mechanical acceleration time constant of the fan, the closed-loop control execution module enters the low-speed smoke control stage and generates a low-speed frequency command according to the lower boundary smoke exhaust wind speed. When the alternating smoke exhaust determination signal is received, and the settling time of the flue gas layer is not greater than the mechanical acceleration time constant of the fan, the closed-loop control execution module directly generates a high-speed forced smoke exhaust frequency command. During the execution of the low-speed smoke control phase, the closed-loop control execution module accumulates the running time within the current alternation cycle; When the running time is not less than the initial judgment threshold, the closed-loop control execution module triggers the high wind speed forced smoke exhaust frequency command; When the upper boundary smoke exhaust velocity is not less than the lower boundary smoke exhaust velocity, the closed-loop control execution module generates the high-speed forced smoke exhaust frequency command based on the upper boundary smoke exhaust velocity. When the upper boundary smoke exhaust velocity is less than the lower boundary smoke exhaust velocity, the closed-loop control execution module generates the high-velocity forced smoke exhaust frequency command based on the anti-backflow protection velocity. After maintaining the forced smoke exhaust duration, the exhaust fan slows down again to switch back to the low-speed smoke control phase.

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