Urban building group fire spreading prediction method based on coupling of wind field and fire flow field

Abstract

The invention relates to an urban building group fire spreading prediction method based on coupling of a wind field and a fire flow field. The technical problem that in the prior art, a large deviation exists between a building group fire spreading prediction result and a fire spreading result under the actual building group multi-point fire catching condition is solved. The invention provides a building group fire spreading prediction method based on coupling of a wind field and a fire flow field, and the method comprises the following steps: S1, calculating the speed of airflow generated by the combustion of a fire building according to the initial fire state of a building group and the fire characteristic parameters of the building; s2, calculating a coupling airflow velocity according to the airflow velocity generated by combustion of the on-fire building and the environmental wind speed; s3, according to the coupling airflow velocity, calculating short-range and long-range fire spreading probabilities of the on-fire building and calculating the on-fire probability of the non-on-fire building; and S4, predicting fire spreading of the building group according to a calculation result.

Description

Technical Field

[0001] The present invention relates to a fire spread prediction method for a building complex in fire fighting technology, and in particular to a fire spread prediction method for an urban building complex based on the coupling of a wind field and a fire flow field. Background Art

[0002] Fires in urban building complexes are a form of disaster that often occurs in scenarios such as accidental explosions and earthquakes in cities. They pose a huge threat to people, urban buildings, etc. Therefore, reasonably predicting the spread of fires in urban building complexes under extreme conditions is of great significance for assessing urban fire risks and formulating emergency rescue plans.

[0003] Currently, common urban fire spread calculation methods include probabilistic methods based on damage level assessment, mathematical prediction methods based on experience, and numerical prediction methods based on physics and semi-physical methods. Among them, the probabilistic methods based on damage level assessment and the mathematical prediction methods based on experience have fast calculation speeds but low calculation accuracy; the numerical prediction methods based on physics have high calculation accuracy, but the calculation process is complex and the calculation speed is slow; the numerical prediction methods based on semi-physical methods usually use simplified empirical formulas to characterize fire spread mechanisms such as thermal radiation, smoke flow and flying fire, taking into account the efficiency of probabilistic empirical methods and the rationality of physical methods. Therefore, they have received widespread attention in practical applications in recent years.

[0004] When calculating the fire spread process of a building complex, semi-physical numerical prediction methods usually assume that the ambient wind speed and direction are constant, and ignore the coupling effect between the airflow generated by building combustion and the ambient wind field. As a result, there is a large deviation between the prediction results of the fire spread of a building complex and the fire spread results under the conditions of multiple fires in the actual building complex. Summary of the Invention

[0005] The purpose of the present invention is to solve the technical problem that there is a large deviation between the existing building complex fire spread prediction results and the actual building complex fire spread results under multi-point fire conditions, and to provide an urban building complex fire spread prediction method based on the coupling of wind field and fire flow field.

[0006] To achieve the above objectives, the technical solutions provided by the present invention are as follows:

[0007] A fire spread prediction method for urban building complexes based on the coupling of wind field and fire flow field is characterized in that it includes the following steps:

[0008] Step S1: Determine the location, number, and fire status of the buildings currently on fire, and the location and number of the buildings currently not on fire, based on the type of fire accident in the urban building complex; determine the fire characteristic parameters of the buildings currently on fire based on the functional type and geometric characteristics of the buildings currently on fire; and determine the ambient wind speed based on a preset ambient wind field within the building complex area;

[0009] Step S2: Calculate the airflow velocity generated by the burning buildings at the current moment according to the location, number, and fire status of the buildings at the current moment;

[0010] Step S3, calculating the coupled airflow velocity at the location of the burning building at the current moment by a vector superposition method based on the airflow velocity generated by the burning building at the current moment and the ambient wind speed;

[0011] Step S4, calculating the short-range fire spread probability and the long-range fire spread probability of the fire building at the current moment based on the coupled airflow velocity at the location of the fire building at the current moment and the fire state of the fire building at the current moment;

[0012] Step S5: Calculate the probability of fire in the unburned building at the current moment using the total probability formula based on the short-range fire spread probability and long-range fire spread probability of the fire-stricken building at the current moment;

[0013] Step S6: predicting the fire status of the unburned building and the fire status of the burned building at the next preset time based on the fire probability of the unburned building at the current time and the fire characteristic parameters of the burned building at the current time;

[0014] Step S7: Based on the fire status of the unburned buildings and the fire status of the burned buildings at the next preset time, obtain the new location, number, and fire status of the burned buildings at the current time, and the new location and number of the unburned buildings at the current time within the urban building complex; and determine the new fire characteristic parameters of the burned buildings at the current time based on the functional types and geometric characteristics of the burned buildings at the new time;

[0015] Step S8, determine whether the fire status of the unburned buildings and the fire status of the burned buildings at the next preset moment meet the preset termination conditions. If so, the prediction of the fire spread of the urban building complex is completed; if not, based on the new position, number and fire status of the burned buildings at the current moment obtained in step S7, the new position and number of the unburned buildings at the current moment, the new fire characteristic parameters of the burned buildings at the current moment, and the ambient wind speed determined in step S1, return to step S2 until the fire status of the unburned buildings and the fire status of the burned buildings at the next preset moment meet the preset termination conditions, and the prediction of the fire spread of the urban building complex is completed.

[0016] Furthermore, in step S1, the fire characteristic parameters of the burning building include the characteristic time of the combustion stage of the burning building and the combustion heat release rate per unit area of the burning building corresponding to the combustion stage; the characteristic time of the combustion stage includes the initial ignition characteristic time, the fire growth characteristic time, the full combustion characteristic time, and the fire decay characteristic time; the combustion heat release rate per unit area of the burning building corresponding to the combustion stage includes the combustion heat release rate per unit area of the building during initial ignition, fire growth, full combustion, and fire decay.

[0017] Furthermore, in step S3, the current coupled airflow velocity is calculated by the following formula:

[0018]

[0019] Where, represents the airflow velocity generated by the burning building, j represents the burning building, and b represents the location of the coupled airflow to be calculated; represents the ambient wind speed, and r represents the distance from the location where the coupled airflow is to be calculated to the geometric center of the fire building.

[0020] Furthermore, in step S2, the airflow velocity generated by the burning building is calculated by the following formula:

[0021]

[0022] Where, F a Indicates the air flow rate entering the fire source area per unit time, L c is the ratio of the fire plume height of the burning building to the distance from the current position to the center of the fire plume, f r It's about L c function, α is a characteristic parameter related to fire intensity, n is the ratio of the fire plume height to its radius, F a The following formula is used for calculation:

[0023]

[0024] In the formula, M represents the air mass consumed by the combustion of unit mass of combustibles. represents the combustion heat release rate of the burning building j, h0 represents the combustion calorific value of the combustible material, ρ ∞ Indicates the air density.

[0025] Furthermore, in step S4, the short-range fire spread probability P is calculated by the following formula: s :

[0026] P s =P e (1-L eff / L d )

[0027] Where, P e Indicates the maximum short-range fire spread probability of a burning building, L eff Indicates the distance between the unburned building and the burned building, L d It indicates the short-range fire spread limit distance between the unburned building and the burned building in the straight line direction. Its size is related to the air flow velocity at the location of the burned building. When the air flow velocity is less than 5 meters per second,

[0028] L d =a r +D

[0029] Where a r is the characteristic length, D is the characteristic scale of the building;

[0030] When the air velocity is greater than 5 meters per second, L d The size of is determined by the boundary position of the ellipse along the airflow velocity direction with the burning building as the upper focus, and its expression is:

[0031]

[0032] Where P is the semi-focal chord of the ellipse, e is the eccentricity, It represents the angle between the line connecting the burning building and the non-burning building and the airflow direction; the specific expression of P is,

[0033]

[0034] Where a and b represent the semi-major axis and semi-minor axis of the ellipse, respectively; their sizes are positively correlated with wind speed.

[0035] The long-range fire spread probability P is calculated by the following steps L :

[0036] Step S4.1: Define the number of flying fire particles generated by the burning building at the current moment as N(t), where N(t) is the number of flying fire particles generated per unit area of the burning building at the current moment. s The product of (t) and the building area S, assuming that the generation rate of flying fire particles is independent of each other on the time axis, then the number of flying fire particles N generated per unit burned area of the building on fire at the current moment is s (t) is determined by Poisson sampling, and the corresponding Poisson distribution function expression is,

[0037]

[0038] Where λ represents the average rate of flying fire particles generated per unit fire area of a building, which is defined as:

[0039]

[0040] Where t3 and t4 represent the duration of the full combustion and fire decay stages of the burning building, respectively. s It represents the number of flying fire particles generated per unit area of a burning building. Its expression is:

[0041]

[0042] Where f is the correction factor, which is related to the building type;

[0043] Step S4.2: Calculate the probability P of a single flying fire particle k causing a building fire k :

[0044] P k =P d,k ×P i,k =[P D,X (x i )·P D,Y (y i )] k ×P i,k

[0045] Where, P d,k P represents the probability of flying fire particles k settling on unburned buildings under the action of wind field; i,k P represents the probability of ignition of an unburned building under the action of the kth flying fire particle; D,X (x i ), P D,Y (y i ) represent the probability of flying fire particles distribution in the X-axis and Y-axis directions, respectively. The X-axis is set along the wind direction, and the Y-axis is perpendicular to the X-axis; i represents an unburned building; x i Indicates the distance from the unburned building to the Y axis; i Indicates the distance from the unburned building to the X-axis;

[0046] In step S4.2, when the wind speed is less than or equal to 5 m / s, the probability of flying fire particle distribution is calculated by the following formula:

[0047]

[0048] Where μ and σ are the expected and standard deviation of the distribution function, μ = 0, σ = 0.92D, D represents the characteristic scale of the burning building, and the square root of the building's bottom surface area can be used in the calculation;

[0049] When the wind speed is greater than 5m / s, the calculation formula for the probability of flying fire particles distribution is as follows:

[0050]

[0051] Where, μ L,X , σ L,X They represent the natural logarithm distance ln(x i )’s mean and standard deviation, σ Y is the standard deviation of the normal distribution function perpendicular to the wind direction,

[0052]

[0053] Where μ X , σ X Represent the expectation and standard deviation of the lognormal distribution function on the X-axis respectively;

[0054]

[0055] Where B * It represents the characteristic parameter of flying fire spread, and the calculation formula is:

[0056]

[0057] Where g represents the acceleration due to gravity, ρ P represents the density of flying fire particles, d P Indicates the size of flying fire particles, T ∞ Indicates the ambient temperature, c P represents the specific heat capacity of air.

[0058] Step S4.3: Calculate the long-range fire spread probability P L :

[0059]

[0060] Where, P k represents the probability that the kth flying fire particle causes an unburned building to catch fire.

[0061] Furthermore, in step S5, the probability of fire of the unburned building P is calculated by the total probability formula. i :

[0062]

[0063] Where, P S,i,j P represents the probability that the burning building j will cause the fire of the unburned building i through the short-range fire spread mechanism, and m represents the total number of burning buildings in the area that may cause the fire of the unburned building i through the short-range fire spread mechanism; L,i,j represents the probability that the burning building j will cause the fire of the unburned building i through the long-range fire spread mechanism, and n represents the total number of burning buildings in the area that may cause the fire of the unburned building i through the long-range fire spread mechanism.

[0064] Furthermore, step S6 is specifically as follows: step S6.1, based on the fire probability of the unburned building calculated at the current moment, sampling is used to determine the fire state of the unburned building at the next preset moment, and the fire state includes fire and no fire; step S6.2, based on the combustion duration of the burned building at the current moment and the characteristic time of the combustion stage of the burned building, the fire state of the burned building at the next preset moment is determined, and the fire state includes initial ignition, fire growth, full combustion, fire decay and combustion termination.

[0065] Furthermore, the step S6.1 is specifically as follows: the fire probability P of the unburned building is calculated according to the current moment. i , determined by (0,1) random sampling, the specific rules are: if the (0,1) random sampling result is less than the fire probability P i , then the fire state of the building that is not on fire at the next moment is on fire, otherwise it is not on fire; the specific step S6.2 is: comparing the burning duration of the building on fire at the current moment with the characteristic time of the burning stage of the building on fire, if the burning duration ≥ the characteristic time of the burning stage, the building enters the next fire state, if the burning duration ≤ the characteristic time of the burning stage, the fire state of the building remains unchanged.

[0066] Furthermore, in step S8, the preset termination condition is that at the next preset moment, the status of all unburned buildings is unburned, and the fire status of all burned buildings is combustion terminated, or the number of unburned buildings is zero, and the fire status of all burned buildings is combustion terminated.

[0067] Beneficial effects of the present invention:

[0068] 1. This invention proposes a fire spread prediction method for urban building complexes based on the coupling of wind fields and fire flow fields. This method couples the airflow velocity generated by building combustion with the wind velocity in the ambient wind field, and predicts the spread of building fires based on the coupled airflow velocity. This improves the rationality of the fire spread prediction results for building complexes under conditions of multiple fires.

[0069] 2. The present invention provides a fire spread prediction method for urban buildings based on the coupling of wind field and fire flow field. The method uses vector superposition method to calculate the coupled airflow velocity, which reduces complex fluid dynamics calculations and improves calculation efficiency.

[0070] 3. This invention proposes a fire spread prediction method for urban building complexes based on the coupling of wind fields and fire flow fields. This method considers both short-range fire spread and the ignition points caused by long-range fire spread, ensuring a more comprehensive prediction result.

[0071] 4. This invention proposes a fire spread prediction method for urban buildings based on the coupling of wind fields and fire flow fields. It uses a full probability formula and combines short-range and long-range fire spread probabilities to effectively calculate the fire probability of unburned buildings, improving the scientific nature and accuracy of the prediction.

[0072] 5. The present invention provides a method for predicting the spread of fire in urban buildings based on the coupling of wind fields and fire flow fields. It can dynamically update the fire probability of unburned buildings and the fire status of burned buildings over time, thereby realizing real-time prediction of fire spread. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Figure 1 This is a flow chart of an embodiment of a method for predicting the spread of fire in urban buildings based on the coupling of wind field and fire flow field according to the present invention;

[0074] Figure 2 This is a schematic diagram of calculating the airflow velocity generated by the burning building in step S3 of an embodiment of a method for predicting the spread of fire in urban buildings based on the coupling of wind field and fire flow field of the present invention;

[0075] Figure 3 This is a schematic diagram of calculating the probability of short-range fire spread caused by a burning building in step S5 of an embodiment of a method for predicting the spread of fire in urban buildings based on the coupling of wind field and fire flow field of the present invention;

[0076] Figure 4 This is a schematic diagram of calculating the probability of long-range fire spread caused by a burning building in step S5 of an embodiment of a method for predicting the spread of fire in urban buildings based on the coupling of wind field and fire flow field of the present invention. DETAILED DESCRIPTION

[0077] The present invention will be further described below with reference to the accompanying drawings and examples.

[0078] Figure 1 This is a flowchart of specific implementation steps of an embodiment of the present invention, such as Figure 1 As shown, this embodiment provides a method for predicting the spread of fire in urban buildings based on the coupling of wind field and fire flow field, which includes the following calculation steps:

[0079] Step S1: Building fire characteristic parameters are given based on the building's functional type and geometric characteristics. Building functional types include ordinary residential buildings, commercial buildings, factory warehouses, etc. Each type of building has six fire states, including no fire, initial ignition, fire growth, full combustion, fire decay, and combustion termination. Building characteristics include building size, building type (such as factory, warehouse), area, and building spacing. Fire characteristic parameters take effect when a building is on fire, including: the characteristic time Δt of the building's initial ignition, fire growth, full combustion, and fire decay.cr1 , Δt cr2 , Δt cr3 , Δt cr4 , and the heat release rate per unit area of the building corresponding to the four combustion stages Q rr1 , Q rr2 , Q rr3 , Q rr4 .

[0080] Step S2: determining the initial fire status of the building complex according to the accident type, where the initial fire status of the building complex includes the location and number of buildings on fire at the current moment, and the location and number of buildings not on fire at the current moment;

[0081] Accident types include accidental explosion and fire and earthquake fire. In the accidental explosion and fire scenario, samples are taken at certain intervals with the explosion point as the center within the predetermined area until the probability of building fire decreases from large to small to 0, and the initial fire state of the building complex is determined; in the earthquake fire scenario, all buildings in the predetermined area are sampled according to their building area to determine the initial fire state of the building complex.

[0082] Step S3: Calculate the airflow velocity generated by the burning building at the current moment:

[0083] The calculation formula for the airflow velocity generated by the burning building at the current moment is:

[0084]

[0085] Where, F a Indicates the air flow rate entering the fire source area per unit time, L c is the ratio of the fire plume height of the burning building to the distance from the current position to the center of the fire plume, f r It's about L c function, α is a characteristic parameter related to fire intensity, n is the ratio of the fire plume height to its radius, F a The following formula is used for calculation:

[0086]

[0087] In the formula, M represents the air mass consumed by the combustion of unit mass of combustibles. represents the combustion heat release rate of the burning building j, h0 represents the combustion calorific value of the combustible material, ρ ∞ represents the air density,

[0088] If the height of the fire plume generated by the burning building is small compared to the distance from the current location to the center of the fire plume, that is, L c It tends to 0 and can be ignored. The calculation formula for the airflow velocity generated by the burning building at the current moment is:

[0089]

[0090] In the formula, all variables are in international units, and the parameter c is 6.1×10 -4 .

[0091] Step S4: Calculate the current airflow velocity at the target position by vector superposition method, such as Figure 2 As shown, the calculation formula for the coupled airflow velocity at the target position at the current moment is as follows:

[0092]

[0093] Where, represents the airflow velocity generated by the burning building, j represents the burning building, and b represents the location of the coupled airflow to be calculated; represents the ambient wind speed, and r represents the distance from the location where the coupled airflow is to be calculated to the geometric center of the fire building.

[0094] Step S5: Calculate the short-range fire spread probability and long-range fire spread probability caused by the burning building at the current moment

[0095] Calculate the probability of short-range fire spread, such as Figure 3 As shown in the figure, the area represented by the blue ellipse is the short-range fire spread area that may be caused by the burning building; the major axis of the ellipse is along the wind direction, and the burning building is located at the focus of the ellipse. a and b represent the semi-major axis and semi-minor axis of the ellipse respectively. The short-range fire spread probability P of any point within the ellipse is S The calculation formula is,

[0096] P s =P e (1-L eff / L d )

[0097] Where, P e Indicates the maximum short-range fire spread probability of a burning building, L eff Indicates the distance between the unburned building and the burned building, L d It indicates the short-range fire spread limit distance between the unburned building and the burned building in the straight line direction. Its size is related to the air flow velocity at the location of the burned building. When the air flow velocity is less than 5 meters per second,

[0098] L d =a r +D

[0099] Where a r is the characteristic length, D is the characteristic scale of the building;

[0100] When the air velocity is greater than 5 meters per second, L dThe size of is determined by the boundary position of the ellipse along the airflow velocity direction with the burning building as the upper focus, and its expression is:

[0101]

[0102] Where P is the semi-focal chord of the ellipse, e is the eccentricity, It represents the angle between the line connecting the burning building and the non-burning building and the airflow direction; the specific expression of P is,

[0103]

[0104] Where a and b represent the semi-major axis and semi-minor axis of the ellipse respectively; their sizes are positively correlated with wind speed;

[0105] Calculate the long-range fire spread probability. The long-range fire spread of a burning building is caused by flying fire particles. The number of flying fire particles generated by the burning building at the current moment is N(t). N(t) is the number of flying fire particles per unit area of the burning building at the current moment. s The product of (t) and the building area S, assuming that the generation rate of flying fire particles is independent of each other on the time axis, then the number of flying fire particles N generated per unit burned area of the building on fire at the current moment is s (t) can be determined by Poisson sampling, and the corresponding Poisson distribution function expression is,

[0106]

[0107] Where λ represents the average rate of flying fire particles generated per unit fire area of a building, which is defined as:

[0108]

[0109] Where t3 and t4 represent the duration of the full combustion and fire decay stages of the burning building, respectively. s It represents the number of flying fire particles generated per unit area of a burning building. Its expression is:

[0110]

[0111] Where f is the correction coefficient, which is related to the building type. The value for ordinary residential and commercial buildings is 1, and the value for factory warehouses is 0.6.

[0112] The distribution of flying fire particles generated by burning buildings is as follows Figure 4 When the wind speed is less than or equal to 5m / s, the distribution of flying fire particles is a normal distribution with the burning building as the center. The corresponding distribution probability calculation formula is:

[0113]

[0114] Where μ and σ are the expected value and standard deviation of the distribution function, μ = 0, σ = 0.92D, D represents the characteristic scale of the burning building, and the square root of the building bottom area can be used in the calculation; P D,X (x i ), P D,Y (y i ) represent the probability of flying fire particles distribution in the X-axis and Y-axis directions, respectively. The X-axis is set along the wind direction, and the Y-axis is perpendicular to the X-axis; i represents a building without fire; x i Indicates the distance from the unburned building to the Y axis; i Indicates the distance from the unburned building to the X-axis;

[0115] When the wind speed is greater than 5m / s, the deposition area of flying fire particles is an elliptical area with the burning building as the upper vertex. The calculation formula for the distribution probability of flying fire particles is:

[0116]

[0117] Where, μ L,X , σ L,X They represent the natural logarithm distance ln(x i )’s mean and standard deviation, σ Y is the standard deviation of the normal distribution function perpendicular to the wind direction,

[0118]

[0119] Where μ X , σ X Represent the expectation and standard deviation of the lognormal distribution function on the X-axis respectively;

[0120]

[0121] Where B * It represents the characteristic parameter of flying fire spread, and the calculation formula is:

[0122]

[0123] Where g represents the acceleration due to gravity, ρ P represents the density of flying fire particles, d P Indicates the size of flying fire particles, T ∞ Indicates the ambient temperature, c P represents the specific heat capacity of air;

[0124] The probability P of a single flying fire particle k causing a building fire k The expression is,

[0125] P k =P d,k×P i,k =[P D,X (x i )·P D,Y (y i )] k ×P i,k

[0126] Where, P d,k P represents the probability of flying fire particles k settling on unburned buildings under the action of wind field; i,k represents the probability of ignition of an unburned building under the action of the kth flying fire particle;

[0127] The probability P of long-range fire spread caused by flying fire from a burning building L The calculation formula is:

[0128]

[0129] Where N(t) represents the number of flying fire particles generated by the burning building at the current moment; P k represents the probability that the kth flying fire particle causes an unburned building to catch fire.

[0130] Step S6: Calculate the fire probability P of the building that is not on fire at the current moment using the total probability formula i ;

[0131]

[0132] Where, P S,i,j P represents the probability that the burning building j will cause the fire of the unburned building i through the short-range fire spread mechanism, and m represents the total number of burning buildings in the area that may cause the fire of the unburned building i through the short-range fire spread mechanism; L,i,j represents the probability that the burning building j will cause the fire of the unburned building i through the long-range fire spread mechanism, and n represents the total number of burning buildings in the area that may cause the fire of the unburned building i through the long-range fire spread mechanism.

[0133] Step S7: Predicting the burning state of the building;

[0134] The next moment state prediction method of the unburned building is to calculate the fire probability P of the unburned building according to the current moment. i , determined by (0,1) random sampling, the specific rules are: if the (0,1) random sampling result is less than the fire probability P i , then the fire status of the building that is not on fire at the next moment is on fire, otherwise it is not on fire;

[0135] The method for predicting the state of a burning building at the next moment is to use the burning state s jk Duration Δt sjkWith this type of building in this burning state jk Characteristic time Δt crk Compare (k value is 1, 2, 3, 4, determined by the combustion state), if Δt sjk >Δt crk , the building enters the next combustion state (until the burning building finally enters the combustion termination state), otherwise its combustion state remains unchanged;

[0136] In this embodiment, based on the fire probability of the unburned building at the current time (assuming the current time is 10 o'clock) and the burning duration of the burned building at that time, the fire status of the unburned building and the fire status of the burned building at 10:05 are predicted.

[0137] Step 8: Simulate and predict the evolution of fire spread in building complexes and save the results;

[0138] In this embodiment, 10.05 is taken as the current moment, and the next round of calculation is continued. That is, the preset moment of this round is taken as the current moment of the next round. The fire spread calculation process given in steps S3 to S7 is repeated until the fire status of all buildings on fire is combustion terminated, and the status of all buildings not on fire is not on fire, or the number of buildings not on fire is zero, and the fire status of all buildings on fire is combustion terminated. Then, the calculation is terminated, and the prediction of the fire spread of the building complex is completed. The fire spread prediction result of the building complex is output and saved. The fire spread prediction result of the building complex includes the fire status of the buildings on fire at each preset moment, the fire status of the buildings not on fire, and the coupled airflow velocity and direction at the location of the buildings on fire.

Claims

1. A fire spread prediction method for urban buildings based on the coupling of wind field and fire flow field, characterized in that: The following steps are involved: Step S1: determining the location, number, and fire status of buildings currently on fire, and the location and number of buildings currently not on fire, based on the type of fire accident in the urban building complex; and determining fire characteristic parameters of the buildings currently on fire based on the functional type and geometric characteristics of the buildings currently on fire; Determine the ambient wind speed based on the preset ambient wind field within the building complex area; Step S2: Calculate the airflow velocity generated by the burning buildings at the current moment according to the location, number, and fire status of the buildings at the current moment; Step S3, calculating the coupled airflow velocity at the location of the burning building at the current moment by a vector superposition method based on the airflow velocity generated by the burning building at the current moment and the ambient wind speed; Step S4, calculating the short-range fire spread probability and the long-range fire spread probability of the fire building at the current moment based on the coupled airflow velocity at the location of the fire building at the current moment and the fire state of the fire building at the current moment; Step S5: Calculate the probability of fire in the unburned building at the current moment using the total probability formula based on the short-range fire spread probability and long-range fire spread probability of the fire-stricken building at the current moment; Step S6: predicting the fire status of the unburned building and the fire status of the burned building at the next preset time based on the fire probability of the unburned building at the current time and the fire characteristic parameters of the burned building at the current time; Step S7: Based on the fire status of the unburned buildings and the fire status of the burned buildings at the next preset time, obtain the new location, number, and fire status of the burned buildings at the current time, and the new location and number of the unburned buildings at the current time within the urban building complex; and determine the new fire characteristic parameters of the burned buildings at the current time based on the functional types and geometric characteristics of the burned buildings at the new time; Step S8: determining whether the fire status of the non-fired buildings and the fire status of the fire-stricken buildings at the next preset time meet the preset termination conditions. If so, the prediction of the spread of the fire in the urban building complex is completed. If not, then based on the new location, number and fire status of the buildings on fire at the current moment obtained in step S7, the new location and number of the buildings not on fire at the current moment, the new fire characteristic parameters of the buildings on fire at the current moment, and the ambient wind speed determined in step S1, return to step S2 until the fire status of the buildings on fire and the fire status of the buildings not on fire at the next preset moment meet the preset termination conditions, and the prediction of the spread of fire in the urban building complex is completed.

2. The method for predicting the spread of fire in urban buildings based on the coupling of wind field and fire flow field according to claim 1 is characterized by: In step S1, the fire characteristic parameters of the burning building include the characteristic time of the burning stage of the burning building and the combustion heat release rate per unit area of the burning building corresponding to the burning stage; The characteristic time of the combustion stage includes the characteristic time of initial ignition, the characteristic time of fire growth, the characteristic time of full combustion, and the characteristic time of fire decay; The combustion heat release rate per unit area of the burning building corresponding to the combustion stage includes the combustion heat release rate per unit area of the building during initial ignition, fire growth, full combustion, and fire decay.

3. The method for predicting the spread of fire in urban buildings based on the coupling of wind field and fire flow field according to claim 2 is characterized by: In step S3, the current coupled airflow velocity is calculated by the following formula: Where, represents the airflow velocity generated by the burning building, j represents the burning building, and b represents the location of the coupled airflow to be calculated; represents the ambient wind speed, and r represents the distance from the location where the coupled airflow is to be calculated to the geometric center of the fire building.

4. The method for predicting the spread of fire in urban buildings based on the coupling of wind field and fire flow field according to claim 3 is characterized by: In step S2, the airflow velocity generated by the burning building is calculated by the following formula: Where, F a Indicates the air flow rate entering the fire source area per unit time, L c is the ratio of the fire plume height of the burning building to the distance from the current position to the center of the fire plume, f r It's about L c function, α is a characteristic parameter related to fire intensity, n is the ratio of the fire plume height to its radius, F a The following formula is used for calculation: In the formula, M represents the air mass consumed by the combustion of unit mass of combustibles. represents the combustion heat release rate of the burning building j, h0 represents the combustion calorific value of the combustible material, ρ ∞ Indicates the air density.

5. The method for predicting the spread of fire in urban buildings based on the coupling of wind field and fire flow field according to claim 4 is characterized by: In step S4, the short-range fire spread probability P is calculated by the following formula: s : P s =P e (1-L eff / L d ) Where, P e Indicates the maximum short-range fire spread probability of a burning building, L eff Indicates the distance between the unburned building and the burned building, L d Indicates the short-range fire spread limit distance in the straight line direction between the unburned building and the burned building; The long-range fire spread probability P is calculated by the following steps L : Step S4.1: Define the number of flying fire particles generated by the burning building at the current moment as N(t), where N(t) is the number of flying fire particles generated per unit area of the burning building at the current moment. s The product of (t) and the building area S, assuming that the generation rate of flying fire particles is independent of each other on the time axis, then the number of flying fire particles N generated per unit burned area of the building on fire at the current moment is s (t) is determined by Poisson sampling, and the corresponding Poisson distribution function expression is: Where λ represents the average rate of flying fire particles generated per unit burned area of the burning building, which is defined as: Where t3 and t4 represent the duration of the fire building's full combustion and fire decay stages, respectively. s It represents the number of flying fire particles generated per unit area of a burning building. Its expression is: Where f is the correction factor, which is related to the building type; Step S4.2: Calculate the probability P of a single flying fire particle k causing a building fire k : P k =P d,k ×P i,k =[P D,X (x i )·P D,Y (y i )] k ×P i,k Where, P d,k P represents the probability of flying fire particles k settling on unburned buildings under the action of wind field; i,k P represents the probability of ignition of an unburned building under the action of the kth flying fire particle; D,X (x i ), P D,Y (y i ) represent the probability of flying fire particles distribution in the X-axis and Y-axis directions, respectively, the X-axis is set along the wind direction, and the Y-axis is perpendicular to the X-axis; i represents an unburned building; x i Indicates the distance from the unburned building to the Y axis; i Indicates the distance from the unburned building to the X-axis; Step S4.3: Calculate the long-range fire spread probability P L : Where, P k represents the probability that the kth flying fire particle causes an unburned building to catch fire.

6. The method for predicting the spread of fire in urban buildings based on the coupling of wind field and fire flow field according to claim 5 is characterized in that: In step S5, the probability of fire in the unburned building P is calculated by the total probability formula. i : Where, P S,i,j P represents the probability that the burning building j will cause the fire of the unburned building i through the short-range fire spread mechanism, and m represents the total number of burning buildings in the area that may cause the fire of the unburned building i through the short-range fire spread mechanism; L,i,j represents the probability that the burning building j will cause the fire of the unburned building i through the long-range fire spread mechanism, and n represents the total number of burning buildings in the area that may cause the fire of the unburned building i through the long-range fire spread mechanism.

7. The method for predicting the spread of fire in urban buildings based on the coupling of wind field and fire flow field according to claim 6, characterized in that: In step S4.2, when the wind speed is less than or equal to 5 m / s, the probability of flying fire particle distribution is calculated by the following formula: Where μ and σ are the expected and standard deviation of the distribution function, μ = 0, σ = 0.92D, D represents the characteristic scale of the burning building, and the square root of the building's bottom surface area can be used in the calculation; When the wind speed is greater than 5m / s, the calculation formula for the distribution probability of flying fire particles is as follows: Where, μ L,X , σ L,X They represent the natural logarithm distance ln(x i )’s mean and standard deviation, σ Y is the standard deviation of the normal distribution function perpendicular to the wind direction, Where μ X , σ X Represent the expectation and standard deviation of the lognormal distribution function on the X-axis respectively; Where B * It represents the characteristic parameter of flying fire spread, and the calculation formula is: Where g represents the acceleration due to gravity, ρ P represents the density of flying fire particles, d P Indicates the size of flying fire particles, T ∞ Indicates the ambient temperature, c P represents the specific heat capacity of air.

8. The method for predicting the spread of fire in urban buildings based on the coupling of wind field and fire flow field according to claim 7 is characterized in that: The step S6 is specifically as follows: Step S6.1, sampling and determining the fire status of the non-fired building at the next preset time based on the fire probability of the non-fired building calculated at the current time, wherein the fire status includes fire and non-fire; Step S6.2: Determine the fire state of the building on fire at the next preset moment based on the combustion duration of the building on fire at the current moment and the characteristic time of the combustion stage of the building on fire. The fire state includes initial ignition, fire growth, full combustion, fire decay and combustion termination.

9. The method for predicting the spread of fire in urban buildings based on the coupling of wind field and fire flow field according to claim 8, characterized in that: The step S6.1 is specifically as follows: the fire probability P of the unburned building is calculated based on the current moment. i , determined by (0,1) random sampling, the specific rules are: if the (0,1) random sampling result is less than the fire probability P i , then the fire status of the building that is not on fire at the next moment is on fire, otherwise it is not on fire; The specific step S6.2 is as follows: the burning duration of the burning building at the current moment is compared with the characteristic time of the burning stage of the burning building. If the burning duration is ≥ the characteristic time of the burning stage, the burning building enters the next fire state; if the burning duration is ≤ the characteristic time of the burning stage, the fire state of the burning building remains unchanged.

10. The method for predicting the spread of fire in urban buildings based on the coupling of wind field and fire flow field according to claim 9, characterized in that: In step S8, the preset termination condition is that at the next preset moment, the status of all unburned buildings is unburned, and the fire status of all burned buildings is combustion terminated, or the number of unburned buildings is zero, and the fire status of all burned buildings is combustion terminated.

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