Real-time judgment method for roof collapse caused by fire between oil storage tanks of nuclear power station

Abstract

The invention discloses a real-time judgment method for roof collapse caused by a fire between nuclear power station oil storage tanks, and relates to the technical field of fire safety design of roof structures between nuclear power station oil storage tanks. Acquiring time sequence temperature data of the grid nodes; establishing a three-dimensional heat conduction model of the roof structure; top plate structure heating surface temperature field mapping is realized; carrying out three-dimensional heat transfer simulation on the top plate structure; analyzing the instability critical condition of the roof structure. According to the real-time judgment method for the roof collapse caused by the fire between the oil storage tanks of the nuclear power station, time sequence temperature field mapping of the heated surface of a complex roof structure between CFD numerical simulation software and FEM software in different fire scenes between the oil storage tanks of the nuclear power station can be realized; real-time structure response behaviors of the nuclear power station oil storage tank roof structure in different fire scenes are simulated, and the method can be used for fire safety design and post-disaster damage evaluation of the nuclear power station oil storage tank roof structure.

Description

Technical Field

[0001] The invention relates to the technical field of fire safety design of roof structures in oil storage tank rooms of nuclear power plants, and in particular to a real-time determination method for roof collapse caused by fire in oil storage tank rooms of nuclear power plants. Background Art

[0002] With the continuous rise in global energy demand and the significant increase in environmental awareness, nuclear power plants, as a clean and efficient way of energy supply, have ushered in rapid development around the world. The internal layout of nuclear power plants is complex. Among them, oil storage tanks are important facilities for storing key media such as lubricating oil and cooling oil required for the nuclear fuel cycle. Their safe and stable operation is directly related to the overall safety of nuclear power plants. However, once the flammable and explosive oil stored in the oil storage tank triggers a fire due to equipment failure, human operating errors or external factors, it will directly threaten the safety of the oil storage tank. The fire is more likely to spread rapidly, posing a major risk to other facilities in the nuclear power plant, and even causing the roof of the oil storage tank room to collapse due to high temperature and load, further exacerbating the severity of the accident.

[0003] The roof structure of the oil tank room in a nuclear power plant is complex. According to actual functional requirements, it is often necessary to make holes to meet ventilation, cable passage and other requirements, and multiple reinforcements are used to enhance the structural strength. However, this complexity makes it difficult to accurately simulate and evaluate the temperature field distribution and thermal response behavior of the roof structure under fire. The high temperature generated by the fire will not only cause the performance of the roof material to deteriorate, but may also cause the internal stress of the structure to be redistributed, thereby increasing the risk of roof instability. Therefore, how to accurately assess the collapse risk of the roof structure under fire and determine the critical conditions for its instability has become a crucial and urgent technical problem to be solved.

[0004] Traditional fire analysis methods, such as full-scale fire experiments or simplified numerical models, show obvious limitations when dealing with specific scenarios such as nuclear power plant oil tank rooms with complex internal structures and large spatial scales. The complexity of the oil tank room is not only due to the precise layout of its internal equipment and the diversity of its structure, but also because of its large size, which greatly increases the difficulty of simulating the dynamic behavior of the fire. The implementation of full-scale fire experiments not only requires a lot of financial and human resources, but also is limited by the controllability of the experimental environment. It is often difficult to accurately replicate the multidimensional complexity of actual fire scenes, including but not limited to the nonlinear spread path of the fire, the complex response of the roof structure under multidimensional thermal loads and other key aspects.

[0005] In addition, most of the current methods use a combination of fluid dynamics CFD numerical simulation software and structural mechanics FEM finite element analysis simulation software to simulate the thermal response behavior of building structures under fire. The invention patent with the authorization announcement number CN104680915B and the name of the subway performance-based fire protection method uses Pyrosim to establish fire physical models of subway tunnels and stations respectively, and obtains the relationship between the actual temperature of smoke and time by arranging detectors, and loads it as the fire temperature of the lining structure to the fire surface of the lining structure, simulating the temperature field and mechanical field of the lining structure under this fire temperature, so as to analyze and obtain the fire safety performance of the tunnel lining structure under real fire. The patent application with the publication number CN114357817A and the name of the fire protection method for building aluminum alloy structures based on fire resistance calculation invention calculates the temperature field of each space in the fire scene through CFD simulation software, calculates the temperature of aluminum alloy components in the fire scene by heat transfer theory, performs thermal-structural coupling analysis and calculation through FEM, and uses the yield of aluminum alloy materials as the overall structural failure judgment criterion. The patent application with publication number CN106815398A and name is "Building Fire Temperature Field Data Conversion Method Based on Multi-Field Coupling". It arranges temperature measurement points in the grid of CFD simulation software and then performs simulation. It uses interpolation or fitting function method to import temperature values ​​into the FEM component surface to obtain the thermal response of the roof structure to the fire.

[0006] Through the investigation and analysis of existing research methods, it can be seen that the existing fire safety performance analysis methods for roof structures under fire have certain limitations, mainly manifested in: 1) Indirectness of temperature field calculation and mapping: The current calculation of the temperature field of the roof structure is based on the basic theory of fire dynamics, and is calculated by heat transfer analysis of the spatial temperature field obtained by CFD simulation (that is, the calculated temperature is the gas phase boundary temperature of the fire scene, and the temperature of the solid surface of the building still needs to be calculated through the heat transfer formula). It is impossible to achieve direct mapping of the surface temperature of the roof structure. In addition, due to the idealized assumptions of the heat transfer formula, the building surface temperature calculated by this method usually has calculation errors, and it takes a lot of time to analyze various fire scenarios.

[0007] 2) Limitations of temperature field mapping methods: Currently, the temperature field mapping methods for fluid dynamics CFD simulation software and structural mechanics finite element analysis FEM simulation software are mainly implemented by arranging temperature measurement points (with limited measurement point arrangement density), and then estimating the temperature of the area without measurement points by interpolation or fitting function method. Due to the diversity of interpolation and fitting function methods, they are not applicable to complex fire scenes and complex roof structures between oil storage tanks in nuclear power plants, such as multiple fire points, non-horizontal roofs containing load-bearing beams, and roofs with multiple holes, which may lead to large errors between the node temperature where temperature measurement points are not arranged and the actual temperature.

[0008] 3) Lack of methods for real-time assessment of critical criteria for structural instability: There is a lack of analytical methods for the structural response behavior of the time-related evolution of the temperature field of the heated surface of the roof structure caused by the development of different fire scenarios.

[0009] Therefore, it is necessary to develop a new method that can efficiently and accurately realize the temperature field mapping between CFD simulation software and FEM simulation software, and simulate the real-time thermal response behavior of the roof structure of the nuclear power plant oil tank room under different fire scenarios, so as to provide reliable theoretical support for the fire safety design and post-disaster damage assessment of the roof structure of the nuclear power plant oil tank room. Summary of the invention

[0010] The purpose of the present invention is to provide a real-time determination method for roof collapse caused by fire in a nuclear power plant oil tank room, to solve the problems raised in the above-mentioned background technology, and to realize three-dimensional heat transfer temperature field analysis, thermal response behavior simulation and structural instability critical condition determination of the roof structure of the nuclear power plant oil tank room under different fire scenarios.

[0011] To achieve the above object, the present invention provides a real-time determination method for roof collapse caused by fire in a nuclear power plant oil storage tank room, comprising the following steps: Step S1, using CFD numerical simulation software to simulate the temporal and spatial evolution of the surface temperature field of the roof structure under fire conditions; Step S2, processing the temperature field of the heated surface of the roof structure obtained by the CFD numerical simulation software, and obtaining the time series temperature data of all grid nodes on the heated surface of the roof structure; Step S3, establishing a three-dimensional heat conduction model of the top plate structure by using FEM software; Step S4, seamlessly mapping the time series temperature data obtained by the CFD numerical simulation software to the three-dimensional heat conduction model established by the FEM software to achieve temperature field mapping of the heated surface of the top plate structure; Step S5, performing three-dimensional heat transfer simulation of the top plate structure by using FEM software; Step S6: Use FEM software to simulate the thermal response behavior of the roof structure based on the mapped temperature field, obtain the change of mechanical parameters and stress field distribution of the roof structure, and analyze the critical conditions for instability of the roof structure.

[0012] Preferably, in step S1, the temporal and spatial evolution of the surface temperature field of the roof structure under fire conditions is simulated by FDS numerical simulation software, and the specific steps are as follows: Step S11: Perform fire hazard analysis based on the actual layout of the nuclear power plant oil storage tank room, design fire scenarios, and complete the construction of the CFD model; Step S12, determine the mesh size range according to the formula in the CFD numerical simulation software user manual, perform temperature comparison analysis, and finally determine the optimal mesh size based on efficiency and accuracy; Step S13, by writing the running code of the CFD numerical simulation software, numbering the top plate structure created in the CFD model group for subsequent data reading, and defining the temperature data of the heating surface of the top plate structure to be output; For composite roof structures, each structural component is numbered in sequence, and the heating surfaces of which the surface temperature field changes due to heat radiation and heat convection under fire are defined respectively, so as to obtain the heating information of different parts of the roof structure; Step S14, define the temperature type to be output, and save the simulation results in the boundary file obtained by the CFD numerical simulation software.

[0013] Preferably, the specific steps of step S2 include: reading the temperature data of all grid nodes on the heated surface of the top plate structure obtained by simulating the CFD numerical simulation software through the Fortran language, saving it in the boundary file, and converting it into n text files containing the coordinates of all grid nodes on the heated surface of the top plate structure in the CFD model and the corresponding temperatures, wherein n=total calculation time of the CFD numerical simulation software / boundary file data output time step.

[0014] Preferably, the step S3 establishes a three-dimensional heat conduction model of the top plate structure by using ABAQUS numerical simulation software, and the specific steps are as follows: Step S31, based on the heated roof structure to be analyzed in the CFD model, establish a roof structure model with the same size and the same material properties; Step S32, setting the heat transfer analysis step and heat transfer unit type of the FEM model; Step S33, the meshing of the FEM model is consistent with the meshing of the CFD model, so as to ensure the consistency of the number of mesh nodes on the heated surface of the top plate structure and achieve a higher precision mapping of the temperature field; Step S34: Finally, the INP file is output as data for subsequent reading and mapping in the Fortran language.

[0015] Preferably, the specific steps of step S4 are as follows: Step S41, using Fortran language to establish a mapping file, correspond the heated surface of the CFD model to the heated surface of the FEM model component, read the node coordinates in the n text files processed by the CFD boundary file and the INP file output by the FEM model, realize one-to-one mapping of the nodes with the same coordinates, and write the corresponding temperature data to generate n text files with the same format as the CFD boundary file; Step S42, reading the n text files obtained from the FEM model by using the Fortran language, generating an AMP file of each coordinate point changing with time step that can be read by the FEM software, and the file will be imported into the FEM model as an external file; Step S43, using Fortran language to encode the AMP file to generate a BC file readable by FEM software, which contains the time series temperature data corresponding to each node in the FEM model; Step S44: All files obtained by programming in the above steps are saved in the same folder as the INP file. When the INP file is imported into the FEM model, the thermal boundary load from the BC file and the time series temperature data from the AMP file will be automatically loaded.

[0016] Preferably, the specific steps of step S5 include: Step S51, applying the temperature data of the heating surface of the top plate structure obtained by temperature field mapping to the heating surface of the top plate structure as a thermal boundary condition; Step S52: By defining constraint relationships, the three-dimensional heat conduction effect of the composite roof structure itself and between the structures is realized, and the temperature field distribution of the composite roof structure under different building fire scenarios is obtained.

[0017] Preferably, in step S6, the temperature field obtained by three-dimensional thermal analysis using the FEM model is used as a predefined field to perform structural mechanics simulation of the FEM model, thereby determining the critical condition for instability of the roof structure.

[0018] Preferably, the specific steps of the FEM model structural mechanics simulation include: Step S61, establishing the internal details of the roof structure model according to the actual situation of the roof structure of the oil storage tank room of the nuclear power plant, including the arrangement and assembly of the number and spacing of the force reinforcement and tension reinforcement inside the component, and setting the interaction; Step S62, setting the analysis step, output variable and unit type according to actual needs; Step S63, applying boundary loads according to the actual functions and layout of the building components, including fixed and hinged loads; Step S64, determining the critical instability condition of the roof structure according to the stress, strain, deflection mechanical performance parameters and the fire resistance limit of the roof structure.

[0019] Therefore, the present invention adopts the above-mentioned real-time determination method of roof collapse caused by fire in the oil storage tank room of a nuclear power plant, which has the following beneficial effects: (1) The present invention can provide an efficient and relatively accurate CFD-FEM temperature field mapping method. By processing the CFD boundary file using the Fortran language, the temperature data of all grid nodes on all different heated surfaces of the composite roof structure obtained by CFD simulation can be directly obtained, avoiding the error caused by interpolation of temperature measurement points.

[0020] (2) The present invention can simulate the three-dimensional heat transfer process and thermal response process of the composite roof structure caused by non-uniform heating under different fire scenarios. By performing CFD-FEM temperature field mapping, the non-uniform temperature field distribution on the heated surface of the roof structure caused by different fire scenarios can be obtained, which solves the problem of uniform heat transfer caused by only one-dimensional heat transfer in CFD and direct loading of thermal boundary conditions on the FEM model, thus forming a uniform temperature field distribution.

[0021] (3) The present invention can realize a comprehensive analysis of the structural response behavior of the composite roof structure under different fire scenarios and the development and evolution process of the actual fire scenario, providing a reference for the determination of thermal instability of the roof structure under different fire scenes and post-disaster damage assessment.

[0022] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The CFD simulation of different fire scenarios of single and composite roof structures of the present invention, where (a) is a single fire source fire scenario, (b) is a double fire source fire scenario, and (c) is a load-bearing beam structure fire scenario; Figure 2 This is the efficient mapping of the CFD and FEM temperature fields of a single fire source at the same time of the present invention, where (a) is the surface temperature field of the roof structure of FDS, and (b) is the surface temperature field of the roof structure of ABAQUS; Figure 3 This is the efficient mapping of the CFD and FEM temperature fields of the dual fire sources at the same time of the present invention, where (a) is the surface temperature field of the roof structure of FDS, and (b) is the surface temperature field of the roof structure of ABAQUS; Figure 4 The present invention is an efficient mapping of the CFD and FEM temperature fields of the load-bearing beam structure floor at the same time, wherein (a) is a schematic diagram of the load-bearing beam structure, (b) is the temperature distribution field of the left floor, (b1) is the FDS surface temperature field, (b2) is the ABAQUS surface temperature field, (c) is the temperature distribution field of the right floor, (c1) is the FDS surface temperature field, and (c2) is the ABAQUS surface temperature field; Figure 5This is the efficient mapping of the CFD and FEM temperature fields of the left heated surface of the load-bearing beam structure at the same time of the present invention, where (a) is a schematic diagram of the left heated surface structure of the load-bearing beam, (b) is the temperature distribution field, (b1) is the FDS surface temperature field, and (b2) is the ABAQUS surface temperature field; Figure 6 This is the efficient mapping of the CFD and FEM temperature fields of the right heated surface of the load-bearing beam structure at the same time of the present invention, where (a) is a schematic diagram of the heated surface structure of the right side of the load-bearing beam, (b) is the temperature distribution field, (b1) is the FDS surface temperature field, and (b2) is the ABAQUS surface temperature field; Figure 7 This is the efficient mapping of the CFD and FEM temperature fields of the heated surface below the load-bearing beam structure at the same time of the present invention, where (a) is a schematic diagram of the heated surface structure below the load-bearing beam, (b) is the temperature distribution field, (b1) is the FDS surface temperature field, and (b2) is the ABAQUS surface temperature field; Figure 8 This is the accuracy verification of the temperature data of the single fire source CFD and FEM mapping of the present invention, where (a) is the CFD simulated temperature field, (b) is the FEM calculated temperature field, and (c) is the CFD-FEM temperature data comparison; Fig. 9 This is the verification of the accuracy of the temperature data mapped by CFD and FEM for the dual-fire source of the present invention, where (a) is the CFD simulated temperature field, (b) is the FEM calculated temperature field, and (c) is the CFD-FEM temperature data comparison; Fig.10 This is the accuracy verification of the temperature data of the CFD and FEM temperature field mapping on the left side of the load-bearing beam structure floor of the present invention, where (a) is the CFD simulated temperature field, (b) is the FEM calculated temperature field, and (c) is the CFD-FEM temperature data comparison; Fig.11 The accuracy verification of the temperature data of the CFD and FEM temperature field mapping of the left heated surface of the load-bearing beam structure of the present invention is shown in Figure 1, where (a) is the CFD simulated temperature field, (b) is the FEM calculated temperature field, and (c) is the CFD-FEM temperature data comparison; Fig.12 The three-dimensional temperature field distribution of the roof structure under the FEM simulation of a single fire source fire condition of the present invention, wherein (a) is the heated surface, (b) is the heated back surface, and (c) is the heated side surface; Fig.13 The three-dimensional temperature field distribution of the roof structure under the double-fire source fire condition simulated by FEM of the present invention, wherein (a) is the heated surface, (b) is the heated back surface, and (c) is the heated side surface; Fig.14 The three-dimensional temperature field distribution of the load-bearing beam floor structure simulated by FEM of the present invention, wherein (a) is the heated surface, (b) is the heated back surface, and (c) is the heated side surface; Fig.15 The thermal response behavior of the load-bearing beam structure at 6s of the present invention, (a) is the temperature field distribution, (b) is the stress field distribution, (c) is the displacement change, and (d) is the damage distribution; Fig.16 The thermal response behavior of the load-bearing beam structure at 21s of the present invention, (a) is the temperature field distribution, (b) is the stress field distribution, (c) is the displacement change, and (d) is the damage distribution; Fig.17 The thermal response behavior of the load-bearing beam structure at 39s of the present invention, (a) is the temperature field distribution, (b) is the stress field distribution, (c) is the displacement change, and (d) is the damage distribution; Fig.18 The diagram is a critical point determination diagram of the instability of the concrete material on the left heated surface of the load-bearing beam structure of the present invention, wherein (a) is a thermal response cloud diagram of the left heated surface structure of the load-bearing beam, (b) is a stress change curve of the concrete on the left heated surface of the load-bearing beam, and (c) is a damage change curve of the concrete on the left heated surface of the load-bearing beam; Fig.19 This is a diagram for determining the critical point of instability of the concrete material of the load-bearing beam structure floor slab of the present invention, wherein (a) is a thermal response cloud diagram of the left floor slab structure, (b) is a stress change curve of the left floor slab concrete, and (c) is a damage change curve of the left floor slab concrete. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0025] Unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The words "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0026] Example See also Figure 1-19 The present invention provides a real-time determination method for roof collapse caused by fire in a nuclear power plant oil storage tank room, comprising the following steps: Step S1, using CFD numerical simulation software (fluid dynamics numerical simulation software) to simulate the spatiotemporal evolution of the temperature field on the roof structure surface under fire conditions. The spatiotemporal evolution of the temperature field on the roof structure surface under fire conditions is simulated by FDS numerical simulation software. FDS numerical simulation software is PyroSim fire simulation software, which can intuitively output the simulation results of the fire process. The simulation process includes establishing a CFD model according to the actual building fire scene, mesh independence analysis, defining the heat output surface of the roof structure, and defining the temperature type of the heating surface of the roof structure. The specific steps are as follows: Step S11: Perform fire hazard analysis based on the actual layout of the nuclear power plant oil storage tank room, design fire scenarios, and complete the construction of the CFD model; Step S12, determine the mesh size range according to the formula in the CFD numerical simulation software user manual, perform temperature comparison analysis, and finally determine the optimal mesh size based on efficiency and accuracy; Step S13, by writing the running code of the CFD numerical simulation software, the roof structure created in the CFD model group is numbered for subsequent data reading, such as obstruction#1; At the same time, define the temperature data of the heated surface of the top plate structure that needs to be output, such as: BNDF_FACE(-3)=.TRUE. / , where 1 represents the positive x direction, 1 represents the negative x direction, 2 represents the positive y direction, -2 represents the positive y direction, 3 represents the positive z direction, and -3 represents the positive z direction; For the composite roof structure, each structural component is numbered in the order of 1, 2, etc., and the heating surfaces of the components whose surface temperature field changes due to heat radiation and heat convection under fire are defined respectively, so as to obtain the heating information of different parts of the roof structure; Step S14, define the temperature type to be output, such as BNDF QUANTITY='WALL TEMPERATURE' / , that is, output the heated surface temperature of the top plate structure. The results will be saved in the boundary files obtained by CFD simulation in the format of CHID_n.bf (n= 0001, 0002...).

[0027] Step S2, processing the temperature field of the heated surface of the roof structure obtained by the CFD numerical simulation software, and obtaining the time series temperature data of all grid nodes on the heated surface of the roof structure. The specific steps include: reading the temperature data of all grid nodes on the heated surface of the roof structure obtained by the CFD numerical simulation software through the Fortran language, saving it in the boundary file, and converting it into n text files containing the coordinates of all grid nodes on the heated surface of the roof structure in the CFD model and the corresponding temperatures, wherein n=the total calculation time of the CFD numerical simulation software / the output time step of the boundary file data.

[0028] Step S3, establish a three-dimensional heat conduction model of the roof structure through FEM software (finite element analysis simulation software). FEM software is a finite element analysis simulation software with a wide range of simulation performance. It simulates and analyzes many problems in the engineering field, such as heat conduction problems under fire conditions. At the same time, it can solve stress / displacement problems after fire and analyze the performance changes of components under fire conditions. The three-dimensional heat conduction model of the roof structure is established through ABAQUS numerical simulation software, including modeling of the roof structure, establishment of thermal analysis model, mesh division, establishment of node set, and creation of FEM model output file. The specific steps are as follows: Step S31, based on the heated roof structure to be analyzed in the CFD model, establish a roof structure model with the same size and the same material properties; Step S32, setting the heat transfer analysis step and heat transfer unit type of the FEM model; Step S33, the meshing of the FEM model is consistent with the meshing of the CFD model, so as to ensure the consistency of the number of mesh nodes on the heated surface of the top plate structure and achieve a higher precision mapping of the temperature field; Step S34: Finally, the INP file (FEM model file) is output as data for subsequent reading and mapping in Fortran language.

[0029] Step S4, seamlessly map the time series temperature data obtained by the CFD numerical simulation software to the three-dimensional heat conduction model established by the FEM software to achieve the temperature field mapping of the heated surface of the roof structure. Since the CFD software simulates the fire development process to obtain the surface temperature field of the roof structure by interpolating each node of the grid, and using the linear interpolation method to achieve a complete one-dimensional temperature field distribution for display. Similarly, after applying thermal boundary temperature conditions to all grid nodes of the heated surface of the FEM model, it also realizes the temperature field distribution display on the one-dimensional plane in a linear interpolation manner. Therefore, by mapping all the grid node temperature data of the heated surface of the roof structure in the CFD model to all the grid nodes of the heated surface of the FEM roof structure, the complete temperature field mapping of the two can be achieved. The mapping process of the node temperature is as follows: Step S41, using Fortran language to establish a mapping file, correspond the heated surface of the CFD model to the heated surface of the FEM model component, read the node coordinates in the n text files processed by the CFD boundary file and the INP file output by the FEM model, realize one-to-one mapping of the nodes with the same coordinates, and write the corresponding temperature data to generate n text files with the same format as the CFD boundary file; Step S42, reading the n text files obtained from the FEM model by Fortran language, generating an AMP file (time series temperature value file) of each coordinate point changing with time step that can be read by the FEM software, and the file will be imported into the FEM model as an external file; Step S43, using Fortran language to encode the AMP file to generate a BC file (thermal boundary load file) readable by FEM software, which contains the time series temperature data corresponding to each node in the FEM model; Step S44: All files obtained by programming in the above steps are saved in the same folder as the INP file. When the INP file is imported into the FEM model, the thermal boundary load from the BC file and the time series temperature data from the AMP file will be automatically loaded.

[0030] Step S5: Perform three-dimensional heat transfer simulation of the top plate structure using FEM software. The specific steps include: Step S51, applying the temperature data of the heating surface of the top plate structure obtained by temperature field mapping to the heating surface of the top plate structure as a thermal boundary condition; Step S52: By defining constraint relationships, the three-dimensional heat conduction effect of the composite roof structure itself and between the structures is realized, and the temperature field distribution of the composite roof structure under different building fire scenarios is obtained.

[0031] Step S6, using FEM software to simulate the thermal response behavior of the roof structure based on the mapped temperature field, obtain the changes in the mechanical parameters of the roof structure and the distribution of the stress field, and analyze the critical conditions for the instability of the roof structure. The temperature field obtained by three-dimensional thermal analysis of the FEM model is used as a predefined field to perform FEM model structural mechanics simulation, and then determine the critical conditions for the instability of the roof structure. The FEM model structural mechanics simulation mainly includes the establishment of internal details of the building component model, the import of temperature field data obtained by three-dimensional thermal analysis, the setting of basic parameters, the application of boundary loads, and the analysis of stress fields. The specific steps include: Step S61, establishing the internal details of the roof structure model according to the actual situation of the roof structure of the oil storage tank room of the nuclear power plant, including the arrangement and assembly of the number and spacing of the force reinforcement and tension reinforcement inside the component, and setting the interaction; Step S62, setting the analysis step, output variable and unit type according to actual needs; Step S63, applying boundary loads according to the actual functions and layout of the building components, including fixed and hinged loads; Step S64, determining the critical instability condition of the roof structure according to the stress, strain, deflection mechanical performance parameters and the fire resistance limit of the roof structure.

[0032] Therefore, the present invention adopts the above-mentioned real-time judgment method for roof collapse caused by fire in the oil tank room of a nuclear power plant, which can simulate the time series three-dimensional heat transfer temperature field distribution, mechanical parameter changes and stress field distribution of the roof structure as different fire scenarios develop. Combined with the fire resistance limit theory of the roof structure, it can be used to determine the critical instability conditions of complex building structures under different fire scenarios, and provide theoretical support for the fire safety performance design of the roof structure and post-disaster damage assessment.

[0033] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A real-time determination method for roof collapse caused by fire in a nuclear power plant oil storage tank room, characterized in that: The following steps are involved: Step S1, using CFD numerical simulation software to simulate the temporal and spatial evolution of the surface temperature field of the roof structure under fire conditions; Step S2, processing the temperature field of the heated surface of the roof structure obtained by the CFD numerical simulation software, and obtaining the time series temperature data of all grid nodes on the heated surface of the roof structure; Step S3, establishing a three-dimensional heat conduction model of the top plate structure by using FEM software; Step S4, seamlessly mapping the time series temperature data obtained by the CFD numerical simulation software to the three-dimensional heat conduction model established by the FEM software to achieve temperature field mapping of the heated surface of the top plate structure; Step S5, performing three-dimensional heat transfer simulation of the top plate structure by using FEM software; Step S6: Use FEM software to simulate the thermal response behavior of the roof structure based on the mapped temperature field, obtain the change of mechanical parameters and stress field distribution of the roof structure, and analyze the critical conditions for instability of the roof structure.

2. A real-time determination method for roof collapse caused by fire in a nuclear power plant oil storage tank room according to claim 1, characterized in that: In step S1, the temporal and spatial evolution of the surface temperature field of the roof structure under fire conditions is simulated by using FDS numerical simulation software. The specific steps are as follows: Step S11: Perform fire hazard analysis based on the actual layout of the nuclear power plant oil storage tank room, design fire scenarios, and complete the construction of the CFD model; Step S12, determine the mesh size range according to the formula in the CFD numerical simulation software user manual, perform temperature comparison analysis, and finally determine the optimal mesh size based on efficiency and accuracy; Step S13, by writing the running code of the CFD numerical simulation software, numbering the top plate structure created in the CFD model group for subsequent data reading, and defining the temperature data of the heating surface of the top plate structure to be output; For composite roof structures, each structural component is numbered in sequence, and the heating surfaces of which the surface temperature field changes due to heat radiation and heat convection under fire are defined respectively, so as to obtain the heating information of different parts of the roof structure; Step S14, define the temperature type to be output, and save the simulation results in the boundary file obtained by the CFD numerical simulation software.

3. A real-time determination method for roof collapse caused by fire in a nuclear power plant oil storage tank room according to claim 2, characterized in that: The specific steps of step S2 include: reading the temperature data of all grid nodes on the heated surface of the top plate structure obtained by simulating the CFD numerical simulation software through the Fortran language, saving it in the boundary file, and converting it into n text files containing the coordinates of all grid nodes and corresponding temperatures on the heated surface of the top plate structure in the CFD model, wherein n=total calculation time of the CFD numerical simulation software / boundary file data output time step.

4. A real-time determination method for roof collapse caused by fire in a nuclear power plant oil storage tank room according to claim 3, characterized in that: The step S3 establishes a three-dimensional heat conduction model of the top plate structure by using ABAQUS numerical simulation software, and the specific steps are as follows: Step S31, based on the heated roof structure to be analyzed in the CFD model, establish a roof structure model with the same size and the same material properties; Step S32, setting the heat transfer analysis step and heat transfer unit type of the FEM model; Step S33, the mesh division of the FEM model is consistent with the mesh division of the CFD model, so as to ensure the consistency of the number of mesh nodes on the heated surface of the top plate structure and achieve a higher precision mapping of the temperature field; Step S34: Finally, the INP file is output as data for subsequent reading and mapping in the Fortran language.

5. A real-time determination method for roof collapse caused by fire in a nuclear power plant oil storage tank room according to claim 4, characterized in that: The specific steps of step S4 are as follows: Step S41, using Fortran language to establish a mapping file, correspond the heated surface of the CFD model to the heated surface of the FEM model component, read the node coordinates in the n text files processed by the CFD boundary file and the INP file output by the FEM model, realize one-to-one mapping of the nodes with the same coordinates, and write the corresponding temperature data to generate n text files with the same format as the CFD boundary file; Step S42, reading the n text files obtained from the FEM model by using the Fortran language, generating an AMP file of each coordinate point changing with time step that can be read by the FEM software, and the file will be imported into the FEM model as an external file; Step S43, using Fortran language to encode the AMP file to generate a BC file readable by FEM software, which contains the time series temperature data corresponding to each node in the FEM model; Step S44: All files obtained by programming in the above steps are saved in the same folder as the INP file. When the INP file is imported into the FEM model, the thermal boundary load from the BC file and the time series temperature data from the AMP file will be automatically loaded.

6. A real-time determination method for roof collapse caused by fire in a nuclear power plant oil storage tank room according to claim 5, characterized in that: The specific steps of step S5 include: Step S51, applying the temperature data of the heating surface of the top plate structure obtained by temperature field mapping to the heating surface of the top plate structure as a thermal boundary condition; Step S52: By defining constraint relationships, the three-dimensional heat conduction effect of the composite roof structure itself and between the structures is realized, and the temperature field distribution of the composite roof structure under different building fire scenarios is obtained.

7. A real-time determination method for roof collapse caused by fire in a nuclear power plant oil storage tank room according to claim 6, characterized in that: The step S6 uses the temperature field obtained by three-dimensional thermal analysis of the FEM model as a predefined field to perform FEM model structural mechanics simulation, thereby determining the critical condition for instability of the roof structure.

8. A real-time determination method for roof collapse caused by fire in a nuclear power plant oil storage tank room according to claim 7, characterized in that: The specific steps of the FEM model structural mechanics simulation include: Step S61, establishing the internal details of the roof structure model according to the actual situation of the roof structure of the oil storage tank room of the nuclear power plant, including the arrangement and assembly of the number and spacing of the force reinforcement and tension reinforcement inside the component, and setting the interaction; Step S62, setting the analysis step, output variable and unit type according to actual needs; Step S63, applying boundary loads according to the actual functions and layout of the building components, including fixed and hinged loads; Step S64, determining the critical instability condition of the roof structure according to the stress, strain, deflection mechanical performance parameters and the fire resistance limit of the roof structure.

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