A real-time determination method for roof collapse caused by a fire in the oil storage tank area of a nuclear power plant

Abstract

The present invention discloses a real-time determination method for roof collapse caused by fire in a nuclear power plant oil storage tank area, which relates to the technical field of fire safety design of the roof structure in the nuclear power plant oil storage tank area, and includes: simulating the spatio-temporal evolution process of the surface temperature field of the roof structure under fire conditions; obtaining the time series temperature data of grid nodes; establishing a three-dimensional heat conduction model of the roof structure; realizing the mapping of the temperature field of the heated surface of the roof structure; conducting three-dimensional heat transfer simulation of the roof structure; and analyzing the critical conditions for roof structure instability. By adopting the above real-time determination method for roof collapse caused by fire in a nuclear power plant oil storage tank area, the present invention can realize the mapping of the time series temperature field of the heated surface of the complex roof structure between the CFD numerical simulation software and the FEM software under different fire scenarios in the nuclear power plant oil storage tank area, simulate the real-time structural response behavior of the roof structure in the nuclear power plant oil storage tank area under different fire scenarios, and can be used for the fire safety design and post-disaster damage assessment of the roof structure in the nuclear power plant oil storage tank area.

Description

Technical Field

[0001] The present invention relates to the technical field of fire safety design for the roof structure of the oil storage tank room in a nuclear power plant, and more particularly to a real-time determination method for the collapse of the roof caused by a fire in the oil storage tank room of a nuclear power plant. Background Art

[0002] With the continuous increase in global energy demand and the significant enhancement of environmental protection awareness, nuclear power plants, as a clean and efficient energy supply method, have witnessed rapid development worldwide. The internal layout of a nuclear power plant is complex. Among them, the oil storage tank, as an important facility for storing key media such as lubricating oil and cooling oil required for the nuclear fuel cycle, its safe and stable operation is directly related to the overall safety of the nuclear power plant. However, once a fire is triggered due to equipment failure, human operation error or external factors in the oil storage tank storing flammable and explosive oils, 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 effects, further exacerbating the severity of the accident.

[0003] The roof structure of the oil storage tank room in a nuclear power plant is complex. According to actual functional requirements, it is often necessary to open holes to meet requirements such as ventilation and cable passing, and at the same time, multiple reinforcement bars 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 not only causes the material properties of the roof to decline, but may also trigger a redistribution of internal stresses in the structure, thereby increasing the risk of roof instability. Therefore, how to accurately evaluate the collapse risk of the roof structure under fire and determine its critical instability conditions 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 the oil storage tank room in a nuclear power plant with intricate internal structures and large spatial scales. The complexity of the oil storage tank room not only stems from the precise layout of its internal equipment and the diversity of its structure, but also greatly increases the difficulty of simulating the dynamic behavior of the fire due to its large volume. Conducting full-scale fire experiments not only requires a large amount of financial and human resources, but also is limited by the controllability of the experimental environment and often difficult to accurately replicate the multi-dimensional complexity in the actual fire scenario, including but not limited to key aspects such as the non-linear spread path of the fire and the complex response of the roof structure under multi-dimensional thermal loads.

[0005] In addition, at present, a combination of fluid dynamics CFD numerical simulation software and structural mechanics FEM finite element analysis simulation software is mostly used to simulate the thermal response behavior of building structures under fire. For the invention patent with the authorization announcement number CN104680915B and the name of "Performance-based Fire Protection Method for Subways", it uses Pyrosim to establish the fire physical models of subway tunnels and stations respectively, obtains the relationship between the real temperature of the smoke and time by arranging detectors, takes it as the fire temperature of the lining structure and loads it onto the fire-exposed surface of the lining structure, and simulates the temperature field and mechanical field of the lining structure under this fire temperature, so as to analyze and obtain the fire resistance safety performance of the tunnel lining structure under real fire. For the patent application with the publication number CN114357817A and the name of "Fire Protection Method for Building Aluminum Alloy Structures Based on Fire Resistance Calculation", it calculates the temperature field of each space under the fire scenario through CFD simulation software, calculates the temperature of aluminum alloy components under the fire scenario by using the heat transfer theory method, and conducts thermal-structural coupling analysis and calculation through FEM, with the yield of aluminum alloy material as the failure criterion for the overall structure. For the patent application with the publication number CN106815398A and the name of "Data Conversion Method for Building Fire Temperature Field Based on Multi-field Coupling", it conducts simulation after arranging temperature measurement points in the grid of CFD simulation software, and uses the interpolation method or fitting function method to import the temperature values onto the surface of FEM components 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 analysis methods for the fire safety performance of roof structures under fire have certain limitations, mainly manifested in:

[0007] 1) Indirectness of temperature field calculation and mapping: At present, the calculation of the temperature field of the roof structure under heat is based on the basic theory of fire dynamics, and is obtained through heat transfer analysis and calculation of the space temperature field obtained by CFD simulation (that is, the calculated temperature is the gas-phase boundary temperature of the fire field, and the temperature of the building solid surface still needs to be calculated through the heat transfer formula), and the direct mapping of the surface temperature of the roof structure cannot be realized. In addition, limited by the idealized assumptions of the heat transfer formula, the calculated building surface temperature usually has calculation errors, and at the same time, a large amount of time is required for the analysis of multiple fire scenarios.

[0008] 2) Limitations of the temperature field mapping method: Currently, the temperature field mapping method for fluid dynamics CFD simulation software and structural mechanics FEM simulation software mainly estimates the temperature of areas without temperature measurement points by arranging temperature measurement points (the density of measurement point arrangement is limited), and then using interpolation or fitting function methods. Due to the diversity of interpolation and fitting function methods, it is not applicable to complex fire scenarios and complex roof structures in nuclear power plant storage tank areas, such as multiple fire points burning, non-horizontal roofs containing load-bearing beams, and roofs with multiple holes, etc., which may lead to a large error between the node temperature without temperature measurement points and the actual temperature.

[0009] 3) Lack of a method for real-time judgment of the critical criterion for structural instability: There is a lack of an analysis method for the structural response behavior of the temperature field evolution of the heated surface of the roof structure associated with time during the development process of different fire scenarios.

[0010] Therefore, it is necessary to develop a new method that can efficiently and accurately achieve the temperature field mapping between CFD simulation software and FEM simulation software, simulate the real-time thermal response behavior of the roof structure in nuclear power plant storage tank areas under different fire scenarios, and thus provide reliable theoretical support for the fire safety design and post-disaster damage assessment of the roof structure in nuclear power plant storage tank areas. Summary of the Invention

[0011] The object of the present invention is to provide a real-time determination method for the roof collapse caused by a fire in a nuclear power plant storage tank area, solve the problems raised in the above background technology, and realize the three-dimensional heat transfer temperature field analysis, thermal response behavior simulation, and critical condition determination of structural instability of the roof structure in nuclear power plant storage tank areas under different fire scenarios.

[0012] To achieve the above object, the present invention provides a real-time determination method for the roof collapse caused by a fire in a nuclear power plant storage tank area, including the following steps:

[0013] Step S1: Use CFD numerical simulation software to simulate the spatio-temporal evolution process of the temperature field on the surface of the roof structure under fire conditions;

[0014] Step S2: Process the temperature field of the heated surface of the roof structure simulated by the CFD numerical simulation software to obtain the time series temperature data of all grid nodes on the heated surface of the roof structure;

[0015] Step S3: Establish a three-dimensional heat conduction model of the roof structure through FEM software;

[0016] Step S4: Seamlessly map the time series temperature data obtained by the CFD numerical simulation software into 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;

[0017] Step S5: Perform three-dimensional heat transfer simulation on the roof structure using FEM software;

[0018] Step S6: Perform thermal response behavior simulation on the roof structure based on the mapped temperature field using FEM software to obtain the changes in mechanical parameters and stress field distribution of the roof structure, and analyze the critical conditions for roof structure instability.

[0019] Preferably, in step S1, the spatio-temporal evolution process of the surface temperature field of the roof structure under fire conditions is simulated using FDS numerical simulation software, and the specific steps are as follows:

[0020] Step S11: Conduct a fire hazard analysis based on the actual layout of the nuclear power plant's oil storage tank area, design a fire scenario, and complete the construction of the CFD model;

[0021] Step S12: Determine the grid size range according to the formula in the user manual of the CFD numerical simulation software, conduct temperature comparison analysis, and finally determine the optimal grid size based on efficiency and accuracy;

[0022] Step S13: Number the roof structure created in the CFD model group by writing the running code of the CFD numerical simulation software for subsequent data reading, and at the same time define the temperature data of the heated surface of the roof structure to be output;

[0023] For the composite roof structure, number each structural component in sequence, and respectively define the heated surfaces of the surface temperature field changes caused by thermal radiation and thermal convection in the fire field for each component, so as to obtain the heating information of different parts of the roof structure;

[0024] Step S14: Define the type of temperature to be output, and save the simulation results in the boundary file obtained by the CFD numerical simulation software.

[0025] Preferably, the specific steps of step S2 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 Fortran language and saving it in the boundary file, so that it is converted into n text files containing the coordinates and corresponding temperatures of all grid nodes on the heated surface of the roof structure in the CFD model, where n = total calculation duration of the CFD numerical simulation software / time step of boundary file data output.

[0026] Preferably, in step S3, a three-dimensional heat conduction model of the roof structure is established using ABAQUS numerical simulation software, and the specific steps are as follows:

[0027] 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;

[0028] Step S32: Set the heat transfer analysis step and heat transfer element type of the FEM model;

[0029] Step S33: Keep the mesh division of the FEM model consistent with that of the CFD model to ensure the same number of grid nodes on the heated surface of the roof structure and achieve a higher-precision mapping of the temperature field;

[0030] Step S34: Finally, output the INP file as the data for subsequent reading and mapping in Fortran language.

[0031] Preferably, the specific steps of step S4 are as follows:

[0032] Step S41: Use Fortran language to establish a mapping file, map 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 after processing the CFD boundary file and the INP file output by the FEM model, achieve a one-to-one mapping of the same coordinate nodes, and write the corresponding temperature data to generate n text files with the same format as the CFD boundary file;

[0033] Step S42: Read the n text files obtained from the FEM model through Fortran language to generate an AMP file that can be read by the FEM software for each coordinate point changing with the time step. This file will be imported into the FEM model as an external file;

[0034] Step S43: Encode the AMP file using Fortran language to generate a BC file that can be read by the FEM software, which contains the time series temperature data corresponding to each node in the FEM model;

[0035] Step S44: All the files obtained through programming in the above steps and the INP file are saved in the same folder. 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.

[0036] Preferably, the specific steps of step S5 include:

[0037] Step S51: Based on the temperature data of the heated surface of the roof structure obtained from the temperature field mapping, apply it as the thermal boundary condition on the heated surface of the roof structure;

[0038] Step S52: By defining the constraint relationship, achieve the three-dimensional heat conduction effect of each structure of the composite roof structure itself and between each structure, and obtain the temperature field distribution of the composite roof structure under different building fire scenarios.

[0039] Preferably, the temperature field obtained by three-dimensional thermal analysis through the FEM model in step S6 is used as a predefined field for structural mechanics simulation of the FEM model, and then the critical condition of roof structure instability is determined.

[0040] Preferably, the specific steps of the structural mechanics simulation of the FEM model include:

[0041] Step S61: Establish the internal details of the roof structure model according to the actual situation of the roof structure of the nuclear power plant oil storage tank area, including the arrangement and assembly of the number and spacing of internal stress bars and tension bars in the components, and set the interactions;

[0042] Step S62: Set the analysis steps, output variables and element types according to actual requirements;

[0043] Step S63: Apply boundary loads according to the actual functions and layouts of building components, including fixed and hinge loads;

[0044] Step S64: Determine the critical condition of roof structure instability according to the mechanical property parameters of stress, strain, deflection and the fire resistance limit of the roof structure.

[0045] Therefore, the present invention adopts the above-mentioned real-time determination method for roof collapse caused by fire in the nuclear power plant oil storage tank area, and has the following specific beneficial effects:

[0046] (1) The present invention can provide an efficient and relatively accurate CFD-FEM temperature field mapping method. By processing the CFD boundary file with 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 errors caused by interpolation with temperature measurement points.

[0047] (2) The present invention can simulate the three-dimensional heat transfer process and thermal response process caused by non-uniform heating of the composite roof structure under different fire scenarios. Through the temperature field mapping of CFD-FEM, the non-uniform temperature field distribution on the heated surface of the roof structure caused by different fire scenarios can be obtained, solving the problems of one-dimensional heat transfer in CFD and uniform heat transfer caused by directly loading thermal boundary conditions on the FEM model, resulting in a uniform temperature field distribution.

[0048] (3) The present invention can realize the comprehensive analysis of the structural response behavior of the composite roof structure under different fire scenarios and the development and evolution process of the real fire scenario, providing a reference for the determination of heat-induced instability of the roof structure in different fire fields and the post-disaster damage assessment.

[0049] The technical solutions of the present invention will be further described in detail below with reference to the drawings and embodiments. Description of the Drawings

[0050] Figure 1 For the CFD simulation of different fire scenarios of the single and composite roof structures of the present invention, where (a) is the single-fire source fire scenario, (b) is the double-fire source fire scenario, and (c) is the fire scenario of the load-bearing beam structure;

[0051] Figure 2 For the efficient mapping of the temperature fields of single-fire source CFD and FEM at the same moment 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;

[0052] Figure 3 For the efficient mapping of the temperature fields of double-fire source CFD and FEM at the same moment 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;

[0053] Figure 4 For the efficient mapping of the temperature fields of the floor slab of the load-bearing beam structure of CFD and FEM at the same moment of the present invention, where (a) is the schematic diagram of the load-bearing beam structure, (b) is the temperature distribution field of the left floor slab, (b1) is the surface temperature field of FDS, (b2) is the surface temperature field of ABAQUS, (c) is the temperature distribution field of the right floor slab, (c1) is the surface temperature field of FDS, and (c2) is the surface temperature field of ABAQUS;

[0054] Figure 5 For the efficient mapping of the temperature fields of the left heated surface of the load-bearing beam structure of CFD and FEM at the same moment of the present invention, where (a) is the schematic diagram of the left heated surface structure of the load-bearing beam, (b) is the temperature distribution field, (b1) is the surface temperature field of FDS, and (b2) is the surface temperature field of ABAQUS;

[0055] Figure 6 For the efficient mapping of the temperature fields of the right heated surface of the load-bearing beam structure of CFD and FEM at the same moment of the present invention, where (a) is the schematic diagram of the right heated surface structure of the load-bearing beam, (b) is the temperature distribution field, (b1) is the surface temperature field of FDS, and (b2) is the surface temperature field of ABAQUS;

[0056] Figure 7 For the efficient mapping of the temperature fields of the lower heated surface of the load-bearing beam structure of CFD and FEM at the same moment of the present invention, where (a) is the schematic diagram of the lower heated surface structure of the load-bearing beam, (b) is the temperature distribution field, (b1) is the surface temperature field of FDS, and (b2) is the surface temperature field of ABAQUS;

[0057] Figure 8 For the verification of the accuracy of the temperature data mapped by single-fire source CFD and FEM of the present invention, where (a) is the CFD simulation temperature field, (b) is the FEM calculation temperature field, and (c) is the comparison of the CFD-FEM temperature data;

[0058] Figure 9 For the verification of the accuracy of the mapped temperature data between the dual - ignition sources of the CFD and FEM of the present invention. Among them, (a) is the CFD - simulated temperature field, (b) is the FEM - calculated temperature field, and (c) is the comparison of the CFD - FEM temperature data;

[0059] Figure 10 For the verification of the accuracy of the mapped temperature data between the CFD and FEM of the left side of the floor slab with a load - bearing beam structure of the present invention. Among them, (a) is the CFD - simulated temperature field, (b) is the FEM - calculated temperature field, and (c) is the comparison of the CFD - FEM temperature data;

[0060] Figure 11 For the verification of the accuracy of the mapped temperature data between the CFD and FEM of the heated surface on the left side of the load - bearing beam structure of the present invention. Among them, (a) is the CFD - simulated temperature field, (b) is the FEM - calculated temperature field, and (c) is the comparison of the CFD - FEM temperature data;

[0061] Figure 12 For the three - dimensional temperature field distribution of the roof structure under the condition of single - ignition - source fire simulated by FEM of the present invention. Among them, (a) is the heated surface, (b) is the back of the heated surface, and (c) is the side of the heated surface;

[0062] Figure 13 For the three - dimensional temperature field distribution of the roof structure under the condition of dual - ignition - source fire simulated by FEM of the present invention. Among them, (a) is the heated surface, (b) is the back of the heated surface, and (c) is the side of the heated surface;

[0063] Figure 14 For the three - dimensional temperature field distribution of the load - bearing beam floor slab structure simulated by FEM of the present invention. Among them, (a) is the heated surface, (b) is the back of the heated surface, and (c) is the side of the heated surface;

[0064] Figure 15 For the thermal response behavior of the load - bearing beam structure at 6 s 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;

[0065] Figure 16 For the thermal response behavior of the load - bearing beam structure at 21 s 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;

[0066] Figure 17 For the thermal response behavior of the load - bearing beam structure at 39 s 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;

[0067] Figure 18This is the determination diagram of the instability critical point of the concrete material on the left heat-receiving surface of the load-bearing beam structure of the present invention. Among them, (a) is the thermal response nephogram of the left heat-receiving surface structure of the load-bearing beam, (b) is the concrete stress change curve of the left heat-receiving surface of the load-bearing beam, and (c) is the concrete damage change curve of the left heat-receiving surface of the load-bearing beam;

[0068] Figure 19 This is the determination diagram of the instability critical point of the concrete material of the floor slab of the load-bearing beam structure of the present invention. Among them, (a) is the thermal response nephogram of the left floor slab structure, (b) is the concrete stress change curve of the left floor slab, and (c) is the concrete damage change curve of the left floor slab. Specific embodiments

[0069] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0070] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the field to which the present invention belongs. The "first", "second" and similar terms used in the present invention do not denote any order, quantity or importance, but are only used to distinguish different components. The terms such as "including" or "comprising" mean that the elements or objects appearing before the term cover the elements or objects listed after the term and their equivalents, without excluding other elements or objects. The terms such as "connected" or "coupled" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The terms such as "upper", "lower", "left" and "right" are only used to represent relative positional relationships, and when the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0071] Embodiment

[0072] Please refer to Figure 1-19 , the present invention provides a real-time determination method for the collapse of the roof caused by a fire in a nuclear power plant oil storage tank room, including the following steps:

[0073] Step S1: Use CFD numerical simulation software (fluid dynamics numerical simulation software) to simulate the spatio-temporal evolution process of the surface temperature field of the roof structure under fire conditions. The spatio-temporal evolution process of the surface temperature field of the roof structure under fire conditions is simulated by FDS numerical simulation software. FDS numerical simulation software is PyroSim fire simulation software, which can visually output the simulation results of the fire process. The simulation process includes establishing a CFD model according to the actual building fire scenario, grid independence analysis, defining the heat output surface of the roof structure, and defining the temperature type of the heat-receiving surface of the roof structure. The specific steps are as follows:

[0074] Step S11: Conduct a fire hazard analysis based on the actual layout of the nuclear power plant's oil storage tanks, design a fire scenario, and complete the construction of the CFD model;

[0075] Step S12: Determine the grid size range according to the formula in the user manual of the CFD numerical simulation software, conduct a temperature comparison analysis, and finally determine the optimal grid size based on efficiency and accuracy;

[0076] Step S13: By writing the running code of the CFD numerical simulation software, number the roof structures created in the CFD model group for subsequent data reading, such as obstruction#1;

[0077] Meanwhile, define the temperature data of the heated surface of the roof structure 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 negative y direction, 3 represents the positive z direction, and -3 represents the negative z direction;

[0078] For the composite roof structure, number each structural component in the order of 1, 2..., and respectively define the heated surfaces of the surface temperature field changes caused by thermal radiation and thermal convection under the fire, so as to obtain the heating information of different parts of the roof structure;

[0079] Step S14: Define the temperature type to be output, such as BNDF QUANTITY='WALL TEMPERATURE' / , that is, output the temperature of the heated surface of the roof structure, and the results will be saved in the boundary files obtained by the CFD simulation, in the format of CHID_n.bf (n = 0001, 0002...).

[0080] Step S2: Process the temperature field of the heated surface of the roof structure obtained by the CFD numerical simulation software to obtain 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 Fortran language and saving them in the boundary file, so that it is converted into n text files containing the coordinates and corresponding temperatures of all grid nodes on the heated surface of the roof structure in the CFD model, where n = the total calculation duration of the CFD numerical simulation software / the data output time step of the boundary file.

[0081] Step S3: Establish a three-dimensional heat conduction model of the roof structure using FEM software (finite element analysis and simulation software). FEM software is a finite element analysis and simulation software with extensive simulation capabilities, capable of simulating and analyzing many problems in the engineering field, such as heat conduction problems under fire conditions, and at the same time being able to solve stress / displacement problems after a fire, and well analyzing the performance changes of components under fire conditions. Establish a three-dimensional heat conduction model of the roof structure using ABAQUS numerical simulation software, including the modeling of the roof structure, the establishment of the heat analysis model, the meshing, the establishment of the node set, and the creation of the FEM model output file. The specific steps are as follows:

[0082] 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;

[0083] Step S32: Set the heat transfer analysis step and the heat transfer element type of the FEM model;

[0084] The meshing of the FEM model is kept consistent with that of the CFD model to ensure that the number of grid nodes on the heated surface of the roof structure is the same, and to achieve a higher-precision mapping of the temperature field;

[0085] Step S34: Finally, output the INP file (FEM model file) as the data for subsequent reading and mapping in Fortran language.

[0086] 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 way the CFD software simulates the temperature field on the surface of the roof structure during the fire development process is to insert the values at each grid node by interpolation method and use the linear interpolation method to present the complete one-dimensional temperature field distribution. Similarly, after applying the heat boundary temperature conditions to all the grid nodes on the heated surface of the FEM model, it also presents the temperature field distribution on this one-dimensional plane in a linear interpolation manner. Therefore, by mapping the temperature data of all the grid nodes on the heated surface of the roof structure in the CFD model to all the grid nodes on the heated surface of the FEM roof structure, the complete temperature field mapping of the two can be achieved. The process of mapping the node temperatures is as follows:

[0087] Step S41: Use Fortran language to establish a mapping file, correspond the heated surface of the CFD model construction to the heated surface of the FEM model components, read the node coordinates in the n text files processed by the CFD boundary file and the INP file output by the FEM model, achieve a 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;

[0088] Step S42: Read the n text files obtained from the FEM model using Fortran language to generate an AMP file (time series temperature value file) that can be read by the FEM software for each coordinate point varying with the time step. This file will be imported into the FEM model as an external file.

[0089] Step S43: Encode the AMP file using Fortran language to generate a BC file (thermal boundary load file) that can be read by the FEM software, which contains the time series temperature data corresponding to each node in the FEM model.

[0090] Step S44: All the files obtained through 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.

[0091] Step S5: Perform three-dimensional heat transfer simulation of the roof slab structure using the FEM software. The specific steps include:

[0092] Step S51: Based on the temperature data of the heated surface of the roof slab structure obtained from the temperature field mapping, apply it as the thermal boundary condition to the heated surface of the roof slab structure.

[0093] Step S52: By defining the constraint relationship, realize the three-dimensional heat conduction effect of each structure of the composite roof slab structure itself and between structures, and obtain the temperature field distribution of the composite roof slab structure under different building fire scenarios.

[0094] Step S6: Perform simulation of the thermal response behavior of the roof slab structure based on the mapped temperature field using the FEM software to obtain the changes in the mechanical parameters and the stress field distribution of the roof slab structure, and analyze the critical conditions for the instability of the roof slab structure. Specifically, the temperature field obtained through three-dimensional thermal analysis by the FEM model is used as the predefined field to perform the structural mechanics simulation of the FEM model, and then the critical conditions for the instability of the roof slab structure are determined. The structural mechanics simulation of the FEM model mainly includes establishing the internal details of the building component model, importing the temperature field data obtained from the three-dimensional thermal analysis, setting the basic parameters, applying the boundary loads, and performing the stress field analysis. The specific steps include:

[0095] Step S61: Establish the internal details of the roof slab structure model according to the actual situation of the roof slab structure of the nuclear power plant oil storage tank area, including the arrangement and assembly of the number and spacing of the internal stress bars and tension bars in the components, and set the interactions.

[0096] Step S62: Set the analysis steps, output variables, and element types according to the actual needs.

[0097] Step S63: Apply boundary loads according to the actual functions and layouts of the building components, including the loads of fixed and hinge supports.

[0098] Step S64: Determine the critical instability condition of the roof structure according to the mechanical property parameters of stress, strain, and deflection, as well as the fire resistance limit of the roof structure.

[0099] Therefore, by adopting the above real-time determination method for roof collapse caused by fire in the nuclear power plant oil storage tank area, the present invention can simulate the three-dimensional heat transfer temperature field distribution, mechanical parameter changes, and stress field distribution of the roof structure during the development process of different fire scenarios. Combining with the fire resistance limit theory of the roof structure, it can be applied to determine the critical instability conditions of complex building structures under different fire scenarios, providing theoretical support for the fire safety performance design and post-disaster damage assessment of the roof structure.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements do not make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A real-time determination method for the collapse of the roof caused by a fire in the oil storage tank area of a nuclear power plant, characterized in that, It includes the following steps: Step S1: Use CFD numerical simulation software to simulate the spatio-temporal evolution process of the surface temperature field of the roof structure under fire conditions; Step S2: Process the temperature field of the heated surface of the roof structure obtained by the CFD numerical simulation software to obtain the time series temperature data of all grid nodes on the heated surface of the roof structure; Step S3: Establish a three-dimensional heat conduction model of the roof structure through FEM software; Step S4: Seamlessly map the time series temperature data obtained by the CFD numerical simulation software into the three-dimensional heat conduction model established by the FEM software to achieve the mapping of the temperature field of the heated surface of the roof structure; The specific steps of step S4 are as follows: Step S41: Use Fortran language to establish a mapping file, map 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, achieve one-to-one mapping of the same coordinate nodes, and write the corresponding temperature data to generate n text files with the same format as the CFD boundary file; Step S42: Read the n text files obtained from the FEM model through Fortran language to generate an AMP file in which the temperature changes with time steps for each coordinate point can be read by the FEM software, and this file will be imported into the FEM model as an external file; Step S43: Encode the AMP file using Fortran language to generate a BC file that can be read by the FEM software, which contains the time series temperature data corresponding to each node in the FEM model; Step S44: All the 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; Step S5: Conduct three-dimensional heat transfer simulation of the roof structure through FEM software; Step S6: Conduct a thermal response behavior simulation of the roof structure based on the mapped temperature field through FEM software to obtain the changes in the mechanical parameters and the stress field distribution of the roof structure, and analyze the critical conditions for the instability of the roof structure.

2. The real-time determination method for roof collapse caused by fire in the nuclear power plant oil storage tank area according to claim 1, characterized in that, In step S1, the spatio-temporal evolution process of the surface temperature field of the roof structure under fire conditions is simulated through FDS numerical simulation software. The specific steps are as follows: Step S11: Conduct a fire risk analysis based on the actual layout of the nuclear power plant oil storage tank area, design a fire scenario, and complete the construction of the CFD model; Step S12: Determine the grid size range according to the formula in the user manual of the CFD numerical simulation software, conduct temperature comparison analysis, and finally determine the optimal grid size based on efficiency and accuracy; Step S13: Number the roof structure created in the CFD model group by writing the running code of the CFD numerical simulation software for subsequent data reading, and at the same time define the temperature data of the heated surface of the roof structure that needs to be output; For the composite roof structure, number each structural component in turn, and respectively define the heated surfaces on which the surface temperature field changes due to thermal radiation and thermal convection in the fire field, so as to obtain the heat receiving 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 from the CFD numerical simulation software.

3. The real-time determination method for roof collapse caused by a fire in a nuclear power plant's oil storage tank area according to claim 2, characterized in that, The specific steps of step S2 are as follows: Read the temperature data of all grid nodes on the heated surface of the roof structure obtained from the CFD numerical simulation software through Fortran language, save it in the boundary file, and convert it into n text files containing the coordinates and corresponding temperatures of all grid nodes on the heated surface of the roof structure in the CFD model, where n = total calculation duration of the CFD numerical simulation software / data output time step of the boundary file.

4. The real-time determination method for roof collapse caused by fire in the nuclear power plant oil storage tank room according to claim 3, characterized in that, In step S3, establish a three-dimensional heat conduction model of the roof structure through the ABAQUS numerical simulation software. 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: Set the heat transfer analysis step and heat transfer element type of the FEM model. Step S33: Keep the mesh division of the FEM model consistent with that of the CFD model to ensure the same number of grid nodes on the heated surface of the roof structure and achieve a higher-precision mapping of the temperature field. Step S34: Finally, output the INP file as the data for subsequent reading and mapping by Fortran language.

5. The real-time determination method for roof collapse caused by a fire in a nuclear power plant's oil storage tank area according to claim 4, characterized in that, The specific steps of step S5 are as follows: Step S51: According to the temperature data of the heated surface of the roof structure obtained from the temperature field mapping, apply it as the thermal boundary condition on the heated surface of the roof structure. Step S52: By defining the constraint relationship, realize the three-dimensional heat conduction effect of each structure of the composite roof structure itself and between structures, and obtain the temperature field distribution of the composite roof structure under different building fire scenarios.

6. The real-time determination method for roof collapse caused by fire in the nuclear power plant oil storage tank area according to claim 5, characterized in that: In step S6, use the temperature field obtained from the three-dimensional thermal analysis of the FEM model as the predefined field to conduct the structural mechanics simulation of the FEM model, and then determine the critical condition of roof structure instability.

7. The real-time determination method for roof collapse caused by fire in the nuclear power plant storage tank area according to claim 6, wherein The specific steps of the structural mechanics simulation of the FEM model are as follows: Step S61: According to the actual situation of the roof structure of the nuclear power plant oil storage tank room, establish the internal details of the roof structure model, including the arrangement and assembly of the number and spacing of internal stress bars and tension bars in the components, and set the interactions. Step S62: Set the analysis step, output variables and element type according to the actual needs. Step S63: Apply boundary loads according to the actual functions and layouts of the building components, including the loads of fixed and hinge. Step S64: Determine the critical condition of roof structure instability according to the mechanical property parameters of stress, strain, deflection and the fire resistance limit of the roof structure.

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