Analysis On The Stability Of Indoor Fire And Three-dimension Numerical Simulation

Fire research includes the cause, the development process, the prevention and control method as well as mechanism of the fire. It relates to the basic theory of catastrophology science, engineering physics, structure engineering, safety engineering, electronic/information engineering, system engineering and computer science, etc. Fire hazard exhaustive, yet the final analysis attributes to the process of ignition, spreading, gas fume transmission, evacuation, and fire extinction, from which we may get access to the law of fire evolution. The evolution of building fire hazards presents both randomness and certainty. The happening time, place and burning process reflect randomness, while the certainty embodies in the whole procedure follow the conservation of energy, momentum, components of concentration. The article focuses on analyzing the basic law of fire occurrence, development and nonlinear dynamic characteristics, and by studying the common matters of supermarket fire hazard, to obtain the mechanism of fire occurrence, development and spreading, thus to verify fire protection design, fire risk detection and the effect of extinguishing system. Base on the analysis above, we may make objective assessment on fire protection design of new buildings like supermarket, and also on fire safety conditions of existing buildings. Consequently, to propose effective, economic and reasonable suggestions on performance-based fire prevention design.The main content and result are as follows:(1) Analyzing the common Structure Characteristics and fire risk of large space buildings (e.g. supermarket), comparing the rationale and application scope of different fire hazard mode and simulation method, laying emphasis on the simulation software and working mechanism of zone mode and field mode, from which to select the zone mode analog software CFAST to simulate fire hazard in the single room, and to select field mode analog software FDS to simulate fire hazard in the large space stores.(2) Building the single chamber mode and set the warehouse as an example, and set the parameters of surrounding environment, the thermal boundary conditions and the heat release rate, to simulate fire evolution process in the single chamber. As a result, we obtain the indoor average temperature variation law over time, and the variation tendency of temperature, gas cloud height and concentration of harmful gas component under different spraying condition, sunch as fire power, ventilation, mechanicl exhaust smoke and sprinkler system;(3) On the basis of fire progress analysis, the article focus on researching the stability of the process and the critical condition of flashover, building differential equations to represent fire procedure, proceeding numerical calculation through MATLAB, finding out characteristic value of system matrix Jacobi and time evolution rule, describing the current stage of fire and the critical condition of flashover in view of characteristic value-time curve. From the temperature-time curve T(n)～T(n+1). the article further verifies the critical condition of flashover, explaining the evolution of fire, the nonlinear dynamic system, burning process;(4) Establish field mode of supermarket via FDS, setting the thermal boundary conditions and fire source parameters, considering different factors under different conditions, to attain dynamic graphic of flue gas diffusion, i.e. time curve over temperature, gas cloud height, CO and O2density, thus to analyze the fire evolution law for the large space buildings.The action of influential factors on fire process is studied by numerical simulation and computation in this paper. It obtains the variation of gas temperature, gas cloud height and density of carbon monoxide with time under different spraying condition; it also analyses the critical stability of flashover in the fire process and the variation of temperature in different condition of wall factors and zone size with time; It gets the special characteristics of fire spread and smoke movement inside supermarket. it analyzed the laws of smoke spread and temperature, speed, concentration of various components distribution. According to the above conclusions, it can analyse fire dangerousness in structure, and provides some theory results and foundations for performance-based fire protection design for different buildings, and make firesafty ecaluation for buildings.