The community is one of the main places in a city where humans reside.Community security is an important part of the development of a harmonious society.Fire disaster is one of the main factors that threaten community security.A large number of accidents show that toxic fire fumes and a high-temperature environment are the main causes of casualties.A numerical simulation model can analyze smoke flow and temperature distribution that are caused by fire.Therefore

research on community fire scene simulation models is important to fire rescue and emergency evacuation.Fire scene simulation requires models for indoor and outdoor objects and the environment

as well as a large number of numerical calculations.However

a traditional map cannot meet the aforementioned requirements. In this study

we propose a fire scene numerical simulation model for community security based on a research on indoor and outdoor maps.The model is required to establish the distribution of community objects through traditional mapping technology.It utilizes indoor mapping technology to create the interior scene of buildings.The contents of the indoor map include the door

fire facility

passage

and room range layers.The contents of the outdoor map include community boundaries

transportation

vegetation

residential buildings

fire facilities

and other layers.A 3D fire scene model is reconstructed using 3D modeling technology.A fire numerical equation is imported to calculate the simulation.The model can be displayed in 3D dynamics.The fire numerical simulation is calculated using the Fire Dynamic Simulation (FDS) software

which was developed by the National Institute of Standards and Technology in the USA.FDS solves the fire numerical simulation equation to calculate the smoke diffusion and heat transfer processes in a single grid as a unit.In theory

a fine grid size provides accurate calculation results.Under the same calculating volume conditions

if a fine grid size is designed

then numerous grids will be generated.A subregional variable-scale meshing method is proposed to improve the efficiency of the fire numerical calculation for the complex structure of a community because computation on numerous grids is costly in terms of time.The following three rules should be followed when setting up a subregional variable-scale meshing.First

a number of calculation regions should be divided according to the shapes of the buildings.The different regions of a grid can overlap

abut

or not be in contact.The details of a fire region should not be divided.Second

the grid size should be set according to the complexity of the community structure and the distance from the fire.The section near the fire scene of the entire indoor and outdoor areas divides the fine grid

and the community near the ground also divides the fine grid.The rough grid is divided at the region that cannot be affected by the fire.Third

the abutting regions should follow the mesh boundary alignment.The most important rule of the mesh boundary alignment is that abutting cells should have the same cross-sectional area or integral ratios.We select the community of Hongshuwan as the study area to conduct the fire numerical simulation experiments.We also use three different meshing methods to experiment on the fire scene simulation in Hongshuwan community

namely

fine meshing

rough meshing

and subregional variable-scale meshing. The burning changes of indoor fires can be observed in the results of a single-layer fire simulation model of Hongshuwan community.The fire-burning changes include smoke flow and temperature distribution.We determine that grid size is positively correlated with calculation accuracy by comparing the three meshing methods.Therefore

we set the results of the fine meshing method as the standard to compare the computational accuracy and computational efficiency of the other two meshing methods.For calculation speed

the results of the subregional variable-scale meshing and rough meshing methods are 8 times and 24 times that of the fine meshing method

respectively.The calculation speeds of the subregional variable-scale meshing and rough meshing method are faster than that of the fine meshing method.The temperature simulation results show that the temperature-changing curves of the subregional variable-scale meshing method approximate those of the fine meshing method.The differences between the rough meshing and fine meshing methods are significant.The correlation coefficient of the temperature simulation results between the subregional variable-scale meshing and fine meshing methods is greater than 0.96

which proves that the results of the two methods are highly correlated.Compared with the smoke diffusion results of the fine meshing method

the minimum visibility error of the subregional variable-scale meshing method is 2 m

whereas that of the rough meshing method is 13.5 m.These results show that the smoke simulation accuracy of the subregional variable-scale meshing method is higher than that of the rough meshing method.The simulation accuracy of the subregional variable-scale meshing method is closer to that of the fine meshing method

and its efficiency is higher than that of the fine meshing method. In this study

a simulation model for a community fire scene is constructed to extend the application of an indoor map.The smoke diffusion and temperature distribution laws can be analyzed through the aforementioned fire scene numerical simulation model.Subregional variable-scale meshing can improve simulation efficiency while maintaining the level of simulated accuracy.The model can be applied to fire rescue and emergency evacuation at the community scale.The new approach has an important application value.