# Construction and Application of Safety Management Scenarios at Construction Sites
## 2 Materials and Methods
### Methods of Spatial and Temporal Analysis of Construction Site Elements  
(1) Air conditions at the construction site This study focuses on simulating the outdoor wind environment on a construction site using natural ventilation. The scope of this paper excludes the use of mechanical or artificial means to regulate air conditions. The air pollution index in the simulated outdoor wind environment is assumed to be zero. When modelling the outdoor wind environment at a construction site, two important parameters in terms of air conditions are air density and air viscosity. Density of Air is the mass per unit volume of air at a given temperature and pressure and is calculated by the following formula  
\[AD=1.293\times(AP/SAP)\times(273.15/AAT) \tag{1}\]  
\[AT=CT+273.15 \tag{2}\]  
According to the above equation, the actual absolute temperature (AAT) range of the average maximum outdoor air temperature in Nanjing for all seasons is between 9 \({}^{\circ}\)C and 31 \({}^{\circ}\)C. The air density (AD) in this temperature range is calculated at an absolute pressure (AP) of 0.1 Mpa and 1 standard atmospheric pressure (SAP). Additionally, the result is 1.2 kg/m\({}^{3}\) with one decimal place, according to which, the air density in the wind environment simulation in this study is set to 1.2 kg/m\({}^{3}\). Air viscosity is the value when the friction force per unit area in the air movement of the velocity gradient of 1, its size, and the temperature are closely connected with the formula for its calculation:  
\[\mu=\tau/\frac{dv}{dn} \tag{3}\]  
Where \(\tau\) is the friction force per unit area, and \(\frac{dv}{dn}\) is the velocity gradient. According to the above equation, the air viscosity enlarges with the increase in temperature, and the calculated air viscosity value is approximately equal to 1.8 \(\times\) 10\({}^{-5}\) PaS in the range of the average annual maximum air temperature of 9 \({}^{\circ}\)C-31 \({}^{\circ}\)C in Nanjing area, according to which, the air viscosity is set to 1.8 \(\times\) 10\({}^{-5}\) PaS in the wind environment simulation process in this study. (2) Spatial and temporal modelling approach to the wind environment on construction sites  
Computational Fluid Dynamics (CFD) is a comprehensive discipline formed from the development of computer technology and fluid dynamics. CFD is the fundamental theory used in constructing scenarios. It emerged in the 1960s, and the continuous development of computer technology ensured rapid improvement in the CFD software series during the 1990s. Currently, CFD has replaced the conventional method of manpower in acquiring flow simulation data and serves as a significant tool for computer-based simulations of indoor and outdoor environmental building conditions [33]. In the simulation of the outdoor wind environment of a building, this paper defines the gas flowing around the building as turbulence in the ideal state, which is viscous and incompressible. The standard \(k\)-\(\varepsilon\) model is used to solve the state of the surrounding environment. The gas motion in the flow field primarily involves the continuity equation, momentum equation, and energy equation; additionally, the numerical values are obtained by solving the differential equations, controlling the fluid motion, and deriving the distribution of the flow field in a specific area [34]. The general equation formulation for modelling the outdoor wind environment of a building is as follows [35]:  
\[\frac{\partial(\rho\varnothing)}{\partial t}+div\Big{(}\rho\overset{\rightarrow }{v}\varnothing\Big{)}=div(\Gamma_{\varnothing}grad\varnothing)+S_{\varphi} \tag{4}\]  
where \(\varnothing\) is velocity, turbulent kinetic energy, but also turbulent dissipation rate, and temperature; \(\rho\) is the density (kg/m\({}^{-3}\)); \(\overset{\rightarrow}{v}\) is the velocity vector (m/s); \(\Gamma_{\varnothing}\) is the generalized diffusion coefficient; and \(S_{\varphi}\) is the original item.