# Numerical Simulation of Oil Pipeline Leakage Diffusion in Dashagou Yellow River Crossing Section
## 3 Geometry of Computational Area  
[PERSON], [PERSON], [PERSON], et al. [32] employs numerical simulation to conduct preliminary studies of the concentration distribution of components under a range of operational conditions, including wind speed, temperature, pipe diameter, leakage direction and leakage aperture ratio. The geometric modeling of this simulation is constructed using ANSYS 2020R1 Spaceclaim software, ANSYS 2020R1 Fluent fluid simulation software is used for the flow calculation of oil leakage, the simulation work is carried out using ANSYS Workbench 2020R1 version, and the simulation is carried out through two stages of simulation work to calculate and analyze the oil leakage of the pipeline.  
In order to simplify the model calculation, the geometric model is generalized to a cube, which is the porous medium fluid domain of the simulation, a round pipe is hollowed out in the cube, and the surface of the round pipe is the wall boundary of the calculation domain (i.e., the leaking oil will not enter into the inside of the pipeline). At the same time, a circular leakage opening is outlined on the surface of the round pipe, in which the \(X\)-axis is the perpendicular pipeline direction, the \(Y\)-axis is the direction of the pipeline, and the \(Z\)-axis is the direction of gravity, i.e., the pendant direction, as shown in the figure below. Direction of gravity, i.e., vertical direction, is shown in Figure 11.  
In order to facilitate the observation of the subsequent simulation results, when the display interface axis shows XZ, the observation direction is the direction of the pipe section, at this time to observe the circular section of the pipe and the soil porous media calculation domain; when the display interface axis is YZ, the observation direction is the direction of the pipe side, at this time to observe the side of the entire pipe and the soil porous media calculation domain.  
Figure 10: Schematic diagram of oil spill process in Dashagou leakage into Yellow River under scenario 4.  
This numerical simulation only simulates the representative leakage port location, leakage port radius and leakage shape. The representative locations of the leakage ports are categorized as (1) the leakage port is located directly above the pipe (top), (2) the leakage port is located directly to the side of the pipe (side) and (3) the leakage port is located directly below the pipe (bottom), as shown in Figure 12.  
Considering that the diameter of the crude oil pipeline in the Dashagou crossing section is \(\Phi\)711 mm and the diameter of the refined oil pipeline is \(\Phi\)508 mm, the size of the leakage opening is usually not larger than 10% of the pipeline diameter; therefore, the radius of the leakage opening in the small leakage scenario is divided into two cases, i.e., (1) 10 mm and (2) 20 mm, and the radius of the leakage opening in the large leakage scenario is 50 mm. In order to examine the change in flow pattern after an oil spill, the flow pattern settings of this simulation work are 30 s after the spill, 15 min after the spill, 30 min after the spill and 1 h after the spill, totaling four flow times. The simulation model of the Dashagou crossing section is buried at a depth of 12 m. Diesel oil is used as the simulation fluid in this simulation model. The simulation flow chart is shown in Figure 13.  
Figure 11: Schematic diagram of geometric modeling of simulation model.  
Figure 12: Schematic diagram of leakage port position (pipeline profile).