## 3 Dynamic Contact Analysis of Traction Arc-Toothed Cylindrical Gear Units
### Imposition of Boundary Conditions and Post-Processing  
Transient dynamics are suitable for modeling and analyzing objects subjected to external loads or impacts over time. Solving transient dynamic problems is much more complex than solving hydrostatic equations, and the computational time can increase considerably. Therefore, to accurately solve the dynamic problem, it is necessary to rationally choose the parameters and impose the boundary conditions. 1. **Defining materials** The strength and durability characteristics of the material directly affect the life and reliability of the gear system. Different materials have different strength and fatigue properties; thus, choosing the right material is essential to ensure that the gear system can withstand the loads it is subjected to. We referred to the current G301 high-speed EMU stock traction gear material and defined the material properties of the curved-tooth cylindrical gear in the Workbench as shown in Table 2.  
Using the association function of CREO and ANSYS Workbench, a 3D model of the gear pair built in CREO was imported into the transient dynamics plate of ANSYS Workbench to establish the finite element model. 2. **Gear finite element model meshing** The sparseness, quality, and quantity of the meshing of the finite element model directly affect the accuracy of the analysis results and the elastic deformation of the gear tooth top. Too many grids can greatly increase the speed of computer calculations, and too few grids can lead to inaccurate results. The reason is that when the number of meshes is too large, the size of each element is small, and the system needs to calculate the interactions between a large number of small elements, which may lead to slower computer calculations. On the contrary, when the number of meshes is too small, the element sizes are larger, and the system gives a coarser approximation of the object. This can lead to inaccurate calculations as it does not capture the detailed features and stress changes in the object. Therefore, meshing is one of the most critical steps. Gear contact areas are places of high stress. In this region, the meshing between the gear teeth induces a concentration of high stresses, and a more detailed mesh is required in order to capture the microscopic changes in the load distribution and stress distribution. By encrypting the gear contact area with a high density, the accuracy of the results can be improved, especially for the evaluation of localized stresses and deformations. As long as the error is within the \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Name** & **Modulus of Elasticity \(E\)(Pa)** & **Poisson’s Ratio \(\mu\)** & **Densities \(\rho\)(kg/m3)** \\ \hline Small gear (main wheel) & 2.06 \(\times\) 1011 & 0.29 & 7850 \\ Large gear (driven wheel) & 2.0 \(\times\) 1011 & 0.31 & 7800 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Material parameters of radial cylindrical gear units. allowable range, it is sufficient to take localized encryption in the part of the gear meshing contact area, and the part of the mesh outside the contact area can be automatically divided by the system. Since curved cylindrical gears usually have complex curved surfaces and geometrical features, tetrahedral meshes provide better geometrical adaptability and are able to delineate these irregular shapes more flexibly to accommodate the curves and surfaces of the gears. Tetrahedral meshes typically have high computational accuracy in capturing complex geometries and curved surfaces. This is important for stress analysis and performance simulation of curved cylindrical gears, and mesh independent validation of the model.