# A Simulation of Tire Hydroplaning Based on Laser Scanning of Road Surfaces
## 3 Test Methods
### Simulation Model
#### 3.2.4. Tire-Fluid-Road Coupling Contact Modeling  
The contact between tires and the road surface is a nonlinear problem, making modeling complex. Abaqus software provides two algorithms for general contact and contact pairs. The general contact algorithm has a simple definition and imposes fewer restrictions on the contact surfaces; the contact pair algorithm is suitable for complex contact behaviors, offering high computational efficiency but requiring strict adherence to contact surfaces. This paper selects the contact pair algorithm to define contact behavior, which includes point-to-surface and surface-to-surface contact types, both of which are solved through discretization. Point-to-surface contact is established by searching for the main surface element from the surface node to create contact elements (Figure 13(a)). The calculation is simple and converges easily, but it tends to produce penetration phenomena, which do not fully match the actual tire-road contact, leading to lower accuracy. Face-to-face contact involves finding adjacent surface patches from nodes and using the N2S method to determine the main surface patch, establishing multiple contact elements (Figure 13(b)). This effectively avoids penetration and aligns with the actual tire-road contact, resulting in higher accuracy. Therefore, this paper adopts face-to-face contact. The main surface and the secondary surface should be defined for face-to-face contact. The selection criteria of the main surface are as follows: the surface with a large stiffness difference is selected; the surface with similar stiffness is selected when the mesh is coarse. In this paper, the road surface contact surface is taken as the main surface, and the tire contact surface is taken as the secondary surface. Contact properties include normal and tangential attributes. Normal contact is divided into hard and soft contact. Hard contact does not allow penetration, with zero clearance allowing infinite pressure (Figure 14(a)); soft contact (exponential, linear, tabular models) allows penetration, with the amount depending on parameters (Figure 14(b)). Hard contact better represents the actual tire-road contact, hence the hard contact model is selected. Figure 14. Contact types: (**a**) node-to-surface contact; (**b**) surface-to-surface contact. Figure 13. Modeling process of water film model: (**a**) water film grid division; (**b**) water film model. Tangential contact includes exponential friction, Coulomb friction and custom model. The Coulomb friction model is simple to calculate and has good convergence, which can be divided into isotropic and anisotropic. In this paper, the isotropic Coulomb friction model is selected to define the tangential contact attribute. The tangential contact properties mainly include the exponential friction model, Coulomb friction model, and custom models. Among these, the Coulomb friction model can describe the running state in the tangential direction of the contact model, which includes two types: isotropic and anisotropic. Compared with other friction models, the Coulomb friction model is characterized by simple calculations and good convergence. Therefore, this paper selects the isotropic Coulomb friction model to define the tangential contact properties between tires and the road surface. To accurately simulate the tire-road contact behavior, the tire boundary conditions are set as follows: release the translational degrees of freedom in the Z direction to simulate vertical loads; constrain the translational and rotational degrees of freedom in the X and Y directions to ensure that the tire only moves vertically. The road surface boundary conditions constrain all six degrees of freedom to simulate a fixed road surface. In static analysis, a tire load along the Z-axis is applied, with a friction coefficient set to 0 to simplify initial contact calculations. In steady-state analysis, the friction coefficient can be adjusted to reflect actual friction behavior.