Experimental study on the instability risk threshold of foot-size vehicles under urban road flooding conditions

Abstract

[Objective] Under the background of rapid urbanization, the frequent occurrence of extreme weather events has led to the intensification of urban road flooding, which has led to vehicle instability, brake failure and other traffic safety problems that are becoming more and more prominent. The study of vehicle instability risk thresholds in flooded water is of great theoretical value and practical significance in the field of flood risk assessment and emergency management. [Methods] The friction coefficients of new and old wheels under different road conditions(dry, wet, and waterlogged) and different loads were investigated experimentally. Taking the Volkswagen Polo as the research object, the rotary bearing and three-axis attitude sensor were used to adjust the direction of the vehicle to meet the flow, and the mechanical sensors and data collector were used to measure the force of the water flow on the vehicle under different water depths and flow rates, so as to reveal the mechanism of the vehicle's destabilization. [Results] The results show that the coefficient of friction μ ranges from 0.320 to 0.898, the coefficient of friction of asphalt pavement with the same wheels is larger than that of cement pavement, and the condition of coefficient of friction under the same pavement condition is as follows: wet condition > dry condition > waterlogged condition, and the coefficient of friction of the new tires is generally larger than that of the old tires. For non-sealed vehicles, when the water depth is greater than 0.45 m, the buoyancy of the car gradually decreases until it sinks to the bottom, and under the same water depth conditions, the buoyancy shows a decreasing trend with the increase of flow velocity. The flow resistance F_D and transverse force F_T of the car increased with the increase of flow velocity and water depth, and the coefficient of flow resistance C_D of the car in different flow directions(0°~180°) ranged from 0.466 to 1.067, and the coefficient of transverse force C_T ranged from 0 to 0.407. [Conclusion] The car is most easily destabilized at 90° in the head-on direction and most difficult to destabilize at 0°. Adopting the bottom line thinking, the friction coefficient is taken as 0.320, and when the product of flow velocity and water depth hυ_min is greater than 0.81 m²·s^-1, the car slides and destabilizes. And fitted curves for the relationship between the critical flow rate threshold for instability and water depth for different headwater directions. The results of the study can provide key parameter support for the development of vehicle instability early warning system, and at the same time, provide scientific basis for the optimization of urban road drainage performance evaluation standard.

Keywords

urban flooding / vehicle instability / risk threshold / friction coefficient / coefficient of resistance to flow bypass / coefficient of lateral force / climate change / risk assessment