Snow contamination of cars: Collisions of ice particles with surfaces

Sammanfattning: Seasonal snow cover on roads causes car accidents that lead to human suffering and economic loss. Snow cover decreases visibility and road-tire friction. Advanced active safety systems have been developed to cope with sudden changes in driving conditions and have been engineered to act as quickly as possible. These systems are heavily reliant on sensors on the exterior of the car that can detect these changes. Snow, however, has a tendency to accumulate and cause sensor blockage, and consequently, the sensors might not be available when they are most needed. The physics of how snow and ice adhere to surfaces must be understood in order to develop measures that avoid snow accumulation. Snow and ice during normal winter temperatures in the northern hemisphere (0 °C to ~-30 °C) are close to the melting point of ice and are therefore thermodynamically active. This fact in combined with small grain sizes causes ice and snow to easily adhere to surfaces. Mathematical models for snow adhesion are developed in this work by studying collisions of ice particles with walls. Based on a general theory for adhesive-elastic interactions, the threshold velocities for ice particles are calculated so that particles that collide with surfaces at velocities below this threshold will adhere to the surface they collide with. Experimental measurements are also conducted on ice particles that collide with different massive walls, and from these measurements, a collisional melting model is proposed to model the abrupt increase in energy loss observed. The two different modeling approaches are combined as a generalized velocity-dependent collision model for ice particles.