A Geometrically Motivated Two-Dimensional Collisional Abrasion Model to Resolve the Evolution of Natural Fragment Shapes

In the present paper we propose a geometrically motivated mathematical model, which reveals the key features of natural coastal and fluvial fragment shape evolution from the earliest stages of the abrasion. Our collisional polygon model governs the evolution through an ordinary differential equation (ODE), which determines the rounding rate of initially sharp corners in the function of the size reduction of the fragment. As an approximation, the basic structure of our model adopts the concept of Bloore’s partial differential equation (PDE) in terms of the curvature-dependent local collisional frequency. We tested our model under various conditions and made comparisons with the predictions of Bloore’s PDE. Moreover, we applied the model to discover and quantify the mathematical conditions corresponding to typical and special shape evolution. By further extending our model to investigate the self-dual and mixed cases, we outline a possible explanation of the long-term preservation of initial pebble shape characteristics.