Slow spreading of fluid mud over a conical surface

Abstract

We investigate the slow spreading of fluid mud over a gently sloped conical surface which may simulate a shallow basin or a hill. The mud is assumed to behave as a Bingham plastic possessing a finite yield stress and the lubrication approximation is used. Because of the finite yield stress, a variety of non-trivial equilibrium profiles can exist, corresponding to the state of deposit at the end of upward or downward motion. Analytical solutions are derived for axially symmetric deposits. It is shown that the front of the final profile in axisymmetric spreading is of a common form in dimensionless variables, independent of the total mud volume. Transient evolutions are then studied numerically by employing a finite-volume scheme for both axially symmetric and asymmetric spreading from a localized source. The characteristic features of the mud pile at different stages of spreading are examined. The final shape in asymmetric spreading is strongly affected by the total volume released and by the rate of discharge.