T. Robinson

A one-dimensional model framework of unsteady free-surface flow through a blocking-drag region is developed, tested, and applied to understand the dam-break flow past a rectangular building. This is achieved by studying the steady-state, adjustment to steady-state, and the unsteady response of a blocking-drag region. Three steady flow regimes are identified based on the Froude number upstream and downstream of a blocking-drag region: a subcritical state, a choked state with a subcritical-supercritical transition, and a supercritical state. The interaction between a dam-break flow and a blocking-drag region can be mostly understood from the quasi-steady analysis using the variation of the Froude number with time, and comparing the upstream and downstream Froude number scatter plots against the steady curve. The force time-series depends on the height of the precursor layer and the position of the blocking-drag region relative to the lock-length. This model provides considerable insight into the types of flow characteristics observed at low/high Froude numbers and goes some way to clarifying the relationship between the drag force and the dam-break flow properties.