Assessment of Vehicle Stability Processes Under Unsteady Flow Conditions

ABSTRACT The vehicle stability criteria are based on experimental and theoretical studies that do not account for the unsteady nature of floods. The rapid variation of depths and velocities in floods causes an additional hydrodynamic force in the direction of the flow, destabilising a vehicle that would otherwise be safe in steady flow conditions. This study shows the changes in drag and lift forces when the vehicle encounters a floodfront or experiences accelerating flow past it. The numerical model built with smoothed particle hydrodynamics (SPH) is first validated for its use in studying unsteady flows by comparing it with 1:14 scale physical model results. The SPH model is then further extended to study the variation in drag and lift forces when the flow is accelerated past the vehicle from a steady state. The results show that the hydrodynamic drag can increase by 40%–50% in unsteady flows. This increase varies linearly with the acceleration of flow. Moreover, the build‐up of water in front of a watertight vehicle can further amplify the destabilising forces on the vehicle. It is the first such study wherein the hydrodynamic forces on a partially submerged object in high Reynolds number flow have been studied.