Swash-flow induced forces on human body standing on a smooth and impermeable slope: A numerical study with experimental validations

Abstract

ABSTRACT Swash flow poses a significant hazard to pedestrians standing on the slope of the seawall. Unlike the forces of overtopping flow or open channel flow on the human body, which have been studied before, swash flow has two distinct cycles within one wave period: onshore flow and offshore flow. Both cycles can risk human safety by exerting hydrodynamic forces on the body. This paper presents a numerical study to examine the hydrodynamic forces exerted on the human body when subjected to swash flow on a smooth and impermeable slope. A Reynolds-averaged Navier-Stokes (RANS) model is set up in OpenFOAM, where the numerical results are compared with experimental data obtained from wave tank tests. Reasonable agreement has been achieved, which validates the numerical model. We examine the kinematics of swash flow generated by plunging and surging breakers. In the case of a plunging breaker, we observe that the instantaneous runup height exhibited asymmetry, whereas it is nearly symmetric for a surging breaker. The velocity profile is then used to compute the momentum flux of the swash flow, which is shown to be associated with the inline forces exerted on the human body. We have defined an instability index to assess the risk of pedestrian mobilisation by swash flow, demonstrating its dependence on the Iribarren number and the body's position. The analysis reveals that the associated risk is substantially reduced as the Iribarren number increases and when the body moves towards the shoreline.