3D numerical simulation for equivalent resistance coefficient for flooded built-up areas

Abstract

An equivalent resistance coefficient including the effect of drag caused by structures as well as a bottom friction was investigated for flooded built-up areas. As applying the coefficient into the bottom friction term in the shallow water equation model, relatively larger grids can be used for the drag effect of structures in inundation simulations, In order to investigate the equivalent resistance coefficient, the existing hydraulic experiment using unsubmerged square piers was simulated by using the RANS equation model of FLOW-3D, a 3-dimensional computational fluid dynamics code. The coefficient (n-value) was evaluated by applying the computed data into the Manning's equation. The computations were compared with the experimental results and the semi-analytical formula derived from momentum analysis including drag interaction effects. The computations agreed well with the experimental results and the semi-analytical formula. From the agreement it was confirmed that the drag interaction coefficient evaluated by the measurements was strongly dependent on the interval of piers. From the computations for the case, in which the water depths were much larger than those of the measurements, it was found that when the unsubmerged piers were arranged in a fully developed open channel, the equivalent resistance coefficient increased with 2/3 power of water depth. © 2010 World Scientific Publishing Co. Pte. Ltd.