A practical drag-equivalent representation method for submerged pile groups in Froude-similar physical models

Study region River, estuarine, and tidal-bay systems containing pile-supported structures, where temporally varying flows can be divided into representative hydraulic conditions. Fangchenggang Port, China, is used as a regional engineering application. Study focus Geometric and Froude similarity preserve the scaled geometry and gravity-dominated flow characteristics of hydrodynamic physical models, but do not necessarily preserve the drag exerted by pile groups on the surrounding flow. This drag dissimilarity can distort how the local influence of pile-supported structures is represented within a larger-scale flow field. We therefore develop drag-similarity criteria based on the overall pile-group drag and the accumulated drag contributions of individual piles, together with an empirical framework accounting for Reynolds number, pile spacing and arrangement, and inflow direction. New hydrological insights for the region The study reveals that pile-supported structures can influence local hydrodynamic responses within regional flow systems and that these effects may be misrepresented when pile groups are scaled only geometrically. Geometric scaling produced excessive pile-group drag, whereas drag-similarity representation provided a closer reproduction of the integrated hydraulic influence of the prototype structure. These findings highlight the importance of considering pile-group drag when representing engineering structures in physical models of natural water systems.