عنوان مقاله [English]
Stilling basins with sudden expansions are one of the main energy dissipater structures. Pressure fluctuations in the hydraulic jump leads to severe damages in the stilling basins and it is necessary to be considered in design of structures . On the other hand, roughness cause changes in the behavior of stream line and vortices. Thus, study of pressure fluctuations under laboratory conditions is vital. Present research aimed to study influence of rough bed on pressure fluctuations of S-jump in abrupt expanding stilling basin. Experiments were conducted in a 0.8 m width and 12 m length flume. Channel expansions ratios were 0.33, 0.5, 0.67, and 1 and within the range of Froude number, 2 to 9.5. Also, roughness elements with 3 cm height and specific distance were located in downstream of abrupt expansion. In order to investigate the roughness effects on hydrodynamic pressures, experiments were carried out in two main steps, including smooth bed (77 experiments) and roughened bed (81 experiments). Results showed that roughness decreases intensity of pressure fluctuations in abrupt expansion stilling basin. Also, in sudden expanding sections, due to the formation of lateral vortices, the energy loss increases and the intensity of pressure fluctuations decreases. The reduction rate of maximum pressure fluctuation was 27%, 46%, and 58% for expansion ratio of 0.67, 0.5, and 0.33, respectively.