Author(s): Y Shoji; E. Kobayashi; K. Ishii; Y. Shimizu; I. Kimura
Linked Author(s): Ichiro Kimura, Yasuyuki Shimizu
Keywords: Horizontal-2D numerical analysis; Sediment transport; Riverbed evolution; Dam reservoir; Broad area; High-speed calculation; Parallelization; Open-MP
Abstract: In Japan, many dams have sediment issues that affect the environment of river basins downstream, cause flood damage in upstream areas, etc. One efficient method for the removal of sediment at dams is to discharge it downstream from spillway gates. This has the advantage of a lower cost for sediment removal and it supplies material to form riverbeds downstream in order to resolve environmental concerns arising from a lack of river sands. For this reason, when discharging sediments from spillway gates, it is necessary to precisely study and investigate hydraulic phenomena in dam reservoirs, especially behind dams. A horizontal-2D numerical calculation is one of the practicable methods for analyzing these phenomena compared with 3D calculation methods due to computation capacity. However, for broad areas such as reservoirs with a length of over 10 km using a computation grid size of approximately 10-20 m, there are cases in which a2D calculation method will also have some difficulty in its calculation time. In this study, firstly, dissimilarities of calculation results such as currents and riverbed fluctuations were confirmed on the basis of differences in computation grid sizes, and different schemes for advective terms and turbulence models. Next, Open-MP was introduced into the calculation process for parallelization. Finally, appropriate combinations of methods were studied in order to practically use the horizontal-2D numerical calculation method (Nays2D) for the event mentioned above in comparison with computation time and calculation results such as reproduction of actual phenomena.