Author(s): Ichiro Kimura; Kakeru Murata; Takaaki Okamoto

Linked Author(s): Ichiro Kimura, Takaaki OKAMOTO

Keywords: Driftwood movement; 3D flow model; URANS; Driftwood capture facility

Abstract: In this study, we developed a 3D-3D type (3D flow – 3D driftwood motion) computational model to simulate the behavior of driftwood movement around an inlet type artificial driftwood capture facility built along a side bank of a channel. URANS type turbulence model was applied to compute unsteady flow behavior duet to shear layer instability at the interface between the inlet and the main channel. A piece of a driftwood was modeled as connected spheres. The collision of driftwood pieces was modeled using discrete element method (DEM). Two-way approach was used between the driftwood movement and the flow. The model was applied to simulate the laboratory experiment by Okamoto et al. (2018). In this experiment, two types of capture inlets with different shapes (rectangular and trapezoidal) were installed at one side of the straight experimental flume with a rectangular shape. Spur dikes were also installed at opposite side of the capture inlet. The experimental results showed that up to 65 % of supplied driftwood pieces were captured at the inlet if the two spur dikes were installed at appropriate locations and the shape of the capture inlet is trapezoidal. However, if spur dikes were not installed, most of driftwood pieces were flown away without entering the capture inlet. The present computations could simulate the fundamental aspects of the behavior of driftwood movement. The computational results also showed that spur dikes and the shape of the inlet are important control factors to increase the capture ratio. It is also pointed out that after some driftwood pieces were captured at the inlet, the capture rate is accelerated because the water flow was decelerated due the drag of the captured driftwood pieces. The computational results also indicated that unsteady large scale turbulent structure due to the shear layer instability at the interface between the capture inlet and the main channel plays important role to entrain driftwood into the capture inlet.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221688

Year: 2022