3D–3D Computations on Submerged-Driftwood Motions in Water Flows with Large Wood Density around Driftwood Capture Facility

Ichiro Kimura,Taeun Kang,Kazuo Kato

doi:10.3390/w13101406

Ichiro Kimura, Taeun Kang + Show 1 more

Open Access

https://doi.org/10.3390/w13101406

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Abstract

The accumulation of driftwood during heavy rainfall may block river channels and damage structures. It is necessary to mitigate such effects by periodically capturing and removing driftwood from rivers. In this study, the behavior of driftwood in open-channel flows with a relatively large wood density was modeled numerically. The water flow and driftwood motion were solved three-dimensionally, with an Euler-type flow model coupled with a Lagrange-type driftwood motion model. A piece of driftwood was modeled as a set of connected spherical elements in a straight line for easy analysis using a discrete element method. Wood with specific gravity exceeding 1 will travel along a position near the riverbed and will be affected by bed friction. In addition, friction forces for sliding and rolling motions are considerably different. Therefore, in the numerical model, a bed friction term was introduced between the bed and driftwood considering the anisotropy of the friction force. The variation in the drag force of water flow on driftwood was also considered depending on the angle between the driftwood trunkwise direction and flow direction. The model was applied under the same conditions as those used in a laboratory experiment on driftwood behavior around an inlet-type driftwood capture facility. The computational results showed that the proposed model could qualitatively reproduce the driftwood behavior around the capture facility. The secondary flow patterns at the approaching reach and the capture ratio were found to be strongly affected by the turbulence model and the Manning roughness coefficient.

Highlights

A common characteristic of recent disasters caused by heavy rainfall is the outflow of a large amount of driftwood and the consequent destruction of river structures such as bridges and houses or the blockage of river channels due to the accumulation of driftwood.To mitigate the effects of these disasters, measures to control the generation of driftwood and to capture and remove driftwood that has flowed out into the river channel can be considered
With regard to the sliding friction μt, we considered the difference between the static friction coefficient μts and dynamic friction coefficient μtk
We examined the structure of the secondary current of the first kind induced by an imbalance in the centrifugal force, which is considered to have a major effect on the driftwood behavior in the curved part

Summary

Introduction

To mitigate the effects of these disasters, measures to control the generation of driftwood and to capture and remove driftwood that has flowed out into the river channel can be considered. The former methods are not realistic because driftwood can be generated from a wide variety of locations. One of the typically used facilities involves the creation of a bypass channel or cove on the side bank of the river to guide the driftwood and capture it. Because the driftwood storage area is inevitably set up at a location that is divergent from the main stream area, it is difficult to efficiently guide the driftwood to the storage area

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