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Effects of an Emergent Cylinder in a Group on Water Flows and Evaluation of Hydrodynamic Force

Author(s): Ryo Tomiyama; Tatsuhiko Uchida; Daisuke Kobayashi; Misako Hatono; Satoshi Yokojima

Linked Author(s): Tatsuhiko Uchida, Daisuke Kobayashi, Satoshi Yokojima

Keywords: Drag coefficient; Pressure coefficient; Undisturbed flow; Disturbed flow; Disturbance

Abstract: The heavy rain in July 2018 caused serious flood damage in Hiroshima prefecture. Emergent vegetation in river brings water level rising which leads to flood. It is important to understand the hydrodynamic forces acting on emergent vegetation in rivers for preventing and mitigating the flood disaster. There are many research papers about the density and arrangement of vegetation, however, the research about the effects of a vegetation element on local flow has not been discussed enough. The objective of this study is to examine the characteristics of hydrodynamic forces acting on emergent cylinders focusing the flow changed by a cylinder in the group. In this study, we investigated the distribution of pressure around a cylinder in a group installed in a channel. We define the terms “undisturbed flow”/ “disturbed flow” as the flow without/with the target cylinder and “water surface disturbance” as the water level difference between the undisturbed and disturbed flows. By measuring disturbance, we found undisturbed flow differed depending on flow condition and effected the drag force acting on the target cylinder. Based on undisturbed flow, we proposed an evaluation method of the hydrodynamic force by clarifying the force being composed of four forces components, i.e., the buoyant force component in the streamwise direction, the base component drag force, the drag force component due to water surface deformation, and the drag force component exerted by the streamwise pressure gradient. We also applied the evaluation method to calculate water surface profile calculation for the validation.


Year: 2022

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