Effects of cobble shape on coefficient of drag force

Sang Deog Park; Min Woo Yoon; Young Ho Yoon

doi:10.3741/JKWRA.2017.50.6.419

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2017 Vol.50, Issue 6 Preview Page Next Page

Effects of cobble shape on coefficient of drag force 항력계수에 미치는 호박돌 형상의 영향

30 June 2017. pp. 419-427

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Abstract

In mountainous rivers, the drag force acting on cobbles abundant in the riverbed surface is important in predicting behavior and response of the river. However there is little research for the drag coefficients of cobbles. This paper is to carry out the experiments for drag force of cobble and analyze the relation between the cobble shape and the drag coefficient. The effects of the shape factor on the drag coefficients when the long axis or the short axis of the cobbles are parallel to the direction of flow velocity were analyzed. The coefficient of drag force increased with the nominal diameter Reynolds number . The drag coefficients are greater in short axis than long axis. The coefficient of determination of the relation between and is greater in long axis than short axis. This means that the drag forces acting on the irregularly-shaped cobbles depend on the axis. A change of the drag force distribution has brought about the alternative swing of cobbles. For > 12,000, the amplitude of the swing has been increased sharply and especially was greater in short axis than long axis.

Keywords

Drag coefficient

Cobble

Drag force

Shape factor

River

산지하천 하상에서 흔히 발견되는 호박돌에 작용하는 항력은 하천의 거동과 반응을 예측하는 데 있어서 중요하나 이를 위한 항력계수 연구는 미흡한 실정이다. 본 연구는 호박돌의 항력 실험을 통해서 호박돌 형상과 항력계수의 관계를 분석하였다. 호박돌의 장축과 단축이 흐름방향을 따를 때 항력계수에 미치는 형상계수의 영향을 분석하였다. 항력계수는 장축보다 단축에서 더 크며 호박돌의 등가직경 Reynolds 수가 증가하면 감소하였다. 항력계수와 등가직경 Reynolds 수의 관계에서 결정계수는 단축보다 장축에서 더 크다. 이는 호박돌 형상의 불규칙성에 따른 항력이 축에 따라 변화하기 때문인 것으로 판단된다. 항력분포 변화는 호박돌의 교호진동을 초래하였다. 그 진폭은 가 약 12,000에서 급격히 증가하였으며 장축보다 단축에서 더 큰 것으로 나타났다.

키워드

항력계수

호박돌

항력

형상계수

하천

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Information

Publisher :KOREA WATER RESOURECES ASSOCIATION
Publisher(Ko) :한국수자원학회
Journal Title :Journal of Korea Water Resources Association
Journal Title(Ko) :한국수자원학회 논문집
Volume : 50
No :6
Pages :419-427
Received Date : 2017-05-06
Revised Date : 2017-05-15
Accepted Date : 2017-05-15
DOI :https://doi.org/10.3741/JKWRA.2017.50.6.419

Journal of Korea Water Resources Association ISSN:2799-8746(Print) 2799-8754(Online) 한국수자원학회 논문집

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