Journal of Korean Society of Disaster and Security (한국방재안전학회논문집)

Korean Society of Disaster & Security (한국방재안전학회)
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Analysis on the Scour Reduction Effect by Controlling Downflow

하강류 제어를 통한 교각세굴 감소 효과 분석

  • Lee, Ho Jin (School of Civil Engineering. 208, E8-6, Chungbuk National University) ;
  • Oh, Hyoun Sik (School of Civil Engineering. 208, E8-6, Chungbuk National University)
  • Received : 2018.11.15
  • Accepted : 2018.11.27
  • Published : 2018.12.31
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Abstract

Scour protection methods can be categorized as two types: The first is to reduce the horseshoe and wake vortices which are the main reasons for local scour. Either small cylindrical structures or separated vertical deflectors can be placed in front of the pier or the horizontal deflector (or collar) can be attached to the pier like the spoiler to reduce the dynamics of vortical structures. The second is to employ the protection layer to keep the bed material in place, which is a common method with a merit of immediate effect by using block mat or tetrapod. This study examined the effect of scour reduction using the former method. The relationship between the reflector interval and reduction of scour was not clear. It is assumed that the width of the reflector is somewhat correlated with the reduction of the scour. As the KC numbers increases, the Effect of Scour reduction rate is shown to decrease. Also, Scour reduction rate showed a rapid change at $U_R=25$ or KC = 8.

세굴보호방법은 두 가지 형태로 구분할 수 있다. 첫 번째 방법은 국부세굴의 주요 원인인 말굽형와류와 후류와를 감소시키는 방법이다. 소형 원통형구조물 또는 분리된 연직반사판은 교각 앞에 설치하거나 스포일러처럼 교각에 부착하여 와류의 세기를 감소시킬 수 있다. 두 번째 방법은 하상재료를 보호하기 위한 보호층을 설치하는 방법이다. 이 방법은 블록매트 또는 테트라포드를 사용함으로써 즉시 효과를 발휘하는 장점이 있다. 본 연구에서는 첫 번째 방법을 사용하여 세굴감소 효과를 평가하였다. 반사판 간격과 세굴의 감소효과의 관계는 명확하게 나타나지 않았다. 이 것은 반사판의 폭이 세굴 감소와 어느 정도 관계가 있기 때문인 것으로 추측된다. KC 수가 증가함에 따라, 세굴감소 효과는 줄어드는 경향을 보였다. 또한, 세굴감소율은 $U_R=25$ 또는 KC = 8 일 때 급격한 변화를 보였다.

Keywords

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Fig. 1. Separation line on the bed boundary layer

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Fig. 2. Horseshoe vortex in phase space (Sümer et al., 1997)

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Fig. 3. Equilibrium scour depth. Circular pile. Live bed condition(Sǜmer et al., 1992a).

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Fig. 4. Experimental setup

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Fig. 5. Schematic description of deflector attached to the pile

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Fig. 6. Schematic description of deflector attached to the pile

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Fig. 7. Scour reduction ratio by deflector interval

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Fig. 8. Scour reduction ratio by deflector width

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Fig. 9. Relative S/D and Scour reduction ratio according to KC number

Table 1. Wave conditions

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Table 2. Deflector conditions

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References

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