Ecology and Resilient Infrastructure

Korean Society of Ecology and Infrastructure Engineering (응용생태공학회)
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Analysis of Bed Shear Stress Distributions in Compound Open Channels Using Large Eddy Simulation.

LES를 이용한 복단면 개수로의 바닥전단응력 분포특성 분석

  • Lee, Du Han (River Experiment Center, Korea Institute of Civil Engineering and Building Technology)
  • 이두한 (한국건설기술연구원 하천실증연구센터)
  • Received : 2018.10.09
  • Accepted : 2018.11.28
  • Published : 2018.12.31
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Abstract

In river design, consideration of bed shear stresses is necessary to secure stability of levee and floodplain. In this study distributions of bed shear stresses in compound open channels are analyzed through numerical simulation for various width and depth. LES solver in OpenFOAM is applied to 12 cases of compound channel shapes considering secondary flow which effects distributions of bed shear stresses. By the results time averaged velocity distributions, secondary currents, and distributions of bed shear stresses are analyzed. Overall distributions of bed shears in floodplain show that higher shear stresses are seen in left of floodplain and the shears decrease toward right of floodplain. However, high local variations in shear stresses are shown due to the secondary flow effects. In shallow floodplain, bed shear stresses show low value below 0.8 times of averaged bed shear. In deep floodplain, bed shear stresses show high value over 1.2 - 1.4 times of averaged bed shear.

하천설계에서 제방과 홍수터의 안정성 확보를 위해서는 바닥전단응력을 고려하는 것이 필수적이다. 본 연구에서는 다양한 하폭과 수심에 따른 복단면의 바닥전단응력을 모의하여 분포 특성을 분석하였다. 바닥전단응력 분포에 지배적인 영향을 주는 이차류를 모의하기 위하여 OpenFOAM의 large eddy simulation (LES)를 적용하였으며 하폭과 수심을 고려하여 12개의 케이스를 모의하였다. 모의 결과를 이용하여 시간 평균 유속 분포, 이차류 분포, 바닥전단응력 분포 등의 특성에 대하여 분석하였다. 홍수터 바닥전단응력 분포는 전체적으로 홍수터 좌안에서 높은 값이 나타나고 우안 방향으로 감소하는 경향을 확인하였으나 이차류에 의해 상당한 국부적인 변화가 나타남을 확인하였다. 홍수터의 수심이 얕은 경우에는 홍수터의 바닥전단응력이 평균전단응력의 0.8배 이하로 낮은 값이 나타나고 있으나 홍수터의 수심이 깊은 경우에는 평균전단응력의 1.2-1.4배의 높은 값이 나타남을 확인하였다. 홍수터의 폭이 좁은 경우에는 홍수터 우안 측벽의 영향으로 국부적으로 높은 값이 나타나는 것도 확인할 수 있었다.

Keywords

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Fig. 1. Schematic diagram of compound open channels used in this study (Lee 2017).

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Fig. 2. Computational setup and boundary conditions for the large eddy simulation (LES) used in this study (Lee 2017).

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Fig. 3. Composition of cross sectional grid points used in this study (Lee 2017).

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Fig. 4. Normalized streamwise mean velocity in case CR01.

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Fig. 5. Normalized streamwise mean velocity in case CR13.

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Fig. 6. Normalized streamwise mean velocity in case CR24.

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Fig. 7. Secondary currents of the case CR01.

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Fig. 8. Secondary currents of the case CR13.

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Fig. 9. Secondary currents of the case CR24.

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Fig. 10. Bed shear stress distribution in case CR01.

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Fig. 11. Bed shear stress distribution in case CR04.

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Fig. 12. Bed shear stress distribution in case CR11.

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Fig. 13. Bed shear stress distribution in case CR14.

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Fig. 14. Bed shear stress distribution in case CR21.

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Fig. 15. Bed shear stress distribution in case CR24.

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Fig. 16. Variation of max bed shear stresses with b/B in main channel.

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Fig. 17. Variation of max bed shear stresses with h/H in main channel.

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Fig. 18. Variation of max bed shear stresses with b/B in floodplain.

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Fig. 19. Variation of max bed shear stresses with h/H in floodplain.

Table 1. Flow conditions of the simulation cases in this study

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