• 한국해양공학회지
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• 제25권1호
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• pp.14-21
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• 2011

The purpose of this study is to quantify the erosional parameters, such as the critical shear stress for erosion and the erosion rate coefficient for cohesive sediments from the Mokpo coast. Using Chonbuk annular flume, five erosion tests were conducted under the uniform bed condition but a different bed density respectively. Erosion test results for Mokpo sediments have shown increases in the range of $0.16{\sim}0.43\;N/m^2$ but decreases exponentially in the range of $272{\sim}4.64\;mg/cm^2{\cdot}hr$ for the given bed shear stress of $1.14{\sim}1.34\;g/cm^3$. The erosional parameters of Mokpo sediments are found to vary remarkably in quantity compared with those for cohesive sediments from other sites. On the whole, the value of Mokpo coast sediments appears to be similar to Kunsan sediments but smaller than Saemankeum and Okeechobee sediments. On the other hand, Mokpo sediments have been shown to be larger than Saemankeum and Okeechobee sediments but smaller than Kunsan sediments.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.403-408
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• 2003

The erosion behavior of :artificially aged HK40 steel was investigated. Erosion tests were conducted at room temperature, $200^{\circ}C$ and $400^{\circ}C$ using $Al_2O_3$ particles. Erosion rates increased with increment of temperature. The maximum erosion rate increased with the impingement angle of 30 degree. The erosion rate increased, reached the maximum at 1000 hours, and after that, decreased with heat treatment time. The mechanism of erosion seems to be the cutting wear which is very much associated with the strength of material. As results, the erosion rates were rather affected by the tensile strength and the strain hardening coefficient than the hardness and the yield strength. Such changes of material properties would be caused by the change of micro-structure due to the precipitation of carbide and the dissolution of solid element within matrix during the heat treatment.

• 한국해안해양공학회지
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• 제17권2호
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• pp.119-128
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• 2005

미세-점착성 퇴적물의 침식률 산정을 목적으로 국내 최초로 환형수조가 제작되었으며, 수조의 성능, 실험 방법 및 결과 등에 대한 타당성 검증을 목적으로 고령토를 이용한 침식실험이 수행되었다. 각기 다른 밀도를 갖는 균일저면 조건하에서 총 4회의 실험이 수행되었으며, 이 결과로부터 점착성 퇴적물의 침식한계 전단응력과 침식률 계수가 산정되었다. 기존의 타 연구결과와의 비교$\cdot$검토를 통하여, 본 연구에서 특수 제작된 환형수조는 성능상에 문제가 없음이 간접적으로 확인되었으며, 균일저면의 제작과정을 포함하는 침식실험 방법 및 실험 결과의 타당성이 입증되었다.

• Geomechanics and Engineering
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• 제25권1호
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• pp.49-58
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• 2021

The resistance of soil to the tractive force of flowing water is one of the essential parameters for the stability of the soil when directly exposed to the movement of water such as in rivers and ocean beds. Biopolymers, which are new to sustainable geotechnical engineering practices, are known to enhance the mechanical properties of soil. This study addresses the surface erosion resistance of river-sand treated with several biopolymers that originated from micro-organisms, plants, and dairy products. We used a state-of-the-art erosion function apparatus with P-wave reflection monitoring. Experimental results have shown that biopolymers significantly improve the erosion resistance of soil surfaces. Specifically, the critical shear stress (i.e., the minimum shear stress needed to detach individual soil grains) of biopolymer-treated soils increased by 2 to 500 times. The erodibility coefficient (i.e., the rate of increase in erodibility as the shear stress increases) decreased following biopolymer treatment from 1 × 10-2 to 1 × 10-6 times compared to that of untreated river-sands. The scour prediction calculated using the SRICOS-EFA program has shown that a height of 14 m of an untreated surface is eroded during the ten years flow of the Nakdong River, while biopolymer treatment reduced this height to less than 2.5 m. The result of this study has demonstrated the possibility of cross-linked biopolymers for river-bed stabilization agents.

• 한국수자원학회논문집
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• 제41권5호
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• pp.473-482
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• 2008

본 연구의 목적은 최근 끝막이 공사가 완료된 새만금 인공호 점착성 퇴적물의 침식특성을 정량적으로 분석하는 것이다. 침식실험은 국내 최초로 제작되고 그 타당성이 검증된 전북대 환형수조를 이용하여 각기 다른 밀도를 갖는 균일저면 조건하에서 수행되었으며, 새만금 인공호 점착성 퇴적물의 침식한계전단응력 및 침식률계수가 정량적으로 산정되었다. 한편, 일반적으로 점착성 퇴적물의 침식특성은 퇴적물의 물리.화학적 기본특성에 따라 크게 변화하므로, 새만금 인공호 점착성 퇴적물의 이러한 특성 또한 조사되었으며, 이와 연계하여 침식특성이 해석되었다. 새만금 인공호 점착성 퇴적물의 경우에, 저면밀도 $1.17{\sim}1.34g/cm^3$ 범위에서 침식한계전단응력은 $0.26{\sim}0.52N/m^2$로 로그함수적으로 증가하였으며, 침식률계수는 $14.28{\sim}6.02mg/cm^2\;hr$ 범위로 지수함수적으로 감소하였다. 산정된 침식 매개변수들은 타 지역 점착성 퇴적물과 또한 비교/분석되었으며, 그 값은 정량적으로 지역마다 크게 다른 것으로 나타났다. 특히 새만금 인공호 점착성 퇴적물의 침식한계전단응력은 군산해역 퇴적물보다는 크며, 시화호 퇴적물과는 유사한 것으로 나타났으며, 반면에 새만금 인공호 퇴적물의 침식률계수는 군산해역 퇴적물보다는 작은 것으로 나타났다.

• 대한토목학회논문집
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• 제28권1B호
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• pp.125-135
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• 2008

본 연구의 목적은 금강하구의 표층에 분포하는 점착성 퇴적물의 침식매개변수를 정량적으로 산정하는 것이다. 또한 본 연구는 침식매개변수들의 금강하구역 내에서의 지엽적 계절적 변화에 대한 조사와 타 지역 분석 결과와의 비교/분석을 통한 공간적 변화에 대한 조사를 포함한다. 점착성 퇴적물의 침식특성은 기본적으로 퇴적물 자체의 물리 화학적 특성에 의해 크게 영향을 받으므로, 본 연구는 또한 퇴적물의 이러한 기본특성이 침식특성에 미치는 영향에 대한 정성적 분석을 포함한다. 침식실험은 전북대 환형수조를 이용하여 균일저면 조건하에서 수행되었으며, 저면밀도와 바닥전단응력을 변화시키면서 총 16회의 실험이 수행되었다. 실험결과에 따르면, 금강하구역 점착성 퇴적물은 저면밀도 $1.14{\sim}1.38g/cm^3$ 범위에서 침식한계전단응력(${\tau}_{ce,s}$)은 $0.19{\sim}0.41N/m^2$, 침식률 계수(${\varepsilon}_{M,s}$)는 $54.26{\sim}7.70mg/cm^2{\cdot}hr$ 범위의 값을 갖는 것으로 나타났다. 또한 산정된 침식 매개변수들은 타 지역 점착성 퇴적물과 비교시 정량적으로 그 값이 크게 다른 것으로 나타났으나, 금강하구역 내에서의 지엽적/계절적 변화는 미미한 것으로 나타났다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 추계학술대회논문집
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• pp.170-176
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• 2009

Flow control butterfly valve(FCBV) is known to have difficulty in controlling flow rate along valve opening due to its high flow rate. In low opening condition, the butterfly valve also has some shortcomings such as noise, vibration and erosion which are mostly caused by cavitation effects. Therefore, the FCBV requires proper remedies to reduce cavitation effects and to improve flow control performance. Numerical analysis is applied to FCBV flow to find effects of design factors such as seat diameter and valve opening rate. Cases with 3 different sizes of seat diameter and various valve opening rate are selected for the numerical analysis. From the analysis results, it is found that the FCBV with small seat diameter shows better pressure loss performance and reduced cavitation effects.

• 한국전산유체공학회지
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• 제15권1호
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• pp.64-70
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• 2010

Flow control butterfly valve(FCBV) is known to have difficulty in controlling flow rate along valve opening due to its high flow rate. In low opening condition, the butterfly valve also has some shortcomings such as noise, vibration and erosion which are mostly caused by cavitation effects. Therefore, the FCBV requires proper remedies to reduce cavitation effects and to improve flow control performance. Numerical analysis is applied to FCBV flow to find effects of design factors such as seat diameter and valve opening rate. Cases with 3 different sizes of seat diameter and various valve opening rate are selected for the numerical analysis. From the analysis results, it is found that the FCBV with small seat diameter shows better pressure loss performance and reduced cavitation effects.

• 한국농공학회논문집
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• 제54권1호
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• pp.99-108
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• 2012

Soil erosion and sediment from agricultural farmland has caused various negative impacts on environment in recent years. The effect of rice straw mat on soil erosion has been investigated by many researchers these days. In this study, the SWAT model was applied to Hongcheon watershed to evaluate SWAT flow and sediment, and the effect of rice straw mat on sediment yield at watershed outlet was evaluated. The Nash-Sutcliffe model efficiency (NSE) and coefficient of determination ($R^2$) values for flow simulation (calibration period) were 0.66 and 0.67, and the NSE values for sediment was 0.90. The calibrated parameters were used to analyze the reduction of sediment yield in the farmland with rice straw mat. Average daily sediment yield without rice straw mat was 49.8 ton/day and sediment yield with rice straw mat was 25.5 ton/day, and the reduction rate was 38.7 %. Also, average daily sediment yield with/without rice straw mat were 97.5 ton/day and 190.7 ton/day during the rainy season (Jun. 2008 - Aug. 2009), with the reduction rate 46.3 %.

• International Journal of Fluid Machinery and Systems
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• 제2권2호
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• pp.165-171
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• 2009

We developed a 'multi-point vibration acceleration method' for accurately predicting the cavitation intensity in pumps. Pressure wave generated by cavitation bubble collapse propagates and causes pump vibration. We measured vibration accelerations at several points on a casing, suction and discharge pipes of centrifugal and mixed-flow pumps. The measured vibration accelerations scattered because the pressure wave damped differently between the bubble collapse location and each sensor. In a conventional method, experimental constants are proposed without evaluating pressure propagation paths, then, the scattered vibration accelerations cause the inaccurate cavitation intensity. In our method, we formulated damping rate, transmittance of the pressure wave, and energy conversion from the pressure wave to the vibration along assumed pressure propagation paths. In the formulation, we theoretically defined a 'pressure propagation coefficient,' which is a correlation coefficient between the vibration acceleration and the bubble collapse pressure. With the pressure propagation coefficient, we can predict the cavitation intensity without experimental constants as proposed in a conventional method. The prediction accuracy of cavitation intensity is improved based on a statistical analysis of the multi-point vibration accelerations. The predicted cavitation intensity was verified with the plastic deformation rate of an aluminum sheet in the cavitation erosion area of the impeller blade. The cavitation intensities were proportional to the measured plastic deformation rates for three kinds of pumps. This suggests that our method is effective for estimating the cavitation intensity in pumps. We can make a cavitation intensity map by conducting this method and varying the flow rate and the net positive suction head (NPSH). The map is useful for avoiding the operating conditions having high risk of cavitation erosion.