• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.3 s.234
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• pp.432-438
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• 2005

CMP characteristics such as material removal rate and edge effect were measured and investigated in accordance with pad grooving effect, groove width, depth and pitch. GSQ (Groove Stiffness Quotient) and GFQ (Groove Flow Quotient) were proposed to estimate pad grooving characteristics. GSQ is defined as groove depth(D) divided by pad thickness(T) and GFQ is defined as groove width(W) divided by groove pitch(P). As GFQ value increased, material removal rate increased some point but gradually saturated. It seems that material removal rate is not affected by each parameter respectively but by interaction of these parameters such as groove dimensions. In addition, an increase in GFQ and GSQ causes edge effect to be improved. Because, pad stiffness decreases as GSQ and GFQ increase. In conclusion, groove influences relative pad stiffness although original mechanical properties of pad are unchanged by grooving. Also, it affects the flow of slurry that has an effect on the lubrication regime and polishing results. The change of groove dimensions has influence on pad stiffness and slurry flow, so that polishing results such as removal rate and edge effect become changed.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.13 no.2
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• pp.95-104
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• 2010

The purpose of this study is to analyze the correlation between physical stream characteristics and bed materials in natural rivers. Accordingly, four natural rivers were selected reference streams, they were Nam river, Sumjin River, Naesung River and Han River. Grain size distributions of bed materials were gravels, cobbles and boulders in Han river and Nam river, were sand, gravels, cobbles and boulders in Sumjin river and were sand in Naesung river. Four reference streams were divided into each two reference reaches (straight and bend) by plan and profile characteristics of naturally meandering stream. Therefore various reference reaches were chosen in the aspect of physical stream characteristics and grain size distributions. The results investigated and analyzed are as follows. The streams that grain sizes distributions of river bed materials were coarse were stable because they had variety of bed slope without sediment deposition, and then the riffles frequency and the physical characteristics were various. Also, velocitydepth regime were various in four kinds, and the response parts for water level change were small, so that channel flow status were stable and excellent condition. On the other hand, sand river that grain sizes distributions of river bed materials were fine had not the variety of parameters as velocity-depth regimes, sediment deposition, channel flow status and riffles frequency, so that the physical stream characteristics were not various.

• Ecology and Resilient Infrastructure
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• v.1 no.2
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• pp.61-67
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• 2014

Dam construction changes flow regime and stream morphology in the downstream reach. These affect the ecosystem of downstream reach. This study provides the assessment of the impact of dam construction on the downstream fish habitat. For this, physical habitat simulations are carried out. The quasi-steady model is used for hydraulic simulation, The hydraulic model used in the present study is capable of simulating the morphological change due to sediment transport. The change of the fish habitat condition is investigated using the flow scenarios before and after the dam construction. Simulation results indicate that the habitat suitability decreases frequently due to hydropeaking after dam construction. In addition, erosion is expected to occur in a reach downstream of dam. This is a long term effect due to the shut-down of sediment supply from the upstream reach.

• Korean Journal of Ecology and Environment
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• v.51 no.4
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• pp.331-344
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• 2018

Lotic organisms in streams are affected by natural and anthropogenic disturbances such as increase of heavy rainfall event caused by climate change and flow regime change caused by weir constructions. Based on domestic and foreign literature, 157 Korean benthic macroinvertebrate taxa were selected species as potential lotic candidates. Three shoreline sites (total 54 samples) were surveyed consecutively before ('08~'09), during ('10~'12) and after ('13~'16) the construction of the weirs (Gangcheon, Yeoju and Ipo weir) in the Namhan-River for tracing changes of lotic communities. As a result, water flow of the Ipo-wier and water quality variables such as T-N, T-P, BOD5, etc. of the weir section revealed no significant changes. Physical habitat conditions such as the flow velocity and streambed substrate evidently changed. Particulary, flow velocity measured at sampling points along with each microhabitat drastically decreased and particle size of streambed substrate steadily decreased after weir constructions. Lotic organisms also decreased after construction, especially Hydropsychidae (insecta: Trichoptera) acutely decreased from $3,526ind.\;m^{-2}$ to $2ind.\;m^{-2}$ As a result of CCA, lotic species such as Hydropsyche valvata, Hydropsyche kozhantschikovi, Cheumatopsyche brevilineata, Cheumatopsyche KUa, Macrostemum radiatum, etc. correlated with the flow velocity, streambed substrate. Therefore, the decrease of the flow velocity and substrate size after weir construction seemed to be closely related to the decrease of the individual abundances of the lotic organisms independently of water quality. In order to evaluate the influence of the ecosystem on the flow regime change more accurately, it is necessary to study the indicator species based on the resistance or preference of the flow.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.6
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• pp.442-450
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• 2011

A three dimensional random walk particle tracking method is applied to the Saemangeum area in order to find stepwise environmental changes according to long term construction. Flow regime around Mangyeong, Dongjin and Geum river estuary changed greatly due to dike construction. It is distinctive that reduction of Byeonsan area's flow field and stagnant change in the northern part of the inner reservoir. Similar characteristics are found through the tidal excursion analysis. By analysis of the vertical mixing structures according to density stratification based on temperature and salinity variation, a salt wedge and very strong stratification arises in the inner part of the reservoir after final closure, while it has been well mixed or partially mixed estuary during construction. Shrinking of horizontal dispersion and vertical mixing capability may cause adverse effect on water quality not only inner part but also outer region of the Saemangeum reservoir.

• Tribology and Lubricants
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• v.3 no.2
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• pp.68-71
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• 1987

This paper deals with some thermal Characteristics of journal bearing such as the behaviour of the maximum bearing temperature, the lubricant's carry-over in the inlet region and so on. Temperatures of the bearing and the lubricants being supplied and discharged were measured along with shaft speed and bearing load. The results showed that with the increase of the Shaft speed, the maximum temperature rose at any shaft speed at a defferent rate of change defending on the flow regime of the lubricant film. And the lower eccentricity ratio is the more lubricant's carry-over occur. Additionally it was partially proved that the oil discharge temperature and the maximum temperature changed in quite different each other.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.648-651
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• 2007

하천의 정상적인 기능을 회복시켜 하천 생태계 보전과 환경적으로 안정된 하천 조성이 이루어지도록 하기 위해서는 하천을 보다 자연스럽고 지속적으로 관리하기 위한 효율적인 환경유량의 관리가 필요하다. 본 연구의 목적은 수리구조물에 의한 하천유황 및 하천환경의 변화를 분석하는 기법을 제안하는데 있다. 이를 위하여 먼저, KModSim모델을 이용하여 금강수계에 위치한 대청댐과 용담댐의 운영 전후 가정조건하에서 1984년부터 2006년까지 22년간의 유량자료를 수통지점과 공주지점에 대하여 생산한 후, 환경유량 설정 도구로서 호주 eWater CRC에서 개발한 RAP(River Analysis Package)을 이용하여 금강유역의 유황변화를 통계적으로 분석하였다. 본 연구결과는 향후 수질, 서식처 등 하천환경 변화를 포함하여 하천의 건강성 평가를 위한 기초자료로 사용될 것이다.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.562-562
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• 2015

하천의 유황특성을 분석하는 것은 하천생태계의 변화를 파악하고 예측하는데 있어 매우 중요하다고 할 수 있다. 최근에는 수문학적인 변화과정을 통계학적 기법을 적용하여 정량적인 지표로 산정하고 분석하는 모델을 개발하여 다양한 연구가 진행되고 있다. 특히 미국 Nature Conservancy에서 개발한 수문변화지표법(IHA)은 일(daily)유출량 자료로부터 수문학적 관점에서의 특성지표와 환경유량 관점에의 변화지표를 분석함으로써 하천 유황변동을 정량화 할 수 있다. 본 연구는 기후변화가 향후 하천유황과 수생태계에 미치는 영향을 분석하기 위해 중규모 하천유역인 만경강을 대상으로 하고 RCP 8.5 기후변화시나리오를 기반으로 준분포형 모형인 SLURP 모형으로부터 일(daily)단위의 유출모의 시나리오를 작성하였다. 그리고 수문변화지표법(IHA)을 이용하여 기후변화에 따른 하천 유황과 수생태계에 미치는 영향을 정량화하였다.

• Journal of Welding and Joining
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• v.7 no.3
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• pp.28-35
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• 1989

It was reported that the toughness for welded region was influenced by various factors such as the gradient for prior austenite grain size, the variation of microhardness and the characteristic microstructure depending on distance from the fusion boundary. Therefore, in order to evaluate the fracture strength of the weldment in which the microstructures change continuously, it is important to assess the peculiar strength of each microstructure in welded region. It was known that the small punch(SP) test technique which was originally developed to study the irradiation damage effect for the structures of nuclear power plant was also useful to investigate the strength evaluating of nonhomogeneous materials. In this paper, by means of a small punch test technique the possibility of evaluating strength of parent and welded region in SS41 and SM53B steels was investigated. The obtained results are summerized as follows: 1) The small punch test which showed markedly the ductile-brittle transition behavior in this experiment may be applied to evaluation for the fracture strength of welded region. 2) It was shown that the ductile-brittle regime lied in Region III(plastic membrane stretching region) of the flow characteristics observed in SP test. 3) The SP test technique which shows a more precipitous energy change transition behavior than the other test technique is able to estimate the more precise transition temperature. 4) It could be seen that in comparision with the structure of parent the structure of weld HAZ in SS41 steel was improved while it in SM53B steel was deteriorated.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.187-190
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• 2006

In the present study, effects of tree-stream turbulence and surface trip wire on the flow past a sphere at $Re\;=\;0.4\;{\times}\;10^5\;{\sim}\;2.8\;{\times}\;10^5$ are investigated through wind tunnel experiments. Various types of grids are installed upstream of the sphere in order to change the tree-stream turbulence intensity. In the case of surface trip wire, 0.5mm and 2mm trip wires are attached from $20^{\circ}\;{\sim}\;90^{\circ}$ at $10^{\circ}$ interval along the streamwise direction. To investigate the flow around a sphere, drag measurement using a load cell, surface-pressure measurement, surface visualization using oil-flow pattern and near-wall velocity measurement using an I-type hot-wire probe are conducted. In the variation of free-stream turbulence, the critical Reynolds number decreases and drag crisis occurs earlier with increasing turbulence intensity. With increasing Reynolds number, the laminar separation point moves downstream, but the reattachment point after laminar separation and the main separation point are fixed, resulting in constant drag coefficient at each free-stream turbulence intensity. At the supercritical regime, as Reynolds number is further increased, the separation bubble is regressed but the reattachment and the main separation points are fixed. In the case of surface trip wire directly disturbing the boundary layer flow, the critical Reynolds number decreases further with trip wire located more downstream. However, the drag coefficient after drag crisis remains constant irrespective of the trip location.