이 연구는 지속가능한 수자원 이용 및 관리대책을 수립하는 데에 필요한 수문학적 자료를 제공할 목적으로 2017~2020년 홍수기 (6~9월)에 발생한 총 59회의 강우 사상에 대한 강우-유출 특성을 파악하였다. 그 결과, 강우량은 5.0~400.8 mm, 유출고는 0.1~176.5 mm, 유출률은 0.1~242.9%의 범위로 나타났다. 그리고 유출수문곡선에서 직접유출과 기저유출을 분리한 결과, 홍수기의 총 유출일 대비 기저유출 (139.3일)이 직접유출 (78.3일)보다 유출기간이 길었지만, 총 유출고에 대한 기여도는 직접유출 (54.2%)이 기저유출 (45.8%)보다 높게 나타났다. 또한, 유출에 영향을 미치는 강우조건을 분석한 결과, 직접 유출과 기저유출의 유출고 및 첨두유출고에 높은 유의성 (p<0.05)을 보이는 강우조건은 강우량과 강우지속시간으로 나타났다. 특히, 유출고와 첨두유출고의 강우량은 각각 5.0~200.4, 10.5~110.5 mm의 범위에서는 기저유출이 우세한 강우사상이 나타났지만, 유출고와 첨두유출고의 강우량이 각각 267.4~400.8, 169.0~400.8 mm의 범위에서는 직접유출이 우세한 강우사상이 나타났다. 앞으로 극한 기후현상에 따른 물 부족이 심화할 것으로 예상되는 가운 데, 산지계류의 직접유출 및 기저유출에 대한 장기적이고도 지속적인 분석이 이루어진다면 지표수-지하수의 이용 및 관리 측면에서의 활용과 자료의 신뢰성을 높일 수 있을 것으로 판단된다.

This paper presents a Raman spectroscopy study of the influence of methane flow on the micro-tribological behavior of diamond-like carbon coatings deposited with an industrial plasma-enhanced chemical vapor deposition system. Results have shown a direct relationship between the methane flow and thickness of the coatings. The analysis of the Raman spectra and deposition parameters allowed establishing the influence of H content with the methane flow, the disorder level and estimation of the sp3 fraction on the carbon coatings. The micro-tribology tests showed a strong dependence of the wear resistance and hardness with Raman parameters. The coating deposited at 72-sccm methane flow presented a thickness of 1.7 μm and a sp3 fraction of 0.33. This sp3 fraction gave rise to a hardness of 24 GPa and an excellent wear resistance of 3.3 × 10–6 mm3 N−1 mm−1 for this DLC coating. Wear tests showed a swelling in the wear profiles on this coating, which was associated with the occurrence of a re-hybridization process.

본 연구의 목적은 슬리브 이음된 배관 사이의 간극과 Re가 변할 때 배관 내의 유동은 어떻게 변하는지 조사함으로써 조정관 설치 시에 압력손실과 난류 강도를 감소시킬 수 있는 배관 간극(Lp)을 파악하는 것이다. 슬리브 이음된 배관 두께(tp)는 5 mm로 고정 하고 Lp는 10, 50, 100 및 200 mm로 하여 슬리브 이음부의 속도, 압력 분포, 재순환 영역에서의 재부착점 길이 및 Re와의 상관관계를 해석하였다. 상용 프로그램인 Ansys fluent 18.1을 이용하였고, Re의 범위는 200 ≤ Re ≤ 5,000으로 하여 층류에서 난류까지 슬리브 이음부의 유동 특성을 파악하였다. 슬리브 이음부의 확대비와 축소비는 각각 1.2와 0.83이였고 Lp가 일정할 때 Re가 커질수록 슬리브 하류가 장자리(edge)의 난류 강도와 압력 변화가 크게 나타났다. 이는 슬리브 벽면에서의 유동이 tp에 의해 흐트러지고 속도 에너지의 손실이 발생하면서 슬리브 이음부의 가장자리에 영향을 미친 것으로 판단된다. Lp가 10 mm 이하의 경우, Re가 증가함에 따라 가장자리의 난류 강도에는 큰 변화가 없었다. 재순환 영역에서의 재부착점은 Lp가 10 mm 이하에서 나타나지 않았으며 와(vortex)의 영향도 없었다. 3,000 ≤ Re의 경우, Lp가 증가함에 따라 슬리브 이음부 벽면에서의 재부착점 길이는 거의 일정하였다.

In this study, the flow rate at the drone and the pressure around the drone were investigated by carrying out the flow analysis due to the wing shape of drone. At models 1, 2 and 3, the positions of areas with the maximum flow rate around the drone according to the shape of the wing were seen to be same at the rear wing of drone. Model 2 has the fastest flow rate, followed by model 1 and model 3. At the distribution of flow pressure by model around the drone according to the wing shape of drone, models 1, 2 and 3 had the same highest pressures at the center of drone. In comparison with the maximum pressures of models near the wing shape of the drone, the flow pressure at model 2 was higher compared with models 1 and 3. At the wing shape of the drone, model 2 is considered to carry the flow performance better than models 1 and 3. So, the result of this study is thought to be useful for designing the wing shape of the drone. Without the test of flow performance due to the shape of drone wing, the flow performance can be seen as the flow rate and pressure are investigated through the flow analysis.

This study was performed to analyze the effect on driving performance by identifying the flow characteristics of the rear diffuser such as drag coefficient, lift coefficient, velocity vector, velocity streamlines, turbulence kinetic energy and vortex-core region according to the angle of the sedan rear diffuser and the shape of the divider. The angle of the diffuser was analyzed at 2° intervals from 0° to 18°, and the divider was analyzed by changing from one to five. The three-dimensional modeling was performed using CATIA V5 and the vehicle model was selected as a sedan car in the form of an LF Sonata. The CFD analysis was performed in order to identify the flow characteristics of rear diffuser using ANSYS CFX 14.5.7. For each model, the analysis was performed under each condition with speeds of 80km/h, 100km/h, 120km/h, 140km/h. The results of the flow analysis showed that the rear diffuser angle was the best result in driving stability at 6°. The results of the study on the number of dividers showed the best result value in driving stability when the rear diffuser angle was 6° and the divider was 3 and selected as the optimal shape.

최근 연안지역의 대규모 개발로 인해 고파랑 내습과 강한 태풍으로 발생된 월파는 연안지역의 많은 인명 및 재산피해를 발생시켰으나 연안지역의 특성을 고려한 침수·범람 연구는 미비한 실정이다. 본 연구는 ADCSWAN(ADCIRC+SWAN) 모델과 FLOW-3D 모델을 적용하여 해일 및 파랑의 복합요소에 대한 침수범람을 재현하기 위한 방법론에 대한 연구이다. 본 연구에서는 ADCSWAN(ADCIRC+SWAN) 모델을 이용하여 FLOW-3D 모델의 경계자료(해수위, 파랑)를 추출하고, FLOW-3D 모델 입력값으로 적용하여 태풍 차바 통과시 부산 마린시 티를 대상으로 해일과 월파에 의한 침수범람을 재현하였다. 또한 기존 월파량 경험식과 FLOW-3D 모델로 계산된 월파량을 비교하였으며, 침수범람은 한국국토정보공사의 침수흔적도를 활용하여 정성적인 검증을 수행하여, 본 연구의 유효성을 검토하였다.

Plastic products molded by injection molding have become an essential element of our lives. In addition, plastics can replace parts that used to be metal in the past. Plastic molded products used as a part of a mechanical system require high precision. At the same time, the appearance quality of molded products is also an important evaluation factor. The appearance quality of a molded product is affected by injection molding conditions, plastic material fluidity, and the condition of the mold surface. In this study, the cause of the short shot of the dog house, which functions to assemble the plastic tailgate parts for automobiles, was analyzed. In order to solve the short shot problem of the dog house, the root thickness of the dog house, injection molding conditions, and fluidity of plastic materials were experimented. Through the injection molding experiment, it was found that when the dog house root thickness was increased from 0.8mm to 1.2mm, the filling amount of the doghouse part increased by 43% in experiment mold. These results were verified by injection molding analysis.

Numerical analysis has been carried out to investigate the flow field characteristics for exhaust gas in automobile engine DPF system. The DPF system performance is largely affected by exhaust gas flow while it passes through the complicated geometry of DOC/DPF system, fan shape structure, and perforated can with air for fuel combustion. Hence the characteristics of fluid velocity, pressure, and streamline are analyzed with velocity uniformity in front of DOC and swirl flow near the fan. It can be seen that the velocity uniformity increases with the gas flow rate including flow acceleration near the lower area of the fan. The air flow also influences the gas flow distribution close to the impeller and fan structure with complicated swirl flow. These results are expected to be applicable as fundamental design data for automobile engine exhaust system.

In this study, the flow analyses were carried out on three kinds of front wing models. The down forces of front wings which influence the stability, cornering at driving were investigated with three models. At model 1, the maximum pressure shown on the main plate of front wing is 3177.539Pa. The maximum pressures at models 2 and 3 are shown to be 3429.677Pa and 3506.494Pa, respectively. The higher the pressure, the more resistance. So, the lower the pressure, the less resistance the model gets. At model 1, the maximum velocity of stream that flows under the front wing was shown to be the smallest among three models. In case of all three models, the pressure at which the air passes through the front wing is high in the upper part of the front wing. Among three models, model 1 is thought to be the most appropriate model to give the effect of the down force while reducing the flow resistance at driving. By utilizing this study result, the flow velocity and pressure are investigated without the flow experiment at driving due to the configuration of automotive front wing, and the flow resistance can be seen.

The effect of flow direction on heat transfer in water cooling channel of lithium-ion battery is numerically investigated. Battery Design StudioⓇ software is used for modeling electro-chemical heat generation in the battery and the conjugated heat transfer is analyzed with the commercial package STAR-CCM+. The result shows that the maximum temperature and temperature difference of battery with Type 1 are the lowest because the heat transfer in the entrance region near the electrode is enhanced. As the inlet velocity is increased, the maximum temperature and temperature difference of battery decreases but the pressure loss increases. The pressure loss in Type 2 channel is the lowest due to the shortest channel length, while the pressure loss with Type 3 or 4 channel is the highest because of the longest channel length. Considering heat transfer performance and pressure loss, Type 1 is the best cooling channel.

In order to satisfy the strengthening automobile exhaust gas regulation and CO2 regulation, the development of eco-friendly vehicles is actively progressing. To cope with these regulations, research on alternative fuel vehicles is being actively conducted. Alternative fuels are one of the best ways to reduce dependence on fossil fuels and respond to emissions and CO2 regulations. Natural gas, one of many alternative fuels, contains methane (CH4) as a main component and has abundant reserves, so it is attracting attention as a fuel that can provide stable long-term supply by replacing fossil fuels. In addition, natural gas has a high octane number, so there is room for improvement in combustion characteristics when used in SI engines, and it has the advantage of reducing harmful emissions and carbon dioxide (CO2) compared to conventional fossil fuels. When using a low-pressure injector in a turbo engine, it is difficult to secure the flow rate of fuel because the pressure difference between the injector and the manifold is small. Therefore, it is necessary to develop a high-pressure injector to improve this. Natural gas is a gaseous fuel and should be developed in consideration of compressible flow, Although the use of a CNG high-pressure injector is required, it is difficult to stabilize the flow due to the Mach disk and shock wave interference caused by compressible flow. If the flow is not stabilized, it is difficult to precisely control the flow. Therefore, it is necessary to develop an injector in consideration of flow characteristics. In this paper, the flow analysis according to the shape change of the injector was conducted to improve the fuel flow rate injected from the 800 kPa high pressure CNG injector.

본 연구는 산악형 설악산 국립공원지역에서 발생한 토석류 발생지 263개소를 대상지로 선정하여 다양한 산림환경 인자별로 조사하고 토석류발생지 특성을 분석하였다. 토석류 평균(침식량, 길이, 폭, 면적)은 각각 1,935㎥, 103.7m, 14.4m, 1,728㎡로 나타났다. 산림환경 인자가 토석류 발생 빈도에 미치는 영향을 분석한 결과, 경사도(31∼40°), 사면방위(남사면), 종단사면(오목凹), 횡단사면(오목凹), 표고(801∼1,200m), 사면위치(산록), 하천차수 (1차), 임상(혼효림), 모암(화강암), 토심(15cm 이하)에서 발생빈도가 높은 것으로 조사되었다. 토석류가 발생한 피해지에서의 침식량과 산림환경 인자와의 상관관계를 분석한 결과는, 종단사면(오목凹, 복합凹凸), 표고(1,201m 이상), 토심(46cm 이상)에서 1% 수준 내에서 정의 상관관계를 보였다.

본 연구의 목적은 골프전공 대학생의 학업적 자기효능감과 학습몰입 및 자기주도학습의 관계를 조사하는데 있다. 본 연구는 골프전공 대학 수업에 참여한 257명의 학생들로 구성되었으며, 270명의 학생들의 데이터를 분석하였다. SPSS 21.0 및 AMOS 22.0의 프로그램을 이용하여 구조방정식 모델을 분석하였다. 그 결과는 다음과 같다. 첫째, 골프전공 대학생의 학업적 자기효능감은 학습몰입에 긍정적인 영향을 주었다. 둘째, 골프전공 대학생들의 학습몰입은 자기주도학습에 긍정적인 영향을 주었다. 셋째, 골프전공 대학생의 학업적 자기효능감은 자기주도학습에 긍정적인 영향을 주었다.

Direct water quenching technique can be used in hot stamping process to obtain higher cooling rate compared to that of the normal die cooling method. In the direct water quenching process, setting proper water flow rate in consideration of material thickness and the size of the area directly cooled in the component is important to ensure uniform microstructure and mechanical properties. In this study, to derive proper water flow rate conditions that can achieve uniform microstructure and mechanical properties, microstructure and hardness distribution in various water flow rate conditions are measured for 3.2 mm thick boron steel sheet. Hardness distribution is uniform under the flow condition of 1.5 L/min or higher. However, due to the lower cooling rate in that area, the lower flow conditions result in a drastic decrease in hardness in some areas in the hot-stamped part, resulting in low martensite fraction. From these results, it is found that the selection of proper water flow rate is an important factor in hot stamping with direct water quenching process to ensure uniform mechanical properties.

The objectives of this study were to develop the optimal structures of recirculating aquaculture tank for improving the removal efficiency of solid materials and maintaining water quality conditions. Flow analysis was performed using the CFD (computational fluid dynamics) method to understand the hydrodynamic characteristics of the circular tank according to the angle of inclination in the tank bottom (0°, 1.5° and 3°), circulating water inflow method (underwater, horizontal nozzle, vertical nozzle and combination nozzle) and the number of inlets. As the angle in tank bottom increased, the vortex inside the tank decreased, resulting in a constant flow. In the case of the vertical nozzle type, the eddy flow in the tank was greatly improved. The vertical nozzle type showed excellent flow such as constant flow velocity distribution and uniform streamline. The combination nozzle type also showed an internal spiral flow, but the vortex reduction effect was less than the vertical nozzle type. As the number of inlets in the tank increased, problems such as speed reduction were compensated, resulting in uniform fluid flow.

There are many disadvantages to existing silencers used in power plants. Recently, high-performance silencers are required in society, so it is necessary to develop silencers accordingly. Therefore, in this study, to develop the flow silencer by taking advantage of the foamed aluminum, the property values such as loss coefficient and porosity were obtained through experiments, based on the Forchheimer's law. CFD analysis was performed by applying a porous modeling technique to foamed aluminum and the results were compared with experimental values. The error rate between the results of the experiment and the flow analysis is within about 2.79%, so the results of the experiment and the analysis agree relatively well. When the foamed aluminum was installed, the flow noise was reduced by about 5.14dB.