The distance between livestock facilities and residential spaces is decreasing. Moreover, livestock odor complaints are increasing due to the large-scale and concentrated livestock breading industry. In order to reduce odor from livestock facilities, bio-curtain that are easy to install and inexpensive are commonly used in Korea. However, there is a lack of basic data on design standards and operation manuals for bio-curtains. The installation density of the bio-curtain material is an important factor that affects the odor reduction rate, increment of the load on the ventilation fans, and the structural stability of the curtain. There are limitations on deriving the design conditions of the bio-curtain by only field experiments targeting invisible air. Therefore, aerodynamic simulation such as CFD (computational fluid dynamics) can be used to obtain quantitative data according to various environmental conditions. Bio-curtain is a porous medium with a complex structure, and it is necessary to derive aerodynamic coefficients to analyze it. In this study, the wind speed and pressure difference according to the design density of the bio-curtain were monitored using the experimental chamber. Using the field results, a pressure resistance curve was created for each flow velocity and installation density. The viscosity and resistance coefficient of the bio-curtain were calculated through the derived resistance curve.

CFD was used to study the change in the operation of the governor to check the effect of response delay due to residual air in the governor cylinder, which adjusts the pump RPM of the Turbine Driven Aux. Feed Water Pump(TD AFWP) in the Nuclear power plant. As a result of analysis, as the amount of internal air increased, the time delay also increased proportionally, and a time delay of up to 0.2 sec. occurred. As in the theory, it was confirmed that the cylinder operation delay occurred depending on the presence or absence of a compressive fluid such as air, but the time delay wat not enough to significantly affect the pump operation.

In this paper, numerical simulations were conducted to secure both flow distribution and uniform flow discharge through a wall mount type air sterilizer. In order to increase the reliability of the simulation results where there is no well-known validation case for air sterilizer, mesh sensitivity study was performed under the constraint that y+ set to one for k-w SST turbulent modeling for both the air sterilizer and the fan. The installation of various guides and structures was reviewed in the point of flow distribution and pressure drop inside the sterilizer, and the exhaust pressure conditions were predicted to secure uniform flow discharge at outlets. This study has been done based on the computational analysis during the development stage of the air sterilizer, and the results will be verified through physical testing after production of prototype.

본 연구에서는 대마난류(Tsushima Warm Current, TWC)의 유동 변화에 영향을 주는 요소를 파악하기 위하여 TWC의 수송량과 태 평양 순년진동(Pacific Decadal Oscillation, PDO) 및 엘니뇨 남방진동(El Niño - Southern Oscillation, ENSO)의 상호 관계 분석을 실시하였다. 25 년(1993~2018년) 동안의 TWC의 월별 수송량을 계산해보면 하계에 가장 크고 동계에 가장 작게 나타나는 계절변동 주기가 뚜렷하다. TWC 수송량과 PDO 및 ENSO의 한 척도인 Oceanic Niño Index(ONI) 각각의 주기성 파악을 위한 power spectrum 분석결과, TWC 수송량은 1년 주기 에서 peak를 보이지만 PDO 및 ONI는 뚜렷한 주기가 나타나지 않았다. 또한, TWC 수송량과 PDO 및 ONI의 상호 관계 파악을 위해 coherence 추정 방법을 이용하여 분석하였다. PDO 및 ONI의 coherence는 3년 이상의 장주기 변동에서 상호 기여도가 높으나 1년 이내의 단주기 변동 에서는 상호 기여도가 낮다. 그러나 TWC 수송량과 PDO 두 요소 간 0.8~1.2년 주기에서 coherence 값은 0.7로 상호 기여도가 높다. 한편 서수 도를 통과하는 TWC 수송량과 PDO는 Ⅰ기간(1993~2002년)과 Ⅲ기간(2010~2018년)에 역상관 관계성을 가진다. TWC 최대 수송량 (2.2 Sv 이 상)이 높게 나타나는 시기에 PDO 지수가 –1.0 이하의 음의 값, 2.2 Sv 이하로 작은 시기에 PDO 지수가 양의 값을 나타낸다. 따라서 장기적 인 PDO 지수 자료를 이용하면 TWC 수송량 변동 및 동해 연안역의 수온변화를 예측 또한 가능할 것으로 판단된다.

In this study, two ventilation holes were considered to prevent condensation in the circular column supporting the provision crane on a training ship(Saenuri) for Mokpo National Maritime University. The ventilation holes could be understood as the most simple and inexpensive way to prevent condensation because it was formed only by drilling. If sufficient ventilation is provided, the insulation and corrosion of an electric motor can be improved, and a comfortable state can be ensured in the circular column. The circular column had an electric motor for driving the provision crane so that the basic principle was to utilize the kinetic energy for the flow field from a cooling fan in the circular column. The ventilation holes attenuated the low-velocity area in the circular column and contributed to internal flow circulation with updrafts. The results were discussed through numerical analysis based on computational fluid dynamics.

AlSi10Mg alloys are being actively studied through additive manufacturing for application in the automobile and aerospace industries because of their excellent mechanical properties. To obtain a consistently high quality product through additive manufacturing, studying the flowability and spreadability of the metal powder is necessary. AlSi10Mg powder easily forms an oxide film on the powder surface and has hydrophilic properties, making it vulnerable to moisture. Therefore, in this study, AlSi10Mg powder was hydrophobically modified through silane surface treatment to improve the flowability and spreadability by reducing the effects of moisture. The improved flowability according to the number of silane surface treatments was confirmed using a Carney flowmeter. In addition, to confirm the effects of improved spreadability, the powder prior to surface treatment and that subjected to surface treatment four times were measured and compared using s self-designed recoating tester. The results of this study confirmed the improved flowability and spreadability based on the modified metal powder from hydrophilic to hydrophobic for obtaining a highquality additive manufacturing product.

In this study, numerical analysis is conducted to investigate the flow characteristics of a turning type flood gate fishway with various design factors. The shapes of the fishway are circular and rectangular type. Baffles are installed to reduce the velocity in the fishway, and the gap and rotational arrangement of the baffles are set as design factors. To reduce the maximum velocity, a cavity-shaped break region is installed to examine the flow characteristics according to the presence of the break region. As a result, in the condition where the shape of the fishway is rectangular, the outlet average flow velocity is larger than that in the circular condition. The highest flow velocity occurs when the baffle is rotated in 90-degree arrangement. As the baffle gap increases, the average velocity increases. The cavity-shaped break region creates a recirculation zone in the fishway, and as a result, shows a decrease in the maximum velocity of up to 5.8%.

국제해사기구(IMO)의 온실가스(GHG) 감축 전략과 같은 환경규제를 강화함에 따라 친환경 선박 및 대체 연료 등 기술 개발이 확대되고 있다. 그의 일환으로 해운사와 조선사를 중심으로 에너지 저감과 풍력 추진 기술을 활용한 선박 추진 기술이 대두되고 있다. 풍 력 추진 기술의 확보와 실증 연구를 조선 및 해운 분야에 도입함으로써 친환경 기술을 활용한 고부가가치 시장을 창출할 수 있으며, 운항 선박의 연료 소비율을 줄임으로써 연비를 약 6~8 % 정도 향상시켜 GHG의 감축을 기대할 수 있다. 로터 세일(Rotor Sail, RS) 기술은 원형 실린더가 일정한 속도로 회전하여 유체를 통과할 때 실린더의 수직 방향으로 유체역학적 힘을 발생시키는 기술이다. 이를 마그누스 효과 (Magnus Effect)라고 하며, 본 연구에서는 선박에 설치된 풍력보조추진 시스템인 RS 주위의 난류 유동특성에 관한 수치해석적 연구를 통하 여 추진효율을 높일 수 있는 방안을 제시하고자 하였다. 그래서 RS의 공기 역학적 힘에 영향을 미치는 매개변수로써 속도비(Spin Ratio, SR)와 종횡비(Aspect Ratio, AR) 변화에 따른 양력계수( )와 항력계수( )를 도출하였고, RS 끝단 플레이트(End Plate, EP) 적용에 따른 RS 주변 유동특성을 비교하였다.

Flow prediction was carried out through observational survey and three dimensional multi-layered numerical diagnostic model experiment to clarify the time and spatial structure of tidal current and residual flow dominant in the sea exchange and material circulation of the waters around Geumo Islands in the southern waters of Korea. The horizontal variation of tidal current is so large that it causes asymmetric tidal mixing due to horizontal eddies and the topographical effect creating convergence and dispersion of flow direction and velocity. Due to strong tidal currents flowing northwest-southeast, counterclockwise and clockwise eddies are formed on the left and right sides of the south of Sori Island. These topographical eddies are created by horizontal turbulence and bottom friction causing nonlinear effects. Baroclinic density flows are less than 5 cm/s at coastal area in summer and the entire sea area in winter. The wind driven currents assuming summer and winter seasonal winds are also less than 5 cm/s and the current flow rate is high in winter. Density current in summer and wind driven current in winter have a relatively greater effect on the net residual flows (tidal residual current + density current + density driven current) around Geumo Islands Sea area.

Among the various causes of the vibration problem of the radial sluice gate used in Saemangeum, the effect of flow-induced vibration was studied by the method of computational fluid analysis. In this study, the effect on the flow-induced vibration of the Saemangeum radial sluice gate was evaluated by 2D unsteady flow numerical analysis using ANSYS Fluent. Gate opening cases of 0.2m, 0.3m, 0.4m, 0.5m, and 1.0m were analyzed. As a result, the flow-induced vibration characteristics due to the instability of turbulent flow were observed through FFT analysis. As the gate opening increases, the frequency of the maximum amplitude moves gradually to a lower frequency region with the reduction of the magnitude. Therefore the flow-induced vibration effects can be considered as small with the gate opening increase.

본 연구에서는 80k Bulk carrier의 저항성능 향상을 목적으로 선미부에 1개의 핀을 부착해 선미 유동을 제어하였고, 저항성능 및 반류의 변화를 분석하였다. 부착된 핀은 직사각형 단면을 가지며, 길이와 폭, 두께는 고정된 채 길이 및 흘수 방향 부착 위치와 유선에 대 한 각도만 변화가 있었다. 나선 및 핀이 부착된 선체에 대한 모형 스케일에서의 CFD 해석이 수행되었고, 그 결과를 실선 확장 후 비교하 였다. 핀은 프로펠러로 유입되는 빌지 볼텍스의 경로를 선미 트랜섬 쪽으로 변화시켰고, 이는 프로펠러 상부와 선미부의 압력을 증가시켰 다. 이로 인해 선체의 압력저항 및 전 저항이 감소되었으며, 감소율은 핀의 부착 위치가 선미 및 선저와 가까울수록 높았다. 또한 핀은 공 칭반류를 감소시켰는데 핀의 각도가 커질수록 반류의 변화가 컸고, 전 저항 저감률은 최대가 되는 특정 각도까지만 비례하였다. 대상 선 박에 단일 핀을 부착했을 시의 최대 전 저항 저감률은 약 2.1 %였고, 선미로부터 수선간장의 12.5%, 선저로부터 흘수의 10 % 위치에 14 의 각도로 부착됐을 때이다.

In general, small and medium-sized computer rooms do not have access floors for reasons of increased floor height and increased construction cost. Therefore, the air conditioning method used here applies the method of directly blowing the cold air of the air conditioner into the computer room. In this case, the hot/cold air is not separated, and as the hot air is recirculated, it is re-introduced to the front of the server rack, resulting in a problem that the server cooling efficiency is decreased. In addition, in such a computer room structure, it is difficult to configure and install a containment system. In this study, we tried to understand the problem of the formation airflow in the case of using the existing air conditioning method, and to find a method of configuring the air conditioning environment to improve the cooling efficiency. The purpose of this study was to understand the airflow/temperature distribution in the computer room using the CFD simulation method. In addition, the thermal characteristics of various air-conditioning environments such as the location of the CRAC cold air discharge location, the layout between server rack and CRAC and the containment were reviewed.