얕은 물에서 선박과 바닥의 상호작용으로 인해, 제한이 없는 깊은 물에서 운항할 때와 비교하여 저항이 증가하는 현상이 발생 한다. 이러한 천수효과에 의해 증가하는 저항은 주로 조파저항에 기인하기 때문에, 본 연구에서는 유람선을 대상으로 LCG(Longitudinal Center of Gravity)의 위치 변경을 통해 성능을 최적화하여 조파저항을 감소시키는 것을 목표로 진행하였다. 수치해석 시뮬레이션을 통해 LCG 위치를 최적화하여 저항의 최소값을 찾고, 이후 수심의 깊이에 따른 영향을 분석하였다. 분석 결과, 37.5% - 52.5% Lpp의 영역에서의 LCG 변화는 총 저항에 큰 영향을 주었으며, 깊은 물의 조건에서는 총 저항의 최대값과 최소값을 비교하였을 때, 72.67%의 큰 차이를 보이 는 반면, 얕은 물 조건에서는 그 차이가 62.97% 정도로 비교적 낮은 차이를 보인다. 수심의 깊이에 따른 효과는 수심이 낮을수록 총 저항 이 증가하는 경향을 보였다. 깊은 물과 비교하여 1.5m의 얕은 물에서는 총 저항이 최대 67.68% 가량 증가하는 것으로 분석되었다. 이 경우 총 저항 증가의 주요 원인은 전체 저항의 84.99%를 차지하는 조파저항에 의한 것으로 판단된다.

A cyclone separator is a device that separates solid particles from a fluid using centrifugal force and gravity in its inner chamber. Among cyclone separators, the separator that uses water as a working fluid is called as hydrocyclone separator, which has been developed for the purpose of dehydrating solid mixtures with a proportion of solids floating in liquids greater than 1, such as soil, coal, and cement slurry. In this paper, a hydrocyclone was designed based on the previously proposed design method, and how different the performance is from the targeted value was investigated using the computational fluid dynamics.

Microclimate analysis was conducted through actual measurement according to land use status in urban, and CFD analysis was conducted to analyze and predict the microclimate characteristics of urban, and compared and analyzed with the actual measurement results. It was measured in high-rise areas and parks, and the temperature of the park area was 0.4 to 0.6℃ lower, and the relative humidity was 1.0 to 3.0% higher. The correlation coefficient was obtained by comparing the results of the computational fluid analysis with the results of the computational fluid analysis at the actual location located within the CFD analysis area for validation. The seasonal correlation coefficients are all higher than 0.8, so it is judged that they can be applied to microclimate analysis in urban area. The computational fluid analysis was divided into three areas (low-rise, low and high-rise, and high-rise) centered on the A2 point. On average, the low-rise area was 0.1 to 0.4% higher than the high-rise area. In the low and high-rise area and high-rise area, the pith of buildings are wide, so the airflow is smooth, so it is judged that the temperature is relatively low.

Micro-climate measurements and computational fluid analysis were conducted to use it as basic data for the preservation and management of the old house of Kim Myung-kwan, a traditional building that is National Folk Cultural Property No. 26. As a result of the actual measurement, the temperature and humidity are relatively evenly distributed indoors unlike outdoors, but the temperature and humidity vary depending on the time change and the installation location in the outdoors. It was found that the temperature increases after dawn and the temperature varies depending on the installation position around 14:00–15:00, when the temperature becomes the highest. In particular, the temperature was high at the outdoor measurement point adjacent to the building and the fence. As a result of the computational fluid analysis, the temperature was high in the buildings and fences in the old house or in the area adjacent to the building, and it was about 1℃ higher than the surrounding area. In this area, it is judged that the thickening of wood will occur more severely than in other locations, and special preservation management is required.

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.

Failure to comply with the performance test requirements for the centrifugal pumps at power plants often results in performance dissatisfaction as a result of field tests. This study proposed a method of reducing the uncertainty of the field test results by evaluating the systematic error in the measurement system caused by failure to follow the test requirements using the computational fluid dynamics(CFD) technique. As a result of the evaluation of the systematic error and reflecting it in the performance test data, it was confirmed that the error occurred at a constant rate with respect to the flowrate and that the pump, which showed a difference in performance actually had the same performance.

Valves are one of the indispensable components in modern industry. Filling and de-pressure connectors in rocket valves used for space launch vehicles are very important parts for smooth fluid supply. For this reason, an optimized design that can improve efficiency, miniaturization, weight reduction, and safety of the valve at the same time is required. In this work, flow analysis and structural analysis were performed through 3D modeling using computational numerical analysis for open type filling and de-pressure valves. As results, the flow velocity and pressure distribution of the fluid were analyzed through the flow analysis of valve, and stress distribution was conducted in structural analysis. Through this study, it is consequently expected to provide valves of various specifications by performing production and performance test evaluation of development prototypes.

When operating at high speed on a vessel, a high-speed planing hull occurs nonlinear movements such as stern trim and large sprays. This phenomenon results in the hindrance of stability, embarkation and mission performance. Excessive stern trim during the slides decreases propulsion efficiency and visibility of helmsman due to porpoising and changing the attack angle of the fluid flowing into the propeller. To improve these problems, an outboard floating plate is installed on the cavitation plate to greatly suppress or eliminate the porpoising phenomenon. In this study, to analyze the performance of the floating plate mounted on the outboard engine, numerical analysis was carried out to investigate the resistance applied to the floating plate and the lift generated according to the change of the angle of attack and the flow velocity. The reliability of the floating plate mounted on the outboard engine was verified by applying the floating plate according to the speed and the angle of attack.

국내 자연재난 피해의 50%는 태풍에 의해 발생하며, 최근 태풍에 동반된 강풍에 의한 인명 피해가 빈번하게 발생하고 있다. 재난 피해 저감을 위한 재난 안전 교육의 일환으로 국내의 강풍체험시설은 대부분 제한된 공간에 설치되어 체험을 위한 내부 유동장의 효과적 설계가 필요하다. 이를 위해 본 연구에서는 전산유체역학 기법을 이용하여 강풍 체험장의 내부 유동장을 해석하였으며, 내부 구조 형상으로 인해 발생하는 압력 저항을 공간 저항으로 정의하였다. 기존 강풍 체험장에 대한 분석 결과 기존의 수평 방향 풍로 구조로 인해 매우 불균질한 내부 유동장이 형성되고 큰 공간 저항이 발생함을 확인하였다. 이를 개선하기 위하여 풍로를 수직 방향으 로 변경함으로써 공간 저항을 80% 가까이 감소시킬 수 있음을 확인하였으며, 체험장 내부 유동장의 균질도도 크게 향상되어 실질적 강풍 체험장 구현이 가능함을 확인하였다.

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.

최근 일본의 건축구조기준(AIJ 2015)에서는 CFD 해석을 통한 풍하중 산정을 허용한 바 있다. 이는 컴퓨터의 연산 능력 향상 및 CFD 해석 이론의 발전으로 인해 해석의 결과가 풍동실험의 결과와 유사한 수준에 도달하였음을 뜻한다. 본 연구에서는 먼저 CFD 해석의 이론적 배경을 살펴보고, 일본의 건축구조기준 및 유럽의 과학기술연구 프로그램인 COST에서 권장한 CFD 해석 절차를 토대 로 해석을 진행하였다. 해석 결과의 신뢰성을 검증하기 위해 Tokyo Polytechnic University에서 제공하는 풍동실험 데이터를 사용하였 고, 해석과 실험의 유사성을 평가하기 위하여 형상비가 3, 4, 5일 때의 풍방향하중을 비교하였다.

Conventional rotary sawing machine for cutting lumber generates severe amount of dust scattering to the environment. In this research, the design improvement of the rotary sawing machine is achieved to significantly reduce the dust scattering by the design process utilizing computational fluid dynamics (CFD) analysis. Several design candidates for the design improvement of the rotary saw system were proposed and modeled, and CFD analyses were performed to choose the best design in viewpoint of the least dust scattering. CFD analysis proved to be very useful to predict the characteristics of the air flow inside the saw system. The movement of dust particles with the air flow during the sawing process was analyzed for various design features of the saw system. The most efficient design to minimize the amount of dust particles ejected from the saw system was chosen based on the CFD analysis results. Then, the prototype of the best candidate of the improved rotary saw machine was built and the amount of dust particles were measured to verify its performance.

This paper presents the dimensionless wall distance, y+ effect on SST turbulent model for wind turbine blade. The National Renewable Energy Laboratory (NREL) Phase VI wind turbine was used for the study, which the wind tunnel and structural test data has publicly available. The near wall treatment and turbulent characteristics have important role for proper CFD simulation. Most of the CFD development in this area is focused on advanced turbulence model closures including second moment closure models, and so called Low-Reynolds (low-Re) number and two-layer turbulence models. However, in many cases CFD aerodynamic predictions based on these standard models still show a large degree of uncertainty, which can be attributed to the use of the  -equation as the turbulence scale equation and the associated limitations of the near wall treatment. The present paper demonstrates the y+ definition effect on SST (Shear Stress Transport) turbulent model with advanced automatic near wall treatment model and Gamma theta transitional model for transition from lamina to turbulent flow using commercial ANSYS-CFX. In all cases the SST model shows to be superior, as it gives more accurate predictions and is less sensitive to grid variations.

In the present numerical study, simple stenotic artery models using pulsatile flow condition were investigated. A reversing sinusoidal velocity for pulsatile flow was imposed at the flow inlet and the corresponding based on the vessel radius. The stenotic geometries modeled using mechanical 3D CAD. It has been used that consist of 0.2, 0.4, 0.5 0.75 and 0.8 stenotic rate in a cylindrical tube. In this paper, numerical solutions are presented for a second harmonic oscillatory flow using commercial code CFX 14. As stenosis rate increases, the maximum wall shear stress(WSS) increases while the minimum WSS decreases. As the stenotic rate increases, the pressure drop at the throat severely decreases to collapse the artery and plaque. It is found that the fluid mechanical disturbances due to the constriction were highly sensitive with rate of stenosis. When stenosis rate increases, the recirculation region exists. In this recirculation region the possibility of plaque attachment is increasingly higher. The present results enhance our understanding of the hemodynamics of a stenotic artery.

고온수증기전기분해(HTSE) 장치의 수소생산 및 열 화학적 특성을 파악하고자 COMSOL Multiphysics®를 사용해 2차원 정상상태 수치해석을 실시하였다. 계산을 위한 주요 파라메터로는 작동전압, ASR(Area-specific Resistance) 및 유입가스의 온도와 압력 등이다. 해석결과 1.2454 V에서 Thermal-neutral Voltage가 나타나고, 작동 전압이 증가함에 따라 Cell의 내부 온도가 단조 증가하는 것이 아니라 Thermal-neutral Voltage를 기준으로 낮은 전압에서는 Cell의 온도가 감소하고, 높은 전압에서는 Cell의 온도가 증가하였다. 또한, ASR 값이 증가함에 따라 Cell 내부의 온도는 하강하고, 수소생산율도 낮아지는 경향을 보였다.

원자력을 이용한 황-요오드 수소생산 공정 중 황산용액을 이송하는 기존의 시스템과 달리 새로운 황산 이송장치는 벨로우즈 박스 내에서 벨로우즈 외측으로 고온 부식성 액체인 황산이 흐르고, 벨로우즈 내측으로는 냉각수가 흐르는 상태에서 주기 운동을 통해 황산용액이 펌핑 되도록 구성된다. 200 ℃ 이상의 고온 부식성 액체인 황산용액을 정량으로 이송할 수 있도록 장치의 주요부품인 벨로우즈 주변의 열해석을 통해 온도분포를 확인하여, 테프론 재질의 벨로우즈의 내식성 및 내열성을 파악하고, 장치의 안전하고 효율적인 운용을 위한 기초자료를 취득하고자 하였으며, 냉각수 입구직경 3 ㎝, 질량유량이 3.9199 ㎏/s로 고정한 경우 벨로우즈의 길이에 관계없이 테프론 변형온도 이하임을 알 수 있었다.

이 연구에서는 친환경적이고, 효율적인 수소생산방식으로 알려진 고온수증기전기분해(HTSE)에 대한 열․화학적 특성 및 수소 생산 특성을 파악하고자 하였으며, 이론적 고찰과 더불어 정밀한 전산유체해석(CFD)를 통하여 획득한 결과를 제시하였다. 연구의 주요 파라메터로는 ASR(Area Specific Resistance)의 영향 및 유입가스의 온도와 압력 등이다. 상용 FEM CODE인 COMSOL Multiphysics ver. 3.3 소프트웨어를 이용하여 2차원 정상상태 전산유체해석을 실시하였으며, 다음과 같은 결론을 얻었다. 1) ASR 값이 증가함에 따라 cell 내부의 온도는 하강하였 고, 수소생산율도 낮아졌다. 2) 입구압력이 0.1MPa과 5MPa인 경우를 비교한 결과 0.1MPa일 때가 5MPa일 때 보다 최대속도를 기준으로 약 52 배 빠른 속도를 나타내며, cell의 최대온도를 기준으로 약 6.6K 가량 높은 것으로 확인되었다.