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.

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.

Numerical analysis has been carried out to analyze seawater flow field and power generation characteristics of the tidal current power generation system for various multi channel shroud systems. Geometrical multi channel arrangement largely affects the flow field characteristics in the shroud system which power generation performance through turbine blade depends on. Sectional averaged velocity in front of the turbine blade which increases more than 2 times compared with channel inlet is much influenced as well as the flow from the rear with curl. And flow variation results in high inlet velocity in horizontal arrangements of multi channels with mechanical output of the turbine. These results are expected to be used as applicable data for the development of the tidal power generation system with shrouds.

Numerical analysis has been carried out to investigate seawater flow field characteristics with various current directions near the manganese nodule mining device. Seawater flow near the collecting device is largely influenced by the sea current direction, especially along the downstream of the rear system. Predicted flow velocity distributions are analyzed with turbulent kinetic energy and drag force. There is big flow field variation when the direction angle between the mining device and seawater current flow approaches to 30°~ 120°, and flow velocity along the rear region of 60° becomes faster than 180°. Averaged turbulent kinetic energy at 180° also becomes low, about 57% higher at 60°. These results from the study can be applicable to the optimum design of manganese nodule collecting system in the deep seawater flow.

In this research, the heat and flow analysis in a condenser of vehicle HVAC system was investigated numerically regarding the different shapes of the condenser tube. The velocity, pressure, and temperature distribution of the test fluid(R-134A) inside the tube were numerically calculated for the optimum design of the condenser tube for two different length with four different inlet velocities. In addition, the local pressure and temperature distributions for total tube length were calculated and the variation of pressure drop of the R-134A with flow rate were also calculated numerically. The tube at case 1 with less curved elbows was determined for the better design than case 2 in the aspect of energy-effective shape of the condenser tube.

For the purpose of the enhancement of the air conditioner performance and fuel effciency, several cases of centrifugal impeller for passenger car air conditioner have been numerically analyzed by changing central angle of blades and length of outlet for shape optimization of the impeller. Commercial CFD program Fluent 6.3.26 has been used to compute velocity, temperature, pressure and turbulence intensity that can lead numerous results. The central angles of two blades and three cases of outlet length led 4～12% and 3.5～6.4% differences of velocity and flow rate, respectively. The velocity distribution near the blade surface was axisymmetric and had a maximum value of 22.19 m/s and velocity of the vertical direction of the impeller showed linear increase with horizontal direction. At case 3 of oultet length, there existed a a minimum pressure value of -133320 Pa.

3차원 실내공간의 상부에서 일정유속이 유입하여 양측면 하부쪽으로 유출될 경우, 책상형의 가열 장애물 영향에 의한 유동장의 변화와 온도분포를 수치계산 한 결과 다음과 같은 결론을 얻었다. (1)표준 k-ε 2 방정식 모델로 난류유동장을 해석한 결과 장애물을 기준으로 상하부에는 독립적인 큰 재순환 영역이 존재함을 알 수 있었다. (2) 유입류의 속도 변화에 따른 전제적인 유동패턴은 큰 변화없이 상사적인 분포를 하는 것을 알 수 있었다. (3) 유입속도가 감소함에 따라서, 공간에 대한 발열체의 온도영향이 커진다. (4) Re수가 작은 범위 (10 상(4)-10 상(5)에서는 열전달이 급격히 상승하여, Re수가 10 상(5)이상이 도면 열전달이 거의 일정하다.

최근 전 지구적인 기후변화의 영향으로 집중호우가 증가하고 있어 산지가 많은 국내에서는 산지재해 발생 위험이 증가하고 있다. 특히 산지에서 발생하는 토석류의 경우는 산지계류를 따라 빠르게 이동하여 하류부에 위치한 도심지까지 피해를 주고 있다. 그러나 토석류 피해지역을 정확히 분석하고 대책을 수립하기 위한 연구는 매우 미진한 상태이다. 따라서 본 연구에서는 지상 LiDAR 장비를 활용하여 토석류 발생 및 피해지역에 대한 3차원 정밀지형정보를 구축하는 방법에 관해 연구를 수행하였다. 구축된 3차원 지형정보는 토석류 피해지역의 복구활동 및 시간경과에 따른 재해현장의 환경변화에 지장을 받지 않고 다양한 연구활동이 가능하다. 따라서 지상 LiDAR로 구축된 지형자료는 토석류 피해지역의 이동과 확산범위 산정을 위해 적용된 RAMMS 모형의 기본자료로 활용하였다.

In order to reduce the uncertainties and improve the air flow field, objective analysis using observational data is chosen as a method that enhances the reality of meteorology. To improve the meteorological components, the radius influence and nudging coefficient of the objective analysis should perform a adequate value on complex area for the objective analysis technique which related to data reliability and error suppression. Several numerical experiments have been undertaken in order to clarify the impacts of the radius influence and nudging coefficient of the objective analysis on meteorological environments. By analyzing practical urban ground conditions, we revealed that there were large differences in the meteorological differences in each case. In order to understand the quantitative impact of each run, the Statistical analysis by estimated by MM5 revealed the differences by the synoptic conditions. The strengthening of the synoptic wind condition tends to be well estimated when using quite a wide radius influence and a small nudging coefficient. On the other hand, the weakening of the synoptic wind is opposite.

Gwangyang Bay is often severely confronted by photochemical pollutants due to its location and dense emissions. It is located in a basin on the south coast of the Korean peninsula and is crossed by a remarkable cluster of hills and mountains of a small horizontal scale that forms a channel. Clearly, the air flow field has a great influence on the dispersion of air pollutants. The characteristics of the wind flow patterns have an important effect on the dispersion of pollutants emitted. In these situations, the distribution of the ozone concentration is extremely complicated because of the superposition of circulations of the air flow fields, especially in complex coastal region. In this study, we examined the distribution of the high level ozone on Gwangyang Bay particularly during the episode day (for 5 years). Among these days, A high level ozone was induced by the development of a sea/land breeze local circulation system, as well as by an anabatic/catabatic flow from the mountains and valley with weakening of the synoptic wind. High level ozone distribution pattern(6 types) on Gwangyang bay is analyzed and the comparison of each pattern reveals substantial localized differences in intensity and distribution of ozone concentration from the site coherence and UPA analysis of ozone concentration. The observed VOC concentration had much difference in concentrations and daily variations between Jungdong and Samil.

VOF법은 유체 체적 비율을 통해 밀도가 다른 두 유체를 한꺼번에 계산할 수 있는 수치해석 기법이다. 상용 CFD프로그램의 VOF옵션을 이용하여 자유수면 부근에서 정속으로 움직이는 물체 주위의 수치해석을 시도하였다. 검증 대상으로는 물 속에 잠겨있는 2차원 날개, 자유수면을 수직으로 관통하는 3원 날개, 그리고 컨테이너 선형이 사용되었다. 검증 결과 정도의 차이는 있지만 상용 코오드의 범용성을 어느 정도 확인할 수 있었고 자유수면 유동장을 모사하는데 VOF법이 무난히 활용될 수 있음을 알 수 있었다.

파력발전장치 중 진동수주(Oscillating Water Column)형은 3단계 에너지 변환과정을 거치게 된다. 그 중 파랑에너지를 공기에너지로 변환하는 장치인 공기실의 형상을 바꿔가며 그에 따른 성능을 상용 CFD 코드인 FLUENT를 이용한 수치 해석 기법으로 연구하여 보았다. 통상 OWC형 파력발전장치는 공기실과, 터빈이 설치되는 덕트 간에 효율적인 이유로 급축소 형태를 취하고 있는데 이 때 공기실과 터빈 연결부의 형상이 파력발전 장치 전체 성능에 중요한 영향을 미치므로 공기실내의 압력을 최소화하고 터빈 유입유속의 가속화가 용이한 가장 적합한 형상을 정상 및 비정상 해석을 통하여 찾고자 하였다.

Enormous apartment complexes in urban areas, temporary inversion state and heat island effect occur due to the strong sunshine and weak wind speeds which hinders the dispersion of air pollutants that are emitted from neighboring areas of apartment complexes. In this study, analysis were conducted by using the Fluent code based on the CFD(Computation Fluid Dynamics), including building layout, material, building height from the ground surface, the heat, analysis of flow field in the apartment complex. It was estimated that the temporal radiation inversion phenomenon during the daytime, which was caused by the weak wind speed and higher temperatures in the upper level, contributed to the stagnation of the air pollutants in the lower layer of the apartment complex.