Air blower has been widely used in many industrial fields such as wind tunnel and large ventilation systems. Its performance is affected by operating conditions and system geometry of inpeller and duct, and these design parameter optimization is essential for the effective development. CFD analysis is carried out to investigate the air flow field characteristics with outlet total pressure in a blower system. Intake air into the impeller blade through the inlet is compressed, and then gradually discharged from the outlet with ascending total pressure, and predicted results are compared with test data. Especially this overall pressure difference in the blower system severely depends on the flow rate. These results are expected to be used as applicable design data for blower performance improvement.
Application areas of floating marine structure systems have been increased with the development of power generation systems using renewable energy. Hence it is necessary to analyze the behavior of these floating systems for efficient design and operation. In this study, a computational analysis was performed to predict the characteristics of mooring lines load variation connected to a floating marine structure with waves. Pressure on the floating body and mooring lines load were analyzed with wave direction and height. The floating body stability severely decreased for 90° of the wave incident direction, and maximum load of the mooring lines increased with the height. These results are expected to be applicable for optimal design of the marine floating system.
Numerical analysis has been carried out to predict the thermal characteristics for a LED lens in mold core system. These thermal characteristics inside the lens are largely affected by geometry, material, and initial conditions of the mold core and lens system. Local temperature and heat flux variation inside the lens are compared for several initial temperatures. Maximum temperature inside the lens was decreased rapidly from the beginning of cooling process up to about 10 seconds. There was also large variation of the heat flux at the upper and lower surfaces of the lens with initial temperature distribution. And the heat flux from the thin lower surface of the lens was relatively higher than the opposite-side thick region. In addition, overall heat transfer rate from the lens through the mold core has similar transient distribution from the beginning. These results can be applied as basic heat transfer data for the LED lens design and manufacturing process in the mold core system.
Structural characteristics have been analyzed for gear system in a commercial iron bending machine which is widely used at many building construction sites. This complicated gear system in the bending machine is fundamental power transfer unit from electrical motors, and it is composed of various configuration structure including various spur and helical gear assembly. Main structural characteristics of the gear system such as stress and deformation distributions are predicted with numerical simulation of FEM method for various operating conditions of torque and rotation speed. Results show that there is large deformation in lower region of driving gear, and high stress near those contact area which is greatly affected by motor torque. These results can be applied for the design improvement of efficient gear system in the iron bar bending machine.
Experimental analysis has been carried out on double glazed glass of a commercial vehicle to analyze thermal characteristics for various air flow conditions. This double glazed glass has an important effect on the blocking performance of heat transfer with the vehicle's moving speed and ambient thermodynamic conditions. Calculated thermal resistances and heat transmission coefficient through the glass were compared with measured air indoor and outdoor temperatures including the glass surfaces using an experimental apparatus. The thermal resistance through the glass was increased with the indoor air temperature while overall heat transmission coefficient was decreased due to the convective heat transfer effect. As indoor air became warmer, the effect of air flow velocity on the heat transmission coefficient was reduced significantly. It is expected that these results can be used as applicable design data for the development of the double glazed glass system for many commercial vehicles.
Numerical analysis has been carried out to investigate the characteristics of seawater flow fields and turbine output in a compact double current tidal power generation system for various level differences. There are growing concerns for the development of efficient tidal power generation which is stable and less affected by environmental circumstances as ocean energy. Especially the flow field characteristics in the compact tidal power generation system have a large influence on the system power generation performance. Flow velocity, pressure, and streamline distributions are compared including vertical type turbine out, and it can be predicted that seawater is accelerated by vortex flow in front of the turbine and there is severe turbine output variation due to the water level difference with pressure difference. These results can be applied as basic data for the effective development of compact tidal power generation system.
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.
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.
환경풍동 내 공기의 온도와 속도 변화에 대한 공기 유동과 전열 특성을 분석하기 위하여 수치해석을 수행하였다. 풍동 시험부 내 각 단면의 평균 속도, 균일도, 그리고 대류 열전달계수는 노즐 출구의 온도와 속도에 따라 큰 영향을 받게 된다. 노즐 출구로부 터 멀어질수록 평균 속도와 균일도가 점차 감소하고, 노즐 출구의 속도가 50km/h일 때 공기온도가 -40~60oC까지 변화함에 따라 단면 평균 속도와 균일도가 각각 약 12.9%와 13.5% 정도까지 증가하였다. 또한 시험부 바닥의 대류 열전달계수는 50~150km/h의 속도 변화에 대해 약 59.7%까지 증가하였으며, 공기의 온도와 속도가 증가함에 따라 시험부 열 유속도 함께 증가하였다. 본 연구에서 수행한 결과들은 최적의 환경풍동 설계에 필요한 주요 설계 자료로 활용될 수 있을 것으로 기대된다.
Agricultural meteorological information is an important resource that affects farmersʼ income, food security, and agricultural conditions. Thus, such data are used in various fields that are responsible for planning, enforcing, and evaluating agricultural policies. The meteorological information obtained from automatic weather observation systems operated by rural development agencies contains missing values owing to temporary mechanical or communication deficiencies. It is known that missing values lead to reduction in the reliability and validity of the model. In this study, the hierarchical Bayesian spatio–temporal model suggests replacements for missing values because the meteorological information includes spatio–temporal correlation. The prior distribution is very important in the Bayesian approach. However, we found a problem where the spatial decay parameter was not converged through the trace plot. A suitable spatial decay parameter, estimated on the bias of root–mean–square error (RMSE), which was determined to be the difference between the predicted and observed values. The latitude, longitude, and altitude were considered as covariates. The estimated spatial decay parameters were 0.041 and 0.039, for the spatio-temporal model with latitude and longitude and for latitude, longitude, and altitude, respectively. The posterior distributions were stable after the spatial decay parameter was fixed. root mean square error (RMSE), mean absolute error (MAE), mean absolute percentage error (MAPE), and bias were calculated for model validation. Finally, the missing values were generated using the independent Gaussian process model.