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이선엽,최원빈,김창기,이석환,오세철,이정우 한국자동차공학회 2022 International journal of automotive technology Vol.23 No.1
The effects of intake pressures and EGR rates on the natural gas/diesel dual-fuel combustion under a high load condition (brake power of 100 kW) were evaluated using a 6-L CI engine in this study. Natural gas fraction was fixed as 80 % of total input energy for all the dual-fuel combustion operations and engine rotation speed was set to 1,800 rpm. Intake pressure was varied from 0.15 to 0.21 MPa by controlling the waste gate type turbocharger system. EGR rate was changed mainly by controlling EGR valve opening from fully closing to mid-opening to fully opening, but it was also affected when intake pressures were varied. In addition to these intake mixture parameters, diesel injection timing was adjusted in two cases–early and late injections and all the experimental results were compared to those of the neat diesel combustion cases. The results emphasized that the dual-fuel combustion was more sensitive to overall equivalence ratio determined by intake pressures and EGR rates than the neat diesel combustion because it had flame propagation process of premixed natural gas and air mixture. Thus, during the dual-fuel operations, in-cylinder temperature and brake thermal efficiency were decreased as intake pressure was increased.
이선엽,조재환,이해각,조무성,박철수,김응찬,김성규,동경래,정운관,신재우,김영재,조영국 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.5
The aim of this study was to reduce the effect of cross-talk artifacts on the region of interest (ROI) and to improve the diagnostic value of an image by conducting an examination using the linear (series) method, rather than the interleave method, based on the time concept, which is a basic principle of MRI, with a focus on the T1-weighted image, which has a strong effect on the cross-talk artifact. A water phantom was placed in the center of a brain coil before using the interleave method and the linear method to obtain cross-sectional images. A sagittal oblique scan was conducted to ensure that the slice groups intersected one another. A reference image was also acquired at TR (time of repetition) = 500 msec. Subsequently, the TR was changed to 600 and 700 msec to conduct scans. The analysis method was to use the interleave method and the linear method to compare the effects of the cross-talk artifacts and the TR. As scanned images were suggested, the SNR (signal to noise ratio) for the ROI was measured. According to the study results, the effects of cross-talk artifacts were reduced more significantly in the image scanned using the linear method than in that using the interleave method. When the SNRs of the images scanned in the interleave method and the linear method were compared, the image scanned in the linear method showed higher SNRs for the anterior and the posterior parts at TR = 500, 600, and 700 msec. On the other hand, the image scanned in the interleave method showed an increase in the SNR for the middle part, where the cross-talk artifacts did not appear. This means that the cross-talk artifacts were reduced in the image scanned using the linear method, which resulted in an increase in the SNR. Overall, the SNRs of each image for the interleave method and the linear method were highest at TR = 700 msec. In conclusion, the linear method is selected to reduce the effects of cross-talk artifacts in a simultaneous and multiple slice plane oblique scan where the TR is extended.
튜브 직경에 따른 과냉각 유동 내 단일 기포 응축의 영향
이선엽,Cong-Tu Ha,이재화 한국가시화정보학회 2023 한국가시화정보학회지 Vol.21 No.1
Bubble condensation, which involves the interaction of bubbles within the subcooled liquid flow, plays an important role in the effective control of thermal devices. In this study, numerical simulations are performed using a VOF (Volume of Fluid) model to investigate the effect of tube diameter on bubble condensation. As the tube diameter decreases, condensation bubbles persist for a long time and disappear at a higher position. It is observed that for small tube diameters, the heat transfer coefficients of condensation bubbles, which is a quantitative parameter of condensation rate, are smaller than those for large tube diameters. When the tube diameter is small, the subcooled liquid around the condensing bubble is locally participated in the condensation of the bubble to fill the reduced volume of the bubble due to the generation of a backflow in the narrow space between the bubble and the wall, so that the heat transfer coefficient decreases.
이선엽,아메드 니아즈,남강현 제어로봇시스템학회 2021 제어로봇시스템학회 국내학술대회 논문집 Vol.2021 No.6
This paper proposes a system modeling and a controller design for omnidirectional motion robots based on Mecanum wheel. Conventional mobile robots are capable of moving longitudinally and rotating, but it is impossible to control each motion independently. To overcome this limitation, we designed a holonomic type of vehicle that allows omnidirectional motion by attaching motors individually to each Mecanum wheel. The Mecanum wheel consists of a central main wheel and a roller placed at a specific angle around main wheel, enabling individual motion of X, Y, and Yaw. By matrixing the relationship between angular velocity of wheels and vehicle velocity, individual motor velocities are calculated as reference inputs to the controller. Base on this matrix and system characteristic of motor, this paper proposes a model-based feedback, feedforward controller and disturbance observer.
이선엽,유솔,이동재,송현선,김보경,윤동민,김성렬 한국생활환경학회 2015 한국생활환경학회지 Vol.22 No.3
Recently, a large number of studies have indicated that exposure to outdoor air pollution, including fine particulate matter (PM2.5), caused serious health risks of lung cancer and cardiovascular diseases. We conducted this study to assess the level of awareness among Korean adults on the characteristics and health risks of PM2.5. We randomly recruited 507 adults aged 20 years or older through a commercially available survey institute. Our questionnaire consisted of five categories, including demographic information, definition of PM2.5, characteristics of PM2.5, health risks of PM2.5, and control policies currently applied in South Korea. Data analyses were conducted using SPSS version21.0. Of the participants, only 10% accurately distinguished the definition of PM2.5 from that of PM10 and 28.8% were aware of the fact that exposure to outdoor particulate matter causes carcinogenic effects. Only 10.5% of all the respondents recognized that reinforced airquality standards were conducted in January 2015. Most of the participants lacked information about the definition of PM2.5 and the potential health risk caused by exposure to PM2.5. Therefore, in this regard, policy makers and public health experts need to improve the public’s awareness and disseminate this information effectively.