• 대한기계학회논문집B
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• 제22권9호
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• pp.1317-1324
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• 1998

In general, DI gasoline engine has the advantages of higher power output, higher thermal efficiency, higher EGR tolerance and lower emissions due to the operation characteristics of increased volumetric efficiency, compression ratio and ultra-lean combustion scheme. In order to apply the concept of stratified charge into direct injection gasoline engine, some kinds of methodologies have been adapted in various papers. In this study, a reflector was adapted around the injector nozzle to apply the concept of stratified charge combustion which leads the air-fuel mixture to be rich near spark plug. Therefore, the mixture near the spark plug is locally rich to ignite while the lean mixture is wholly introduced into the combustion chamber. The characteristics of combustion is analyzed with the variations of fuel injection pressure and load in a stratified -charge direct injection single cylinder gasoline engine. The obtained results are summarized as follows ; 1. The MBT spark timing approached to TDC with the increase of load on account of the increase of evaporation energy, but has little relation with fuel injection pressure. 2. The stratification effects are apparent with the increase of injection pressure. It is considered by the development of secondary diffusive combustion and the increase of heat release of same region, but proceed rapidly than diesel engine. Especially, in the case of high pressure injection (l70bar) and high load (3.0kgf m), the diffusive combustion parts are developed excessively and results in the decrease of peak pressure than in the case of middle load. 3. The index of engine stability, COVimep value, is drastically decreased with the increase of load. 4. To get better performance of DI gasoline engine development, staged optimizaion must be needed such as injection pressure, reflector, intake swirl, injection timing, chamber shape, ignition system and so on. In this study, the I50bar injection pressure is appeared as the optimum.

• 대한기계학회논문집A
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• 제34권3호
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• pp.273-281
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• 2010

본 논문은 교정가속수명시험법을 이용하여 액슬구동축의 피로수명을 예측하는 법을 제안한다. 교정가속 수명시험법은 수명예측, 시험시간 절감, 신뢰성 정량화시에 매우 효과적이다. 피로시험은 두 개의 고 부하 수준과 한 개의 저 부하 수준에서 수행되고, 외삽법을 사용하여 사용수준에서의 수명시간을 예측하게 된다. 본 논문에서는 수행시험 결과로부터 획득한 수명시간, 가속지수, 형상모수, 척도모수등과 같은 주요 신뢰성 인자들을 보여주고 있다. 액슬구동축의 수명예측은 부하스펙트럼 데이터와 시험데이터와의 비교 연구를 수행하여 검증하였다. 교정가속수명시험법을 사용한 수명예측법은 짧은 시간내에 수명을 예측하는데 매우 효과적인 방법임을 확인하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제34회 춘계학술대회논문집
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• pp.377-382
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• 2010

젤 추진제와 유변학적 특성이 유사한 모사 젤 추진제를 물, Carbopol 941, NaOH 농축액을 혼합하여 제작하였고, $Al_2O_3$ 나노 입자를 첨가하여 점도 특성을 비교하였다. 두 가지 모사 추진제의 물성치를 바탕으로 곡관 덕트 내에서의 유동특성을 수치모사하여 해석하였고 덕트에 Dean vortices가 발생하는 임계 Dean 수를 도출하였다. 젤-나노 추진제의 경우 비록 높은 겉보기 점성계수를 가지나 젤 추진제와 비교시 같은 범위의 임계 Dean 수가 도출되었다. 이는 Fellouah et al.[1]이 제시한 바와 같이 비슷한 값의 Power law 지수에 기인하는 것으로 판단된다.

• 한국광학회지
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• 제10권3호
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• pp.248-253
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• 1999

본 논문에서는 측면이 연마된 단일모드 광섬유와 폴리머 다중 평면도파로가 결합했을 때 발생하는 모드 결합현상을 이용한 능동형 광결합기를 연구하였다. 제안된 소자는 파장가변 광필터나 광변조기로 이용할 수 있을 뿐만 아니라, 광도파로 물질의 굴절률, 복굴절, 전기광학 계수, 열광학 계수 등을 측정하는 도구로 응용할 수 있다. BPM으로 최적화된 결합기를 설계하였고, 열광학 폴리머를 능동 평면 도파로층으로 이용하여 결합기를 제작하였다. 제작된 소자는 -0.5dB 이하 손실, 공진파장 -13dB 소멸비. 그리고 열광학 효과에 의해 -1.5nm/$^{\circ}C$ 정도의 파장 가변성을 보였다. 본 연구의 결과로 볼 때 열광학 능동형 광결합기는 광변조기, 파장가변 광필터, 광센서 등으로 이용될 가능성이 높다.

• 한국수자원학회논문집
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• 제38권1호
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• pp.37-48
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• 2005

본 연구에서는 국내ㆍ외의 하천자연도평가에 관한 방법을 조사하고, 국내에서 연구ㆍ제안된 하천자연도평가방법에 따라 내린천, 복하천과 안양천의 3개하천의 시범평가를 시행하였다. 시범평가 결과, 자연상태가 비교적 잘 보전된 내린천은 2등급, 인위적인 훼손에서 회복단계에 있는 복하천은 3등급, 인위적인 훼손이 심각한 안양천은 4등급으로 평가되어 비교적 하천의 생물서식처의 훼손정도를 적절히 반영하고 적용성이 우수한 것으로 검토되었다. 따라서 본 평가방법을 국가하천 및 지방1급하천 등 대하천에서도 적용이 가능하도록 평가부문 및 평가항목을 개선하여 하천의 생물서식처 복원을 위한 하천자연도평가 방법과 절차를 제안하였다. 금번 제안한 하천자연도평가는 하천형태와 하천환경의 2개 평가부문과 14개의 평가항목으로 구성하고, 평가척도는 자연성 저감정도에 따라 5등급으로 구분하였으며, 평가단위는 최적간격을 2,000m∼3,000m로 하였다.

• 지질공학
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• 제18권2호
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• pp.197-205
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• 2008

보강효과 및 계측조건의 영향이 배제된 무보강 상태의 전변위는 터널 굴착에 따른 암반 거동의 정량적 지표가 될 수 있으며, 이러한 변위는 지질학적 특성에 의존한다. 본 연구는 암반 상태별로 굴착에 따른 암반의 거동 특성을 잘 반영할 수 있는 암반 평가법의 제안을 목적으로 한다. 이를 위해 퇴적암을 기반으로 하는 터널을 대상으로 형상, 굴진장 및 굴착 조건 등이 고려된 3차원 수치해석을 수행하였으며, 이를 통긍 암반 상태에 따른 무보강 상태의 전변위를 산정하였다. 그리고 산정된 전변위를 외적기준으로 하고, 각 RMR 인자들을 설명변수로 하는 수량화분석을 수행하였다. 그 결과 각 RMR 인자의 변위 영향도를 결정하였으며, 최종적으로 수정된 RMR 배점 체계를 제안하였다.

• 한국환경복원기술학회지
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• 제19권3호
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• pp.29-44
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• 2016

The purpose of this study is to quantitatively and visually analyze the degree of green biotope fragmentation caused by road construction and other development work using FRAGSTATS and GUIDOS tool. Moreover, linking of the endangered species research, we mapped "Biotope Fragmentation Map" of Daejeon-city. The findings of the study are summarized as follows: First, as the result of FRAGSTATS, landscape indices : number of patch(NP), mean patch size (MPS), edge length(TE), mean nearest neighbor distance(MNN), edge shape(LSI) showed meaningful change from fragmentation. Moreover, the result of GUIDOS analysis, middle core-small core-bridge-branch-edge-islet-perforation showed increase of area percentage without large core. Lastly, analysis result of 'Biotope Fragmentation Map' revealed that changing site of large core's size appeared eighteen-site and designated as the special protection area appeared forty-one site. As the result of the two data, overlapping areas that showed both change of core size and revealed special protection areas revealed four site. For example, five species of endangered species appeared on the NO. 4 site in 'Biotope Fragmentation Map'. The findings of this study as summarized above are considered to play an important role in basic data preventing green biotope fragmentation at the planned level from various development work.

• 대한지역사회영양학회지
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• 제5권2호
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• pp.280-288
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• 2000

This study was undertaken to compare the obesity related dietary factors among rural middle school students living in Korea. Anthropometric data showed that mean height and weigh were 161.7$\pm$13.0 and 49.8$\pm$10.3kg in 226 male students and 158.3$\pm$6.1 and 48.2$\pm$7.5kg in 212 female students. Mean BMIs for boys and girls were 19.10$\pm$2.47 and 19.26$\pm$2.35, respectively. 71.68% of male students and 72% of female students were underweight by the BMI index. The BMI of older students was higher than young ones in both sexes. Most nutrient intakes of the subjects were below the RDA. In particular Ca and Fe intakes were extremely low in both sexes. 66.88% of the students skipped breakfast and it was found that the reasons for missing a meal for both sexes were significantly different. Compared to males, more female respondents felt guilty and depressed related to eating. Furthermore, females were more significantly concerned with body image, diet, and body weight(p〈0.001), and they were not satisfied with their weight. The sources of information on obesity and diet were from radio and TV in males while females got information from magazines and friends. In male students their ideal body weight was higher was higher than actual body weight. In contrasting, female students desired a thin body shape. A different approach for nutrition education for adolescents should be developed and implemented based on sex.

• 대한지역사회영양학회지
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• 제11권6호
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• pp.695-706
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• 2006

This study was to investigate the relationship between time spent on lunch and degree of obesity, eating habits in culinary college male students. This survey was conducted using questionnaires for 106 male students in a Hongseung-located culinary college. Over 16 minutes of time spent on lunch group had significantly lower body weights, obesity degrees and body mass index (BMI) and tended to have lower body fat % than the other groups. It suggests that shorter time spent on lunch is related with lower body weight, obesity degree and BMI. Those who ate the meal prepared by mother had longer time spent on lunch. The shorter times spent on lunch group recognized their body shape was lean, the longer time spent on lunch group recognized the overweight or obesity significantly. The shorter time spent on lunch group tended to eat the cooked rice in the gug and recognized that they were not healthy. Those who had diseases in the past tended to have shorter time spent on lunch. The more they chewed cooked rice and then longer time spent on lunch they had, they recognized their eating speed was not significantly speedy. The shorter time spent on lunch they had, the fewer fruits and salty foods they ate significantly. This study suggests that more chewing time. slower eating speed and longer time spent on eatmg lunch is very related with lowering weight, BMI, body fat % and obesity degrees, so male college students should be educated to have correct eating habits.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 추계학술대회 논문집
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• pp.291-291
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• 2013

The interior vehicle noise due to the exterior aerodynamic field is an important topic in the acoustic design of a car. The air flow detached from the A-pillar and impacting the side windows are of particular interest as they are located close to the driver / passenger and provides a lower insulation index than the trimmed car body parts. HMC is interested in the numerical prediction of this aerodynamic noise generated by the car windows with the final objective of improving the products design and reducing this noise. The methodology proposed in this paper relies on two steps: the first step involves the computation of the exterior flow and turbulence induced non-linear acoustic field using the CAA(Computational aeroacoustics) solver CAA++. The second step consists in the computation of the vibro-acoustic transmission through the side window using the finite element vibro-acoustic solver Actran. The internal air cavity including trim component are included in the simulation. In order to validate the numerical process, an experimental set-up has been created based on a generic car shape. The car body includes the windshield and two side windows. The body is made of aluminum and trimmed with porous layers. First, this paper describes the method including the CAA and the vibro-acoustic models, from the boundary conditions to the different components involved, like the windows, the trims and the car cavity is detailed. In a second step, the experimental set-up is described. In the last part, the vibration of the windshield and windows, the total wind noise level results and the relative contributions of the different windows are then presented and compared to measurements. The influence of the flow yaw angle (different wind orientation) is also assessed.