• 대한기계학회논문집B
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• 제34권10호
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• pp.933-939
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• 2010

본 연구는 타원형 노즐과 원형 노즐 내부에서 발생되는 cavitation의 발생 및 성장을 실험적으로 관찰하였다. 원형 노즐과 타원형 노즐의 cavitation 특성을 가시화 하기위해 투명한 아크릴로 노즐을 제작하였다. 실험에 사용된 노즐들은 같은 단면적으로 제작되었으며, 타원형 노즐의 경우 형상비(a/b)를 다르게 하였다. 분사압력의 증가에 따라 노즐내부 유동은 no cavitation, cavitation, hydraulic flip 영역으로 나뉘어졌다. 노즐의 형상에 상관없이 no cavitation과 cavitation 영역에서는 분사압력의 증가에 따라 유량은 증가하며, 유출계수는 감소하는 경향을 나타냈다. 그러나 hydraulic flip 영역에서의 유량계수는 일정한 값을 나타냈다. 타원형 노즐은 원형 노즐에 비해 높은 cavitation number에서 cavitation이 성장, 발달하였다. 특히 타원형 노즐에서는 장축의 cavitation length가 단축보다 길게 나타났다.

• 한국해양공학회지
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• 제22권5호
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• pp.25-30
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• 2008

A B-spline based high order panel method was developed for the motion of bodies in an ideal fluid, either of infinite extent or with a free boundarysurface. In this method, both the geometry and the potential are represented by the B-spline, which guarantees more accurate results than most potential based low order methods. In the present work, we applied this B-spline based high order method to the radiation problem of floating bodies. The boundary condition on the free surface was satisfied by adopting a Kelvin-type Green function and irregular frequencies were removed by placing additional control points on the free surface surrounding the body. The numerical results were validated by comparison with existing numerical and experimental results.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2010년도 정기 학술발표대회
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• pp.53.2-53.2
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• 2010

국내 홍수빈도해석 지침서 제공을 위한 기초 연구로서 미국 홍수빈도해석 지침서인 Bulletin 17B과 같이 국내 적합한 홍수빈도해석 기법을 제시하고자 하였다. 홍수빈도해석 지침서의 핵심은 확률분포형과 매개변수 추정법을 제시하는 것이며 이에 GEV(Generalized Extreme Value), GLO(Generalized Logistic) 분포, B-GLS(Bayesian Generalized Least Square) 기법을 대상으로 다양한 연구를 수행하였다. B-GLS 기법을 이용하여, 국내 대유역에 골고루 위치하며 댐의 영향을 받지 않는 31개 지점의 연최대 일유량 시계열의 L-변동계수(L-moment coefficient variation)와 L-왜도계수(L-moment coefficient skewness)를 추정할 수 있는 회귀모형을 제안하였다. 위 회귀모형을 구성하기 위한 유역특성으로는 유역면적, 유역경사, 유역평균강우 등을 사용하였다. Bayesian-GLS(B-GLS) 적용 결과를 OLS(Ordinary Least Square) 및 B-GLS 기법에서 지점간의 상관관계를 고려하지 않는 Bayesian-WLS(Weighted Least Square)와 비교 평가하여 그 우수성을 입증하였다. 따라서 본 연구에서 제안된 B-GLS에 의한 지역회귀모형은 국내의 미계측유역이나 또는 관측 길이가 짧은 계측유역의 홍수빈도분석을 위해 매우 유용할 것으로 기대된다. 또한 수행된 연구의 내용을 공론화하는 노력이 계속된다면 공감대가 형성된 가이드라인을 제정되는데 일조를 하리라 확신한다.

• 한국환경보건학회지
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• 제23권4호
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• pp.91-96
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• 1997

In order to investigate the behavior of particulate carbon and benzo(a)pyrene(B(a)P) in the ambient air, suspended particle matters were collected from April, 1990 to February, 1992, and total carbon(TC), organic carbon(OC), elemental carbon(EC) and B(a)P were measured by an elemental analyzer and a HPLC. The results were as follows the average concentration of TC was 38.6 $\mug/m^3$ and its concentration was higher in winter(45.4 $\mug/m^3$) and fa11(44.3 $\mug/m^3$) than in summer(36.8 $\mug/m^3$) and spring(28.9 $\mug/m^3$). The monthly concentration trends both of EC and OC was similar, but seasonal variation of EC concentrations was larger than that of OC. The average concentration of B (a)P was 2.2 ng/m$^3$, and was higher in winter(4.1 ng/m$^3$) and fall(3.2 ng/m$^3$) than in spring(1.2 ng/m$^3$) and summer(0.6 ng/m$^3$). The seasonal behavior of carbon and B(a)P was to similar except for summer. The correlation coefficient(r) between EC and B(a)P was 0.71, and the correlation coefficient(r) between OC and B(a)P was 0.66.

• 수산해양기술연구
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• 제42권4호
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• pp.217-227
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• 2006

This research aims at establishing the application of canvas kite to the fishing gear through the analysis of the lift/drag tests of the kites have been performed in our previous finding. Now that several methodologies were designed to find the most effective triangular model as a buoyancy device applied to the fishing gear. Comparisons of drag/lift were made by installing the model in an installation frame instead of the prototype. Also, we have considered the application of canvas kite to the prototypic fishing gear by calculation using the result of this test. The results obtained from the above approaches are summarized as follows, where attack angle, lift coefficient, maximum lift coefficient and drag coefficient are denoted as $B,\;C_L,\;C_Lmax\;and\;C_D$ respectively. The camber showed a gradual increase with an increase of fluid velocity. There was a big discrepancy in B=20 unlike B=30. Even if the kite retreats along the fluid flow, there is little relationship with the velocity variation. Lifts calculated with the kites were bigger and drags were smaller than those of the calculations with the float only. The kite as the buoyancy device will be very useful when the appropriate applications and the stability are met.

• 대한지역사회영양학회지
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• 제18권1호
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• pp.45-54
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• 2013

This study was conducted to investigate the physical activity pattern, activity coefficient, basal metabolic rate and energy expenditure of female university students. One-day activity diaries were collected from 95 female university students in Seoul. Body composition was measured by Inbody 720. Subjects spent 7 hr 8min on sleeping, 6 hr 31min on studying, 2 hr 50min on physiological activity, 2 hr 3min on leisure, 2 hr 2min on walking and jogging, 1 hr 58 min on commuting and 22min on house chores. The activity coefficient of these subjects was 1.58. The comparison of body composition of subjects according to PAL showed that body weight, body fat mass, arm circumference and arm muscle circumference of physically active group were significantly higher than those of the sedentary group. BMR calculated by Harris-Benedict (H-B) formula and DRI formula and BMR measured by Inbody 720 was 1375 kcal, 1306 kcal and 1209 kcal, respectively. Total energy expenditure (TEE) examined by one-day activity diaries and calculated by H-B formula and estimated energy requirement (EER) formula in DRI was 2102.1 kcal, 2184.4 kcal, and 2164.5 kcal, respectively. The Pearson correlation coefficient between TEE examined by one-day activity diaries and H-B TEE was 0.795 (p < 0.001) while that between TEE examined and DRI EER was 0.604 (p < 0.001). Overall data indicated that female university students seemed to be less active. Therefore it is recommended that universities develop good exercise programs for their students. Further studies are needed to generate more meaningful results with a larger sample size and using machine attached to the body, which are able to detect physical activity more accurately.

• 한국지형학회지
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• 제25권2호
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• pp.15-29
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• 2018

The sediment transport process in a river reflects the process of geomorphological change in the watershed, influencesthe river bed variation and the river channel migration, and is a parametric phenomenon that exhibits a dynamic self-adjusting process. Sediment load is divided into bedload and suspended load depending on the dominant mechanism. Quantitative sediment load is important information for solving river problems. Because it is difficult and time consuming to measure bedload, compared to that ofsuspended load, data on the sediment transport load and the research required for the gravel-bed rivers are insufficient. This study is to analyze the ratio of the bedload to the total sediment load in gravel-bed rivers. The sediment load ratio in gravel-bed rivers increases with the flow rate per unit width, and the rate of the bedload varies more rapidly than the suspended load. The sediment transport efficiency coefficient has been affected by the ratio of the flow depth to the mean diameter of particles and has been dependent on the shear velocity Reynolds number. So $A^{\ast}$ and $B^{\ast}$ are introduced to compensate for the uncertainties such as bed materials, sediment transport, and flow velocity distribution, and the coefficient of bedload ratio has been presented. For the sediment load data in experimental channels and rivers, A* was 3.1. The dominant variables of $B^{\ast}$ were $u_*d_m/{\nu}$ in the gravel-bed and h/dm in the sand-bed. When $B^{\ast}$ the is the same, in the experimental channels the coefficient of bedload ratio was affected by the bed forms, but in the rivers it was of little difference between the gravel-bed and sand-bed.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.429-430
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• 2002

In this study, three kinds of brake: discs including two coated brake discs and one steel disc were tested under the same experimental conditions on a reduced scale braking test bench. Plasma spray coating technique was used to coat ceramic powder on the discs. In the test, four commercial sintered brake pads were coupled with discs. Ceramic coated discs have shown good stability in friction coefficient at high speed and high energy braking conditions. However, ceramic coated discs caused more wear loss of pad mass than the steel disc. It was shown that thermal barrier effect in ceramic coated discs adjusted the thermal partition between pad and disc. Steel disc showed fluctuating friction coefficient at high speed but less wear loss of pad mass than ceramic coated discs.

• 대한기계학회논문집B
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• 제23권3호
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• pp.364-373
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• 1999

A combination of conjugate gradient and Levenberg-Marquardt method is used to estimate the spatially varying scattering coefficient, ${\sigma}(r)$, in the solid and hollow spheres by utilizing the measured transmitted beams from the solution of an inverse analysis. The direct radiation problem associated with the inverse problem is solved by using the $S_{12}-approximation$ of the discrete ordinates method. The accuracy of the computations increased when the results from the conjugate gradient method are used as an initial guess for the Levenberg-Marquardt method of minimization. Optical thickness up to ${\tau}_0=3$ is used for the computations. Three different values of standard deviation are considered to examine the accuracy of the solution from the inverse analysis.

• 대한기계학회논문집B
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• 제21권2호
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• pp.294-302
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• 1997

Falling-film evaporation experiments for aqueous solution of lithium bromide (LiBr) were performed on a horizontal smooth 19.05-mm-dia copper tube. Average heat transfer coefficients were obtained with varied film Reynolds numbers, system pressures, LiBr concentrations and degrees of wall superheat. Heat transfer coefficients increase with increasing system pressure and decreasing concentration. For degrees of wall superheat, the heat transfer coefficient did not't show the distinct trend. For this experimental ranges, heat transfer coefficients showed maximum values at an optimal film Reynolds number. The results of this work were compared with pool boiling data reported previously, and it was shown that the heat transfer performance is superior to the pool boiling.