• 한국전산구조공학회논문집
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• 제17권1호
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• pp.75-82
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• 2004

본 논문에서는 응력파 전파를 수치모의할 때 발생하는 수치적인 분산효과를 제거하기 위해 파동방정식에 기초한 일차원 유한요소모형을 이용하여 수치분산오차의 특성을 분석하고 분산오차를 제어할 수 있는 방법을 제안하였다. 질량행렬을 그대로 사용하는 경우와 집중질량행렬을 사용하는 경우에 대한 수치분산오차를 분석하였다. 개발된 분산제어기법은 공간미분항의 시간단계 가중치 및 질량집중도를 조정하는 음해법과 인위적인 분산항을 추가하는 양해법의 두가지 방법이다. 제안된 분산보정기법을 이용하여 계산한 수치해와 파동방정식의 해석해를 비교한 결과 본 연구에서 제안한 분산보정기법의 타당성을 확인하였다.

• 항공우주기술
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• 제10권1호
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• pp.63-69
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• 2011

본 연구에서는 기존의 가스발생기 사이클 액체로켓 엔진 모드해석 프로그램(GEMAT)을 개선하여 엔진 구성품이 가지는 성능 분산으로 인한 시스템 수준에서의 성능 분산을 계산 하는 프로그램을 개발하였다. 본 프로그램을 이용하여 엔진 내부 인자의 성능 분산을 보정하기 위해 필요한 각 배관에서의 보정용 여유차압을 산정하는 방법을 제시하였다. 또한 이를 활용하여 기존의 엔진 보정 방법을 보완하여 보정용 차압을 최적화하고 이를 통해 펌프 토출압을 감소시키거나 연소실의 연소압을 높임으로써 전체 엔진의 비추력 향상을 꾀할 수 있는 보정 방법을 제시하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제23회 추계학술대회 논문집
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• pp.87-91
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• 2004

우주 발사체의 성공적인 비행을 위해서는 로켓 엔진의 성능 분산 관리가 필수적이다. ANASYN을 이용해 가스발생기 사이클 액체 로켓 엔진의 성능 오차 분석을 수행하였다. 별도의 추력제어 시스템을 갖추지 않은 엔진의 진공 추력 분산은 $+5.34\%,\;-5.27\%$로 나타났으며 연소기 혼합비 오차는 $+9.07\%,\;-9.82\%$에 달했다. 가스발생기의 혼합비를 제어할 경우 추진제 유량의 제어 없이 혼합비만을 제어하면 엔진성능의 분산이 증가한다. 분산 요인에 대한 민감도 해석에 의하면 터빈 효율에서의 오차가 엔진 성능 분산에 가장 큰 영향을 미친다.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• 제10권S_1호
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• pp.11-22
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• 2001

Observations related to the along-wind dispersion of puffs were collected from 12 field sites and from a wind tunnel experiment and used to test simple similarity relations. Because most of the date made use of concentration time series observation from fixed monitors, the basic observation was t, the standard deviation of the concentration time series. This data also allowed the travel time, t, from the source to the receptor to be estimated, from which the puff advective speed ue, could be determined. The along-wind dispersion coefficient, x, was then assumed to equal tue. The data, which extended over four orders of magnitude, supported the similarity relations t=0.1 t and x=1.8 $u^*$t, where t is the travel time and $u^*$ is the friction velocity. About 50% of the observations were within a factor of two of the predictions based on the similarity relations.

• KDI Journal of Economic Policy
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• 제37권3호
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• pp.31-53
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• 2015

According to the macroeconomic allocation efficiency measure, particularly based on the methodology of Hsieh and Klenow (2009), Korea's allocation efficiency in the manufacturing industry deteriorated in the 2000s compared to that in the 1990s. This study compares the potential TFP gain when resource allocation is removed, an indicator of allocation inefficiency according to Hsieh and Klenow (2009), and the productivity dispersion in the Korean manufacturing industry. It finds that the TFP gain may be better explained by TFP dispersions rather than proxies related to factors of distortion. The findings imply that we should investigate the sources of TFP dispersion rather than the sources of distortion to explain increases in the TFP gain (or TFP loss), which is considered as allocation inefficiency in the literature.

• Current Optics and Photonics
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• 제5권3호
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• pp.250-260
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• 2021

A tapered As₂S₃ photonic crystal fiber (PCF) with four layers of air holes in a hexagonal array around the core is designed in this paper. Numerical simulation shows that the dispersion D decreases and the nonlinearity coefficient γ increases from the thick to the thin end along the tapered PCF. We simulate the midinfrared pulse compression in the tapered As₂S₃ PCF using the adaptive split-step Fourier method. Initial Gaussian pulses of 4.4 ps and a central wavelength of 2.5 ㎛ propagating in the tapered PCF are located in the anomalous dispersion region. With an average power of assumed input pulses at 3 mW and a repetition frequency of 81.0 MHz, we theoretically obtain a pulse duration of 56 fs and a compression factor of 78 when the pulse propagates from the thick end to the thin end of the tapered PCF. When confinement loss in the tapered PCF is included in the simulation, the minimum pulse duration reaches 72 fs; correspondingly, the maximum compression factor reaches 61. The results show that in the anomalous-dispersion region, midinfrared pulses can be efficiently compressed in a dispersion-decreasing and nonlinearity-increasing tapered As₂S₃ PCF. Due to confinement loss in the tapered fiber, the efficiency of pulse compression is suppressed.

• 폴리머
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• 제35권1호
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• pp.60-65
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• 2011

고분자 나노복합재의 성능을 극대화 하기 위해서는 나노업자 분산도의 향상과 더불어 분산상태가 물성 변화에 미치는 영향을 정확히 이해하는 것이 매우 중요하다. 본 연구에서는 탄소나노튜브 첨가 고분자 복합재의 분산상태를 정량적으로 평가할 수 있는 방법을 제시하고자 하였다. 자외선-가시광선 분광광도법을 이용하여 탄소나노튜브의 분산상태에 따른 투과도를 측정하였으며, 동일 농도에서 분산상태가 향상됨에 띠라 투과도가 감소하는 것을 확인하였다. 이러한 결과를 바탕으로 기존의 Beer-Lambert 투과도 법칙에 분산상태의 변화를 포함할 수 있는 새로운 분산도 평가인자인 유효 농도 인자를 제시하였다. 이를 통해 탄소나노튜브의 분산상태의 변화와 함께 다양한 탄소나노튜브의 농도 및 시편 두께에 따른 투과도 결과를 분석함으로써 제시한 분산도 평가방법과 유효 농도 인자의 유효성을 확인하였다.

• 한국재료학회지
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• 제26권3호
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• pp.136-142
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• 2016

To study the dispersion factors of silica sol prepared from fumed silica powder, we prepared silica sol under an aqueous system using a batch type bead mill. The dispersion properties of silica sol have a close relationship to dispersion factors such as pH, milling time and speed, the size and amount of zirconia beads, the solid content of fumed silica, and the shape and diameter of the milling impellers. Especially, the silica particles in silica sol were found to show dispersion stability on a pH value above 7, due to the electrostatic repulsion between the particles having a high zeta potential value. The shape and diameter of the impellers installed in the bead mill for the dispersion of fumed silica was very important in reducing the particle size of the aggregated silica. The median particle size ($D_{50}$) of silica sol obtained after milling was also optimized according to the variation of the size and amount of the zirconia beads that were used as the grinding medium, and according to the solid content of fumed silica. The dispersion properties of silica sol were investigated using zeta potential, turbiscan, particle size analyzer, and transmission electron microscopy.

• 한국환경과학회지
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• 제14권9호
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• pp.851-860
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• 2005

In order to how well predict ISCST3(lndustrial Source Complex Short Term version 3) model dispersion of air pollutant at point source, sensitivity was analysed necessary parameters change. ISCST3 model is Gaussian plume model. Model calculation was performed with change of the wind speed, atmospheric stability and mixing height while the wind direction and ambient temperature are fixed. Fixed factors are wind direction as the south wind(l80") and temperature as 298 K(25 "C). Model's sensitivity is analyzed as wind speed, atmospheric stability and mixing height change. Data of stack are input by inner diameter of 2m, stack height of 30m, emission temperature of 40 "C, outlet velocity of 10m/s. On the whole, main factor which affects in atmospheric dispersion is wind speed and atmospheric stability at ISCST3 model. However it is effect of atmospheric stability rather than effect of distance downwind. Factor that exert big influence in determining point of maximum concentration is wind speed. Meanwhile, influence of mixing height is a little or almost not.

• 대한교통학회지
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• 제6권1호
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• pp.55-64
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• 1988

Prior to using any computer model, the program-embedded palameters showing significant differences from real world should be calibrated. This is especially true when the model is expected to be used fro various roadway and traffic condition. The calibration of TRANSYT model was conducted for the parameters of start-up delay, and lag, stop penalty(K), platoon dispersion factor, and saturation flow rate. The values of the parameters were obtained by theoretical methods from actual field measurements for discharging and arrival pattern. The sites elected for the study was an intersection of Dongil-Ro and Hwarang-Ro, and a 334 meter downstrean section from the intersection stop line on westbound Hwarang-Ro. The study results showed that the start-up delay was 2.6 sec, end lag was 1.0 sec, saturation flow rate was 2287 pcphgpl, platoon dispersion factor was 0.2-03, and stop penalty(K) was 32. However, since these parameters re apt to depend on traffic and roadway condition, it is doubtful whether the obtained values will be applicable to the area-wide situation other than this particular site.