• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.7
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• pp.607-618
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• 2014

An experimental investigation of turbulent heat transfer during the vertical upward flow of supercritical $CO_2$ was conducted in a circular tube with inner diameter of 4.5 mm. The experiments were conducted at bulk fluid temperatures ranging from 29 to $115^{\circ}C$, pressures from 74.6 to 102.6 bar, local wall heat fluxes from 38 to $234kW/m^2$, and mass fluxes from 208 to $874kg/m^2s$. At moderate wall heat and low mass fluxes, the wall temperature had a noticeable peak value. For observing the buoyancy and flow acceleration effects on heat transfer, the ratios of Nusselt numbers from the experimental data and a reference correlation were compared with the $Bo^*$ and $q^+$ distributions. The flow acceleration parameter $q^+$ appropriately represented the heat transfer phenomena in the experiments. A new heat transfer correlation for the vertical upward flow of the supercritical pressure fluid was developed, and was found to agree with the experimental data with an error margin of ${\pm}30%$.

• Journal of the Korean Society of Food Science and Nutrition
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• v.45 no.8
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• pp.1162-1169
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• 2016

A new method based on accelerated solvent extraction (ASE) combined with response surface methodology (RSM) has been developed for optimization of the extraction of ginsenoside [Rb1, Rg1, and Rg3(20S)], total phenolics, and benzopyrene in red ginseng. The RSM method, based on a five level and two variable central composite design, was employed to obtain the optimal combination of extraction conditions. In brief, ginsenosides Rb1, Rg1, and Rg3(20S) and total phenolics with undetectable benzopyrene were optimally extracted with 50% ethanol as an extraction solvent, extraction temperature of $158^{\circ}C$, extraction time of 20 min, extraction pressure of 2,500 psi, flush volume of 60%, and one extraction cycle. The contents of ginsenosides and total phenolics in red ginseng extracted by ASE under optimum conditions were significantly higher than those extracted by sonication and reflux extraction.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.9
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• pp.731-740
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• 2014

Occupants induced floor vertical vibrations may cause other occupant's annoyance and lead to social loss. To help control such floor vibrations, several criteria have been developed mostly based on human perception tests and floor vibration tests. Floor vibration is evaluated by comparison with criteria and vibration parameters of subject floor, such as frequency, damping ratio, acceleration value, vibration duration time and occurrence frequency. Three acceleration value parameters are used in criteria; peak acceleration, rms acceleration and VDV, when a floor vibration serviceability is evaluated. Meanwhile rms acceleration and peak acceleration are adopted as vibration limit value in criteria and researches of human perception for vibration. Occupants induced floor vibration is transient rather than steady state. However, rms acceleration is not reliable parameter for evaluating transient vibration. The objective of this study is to investigate the characters of human perception level according to acceleration value parameters for vibration induced by heel impacts and walking activities.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.38.2-38.2
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• 2009

마이크로노즐은 우주공간에서 인공위성의 자세를 바로잡는 데 필요한 마이크로 로켓에 들어가는 필수적인 부품이다. 마이크로 노즐은 또한 나노입자 적층 시스템(nano-particle deposition system, NPDS)에 들어갈 수 있다. NPDS는 세라믹 또는 금속 나노분말 입자를 노즐을 통해 초음속으로 가속시킨 뒤 상온에서 이를 기판에 적층시키는 새로운 시스템이다. 본 연구의 목표는 NPDS에 쓰이는 노즐을 일반적인 반도체 공정을 이용하여 마이크론 스케일의 목을 갖도록 한 마이크로노즐을 제작하는 데 있다. 보쉬 공정은 이러한 마이크로노즐을 제작하는데 필수적인 공정으로, 유도결합플라즈마를 이용해 실리콘 웨이퍼를 식각시키는 기술을 말한다. 보쉬 공정에 사용되는 플라즈마 기체는 $SF_6$와 $C_4F_8$인데, 이 두 가지 기체를 번갈아가면서 사용하여 실리콘 웨이퍼를 이방성 식각하는 것이 그 특징이다. 보쉬 공정에는 다양한 변수가 존재하며 이를 적절히 통제하면 마이크로노즐에 적합한 프로파일을 실리콘 웨이퍼 내에 형성시킬 수 있다. 본 연구에서는 보쉬 공정을 이용하여 3차원 마이크로 노즐을 제작하였다. 기존에 반응성이온식각(deep reactive ion etching, DRIE) 공정을 통해 마이크로노즐을 제작한 사례가 많이 보고되었지만 이들은 모두 2차원적으로 마이크로노즐을 제작하였다. 2차원적으로 제작한 마이크로노즐은 마이크로 로켓에 주로 사용되었지만, 초음속으로 가속된 분말이 노즐의 형상으로 인한 유체 흐름의 불안정성 때문에 NPDS에서는 오래도록 사용할 수 없다는 문제점이 있다. 그러므로 본 연구에서는 마이크로노즐을 3차원 형상으로 제작함으로써 이러한 문제점을 해결하고자 하였다.

• Journal of the Korea Convergence Society
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• v.10 no.11
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• pp.327-333
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• 2019

The Fuel-cut driving is started when the acceleration pedal released with transmission gear engaged. Fuel economy of the vehicle improves by active fuel-cut driving. A deep-learning technique is proposed to predict fuel-cut driving with vehicle speed, acceleration and road gradient data in the study. It's 3~10 of hidden layers and 10~20 of variables and is applied to the 9600 data obtained in the test driving of a vehicle in the road of 12km. Its accuracy is about 84.5% with 10 variables, 7 hidden layers and Relu as activation function. Its error is regarded from the fact that the change rate of input data is higher than the rate of fuel consumption data. Therefore the accuracy can be better by the normalizing process of input data. It's unnecessary to get the signal of vehicle injector or OBD, and a deep-learning technique applied to the data to be got easily, like GPS. It can contribute to eco-drive for the computing time small.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.3
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• pp.159-169
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• 2020

Acceleration amplification factors, which are variables used in the seismic design of power facilities installed inside substation structures, are presented in the seismic design standards of the United States (US), Japan, and Korea. Unlike the coefficients presented in the design standards of the US and Japan, those presented in domestic design standards can be obtained only by performing dynamic analysis when the substation structure has more than four floors. Because most substation structures in Korea have 4-5 stories, the existing acceleration amplification factor is insufficient to be applied to actual substation structures. To suggest an acceleration amplification factor suitable for domestic substation structure types, the acceleration amplification factor was evaluated for seven representative substation structures. The acceleration amplification factors were evaluated by constructing in-structure response spectra based on a study of far-field and near-fault earthquakes. In general, the acceleration amplification coefficients α_J and α_A according to the US and Japan seismic design criteria tend to be overestimated compared with the acceleration amplification factors obtained through dynamic analysis based on the study of near-fault and far-field earthquakes.

• International Journal of Highway Engineering
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• v.9 no.4
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• pp.11-20
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• 2007

This thesis develops a fatigue model for the asphalt black base using the APT(Accelerated Pavement Testing) and analyzes the correlation of the APT analysis result with results of previous laboratory tests. For the APT testing, aggregate of the maximum grain size of 25mm(BB-3) was used as the material for the asphalt black base. The result of the APT revealed that the variable of the fatigue model, i.e. the maximum tensile stress on the bottom part of the pavement, increased as the number of loading increased while the modulus of elasticity for the pavement layer decreased gradually. The tensile strain was obtained from a strain gauge, and it was used to derive the values of $k_1=1.29{\times}10^{-6}$ and $k_2=3.02$ from the basic equation of the asphalt fatigue model, $N_f=k_1(\frac{1}{\epsilon})^{k_2}$. The fatigue life predicted from the asphalt fatigue model was greater than that obtained from laboratory experiments, given the same tensile strain. Additionally, a theory to estimate the remaining life of the pavement was developed using FWD, a non-destructive experiment.

• Progress in Medical Physics
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• v.17 no.4
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• pp.224-231
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• 2006

The electron energy spectra for 6 MeV electron beam were calculated using a MCNPX code. The head of the linear accelerator (ML6M; Mitsubishi, Japan) was modelled for this study. The energy spectrum of the initial electron beam was assumed to be Gaussian and the mean energy was determined by evaluating the measured and calculated values of $R_{50}$ and dose profiles in air. The energy distributions for electrons and photons at the interested points in the head of the linear accelerator were calculated by appling the Initial beam parameters. The effect of contaminant photons on depth dose curves were estimated by the photon energy spectra at the end of the applicator.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.445-445
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• 2010

전자빔 플라즈마는 전자 소스 부분, 전자 가속 부분, 전자빔 플라즈마 생성 부분으로 구성되어 있다. Hollow cathode형태의 전극과 anode역할을 하는 안쪽 그리드로 DC방전을 일으켜 전자를 발생시키고 안쪽 그리드와 바깥쪽 그리드 사이의 전압차이로 전자를 가속시킨다. 가속된 전자는 중성 가스와 비탄성 충돌을 하게 되어 플라즈마가 생성이 된다. 이러한 방식으로 생성된 전자빔 플라즈마는 플라즈마 형성 공간에 전기장이 없어 전자가 에너지를 얻을 수 없으며, 중성가스와 비탄성 충돌로 인해 에너지를 쉽게 잃기 때문에 전자 온도가 낮게 유지가 된다. 일반적으로 바깥쪽 그리드는 접지를 시켜 전자빔 플라즈마를 발생시키지만, DC 전원을 연결하여 양의 전압을 걸어주면 전자빔 플라즈마의 밀도는 크게 변하지 않고 전자 온도가 급격히 상승하게 된다. Ar 전자빔 플라즈마의 경우 바깥쪽 그리드가 접지에 연결되었을 경우 전자 온도는 0.5eV 정도인 것에 비해 바깥쪽 그리드에 20V DC전압을 걸어주면 전자 온도가 1eV 정도로 크게 증가를 한다. 그 이유는 바깥쪽 그리드 전압의 영향으로 전자빔 플라즈마 전위가 상승하게 되고 그 결과 높은 에너지를 가진 전자가 플라즈마 전위에 갇히게 되기 때문이다.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2006.11a
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• pp.297-300
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• 2006

본 논문에서는 비선형 기동표적의 추적에 대한 새로운 접근 방식을 소개한다. 이 논문에서는 표적의 가속도를 시변 변수인 표적의 추가적인 잡음으로 두고 각각의 가속도 간격의 정도에 따라 얻어지는 모든 잡음에 대한 변수에 의해 각각의 하부 모델들을 특성화시켰다. 표적의 기동중에 나타나는 가속도를 효과적으로 다루기 위하여, 잡음의 크기가 급격히 증가할 경우 증가분을 가속도로 인식하여 기동표적 관계식에 이용하였다. 또한 모르는 가속도에 따른 시변 변수를 적응적으로 어립잡기는 어렵기 때문에 정밀한 계산을 위하여 퍼지 뉴럴 네트워크와 적응 상호작용 다중모델 기법을 이용하였다. 퍼지 뉴럴 네트워크의 동정을 위해서는 오차 역전파 학습법을 사용하였다. 그리고 제안된 알고리즘의 수행 가능성을 보여주기 위하여 몇 가지 예를 제시하였다.