• 한국자동차공학회논문집
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• 제19권5호
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• pp.92-99
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• 2011

To measure the traffic pollutants with high temporal and spatial resolution under real conditions, a mobile emission laboratory (MEL) was designed. The equipment of the mini-van provides gas phase measurements of CO, NOx, $CO_2$, THC (Total hydrocarbon) and number density & size distribution measurements of fine and ultra-fine particles by a fast mobility particle sizer (FMPS) and a condensation particle counter (CPC). The inlet sampling port above the bumper enables the chasing of different type of vehicles. This paper introduces the technical details of the MEL and presents data from the car chasing experiment of diesel bus equipped with aftertreatment system. The dilution ratio was calculated by the ratio of ambient NOx and tail-pipe NOx. Most particles from the diesel bus were counted under 300 nm and the peak concentration of the particles was located between 30 and 60 nm. The total PM number emission from diesel bus equipped with DPF was 10 orders of magnitude lower compared to those emitted from base diesel bus. And the total PM number emission from diesel bus equipped with SCR was comparable to the particle emission from base diesel bus.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.612-619
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• 2002

The dynamic behavior of Al-Mg alloys plasma was very unstable and this instability was closely related to the unstable motion of keyhole during laser irradiation. The keyhole fluctuated both in size and shape and its fluctuation period was about 440 ${\mu}{\textrm}{m}$. This instability has been estimated to be caused by the evaporation phenomena of metals with different boiling point and latent heats of vaporization. Therefore, the authors have conducted the spectroscopic diagnostics of plasma induced in the pulsed YAG laser welding of Al-Mg alloys in air and argon atmospheres. In the air environment, the identified spectra were atomic lines of Al, Mg, Cr, Mn, Cu, Fe and Zn, and singly ionized Mg line, as well as strong molecular spectrum of AlO, MgO and AIH. It was confirmed that the resonant lines of Al and Mg were strongly self-absorbed, in particular in the vicinity of pool surface. The self-absorption of atomic Mg line was more eminent in alloys containing higher Mg. These facts showed that the laser-induced plasma was relatively a low temperature and high density metallic vapor. The intensities of molecular spectra of AlO and MgO were different each other depending on the power density of laser beam. Under the low power density irradiation condition, the MgO band spectra were predominant in intensity, while the AlO spectra became much stronger in higher power density. In argon atmosphere the band spectra of MgO and AlO completely vanished, but AlH molecular spectra was detected clearly. The hydrogen source was presumably the hydrogen solved in the base Metal, absorbed water on the surface oxide layer or H$_2$ and $H_2O$ in the shielding gas. The temporal change in spectral line intensities was quite similar to the fluctuation of keyhole. The time average plasma temperature at 1 mm high above the surface of A5083 alloy was determined by the Boltzmann plot method of atomic Cr lines of different excitation energy. The obtained electron temperature was 3, 280$\pm$150 K which was about 500 K higher than the boiling point of pure aluminum. The electron number density was determined by measuring the relative intensities of the spectra1lines of atomic and singly ionized Magnesium, and the obtained value was 1.85 x 1019 1/㎥.

• Biotechnology and Bioprocess Engineering:BBE
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• 제4권1호
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• pp.51-58
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• 1999

A mathematical model for a three phase fluidized bed bioreactor (TFBBR) was proposed to describe oxygen utilization rate, biomass concentration and the removal efficiency of Chemical Oxygen Demand (COD) in wastewater treatment. The model consisted of the biofilm model to describe the oxygen uptake rate and the hydraulic model to describe flow characteristics to cause the oxygen distribution in the reactor. The biofilm model represented the oxygen uptake rate by individual bioparticle and the hydrodynamics of fluids presented an axial dispersion flow with back mixing in the liquid phase and a plug flow in the gas phase. The difference of setting velocity along the column height due to the distributions of size and number of bioparticle was considered. The proposed model was able to predict the biomass concentration and the dissolved oxygen concentration along the column height. The removal efficiency of COD was calculated based on the oxygen consumption amounts that were obtained from the dissolved oxygen concentration. The predicted oxygen concentration by the proposed model agreed reasonably well with experimental measurement in a TFBBR. The effects of various operating parameters on the oxygen concentration were simulated based on the proposed model. The media size and media density affected the performance of a TFBBR. The dissolved oxygen concentration was significantly affected by the superficial liquid velocity but the removal efficiency of COD was significantly affected by the superficial gas velocity.

• Smart Structures and Systems
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• 제22권5호
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• pp.561-574
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• 2018

In this paper, for efficiently reducing the computational cost of the model updating during the optimization process of damage detection, the structural response is evaluated using properly trained surrogate model. Furthermore, in practice uncertainties in the FE model parameters and modelling errors are inevitable. Hence, an efficient approach based on Monte Carlo simulation is proposed to take into account the effect of uncertainties in developing a surrogate model. The probability of damage existence (PDE) is calculated based on the probability density function of the existence of undamaged and damaged states. The current work builds a framework for Probability Based Damage Detection (PBDD) of structures based on the best combination of metaheuristic optimization algorithm and surrogate models. To reach this goal, three popular metamodeling techniques including Cascade Feed Forward Neural Network (CFNN), Least Square Support Vector Machines (LS-SVMs) and Kriging are constructed, trained and tested in order to inspect features and faults of each algorithm. Furthermore, three wellknown optimization algorithms including Ideal Gas Molecular Movement (IGMM), Particle Swarm Optimization (PSO) and Bat Algorithm (BA) are utilized and the comparative results are presented accordingly. Furthermore, efficient schemes are implemented on these algorithms to improve their performance in handling problems with a large number of variables. By considering various indices for measuring the accuracy and computational time of PBDD process, the results indicate that combination of LS-SVM surrogate model by IGMM optimization algorithm have better performance in predicting the of damage compared with other methods.

• 대한기계학회논문집A
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• 제35권7호
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• pp.753-758
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• 2011

초내열합금인 GTD-111은 고온강도와 내산화성이 우수하여 가스터빈에서 사용되는 소재이다. 초내열합금의 피로 수명 예측은 가스터빈의 효율을 개선하기 위하여 매우 중요하다. 본 연구에서의 저주기 피로시험은 실제 운전 환경과 유사하게 변형률 범위, 온도를 다양하게 설정하여 시험을 수행하였다. GTD-111의 저주기 피로수명을 예측하기 위하여 변형률 에너지 밀도와 파단 사이클과의 관계를 이용하였다. 시험결과를 토대로 변형률 에너지법과 Coffin-Manson법에 의하여 피로수명을 예측하였다.

• Elastomers and Composites
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• 제35권4호
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• pp.288-295
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• 2000

가황 EPDM(ethylene-propylene-diene terpolymer) 고무를 화학적 탈황처리 방법을 통하여 가교 밀도를 감소시키고자 시도하였다. 화학적 탈황처리를 위하여 상이동 촉매(phase transfer catalyst), 알카리 금속인 sodium, triphenylphosphine 등을 탈황 조제로 사용하였으며 또한 2-butanol을 탈황반응의 반응용매로 사용한 경우에 대한 탈황처리 효과도 아울러 조사하였다. 4급 암모니움염 형태의 상이동 촉매를 탈황반응에 이용할 경우 촉매의 분자량에 따른 변화 그리고 bromide(Br) 음이온 대비 chloride(Cl)음이온 사용에 따른 변화 등을 비교하였다. Sodium(Na)을 탈황반응에 투여할 경우 Na의 사용량, 반응온도, 반응시간 그리고 반응 분위기로 이용된 수소가스의 압력 등 반응변수에 따른 탈황효과를 살펴보았다. 가교밀도를 정량적으로 나타내는 수치인 $M_c$값(가교점 사이의 수평균 분자량)을 평형팽윤법을 이용하여 실험적으로 결정하였고 가황 EPDM 고무시료의 탈황효과 분석은 탈황 전과 탈황 후 시료에 대한 $M_c$ 값을 비교함으로써 수행되었다.

• Safety and Health at Work
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• 제6권1호
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• pp.30-34
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• 2015

Background: The purpose of this study was to examine the cohesions status of the coordination within response teams in the emergency response team (ERT) in a refinery. Methods: For this study, cohesion indicators of social network analysis (SNA; density, degree centrality, reciprocity, and transitivity) were utilized to examine the coordination of the response teams as a whole network. The ERT of this research, which was a case study, included seven teams consisting of 152 members. The required data were collected through structured interviews and were analyzed using the UCINET 6.0 Social Network Analysis Program. Results: The results reported a relatively low number of triple connections, poor coordination with key members, and a high level of mutual relations in the network with low density, all implying that there were low cohesions of coordination in the ERT. Conclusion: The results showed that SNA provided a quantitative and logical approach for the examination of the coordination status among response teams and it also provided a main opportunity for managers and planners to have a clear understanding of the presented status. The research concluded that fundamental efforts were needed to improve the presented situations.

• Design & Manufacturing
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• 제13권2호
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• pp.37-43
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• 2019

This study conducted a research as to condensation heat transfer friction loss headby using three types of flat micro multi-channel tubes with different processing of micro-fin and number of channels inside the pipes and different sizes of appearances. In addition, identical studies were conducted by using smoothing circular tubes with 5mm external diameter to study heat enhancement factor and pressure drop penalty factor. 1) The friction head loss showed an increase as the vapor quality and mass flux increased. In case of saturation temperature, it shows an increase as it gets lower. These factors are the reason occurring as the lower the saturation temperature is, the higher the density of refrigerant vapor gets. The influence of heat flux is similar as the dryness is low, but as it gets higher, it lowers in heat flux, and as the high temperature of high heat flux, it is a factor that occurs as the density gets lower. 2) RMS error of the in case of friction head loss, it showed to be predicted as 0.45~0.67 by Chisholm, Friedel, Lockhart and Martinelli. 3) As forfriction head loss penalty factor, the smaller the aspect ratio is, the larger the penalty factor gets, and as for the effect of micro-fin, the penalty factor increased because it decreases to the gas fluid the way groove for the refrigerant's flow.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.3377-3382
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• 2007

In proton exchange membrane fuel cell, the heat is generated at the catalyst layer as result of exothermic electrochemical reaction. This heat increases temperature of gas diffusion layer and membrane whose conductivity is very sensitive to humidity, function of temperature. So it is very important to analysis heat transfer through fuel cell to maintain temperature at specified range. In this paper numerical simulation was done including reversible, irreversible, ionic resistance, water formation loss to source term of energy equation. Results show that irreversible and water formation loss contributes mainly to energy source term and as current density increases, all of energy source terms become increased and Nusselt number is increased as results of more heat generation. Particularly irreversible loss is found to be predominant among the all energy source and water formation at cathode channel influences the temperature distribution of fuel cell greatly.

• Journal of Astronomy and Space Sciences
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• 제18권1호
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• pp.1-6
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• 2001

In this paper we investigate the properties of advection-dominated accretion flows (ADAFs) in case that outflows carry away infalling matter with its angular momentum and energy. Positive Bernoulli number in ADAFs allow a fraction of the gas to be expelled in a form of outflows. The ADAFs are also unstable to convection. We present self-similar solutions for advection-dominated accretion flows in the presence of outflows from the accretion flows(ADIOS). The axisymmetric flow is treated in variables integrated over polar sections and the effects of outflows on the accretion flow are parameterized for possible configurations compatible with the one dimensional self-similar ADAF solution. We explicitly derive self-similar solutions of ADAFs in the presence of outflows and show that the strong outflows in the accretion flows result in a flatter density profile, which is similar to that of the convection-dominated accretion flows(CDAFs) in which convection transports the angular momentum inward and the energy outward. There two different versions of the ADAF model should show similar behaviors in X-ray spectrum to some extent. Even though the two models may show similar behaviors, they should be distinguishable due to different physical properties. We suggest that for a central object of which mass is known these two different accretion flow should have different X-ray flux value due to deficient matter in the wind model.