• 한국조경학회지
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• 제29권1호
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• pp.22-31
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• 2001

The purpose of this study is to compare calculated pollutant loadings using pollutant load unit factors and vector type coverage, and expected mean concentration(EMC) and raster type of digital elevation model(DEM). This study is also focusing on comparison of the advantages and the disadvantages of the two methods, and seeking for a method of calculation of pollutant loadings using DEM. Estimation of pollutant inputs using pollutant load unit factors has limitations in identifying seasonal variations of pollutant loadings. Seasonal changes of runoffs should be considered in the calculation of pollutant loadings from catchments into reservoirs. Evaluation of pollutant inputs using runoff-coefficient and EMC can overcome these drawbacks. Proper EMC and runoff-coefficient values for the Koeup stream catchments of the Koheung estuarine lake were drawn from review of related papers. Arc/Info was employed to establish database of spatial and attribute data of point and non-point pollutant sources and characteristics of the catchments. ArcView was used to calculate point and non-point pollutant loadings. Pollutant loads estimated with either unit factors-coverages, i.e., pollutant load unit factors and vector coverages f point sources and land use, or EMC and digital elevation mode(DEM) were compared with stream monitoring loads. We have found that some differences were shown between monitoring results and estimated loads by Unit Factors-Coverage and EMC-DEM. Monthly variations of pollutant loads evaluated with EMC-DEM were similar to those with monitoring result. The method using EMC-DEM can calculate accumulated flows and pollutant loads and can be utilized to identify stream networks. A future research on correcting the difference between vector type stream using flow direction grid and digitalizing vector type should be conducted in order to obtain more exact calculation of pollutant loadings.

• 한국화재소방학회논문지
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• 제27권2호
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• pp.75-79
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• 2013

본 연구는 구획화재의 출입구를 통한 연기밀도를 정량적으로 측정하고 측정기법의 신뢰성을 평가하기 위해 불확실성 해석을 수행한다. 메탄 화재 강도에 따른 축소모형 구획공간의 출입구 상층부를 통해 유출되는 연기 유동에 대해 광소멸 측정을 수행하고 Bouguer's의 법칙을 적용하여 연기밀도를 산정하였다. 광투과율, 경로길이, 질량비광소멸상수에 대하여 연기밀도의 측정 불확실도를 평가하였으며 계산된 연기밀도 측정의 확장불확실도는 20% 정도이며 신뢰수준은 95% 이다. 준정상상태의 화재 발열량에 대하여 출입구에서의 평균 연기밀도를 산정하였으며 구획공간내부의 총괄당량비 증가에 따라 출입구의 연기농도가 선형적으로 증가하는 경향을 보였다.

• Journal of Mechanical Science and Technology
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• 제20권12호
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• pp.2230-2241
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• 2006

This paper presents a sole application of boundary element method to the conjugate heat transfer problem of thermally developing laminar flow in a thick walled pipe when the fluid velocities are fully developed. Due to the coupled mechanism of heat conduction in the solid region and heat convection in the fluid region, two separate solutions in the solid and fluid regions are sought to match the solid-fluid interface continuity condition. In this method, the dual reciprocity boundary element method (DRBEM) with the axial direction marching scheme is used to solve the heat convection problem and the conventional boundary element method (BEM) of axisymmetric model is applied to solve the heat conduction problem. An iterative and numerically stable BEM solution algorithm is presented, which uses the coupled interface conditions explicitly instead of uncoupled conditions. Both the local convective heat transfer coefficient at solid-fluid interface and the local mean fluid temperature are initially guessed and updated as the unknown interface thermal conditions in the iterative solution procedure. Two examples imposing uniform temperature and heat flux boundary conditions are tested in thermally developing region and compared with analytic solutions where available. The benchmark test results are shown to be in good agreement with the analytic solutions for both examples with different boundary conditions.

• 대한기계학회논문집B
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• 제27권3호
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• pp.381-388
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• 2003

An experimental study was carried out to measure the heat transfer coefficient in flow boiling to mixtures of HFC-l34a and HCFC-123 in a uniformly heated horizontal tube. Tests were run at a pressure of 0.6 MPa and in the ranges of heat flux 1-50 kw/$m^2$, vapor quality 0-100 % and mass velocity 150-600 kg/$m^2$s. Heat transfer coefficients of mixture were less than the interpolated values between pure fluids both in the low quality region where the nucleate boiling is dominant and in the high quality region where the convective evaporation is dominant. Measured data of heat transfer are compared to a few available correlations proposed for mixtures. The correlation of Jung et. al. satisfactorily predicted the present data, but the data in lower quality was overpredicted and underpredicted the high quality data. The correlation of Kandlikar considerably underpredicted most of the data. and showed the mean deviation of 35.1%.

• 한국농공학회지
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• 제37권2호
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• pp.31-40
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• 1995

This study was conducted to get best fitting frequency distribution for the annual run- off and to simulate long series of annual flows by single-season first order Markov Model with comparison of statistical parameters which were derived from observed and synthetic flows at four watersheds in Seom Jin and Yeong San river systems. The results summarized through this study are as follows. 1. Hydrologic persistence of observed flows was acknowledged by the correlogram analysis. 2. A normal distribution of the annual runoff for the applied watersheds was confirmed as the best one among others by Kolmogorov-Smirnov test. 3. Statistical parameters were calculated from synthetic flows simulated by normal dis- tribution. In was confirmed that mean and standard deviation of simulated flows are much closer to those of observed data than except coefficient of skewness. 4. Hydrologic persistence between observed flows and synthetic flows simulated was also confirmed by the correlogram analysis. 5. It is to be desired that generation technique of synthetic flow in this study would be compared with other simulation techniques for the objective time series.

• 한국태양에너지학회 논문집
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• 제21권1호
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• pp.61-69
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• 2001

The heat transfer characteristics of horizontal and vertical mantle heat storage tanks are studied in order to replace the tank-coil heat exchanger for application in thermosyphon solar water heaters. In this study, 5 mantle storage tanks with different geometric shape are manufactured into stainless steel and each tank is tested. For the test, The inlet flow rate of the heat transfer fluid is maintained 1.2 lpm consistently. The heat transfer fluid temperature through the mantle is $70{\pm}1^{\circ}C$. The temperatures of 26 points included the ambient temperature are measured at every one minute. The measured data are used to calculate the overall heat transfer coefficient(UA) using the LMTD(Log Mean Temperature Difference) method and it is used on the analysis of the heat transfer characteristics to search for optimum arrangement.

• 대기
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• 제31권1호
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• pp.61-71
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• 2021

The relationship between the Arctic Oscillation (AO) and surface air temperature (SAT) over Korea is re-examined using the long-term observation and reanalysis datasets for the period of December 1958 to February 2020. Over the entire period, Korean SAT is positively correlated with the AO index with a statistically significant correlation coefficient, greater than 0.4, only in the boreal winter. It is found that this correlation is not static but changes on the decadal time scale. While the 15-year moving correlations are as high as 0.6 in 1980s and 1990s, they are smaller than 0.3 in the other decades. It is revealed that this decadal variation is partly due to the AO structure change over the North Pacific. In the period of 1980s-1990s, the AO-related sea level pressure fluctuation is strong and well defined over the western North Pacific and the related temperature advection effectively changes the winter SAT over Korea. In the other periods, the AO-related circulation anomaly is either weak or mostly confined within the central North Pacific. This result suggests that Korean SAT-AO index relationship, which becomes insignificant in recent decades is highly dependent on mean flow change in the North Pacific.

• Wind and Structures
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• 제35권2호
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• pp.109-120
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• 2022

The force coefficients of rotating plates in the acceleration stage will vary with rotation rate from 0 to stable rotation rate w₀, which are important for quasi-steady theory of plate-like windborne debris to simulate the trajectory. In this paper, a wind tunnel experiment is carried out to study the effects of geometry and the Reynolds number on the variations of mean force coefficients of rotating plates. The rotational lift coefficients are sensitive to both geometry effect and Reynolds number effect, while the rotational drag and moment coefficients are only sensitive to geometry effect. In addition, new empirical formulas for the rotational lift coefficient and moment coefficients are proposed. Its accuracy is verified by comparing the predicted results with existing test data. Based on the experimental data of rotating plates, a new rotational force model for quasi-steady theory, which can be applied to a wider scope, is proposed to calculate the trajectory of plate-like windborne debris. The results show that the new model provides a better match with the tested trajectories than previous quasi-steady theories.

• 한국재료학회지
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• 제33권4호
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• pp.164-174
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• 2023

The bandgap characteristics of semiconductor materials are an important factor when utilizing semiconductor materials for various applications. In this study, based on data provided by AFLOW (Automatic-FLOW for Materials Discovery), the bandgap of a semiconductor material was predicted using only the material's compositional features. The compositional features were generated using the python module of 'Pymatgen' and 'Matminer'. Pearson's correlation coefficients (PCC) between the compositional features were calculated and those with a correlation coefficient value larger than 0.95 were removed in order to avoid overfitting. The bandgap prediction performance was compared using the metrics of R² score and root-mean-squared error. By predicting the bandgap with randomforest and xgboost as representatives of the ensemble algorithm, it was found that xgboost gave better results after cross-validation and hyper-parameter tuning. To investigate the effect of compositional feature selection on the bandgap prediction of the machine learning model, the prediction performance was studied according to the number of features based on feature importance methods. It was found that there were no significant changes in prediction performance beyond the appropriate feature. Furthermore, artificial neural networks were employed to compare the prediction performance by adjusting the number of features guided by the PCC values, resulting in the best R² score of 0.811. By comparing and analyzing the bandgap distribution and prediction performance according to the material group containing specific elements (F, N, Yb, Eu, Zn, B, Si, Ge, Fe Al), various information for material design was obtained.

• 한국수산과학회지
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• 제30권5호
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• pp.700-707
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• 1997

본 연구에서는 유수저항과 해저 마찰력을 동시에 받는 저층 트롤그물의 예망저항을 정도 높게 표현해낼 목적으로, 전보에서 구한 유수저항만을 받을 때의 저항식에 해저 마찰력의 영향을 추가하고, 지금까지 행해진 실험 결과들을 수집하여 분석하였다. 그 결과, 벽 면적이 $S(m^2)$ 되는 저층 트롤그물이 예망속도 $\nu(m/sec)$에서 받는 예망저항 R(kg)은 그물 입구의 단면적을 $S_m\;(m^2)$, 흐름에 수직인 평면에 대한 그물의 총 투영면적을 $S_n\;(m^2)$, 자루그물 앞끝의 완성 둘레를 B(m)라 할 때 $$R=4.5(\frac{S_n}{S_m})^{1.2}S\;v^{-1.8}+20(Bv)^{1.1}$$으로 주어졌다. 그러나, 실용적으로는 윗 식보다 $R=kS\nu^2$의 형태로 표시하는 것이 더욱 편리하다고 볼 수 있기 때문에, 실험 결과들을 이 식에 적용하여 저항계수 $k(kg{\cdot}sec^2/m^4)$를 여러 가지 측면에서 검토해 본 결과, k는 근사적으로딜만의 함수로 표시할 수 있다는 것을 알 수 있었으며, 그물의 완성 전장을 L (m)이라 할 때 $S{\propto}BL$이어서 $S/BL=\alpha$라 둘 수 있기 때문에 R(kg)은 근사적으로 $$R=18{\alpha}B^{0.5}L\;v^{1.5}$$으로 표시해도 좋다는 것을 알 수 있었다. 또한, $\alpha$의 값은 그물마다 달라 $0.40\~0.55$의 범위이긴 하나 전체 평균치 0.48에서 크게 벗어나지 않았기 때문에, 저층 트롤그물들을 총괄해서 표시할 때는 $\alpha=0.48$을 적용함으로써 R (kg)을 $$R=9\;B^{0.5}\;L\;v^{1.5}$$ 으로 대신해도 좋다는 것을 알 수 있었다.