• 한국산학기술학회논문지
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• 제20권1호
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• pp.329-338
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• 2019

본 연구에서는 농산물 꾸러미 속성별 소비자선호 분석을 통해 사업 활성화 방안을 제시하고자 하였다. 꾸러미의 속성을 구성함에 있어서 상품묶음 방식과 배송 방식 및 가격으로 구분하여 설정하고, 선택실험법에 의해 각 속성의 수준변화에 대한 한계지불의사금액을 추정하였다. 계량적 분석을 수행함에 있어서 보다 효율적인 모형을 선택하기 위하여 잔차항에 대한 가정이 서로 다른 조건부로짓 모형, 이분산 극한치 모형, 다항프로빗 모형, 혼합로짓 모형 등 네 모형을 추정하였으며, 그 결과 상품묶음 방식과 배송 방식 및 가격에 대한 추정계수 값이 모두 통계적으로 유의한 것으로 나타났다. 로그우도 값의 크기를 기준으로 볼 때 이분산 극한치 모형이 자료에 가장 적합하는 것으로 나타났다. 이분산 극한치 모형의 추정계수를 활용한 한계지불의사금액은 상품묶음 방식을 고정형에서 선택형으로 변경 할 경우 1회당 7,096.6원, 배송방식 중 직접배송에 대한 소비자의 한계지불의사금액은 1회당 3,497.5원, 콜드체인 배송에 대한 한계지불의사금액은 1회당 4,035.2원으로 나타났다. 이러한 분석결과는 정부의 로컬푸드 활성화를 위한 정책수립에 기초자료로 활용될 수 있을 것이다.

• 한국지하수토양환경학회지:지하수토양환경
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• 제23권1호
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• pp.41-53
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• 2018

Comprehensive statistical analysis for the 127 groundwater monitoring stations in Jeju Island during 2005~2015 was carried out for the re-establishment of management groundwater level. Three probability distribution functions such as normal distibution, GEV (General Extreme Value) distribution, and Gumbel distribution were applied and the maximum likelihood method was used for parameter estimation of each distribution. AIC (Akaike information criterion) was calculated based on the estimated parameters to determine the proper probability distribution for all 127 stations. The results showed that normal distribution and Gumble distribution were found in 11 stations. Whereas GEV distribution were found in 105 stations, which covered most of groundwater monitoring stations. Therefore, confidence levels should be established in accord with the proper probability distribution when groundwater level management is determined.

• 한국농공학회논문집
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• 제51권3호
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• pp.53-62
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• 2009

This study was carried out to select optimal probability distribution based on design accumulated monthly mean inflow from the viewpoint of drought by Gamma (GAM), Generalized extreme value (GEV), Generalized logistic (GLO), Generalized normal (GNO), Generalized pareto (GPA), Gumbel (GUM), Normal (NOR), Pearson type 3 (PT3), Wakeby (WAK) and Kappa (KAP) distributions for the observed accumulative monthly mean inflow of Chungjudam. L-moment ratio was calculated using observed accumulative monthly mean inflow. Parameters of 10 probability distributions were estimated by the method of L-moments with the observed accumulated monthly mean inflow. Design accumulated monthly mean inflows obtained by the method of L-moments using different methods for plotting positions formulas in the 10 probability distributions were compared by relative mean error (RME) and relative absolute error (RAE) respectively. It has shown that the design accumulative monthly mean inflow derived by the method of L-moments using Weibull plotting position formula in WAK and KAP distributions were much closer to those of the observed accumulative monthly mean inflow in comparison with those obtained by the method of L-moment with the different formulas for plotting positions in other distributions from the viewpoint of RME and RAE.

• Smart Structures and Systems
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• 제15권1호
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• pp.41-55
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• 2015

This study proposes a laser based impedance measurement system and impedance based pipe corrosion and bolt-loosening monitoring techniques under temperature variations. For impedance measurement, the laser based impedance measurement system is optimized and adopted in this paper. First, a modulated laser beam is radiated to a photodiode, converting the laser beam into an electric signal. Then, the electric signal is applied to a MFC transducer attached on a target structure for ultrasonic excitation. The corresponding impedance signals are measured, re-converted into a laser beam, and radiated back to the other photodiode located in a data interrogator. The transmitted impedance signals are treated with an outlier analysis using generalized extreme value (GEV) statistics to reliably signal off structural damage. Validation of the proposed technique is carried out to detect corrosion and bolt-loosening in lab-scale carbon steel elbow pipes under varying temperatures. It has been demonstrated that the proposed technique has a potential to be used for structural health monitoring (SHM) of pipe structures.

• 산업경영시스템학회지
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• 제45권4호
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• pp.61-69
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• 2022

The function of coolant in machining is to reduce the frictional force in the contact area in between the tool and the material, and to increase the precision by cooling the work-piece and the tool, to make the machining surface uniform, and to extend the tool life. However, cutting oil is harmful to the human body because it uses chlorine-based extreme pressure additives to cause environmental pollutants. In this study, the effect of cutting temperature and surface roughness of titanium alloy for medical purpose (Ti-6Al-7Nb) in eco-friendly ADL slot shape machining was investigated using the response surface analysis method. As the design of the experiment, three levels of cutting speed, feed rate, and depth of cut were designed and the experiment was conducted using the central composite planning method. The regression expressions of cutting temperature and surface roughness were respectively obtained as quadratic functions to obtain the minimum value and optimal cutting conditions. The values from this formula and the experimental values were compared. As a result, this study makes and establishes the basis to prevent environmental pollution caused by the use of coolant and to replace it with ADL (Aerosol Dry Lubricant) machining that uses a very small amount of vegetable oil with high pressure.

• Coupled systems mechanics
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• 제13권2호
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• pp.95-113
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• 2024

In this paper, we will analyse the thermo-elastic behavior of the plate element of a structure arranged in a climatically aggressive environment (extreme temperature), we use a refined four-variable thick plate theory to take the shear effect into consideration, the proposed theory less computationally expensive and more accurate so that it incorporates the shear effect into the formulation. The plate is assumed to be simply supported on its four edges, so exact (closed-form) solutions are found according to the Navier expansion, and the governing stability equations and associated boundary conditions of the problem are obtained via the virtual works principle. The plate studied ismade of laminated composite materials, so a parametric study is needed to see the effect of different types of parameters and coupling on the critical temperature value causing thermo-elastic instability of the plate and also on the natural frequency of free vibration, as well as for other parameters such as anisotropy, slenderness and aspect ratio of the plate and finally the lamination angle. Numerical results are obtained for specially orthotropic and antisymmetrical plates and are compared with those obtained by othertheoriesin the literature to validate the analysis approach used.

• 한국수자원학회논문집
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• 제55권3호
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• pp.177-189
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• 2022

본 연구는 저빈도·고강도의 확률강우량 산정을 위해, 대규모 기후 앙상블 모의실험으로 생성된 d4PDF (Data for Policy Decision Making for Future Change)를 적용하는 것을 목적으로 수행되었다. 또한, d4PDF를 이용하여 산정된 확률강우량과 관측 자료 및 빈도해석을 통해서 산정된 확률강우량을 비교함으로써 빈도해석 과정의 적용에 따라 발생하는 불확실성을 분석하였다. 이와 같은 연구는 금산, 임실, 전주, 장수 관측소를 대상으로 수행되었다. d4PDF 자료는 총 50개의 앙상블로 구성되어있으며, 하나의 앙상블은 60년동안의 기상자료를 제공하기 때문에 한 지점에서 3,000개의 연 최대 일 강우량을 수집하는 것이 가능했다. 이와 같은 d4PDF의 특징을 토대로 본 연구는 빈도해석 방법을 적용하지 않고, 3000개의 연 최대 일강수량을 비모수적 접근법(Non-parametric approach)에 따라 규모별로 나열하여, 10년부터 1000년의 재현기간을 갖는 확률강우량을 산정했다. 그 후, 관측 자료와 Gumbel 및 GEV (General extreme value) 분포를 토대로 산정된 확률강우량과의 편차를 산정하였다. 그 결과, 재현기간과 관측 기간의 차이가 증가할수록 이 편차가 증가하였으며, 이 결과는 짧은 관측 기간과 빈도해석의 적용은 재현기간이 증가할수록 신뢰하기 어려운 확률강우량을 제시한다는 것을 의미한다. 반면에, d4PDF는 대규모 표본을 이용함으로써 이와 같은 불확실성을 최소화시켜 합리적인 저빈도·고강도의 확률강우량을 제시하였다.

• Journal of the Korean Data Analysis Society
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• 제20권6호
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• pp.2829-2840
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• 2018

음이 아닌(non-negative) 측정값을 가지는 확률변수에 있어서, 영(0)이 과도하게 측정되는 자료를 반연속형(semi-continuous) 자료와 영-과잉(zero-inflated) 자료로 구분한다. 이러한 자료에서는 특정 확률 분포(probability distribution) 하에서의 확률보다 훨씬 큰 확률로 0을 관측하게 되는데, 연속형(continuous) 확률분포를 고려하는 경우에는 반연속형으로, 이산형(discrete) 확률분포를 고려하는 경우에는 영-과잉이라고 한다. 본 연구에서는 경계값(0)의 측정 여부에 관한 모형과 0보다 큰 확률변수에 대한 확률분포를 활용한 모형 등 두 개의 부문으로 이루어진 모형, 즉 2-부문 모형(two-part model)을 소개하고자 한다. 특히, 이산형 확률분포 중 포아송 분포와 음이항 분포를 고려한 영-과잉 회귀모형(regression model)을 설명하고 그 특성을 파악하고자 한다. 실증연구에서는 이러한 영-과잉 회귀모형을 활용하여 지난 10년(2009년부터 2018년) 간 한국의 여름철(6-8월) 폭염주의보(heat-wave advisory) 및 폭염경보(heat-wave warning) 발생일수를 적합하였다. 또한 공간예측기법 중 하나인 범용크리깅(universal kriging)을 이용하여 적합결과를 바탕으로 한 폭염 발생일수에 대한 예측지도를 작성하였다.

• 한국농공학회지
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• 제44권5호
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• pp.41-53
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• 2002

This study was conducted to derive the regional design rainfall by the regional frequency analysis based on the regionalization of the precipitation suggested by the first report of this project. According to the regions and consecutive durations, optimal design rainfalls were derived by the regional frequency analysis for L-moment in the second report of this project. Using the LH-moment ratios and Kolmogorov-Smirnov test, the optimal regional probability distribution was identified to be the Generalized extreme value (GEV) distribution among applied distributions. regional and at-site parameters of the GEV distribution were estimated by the linear combination of the higher probability weighted moments, LH-moment. Design rainfall using LH-moments following the consecutive duration were derived by the regional and at-site analysis using the observed and simulated data resulted from Monte Carlo techniques. Relative root-mean-square error (RRMSE), relative bias (RBIAS) and relative reduction (RR) in RRMSE for the design rainfall were computed and compared in the regional and at-site frequency analysis. Consequently, it was shown that the regional analysis can substantially more reduce the RRMSE, RBIAS and RR in RRMSE than at-site analysis in the prediction of design rainfall. Relative efficiency (RE) for an optimal order of L-moments was also computed by the methods of L, L1, L2, L3 and L4-moments for GEV distribution. It was found that the method of L-moments is more effective than the others for getting optimal design rainfall according to the regions and consecutive durations in the regional frequency analysis. Diagrams for the design rainfall derived by the regional frequency analysis using L-moments were drawn according to the regions and consecutive durations by GIS techniques.

• 한국수자원학회논문집
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• 제45권4호
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• pp.393-407
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• 2012

본 연구에서는 과거에서부터 기록된 우리나라 65개의 관측소들을 대상으로 강수량 데이터를사용하여 강수빈도와 극한 지표들을 산출해 냄으로써, 지표에 따라 지역별 분포를 살펴보고 시공간적인 증 감율에 대한 결과를 제시하였다. 그 결과를 시계열로 도시함으로 쉽게 파악할 수 있지만경향이 뚜렷하게 나타나지 않는 경우에는 통계적 방법인 Mann-Kendall 경향성 분석을 실시하여 이에 대해 파악하였다. 더불어 FARD를 이용하여 100년과 200년의 빈도확률강수량을 산정하고 이를 비교하였다. 강우특성을 크게 Amount, Extreme, Frequency로 분류하고 각각의 지수를 강우량 지수(Rainfall Index for Amount), 강우극치 지수(Rainfall Index for Extremes), 강우빈도 지수(Rainfall Index for Frequency)로 정의하고 RIA, RIE, RIF를 산술평균하여 홍수에 대한 종합적인 강우 위험도를 나타내는 평균 강우지수(Average Rainfall Index, ARI)를 산정하였다. 그 결과 과거에 비해 최근 10년간 강우량의 정량적인 평가 특성은 양적으로 22.3%, 극치사상 발생측면은 26.2%, 빈도측면은 5.1% 증가하였음을 확인 할 수 있었다. 본연구의 결과는 최근 우리나라 기후변화 경향을 구체적으로 제시하고 있으므로 기후변화 대비 적응 연구의 기초 자료로 활용될 수 있다.