• 한국농공학회지
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• 제37권E호
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• pp.1-9
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• 1995

It is shown that two step power transformation is more efficient for the normalization of frequency distribution with the coefficient of skewness of zero in comparison with others including SMEMAX and power transformations. It is confirmed that the design low flows calculated using power and two step power transformations used in this study are generally nearer to the observed data as compared with those of SMEMAX transformation at all return periods in the applied watersheds of the Kum, Naktong and Yongsan rivers in Korea.

• Journal of the Korean Data and Information Science Society
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• 제21권4호
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• pp.803-811
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• 2010

This study analyzes the characteristics of preference ratings by dividing estimated values into four groups according to rank correlation coefficient after obtaining preference estimated value to user's ratings by using collaborative filtering algorithm. It is known that the value of standard error of skewness and standard error of kurtosis lower in the group of higher rank correlation coefficient This explains that the preference of higher rank correlation coefficient has lower extreme values and the differences of preference rating values. In addition, top n recommendation lists are made after obtaining rank fitting by using the result ranks of prediction value and the ranks of real rated values, and this top n is applied to the four groups. The value of top n recommendation is calculated higher in the group of higher rank correlation coefficient, and the recommendation accuracy in the group of higher rank correlation coefficient is higher than that in the group of lower rank correlation coefficient Thus, when using standard error of skewness and standard error of kurtosis in recommender system, rank correlation coefficient can be higher, and so the accuracy of recommendation prediction can be increased.

• 한국농공학회지
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• 제32권E호
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• pp.20-32
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• 1990

Abstract This study was conducted to pursue the normalization of frequency distribution by making an approach to the coefficient of skewness to nearly zero through the Box-Cox transformation, to get probable flood flows can be calculated by means of the transformation equation which has been derivated by Box-Cox transformation in the annual maximum series of the applied watersheds. It has been concluded that Box-Cox transfromation is proved to be more efficient than logarithmic, square root and SMEMAX transformation which is based on the trigonometric solution of a right triangle whose three verteces repesent the smallest, median and largest observed values of a population in making the coefficient of skewness nearer to zero. Consequently it is shown that probable flood flows according to the return period based on Box-Cox transformation are closer to the observed data as compared to other methods including SMEMAX transformation and fitted probability distributions such as the three parameter lognormal and the type I extremal distribution for the applied watersheds.

• Wind and Structures
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• 제36권6호
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• pp.393-404
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• 2023

Skewness and kurtosis are important higher-order statistics for simulating non-Gaussian wind pressure series on low-rise buildings, but their predictions are less studied in comparison with those of the low order statistics as mean and rms. The distribution gradients of skewness and kurtosis on roofs are evidently higher than those of mean and rms, which increases their prediction difficulty. The conventional artificial neural networks (ANNs) used for predicting mean and rms show unsatisfactory accuracy in predicting skewness and kurtosis owing to the limited capacity of shallow learning of ANNs. In this work, the deep neural networks (DNNs) model with the ability of deep learning is introduced to predict the skewness and kurtosis on a low-rise building. For obtaining the optimal generalization of the DNNs model, the hyper parameters are automatically determined by Bayesian Optimization (BO). Moreover, for providing a benchmark for future studies on predicting higher order statistics, the data sets for training and testing the DNNs model are extracted from the internationally open NIST-UWO database, and the prediction errors of all taps are comprehensively quantified by various error metrices. The results show that the prediction accuracy in this study is apparently better than that in the literature, since the correlation coefficient between the predicted and experimental results is 0.99 and 0.75 in this paper and the literature respectively. In the untrained cornering wind direction, the distributions of skewness and kurtosis are well captured by DNNs on the whole building including the roof corner with strong non-normality, and the correlation coefficients between the predicted and experimental results are 0.99 and 0.95 for skewness and kurtosis respectively.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.819-822
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• 2002

It is necessary for the numerical simulation of 3-dimensional incompressible isotropic decaying turbulence to construct 3-dimensional initial velocity field which resembles the fully developed turbulence. Although the previous velocity field generation method proposed by Rogallo(1981) satisfies continuity equation and 3-dimensional energy spectrum, it has limitation, as indicated in his paper, that it does not produce the higher velocity moments(e. g. velocity derivative skewness) characteristic of real turbulence. In this study, a new velocity field generation method which is able to control velocity derivative skewness of initial velocity field is proposed. Brief descriptions of the new method and a few parameters which is used to control velocity derivative skewness are given. A large eddy simulation(LES) of isotropic decaying turbulence using dynamic subgrid-scale model is carried out to evaluate the performance of the initial velocity field generated by the new method. It was shown that the resolved turbulent kinetic energy decay curve and the resolved enstrophy decay curve from the initial field of new method were more realistic than those from the initial field of Rogallo's method. It was found that the dynamic model coefficient from the former was initially half the stationary value and experienced relatively short transition period, though that from the latter was initially zero and experienced relatively longer transition period.

• 한국수자원학회논문집
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• 제47권2호
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• pp.161-170
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• 2014

수공구조물의 설계 시 적절한 확률수문량을 추정하는 것은 매우 중요하며, 이러한 확률수문량을 추정하기 위해서는 표본으로서의 수문자료를 잘 표현할 수 있는 확률분포형을 찾아야 한다. 이와 같이 수문자료에 통계적 특성을 잘 표현할 수 있는 확률분포형을 찾기 위해서 적합도 검정을 실시하며, 적합도 검정 중 하나인 확률도시 상관계수 검정은 비교적 최근에 개발되어 그 사용법이 간단하며 높은 기각능력을 갖는다고 알려져 있다. 본 연구에서는 왜곡도 계수의 영향을 고려할 수 있는 도시위치공식을 이용하여 확률도시 상관계수 검정통계량을 유도하고 그 기각능력을 검토하였으며, 그 결과를 기존에 왜곡도 계수를 고려하지 않은 확률도시 상관계수 검정 방법과 비교해보았다. 그 결과 본 연구에서 유도된 확률도시 상관계수 검정에 의한 기각능력이 기존의 검정 방법들 보다 뛰어났으며, 특히 표본 크기가 작을수록, 발생 분포형이 형상 매개변수를 가질 경우 기각능력이 높게 나타나는 것으로 나타났다.

• 한국기계가공학회지
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• 제3권2호
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• pp.18-24
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• 2004

The effect of surface characterization parameters, such as surface roughness, skewness and kurtosis, on sliding friction and wear was studied experimentally. The friction coefficient was examined under the various parameters and sliding speed, normal load and type of lubricant with ball-on-disk type tribo-meter. The surface of the lower skewness in negative or the higher kurtosis between the same arithmetic mean value tends to indicate low friction.

• 대한설비공학회지:설비저널
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• 제16권5호
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• pp.516-524
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• 1987

This paper presents experimental data of fluctuation characteristics of local void fraction of air-water two-phase flow which are associated with the flow pattern, annular gap size and radial location in vertical concentric annuli with coefficient of skewness and kurtosis. The annular gap widths are 13mm, 11mm, and 9mm for a 38m inner diameter as the lucite outer tube. A electrical conductivity probe was used to measure the local void fraction and traversed diametrically from inner wall to outer wall using radial increments of 2mm. It was shown that distribution of the coefficient of skewness and kurtosis, which is related that the one is the asymmetry and the other peakness of local void fraction distribution was influenced by flow pattern, annular gap size and radial location.

• Journal of the Korean Data and Information Science Society
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• 제28권5호
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• pp.959-970
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• 2017

본 연구에서는 두 변수의 상관계수를 반영한 이변량 자료의 왜도와 첨도 통계량을 제안하고, 시각적으로 표현할 수 있는 표면그림을 개발한다. 이변량 왜도 통계량은 이변량 확률표본 자료의 치우침 방향과 정도를 표현하는 실수 한 쌍으로 정의한다. 첨도는 양의 값을 가지며 이변량 정규분포를 기준으로 꼬리 부분의 두터운 정도를 파악할 수 있다. 그리고 표면그림은 분위벡터를 바탕으로 평면에 구현한다. 다양한 형태의 이변량 자료를 생성하여 표면그림을 작성하고 왜도와 첨도를 계산하여 탐색해 본 결과, 왜도와 첨도 값들은 표면그림으로 구현한 이변량 자료의 특징을 잘 반영하는 것을 발견할였다. 그러므로 본 논문에서 제안한 왜도, 첨도 그리고 표면그림은 이변량 분포를 분석하는 기술통계학적 방법으로 활용할 수 있다.

• 한국농공학회지
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• 제29권3호
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• pp.138-144
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• 1987

This study was conducted to pursue the normalization of frequency distribution by making approach the coefficient of skewness to nearly zero tbrough SMEMAX transformation and to get probable minimum flows can be acquired by means of transforrnation equation which has been derivated by SMEMAX method to the annual minimum flow series of five watersheds along Geum river basin. The results obtained through SMEMAX method were compared with probable minimum flows according to return periods by Type III extremal distribution which has been determined as the best fitted one among probablility distributions for the analysis of minimum flow. All the results obtained through this study are summarized as follows. 1.SMEMAX transformation based on median value was proved to be the best method when the coefficient of skewness has less reliability because of the short duration for the observation and were not affected by accidental outliers. 2.SMEMAX transformation has found to be the best one for the coefficient of skewness to be made nearly zero in comparison with log and cubic root transformation. 3.Probable minimum flows according to the return periods were derivated by transformation equations obtained through theoretical analysis of SMEM AX transformation. 4.In general, probable minimum flows by SMEMAX method were appeared as higher values in the range of five and twenty years and as lower ones in the range of below than five and more than fifty years in return periods respectively, in comparison with the results of type III extremal distribution. 5.Relative errors in the probable minimum flows of SMEMAX method to the results of type III extremal distribution were shown to be within ten percent except those of one hundred years in return periods. 6.SMEMAX method was also confirmed to be useful for the analysis of minimum flow frequency as well as flood frequency analysis.