• Journal of Korean Society of Coastal and Ocean Engineers
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• v.27 no.4
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• pp.217-227
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• 2015

In this study, two-dimensional physical experiment was carried out to examine the applicability of the three formulas(Takahashi and Shimosako, 1994; Tabet-Aoul and Lambert, 2003; Li, 2007), which were proposed to calculate the wave forces acting on perforated caisson breakwaters. In order to quantitatively compare the measured with the estimated values based on the wave formulas, the refined index of agreement and the coefficient of determination were calculated, by which the degree of agreement was evaluated. Among the three wave formulas, DUT formula (Li, 2007) showed the smallest deviation from the measured forces, whereas Takahashi formula (Takahashi and Shimosako, 1994) showed the largest deviation. Meanwhile, comparison of the magnitude of the measured wave forces with those from the three formulas revealed that DUT formula slightly underestimate, while the others overestimate the measured forces.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.3
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• pp.2263-2271
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• 2015

The thin cylindrical shell structure under compression should be checked with buckling stability. Initial imperfection effects on buckling strength has been investigated by many researchers. Even though there have been a number of these studies, more studies of buckling strength with various initial imperfections are still necessary. In Eurocode, there is a design parameter that is applicable only on specific imperfection by section thickness rather than on various initial imperfection. In this study, structural analyses, using geometry and material nonlinear analysis, of cylindrical buckling strength with various initial imperfection were performed and compared with Eurocode design strength and Finite Element Method (FEM) analysis results. Moreover, the modified design parameter, which gives more exact prediction result of buckling strength under bending with initial imperfection, is proposed for various initial imperfections.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.3
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• pp.289-296
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• 2009

Natural frequency is a key parameter to determine the seismic and wind loading of tall flexible structures, and to assess the wind-induced vibration for serviceability check. In this study, natural frequencies and associated mode shapes were obtained from measured acceleration data and system identification technique. Subsequently, finite element(FE) models for a tall reinforced concrete buildings were built using a popular PC-based finite element analysis program and calibrated to match their natural frequencies and mode shapes to actual values. The calibration of the FE model included: 1) compensation of modulus of elasticity considering the mix design strength, 2) flexural stiffness of floor slabs, and 3) major non-structural components such as plain concrete walls. Natural frequencies and mode shapes from the final FE model showed best agreement with the measured values.

• Journal of the Earthquake Engineering Society of Korea
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• v.5 no.3
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• pp.1-8
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• 2001

Seismic design forces for bridge components may be determined by modifying elastic member forces of design earthquakes using appropriate response modification factors according to the national design code of bridges Modeling technique of pile foundation system is one of the important parameters which greatly affects the results in the process of the elastic seismic analysis of a bridge system with pile foundation. In this paper, a approximate and simplified modeling technique of a pile foundation system for the practical purposes is presented. The modeling technique is based on the stiffnesses of pile foundation during earthquake. The horizontal stiffnesses are determined from the resistance-deflection curves derived from the results of dynamic field tests using cyclic loads and the vertical stiffness includes the effects of the end bearing capacities and side friction of piles as well as the pile compliances under the expected vertical load level. The applicability of the proposed technique has been validated through the some example bridge analyses.

• The Journal of the Korea Contents Association
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• v.16 no.1
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• pp.140-150
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• 2016

This study aims to investigate the effect of vegetation type, length of vegetative filter strip, and rainfall on trapping efficiency of the non-point source water pollution. Numerical experiments are carried out using VFSMOD-w. It is known from this study that the vegetation having the same value of revised Manning roughness coefficient shows the similar trapping efficiency in VFSMOD-w. When the length of vegetative filter strip increases twice, the trapping efficiency increases negligibly small under the same condition of rainfall. From this finding, it is also known that most of sediment are removed within a certain length of vegetative filter strips. It is concluded that the installation of vegetative filter strip is determined under the consideration of the rainfall characteristics, space of vegetation, and length of vegetative filter strip.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.2
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• pp.489-500
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• 2016

This study examined the influencing factors of depression on the physical appearance satisfaction and the trends of personal relationships in Korean nursing college students. A total of 247 subjects between 17 and 27 years of age were selected through random sampling. Data were collected using a self-reported questionnaire from November 1, 2012 to March 30, 2013. The depression acceptance differed significantly according to rank between siblings, religion, school record, socioeconomic status, cohabitation, and stress resolving methods. There was a positive correlation between depression and the appearance satisfaction and the trends of personal relationship. 26.8% variance in depression was explained by the appearance, socioeconomic status, sympathy-acceptance, resistance-mistrust, body figure, and cohabitation. These findings may be useful for understanding depression in nursing college students and developing more specific personal interrelationship and depression programs.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.12
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• pp.1343-1352
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• 1992

This paper presents a new and easy method to obtain the Fourier transforms of the n-th order cosine-pulses whose maximum amplitudes are uniform. The new method is focused on deriving a formula which is recursively related following their orders and can be well applied to some numerical solutions. On the other hand, this method also offers more compact procedures in view of analytical solutions than the conventional methods because the results are consist of the sum of two functions which are easily calculated. Especially, the formula can be represented as a complete recursion by the separation of coefficients originated by the authors and the resulting difference equation is given by the sum of the original 'sinc' functions shifted by some symmetrical factors and multiplied by some constants. The constants are easily decided from the binomial coefficients and the shifting factors from the corresponding exponential differences in the expansion of $(a+b)^n$.

• Fire Science and Engineering
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• v.28 no.2
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• pp.69-75
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• 2014

This study derives the factors which affect the occurrence of arson from statistical data (population, economic, and social factors) by multiple regression analysis. Multiple regression analysis applies to 4 forms of functions, linear functions, semi-log functions, inverse log functions, and dual log functions. Also analysis respectively functions by using the stepwise progress which considered selection and deletion of the independent variable factors by each steps. In order to solve a problem of multiple regression analysis, autocorrelation and multicollinearity, Variance Inflation Factor (VIF) and the Durbin-Watson coefficient were considered. Through the analysis, the optimal model was determined by adjusted Rsquared which means statistical significance used determination, Adjusted R-squared of linear function is scored 0.935 (93.5%), the highest of the 4 forms of function, and so linear function is the optimal model in this study. Then interpretation to the optimal model is conducted. As a result of the analysis, the factors affecting the arson were resulted in lines, the incidence of crime (0.829), the general divorce rate (0.151), the financial autonomy rate (0.149), and the consumer price index (0.099).

• Journal of the Korea Society of Computer and Information
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• v.17 no.12
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• pp.83-93
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• 2012

This paper proposes an image segmentation framework that modifies the objective function of Fuzzy C-Means (FCM) to improve the performance and computational efficiency of the conventional FCM-based image segmentation. The proposed image segmentation framework includes a locally weighted fuzzy c-means (LWFCM) algorithm that takes into account the influence of neighboring pixels on the center pixel by assigning weights to the neighbors. Distance between a center pixel and a neighboring pixels are calculated within a window and these are basis for determining weights to indicate the importance of the memberships as well as to improve the clustering performance. We analyzed the segmentation performance of the proposed method by utilizing four eminent cluster validity functions such as partition coefficient ($V_{pc}$), partition entropy ($V_{pe}$), Xie-Bdni function ($V_{xb}$) and Fukuyama-Sugeno function ($V_{fs}$). Experimental results show that the proposed LWFCM outperforms other FCM algorithms (FCM, modified FCM, and spatial FCM, FCM with locally weighted information, fast generation FCM) in the cluster validity functions as well as both compactness and separation.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.338-338
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• 2015

하천으로 유입되어 수질 오염을 야기하는 오염원은 오염 배출원이 명확하여 하나의 점으로 나타낼 수 있는 점오염원(Point Source)과 오염원이 명확치 않은 비점오염원(Non-point)으로 구분된다. 생활하수, 축산폐수와 같이 오염원이 명확한 점오염원은 하천 유입 이전에 처리장을 거쳐 정화작업이 가능한 반면, 비점오염원은 오염원이 명확치 않아 처리에 어려움이 따른다. 또, 오염물의 양과 이동 경로가 예측이 불가능하고 강우시에는 특별한 처리 없이 하천으로 바로 유입된다. 비점 오염원의 종류는 토사, 영양물질, 유기물질, 농약, 바이러스 등 다양하다. 이 중에서 토양에 흡착되어 이동하는 질소와 인은 하천으로 유입되어 부영양화를 야기하는 특성이 있어 더욱 처리가 필수적이다. 이러한 비점오염원으로 인한 수질 오염을 줄이기 위해 여러 최적관리기법(Best Management Practices, BMPs)이 제시되어 있으며 오염 물질의 하천 유입을 차단하는 것에 중점을 둔다. 가장 널리 이용되는 방법으로는 비점오염원 저감시설 중 하천변에 식물체를 설치하여 토양의 유실을 막는 식생대(Vegetative Filter Strip, VFS)가 있다. 식생 밀집 지역의 설치를 통해 표면 유출을 차단하고 토양 유실 감소와 수체로의 오염물질 확산을 막을 수 있다. 이에 VFSMOD-w를 이용하여 강우시 식생대를 통한 토양 유실 감소 효율에 대한 연구를 수행하였다. 연구 대상 지역으로 비교적 수문 및 토양 자료가 풍부한 청미천 유역을 선정하였다. 그 결과, 식생대의 길이와 식생대 내 식물체의 파종간격이 가장 지배적인 영향을 미치는 것이 확인된다. 이때, 식물체의 종류는 식물체 파종으로 인해 변화되는 토양의 수정된 Manning의 조도계수로 구분한다. 모든 강우 및 식물체 조건이 동일할 때, 식생대 내 식물의 파종 간격이 좁고 식생대의 길이가 길수록 토사 저감 효율이 증가하는 결과가 도출되었다. 식물체의 높이, 식물체의 종류 및 식물의 파종간격이 입력 자료로 요구되나 이 중 식물체의 높이는 토사 저감 효율에 영향을 미치지 않는 것으로 나타났다. 또, 동일한 강우 조건에서 식생대의 길이가 0.5 m에서 1.0 m로 2배 증가하였을 때 토사 저감 효율이 두 경우 모두 95% 이상의 효율을 보이는 것이 나타났다. 이는 식생대의 길이가 증가할수록 토사 저감 효율이 증가하나 일정 길이 이상이 되면 대부분의 토사가 저감되는 것을 의미한다. 결론적으로 식생의 파종 간격이 좁을수록 토사 저감 효율이 증가하더라도 식물체의 성장을 고려한 적절한 파종 간격을 선정하여야 한다. 즉, 식생대의 설치는 적절한 파종 간격 및 식생대 길이를 식생대 설치지역의 강우 특성에 따라 결정지어야 한다고 판단된다.