• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.1
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• pp.87-94
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• 2017

Reliability analysis(RA) and Reliability-based design optimization(RBDO) require statistical modeling of input random variables, which is parametrically or nonparametrically determined based on experimental data. For the parametric method, goodness-of-fit (GOF) test and model selection method are widely used, and a sequential statistical modeling method combining the merits of the two methods has been recently proposed. Kernel density estimation(KDE) is often used as a nonparametric method, and it well describes a distribution function when the number of data is small or a density function has multimodal distribution. Although accurate statistical models are needed to obtain accurate RA and RBDO results, accurate statistical modeling is difficult when the number of data is small. In this study, the accuracy of two statistical modeling methods, SSM and KDE, were compared according to the number of data. Through numerical examples, the RA results using the input models modeled by two methods were compared, and appropriate modeling method was proposed according to the number of data.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.4
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• pp.457-465
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• 2010

In this study, a Taylor series (T-S) model based on the Arrhenius, McVetty, and Monkman-Grant equations was developed using a mathematical analysis. In order to reduce fitting errors, the McVetty equation was transformed by considering the first three terms of the Taylor series equation. The model parameters were accurately determined by a statistical technique of maximum likelihood estimation, and this model was applied to the creep data of alloy 617. The T-S model results showed better agreement with the experimental data than other models such as the Eno, exponential, and L-M models. In particular, the T-S model was converted into an isothermal Taylor series (IT-S) model that can predict the creep strength at a given temperature. It was identified that the estimations obtained using the converted ITS model was better than that obtained using the T-S model for predicting the long-term creep life of alloy 617.

• Journal of the Korean Chemical Society
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• v.19 no.2
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• pp.142-146
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• 1975

The formation of iron oxide hydroxide in a ferrous sulfate was studied in different contents of iron in the solution at a temperature range of 90 to $100^{\circ}C$ under 1${\sim}$3 atmospheres. The Mohr's salt thus formed was hydrolyzed under 1 to 3 atmospheres, in 14 to 72 g/l of iron content in the solution pH 3 or 6 for two hours at 90 to $100^{\circ}C$. The results obtained was as follows; 1) In Mohr's salt solution, as the iron content was increased, with decreasing the concentration of hydrogen ion, the yield of iron oxide hydroxide was gradually increased. 2) When iron content in Mohr's salt solution was 42.81 g/l, 91.5% of iron was recovered in the form of $\alpha$-goethite similar to yellow grade of natural goethite. 3) When $\alpha$-goethite obtained was calcined of $500^{\circ}C$, it was turned into ${\alpha}$-ferric oxide with a redish brown colour.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.6 no.2
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• pp.67-75
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• 1986

This paper introduces the nonlinear Stream Function Wave Theory for design waves efficiently to compute the wave energy and energy transport quantities and to analyze the effects of nonlinearities on them. The Stream Function Wave Theory was developed by Dean for case of the observed waves with assymmetric wave profiles and of the design waves with symmetric theoretical wave profiles. Dalrymple later improved the computational procedure by adding two Lagrangian constraints so that more efficient convergence of the iterative numerical method to a specified wave height and to a zero mean free surface displacement resulted. And the Stream Function coefficients are computed numerically by the improved Marquardt algorithm developed for this study. As the result of this study the effects of nonlinearities on the wave quantities of the average potential energy density, the average kinetic energy density result in overestimation by linear wave theory compared to the Stream Function Wave Theory and increase monotonically with decreasing $L^*/L_O$ and with increasing $H/H_B$. The effects of nonlinearities on the group velocity and the wavelength quantities result in underestimation by linear wave theory and increase monotonically with increasing $H/H_B$. Finally the effect of nonlinearity on the average total energy flux results in overestimation for shallow water waves and underestimation for deep water waves by linear wave theory.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.3
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• pp.229-235
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• 2016

In this paper, a methodology, which is able to predict the thermal stresses accurately yet efficiently, is presented for beam structures via Saint-Venant's principle. In general, higher-order beam theories have been known to be effective for the prediction of thermal stresses. In contrast to this, we propose the method to predict the thermal stresses of beam structures by post-processing the classical beam theory via Saint-Venant's principle. The approach includes an out-of-plane warping displacement to account for the through-the-thickness thermal deformation. With this, one can accurately recover the thermal stresses as compared to the elasticity solutions. In fact, they are identical for the beams made of isotropic materials. The effect of out-of-plane warping is also investigated, it turns out that the effect is negligible in mechanical stress analysis but not in thermal stress analysis.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.4
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• pp.393-398
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• 2015

A very important part in vibration analysis is to calculate the frequency response function (FRF). In general, a large sized or/and complicated structure has many thousands to millions of degrees. Therefore, the FRF cannot be calculated by the traditional analysis method using an inverse matrix. This paper presents a new FRF calculation method of a superstructure by synthesizing sub-structure modes, of which the DOF can be deduced by partitioning into some sub-structures. To confirm its analysis results, the method was applied to an assembled plate ($B300{\times}L900{\times}t5mm$) with three diagonal sub-plates($B300{\times}L300{\times}t5mm$) in series and compared with the measured data. The test results have were comparable those of the calculated ones with an error less than 5%.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.7 no.1
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• pp.11-18
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• 1989

Observations to precise levelling nets contain different types of error because it has been caried out with various instruments and techniques, and also completed through long period. In order to establish a precise levelling nets, therefore, the weight function has to be selected adequately in the adjustment of nets. The purpose of the study is to determine a suitable weight function for the first order geodetic levelling nets in Korea and, therefore, the various numerical tests are performed with different statistical error models. The result of the study shows that the weight function, W＝1/$L^2$ is more efficient than W＝1/L in the first order levelling nets in the Korea.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.90-94
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• 2005

본 연구의 목적은 현 국내 홍수 예경보시스템에 사용되고 있는 저류함수모형의 매개변수 변화에 따른 유량해석의 불확실성을 평가하는데 있다. 적용 대상지점으로는 개진을 출구로 하는 낙동강 회천유역($747.5km^2$)이며 비교적 양호한 수문자료를 가지고 있는 단일 호우사상을 선정하였다. 불확실성 평가에 사용된 매개변수는 관측수문곡선을 비교적 정확하게 모의하는 경험적인 값을 기준으로 Monte Carlo 기법을 이용하여 각각의 매개변수(K, P, $T_{1},\;f_{l},\;R_{sa}$)에 대한 정규분포를 가지는 100개의 난수를 발생시켜 저류함수 모형으로 모의되는 유량 앙상블을 평가하였다. 최적화된 매개변수를 이용하여 유량해석을 실시한 결과, 각각의 매개변수가 유출해석에 미치는 영향을 파악할 수 있었으며, 그 중 저류상수 K와 포화누가우량 Rsa가 불확실성이 제일 큰 매개변수로 나타났고, 이들의 혼합 앙상블 유출결과도 매우 큰 불확실성을 내포하는 것으로 나타났다.

• The Journal of the Korea Contents Association
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• v.7 no.2
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• pp.125-131
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• 2007

An iterative Green's function method (IGFM) is introduced in order to analyze complex electromagnetic waveguide stub structures in view of a university student. The IGFM utilizes a Green's function approach and an regional iteration scheme. A physical iteration mechanism with simple mathematical equations facilitates clear formulations of the IGFM. Scattering characteristics of a standard E-plane T-junction stub in a parallel-plate waveguide are theoretically investigated in terms of the IGFM. Numerical computations illustrate the characteristics of reflection and transmission powers versus frequency.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.9
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• pp.773-779
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• 2014

A qualitative and quantitative analysis on flame dynamics is required to model combustion instability characteristics in gas turbine lean premixed combustors. The current paper shows the flame transfer function modeling results using CFD(Computational Fluid Dynamics) techniques for the flame dynamics study. It is generally known that flame shapes determine the basic characteristics of the flame transfer function. The comparisons of the modeled flame shapes with the measured ones were made using the optimized heat transfer conditions. Modeling results of the flame transfer function show the close behaviors to the measured data with a reasonable accuracy if the flame geometry can be exactly captured.