• Geomechanics and Engineering
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• 제5권6호
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• pp.519-540
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• 2013

This paper presents an optimal design method for determining pile lengths of piled raft foundations. The foundation settlement is evaluated by taking into account the raft-pile-soil interaction. The analysis of settlement is simplified by using Steinbrenner's equation. Then the total pile length is minimized under the settlement constraint. An extended sequential linear programming technique combined with an adaptive step-length algorithm of pile lengths is used to solve the optimal design problem. The accuracy of the simplified settlement analysis method and the validity of the obtained optimal solution are investigated through the comparison with the actual measurement result in existing piled raft foundations.

• 산업기술연구
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• 제18권
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• pp.125-130
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• 1998

The undergound space is widely developed because of dometic industry and protection of enviornment. The existence and exact location of tunnel is very important for stability of the enormous underground storage house or building. Various types of prospecting methods have been applied to detection of underground tunnel. In this study, electrical prospecting method is applied to detect tunnel because the development of underground space is very connected with groundwater. Sensitivity analysis is introduced for the calculation of elctrical inversion data. The governing equation is Fourier transformed into the 2-dimensional wave number space and solved by using the finite element method.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2010년도 정기 학술대회
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• pp.508-511
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• 2010

본 논문에서는 정상상태 유체-구조 연성문제를 연속체 기반으로 정식화하고 유한요소법을 이용하여 완전 연성된 해를 구하였다. 대 변형을 고려하기 위하여 토탈 라그란지안 정식화를 사용하였으며 유체 및 구조의 비선형성이 고려되었다. 유체와 구조 영역의 형상을 NURBS 곡면을 이용하여 매개화하여 표현하였으며, 형상 최적화를 위해 효율적인 설계민감도 해석법인 애조인 기법을 이용하여 압력, 속도, 변위 등에 대한 설계민감도를 구하였다. 이를 이용하여 최소 컴플라이언스를 갖게 하는 구조물 내부의 유체영역의 설계 등의 수치예제를 통하여 개발된 방법론의 타당성을 확인하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제34회 춘계학술대회논문집
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• pp.264-267
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• 2010

This research focuses on the development of numerical code to deal with compressible two phase flow around three dimensional objects combined with cavitation model suggested by Weishyy et al. with k-e turbulent model. The cryogenic cavitation is carried out by considering the thermodynamic effect on physical properties of cryogenic fluids in physical point of view and implementing the temperature sensitivity in the energy equation of the government equations in numerical point of view, respectively. The formulation has been extensively validated for both liquid nitrogen and liquid hydrogen by simulating the experiments of Hord on hydrofoils. Then, simulations of cavitating turbopump inducers at their design flow rate are presented. Results over a broad range of Nss numbers extending from single-phase flow conditions through the critical head break down point are discussed. In particular, thermal depression effects arising from cavitation in cryogenic fluids are identified and their impact on the suction performance of the inducer quantified.

• 대한전기학회논문지:전력기술부문A
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• 제50권1호
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• pp.1-5
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• 2001

In this paper, a new method for calculating the penalty factors of all generators including the slack bus is presented. A simple transposition of the angle reference, from the conventional slack bus to another bus where no generation exists, enables the derivation of the loss sensitivity of the slack bus. Penalty factors are obtained without any physical assumption through a simple substitution of the bus loss sensitivities. Penalty factors calculated by proposed method are not dependent on reference bus and can also be directly substituted into the general ELD equation for computing the optimal dispatch. Equations for loss sensitivities, Penalty factors and ELD are calculated simultaneously in normal power flow computation. A case study on a test system has proved the effectiveness of the proposed' angle reference transposition' method.

• 한국해양공학회지
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• 제30권4호
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• pp.320-326
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• 2016

Rip current forecasts, based on intensity, are marked in four levels—notice, watch, warning, and danger. However, numerical results are represented by current vectors, whose magnitudes are then converted into predictive levels. In the present study, the rose diagram is adapted as a determinative forecasting index and examined for the case of an ideal rip channel consisting of surface, bottom, and averaged currents. Further, it is employed in the sensitivity analysis of wave-induced currents generated by wave conditions at the Haeundae Beach. The simulation of surface onshore and bottom undertow currents is accomplished by including a mass flux term in the wave-averaged continuity equation.

• 한국지구과학회지
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• 제40권4호
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• pp.392-405
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• 2019

Biogeochemical processes play an important role in ocean environments and can affect the entire Earth's climate system. Using an ocean-biogeochemistry model (NEMO-TOPAZ), we investigated the effects of changes in albedo and wind stress caused by phytoplankton in the equatorial Pacific. The simulated ocean temperature showed a slight decrease when the solar reflectance of the regions where phytoplankton were present increased. Phytoplankton also decreased the El $Ni{\tilde{n}}o$-Southern Oscillation (ENSO) amplitude by decreasing the influence of trade winds due to their biological enhancement of upper-ocean turbulent viscosity. Consequently, the cold sea surface temperature bias in the equatorial Pacific and overestimation of the ENSO amplitude were slightly reduced in our model simulations. Further sensitivity tests suggested the necessity of improving the phytoplankton-related equation and optimal coefficients. Our results highlight the effects of altered albedo and wind stress due to phytoplankton on the climate system.

• Nuclear Engineering and Technology
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• 제53권1호
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• pp.142-147
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• 2021

Hydrogen peroxide is a radiolysis product of water formed under gamma-irradiation; therefore, its reliable detection is crucial in the nuclear industry for spent fuel management and coolant chemistry. This study proposes an electrochemical sensor for hydrogen peroxide detection. Cysteamine (CYST), gold nanoparticles (GNPs), and horseradish peroxidase (HRP) were used in the modification of a gold electrode for fabricating Au/CYST/GNP/HRP sensor. Each modification step of the electrode was investigated through electrochemical and physical methods. The sensor exhibited strong sensitivity and stability for the detection and measurement of hydrogen peroxide with a linear range of 1-9 mM. In addition, the Michaelis-Menten kinetic equation was applied to predict the reaction curve, and a quantitative method to define the dynamic range is suggested. The sensor is highly sensitive to H₂O₂ and can be applied as an electrochemical H₂O₂-sensor in the nuclear industry.

• 한국정밀공학회지
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• 제12권6호
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• pp.145-151
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• 1995

The first-order Taylor series expansion can be evaluated analytically from the formulated symbolic nonlinear dynamic equations. A closed-form linear dynamic euation is derived about a nominal trajectory. The state space representation of the linearized dynamics can be derived easily from the closed-form linear dynamic equations. But manual symbolic expansion of dynamic equations and linearization is tedious, time-consuming and error-prone. So it is desirable to manipulate the procedures using a computer. In this paper, the analytic linearization is performed using the symbolic language MATHEMATICA. Two examples are given to illustrate the approach anbd to compare nonlinear model with linear model.

• Current Optics and Photonics
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• 제7권5호
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• pp.537-544
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• 2023

Differential phase contrast (DPC) microscopy, a central quantitative phase imaging (QPI) technique in cell biology, facilitates label-free, real-time monitoring of intrinsic optical phase variations in biological samples. The existing DPC imaging theory, while important for QPI, is grounded in paraxial diffraction theory. However, this theory lacks accuracy when applied to high numerical aperture (NA) systems that are vital for high-resolution cellular studies. To tackle this limitation, we have, for the first time, formulated a nonparaxial DPC imaging equation with a transmission cross-coefficient (TCC) for high NA DPC microscopy. Our theoretical framework incorporates the apodization of the high NA objective lens, nonparaxial light propagation, and the angular distribution of source intensity or detector sensitivity. Thus, our TCC model deviates significantly from traditional paraxial TCCs, influenced by both NA and the angular variation of illumination or detection. Our nonparaxial imaging theory could enhance phase retrieval accuracy in QPI based on high NA DPC imaging.