• Journal of the Korean GEO-environmental Society
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• v.4 no.3
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• pp.79-88
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• 2003

This paper presents a numerical study of the spatial behavior of a linear absorbing solute in a heterogeneous porous medium. The spatially correlated log-normal hydraulic conductivity field is generated in a given two-dimensional domain by using the geostatistical method (Turning Bands algorithm). The velocity vector field is calculated by applying the two-dimensional saturated groundwater flow equation to the Galerkin finite element method. The simulation of solute transport is carried out by using the random walk particle tracking model with CD(constant displacement) scheme in which the time interval is automatically adjusted. In this study, the spatial behavior of a solute is analyzed by the longitudinal center-of-mass displacement, longitudinal spatial spread moment and longitudinal plume skewness.

• Journal of the Korean Geotechnical Society
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• v.34 no.7
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• pp.29-38
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• 2018

Three-dimensional continuum modeling of dynamic soil-pile-structure interaction embedded in a liquefiable sand was carried out. Finn model which can model liquefaction behavior using effective stress method was adopted to simulate development of pore water pressure according to shear deformation of soil directly in real time. Finn model was incorporated into Non-linear elastic, Mohr-Coulomb plastic model. Calibration of proposed modeling method was performed by comparing the results with those of the centrifuge tests performed by Wilson (1998). Excess pore pressure ratio, pile bending moment, pile head displacement-time history according to depth calculated by numerical analysis agreed reasonably well with the test results. Validation of the proposed modeling method was later performed using another test case, and good agreement between the computed and measured values was observed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.2
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• pp.137-148
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• 2014

A multi-rotor is an autonomous flying robot with multiple rotors. Depending on the number of the rotors, multi-rotors are categorized as tri-, quad-, hexa-, and octo-rotor. Given their rapid maneuverability and vertical take-off and landing capabilities, multi-rotors can be used in various applications such as surveillance and reconnaissance in hostile urban areas surrounded by high-rise buildings. In this paper, the unified dynamic model of each tri-, quad-, hexa-, and octo-rotor are presented. Then, based on derived mathematical equations, the operation and control techniques of each multi-rotor are derived and analyzed. For verifying and validating the proposed models, operation and control technique simulations are carried out.

• Journal of the Korean Institute of Intelligent Systems
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• v.19 no.5
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• pp.667-673
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• 2009

This paper presents an efficient facial expression recognition method by measuring the histogram distance based on preprocessing. The preprocessing that uses both centroid shift and histogram equalization is applied to improve the recognition performance, The distance measurement is also applied to estimate the similarity between the facial expressions. The centroid shift based on the first moment balance technique is applied not only to obtain the robust recognition with respect to position or size variations but also to reduce the distance measurement load by excluding the background in the recognition. Histogram equalization is used for robustly recognizing the poor contrast of the images due to light intensity. The proposed method has been applied for recognizing 72 facial expression images(4 persons * 18 scenes) of 320*243 pixels. Three distances such as city-block, Euclidean, and ordinal are used as a similarity measure between histograms. The experimental results show that the proposed method has superior recognition performances compared with the method without preprocessing. The ordinal distance shows superior recognition performances over city-block and Euclidean distances, respectively.

• Aerospace Engineering and Technology
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• v.4 no.1
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• pp.39-44
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• 2005

To validate the rotor performance analysis, 3D Computational Fluid Dynamics(CFD) analysis was performed for tilt rotor aeroacoustic model(TRAM). Also, 3D vehicle with rotating rotors was simulated for rotor power effect analysis. Multiple reference frame(MRF) and sliding mesh techniques were implemented to capture the effect of rotor revolution. CFD results were compared with the wind tunnel test results to validate their accuracy. At helicopter mode, CFD analysis predicted lower thrust than the wind tunnel test but CFD results showed good agreement with the test result at cruise mode. Rotor power effect decreased the lift but did not change drag and pitching moment.

• Nuclear Engineering and Technology
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• v.16 no.2
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• pp.97-105
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• 1984

A method and computer code for the uncertainty analysis in the top event unavailability are developed and tested by combining Monte Carlo Method and Moments method with fault tree reduction technique. Using system fault trees and unavailability data selected in WASH-1400, the efficiency of the proposed method is tested and these results are compared with those obtained by Monte Carlo method. It is shown that the results are sufficiently good in accuracy and computation time is considerably reduced compared with those by Monte Carlo method.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.12
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• pp.1906-1913
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• 2004

A new method has been proposed for the calibration of frictional forces in atomic force microscopy. Angle conversion factor is defined using the relationship between torsional angle and frictional signal. Once the factor is obtained from a cantilever, it can be applied to other cantilevers without additional experiments. Moment balance equations on the flat surface and top edge of a commercial step grating are used to obtain angle conversion factor. Proposed method is verified through another step grating test and frictional behavior of Mica.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.93-96
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• 2009

바퀴동력계는 차량에 지면으로부터 전달되는 힘과 모멘트를 측정하는 로드셀이다. 본 연구에서 개발한 바퀴동력계는 스트레인 게이지식 로드셀로써 이러한 로드셀을 설계하는데 있어서 몇가지 고려해야 하는 사항이 있다. 우선 스트레인 게이지를 부착하기 쉬운 구조가 되어야 하고 조립시의 오차를 줄이기 위하여 한 몸체로 제작되어야 한다. 이와 동시에 가장 중요하게 고려되어야 하는 인자로 감도를 위해 재료가 허용하는 응력내에서 되도록 큰 변형률이 발생해야 하고 상호 간섭 오차가 발생하지 말아야 한다. 본 연구에서는 수식을 이용하여 이론적으로 상호 간섭 오차를 0으로 만들 수 있었다. 또한 설계 변수 및 재료 물성치의 산포를 고려한 신뢰성 기반 최적설계 기법을 사용하였으며, 이를 통해 허용 응력하에서 최대의 변형률이 발생하는 바퀴동력계를 설계하였다.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.846-851
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• 2004

A new method has been proposed for the calibration of frictional forces in atomic force microscopy. Angle conversion factor is defined using the relationship between torsional angle and frictional signal. Once the factor is obtained from a cantilever, it can be applied to other cantilevers without additional experiments. Moment balance equations on the flat surface and top edge of a commercial step grating are used to obtain angle conversion factor. Proposed method is verified through another step grating test and frictional behavior of Mica.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.14 no.2
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• pp.213-224
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• 2001

확률론적 구조설계 최적화는 구조물의 역학적 특성이나 하중의 불확실성이나 임의성과 같은 변동성을 정량적이고 합리적으로 고려할 수 있다는 점에서 기존의 전통적인 확정론적 최적화와 비교된다. 확률론적 최적화의 방법론으로는 개선된 일계이차모멘트법을 이용하는 신뢰도지수에 기반한 접근법(MPFP search)이 널리 알려져 있으며, 최근 목표성능치에 기반한 접근법(MPTP search)이 새롭게 제안되었다. 본 논문에서는 이들 두 가지 접근법에 대한 정식화를 수행하고, 특히 탐색과정에서 소모적인 반복계산을 발견하고 제거하는 알고리즘을 제시하였다. 예제에서 두 접근법에 의한 확률론적 최적화를 수행하고 구조설계 최적화의 관점에서 두 접근법의 장단점을 비교·검토하였다.