• Applied Microscopy
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• 제38권1호
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• pp.63-72
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• 2008

Allen et al. (2004)에 의해 개발된 IWFR 방법에 대해서 응용성에 관심을 가지고 고찰되었다. 이 고찰에는 문헌에 보고된 GaAs, $YBa_2CuO_7$ 및 $Al_2CuMg$의 재료에 대한 HRTEM 연구물들이 이용되었다. 이 고찰 과정에서 이 방법의 타당성에 대한 이론적 근거, 제한조건 및 정보한계들을 명확히 제시되었다. IWFR 방법을 통해 얻은 결정 밑 표면에 전자 파동함수의 상(phase)-영상은 구면수차에 의한 영상 왜곡이 교정된 정보한계 범위 내에서 원자분해상을 나타낼 뿐만 아니라 결정의 구성원자의 원자번호에 대체적으로 비례하는 강도 분포를 나타내는 강한 경향이 있음이 특히 주목되었다.

• 한국초전도ㆍ저온공학회논문지
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• 제22권1호
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• pp.7-11
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• 2020

As demand for electricity in urban areas increases, it is necessary to improve electric power stability by interconnecting neighboring substations and high temperature superconductor (HTS) power cables are considered as a promising option due to its large power capacity. However, the interconnection of substations reduces grid impedance and expected fault current is over 45 kA, which exceeds the capacity of a circuit breaker in Korean grid. To reduce the fault current below 45 kA, a HTS power cable having a fault current limiting (FCL) function is considered by as a feasible solution for the interconnection of substations. In this study, a FCL HTS power cable of 600 MVA/154 kV, transmission level class, is considered to reduce the fault current from 63 kA to less than 45 kA by generating an impedance over 1 Ωwhen the fault current is induced. For the thermal design of FCL HTS power cable, a parametric study is conducted to meet a required temperature limit and impedance by modifying the cable core from usual HTS power cables which are designed to bypass the fault current through cable former. The analysis results give a minimum cable length and an area of stainless steel former to suppress the temperature of cable below a design limit.

• 한국해안·해양공학회논문집
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• 제23권6호
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• pp.407-413
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• 2011

응답면 기법을 사용하여 잔교식 안벽의 신뢰성 해석을 수행하였다. 잔교식 안벽은 중력식 안벽과 달리 상부가 강관파일에 의해 지지되는 유연구조물로 한계상태함수가 음함수로 존재한다. 따라서, 한계상태함수를 양함수로 근사하기 위해 응답면 기법을 사용하였다. 응답면 기법을 이용한 LevelII신뢰성해석 방법을 통해 지진하중에 의한 잔교식 안벽의 신뢰도지수를 계산하고, 중요도 추출법을 통해 검증하였다. 수치해석으로는 직항식, 사항식을 각각 해석하였다.

• 한국구조물진단유지관리공학회 논문집
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• 제8권3호
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• pp.225-233
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• 2004

본 연구에서는 응답면기법을 이용하여 격납건물의 내진안전성 평가를 하였다. ABAQUS를 이용하여 하중, 저항과 해석에서의 랜덤변수를 고려한 구조해석을 수행하였고 이로부터 변수의 다항식으로 표현되는 구조물의 응답을 얻었다. 그리고 Level II에 의해 신뢰성해석을 하였다. 한계상태함수로는 콘크리트의 2축응력 상태를 고려하기 위해 Drucker-Prager 파괴기준을 이용하였다. 구조물의 수명, 지진의 연발생율과 조건부 파괴확률을 고려하여 격납건물의 파괴확률을 계산하였다. 또한 응답면기법의 안정적인 결과를 얻기 위해 표본점 선정에 대한 민감도해석을 수행하였다.

• 한국컴퓨터정보학회논문지
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• 제18권5호
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• pp.19-23
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• 2013

본 논문에서는 컬러 영상에 삼각형 타입의 소속 함수를 적용하여 스트레칭의 상한과 하한을 동적으로 설정하여 컬러영상을 퍼지 스트레칭 하는 방법을 제안한다. 제안된 퍼지 스트레칭 방법은 평균 밝기 값을 기준으로 가장 어두운 픽셀 값과 가장 밝은 픽셀 값의 거리를 계산하여 밝기의 조정률을 결정한 후, 최소 밝기 값과 최대 밝기 값을 구하고 삼각형 타입 소속 함수의 구간에 적용한다. 영상의 픽셀 값들을 소속 함수에 적용하여 소속도를 구하고 가장 낮은 픽셀 값을 스트레칭 하한으로 설정하고 가장 높은 픽셀 값을 스트레칭 상한으로 설정하여 컬러 영상을 스트레칭 한다. 다양한 영상에 적용한 결과, 앤드인 탐색 방법보다 제안된 퍼지 스트레칭 방법이 효율적인 것을 확인하였다.

• Geomechanics and Engineering
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• 제18권6호
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• pp.595-603
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• 2019

A modified model combining Kriging and Monte Carlo method (MC) is proposed for probabilistic estimation of tunnel face stability in this paper. In the model, a novel uniform design is adopted to train the Kriging, instead of the existing active learning function. It has advantage of avoiding addition of new training points iteratively, and greatly saves the computational time in model training. The kinematic approach of limit analysis is employed to define the deterministic computational model of face failure, in which the Hoek-Brown failure criterion is introduced to account for the nonlinear behaviors of rock mass. The trained Kriging is used as a surrogate model to perform MC with dramatic reduction of calls to actual limit state function. The parameters in Hoek-Brown failure criterion are considered as random variables in the analysis. The failure probability is estimated by direct MC to test the accuracy and efficiency of the proposed probabilistic model. The influences of uncertainty level, correlation relationship and distribution type of random variables are further discussed using the proposed approach. In summary, the probabilistic model is an accurate and economical alternative to perform probabilistic stability analysis of tunnel face excavated in spatially random Hoek- Brown media.

• Geomechanics and Engineering
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• 제16권6호
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• pp.655-667
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• 2018

To evaluate the stability of a rock slope with one pre-exiting vertical crack, this paper performs corresponding probabilistic stability analysis. The existence of cracks is generally ignored in traditional deterministic stability analysis. However, they are widely found in either cohesive soil or rock slopes. The influence of one pre-exiting vertical crack on a rock slope is considered in this study. The safety factor, which is usually adopted to quantity the stability of slopes, is derived through the deterministic computation based on the strength reduction technique. The generalized Hoek-Brown (HB) failure criterion is adopted to characterize the failure of rock masses. Considering high nonlinearity of the limit state function as using nonlinear HB criterion, the multivariate adaptive regression splines (MARS) is used to accurately approximate the implicit limit state function of a rock slope. Then the MARS is integrated with Monte Carlo simulation to implement reliability analysis, and the influences of distribution types, level of uncertainty, and constants on the probability density functions and failure probability are discussed. It is found that distribution types of random variables have little influence on reliability results. The reliability results are affected by a combination of the uncertainty level and the constants. Finally, a reliability-based design figure is provided to evaluate the safety factor of a slope required for a target failure probability.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권1호
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• pp.211-224
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• 2019

This paper deals with a nonlinear controller based on saturation functions with variable parameters for set-point regulation and trajectory tracking control of an Autonomous Underwater Vehicle (AUV). In many cases, saturation functions with constant parameters are used to limit the input signals generated by a classical PD (Proportional-Derivative) controller to avoid damaging the actuators; however this abrupt bounded harms the performance of the controller. We, therefore, propose to replace the conventional saturation function, with constant parameters, by a saturation function with variable parameters to limit the signals of a PD controller, which is the base of the nonlinear PD with gravitational/buoyancy compensation and the nonlinear PD + controllers that we propose in this paper. Consequently, the mathematical model is obtained, considering the featuring operation of the underwater vehicle LIRMIA 2, to do the stability analysis of the closed-loop system with the proposed nonlinear controllers using the Lyapunov arguments. The experimental results show the performance of an AUV (LIRMIA 2) for the depth control problems in the case of set-point regulation and trajectory tracking control.

• 자동차안전학회지
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• 제14권3호
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• pp.23-29
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• 2022

Among the various functions of ADAS (Advanced Driver Assistance System), the most important and representative function to the safety of vehicle passengers is AEB (Autonomous Emergency Braking system). In South Korea, laws are in progress from 2022 for making it mandatory for passenger vehicles to be installed. And as AEB-equipped vehicles continues to increase in the future, the demand for accident analysis related to the AEB function is expected to increase in the future. In order to find out the operating limits of AEB, it is necessary to consider the situations exceeding the standards covered by EuroNCAP. Therefore we have performed four experiments in this study, including situations encountered in real-word traffic conditions, i.e., an oblique stop of Global Vehicle Target (GVT) and ADAS sensor failures. These experimental results are expected to be of great help in accurate and reliable accident analysis by considering them when analyzing traffic accidents for ADAS vehicles.

• Geomechanics and Engineering
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• 제11권2호
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• pp.235-252
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• 2016

This paper presents a new numerical solution of the ultimate lateral capacity of rectangular piles in clay. The two-dimensional plane strain finite element was employed to determine the limit load of this problem. A rectangular pile is subjected to purely lateral loading along either its major or minor axes. Complete parametric studies were performed for two dimensionless variables including: (1) the aspect ratios of rectangular piles were studied in the full range from plates to square piles loaded along either their major or minor axes; and (2) the adhesion factors between the soil-pile interface were studied in the complete range from smooth surfaces to rough surfaces. It was found that the dimensionless load factor of rectangular piles showed a highly non-linear function with the aspect ratio of piles and a slightly non-linear function with the adhesion factor at the soil-pile interface. In addition, the dimensionless load factor of rectangular piles loaded along the major axis was significantly higher than that loaded along the minor axis until it converged to the same value at square piles. The solutions of finite element analyses were verified with the finite element limit analysis for selected cases. The empirical equation of the dimensionless load factor of rectangular piles was also proposed based on the data of finite element analysis. Because of the plane strain condition of the top view section, results can be only applied to the full-flow failure mechanism around the pile for the prediction of limiting pressure at the deeper length of a very long pile with full tension interface that does not allow any separation at soil-pile interfaces.