• 한국안전학회지
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• 제35권3호
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• pp.49-57
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• 2020

In comparison with the existing static reliability analysis methods, the dynamic reliability analysis(DyRA) method is more suitable for estimating the failure probability of a structure subjected to earthquake excitations because it can take into account the frequency characteristics and damping capacity of the structure. However, the DyRA is known to have an issue of numerical stability due to the uncertainty in random sampling of the earthquake excitations. In order to solve this numerical stability issue in the DyRA approach, this study proposed two earthquake-scale factors. The first factor is defined as the ratio of the first earthquake excitation over the maximum value of the remaining excitations, and the second factor is defined as the condition number of the matrix consisting of the earthquake excitations. Then, we have performed parametric studies of two factors on numerical stability of the DyRA method. In illustrative example, it was clearly confirmed that the two factors can be used to verify the numerical stability of the proposed DyRA method. However, there exists a difference between the two factors. The first factor showed some overlapping region between the stable results and the unstable results so that it requires some additional reliability analysis to guarantee the stability of the DyRA method. On the contrary, the second factor clearly distinguished the stable and unstable results of the DyRA method without any overlapping region. Therefore, the second factor can be said to be better than the first factor as the criterion to determine whether or not the proposed DyRA method guarantees its numerical stability. In addition, the accuracy of the numerical analysis results of the proposed DyRA has been verified in comparison with those of the existing first-order reliability method(FORM), Monte Carlo simulation(MCS) method and subset simulation method(SSM). The comparative results confirmed that the proposed DyRA method can provide accurate and reliable estimation of the structural failure probability while maintaining the superior numerical efficiency over the existing methods.

• Smart Structures and Systems
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• 제25권6호
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• pp.719-732
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• 2020

Real-time hybrid simulation (RTHS) which combines physical experiment with numerical simulation is an advanced method to investigate dynamic responses of structures subjected to earthquake excitation. The desired displacement computed from the numerical substructure is applied to the experimental substructure by a servo-hydraulic actuator in real time. However, the magnitude decay and phase delay resulted from the dynamics of the servo-hydraulic system affect the accuracy and stability of a RTHS. In this study, a robust stability analysis procedure for a general single-degree-of-freedom structure is proposed which considers the uncertainty of servo-hydraulic system dynamics. For discussion purposes, the experimental substructure is a portion of the entire structure in terms of a ratio of stiffness, mass, and damping, respectively. The dynamics of the servo-hydraulic system is represented by a multiplicative uncertainty model which is based on a nominal system and a weight function. The nominal system can be obtained by conducting system identification prior to the RTHS. A first-order weight function formulation is proposed which needs to cover the worst possible uncertainty envelope over the frequency range of interest. Then, the Nyquist plot of the perturbed system is adopted to determine the robust stability margin of the RTHS. In addition, three common delay compensation methods are applied to the RTHS loop to investigate the effect of delay compensation on the robust stability. Numerical simulation and experimental validation results indicate that the proposed procedure is able to obtain a robust stability margin in terms of mass, damping, and stiffness ratio which provides a simple and conservative approach to assess the stability of a RTHS before it is conducted.

• 대한기계학회논문집A
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• 제38권11호
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• pp.1283-1290
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• 2014

최근에는 법공학 분야에 구조해석 및 구조-유동 연성해석을 이용한 다양한 시뮬레이션 기법을 활용하여 안전사고 및 재난사고에 대한 법적 책임문제를 해명하고 보다 정확한 원인분석을 통해 원인을 규명하고 있는 추세이다. 본 연구에서는 법공학적 관점에서 DCM(Deep Cement Mixing) 선박의 침몰 사고의 원인을 밝혀내고자 하였다. 사고 선박은 선박 건조 당시 SCP(Sand Compaction Pile) 전용 선박으로 건조되었으며, DCM 선박으로 구조 변경을 위해 안정성 검토 없이 리더부 높이 변경 및 증설을 하였다. 이러한 구조물의 증설 및 변경이 본 침몰 사고에 미치는 영향을 알아내고자 상용 구조 해석프로그램인 ADINA를 이용하여 구조안정성 평가를 수행하였으며, 본 연구를 통하여 구조물의 증설 및 변경에 따른 ADINA 해석 결과를 비교, 분석함으로써 DCM 선박 침몰 사고의 정확한 원인을 밝혀낼 수 있었다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1988년도 한국자동제어학술회의논문집(국제학술편); 한국전력공사연수원, 서울; 21-22 Oct. 1988
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• pp.973-980
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• 1988

This two-part paper presents a control method that allows for stable interaction of a robot manipulator with the environment. In part 1, we focus on the input ouput relationships (unstructured modeling) of the robot and environment dynamics. This analysis leads to a general condition for stability of the robot and environment taken as a whole. This stability condition, for stable maneuver, prescribes a finite sensitivity for robot and environment where sensitivity of the robot(or the environment) is defined as a mapping forces into displacement. According to this stability condition, smaller sensitivity either in robot or in environment leads to narrower stability range. In the limit, when both systems have zero sensitivity, stability cannot be guaranteed. These models do not have any particular structure, yet they can model a wide variety of industrial and research robot manipulators and environment dynamic behavior. Although this approach of modeling may not lead to any design procedure, it will allow us to understand the fundamental issues in stability when a robot interacts with an environment.

• Journal of Electrical Engineering and information Science
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• 제2권4호
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• pp.28-36
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• 1997

In this paper, robust stability analysis for the fuzzy feedback linearization regulator is presented. Well-known Takagi-Sugeno fuzzy model is used as the MISO nonlinear plant model. Uncertainty and disturbance are assumed to be included in the model structure with known bounds. For these structured uncertainty and disturbances, robust stability of the close system is analyzed in both input-output sense and Lyapunov sense. The robust stability conditions are proposed by using multivariable circle criterion and the relationship between input-output stability and Lyapunov stability. The proposed stability analysis is illustrated by a simple example.

• 대한전기학회논문지
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• 제38권11호
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• pp.941-949
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• 1989

This two-part paper presents a control method that allows for stable interaction of a robot manipulator with environment. In part 1, we focus on the input output relationships (unstructured modeling) of the robot and environment dynamics. This analysis leads to a general condition for stability of the robot and environment taken as a whole. This stability condition, for stable maneuver, prescribes a finite sensitivity for robot and environment where sensitivity of the robot (or the environment) is defined as a mapping forces into displacement. According to this stability condition, smaller sensitivity either in robot or in environment leads to narrower stability range. In the limit, when both systems have zero sensitivity, stability cannot be guaranteed. These models do not have any particular structure, yet they can model a wide variety of industrial and research robot manipulators and environment dynamic behavior. Although this approach of modeling may not lead to and design procedure, it will allow us to understand the fundamental issues in stability when a robot interacts with an environment.

• 대한토목학회논문집
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• 제39권6호
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• pp.769-777
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• 2019

이안제와 잠제(인공리프)와 같은 저 마루높이 구조물은 수중구조물은 연안역의 침식 등의 대책으로 일반적으로 사용되고 있다. 이러한 구조물의 피복재 안정성은 비월파조건의 구조물 보다 낮을 수 있다. 기존 연구에서는 대부분 사석으로 피복된 구조물을 대상으로 안정성을 검토하였다. 본 연구에서는 테트라포드로 피복된 저 마루높이 구조물과 수중구조물을 대상으로 안정성을 검토하기 위해 2차원 수리실험을 수행하였다. 피복재 안정성은 구조물 상부, 전사면 및 후사면을 대상으로 파형경사와 여유고를 변화시키며 검토하였다. 피복재의 주된 피해는 전사면 상부와 바다측 마루부에서 발생하였다. 실험결과를 이용하여 테트라포드의 안정계수를 산정할 수 있는 경험식을 제안하였다.

• The Journal of Advanced Prosthodontics
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• 제3권1호
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• pp.10-15
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• 2011

PURPOSE. This study investigated the influence of bone quality and surgical technique on the implant stability quotient (ISQ) value. In addition, the influence of interfacial bone quality, directly surrounding the implant fixture, on the resonance frequency of the structure was also evaluated by the finite element analysis. MATERIALS AND METHODS. Two different types of bone (type 1 and type 2) were extracted and trimmed from pig rib bone. In each type of bone, the same implants were installed in three different ways: (1) Compaction, (2) Self-tapping, and (3) Tapping. The ISQ value was measured and analyzed to evaluate the influence of bone quality and surgical technique on the implant primary stability. For finite element analysis, a three dimensional implant fixture-bone structure was designed and the fundamental resonance frequency of the structure was measured with three different density of interfacial bone surrounding the implant fixture. RESULTS. In each group, the ISQ values were higher in type 1 bone than those in type 2 bone. Among three different insertion methods, the Tapping group showed the lowest ISQ value in both type 1 and type 2 bones. In both bone types, the Compaction groups showed slightly higher mean ISQ values than the Self-tapping groups, but the differences were not statistically significant. Increased interfacial bone density raised the resonance frequency value in the finite element analysis. CONCLUSION. Both bone quality and surgical technique have influence on the implant primary stability, and resonance frequency has a positive relation with the density of implant fixture-surrounding bone.

• 지질공학
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• 제12권3호
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• pp.345-360
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• 2002

이 연구는 활동 가능성이 높은 퇴적암 사면에 대한 안정성을 분석하기 위해 수치해석을 수행하고, 안정성을 확보할 수 있는 보강공법을 제시하기 위한 목적으로 수행되었다. 연구지역은 백악기 하양층군의 학봉 현무암층에 해당하는 지역으로 대부분이 현무암질 응회암으로 구성되어 있으며, 지질 구조요소로는 크게 1차 구조 요소인 층리와 2차 구조요소인 절리 및 단층이 확인되었다 층리는 단사구조를 보이는데, 대부분의 경우 경사방향이 120~160/15~25(dip direction/dip)이고, 절리의 경우에는 크게 3개 조의 절리군이 확인되는데 세트 1은 310~330/65~85, 세트 2는 230~250/70~85이며, 세트 3은 뚜렷한 연장성을 보이지는 않지만 020의 경사방향에 85$^{\circ}$이상의 고각을 보이고 있다. 사면에 대한 안정성 해석은 운동학적 해석과 한계평형 해석을 수행한 후, 수치해석 방법으로 FLAC을 이용하였다. FLAC은 유한차분법을 이용하는 연속체 역학모델이지만, Interfaces Module을 이용하여 UDEC과 같은 불연속체 모델의 해석효과를 얻을 수 있었다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 춘계 학술발표회
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• pp.579-584
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• 2009

Arrangement of the facilities for improving harbor functions depends on sea and land conditions such as the ship's arrival and departure conditions, waves and tide. And the plan and the size of the facilities depend much on harbor and marine environment condition such as cargo quantity, ship size, ship traffic and seawater circulation. Among these, waves have so much effect on a breakwater design that it is the most important to understand their characteristics and to apply them to breakwater design. Therefore, to analyze the effect of waves characteristics over a rubble mound breakwater, we have calculated wave pressure by using numerical analysis at each tide level and have analyzed the effect of wave pressure on structure stability by conducting the stability analysis with the wave pressure. As a result, it is found that during low and mean tide level time the biggest wave pressure is estimated near calm water level. But during high tide time, the biggest wave pressure is estimated in front of capping. And the stability analysis indicates also that a structure is most unstable when low tide time wave pressure is acting on. After reviewing the stability of a structure by applying vertical and horizon wave forces, it is concluded that safety factor is lower than ordinary time(max. about 15%), is also reviewed when designing a rubble mound breakwater.