• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 추계학술대회논문집
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• pp.608-613
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• 2003

In this paper, the variability of modal properties caused by temperature effects is assessed to adjust modal data used for frequency-based damage detection in plate-girder bridges. First, experiments on model plate-girder bridges are described. Next, the relationship between temperature and natural frequencies is assessed and a set of empirical frequency-correction formula are analyzed for the test structure. Finally, a frequency-eased method is used to locate and estimate severity of damage in the test structure using experimental modal data which are adjusted by the frequency-correction formula. Here, local damage in beam-type structures is detected by using measured frequencies and analytical mode shapes.

• 한국해양공학회지
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• 제30권4호
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• pp.287-293
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• 2016

This paper presents an effective damage detection method for offshore jackets using natural frequency change ratios. Two parameters, cosine similarity and magnitude index, are considered to estimate the location and severity of the damage in the structure. A numerical jacket structure model is considered to verify the performance of the proposed method. As observed through analysis, the damages in the structure are detected accurately.

• Smart Structures and Systems
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• 제23권1호
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• pp.15-29
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• 2019

This paper addresses the problem of damage detection in suspension bridge hangers, with an emphasis on the modal flexibility method. It aims at evaluating the capability and the accuracy of the modal flexibility method to detect and locate single and multiple damages in suspension bridge hangers, with different level of severity and various locations. The study is conducted numerically and experimentally on a laboratory suspension bridge mock-up. First, the covariance-driven stochastic subspace identification is used to extract the modal parameters of the bridge from experimental data, using only output measurements data from ambient vibration. Then, the method is demonstrated for several damage scenarios and compared against other classical methods, such as: Coordinate Modal Assurance Criterion (COMAC), Enhanced Coordinate Modal Assurance Criterion (ECOMAC), Mode Shape Curvature (MSC) and Modal Strain Energy (MSE). The paper demonstrates the relative merits and shortcomings of these methods which play a significant role in the damage detection ofsuspension bridges.

• Structural Engineering and Mechanics
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• 제30권4호
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• pp.445-466
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• 2008

This paper presents a novel structural damage detection method with a new damage index based on the statistical moments of dynamic responses of a structure under a random excitation. After a brief introduction to statistical moment theory, the principle of the new method is put forward in terms of a single-degree-of-freedom (SDOF) system. The sensitivity of statistical moment to structural damage is discussed for various types of structural responses and different orders of statistical moment. The formulae for statistical moment-based damage detection are derived. The effect of measurement noise on damage detection is ascertained. The new damage index and the proposed statistical moment-based damage detection method are then extended to multi-degree-of-freedom (MDOF) systems with resort to the leastsquares method. As numerical studies, the proposed method is applied to both single and multi-story shear buildings. Numerical results show that the fourth-order statistical moment of story drifts is a more sensitive indicator to structural stiffness reduction than the natural frequencies, the second order moment of story drift, and the fourth-order moments of velocity and acceleration responses of the shear building. The fourth-order statistical moment of story drifts can be used to accurately identify both location and severity of structural stiffness reduction of the shear building. Furthermore, a significant advantage of the proposed damage detection method lies in that it is insensitive to measurement noise.

• 대한원격탐사학회지
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• 제35권6_4호
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• pp.1341-1350
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• 2019

본 연구는 산불 전후 KOMPSAT-3A 영상을 사용하여 산불피해지역을 분석하는 것을 목적으로 한다. KOMPSAT 시리즈 중 KOMPSAT-3A는 적외선 및 고해상도의 멀티 스펙트럼 밴드를 가진 VHR위성이다. 하지만, KOMPSAT-3A를 활용하여 산불피해강도를 분류하는 연구는 부족한 실정이다. 따라서 본 연구에서는 KOMPSAT-3A의 산불 피해강도를 분류하기 위한 새로운 알고리즘을 제시하는 것을 목표로 한다. 또한, 본 연구에서는 산불 피해지역에 대한 참조자료로 Sentinel-2로 생성한 dNBR을 사용하였다. 본 연구의 연구 지역은 2019년 4월 4일 강릉에서 발생한 산불 피해지역으로 선정하였다. 본 연구에서는 산불피해구간을 산정하기 위한 알고리즘으로 오픈 소스 통계 프로그램인 R software의 확률분포함수를 사용하였다. KOMPSAT-3A에서 산불 피해지역은 산불 전, 후 NDVI의 변화에 따라 생성되었다. 산불피해강도는 분포 함수의 표준 편차를 사용하여 각 등급 크기를 산정하였다. 총 5개 구간에 따른 산불 피해 강도가 효과적으로 분류되었다.

• Structural Monitoring and Maintenance
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• 제5권2호
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• pp.243-260
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• 2018

Detection of damages in fibre reinforced plastic (FRP) composite structures is important from the safety and serviceability point of view. Usually, damage is realized as a local reduction of stiffness and if dynamic responses of the structure are sensitive enough to such changes in stiffness, then a well posed inverse problem can provide an efficient solution to the damage detection problem. Usually, such inverse problems are solved within the framework of pattern recognition. Support Vector Machine (SVM) Algorithm is one such methodology, which minimizes the weighted differences between the experimentally observed dynamic responses and those computed using the finite element model- by optimizing appropriately chosen parameters, such as stiffness. A damage detection strategy is hereby proposed using SVM which perform stepwise by first locating and then determining the severity of the damage. The SVM algorithm uses simulations of only a limited number of damage scenarios and trains the algorithm in such a way so as to detect damages at unknown locations by recognizing the pattern of changes in dynamic responses. A rectangular fiber reinforced plastic composite plate has been investigated both numerically and experimentally to observe the efficiency of the SVM algorithm for damage detection. Experimentally determined modal responses, such as natural frequencies and mode shapes are used as observable parameters. The results are encouraging since a high percentage of damage cases have been successfully determined using the proposed algorithm.

• Structural Engineering and Mechanics
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• 제24권6호
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• pp.665-682
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• 2006

A vibration-based nondestructive damage evaluation technique for a curved thin beam is introduced. The proposed method is capable of detecting, locating, and sizing structural damage simultaneously by using a few of the lower natural frequencies and their corresponding mode shapes before and after a small damage event. The proposed approach utilizes modal flexibilities reconstructed from measured modal parameters. A rigorous system of equations governing damage and curvature of modal flexibility is derived in the context of elasticity. To solve the resulting system of governing equations, an efficient pseudo-inverse technique is introduced. The direct inspection of the resulting solutions provides the location and severity of damage in a curved thin beam. This study confirms that there is a strong linear relationship between the curvature of modal flexibility and flexural damage in the selected class of structures. Several numerical case studies are provided to justify the performance of the proposed approach. The proposed method introduces a way to avoid the singularity and mode selection problems from earlier attempts.

• Structural Engineering and Mechanics
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• 제29권3호
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• pp.311-325
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• 2008

Noting that damage occurrence of offshore jacket platforms is concentrated in two structural regions that are in the vicinity of still water surface and close to the seabed, a damage detection method by using only partial measurement of vibration in a suspect region was presented in this paper, which can not only locate damaged members but also evaluate damage severities. Then employing an experiment platform model under white-noise ground excitation by shaking table and using modal parameters of the first three modes identified by a scalar-type ARMA method on undamaged and damaged structures, the feasibility of the damage detection method was discussed. Modal parameters from eigenvalue analysis on the structural FEM model were also used to help the discussions. It is demonstrated that the damage detection algorithm is feasible on damage location and severity evaluation for broken slanted braces and it is robust against the errors of baseline FEM model to real structure when the principal errors is formed by difference of modal frequencies. It is also found that Z-value changes of modal shapes also play a role in the precise detection of damage.

• 인지과학
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• 제32권4호
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• pp.169-191
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• 2021

인공지능이 발달함에 따라 많은 인간 전문가들의 일자리가 위협당하고 있으며 이는 법조계 또한 해당한다. 본 연구는 실제로 인공지능이 법조계에 종사하는 사람들, 특히 최종 판결을 내리는 판사의 역할까지 대체할 수 있을지에 대해 다루어보고자 하였다. 본 연구는 고유성 무시의 관점에서, 이를 판결 대상자와 얼마나 가까운 사이인지(관여도)와 사건이 얼마나 심각한지(심각성)가 인공지능 판사(실험 1)가 내리는 판결을 수용하는 정도와 전체 배심원 중 인공지능 배심원(실험 2)을 배치하는 정도에 미치는 효과를 확인하는 것으로 시행하였다. 실험 1에서는 관여도와 심각성의 상호작용 효과가 나타났다. 구체적으로, 관여도가 낮을 때는 심각성이 높은 사건(vs. 낮은 사건)에서 더 인공지능 판사 수용도가 높았지만, 관여도가 높을 때는 심각성이 낮은 사건(vs. 높은 사건)에서 더 인공지능 판사 수용도가 높았다. 실험 2에서도 실험 1과 동일한 상호작용이 발생하였다. 구체적으로, 관여도가 낮을 때는 심각성이 높은 사건(vs. 낮은 사건)에서 인공지능 배심원 수를 더 많이 배정하였지만, 관여도가 높을 때는 심각성이 낮은 사건(vs. 높은 사건)에서 인공지능 배심원 수가 더 많아졌다. 본 연구는 인공지능의 법적 판단에 대한 국내 최초의 실험연구라는 점과 법률 전문가들의 일자리에 대한 전망을 제시한다는 점에서 시사점을 가진다.

• 한국화재소방학회논문지
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• 제12권1호
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• pp.15-21
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• 1998

본 연구에서는 국내의 30년간 발생한 백화점 화재 사고사례를 토대로 그 심각성 예측을 위해 확률적 인 접근을 하였다. 백화점 화재의 년간 발생 건수와 그 피해액 정도를 고려하여 위험 수준을 산정해 보 았다 또한 본 연구에서는 백화점 화재발생 시나리오를 작성해 미국 NIST에서 개발한 FPETOOL 프로그 램을 이용하여 백화점에서의 화재에 대한 심각성을 예측하였다 . FPETOOL 프로그햄 실행 결과로 화재 발생시 인체가 위험해지는 용도, 연기충, 가스 농도의 수준에 도탈하는 시간올 알 수 있었다. 백화점에서 화재가 발생했을 경우 그에 따른 재산피해, 인명피해가 매우 크며, 잠재하는 위험성이 매 우 크므로 미연에 방지해야 한다.