• Structural Engineering and Mechanics
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• 제26권3호
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• pp.315-341
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• 2007

A sudden change of stiffness in a structure, associated with the events such as weld fracture and brace breakage, will cause a discontinuity in acceleration response time histories recorded in the vicinity of damage location at damage time instant. A new damage index is proposed and implemented in this paper to detect the damage time instant, location, and severity of a structure due to a sudden change of structural stiffness. The proposed damage index is suitable for online structural health monitoring applications. It can also be used in conjunction with the empirical mode decomposition (EMD) for damage detection without using the intermittency check. Numerical simulation using a five-story shear building under different types of excitation is executed to assess the effectiveness and reliability of the proposed damage index and damage detection approach for the building at different damage levels. The sensitivity of the damage index to the intensity and frequency range of measurement noise is also examined. The results from this study demonstrate that the damage index and damage detection approach proposed can accurately identify the damage time instant and location in the building due to a sudden loss of stiffness if measurement noise is below a certain level. The relation between the damage severity and the proposed damage index is linear. The wavelet-transform (WT) and the EMD with intermittency check are also applied to the same building for the comparison of detection efficiency between the proposed approach, the WT and the EMD.

• 한국전산구조공학회논문집
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• 제37권4호
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• pp.283-293
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• 2024

본 논문에서는 지진 하중으로 인한 급격한 구조손상탐지를 수행하기 위해 분산점 칼만필터(Unscented Kalman Filter, UKF)와 파티클 필터(Particle Filter)를 소개하고 지진 손상 시나리오에 적용 및 비교·검토하였다. 이때, 비선형 전단 빌딩을 모사하기 위해 Bouc-Wen 모델을 사용하였고, 급격한 변화를 추정하기 위해 추가적으로 적응형 기법(Adaptive rule)인 Adaptive Jumping Method를 두 필터 모두에 적용하였다. 적용 결과 두 오리지날 필터 모두 급격한 손상 시점과 정도를 파악하지 못하였고, 적응형 기법을 반영하였을 경우에만 시점 파악이 가능하였다. 하지만, 여전히 손상 정도를 정확히 파악하지 못하였고, 두 방법 모두 제안된 적응형 기법을 새로이 조정하였을 경우에 정확한 추정이 가능함을 확인하였다. 최종적으로 계산시간을 고려하였을 때, 새로운 형태의 적응형 기법을 적용한 UKF 사용을 제안하는 것으로 비교 검토를 수행하였다.

• 대한한의학방제학회지
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• 제11권1호
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• pp.57-90
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• 2003

The result of Bibliographic studies on the pathological mechanism of the sudden coma, we got the conclusion like this. 1. The sudden coma is an acute syndrome that refers to be a sudden fainting, an unconsciousness, an aphasia or a cold clammy limb, and immediately awakes or dies, and awakes in a short time, and if we awake, it doesn't leave over and above a sequela. 2. The clinical presentation of the sudden coma can be summarized as follows : The 1st is a disease raising the sudden death due to unconsciousness accompanied by wry mouth & sudden syncope with coma. The 2nd is simply the state of cold limbs. The 3rd is the meaning of the physique and symptomes of the six meridians. The last is the ancient method of expression in contrast of the beriberi. 3. The pathological mechanism of the sudden coma consists of the toxoid from outside, Qi and Xie, fatigue, damp phegm, the damage from seven emotions and the damage from five mental elements, especially the mental disorder due to the angry energy, causes the problems when the fleming-up of liver fire and the depressed of liver qi raise the physiological disorder. 4. Therapeutic methods of sudden coma are soothing the liver and remove stasis, soothing depression and circulating of the qi, calming the liver and suppressing yang. When that is early stage, at first, we must checking upward adverse flow of the qi after promoting the circulation of qi and awakening, and then, we must regulate excessive deficiency of yin yang by therapy that is based on differentiated in symptoms according to heat & cold, deficiency & excess, and use invigorating herb medicine for supporting vigour.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2021년도 추계학술대회
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• pp.338-340
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• 2021

최근 발생하는 자연 재난 중 홍수피해는 여름철에 집중되면서 태풍 장마로 인해 인명 피해나 재산피해로 이어진다. 이러한 피해를 줄이기 위해 많은 연구가 진행되고 있다. 본 논문에서는 이러한 돌발홍수 발생 시 최단 거리 알고리즘을 사용하여 경로를 검출하고 사용자에게 제공하는 시스템을 설계하고 구현한다. 제안하는 시스템은 QGIS를 사용하여 트랙과 포인터를 생성한 지형 데이터를 활용하여 경로를 검출한다. 또한 시나리오를 통하여 검출된 경로로 대피하는 과정에서 돌발홍수가 발생 시 다른 최단 경로를 검출하여 사용자에게 제공한다. 따라서 사용자는 제안하는 시스템을 통하여 향후 발생하는 재난 안전 사고 위험에 안전한 대피를 할 수 있을 것으로 사료한다.

• Structural Engineering and Mechanics
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• 제32권4호
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• pp.489-500
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• 2009

The aim of this paper is to compare wavelet, kurtosis and pseudofractal based techniques for structural health monitoring in the presence of measurement noise. A detailed comparison and assessment of these techniques have been carried out in this paper through numerical experiments for the calibration of damage extent of a simply supported beam with an open crack serving as an illustrative example. The numerical experiments are deemed critical due to limited amount of experimental data available in the field of singularity based detection of damage. A continuous detectibility map has been proposed for comparing various techniques qualitatively. Efficiency surfaces have been constructed for wavelet, kurtosis and pseudofractal based calibration of damage extent as a function of damage location and measurement noise level. Levels of noise have been identified for each technique where a sudden drop of calibration efficiency is observed marking the onset of damage masking regime by measurement noise.

• Smart Structures and Systems
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• 제8권3호
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• pp.253-274
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• 2011

In this paper, the harmonic displacement response of a damaged square plate with all-over part-through damage parallel to one edge is utilized as the input signal function in wavelet analysis. The method requires the properties of the damaged plate, i.e., no information about the original undamaged structure is required. The location of damage is identified by sudden changes in the spatial variation of transformed response. The incurred damage causes a change in the stiffness or mass of the plate. This causes a localized singularity which can be identified by a wavelet analysis of the displacement response. In this study via numerical examples shown by using harmonic response is more versatile and effective compared with the static deflection response, specially in the presence of noise. In the light of the obtained results, suggestions for future work are presented and discussed.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2004년도 가을 학술발표회 논문집
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• pp.534-541
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• 2004

The modeling of crack initiation and propagation is very important for the failure analysis of concrete. The cracking process in concrete is quite different from that of other materials, such as metal and glass, in that it is not a sudden onset of new free surface but a continuous forming and connecting of microcracks. The failure process of concrete by cracking causes irreversible deformations and stiffness degradation. Those phenomenon can be modeled using plasticity and damage theory in macroscopic aspect. In this study, a plastic-damage model based on homogenized crack model considering velocity discontinuity and damage variable which is a function of plastic strain is proposed for fracture analysis of concrete. Finally, the plastic-damage model is verified with experimental data.

• Structural Monitoring and Maintenance
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• 제2권4호
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• pp.383-397
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• 2015

This article identifies and addresses current limitations on the use of numerical models for validation and/or calibration of damage detection methodologies that are based on the analysis of the high frequency response of the structure to identify the occurrence of abrupt anomalies. Distributed-plasticity non-linear fiber-based models in combination with experimental data from a full-scale reinforced concrete column test are used to point out current modeling techniques limitations. It was found that the numerical model was capable of reproducing the global and local response of the structure at a wide range of inelastic demands, including the occurrences of rebar ruptures. However, when abrupt sudden damage occurs, like rebar fracture, a high frequency pulse is detected in the accelerations recorded in the structure that the numerical model is incapable of reproducing. Since the occurrence of such pulse is fundamental on the detection of damage, it is proposed to add this effect to the simulated response before it is used for validation purposes.

• 한국유체기계학회 논문집
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• 제15권6호
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• pp.64-69
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• 2012

This paper deals with the study on repair case of journal shaft and bearing damage in 25MW industrial gas turbine caused by sudden blackout, operation mistake, and logic abnormal, etc. When a serious accident such as journal and bearing damage in a gas turbine occurs, the domestic local companies having the gas turbine are dependent on manufacturer for all maintenance and repair schedule until now. This case study shows that the damaged gas turbine is normally re-operated itself in domestic by establishing repair schedule in a short period of time, repairing damage journal shaft and tilting pad bearings, and performing rotating test for a reliability check. This paper can be regarded as the important case study of emergency test run experience of the refurbished 25MW gas turbine rotor.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.199-210
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• 2008

Acoustic emission(AE)/Microseimsic(MS) activities are low-energy seismic events associated with a sudden inelastic deformation such as the sudden movement of existing fractures, the generation of new fractures or the propagation of fractures. These events rapidly increase before major failure and happen within a given rock volume and radiate detectable seismic waves. The main difference between AE and MS signals is that the seismic motion frequencies of AE signals are higher than those of MS signals. As the failure of geotechnical structures usually happens as a high velocity and small displacement, it is not easy to determine the precursor and initiation stress level of failure in displacement detection method. To overcome this problem, AE/MS techniques for detection of structure failure and damage have recently adopt in civil engineering. In this study, AE/MS monitoring system, which consist of sensor, data acquisition and operation program, is constructed with domestic technology. To verify and optimize the developed system, we are now carrying out the field application at an underground research laboratory and the developed AE/MS monitoring will be used in detecting of seismic events with various scales.