• 한국지반신소재학회논문집
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• 제5권4호
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• pp.43-47
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• 2006

다짐조건을 달리하여 3가지 종류 지오그리드의 내시공성을 측정하였다. 이 실험은 ENV ISO 10722-1에 근거하여 실행되었다. 채움재와 관계없이 다짐횟수가 증가할수록 지오그리드의 인장강도는 감소하였으며, 지오그리드 종류에 따라 감소되는 경향이 다르게 나타남을 알 수 있었다. Woven 및 warp-knitted type 지오그리드의 경우 접합형 지오그리드에 비해 더 큰 감소경향을 나타내었다.

• Smart Structures and Systems
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• 제22권3호
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• pp.291-302
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• 2018

This paper presents a flexibility based method for damage identification from static measurements in beam-type structures. The response of the beam at the Damaged State is decomposed into the response at the Reference State plus the response at an Incremental State, which represents the effect of damage. The damage is localized by detecting slope discontinuities in the deflection of the structure at the Incremental State. A denoising filtering technique is applied to reduce the effect of experimental noise. The extent of the damage is estimated through comparing the experimental flexural stiffness of the damaged cross-sections with the corresponding values provided by analytical models of cracked beams. The paper illustrates the method by showing a numerical example with two cracks and an experimental case study of a simply supported steel beam with one artificially introduced notch type crack at three damage levels. A Digital Image Correlation system was used to accurately measure the deflections of the beam at a dense measurement grid under a set of point loads. The results indicate that the method can successfully detect and quantify a small damage from the experimental data.

• 한국해양공학회지
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• 제8권1호
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• pp.144-153
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• 1994

본 연구에서는, 소수의 모드형상의 진동반응만이 측정된 자켓형 해양구조물에 존재하는 손상의 위치와 그 크기를 결정할 수 있는 알고리듬이 제시된다. 먼저, 모드형상의 변화로 부터 직접 손상위치와 크기를 결정하는 이론이 제시된다. 다음으로, 세개의 진동모드형상이 측정된 자켓형 해양구조물의 수치예를 이용하여 알고리듬의 적합성이 예증된다. 본 연구의 결과는 다음과 같다. 첫째로, 자켓형 해양구조물에 존재하는 손상의 위치가 정확하게 예측 되었다. 둘째로, 예측된 손상의 크기가 비교적 정확하게 예측되었다.

• 한국해양공학회지
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• 제26권1호
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• pp.34-40
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• 2012

This paper presents an experimental modal analysis of a caisson-type breakwater to produce basic information for the structural health assessment of a caisson structure. To achieve the objective, the following approaches are implemented. First, modal analysis methods are selected to examine the modal characteristics of a caisson structure. Second, experimental modal analyses are performed using finite element analyses and lab-scale model tests. Third, damage scenarios that include several damage levels in a foundation-structure interface are designed. Finally, the effects of damage on the modal characteristics are analyzed for the purpose of utilizing them for damage identification.

• 보건의료산업학회지
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• 제14권1호
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• pp.67-78
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• 2020

Objectives: Using data from the 1styear of the 7th National Health and Nutrition Survey, this study administered a questionnaire to patients with oral damage and examined the type of medical care used based on the nature of the injury, further characterized by age group and sex. Methods: Of the 8,150 respondents, this study selected those who participated in the health survey and oral exam survey, excluding surveys with missing values, and set 7,681 people as the research participants. This study used SPSS Windows version 23.0(SPSS Inc. IL, USA) as the statistics program and applied the chi-square test (p) based on a complex sample and logistic regression analysis. Results: In the analysis of the type of tooth damage, there was a significant difference (p<.001) in the number of male patients who were injured due to exercise, violence, and safety accidents compared to females. However, there was no significant difference in their type of medical security and whether or not they visited a dental clinic. The patients with private insurance showed relatively high use for tooth extraction and oral surgery (p<.001). Conclusions: The best way to prevent tooth damage is to prevent the accident. For sports or exercises which may cause tooth damage, protective gear, such as a mouthpiece, should be used to prevent tooth damage.

• 비파괴검사학회지
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• 제27권6호
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• pp.541-549
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• 2007

This work describes an investigation into the feasibility of using an acoustic emission (AE) technique to evaluate the integrity of a composite actuator with a PZT ceramic under electromechanical cyclic loading. AE characteristics have been analyzed in terms of the behavior of the AE count rate and signal waveform in association with the performance degradation of the composite actuator during the cyclic tests. The results showed that the fatigue cracking of the composite actuator with a PZT ceramic occurred only in the PZT ceramic layer, and that the performance degradation caused by the fatigue damage varied immensely depending on the existence of a protecting composite bottom layer. We confirmed the correlations between the fatigue damage mechanisms and AE signal types for the actuators that exhibited multiple modes of fatigue damage; transgranular micro damage, intergranular fatigue cracking, and breakdown by a short circuiting were related to a burst type signal showing a shortly rising and slowly decaying waveform with a comparably low voltage, a continuous type signal showing a gradual rising and slowly decaying waveform with a very high voltage and a burst and continuous type signal with a high voltage, respectively. Results from the present work showed that the evolution of fatigue damage in the composite actuator with a PZT ceramic can be nondestructively identified via in situ AE monitoring and microscopic observations.

• 한국농공학회지
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• 제45권4호
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• pp.98-106
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• 2003

In order to set up structural improvement strategy against meteorological disasters of the shading structures in ginseng fields, structural safety analyses as well as some case studies of structural damage patterns were carried out. According to the results of structural safety analysis, allowable safe snow depth for type B(wood frame with single span) was 25.9 cm, and those for type A(wood frame with multi span) and type C and D (steel frame with multi span) were 17.6 cm, 25.8 cm, and 20.0 cm respectively. So types of shading structures should be selected according to the regional design snow depth. An experiential example study on meteorological disasters indicated that a strong wind damage was experienced once every 20 years, and a heavy snow damage once every 9.5 years. The most serious disasters were caused by heavy snow and it was found that a half break and complete collapse of structures were experienced by about 70% of snow damage. In addition to maintenance, repair and reinforcement, it is also recommended that improved model of shading structures for ginseng cultivation should be developed as a long term countermeasures against meteorological disasters.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1999년도 가을 학술발표회 논문집
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• pp.283-290
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• 1999

A practical damage identification scheme for PS concrete bridges via modal testing and system identification (SID) procedures is presented. The potential damage types are classified and the possible approaches which can be implemented into each damage type are designed. Damage identification algorithms are developed on the basis of the SID and modal analysis. The feasibility of the algorithms is verified from experimental tests to detect damage in PS concrete beam structures.

• 한국환경복원기술학회지
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• 제19권1호
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• pp.185-193
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• 2016

Purpose of this study is to classify damaged lands according to the cause of the damage and their influences based on characteristic of the damaged lands in DeMilitarized Zone(DMZ) area, and utilize this study as a fundamental study for establishment of ecosystem restoration system. Literature review and field survey have been conducted to review the damage status of DMZ area. For field survey, first year and second year have been conducted, in which type of the damage has been reviewed in this study. In the result, types of damage have been classified into 6 categories: 'alteration of initial landform', 'loss of surface layer', 'land pollution', 'alteration of soil chemical property', 'decline of vegetation', and 'invasion of foreign species'. Restoration for each damage type is as following. First, for alteration of initial landform, the land is restored to the original landform prior to the damage and connection to surrounding ecosystem is considered. Second, for loss of surface layer, lost surface layer is restored or further loss is prevented with stabilization. Third, for land pollution, source of the pollution is eradicated or self-circulation with purification of polluted land is encouraged. Fourth, for alteration of soil chemical property, soil is restored of its original property with eradication of the pollution source and improvement of soil. Fifth, for decline of vegetation, current vegetation and anticipated alteration in future are considered and number of wild species is to be increased based on structure and characteristic of nearby vegetation. Sixth, for invasion of foreign species, prevention of dominance by risky species and facilitation ecological stability with ecological management are to be considered. Influence according to the cause of damage has occurred in secondary(indirect) influence or simultaneous occurrence of several damage types. Considering all these aspects, when type of the damage is complex, restoration process for each of former mentioned 6 damage types with solitary influence should be considered in unison.

• 한국산학기술학회논문지
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• 제18권8호
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• pp.64-71
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• 2017

본 연구에서는 재킷식 해상풍력터빈 지지구조물의 효과적인 건전성 모니터링을 위하여, 손상에 의한 구조물의 모드 특성 변화 및 군집신경망기법을 이용한 손상추정기법을 제안한다. 실용적 적용을 위하여 제한된 계측자료를 활용하고, 구조적으로 중요하며 손상이 발생될 확률이 큰 것으로 판단되는 중요부재를 대상으로 손상을 추정한다. 즉, 재킷식 지지구조물은 부재 개수가 많기 때문에, 모든 부재를 적절히 식별하기 위해서는 이에 상당하는 많은 수의 계측 데이터 채널 및 센서를 설치해야 한다. 이는 건전성 모니터링의 경제적 및 실용적인 측면에서 적절치 않다고 판단되며, 본 연구에서는 중요 구조부재에 대하여 제한된 계측자료를 활용하여 집중적으로 손상추정을 수행하기 위한 연구를 수행한다. 5 MW 해상풍력터빈에 적용될 수 있는 재킷식 해상풍력터빈 지지구조물을 모델링한 후, 수치 시뮬레이션을 수행하여 신경망의 훈련패턴을 생성한다. 이후, 군집신경망기법을 이용하여 중요부재에 대한 손상위치 및 손상정도를 20가지 손상경우에 대하여 추정한 결과, 모든 손상 경우에 대하여 성공적으로 손상을 판정할 수 있었으며, 군집신경망기법을 적용함으로써 추청결과의 정확성이 향상됨을 알 수 있었다. 또한 실험연구를 통하여 기법을 검증하였는데, 3가지 손상경우에 대하여 손상을 추정한 결과 합리적으로 손상을 추정할 수 있었다.