• Earthquakes and Structures
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• 제8권4호
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• pp.821-841
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• 2015

This paper proposes a two-stage imaging approach for quantitative inspection of damages in metallic plates using the fundamental anti-symmetric mode of ($A_0$) Lamb wave. The proposed approach employs a number of transducers to transmit and receive $A_0$ Lamb wave pulses, and hence, to sequentially scan the plate structures before and after the presence of damage. The approach is applied to image the corrosion damages, which are simplified as a reduction of plate thickness in this study. In stage-one of the proposed approach a damage location image is reconstructed by analyzing the cross-correlation of the wavelet coefficient calculated from the excitation pulse and scattered wave signals for each transducer pairs to determine the damage location. In stage-two the Lamb wave diffraction tomography is then used to reconstruct a thickness reduction image for evaluating the size and depth of the damage. Finite element simulations are carried out to provide a comprehensive verification of the proposed imaging approach. A number of numerical case studies considering a circular transducer network with eight transducers are used to identify the damages with different locations, sizes and thicknesses. The results show that the proposed methodology is able to accurately identify the damage locations with inaccuracy of the order of few millimeters of a circular inspection area of $100mm^2$ and provide a reasonable estimation of the size and depth of the damages.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2004년도 춘계학술대회 논문집
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• pp.1142-1147
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• 2004

In this study, two damage detection techniques are applied to the railway tunnel liner based on the static deformation data. Models based on uniform reduction of stiffness and smeared crack concept are both employed, and the efficiency and relative advantage are compared with each other. Numerical analyses are performed on the idealized tunnel structure and the effect of white noise, common in most measurement data, is also investigated to better understand the suitability of the proposed models. As a result, model 1 based on uniform stiffness reduction method is shown to be relatively insensitive to the noise, while model 2 with the smeared crack concept is proven to be easily applied to the field situation since the effect of stiffness reduction is rather small. Finally, real deformation data of a rail tunnel in which health monitoring system is in operation are introduced to find the possible damage and it is shown that the prediction shows quite satisfactory result.

• 한국지반공학회논문집
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• 제28권7호
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• pp.55-65
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• 2012

지오그리드의 장기허용강도를 산출할 때 사용되는 총 감소계수는 내시공성 감소계수($RF_{ID}$), 내화학성 감소계수($RF_D$), 크리프 감소계수($RF_{CR}$) 등이 적용된다. 지오그리드의 단기인장강도에 대한 감소계수를 고려한 허용인장강도 산출 모델의 경우 감소계수들 사이의 상호 작용력을 고려하지 않는 한계를 가지고 있다. 접점강도는 인장강도와 마찬가지로 시공 시 손상이나 화학적 분해에 의하여 감소하게 된다. 기존의 단일접점강도 시험 방법은 치수효과를 고려할 수 없기에 결과의 편차가 큰 시공 시 손상된 시험편의 접점강도를 측정하는데 적합하지 않다. 또한 시공 시 손상에 의한 전단강도 변화에 대한 연구도 전혀 이루어지지 않은 실정이다. 따라서 본 연구에서는 다양한 조건을 고려하여 지오그리드의 장기성능에 영향을 미치는 감소계수들을 재평가하고 감소계수 사이의 상호 작용을 고려하여 정확한 장기허용강도를 구하려고 한다. 내시공성 시험과 내화학성 시험 후 크리프 시험결과 총 감소계수는 GRI GG-4 시험값보다 작게 나타났다. 내시공성 시험과 내화학성 시험 후 접점강도의 감소계수는 인장강도 감소계수보다 더 작게 나타났다. 내시공성 시험후 전단강도 차이가 나타나지 않거나 증가함을 나타내었다.

• Structural Monitoring and Maintenance
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• 제7권2호
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• pp.125-147
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• 2020

Damage detection of structures is one of the most important topics in structural health monitoring. In practice, the response is not available at all structural degrees of freedom, and due to the installation of sensors at some degrees of freedom, responses exist only in limited number of degrees of freedom. This paper is investigated the damage detection of structures by applying two approaches, AllDOF and Dynamic Condensation Method (DCM), based on the Modified Modal Strain Energy Method (MMSEBI). In the AllDOF method, mode shapes in all degrees of freedom is available, but in the DCM the mode shapes only in some degrees of freedom are available. Therefore by methods like the DCM, mode shapes are obtained in slave degrees of freedom. So, in the first step, the responses at slave degrees of freedom extracted using the responses at master degrees of freedom. Then, using the reconstructed mode shape and obtaining the modified modal strain energy, the damages are detected. Two standard examples are used in different damage cases to evaluate the accuracy of the mentioned method. The results showed the capability of the DCM is acceptable for low mode shapes to detect the damage in structures. By increasing the number of modes, the AllDOF method identifies the locations of the damage more accurately.

• Wind and Structures
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• 제16권3호
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• pp.263-278
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• 2013

The fatigue load of a turbine blade has become more important because the size of commercial wind turbines has increased dramatically in the past 30 years. The reduction of the fatigue load can result in an increase in operational efficiency. This paper numerically investigates the load reduction of large wind turbine blades using active aerodynamic load control devices, namely trailing edge flaps. The PD and LQG controllers are used to determine the trailing edge flap angle; the difference between the root bending moment and its mean value during turbulent wind conditions is used as the error signal of the controllers. By numerically analyzing the effect of the trailing edge flaps on the wind turbines, a reduction of 30-50% in the standard deviation of the root bending moment was achieved. This result implies a reduction in the fatigue damage on the wind turbines, which allows the turbine blade lengths to be increased without exceeding the designed fatigue damage limit.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2016년도 추계 학술논문 발표대회
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• pp.150-151
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• 2016

In previous study, researchers studied development of early anti-freezing cement at low temperature (-5℃) using hydration characteristics of reduction slag. In this study, the durability of concrete using reduction slag was conducted. The experiment result, reduction slag makes high temperature and improves compressive strength due to quick setting. And then result of durability show that it is no problem. However, it is considered that further study is needed about high shrinkages which was indicated in dry shrinkage.

• 한국의류학회지
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• 제25권7호
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• pp.1332-1340
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• 2001

This study was designed (1) to examine the results of previous qualitative research on clothing-wearing motives by quantitative approach, (2) to explore the concept of clothing utility, utility-reduction and discard, and (3) to investigate the impact of clothing-wearing motives on consumer attitudes and consuming-behaviors. Date were collected by questionnaire from 443 collegiate students between August and September of 2000, and 396 questionnaires were analyzed. 3 groups were identified on the basis of clothing-wearing motives and named by extroversion group, introversion group, and least clothing-congnizing group respectively. This supported the qualitative results in part, especially in the direction of motives. Clothing utility-reduction factors were identified as appearance demage, social-psychological damage, and abandonment-causing damage. The 3 groups were responded on utility-reduction differently, thus clothing-wearing motive variable was determined as useful in fashion marketing.

• Structural Engineering and Mechanics
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• 제24권1호
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• pp.91-105
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• 2006

In this paper, post-earthquake capacity evaluation method of reinforced concrete buildings was studied. Substructure pseudo-dynamic test and static loading test of first story column in a four-story R/C building was carried out in order to investigate the validity of the evaluation method proposed in the Damage Assessment Guideline (JBDPA 2001). In pseudo-dynamic test, different levels of damage were induced in the specimens by pre-loading, and input levels of seismic motion, at which the specimens reached to the ultimate stage, were examined. From the experimental result, no significant difference in damage levels such as residual crack width between the specimens under static and pseudo-dynamic loading was found. It is shown that the seismic capacity reduction factors ${\eta}$ can provide a reasonable estimation of post-earthquake seismic capacity of R/C buildings suffered earthquakes.

• 원예과학기술지
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• 제28권6호
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• pp.990-995
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• 2010

본 시험은 이상저온($-3.5^{\circ}C$ 이하에서 7시간 지속)에 의해 수체 상에서 동결된 사과 '후지' 과실들의 수확시기에 따른 품질차이를 비교하고자 실시하였다. 수확 시기는 동결피해 1일 전, 동결피해 2일 후, 동결피해 6일 후였다. 시험에 조사된 과실들의 수확시 가용성 고형물 함량은 $14^{\circ}Bx$ 이상이었다. 동결피해 후 수확한 과실의 수확 시 경도 및 산 함량은 동결피해 전에 수확한 과실보다 낮았다. 저온저장 중의 에틸렌 발생량은 동결피해 후 수확한 과실이 동결피해 전에 수확한 과실보다 높았다. 동결피해 후 수확한 과실의 저온 저장 동안의 품질저하는 동결피해 전에 수확한 과실보다 심하였다. 동결피해 후에 수확한 과실의 저온저장 출고 후 실온 1주일째의 품질 저하는 동결피해 전에 수확한 과실보다 더 심하였다. 동결피해 후에 수확한 시험구들간의 비교에서는 저온저장 8주까지 동결피해 6일 후에 수확한 시험구의 에틸렌 발생량 및 과실품질 저하가 동결피해 2일 후에 수확한 시험구보다 낮았으나, 이러한 차이는 저온저장 8주 이후로는 없었다. 과육 갈변증상 발생률은 $-3.5^{\circ}C$ 이하에서 7시간 동결될 경우 영향을 받지 않은 것으로 나타났다.

• Journal of Ginseng Research
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• 제33권4호
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• pp.305-310
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• 2009

Phenanthrene, one of the polycyclic aromatic hydrocarbons, has been known to be toxic to the environment. In this investigation, the protective effect of red ginseng on phenanthrene-induced oxidative DNA damage was evaluated using Comet assay in A549 cells. Red ginseng's cytoprotective effect on phenanthrene-induced hemolysis was also investigated. This study's findings show that oxidative DNA damage and hemolysis were significantly prevented by red ginseng treatment. Notably, it was found that pulverizing red ginseng into ultra-fine particles even enhanced its protective effects against DNA damage and hemolysis. The results suggest that particle size reduction seems to effectively enhance red ginseng's pharmacological efficacies.