• KEPCO Journal on Electric Power and Energy
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• v.3 no.2
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• pp.107-111
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• 2017

The reliability on high cycle fatigue damage mechanism for new blades manufactured by reverse-engineering is demonstrated by success-run test. Turbine blades always experience various dynamic loads in turbine operation, as well as being in resonance condition and forced by fluid-induced vibrations mostly during run-up/down, which may accumulate high cycle damage to the blades. The accidents caused by blade failure especially incur not only a lot of troubles to the machinery but also huge financial losses. Therefore it is necessary to verify the reliability of blades in advance for the safe use. The success run test for the reliability demonstration is designed and performed for the new blades using the technique known as resonant high cycle fatigue testing.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.22 no.2
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• pp.126-132
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• 2010

An approach to calculating expected damage of breakwater assisted by artificial neural network was developed. Wave height in front of a breakwater was predicted by a trained artificial neural network with inputs of wave height in deep ocean and tidal level. Prediction results by the neural network can be comparable to that by professional numerical model for wave transformation. Using the wave prediction neural network, it was very easy and fast to obtain a number of significant waves at breakwater and finally analysis time for expected damage can be shortened. In addition, the effect of considering tidal level in the calculation of expected damage was revealed by comparing the expected damages with and without tidal variation. Therefore, it was pointed out that tidal variation should be considered to improve prediction accuracy.

• Journal of the Korean Institute of Landscape Architecture
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• v.41 no.4
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• pp.68-76
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• 2013

Effortful directed attention becomes fatigued if it is demanded by environment. Kaplan and Kaplan's Attention Restoration Theory (ART) proposes that the fatigued directed attention can be restored by a restorative landscape. The four restorative components are being away, fascination, extent, and compatibility. The restorative effect of landscape has been mainly investigated in terms of nature vs. urban dichotomy, although ART acknowledges that various types of landscapes can induce restorative effect. The purpose of this study is to examine whether sense of place of landscape has an influence on the restorative effect, and how the effect relates to the visiting experience. This study was performed in An-Ap-Ji with 200 Korean visitors who participated in the questionnaire survey. Hartig et al.'s PRS (Perceived Restorativeness Scale) was used as the research instrument to measure the restorative quality. The Analysis results are summarized as: 1) PRS was a very reliable measurement for Koreans' assessment of traditional landscape. Especially, the factor analysis produced four restorative components which fully supported ART. 2) The sense of place of landscape was found to have a positive influence on the restorative effect. 3) Landscape beauty was also discovered to be influential in the restoration even though the effect of beauty was lower than that of the sense of place. 4) Among the four restorative components, three components (fascination, escape, compatibility) influenced both visiting satisfaction and revisit intention, where the order of the relevant importance was fascination, escape, and compatibility. Based on the results, it was suggested that PRS should be used in landscape restoration research in Korea in order to re-examine its' reliability. It was also proposed that more research should be directed to investigate the relationship between the sense of place and the restorative effect of landscape.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.1908-1918
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• 1991

Fatigue tests have been carried out to measure the degradation of the residual strength and the fatigue life in carbon/epoxy (0/45/90/-45)$_{2s}$ composite materials. Theoretical predictions of residual strength and fatigue life were compared with experimental results. Distribution characteristics were studied using the probability of failure based on the cumulative distribution function and median rand. The static ultimate strength of carbon/epoxy composites used herein is observed to be relatively higher than that of existing similar composites ; while fatigue life is shorter due to the brittleness of matrix. The fatigue life obtained in these experiments is shorter than that estimated by residual strength degradation model when the stress level above 0.6 For the stress level of 0.6, the experimental value was abruptly increased. The cumulative distribution function for the static ultimate strength is well correlated to that for the strength converted from the measured fatigue life. Also, the predicted distribution of residual strength shows good agreement with the experimental results. Therefore, it is proven that the residual strength degradation model is reasonable.e.

• Journal of the Korean Society for Railway
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• v.8 no.4
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• pp.348-353
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• 2005

In designing the structures of railway rolling stocks, deterministic methods associated with the concept of a safety factor have been traditionally used. The deterministic approaches based on the mean values of applied loads and material properties have been used as safety verification for the design of rolling-stock car body structures. The uncertainties in the applied loading for the high speed train and the strength of new materials in the rolling stocks require the application of probabilistic approaches to ensure fatigue safety in the desired system. Pressure loadings acting on the car body when the train passes through tunnels show reflected pressure waves for high-speed trains and they may cause a fatigue failure in vehicle bodies. Use of new material technology as body structures also introduces uncertainties in the material strength. A probabilistic approach is more adaptable in designing reliable structures when the pressure waves from the tunnels pounds and new material technology is adopted. In this paper, it is proposed that a fatigue design and assessment method based on a reliability which deals with the loading variations on a railway vehicle due to the pressure reflected in tunnels and the strength variations of material. Equation for the fatigue reliability index has been formulated to calculate the reliability assessment of a vehicle body under fluctuating pressure loadings in a tunnel. Considered in this formulation are the pressure distribution characteristics, the fatigue strength distribution characteristics, and the concept of stress-transfer functions due to the pressure loading.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.98.2-98.2
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• 2011

지구 온난화의 원인이 되는 이산화탄소를 저감하며 유해한 배기가스를 배출하지 않는 수소연료전지자동차(FCV)에 대한 관심이 높아지고 있다. 한국가스안전공사에서 현재 구축하고 있는 평가장비는 이러한 수소연료전지자동차용으로 사용되는 고압용기의 수압반복시험 및 밸브류로 구성된 고압수소저장시스템의 단품 및 시스템 평가를 통한 안전신뢰성 검증을 목적으로 하고 있다. 현재 수소연료전지자동차는 차량이나 부품의 시험 방법에 대한 통일된 기준/표준/시험법이 아직 완전하게 정비되어 있지 않고, 시장에서의 도입 제도, 기준 등이 만들어지고 있는 현실이다. 또한 연료로 수소를 사용하는 도입단계에 있기 때문에, 수소용기가 반복압력변동에 따라 어떤 거동을 나타내는지에 대한 실험관련 연구가 미진한 상태이다. 따라서 수소연료전지자동차용 고압수소저장시스템에 대한 내구성, 안전성 확보를 위하여 수소연료전지자동차에서 중요한 부품인 용기에 대한 반복피로시험이 필요하다. 특히 복합재 용기 분야에서 Type3용기에 대한 높은 안전성과 내구성이 보고되고 있지만 실질적으로 얼마나 다른 용기에 비해 높은 성능을 가지고 있는지 국내에서는 체계적으로 검증된바 없다. 따라서 구축된 수압반복 장비를 이용하여 Type3 용기에 대한 수압반복시험을 실시하였으며, 이를 통해 수소용기의 거동을 확인하고자 한다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.10
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• pp.1275-1282
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• 2012

Helicopter rotor systems are dynamically loaded structures with many composite components such as the main and the tail rotor blades. The fatigue properties of composite materials are extremely important to design durable and reliable helicopter rotor blades. The safe-life methodology has generally been used in the helicopter industry to substantiate dynamically loaded composite components. However, it cannot be used to evaluate the strength reducing effects of flaws and defects that may occur during manufacturing and operational usage. The damage tolerance methodology provides a proper means to overcome this shortcoming; however, it is difficult to economically apply it to every composite component. The flaw tolerant methodology is an equivalent option to the damage tolerance methodology for civil and military rotorcraft. In this study, the flaw tolerant safe-life evaluation is described and illustrated by means of successful application to substantiate the retirement time of composite rotor blades.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.8
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• pp.721-728
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• 2017

High-grade gray cast iron (HCI350) was prepared by adding Cr, Mo and Cu to the gray cast iron (GC300). Their microstructure, mechanical properties and fatigue strength were studied. Cast iron was made from round bar and plate-type castings, and was cut and polished to measure the percentage of each microstructure. The size of flake graphite decreased due to additives, while the structure of high density pearlite increased in volume percentage improving the tensile strength and fatigue strength. Based on the fatigue life data obtained from the fatigue test results, the probability - stress - life (P-S-N) curve was calculated using the 2-parameter Weibull distribution to which the maximum likelihood method was applied. The P-S-N curve showed that the fatigue strength of HCI350 was significantly improved and the dispersion of life data was lower than that of GC300. However, the fatigue life according to fatigue stress alleviation increased further. Data for reliability life design was presented by quantitatively showing the allowable stress value for the required life cycle number using the calculated P-S-N curve.

• Journal of the Microelectronics and Packaging Society
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• v.16 no.3
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• pp.25-29
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• 2009

High temperature high humidity and thermal shock reliability tests were performed for the board level COB(chip-on-board) flip chip packages using self-formulated and commercial NCPs(non-conductive pastes) to ensure the performance of NCP flip chip packages. It was considered that the more smaller fused silica filler in prototype NCPs is more favorable for high temperature high humidity reliability. The failure of NCP interconnection was affected by the expansion of epoxy due to moisture absorption rather than the fatigue due to thermal stress. It was considered that the NCP having more higher adhesive strength seems to be more favorable to increase the thermal shock reliability.

• 한국IT서비스학회:학술대회논문집
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• 2006.05a
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• pp.380-387
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• 2006

정보화가 급격히 확산되면서 정보화로 인한 파급효과와 더불어 정보화의 위험과 역기능 방지와 정보시스템의 품질을 제고하기 위한 최적의 방법중 하나로서 정보시스템 감리에 대한 중요성과 그 수요가 증가하고 있다. 더불어 감리내실화와 신뢰성제고를 위한 기술연구와 제도연구도 지속적으로 수행되어왔다. 많은 감리의뢰기관이 감리자체를 시업성공을 위한 품질보증 및 생산성 향상을 도모하기 위해 실시하는 중간평가로 보지 않고 있고, 감리인의 학력.경력.자격수준 및 신기술에 대한 이해도, 숙련도 부족과 감리대상업무파악 미흡으로 현장감각이 부족하여 실제보다 형식에 치우쳐 있다. 따라서, 정보시스템 감리의 서비스품질이 상대적으로 취약하여 감리의뢰기관이나 피감리 기관으로부터 신뢰를 얻지 못하고 있다. 본 연구에서는 마케팅분야의 서비스품질평가모형을 일부 도입하여 감리서비스 품질요인과 감리품질 또는 감리충실도간의 관계를 규명하고, 나아가서 감리충실도에 영향을 끼치는 요소는 외적서비스요인과 내적서비스요인으로 구분하였으며, 이요인들이 감리충실도에 미치는 영향을 규명코자 하였다, 더불어 감리충실도가 감리효과 및 만족도와 프로젝트성과에 미치는 영향을 규명코자 하였다.