• Wind and Structures
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• 제21권6호
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• pp.693-707
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• 2015

The efficiency of wind turbines (WT) is primarily reflected in their ability to generate electricity at any time. Downtimes of WTs due to "conventional" inspections are cost-intensive and undesirable for investors. For this reason, there is a need for structural health monitoring (SHM) systems, to enable service and maintenance on demand and to increase the inspection intervals. In general, monitoring increases the cost effectiveness of WTs. This publication concentrates on the application of two vibration-based SHM algorithms for stability and structural change monitoring of offshore WTs. Only data driven, output-only algorithms based on stochastic subspace identification (SSI) in time domain are considered. The centerpiece of this paper deals with the rough mathematical description of the dynamic behavior of offshore WTs and with the basic presentation of stochastic subspace-based algorithms and their application to these structures. Due to the early stage of the industrial application of SHM on offshore WT on the one side and the required confidentiality to the plant manufacturer and operator on the other side, up to now it is not possible to analyze different isolated structural damages resp. changes in a systematic manner, directly by means of in-situ measurement and to make these "acknowledgements" publicly available. For this reason, the sensitivity of the methods for monitoring purposes are demonstrated through their application on long time measurements from a 1:10 large scale test rig of an offshore WT under different conditions: undamaged, different levels of loosened bolt connections between tower parts, different levels of fouling, scouring and structure inclination. The limitation and further requirements for the approaches and their applicability on real foundations are discussed along the paper.

• Computers and Concrete
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• 제20권3호
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• pp.319-327
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• 2017

Studying the structural behavior of prestressed segmented girders is quite important due to the large use this type of solution in viaducts and bridges. Thus, this work presents a nonlinear three-dimensional structural analysis of an externally prestressed segmented concrete girder through the Finite Element Method (FEM), using a customized ANSYS platform, version 14.5. Aiming the minimization of the computational effort by using the lowest number of finite elements, a new viscoelastoplastic material model has been implemented for the structural concrete with the UPF customization tool of ANSYS, adding new subroutines, written in FORTRAN programming language, to the main program. This model takes into consideration the cracking of concrete in its formulation, being based on fib Model Code 2010, which uses Ottosen rupture surface as the rupture criterion. By implementing this new material model, it was possible to use the three-dimensional 20-node quadratic element SOLID186 to model the concrete. Upon validation of the model, an externally prestressed segmented box concrete girder that was originally lab tested by Aparicio et al. (2002) has been computationally simulated. In the discretization of the structure, in addition to element SOLID186 for the concrete, unidimensional element LINK180 has been used to model the prestressing tendons, as well as contact elements CONTA174 and TARGE170 to simulate the dry joints along the segmented girder. Stresses in the concrete and in the prestressing tendons are assessed, as well as joint openings and load versus deflection diagrams. A comparison between numerical and experimental data is also presented, showing a good agreement.

• 한국터널지하공간학회 논문집
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• 제16권1호
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• pp.13-24
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• 2014

본 논문에서는 TBM 터널의 세그먼트 라이닝 설계 자동화 기술 개발의 일환으로 인공신경망기법을 이용한 세그먼트 라이닝 부재력 산정기법 개발에 관한 내용을 다루었다. 부재력 평가가 가능한 인공신경망을 개발하기 위해 먼저 다양한 설계조건을 도출하고 이에 대해 2-Ring Beam 모델을 이용한 유한요소해석을 수행하여 인공신경망 학습에 필요한 설계조건별 부재력에 관한 DB를 구축하였다. 구축된 DB를 활용하여 인공신경망의 최적화 과정을 통해 최대 부재력 및 분포도를 예측할 수 있는 인공신경망을 구축하였다. 검토 결과 구축된 인공신경망은 유한요소해석과 동일한 정밀도의 부재력 산정 기능을 확보하는 것으로 검토되었으며 따라서 TBM 세그먼트 라이닝 설계시 필요한 부재력 평가를 위한 효율적인 수단으로 활용될 수 있는 것으로 판단된다.

• 여성건강간호학회지
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• 제3권1호
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• pp.82-92
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• 1997

The purpose of this study was attempted to understand the substance and meaning of menopause experienced by women through informal interviews with oral consent. The informants were 6 perimenopausal women of 50-55 years old who are executing menopause. Colaizz's analytical method, a type of phenomenological analysis, was used to analyze data recorded by audiotape. One professor and a master's degree student who understand phenomenology, and the one who has a master of arts examined the validity between the meanings composed of the clusters of themes. Findings were turned out to be valid through validation process as the last step. The meaning of menopause implied both 'concept about menopause' and 'menopause as a time of change'. Menopause was mostly considered as cessation of menstruation as a physiological, natural, and normal process by aging. However, some people regarded menopause as a loss of youth and womanhood and lessening of every function of the body. Menopause as the time of changes means 'the period of' 'hormonal changes' such as change of menstruation, hot flushes, perspiration, and palpitation ; 'body function changes' of visual acuity, physical strength, sleeping, digestion, thoughts, bone and joints, skin sensibility, sexual pattern and intelligence ; 'emotional changes' such as anxiety, loneliness, gloominess, and nervousness. Menopause is a turning point on the women's life cycle accompanying various kind of changes and health problems. Therefore it is inevitable to develop strategy helping menopausal women pass through the critical successfully by adapting and coping with their critical period toward the healthy and better quality of life individually rather than putting them all into the standardized hormonal replacement protocol.

• Steel and Composite Structures
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• 제35권6호
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• pp.789-798
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• 2020

The effect of Chitosan (CS), Carbon Nanotube (CNT) and hybrid (CS-CNT) fillers on the natural frequency of drilled composite plate is investigated by experimentally in this study. The numerical validation is also made with a program based on Finite Element Method (SolidWorks). Nine types filled and one neat composite plates are used in the study. The fillers ratios are 1% CS, 2% CS, 3% CS, 0.1% CNT, 0.2% CNT, 0.3% CNT, 1% CS+0.3% CNT, 2% CS+0.3% CNT, 3% CS+0.3% CNT. The specimens cut to certain sizes by water jet from the plates 400 mm × 400 mm in dimensions. Some of them are drilled in certain dimensions with drill. The natural frequency of each specimen is measured by the vibration test set up to determine the vibration characteristic. The vibration test set up includes an accelerometer, a current source power unit, a data acquisition card and a computer. A code is written in Matlab^® program for the signal processing. The study are investigated and discussed in four main points to understand the effect of the fillers on the natural frequency of the composite plate. These are the effect of fillers contents and amounts, orientation angles of fibers, holes numbers and holes sizes. As results, the natural frequency of the plate with 1% CS and 0.1% CNT hybrid filler is lower than those of the plates with other fillers ratios for 45° orientation angle. Besides, in the composite plate with 0° orientation angle, the natural frequency increases with increasing the filler ratio. Moreover, the natural frequency increases until a certain hole number and then it decreases. Furthermore, the natural frequency is not affected until a certain hole diameter but then it decreases.

• 한국농공학회논문집
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• 제53권6호
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• pp.111-119
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• 2011

The main objective of this study was to evaluate the effects of control-release fertilizer (CRF) on pollutant loadings from a small watershed. The Baran watershed, 386 ha in size, was selected as the study site, and the AGNPS (Agricultural Non-point Source Pollution) model was used to evaluate the effects of fertilizer types. Digital maps of digital elevation (DEM), slope distribution, channel, flow direction, landuse, soil, and curve number were extracted from the study watershed. Model parameters related to hydrology and water quality were calibrated and validated by comparing model predictions with the observed data collected for 2 years (1999 to 2000). Calibration and validation resulted in $R^2$ values of 0.75-0.91 for all the water quality parameters. All the paddy fields (21.2 %) of the study watershed were sprayed by either CRF or NPK (standard fertilizer). In CRF application, total nitrogen (TN) load was 4.9% less than NPK application, however total phosphorus (TP) load was 0.7 % more than NPK application. In CRF application, considering only paddy fields in the study area, TN load was 38.7 % less than NPK application. Using CRF in paddy fields could be one of the ways to reduce pollutant loadings from agricultural watersheds, however, in order to confirm it, more researches about effects of using CRF are necessary.

• 시스템엔지니어링학술지
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• 제12권1호
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• pp.59-71
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• 2016

The Nuclear and Fossil Steam Turbines record a considerable number of failures annually. Some of these failures reported are as result of blade failure. The failure of the L-0 blade in a Steam Turbine is one of the most reported blade failure in Nuclear and Fossil steam turbines. This paper seeks to identify the best Non Destructive Evaluation (NDE) method or methods to be used in the steam turbine L-0 blades inspection process. The development of systems engineering processes presents an opportunity to apply NDE inspection to the L-0 blades. This process apply computer modelling of the L-0 using ANSYS and by simulating the stresses experienced by the L-0 blade during operation it is possible to identify the most susceptible areas for crack formation and growth. The results from these models compared to industry data for validation. The analysis of these results used to predict the most probable failure location and failure modes. Therefore NDE inspection can be applied to these areas with greater degree of accuracy. This would be beneficial in the increasing the accuracy in the detection of cracks and hence save inspection time and the overall inspection cost. Furthermore, not only the location for crack formation and NDE inspection determined but also best the NDE inspection technique/techniques to be applied appropriately on the L-0 blade are prescribed.

• 유통과학연구
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• 제17권11호
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• pp.93-101
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• 2019

Purpose: Blockchain technology suggests ways to solve the problems in the existing industry. Among them, Cryptocurrency system, which is an element of Blockchain technology, is a very important factor for operating Blockchain. While Blockchain cryptocurrency has attracted attention, studies on cryptocurrency prices have been mainly conducted, however previous studies mainly conducted on Bitcoin prices. On the other hand, in the context of the creation and trading of various cryptocurrencies based on the Blockchain system, little research has been done on cryptocurrencies other than Bitcoin. Hence, this study attempts to find variables related to the prices of Dash, Litecoin, and Monero cryptocurrencies using machine learning techniques. We also attempt to find differences in the variables related to the prices for each cryptocurrencies and to examine machine learning techniques that can provide better performance. Research design, data, and methodology: This study performed Dash, Litecoin, and Monero price prediction analysis of cryptocurrency using Blockchain information and machine learning techniques. We employed number of transactions in Blockchain, amount of generated cryptocurrency, transaction fees, number of activity accounts in Blockchain, Block creation difficulty, block size, umber of created blocks as independent variables. This study tried to ensure the reliability of the analysis results through 10-fold cross validation. Blockchain information was hierarchically added for price prediction, and the analysis result was measured as RMSE and MAPE. Results: The analysis shows that the prices of Dash, Litecoin and Monero cryptocurrency are related to Blockchain information. Also, we found that different Blockchain information improves the analysis results for each cryptocurrency. In addition, this study found that the neural network machine learning technique provides better analysis results than support-vector machine in predicting cryptocurrency prices. Conclusion: This study concludes that the information of Blockchain should be considered for the prediction of the price of Dash, Litecoin, and Monero cryptocurrency. It also suggests that Blockchain information related to the price of cryptocurrency differs depending on the type of cryptocurrency. We suggest that future research on various types of cryptocurrencies is needed. The findings of this study can provide a theoretical basis for future cryptocurrency research in distribution management.

• 한국콘텐츠학회논문지
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• 제16권9호
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• pp.160-169
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• 2016

자기자비 척도(Self-Compassion Scale: SCS)는 Neff(2003a)에 의해 개발되었고, 국내에서는 김경의, 이금단, 조용래, 채숙희, 이우경(2008)에 의해 번안 및 타당화 되었다. 하지만, 원척도와 한국판 자기자비 척도가 대학생만을 대상으로 타당화 한 제한점이 있고, 자기자비 척도의 요인 구조가 일관되지 않는다는 국외 연구 결과도 보고되고 있다. 따라서 본 연구에서는 18세에서 79세의 성인 435명을 대상으로 설문한 자료를 바탕으로 자기자비 척도의 요인 타당성을 검증하였다. 이를 위해 탐색적 요인분석과 확인적 요인분석을 실시하였고, 확인적 요인분석에서는 2요인, 3요인, 6요인 구조 세 가지 모형으로 구성하여 모델의 적합도를 비교 검증하였다. 분석결과, 탐색적 요인분석에서 6개의 요인이 나타났으며, 확인적 요인분석에서도 6요인 구조가 가장 적합한 것으로 나타났다.

• 기술혁신학회지
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• 제18권1호
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• pp.176-203
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• 2015

클라우드 컴퓨팅은 지속적 성장세를 보이고 있고, 개인 클라우드 컴퓨팅 서비스의 중요성이 확대되고 있다. 이러한 중요성에 견주어, 본 연구의 목적은 어떤 이유로 기존 컴퓨팅 환경에서 클라우드 컴퓨팅 환경으로 전환을 하는 것인지, 또 어떤 요인들이 전환을 저해하는지에 대한 판단의 근거를 탐색하고자 한다. 본 연구에서는 사회교환이론을 연구의 이론적 프레임워크로 하여, 지각된 가치와 전환의도와의 관계를 실증적으로 분석하였다. 이를 위해 선행연구를 기초로 클라우드 컴퓨팅 서비스의 특성요인을 도출하였고, 이러한 요인들이 지각된 가치를 매개로 전환의도에 영향을 주는지를 파악하는 연구모형을 설정하였다. 총 7개의 연구가설을 제안하였으며, 총 204개의 데이터를 SmartPLS를 통해 가설을 검증하였다. 검증결과, 제안한 7개의 가설 중, 5개의 가설이 지지되었다. 동기요인 중에서는 효율성과 경제성이 지각된 가치를 매개로 전환의도에 영향을 미치는 것으로 나타났고, 저해요인 중에서는 전환 비용과 보안우려가 전환의도의 선행요인임을 규명하였다. 본 연구는 실무적 차원 혹은 조직관점에서 논의되어 온 클라우드 컴퓨팅 서비스를 개인 수준에서 접근하였다는데 의의가 있다. 또한 클라우드 컴퓨팅 서비스로의 전환의도를 동기요인과 저해요인의 이요인 관점에서 논의하였다는데 또 다른 의의를 갖고 있다.