• 전산구조공학
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• 제10권4호
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• pp.315-325
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• 1997

본 논문에서는 이산성 연속형 최적성규준방법을 이용하여 다지간 부분프리스트레스트 콘크리트보의 최적설계 알고리즘을 유도하였고, 최적설계프로그램을 개발하였다. 목적함수로서 건설 경비는 콘크리트 경비, 긴장재 경비, 철근 경비, 그리고 거푸집 경비를 포함하였으며 이를 최소화하였다. 설계제약조건으로는 시방서상의 최대처짐제약, 휨 및 전단강도제약, 연성제약 그리고 설계변수에 대한 상.하한계제약을 고려하였다. Kuhn-Tucker 필요조건을 이용하여 최적성규준을 설계변수의 항으로 명시적으로 유도하였으며, 이때 설계변수로는 보의 유효깊이, 긴장재의 편심거리 그리고 철근비를 취하였다. 긴장재의 형상은 포물선함수로 고려하였으며, 구조물 자중의 영향은 긴장력에 의한 이차효과와 마찬가지로 실제시스템의 평형방정식에서 고려하였다. 설계변수들의 개선을 위한 반복과정과 컴퓨터프로그램을 개발하였으며, 수치예를 들어 개발된 기법의 응용성 그리고 효율성을 보였다.

• Structural Engineering and Mechanics
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• 제74권2호
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• pp.157-173
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• 2020

In the finite element modelling of long-span cable-stayed bridges, there are a lot of uncertainties brought about by the complex structural configuration, material behaviour, boundary conditions, structural connections, etc. In order to reduce the discrepancies between the theoretical finite element model and the actual static and dynamic behaviour, updating is indispensable after establishment of the finite element model to provide a reliable baseline version for further analysis. Traditional sensitivity-based updating methods cannot support updating based on static and dynamic measurement data at the same time. The finite element model is required in every optimization iteration which limits the efficiency greatly. A convenient but accurate Kriging surrogate model for updating of the finite element model of cable-stayed bridge is proposed. First, a simple cable-stayed bridge is used to verify the method and the updating results of Kriging model are compared with those using the response surface model. Results show that Kriging model has higher accuracy than the response surface model. Then the method is utilized to update the model of a long-span cable-stayed bridge in Hong Kong. The natural frequencies are extracted using various methods from the ambient data collected by the Wind and Structural Health Monitoring System installed on the bridge. The maximum deflection records at two specific locations in the load test form the updating objective function. Finally, the fatigue lives of the structure at two cross sections are calculated with the finite element models before and after updating considering the mean stress effect. Results are compared with those calculated from the strain gauge data for verification.

• 설비공학논문집
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• 제29권8호
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• pp.408-418
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• 2017

Supercritical carbon dioxide ($sCO_2$) power system is emerging technology because of its high cycle efficiency and compactness. Meanwhile, PCHE (Printed Circuit Heat Exchanger) is gaining attention in $sCO_2$ power system technology because PCHE with high pressure-resistance and larger heat transfer surface per unit volume is fundamentally needed. Thermo-fluidic characteristics of $sCO_2$ in the micro channel of PCHE should be investigated. In this study, heat transfer characteristics of $sCO_2$ of various inlet conditions and cross-sectional shapes of single micro channel were investigated experimentally. Experiment was conducted at supercritical state of higher than critical temperature and pressure. Test sections were made of copper and hydraulic diameter was 1 mm. Convective heat transfer coefficients were measured according to each interval of the channel and pressure drop was also measured. Convective heat transfer coefficients from experimental data were compared with existing correlation. In this study, using measured data, a new empirical correlation to predict near critical region heat transfer coefficient is developed and suggested. Test results of single channel will be used for design of PCHE.

• Physical Therapy Rehabilitation Science
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• 제9권2호
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• pp.74-81
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• 2020

Objective: To prevent low back pain, an objective evaluation tool to evaluate pelvic mobility and exercise to improve the flexibility of the lumbar region is needed. The purpose of this study was to compare the results of pelvic mobility measurements using the Wii Balance Board (WBB) and Sensbalance Therapy Cushion (STC), evaluate the usefulness of the STC as a tool for measuring pelvic mobility. Design: Cross-sectional study. Methods: Fifty healthy subjects participated in this study. The subjects performed pelvic mobility range, proprioception, reaction time and reach of the arm using the STC. The pelvic movement parameter was measured two times to determine the intra-rater reliability. To measure the correlation between lumbar muscle tension and pelvic mobility, Myovision was used to measure tension of L4, L5 level erector spinae muscle. Correlations between measured variables were checked to determine the validity of the pelvic mobility assessment tool. Results: STC showed high test-retest reliability in pelvic tilt measurement and reaching task [intraclass correlation coefficients (3,1)=0.804-0.915]. The relationship between WBB and STC showed a significant positive correlation with the pelvic tilt and reaching task (p<0.05). Posterior tilt and erector spinae activation (Lt. L5) showed a significant negative correlation (p<0.05). Left, right tilt and erector spinae activation (L5) showed a significant negative correlation (p<0.05). Conclusions: This study confirmed the advantages of the STC and found efficiency as an objective measuring device of pelvic mobility.

• 한국유체기계학회 논문집
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• 제18권2호
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• pp.14-21
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• 2015

Design lifetime of a wind turbine is required to be at least 20 years. The most important step to ensure the deign is to evaluate the loads on the wind turbine as accurately as possible. In this study, extreme design load of a offshore wind turbine using Garrad Hassan (GH) Bladed and National Renewable Energy Laboratory (NREL) FAST codes are calculated considering structural dynamic loads. These wind turbine aeroelastic analysis codes are high efficiency for the rapid numerical analysis scheme. But, these codes are mainly based on the mathematical and semi-empirical theories such as unsteady blade element momentum (UBEM) theory, generalized dynamic wake (GDW), dynamic inflow model, dynamic stall model, and tower influence model. Thus, advanced CFD-dynamic coupling method is also applied to conduct cross verification with FAST and GH Bladed codes. If the unsteady characteristics of wind condition are strong, such as extreme design wind condition, it is possible to occur the error in analysis results. The NREL 5 MW offshore wind turbine model as a benchmark case is practically considered for the comparison of calculated designed loads. Computational analyses for typical design load conditions such as normal turbulence model (NTM), normal wind profile (NWP), extreme operation gust (EOG), and extreme direction change (EDC) have been conducted and those results are quantitatively compared with each other. It is importantly shown that there are somewhat differences as maximum amount of 18% among numerical tools depending on the design load cases.

• 한국전자파학회논문지
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• 제25권10호
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• pp.1087-1094
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• 2014

본 연구에서는 유전체의 산란 특성 분석을 위해 이용되는 CFIE(Combined Field Integral Equation) 모멘트법의 계산효율을 높이기 위해 임피던스 경계면 조건을 적용시킨 수치해석 기법과 그 적용 범위에 대한 분석결과를 제시한다. 임피던스 경계면의 적용은 유전체의 등가 표면 전류(Js)와 등가 표면 자류(Ms)를 하나의 전류 또는 자류 성분으로 표현할 수 있으며, 임피던스 경계면 조건을 적용해 계산효율을 높인 수치해석 기법의 정확도는 기존의 CFIE 모멘트법과 이론값(Mie-series 해법, Small Perturbation 산란모델)을 이용하여 비교/분석하였다. 임피던스 경계면 조건을 적용한 수치해석 기법의 적용 범위 상대유전율 허수부 12 이상에서 1 dB 이내의 계산 편차를 확인하였다.

• Journal of electromagnetic engineering and science
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• 제18권2호
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• pp.117-128
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• 2018

In this paper, compact linear dual polarized series-fed $1{\times}2$ linear and $2{\times}2$ planar arrays antennas for airborne SAR applications are proposed. The proposed antenna design consists of a square radiating patch that is placed on top of the substrate, a quarter wave transformer and $50-{\Omega}$ matched transformer. Matching between a radiating patch and the $50-{\Omega}$ microstrip line is accomplished through a direct coupled-feed technique with the help of an impedance inverter (${\lambda}/4$ impedance transformer) placed at both horizontal and vertical planes, in the case of the $2{\times}2$ planar array. The overall size for the prototype-1 and prototype-2 fabricated antennas are $1.9305{\times}0.9652{\times}0.05106{{\lambda}_0}^3$ and $1.9305{\times}1.9305{\times}0.05106{{\lambda}_0}^3$, respectively. The fabricated structure has been tested, and the experimental results are similar to the simulated ones. The CST MWS simulated and vector network analyzer measured reflection coefficient ($S_{11}$) results were compared, and they indicate that the proposed antenna prototype-1 yields the impedance bandwidth >140 MHz (9.56-9.72 GHz) defined by $S_{11}$<-10 dB with 1.43%, and $S_{21}$<-25 dB in the case of prototype-2 (9.58-9.74 GHz, $S_{11}$< -10 dB) >140 MHz for all the individual ports. The surface currents and the E- and H-field distributions were studied for a better understanding of the polarization mechanism. The measured results of the proposed dual polarized antenna were in accordance with the simulated analysis and showed good performance of the S-parameters and radiation patterns (co-pol and cross-pol), gain, efficiency, front-to-back ratio, half-power beam width) at the resonant frequency. With these features and its compact size, the proposed antenna will be suitable for X-band airborne synthetic aperture radar applications.

• 지능정보연구
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• 제8권2호
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• pp.91-103
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• 2002

기존의 인터넷 웹사이트에서는 사용자의 만족을 극대화시키기 위하여 사용자별로 개인화 된 서비스를 제공하는 협력적 필터링 방식을 적용하고 있다. 협력적 여과 기술은 비슷한 선호도를 가지는 사용자들과의 상관관계를 기반으로 취향에 맞는 아이템을 예측하여 특정 사용자에게 추천하여준다. 그러나 협력적 필터링은 추천을 받기 위해서 특정 수 이상의 아이템에 대한 평가를 요구하며, 또한 전체 사용자에 대해 단지 비슷한 선호도를 가지는 일부 사용자 정보에 의지하여 추천함으로써 나머지 사용자 정보를 무시하는 경향이 있다. 그러나 나머지 사용자 정보에도 추천을 위한 유용한 정보가 숨겨져 있다. 우리는 이러한 숨겨진 유용한 추천 정보를 발견하기 위하여 본 논문에서는 협력적 여과 방식과 함께 데이터 마이닝(Data Mining)에서 사용되는 연관 규칙(Association Rule)을 추천에 사용한다. 연관 규칙은 한 항목 그룹과 다른 항목 그룹 사이에 존재하는 연관성을 규칙(Rule)의 형태로 표현한 것이다. 이와 같이 생성된 연관 규칙은 개인 구매도 분석, 상품의 교차 매매(Cross-Marketing), 카탈로그 디자인, 염가 매출품(Loss Leader)분석, 상품 진열, 구매 성향에 따른 고객 분류 다양하게 사용되고 있다. 그러나 이런 연관 규칙은 추천 시스템에서 잘 응용되지 못하고 있는 실정이다. 본 논문에서 우리는 연관 규칙을 추천 시스템에 적용해, 항목그룹 사이에 연관성을 유도함으로써 추천에 효율적으로 사용할 수 있음을 보였다 즉 전체 사용자의 히스토리(History) 정보를 기반으로 아이템 사이의 연관 규칙을 유도하고 협력적 여과 방식과 함께 보조적으로 연관 규칙을 추천을 위해 사용함으로써 추천 시스템에 효율성을 높였다.

• 대한교통학회지
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• 제28권2호
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• pp.21-32
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• 2010

교통섬으로 대표되는 도류화 시설은 교통소통과 안전에 크게 기여하면서 신규 도로설계와 교통사고잦은곳 개선사업과 같은 교통안전대책사업에 광범위하게 적용되고 있으나, 다양한 도로환경 조건에서 교통섬 설치로 인한 교통사고 감소효과 등은 구체적으로 제시되지 못하고 있는 실정이다. 이에 본 연구에서는 전국 54개 교차로를 대상으로 공사 전 후 각 3년간의 교통사고자료와 도로환경 자료를 이용하여 정규성 검정과 대응표본 t-검정, 윌콕슨 부호검정을 실시하여 다양한 도로 환경조건에서 교통섬 설치로 인한 교통사고 감소 효과와 경제성 분석을 실시하였다. 교통섬 설치 이후 대부분의 경우 교통사고가 감소하였으나 교통섬의 이용효율이 낮은 시외곽/농업지역과 운전자의 전방 교차로와 교통섬에 대한 시인성이 불량한 곡선부나 교차로 접근부와 유출부의 도로선형이 꺽인구간, 교통섬 설치시 가감속차로가 병행 설치되지 않아 분 합류되는 교차로간상충이 있는 경우 및 부도로 차로수가 1차로인 경우에는 교통섬의 잇점을 충분히 살리지 못해 교통사고감소에 미치는 영향이 미미한 것으로 분석되었다.

• 임상간호연구
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• 제26권1호
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• pp.10-25
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• 2020

Purpose: The purpose of this study was to update the previously developed nursing practice guideline for enteral nutrition (EN). Methods: The guideline update was done in 22 steps using standardized methodology for nursing practice guidelines. Results: The updated EN guideline consisted of 16 domains and 228 recommendations. The domains and number of recommendations in each domain were for IDSA (Infectious Diseases Society of America): 8 on general instruction, 9 on general instruction for special nutrition, 9 on general instruction for EN, 3 on assessment of EN, 10 on access to EN, 18 on EN device insertion, 16 on selection and preparation of nutritional supplements, 46 on administration and stopping EN, 22 on maintenance and management of EN, 9 on monitoring EN, 16 on prevention and management of complications of EN, 18 on medication administration, 20 on EN in various situations, 20 on prevention of errors, 1 on nursing education, and 3 on nursing documentation. For the levels of evidence, there were 9.7% for level I, 13.1% for level II, 62.5% for level III and 1.1% for GRADE (Grading of Recommendations Assessment, Development and Evaluation): 3.3% for low, 0.8% for moderate, 9.3% for very low. A total of 133 recommendations were newly developed and 10 previous recommendations were modified. Conclusion: This updated EN nursing practice guideline can be used to enhance evidence-based practice in fundamentals of nursing practice and it should be disseminated to nurses nationwide in order to improve the efficiency of EN practice.