• Structural Engineering and Mechanics
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• 제9권1호
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• pp.69-88
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• 2000

A relatively simple model of a buried structure response to a surface loading that can simulate a possible opening and closure of a gap between the soil and the structure is presented. Analysis of the response of small and medium scale buried roof slabs under surface impulsive loading shows that the model's predictions are in fairly good agreement with the experimental results. Application of the model to a study case shows the relative influence of system parameters such as, the depth of burial, the arching coefficient, and the roof thickness, on the interface pressure and on the roof displacement. This model demonstrates the effect of a gap between the structure and the soil. The relative importance of including a gap opening and closure in the analysis is examined by the application of the model to a study case. This study results show that the deeper the depth of burial, the longer the gap duration, and the shorter the duration of the initial interface impact, while the higher the soil's shear resistance, the higher the gap duration, and the shorter the initial interface impact duration.

• 대한기계학회논문집B
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• 제28권5호
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• pp.526-534
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• 2004

A new second-moment closure model for turbulent heat fluxes is proposed on the basis of the elliptic equation. The new model satisfies the near-wall balance between viscous diffusion, viscous dissipation and temperature-pressure gradient correlation, and also has the characteristics of approaching its respective conventional high Reynolds number model far away from the wall. The predictions of turbulent heat transfer in a channel flow have been carried out with constant wall heat flux and constant wall temperature difference boundary conditions respectively. The velocity field variables are supplied from the DNS data and the differential equations only fur the mean temperature and the scalar flux are solved by the present calculations. The present model is tested by direct comparisons with the DNS to validate the performance of the model predictions. The prediction results show that the behavior of the turbulent heat fluxes in the whole region is well captured by the present model.

• 한국항공우주학회지
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• 제42권9호
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• pp.745-751
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• 2014

멀티 노즐로 구성된 추진기관의 경우, 각 노즐별 노즐마개 파열압력의 편차가 초기 분력을 유발하고 유도탄의 비행안정성에 영향을 미친다. 따라서 노즐마개 설계 시 먼저 형태별로 파열거동을 분석하여 원하는 파열압력에서 균일하게 파열되는지를 확인해야 한다. 본 연구에서는 평판형, "+" 노치형 노즐마개에 대한 파열거동을 실험적, 해석적인 방법으로 분석하였다. 실험 시 저장온도, 노치의 유무, 노치방향에 따른 노즐마개 파열압력 및 편차를 분석하였다. 그리고 유한요소해석을 통해 노즐마개의 파열거동을 순차적으로 분석하고, 그 결과를 실험값과 비교하여 정확성을 검증하고자 하였다. 해석 시 상용프로그램인 Abaqus/Explicit를 사용하였고, 파손모델은 Johnson-cook 전단파손모델을 적용하였다.

• 대한기계학회논문집B
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• 제20권5호
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• pp.1661-1670
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• 1996

Incompressible flow over a backward-facing step is computed by low Reynolds number turbulence models in order to compare with direct simulation results. In this study, selected low Reynolds number 1st and 2nd (Algebraic Stress Model : ASM) moment closure turbulence models are adopted and compared with each other. Each turbulence model predicts different flow characteristics, different re-attachment point, velocity profiles and Reynolds stress distribution etc. Results by .kappa.-.epsilon. turbulence models indicate that predicted re-attachment lengths are shorter than those by standard model. Turbulent intensity and eddy viscosity by low Reynolds number .kappa.-.epsilon. models are still greater than DNS results. The results by algebraic stress model (ASM) are more reasonable than those by .kappa.-.epsilon. models. The convective scheme is QUICK (Quadratic Upstream Interpolation for Convective Kinematics) and SIMPLE algorithm is adopted. Reynolds number based on step height and inlet free stream velocity is 5100.

• 한국산학기술학회논문지
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• 제21권10호
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• pp.166-173
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• 2020

이 연구의 목적은 인지적 종결 욕구를 측정하는 단축형 종결 욕구 척도(NFCS-SF: Need for Closure Scale-Short Form)를 타당화하기 위함이었다. 참가자들은 인지적 종결 욕구, 불확실성에 대한 인내력 부족, 우울과 불안 설문지를 작성하였다. 2017년 5월~7월 동안 수집된 536개의 자료 중, 총 495명의 참가자의 자료를 SPSS 20.0과 M-Plus로 분석하였다. 연구결과는 다음과 같다. 첫째, 탐색적 요인분석 결과를 토대로 각 하위 영역에서 3문항을 선정하여 15문항의 NFCS-SF를 구성하였다. 둘째, NFCS-SF의 내적 일치도가 양호했다(연구 1, Cronbach's α=.85; 연구 2, Cronbach's α=.84). 셋째, 확인적 요인분석 결과 5요인 구조가 지지되었다(χ²(80)=178.34, p<.001, CFI=.87, TLI=.83, RMSEA=.07, SRMR=.08). 넷째, NFCS-SF는 NFCS(r=.86, p<.01) 뿐 아니라 불확실성에 대한 인내력 부족(r=.58, p<.01), 우울(r=.16, p<.05)과 불안(상태 불안, r=.31, p<.01; 특성 불안, r=.29, p<.01) 척도와의 상관이 유의하였다. 이러한 연구결과를 토대로, 연구의 의의 및 한계와 후속 연구를 위한 제안을 토의하였다.

• Journal of applied mathematics & informatics
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• 제32권5_6호
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• pp.649-663
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• 2014

Presence of eyelid on anterior ocular surface and its thermal effects play significant role in maintaining eye temperature. In most of the literatures of thermal modeling in human eye, the eyelid is not considered as an eye component. In this paper, finite element model is developed to investigate the thermal effects of eyelid closure and opening in human eye. Based on different properties and parameter values reported in literatures, the bio-heat transfer process is simulated and compared with experimental results in steady and transient state cases. The sensitivity analysis using various ambient temperatures, evaporation rates, blood temperatures and lens thermal conductivities is carried out. The temperature values so obtained in open eye show a good agreement with past results. The closure of eyelid is found to increase/decrease the eye temperature significantly than its opening, when the parameter values are considered to be at extreme.

• 한국농공학회:학술대회논문집
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• 한국농공학회 1998년도 학술발표회 발표논문집
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• pp.287-292
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• 1998

The phenomena of local scour due to a current from a seadike closure gap which is protected by rock, then on to an erodible bed, have been studied. Based on the data of hydraulic model test, the scour characteristics have been investigated for the variation of maximum scour depth with time until reaching equilibrium stage and the shape of ultimate scour hole. A brief evaluation of DHL formula for the relationship between maximum scouring depth and time and a dimensionless form leading to time-scale introduced. On the basis of DHL formula, modified DHL formula denoted DHL-RDC formula is extend to the range of estimation of scour depth compared to DHL formula verified by model test.

• 한국연소학회지
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• 제15권1호
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• pp.1-11
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• 2010

In this study, the coupled simulation of fuel injection model and three-dimensional KIVA-3V code was tried to develop an algorism for predicting the effects of varying fuel injection parameter on the characteristics of fuel injection and emissions. The numerical simulations were performed using STAR-CD code in order to calculate the intake air flow, and the combustion characteristics is examined by KIVA-3V code linked with the conditional moment closure(CMC) model to predict mean turbulent reaction rate. Parametric investigation with respect to twelve relevant injection parameters shows that appropriate modification of control chamber orifice diameter, needle valve spring constant and nozzle chamber orifice diameter can significantly reduce NOx and soot emissions. Consequently, it is needed to optimize the fuel injection system to reduce the specific emissions such as NOx and soot.

• 한국농공학회지
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• 제41권5호
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• pp.77-85
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• 1999

Irrigation pipeline systems have been recently adopted for irrigation purposes, which was thought to improve irrigation efficiencies. However, if hydraulic characteristics are not evaluated in designing , overpressure due to waterhammer may occur and result in serious problems. Therefore, in this study a model was formulated to simulate unsteady motion of water in a pipeline resulting from valve closure, the applicability of the model owas tested with fiedld data, and the results showed good agreement in maximum piezometric head. Also, simulated maximum piezometric head was compared with designed piezometric head computed by empirical method, and maximum piezometric head in a pipeline resulting from valve closure was simulated and analyzed with varing surge tank's position and diameter.

• 물과 미래
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• 제29권2호
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• pp.199-207
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• 1996

온배수의 거동해석에 $\kappa-\imath$ 난류모델의 사용성 평가를 위해 수심적분 2차원 수치모형을 개발하였다. 개발된 모형은 간단한 단면을 갖는 개수로 정상류의 경우에 적용하였으며, 기존의 실험결과와 비교적 잘 일치하였다. 온수의 재순환, 재부착 및 초과온도 상승분포의 적절한 모의해석은 $\kappa-\imath$ 난류모델에 의한 적절한 난류 점성 및 확산계수의 산정때문이라 생각된다. 예측의 정확성을 위하여 부력생성항의 도입, Source/Sink 항의 수정 및 그에 따른 적절한 난류 상수의 규명이 필요하다.