• Structural Engineering and Mechanics
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• 제6권1호
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• pp.115-124
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• 1998

A novel boundary stress resolution method is suggested in this paper, which is based upon the displacements of finite element analysis and of high precision with stress boundary condition strictly satisfied. The method is used to modify the Zienkiewicz-Zhu ($Z^2$) a posteriori error estimator and for the h-version adaptive finite element analysis of crack problems. Successful results are obtained.

• 대한음성학회지:말소리
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• 제42호
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• pp.71-88
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• 2001

This study is on the constraints of English Poetic Meter. In English poems, the metrical pattern doesn't always match the linguistic stress on the lines. These mismatches are found differently among the poets. The peaks mismatched with the weak metrical position are divided into the two ways according as they are adjacent to the boundary of a phonological domain or not. PAF and $^*UV$] are suggested for the mismatched peak which are not adjacent to the boundary of a phonological domain ; $^*Peak$] and BT for the mismatched peak which are adjacent to the boundary of a phonological domain. For the lexical stress mismatched with the weak metrical position, $^*W{\;}{\Rightarrow}{\;}Strength$ is set up by the concept of the strong syllable. $MPS{\;}{\Rightarrow}{\;}\Phi_{max}$ for the metrical position size can replace the resolution which is used to control the number of syllables in English poems. These constraints show the different hierarchies among the poets.

• Journal of Advanced Marine Engineering and Technology
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• 제22권6호
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• pp.935-941
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• 1998

Experiments were carried out for a cubic cavity flow. Contrinuous shear stress is supplied by driven flow for high Reynolds number and three kinds of aspect ratios. Velocity vectors are obtained by PIV and they are used as velocity components for Poisson equation for pressure, Related boundary conditions and no-slip condition at solid wall and the linear velocity extrapolation on the upper side of cavity are well examined for the present study. For calculation of pressure resolution of grid is basically $40{\times}40$ and 2-dimensional uniform mesh using MSC staggered grid is adopted. The flow field within the cavity maintains a forced-vortex formation and almost of the shear stress from the driving inflow is transformed into rotating flow energy and the size of the distorted forced-vortex increases with increment of Reynolds number

• 한국안전학회지
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• 제9권1호
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• pp.146-154
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• 1994

A series of numerical calculations are performed in order to investigate the dispersion mechanism of toxic gaseous and solid pollutants in extremely short-term and short range. The calculations are carried out in an open space characterized by turbulent boundary layer. The simulation is made by the use of numerical model, in which a control-volume based finite difference method is used together with the SIMPLEC algorithm for the resolution of the pressure-velocity coupling problem. The Reynolds stresses are solved by two-equation, k-$\varepsilon$ model modified for buoyancy. The major parameters consider-ed in this study are temperature, velocity and Injection height of toxic gases, environmental conditions such as temperature and velocity of free stream air, and topographic factor. The results are presented and discussed in detail. The flow field is commonly characterized by the formation of a strong recirculation zone due to the upward motion of the hot toxic gas and ground shear stress. The driving force of the upward motion is explained by the effect of thermal buoyancy of hot gas and the difference of inlet velocity between toxic gas and free stream.

• Ocean and Polar Research
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• 제28권3호
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• pp.245-258
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• 2006

We investigated seasonal variations of the upper ocean temperature and the mixed layer depth (MLD) in an eddy-permitting global ocean general circulation model (OGCM) to assess the OGCM perfermance. The OGCM is based on the GFDL MOM3 which has a horizontal resolution of 0.5 degree and 30 vertical levels. The OGCM was integrated for 68 years using a monthly-mean climatological wind stress forcing. The model sea surface temperature (SST) and sea surface salinity were restored to the Levitus climatology with a time scale of 30 days. Annual-mean model SST shows a cold bias $(<\;-2^{\circ}C)$ in the summer hemisphere and a warm bias $(>\;1^{\circ}C)$ in the winter hemisphere mainly due to the restoring boundary condition of temperature. The model MLD captures well the observed features in most areas, with a slightly deep bias. However, in the Ross Sea and Weddell Sea, the model shows significantly deeper MLD than the climatology-mainly due to weak salinity stratifications in the model. For amplitude of seasonal variation, the model SST is smaller $(1{\sim}3^{\circ}C)$ than the observation largely due to the restoring surface boundary condition while the model MLD has larger seasonal variation $({\sim}50m)$. It is suggested that for more realistic simulation of the upper ocean structure in the present eddy-permitting ocean model, more refinements in the surface boundary condition for the thermohaline forcing and parameterization for vertical mixing are required, together with the incorporation of a sea-ice model.

• 한국압력기기공학회 논문집
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• 제14권1호
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• pp.15-23
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• 2018

A compact heat exchanger is one of critical components in a very high temperature gas-cooled reactor (VHTR). Alloy 617 (Ni-Cr-Co-Mo) is considered as one of leading candidates for this application due to its excellent thermal stability and strengths in anticipated operating conditions. On the basis of current ASME code requirements, sixty sheets of this alloy are prepared for diffusion welding, which is the key technology to have a reliable compact heat exchanger. Optical microscopic analysis show that there are no cracks, incomplete bond, and porosity at/near the interface of diffusion weldment, but Cr-rich carbides and Al-rich oxides are identified through high resolution electron microscopic analysis. In high-temperature tensile testing, superior yield strengths of the diffusion weldment compared to the code requirement are obtained up to 1223 K ($950^{\circ}C$). However, both tensile strength and ductility drop rapidly at higher temperature due to the insufficient grain boundary migration across the interface of diffusion weldment. Best fit curves for minimum yield strength and average tensile strength are drawn from the experimental tensile results of this study.

• 한국CDE학회논문집
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• 제2권3호
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• pp.175-185
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• 1997

Given the widespread use of the Finite Element Method in strength analysis, automatic mesh generation is an important component in the computer-aided design of parts and assemblies. For a given resolution of geometric accuracy, the purpose of mesh generators is to discretize the continuous model of a part within this error limit. Sticking to this condition often produces many small elements around small features in spite that these regions are usually of little interest and computer resources are thus wasted. Therefore, it is desirable to selectively suppress small features from the model before discretization. This can be achieved by low-pass filtering a CAD model. A spatial function of one dimension higher than the model of interest is represented using the Fourier basis functions and the region where the function yields a value greater than a prescribed value is considered as the extent of a shape. Subsequently, the spatial function is low-pass filtered, yielding a shape without the small features. As an undesirable effect to this operation, all sharp corners are rounded. Preservation of sharp corners is important since stress concentrations might occur there. This is why the LPF (low-pass filtered) model can not be directly used. Instead, the distances of the boundary elements of the original shape from the LPF model are calculated and those that are far from the LPF model are identified and removed. It is shown that the number of mesh elements generated on the simplified model is much less than that of the original model.

• Nuclear Engineering and Technology
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• 제54권11호
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• pp.4296-4309
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• 2022

Mesh and turbulence model sensitivity analyses have been performed on computational fluid dynamics simulations executed with Hydra and ANSYS Fluent for a single CANadian Deuterium Uranium (CANDU) 37M nuclear fuel bundle placed within a standard pressure tube. The goal of this work was to perform a methodical analysis to objectively determine an appropriate mesh and to gauge the sensitivity of different turbulence models for CANDU subchannel flow under isothermal conditions. The boundary conditions and material properties are representative of normal operating conditions in a high-powered channel of the Darlington Nuclear Generating Station. Four meshes were generated with ANSYS Workbench Meshing, ranging from 22 to 84 million cells, and analyzed here to determine an appropriate level of mesh resolution and quality. Five turbulence models were compared in the turbulence model sensitivity analysis: standard k - ε, RNG k - ε, realizable k - ε, SST k - ω, and the Reynolds Stress Model. The intent of this work was to gain confidence in mesh generation and turbulence model selection of a single bundle to inform the decision making of subsequent investigations of an entire fuel channel containing a string of twelve bundles.

• 대한토목학회논문집
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• 제8권2호
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• pp.67-76
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• 1988

본(本) 연구(硏究)에서는 아라비아만(灣)(페르시아만(灣))의 기본적(基本的)인 조석역학(潮汐力學)을 연구(硏究)하기 위한 2차원(次元) 조석수치(潮汐數値) 모델을 수립(樹立)하였다. 모델외해경계(外海境界)는 만동측(灣東側)의 육붕단(陸棚端)에 위치(位置)하며 위도상(緯度上) $1/12^{\circ}$, 경도상(經度上) $1/10^{\circ}$의 격자해상도(格子解像度)를 갖는다. 수립(樹立)된 모델은 $M_2$, $S_2$, $K_1$, $O_1$ 및 $N_2$ 분조(分潮)의 분포(分布)를 조사(調査)하기 위해 일차적으로 이용(利用)되었는데 외해개방경계조건(外海開放境界條件)은 Schwiderski의 해양조석(海洋潮汐) 모델로부터 취하였다. 주분조(主分潮)의 독립적(獨立的)인 등진폭(等振幅)과 등위상도(等位相圖)가 제시(提示)되었으며, 기존영국수로부(旣存英國水路部)의 조석도(潮汐圖)와도 비교검토(比較檢討)되었다. $M_2$분조(分潮)와 $M_4$분조(分潮)에 의한 반일주기(半日週期)의 최대해저응력(最大海底應力)벡터가 이 해역(海域)의 토사이동(土砂移動) 방향(方向)을 추정(推定)하기 위해 제시(提示)되었다.

• 대한원격탐사학회지
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• 제38권6_1호
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• pp.1231-1244
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• 2022

이상기상으로 인해 노지 작물이 스트레스 상황에 노출되는 빈도가 증가하고 있다. 우리나라에서도 대표적인 벼 재배지역에서 대규모의 병해가 발생하는 사례가 나타났으며, 특정 시기에 대규모 필지에서 발생하는 피해를 현장방문으로 조사하는 것은 한계가 있다. 위성 기반의 원격탐사 기법은 시군 영역을 대상으로 작물을 모니터링하기에 유용하나 작물의 생육이상에 따른 민감도 평가가 선행되어야 한다. 본 연구에서는 벼 병해 발생 지역에서 서로 다른 공간해상도를 가지는 위성 기반의 정규화식생지수(normalized difference vegetation index, NDVI)를 드론 영상을 이용하여 평가하였다. 10 m와 30 m의 공간해상도를 가지는 Sentinel-2, Landsat-8 위성 영상을 평가하였으며, 드론 영상은 약 8-10 cm의 공간해상도를 가졌다. 위성 영상에 맞춰 리샘플링(resampling)된 드론 NDVI는 Sentinel-2 NDVI 와 0.867-0.940의 상관관계를 가졌으며, Landsat-8 NDVI와는 0.813-0.934의 상관관계를 가졌다. 센서의 차이, 관측 시점의 차이 등으로 인한 편향(bias) 영향을 최소화하였을 때, Sentinel-2 NDVI는 Landsat-8 NDVI에 비해 드론 NDVI와 0.2-2.8% 더 적은 정규화된 평균 제곱근 오차를 가졌다. 또한, Sentinel-2 NDVI는 드론 NDVI와 병해 피해 정도와 관계없이 일정한 오차를 가졌으나 Landsat-8 NDVI는 병해 피해 정도에 따라 드론 NDVI와 오차 특성이 다르게 나타났다. 농경지 경계에서 오차가 크다는 것을 고려했을 때 공간해상도가 높은 영상을 활용하는 것이 작물 모니터링에 효과적이라고 판단된다.