• 한국해양학회지
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• v.30 no.3
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• pp.170-183
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• 1995

Eddies and surface current field in the southwestern part of the East Sea were investigated using satellite-tracked drifters, CTD, and ADCP from November 1992 to September 1993. Trajectories of surface drifters provided information for the first time on the meandering motion of the East Korean Warm Current in the Ullung Basin (referred as UB) and clearly indicated the existence of cyclonic and anticyclonic eddies of various scales. Anticyclonic eddies persisting for a relatively long period were observed in UB and the southwestern corner of the Northern (Japan) Basin (SNB), while a cyclonic eddy was found in the coastal area between Sokcho and Donghae during the summer. Analysis shows that the eddy in UB behaved as a stationary eddy at least during the observation period and the cyclonic eddy was closely related to the existence of a cold water mass. The anticyclonic eddy in SNB was larger than that in UB, but much elongated in shape. The eddy in UB is characteristic of major and minor axes of about 120 and 70 km, revolution period of 13.6 days, mean swirl velocity of about 24 cm/s, and mean eddy kinetic energy of 392 cm$\^$2//s$\^$2/. The eddy in SNB is described as follows; major and minor axes of 168 and 86 km, period of 14.9 days, mean swirl velocity of 29 cm/s and mean eddy kinetic energy of 629 cm$\^$2//s$\^$2/. The mean translational speed is about 3 cm/s for both eddies. The agreement of the surface current pattern in UB observed by ADCP with the geostrophic flow pattern may suggest that the eddy in UB was nearly in geostrophic balance. The eddy was found to be strongly bottom-controlled.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.12
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• pp.18-25
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• 2005

This paper presents a supercompact multi-wavelet scheme and its application to fluid simulation data. The supercompact wavelet method is an appropriate wavelet for fluid simulation data in the sense that it can provide compact support and avoid unnecessary interaction with remotely located data (e.g. across a shock discontinuity or vortices). thresholding for data compression is applied based on a covariance vector structure of multi-wavelets. The extension of this scheme to three dimensions is analyzed. The numerical tests demonstrate that it can allow various analytic advantages as well as large data compression ratios in actual practice.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.7
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• pp.905-914
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• 2001

A large eddy simulation(LES) is performed for turbulent flow around a bluff body inside a sudden expansion cylinder chamber, a configuration which resembles a premixed gas turbine combustor. To promote turbulent mixing and to accommodate flame stability, a flame holder is installed inside the combustion chamber. The Smagorinsky model is employed and the calculated Reynolds number is 5,000 based on the bulk velocity and the diameter of the inlet pipe. The simulation code is constructed by using a general coordinate system based on the physical contravariant velocity components. The predicted turbulent statistics are evaluated by comparing them with the laser-doppler velocimetry (LDV) measurement data. The agreement of LES with the experimental data is shown to be satisfactory. Emphasis is placed on the time-dependent evolutions of turbulent vortical structure behind the flame holder. The numerical flow visualizations depict the behavior of large-scale vortices. The turbulent mixing process behind the flame holder is analyzed by visualizing the sectional views of vortical structure.

• Restorative Dentistry and Endodontics
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• v.36 no.6
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• pp.465-476
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• 2011

In current endodontic practice, introduction of operating microscope, ultrasonic instruments, and microinstruments has induced a big change in the field of surgical retreatment. In this study, we aimed to offer key steps of endodontic microsurgery procedure compared with traditional root-end surgery, and to evaluate factors influencing success and failure based on published articles. Endodontic microsurgery is a surgical procedure performed with the aid of a microscope, ultrasonic instruments and modern microsurgical instruments. The microscope provides magnification and illumination - essential for identifying minute details of the apical anatomy. Ultrasonic instruments facilitate the precise root-end preparation that is within the anatomical space of the canal. Modern endodontics can therefore be performed with precision and predictability, thus eliminating the disadvantages inherent in traditional periapical surgery such as large osteotomy, beveled apicoectomy, inaccurate root-end preparation and the inability to observe isthmus. Factors influencing the outcomes of endodontic microsurgery may be diverse, but standardization of procedures can minimize its range. Among patient and tooth-related factors, periodontal status and tooth position are known to be prognostic, but there are only few articles concerning this matter. High-evidence randomized clinical trials or prospective cohort studies are needed to confirm these findings.

• Journal of the korean academy of Pediatric Dentistry
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• v.45 no.3
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• pp.290-298
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• 2018

This study aimed to evaluate surface morphology and resin tag penetration of resin infiltration into primary anterior teeth after enamel deproteinization with sodium hypochlorite (NaOCl) prior to phosphoric acid ($H_3PO_4$) etching. Ninety primary anterior teeth with non-cavitated caries lesion were devided five groups according to enamel pretreatment as follows, group I-15% hydrochloric acid (HCl) 2min. ; group II-5.25% NaOCl 1min., 35% $H_3PO_4$ 1min. ; group III-5.25% NaOCl 2min., 35% $H_3PO_4$ 1min. ; group IV-5.25% NaOCl 1min., 35% $H_3PO_4$ 2min. ; group V-5.25% NaOCl 2min., 35% $H_3PO_4$ 2min. Fifteen teeth were examined etched surface structure using field emission-scanning electron microscope. Seventy five teeth were infiltrated with resin, maximum penetration depth and percentage penetration were analysed using dual fluorescence confocal microscopy. As the application time of NaOCl increased, ratio of enamel type I, II were increased. Percentage penetration (PP) was higher in group V than group II, III (p < 0.05). PP of group IV, V did not show any differences. Non-cavitated caries of primary anterior teeth can be treated with resin infiltration. Enamel deproteinization with NaOCl prior to 35% $H_3PO_4$ etching could be an alternative of 15% HCl etching in resin infiltration.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.34 no.6
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• pp.713-719
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• 2001

The aim of this study is to check the application criteria of the conventional techniques and clarify the effects of breaker depth, seabed conditions on the stability in relation to the effects of uncertainty of storm duration and directional irregular waves. The typical damage modes were divided by the direct wave force on the armor unit and by the local scouring around the toe of a breakwater head by the model experiments. The destruction modes are defined, and some criteria on the damage modes and scouring/deposition at the toe of a breakwater head in relating the wave-bottom-structural conditions can be checked using the multi-directonal irregular wave generator system. According to the results, it is emphasized that the 3-D effects on the stability should be analyzed in the design of multi-purpose/function coastal structures in consideration of the evaluation of spatial variation of damage modes and hydraulic characteristics as well as the wave distribution along the structures.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.2
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• pp.1-9
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• 2014

To investigate the flame dynamics in an annular combustor with single swirl injector, a 3D large-eddy simulation (LES) and a level-set flamelet turbulent combustion model have been implemented. The LM6000 developed by GEAE has been used as the combustor of concern and boundary conditions are based on experimental data. The strong central toroidal recirculation zone induced by the volume expansion of the combustion gas and the vortex breakdown continuously occurred through the procession of the vortex with decreasing strength, are observed.

• Proceeding of EDISON Challenge
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• 2013.04a
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• pp.354-359
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• 2013

일반적으로 건축물의 설계시 풍동 실험을 통한 풍환경의 평가를 수행하고 있으며, 이는 환경 영향 평가법에서 정한 건축 사업 시행 시 수반되어야 할 자연환경, 생활환경 그리고 사회경제환경의 영향 평가의 일환으로 실시되고 있다. 그러나, 풍동 실험의 경우 여러 가지 현실적 제약조건으로 설계와 실험의 피드백 (Feedback)이 원활하지 못하며, 특히 대상 건축물이 공장과 같이 대기 오염원이 되는 경우 실험은 더욱 어려운 형편이다. 이에 대한 보완책으로 전산 유체 역학을 이용한 건축물의 풍압 해석에 의한 풍하중 추정이나 인접 지형-지물의 영향을 고려한 건축물 주위의 풍환경 평가가 있다. 전산 모사에 의해 풍동 실험의 미비점을 보완하고, 보다 상세한 정보를 확보함으로써 건축물의 구조적 안전성의 증대와 환경 피해 감소를 기할 수 있다. 그러나 복잡한 지형-지물이나 건축물 주위의 풍환경에 대한 전산 모사는 주로 두 가지의 기술적 어려움을 수반하게 되다. 그 중 하나는 고정 경계면을 이루는 형상의 복잡성으로 인해 기존에 많이 이용하고 있는 Body-fitted 격자계를 이용하는 경우, 격자 생성 과정이 매우 복잡하고 어려울 뿐 만 아니라 생성된 격자가 주로 비정렬 (unstructured) 특성을 갖게 되어 수치해석 과정의 효율을 저하시키는 요인이 되며, 격자의 형상도 수치해석의 수렴성을 저하시키는 예가 많다. 다른 어려움으로 풍환경은 전형적인 난류 유동장으로서 난류의 전산 해석은 아직도 해결하지 못한 부분이 많다는 점이다. 이에 본 논문에서는 복잡한 지형-지물이나 건축물의 풍하중과 풍환경의 전산 모사 기술 확보를 위하여 수행중인 연구의 일환으로 물체 형상의 기하학적 복잡성의 극복을 위한 가상경계법 (Immersed Boundary Method)과 난류 유동장의 물리적 엄밀성을 높이기 위한 다와동 모사 (Large Eddy Simulation)을 이용한 물체 형상과 무관한 유동장 해석 기술 개발에 대하여 다루고자 한다. 먼저 최근에 유동 해석에 이용되는 방법인 가상경계법(IBM)은 물체를 포함한 전체 전산 영역을 직교 좌표계에 의해 이산화하고, 유동장내 존재하는 물체의 표면에서의 점착 조건을 만족시키기 위하여 지배 방정식에 적절한 외력을 추가로 고려하는 방법이다. 본 연구에서는 가상경계법을 이용하여 경계층에 위치한 건물 형상의 각진 물체 주위 사이에 형성되는 공동 내부의 비정상 유속 및 압력에 대한 전산 해석을 수행하고, 풍상측 전면에 형성되는 경계층에 의한 영향을 분석하였다.

• Fire Science and Engineering
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• v.29 no.5
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• pp.42-50
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• 2015

Three simulation approaches for turbulence were applied for the computation of propane dispersion in a simplified real-scale urban area with one building:, Large Eddy Simulation (LES), Detached Eddy Simulation (DES), and Unsteady Reynolds Averaged Navier-Stokes (RANS). The computations were performed using FLUENT 14, and the grid system was made with ICEM-CFD. The propane distribution depended on the prediction performance of the three simulation approaches for the eddy structure around the building. LES and DES showed relatively similar results for the eddy structure and propane distribution, while the RANS prediction of the propane distribution was unrealistic. RANS was found to be inappropriate for computation of the gas dispersion process due to poor prediction performance for the unsteady turbulence. Considering the computational results and cost, DES is believed to be the optimal choice for computation of the gas dispersion in a real-scale space.

• Journal of Energy Engineering
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• v.24 no.3
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• pp.109-114
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• 2015

Heat exchanger tube array in a heat recovery steam generator is exposed to the hot exhaust gas flow and it could cause the flow induced vibration, which could damage the heat exchanger tube array. It is needed for the structural safe operation of the heat exchanger to establish the characteristics of flow induced vibration in the tube array. The researches for the flow induced vibration of typical heat exchangers have been conducted and the nondimensional PSD(Power Spectral Density) function with the Strouhal number, fD/U, had been derived by experimental method. The present study examined the results of the previous experimental researches for the nondimensional PSD characteristics by CFD analysis and the basis for the application of flow induced vibration to the heat recovery steam generator tube array would be prepared from the present CFD analysis. For the previous mentioned purpose, the present CFD analysis introduced a single circular cylinder and calculated with the unsteady laminar flow over the cylinder. The characteristics of vortex shedding and lift fluctuation over the cylinder was investigated. The derived nondimensional PSD was compared with the results of the previous experimental researches and the characteristics of lift PSD over a single circular cylinder was established from the present CFD study.