• Title/Summary/Keyword: averaged flat

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Development of Wind Noise Analysis Procedure and Its Verification Using CFD Tool around an OSRVM (CFD를 이용한 OSRVM 주변의 공력소음 해석과정 개발 및 검증)

  • Park, Hyun-Ho;Han, Hyun-Wook;Kim, Moon-Sang;Ha, Jong-Paek;Kim, Yong-Nyun
    • Transactions of the Korean Society of Automotive Engineers
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    • v.20 no.4
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    • pp.92-102
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    • 2012
  • The process of the wind noise analysis around an OSRVM is developed and is verified by simulating unsteady flow field past a generic OSRVM mounted on the flat plate at the Reynolds number of $Re_D=5.2{\times}10^5$ based on the mirror diameter. The transient flow field past a generic OSRVM is simulated with various turbulence models, namely DES-SA, LES Constant SGS, and LES Dynamic SGS. The sound radiation is predicted using the Ffowcs- Williams and Hawkings analogy. For the present simulation, the 6.35million cells are generated. Time averaged pressure coefficients at 34 locations on the surface of the generic OSRVM are compared with the available experimental data. Also, 12 Sound Pressure Levels located on the surrounding mirror are compared with the available experimental data. Both of them show good agreements with experimental data.

Turbulent Flow over 2-D Rectangular-Shaped Roughness Elements with Various Spacings(Part 1 : Time Averaged Flow) (사각단면을 갖는 환경 거칠기 요소의 거칠기 간격에 따른 유동 변화 (제1보: 평균유동장))

  • Hyun B.S.;Suh E.J.;Kim M.R.;Choi K.C.
    • Journal of the Korean Society for Marine Environment & Energy
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    • v.9 no.2
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    • pp.79-84
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    • 2006
  • The present study deals with the flow over a flat plate with repeated roughness elements of 2-dimensional rectangular shape, which can be applied into the study on the natural geographical roughness and the turbulent flow on roughened solid surface. Experiment was performed using PIV technique in the circulating water channel. Results showed that the flow over roughness elements was characterized by the high shear flow emanating from top of roughness element and the recirculating region formed at the trough of two roughness elements. In general, the ratio between the spacing and the height of roughness elements plays a crucial role in developing the flow pattern near wall surface.

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Characterization of the Anatomic Location of the Pituitary Stalk and Its Relationship to the Dorsum Sellae, Tuberculum Sellae and Chiasmatic Cistern

  • Gulsen, Salih;Dinc, Ahmet Hakan;Unal, Melih;Canturk, Nergis;Altinors, Nur
    • Journal of Korean Neurosurgical Society
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    • v.47 no.3
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    • pp.169-173
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    • 2010
  • Objective : The normal anatomic relationships characteristic of the pituitary stalk area were previously thought to involve only one location. The purpose of this study was to re-evaluate the anatomic location of the pituitary stalk and possible varying locations in relation to the tuberculum sellae and dorsum sellae using morphometric evaluation and anatomic dissection of human cadaveric specimens. The surgical implications of the variations are discussed. Methods : The calvaria were removed via routine autopsy dissections, and the brains were removed from the skull while preserving the pituitary stalk. The diaphragma sellae, tuberculum sellae, and the location of the pituitary stalk were examined in 60 human cadaveric heads obtained from fresh adult cadavers. Empty sellae were excluded. Results : The openings of the diaphragma sellae averaged $6.62{\pm}1.606mm$ (range, 3-9 mm). The distance between the tuberculum sellae and the posterior part of the pituitary stalk was 1 to 8 mm. The upper face of the diaphragma sellae appeared flat in 26 (43%), concave in 24 (40%), and convex in 6 cases (10%), with a prominent tuberculum sellae in 4 cases (7%). The location of the chiasm was normal in 47 cases (78%), with a prefixed chiasm in 3 cases (5%) and a postfixed chiasm (17%) in the 10 cases. Four cadaver specimens had prominent tuberculum sellae and other parameters were not evaluated. Conclusion : When opening the chiasmatic cistern, neurosurgeons should be aware about the relationship between the pituitary stalk and the surrounding structures to prevent inadvertent injury to the pituitary stalk.

SPATIAL AND ENERGY RESOLUTIONS OF A HEXAGONAL ANIMAL PET SCANNER BASED ON LGSO CRYSTAL AND FLAT-PANEL PMT

  • Lee, Chan-Mi;Hong, Seong-Jong;Yoon, Hyun-Suk;Ito, Mikiko;Kwon, Sun-Il;Park, Sang-Keun;Lee, Dong-Soo;Sim, Kwang-Souk;Lee, Jae-Sung
    • Nuclear Engineering and Technology
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    • v.44 no.1
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    • pp.53-60
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    • 2012
  • The aim of this study was to explore the spatial and energy resolutions of a PET scanner that we have recently developed. The scanner, which consists of six detector modules with 1-layer LGSO crystals, has a hexagonal configuration with a faceto- face distance of 86.4 mm between two opposite PET modules; such properties facilitate the imaging of small animals. A $^{22}Na$ point source was employed to estimate horizontal and vertical spatial resolutions. To assess the energy resolution, a uniform $^{18}F$ cylindrical phantom was scanned. A software-based spectrum analysis of list-mode data was used to assign a local energy window centered on the photopeak position for every single crystal. For the image reconstruction, an ML-EM algorithm was used. The spatial resolutions at the center of the scanner were 0.99 mm in the horizontal direction and 1.13 mm in the vertical direction. The energy resolution averaged over each PMT ranged from 13.3%-14.3%, which gave an average value of 13.8%. These results show that this simple system is promising for small animal imaging with excellent spatial and energy resolutions.

Heat/Mass Transfer Characteristics on Stationary Turbine Blade and Shroud in a Low Speed Annular Cascade (II) - Tip and Shroud - (환형 캐스케이드 내 고정된 터빈 블레이드 및 슈라우드에서의 열/물질전달 특성 (II) - 끝단 필 슈라우드 -)

  • Lee Dong-Ho;Cho Hyung Hee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.29 no.4 s.235
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    • pp.495-503
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    • 2005
  • Experiments were conducted in a low speed stationary annular cascade to investigate local heat transfer characteristics on the tip and shroud and the effect of inlet Reynolds number on the tip and shroud heat transfer. Detailed mass transfer coefficients on the blade tip and the shroud were obtained using a naphthalene sublimation technique. The turbine test section has a single stage composed of sixteen guide vanes and blades. The chord length and the height of the tested blade are 150 mm and about 125 mm, respectively. The blade has flat tip geometry and the mean tip clearance is about $2.5{\%}$of the blade chord. The inlet flow Reynolds number based on chord length and incoming flow velocity is changed from $1.0{\times}10^{5}\;to\;2.3{\times}10^{5}.$ to investigate the effect of Reynolds number. Flow reattachment after the recirculation near the pressure side edge dominates the heat transfer on the tip surface. Shroud surface has very intricate heat/mass transfer distributions due to complex flow patterns such as acceleration, relaminarization, transition to turbulent flow and tip leakage vortex. Heat/mass transfer coefficient on the blade tip is about 1.7 times as high as that on the shroud or blade surface. Overall averaged heat/mass transfer coefficients on the tip and shroud are proportional to $Re_{c}^{0.65}\;and\;Re_{c}^{0.71},$ respectively.

Heat/Mass Transfer Characteristics on Stationary Turbine Blade and Shroud in a Low Speed Annular Cascade (I) - Near-tip Blade Surface - (환형 캐스케이드 내 고정된 터빈 블레이드 및 슈라우드에서의 열/물질전달 특성 (I) - 블레이드 끝단 인접 표면 -)

  • Rhee Dong-Ho;Cho Hyung Hee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.29 no.4 s.235
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    • pp.485-494
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    • 2005
  • For the extensive investigation of local heat/mass transfer on the near-tip surface of turbine blade, experiments were conducted in a low speed stationary annular cascade. The turbine test section has a single stage composed of sixteen guide vanes and blades. The chord length and the height of the tested blade are 150 mm and about 125 mm, respectively. The blade has flat tip geometry and the mean tip clearance is about $2.5{\%}$ of the blade chord. Detailed mass transfer coefficient on the blade near-tip surface was obtained using a naphthalene sublimation technique. The inlet flow Reynolds number based on chord length and incoming flow velocity is changed from $1.0{\times}10^{5}\;to\;2.3{\times}10^{5}.$ Extremely complex heat transfer characteristics are observed on the blade surface due, to complicated flow patterns, such as flow acceleration, laminarization, transition, separation bubble and tip leakage flow. Especially, the suction side surface of the blade has higher heat/mass transfer coefficients and more complex distribution than the pressure side surface, which is related to the leakage flow. For all the tested Reynolds numbers, the heat/mass transfer characteristics on the turbine blade are the similar. The overall averaged $Sh_{c}$ values are proportional to $Re_{c}^{0.5}$ on the stagnation region and the laminar flow region such as the pressure side surface. However, since the flow is fully turbulent in the near-tip region, the heat/mass transfer coefficients are proportional to $Re_{c}^{0.8}.$

Wave Drag Reduction due to Repetitive Laser Pulses (반복 레이저 펄스를 이용한 초음속 비행체의 항력저감)

  • Kim, Jae-Hyung;Sasoh, Akihiro;Kim, Heuy-Dong
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2011.04a
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    • pp.381-384
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    • 2011
  • Wave drag reduction due to the repetitive laser induced energy deposition over a flat-nosed cylinder is experimentally conducted in this study. Irradiated laser pulses are focused by a convex lens installed in side of the in-draft wind tunnel of Mach 1.94. The maximum frequency of the energy deposition is limited up to 80. Time-averaged drag force is measured using a low friction piston which was backed by a load cell in a cavity as a controlled pressure. Stagnation pressure history, which is measured at the nose of the model, is synchronized with corresponding sequential schlieren images. With cylinder model, amount of drag reduction is linearly increased with input laser power. The power gain only depends upon the pulse energy. A drag reduction about 21% which corresponds to power gain of energy deposition of approximately 10 was obtained.

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Emission Characteristics of VOCs Distributions in Semiconductor Workplace (반도체 작업환경의 VOCs 농도분포 특성)

  • Lee, Jeong Joo
    • Journal of the Korean Society of Urban Environment
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    • v.18 no.4
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    • pp.503-509
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    • 2018
  • In this study, a Proton-Transfer Reaction-Time-of-Flight Mass spectrometer (PTR-TOF-MS) was used for the continuous monitoring of Volatile Organic Compounds (VOCs) emitted from semiconductor workplace such as photolithography (PHOTO), flat panel display (FPD), organic light emitting diode (OLED), etching (WET) process. The averaged VOCs mixing ratio in the such workplace, PHOTO was 6.5 ppm, FPH was 6.4 ppm, WET was 2.0 ppm and OLED was 1.3 ppm, respectively. The abundance of VOCs in the workplace were methyl ethyl ketone (MEK) with 2.8 ppm (69%) and acetaldehyde with 0.5 ppm (13.2%). Depending on the semiconductor process characteristics, various VOCs have been observed in the workplace. The VOCs mixing ratio are lower than the workplace regulation standard (TWA), it is necessary to continuously monitor and effectively manage these VOCs.

Study on the Skin-frictional Drag Reduction Phenomenon by Air Layer using CFD Technique (CFD 기법을 활용한 공기층에 의한 마찰항력 감소 현상 연구)

  • Kim, Hee-Taek;Kim, HyoungTae;Lee, Dong-Yeon
    • Journal of the Society of Naval Architects of Korea
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    • v.56 no.4
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    • pp.361-372
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    • 2019
  • The flow pattern of air layers and skin-friction drag reduction by air injection are investigated to find the suitable multiphase flow model using unstructured finite-volume CFD solver for the Reynolds-averaged Navier-Stokes equations. In the present computations, two different multiphase flow modeling approaches, such as the Volume of Fluid (VOF) and the Eulerian Multi-Phase (EMP), are adopted to investigate their performances in resolving the two-phase flow pattern and in estimating the frictional drag reduction. First of all, the formation pattern of air layers generated by air injection through a circular opening on the bottom of a flat plate are investigated. These results are then compared with those of MMkiharju's experimental results. Subsequently, the quantitative ratios of skin-friction drag reduction including the behavior of air layers, within turbulent boundary layers in large scale and at high Reynolds number conditions, are investigated under the same conditions as the model test that has been conducted in the US Navy's William B. Morgan Large Cavitation Channel (LCC). From these results, it is found that both VOF and EMP models have similar capability and accuracy in capturing the topology of ventilated air cavities so called'air pockets and branches'. However, EMP model is more favorable in predicting quantitatively the percentage of frictional drag reduction by air injection.

Dispersion of Standing Stones at Noseongsan(Mt.Noseong) and Aspect of the Stone Decorated Garden(Soo-suk Jeongwon) at Chongsuk-Sa(Chongsuk Buddhist Temple) in Nonsan City (논산 노성산(魯城山)의 입석(立石) 분포와 총석사(叢石寺) 수석(樹石)의 정원적 면모)

  • Rho, Jae Hyun;Huh, Joon;Jang, Il Young
    • Korean Journal of Heritage: History & Science
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    • v.43 no.1
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    • pp.160-189
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    • 2010
  • This study has been designed to grasp the present situation, shapes and meaning of the standing stones and rock pillars in the whole area of Noseong Mountain Fortress in Nonsan City which have never been academically reported yet. Accordingly, the research was carried out to grasp the spatial identity of Noseong Mt. and Noseong Mountain Fortress and the dispersion of standing stones scattered around inside and outside Noseong Mountain Fortress, while the shapes and structural characteristics of stones were investigated and analyzed focusing on Chongsuk Temple, which was considered to have the highest density of standing stones and greatest values for preservation as a cultural property. In consideration of the reference to the 'Top Sa' (tower temple) at the 'Bul Woo Jo' (Article about Buddhism Houses) of 'Shinjoong Dongguk Yeoji Seungram', theoretical existence of the temple according to surveying investigation, and the excavation records of roof tile pieces with the name of 'Gwan Eum Temple', it is presumed that there had been a Buddhist sanctum inside the fortress and it could be connected to the carved letters, 'Chongsuk Temple'. According the observation survey, the 6th place of standing stones among many other places inside the fortress shows that Chongsuk Temple appears to have the strong characteristics of artificially constructed space in consideration of the size of trees and stones, the composite trend of tree and stone composition, and trace of the adjacent well and strand and the construction of stairway leading to the stone gate. Along with the constellation of the Big Dipper carved on a rock at the same space, the stones, on which the letters of 'Shinseonam', 'Chilseongam' and 'Daejangam' were carved, including 'Chongsuksa', and the carved statue of Buddha, which was assumed to be Avalokitesvara Guan Yin, have offered clue which make it possible to infer that the space was a space for Chilseong and Mountain god(Folk Belief) that had originated from the combination of Buddhism, Taoism and folk religion. According to the actual measurement of standing stones at Chonsuk Temple, it was identified that there were big differences in height among 24 stones in total, ranging from 402~29cm and the averaged distance between each stone appeared to be 23.6cm. And the shape of stones appeared to be standing or flat, and various stones such as mountain-like stones and Buddha-like stones were placed in a special arrangement or assorted arrangement, but the direction of the stones had a consistency pointing to the west. And comparing to the trace of construction of ZEN Landscape Garden well known in the country, the three flat stones except for the standing and shaped stones appeared to have the shape of meditation statue, which is the typical formational factors of a ZEN Landscape Garden, on the basis of formational technique of stones. Among them, the flat stone facing the Buddhist saint statue, was formed by way of symbolization of three-mountain stone, which was assumed to be an offering stone for sacrificial food rather than carrying out ZEN Meditation. In consideration of the formation of standing stones at Chong-suk Temple, which was carried out in the composite stoning method based using the scalene triangle with ratio of 3:5:7 in order to seek the in-depth beauty based on the stone statues of three Buddhas where the three factors such as heaven, earth and humans are embodied in the elevated or flat formation, the stones at Chongsuk Temple and the space seemed to the trace of contracted garden construction that was formed with stones for a temple, so that could be used for ZEN meditation.