• Title/Summary/Keyword: Entrance Region

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Measurement of Inward Turbulent Flows in a Rotating with Square Cross-Section $90^{\circ}$ Duct (회전하는 정사각단면 $90^{\circ}$ 곡덕트 내 내향 난류유동 측정)

  • Kim, Dong-Chul;Chun, Kun-Ho;Choi, Young-Don
    • Proceedings of the KSME Conference
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    • 2000.11b
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    • pp.627-632
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    • 2000
  • Developing turbulent flows in a rotating 90 degree bend with square cross-section were measured by a hot-wire anemometer. The six orientation hot-wire technique was applied to measured the distributions of 3 mean velocities and 6 Reynolds stress components. Effects of Coriolis and centrifugal forces caused by the curvature and rotation of bend on the mean motion and turbulence structures were experimentally investigated Productive addition of Coriolis and centrifugal forces to the outward radial direction in the entrance region of bend increases the secondary flow intensity according to the rotational speeds. However, after 45 degree of bend, centrifugal force due to the rotation of bend may promote the break down of counter rotating vortex pair into multi-cellular pattern, thereby decreasing the production rate of turbulence energy and Reynolds stresses.

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Numerical Analysis of Fully Developed Turbulent Recirculating Flow and Heat Transfer for The Periodic Variations of Cross Sectional Area (周期的으로 斷面이 變化하는 完全確立된 亂流再循環 流動과 亂流熱傳達의 數値分析)

  • 이병곤;최영돈
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.10 no.1
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    • pp.138-149
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    • 1986
  • A numerical method is developed for the solution of fully developed turbulent recirculating flow whose cross-sectional area varies periodically. This enalbes the flow field analysis to be confined to a single isolated module, without involvement with the entrance region problem. This method are applied to the analysis of the turbulent flow field and heat transfer in artificially roughened annulus with repeated square rib.

An Experimental Investigation on Combined Convective Heat Transfer of NonNewtonian Fluids (비뉴톤유체의 복합대류 열전달에 관한 실험적 연구)

  • 김용진
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.7
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    • pp.1770-1779
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    • 1995
  • A combined convective heat transfer study for non-Newtonian fluids was experimentally performed in uniformly heated horizontal tubes with laminar flow in the thermal entry region. Velocity profiles were fully developed at the entrance of the heated sections in the tubes. Aqueous solutions of sodium carboxymethylcellulose(CMC ) were used; their behavior showed a reasonably good fit into the power-law model, .tau.=K.gamma.$^{n}$ . The test sections were made of copper with inside diameters of 3.23 cm and 5.042 cm and lengths of approximately 300 cm. Most experimental runs displayed noticeable secondary flows caused by buoyancy ; when present, secondary flows caused significant increase in the rate of heat transfer over the purely forced-convection case. A correlation, which relates the rate of heat transfer for flows with temperature-dependent properties, free convection effects, and non-newtonian effects, was suggested.

Deformation of multiple non-Newtonian drops in the entrance region

  • Kim, See-Jo;Kim, Sang-Dae;Youngdon Kwon
    • Korea-Australia Rheology Journal
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    • v.15 no.2
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    • pp.75-82
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    • 2003
  • In this study, with the finite element method we numerically investigate the deformation of liquid drops surrounded by Newtonian or non-Newtonian viscous medium in the axisymmetric contraction flow. 1, 2 or 4 Newtonian or non-Newtonian drops are considered and the truncated power-law model is applied In order to describe non-Newtonian viscous behavior for both fluids. In this type of flow the drop exhibits considerably large deformation, and thus techniques of unstructured mesh generation and auto-remeshing are employed to accurately express the fluid mechanical behavior. We examine the deformation pattern of liquid drops with viscosity dependence different from that of the surrounding medium and also explain their interactions by comparing relative position or speed of drop front.

Prediction of Roll Force Profile in Cold Rolling - Part I : Development of a Mathematical Model (냉간 압연에서 압하력 분포 예측 - Part I : 수식 모델 개발)

  • Nam, S.Y.;Hwang, S.M.
    • Transactions of Materials Processing
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    • v.28 no.4
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    • pp.190-196
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    • 2019
  • The capability of accurately predicting the roll force profile across a strip in the bite zone in cold rolling process is vital for the calculation of strip profile. This paper presents a derivation of a precision mathematical model for predicting variations in the roll force across a strip in cold rolling. While the derivation is based on an approximate 3-D theory of rolling, this mathematical model also considers plastic deformation in the pre-deformation region which is located close to the roll entrance before the strip enters the bite zone. Finally, the mathematical model is expressed as a boundary value problem, and it predicts the roll force profile and tension profile in addition to lateral plastic strain profile.

Coastal Circulation and Bottom Change due to Ocean Resort Complex Development

  • Kim, Pill-Sung;Lee, Joong-Woo;Kim, Jeong-Seok
    • Journal of Navigation and Port Research
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    • v.36 no.7
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    • pp.585-590
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    • 2012
  • On the basis of the potentials for the growth of local economy and the result of investigation of the ocean space development status, an ocean resort complex was proposed at the small harbor with a parallel beach in the east coast of Korea. As the development plan needs to reclaim the noticeable amount of coastal water area together with the applied shore facilities, it is necessary to analyze their impacts. Here, it was intended to analyze the coastal environment change such as water circulation and bottom change because of the development plan. A horizontal two-dimensional numerical model was applied to represent the combined impact of wind waves and tidal currents to sediment transport in that coastal region. Based on the result of 30 days tidal current simulations considering major four tidal components of $M_2$,$S_2$,$K_1$ and $O_1$ for the upper and lower boundaries and wind field data, bottom change was discussed. Flow velocities were not changed much at outer breakwater of Yangpo harbor. Bottom was eroded by maximum 1.7m after construction but some locations such as lee side of outer breakwater and some islets near the entrance shows isolated accretions. Although it needs more field observations for bottom change in the period of construction, the numerical calculation shows that there exist small impacts near the entrance area and coastal boundaries because of the development.

Design of flat-field XUV spectrograph with a toroidal mirror (광집속 Toroidal mirror를 이용한 평면결상)

  • 이병훈;최일우;남창희
    • Korean Journal of Optics and Photonics
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    • v.3 no.2
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    • pp.77-85
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    • 1992
  • The design of a flat-field XUV spectrograph is optimized for a high throughput, aberration-corrected spectral image in the wavelength region of 50-300 $\AA$ The varied-line spacing (VLS) concave grating theory for an XUV spectrograph with a toroidal mirror in front of an entrance slit is derived. Since the derived theory includes the arbitrary shaped source, it is able to correct the limit of the simple optimization theory which considers only a point source at the center of the entrance slit. The reflection matrix at the toroidal mirror and the diffraction matrix at VLS grating are derived and compared with those of a holographic grating. The absolute energy efficiency of a flat-field spectrograph is calculated by considering the reflectivities of the toroidal mirror and the Au coated concave grating and the grating efficiency. The alignment sensitivity of the toroidal mirror and the concave grating is investigated, and the method to achieve the best imaging of XUV spectrum is discussed. The calculated resolving power of the flat-field XUV spectrograph is more than 4000 in the aberration-corrected wavelength range. The focused spot size at the dispersion plane is less than $20\mu \textrm m\times \mu \textrm m$at the wavelength 100$\AA$ It is shown that a high throughput characteristic can also be achieved through a careful adjustment of alignment parameters.

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Analysis of the Entrance Surface Dose (ESD) and Contrast Usage of Trance Femoral Cerebral Angiography (TFCA) and Cerebral Computed Tomographic Angiography (CCTA) for Cerebrovascular Disease Examining (뇌혈관 질환 검사를 위한 뇌혈관 조영술(TFCA)과 뇌혈관 전산화 단층 촬영 검사(CCTA)의 입사표면선량(ESD) 및 조영제 사용량 분석)

  • Seo, Young-Hyun;Hong, Cheon-Gi;Song, Jong-Nam
    • Journal of the Korean Society of Radiology
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    • v.13 no.4
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    • pp.495-502
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    • 2019
  • A typical cerebrovascular disease among cerebrovascular diseases is vascular diseases such as cerebral infarction, cerebral hemorrhage, cerebral aneurysm, cerebrovascular stenosis. If the disease occurs and causes cerebral damage, it may be difficult to recover completely. So that, Must continue to perform health care through examination early. In particular, Because most cerebrovascular disease examining use radiation equipment and Thus this study was to find out how to select about the optimal examining method and X-ray dose decrease method among different examining method though comparison and analysis for the entrance surface dose (ESD) on cerebrovascular examining with Trance Femoral Cerebral angiography (TFCA) and Cerebral Computed Tomographic Angiography (CCTA). Also, want to find out how to select about the optimal examining method for worried patient that contrast medium side effect though measuring and evaluating for contrast usage. Data were collected from 70 patients (43 males and 27 females) who underwent CCTA at Yeosoo region hospital from June 2018 to December 2018 and 61 patients (34 males and 27 females) who underwent TFCA at Pyeongtaek region hospital from June 2018 to November 2018. ESD analysis method collected retrospective data though M-view and PACS PLUS program, Used contrast usage measuring method did reality measuring method. In the analysis using SPSS, the ESD of TFCA was $245.74{\pm}71.91$, which was $32.05{\pm}7.74$ lower than the dose of $277.79{\pm}79.65$ of CCTA ESD, and statistically significant at t = 3.249, p = 0.017 (p<0.05). As a result of the comparison of the total amount of contrast agent, the mean contrast agent used in TFCA was $55.05{\pm}17.68ml$, which was about 14.95 smaller than the amount of contrast agent used in CCTA, and statistically significant t = -4.548, p<0.001. In conclusion, the ESD of TFCA was statistically significantly lower than that of CCTA, and also the used contrast usage was significantly tiny than that of CCTA. Therefore, Select the method to increase the utilization of TFCA for cerebral disease examining, we can consider X-ray dose decrease method at the same time as to decrease side effect of contrast medium.

A Study on the composition factors for making-up Urban image -with special reference to the facade and sign (도시환경 이미지 조성을 위한 구성요소에 관한 연구 -Facade와 Sign(옥외광고물)을 중심으로-)

  • 우영희
    • Archives of design research
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    • v.13 no.2
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    • pp.133-143
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    • 2000
  • Recently there are increasing demands for establishing its peculiar city image in Korea. In establishing a urban image, streetscapes of various functional regions in city have very important roles. And many streetscape were designed and are under design for that purpose. There are many factors involved in the image-generation of streetscape, and the facade is one of the most important factors. In this study, we surveyed many factors in the city-regions of various functions to find out desirable characteristics of facade for each region. And we are going to use there findings as a basic data in the future streetscape design. We selected traditional region(Insadong, Chongro-gu, Seoul), apartment-type residential region (Apkujung-dong, Kangnam-gu, Seoul), and newly developed-downtown (Dunsan-dong, Seo-gu, Daejun) as streetscapes of various functions for facade study. Texture, color, form, size, structure and location of the following facade components were surveyed and analyzed. The surveyed components were window, entrance, equipment, signboard, show window.

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The Ruling System of Silla to Gangneung Area Judged from Archaeological Resources in 5th to 6th Century (고고자료로 본 5~6세기 신라의 강릉지역 지배방식)

  • Shim, Hyun Yong
    • Korean Journal of Heritage: History & Science
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    • v.42 no.3
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    • pp.4-24
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    • 2009
  • This paper examined archaeological resources that discuss how Silla entered the Gangneung area, the coastal region along the East Sea that has been excavated most actively. Silla expanded its territories while organizing the its system as an ancient state and acquired several independent townships in various regions, stretching its forces to the East Sea area faster than any other ancient states of the time. In particular, many early relics and heritages of Silla have been found in Gangneung, the center of the East Sea area. Many archaeological resources prove these circumstances of that time and provide brief texts that are valuable for our interpretation of historical facts. In this respect, it was possible for me to examine these resources to answer my question as to why early relics and heritages of Silla are found in the Gangneung area. Based on my research on Silla's advancement into the Gangneung area, I have acquired the following results: How did Silla rule this area after conquering Yeguk in the Gangneung area? After conquering the Gangneung area, Silla attempted an indirect ruling at first. Later, Silla adopted a direct ruling system. I divided the indirect ruling period into two phases: introduction and settlement. In detail, Silla's earthenware and stone chamber tombs first appeared in Hasi-dong in the fourth quarter of the 4th Century and the tombs spread to Chodang-dong in the second quarter of the 5th Century. A belt with dragon pattern openwork, which seems to be from the second quarter of the 5th Century, was found to tell us that the Gangneung region began receiving rewards from Silla during this time. Thus, the period from the fourth quarter of the 4th Century to the second quarter of the 5th Century is designated as the 1st Phase (Introduction) of indirect ruling in terms of aechaeological findings. This is when Silla was first advanced to the Gangneung area and tolerated independent administration of the conquered. In the third and fourth quarters of the 5th Century, old mound tombs appeared and burials of relics that symbolized power emerged. In the third quarter of the 5th Century, stone chamber tombs were prevalent, but wooden chamber tombs, stone mounded wooden chamber tombs, and lateral entrance stone chamber tombs began to emerge. Also, tombs that were clustered in Hasi-dong and Chodang-dong began to scatter to Byeongsan-dong, Yeongjin-ri, and Bangnae-ri nearby. Steel pots were the symbol of power that emerged at this time. In the fourth quarter of the 5th Century, stone chamber tombs were still dominating, but wooden chamber tombs, stone mounded wooden chamber tombs, and lateral entrance stone chamber tombs became more popular. More crowns, crown ornaments, big daggers, and belts were bestowed by Silla, mostly in Chodang-dong and Byeongsan-dong. The period from the third quarter to the fourth quarter of the 5th Century was designated as the 2nd Phase (Settlement) of indirect ruling in terms of aechaeological findings. At this time, Silla bestowed items of power to the ruling class of the Gangneung area and gave equal power to the rulers of Chodang-dong and Byeongsan-dong to keep them restrained by each other. However, Silla converted the ruling system to direct ruling once it recognized the Gangneung area as the base of its expedition of conquest to the north. In the first quarter of the 6th Century, old mound tombs disappeared and small/medium-sized mounds appeared in the western inlands and the northern areas. In this period, the tunnel entrance stone chamber tombs were large enough for people to enter with doors. A cluster of several tunnel entrance stone chamber tombs was formed in Yeongjin-ri and Bangnae-ri at this time, probably with the influence of Silla's direct ruling. In the first quarter of the 6th Century, Silla dispatched officers from the central government to complete the local administration system and replaced the ruling class of Chodang-dong and Byeongsan-dong with that of Silla-friendly Yeonjin-ri and Bangnae-ri to reorganize the local administration system and gain full control of the Gangneung area.