• Title/Summary/Keyword: stream side

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Numerical Study on Uniform-Shear Flow Over a Circular Cylinder (원형실린더를 지나는 균일전단 유동에 관한 수치연구)

  • Choi, Won-Ho;Kang, Sang-Mo
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.29 no.1 s.232
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    • pp.139-150
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    • 2005
  • The present study has numerically investigated two-dimensional laminar flow over a circular cylinder with a uniform planar shear, where the free-stream velocity varies linearly across the cylinder. Numerical simulations using the immersed boundary method are performed for the ranges of $50{\le}Re{\le}160,\;K{\le}0.2$, and B=0.1 and 0.05 where Re, K and B are the Reynolds number, the non-dimensionalized velocity gradient and the blockage ratio, respectively. Results show that the flow depends significantly on B as well as Re and K. It is found, especially, that the blockage effect accounts for some causes of apparent discrepancies among previous studies on the flow. With increasing K, the vortex shedding frequency and the mean drag stay nearly constant or slightly decrease whereas the mean lift, acting from the higher-velocity side to the lower, increases linearly. Flow statistics as well as instantaneous flow fields are presented to identify the characteristics of the flow and then to understand the underlying mechanism.

A Study on the Combustion Characteristics of Diffusion Flame Formed in the Wake of Cylindrical Bluff Body (원통형 보염기 후류에 형성되는 확산화염의 연소특성에 관한 연구)

  • An, J.G.;Lim, D.J.;Ro, T.S.;Song, K.K.
    • 한국연소학회:학술대회논문집
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    • 1998.10a
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    • pp.23-30
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    • 1998
  • The stabilization characteristics of diffusion flame formed in the wake of a cylindrical flame holder were investigated. Distribution of turbulence intensity, concentration distribution of combustion gas, and ion currents were measured. The turbulence intensity in the wake of cylindrical- game holder is increased with increase of diameter or blockage ratio of grid. If the auxiliary fuel is injected into recirculation zone, the concentration of $C_3H_8$ is high, but the concentration of $CO_2$ is low at the boundary of recirculation zone. The region with highest average value of ion currents in the middle of flame is moved to the upstream side by the turbulent components of main stream. The flame mass with partially active reaction is moved fast for uniform flow and turbulence generator G3, but the flame mass with relatively slow reaction is moved slowly for turbulence generator G1.

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An Experimental Study of Heat Transfer Characteristics on the Electronic Module Arrangement (전자모듈의 배열에 따른 열전달특성의 실험적 연구)

  • Lee, Dae-Hee;Lee, Dae-Keun;Cha, Yoon-Seok;Lee, Jun-Sik
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.32 no.6
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    • pp.407-412
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    • 2008
  • Heat transfer from three-dimensional heat-generating modules was investigated. Simulated electronic module in an array configured with dummy module elements were used to measure the average heat transfer coefficients. Various module arrangements were tested using module spacings of 0.85 and 1.15 cm for six Reynolds numbers ranging from 500 to 975. The results show that a module placed in-line with and upstream of a heated module results in the heat transfer enhancement due to high turbulence intensity prompted by upstream modules. The highest enhancement occurs when the separation distance between modules is close to the module length in the flow direction. The laminar flow was observed on the front of the first module, slow recirculation regions on the sides parallel to the airstream, and turbulent flow on the back side. It appears that the first module serves to trip the air stream and produce a high level of turbulence, which enhances the heat transfer rate downstream.

Application of the QUAL2Kw model to a Polluted River for Automatic Calibration and Sensitivity Analysis of Genetic Algorithm Parameters (오염하천의 자동보정을 위한 QUAL2Kw 모형의 적용과 유전알고리즘의 매개변수에 관한 민감도분석)

  • Cho, Jae-Heon
    • Journal of Environmental Impact Assessment
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    • v.20 no.3
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    • pp.357-365
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    • 2011
  • The QUAL2K has the same basic characteristics as the QUAL2E model, which has been widely used in stream water quality modeling; in QUAL2K, however, various functions are supplemented. The QUAL2Kw model uses a genetic algorithm(GA) for automatic calibration of QUAL2K, and it can search for optimum water quality parameters efficiently using the calculation results of the model. The QUAL2Kw model was applied to the Gangneung Namdaecheon River on the east side of the Korean Peninsula. Because of the effluents from the urban area, the middle and lower parts of the river are more polluted than the upper parts. Moreover, the hydraulic characteristics differ between the lower and upper parts of rivers. Thus, the river reaches were divided into seven parts, auto-calibration for the multiple reaches was performed using the function of the user-defined automatic calibration of the rates worksheets. Because GA parameters affect the optimal solution of the model, the impact of the GA parameters used in QUAL2Kw on the fitness of the model was analyzed. Sensitivity analysis of various factors, such as population size, crossover probability, crossover mode, strategy for mutation and elitism, mutation rate, and reproduction plan, were performed. Using the results of this sensitivity analysis, the optimum GA parameters were selected to achieve the best fitness value.

Numerical Study on NO Emission with Flue Gas Dilution in Air and Fuel Sides

  • Cho Eun-Seong;Chung Suk Ho
    • Journal of Mechanical Science and Technology
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    • v.19 no.6
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    • pp.1358-1365
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    • 2005
  • Flue gas recirculation (FGR) is widely adopted to control NO emission in combustion systems. Recirculated flue gas decreases flame temperature and reaction rate, resulting in the decrease in thermal NO production. Recently, it has been demonstrated that the recirculated flue gas in fuel stream, that is, the fuel induced recirculation (FIR), could enhance much improved reduction in NO per unit mass of recirculated gas, as compared to conventional FGR in air. In the present study, the effect of dilution methods in air and fuel sides on NO reduction has been investigated numerically by using $N_2$ and $CO_2$ as diluent gases to simulate flue gases. Counterflow diffusion flames were studied in conjunction with the laminar flamelet model of turbulent flames. Results showed that $CO_2$ dilution was more effective in NO reduction because of large temperature drop due to the larger specific heat of $CO_2$ compared to $N_2$. Fuel dilution was more effective in reducing NO emission than air dilution when the same recirculation ratio of dilution gas was used by the increase in the nozzle exit velocity, thereby the stretch rate, with dilution gas added to fuel side.

A Study on the Estimation of Initial Design-Width for Small Stream in the West Side Area of GangWon Provinc (강원영서지역 소하천의 초기계획하폭 산정에 관한 연구)

  • Bang, Yoon Hyun;Kim, Sang Ho
    • Proceedings of the Korea Water Resources Association Conference
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    • 2017.05a
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    • pp.447-451
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    • 2017
  • 하천은 지역별, 하천별 고유한 유역형상과 유출특성을 갖고 있어 계획과 관리를 위한 계획하폭 산정공식은 지역고유의 수문학적, 지역적 특성에 따라 달라야 하지만, 현재 적용되고 있는 설계기준의 계획하폭 산정공식은 최근 강우 경향 및 하천 주변 토지이용 고도화 등의 지역특성 여건변화가 고려되지 못하고 있는 실정이다. 특히 소하천의 경우에는 중 대규모의 하천과 달리 계획하폭 산정을 위한 지역별 매개변수의 편차가 커기존 산정된 공식을 활용함에 있어 어려움이 따르며, 토지이용 효율성 및 치수 경제성이 낮은 비효율적 계획하폭이 결정될 개연성이 있는 것으로 판단된다. 따라서 본 연구에서는 한반도 내륙기후특성을 가지는 강원영서지역 소하천에 대한 초기계획하폭 제안식을 산정하기 위해 계획홍수량(Q), 유역면적(A), 하상경사(S)에 대한 회귀분석을 실시하였다. 이를 통해 산정된 관계식은 기초 매개변수만 가지고 쉽게 초기계획하폭을 산정할 수 있어 지역 및 하천특성에 부합되는 개수계획 수립에 활용할 수 있다.

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Characteristics of Droplet Properties in the Two-Phase Spray into a Subsonic Cross Flow

  • Lee, I.C.;Cho, W.J.;Koo, J.Y.
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2008.03a
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    • pp.358-363
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    • 2008
  • The spray cross-section characteristics of two-phase spray that using external-mixing nozzle injected into a subsonic cross flow were experimentally studied with various ALR ratio that is $0{\sim}59.4%$. Suction type wind tunnel was used and experiments were conducted to ambient environment. Several plain orifice nozzles with L/d of 30 and orifice diameter of 0.5 mm and orifice length 1.5 mm were tested. Free stream velocity profiles at the injection location were measured using hot wire. Spray images were captured to study collision point and column trajectory. Phase Doppler particle analyzer(PDPA) was utilized to quantitatively measuring droplet SMD, volume flux. Measuring probe of PDPA positions was moved 3-way transverse machine. SMD distributions were layered structure and peaked at the top of the spray plume and low value at bottom of the spray. Volume flux of spray was distributed to the two side region and volume flux quantity decreased when ALR ratio increased. It was found that the perpendicularly injected two-phase spray jet of external mixing into a cross flow showing that mistlike spray moved away from the test section bottom region.

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Epidemiological Studios on Clonorchis sinensis Infection along the Nam-river in Gyeongnam Province, Korea (남강유역 간흡충감염의 역학적 조사연구)

  • 배경훈;안영겸
    • Parasites, Hosts and Diseases
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    • v.21 no.2
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    • pp.116-186
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    • 1983
  • An epidemiological study on Clonorchis sinensis infection along the Nam-river (total length ; 186km) flowing in Gyeongsang-nam-do, southern part of Korea, was carried out. Formalin-ether concentration technique and Stoll's egg counting method were employed to figure out the prevalence of C. sinensis infection. For the detection of cercariae from Parafossarulus sp., the snail host of C. sinensis, each snail was placed in aerated tap water, and examined for expelled cercariae. For observing the metacercariae the fresh water fish favorably eaten in raw conditions wore prepared by means of pressing the muscles between two slide glasses and/or by digesting them with artificial gastric juice. The fresh water fish were fed to the rabbits to get the worms and to identify the morphology of adult C. sinensis. The results are summarized as follows: 1. Overall Prevalence of C. sinensis infection was 38.75 from 5,291 examinees; 44.15 (1,408 out of 3,196) in male and 30.4% (637 out of 2,095) in female. 2. The prevalence rates were 42.0% at the upper stream, 41.2% around the vicinity of Jinyanglake, 34.2% at Jinju city, 34.2% at middle stream and 40.3% at down stream regions, respectively. 3. By age, the highest positive rate (53.4∼54.3%) was observed in 30 to 59 years of age. In this age group, the rate in males was 59.7∼62.2%, and in females 42.2∼44.4%, In the age group of less than 19 years it was 7.5∼20.9%. 4. By social strata, the positive rate was 16.5% in the primary school children, 22.6% in school students, 46.2% in teachers and local officers and 49.6% in the general inhabitants. 5. The quantitative examinations with the stool collected from clonorchiasis cases revealed that the light infection (less than 4,000/EPG) was 53.6%, moderate infection (4,001∼10,000 /EPG) 30.3% and heavy infection (more than 10,001/EPG) 16.1%, respectively. More than half of total cases examined were light infection, and 73.2% of female examinees were lightly infected with this cuke. 6. The average value of EPG was 4,963 (male, 6,057; female, 2,557 and the highest value was obtained from the age group of 30 to 59 years (5,240∼6,454). 7. The prevalence of Metagonimus yokogawai infection in humans was 5.5%, and 89.8% of metagonimiasis cases wore double-infected arith C. sinensis. The highest prevalence rate was observed in Jinju city (11.2%). 8. Total of 5,005 Parafossarulus sp., the snail intermediate host of C. sinensis, were examined for the detection of cercariae. The cercarial expulsion rate was 0.34%, and the snails collected in Jin-yang-lake side and in the down stream expelled mainly the cercariae of C, sinensis. 9. About 788 cercariaejday (range: 127∼1,503) were expelled daily from a snail naturally infected with C. sinensis. The snails which released more than 1,000 cercariae/day were 30.8% out of total collected. A snail uniquely released 5,840 cercariae/day in this study. 10. The other trematode cercariae besides C. sinensis were also detected, and the rates out of total snails were the cercariae of Losogenes liberum 6.71%, Cyathocotyle orientalis 0.26%, Notocotylus attenuatus 2.52% and Mucobucaris 0.54%, 11. Ten out of 18 species of fresh water fish caught along the river harbored the metacercariae of C, sinensis. The highest rate of metacercarial infection in fish was detected in Pseudorasbora larva (85.9%). The fish mainly eaten by the inhabitants along the Nam-river, and the metacercarial infection rates were: Zacco platypus 8.0%, Hemibarbus sp. 18.2∼26.7%, Gnathepcgcn sp. 37.5%, Ischikauia steenackeri 42.9% and Pseudogobio esocinus 16.7%. 12. Out of 36 P. larva, the number of metacercariae were about 109 (ranEe; 18∼446) per fish and 27 per gram of flesh. The fish caught in spring harbored the highest number of metacercariae. As indicated above, the prevalence of C. sinensis infection in the inhabitants residing around the Nam-river was relatively high. The farther toward the upper stream areas, the higher was the positive rate of C. sinensis infection, and most of clonorchiasis cases were lightly infected. The snail hosts of C. sinensis distributed all around the Nam-river. Several species of freshwater fish were infected with the metacercariae of C. sinensis and the infection rates were relatively high. To prevent C. sinensis infection in the endemic areas, the effective health education system is suggested as a control measure, although mass treatment is also expected to be useful, using chemotherapeutic agents such as "praziquantel", a recently developed anthelminthic for C. sinensis inftraction.

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A Study on the Byung-Su Jo's House in Yongyu Island (인천 용유도의 조병수가옥에 대한 연구)

  • Han, Jong-Koo
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.18 no.8
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    • pp.332-337
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    • 2017
  • This study investigates the site and architectural space of Byung-Su Jo's traditional house on Yongyu Island in Incheon. The house is located on a peaceful, warm site that is well protected by surrounding mountains, such as Hyunmubong to the rear, Jwacheongyong to the left, Wubackho to the right, and Ansan in front. The house was designed with an open layout with a sarangchae and anchae. There is a spring on the left side of the sarangchae, and a stream auspiciously flows from the west to the east in front of the sarangmadang. The house generally faces south, but to avoid pressure by the height of Ansan in the south direction, it is slightly turned to the east. There is a wide, rectangular pond that covers the pungsu weak point of the empty open view between the right and left mountains. The sarangchae space is composed of front 6 Gan and side 3 Gan. The anchae space is also composed of front 6 Gan and side 3 Gan,and it has a typical L-shaped anchae layout for the middle region of Korea. There is no shrine in the backyard, where yongmag is descending from hyunmubong, and a jangdokdae is installed to the west direction of the anbang due to narrow and slope backyard space.

A Reinvestigation on Key Issues Associated with the Yimjin(1712) Boundary Making and Demarcation: The Distribution of Soil Piles and the Location of 'Suchul(水出)' written on the Mukedeng's Map (임진정계 경계표지 토퇴의 분포와 목극등 지도에 표시된 '수출(水出)'의 위치)

  • Lee, Kang-Won
    • Journal of the Korean Geographical Society
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    • v.52 no.1
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    • pp.73-103
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    • 2017
  • This paper reports the distribution of soil piles set up during the Yimjin(1712) Boundary Making and Demarcation(YBMD). Through the survey on the distribution of soil piles the location of 'Suchul'(水出: seepage zone) could be identified. The endpoint soil pile set up on the east-south bank of Heishigou(黑石溝) stream locates on $42^{\circ}04^{\prime}20.09^{{\prime}{\prime}}N$, $128^{\circ}16^{\prime}08.42^{{\prime}{\prime}}E$. The west beginning point of soil piles distributed in the south side of Tuhexian road locates on $42^{\circ}02^{\prime}20.14^{{\prime}{\prime}}N$, $128^{\circ}18^{\prime}53.40^{{\prime}{\prime}}E$. And the east endpoint of them locates $42^{\circ}01^{\prime}32.97^{{\prime}{\prime}}N$, $128^{\circ}21^{\prime}24.59^{{\prime}{\prime}}E$. From the west beginning point to the soil pile located in 2.1km distance from the beginning point, the distribution direction is west-east. The direction of soil piles after them is northwest-southeast. The total real length of soil piles distributed in the south side of Tuhexian(圖和線) road is about 4.2km more or less. The location of 'Suchul' written on the Mukedeng's map locates on $42^{\circ}01^{\prime}30.36^{{\prime}{\prime}}N$, $128^{\circ}21^{\prime}3.62^{{\prime}{\prime}}E$, The point locates in southeastward 222m distance from the soil piles endpoint of the south side of Tuhexian road. In reference of these reports this paper develops some reinterpretation on the YBMD.

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