• Title, Summary, Keyword: 입구 부

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세계의 동굴 개관<2> 미대륙의 (남북아메리카)의 동굴

  • 한성인;홍승달
    • Journal of the Speleological Society of Korea
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    • v.29 no.30
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    • pp.79-86
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    • 1992
  • 드문드문 펼쳐진 켄터키의 한 시골에 구부러 흘러내리는 그린천이 있다. 흐름은 유연하고, 강가에는 수목이 무성하다. 그곳 숲에 가리워진 커다란 물이 없는 동굴의 입구가 있다. 반대편에는 지평선 저쪽까지 푸른 초원이 펼쳐져 있다. 특별히 이렇다할 정도의 풍경은 아니지만, 여기에 세계 제일의 경이로운 동굴의 하나를 볼 수 있다. 이 동굴이 맘모스(매머드)동굴의 입구다. 여기서부터 전장 290km의 새끼모양의 동굴이 시작되는 것이다. 세계 최장의 동굴이다. 이 거대한 동굴은 관목이 번성한 프린트 대지와 맘모스 케이프대지, 그 사이를 침식하고 있는 호친스 계곡의 지하에까지 펼쳐진다. 10개 이상의 입구가 있고, 크고 넓은 광장, 폭넓고 긴 터널, 비뚤비뚤한 지하천이 계속된다. 수직굴은 적고, 또 낙차도 적다. 그 때문에, 물이 없는 주굴부는 이상적인 관광동굴로 개발되어 있다. 케이브대지에는 여기저기에 동굴의 일부가 관광에 이용되고 있다. 한 관광동굴에서는, 벌꿀통과 같은 동굴안을 걸어가기 위해 4시간 이상 걸린다. 프린트대지 쪽은 동굴이 복잡하고, 지금도 많은 새로운 동굴이 발견되며, 되어 지고 있다. (중략)

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A Computation of Viscous Flows on an Axisymmetric Body (축 대칭 물체 주위의 점성유동 계산)

  • Jae-Moon Lew
    • Journal of the Society of Naval Architects of Korea
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    • v.28 no.1
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    • pp.19-26
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    • 1991
  • The complete, fully-elliptic Reynolds-averaged Navier-Stokes equations have been solved using a two-layer model, in the $\kappa-\varepsilon$ turbulence model, for the axisymmetric body. Numerically generated boundary-fitted coordinate system and the finite analytic methods are used to solve the governing equations. Calculations are started after the middle body with given inlet conditions. The velocities and the turbulent quantities at the inlet section are specified by solving the boundary layer equations or by standard flat-plate boundary profiles. The effects of the inlet conditions on the solution are investigated.

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Synthetic Turbulence Effect in Subsonic Backward Facing Step Flow Using LES (LES을 이용한 후향 계단 유동에서의 Synthetic turbulence 효과 연구)

  • Ahn, Sang-Hoon;Sung, Hong-Gye
    • Journal of Aerospace System Engineering
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    • v.13 no.6
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    • pp.1-8
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    • 2019
  • The synthetic turbulence generation model for inlet boundary conditions of subsonic Backward Facing Step (BFS) was investigated. The average u-velocity and Reynolds stress at inlet boundary follows experimental data. Synthetic Eddy Method (SEM), random noise, and uniform flow conditions were implemented relative to the synthetic turbulence generation method. A three dimensional Large Eddy Simulation (LES) was applied for turbulent flow simulation. Turbulent and mean flow characteristics such as flow reattachment length, velocity profiles, and Reynolds stress profiles of BFS were compared with respect to the turbulent effects.

Effects of Prandtl Numbers on Heat Transfer of Backward-Facing Step Laminar Flow with a Pulsating Inlet (입구유동 가진이 있는 층류 후향계단 유동에서 열전달에 대한 프란틀수 효과해석)

  • Kim, Won-Hyun;Park, Tae-Seon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.36 no.9
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    • pp.923-930
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    • 2012
  • The wall heat transfer of backward-facing step laminar flows with different Prandtl numbers and a pulsating inlet is investigated by unsteady simulations. The inlet is perturbed by the variation of frequency and amplitude. Temperature-dependent transport properties are adopted. Various characteristics of the wall heat transfer are explained by the variation of the thermal boundary layer. For Pr < 1, the wall heat transfer of temperature-dependent properties is decreased compared to that of constant properties, whereas it increases for Pr < 1. In addition, the wall heat transfer increases depending on the pulsating amplitude. However, the results of frequency variation for St < 0.2 show that the heat transfer is strongly enhanced at a specific frequency. In particular, the increase in the wall heat transfer is strongly related to the root mean square of the fluctuations of the reattachment length.

Numerical Analysis of the Blood Flow in the Korean Artificial Heart Using Two Dimensional Model (2차원 모델을 이용한 한국형 인공심장 내 혈액 유동에 대한 수치적 해석)

  • 박명수;심은보;고형종;사종엽;박찬영;민병구
    • Journal of Biomedical Engineering Research
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    • v.24 no.4
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    • pp.301-307
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    • 2003
  • In this study, we Presented computational results on the blood flow in the sac of the Korean artificial heart. Two dimensional unsteady flow was assumed and we utilized a finite element commercial code ADINA to simulate the blood flow. Rigid body-solid contact were considered between the actuator and the blood sac and fluid-structure interaction between the blood and the sac. The three geometric models proposed in the design process were simulated to assess the hemodynamic characteristics of the models According to the computational results, a strong flow to the outlet and a stagnated flow region near the inlet were observed during systole. The sac was filled with blood and recirculating flow was generated near the outlet during diastole. Shear stress during systole had its extreme values near the outlet edge whereas the magnitude of shear stress values were relative)v high near the inlet edge and the contacting surface with the actuator.

Effect of Fuel Equivalence Ratio on Scramjet-to-Ramjet Mode Transition (스크램-램제트 모드 천이에 미치는 연료 당량비의 영향)

  • Ha, Jeong Ho;Yoon, Youngbin;Ladeinde, Foluso;Kim, Tae Ho;Kim, Heuy Dong
    • Journal of the Korean Society of Propulsion Engineers
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    • v.22 no.1
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    • pp.45-51
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    • 2018
  • The generation mechanism of NAR is not yet understood. In the present study, an in-depth analysis of the computational results previously obtained by the authors is conducted to investigate the flow mechanism responsible for NAR. A theoretical analysis has also been performed to understand the gas dynamic features during transition from scramjet to ramjet mode. It is known that there exists a critical value of the fuel equivalence ratio at which the flow states at the inlet of isolator remain unchanged. An increase in the equivalence ratio over the critical value leads to a sudden change in the static pressure and the Mach number at the inlet of the isolator, which is responsible for the generation of NAR.

Enhancement of the Performance a Centrifugal Compressor in an Automobile Turbocharger by Modifying the Circumferential Inlet Height of Volute (원주방향 볼류트 입구 높이를 수정한 자동차용 터보차저 원심압축기의 성능 향상)

  • Zhou, Tianjun;Lee, Geun Sik
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.38 no.2
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    • pp.115-120
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    • 2014
  • To enhance the performance of an automobile turbocharger compressor, the circumferential inlet heights of the volute were modified and the flow field for the combined region of the diffuser and volute was numerically investigated using commercial software. Basically, a well-designed volute should have a high pressure recovery coefficient and a low loss coefficient for the total pressure. In this study, two circular volutes with the same cross sectional shape and tongue angle, but circumferentially different volute inlet heights, were selected. One volute had the middle inlet in the cross-section at the circumferential angle of $90^{\circ}$ but gradually lower inlet heights for the angles between $90^{\circ}$ to $360^{\circ}$ with respect to the cross sectional center of the volute, while maintaining the same height between the tangential line connecting the lowest positions of the cross section and the line connecting the volute inlets in the circumferential direction (case 1 volute). The other volute has an inlet height that is 2 mm lower than in case 1 volute such that the tongue section has a tangential inlet (case 2 volute). The results showed that the case 2 volute had a higher total pressure ratio because of its higher pressure recovery coefficient and higher isentropic efficiency, resulting from the lower loss coefficient along the circumferential position than the case 1 volute.

Microbial structures and their distributions in cave tufa formations from a twilight zone of the Baeg-nyong Cave (백룡동굴 입구부 튜파(tufa)의 미생물 구조와 그 분포 특성)

  • Jung, Da-Yea;Jo, Kyoung-Nam;Lee, Jung-Shin;Park, Shinae
    • Journal of the Geological Society of Korea
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    • v.53 no.5
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    • pp.743-758
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    • 2017
  • Microbial mats which formed at various terrestrial environments including the Earth's critical zone have a significant implication on the relationship between microbial activities and formations (and/or degradations) of minerals. Up to date, however, there is no geological survey for the microbial mats of tufa deposits in a twilight zone of Korean limestone caves. In this study, we aimed to report a variety of microbial structures and their distributions on tufa deposits in the Baeg-nyong Cave (Natural monument no. 260), Pyeongchang, South Korea. The sedimentary petrographic results for 7 tufa specimens collected near the cave entrance show that both of clotted and filamentous textures are largely dominant and their detailed types are different from each other. These characteristics of the tufa deposits are clearly different from those of the typical meteoric speleothems composed mainly of clean carbonate crystals and may indicate the past presence of microbial mats on the surface. Through the scanning electron microscopy, we have identified the various shapes of microbial structures including diatoms, hyphal filaments and coccoids. The microbial structures observed in this study have been classified to 2 and 7 types of coccoids and filaments, respectively, based on shape, size and arrangements between individual structures. Interestingly, our results show that the diversity of microbial structures in the Baeg-nyong Cave is gradually increasing to the inner cave with a distinct threshold area which is abruptly decreased in the microbial structural diversity. This may imply that an entrance area of the limestone cave is one of the microbe growth stimulating environments and has been affected by complex factors on geological, geographical and micro-meteorological conditions.

Effect of Inlet Humidity Condition at Cathode Side on Performance of a Polymer Exchange Membrane Fuel Cell (캐소드극 입구 가습 조건이 고분자 전해질 연료전지의 성능에 미치는 영향)

  • Moon, Cheor-Eon;Lee, Seo-Hee;Ko, Dong-Soo;Yang, Jang-Sik;Choi, Gyung-Min;Kim, Duck-Jool
    • Proceedings of the KSME Conference
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    • pp.3423-3428
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    • 2007
  • This paper shows that inlet humidity condition at cathode side is one of dominant parameters affecting the performance of PEMFC. To investigate effects of inlet humidity condition, the performance measurements were conducted for a single PEMFC with two operating variables : cathode relative humidity and dry condition in anode dry. The fuel cell employed for the experiments is a unit PEMFC with a 25$Cm^2$, Nafion$^(R)$112 membrane. As a result of this study, the cell performance is getting higher by increasing inlet humidity condition at cathode side. The cell performance is different from each operating temperature an it has maximum30% higher than dry condition at 60$^{\circ}C$ operating temperature with 80% relative humidity.

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Optical Resource Reservation Protocol for OBS Networks (OBS 네트워크를 위한 광 자원 예약 프로토콜)

  • 엄태원;최준균
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.40 no.10
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    • pp.43-50
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    • 2003
  • This paper describes the optical resource reservation protocol for Optical Burst Switching(OBS) networks, in which the burst sending time and the burst size at an ingress node are determined by the available resources between the ingress and egress nodes. Our scheme attempts to improve the burst contention resolution and optical channel utilization. We analyze the performance of the optical resource reservation protocol by using NS2 simulator.