• Title/Summary/Keyword: momentum exchange

Search Result 88, Processing Time 0.024 seconds

GENERAL RELATIVISTIC RADIATION HYDRODYNAMICS: FREQUENCY-INTEGRATED RADIATION MOMENT FORMALISM

  • Park, Myeong-Gu
    • Journal of The Korean Astronomical Society
    • /
    • v.45 no.4
    • /
    • pp.101-110
    • /
    • 2012
  • I present here one approach to general relativistic radiation hydrodynamics. It is based on covariant tensor conservation equations and considers only the frequency-integrated total energy and momentum exchange between matter and the radiation field. It is also a mixed-frame formalism in the sense that, the interaction between radiation and matter is described with quantities in the comoving frame in which the interaction is often symmetric in angle while the radiation energy and momentum equations are expressed in the fixed frame quantities in which the derivatives are simpler. Hence, this approach is intuitive enough to be applied straightforwardly to any spacetime or coordinate. A few examples are provided along with caveats in this formalism.

An experimental study of convective smoke filling (유동에 의한 연층 확산에 관한 실험적 연구)

  • 김명배;한용식
    • Fire Science and Engineering
    • /
    • v.11 no.3
    • /
    • pp.3-14
    • /
    • 1997
  • An experimental investigation of smoke spread in a corridor is made using thermocouples and visualization technique with a laser beam sheet. A speed of smoke front under a ceiling is measured by thermocouple trees. Visualization of the ceiling jet formation and of smoke filling process is carried out to observe lowering of the smoke layer. From the results, a large-scale convective motion the corridor plays dominant roles for smoke spread from visualized photos together with temperature records. A circulating motion of fluid transports some smokes to some regions where its momentum is effective. It is therefore showed that the conventional concept of lowering smoke with two-layer zone model has some restrictions for the corridor because the lowering of smoke layer has been thought to be mass transport due to relatively small scale motion such as decrease of buoyancy, mass diffusion and momentum exchange.

  • PDF

Effects of Liquid Fuel on Spacecraft's Moment of Inertia and Motion during Reorientation (방향전환 기동 시 액체연료가 위성체의 관성모멘트 및 자세운동에 미치는 영향 분석)

  • Kang, Ja-Young;Lee, Sang-Chul
    • Journal of the Korean Society for Aviation and Aeronautics
    • /
    • v.17 no.1
    • /
    • pp.1-8
    • /
    • 2009
  • In this paper, reorientation based on angular momentum exchange is applied for a bias momentum stabilized satellite, which is equipped with a spherical fuel tank, and the effect of liquid slosh on the attitude properties such as inertia tensor and angular rate is investigated. In order to represent the slosh motion of liquid an equivalent mechanical model is adopted and full nonlinear equations of motion for three-body system are derived. Computer simulations are performed for several cases, which use the viscosity of liquid and the center location of the tank as input parameters, mainly in order to observe how the viscosity of liquid and the center location of the tank influence the spacecraft’s attitude. The investigation includes observing time-variations of the inertia tensor, especially presence of components of product of inertia during the maneuver.

  • PDF

Stabilization Control Method Development for Single Axis Unstable System Using SGCMG (SGCMG를 이용한 단축 불안정 시스템의 안정화 제어 기법 개발)

  • Lee, Junsik;Yi, Junyong;Yoo, Jihoon;Kim, Jichul;Cheon, Dongik;Oh, Hwa-Suk
    • Journal of Aerospace System Engineering
    • /
    • v.7 no.4
    • /
    • pp.12-17
    • /
    • 2013
  • Control Moment Gyroscope(CMG) is one of the most efficient momentum exchange devices for satellite attitude control and essential device for agile maneuver system. This paper presents the details of a designed Single Gimbal CMG with a constant speed momentum wheel and single axis attitude control unstable to stable. In order to keep the naturally unstable equivalent point, it should be controlling the gimbal constantly. The experimental data are compared with theoretical result and requirements are used to verify their performance specifications.

Numerical simulations of rotating star clusters with 2 mass components

  • Hong, Jong-Suk;Kim, Eun-Hyeuk;Lee, Hyung-Mok
    • The Bulletin of The Korean Astronomical Society
    • /
    • v.36 no.1
    • /
    • pp.56.1-56.1
    • /
    • 2011
  • To understand the effect of the initial rotation for tidally bounded clusters with mass spectrum, we performed N-body simulations for the clusters with different degrees of initial rotation and compared to Fokker-Planck results. We confirmed that the cluster evolution is accelerated by the initial rotation as well as the mass spectrum. For the slowly rotating models, the time evolution of mass, energy and angular momentum show good agreements between N-body and Fokker-Planck calculations. On the other hand, for the rapidly rotating models, there are significant differences between two approaches at the beginning of the evolution. By investigating cluster shapes, we concluded that these differences are mainly due to secular instability that takes place for very rapidly rotating clusters. The shape of cluster for N-body simulations becomes tri-axial or even prolate, while the 2-dimensional Fokker-Planck simulation can treat only oblate type axisymmetric systems. We also founded that there is the angular momentum exchange from high mass to low mass.

  • PDF

Development of Spatial Data Management System to Estimate Regional Evapotranspiration Using a Land Surface Parameterization

  • Kim, Kwang-Soo;Chung, U-Ran
    • Proceedings of The Korean Society of Agricultural and Forest Meteorology Conference
    • /
    • 2003.09a
    • /
    • pp.58-61
    • /
    • 2003
  • A land surface parameterization has been used to simulate influences of the terrestrial surface on the atmosphere. A simple biosphere model (SiB2), one of land surface parameterization, calculates exchange of radiation, sensible heat, latent heat, and momentum between the surface and the atmosphere (Sellers, et al., 1996).(omitted)

  • PDF

Stack Performances of Proton Exchange Membrane Fuel Cell

  • Kho, Young-Tai;Cho, Won-Ihl;Park, Yong-Woo-
    • Proceedings of the Korea Society for Energy Engineering kosee Conference
    • /
    • 1994.11a
    • /
    • pp.14-16
    • /
    • 1994
  • The development of proton exchange membrane fuel cells(PEMFCs) with high energy efficiencies and high power densities is gaining momentum because their performance characteristics are attractive for terrestrial(power sources for electrical vehicles, stand-by power), space and underwater application[1]. Fuel cells are capable of running on non-petroleum fuels such as methanol, natural gas or hydrogen and also have major impact on improving air quality. They virtually eliminate particulates, NO$_{x}$, SO$_{x}$, and significant reduce hydrocarbons and carbon monoxide. Especially, fuel cell-battery hybrid power sources appear to be well suited to overcome both the so-called battery problem(low energy density) and the fuel cell problem(low power density)[2].[2].

  • PDF

An Analytic Study on the Present Condition of Internet Knowledge Exchange Market (인터넷 지식거래소의 현황분석에 관한 조사연구)

  • Noh Young-Hee
    • Journal of Korean Library and Information Science Society
    • /
    • v.37 no.3
    • /
    • pp.33-57
    • /
    • 2006
  • Upon the growing popularity of knowledge information and paid digital content, the Internet knowledge exchange market had emerged. A Internet knowledge exchange market consists of general characteristics of a market where a wide variety of knowledge is exchanged at market-appropriate prices, the Internet knowledge exchange market is recently gaining momentum with specialized knowledge items such as design, program source, patent information, consulting service, multimedia, or resumes, as it seeks to secure competitive advantage over its peer markets. Considering the immense influence that these Internet markets will exert on the existing system of knowledge circulation including libraries and information centers, this study aims to contribute to a better understanding of Korea's knowledge circulation structure by analyzing the current standing of the Internet knowledge exchange market.

  • PDF

Flow-Field Analysis for Designing Bipolar Plate Patterns in a Proton Exchange Membrane Fuel Cell (연료전지 분리판의 형상설계를 위한 유동해석)

  • Park, Jeong-Seon;Jeong, Hye-Mi
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.26 no.9
    • /
    • pp.1201-1208
    • /
    • 2002
  • A numerical flow-field analysis is performed to investigate flow configurations in the anode, cathode and cooling channels on the bipolar plates of a proton exchange membrane fuel cell (PEMFC). Continuous open-faced flow channels are formed on the bipolar plate surface to supply hydrogen, air and water. In this analysis, two types of channel pattern are considered: serpentine and spiral. The averaged pressure distribution and velocity profiles of the hydrogen, air and water channels are calculated by two-dimensional flow-field analysis. The equations for the conservation of mass and momentum in the two-dimensional fluid flow analysis are slightly modified to include the characteristics of the PEMFC. The analysis results indicate that the serpentine flow-fields are locally unstable (because two channels are cross at right angles). The spiral flow-fields has more stable than the serpentine, due to rotational fluid-flow inertia forces. From this study, the spiral channel pattern is suggested for a channel pattern of the bipolar plate of the PEMFC to obtain better performance.

One-Dimensional Model for Flow Resistance of Floodplain Vegetation in Compound Open-Channel Flow (복단면 개수로흐름에서 홍수터 식생의 흐름저항을 반영한 1차원 모형)

  • Park, Moon-Hyeong
    • Journal of Korea Water Resources Association
    • /
    • v.43 no.6
    • /
    • pp.517-524
    • /
    • 2010
  • In this study, the 1D apparent shear stress model for vegetated compound open-channel flows was suggested. To consider the effect of momentum exchange between main channel and floodplain, the eddy viscosity concept was used in the present model. The interfacial eddy viscosity in the interface of main channel and floodplain was determined from the 3D Reynolds stress model. The evaluated interfacial eddy viscosity appears to be good agreement with those proposed previously. To investigate the effect of interfacial eddy viscosity, sensitive analysis was carried out. the computed backwater profiles are nearly identical with respect to the value of the interfacial eddy viscosity. However, the discharge conveyed by the floodplain changes is proportional to the interfacial eddy viscosity. Finally, the changes of the interfacial eddy viscosity due to the vegetation density and vegetation height were examined. The computed results of interfacial eddy viscosity are in proportion to the vegetation density and vegetation height, and the interfacial eddy viscosity has a range of $(2-5)\;{\times}\;10^{-4}$.