• Title/Summary/Keyword: Interface Numbers

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Reynolds and froude number effect on the flow past an interface-piercing circular cylinder

  • Koo, Bonguk;Yang, Jianming;Yeon, Seong Mo;Stern, Frederick
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.6 no.3
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    • pp.529-561
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    • 2014
  • The two-phase turbulent flow past an interface-piercing circular cylinder is studied using a high-fidelity orthogonal curvilinear grid solver with a Lagrangian dynamic subgrid-scale model for large-eddy simulation and a coupled level set and volume of fluid method for air-water interface tracking. The simulations cover the sub-critical and critical and post critical regimes of the Reynolds and sub and super-critical Froude numbers in order to investigate the effect of both dimensionless parameters on the flow. Significant changes in flow features near the air-water interface were observed as the Reynolds number was increased from the sub-critical to the critical regime. The interface makes the separation point near the interface much delayed for all Reynolds numbers. The separation region at intermediate depths is remarkably reduced for the critical Reynolds number regime. The deep flow resembles the single-phase turbulent flow past a circular cylinder, but includes the effect of the free-surface and the limited span length for sub-critical Reynolds numbers. At different Froude numbers, the air-water interface exhibits significantly changed structures, including breaking bow waves with splashes and bubbles at high Froude numbers. Instantaneous and mean flow features such as interface structures, vortex shedding, Reynolds stresses, and vorticity transport are also analyzed. The results are compared with reference experimental data available in the literature. The deep flow is also compared with the single-phase turbulent flow past a circular cylinder in the similar ranges of Reynolds numbers. Discussion is provided concerning the limitations of the current simulations and available experimental data along with future research.

A Study on Wave Run-up Height and Depression Depth around Air-water Interface-piercing Circular Cylinder

  • Koo, Bon-Guk;Park, Dong-Woo;Paik, Kwang-Jun
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.20 no.3
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    • pp.312-317
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    • 2014
  • In this paper, the wave run-up height and depression depth around air-water interface-piercing circular cylinder have been numerically studied. The Reynolds Averaged Navier-Stokes equations (RANS) and continuity equations are solved with Reynolds Stress model (RSM) and volume of fluid (VOF) method as turbulence model and free surface modeling, respectively. A commercial Computational Fluid Dynamics (CFD) software "Star-CCM+" has been used for the current simulations. Various Froude numbers ranged from 0.2 to 1.6 are used to investigate the change of air-water interface structures around the cylinder and experimental data and theoretical values by Bernoulli are compared. The present results showed a good agreement with other studies. Kelvin waves behind the cylinder were generated and its wave lengths are longer as Froude numbers increase and they have good agreement with theoretical values. And its angles are smaller with the increase of Froude numbers.

Collapse Characteristics of CFRP Hat Shaped members According to Variation of Interface Numbers under the Hygrothermal Environment (고온.고습 환경 하에서의 계면수 변화에 따른 CFRP모자형 단면 부재의 압궤특성)

  • Yang, Yong-Jun;Cha, Cheon-Seok;Yang, In-Young
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.18 no.3
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    • pp.241-247
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    • 2009
  • It is important to satisfy the requirements and standards for the protections of passengers in a car accident. There are lots of studies on the crushing energy absorption of a structure members in automobiles. We have studied to investigate collapse characteristics and moisture absorption movements of CFRP(Carbon Fiber Reinforced Plastics) hat shaped sectional members when CFRP laminates are under the hygrothermal environment. In particular, the absorbed energy, mean collapse load and deformation mode were analyzed for side members which absorbed most of the collision energy. Variation of CFRP interlaminar numbers is important to increase the energy absorption capability. Therefore we have made a static collapse experiment to research into the difference of absorbed energy and deformation mode between moisture absorbed specimen and non-moisture absorbed.

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A Study on Two Dimensional Phase Change Problem (상변화 축열계의 비정상 해석)

  • Won, Sung-Pil;Ro, Sung-Tack
    • The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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    • v.10 no.1
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    • pp.12-21
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    • 1981
  • The Enthalpy Model was verified in order to analyze two- dimensional phase change problems. By using the Enthalpy Model, interface locations, frozen fraction rates, heat flux distribution rut cooled surfaces, and surface-integrated heat flux were purely numerically calculated in rectangular thermal storage units, whose initial condition was saturated liquid and phase change material was cooled on its boundaries by convective heat transfer. The calculations were performed for various Stefan numbers and Biot numbers. The effect on those dimensionless numbers were explained.

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A Study on the Cost Model for Implementation of SE for the Light Rail Transit Project (경량전철 사업의 SE 적용을 위한 비용 추정 모델 연구)

  • Kim, Chul Whan;Han, Myeong-Deok;Lee, Jae Hong;Lee, Chang Young
    • Journal of the Korean Society of Systems Engineering
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    • v.8 no.1
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    • pp.1-7
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    • 2012
  • This research aims to propose a model to estimate the appropriate SE Cost rate to the total project cost when systems engineering applied to light rail transit project. In this research an investment cost estimation model is proposed with reference to COSYSMO (Constructive System Engineering Cost Model). This model includes four input factors such as requirement numbers, interface numbers, algorithm numbers, and scenario numbers. When 2600 requirement numbers are considered on a proposal document with 350 pages in a light rail transit specification of 500 billion~trillion won scale, COSYSMO demo version estimates 42.5 billion won of SE cost (about 5% of total project cost or about 10% of E&M cost).

SINGLE OBJECTIVE LAYOUT DESIGN OF USER INTERFACE COMPONENTS WITH MULTIPLE QUALITATIVE FACTORS

  • Peer, S.K.;Sharma, Dinesh-K.
    • Journal of applied mathematics & informatics
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    • v.14 no.1_2
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    • pp.353-363
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    • 2004
  • The purpose of this paper is to present a model to design the layout of the user interface components that handles many numbers of qualitative factors. An alternate rating system is also proposed for the closeness relationship ratings between the various pairs of components evaluated by using GOMS (goals, operators, methods and selection rules) technique. The proposed model is applied to the design of the part of the user interface in order to obtain the best layout of the components. The results of the proposed model are compared with that of an existing model, which handles single qualitative factor applied to obtain the layouts of user interface components.

Instabilities of Natural Convection in a Shallow Fluid Layers (얇은 유체층(流體層)에 있어서 자연대류(自然對流)의 불안정성(不安定性))

  • Yang, Soong-Hyo;Park, Chan-Kuk
    • Solar Energy
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    • v.8 no.1
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    • pp.33-40
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    • 1988
  • The characteristics of thermal instabilities of natural convection in a horizontal fluid layer bounded below by a rigid plate and above by an interface with a passive gas is presented. The critical Grashof number decreases as the surface tension gradient effect (Marangoni effect) at the interface increases and the flow remains unstable for a critical Marangoni number depending on Prandtl numbers. These results are in substantial agreement with those of Smith and Davis.

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Structural Study of Tetragonal-Ni1-xPdxSi/Si (001) Using Density Functional Theory (DFT) (Density Functional Theory (DFT)를 이용한 Tetragonal-Ni1-xPdxSi/Si (001)의 구조 연구)

  • Kim, Dae-Hee;Seo, Hwa-Il;Kim, Yeong-Cheol
    • Korean Journal of Materials Research
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    • v.18 no.9
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    • pp.482-485
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    • 2008
  • Tetragonal-$Ni_{1-x}Pd_x$Si/Si (001) structure was studied by using density functional theory (DFT). An epitaxial interface between $2{\times}2{\times}4$ (001) tetragonal-NiSi supercell and $1{\times}1{\times}2$ (001) Si supercell was first constructed by adjusting the lattice parameters of B2-NiSi structure to match those of the Si structure. We chose Ni atoms as a terminating layer of the B2-NiSi; the equilibrium gap between the tetragonal-NiSi and Si was calculated to be 1.1 ${\AA}$. The Ni atoms in the structure moved away from the original positions along the z-direction in a systematic way during the energy minimization. Two different Ni sites were identified at the interface and the bulk, respectively. The two Ni sites at the interface have 6 and 7 coordination numbers. The Ni sites with coordination number 6 at the interface were located farther away from the interface, and were more favorable for Pd substitution.

Unstable Interface Phenomena in a Micro Channel

  • Inamuro T.;Kobayashi K.;Yamaoka Y.;Ogino F.
    • 한국전산유체공학회:학술대회논문집
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    • 2003.10a
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    • pp.118-120
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    • 2003
  • The behavior of viscous fingerings caused by an external force is investigated by using a two­phase lattice Boltzmann method. The effects of the modified capillary number, the viscosity contrast, and the modified Darcy-Rayleigh number on the instability of interfaces are found. The calculated wave numbers are in good agreement with the theoretical ones in the range of wave numbers smaller than 10, but the calculated ones tend to become smaller than the theoretical ones in higher wave numbers.

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