• Title/Summary/Keyword: Reynolds-averaged navier-stokes analysis

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Numerical Analysis of the Beach Stabilization Effect of an Asymmetric Ripple Mat (왜도 된 연흔모양 매트의 해빈 안정화 효과 수치해석)

  • Cho, Yong Jun
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.31 no.4
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    • pp.209-220
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    • 2019
  • Even though the scale of hard structures for beach stabilization should carefully be determined such that these structures do not interrupt the great yearly circulation process of beach sediment in which the self-healing ability of natural beach takes places, massive hard structures such as the submerged breakwater of wide-width are frequently deployed as the beach stabilization measures. On this rationale, asymmetric ripple mat by Irie et al. (1994) can be the alternatives for beach stabilization due to its small scale to replace the preferred submerged breaker of wide-width. The effectiveness of asymmetric ripple mat is determined by how effectively the vortices enforced at the contraction part of flow area over the mat traps the sediment moving toward the offshore by the run-down. In order to verify this hypothesis, we carry out the numerical simulations based on the Navier-Stokes equation and the physically-based morphology model. Numerical results show that the asymmetric ripple mat effectively capture the sediment by forced vortex enforced at the apex of asymmetric ripple mat, and bring these trapped sediments back to the beach, which has been regarded to be the driving mechanism of beach stabilization effect of asymmetric ripple mat.

NUMERICAL ANALYSIS OF THREE-DIMENSIONAL FLOW IN A MIXED-FLOW PUMP (사류펌프 내 삼차원 유동의 수치해석)

  • Ahn, H.J.;Kim, J.H.;Kim, K.Y.
    • 한국전산유체공학회:학술대회논문집
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    • 2009.04a
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    • pp.223-226
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    • 2009
  • This paper presents three-dimensional flow analysis for a mixed-flow pump which consists of a rotor and a stator. Reynolds-averaged Navier-Stokes equations with shear stress transport turbulence model are discretized by finite volume approximations and solved by the commercial CFD code CFX 11.0. Structured grid system is constructed in the computational domain, which has O-type grids near the blade surfaces and H-type grids in other regions. Validation of the numerical results was performed with experimental data for head coefficients and hydraulic efficiencies at different flow coefficients. This paper shows that the pump characteristics can be predicted effectively by numerical analysis.

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A Study on the Flow Characteristics in Urban Stream Using 3-D Numerical Model (3차원 수치모형을 이용한 도시하천의 흐름특성에 관한 연구)

  • Yoon, Sun-Kwon;Kim, Jong-Suk;Moon, Young-Il;Lee, Il-Ju
    • Proceedings of the Korea Water Resources Association Conference
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    • 2007.05a
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    • pp.1287-1292
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    • 2007
  • Recently, the frequency of unexpecting heavy rains has been increased due to abnormal climate and extreme rainfall. There was a limit to analyze 1D or 2D stream flow that was applied simple momentum equation and fixed energy conservation. Therefore, hydrodynamics flow analysis in rivers has been needed 3D numerical analysis for correct stream flow interpretation. In this study, CFD model on FLOW-3D was applied to stream flow analysis, which solves three dimenson RANS(Reynolds Averaged Navier-Stokes Equation) control equation to find out physical behavior and the effect of hydraulic structures. Numerical simulation accomplished those results was compared by using turbulence models such as ${\kappa}-{\varepsilon}$, RNG ${\kappa}-{\varepsilon}$ and LES. Those numerical analysis results have been illustrated by the turbulence energy effects, velocity of flow distributions, water level pressure distributions and eddy flows around the piers at Jangwall bridge in urbarn stream.

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Analysis of Hydraulic effect on Removing Side Overflow Type Structures in Woo Ee Stream Basin (우이천 유역의 횡단 월류형 구조물 철거에 의한 수리영향 분석)

  • Moon, Young-Il;Yoon, Sun-Kwon;Chun, Si-Young;Kim, Jong-Suk
    • 한국방재학회:학술대회논문집
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    • 2008.02a
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    • pp.687-690
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    • 2008
  • Currently, Stream flow analysis has been accomplished by one or two dimensional equations and was applied by simple momentum equations and fixed energy conservations which contain many reach uppermost limit. In this study, FLOW-3D using CFD(Computational Fluid Dynamics) was applied to stream flow analysis which can solve three dimensional RANS(Reynolds Averaged Navier-Stokes Equation) control equation to find out physical behavior and the effect of hydraulic structures. Numerical simulation accomplished those results was compared by using turbulence models such as $k-\varepsilon$, RNG(Renomalized Group Theory) $k-\varepsilon$ and LES(Large Eddy Simulation). Numerical analysis results have been illustrated by the turbulence energy effects, velocity of flow, water level pressure and eddy flows around the side overflow type structures at Jangwall bridge in urban stream.

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Numerical Analysis of Nonlinear Shoaling Characteristics over Surf Zone Using SPH and Lagrangian Dynamic Smagronsky Model (Lagrangian Dynamic Smagronsky 난류모형과 SPH를 이용한 쇄파역에서의 비선형 천수거동에 관한 연구)

  • Cho, Yong-Jun;Lee, Heon
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.19 no.1
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    • pp.81-96
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    • 2007
  • Nonlinear shoaling characteristics over surf zone are numerically investigated based on spatially averaged NavierStokes equation. We also test the validity of gradient model for turbulent stresses due to wave breaking using the data acquainted during SUPERTANK LABORATORY DATA COLLECTION PROJECT(Krauss et al., 1992). It turns out that the characteristics length scale of breaking induced current is not negligible, which firmly stands against ever popular gradient model, ${\kappa}-{\varepsilon}$ model, but favors Large Eddy Simulation with finer grid. Based on these observations, we model the residual stress of spatially averaged NavierStokes equation after Lagrangian Dynamic Smagorinsky(Meneveau et al., 1996). We numerically integrate newly proposed wave equations using SPH with Gaussian kernel function. Severely deformed water surface profile, free falling water particle, queuing splash after landing of water particle on the free surface and wave finger due to structured vortex on rear side of wave crest(Narayanaswamy and Dalrymple, 2002) are successfully duplicated in the numerical simulation of wave propagation over uniform slope beach, which so far have been regarded very difficult features to mimic in the computational fluid mechanics.

2D Computational Analysis of Overtopping Wave Energy Convertor

  • Liu, Zhen;Hyun, Beom-Soo;Jin, Ji-Yuan
    • Journal of Ocean Engineering and Technology
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    • v.23 no.6
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    • pp.1-6
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    • 2009
  • An Overtopping Wave Energy Convertor (OWEC) is an offshore wave energy convertor used for collecting overtopping waves and converting the water pressure head into electric power through hydro turbines installed in a vertical duct affixed to the sea bed. A numerical wave tank based on the commercial computational fluid dynamics code Fluent is established for the corresponding analysis. The Reynolds Averaged Navier-Stokes equation and two-phase VOF model are utilized to generate the 2D numerical linear propagating waves, which are validated by the overtopping experiment results. Calculations are made for several incident wave conditions and shape parameters for the overtopping device. Both the incident wave periods and heights have evident effects on the overtopping performance of the OWEC device. The computational analysis demonstrates that the present overtopping device is more compatible with longer incident wave periods.

Numerical Analysis of Aerodynamic Performance for Tilt Rotor Aircraft in Cruise Mode Using Chimaera Grid Method (겹침격자 기법을 이용한 틸트로터의 순항모드에 대한 공력성능 수치해석)

  • Ko S. H.;Ahn S. W.;Kim B. S.
    • 한국전산유체공학회:학술대회논문집
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    • 2004.10a
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    • pp.87-90
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    • 2004
  • A numerical analysis was made for the unsteady flow fields of rotor system of a Tilt-Rotor aircraft in cruise mode. The Reynolds-averaged thin-layer Navier-Stokes equations were discretized by Roe's upwind differencing scheme and integrated in time by the LU-SGS algorithm. The computational domain of the rotor system was constructed by six multi-block Chimera grids. Simulated unsteady flow fields of rotating blades were studied in several different view points.

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Analysis of crosswind around G7 and TTX (G7 TTX 및 차량의 측풍 해석)

  • Kim Tae-yoon;Lee Bo-sung;Kwon Hyeok-Bin;Ko Tae-hwan;Lee Dong-ho
    • Proceedings of the KSR Conference
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    • 2005.05a
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    • pp.138-143
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    • 2005
  • In this study, the cross-wind stability of the G7 train and TTX running under the high speed was investigated by using 2-dimensional Reynolds Averaged Navier-Stokes equations. It is very important to analysis the aerodynamic characteristic of bluff body located near a ground at the field of the aeronautical, wind engineering, ground vehicle system. To the point of running stability, it is meaningful to analysis the cross-wind effect to the G7 train and TTX developed by domestic technology. The aerodynamic characteristics of the G7 train equipped by bogie-cover is more superior to the case without bogie-cover. Also 2nd model of TTX has stream-shape body has the more good performance than 1st model of TTX.

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Numerical Study on Effects of Geometrical Variables on Performance of A Centrifugal Compressor (원심압축기의 성능에 미치는 형상변수들의 영향에 대한 수치적 연구)

  • Kim, Jin-Hyuk;Kim, Kwang-Yong
    • 한국전산유체공학회:학술대회논문집
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    • 2008.03b
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    • pp.152-155
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    • 2008
  • In this paper, the effect of modification of geometric variables on the performance of a centrifugal compressor blade has been studied numerically. The compressor contains six main blades and six splitter blades. Reynolds averaged Navier-Stokes (RANS) equations with shear stress turbulence (SST) model are discretized by finite volume approximations and solved on hexahedral grids for flow analysis. The design variables from blade lean angle at tip and middle of the blade have been modified. The isentropic blade efficiency and pressure have been predicted with the variation of the variables. Frozen rotor simulation is performed and adiabatic wall condition has been used. One of the six blades of compressor has been used for simulation to reduce the computational load. Optimum number of meshes has been selected by grid-dependency test, and this is used for all the simulations with changing geometric variables. The detailed flow analysis results have been reported as well as the effects of the variables.

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Numerical Analysis of the Differential Pressure Venturi-cone Flowmeter (차압식 Venturi-cone 유량계에 대한 유동해석)

  • Yoon J. Y.;Maeng J. S.;Lee J. W.
    • 한국전산유체공학회:학술대회논문집
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    • 1997.10a
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    • pp.143-148
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    • 1997
  • Differential pressure Venturi cone flowmeter is an advanced flowmeter which has many advantages such as wide range of measurement, high accuracy, excellent flow turndown ratio, low headless, and short installation pipe length requirement, etc. Like other differential pressure flowmeter, Venturi cone flowmeter uses the law of energy conservation, but its shape and position make it perform better than others. The cone acts as its own flow conditioner and mixer, fully conditioning and mixing the flow prior to measurement. For the analysis, we use Reynolds-averaged Navier-Stokes equations and $k-{\omega}$ turbulence model. The equations are fully trans-formed in the computational coordinates, the pressure-velocity coupling is made through SIMPLER algorithm, and the equations are discretized using analytic solutions of the linearized equations(Finite Analytic Method). At the end of the paper, using the result of analysis, We propose a new shape of cone with the hope of drag reduction and high performance.

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