• Title/Summary/Keyword: Keulegan-Carpenter number

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Numerical Simulation of the Vortical flow around an Oscillating Circular Cylinder (진동하는 원형주상체 주위의 와류 수치 모사)

  • 김광수;이승재;서정천
    • Journal of the Society of Naval Architects of Korea
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    • v.40 no.2
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    • pp.21-27
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    • 2003
  • The phenomena of vortex shedding around a cylinder oscillating harmonically in a fluid at rest are investigated by a two-dimensional numerical simulation of the Navier-Stokes equations. The simulation is based on a vorticity-velocity integro-differential formulation dealing with vorticity, velocity and pressure variables. Three combinations of Reynolds number(Re) and Keulegan-Carpenter number(KC) were taken to investigate the associated vortex development around the cylinder in the different flow regimes. Drag and lift forces are computed to describe their dominant frequency modulation which is related to the vortex shedding and to the harmonic motion of the cylinder.

Characteristics of the Local Scour Around Submarine Imbeded Pipelines Due to Waves (파랑에 의한 해저 매설관로 주변의 국부세굴특성)

  • Kim Kyoung Ho;Kim Hong Hoon;Oh Hyoun Sik;Yeun Ju Heum
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.17 no.2
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    • pp.106-118
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    • 2005
  • It is well-known that when pipelines are positioned on a sandy seabed, they have a tendency to bury themselves. This paper presents the results of an experimental investigation on the characteristics of the local scour around the submarine imbeded pipelines exposed to waves. Scour depths were measured according to the imbedment ratios of the pipelines. The results indicated that the effect of lee-wake of the pipe is the key element in the scour process of the submarine imbeded pipelines. In general, scour depths are smaller as the imbedment ratios are larger. Using the experimental results, the relative scour depths are related to Keulegan -Carpenter number and modified Ursell number, and the empirical equations are established. These equations show that the relative scour depths are proportional to above two parameters and the scour region is extended as Keulegan-Carpenter number and modified Ursell number are larger.

Experimental Study of VIV Characteristics of Free Hanging PVC Pipe under Forced Oscillation Conditions (강제가진조건에서 자유롭게 매달린 PVC 파이프의 와류유기진동 특성에 관한 시험 연구)

  • Kwon, Yong-Ju;Jung, DongHo;Park, Byeong-Won;Jung, Jae-Hwan;Oh, Seunghoon
    • Journal of Ocean Engineering and Technology
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    • v.32 no.5
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    • pp.341-350
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    • 2018
  • A series of model tests was carried out to investigate the vortex-induced vibration (VIV) characteristics of a free hanging PVC pipe under forced oscillation conditions. The prescribed displacement with a period and amplitude was forced at the top of the riser. The motion of the riser along its length was measured with underwater cameras in three dimensions. The top-excited responses in the inline direction and vortex-induced vibration in the cross-flow direction were examined in the time and frequency domains. Multi-peak frequencies in the VIV were demonstrated to be strongly dependent upon the Keulegan-Carpenter number, corresponding with the results of Blevin. It was found that the Reynolds numbers (excitation period) was a critical parameter for the dominant VIV characteristics, even under the condition of using the same Keulegan-Carpenter number, under the top-excited condition. In the resonance at the nth natural frequency by the forced-motion induced VIV frequency, the riser responded with a large amplitude and forced frequency, dominantly in the VIV CF direction.

The Local Scour around a Slender Pile in Combined Waves and Current (파랑과 흐름이 결합된 공존역에서 파일 주변의 국부세굴)

  • Park, Jong-Hwan;Kim, Kyoung-Ho
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.22 no.6
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    • pp.405-414
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    • 2010
  • In the study, experiments are performed in the mixing region combined wave and current to investigate the characteristics of local scour around a slender pile. Wave generator and current generator are used for the experiments and currents are co-directions with the waves. The local scour depths around the pipeline are obtained according to the various pipe diameters, wave periods, wave heights, and current velocities. The experiments show that the maximum equilibrium local scour depth increases with pipe diameter, wave period, wave height, and current velocity. Using the experimental results, the correlations of scour depth and parameters such as Shields parameter ($\theta$), Froude number (Fr), Keulegan-Carpenter number (KC), Ursell number ($U_R$), modified Ursell number ($U_{RP}$) and ratio of velocities ($U_c/U_c+U_m$) are analyzed. In the mixing region combined with waves and currents, The Froude number of single parameters is the main parameter to cause the local scour around a slender pile due to waves and current and this means that current governs the scour within any limits of the currents.

The Local Scour around Submarine Pipelines in the Interaction Region Combined with Waves and Currents (파랑과 정상흐름의 공존역에서 해저관로 주변의 국부세굴)

  • Kim, Kyoung-Ho;Lee, Ho-Jin;Kim, Wan-Shik
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.20 no.5
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    • pp.510-521
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    • 2008
  • In the study, experiments are performed in the interaction region combined with wave and current to investigate the characteristics of local scour around submarine pipelines. Wave generator and current generator are used for the experiments and two current directions were used; co-direction and counter direction to the wave. The local scour depths around the pipeline are obtained according to the various pipe diameters(D), wave periods(T), wave heights(H), and current velocities(V). The experiments show that the maximum equilibrium local scour depth increases with pipe diameter, wave period, wave height, and current velocity. Using the experimental results, the correlations of scour depth and parameters such as Shields parameter($\theta$), Froude number(Fr), period parameter, Keulegan-Carpenter number(KC), Ursell number($U_R$), modified Ursell number($U_{RP}$) and ratio of velocities($U_{c}/(U_{c}+U_{m})$) are analyzed. In the interaction region combined with waves and currents, Froude number and Shields parameter are found the main parameters to cause the local scour around the submarine pipelines and this means that current governs the scour within any limits of the currents.

A Study of Artificial Reef Subsidence in Unsteady Flow-Wave Field (비정상 흐름-파랑 공존장의 인공어초 침하특성에 관한 연구)

  • Yun, Sang Jun;Kim, Heon Tae
    • Journal of Ocean Engineering and Technology
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    • v.15 no.3
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    • pp.28-34
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    • 2001
  • The experimental studies for the artificial reef (AFR) subsidence characteristics in the unsteady flow field and in the unsteady flow-wave field were carried out. The difference of scou $r_sidence characteristics between in the steady flow field and in the unsteady flow field wad discussed and also the long-term subsidence characteristics in the unsteady flow field were investigated. AFR subsidence characteristics was discussed with Keulegan - Carpenter number(KC), Reynolds number (Re),. Shields number (Sn) and dimensionless time (t/Tt). And the difference of subsidence characteristics between in the unsteady flow and in the unsteady flow-wave field was discussed.ed.

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A Study of Artificial Reef Subsidence in Unsteady Flow-Wave Field (비정상 흐름-파랑 공존장의 인공어초 침하특성에 관한 연구)

  • Yun, Sang Jun;Kim, Heon Tae
    • Journal of Ocean Engineering and Technology
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    • v.15 no.3
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    • pp.29-29
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    • 2001
  • The experimental studies for the artificial reef (AFR) subsidence characteristics in the unsteady flow field and in the unsteady flow-wave field were carried out. The difference of scour/subsidence characteristics between in the steady flow field and in the unsteady flow field wad discussed and also the long-term subsidence characteristics in the unsteady flow field were investigated. AFR subsidence characteristics was discussed with Keulegan - Carpenter number(KC), Reynolds number (Re),. Shields number (Sn) and dimensionless time (t/Tt). And the difference of subsidence characteristics between in the unsteady flow and in the unsteady flow-wave field was discussed.

Parameter Analysis for Influence on the Scour Width around Submarine Pipelines in Waves (파랑하 해저관로 주변의 세굴폭에 영향을 주는 매개변수 분석)

  • Oh, Hyoun-Sik;Kim, Kyoung-Ho;Son, Kwang-Sik;Kim, Heung-Guk
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.21 no.6
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    • pp.470-479
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    • 2009
  • The local scour in waves can be thought of as very complex synthetic processes which is influenced by geology of bed material, bed flow in the sea and hydraulics condition. The most research until now be targeted at the scour depth and therefore the local scour width in waves has not been investigated as well. The size of wave or bottom velocity at the bed is direct cause of the local scour among lots of the scour effect factors, and the scour depth and width can be estimated through interrelationship analysis with scour area to use the dimensionless parameters including these such as Keulegan-Carpenter number, Ursell number etc. In this paper, to find out closely relation with the dimensionless parameters and scour width, performed an experiment with the variations of pipe diameters, wave heights and wave periods and then analyzed it. As the result, while Reynolds number and period parameter were seen to disperse local scour width largely, Shields number, KC number and Ursell number appeared good interrelationship. Specially, Shields number doesn't much affect the scour depth but has good relation for the scour width.

A Review-Status of Development and Research of Artificial Reefs in the East Asian Countries- (동아시아의 인공어초 개발과 연구 현황)

  • LEE, Moon-Ock;KIM, Jong-Kyu;KIM, Byeong-Kuk
    • Journal of Fisheries and Marine Sciences Education
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    • v.28 no.3
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    • pp.630-644
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    • 2016
  • We conducted a comprehensive review on artificial reefs (ARs) including seaweed reefs for marine afforestation in relation to their development and research from 1972 to 2016, and then systematically analyzed their current a state-of-the-art and practice. From the review, the followings conclusions are made. First, the objectives of AR projects in the Southeast Asia can be classified into three, i.e. protection and increase of fishery resources, local community's profits, and ecological tourism. Second, fish gathering effects by ARs can be determined in terms of wake region or wake length that tends to increase with the K-C (Keulegan-Carpenter) number. Third, ARs are desirable to deploy across a direction of the main flow but it is essential to keep the deployment interval two to four times the length of a single reef. Fourth, stability of ARs depends on how to evaluate drag coefficient, and Morison formula turns out to be practical. Fifth, local scours of ARs are likely to occur due to a downward flow around the center of the front surface. Finally, it is natural for ARs to positively contribute to the marine ecosystem but it is imperative to develop an evaluation method for the effects of ARs on the marine ecosystem.

IMPLEMENTATION OF IMMERSED BOUNDARY METHOD TO INCOMPRESSIBLE NAVIER-STOKES SOLVER USING SIMPLE ALGORITHM (SIMPLE Algorithm기반의 비압축성 Navier-Stokes Solver를 이용한 Immersed Boundary Method의 적용)

  • Kim, G.H.;Park, S.O.
    • Journal of computational fluids engineering
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    • v.17 no.1
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    • pp.44-53
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    • 2012
  • Immersed boundary method(IBM) is a numerical scheme proposed to simulate flow field around complex objectives using simple Cartesian grid system. In the previous studies, the IBM has mostly been implemented to fractional step method based Navier-Stokes solvers. In this study, we implement the IBM to an incompressible Navier-Stokes solver which uses SIMPLE algorithm. The weight coefficients of the bi-linear and quadratic interpolation equations were formulated by using only geometric information of boundary to reconstruct velocities near IB. Flow around 2D circular cylinder at Re=40 and 100 was solved by using these formulations. It was found that the pressure buildup was not observed even when the bi-linear interpolation was adopted. The use of quadratic interpolation made the predicted aerodynamic forces in good agreement with those of previous studies. For an analysis of moving boundary, we smulated an oscillating circular cylinder with Re=100 and KC(Keulegan-Carpenter) number of 5. The predicted flow fields were compared with experimental data and they also showed good agreements.