• Title/Summary/Keyword: Marine boundary layer

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A study for the pressure distribution and the boundary layer around a circular cylinder in a shear flow (Shear Flow 속에 있는 Circular Cylinder 표면의 압력분포 및 경계층 연구)

  • 이상섭
    • Journal of Advanced Marine Engineering and Technology
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    • v.27 no.6
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    • pp.753-758
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    • 2003
  • In this study. an experiment has been performed to investigate distributions of static pressure around a circular cylinder in a uniform shear flow which is made by a specially designed wind tunnel. From the computation program(BLAYER), various boundary layer value are obtained depending on the shear flow rate. It is basical design data that boundary layer flow phenomenon of nuclear power plant heat exchanger tube surroundings. airfoil. and others flow fields.

Flow-induced interior noise from a turbulent boundary layer of a towed body

  • Abshagen, J.;Kuter, D.;Nejedl, V.
    • Advances in aircraft and spacecraft science
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    • v.3 no.3
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    • pp.259-269
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    • 2016
  • In this work results from an underwater experiment on flow-induced noise in the interior of a towed body generated from a surrounding turbulent boundary layer are presented. The measurements were performed with a towed body under open sea conditions at towing depths below 100 m and towing speeds ranging from 2.4 m/s to 6.2 m/s (4 kn to 12 kn). Focus is given in the experiments to the relation between (outer) wall pressure fluctuations and the (inner) hydroacoustic near-field on the reverse side of a flat plate. The plate configuration consists of a sandwich structure with an (thick) outer polyurethane layer supported by an inner thin layer from fibre-reinforced plastics. Parameters of the turbulent boundary layer are estimated in order to analyse scaling relations of wall-pressure fluctuations, interior hydroacoustic noise, and the reduction of pressure fluctuations through the plate.

Reduction of Skin Friction Force for Turbulent Boundary Layer (난류 경계층의 표면 마찰력 감소화)

  • Kim, Si-Young
    • Journal of Fisheries and Marine Sciences Education
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    • v.5 no.2
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    • pp.128-137
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    • 1993
  • This paper presents a new concept to reduce turbulent frictional drag by injecting micro-bubble into buffer layer of turbulent boundary layer on flat plate. The buffer layer of boundary was specified by minus velocity gradient of law of the wall. When the buffer layer region of turbulent boundary layer is filled with micro-bubble of air and viscous of the region is kept low, the velocity profile in the region should be changed substantially. Then the Reynolds stress in the buffer layer region becomes less, which guide to higher velocity gradient there. It results in reduction of velocity gradient at the viscous sublayer, which gives the reduction of shear stress at the wall.

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A study on the boundary layer characteristics of TP620 hydrofoil in the steady state (정상상태인 박용 TP620 익형의 경계층 특성 연구)

  • 서봉록;김시영
    • Journal of Advanced Marine Engineering and Technology
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    • v.10 no.4
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    • pp.50-56
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    • 1986
  • This report deals with a study on the boundary layer characteristics of TP620 hydrofoil in the steady state by using two dimensional boundary layer theory. On the basis of complex velocity and laminar and turbulent boundary layer theory, the author attempts to know some tendency by evaluating the performance characteristic values of TP620 hydrofoil working in a uniform flow. In deriving characteristic values, he calculates numerically velocity, momentum thickness, skin friction coefficient, shape factor, and displacement thickness on the TP620 hydrofoil working at each attack angle in a uniform flow. Applying this present numerical calculation using Thwaites' and Head's method, the results of boundary layer on the hydrofoil are shown to be influenced by surface velocity and attack angle.

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A Numerical Analysis of Streamwise Vortices in Turbulent Boundary Layers (주유동방향 와동과 난류경계층과의 상호작용에 관한 수치적 연구)

  • 김정한;양장식;김봉환;이기백
    • Journal of Advanced Marine Engineering and Technology
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    • v.24 no.1
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    • pp.31-40
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    • 2000
  • This paper describes the numerical computations of the interaction between the streamwise vortex and a flat plate 3-D turbulent boundary layer. In the present study, the main interest is in the behavior of the streamwise vortices introduced in turbulent boundary layers. The flow behind a vortex generator is modeled by the information that is avilable from studies on the dalta winglet. An algorithm of the solution of the incompressible Navier-Stokes equations for three-dimensional turbulent flows, together with a two layer turbulent model to resolve the near-wall flow, is based on the method of artificial compressibility. The present results show boundary layer distortion due to vortices, such as strong spanwise flow divergence and boundary thinning, and have a good agreement with the experimental data.

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The effects of tripping structure on the development of turbulent boundary layer subjected to adverse pressure gradient (역압력 구배가 존재하는 난류 경계층의 발달에 트리핑 구조물이 미치는 영향에 관한 연구)

  • 임태현;김대성;윤순현
    • Proceedings of the Korean Society of Marine Engineers Conference
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    • 2001.11a
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    • pp.36-44
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    • 2001
  • The effects of various tripping structures on turbulent boundary layer subjected to adverse pressure gradient were examined. The profiles are compared to zero pressure gradient and adverse pressure gradient. The increases of tripping structures of height, k are affects almost flow parameter included velocity fluctuation, skin friction coefficient and turbulent boundary thickness.

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A Case Study on the Heat budget of the Marine Atmosphere Boundary Layer due to inflow of cloud on observation at Ulleungdo (울릉도에서 구름 유입시 관측한 해양대기경계층의 열수지에 관한 사례연구)

  • Kim, Hee-Jong;Yoon, Ill-Hee;Kwon, Byung-Hyuk
    • Journal of the Korean earth science society
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    • v.25 no.7
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    • pp.629-636
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    • 2004
  • In order to study developments of the marine atmosphere boundary layer in cloud incoming, important parameters like heat advection, surface layer heat flux, and radiation energy were estimated using the rawinsonde, AWS data, satellite images, and buoy data which was installed at the East Sea. We explained the variation and the development of mixed layer in terms of surface layer heat flux and long wave radiation under the cloudy sky. The heat flux was obtained by means of the bulk method. Conservation of heat was analysed by heat budget equation, which was consist of buoy data in the East sea, and sounding data at Ulleungdo and at Pohang. During the inflow of cloud, radiative cooling at the surface after was suppressed and long wave radiation from cloud played a role of warming. The surface layer temperature was also remained warm by influence of warm advection from south-easterly direction. The air temperature in night was increased, as a result, mixed layer was not destroyed and The nocturnal boundary layer was composed of the mixed layer and the residual layer.

Spatial Analysis on Marine Atmosphere Boundary Layer Features of SAR Imagery Using Empirical Mode Decomposition

  • Jo, Young-Heon;Oliveira, Gustavo Henrique;Yan, Xiao-Hai
    • Korean Journal of Remote Sensing
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    • v.33 no.4
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    • pp.351-358
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    • 2017
  • A new method to decompose the footprints of marine atmosphere boundary layer (MABL) on Synthetic Aperture Radar (SAR) imagery into characteristic spatial scales is proposed. Using two-dimensional Empirical Mode Decomposition (EMD) we obtain three Intrinsic Mode Functions (IMFs), which mainly present longitudinal rolls, three-dimensional cells and atmospheric gravity waves (AGW). The rolls and cells have spatial scales between 3.0 km and 3.8 km and between 5.3 km and 7.1 km, respectively. Based on previous observations and mixed-layer similarity theory, we estimated MABL's depths that vary from 0.95 km to 1.2 km over the rolls and from 3.0 km to 3.8 km over the cells. The AGW has maximum spectrum at 14.3 km wavelength. The method developed in this work can be used to decompose other satellite imageries into individual features through characteristic spatial scales.

A Laboratory Study of Formation of 'The Warm Core' in the East Sea of Korea

  • NA Jung Yul;KIM Bong Ho
    • Korean Journal of Fisheries and Aquatic Sciences
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    • v.22 no.6
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    • pp.415-423
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    • 1990
  • In a laboratory model the response of the boundary layer flow over topography is studied in a rotating sliced cylinder by employing the source-sink analogy with Ekman layer dynamics. The boundary layer flow is produced by two different fluid. In the first experiment homogeneous fluid is used both for the source and the working fluid of the container. In the second experiment a denser fluid is used for the source with the same working fluid. For the homogeneous western boundary layer flow both the northward and the southward flow were affected by the topography(ridge) to produce a cyclonic motion near the ridge. When woughward moving heavy boundary flow of slower speed and the northward moving faster flow were present at the same time, the splitting of southward flow and the separating of the northward flow were observed with a cyclonic motion at the ridge. The most important factor that influence production of the cyclonic motion has been turned out to be the presence of the topography in the western boundary layer. In particular the role of the southward moving heavy flow over the interior flow pattern was found to be very significant.

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The Effect of Surface Roughness on the Zero Pressure Gradient Turbulent Boundary Layers (영압력 구배 난류 경계층에서 표면조도가 미치는 영향)

  • Kim Moon-Kyung;Yoon Soon-Hyun;Kim Dong-Keon
    • Journal of Advanced Marine Engineering and Technology
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    • v.29 no.4
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    • pp.453-460
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    • 2005
  • Experiments were conducted to investigate the effect of the surface roughness on the flat plate turbulent boundary layer. The square rods were installed at the leading edge to make surface roughness. The particle image velocimetry was used to measure the mean velocities and velocity fluctuation component. All measurements were made over a range of w/k=1. 2 5 and $Re_x=80.000{\sim}360,000$. Friction velocity was measured by using Clauser plot method. The level of turbulent intensities on roughness surface appears more strongly than that of turbulent intensities on flat plate. A correlation of boundary layer thickness in term of $Re_x$ and w/k are presented.