• Title/Summary/Keyword: Two-dimensional Wedge

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An Experimental Study on Wake Cavity Flow Characteristics of Two-dimensional Wedge Shaped Control Fins (2차원 쐐기형 제어핀 후류의 공동유동 특성에 대한 실험연구)

  • Jeong, So-Won;Ahn, Byoung-Kwon
    • Journal of the Society of Naval Architects of Korea
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    • v.53 no.3
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    • pp.180-187
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    • 2016
  • As distinct from a slender body, the separation of the boundary layer on a bluff body give rise to complex wakes in which various kinds of vortices form, develop and interact with each other. In this paper, we investigate cavitation wake field behind wedge shaped two-dimensional fin models. Eight different models are tested at the Chungnam National University Cavitation Tunnel (CNU-CT). First, we measure wake cavity shapes and compare with numerical results, which shows the good agreement with each other. In addition, we demonstrate that wake flow characteristics of the control fin are clearly identified by the correlation analysis of high-speed camera images and pressure fluctuation measurements.

NUMERICAL ANALYSIS OF SUPER-CAVITATING FLOW AROUND TWO-DIMENSIONAL AND AXISYMMETRIC BODIES (2차원 및 축대칭 운동체 주위의 초공동 현상에 대한 수치해석)

  • Park, Sun-Ho;Rhee, Shin-Hyung
    • Journal of computational fluids engineering
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    • v.16 no.1
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    • pp.14-21
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    • 2011
  • Super-cavitating flows around under-water bodies are being studied for drag reduction and dramatic speed increase. In this paper, high speed super-cavitating flow around a two-dimensional symmetric wedge-shaped body were studied using an unsteady Reynolds-averaged Navier-Stokes equations solver based on a cell-centered finite volume method. To verify the computational method, flow over a hemispherical head-form body was simulated and validated against existing experimental data. Various computational conditions, such as different wedge angles and caviation numbers, were considered for the super-cavitating flow around the wedge-shaped body. Super-cavity begins to form in the low pressure region and propagates along the wedge body. The computed cavity lengths and velocities on the cavity boundary with varying cavitation number were validated by comparing with analytic solution.

Pseudo-static stability analysis of wedges based on the nonlinear Barton-Bandis failure criterion

  • Zhao, Lianheng;Jiao, Kangfu;Zuo, Shi;Yu, Chenghao;Tang, Gaopeng
    • Geomechanics and Engineering
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    • v.20 no.4
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    • pp.287-297
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    • 2020
  • This paper investigates the stability of a three-dimensional (3D) wedge under the pseudo-static action of an earthquake based on the nonlinear Barton-Bandis (B-B) failure criterion. The influences of the mechanical parameters of the discontinuity surface, the geometric parameters of the wedge and the pseudo-static parameters of the earthquake on the stability of the wedge are analyzed, as well as the sensitivity of these parameters. Moreover, a stereographic projection is used to evaluate the influence of pseudo-static direction on instability mode. The parametric analyses show that the stability coefficient and the instability mode of the wedge depend on the mechanical parameter of the rock mass, the geometric form of the wedge and the pseudo-static state of the earthquake. The friction angle of the rock φb, the roughness coefficient of the structure surface JRC and the two angles related to strikes of the joints θ1 and θ2 are sensitive to stability. Furthermore, the sensitivity of wedge height h, the compressive strength of the rock at the fracture surface JCS and the slope angle α to the stability are insignificant.

A Numerical Analysis of Gravity and Free Surface Effects on a Two-Dimensional Supercavitating Flow (2차원 초공동 유동의 중력과 자유표면 효과에 대한 수치해석)

  • Kim, Hyoung-Tae;Lee, Hyun-Bae
    • Journal of the Society of Naval Architects of Korea
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    • v.51 no.5
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    • pp.435-449
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    • 2014
  • The effects of the gravity field and the free surface on the cavity shape and the drag are investigated through a numerical analysis for the steady supercavitating flow past a simple two-dimensional body underneath the free surface. The continuity and the RANS equations are numerically solved for an incompressible fluid using a $k-{\epsilon}$ turbulence model and a mixture fluid model has been applied for calculating the multiphase flow of air, water and vapor using the method of volume of fluid and the Schnerr-Sauer cavitation model. Numerical solutions have been obtained for the supercavitating flow about a two-dimensional $30^{\circ}$ wedge in wide range of depths of submergence and inflow velocities. The results are presented for the cavity shape, especially the length and the width, and the drag of the wedge in comparison with those of the case for the infinite fluid flow neglecting the gravity and the free surface. The influences of the gravity field and the free surface on the aforementioned quantities are discussed. The length and the width of the supercavity are reduced and the centerline of the cavity rises toward the free surface due to the effects of the gravity field and the free surface. The drag coefficient of the wedge, however, is about the same except for shallow depths of submergence. As the supercavitating wedge is approaching very close to the free surface, it is found the length and the width of a cavity are shorten even though the cavitation number is reduced. Also the present result suggests that, under the influence of the gravity field and the free surface, the length of the supercavity for a certain cavitation number varies and moreover is proportional to the inverse of the submergence depth Froude number.

Numerical Analysis of Cavitating Flow around Two-dimensional Wedge-shaped Submerged Bodies under the Wall Effect (벽면효과를 받는 2차원 쐐기형 몰수체의 공동 유동에 대한 수치해석)

  • Kim, Ji-Hye;Ahn, Byoung-Kwon
    • Journal of the Society of Naval Architects of Korea
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    • v.54 no.4
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    • pp.321-328
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    • 2017
  • In practice, cavitation phenomena occur in unbounded flows. However, the wall effect is unavoidable during experiments at a closed section such as a cavitation tunnel. Especially, supercavity generated behind a cavitator is relatively large and thick, so that geometric and dynamic characteristics of the cavity are affected by the tunnel wall. In order to apply experimental results into the unbounded flow field, physical correlations are necessary. In this paper, we proposed an image method based on a potential flow to simulate the wall effect. Considering two-dimensional wedge-shaped bodies, configurations and drag characteristics of the cavity were examined according to the distance ratio to the wall surface. The results were compared and verified with existing theoretical and experimental results.

Experimental Study of Water Impact Loads on Symmetric and Asymmetric Wedges (대칭 및 비대칭 2차원 쐐기의 입수 충격에 관한 실험적 연구)

  • Kim, Kyong-Hwan;Lee, Dong Yeop;Hong, Sa Young;Kim, Young-Shik;Kim, Byoung Wan
    • Journal of Ocean Engineering and Technology
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    • v.28 no.3
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    • pp.209-217
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    • 2014
  • In the present study, the water impact loads on two-dimensional symmetric and asymmetric wedges were mainly studied. The impact pressure and force were measured during a vertical drop of the symmetric and asymmetric wedges. The measured pressure was compared with analytic solutions. The measured force at a local area of the wedge was compared with the integrated pressures and analytic solutions. Some findings on symmetric and asymmetrical wedge drops are presented, and the reliability of the force sensor used for the measurement of the local impact force is discussed.

CFD PARAMETRIC STUDY FOR 2D WATER ENTRY

  • Lee, H.H.;Rhee, S.H.
    • 한국전산유체공학회:학술대회논문집
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    • 2009.04a
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    • pp.191-195
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    • 2009
  • A parametric study for for the water entry of a two dimensional symmetric wedge with deadrise angle of 10 degrees was carried out to find out the most dominant parameter. Water entry problem with constant velocity is simplified as the stationary wedge in the way of the upcoming water surface. The calculated impact loads showed that the effect of the viscosity was not so important in this problem. For a given grid system a suitable time step size can be found. The most sensitive parameter was found to be the grid size.

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Nonlinear Vortical Forced Oscillation of Floating Bodies (부유체의 대진폭 운동에 기인한 동유체력)

  • 이호영;황종흘
    • Journal of the Society of Naval Architects of Korea
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    • v.30 no.2
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    • pp.86-97
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    • 1993
  • A numerical method is developed for the nonlinear motion of two-dimensional wedges and axisymmetric-forced-heaving motion using Semi-Largrangian scheme under assumption of potential flows. In two-dimensional-problem Cauchy's integral theorem is applied to calculate the complex potential and its time derivative along boundary. In three-dimensional-problem Rankine ring sources are used in a Green's theorem boundary integral formulation to salve the field equation. The solution is stepped forward numerically in time by integrating the exact kinematic and dynamic free-surface boundary condition. Numerical computations are made for the entry of a wedge with a constant velocity and for the forced harmonic heaving motion from rest. The problem of the entry of wedge compared with the calculated results of Champan[4] and Kim[11]. By Fourier transform of forces in time domain, added mass coefficient, damping coefficient, second harmonic forces are obtained and compared with Yamashita's experiment[5].

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PIV Measurements of Non-cavitating and Cavitating Flow in Wake of Two-dimensional Wedge-shaped Submerged Body (PIV를 이용한 2차원 쐐기형 몰수체 후류의 비공동 및 공동 유동장 계측)

  • Hong, Ji-Woo;Jeong, So-Won;Ahn, Byong-Kwon
    • Journal of Ocean Engineering and Technology
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    • v.33 no.1
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    • pp.26-32
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    • 2019
  • The vortex flow behind a bluff body has been a subject of interest for a very long time because of its engineering applicability such as to vortex induced vibration. In the near wake of a bluff body, vortices are periodically shed in two shear layers, which originate in the trailing edges. The far wake is made up of the classical Karman vortices, which are connected together by streamwise and spanwise vortices. These vortex formations have been studied in many experimental and numerical ways. However, most of the studies considered non-cavitating flow. In this study, we investigated cavitating flow in the wake of a two-dimensional wedge. Experiments were conducted in a cavitation tunnel of Chungnam National University. Using a particle image velocimetry (PIV), we measured the velocity fields under two different flow conditions: non-cavitating and cavitating regimes. We also investigated the vortex shedding frequencies using an absolute pressure transducer mounted on the top of the test window. Throughout the experiments, it was found that the shedding frequency of the vortex was strongly affected by cavitation, and the Strouhal number could exceed its value in the non-cavitating regime.