• Title/Summary/Keyword: buoyancy method

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Hall and Ion-Slip effects on magneto-micropolar fluid with combined forced and free convection in boundary layer flow over a horizontal plate

  • Seddeek, M.A.;Abdelmeguid, M.S.
    • Journal of the Korean Society for Industrial and Applied Mathematics
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    • v.8 no.2
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    • pp.51-73
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    • 2004
  • A boundary layer analysis is used to study the effects of Hall and ion-slip currents on the steady magneto-micropolar of a viscous incompressible and electrically conducting fluid over a horizontal plate. By means of similarity solutions, deviation of fundamental equations on the assumption of small magnetic Reynolds number are solved numerically by using the shooting method. The effects of various parameters of the problem, e.g. the magnetic parameter, Hall parameter, ion-slip parameter, buoyancy parameter and material parameter are discussed and shown graphically.

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Double-Diffusive Convection in Molten Pb-Sn Alloy (용융상태인 납-주석 합금의 이중확산유동)

  • ;Bergman, T. L.
    • Journal of Advanced Marine Engineering and Technology
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    • v.19 no.2
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    • pp.27-35
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    • 1995
  • 액체 상태인 Pb-Sn 합금에 의한 이중확산유동에 대해 체비세프 콜로케이션 기법을 이용하여 수치해석하였다. 온도차에 의한 부력과 농도차에 의한 부력이 작을때에는 유동형태가 서서히 준정상상태에 이르러 아무런 진동현상을 볼 수 없다. 부력이 증가함에 따라 유동은 수직 농도 경계층을 파괴하여 플륨(Plume)형태의 유동을 생성시키고, 이는 시스템 내부로 성장한 후 소멸된다. 이러한 현상이 반복되면서 높은 주파수의 진동현상을 관찰할 수 있다.

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On the Time-Mean Drift Force Acting on a Floating Offshore Structure in Wave (부유식 해양구조물에 작용하는 시감평균 파표류력에 관한 고찰)

  • 홍도천
    • Journal of Ocean Engineering and Technology
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    • v.16 no.3
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    • pp.8-18
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    • 2002
  • Formulation of the far-field method for the prediction of time-mean hydrodynamic force and moment acting on a 3-D surface-piercing body in waves is reviewed. It is found that the inequality between the weight of the floating body and its buoyancy force permits the replacement of the fluid particles inside the control surface by the fluid particles outside the control surface. Under such circumstances, momentum exchanges across the control surface make the time-mean value of the time rate of the momentum of the fluid inside the control surface non-vanishing. It is a second-order quantity which is hard to calculate by the far-field method. The drift forces and moments on half-immersed ellipsoids are calculated by both the far-field method and the near-field method. The discrepancy between two numerical results is presented and discussed.

Numerical analysis of two and three dimensional buoyancy driven water-exit of a circular cylinder

  • Moshari, Shahab;Nikseresht, Amir Hossein;Mehryar, Reza
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.6 no.2
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    • pp.219-235
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    • 2014
  • With the development of the technology of underwater moving bodies, the need for developing the knowledge of surface effect interaction of free surface and underwater moving bodies is increased. Hence, the two-phase flow is a subject which is interesting for many researchers all around the world. In this paper, the non-linear free surface deformations which occur during the water-exit of a circular cylinder due to its buoyancy are solved using finite volume discretization based code, and using Volume of Fluid (VOF) scheme for solving two phase flow. Dynamic mesh model is used to simulate dynamic motion of the cylinder. In addition, the effect of cylinder mass in presence of an external force is studied. Moreover, the oblique exit and entry of a circular cylinder with two exit angles is simulated. At last, water-exit of a circular cylinder in six degrees of freedom is simulated in 3D using parallel processing. The simulation errors of present work (using VOF method) for maximum velocity and height of a circular cylinder are less than the corresponding errors of level set method reported by previous researchers. Oblique exit shows interesting results; formation of waves caused by exit of the cylinder, wave motion in horizontal direction and the air trapped between the waves are observable. In 3D simulation the visualization of water motion on the top surface of the cylinder and the free surface breaking on the front and back faces of the 3D cylinder at the exit phase are observed which cannot be seen in 2D simulation. Comparing the results, 3D simulation shows better agreement with experimental data, specially in the maximum height position of the cylinder.

Study of the Resistance Test and Wall Blockage Correction Method for the Submerged Body in LCT (대형 캐비테이션터널에서 몰수체 저항시험 및 위벽효과 수정 기법 연구)

  • Ahn, Jong-Woo;Seol, Han-Shin;Park, Young-Ha;Kim, Ki-Sup
    • Journal of the Society of Naval Architects of Korea
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    • v.57 no.3
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    • pp.133-139
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    • 2020
  • In order to study the resistance test technique for the submerged body in Large Cavitation Tunnel (LCT), DARPA Suboff, submarine model publicly available was manufactured. DTRC released the resistance test data of DARPA Suboff conducted at ship speeds up to 18.0 knots in high-speed towing tank in 1990. As LCT is considered restricted waterways with walls, the resistance test results must be corrected with three wall blockage effects called buoyancy effect, solid blockage effect and wake blockage effect. Before correction, the resistance of LCT was 16~20 % higher than that of DTRC. After correction, the resistance and the resistance coefficients were compared with those of DTRC. The corrected resistance of LCT shows good agreement with that of DTRC. The residual resistance coefficient shows the difference according to the calculation method of buoyancy and frictional resistance coefficient. This paper suggests the best way for the calculation of residual resistance coefficient, On the basis of the present study, it is thought that the operating conditions for the propeller cavitation and noise tests can be drawn through LCT tests.

The Efficient Algorithm for Simulating the Multiphase Flow

  • Yoon Seong Y;Yabe T.
    • Journal of computational fluids engineering
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    • v.9 no.1
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    • pp.18-24
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    • 2004
  • The unified simulation for the multiphase flow by predictor-corrector scheme based on CIP method is introduced. In this algorithm, the interface between different phases is identified by a density function and tracked by solving an advection equation. Solid body motion is modeled by the translation and angular motion. The mathematical formulation and numerical results are also described. To verify the efficiency, accuracy and capability of proposed algorithm, two dimensional incompressible cavity flow, the motion of a floating ball into water and a single rising bubble by buoyancy force are numerically simulated by the present scheme. As results, it is confirmed that the present scheme gives an efficient, stable and reasonable solution in the multiphase flow problem.

A Study on Rescue Technique and Safe Tow of Damaged Ship(1) - Prediction of Final Drafts and Residual Stability of Ship in Damage - (손상된 선박의 구난 기술 및 안전 예항에 관한 연구(1) - 손상시의 선체 자세 및 잔존 복원성 평가법 -)

  • 손경호;이상갑;최경식;안영규;김윤수
    • Journal of the Korean Institute of Navigation
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    • v.21 no.3
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    • pp.83-90
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    • 1997
  • Damage stability is generally very important as a part of rescue technique of damaged ship and also in connection with the requirements of MARPOL73/78[2]. Damage stability calculation program has been developed and suggest, which can be used on an onboard computer for any operating drafts. The program is based on lost buoyancy method for calculation of final drafts, and also based on added mass method for calculation of residual righting arm. The numerical method suggested by Hamamoto-Kim[6] is adopted for calculation of intact righting arm(GZ). The model experiments on damage stability are also carried out in a small tank with tanker model 2.385 meters long. The experimental results are compared with the calculations by the suggested method.

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An Immersed-Boundary Method for Simulation of Density-Stratified Flows (밀도 성층 유동 해석을 위한 가상경계법)

  • Yoon, Dong-Hyeog;Yang, Kyung-Soo;Hwang, Jong-Yeon;Lee, Sung-Su
    • Proceedings of the KSME Conference
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    • 2004.04a
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    • pp.1909-1914
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    • 2004
  • An immersed boundary method for simulation of density-stratified flows is developed and applied to computation of viscous flows over two-dimensional obstacles in a bounded domain under stable density stratification. Density sources/sinks are introduced on the body surface. Two obstacle shapes are used, a vertical barrier and a smooth cosine-shaped hill; weak stratification, defined by $K=ND/{\pi}U{\leq}1$, where U, N, and D are the upstream velocity, buoyancy frequency, and domain height, respectively, is considered. The results are consistent with other authors' calculations, and shed light on computation of density-stratified flows in complex geometries.

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Study on the Application of Press in Steel Pipe Pile for Restoring Building of different settlement (부동침하 건축물 복원을 위한 압입강관파일 공법 현장 적용에 관한 연구)

  • Sin, Jae-Kwon;Lee, Hee-Seok;Sho, Kwang-Ho
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2015.11a
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    • pp.85-86
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    • 2015
  • Recently, As the high rise buildings have been demanded due to the rising current of land price, the permanent drainage method have been applied during and after the construction as a way to reduce the buoyancy acting on the bottoms of the foundations in the basement. This method has brought about the consolidation subsidence of the ground and turned out to be the problems of sinking hole and foundation re-settlement. The representative methods to be used for extending the life cycle of the existing building structure which is tilted by the foundation re-settlement or differential settlement of the foundation can be divided into the building structures reinforcement and soil reinforcement. The purpose of this study is to analyze and present the application example of steel pipe pile method to extend the life cycle of the six -stories building tilted in a soft ground.

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A Study on the Flow Analysis for Natural Convection of Magnetic Fluid in a Cubic Cavity (밀폐공간내 자성유체의 유동특성에 관한 연구)

  • Ryu, Shin-Oh;Park, Joung-Woo;Seo, Lee-Soo
    • Proceedings of the KSME Conference
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    • 2001.06e
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    • pp.142-147
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    • 2001
  • Natural convection of a magnetic fluid is different from that of Newtonian fluids because magnetic body force exists in an addition to gravity and buoyancy. In this paper, natural convection of a magnetic fluids(W-40) in a cubic cavity is examined by numerical and experimental method. One side wall was kept at a constant temperature($25^{\circ}C$), and the opposite side wall was also held at a constant but lower temperature($20^{\circ}C$). Under above conditions, various magnitudes of the magnetic fields were applied up. GSMAC scheme is used for a numerical method, and the thermo-sensitive liquid crystal film(R20C5A) is utilized in order to visualize wall-temperature distributions as an experimental method. This study has resulted in the following fact that the natural convection of a magnetic fluids is controlled by the direction and intensity of the magnetic fields.

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