• Title/Summary/Keyword: Drag effects

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Analysis of a Two-Dimensional Section of Deforming Yacht Sails (변형을 고려한 요트 세일의 2차원 단면 해석)

  • Lee, Hee-Bum;Rhee, Shin-Hyung;Yoo, Jae-Hoon
    • Journal of the Society of Naval Architects of Korea
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    • v.48 no.4
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    • pp.308-316
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    • 2011
  • Although a yacht sails operate with large displacement due to very thin thickness, many studies for flow around yacht sails have not considered the sail deformation. The sail deformation not only caused a change in the center of effect(CE) on the sail but also a change in the thrust of the sail. The change of the CE and thrust affects the center of lateral resistance(CLR) and side forces of the hull, and the balance of the yacht. These changes affect the motion of the yacht which changes the velocity of the yacht. Thus, when analyzing the flow around yacht sails, the sail deformation should be considered. In the present study, fluid-structure-interaction(FSI) analysis of a two dimensional section of yacht sails was performed to consider the effects of sail deformation on the lift and drag performance. FSI and moving mesh methods were studied. Computational methods were verified using benchmark test cases such as the flow around horizontal and vertical cantilever beams. Shape deformation, pressure distribution, lift forces and separation flow were compared for both rigid and deformable sail.

Fundamental Studies on the Net-Shape of the Drag Net ( III ) - The Relationship between the Section Shape and the Porosity of Netting in the Bag Net - (저예망의 어구형상에 관한 기초적 연구 III)

  • 이주희
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.21 no.2
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    • pp.89-98
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    • 1985
  • As a primary step in studying the effects of the netting porosity on the net-shape in the four-seam trawling net, a series of experiments were performed changing the porosity of each panel, with the simplified mo:iel of the bag net made of porous vinyl film and that ma:ie of net webbing. These models were suspended horizontally in circularly flowing water, with two pairs of susp~nding threais to four points of symetry at the border of the bag mouth in place of both wing nets. And then, the section shape of the bag mouth photographed and the tensions on both pairs of suspending threads were measured with two load cells in circularly flowing water. From the results, the auther estimated an experimental equation from the relationship between the porosity of each panel in the bag net and the section shape of the bag mouth, h/w=k (l-Pr_u/lPr_s)

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Design and Analysis of Wing-Tip and Wing-Body Fairings (날개 끝과 날개 동체 페어링의 설계 및 공력해석)

  • Park, Sang-Il;Kwak, Ein-Keun;Lee, Seung-Soo
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.39 no.4
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    • pp.289-296
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    • 2011
  • In this study, fairing configurations for an aircraft are designed and the aerodynamic analyses of the fairings are performed to find the best choice for the aircraft. Fairings considered are wing-tip fairing and wing-body fairing. Wing alone analyses are done for the wing-tip faring selection, while wing-body-tail analyses are done for the wing-body fairing selection. A 3-D RANS solver with Menter's ${\kappa}-{\omega}$ SST turbulence model are used for the aerodynamic analyses. The effects on the drag of the aircraft are examined by comparing the analysis results with and without the farings.

A Study on Longline Type Aquaculture Facilities in the Open Sea : Frequency Domain Analysis of Cable-Buoy-Weight Mooring System (내파성 가리비 연승식 양식시설에 관한 연구 - 케이블-부이-중량물 계류시스템의 주파수 영역 해석 -)

  • Shin, H.;Kim, D.S.
    • Journal of the Society of Naval Architects of Korea
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    • v.33 no.4
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    • pp.162-174
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    • 1996
  • Longline type aquaculture facilities in the open sea are based on the cable-buoy-weight mooring system. For their optimal design it is necessary to estimate tensions along the mooring lines including the attachment points of buoys and weights. However, the dynamic analysis is very complicated due to the nonlinear behaviors of the mooring lines and the effects of wave and current. In this paper, parametric studies for various buoy-weight cases are shown. Finite difference scheme is employed in obtaining eigenfrequencies in the frequency domain. Nonlinear hydrodynamic drag forces are equivalently linearized.

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Numerical Simulation of Laminar Flows for a Circular Cylinder Vertically Piercing Free Surface (수직원통 주위의 자유표면 층류운동의 수치해석)

  • Bum-Sang Yoon;Yoon-Ho Kim
    • Journal of the Society of Naval Architects of Korea
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    • v.30 no.1
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    • pp.104-114
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    • 1993
  • In this paper, effects of free surface on viscous flow is investigated. Continuity equation coupled with Navier-Stokes equations are solved numerically by using an artificial compressibility method[1, 2]. The body-fitted generalized curvilinear coordinate system is employed to deal with arbitrary body shape. The IAF scheme with finite difference method is used to solve the equations, and a diagonal algorithm is applied to time-varying Jacobian matrices for the computational economics. Free surface shape is obtained by applying zero pressure condition to still water surface at each time step. A numerical test is made for larminar flow around a circular cylinder vertically piercing the free surface. Computed flow patterns are largely affected by the existance of free surface in low Reynolds number flows treated in this paper. Free surface causes viscous pressure drag to vary much in depth direction in accordance with the variations of flow pattern.

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Modelling cavitating flow around underwater missiles

  • Petitpas, Fabien;Saurel, Richard;Ahn, Byoung-Kwon;Ko, Sung-Ho
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.3 no.4
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    • pp.263-273
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    • 2011
  • The diffuse interface model of Saurel et al. (2008) is used for the computation of compressible cavitating flows around underwater missiles. Such systems use gas injection and natural cavitation to reduce drag effects. Consequently material interfaces appear separating liquid and gas. These interfaces may have a really complex dynamics such that only a few formulations are able to predict their evolution. Contrarily to front tracking or interface reconstruction method the interfaces are computed as diffused numerical zones, that are captured in a routinely manner, as is done usually with gas dynamics solvers for shocks and contact discontinuity. With the present approach, a single set of partial differential equations is solved everywhere, with a single numerical scheme. This leads to very efficient solvers. The algorithm derived in Saurel et al. (2009) is used to compute cavitation pockets around solid bodies. It is first validated against experiments done in cavitation tunnel at CNU. Then it is used to compute flows around high speed underwater systems (Shkval-like missile). Performance data are then computed showing method ability to predict forces acting on the system.

PWR Hot Leg Natural Circulation Modeling with MELCOR Code

  • Park, Jae-Hong;Lee, Jong-In;Randall. K. Cole;Randall. O. Gauntt
    • Proceedings of the Korean Nuclear Society Conference
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    • 1997.10a
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    • pp.772-777
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    • 1997
  • Previous MELCOR and SCDAP/RELAP5 nodalizations for simulating the counter-current, natural circulation behavior of vapor flow within the RCS hot legs and SG U-tubes when core damage progress can not be applied to the steady state and water-filled conditions during the initial period of accident progression because of the artificially high loss coefficients in the hot legs and SG U-tubes which were chosen from results of COMMIX calculation and the Westinghouse natural circulation experiments in a 1/7-scale facility for simulating steam natural circulation behavior in the vessel and in the hot leg and SG during the TMLB' scenrio. The objective of this study is to develop a natural circulation modeling which can be used both for the liquid flow condition at steady state and for the vapor flow condition at the later period of in-vessel core damage. For this, the drag forces resulting from the momentum exchange effects between the two vapor streams in the hot leg was modeled as a pressure drop by pump model. This hot leg natural circulation modeling of MELCOR was able to reproduce similar mass flow rates with those predicted by previous models.

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Interface Chemical and Hydrodynamic Aspects of Deinking Process Using Flotation for Waste paper Recycling(II) (부유선별법을 적용한 탈묵공정의 계면화학적 및 수력학적 원리(II) -수력학적 원리를 중심으로-)

  • Sun-Young Park
    • Resources Recycling
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    • v.5 no.4
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    • pp.11-16
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    • 1996
  • In the flotation system for deinking process, the ink partcles musl collidc with the air bubbles for adhesion The probability of bubble-particle collision is largely dependent on the hydrodynamic conditions The main reason for the very small ink particles not to be able to float easily may be tound in the hydrodynamic effects, which make small ink particlcs move following the slreamlines around the bubbles rather than achually collide with bubbles. Also. the low floatabdily of the large and heavy ink particles is due to the gravity force and viscous drag which affect uprising molinn of particles through the liquid. Therefore, it is vely important to control not only the surface chemical conditions but the hydrodynamic conditions in practical floialion system

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Study on the Vortex Shedding Phenomena Near Free Surface (자유수면 근처에서의 보오텍스 방출 현상에 관한 고찰)

  • Seok-Won Hong;Pan-Mook Lee
    • Journal of the Society of Naval Architects of Korea
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    • v.28 no.2
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    • pp.118-131
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    • 1991
  • The effects of free surface on vortex shedding phenomena around a bluff body were studied by both numerical simulation and flow visualization experiments. A vortex method, which approximates the vorticity field as the sum of discrete vortices; was used for the numerical simulation. Flow visualization experiments were performed in the KRISO cavitation tunnel. Hydrogen bubble was used as illumination material. Free surface elevation was also measured during experiments. The hydrodynamic drag and lift were predicted by numerical simulation. The predicted period of vortex shedding was compared with the results of experiments.

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Study on Dynamics Modeling and Depth Control for a Supercavitating Underwater Vehicle in Transition Phase (초공동 수중운동체의 천이구간 특성을 고려한 동역학 모델링 및 심도제어 연구)

  • Kim, Seon Hong;Kim, Nakwan
    • Journal of the Society of Naval Architects of Korea
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    • v.51 no.1
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    • pp.88-98
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    • 2014
  • A supercavitation is modern technology that can be used to reduce the frictional resistance of the underwater vehicle. In the process of reaching the supercavity condition which cavity envelops whole vehicle body, a vehicle passes through transition phase from fully-wetted to supercaviting operation. During this phase of flight, unsteady hydrodynamic forces and moments are created by partial cavity. In this paper, analytical and numerical investigations into the dynamics of supercavitating vehicle in transition phase are presented. The ventilated cavity model is used to lead rapid supercavity condition, when the cavitation number is relatively high. Immersion depth of fins and body, which is decided by the cavity profile, is calculated to determine hydrodynamical effects on the body. Additionally, the frictional drag reduction associated by the downstream flow is considered. Numerical simulation for depth tracking control is performed to verify modeling quality using PID controller. Depth command is transformed to attitude control using double loop control structure.