• Title, Summary, Keyword: Free surface depth

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Hamilton제s Principle for the Free Surface Waves of Finite Depth (유한수심 자유표면파 문제에 적용된 해밀톤원리)

  • 김도영
    • Journal of Ocean Engineering and Technology
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    • v.10 no.3
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    • pp.96-104
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    • 1996
  • Hamilton's principle is used to derive Euler-Lagrange equations for free surface flow problems of incompressible ideal fluid. The velocity field is chosen to satisfy the continuity equation a priori. This approach results in a hierarchial set of governing equations consist of two evolution equations with respect to two canonical variables and corresponding boundary value problems. The free surface elevation and the Lagrange's multiplier are the canonical variables in Hamilton's sense. This Lagrange's multiplier is a velocity potential defined on the free surface. Energy is conserved as a consequence of the Hamiltonian structure. These equations can be applied to waves in water of finite depth including generalization of Hamilton's equations given by Miles and Salmon.

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On the Vertical Plane Dynamics Modeling and Depth Control of a Submerged Body Moving beneath Free Surface (수면 근처에서 운동하는 잠수체의 수직면 운동 모델링 및 심도 제어)

  • Yeo, Dong-Jin;Rhee, Key-Pyo;Park, Jeong-Yong;Choi, Ju-Hyuck
    • Journal of the Society of Naval Architects of Korea
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    • v.43 no.6
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    • pp.647-655
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    • 2006
  • In this paper, submerged body dynamics model in vertical plane which can include the effect of free surface and wave is suggested to simulate the motions of submerged body moving beneath free surface precisely. A controller is designed, which can maintain a constant depth below the mean sea level and minimize the pitch angle. Numerical simulations show that the designed controller is effective on depth keeping and minimizing pitch angle in regular waves and irregular waves.

Machining Characteristics in Turning Circular Free Formed Surface with Coated Tool (코팅공구에 의한 원형곡면 선삭가공시 절삭특성)

  • Wang, Duck Hyun;Kim, Won Il;Eom, Phil Hwan
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.2 no.1
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    • pp.85-91
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    • 2003
  • The experimental study for turning circular free fanned surface with TiN coated insert tool was conducted for different cutting conditions such as cutting speed, feed rate and depth-of-cut. For the fluctuation of 1.0mm depth-of-cut, the characteristics for machined surface and tool wear were less influenced by the feed rate and cutting speed than those of higher depth of cut. The higher surface roughness and surface precision were obtained in lower cutting speed. For the fluctuation of 1.5mm depth-of-cut, the higher surface roughness was obtained for the case of the lower feed rate of 0.05-10mm/rev and the higher cutting speed of 80m/min. For the fluctuation of 2.0mm depth-of-cut, the surface roughness and surface precision were too worse to machine the specimen And the flank wear on the tool was increased rapidly rather than the crater wear.

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PIV analysis of free surface effects on flow around a rotating propeller with varying water depth (자유표면과 수심깊이가 회전하는 프로펠러 주위 유동에 미치는 영향에 대한 PIV 해석)

  • Paik Bu Geun;Lee Jung Yeop;Lee Sang Joon
    • 한국가시화정보학회:학술대회논문집
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    • pp.40-43
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    • 2004
  • The effects of free surface on wake behind a rotating propeller were investigated experimentally in a circulating water channel with the variation of water depth. Instantaneous velocity fields were measured using two-frame PIV technique at tow different blade phases and ensemble-averaged to investigate the phase-averaged flow structure in the wake region. For an isolated propeller, the flow behind the propeller is influenced by the propeller rotation and the free surface. The phase-averaged mean velocity fields show that the potential wake and the viscous wake are formed by the boundary layers developed on the blade surfaces. The interaction between the tip vortices and the slipstream causes the oscillating trajectory of tip vortices. Tip vortices are generated periodically and the slipstream contracts in the near-wake region. The presence of free surface affects the wake structure largely, when the water depth is less than 0.6D. The free surface modifies the vortex structure, especially the tip and trailing vortices and flow structure in slipstreams of the propeller wake behind X/D = 0.3.

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PIV Analysis of Free Surface Effects on Flow Around a Rotating Propeller with Varying Water Depth (자유표면과 수심깊이가 회전하는 프로펠러 주위 유동에 미치는 영향에 대한 PIV 해석)

  • Paik, Bu-Geun;Lee, Jung-Yeop;Lee, Sang-Joon
    • Journal of the Society of Naval Architects of Korea
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    • v.42 no.5
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    • pp.427-434
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    • 2005
  • The free surface influenced the wake behind a rotating propeller and its effects were investigated experimentally in a circulating water channel with the variation of water depth. Instantaneous velocity fields were measured using two-frame PIV technique and ensemble-averaged to study the phase-averaged flow structure in the wake region. For an isolated propeller, the flow behind the propeller is affected only by the propeller rotation speed, the leading on the blades and the proximity of the propeller to the free surface. The phase-averaged mean velocity fields show that the potential wake and the viscous wake developed on the blade surfaces. The interaction between the tip vortices and the slipstream causes the oscillating trajectory of tip vortices. The presence of the free surface greatly affected the wake structure, especially for propeller immersion depth of 0.6D. At small immersion depths, the free surface modified the tip and trailing vortices and the slipstream flow structure downstream of X/D = 0.3 in the propeller wake.

Flow Structure of the Wake behind an Elliptic Cylinder Close to a Free Surface

  • Daichin;Lee, Sang-Joon
    • Journal of Mechanical Science and Technology
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    • v.15 no.12
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    • pp.1784-1793
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    • 2001
  • The flow fields around an elliptic cylinder of axis ratio AR=2 adjacent to a free surface were investigated experimentally using a water channel. The main objective is to understand the effect of the free surface on the flow structure in the near-wake. The flow fields were measured by varying the depth of cylinder submergence, for each experimental condition, 350 velocity fields were measured using a single-frame PIV system and ensemble-averaged to obtain the spatial distribution of turbulent statics. For small submergence depths a large-scale eddy structure was observed in the near-wake, causing a reverse flow near the free surface, downstream of the cylinder. As the depth of cylinder submergence was increased, the flow speed in the gap region between the upper surface of the cylinder and the free surface increased and formed a substantial jet flow. The general flow structure of the elliptic cylinder is similar to previous results for a circular cylinder submerged near to a free surface. However, the width of the wake and the angle of downward deflection of the shear layer developed from the lower surface of the elliptic cylinder are smaller tan those for a circular cylinder.

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Wave Patterns Due to a Point Impulse Travelling over Free Surface of Water of Finite Depth

  • Lee, G.J.;Chung, Y.K.
    • Journal of Hydrospace Technology
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    • v.2 no.1
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    • pp.10-17
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    • 1996
  • If a point impulse travels over free surface of water of finite depth, surface waves consist of divergent waves. The crestlines of those divergent waves are short and end on the cusp line if the impulse travels at a subcritical speed. But the crestlines become infinitely long and there are no cusps if the impulse travels at a supercritical speed.

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A study of low-power density laser welding process with evolution of free surface (자유표면변형을 고려한 저에너지밀도 레이저 용접공정 해석)

  • Ha, Eung-Ji;Kim, Woo-Seung
    • Proceedings of the KSME Conference
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    • pp.133-138
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    • 2003
  • In this study, numerical investigation has been performed on the evolution of weld pool geometry with moving free surface during low-energy density laser welding process. The free surface elevates near the weld pool edge if ${\partial}{\sigma}/dT$ is dominantly negative. On the contrary, the free surface rise at the center of weld pool in case of mainly positive ${\partial}{\sigma}/dT$. The predicted weld pool width and depth with moving free surface are 5∼15%$5{\sim}15%$ greater than those with flat weld pool surface. It is considered that weld pool surface oscillation during melting process augments convective heat transfer rate in the weld pool.

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Depth Controller Design for Submerged Body Moving near Free Surface Based on Adaptive Control (적응제어기법을 이용한 수면근처에서 운항하는 몰수체의 심도제어기 설계)

  • Park, Jong-Yong;Kim, Nakwan;Yoon, Hyeon Kyu;Kim, Su Yong;Cho, Hyeonjin
    • Journal of Ocean Engineering and Technology
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    • v.29 no.3
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    • pp.270-282
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    • 2015
  • A submerged body moving near the free surface needs to maintain its attitude and position to accomplish missions. It is necessary to validate the performance of a designed controller before a sea trial. The hydrodynamic coefficients of maneuvering are generally obtained by experiments or computational fluid dynamics, but these coefficients have uncertainty. Environmental loads such as the wave exciting force and suction force act on the submerged body when it moves near the free surface. Thus, a controller for the submerged body should be robust to parameter uncertainty and environmental loads. In this paper, the six-degree-of-freedom equations of motions for the submerged body are constructed. The suction force is calculated using the double Rankine body method. An adaptive control method based on an artificial neural network and proportional-integral-derivative control are used for the depth controller. Simulations are performed under various depth and speed conditions, and the results show the effectiveness of the designed controller.

A Study of tow-Power Density Laser Welding Process with Evolution of me Surface (자유표면변형을 고려한 저에너지밀도 레이저 용접공정 해석)

  • Ha Eung-Ji;Kim Woo-Seung
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.28 no.10
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    • pp.1202-1209
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    • 2004
  • In this study, numerical investigation has been performed on the evolution of weld pool geometry with moving free surface during low-energy density laser welding process. The free surface elevates near the weld pool edge and descends at the center of the weld pool if d$\sigma$/dT is dominantly negative. It is shown that the predicted weld pool width and depth with moving free surface are a little greater than those with flat weld pool surface. It is also believed that the weld pool surface oscillation during the melting process augments convective heat transfer rate in the weld pool. The present analysis with moving free surface should be considered when We number is very small compared to 1.0 since the deformation of the weld pool surface is noticeable as We number decreases.