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전파하는 변동유장 중 전진하며 동요하는 2차원 수중익에 의한 추력
최윤락(Yoon-Rak Choi) 한국해양환경·에너지학회 2012 한국해양환경공학회 학술대회논문집 Vol.2012 No.5
This study considers a two-dimensional hydrofoil that is fully submerged and oscillating with forward speed. The flow field is assumed as the propagating vertical velocity field Using the perturbation theory, the problem is linearized, and the leading-order lift force is surveyed. The thrust force is analytically derived as the second-order horizontal force. As an example, the lift ana thrust for a flapping flat plate in heaving and pitching modes are analyzed. The parameters affecting the thrust is listed.
전파하는 변동유장 중 전진하며 동요하는 2차원 수중익에 의한 추력
최윤락(Yoon-Rak Choi) 대한조선학회 2012 대한조선학회 학술대회자료집 Vol.2012 No.5
This study considers a two-dimensional hydrofoil that is fully submerged and oscillating with forward speed. The flow field is assumed as the propagating vertical velocity field. Using the perturbation theory, the problem is linearized, and the leading-order lift force is surveyed. The thrust force is analytically derived as the second-order horizontal force. As an example, the lift and thrust for a flapping flat plate in heaving and pitching modes are analyzed. The parameters affecting the thrust is listed.
최윤락(Yoon-Rak Choi) 한국해양공학회 2013 韓國海洋工學會誌 Vol.27 No.1
In this paper, the effects of a foil attached to a ship on the ship motion, added resistance, and thrust generation in waves are analyzed. The unsteady theory for a two-dimensional foil is introduced to determine the coupled motion responses of the ship and foil. The thrust caused by the oscillating foil if evaluated and compared to the added resistance of the ship, so that a positive net thrust can be possible in waves. A comparison of the results of unsteady, quasi-steady, and experimental analysis is performed.
전파하는 변동유장 중 전진하며 동요하는 2차원 수중 날개에 의한 추력
최윤락(Yoon-Rak Choi) 한국해양공학회 2012 韓國海洋工學會誌 Vol.26 No.5
This paper considers a two-dimensional hydrofoil that is fully submerged and oscillating with forward speed. The flow field is assumed to be a propagating vertical velocity field. Using the perturbation theory, the problem is linearized, and the leading-order lift force is surveyed. The thrust force is analytically derived as the second-order horizontal force. As an example, the lift thrust for a flapping flat plate in heaving and pitching modes are analyzed. The parameters affecting the thurst are listed. The thrust is expressed in terms of the quadratic transfer functions in relation to the disturbances. The quadratic transfer functions are studied parametrically to assess the most favorable thrust.
수평 지반에 놓인 액체 저장용 막구조물 형상의 단면 체적에 따른 해석적 해
최윤락(Yoon-Rak Choi) 한국해양공학회 2011 韓國海洋工學會誌 Vol.25 No.2
In this paper, a liquid-filled long membrane container resting on a horizontal foundation is considered. All of the quantities are normalized to obtain similarity solutions. A system of nonlinear ordinary differential equations with undetermined boundary conditions is solved analytically. The integration of the curvature gives the solutions, which are expressed in terms of the elliptic integrals. A method for finding the shape and characteristic values is proposed for a given cross-sectional volume. The validity of these solutions is confirmed, and some results are shown for characteristic values and shapes.
최윤락(Yoon-Rak Choi) 한국해양공학회 2011 韓國海洋工學會誌 Vol.25 No.1
A compact array system of small buoys is used for wave energy extraction. To evaluate the performance of this system, hydrodynamic analysis is carried out in regular waves using the higher order boundary element method. The motion response of each buoy is calculated considering hydrodynamic interactions caused by other buoys. The effect of energy extraction device is modeled as a linear damping load. The efficiencies of energy conversion are compared using the various sizes and arrangements of the array system and the damping coefficients for energy extraction. The increase in size or the packing ratio of the system gives better efficiency. However, the wave condition and the cost for the system should be considered to optimize performance from the perspective of engineering and economics. The proposed nondimensionalized damping coefficient for energy extraction is 0.1~0.5.
최윤락(Yoon-Rak Choi) 한국해양공학회 2009 韓國海洋工學會誌 Vol.23 No.4
An analytic similarity shape solution was studied for a two-dimensional floating and fluid-filled membrane structure. The static shape of a membrane structure can be expressed as a set of nonlinear ordinary differential equations. The integration of curvature leads to an analytic solution for the shape, which contains unknown boundary values. Matching the upper and lower shapes at the free surface incorporated with their buoyancy allowed the unknowns to be determined. Same characteristic values of similarity shapes were evaluated and shapes are illustrated for various density ratios and volume efficiency ratios.
최윤락(Yoon-Rak Choi),여환태(Hwan-Tae Yeo) 한국해양공학회 2009 韓國海洋工學會誌 Vol.23 No.6
The dynamic responses and drift forces in waves of a floating circular fish cage are analyzed considering hydroelastic effects. The method of generalized mode is used to calculate the hydroelastic responses of the floater of cage. The elastic mode shapes, generalized mass, and stiffness in dry mode are evaluated by using a structural analysis code. The higher-order boundary element method is adopted to analyze the interaction between fluid and deformable structure. Some results of vertical motions and drift forces are sho주 and compared with those for a rigid body.
전파하는 파동유장 중 전진하며 동요하는 2차원 날개의 동력해석
최윤락(Yoon-Rak Choi) 한국해양공학회 2019 韓國海洋工學會誌 Vol.33 No.3
In this study, a two-dimensional oscillating foil with forward speed in a propagating wave flow field was considered. The time-mean power to maintain the heaving and pitching motions of the foil was analyzed using the perturbation theory in an ideal fluid. The power, which was a non-linear quantity of the second-order, was expressed in terms of the quadratic transfer functions related to the mutual product of the heaving and pitching motions and incoming vertical flow. The effects of the pivot point and phase difference among the disturbances were studied. The negative power, which indicates energy extraction from the fluid, is shown as an example calculation.
3차원 정적 집중하중을 받는 복합 탄성 케이블의 정적 해석
최윤락(Yoon-Rak Choi) 한국해양공학회 2014 韓國海洋工學會誌 Vol.28 No.3
An elastic cable with piecewise constant properties under the action of concentrated static loads is studied analytically. Analytic solutions for catenary cables are combined at the discontinuous points caused by the discontinuous elastic properties or concentrated loads. The application of the boundary conditions at both ends of the multi-component cable results in three algebraic non-linear equations for three unknown parameters, which are determined numerically. The solutions for the shape, tension, elongation, and cross-sectional contraction of the cable are expressed in dosed forms. Some examples are given for cases of two-and three-dimensional loads.