• International Journal of Naval Architecture and Ocean Engineering
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• 제7권5호
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• pp.785-794
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• 2015

To obtain low resistance and high efficiency energy-saving ship, minimum total resistance hull form design method is studied based on potential flow theory of wave-making resistance and considering the effects of tail viscous separation. With the sum of wave resistance and viscous resistance as objective functions and the parameters of B-Spline function as design variables, mathematical models are built using Nonlinear Programming Method (NLP) ensuring the basic limit of displacement and considering rear viscous separation. We develop ship lines optimization procedures with intellectual property rights. Series60 is used as parent ship in optimization design to obtain improved ship (Series60-1) theoretically. Then drag tests for the improved ship (Series60-1) is made to get the actual minimum total resistance hull form.

• 대한기계학회논문집B
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• 제27권5호
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• pp.655-667
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• 2003

Turbulent flow over a fully-developed wavy channel is investigated by the nonlinear $k-\varepsilon-f_\mu$ model of Park et al.⁽¹⁾ The Reynolds number is fixed at $Re_{b}$ = 6760 through all wave amplitudes and the wave configuration is varied in the range of $0\leq\alpha/\lambda\leq0.15$ and $0.25\leq{\lambda}/H\leq4.0$. The predicted results for wavy channel are validated by comparing with the DNS data of Maa$\beta$ and Schumann⁽²⁾ The model performance Is shown to be generally satisfactory. As the wave amplitude increases, it is found that the form drag grows linearly and the friction drag is overwhelmed by the form drag. In order to verify these characteristics, a large eddy simulation is performed for four cases. The dynamic model of Germane et al.⁽³⁾ is adopted. Finally, the effects of wavy amplitude on separated shear layer are scrutinized.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.101-104
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• 2008

The sailfish is the fastest sea animal, reaching its maximum speed of 110km/h. On its skin, a number of V-shaped protrusions pointing downstream exist. Thus, in the present study, the possibility of reducing the skin friction using its shape is investigated in a turbulent boundary layer. We perform a parametric study by varying the height and width of the protrusion, the spanwise and streamwise spacings between adjacent ones, and their overall distribution pattern, respectively. Each protrusion induces a pair of streamwsie vortices, producing low and high shear stresses at its center and side locations, respectively. These vortices also interact with those induced from adjacent protrusions. As a result, the drag is either increased or unchanged for all the cases considered. In some cases, the skin friction itself is reduced but total drag including the form drag on the protrusions is larger than that of a smooth surface. Since the shape of present protrusions is similar to that used by Sirovich and Karlsson [Nature 388, 753 (1997)] where V-shaped protrusions pointing upstream were considered, we perform another set of experiments following their study. However, we do not obtain any drag reduction even with random distribution of those V-shaped protrusion.

• 한국해양공학회지
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• 제10권1호
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• pp.75-80
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• 1996

The importance of the impact force on the vertical offshore circular structure member in the surf zone due to the breaking wave has been recognized recently. In this paper characteristics of breaking wave forces and the corresponding estimation procedures for them are investigated. For the characterization of the wave forces, three parts, drag force, inertia force, impact force are categorized and identified, respectively. Among them the impact force is maimly studied and the concise form of the force is proposed with the application scheme for the design of offshore circular structure member. The resulting form porposed here for impact force is well coincided with former research results by other people. Except the impact force, so called Morison equation can be employed for the common offshore structure design. The drag force and inertia force are represented as convertionally for the profile except the breaking part. In the numerical example, for thpical sea condition and the member size, the proposed procedures for the breaking wave forces calculation are demonstrated. It is found that the impact force is the most deminant one comparing with inertia and drag forces in the surf zone.

• 대한조선학회논문집
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• 제40권5호
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• pp.10-16
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• 2003

To investigate the jet effect on circulation control, a segment of model was prepared and inserted horizontally across the test section of the cavitation tunnel. The hydrodynamic forces acting on the model were measured under the 2 dimensional flow behavior. Circulation flow control requires higher flow rate of water jet than boundary layer control does. Jet injection is effective in increasing lift coefficient and the increments reach to 160% in a certain combination of parameters such as an angle of attack, jet flow rate and flap angle. The blown water jet not only reduces form drag but also thrust effect, which is sometimes greater than the form drag in specific conditions.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 춘계학술대회 초록집
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• pp.183.3-183.3
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• 2010

This is the research of wind turbine that is designed to supply power to offshore buoy system. In order to reach maximum efficiency in limited space, vertical axis wind turbine was used. Vertical axis wind turbine system that was applied in this research has the form of lift and drag blade combined to achieve high efficiency at both high and low speed. In addition, support system was designed and developed to suit the offshore condition.

• 대한기계학회논문집
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• 제7권2호
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• pp.175-185
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• 1983

When a circular cylinder near the plane fluid-interface of different viscosities is in parallel and normal motion, solutions of the Oseen equation are obtained. Classical image method with Faxen's integral form is used to satisfy the boundary conditions on the plane interface. Coefficients of drag and lift increase as a cylinder approaches to the interface. But drag-coefficients of parallel motions with viscosity-ratio less than unity are decreased slightly. They show monotonic increase with Reynolds number in case of parallel motion, but minimum values of drag coefficients in normal motion are appeared. On the other hand Stokes' solution are obtained by taking limits of low Reynolds number except the case of parallel motion with viscosity-ratio not equal to infinity.

• 정보저장시스템학회:학술대회논문집
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• 정보저장시스템학회 2005년도 추계학술대회 논문집
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• pp.113-118
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• 2005

Small form factor optical disks for near-field optics using solid immersion lens were developed. Disk durability properties in terms of head-disk interface (HDI) properties were investigated by drag test, diamond like carbon film and lubricant film were coated on the small form factor disk to enhance HDI. Disks with glass substrates and lubricant films after heat treatment showed more durable characteristics. Coverlayers made of UV resin were uniformly coated by spin coating In which the ski-jump could not be formed by adopting outer ring technique.

• 정보저장시스템학회논문집
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• 제2권1호
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• pp.26-31
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• 2006

Small form factor optical disks for near-field optics using solid immersion lens were developed. Diamond like carbon film and lubricant film were coated on the small form factor optical disk to enhance the head-disk interface(HDI) characteristics. The disk durability properties in terms of HDI phenomena were investigated by drag test. Disks with glass substrates and the lubricant films experienced heat treatment showed more durable characteristics. Coverlayers made of UV resin were uniformly coated by spin coating in which the ski-jump could be removed by adopting outer ring technique

• 한국항공우주학회지
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• 제35권4호
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• pp.308-315
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• 2007

연구는 경비행기인 창공-91의 인증 획득을 위한 비행시험의 일부로서 상승성능을 파악하기 위하여 수행되었다. 창공-91은 1993년에 대한민국의 건설교통부로부터 최초로 인증을 취득한 단발엔진을 장착한 일반유형의 5인승 항공기이다. 상승을 위한 비행시험 절차 및 자료는 형식증명을 획득하는데 사용되었다. 톱니형 상승 데이터로부터 양항곡선방법으로 데이터를 처리하여 창공-91의 최대상승률, 최대상승각 속도, 최대상승률 속도, 그리고 절대상승한도를 구하였다. 또한, 상승성능의 결과로부터 양항곡선식을 구함으로써 형상항력계수와 오스왈드 효율계수를 비행기 설계시의 값과 비교하였다.