• Journal of the Korean Society of Marine Environment & Safety
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• v.16 no.4
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• pp.393-399
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• 2010

Recently, a vessel's maneuvering performance is considered to be an important subject as marine pollution from the ships that stranded on a rock becomes more severe. So, IMO(International maritime organization) has adopted Resolution MSC.l37 to enhance international standards of ship's maneuverability. There's more than one way to improve ship's maneuverability. This research focused on improving ship's maneuverability by high-lift rudder. To predict the maneuverability, the numerical simulation model was used. The evaluation of maneuverability was carried out by turning test and zig-zag test. The results obtained with these simulation showed that the high-lift rudder would be effective in improving the turning ability of the ship. But it was clarified that there Has a possibility that course changing ability night become bad through an increase of rudder lift.

• Bulletin of the Society of Naval Architects of Korea
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• v.26 no.4
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• pp.27-34
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• 1989

A potential-based panel method is formulated for the analysis of a partially cavitating 2-dimensional hydrofoil. The method employs dipoles and sources distributed on the foil surface to represent the lifting and cavity problems, respectively. The kinematic boundry condition on the wetted portion of the foil surface is satisfied by requiring that the total potential vanish in the inner flow region of the foil. The dynamic boundary condition on the cavity surface is satisfied by requiring that the potential vary linearly, i.e., the velocity be constant. Green's theorem then results in a potential-based boundary value problem rather than a usual velocity-based formulation. With the singularities distributed on the exact hydrofoil surface, the pressure distributions are predicted with more improved accuracy than the zero-thickness hydrofoil theory, especially near the leading edge. The theory then predicts the cavity shape and cavitation number for an assumed cavity length. To improve the accuracy, the sources and dipoles on the cavity surface are moved to the newly computed cavity surface, where the boundary conditions are satisfied again. It was found that five iterations are necessary to obtain converged values, while only two iterations are sufficient for engineering purpose.

• 한국항공운항학회:학술대회논문집
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• 2015.11a
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• pp.35-38
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• 2015

본 연구에서는 스포츠급 경항공기 모형의 공력 특성을 공군사관학교 아음속 풍동에서 측정하였다. 풍동시험은 유속 40m/s에서 이전 모델과 최근 공력성능 향상을 위해 보완된 모델에 대해 비교 실험 수행하였으며, 정확한 데이터를 얻기 위하여 흐름각 효과, 벽면효과, 지지대 간섭효과를 보정하여 공력계수를 산출하였다. 실험 결과, 두 모델의 항력계수와 양력계수가 전체적으로 유사한 경향성을 보이나 고받음각에서의 양력특성의 차이가 발생하였다. 또한 실제 비행 시의 레이놀즈 수 유동을 모사하기 위하여 Trip strip의 영향에 대하여 실험하였다. 그 결과 Trip strip을 부착하였을 경우 항력계수가 증가하고 최소항력받음각이 낮아지는 결과를 획득하였다.

• Proceeding of EDISON Challenge
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• 2013.04a
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• pp.343-348
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• 2013

초임계 익형은 천음속 영역에서 비행하는 상업용 민간 항공기와 전투기 날개의 공력성능을 향상시키기 위해 Whitcomb R. T.가 제안 하였다. 초임계 익형은 상부표면을 평평하게 디자인하여 임계마하수보다 큰 마하수에서 나타나는 익형 주위의 충격파 출현을 지연시킴으로써 항력을 줄일 수 있고, 상부 표면의 평면 설계로 인한 양력 감소를 보정하기 위하여 하부 표면의 꼬리부분에 캠버가 있는 형상을 하고 있다. 본 연구에서는 EDISON CFD를 이용하여, 초임계 익형의 공력특성을 해석하고 Xfoil의 data와 비교 분석하였다. 또한, 초임계 익형의 형상을 변경하여 두께와 뒷전 캠버가 다른 초임계 익형을 설계하였다. 새로운 초임계 익형의 형상은 상용 프로그램 Maple12을 이용하여 Whitcomb Integral Supercritical Airfoil의 형상을 수정하여 구할 수 있다. 초임계 익형 주위의 유동을 2D압축성 유동으로 가정하고 EDISON CFD의 2D_Comp-2.0 솔버를 사용하여 수치해석을 수행하였다.

• Journal of the Society of Naval Architects of Korea
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• v.37 no.3
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• pp.57-68
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• 2000

The Power Augmented Ram(PAR) effect, which blows the down stream of the propellers into the underside of the wings and hence increases the pressure between the lower surface of the wings and the sea surface, is known significantly to enhance the performance of the WIG concept by reducing the take-off and landing speeds. The aerodynamic characteristics of a 20 passenger PARWIG are investigated by wind tunnel tests with the 1/20 scale model. The efflux of the forward mounted propellers are simulated by jet flows with a blower and duct system. The lift, drag, and pitch moment of the model with various ground clearances, angles of attack and flap angles are measured for the various jet velocities, jet nozzle angles, horizontal and vertical positions of the nozzle, and the nozzle diameters. The aerodynamic characteristics of the PARWIG due to these parametric changes are compared and pertinent discussions are included. It is shown that the proper use of the PAR can increase the lift coefficient of as much as up to 4.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.4
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• pp.345-352
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• 2011

In the present study, a three-dimensional CFD simulation on aerodynamic lift acting on windshield wiper blades was performed to improve the wiping performance of a vehicle moving at a high speed. To predict the reliable flow characteristics around the windshield wiper system, the computational domain included the full vehicle model with detailed geometry of wiper blades in the wind tunnel. From the numerical results, the drag and lift coefficients of wiper blade were obtained for the performance of windshield wiper. With this aerodynamic characteristics of windshield wiper, the effects of wiping angles and hood tip angle on the wiping performance of the windshield wiper were evaluated.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.24 no.1
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• pp.17-21
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• 1988

To the purpose of keeping net mouth of seine with bag open in the seining operation a novel method was devised and tested with model gear that double textile strips were fixed at both side edges of bag net mouth as sheering devices. The angles of attack of inner and outer strips were the 40 in degrees by adjusting rigging. In seining operation current that flowed between the double strips and generated side force on the strips sheered and opened the net mouth automatically. This paper described dynamic characteristics of the sheering strips and its automatic opening function of net mouth.

• Aerospace Engineering and Technology
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• v.9 no.1
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• pp.78-83
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• 2010

In the present paper, a flap was optimized to maximize the lift. A 2-element fowler flap system was utilized for optimization with an initial shape of general aviation airfoil and a flap shape designed by Wentz. Response surface method and Hicks-Henne shape function were implemented for optimization. 2-D Navier-Stokes method was used to solve flow field around aGA(W)-1 airfoil with a fowler flap. Commercial programs including Visual-Doc, Gambit/Tgridand Fluent were used. Upper surface shape and the flap gap were optimized and lift for landing condition was improved considerably. The original and optimized flaps were tested in the KARI's 1-m low speed wind tunnel to examine changes in aerodynamic characteristics. For optimized flap tests, the similar trend to prediction could be seen but stall angle of attack was lower than what was expected. Also, less gap than optimized design delayed stall and produced better lift characteristics. This is believed to be the effect of turbulence model.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.6
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• pp.591-596
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• 2012

Recently, a vessel's maneuvering performance is considered to be an important subject to secure safety at short sea shipping. Especially the high turning performance, which is required to avoid the marine pollution by the ships that was grounded, becomes more severe. In this paper, we discuss the effect of increasing rudder force on turning performance of short sea shipping ship by free running test in towing tank. First of all, we make the 47K PC model ship and high-lift rudder using Coanda effect. And we make the free running test system for the turning test in towing tank. And also we perform the turing test of 47K PC model in several changes of Coanda jet momentum and evaluate the turing performance such as advance and tactical diameter. Finally, we confirm that the increasing of rudder force is very effective to improvement of turning performance of short sea shipping ship.

• Aerospace Engineering and Technology
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• v.7 no.1
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• pp.24-29
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• 2008

Aircraft fuel efficiency is one of main concerns to aircraft manufacturers and to aviation companies because jet fuel price has tripled in last ten years. One of simple and effective methods to increase fuel efficiency is to reduce aircraft induced drag by using of wingtip devices. Induced drag is closely related to the circulation distribution, which produces strong wingtip vortex behind the tip of a finite wing. Wingtip devices including winglets can be successfully applied to reduce induced drag by wingtip vortex mitigation. Winglet design, however, is very complicated process and has to consider many parameters including installation position, height, taper ratio, sweepback, airfoil, toe-out angle and cant angle of winglets. In current research, different shapes of winglets are compared in the view of vortex mitigation. Appropriately designed winglets are proved to mitigate wingtip vortex and to increase lift to drag ratio. Also, the results show that winglets are more efficient than wingtip extension. That is the reason B-747-400 and B-737-800 chose winglets instead of a span increase to increase payload and range. Drag polar comparison chart is presented to show that minimum drag is increased by viscous drag of winglet, but at high lift, total drag is reduced by induced drag decrease. So, winglets are more efficient for aircraft that cruises at a high lift condition, which generates very strong wingtip vortex.