• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.12
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• pp.1192-1200
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• 2009

This paper deals with an analytical study on the aileron reversal characteristics of anisotropic composite aircraft wings modelled as thin-walled beam and having bending-torsion structural couplings caused by Circumferentially Asymmetric Stiffness layup scheme. For a study on the aileron reversal of CAS composite wings, it is essential to consider the following effects such as warping restraint, transverse shear flexibility, bending-twist structural coupling, wing aspect ratio, ratio of span-wise and chord-wise length of aileron to wing, and sweep angle, etc. The results on the aileron reversal could have a significant role in more efficient designs of thin-walled composite wing aircraft for which this aeroelastic instability is one of the most critical ones.

• International Journal of Naval Architecture and Ocean Engineering
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• v.4 no.4
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• pp.447-459
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• 2012

The present study numerically investigates the effect of the wavy leading edge on hydrodynamic characteristics for the flow of rectangular wings with the low aspect ratio of 1.5. Five different wave lengths at fixed wavy amplitude have been considered. Numerical simulations are performed at a wide range of the angle of attack ($0^{\circ}{\leq}{\alpha}{\leq}40^{\circ}$) at one Reynolds number of $10^6$. The wavy wings considered in this study did not experience enough lift drop to be defined as the stall, comparing with the smooth wing. However, in the pre-stall region, the wavy wings reveal the considerable loss of the lift, compared to the smooth wing. In the post-stall, the lift coefficients of the smooth wing and the wavy wings are not much different. The pressure coefficient, limiting streamlines and the iso-surface of the spanwise vorticity are also highlighted to examine the effect of the wave length on the flow structures.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.5
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• pp.381-389
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• 2011

In this study, we are focusing our attention on lift characteristics of the low aspect wings for Wing-In Ground effect crafts (WIG). Experimental measurements at an open-type wind tunnel are carried out and results are comparatively presented. In order to simulate the realistic ground condition in where the WIG craft is flying, moving ground is implemented by a conveyor belt rotating with the same velocity of the inflow. We consider two different wings (NACA0012 and DHMTU section) which have four different aspect ratios (0.5, 1.0, 1.5 and 2.0). Forces acting on the wings are measured and lift characteristics are elaborately investigated for various different conditions. In addition, end-plate effects are estimated. Results are validated by comparing with theoretic solutions of the symmetric airfoil. Present results show that ground effects are differently generated in moving or fixed ground conditions, and hence left characteristics are affected by the ground condition. Consequently, accurate aerodynamic forces acting on the WIG craft are guaranteed in a realistic moving ground condition.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2857-2861
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• 2007

Flow and aerodynamic characteristics were analyzed numerically for a commercial passenger airplane, Boeing 747-400, flying in the cruising condition. The model geometry with 100:1 in scale was obtained by the photo scanning measurement with the maximum error of 1.4% comparing with the real airplane dimension. The three-dimensional inviscid steady compressible governing equations were solved by the finite volume method in the unstructured grid system. The convective terms were treated by the Crank-Nicholson and first-order upwind schemes. In the computational results, the strong wing-tip vortices were clearly observed and the pressure contours on the airplane surface were suggested. The lift and drag forces in the wing with engines increase by 1.49% and 3.9%, respectively compared with the case without engines. The aerodynamic forces were estimated quantitatively for each element which consists of the airplane.

• Journal of the Society of Naval Architects of Korea
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• v.50 no.5
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• pp.343-348
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• 2013

When a natural frequency of the trailing edge of a wing is close to a vortex shedding frequency, an amplitude of the edge oscillation becomes maximal; it makes intensive noise called singing. Motion of the trailing edge may also feedback to the vortex shedding so that self-sustained oscillation appears, and a resonant frequency is locked in some interval of the speed of the incident flow. In this study, we first evaluate main features of oscillating characteristics of the wing. Second we simulate fluid-structure interaction of the wing with a flap using a commercial code, ANSYS-CFX, and investigate lift characteristics in a frequency domain.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.3 s.234
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• pp.295-305
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• 2005

To improve the aerodynamic effciency of TR-E2, a new configuration so called TR-E2Sl was introduced. TR-2251 is composed of different wing airfoil section and T-tail shape compared with TR-E2. Wind tunnel test for TR-EBS1 had been performed by changing the incidence angles of wing and deflection angles of control surfaces such as elevator and rudder. Also the on/off effect of ventral fin attached underneath of AFT fuselage was tested. Test result showed that variations of wing incidence angle did not cause any severe differences in aerodynamic characteristics. Longitudinal and directional characteristics of TR-E2S1 show stable for the pitch and yaw motions. However, the lateral stability of TR-E2S1 is not stable for a certain control surface deflection.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.331-334
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• 2010

The supersonic speeds slowing down by shock waves is a common problem during the transonic region. So how to study the status of shock on the surface of airplane and wings is crucial adjective during transonic region. However, the theoretical and computational transonic flow problems were very hard. This paper introduced using Navier-Stokes Schemes to study characteristics of AGARD Wing 445.6 by ANSYS CFX in transonic region. From simulations results, as the Mach number increases, shock waves appear in the flowfield, getting stronger as the speed increases, these shock waves will lead to a rapid increase in drag.

• Journal of Ship and Ocean Technology
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• v.12 no.3
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• pp.14-25
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• 2008

Recently, there has been a serious effort to design a wing in ground effect (WIG) craft. Vehicles of this type might use low aspect ratio wings defined as those with smaller than 3. Design and prediction techniques for fixed wings of relatively large aspect ratio are reasonably well developed. However, Aerodynamic problems related to vortex lift on wings of low aspect ratio have made it difficult to use existing techniques. In this work, we firstly focus on understanding aerodynamic characteristics of low aspect ratio wings and comparing the results from experimental measurements and currently available numerical predictions for both inviscid and viscous flows. Second, we apply an improved numerical method, "B-spline based high panel method with wake roll-up modeling", to the same problem.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.35 no.6
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• pp.535-544
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• 2017

UAVs (Unmanned Aerial Vehicle) are generally classified into fixed-wing and rotary-wing type, and both have very different flight characteristics each other during photographing. These can greatly effect on the quality of images and their productions. In this paper, the change of the camera rotation angle at the moment of photographing was compared and analyzed by calculating orientation angles of each image taken by both types of payload. Study materials were acquired at an altitude of 130m and 260m with fixed-wing, and at an altitude of 130m with rotary-wing UAV over an agricultural land. In addition, an accuracy comparison of boundary surveying methods between UAV photogrammetry and terrestrial cadastral surveying was conducted in two parcels of the study area. The study results are summarized as follows. The differences at rotation angles of images acquired with between two types of UAVs at the same flight height of 130m were significantly very large. On the other hand, the distance errors of parcel boundary surveying were not significant between them, but almost the same, about within ${\pm}0.075m$ in RMSE (Root Mean Square Error). The accuracy of boundary surveying with a fixed-wing UAV at 260m altitude was quite variable, $0.099{\sim}0.136m$ in RMSE. In addition, the error of area extracted from UAV-orthoimages was less than 0.2% compared with the results of the cadastral survey in the same two parcels used for the boundary surveying, In conclusion, UAV photogrammetry can be highly utilized in the field of cadastral surveying.

• Ocean Systems Engineering
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• v.6 no.3
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• pp.245-264
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• 2016

The iterative boundary element method (IBEM) developed originally before for cavitating two-dimensional (2-D) and three-dimensional (3-D) hydrofoils moving under free surface is modified and applied to the case of 2-D (two-dimensional) airfoils and 3-D (three-dimensional) wings over water. The calculation of the steady-state flow characteristics of an inviscid, incompressible fluid past 2-D airfoils and 3-D wings above free water surface is of practical importance for air-assisted marine vehicles such as some racing boats including catamarans with hydrofoils and WIG (Wing-In-Ground) effect crafts. In the present paper, the effects of free surface both on 2-D airfoils and 3-D wings moving steadily over free water surface are investigated in detail. The iterative numerical method (IBEM) based on the Green's theorem allows separating the airfoil or wing problems and the free surface problem. Both the 2-D airfoil surface (or 3-D wing surface) and the free surface are modeled with constant strength dipole and constant strength source panels. While the kinematic boundary condition is applied on the airfoil surface or on the wing surface, the linearized kinematic-dynamic combined condition is applied on the free surface. The source strengths on the free surface are expressed in terms of perturbation potential by applying the linearized free surface conditions. No radiation condition is enforced for downstream boundary in 2-D airfoil and 3-D wing cases and transverse boundaries in only 3-D wing case. The method is first applied to 2-D NACA0004 airfoil with angle of attack of four degrees to validate the method. The effects of height of 2-D airfoil from free surface and Froude number on lift and drag coefficients are investigated. The method is also applied to NACA0015 airfoil for another validation with experiments in case of ground effect. The lift coefficient with different clearance values are compared with those of experiments. The numerical method is then applied to NACA0012 airfoil with the angle of attack of five degrees and the effects of Froude number and clearance on the lift and drag coefficients are discussed. The method is lastly applied to a rectangular 3-D wing and the effects of Froude number on wing performance have been investigated. The numerical results for wing moving under free surface have also been compared with those of the same wing moving above free surface. It has been found that the free surface can affect the wing performance significantly.