• Journal of Ocean Engineering and Technology
• /
• v.9 no.2
• /
• pp.75-82
• /
• 1995

The free surface effects on the aerodynamic performance of 2-D wings are investigated based on the potential flow approximation. The wing is represented b source and vortex distributions on the wing surface. The steady free surface effect is taken into account by source distribution on the free surface and the velocity potentials of air and water flows are obtained. Using three different techniques, namely, positive image method, inverse image method and source distribution method, numerical results are obtained for wave elevation, pressure distribution and lift coefficient with various foil sections. The wave elevation calculated by the inverse image method is shown to be very small even at higher speeds so that the free surface effect on the performance of wings is regraded negligible. However, the wave elevations by the positive image method and source distribution method are relatively high at higher speeds and accordingly the free surface effects on wings can not be neglected.

• Journal of Ship and Ocean Technology
• /
• v.11 no.3
• /
• pp.39-50
• /
• 2007

This study aims the observation of wing-in-ground effect near free surface. Numerical computations are carried out to observe the deformation of free surface and the effects on lift and drag. The detailed flow fields around two- and three-dimensional wings with NACA 0012 section are observed from the results of a commercial CFD program, FLUENT, and the local deformations of free surface are obtained by applying a Rankine panel method. In the present cases, the small deformation of free surface under the wings is observed, but different forces are found between solid wall and free surface when the speed of wings becomes large.

• Journal of Ocean Engineering and Technology
• /
• v.11 no.1
• /
• pp.55-64
• /
• 1997

A wing operating in close proximity to the ground exhibits a reduction in induced drag, which increase the lift/drag ratio. The poert-augmented ram (RAR) phenomenon involves directiing the efflux from forward mounted propulsion ststem under the wings, with the efflux nearly stagnated under the wings. In the present paper, 3 dimentional PAR was numerically studied by solving the Navier-Stokes equations. Pressure distribution and velocity vectors are calculated around the wing surface and the ground. Through the numerical simulation, Cp values and lift/drag ratio are carefully reviewed by changing the height/chord; 0.05, 0.1, 0.3 and 0.8. The shape of model is NACA 0012 with a span/chord ratio of 3.0. According to the numerical results, the relationship between lift/drag and height/chord is fairly reasonable.

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

• Composites Research
• /
• v.23 no.1
• /
• pp.44-50
• /
• 2010

In this paper, two different experiments, namely, salt water spray and salt water immersion, were performed to reproduce the contact of composites with the seawater for three kinds of woven fabric composite material systems which would be used for the WIG(wing in ground effect)craft. After aging 140 days in the salt water environment, material properties of carbon/epoxy and glass/epoxy composite such as tensile, compressive and shear stiffness and strength, and inter-laminar shear strength (ILSS) were measured. By comparing baseline material properties with degraded ones, the effects of the salt water environment on the composite mechanical properties were evaluated. From the experiments, it was confirmed that the difference in aging conditions had very small influence on composite properties. And it was found that tensile strength of carbon/epoxy composites showed little degradation, but much more degradation was observed in glass/epoxy composites. And large degradations on matrix dominant properties were observed. The salt water could damage the fiber-matrix interface, matrix properties and the glass fiber.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.19 no.5
• /
• pp.491-496
• /
• 2013

Since IMO(International Maritime Organization, hereafter IMO) has decided the Wing-In-Ground craft as one of the ships, A few regulations and recommendations have been revised and approved internationally and domestically. However, the navigation rules considering types and navigation characteristics to secure the safe navigation of Wing-In-Ground craft are not sufficient and especially, there are no navigation rule between Wing-In-Ground crafts. In this situation, it is judged that the navigation rules related to the Wing-In-Ground crafts in any condition of visibility should be moved to the section of the ones in sight of one another to define the responsibilities between WIG and other vessels, and the new regulation, which Type 'B' and 'C' WIGs should avoid Type 'A' WIG, has to be established to ensure the safe navigation between WIGs on the current laws.

• Bulletin of the Society of Naval Architects of Korea
• /
• v.32 no.5
• /
• pp.19-26
• /
• 1995

표면효과익선(WIG : Wing-In-Ground Effect Ship)은 해면 위를 낮게 비행함으로써 표면효과에 의한 양력 증가를 얻게 되어 초고속으로 운행할 수 있는 선박과 항공기의 중간형태의 차세대 해상운송 수단이다. 해면 위에 직접 이.착륙이 가능하기 때문에 별도의 활주로가 필요 없으며 수륙양용으로 사용 가능하다. 연근해 도서지방 관광 및 신선도 유지가 필수적인 신속화물의 수 송에도 사용될 수 있으며 해난사고 구난 및 해양 경비용으로도 사용가능한 해상 운송수단이다. 본 고에서는 표면효과익선의 특징을 간략히 살펴보고 21세기 고속해상운송수단으로 사용될 가 능성에 대한 경제성 검토 및 핵심애로기술을 살펴보았으며 러시아 표면효과익선의 발달과정과 개발된 선종의 특징을 조사하였다.

• Journal of Ocean Engineering and Technology
• /
• v.9 no.2
• /
• pp.71-74
• /
• 1995

A numerical model capable of simulating a 2-D airfoil flying over in the vicinity of the waves is discussed. Instead of treating the problem as a heaving oscillation one above the rigid flat wall, sources are distributed on the prescribed wave profile. The wave deformation due to the airfoil is assumed to be negligible and treated as a rigid undulated wall. The source and vortex are distributed on the surface of the foil. It is found that the variation of $C_L$ with wave steepness in severe and that the lift variation due to waves decreases as the wing height above the water surface increases.

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

• Microbiology and Biotechnology Letters
• /
• v.18 no.6
• /
• pp.620-623
• /
• 1990

To examine the inhibitory effect of nisin on Kimchi, comparison of the fermentation pattern was studied between the Kimchi added nisin (100 WIg) and the control Kimchi at 15cC. The Kimchi added nisin was showed pH 4.03 at 7 days fermentation, on the other hand the control Kimchi showing pH 4.04 at 5 days. And total acidity (lactic acid%) showed 0.47,0.69,0.88 at 5,9, 14 days fermentation compared with the control Kimchi showing 0.57,0.93, 1.13 respectively. Maximum growth of lactic acid bacteria on the control Kimchi indicated 1.8, 1.6 x 108 CFU/ml at 7 days but on presence of nisin indicated 9.5,6.4 x 107 CFU/ml at 5 days. In conclusion, nisin showed inhibitory action to Kimchi fermentation from pH, total activity and lactic acid bacteria count results.