• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 추계학술대회 논문집
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• pp.1835-1842
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• 2007

The purpose of this paper describes the changes of TGV & ICE series' nose shape by increasing train speed and according to the periodical characteristics. As the speed increases, the length of the nose shape trends to lengthen longer. But the nose shape length does not increase as speed improves by optimized nose shape to reduce aerodynamic drag and micro-pressure wave in tunnels. TGV & ICE series' nose shape can be classified into Advanced paraboloid type, Shape-nosed type, Organic double-edged type and Flat-nosed type by the advance research(the changes of Shinkansen vehicle' nose shape) of high speed railway. Because it trends to be diversified and characterized more and more. This paper analyzed and introduced as TGV & ICE series' nose shape by top 2 nation (Germany, France) and high speed railway in the past years(1980-2007) for their railway design trends by new positioning(Advance research).

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 춘계학술대회논문집
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• pp.57-65
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• 2009

An efficient and high-fidelity design approach for wing-body shape optimization is presented. Depending on the size of design space and the number of design of variable, aerodynamic shape optimization process is carried out via different optimization strategies at each design stage. In the first stage, global optimization techniques are applied to planform design with a few geometric design variables. In the second stage, local optimization techniques are used for wing surface design with a lot of design variables to maintain a sufficient design space with a high DOF (Degree of Freedom) geometric change. For global optimization, Kriging method in conjunction with Genetic Algorithm (GA) is used. Asearching algorithm of EI (Expected Improvement) points is introduced to enhance the quality of global optimization for the wing-planform design. For local optimization, a discrete adjoint method is adopted. By the successive combination of global and local optimization techniques, drag minimization is performed for a multi-body aircraft configuration while maintaining the baseline lift and the wing weight at the same time. Through the design process, performances of the test models are remarkably improved in comparison with the single stage design approach. The performance of the proposed design framework including wing planform design variables can be efficiently evaluated by the drag decomposition method, which can examine the improvement of various drag components, such as induced drag, wave drag, viscous drag and profile drag.

• 문화기술의 융합
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• 제6권1호
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• pp.501-506
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• 2020

본 실험 연구에서는 대표적인 네 가지 타입의 승용차 차량형태에 대한 공기역학(공력) 성능 분석, 측면 유리의 각도에 따른 공력 성능 분석, 엔진후드(엔진 덮개)의 각도차이에 따른 공력 성능 분석, 루프 라인의 각도 차이에 따른 공력 성능 분석을 통해 차량의 형태 변화에 따라 공력 성능이 어떻게 변화하는지를 종합적으로 분석해 보았다. 실험결과 비스듬히 떨어지는 후면 유리 라인은 공력 성능을 저하시켰고, 루프의 각도 차이에 따른 공력 성능 차이는 거의 나타나지 않았으며 일찍 떨어지는 후면 라인은 공력 성능에 가시적인 영향을 끼치지 않았다. 차량의 루프라인이 수평으로 늦게까지 이어지다 천천히 떨어지는 후면 유리 라인은 스타일링에 도움이 될지언정 공력 성능은 저하시켰다. 후방 디퓨저의 경우 차체의 형태에 따라 그 성능 효과가 달라지는 것으로 판단되었다.

• 한국항공우주학회지
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• 제49권11호
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• pp.901-907
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• 2021

본 연구에서는 다양한 유도탄 노즈 형상과 유동조건에 대한 공력계수를 예측할 수 있는 인공신경망 기반의 공력 산출 기법을 제시한다. Missile DATCOM를 통해 유도탄 노즈 형상, 유동조건, 유도탄 공력계수로 구성된 학습 데이터셋을 구축하였다. 인공신경망의 예측 성능을 향상시키기 위해 데이터 전처리 과정으로 데이터 정규화를 진행하였고, 과대적합을 방지하기 위해 신경망 학습 과정 중 드롭아웃 기법을 사용하였다. 신경망을 통해 학습하지 않은 유도탄 노즈 형상과 유동조건에 대한 공력계수를 예측하였고 이를 Missile DATCOM 해석 결과와 비교하여 신경망의 성능을 검증하였다. 그 결과 본 연구에서 구축한 신경망은 학습하지 않은 유도탄 노즈 형상과 유동조건에 대한 유도탄 공력계수를 정확하게 산출할 수 있음을 확인하였다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 춘계학술대회 논문집
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• pp.1-6
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• 2011

In this study, wind tunnel test were conducted to improve an aerodynamic performance of HEMU400X pantograph system with 4 types of pantograph housing models. Experimental models were 1/4 scaled pantograph system, 1/4 scaled ground plate which is scaled down to real roof shape of HEMU-400x, and 4 types of pantograph housing models. The free stream of wind tunnel were 20, 40, 60, 70m/s. The lift and drag forces were measured with 2-axis load cell. And, Total pressure were measured with rake in the wake region of panhead. In addition, Surface flow visualization by tufts were performed to know flow characteristics around pantograph housing. According to the results of force tests and surface visualizations, pantograph housing shape is important part because the shape affects to pantograph system. Therefore, it is considered that adaption of pantograph housing is more advantageous to decrease drag and acoustic noise.

• 한국전산유체공학회지
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• 제11권1호
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• pp.57-66
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• 2006

An optimal shape design approach is presented for a subsonic S-shaped intake using aerodynamic sensitivity analysis. Two-equation turbulence model is employed to capture strong counter vortices in the S-shaped duct more precisely. Sensitivity analysis is performed for the three-dimensional Navier-Stokes equations coupled with two-equation turbulence models using a discrete adjoint method For code validation, the result of the flow solver is compared with experiment data and other computational results of bench marking test. To study the influence oj turbulence models and grid refinement on the duct flow analysis, the results from several turbulence models are compared with one another and the minimum number of grid points, which can yield an accurate solution is investigated The adjoint variable code is validated by comparing the complex step derivative results. To realize a sufficient and flexible design space, NURBS equations are introduced as a geometric representation and a new grid modification technique, Least Square NURBS Grid Approximation is applied With the verified flow solver, the sensitivity analysis code and the geometric modification technique, the optimization of S-shaped intake is carried out and the enhancement of overall intake performance is achieved The designed S-shaped duct is tested in several off-design conditions to confirm the robustness of the current design approach. As a result, the capability and the efficiency of the present design tools are successfully demonstrated in three-dimensional highly turbulent internal flow design and off-design conditions.

• 한국유체기계학회 논문집
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• 제2권3호
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• pp.30-36
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• 1999

Blade shape profile in the axial compressor is one of the most important factors governing its aerodynamic characteristics. Manufacturing tolerance, which is inevitable in the blade manufacturing processes, may change blade profile and as a consequence, it will affect the compressor performance. In this paper, influence of manufacturing tolerance on the aerodynamic characteristics of axial compressor blades with distortion of blade profile curvatures is investigated by using a flow simulation technique. It is found that manufacturing tolerance can be an important factor affecting the source of both profile and wake losses of the axial compressor blades.

• 한국군사과학기술학회지
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• 제10권1호
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• pp.33-43
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• 2007

Using the more common conventional chordwise aerodynamic approach, flapping a flat plate wing with zero degree chordwise pitch angle of attack and no relative wind should not produce lift. However, in hover, with no forward relative velocity and zero degree chordwise pitch angle of attack, flapping flat plate wings does in fact produce lift. In the experiments peformed for this paper, the flapping motion is considered pure(downstroke and upstroke) with no flapping stroke plane inclination angle. No changes in chordwise pitch angle are made. The total force is measured using a force transducer and the net aerodynamic force is determined from this measured total force by subtracting the experimentally determined inertial contribution. These experiments were repeated at various flapping frequencies and for various wing planform sizes for flat plate wings. The trends in the aerodynamic lift variation found using a force transducer have nearly identical shape for various flapping frequencies and wing planform sizes.

• Wind and Structures
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• 제26권4호
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• pp.253-266
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• 2018

In this paper, the aerodynamic performance of two new cable surfaces with concave fillets (strakes) is examined and compared to plain, dimpled and helically filleted surfaces. To this end, an extensive wind-tunnel campaign was undertaken. Different samples with different concave fillet heights for both new surfaces were tested and compared to traditional surfaces in terms of aerodynamic forces (i.e. drag and lift reduction) and rain-rivulet suppression. Furthermore, flow visualization tests were performed to investigate the flow separation mechanism induced by the presence of the concave fillet and its relation to the aerodynamic forces. Both new cable surfaces outperformed the traditional surfaces in terms of rain-rivulet suppression thanks to the ability of the concave shape of the fillet to act as a ramp for the incoming rain-rivulet. Furthermore, both new surfaces with the lowest tested fillet height were found to have drag coefficients in the supercritical Reynolds range that compare favorably to existing cable surfaces, with an early suppression of vortex shedding.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2010년 춘계학술대회논문집
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• pp.464-467
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• 2010

Ice accretion on aircraft surface in icing condition induces external shape changes that may result in a hazard factor for aircraft safety. In case of aircraft main wing with high lift equipment, ice accretion is observed around leading edge and flap. During the design phase, location of ice accretion and associated aerodynamic characteristics must be investigated. In this study, icing effects on aerodynamic characteristics of the main wing section of KC-100 aircraft are investigated using an Eulerian-based FENSAP-ICE code in various icing conditions.