• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2002년도 춘계학술대회 논문집
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• pp.140-145
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• 2002

At present, wind tunnel test or CFD is used for predicting aerodynamic drag coefficient in motor company. But, wind tunnel test requires much cost and time, and CFD has about 30% error. In this study a predicting program of the aerodynamic drag coefficient based on empirical techniques was developed. Also a mathematical optimization method using GRG method was added to the program. The program was applied to six cars. Aerodynamic drag coefficient values of six cars were Predicted with 4.857% average error. The optimization method was also applied to six cars. Three parameters selected from sensitivity analysis were determined to reduce the afterbody drag coefficient to the value established by a designer and when some parameters were changed for a developing automotive, optimal modifiable parameters were determined to preserve the same drag coefficient as the original automotive. It was verified that this program could predict the aerodynamic drag coefficient effectively and accurately, and this program with GRG method could determine optimal values of parameters.

• 한국자동차공학회논문집
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• 제10권5호
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• pp.223-227
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• 2002

Wind tunnel test or CFD is used for predicting aerodynamic drag coefficient in domestic motor companies. But, wind tunnel test requires much cost and time, and CFD has a relatively large error. In this study a predicting program of the aerodynamic drag coefficient based on empirical techniques was developed. Also GRG method was added to the program in order to decide optimal values of some parameters. The program was applied to 24 cars and the aerodynamic drag coefficients were predicted with 4.82% average error. Optimization was also accomplished to 6 cars. Some parameters to be modified were determined (1) to reduce the afterbody drag coefficient to the value established by a designer and (2) to preserve the same drag coefficient as the original automotive when some parameters have to be changed in the viewpoint of design. It was verified that the developed program can predict the aerodynamic drag coefficient appropriately and determine optimal values of some parameters.

• 한국추진공학회지
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• 제21권1호
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• pp.98-103
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• 2017

본 논문은 비행시험의 결과를 이용하여 항력 및 항력감소 분석을 위한 항력계수 산출기법에 대하여 기술하였다. 2차원 탄도운동방정식의 역산을 통하여 비행시험을 이용한 항력계수 산출방법에 대하여 정리하였으며 155 mm 탄의 비행시험을 통하여 이론적인 항력계수와 시험결과로부터 산출된 항력계수를 비교하여 항력계수 산출 기법에 대한 검증을 수행하였다. 항력감소제가 적용된 탄의 비행시험결과를 이용하여 항력계수 산출 및 항력감소 양상을 분석하였다.

• Wind and Structures
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• 제16권2호
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• pp.193-211
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• 2013

This paper presents results from a wind tunnel study that examined the drag coefficient and wind flow over an asymmetric wave train immersed in turbulent boundary layer flow. The modeled wavy surface consisted of eight replicas of a statistically-valid hurricane-generated wave, located near the coast in the shoaling wave region. For an aerodynamically rough model surface, the air flow remained attached and a pronounced speed-up region was evident over the wave crest. A wavelength-averaged drag coefficient was determined using the wind profile method, common to both field and laboratory settings. It was found that the drag coefficient was approximately 50% higher than values obtained in deep water hurricane conditions. This study suggests that nearshore wave drag is markedly higher than over deep water waves of similar size, and provides the groundwork for assessing the impact of nearshore wave conditions on storm surge modeling and coastal wind engineering.

• 한국수자원학회논문집
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• 제50권6호
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• pp.419-427
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• 2017

산지하천 하상에서 흔히 발견되는 호박돌에 작용하는 항력은 하천의 거동과 반응을 예측하는 데 있어서 중요하나 이를 위한 항력계수 연구는 미흡한 실정이다. 본 연구는 호박돌의 항력 실험을 통해서 호박돌 형상과 항력계수의 관계를 분석하였다. 호박돌의 장축과 단축이 흐름방향을 따를 때 항력계수에 미치는 형상계수의 영향을 분석하였다. 항력계수는 장축보다 단축에서 더 크며 호박돌의 등가직경 Reynolds 수가 증가하면 감소하였다. 항력계수와 등가직경 Reynolds 수의 관계에서 결정계수는 단축보다 장축에서 더 크다. 이는 호박돌 형상의 불규칙성에 따른 항력이 축에 따라 변화하기 때문인 것으로 판단된다. 항력분포 변화는 호박돌의 교호진동을 초래하였다. 그 진폭은 $R_{ep}$가 약 12,000에서 급격히 증가하였으며 장축보다 단축에서 더 큰 것으로 나타났다.

• 한국자동차공학회논문집
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• 제6권5호
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• pp.86-96
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• 1998

A numerical study has been carried out of three-dimensional turbulent flows around a MIRA reference vehicle model both with and without wheels in computation. Two convective difference schemes with two k-$\varepsilon$ turbulence models are evaluated for the performance such as drag coefficient, velocity and pressure fields. Pressure coefficients along the surfaces of the model are compared with experimental data. The drag coefficient, the velocity and pressure fields are found to change considerably with the adopted finite difference schemes. Drag forces computed in the various regions of the model indicate that design change decisions should not rely just on the total drag and that local flow structures are important. The results also indicate that the RNG model with the QUICK scheme predicts fairly well the tendency of velocity and pressure fields and gives more reliable drag coefficient rather than the other cases.

• 대한기계학회논문집B
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• 제38권10호
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• pp.797-805
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• 2014

본 연구의 목적은 해수 흡입구를 고려한 초공동 수중운동체 캐비테이터의 항력과 양력특성 및 해수 흡입유로의 입구에서 압력손실에 대해 예측하는 것이다. 흡입구 직경과 유로에서의 속도, 흡입구의 곡률반경 및 캐비테이터의 받음각이 미치는 영향에 대해 유동해석을 수행하였다. 연구 결과 직경비가 커지면, 항력계수와 압력손실계수가 감소하며, 속도비가 증가할 때 항력계수와 양력계수는 감소하고 압력손실계수는 증가한다. 해수 흡입구에 곡률을 주면 항력계수와 양력계수에는 영향을 미치지 않지만, 압력손실계수가 크게 감소한다. 캐비테이터의 받음각은 항력계수와 압력손실계수에 미소한 영향만을 주나, 양력계수를 크게 변화시킨다. 초공동 수중운동체 설계 시 본 연구 결과를 반영할 수 있다.

• 한국항공우주학회지
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• 제48권7호
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• pp.489-495
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• 2020

충격파 터널에서 항력 측정을 위하여 가속도계 기반 시스템을 설계 및 구축하고, 마하 6 유동조건에서 원뿔형 모델의 항력계수를 측정하였다. 항력 측정 시스템의 마찰력을 보정하기 위하여 간단하고 직관적인 교정 방식을 제시하고, 항력 측정 결과를 단순 원뿔형 모델의 전산유체역학 해석 결과와 비교, 분석하였다. 다양한 형상의 지지대를 이용하여 지지대에 의한 항력 측정 간섭 영향을 파악하고 이를 최소화하기 위한 디자인을 제시하였다. 수정된 지지대를 이용하여 항력계수를 측정한 결과, 지지대에 의한 항력계수 오차가 작아지는 것이 확인되었다.

• 한국전산유체공학회지
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• 제4권1호
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• pp.34-40
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• 1999

Drag reduction on vehicles are the main concern for the body shape designers in order to lower the fuel consumption rate and to aid the driving stability. The drag of bluff bodies like transportation vehicles is mostly pressure drag due to the flow separation, which can be minimized by controlling the location and size of the separation bubble. In the present study, the TURBO-3D code is incorporated with optimal algorithm based on analytical approximation method to obtain an optimal afterbody shape of the MIRA Model corresponding to the lowest drag coefficient. For this purpose three mutually independent afterbody angles are chosen as design variables, while the drag coefficient is chosen as an objective function. It is demonstrated in the present study that an optimal body shape having the lowest drag coefficient which is about 6% lower than that of the original shape has been successfully obtained within number of iterations of tile optimal design loop.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1998년도 춘계 학술대회논문집
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• pp.67-74
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• 1998

Reducing drag of vehicles are the main concern for the body shape designers in order to lower fuel consumption rate and to aid the driving stability. The drag of bluff bodies like transportation vehicles is mostly pressure drag due to the flow separation, which can minimized by controlling the location and size of the separation bubble. In the present study, the TURBO-3D code is incorporated with optimal algorithm based on analytical approximation method to obtain optimal afterbody shape of the MIRA Model corresponding to the lowest drag coefficient. For this purpose three mutually independent afterbody angles are chosen as design variables, while the drag coefficient is chosen as an objective function. It is demonstrated in the present study that an optimal body shape having lowest drag coefficient which is about $6\%$ lower than that of the original shape has been successfully obtained within number of iterations of the optimal design loop.