• 한국해안·해양공학회논문집
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• 제21권3호
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• pp.216-223
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• 2009

수면보다 높은 사각기둥 저항체가 등간격으로 배치되어 있는 경우의 상당저항계수 식의 횡방향에 따른 항력상호작용계수를 연구하여 제안하였다. 저항체의 횡방향 이격거리에 따른 에너지 손실이 오리피스의 공극률에 따른 에너지 손실과 동일하다고 가정하고 오리피스의 에너지 손실계수를 차용하여 횡방향 항력상호작용계수를 제안하였다. 이 항력상호작용계수를 사용하는 상당저항계수 식을 김 등(2008)에 의해 사용된 수리조건에 대해 그 해석능력이 검증된 FLOW-3D를 이용하여 수치실험한 결과와 비교하였다. 그 결과가 잘 일치하였고 이로부터 바닥마찰뿐만 아니라 수면보다 높은 정방형 다열기둥의 종방향 및 횡방향 이격거리에 따라 변화되는 저항정도를 고려할 수 있는 제안된 상당저항계수 식의 타당성을 검증하였다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2001년도 ICCAS
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• pp.92.4-92
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• 2001

Estimation of the general along-track acceleration was performed in the KOMPSAT-1 orbit determination process. Several sets of the atmospheric drag and solar radiation pressure coefficients were also derived with the different spacecraft area. State vectors in the orbit determination with the different spacecraft area were compared in the time frame. The orbit prediction using the estimated coefficients was performed and compared with the orbit determination results. The orbit prediction with the different general acceleration values was also carried out for the comparison.

• 한국환경과학회지
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• 제23권6호
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• pp.1199-1211
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• 2014

The momentum flux and the sensible heat flux were measured with the scintillometers and ultrasonic anemometers at 6 sites of which surface characteristics like roughness length and zero-displacement are different each other. We estimated the momentum flux and the sensible heat flux based on the bulk transfer method with the drag coefficient and the heat transfer coefficient calculated from the temperature and wind speed at two heights. The variation of bulk transfer coefficients showed a remarkable difference depending on the atmospheric stability which is less influenced by the zero-displacement than the roughness length. The estimated sensible heat fluxes were in good agreement with those measured at 3 m, showing 23.7 $Wm^{-2}$ of the root mean square error that is less than 10% of its maximum. Since the estimated momentum flux is not only effected by drag coefficient but also by wind speed square, the determination of wind speed in the bulk transfer method is critical.

• 한국해양공학회지
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• 제10권1호
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• pp.75-80
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• 1996

The importance of the impact force on the vertical offshore circular structure member in the surf zone due to the breaking wave has been recognized recently. In this paper characteristics of breaking wave forces and the corresponding estimation procedures for them are investigated. For the characterization of the wave forces, three parts, drag force, inertia force, impact force are categorized and identified, respectively. Among them the impact force is maimly studied and the concise form of the force is proposed with the application scheme for the design of offshore circular structure member. The resulting form porposed here for impact force is well coincided with former research results by other people. Except the impact force, so called Morison equation can be employed for the common offshore structure design. The drag force and inertia force are represented as convertionally for the profile except the breaking part. In the numerical example, for thpical sea condition and the member size, the proposed procedures for the breaking wave forces calculation are demonstrated. It is found that the impact force is the most deminant one comparing with inertia and drag forces in the surf zone.

• 대한기계학회논문집B
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• 제30권12호
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• pp.1155-1163
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• 2006

Calculation was carried out for phase velocity and deformation wave decay in a layer of viscoelastic material fixed tightly on the solid substrate. Analysis has been performed regarding the inner structure of the wave, i.e., the proportions between the vertical and horizontal displacements and their profiles. The wave characteristics depend strongly on media compressibility factor. The effect of viscous losses on parameters of the main oscillation mode was studied in detail. Results were compared with the model of coating with local deformation. A new experimental approach was made in order to measure such wave properties of a compliant coating as the dependency of deformation wave velocity on frequency and decay factor was made. The method for estimation of coating parameters enabling the drag reduction in turbulent flow was then refined.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 춘계 학술대회논문집
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• pp.50-52
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• 2007

In the present paper, some difficulties encountered in predicting airfoil characteristics are described and solutions for those problems are discussed Since drag is determined by the amounts of pressure and, especially, shear stress, accurate estimation of shear stress is very crucial. However shear stress computation is dependent on the grid density and turbulence model, it should be consistent in preparing grid and turbulence model. When the transition from laminar to turbulent happen at the middle of airfoil, CFD solver should divide the region into laminar and turbulent region based on the transition location.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권1호
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• pp.225-232
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• 2019

In recent years, nonlinear dynamic models have been developed for flapping-type energy harvesting systems with a rigid wing, but not for those with a flexible wing. Thus, in this study, flexible wing designs of NACA0012 section are proposed and measurements of the forces of rigid cambered wings, which are used to estimate the performance of the designed wings, are conducted. Polar curves from the measured lift and drag coefficients show that JavaFoil estimation is much closer to the measured values than Eppler over the entire given range of angles of attack. As the camber of the rigid cambered wings is increased, both the lift and drag coefficients increase, in turn increasing the resultant forces. Moreover, the maximum resultant forces for all rigid cambered wings are achieved at the same angle of attack as the maximum lift coefficient, meaning that the lift coefficient is dominant in representations of the wing characteristics.

• 한국해안해양공학회지
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• 제11권2호
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• pp.107-115
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• 1999

정수 또는 유수중 투하 석재의 이동거리를 산정하기 위한 간편한 방법을 도출하기 위하여 간단하면서도 어느 정도 정밀성을 갖고 있는 항력계수 산정식을 도입하였다. 도입된 항력계수 산정식은 매끈한 구형체인 경우 정밀식의 해와 거의 유사한 산정치를 제공하고 있음을 확인하였으며, 투하 석재의 형상이나 조면의 상태에 따라 경험계수의 조정으로 산정치를 제공하고 있음을 확인하였으며, 투하 석재의 형상이나 조면의 상태에 따라 경험계수의 조정으로 흐름상태를 반영할 수 있었다. 정수중의 침강속도 또는 낙하거리를 산정하기 위한 이론식을 유도하였으며, 항력계수의 조정으로 관측결과와 일치하는 산정결과를 얻을 수 있었다. 유수중의 이동거리 산정을 위하여 2차 상미분방정식을 유도하였고, 이의 해를 Runge-Kutta법으로 구하는 수치모형을 개발하였다. 또한 여러 가지 조건에 대한 산정치를 구하여 비교하였다.

• 대한조선학회논문집
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• 제44권5호
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• pp.534-541
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• 2007

This paper suggests the mathematical method for the estimation of the required engine output for WIG crafts. The engine size of a WIG craft Is a key parameter in the design stage, because WIGs should overcome the hump drag during the take-off. Therefore, it is very important for a WIG designer to estimate required power and state change during take-off. The mathematical method was developed based on the steady planing state model of a planing boat. Through numerical calculations on various take-off states, it was found that the suggested method could give reasonable estimation of required power and state change during take-off.

• 대한토목학회논문집
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• 제34권1호
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• pp.107-116
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• 2014

본 연구는 조도보정 블록수로에서의 체적밀집도를 정의하고, 평균유속(V)과 수리반경(R)의 곱인 VR, 블록 Reynolds수($Re^*$), 항력계수($\acute{C}_D$) 및 바닥전단특성의 바닥조도계수($n_b$)를 분석하여 조도계수(n)를 산정하였다. VR과 블록Reynolds수가 증가함에 따라 조도계수가 감소하여 일정함에 수렴하는 경험적인 양상을 확인하였다. 블록Reynolds수의 증가에 따라 항력계수는 감소하여 일정한 값에 수렴하는 것으로 나타났다. 블록Reynolds수가 큰 난류구간에서는 항력계수는 밀집도로 정의한 조도블록의 형상에 지배적임을 볼 수 있다. 정확한 조도계수의 산정을 위해서는 블록Reynolds수와 체적밀집도에 의한 상관식의 개발이 요구된다. n-VR, $\acute{C}_D-Re^*$, $n_b-\acute{C}_D$상관에 대한 관계곡선식을 제시하였다. 조도계수를 산정할 수 있는 블록Reynolds수와 체적밀집도와의 상관관계식을 제시하였다. 실험결과를 토대로 블록Reynolds수와 체적밀집도에 의한 조도 계수 산정식을 이용한 HEC-RAS의 수리특성 분석결과는 실험결과와 잘 일치함을 보여주어 산정한 조도계수 추정식의 적용성을 확인하였다.