• Proceeding of EDISON Challenge
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• 2012.04a
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• pp.65-68
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• 2012

본 연구에서는 XFOIL을 사용하여 설계된 30% 두께를 가지며 팁에서의 두께가 코드의 1.5%인 풍력터빈용 에어포일의 공력 특성을 해석하였다. 받음각에 따른 양력 항력 곡선 및 양항비를 XFOIL에서 얻어낸 결과와 EDISON_CFD 해석 결과를 상호 비교 하였다. EDISON_CFD에서의 해석을 위한 격자의 형태를 격자균일성을 생각하여 큰 타원과 작은 타원을 합쳐 만들었다. 수치 기법으로 Roe의 FDS를 선택하여 데이터를 수집하였다. 그 결과로 나타낸 압력계수와 양항비 그래프를 보면 선형 구간에서 양력은 XFOIL 해석 결과와 잘 일치하는 결과를 보여주었다. 그러나 항력에서 약1.5배 정도 EDISON_CFD의 결과가 크게 나옴으로써 양항비의 차이를 보이는 것으로 나타났다. 실속이후에서는 XFOIL의 신뢰도가 떨어지는 경향이 있어 특히 실속이후에서는 CFD의 해석결과가 필요한 것으로 보인다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.3 no.3
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• pp.126-136
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• 1991

This study is concerned with the nonlinear dynamic behaviors of guyed towers for wave loadings. In order to analyze the nonlinear responses of guyed towers efficiently, the main tower is modeled as an equivalent stick, the guyline system is idealized as a spring with nonlinear stiffness in the horizontal direction. and the pile foundation system is represented as a linear spring in the rotational direction. The wave forces on the main tower are evaluated by using Morison's equation. In order to consider adequately the nonlinearities of the guying system and drag forces due to fluid viscosity. the analyses are performed in the time domain. The mode superposition method is adopted for solving the nonlinear equation of motion efficiently. which is based on the Newmark integration scheme. Numerical analyses are carried out to investigate the sensitivity of two major design parameters for guyed towers. i.e., the clump weight conditions and the base renditions of the tower.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.138-138
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• 2011

식생된 개수로에서 식생의 영향을 파악하기 위해 k-$\in$ 난류 모형을 이용하여 수치모의를 하였다. 식생의 영향을 고려하기 위해 항력항을 추가한 지배방정식을 구성하였으며, 지배방정식을 해석하기 위하여 유한체적법을 사용하였다. 수치모의에서 구한 식생된 개수로의 흐름구조를 기존의 수리실험 결과와 비교하여 비교적 잘 일치함을 확인할 수 있다. 난류의 생성과 소멸을 수치모의한 결과, 부분구간 식생된 경우 식생높이 보다 낮은 구간에서는 후류에 의한 난류 생성이 지배적이며, 식생높이보다 높은 구간에서는 주로 마찰에 의한 난류 생성이 지배적임을 보였다. 기존의 연구들은 식생의 영향을 고려하여 개수로의 흐름을 연구한 예는 드물며, 현재까지 진행되어진 국내의 연구는 난류모형을 이용하여 식생된 개수로에서의 흐름 구조를 모의하였다. 따라서 난류흐름을 모의하는데 가장 보편적인 k-$\in$ 난류모형을 이용하여 식생된 개수로에서 수직방향으로의 흐름구조와 식생의 영향을 해석하는 것은 그 자체로도 의미 있는 연구이며, 앞으로의 환경수리 문제를 해결하기 위해 선행되어야 하는 연구이다. 식생된 개수로에서의 난류구조와 부유사 이동에 대한 식생의 영향을 비정상 1차원 수직모형으로 해석하였으며, 폐합문제를 위해 2-방정식인 k-$\in$ 난류모형을 사용하였다. k-$\in$ 난류모형에 식생에 의한 항력항을 더하여 지배방정식을 구성하였다. 수직방향에 대해 흐름방향 유속 u, 난류에너지 k, 그리고 난류에너지 소산율 $\in$의 분포를 구하고, 부유사에 대한 수송방정식을 풀었다. 식생된 개수로와 식생되지 않은 개수로에서의 유속분포, 난류강도, 레이놀즈 응력 분포와 난류의 생성과 소멸을 구하여 식생이 난류흐름에 미치는 영향을 분석하였다.

• Journal of the Korean Society for Railway
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• v.17 no.6
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• pp.397-401
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• 2014

In order to rationally design a new conceptual submerged floating railway, prediction of wave forces applied to the structure is very important. In this paper, equations to calculate such forces based on hydrodynamic theories were proposed and model tests were carried out. Inertia forces and drag forces, calculated using Morison's equation and the linear small amplitude wave theory, were in good agreement with the results from model tests conducted in a wave making tank. Drag forces were negligible compared with inertia forces. Also, wave forces showed linear variation with the changing wave heights. It was revealed that the linear wave theory and Morison's equation can give a simple and useful solution for the prediction of wave forces in the initial design stage of a submerged floating railway.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.3
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• pp.813-820
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• 2014

This study presents a numerical modeling of mean flow and turbulence structures of partly-vegetated open-channel flows. For this, Reynolds-averaged Navier-Stokes equations with vegetation drag terms are solved numerically using the non-linear k-${\varepsilon}$ model. The numerical model is applied to laboratory experiments of Nezu and Onitsuka (2001), and simulated results are compared with data from measurement and computations by Kang and Choi's (2006) Reynolds stress model. The simulation results indicate that the proposed numerical model simulates the mean flow well. Twin vortices are found to be generated at the interface between vegetated and non-vegetated zones, where turbulence intensity and Reynolds stress show their maximums. The model simulates the pattern of the Reynolds stress well but under-predicts the intensity of Reynolds stress slightly.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.4
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• pp.661-674
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• 2002

The objective of this study is to develop efficient numerical method to enable solution of optimal control problems of Navier-Stokes flows and to apply these technique to the problem of viscous drag minimization on a bluff body by controlling boundary velocities on the surface of the body. In addition to the industrial importance of the drag reduction problem, it serves as a model for other more complex flow optimization settings, and allows us to study, modify, and improve the behavior of the optimal control methods proposed here. The control is affected by the suction or injection of fluid on portions of the boundary, and the objective function represents the rate at which energy is dissipated in the fluid. This study shows how reduced Hessian successive quadratic programming method, which avoid converging the flow equations at each iteration, can be tailored to these problems.

• Journal of the Society of Naval Architects of Korea
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• v.33 no.4
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• pp.162-174
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• 1996

Longline type aquaculture facilities in the open sea are based on the cable-buoy-weight mooring system. For their optimal design it is necessary to estimate tensions along the mooring lines including the attachment points of buoys and weights. However, the dynamic analysis is very complicated due to the nonlinear behaviors of the mooring lines and the effects of wave and current. In this paper, parametric studies for various buoy-weight cases are shown. Finite difference scheme is employed in obtaining eigenfrequencies in the frequency domain. Nonlinear hydrodynamic drag forces are equivalently linearized.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.5
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• pp.655-667
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• 2003

Turbulent flow over a fully-developed wavy channel is investigated by the nonlinear $k-\varepsilon-f_\mu$ model of Park et al.⁽¹⁾ The Reynolds number is fixed at $Re_{b}$ = 6760 through all wave amplitudes and the wave configuration is varied in the range of $0\leq\alpha/\lambda\leq0.15$ and $0.25\leq{\lambda}/H\leq4.0$. The predicted results for wavy channel are validated by comparing with the DNS data of Maa$\beta$ and Schumann⁽²⁾ The model performance Is shown to be generally satisfactory. As the wave amplitude increases, it is found that the form drag grows linearly and the friction drag is overwhelmed by the form drag. In order to verify these characteristics, a large eddy simulation is performed for four cases. The dynamic model of Germane et al.⁽³⁾ is adopted. Finally, the effects of wavy amplitude on separated shear layer are scrutinized.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.9 no.1
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• pp.11-23
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• 1989

This paper presents the results of the numerical analysis on the behaviour of mooring system of offshore guyed tower. Finite element method is used and geometric nonlinearities are considered in the analysis of mooring line. The governing equilibrium equations are derived by the principle of virtual work, and modified Newton-Raphson method and Newmark-${\beta}$ method are employed in response calculations. The drag and inertia effects of fluid are included using a Morrison type equation. The influences of changing typical parameters like initial inclination and tension of line at the guy attachment point, the length of clump weight, its unit weight and the anchor line length are examined. The effects of idealising the clump weight as a point load(lumped clump weight) on the behaviour of mooring lines are also discussed. Numerical examples demonstrate the validity and capability of the mathematical formulation.

• Journal of the Society of Naval Architects of Korea
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• v.36 no.2
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• pp.22-28
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• 1999

Small amplitude in-phase oscillations of multi-cylinders are considered both numerically and experimentally. Flow field is separated into inner and outer regions. The basic unsteady solution is obtained analytically and the secondary flow, termed as steady streaming flow, can be obtained numerically by using Finite Volume Code with Panel Method. The Particle Induced Velocimetry, one of whole field measurements, is introduced for comparison with numerical flow visualization quantitatively. Among the algorithms for PIV, the Three Step Vector Searching Technique is applied to reduce CPU time. Small but non-zero damping coefficient, that is important in lightly damped system can be obtained with varying number of bodies and distances.