• Wind and Structures
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• 제21권1호
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• pp.105-117
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• 2015

This paper presents a numerical characterization of real railway overhead cables based on computational fluid dynamics (CFD). Complete analysis of the aerodynamic coefficients of this type of cross section yields a more accurate modelling of pressure loads acting on moving cables than provided by current approaches used in design. Thus, the characterization of certain selected commercial cables is carried out in this work for different wind speeds and angles of attack. The aerodynamic lift and drag coefficients are herein determined for two different types of grooved cables, which establish a relevant data set for the railway industry. Finally, the influence of this characterization on the fluid-structure interaction (FSI) is proved, the static behavior of a catenary system is studied by means of the finite element method (FEM) in order to analyze the effect of different wind angles of attack on the stiffness distribution.

• International Journal of Aeronautical and Space Sciences
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• 제12권1호
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• pp.63-68
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• 2011

Aerodynamic characteristics of a wing during fold motion were investigated in order to understand how variations or changes in such characteristics increase aircraft performance. Numerical simulations were conducted, and the results were obtained using the unsteady vortex lattice method to estimate the lift, drag and the moment coefficient in subsonic flow during fold motion. Parameters such as the fold angle and the fold angular velocity were summarized in detail. Generally, the lift and pitching moment coefficients decreased as the angle increased. In contrast, the coefficients increased as the angular velocity increased.

• Journal of Astronomy and Space Sciences
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• 제19권2호
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• pp.89-96
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• 2002

General along-track acceleration was estimated 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

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.434-440
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• 2011

Oscillating airfoil haw been challenged for the dynamic stalls of airfoil am wind turbines at high angle of attach. Especially, the pressure oscillation has a huge effect on noise generation, structure damage, aerodynamic performance am safety, because the flow has strong unsteadiness at high angle of attack. In this paper, the unsteady aerodynamics coefficients were analyzed for the oscillating airfoil at high angle of attack around two dimensional NACA0012 airfoil. The two dimensional unsteady compressible Navier-Stokes equation with a LES turbulent model was calculated by OHOC (Optimized High-Order Compact) scheme. The flow conditions are Mach number of 0.2 and Reynolds number of $1.2{\times}10^4$. The lift, drag, pressure distribution, etc. are analyzed according to the pitching oscillation. Unsteady velocity field, periodic vortex shedding, the unsteady pressure distribution, and the acoustic fields are analyzed. The effects of these unsteady characteristics in the aerodynamic coefficients are analyzed.

• 대한조선학회논문집
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• 제45권3호
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• pp.280-287
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• 2008

In this paper, a mathematical model for a ship manoeuvring with low forward speed in shallow water was suggested. Based on the cross flow model with low forward speed in deep sea, hull, propeller and rudder models were modified to consider the shallow water effects. Static drift and PMM tests were performed to obtain the cross flow drag coefficients and hydrodynamic coefficients. To validate suggested mathematical model, numerical simulation results were compared with those of sea-trials. Through comparisons, it was concluded that suggested mathematical model could give proper estimation on turning test results.

• Wind and Structures
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• 제15권4호
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• pp.345-354
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• 2012

This work discusses the wind stability requirements specified by UN Reg. 27 on emergency car warning triangles, which are of mandatory use in many countries. Wind tunnel experiments have been carried out in order to determine aerodynamic coefficients of commercial warning triangles and the friction coefficients between the triangle legs and an asphalt base that fulfils the roughness requirements stated by Reg. 27 for wind stability certification. The wind stability specifications for warning triangles are reviewed, compared with pressure field measurements and discussed. Results of wind tunnel tests and comparison with field measurements reported in the literature show that the requirements could be excessively conservative.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2001년도 춘계학술대회 논문집
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• pp.52-57
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• 2001

Laminar two-dimensional time-dependent flow past a circular cylinder is numerically investigated using direct numerical simulation for the low Reynolds number (Re=164∼280). The higher-order finite difference scheme is employed for the spatial distributions along with the second order Adams-Bashforth and the first order backward-Euler time integration. The convection term is applied by the 7th order up wind scheme and the pressure and viscosity terms are applied by the 4th order central difference. The grid system makes use of the regular grid system and it is generated by an equation. The calculated results of drag coefficients, lift coefficients, pressure distributions, and vorticity contours and other information are compared with experimental and numerical ones. These results obtained by the present DNS show good agreement with the previous studies.

• Journal of Advanced Research in Ocean Engineering
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• 제3권4호
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• pp.165-173
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• 2017

This study aims at validating simulations of the forced and freely vibrating cylinders at Reynolds number of approximately 500 in order to identify the capability of the CFD code, and to establish the analysis process of the vortex-induced vibration (VIV). The direct numerical and large eddy simulations were employed to resolve the various length scales of the vortices, and the morphing technique was used to consider a motion of the circular cylinder. For the forced vibration case, both in- and anti-phase VIV processes were observed regarding the frequency ratio. Namely, when the frequency ratio approaches to unity, the synchronization/lock-in process occurs, leading to substantial increases in drag and lift coefficients. This is strongly linked with the switch in timing of the vortex formation, and this physical tendency is consistent with that of Blackburn and Henderson (J. Fluid Mech., 1999, 385, 255-286) as well as force coefficients. For the free oscillation case, the mass and damping ratio of 50.8 and 0.0024 were considered based on the study of Blackburn et al. (J. Fluid Struct., 2000, 15, 481-488) to allow the direct comparison of simulation results. The simulation results for a peak amplitude of the cylinder and a shedding mode are reasonably comparable to that of Blackburn et al. (2000). Consequently, based on aforementioned results, it can be concluded that numerical methods were successfully validated and the calculation procedure was well established for VIV analysis with reasonable results.

• 한국습지학회지
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• 제18권1호
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• pp.84-93
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• 2016

해양과 육지 사이에 있는 연안습지는 연안의 수질을 개선하고 다양한 생물의 자연적인 서식처로 이용될 뿐 아니라 연안침식을 억제하는 기능을 가지고 있다. 연안식생은 외해에서 입사하는 파에너지 또는 폭풍해일을 감소하며 해저 안정화를 통해 습지를 유지하는 기능을 가지고 있다. 식생에 의한 파랑감쇠의 특성을 위해서는 식생과 파랑의 역학적 과정의 검토가 필수적이며 이를 통해 연안과정이나 연안의 동수역학적 특성을 이해할 수 있다. 본 연구에서는 파랑조건 이외에 식생형태에 따른 파랑감쇠 특성을 정량화하기 위해 수리실험을 통해 검토하였으며, 식생모형은 강성식생을 대상으로 규칙파가 작용하는 경우에 대해 파악하였다. 파형경사 ak와 상대수심 kh에 따른 수면위로 돌출된 식생에 대한 파랑감쇠를 검토하기 위하여 수리실험과 수치해석을 수행하였다. 실험결과에 대한 파고감쇠는 Dalrymple et al.(1984)의 파고감쇠식을 통해 식생에 의한 파고전달율, 감쇠율 및 항력계수를 해석하였다. 실험결과 식생에 작용하는 항력계수는 Reynolds수 보다는 Keulegan-Carpenter 수와 상관성이 있고, 파형경사가 증가할수록 파고감쇠율이 증가하고 있음을 확인하였다.

• 한국전산유체공학회지
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• 제21권1호
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• pp.30-35
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• 2016

In order to investigate effects of grid resolution on large-eddy simulation of flow over a heavy vehicle, large-eddy simulations over the vehicle with coarse grid and fine grid are conducted. In addition, comparison of drag coefficients with the experimental data obtained by a wind tunnel experiment is conducted. Both of the drag coefficients of coarse grid and fine grid large-eddy simulation show good agreement with the experimental data. Flow fields obtained by the coarse and the fine grid large-eddy simulation are compared in the vehicle frontal-face region, the vehicle rear wheel region, and the vehicle base region. Coarse grid large-eddy simulation shows good agreement with the fine grid large-eddy simulation in the vehicle front face region and the vehicle rear wheel region, since the flow over the present vehicle is dominated by flow separation which is geometrically pre-determined, not by the skin friction which is known to be sensitive to grid resolution.