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Free Surface Suction Force Acting on a Submerged Slender Body Moving Beneath a Free Surface
윤범상,담반퉁,Yoon, Bum-Sang,Trung, Dam Vam The Society of Naval Architects of Korea 2009 大韓造船學會 論文集 Vol.46 No.6
In this paper, the steady lift force acting on a slender body moving beneath regular wave systems of arbitrary wavelengths and directions of propagation is considered. The momentum conservation theorem and the strip method are used to obtain the hydrodynamic forces acting on the body and affecting its motions on the assumption that the body is slender. In order to obtain the vertical steady force acting on it, or the free surface suction force, the second-order hydrodynamic forces caused by mutual interactions between the components of the first-order hydrodynamic forces are averaged over time. The validity of the method is tested by comparison of the calculated results with experimental data and found to be satisfactory. Through some parametric calculations performed for a typical model, some useful results are obtained as to the depth of submergence of the body, wavelengths, directions, etc.
이혁준(Hyuck-Joon Yi),윤범상(Bum-Sang Yoon) 한국해양환경·에너지학회 2012 한국해양환경공학회 학술대회논문집 Vol.2012 No.5
The flow around a circular cylinder advancing beneath the free surface is numerically investigated with a VOF method. The simulations cover for Froude numbers 0.2~0.6 and gap ratio(h/d) 0.1~2.0, where h is a distance from the free surface to a cylinder and d is a diameter of a cylinder at Reyndds number 180. It is doserved that vortex suppression effect and surface deformation increases as a gap ratio decreases or Froude number increases. Noticable results of the present study are as follows. The prodimity of the free surface cause an initial increase in the Strouhal number and the drag coefficient and the maximum Strouhal number and drag coefficient occurs in the range 0.6~0.7. But this trend reverses as the gap ratio becomes small. And lift coefficient decresses as gap ratio decresses.
변분다중스케일법을 이용한 파형벽면이 있는 채널 난류 유동의 대와류모사
장경식(Kyoung sik Chang),윤범상(Bum Sang Yoon),이주성(Joo Sung Lee) 한국전산유체공학회 2011 한국전산유체공학회지 Vol.16 No.2
Turbulent flows with wavy wall are simulated using Residual-based Variational Multiscale Method (RB-VMS) which is proposed by Bazilves et al(2007) as new Large Eddy Simulation methodology. Incompressible Navier-Stokes equations are integrated using Isogeometric analysis which adopt the basis function as NURBS The Reynolds number is 6760 based on the bulk velocity and averaged channel height. And the amplitude (α/λ) of wavy wall is 0.05. The computational domain is 2λ×1.05λ×λ in the streamwise, wall normal and span wise direction. Mean quantities and turbulent statistics near wavy wall are compared with DNS results of Cherukat et al. (1998). The predicted results show good agreement with reference data.
이혁준(Hyuck-Joon Yi),윤범상(Bum-Sang Yoon) 대한조선학회 2012 대한조선학회 학술대회자료집 Vol.2012 No.5
The flow around a circular cylinder advancing beneath the free surface is numerically investigated with a VOF method. The simulations cover for Froude numbers 0.2~0.6 and gap ratio(h/d) 0.1~2.0, where h is a distance from the free surface to a cylinder and d is a diameter of a cylinder at Reynolds number 180. It is observed that vortex suppression effect and surface deformation increases as a gap ratio decreases or Froude number increases. Noticeable results of the present study are as follows: The proximity of the free surface cause an initial increase in the Strouhal number and the drag coefficient and the maximum Strouhal number and drag coefficient occurs in the range 0.6 ~0.7. But this trend reverses as the gap ratio becomes small. And lift coefficient decreases as gap ratio decreases.
손영이(Young Ee Shon),윤범상(Bum Sang Yoon) 대한조선학회 2011 대한조선학회 학술대회자료집 Vol.2011 No.11
초발수성표면이 마찰저항감소방안의 하나로 주목 받고 있다. 이 사실은 비록 낮은 유속영역에서이긴 하나, 이미 몇몇 실험을 통해 입증되고 있다. 본 연구에서는 초발수성표면 주위 유동을 수치해석하여, 표면의 미세구조가 유동장, 압력장, 저항 등에 미치는 영향을 조사하였다. 실제유동과는 차이가 있는 층류유동을 전제하였지만, 마찰저항 감소 가능성 등, 몇 가지 유용한 결과가 얻어져 이를 보고한다 Surface super-hydrophobicity is now being strongly expected as one of the possible friction drag reduction technologies, which is verified by some experiments even though performed in very low flow velocity range. In the present study, flows around surface with various micro-scale roughnesses are investigated numerically. Some useful discussions about drag reduction, velocity patterns, pressure fields and etc. with respect to the surface structure are made in the present paper.
이혁준(Hyuck-Joon Yi),신현경(Hyun-Kyung Shin),윤범상(Bum-Sang Yoon) 한국해양공학회 2013 韓國海洋工學會誌 Vol.27 No.5
The flow around a circular cylinder advancing beneath the free is numerically investigated using a VOF method. The simulations cover Froude numbers in the range of 0.2~0.6 and gap ratios (h/d) in the range of 0.1~2.0, where h is the distance from the free surface to a cylinder, and d is the diameter of a cylinder at Reynolds number 180. It is observed that the vortex suppression effect surface deformation increase as the gap ratio decreases or the Froude number increase. The most important results of the present study are as follows. The proximity of the free surface causes an initial increase in the Strouhal number and drag coefficient, and the maximum Strouhal number and drag coefficient occur in the range of 0.5~0.7. However, this trend reverses as the gap ratio becomes small, and the life coefficient increases downward as the gap ratio decreases.