PIV시스템을 이용한 규칙파중 2차원 사각형 부유식 구조물 주위의 유동특성 연구

정광효(KWANG-HYO JUNG),전호환(HO-HWAN CHUN) 한국해양공학회 2006 한국해양공학회지 Vol.20 No.6

This experimental study investigated the flow characteristics for regular waves passing a rectangular floating structure in a two-dimensional wave tank. The particle image velocimetry (PIV) was employed to obtain the velocity field in the vicinityof the structure. The phase average was used to extract the mean flow and turbulence property from repeated instantaneous PIV velocity profiles.The mean velocity field represented the vortex generation and evolution on both sides of the structure. The turbulence properties, including the turbulence length scale and the turbulent kinetic energy budget were investigated to characterize the flow interactionbetween the regular wave and the structure. The results show the vortex generated near the structure corners,which are known as the eddy-making damping or viscous damping. However, the vortex induced by the wave is longer than the roll natural period of the structure, whichpresents the phenomena opposing the roll damping effect; that is, the vortex may increase the roll motion under the wave condition longer than the roll natural period.

PIV기법을 이용한 회류수조의 유속 분포 교정

정광효(Kwang-Hyo Jung),서성부(Sung-Bu Suh),박성부(Sung-Boo Park) 대한조선학회 2011 대한조선학회 학술대회자료집 Vol.2011 No.6

This study is to calibrate the surface flow accelerator to make a uniform vertical velocity distribution. This experiment is carried out circulating water channel with employing PIV technique. The vertical and horizontal velocity distributions are illustrated for two different impeller rpm with varying surface flow accelerator rpm. This experimental approach suggests how to measure, the velocity uniformity near free surface. Also, the velocity uniformity could be quantified in direction vertical and horizontal.

사각형 바지선의 횡동요 와류 감쇠에 대한 실험적 연구

정광효(Kwang Hyo Jung),서성부(Sung Bu Suh),전호환(Ho Hwan Chun) 대한조선학회 2007 大韓造船學會 論文集 Vol.44 No.3

This experimental study investigated on the eddy making effect on the roll motion of a rectangular barge in a two-dimensional wave tank. The structure was used to simulate a simplified rectangular barge in the beam sea condition. The structure with a draft one half of its height was hinged at the center of gravity and free to roll by waves. The rectangular barge was tested with regular waves with a range of wave periods that are shorter. equal to. and longer than its roll natural period. Particle image velocimetry (PIV) was employed to obtain the velocity field in the vicinity of the structure. The coupled interactions between the incident wave and the barge were demonstrated by examining the vortical flow fields to elucidate the eddy making effect during the roll motion. For incoming wave with a wave period same as the roll natural period. the barge roll motion was reduced by the eddy making damping effect. At the wave period shorter than the roll natural period. the structure roll motion was slightly reduced by the vertical flow around the barge. However. at the wave period longer than the roll natural period. the eddy making effect due to flow separation at structure corners indeed amplifies the roll motion. This indicates that not only can the eddy making effect damp out the roll motion. it can also increase the roll motion.

부방파제의 유동과 와의 생성 및 소멸에 관한 연구

윤종성(JUNG-SUNG YOON),김명규(MYOUNG-KYU KIM),정광효(KWANG-HYO JUNG),김가야(GA-YA KIM) 한국해양공학회 2008 한국해양공학회지 Vol.22 No.3

In this study, flow and creation and dissipation of vorticity around rectangular floating breakwater is investigated both experimentally and numerically. The PIV system(Particle image velocimetry) is employed to obtain the velocity field in the vorticity of rectangular structure. The numerical model, combined with k-ε turbulence model and the VOF method based on RANS equation, is used to analyze the turbulence structure. In the results of this study, the vorticity is found around conner of rectangular structure at all time domain, and creation and dissipation of vorticity are closely related to wave period. Separation points of phase of vortex due to flaw separation for longer period waves are faster then for shorter period waves.

Round-Bilge 고속 반활주선의 선형특성 및 설계에 관한 연구

이정관(Jung Gwan Lee),정광효(Kwang Hyo Jung),서성부(Sung Bu Suh),전호환(Ho-Hwan Chun),이인원(Inwon Lee) 한국해양공학회 2010 한국해양공학회지 Vol.24 No.4

This study presents the design procedure for optimizing the semi-planing hull form, including appendages, using numerical and experimental methods. Four different referenced semi-planing hull forms were compared to determine their hydrodynamic performances, and one at the hull forms was modified for optimum operation at high-speed conditions (0.4 < F<SUB>NL</SUB> < 0.9). The optimized, semi-planing hull form was tested in the towing tank to investigate its resistance characteristics. Also, the results of the model tests with differing design parameters were used to choose the stem wedge and the spray strip to improve the hydrodynamic performance at high speeds.

부산 연안지형 VRS-GPS 계측을 통한 태풍해일 침수예측

김가야(Ga-Ya Kim),정광효(Kwang-Hyo Jung),김정호(Jeong-Ho Kim) 한국해양공학회 2012 한국해양공학회지 Vol.26 No.1

A coastal flood area was predicted using the empirical superposition of the typhoon surge level and typhoon wave height along the Busan coastal area. The historical typhoon damages wore reviewed, and the coastal topography was measured using VRS-GPS. A FEMA formula was applied to estimate the coastal. flood area in a typhoon case when the measured and predicted dam of typhoon waves are not available. The results in the area of Haeundae beach and Gwangalli beach were verified using the flood area dam from the case of Typhoon Maemi (2003). If a Hurricane Katrina class typhoon were to pass through the Maemi trajectory, the areathat would be flooded along the Busan coastal. area was predicted and compared with the results of the Maemi case. Because of the lack of ocean environment data such as data for the sea level, waves, bathymetry, wind, pressure, etc., it is hard to improve the prediction accuracy for the coastal flood area in the typhoon case, which could be reflected in the policy to mitigate a typhoon’s impact. This paper discusses the kinds of ocean environment information that is needed to predict a typhoon’s impact with better accuracy.

다위상 유체 속도 계측을 위한 영상기법 적용

류용욱(Yong-Uk Ryu),정광효(Kwang-Hyo Jung) 한국해양공학회 2012 한국해양공학회지 Vol.26 No.3

Air-water flow measurements are if importance for the coastal and ocean engineering fields. Although kinematic investigations if the multi-phase flows have been conducted for long time, velocity measurements still are concerned with many researchers and engineers in coastal and ocean areas. In the present study, an imaging technique using shadowgraphy and fiber optic probe for velocity measurements of air bubbles is introduced. The shadow graphy image technique is modified from the typical image velocimetry methods, and optical fibers are used for the well-known intrusive coupled phase-detection probe system. Since the imaging technique is a non-intrusive optical method from the air, it is usually applied for 2D flows. On the other hand, the double fiber optic probes touch flows regardless if flow patterns. The results of the flow measurements by both methods are compared and discussed. The methods are also applied to the measurements of overtopping flows by a breaking wave over the structure fixed on the free surface.

댐 붕괴 유동에 미치는 표면 거칠기와 난류강도 변화의 영향 연구

박일룡(Il-Ryong Park),정광효(Kwang-Hyo Jung) 대한조선학회 2012 大韓造船學會 論文集 Vol.49 No.3

Dam-break flows, a type of very shallow gravity-driven flow, are substantially influenced by resistance forces due to viscous friction and turbulence. Assuming turbulent flow, the main focus of this study is to validate the increase of drag forces caused by surface roughness and especially turbulence intensity. A Reynolds Averaged Navier-Stokes(RANS) approach with the standard k-? turbulence model is used for this study, where the free surface motion is captured by using a volume of fluid(VOF) method. Surface roughness effects are considered through the law of the wall modified for roughness, while the initial turbulence intensity which determines the lowest level of turbulence in the flow domain of interest is used for the variation of turbulence intensity. It has been found that the numerical results at higher turbulence intensities show a reasonably good agreement with the physical aspects shown by two different dam-break experiments without and with the impact of water.

투과성 잠제 주변의 와류특성에 관한 고찰

허동수(Hur Dong Soo),정광효(Jung Kwang Hyo),김인철(Kim In Chul),이경섭(Lee Kyung Sub) 대한토목학회 2009 대한토목학회 학술대회 Vol.2009 No.10

터렛 계류된 LNG-FSRU의 극한 계류 해석

이민경(Min-Kyeong Lee),정광효(Kwang-Hyo Jung),박성부(Sung-Boo Park),유병석(Byeong-Seok Yu),정윤석(Yun-Suk Chung) 대한조선학회 2016 大韓造船學會 論文集 Vol.53 No.5

In this study, hydrodynamic and mooring analysis for LNG FSRU moored by an internal turret with 9 mooring lines are numerically performed using commercial softwares, Hydrostar and Ariane. Met-ocean combinations for screening method are taken from wave governed condition(BV Rule Note NR 493) with relative heading between wave and wind between -45° and +45° and relative heading between wind and current between -30° and +30°. Extreme mooring analysis and sensitivity analysis are performed for intact and damaged (=one line missing) conditions and the parameters for sensitivity analysis are wave peak period, peak enhancement factor and line pretension. In the viewpoint of the design tension in mooring line, chain diameter is designed to satisfy safety factor for each conditions. As the chain diameter is increased from 152mm to 171mm, the designtension is reduced while the minimum breaking load is increased.