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Free surface simulation of a two-layer fluid by boundary element method
구원철 대한조선학회 2010 International Journal of Naval Architecture and Oc Vol.2 No.3
A two-layer fluid with free surface is simulated in the time domain by a two-dimensional potential-based Numerical Wave Tank (NWT). The developed NWT is based on the boundary element method and a leap-frog time integration scheme. A whole domain scheme including interaction terms between two layers is applied to solve the boundary integral equation. The time histories of surface elevations on both fluid layers in the respective wave modes are verified with analytic results. The amplitude ratios of upper to lower elevation for various density ratios and water depths are also compared.
Numerical Modeling and Analysis of Waves Induced by Submerged and Aerial/Sub-aerial Landslides
구원철,김무현 대한토목학회 2008 KSCE JOURNAL OF CIVIL ENGINEERING Vol.12 No.2
Two dimensional tsunami waves induced by submerged or aerial/sub-aerial rigid slider with and without sudden stop are simulatedin time domain by using fully-nonlinear NWT (numerical wave tank) technique. Special attentions are paid on the maximum free-surface depression/rise and the resultant run-up near shoreline to assess relevant potential hazard. The fully-nonlinear results arecompared with linear results. mass height and sliding velocity and the growthrate can be better predicted by using the nonlinear simulation. The cases with or without sudden stop are next compared. Themaximum free-surface rise/fall as well as shoreline run-up significantly increases in the case of sudden stop due to additionaltransient waves generated by the impact-like change of motion. The aerial/sub-aerial cases are also compared with submerged/underwater cases. Through a series of parametric investigations, it is clearly seen that the potential tsunami risk of aerial/sub-aerialland slide is much higher than that of submerged underwater land slide.
구원철,김동준 대한조선학회 2015 International Journal of Naval Architecture and Oc Vol.7 No.1
The aim of this study is to develop a simplified formula for added mass coefficients of a two-dimensional floating body moving vertically in a finite water depth. Floating bodies with various sectional areas may represent simplified structure sections transformed by Lewis form, and can be used for floating body motion analysis using strip theory or another relevant method. Since the added mass of a floating body varies with wave frequency and water depth, a correction factor is developed to take these effects into account. Using a developed two-dimensional numerical wave tank technique, the reference added masses are calculated for various water depths at high frequency, and used them as basis values to formulate the correction factors. To verify the effectiveness of the developed formulas, the predicted heave added mass coefficients for various wetted body sections and wave frequencies are compared with numerical results from the Numerical Wave Tank (NWT) technique.
수치 파동 수조를 이용한 비선형파의 파형변화와 속도분포 해석
구원철(Weon-Cheol Koo),최가람(Ka-Ram Choi) 한국해양공학회 2009 韓國海洋工學會誌 Vol.23 No.6
In this study, the wave profiles and kinematics of highly nonlinear waves at various water depths were calculated using a 2D fully nonlinear Numerical Wave Tank (NWT). The NWT was developed based on the Boundary Element Method (BEM) with the potential theory and the mixed Eulerian-Lagrangian (MEL) time marching scheme by 4th-order Runge-Kutta time integration. The spatial variation of intermediate-depth waves along the direction of wave propagation was caused by the unintended generation of 2nd-order free waves, which were originally investigated both theoretically and experimentally by Goda (1998). These free waves were induced by the mismatch between the linear motion of wave maker and nonlinear displacement of water particles adjacent to the maker. When the 2nd-order wave maker motion was applied, the spatial modulation of the waves caused by the free waves was not observed. The respective magnitudes of the nonlinear wave components for various water depths were compared. It was found that the high-order wave components greatly increase as the water depth decreases. The wave kinematics at various locations were calculated and compared with the linear and the Stokes 2nd-order theories.
유한 수심에서 반원형 부유체의 부가질량계수 약산식 개발
구원철(Weoncheol Koo),김준동(Jun-Dong Kim) 한국해양공학회 2013 韓國海洋工學會誌 Vol.27 No.1
This study is to develop the simplified formulae for added mass coefficient of a 20D floating body with a semi-circle section in a finite water depth. The semi-circle floating body may represent a simplified midship section transformed by Lewis form, which can be used for the ship motion analysis by strip theory. Since the added mass coefficient varies with motion frequencies and sea bottom effect, the correction factor representing the effect of water depth and frequencies is developed for accurate prediction of added mass. Using a two-dimensional numerical wave tank (NWT) technique based on the boundary element method(BEM) including sea bottom boundary the reference values of added mass are calculated to develop the correction factor. For verification and effectiveness of the formulae, the predicted added mass coefficients for various frequencies and water depth ratios are compared with the calculated values from NWT technique.
고정식 진동 수주형 파력 발전기(OWC) 형상 파라미터의 실험 연구
구원철(Weon-Cheol Koo),권진성(Jin-Sung Kwon),김준동(Jun-dong Kim),김성재(Sung-Jae Kim),김민우(Min-Woo Kim),최문관(Mun-Kwan Choi) 한국해양공학회 2012 韓國海洋工學會誌 Vol.26 No.3
The aim of this experimental study was to analyze the effect if the shape parameters and chamber pressure of a land-based oscillating water column (OWC) in regular incident waves. The magnitude of the free surface elevations inside the chamber was measured in a two-dimensional wave tank for various chamber skirt drafts and bottom slope angles. The surface elevations were also measured under both open chamber and partially open chamber conditions. From these measurements, the optimum shape of the OWC device could be predicted for the maximum wave energy conversion efficiency. It was found that the resonance frequency of the OWC system associated with incident waves moved toward the long wave region with increments of the draft if the chamber skirt and bottom slope. The behavior of the free surface elevation inside the chamber was also found to be dependent on the chamber pressure.