Sa Young Hong

Experimental and Numerical Study on Towing Stability of Transportation Barge

This paper presents the results of an experimental and numerical study on the towing characteristics of a barge. A series of model tests were carried out at the Ocean Engineering Basin of KRISO. A model with a 1:50 scale ratio was constructed out of wood. First, force coefficient tests were performed in order to obtain the surge, sway, and yaw force coefficients of the barge. The focus was the effect of skeg on the force coefficients. The stability parameter was calculated from the force coefficients. Next, towing tests in calm sea were carried out with different towline lengths and towing speeds. The trajectories of the barge and the towline tensions were measured during the tests. The measured trajectories were compared with numerical simulation results using a cross-f low model. The towing stability of the barge in a calm sea is discussed in detail.

Numerical Simulation of Towing Stability of Barges in Calm Water

This paper presents the results of a numerical study on the towing stability of barges. Towing simulations were carried out by using two different numerical models (MMG model and cross-flow model). Stability criteria are also suggested based on the analysis of the linearized governing equations for towed vessel motion. In order to validate the present numerical models, the experimental data of Yasukawa et al. (2006) were used. Simulations were conducted for single and double barges under constant towing speed and direction conditions. The time histories of the heading angle, yaw rate, and towline tension were compared between the numerical results and experiments. The effects of the towline length on the slewing frequency and maximum heading angle were also observed. In addition, a series of numerical simulations using variable hydrodynamic coefficients were performed to investigate the effects of the hydrodynamic forces on the towing stability.

Experimental Study of Wave Run-up on Semi-submersible Offshore Structures in Regular Waves

This paper presents the results of an experimental study of wave run-ups on a semi-submersible offshore structure. A series of model tests with a 1:80 scale ratio were carried out in the two-dimensional wave basin of MOERI/KIOST. The experimental model had two columns and one pontoon. The model was fixed and wave elevations were measu red at five points per column. Two different draft (operational & survival) conditions and three wave heights were considered under regular wave conditions. First, the nonlinear characteristics of wave run-ups are discussed by using the time series data. Then, the wave heights are compared with numerical results based on the potential flow model. The comparison shows fairly good correlation between the experiments and compu tations. Finally, wave run-ups under the operational and survival conditions are suggested.

Numerical Study on Wave-Induced Motion Response of Tension Leg Platform in Waves

ABSTRACT: A numerical method to investigate the non-linear motion charact eristics of a TLP is established. A time domain simulation that includes the memory effect using the convolution integral is used to consider the transient effect of TLP motion. The hydrodyn amic coefficients and wave force are calculated using a potential flow model based on the HOBEM(higher order boundary element method). The viscous d rag force acting on the platform and tendons is also considered by using Morison ’s drag. The results of the present numerical method are compar ed with experimental data. The focus is the nonlinear effect due to the viscous drag force on the TLP motion. The ringing, springing, and drift motion are due to the drag force based on Morisons formula. 1. 서 론 TLP(Tension leg platform)는 텐던(Tendon)과 반잠수식 형태의 플랫폼으로 구성되며, 선장력(Pretension)을 갖는 텐던에 의해 수직면 운동의 공진주기를 파주파수영역에서 벗어나도록 하는 개념의 해양구조물이다. 우수한 수직면 운동성능으로 인하여 멕시코만 지역 혹은 Dry tree가 사용되는 지역에 주로 운영되어 왔으며, 최근에는 해상풍력 연구가 연안에서 깊은 수심으로 이동함에 따라 TLP형태의 구조물을 이용하는 사례가 늘어나고 있다. TLP형태의 구조물은 텐던이 갖는 강한 강성 때문에 고주파수 공진 운동응답인 링잉(Ringing) 혹은 스프링잉(Springing) 현상이 발생되며, 이 현상은 텐던의 피로도에 심각한 영향을 미친다. 이로 인해 고주파수 운동응답은 TLP 설계시 반드시 고려되어야 하는 중요한 요소이다.TLP의 거동에 관한 실험은 주로 고주파수 운동에 초점을 두고 이루어졌으며, 주요 연구는 다음과 같다. Stansberg et al.(1995)은 다양한 모양의 원형 실린더에 대한 고주파수 힘을 측정하였으며, 링잉현상에서 3차 조화 성분이 지배적으로 나타난다는 점을 지적하였다. Huse and Stansberg(1995)은 스프링잉 현상은 링잉 현상보다 비교적 낮은 해상상태에서 발생하며 파고의 제곱에 지배적인 점을 지적한 바 있다 .실린더 형태의 구조물에 작용하는 표류력을 계산하기 위해 많은 연구가 이루어졌으며, 주요 연구는 다음과 같다. Pijfer and Brink(1977)은 무한수심에서 파와 조류가 동시에 작용할 때, 반잠수식 시추선에 작용하는 표류력을 계산하였다. 이 계산 모델에서는 모리슨 식으로 단위플랫폼에 작용하는 동유체력을 적분하여 계산하고, 정수중의 조류력을 소거하였다. Hong(1985)은 이 모델508