• 한국농공학회지
• /
• 제33권4호
• /
• pp.73-83
• /
• 1991

A numerical simulation of a 2-dimensional tidal flow in a shallow sea was performed using the frequency domain finite element method. In this study, to overcome the inherent problems of a time domain model which requires high eddy viscosity and small time steps to insure numerical stability, the harmonic function incorporated with the linearized function of governing equations was applied. Calculations were carried out using the developed tidal model(TIDE) in a rectangular channel of lOm(depth) X 4km (width) X 25km(length) under the condition of tidal waves entering the channel closed at one end for both with and without bottom friction damping. The predicted velocities and water levels at different points of the channel were in close agreement with less than 1 % error between the numerical and analytical solutions. The results showed that the characteristics of the tidal flow were greatly affected by the magnitude of tidal elevation forcing, and not by on surface friction, wind, or the linear bottom friction when the value was less than 0.01. For the optimum size of grid to obtain a consistent solution, the ratio between the length of the maximum grid and the tidal wave length should be less than 0.0018. It was concluded that the finite element tidal model(TIDE) developed in this study could handle the numerical simulation of tidal flows for more complex geometrical conditions.

• 대한원격탐사학회:학술대회논문집
• /
• 대한원격탐사학회 2006년도 Proceedings of ISRS 2006 PORSEC Volume I
• /
• pp.166-169
• /
• 2006

Our country's coast is vulnerable area to natural disaster which the repetitive damages occur every year including a loss of lives, the damage of facilities and erosion mostly except for the east coast because of a typhoon, tidal waves, sea water overflowing by topographic structure of low-lying gentle slope and shallow sea. However, as for prevention of natural disaster occurring every year, the situation is that it's centered on the restorationcentered measures and the general disaster prevention research to minimize damages at the time of disaster occurrence is insufficient. This study intendedlop t to devehe techniques possible for real time sampling of damage prediction areas on Web in order to support decision making for damage prevention and establishment of disaster prevention policy. For this, the thematic map was produced related to disaster based on high-resolution satellite picture, and the environmental DB similar to real world was constructed through topographic construction of three-dimension integrating the parts of land and the sea. In addition, the system was developed possible for the expression of damageable regions by real time grasp of dangerous regions at the time of disaster occurrence through over flowing simulation of three-dimension, and it's intended to prepare a basis to minimize damages to disaster situations through it.

• 대한조선학회논문집
• /
• 제42권1호
• /
• pp.43-49
• /
• 2005

in this paper a dolphin-fender moored pontoon-type floating structure in shallow water depth is studied focusing on mooring force. The pontoon-type floating structure is 500m long, 300m wide. The structure has partially non-uniform drafts of 2.0m and 3.0m. The employed mooring system is a guyed frame type dolphin-fender system. The 1/125 scale model fender system is made of rubber tube to have hi-linear load deflection characteristics. A series of model tests has been conducted focusing on motion and fender force responses in regular and irregular waves at KRISO's ocean engineering basin Non-linear numerical simulation of fender reaction force has been carried out and the results are compared with those of model tests. The simulated rigid body motion and mooring forces also have been compared with the test results.

• Nuclear Engineering and Technology
• /
• 제44권8호
• /
• pp.871-888
• /
• 2012

This paper aims at presenting the state of the art, the recent progress, and the perspective for the future, in the modelling of two-phase flow in the horizontal legs of a PWR. All phenomena relevant for safety analysis are listed first. The selection of the modelling approach for system codes is then discussed, including the number of fluids or fields, the space and time resolution, and the use of flow regime maps. The classical two-fluid six-equation one-pressure model as it is implemented in the CATHARE code is then presented and its properties are described. It is shown that the axial effects of gravity forces may be correctly taken into account even in the case of change of the cross section area or of the pipe orientation. It is also shown that it can predict both fluvial and torrential flow with a possible hydraulic jump. Since phase stratification plays a dominant role, the Kelvin-Helmholtz instability and the stability of bubbly flow regime are discussed. A transition criterion based on a stability analysis of shallow water waves may be used to predict the Kelvin-Helmholtz instability. Recent experimental data obtained in the METERO test facility are analysed to model the transition from a bubbly to stratified flow regime. Finally, perspectives for further improvement of the modelling are drawn including dynamic modelling of turbulence and interfacial area and multi-field models.

• 한국해안해양공학회지
• /
• 제3권3호
• /
• pp.176-183
• /
• 1991

본 연구는 경계요소법을 이용하여 비선형 자유표면파을 해석한 것이며, 가상경계처리는 유체 연속성을 고려하여 mass-flux와 energy-flux를 사용하여 유한진폭파동의 해석수법을 제시했다. 유체의 비선형성 때문에 증분법을 적용했으며 경계요소법에 의해 얻어진 결과는 유한요소법의 결과와 실험치와 비교하여 보았으며 좋은 일치가 얻어 졌다. 따라서, 이 방법은 광범위한 파동문제 해석에 유효하게 이용될 수 있으리라 사료된다.

• 한국해안해양공학회지
• /
• 제15권2호
• /
• pp.108-115
• /
• 2003

천수방정식에 기초한 ADCIRC 유한요소모형을 이용하여 지진해일 전파를 수치모의할 때 분산효과를 고려하기 위한 두 가지 일차원 분산보정기법을 개발하였다. 첫 번째 방법은 음해법으로, 각 시간단계의 공간미분항에 부여되는 가중치를 조정함으로써 분산보정을 수행한다. 두 번째는 양해법으로, 유한요소의 크기를 조정하여 분산을 고려한다. 새로운 기법을 이용하여 계산한 수치해와 파의 분산효과를 고려한 해석해의 비교를 통해 본 연구에서 제안한 분산보정기법의 타당성을 확인하였다.

• 한국해안·해양공학회논문집
• /
• 제20권1호
• /
• pp.121-127
• /
• 2008

비선형의 정도에 따른 Boussinesq 모형의 특성을 비교하기 위해 약비선형 모형인 MIKE21 BW 모듈과 완전비선형 모형인 FUNWAVE 모형을 이용하여 수치실험을 수행하였다. 진폭별 조파실험, 심해 파형경사별 천수실험 그리고 사주 지형상의 파랑 전파실험을 수행하였고, 이상의 실험을 통해 비선형성이 부각되는 천해역에서 비선형 모형의 중요성을 확인하였다. 특히 완전 비선형 모형이 약비선형 모형에 비해 비대칭 파형의 재현성이 우수하고, 천수현상에 따른 파고의 증가가 상대적으로 크게 나타나는 모형 간 특성을 확인하였다.

• 한국해안·해양공학회논문집
• /
• 제27권4호
• /
• pp.228-237
• /
• 2015

본 연구에서는 사질 해안인 해운대 해수욕장을 대상으로 수리 퇴적 작용의 동적구조 규명에 필요한 현장 관측실험을 수행하였다. 연안에서 발생하는 계절별 파랑 및 수리 현상을 정량적으로 파악하기 위하여, 동계 및 하계 집중 관측기간 중 해안선의 법선 방향으로 3개 정점 및 해안선 방향으로 3개 정점 등 공간적으로 여러 정점에 파랑 및 층별 유속 관측장비를 설치하였다. 파랑 관측자료의 분석결과, 동계에는 동해안으로부터 입사하는 E계열 파랑이 대부분이며, 하계에는 S계열과 ESE 계열이 공존하는 분포를 가지고 있다. 대상 해역에서 유속의 공간적분포는 전체적으로 주 흐름방향이 동계와 하계에 조석운동의 영향으로 동서방향으로 형성되어 있다. 심해역에서 천해역로 갈수록 연안지형의 영향으로, 유속의 세기는 약해지며 유속의 방향은 해안선 및 등수심선과 나란하게 변형되어 나타나고 있다. 본 연구를 통하여 제시된 파랑 및 흐름 등 수리특성에 관한 기초 분석자료는 동 기간에서 측정된 모래이동량 및 지형변화 관측자료와 연계하여, 대상 해역의 침퇴적 정도를 정량적으로 산출하는데 활용될 수 있다.

• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2006년 창립20주년기념 정기학술대회 및 국제워크샵
• /
• pp.285-289
• /
• 2006

Recently the target area for the installation of structures have been changed from shallow water into deep one by reservation and use of the wider coastal region, and development of deep water. Additionally, great emphasis in the improved human life quality has been placed on the necessities for the preservation of the agreeable natural and coastal environments and development waterfront, recreation, and resort in the sea. However, the existing gravity-type breakwater did not appropriately cope with the recent changes of circumstances, but required the enormous construction coat for coping with them. Until now, floating breakwuater, which was adequate for the environment and construction cost, has been actively studied in the other countries including Japan. This floating breakwater has been already constructed in many places and satisfactory in poor subsoil and deep water in Japan. Also it showed the same function as a gravity-type breakwater. But floating breakwater was not control long period waves by reason of constructive characteristic. The aim of this study is to discuss field application of Floating Breakwater with Compound Plate Type(FBCPT) in coastal region by using numerical analyses and hydraulic model test.

• Ocean and Polar Research
• /
• 제34권3호
• /
• pp.325-335
• /
• 2012

It is well known that sound waves in the sea propagates under the influence of sea surface and bottom roughness, the sound speed profile, the water depth, and the density of sea floor sediment. In particular, an abrupt change of sound speed with depth can greatly affect sound propagation through an eddy. Eddies are frequently generated in the East Sea near the Korean Peninsula. A warm eddy with diameter of about 150 km is often observed, and the sound speed profile is greatly changed within about 400 m of water depth at the center by the eddy around the Ulleung Basin in the East Sea. The characteristics of low-frequency sound propagation across a warm eddy are investigated by a sound propagation model in order to understand the influence of warm eddies. The acoustic rays and propagation losses are calculated by a range-dependent acoustic model in conditions where the eddy is both present and absent. We found that low-frequency sound propagation is affected by the warm eddy, and that the phenomena dominate the upper ocean within 800 m of water depth. The propagation losses of a 100 Hz frequency are variable within ${\pm}15$ dB with depth and range by the warm eddy. Such variations are more pronounced at the deep source near the sound channel axis than the shallow source. Furthermore, low-frequency sound propagation from the eddy center to the eddy edge is more affected by the warm eddy than sound propagation from the eddy edge to the eddy center.