• 한국해양공학회지
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• 제31권3호
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• pp.208-218
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• 2017

The performance of a wave energy converter (WEC) that uses the rolling motion of a partially submerged pendulum plate in front of a quay wall was analyzed. The wave exciting moment and hydrodynamic moment were obtained using a matched eigenfunction expansion method (MEEM) based on the linear potential theory, and then the roll motion response of a pendulum plate, time averaged extracted power, and efficiency were investigated. The optimal PTO damping coefficient was suggested to give the optimal extracted power. The peak value of the optimal extracted power occurs at the resonant frequency. The resonant peak and its width increase as the submergence depth of the pendulum plate decreases and thickness of the pendulum plate increases. An increase in the wave incidence angle reduces the efficiency of the wave energy converter. In addition, the WEC using a rolling pendulum plate contributes not only to the extraction of the wave energy, but also to a reduction in the waves reflected from the quay wall, which helps to stabilize ships going near the quay wall.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제29회 추계학술대회논문집
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• pp.367-370
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• 2007

Present study examines detonation wave propagation characteristics in annular channel. A normalized value of channel width to the annular radius was considered as a geometric parameter. A parametric study was carried out for a various regimes of detonation waves from weakly unstable to highly unstable detonation waves. Numerical approaches that used in the previous study of numerical requirements of the simulation of detonation wave propagations in 2D and 3D channel were used also for the present study with OpenMP parallization for multi-core SMP machines. The major effect of the curved geometry on the detonation wave propagation seems to be a flow compression effect, regardless of the detonation regimes. The flow compression behind the detonation wave by the curved geometry of the circular channel pushes the detonation wave front and results in the overdriven detonation waves with increased detonation speed beyond the Chapmann-Jouguet speed. This effect gets stronger as the normalized radius smaller, as expected. The effect seems to be negligible beyond the normalized radius of 10.

• 한국해양공학회지
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• 제28권3호
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• pp.227-235
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• 2014

Using a 3-D numerical scheme (LES-WASS-3D) that considered wave-structure-sandy seabed interactions in a 3-D wave field, we analyzed the wave reflection and hydraulic characteristics inside a slit caisson with two chambers in a 3-D oblique wave field. To verify the 3-D numerical analysis method suggested in this study, we compared the numerical results with existing experimental results and found good agreement. The numerical analysis revealed that a standing wave field is generated on the front side of the slit caisson due to the effect of wave reflection. For incident waves propagating perpendicular to the slit caisson, the nodes and anti-nodes of the standing wave are apparent and symmetrical. However, in an oblique wave field, as the incident wave angle decreases, the nodes and anti-nodes of the standing wave become ambiguous and unsymmetrical. It was also found that the wave reflection coefficient decreases as the incident wave angle decreases. It can be pointed out that as the incident wave angle decreases, the turbulent intensity in the chamber increases. Thereby, the increased wave energy dissipation by the increased turbulent intensity reduces the rate of wave reflection. In addition, a strong turbulent intensity generally occurs in the first chamber.

• 한국해안·해양공학회논문집
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• 제21권1호
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• pp.54-62
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• 2009

본 연구에서는 소파블록피복 케이슨 방파제 후면으로 떨어지는 월파의 거동을 분석하기 위하여 수리모형실험을 수행하였다. 방파제 후면으로 낙하하는 월파는 배후사면으로 내습하며 배후사면의 안정성에 직접적인 영향을 준다. 본 연구에서는 배후면에서의 월파거동을 검토하기 위해 월파의 전면유속, 파형 및 관입거리를 측정하였으며, 다양한 파랑조건에 대한 월파의 특성변화를 비교 분석하였다. 수리모형실험은 파랑조건과의 상관성에 초점을 두기 위해 규칙파를 대상으로 하였으며, 월파수괴의 전면유속, 파형, 관입거리를 측정하기 위하여 그림자기법과 교차상관기법을 응용한 화상유속기법을 이용하여 측정하였다. 실험결과에 의하면 배후면에서 월파의 관입거리와 유속은 입사파의 주기와 파고가 커짐에 따라 증가함을 알 수 있었으며, 무차원변수 사이의 상사관계로부터 유속 및 거리분포에 대한 경험식을 유도하였다.

• 한국해양공학회지
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• 제31권2호
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• pp.130-140
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• 2017

Typically, a submerged breakwater is one of the good scene-friendly coastal structures used to reduce wave energy and coastal erosion. However, sometimes, a submerged breakwater also has a negative aspect in that a strong rip current occurring around an open inlet due to a difference in mean water levels on the front and rear sides of the structure leads to scouring. Such scouring has a bad effect on its stability. In order to eliminate this kind of demerit, this study investigated four new types of submerged breakwaters with drainage channels. First, hydraulic experiments were performed the typical and new structures. Then, the wave height and mean water level distributions around the structures were examined using the experimental results. Finally, it was revealed that the new type of submerged breakwater could efficiently reduce the mean water level on its rear side. In particular, in the case of new-type submerged breakwater 2, an average reduction efficiency of 71.2% for the difference between the mean water levels at the front and rear sides was shown in comparison with the typical one.

• 한국항만학회지
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• 제13권2호
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• pp.399-408
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• 1999

Copeland’s(1985) hyperbolic mild-slope equation including diffraction refraction and reflection in the wave field is used as a governing equation in this study. The result of Maruyama & Kajima(1985) is used to calculate wave direction and that of Watanabe & Maruyama(1986) is used as a energy dissipation formula. Numerical solutions are obtained by the Leap-Frog scheme and compared with Watanabe & Maruyama’s (1984) hydraulic experimental results and numerical simulation results for the detached breakwater. This wave model is applied to a detached breakwater and compared with Watanabe and Maruyama’s (1984) hydraulic model results to check the characteristics of reflected wave field around a detached breakwater. The distribution of wave height and we phase in front of a detached breakwater is more accurate than the Watanabe and Maruyama’s numerical results. The results from our wave model show good agreements with the others and also show nonlinear effects around the detached breakwater. This model is applied to the Gamcheon harbor of pusan. the field observations were carried out at Pusan harbor wave station in 1986-1995 and the results were accepted as a design wave condition in this study. The wave height and wave period was measured by Dong-A university at one station in the Gamcheon harbor in 1996-1997 and used as a calibration criterion. The measured data were used as input data for the numerical simulation and also compared with simulated results. The numerical simulation shows a fairly good results which considering the effect of topographic characteristics and effect of narrow entrance due to two separated breakwaters in Gamcheon harbor. The wave distribution characteristics inside Gamcheon harbor is quite different with the offshore wave direction and wave period.

• 한국해안해양공학회지
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• 제16권3호
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• pp.178-189
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• 2004

본 논문에서는 장기간 측정된 파랑자료를 이용하여 신뢰성 있는 항만설계를 하기 위한 평상파 산정에 대한 방법론을 제시하였다. 제안된 방법론을 부산항 내 해경부두 설계에 적용하여, 부산항 입구 조도 전면해상에서 장기간 측정된 파랑자료를 이용하여 97.5% 평상파를 산정하였다. 1993년 2월부터 2002년 12월까지 측정된 파랑자료를 파향별로 유의파고와 유의파주기의 결합분포를 구한 후, 포물선형 완경사 방정식 파랑모델을 이용하여 해경부두에서의 평상파 조건을 산정하였다. 해경부두 위치에서의 항만설계를 위한 97.5% 평상파의 파고는 1.06 m 이며, 이는 부산항 항외에서 입사되는 파향 E, 유의파고 1.75 m, 유의파주기 7 sec에 의해 생성되는 것으로 분석되었다. 부산항 내 풍파에 의한 평상파에의 영향을 검토하였으나, 항내 풍파는 평상파 산정에 영향이 없으며 항외에서 항내로 진입하는 너울성 파고의 영향이 지배적임이 밝혀졌다. 따라서 항내의 풍파의 영향만을 고려하여 평상파를 추정하였을 경우 심각한 오류가 있음을 알 수 있었다.

• 한국해안·해양공학회논문집
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• 제22권1호
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• pp.10-17
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• 2010

투과성 이중 반원통 구조물과 경사 입사파간의 상호작용문제를 선형포텐셜 이론을 사용하여 살펴보았다. 투과성 이중 반원통 구조물은 바닥에 고정된 동심원상으로 배열된 2개의 원통 구조물로 이루어지며 각 원통 구조물의 전면은 일정한 공극율을 갖는 투과벽으로 후면은 투명한 벽으로 구성된다. 전면 투과벽의 공극율과 간격 그리고 파랑특성(주파수, 입사각)을 변화시키면서 파랑하중과 처올림 파형 그리고 파 차단성능을 살펴보았다. 파 차단 성능의 척도로서 차단영역내의 평균제곱 변위의 제곱근(R.M.S.)을 사용하였다. 투과성 반원통 구조물은 불투과성 구조물과 비교하여 차단영역내의 파도응답을 감소시키며 구조물에 작용하는 파랑하중을 크게 줄여준다. 특히 이중 구조물은 고주파주 영역에서 단일 구조물보다 파를 차단하는데 효과적이다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.617-621
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• 2017

본 연구에서는 Al 입자가 함유된 고폭약의 성능 특성을 2 상 모델(two-phase model)을 이용하여 수치 해석을 수행하였다. Al 입자의 점화와 연소시간은 고폭약에 비해 상대적으로 긴 시간이 요구되기 때문에, Al 입자연소에 의한 에너지 발산은 고폭약의 데토네이션 후방에서 이루어진다. Al 입자를 함유하는 고폭약은 Al 함유량이 증가함에 따라 데토네이션 속도의 감소와 고폭약 데토네이션 후방에서 Al 입자 연소가 일어나며 이중 데토네이션이 관찰되는 특징이 있다. 본 연구에서는 Al 입자가 함유된 HMX의 데토네이션 특성을 재현하기 위해 최대 Al 함유량 50%를 갖는 confined rate stick이 고려되었으며, 수치해석 결과는 5-25% 함유량에 대한 실험결과와 비교되었다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.364-370
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• 2008

Spinning detonations propagating in a circular tube were numerically investigated with a one-step irreversible reaction model governed by Arrhenius kinetics. The time evolution of the simulation results was utilized to reveal the propagation mechanism of single-headed spinning detonation. The track angle of soot record on the tube wall was numerically reproduced with various levels of activation energy, and the simulated unique angle was the same as that of the previous reports. The maximum pressure histories of the shock front on the tube wall showed stable and unstable pitch modes for the lower and higher activation energies, respectively. The shock front shapes and the pressure profiles on the tube wall clarified the mechanisms of two modes. The maximum pressure history in the stable pitch remained nearly constant, and the single Mach leg existing on the shock front rotated at a constant speed. The high and low frequency pressure oscillations appeared in the unstable pitch due to the generation and decay of complex Mach interaction on the shock front shape. The high frequency oscillation was self-induced because the intensity of the transverse wave was changed during propagation in one cycle. The high frequency behavior was not always the same for each cycle, and therefore the low frequency oscillation was also induced in the pressure history.