• Ocean Systems Engineering
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• 제10권2호
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• pp.201-226
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• 2020

A systematic numerical comparative study of the performance of semicircular and rectangular submerged breakwaters interacting with solitary waves is the basis of this paper. To accomplish this task, Nwogu's extended Boussinesq model equations are employed to simulate the interaction of the wave with breakwaters. The finite difference technique has been used to discretize the spatial terms while a fourth-order predictor-corrector method is employed for time discretization in our numerical model. The proposed computational scheme uses a staggered-grid system where the first-order spatial derivatives have been discretized with fourth-order accuracy. For validation purposes, five test cases are considered and numerical results have been successfully compared with the existing analytical and experimental results. The performances of the rectangular and semicircular breakwaters have been examined in terms of the wave reflection, transmission, and dissipation coefficients (RTD coefficients) denoted by K_R, K_T, K_D. The latter coefficient K_D emerges due to the non-energy conserving K_R and K_T. Our computational results and graphical illustrations show that the rectangular breakwater has higher reflection coefficients than semicircular breakwater for a fixed crest height, but as the wave height increases, the two reflection coefficients approach each other. un the other hand, the rectangular breakwater has larger dissipation coefficients compared to that of the semicircular breakwater and the difference between them increases as the height of the crest increases. However, the transmission coefficient for the semicircular breakwater is greater than that of the rectangular breakwater and the difference in their transmission coefficients increases with the crest height. Quantitatively, for rectangular breakwaters the reflection coefficients K_R are 5-15% higher while the diffusion coefficients K_D are 3-23% higher than that for the semicircular breakwaters, respectively. The transmission coefficients K_T for rectangular breakwater shows the better performance up to 2.47% than that for the semicircular breakwaters. Based on our computational results, one may conclude that the rectangular breakwater has a better overall performance than the semicircular breakwater. Although the model equations are non-dissipative, the non-energy conserving transmission and reflection coefficients due to wave-breakwater interactions lead to dissipation type contribution.

• 한국해양공학회지
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• 제23권3호
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• pp.6-13
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• 2009

Based on the boundary element method, the motion responses and transmission coefficients of a moored floating breakwater were investigated in oblique waves. To satisfy the outgoing radiation condition in the far field, the fluid domain was divided into inner and outer regions. The complete solution could be obtained by applying the matching conditions between the eigenfunction-based outer solution and BEM-based inner solution. Using the developed predictive tools, the wave exciting forces, added mass, damping coefficients, motion responses, and transmission coefficients were assessed for various combinations of breakwater configuration, wave heading, mooring cables properties, and wave characteristics. It was found that the transmission coefficient for a moored floating breakwater was closely dependent on the motion responses, which were greatly amplified at the resonant frequencies.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계 학술대회논문집(수송기계편)
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• pp.170-173
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• 2005

The objective of this paper is to perform measurements of power transmission and reflection coefficients in a coupled plate. The coupled plate has been divided into 2 subsystems. The out-of-plane vibration has been only considered with assumption of relatively small in-plane vibration. The coupling loss factors have been measured with consideration of the power balance condition. The power transmission and reflection coefficients has been estimated from the measured values of the coupling loss factors. The measured power transmission and reflection coefficients have been compared with the corresponding theoretical coefficients in a semi-infinite coupled plate.

• ETRI Journal
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• 제25권1호
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• pp.41-48
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• 2003

This paper presents a theoretical investigation of power reflection and transmission coefficients for a meander-line polarizer placed periodically on a chiral slab. It is assumed that a linearly polarized transverse magnetic wave is incident on a chiral slab from the air region. In the analysis, we derive the electric and magnetic fields in the modal form in the air and chiral regions. We obtain power reflection and transmission coefficients in a straightforward manner after matching the tangential components of the electric and magnetic fields at the boundaries. We present numerical results for the power reflection and transmission coefficients versus frequency and incident angle for different values of the chirality admittance. A meander-line polarizer placed on a dielectric slab can convert a linearly polarized wave to a circularly polarized wave. The design parameters for a meander-line polarizer are the dimensions of the meander-line and the values of the dielectric slab. Replacing a dielectric slab with a chiral slab introduces a new independent parameter which controls the wave polarization.

• International Journal of Naval Architecture and Ocean Engineering
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• 제8권1호
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• pp.53-65
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• 2016

The interaction between incident waves and a floating rectangular breakwater with the vertical porous side plates has been investigated in the context of the two-dimensional linear potential theory. The matched eigenfunction expansion method(MEEM) for multiple domains is applied to obtain the analytic solutions. The dependence of the transmitted coefficients and motion responses on the design parameters, such as porosity and protruding depth of side plates, is systematically analyzed. It is found that the non-dimensional wavelength where the sudden drop of transmission coefficients occurs, corresponds to the heave resonant frequency obtained from Ruol et al. (2013) for $\pi$-type floating breakwater. It is concluded that both properly selected porosity and deeper protruding depth of side plates are helpful in reducing the transmission coefficients and also extending the wider applicable extent of incident wavelength for performance enhancement.

• 한국해안해양공학회지
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• 제13권1호
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• pp.61-72
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• 2001

천해영역에서 적용 가능한 동수역학적 수치모형을 이용하여 규칙 입사파군이 수직으로 입사할 때 잠제에 의하여 발생되는 반사와 투과의 거동 특성을 해석하였다. 여러 입사파군 조건에서 계산된 잠제의 반사율과 투과율이 파군의 발달정도를 해석하기 위하여 제시된 변수들의 함수로 표시되었다. 입사파군과 잠제의 반사율 및 투과율의 관계를 정성적으로 해석한 결과, 고파군이 발달될수록 잠제에 의하여 발생되는 입사파랑의 반사율과 투과율의 크기가 감소하는 것으로 나타났다. 특히 파군으로 입사하는 경우의 반사율과 투과율이 단일 파랑으로 입사하는 경우의 반사율과 투과율에 비하여 상대적으로 작게 나타났다. 그러나 고파군과 고파군의 간격에 따른 반사율과 투과율의 차이는 크지 않은 것으로 나타났다. 비록 제한적이지만 본 연구에서 해석된 결과에 의하면 파랑 연이음의 평균을 이용할 때 입사파군과 잠제의 반사율 및 투과율의 관계가 가장 잘 해석될 수 있다.

• 한국해양공학회지
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• 제27권6호
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• pp.90-94
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• 2013

This paper reports the results obtained for there flection and transmission coefficients on rubble mound breakwaters in Busan Yacht Harbor. A2D physical model test was conducted in the wave flume at the Coastal Engineering Research Laboratory at Pusan National University, Busan, South Korea. In this study, physical model tests were completed to further our understanding of the hydrodynamic processes that surround a rubble mound structure subjected to irregular waves. In particular, the reflection and transmission coefficients, as well as the spectrum transformation, were analyzed. This analysis suggests that with an increase in wave height around a rubble mound, the reflection coefficient drastically increases at each water level (HHW or MSL or LLW). Moreover, when the water level changes from HHW to LLW, the reflection coefficient is suddenly reduced. A further result of the analysis is that the transmission coefficient strongly drops away from the rear of the structure. Finally, in regard to the rubble mound breakwater in Busan Yacht Harbor, a consideration of the reflection and transmission coefficients plays an important role in the design.

• Ocean Systems Engineering
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• 제11권1호
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• pp.83-97
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• 2021

The submerged U-shape breakwater interaction with the solitary wave is simulated by the Boussinesq equations using the finite-difference scheme. The wave reflection, transmission, and dissipation (RTD) coefficients are used to investigate the U-shape breakwater's performance for different crest width, Lc1, and indent breakwater height, du. The results show that the submerged breakwater performance for a set of U-shape breakwater with the same cross-section area is related to the length of submerged breakwater crest, Lc1, and the distance between the crests, Lc2 (or the height of du). The breakwater has the maximum performance when the crest length is larger, and at the same time, the distance between them increases. Changing the Lc1 and du of the U-shape breakwaters result in a significant change in the RTD coefficients. Comparison of the U-shape breakwater, having the best performance, with the averaged RTD values shows that the transmission coefficients, Kt, has a better performance of up to 4% in comparison to other breakwaters. Also, the reflection coefficients KR and the diffusion coefficients, Kd shows a better performance of about 30% and 55% on average, respectively. However, the model governing equations are non-dissipative. The non-energy conserving of the transmission and reflection coefficients due to wave and breakwater interaction results in dissipation type contribution. The U-shape breakwater with the best performance is compared with the rectangular breakwater with the same cross-section area to investigate the economic advantages of the U-shape breakwater. The transmission coefficients, Kt, of the U-shape breakwater shows a better performance of 5% higher than the rectangular one. The reflection coefficient, KR, is 60% lower for U-shape in comparison to rectangular one; however, the diffusion coefficients, Kd, of U-shape breakwater is 35% higher than the rectangular breakwater. Therefore, we could say that the U-shape breakwater has a better performance than the rectangular one.

• 한국해안해양공학회지
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• 제18권2호
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• pp.97-111
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• 2006

고유함수전개법을 이용하여 다열 커튼월-파일 방파제로부터의 규칙파의 반사율과 투과율을 계산할 수 있는 수학적 모형을 제안하였으며, 파일 부분의 유공율, 커튼월의 흘수 그리고 방파제 열 사이의 간격 등을 다르게 하면서 수리모형실험을 실시하였다. 상대수심이 감소하면서 반사율은 감소하고 투과율은 증가하는 경향을 보이다가, 상대수심이 아주 작아지면 반사율은 다시 증가하고 투과율은 감소하는 경향을 보였다. 다른 실험 변수들은 고정시킨 상태에서, 커튼월의 흘수만 변화시키거나 파일 부분의 유공율만 변화시키는 경우에는 반사율과 투과율의 상대적인 크기는 달라지지만 전반적인 거동은 유사했다. 입사파의 파장과 열 사이의 간격이 일치하는 경우에는 반사율과 투과율이 급격하게 변화하였다. 3열로 구성된 방파제의 경우에도 수학적 모형과 실험 결과가 대체로 잘 일치하였다.

• 대한토목학회논문집
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• 제40권5호
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• pp.485-496
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• 2020

잠제와 인공리프와 같은 수중구조물은 연안역의 침식 등의 대책으로 일반적으로 사용되고 있다. 본 연구에서는 Tetrapod로 제체를 형성한 투과형 수중구조물을 대상으로 파랑의 전달에 대한 2차원 수리실험을 수행하였다. 수리실험은 서로 다른 상대여유수심, 상대여유고, 상대상단폭 및 파형경사 등을 적용하여 수행되었다. 수리실험결과를 이용하여 투과형 수중구조물에 의한 파고전달계수 산정식을 제안하였다. 제안된 경험식은 파고전달계수를 충분한 정도로 예측함을 확인하였으며, 기존 경험식을 개선하였다.