• Geomechanics and Engineering
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• 제5권6호
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• pp.595-611
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• 2013

This paper presents a three-dimensional (3D) integrated numerical model where the wave-induced pore pressures in a porous seabed around breakwater heads were investigated. Unlike previous research, the Navier-Stokes equation is solved with internal wave generation for the flow model, while Biot's dynamic seabed behaviour is considered in the seabed model. With the present model, a parametric study was conducted to examine the effects of wave and soil characteristics and breakwater configuration on the wave-induced pore pressure around breakwater heads. Based on numerical examples, it was found that the wave-induced pore pressures at breakwater heads are greater than that beneath a breakwater. The wave-induced seabed response around breakwater heads become more important with: (i) a longer wave period; (ii) a seabed with higher permeability and degree of saturation; and (iii) larger angle between the incident waves and breakwater. Furthermore, the relative difference of wave-induced pore pressure between fully-dynamic and quasi-static solutions are larger at breakwater heads than that beneath a breakwater.

• 한국해양공학회지
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• 제15권2호
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• pp.22-32
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• 2001

The numerical investigation of obliquely incident wave interactions with fully submerged dual buoy/porous-membrane floating breakwaters placed in parallel with spacing is studied based on linear potential theory and Darcy's law. The numerical solutions are obtained by using a discrete-membrane dynamic model and second-kind modified Bessel function distribution over the entire boundaries of fluid regions. First, numerical solutions for an idealized dual submerged system without buoys are obtained. Second, a more practical dual submerged system with membrane tension provided by buoys at its tops is investigated by the multi-domain boundary element method particularly devised for dual buoy/porous-membrane problems with gaps. The velocity potentials of wave motion are coupled with porous-membrane deformation, and solved simultaneously since the boundary condition on porous-membrane is not known in advance. The effects of varying permeability on membranes and wave characteristics are discussed for the optimum design parameters of systems previously studied. The inclusion of permeability on membrane eliminates the resonances that aggravate the breakwater performance. The system is highly efficient when waves generated by the buoys and membranes were mutually canceled and its energy at resonance frequency dissipates through fine pores on membranes.

• 한국해안·해양공학회논문집
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• 제32권6호
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• pp.420-433
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• 2020

기존 케이슨방파제의 안정성을 높이기 위해 케이슨 전면 또는 후면에 추가로 신규 케이슨을 설치하여 보강하는 경우 박리에 의한 에너지 손실효과와 케이슨과 케이슨 사이의 공극률 변화에 따른 개별 원형케이슨에 작용하는 파력 및 파처오름 특성 평가는 중요하다. 본 연구에서는 고유함수전개법에 투과성판에서의 속도는 판 전후의 압력차에 선형적으로 비례한다는 Darcy의 법칙을 이용하여 원형케이슨들간의 공극률 계수 변화에 따른 2열 배치된 원형방파제에 작용하는 파랑 특성을 분석하였다. 수치해석의 신뢰성을 확보하기 위해 Sankarbabu et al.(2008)의 수치 해석결과와 비교를 수행하였으며, 다양한 변수에 따른 개별 이중 원형케이슨에 작용하는 파력 및 파처오름 특성을 나타내었다.

• 한국해양공학회지
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• 제16권5호
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• pp.7-14
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• 2002

in the present paper, the hydrodynamics properties of a Rahmen type flexible porous breakwater interacting with obliquely or normally incident small amplitude waves are numerically investigated. This system is composed of dual vertical porous membranes hinged at th side edges of a submerged horizontal membrane. The dual vertical membranes are extended downward and hinged at seabed. The effects of permeability, Rahmen type membrane breakwater geometry pre-tensions on membranes, relative dimensionless wave number, and incident Wave headings are thoroughly examined.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권1호
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• pp.60-73
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• 2014

The seaward reverse wave, occurring on the submerged dual porous horizontal plate, can contribute to the reduction of the transmitted wave as it reflects the propagating wave. However, the collision between the propagating and seaward reverse waves increases the water level and acts as a weight on the horizontal plate. This study investigated the characteristics of the wave pressure created by the seaward reverse wave through the analysis of experimental data. The analysis confirmed the following results: 1) the time series of the wave pressure showed reverse phase phenomena due to the collision, and the wave pressures acted simultaneously on both upper and lower surfaces of the horizontal plate; 2) the horizontal plate became repeatedly compressed and tensile before and after the occurrence of the seaward reverse wave; and 3) the seaward reverse wave created the total wave pressure to the maximum towards the direction of gravity, primarily on the upper plate. It was also confirmed that the wave distributions showed a similar trend to the wave steepness. Such outcome of the analysis will provide basic information to the structural analysis of the horizontal plate as a wave dissipater of the steel-type breakwater (STB).

• 한국수자원학회논문집
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• 제49권1호
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• pp.51-60
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• 2016

본 연구에서는 투과성 잠제의 형상 및 평면배치에 따른 방류 흐름제어 기능을 분석하기 위하여 유체 투과성 구조물 해저지반의 비선형 상호간섭을 직접해석 할 수 있는 PBM (Porous Body Model) 기반의 3차원 수치파동수조(NWT; numerical water tank) LES-WASS-3D를 이용하였다. 먼저 이용하는 LES-WASS-3D의 타당성 및 유효성을 확보하기 위하여 투과성 구조물를 통과하는 댐 붕괴파의 전파특성에 관한 수리모형실험과 계산결과를 비교 분석하였다. 투과성 잠제를 고려한 방류시뮬레이션으로부터 투과성 잠제의 적절한 형상 및 평면배치는 방류유속을 저감하고 흐름을 유도하는 데 상당히 효과적인 것을 알 수 있었다. 또한 투과성 잠제의 형상 및 평면배치에 따른 흐름제어에 대한 적용성은 평균류분포, 연직유속분포를 통하여 확인할 수 있었다.

• 한국해안·해양공학회논문집
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• 제20권4호
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• pp.363-371
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• 2008

본 연구에서는 투과성잠제 주변의 파동장 해석을 위한 2-D 수치해석기법과 3-D 수치해석기법에 의한 결과를 비교하기 위하여 투과성구조물에 의한 유체저항(관성저항, 층류저항 및 난류저항)을 고려할 수 있는 수치해석기법을 이용하고, 난류모델로서 LES 모델을 도입하여 기존에 수행되었던 수리모형실험과의 비교를 통하여 검증하였다. 수치해석결과로부터 투과성잠제의 배후에서 2-D해석에 의한 결과가 3-D해석의 경우보다 높은 파고분포를 나타내었으며, 잠제 주변의 평균류에 대해서도 비교, 논의하였다.

• 대한토목학회논문집
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• 제28권2B호
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• pp.249-259
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• 2008

본 연구에서는 투과성잠제의 비탈면경사가 주변 파동장에 미치는 영향을 검토하기 위해 투과성구조물에 의한 유체저항(관성저항, 층류저항 및 난류저항)을 고려할 수 있는, 즉 파-구조물-지반의 상호작용을 해석할 수 있는 수치모델에 LES 난류모델을 도입한 새로운 수치해석기법(LES-WASS-2D)을 제안하여 기존에 수행되었던 수리모형실험과의 비교를 통하여 검증하였다. 이러한 수치해석기법을 이용하여 투과성잠제의 비탈면경사의 변화에 대한 수치모의를 수행한 결과, 비탈면경사가 완만해질수록 반사율 및 투과율이 감소함과 동시에 에너지손실(Energy loss)이 커지는 것을 알 수 있었다. 또한, 잠제의 비탈면경사의 변화에 따른 마루에서 쇄파점의 위치 및 잠제 배후에서의 순환류와 평균와도의 규모에 대해서도 논의하였다.

• 한국수자원학회논문집
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• 제36권5호
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• pp.741-749
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• 2003

본 연구에서는 사다리꼴형상 투과성 수중방파제에 의한 정현파의 Bragg반사에 대해 수리모형실험과 수치모형실험을 수행하였으며, 두 실험결과를 비교하였다. 수치해석에 적용된 모형에서는 공간 평균된 Wavier-Stokes 방정식을 투과체 내에서의 지배방정식으로 사용하였고, 자유수면변위를 추적하기 위해 VOF기법을 적용하였다. 수리실험결과와 수치해석결과는 비교적 잘 일치하였으며, 투과성 수중방파제에 의한 반사계수는 불투과성에 비해 낮게 나타나고, 방파제의 배열이 증가함에 따라 반사계수는 증가함을 보였다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제5권4호
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• pp.569-579
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• 2013

A steel-type breakwater that uses a submerged dual horizontal porous plate was originally proposed by Kweon et al. (2005), and its hydrodynamic characteristics and design methodology were investigated in a series of subsequent researches. In particular, Kweon et al. (2011) proposed a method of estimating the vertical uplift force that acts on the horizontal plate, applicable to the design of the pile uplift drag force. However, the difference between the method proposed by Kweon et al. (2011), and the wave force measured at a different time without a phase difference, have not yet been clearly analyzed. In this study, such difference according to the method of estimating the wave force was analyzed, by measuring the wave pressure acting on a breakwater model. The hydraulic model test was conducted in a two-dimensional wave flume of 60.0 m length, 1.5 m height and 1.0 m width. The steepness range of the selected waves is 0.01~0.03, with regular and random signals. 20 pressure gauges were used for the measurement. The analysis results showed that the wave force estimate in the method of Kweon et al. (2011) was smaller than the wave force calculated from the maximum pressure at individual points, under a random wave action. Meanwhile, the method of Goda (1974) that was applied to the horizontal plate produced a smaller wave force, than the method of Kweon et al. (2011). The method of Kweon (2011) was already verified in the real sea test of Kweon et al. (2012), where the safety factor of the pile uplift force was found to be greater than 2.0. Based on these results, it was concluded that the method of estimating the wave force by Kweon et al. (2011) can be satisfactorily used for estimating the uplift force of a pile.