• 한국해안해양공학회:학술대회논문집
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• 한국해안해양공학회 1994년도 정기학술강연회 발표논문 초록집
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• pp.33-38
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• 1994

• Current Optics and Photonics
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• 제1권2호
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• pp.138-142
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• 2017

Terahertz (THz) generation by periodically-poled $KTiOPO_4$ (PPKTP) with a quasi-phase-matching scheme based on cascaded difference frequency generation (DFG) processes is theoretically analyzed. The cascaded Stokes interaction processes and the cascaded anti-Stokes interaction processes are investigated from coupled wave equations. THz intensities and quantum conversion efficiency are calculated. Compared with non-cascaded DFG processes, THz intensities from 10-order cascaded DFG processes are increased to 5.53. The quantum conversion efficiency of 479.4% in cascaded processes, which exceeds the Manley-Rowe limit, can be realized.

• 대한조선학회논문집
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• 제44권2호
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• pp.148-153
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• 2007

Two typical impact loadings, shock wave and gas bubble pulse, due to UNDEX(UNDerwater EXplosion), should be considered together for the closest response analysis of structure subjected to UNDEX to a reality. Since these two impact loadings have different response time bands, however, their response characteristics of structure are different from each other. It is impossible to consider these effectively under the current computational environment and the mathematical model has not yet been developed. Whereas Hicks model approximates the fluid-structure interaction due to gas bubble pulse as virtual mass effect, treating the flow by the response of gas bubble after shock wave as incompressible ideal fluid contrary to the compressible flow due to shock wave, Geers-Hunter model could make the closest response analysis of structure under UNDEX to a real one as a mathematical model considering the fluid-structure interaction due to shock wave and gas bubble pulse together using acoustic wave theory and DAA(Doubly Asymptotic Approximation). In this study, the application and effectiveness of integrated dynamic response analysis of submerged structure was examined with the analysis of the shock wave and gas bubble pulse together.

• 대한토목학회논문집
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• 제32권5B호
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• pp.321-329
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• 2012

파향이 약간 다르게 진행하는 두 규칙파는 비선형적 상호작용에 기인하여 파봉선이 벌집구조와 유사한 모습을 갖는 현상이 발생하고, 벌집구조 모양의 파봉선 사이에 일정하게 파랑에너지가 매우 낮게 유지되는 노드선 영역이 생성된다. 이러한 파봉선 벌집구조 모양이 해변에 형성되면, 해안선 직각방향으로 생성되는 노드선 영역을 통하여 이안류가 발달하게 된다. 본 연구에서는 해변가에 형성되는 벌집구조 파봉선 현상이 해운대에서 발생하는 이안류의 주요한 메카니즘임을 확인하기 위하여, Boussinesq 파랑모형을 이용하여 일방향 규칙파에 의한 해운대 연안흐름의 수치해석을 수행하고 이를 분석하였다. 그 결과, 해운대 앞바다의 해저천퇴에 따른 파랑굴절로 파향이 서로 약간 다른 파랑들이 해안에 전파되고, 이에 따라 벌집구조가 형성되어 노드영역을 따라 이안류가 매우 잘 발달함을 확인할 수 있었다. 또한, 일정한 파고와 주기를 갖는 다양한 폭의 스펙트럼에 따른 불규칙파 수치모의를 수행하므로, 폭이 넓은 스펙트럼 파랑조건보다 규칙파에 가까운 폭이 좁은 스펙트럼의 파랑조건에서 이안류가 더 잘 발달하는 것을 확인하였다.

• 대한토목학회논문집
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• 제32권4B호
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• pp.243-251
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• 2012

국립해양조사원의 해운대 부이로 부터 관측된 자료와 CCTV 영상자료를 분석하고 수치실험을 수행하여 해운대 해변에서 발생하는 이안류의 특성을 연구하였다. CCTV 영상자료를 분석한 결과로 부터 이안류가 발생할 때 규칙파에 가깝고 진행방향이 약간 다른 파랑이 중첩되어 입사되고 있는 것을 관찰할 수 있었으며, 부이 관측자료의 웨이브릿 분석으로부터 한 주기에 파랑에너지가 집중된 협대역 스펙트럼을 확인할 수 있었다. 이로부터 이미 알려진 이안류 발생 메커니즘가운데 하나인 벌집구조의 절점선 영역을 통한 이안류의 발생이 해운대 이안류의 주요한 발생 메커니즘임을 추론할 수 있었다. 이러한 이안류 발생 메커니즘은 다음과 같이 설명할 수 있다. 진행방향이 약간 다른 규칙파가 해안으로 전파될 때 서로 중첩되어 비선형 상호작용으로 파봉선이 벌집구조 형상으로 변형된다. 여기서, 파고가 영(zero)인 절점선이 해안선에서 외해방향으로 발달하게 된다. 파고가 상대적으로 작은 이 절점선 영역을 향하여 연안류의 질량수송이 집중되며 일시에 외해로 이안류를 발생시키게 된다. 벌집구조 파봉형상 입사파에 의한 이안류 발생을 재현하기 위해 완전 비선형 Boussinesq 방정식 모형을 이용해 수치모의를 수행하였다. 이 수치모의로부터 진행방향이 서로 다르므로, 그리고 일방향 파랑이 수중천퇴에 의하여 변형되므로 발생된 벌집구조 현상에 의하여 이안류가 잘 발생함을 확인하였다.

• 대한조선학회지
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• 제23권4호
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• pp.25-34
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• 1986

A two-dimensional linear method has been developed for the motion and the second-order steady force arising from the hydrodynamic coupling between waves and currents in the presence of a body of arbitrary shape. Interaction between the incident wave and current in the absence of the body lies in the realm beyond our interest. A Fredholm integral equation of the second kind is employed in association with the Haskind's potential for a steadily moving source of pulsating strength located in or below the free surface. The numerical calculations at the preliminary stage showed a significant fluctuation of the hydrodynamic forces on the surface-piercing body. The problem is approximately solved by using the asymptotic Green function for $U^2{\rightarrow}0$. The original Green function, however, is applied for the fully submerged body. Numerical calculations are made for a submerged and for a half-immersed circular cylinder and extensively for the mid-ship section of a Lewis-form. Some of the results are compared with other analytical results without any available experimental data. The current has strong influence on roll motion near resonance. When the current opposes the waves, the roll response are generally negligible in the low frequency region. The current has strong influence on roll motion near resonance. When the current opposes the wave, the roll response decreases. When the current and wave come from the same direction, the roll response increases significantly, as the current speed increases. The mean drift forces and moment on the submerged body are more affected by current than those on the semi-immersed circular cylinder or on the ship-like section in the encounter frequency domain.

• 대한토목학회논문집
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• 제11권2호
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• pp.77-89
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• 1991

수심(水深)이 변하고 흐름이 존재(存在)하는 곳에서 천해파(淺海波)의 파랑변형(波浪變形) 해석(解析)에는 Boussinesq방정식(方程式)에 기초(基礎)한 포물형방정식(抛物形方程式)이 이용된다. 이안류(離岸流)는 Stokes파(波) 이론(理論)의 적용한계(適用限界)를 넘어선 곳에서 발생하므로 본(本) 연구(硏究)에서는 흐름이 존재하는 천해역(淺海域)에서 적용이 가능한 비선형(非線形) 포물형방정식(抛物形方程式)으로 수심변화(水深變化)에 의한 천수현상(淺水現象)과 흐름과의 상호작용(相互作用)에 의한 파(波)의 굴절(屈折) 및 회절현상(回折現象)을 해석(解析)하였고, 흐름은 상대적(相對的)으로 강한 흐름과 약한 흐름을 발생시켜 흐름의 세기에 의한 영향(影響)에 대해 비교(比較) 검토(檢討)하였으며, 수치해석(數値解析)은 쇄파(碎波)가 일어나기 전까지 수행(遂行)하였다.

• 한국해양공학회지
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• 제31권1호
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• pp.47-59
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• 2017

This study conducted numerical simulations using LES-WASS-3D ver. 2.0 to analyze the seawater intrusion characteristics of the incident waves in a coastal aquifer. LES-WASS-3D directly analyzed the nonlinear interaction between the seawater and freshwater in a coastal aquifer, as well as the wave-current interaction in the coastal area. First, the LES-WASS-3D results were compared with the existing experimental results for the mean water level under wave action in the coastal aquifer and seawater penetration into the coastal aquifer. The mean water level, shape and position of the seawater-freshwater interface, and intrusion distance were well implemented in the results. This confirmed the validity and effectiveness of LES-WASS-3D. The overall seawater penetration distance increases in the coastal aquifer as a result of wave set-up and run-up in the swash zone caused by continuous wave actions, and it increases with the wave height and period. Furthermore, a numerical verification was performed by comparing the suggested existing structure and newly suggested curtain wall as a measure against seawater penetration. An existing underground dam showed a better effect with increased height. Additionally, the suggested curtain wall had a better effect when the embedded depth was increased.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권1호
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• pp.530-541
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• 2019

To improve our current understanding of tsunami-like solitary waves interacting with a row of vertical slotted piles on a sloping beach, a 3D numerical wave tank based on the CFD tool $OpenFOAM^{(R)}$ was developed in this study. The Navier-Stokes equations were employed to solve the two-phase incompressible flow, combining with an improved VOF method to track the free surface and a LES model to resolve the turbulence. The numerical model was firstly validated by our laboratory measurements of wave, flow and dynamic pressure around both a row of piles and a single pile on a slope subjected to solitary waves. Subsequently, a series of numerical experiments were conducted to analyze the breaking wave force in view of varying incident wave heights, offshore water depths, spaces between adjacent piles and beach slopes. Finally, a slamming coefficient was discussed to account for the breaking wave force impacting on the piles.

• International Journal of Aeronautical and Space Sciences
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• 제3권1호
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• pp.74-85
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• 2002

The numerical experiment has been conducted to investigate the unsteady shock wave reflecting phenomena. The cell-vertex finite-volume, Roe's upwind flux difference splitting method with unstructured grid is implemented to solve unsteady Euler equations. The $4^{th}$-order Runge-Kutta method is applied for time integration. A linear reconstruction of the flux vector using the least-square method is applied to obtain the $2^{nd}$-order accuracy for the spatial derivatives. For a better resolution of the shock wave and slipline, the dynamic grid adaptation technique is adopted. The new concept of grid adaptation technique, which is much simpler than that of conventional techniques, is introduced for the current study. Three error indicators (divergence and curl of velocity, and gradient of density) are used for the grid adaptation procedure. Considering the quality of the solution and the numerical efficiency, the grid adaptation procedure was updated up to $2^{nd}$ level at every 20 time steps. For the convenience of comparison with other experimental and analytical results, the case of interaction between the straight incoming shock wave and a sharp wedge is simulated for various flow conditions. The numerical results show good agreement with other experimental and analytical results, in the shock wave reflecting structure, slipline, and the trajectory of the triple points. Some critical cases show disagreement with the analytical results, but these cases also have been proven to show hysteresis phenomena.