• 한국해양공학회지
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• 제24권1호
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• pp.39-46
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• 2010

The calmness inside a harbor plays an important role in the appropriate disposition of harbor structures. However, it is not easy to acquire accurate computational results because these are affected by many factors concerned with wave transformation. Recently, numerical model tests, which are quicker and more economical than hydraulic model experiments, were carried out for the purpose of analyzing wave height distributions in harbors. This paper presents a numerical model that is able to calculate wave heights inside a harbor. It is based on a time-dependent mild slope involving wave refraction, diffraction, shoaling effect, and reflection. In particular, arbitrary reflectivity is used at the boundary in order to simulate the real harbor reflection condition. The proposed numerical model is applied to Samcheon new-harbor in order to investigate harbor calmness.

• 한국해양공학회지
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• 제6권2호
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• pp.94-102
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• 1992

This paper presents the method of numerical analysis concerned with the hydropdynamic forces and moments of the floating bodies exerted by waves. The analytic methods of hydrodynamic wave forces and moments for large volume structures are generally classified into four categories ; the strip method, the boundary element method, the finite element method, and the potential matching method. In the case of the comparatively large structures, diffraction theory can be applied. However, there are no application limits of diffraction theory which have been known concerning with the analytic method of the rectangular structures. In this paper, the two-dimensional B.E.M. is treated for a moored small rectangular structure in order to evaluate applicability of diffraction theory. Numerical calculation is carried out for the structure. The results are compared with some other ones for verification. The result shows that diffraction theory is applicable to structures smaller than 0.15 in the ratio of the representative structure length d to wave length L for rectangular ones.

• 한국통신학회논문지
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• 제38C권9호
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• pp.757-763
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• 2013

본 논문에서는 수도권 서북부 지역의 3차원 지리정보를 바탕으로 다중예봉모형을 (multiple knife-edge model) 적용해 전파교란기와 수신기의 지리적 위치에 따른 회절손실을 (diffraction loss) 계산하고, 이를 바탕으로 광대역 잡음재밍 (wideband Gaussian null-to-null noise jamming), 스펙트럼일치형재밍 (matched spectrum jamming), 연속파재밍에 (continuous wave jamming) 의한 GPS (global positioning system) L1 C/A (coarse/acquisition) 신호의 여유재밍전력을 (marginal jamming power) 보인다.

• 대한조선학회논문집
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• 제47권3호
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• pp.369-376
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• 2010

In this study, a radiation and a diffraction problems of a floating body in two-layer fluids were solved by the Numerical Wave Tank(NWT) technique in the frequency domain. In two-layer fluids, two different wave modes exist and the hydrodynamic coefficients can be obtained separately for each mode. The two-domain Boundary Element Method(BEM) in the potential fluid using the whole-domain matrix scheme was used to investigate the characteristics of wave forces, added mass and damping coefficients. The effects of the ratio of density and water depth in the lower domain were also evaluated and compared with given references.

• 대한안전경영과학회지
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• 제11권4호
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• pp.139-145
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• 2009

The present study is to investigate the effect of wave-structure interaction such as wave oscillation. The theoretical method is based upon the linear diffraction theory obtained by the boundary element method. The water depth and incident wave period in fluid region are assumed to be constant. To investigate the wave interaction due to offshore structures, the numerical program has been developed and the simulation has been carried out by varying the conditions of distance and width of offshore structures. This study can effectively be utilized for safety assessment to various breakwater systems and layout of offshore breakwater in the ocean and coastal field. It can give information for the safety to construct offshore structure and revetment in coastal region.

• 한국안광학회지
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• 제4권1호
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• pp.37-43
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• 1999

굴절률이 같은 안경렌즈에 탄성파를 이용한 단색광의 회절무늬로부터 렌즈에 전달되는 탄성파의 속도를 측정하여 렌즈의 불량 유무(有無)를 확인 할 수 있다. 광학적 heterodyne 방법으로 광의 회절무늬를 얻어 종 탄성파의 속도를 측정한 결과 안경렌즈의 경우 중굴절 렌즈는 평균 6588.5575 m/s이고, 고굴절 렌즈는 평균 3973.53 m/s로 측정되었다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제2권3호
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• pp.146-154
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• 2010

In the present study, the wave excitation forces acting on an array of porous circular cylinders are examined based on diffraction problems. To calculate the wave forces, the fluid domain is divided into three regions i.e. a single exterior region, N interior regions and N beneath regions, and the diffraction in each fluid region is expressed by an eigenfunction expansion method with using 3-dimension liner potential theory (Williams and Li, 2000). Especially, the present method is extended to the case of an array of truncated porous circular cylinders to calculate the heave forces as well as surge and sway forces. To verify this method, the numerical results obtained by eigenfunction are compared with these results obtained by higher order boundary element method (Choi et al., 2000). The numerical results obtained by this study are in good agreement with those results. By changing the numbers of porous circular cylinders, the angle of incident wave and the porosity rate of circular cylinders, the wave excitation forces such as surge, sway and heave on an array of truncated porous circular cylinders are investigated.

• 대한조선학회지
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• 제18권1호
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• pp.19-27
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• 1981

The surge motion of a freely-floating sphere in a regular wave is studied within the framework of a linear potential theory. The fluid is assumed to be perfect and only the steady-state harmonic motion in a water of infinite depth is considered. A velocity potential describing the fluid motion is decomposed into three parts; the incident wave potential, the diffraction potential and the radiation potential. In this paper the diffraction potential and the radiation potential are analysed by using multipole expansion method. Upon calculating pressures over the immersed surface of the sphere, the hydrodynamic forces are evaluated in terms of Froude-Krylov, diffraction, added mass and damping forces as functions of the frequency of the incident wave. Finally the frequency dependence of two pertinent parameters, the amplitude ratio and the phase lag between the motion of the sphere and that of the incident wave is derived from the equation of motion. As for numerical results the general tendency of the present calculation shows good agreement with Kim's work who also treated this problem utilizing the Green's function method.

• 한국해안·해양공학회논문집
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• 제28권6호
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• pp.397-407
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• 2016

이안제 좌 우측으로 각각 분기되어 진행하는 파랑은 회절에 의해 이안제 배후 안쪽으로 휘어져 위상간 간섭을 일으키며 중첩되면서 전파된다. 지형적인 여건으로 진행방향이 같아지게 되고 항 입구부로 향한다면 파랑의 에너지 중첩에 의한 영향이 항내로 나타날 수 있다. 본 연구에서는 항 입구부에 이안제가 설치되는 경우, 이안제 길이에 따라 발생하는 좌 우측 회절 파랑의 위상차가 항내 파고에 미치는 영향을 수치실험을 통해 검토하였다. 이로부터 항내에서의 파고는 이안제의 길이에 따른 좌 우측 회절파랑의 위상차에 의한 중첩의 영향으로 증폭 혹은 상쇄되어 나타남을 확인하였다.

• 한국해안·해양공학회논문집
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• 제25권6호
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• pp.349-356
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• 2013

본 연구에서는 만 또는 도서지역과 같이 지형적으로 차폐되어 외해로부터 직접적인 파랑전파가 어렵고 바람에 의해 발달된 파랑의 영향이 클 것으로 판단되는 지역에 사용되는 기존 만내설계파 모델의 문제점을 분석하고 개선방안을 검토하였다. 기존 만내설계파 모델은 바람을 고려할 수 있고 타 모델에 비해 복잡한 지형에도 비교적 간편하게 사용할 수 있는 장점을 지니는 반면 인근 대형 구조물 또는 지형에 의한 파랑의 회절 및 반사 등의 고려가 곤란하다. 기존모델의 단점을 극복하기 위해 회절 및 반사각, 수심변화 등의 고려가 가능한 개량된 만내설계파 모델을 현지에 적용하고 기존 모델과 비교 검토한 결과 구조물 주변에서 설계파고의 값에 신뢰성이 향상되는 것을 확인하였다. 따라서 개선된 만내설계파 모델은 차폐되어 있는 해역에서 항만 구조물 설계 시 기존의 방법에 비해 보다 고정도의 설계파를 산정하는 방법으로서 이용될 수 있을 것으로 판단된다.