• 한국전자파학회논문지
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• 제14권10호
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• pp.1060-1070
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• 2003

국내 위성통신용 Ku/Ka 대역 파라볼라 안테나에 적용될 수 있는 삼중 사각 루프 슬롯 배열 형태인 새로운 주파수 선택 반사기 구조를 제시하였다. 본 논문에서 설계, 제작된 주파수 선택 반사기 구조는 다층 유전체인 하니콤 위에 삼중의 사각 루프 슬롯으로 구성되는 단위 소자가 평면에 2차원적으로 주기적인 배열 형태를 지닌다. 주파수 선택 반사기를 제작하여 측정한 결과 계산 결과와 일치되었으며, 요구되는 사양대로 14/12 GHz대 주파수에서는 입사파의 대부분이 투과되는 반면, 30/20 GHz대 주파수에서는 전반사가 일어남을 확인하였다.

• 한국해안해양공학회지
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• 제4권4호
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• pp.187-200
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• 1992

Taylor 정리를 이용하여 평균위치에서의 Eulerian유속으로부터 수립자의 시간에 따른 Lagrangian 운동궤적을 결정하는 방법이 제안되었다. 이 방법을 Stokes 유한진폭파이론에 적용하여 고차 파성분을 포함하는 수립자의 운동궤적과 질양이동속도를 결정하였다. Stokes 5차파이론의 적용 결과, 평균위치에서의 Eulerian 유속으로부터 결정한 수립자의 운동궤적은 자유수면 부근을 제외하고는 5차파이론에 의한 순간속도에 의해 계산된 값과 매우 좋은 일치를 보여주었다. Stokes 5차파 이론에 의한 질양이동속도는 종전의 2차파이론에 의한 질양이동속도보다 전수심에서 작은 값을 보여준다.

• 대한조선학회논문집
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• 제47권3호
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• pp.388-397
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• 2010

A two-dimensional time-domain, potential-theory-based fully nonlinear numerical wave tank (NWT) was developed by using boundary element method and the mixed Eulerian-Lagrangian (MEL) approach for free-surface node treatment. The NWT was applied to prediction of primary wave energy conversion efficiency of a bottom-mounted oscillating water column (OWC) wave power device. The nonlinear free-surface condition inside the chamber was specially devised to represent the pneumatic pressure due to airflow velocity and viscous energy loss at the chamber entrance due to wave column motion. The newly developed NWT technique was verified through comparison with given experimental results. The maximum energy extraction was estimated with various chamber-air duct volume ratios.

• 수산해양기술연구
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• 제35권3호
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• pp.335-342
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• 1999

The purpose of present research is to develop and efficient numerical method for the calculation of potential flow and predict the wave-making resistance for the application to ship design of tuna purse seiner. Havelock was considered the wave resistance of a post extending vertically downwards through the water from the surface, its section by a horizontal plane being the same at all depths and having its breadth small compared with its length. This enables us to elucidate certain points of interest in ship resistance. However, the ship has not infinite draft. So, the problem which is investigated ind detail in this paper is the wave resistance of a mathematical quadratic model in a uniform stream. The paper deals with the numerical calculation of potential flow around the series 60 with forward velocity by the new slender ship theory. This new slender ship theory is based on the asymptotic expression of the Kelvin-source, distributed over the small matrix at each transverse section so as to satisfy the approximate hull boundary condition due to the assumption of slender body. The numerical results using the panel shift method and finite difference method are compared with the experimental results for wigley mono hull. There are no differences in the wave resistance. However, it costs much time to compute not only wave resistance but also wave pattern over some range of Froude numbers. More improvements are strongly desired in the numerical procedure.

• Journal of Ship and Ocean Technology
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• 제8권2호
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• pp.61-69
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• 2004

Unsteady nonlinear wave motions on the free surface over a plane beach of constant slope are numerically simulated using a finite difference method in rectangular grid system. Two-dimensional Navier-Stokes equations and the continuity equation are used for the computations. Irregular leg lengths and stars are employed near the boundaries of body and free surface to satisfy the boundary conditions. Also, the free surface which consists of markers or segments is determined every time step with the satisfaction of kinematic and dynamic free surface conditions. Moreover, marker-density method is also adopted to allow plunging jets impinging on the free surface. The second-order Stokes wave theory is employed for the generation of waves on the inflow boundary. For the simulation of wave breaking phenomena, the computations are carried out with the plane beach of constant slope in surf zone. The results are compared with other existing experimental results. Agreement between the experimental data and the computation results is good.

• 대한조선학회논문집
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• 제35권2호
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• pp.38-50
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• 1998

부유식 방파제의 특성을 파악하기 위하여 수면 근처에 고정된 상자형 방파제 경우의 방파성능을 실험하고 수치계산과 비교하였다. 상자의 폭과 흘수를 변화시키고 파의 주기와 경사도(wave steepness)를 변화시킴으로써 비교적 다양한 변수변화에 따른 영향을 확인하고자 하였다. 투과계수와 방파제에 작용하는 힘을 실험으로부터 측정하고 선형포텐셜이론에 의해 계산된 결과와 비교함으로써 방파제가 수면근처에 고정된 경우 투과계수와 파력에 대한 흘수 및 파장의 영향을 논하였다. 배열의 경우 폰툰사이의 간격이 투과계수와 파력에 미치는 효과를 논하였고, 전반적으로 계산이 실험의 결과를 효과적으로 예측할 수 있음을 확인하였다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제5권4호
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• pp.513-528
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• 2013

A floating Oscillating Water Column (OWC) wave energy converter, a Backward Bent Duct Buoy (BBDB), was simulated using a state-of-the-art, two-dimensional, fully-nonlinear Numerical Wave Tank (NWT) technique. The hydrodynamic performance of the floating OWC device was evaluated in the time domain. The acceleration potential method, with a full-updated kernel matrix calculation associated with a mode decomposition scheme, was implemented to obtain accurate estimates of the hydrodynamic force and displacement of a freely floating BBDB. The developed NWT was based on the potential theory and the boundary element method with constant panels on the boundaries. The mixed Eulerian-Lagrangian (MEL) approach was employed to capture the nonlinear free surfaces inside the chamber that interacted with a pneumatic pressure, induced by the time-varying airflow velocity at the air duct. A special viscous damping was applied to the chamber free surface to represent the viscous energy loss due to the BBDB's shape and motions. The viscous damping coefficient was properly selected using a comparison of the experimental data. The calculated surface elevation, inside and outside the chamber, with a tuned viscous damping correlated reasonably well with the experimental data for various incident wave conditions. The conservation of the total wave energy in the computational domain was confirmed over the entire range of wave frequencies.

• 한국해양공학회지
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• 제17권6호
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• pp.7-15
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• 2003

A Digital Wave Tank simulation technique, based on a finite-difference method and a modified marker-and-cell (MAC) algorithm, is applied in order to investigate the characteristics of nonlinear Tsunami propagations and their interactions with a 2D sloping beach, Ohkushiri Island, and to predict maximum wove run-up around the island. The Navier-Stokes (NS) and continuity equation are governed in the computational domain, and the boundary values are updated at each time step, by a finite-difference time-marching scheme in the frame of the rectangular coordinate system. The fully nonlinear, kinematic, free-surface condition is satisfied by the modified marker-density function technique. The near shore Tsunami is assumed to be a solitary wave, and is generated from the numerical wave-maker in the developed Digital Wave Tank. The simulation results are compared with the experiments and other numerical methods, based on the shallow-water wave theory.

• International Journal of Ocean Engineering and Technology Speciallssue:Selected Papers
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• 제4권1호
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• pp.22-30
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• 2001

A new concept wave absorber is proposed. It is a net type wave absorber. Its efficiency was reported in another publication. Since it is based on new concept, the traditional wave absorber theory is not applicable. It is modeled by introducing damping terms in linearized free surface boundary conditions in this study. The length and the thickness of the wave absorber are modeled by the length and the coefficient of the damping terms. Series of experiments are carried out to get the data for the coefficients of the damping term. The boundary element method is adopted to solve the system. The predicted wave heights show excellent agreement with those of experiments when the lengths of the incoming waves are within the length of the wave absorber.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 춘계학술대회 논문집
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• pp.231-239
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• 2003

A Digital Wave Tank simulation technique based on a finite-difference method and a modified marker-and-cell (MAC) algorithm is applied to investigate the characteristics of nonlinear Tsunami propagations and their interactions with a 2D sloping beach and Ohkushiri island, and to predict maximum wave run-up around the island. The Navier-Stokes (NS) and continuity equation are governed in the computational domain and the boundary values updated at each time step by a finite-difference time-marching scheme in the frame of rectangular coordinate system. The fully nonlinear kinematic free-surface condition is satisfied by the modified marker-density function technique. The Nearshore Tsunami is assumed to be a solitary wave and generated from the numerical wavemaker in the developed Digital Wave Tank. The simulation results are compared with the experiments and other numerical methods based on the shallow-water wave theory.