• 한국해안해양공학회지
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• 제1권1호
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• pp.63-70
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• 1989

단일 및 2개의 연직 불투과성 구조물이 해역에 설치되어 있는 경우 파랑의 회절 및 상호간섭 효과를 일정요소를 사용한 경계요소법에 의해 수치 해석하였다. 파랑은 2차원 선형 회절파 이론으로부터 해석하였으며 구조물 경계상에서 뿐만 아니라 구조물 주위에서의 회절계수를 계산하였다. 본 계산의 신뢰도를 검증하기 위하여 기존의 해석결과와 비교하였으며 대체로 잘 일치하고 있음을 알 수가 있었다.

• 비파괴검사학회지
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• 제20권2호
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• pp.91-101
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• 2000

초음파 탐촉자로부터 방사된 음장을 모델링하는 것은 초음파 측정 모델을 구성하는 첫 번째 단계이며, 그 정확도를 결정짓는 핵심 요소이기 때문에 지금까지 다양한 연구가 진행되었다. 본 논문에서는 지금까지 제안된 다양한 기법 중에서 현재 널리 사용되고 있는 Rayleigh-Sommerfeld 적분 모델, 경계회절파모델(boundary diffraction wave model), 가장자리요소모델(edge element model)에 대해 간략하게 논의하고, 이 세가지 모델을 적용하여 평면 원형 및 사각형 초음파 탐촉자의 방사 음장을 계산하고, 각 기법의 정확성과 계산 효율을 비교하였다.

• 비파괴검사학회지
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• 제34권1호
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• pp.1-9
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• 2014

A two-dimensional numerical model based on the finite element method was built to simulate the wave propagation phenomena that occur during the ultrasonic time of flight diffraction (TOFD) process. First, longitudinal-wave TOFD was simulated, and the numerical results agreed well with the theoretical results. Shear-wave TOFD was also investigated because shear waves have higher intensity and resolution. The shear wave propagation was studied using three models with different boundary conditions, and the tip-diffracted shear-to-longitudinal wave was extracted from the A-scan signal difference between the cracked and non-cracked specimens. This signal showed very good agreement between the geometrical and numerical arrival times. The results of this study not only provide better understanding of the diffraction phenomena in TOFD, but also prove the potential of shear-wave TOFD for practical application.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권2호
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• pp.952-969
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• 2019

This study develops new analytical solutions to water wave diffraction by vertical truncated cylinders in the context of linear potential theory. Three typical truncated surface-piercing cylinders, a submerged bottom-standing cylinder and a submerged floating cylinder are examined. The analytical solutions utilize the multi-term Galerkin method, which is able to model the cube-root singularity of fluid velocity near the edges of the truncated cylinders by expanding the fluid velocity into a set of basis function involving the Gegenbauer polynomials. The convergence of the present analytical solution is rapid, and a few truncated numbers in the series of the basis function can yield results of six-figure accuracy for wave forces and moments. The present solutions are in good agreement with those by a higher-order BEM (boundary element method) model. Comparisons between present results and experimental results in literature and results by Froude-Krylov theory are conducted. The variation of wave forces and moments with different parameters are presented. This study not only gives a new analytical approach to wave diffraction by truncated cylinders but also provides a reliable benchmark for numerical investigations of wave diffraction by structures.

• 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.

• 한국안전학회지
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• 제23권5호
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• pp.91-96
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• 2008

A reflected breakwater can be affected by wave pressure and power because it is to be concentrated by wave energy. The present study is to estimate hydraulic behavior affecting around a reflected breakwater, which is discontinuity cases and various angle of coner at the breakwater. The numerical model to investigate wave diffraction, which is important hydraulic factor in the ocean, is performed by using direct boundary element method. The present numerical results are compared with the solutions of approximate and absolute based on an eigenfunction, and the solution of analytical by Fresnel integral. The results of the present numerical simulation agreed well with those of the published numerical and analytical data. As a result of this study, wave height is high at the comer of breakwater, and it is to be high if angle of conner at the reflected breakwater is small.

• 대한조선학회논문집
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• 제47권3호
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• pp.291-305
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• 2010

A three-dimensional time-domain calculation method is of crucial importance in prediction of the motions and wave loads of a ship advancing in a severe irregular sea. The exact solution of the free surface wave-ship interaction problem is very complicated because of the essentially nonlinear boundary conditions. In this paper, an approximate body nonlinear approach based on the three-dimensional time-domain forward-speed free-surface Green function has been presented. The Froude-Krylov force and the hydrostatic restoring force are calculated over the instantaneous wetted surface of the ship while the forces due to the radiation and scattering potentials over the mean wetted surface. The time-domain radiation and scattering potentials have been obtained from a time invariant kernel of integral equations for the potentials which are discretized according to the second-order boundary element method (Hong and Hong 2008). The diffraction impulse-response functions of the Wigley seakeeping model advancing in transient head waves at various Froude numbers have been presented. A simulation of coupled heave-pitch motion of a long rectangular barge advancing in regular head waves of large amplitude has been carried out. Comparisons between the linear and the approximate body nonlinear numerical results of motions and wave loads of the barge at a nonzero Froude number have been made.

• 한국항만학회지
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• 제7권1호
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• pp.79-88
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• 1993

This study deals with the case of a fixed floating structure(FFS) at the mouth of a rectangular harbor under the action of waves represented by the linear wave theory. Modified forms of the mild-slope equation is applied to the propagation of regular wave over constant water depth. The model is extended to include bottom friction and boundary absorption. A hybrid element approximation is used for calculation of linear wave oscillation in and near coastal harbor. Modification of the model was necessary for the FFS. For the conditions tested, the results of laboratory experiments by Ippen and Goda(1963), and Lee (1969) are compared with the calculated one from this model. The cases of flat cylinderical structures, both fixed and floating, were taken to be in an intermediate water depth.

• 한국항해학회지
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• 제17권1호
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• pp.61-78
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• 1993

Large offshore structure are to be considered for oil storage facilities , marine terminals, power plants, offshore airports, industrial complexes and recreational facilities. Some of them have already been constructed. Some of the envisioned structures will be of the artificial-island type, in which the bulk of structures may act as significant barriers to normal waves and the prediction of the wave intensity will be of importance for design of structure. The present study deals wave scattering problem combining reflection and diffraction of waves due to the shape of the impermeable rigid upright structure, subject to the excitation of a plane simple harmonic wave coming from infinity. In this study, a finite difference technique for the numerical solution is applied to the boundary integral equation obtained for wave potential. The numerical solution is verified with the analytic solution. The model is applied to various structures, such as the detached breakwater (3L${\times}$0.1L), bird-type breakwater(318L${\times}$0.17L), cylinder-type and crescent -type structure (2.89L${\times}$0.6L, 0.8L${\times}$0.26L).The result are presented in wave height amplification factors and wave height diagram. Also, the amplification factors across the structure or 1 or 2 wavelengths away from the structure are compared with each given case. From the numerical simulation for the various boundary types of structure, we could figure out the transformation pattern of waves and predict the waves and predict the wave intensity in the vicinity of large artificial structures.

• 물과 미래
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• 제26권2호
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• pp.39-48
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• 1993

해안에서 발생하는 재해의 큰 원인은 파랑작용에 기인되기 때문에 해양 기술자는 정확한 파랑변형을 예측하는 것이 매우 중요하다. 파랑변형의 주요인은 간수효과, 반사, 회석, 굴석, 산란, 방사등을 들 수 있다. 최근, 파랑변형에 대하여 수치모델이 이용되고 있다. 본 연구는 굴석과 회석을 동시에 고려할 수 있는 완경사방정식을 이용하여 유한요소법으로 수치모델을 수립했다. 이 방법은 복잡한 경계조건을 갖는 해안에 정확한 파랑예측을 할 수 있는 장점이 있지만 몇 가지의 개선해야할 문제점도 있는 것으로 나타났다. 본 계산결과를 검정하기 위해 모형실험을 실시했다. 완경사 방정식을 유한요소법으로 계산한 계산값과 Lee의 방법(Helmholtz 방정식을 유한차분법으로 수치계산한 방법)으로 계산한 값, 그리고 실험값과 비교한 결과 타당성있는 일치를 얻었다.