• Ocean Systems Engineering
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• 제4권1호
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• pp.21-37
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• 2014

This paper provides a practical stochastic method by which the burial and scour depths of truncated cones exposed to long-crested (2D) and short-crested (3D) nonlinear random waves can be derived. The approach is based on assuming the waves to be a stationary narrow-band random process, adopting the Forristall (2000) wave crest height distribution representing both 2D and 3D nonlinear random waves. Moreover, the formulas for the burial and the scour depths for regular waves presented by Catano-Lopera et al. (2011) for truncated cones are used. An example of calculation is also presented.

• Ocean Systems Engineering
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• 제2권4호
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• pp.257-269
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• 2012

This paper provides a practical stochastic method by which the maximum equilibrium scour depth around spherical bodies exposed to long-crested (2D) and short-crested (3D) nonlinear random waves can be derived. The approach is based on assuming the waves to be a stationary narrow-band random process, adopting the Forristall (2000) wave crest height distribution representing both 2D and 3D nonlinear random waves, and using the regular wave formulas for scour and self-burial depths by Truelsen et al. (2005). An example calculation is provided.

• 한국해안해양공학회지
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• 제5권2호
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• pp.58-65
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• 1993

풍파가 그 생위영역을 벗어나 전이해 갈 경우 스펙트럼의 폭은 side band instability 등으로 인해 증가하게 되는데 이 경우 비선형불규칙파의 추계학적 성질에 대해서는 거의 규명된 바 없으나 간략화된 Longuet-Higgins의 파랑모형을 토대로 비선형 불규칙파의 파봉에 대한 확률밀도함수를 유도하였으며 모의 결과 스펙트럼 폭이 peak의 분포에 지대한 영향을 미치며 비선형의 정도가 심화될 경우 유의파고는 증가하는 것으로 밝혀졌다.

• Ocean Systems Engineering
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• 제1권4호
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• pp.355-372
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• 2011

Based on the fully nonlinear velocity potential theory, the liquid sloshing in a three dimensional tank under random excitation is studied. The governing Laplace equation with fully nonlinear boundary conditions on the moving free surface is solved using the indirect desingularized boundary integral equation method (DBIEM). The fourth-order predictor-corrector Adams-Bashforth-Moulton scheme (ABM4) and mixed Eulerian-Lagrangian (MEL) method are used for the time-stepping integration of the free surface boundary conditions. A smoothing scheme, B-spline curve, is applied to both the longitudinal and transverse directions of the tank to eliminate the possible saw-tooth instabilities. When the tank is undergoing one dimensional regular motion of small amplitude, the calculated results are found to be in very good agreement with linear analytical solution. In the simulation, the normal standing waves, travelling waves and bores are observed. The extensive calculation has been made for the tank undergoing specified random oscillation. The nonlinear effect of random sloshing wave is studied and the effect of peak frequency used for the generation of random oscillation is investigated. It is found that, even as the peak value of spectrum for oscillation becomes smaller, the maximum wave elevation on the side wall becomes bigger when the peak frequency is closer to the natural frequency.

• 한국수자원학회논문집
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• 제38권6호
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• pp.429-438
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• 2005

본 연구에서는 Boussinesq 방정식을 이용하여, 불규칙 파랑의 직접적인 해석이 가능한 한 쌍의 상미분방정식을 유도하였다. 입사파랑은 TMA(TEXEL storm, MARSEN, ARSLOE) 천해 스펙트럼을 이용하여 재현하였으며, 지배방정식은 4차 Runge-Kutta 법을 이용하여 적분하였다. 새로 유도된 파랑 방정식을 이용하여, 일정 수심을 진행하는 파랑의 비선형 에너지 교환효과를 계산하였다. 또한, 일정 경사면의 정현파형 지형을 통과하는 불규칙파랑의 특성에 관해 수치적으로 검토하였다. 비선형성이 불규칙파랑의 통과와 반사에 큰 영향을 주었다.

• 한국해양공학회지
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• 제15권1호
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• pp.12-18
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• 2001

This study concentrates on the second-order diffraction problem around circular cylinders in multi-frequency waves. The method of solution is a time-domain Rankine panel method which adopts a higher-order approximation for the velocity potential and wave elevation. In the present study, the multiple second-order quadratic transfer functions are extracted from the second-order time signal generated in random waves, and the comparison with other bench-mark test results shows a good agreement. This approach is directly applicable to prediction of nonlinear forces on offshore structures in random ocean.

• 한국해안해양공학회:학술대회논문집
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• 한국해안해양공학회 1998년도 정기학술강연회 발표논문 초록집 Annual Meeting of Korean Society of Coastal and Ocean Engineers
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• pp.5-11
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• 1998

Wave nonlinearity and dispersivity have mutually counteracting effects on the wave evolution process; i.e., the former makes the wave profile steeper, while the latter milder. Therefore to describe evolution of nonlinear water waves under general condition such as nonlinear random waves over arbitrary depths, both the wave nonlinearity and dispersivity must be properly taken into account in the wave modeling. (omitted)

• 한국해양공학회지
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• 제7권2호
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• pp.114-120
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• 1993

Responses of marine vehicles and ocean structures in a seaway can be predicted by applying the probabilistic approach. When we consider a linear system, the responses in a random seaway can be evaluated through spectral analysis in the frequency domain. But when we treat nonlinear system in irregular waves, it is necessary to get time history of waves. In the previous study we introduced one-directional waves (long crested waves)as wave environment and carried out calculations and experiments in the waves. But the real sea in which marine vehicles and structures are operated has multi-directional waves (short crested waves). It is important to get a simulated random sea and analyse dynamic problems in the sea. We need entire sample function or probabillty density function to infer statistical value of random process. However if the process are ergodic process, we can get statistical values by analysis of one sample function. In this paper, we developed the simulation technique of multi-directional waves and proved that the time history given by this method keep ergodic characteristics by the statistical analysis.

• 한국수자원학회논문집
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• 제30권3호
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• pp.225-233
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• 1997

부체의 장주기동요, 연안구조물과 계류선의 파괴 등과 같은 역기능으로 인해 파군현상의 정확한 해석은 시급한 과제라 하겠다. 본고에서는 연안계에서 발생하는 파랑과 가장 근접한 비선형불규칙 파랑계를 산정하여 해안구조물의 피로거동에 지대한 영향을 미치는 파군당 파랑의 수와 해안구조물의 first excursion failure mode를 결정하는 high run에서의 파랑수를 중심으로 파군현상을 해석하였다. 해석과정에 mapping technique과 유의파경사를 perturbation parameter로 섭동이론이 사용되었다. 해석결과 Gaussian wave계에서 균등분포하는 것으로 알려진 위상함수는 평균값 주위에 집중분포하였고, 그 정도는 비선형성이 증가할수록 심화되었다. threshold crossing rate의 경우 비선형성이 심화될수록 평균해수위보다 큰 쪽으로 분포형이 이동하였으며 파군당 파랑수와 high run에서의 파랑수도 비슷한 경향을 보여 최근 설치범위가 심해쪽으로 확대되는 해안구조믈의 경우 피로거동에 대한 보강이 요만된다.

• 한국연안방재학회지
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• 제4권1호
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• pp.1-6
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• 2017

Most of the short period waves are blocked by the breakwaters when the short period irregular waves propagate into the ports. However, nonlinear irregular wave numerical experiments show that the long waves generated by the nonlinear interaction is predominant in the port. Seiches phenomenon in Geumjin Fishing Port is very similar to 60 and 300 second harbor oscillations. By arranging the inner breakwater of the proper length in the inside of the port, it is possible to effectively reduce seiches, as well as the short-period wave, and significantly improve the harbor tranquility. In the case of rectangular basin type such as the Geumjin Fishing Port, the multi-directional irregular wave numerical model should be used for the investigation and countermeasures for the harbor tranquility.