• Proceeding of EDISON Challenge
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• 2016.03a
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• pp.588-592
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• 2016

선박의 최적 운항 자세를 찾기 위해 자유 수면을 포함한 저항 해석을 수행할 경우 많은 격자를 이용한 비정상 해석으로 인해 계산 시간이 오래 소요되는 단점이 있다. 본 연구에서는 이를 개선하여 이중 모형을 이용한 정상 해석을 통해 보다 효율적으로 선박의 최적 운항 자세를 도출하는 방법을 연구하였다. KCS를 대상선으로 선정하여 설계속도(24knots)와 저속(15knots)인 경우에 대하여 평형 상태 및 선수/선미 트림 상태에서 이중 모형 수치해석을 수행하고 기존의 연구결과와 비교하였다. 그 결과 자유수면 유무와 속도에 상관없이 선체 자세에 따른 저항 값은 동일한 경향을 갖는 것을 확인하였다. 하지만 저속일 경우 트림조건에 따른 저항의 변화의 폭에서 차이를 보였으며, 이는 압력저항에 기인한 것이다. 따라서 이중 모형을 이용한 저항 해석은 압력저항의 변동이 큰 경우에는 적용되기 어렵다는 한계점이 있다. 하지만 마찰 저항이 주요한 경우에 적용되어 계산효율을 획기적으로 높일 수 있으며, 정성적인 경향을 제시할 수 있는 타당한 방법이라 사료된다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.5
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• pp.126-134
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• 2020

In the case of an earthquake, the fluid storage structure generates hydraulic pressure due to the fluctuation of the fluid. At this time, the hydraulic pressure of the fluid changes not only the peaked acceleration of the earthquake but also the sloshing height of the fluid free water surface. Factors influencing this change in load include the shape of the seismic wave, the maximum seismic strength, the size of the fluid storage structure, the width of the structure, and the height of the fluid. In this study, the effect of the ratio between the height of the fluid and the width of the structure was investigated on the fluctuation characteristics of the fluid. 200mm and 140mm of fluid were placed in a water storage tank with a width of 500mm, and a real seismic wave was applied to measure the shape of the fluctuation of the fluid free water surface. The similarity between the experiment and the analysis was verified through the S.P.H(Smoothed Particle Hydrodynamic) technique, one of the numerical analysis techniques. It was confirmed that the free water surface of the fluid showed a similar shape, through comparison of experiment and analysis. And based on this results, SPH technique was applied to analyze the fluctuation shape of the fluid free water surface while varying the ratio between the fluid height and the structure width. An equation to predict the maximum and minimum heights of the fluid free water surface during an earthquake was proposed, and it was confirmed that the error between the maximum and minimum heights of the fluid free water surface predicted by the proposed equation was within a maximum of 3%.

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 2000.06a
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• pp.241-246
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• 2000

최근 들어 집중호우 및 게릴라성 호우 등 이상강우로부터 야기되는 급격한 하천유량의 증가는 교량에서의 세굴에 대한 안정성 여부에 큰 문제를 야기하고 있다. 홍수시에는 유량이 교량의 상관 위로 월류하게 되는 경우가 생기게 되며, 수심의 증가에 따라 상판의 일부분 또는 전체가 물이 잠기게 된다. 이때의 흐름은 압력흐름 상태를 가지게 되어 세굴의 발달을 더욱 크게 만들게 된다. 흥수시 압력흐름에 대한 위험은 일반 흐름에서보다 훨씬 크며 100년 빈도의 홍수사상일 지라도 그 효과는 500년 빈도의 홍수사상보다 더욱 크게 될 것이다. 기존의 세굴에 대한 연구의 대부분은 자유수면을 기초로 하고 있으며 이에 따라 많은 세굴방정식들도 자유수면에 대해서만 이루어지고 있다. (중략)

• Proceedings of the Korea Contents Association Conference
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• 2010.05a
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• pp.319-321
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• 2010

수리학에서 다루는 유체 현상은 물과 공기의 경계면인 자유수면을 포함할 때가 많다. 수표면의 곡률이 작은 경우에는 정수압 가정이 적절하지만, 그렇지 않은 경우에는 비정수압 분포를 고려하여야 한다. 이와 같은 문제에서는 수심적분된 천수방정식이 아닌, 네비어-스토크스 방정식(Navier-Stokes equations)에 의존해야 할 때가 많다. 특성이 다른 두 유체, 예를 들면, 물과 공기, 물과 기름과 같이 섞이지 않는 두 유체의 모의를 위하여 본 연구에서는 레블? 기법을 적용하였다. 고전적인 문제인 댐파괴 문제에 적용하여 이를 실험결과, 기존 수치모델링 결과와 비교하여 이의 효율성을 확인하였다.

• Proceedings of the Korea Water Resources Association Conference
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• 2004.02a
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• pp.223-245
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• 2004

최근, 자유수면을 갖는 비압축성 유체의 해석을 위해 Hirt and Nichols(1981)가 제안한 VOF법이 자유수면을 취급하는 많은 학문분야에서 활발히 활용되고 있다. 특히, 일본에서 잠제에 의한 쇄파해석에 암전 등(1994)이 처음으로 VOF법을 적용한 이래 많은 연구자에 의한 공동연구의 결과로 개발된 CADMAS-SURF(해안개발기술연구 Center, 2001)는 사용자가 직접 입·출력을 제어할 수 있는 효과적인 2차원파동장의 해석프로그램으로 알려져 있다. 국내에서는 김 등(2001, 2002)이 최초로 VOF-SOLA법을 이용한 수치파동수로를 제안하고 잠제주변의 파동장해석을 수행하고 있다. (중략)

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.29 no.1
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• pp.41-46
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• 2005

In this paper, the flow phenomena and free surface wave pattern around the hull with a transom stern advancing on the free surface in steady state had been studied and the numerical analysis program had been developed using Rankine source panel method based on potential flow analysis in which the non-linearities of the free surface boundary conditions had been fully satisfied. To verify the validity of the developed program the numerical calculations for Athena hull and KCS(KRISO container ship) hull had been performed and the results of the numerical computation had been compared with the ones of the model test experiment.

• Journal of the Society of Naval Architects of Korea
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• v.32 no.3
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• pp.72-82
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• 1995

In the present paper, flow characteristics and free surface waves generated by a submerged hydrofoil advancing with an uniform speed are calculated. Using a numerical method based on a MAC(Marker And Cell) method, the Navier-Stokes and the continuity equations are solved to simulate flow fields around the hydrofoil. Computations are carried out in a rectangular grid system in which grids are concentrated near the foil and the free surface to improve numerical accuracies. Viscous flow phenomenas including pressure distributions are computed. Moreover, the influences of submerged depths upon the generated wave profiles and the wave breaking phenomena are also investigated. Experiments are performed at the towing tank of Inha University to measure free surface wave elevations due to the advancing hydrofoil. The computational results are compared with the present and the other available experimental data to show the accuracy of the numerical method developed.

• Journal of the Korean Society for Marine Environment & Energy
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• v.16 no.4
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• pp.255-262
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• 2013

The boltzmann equation is based on the particle distribution function while the Navire-Stokes equation based on the continuum theory. In order to simulate free surface flow, this paper used the Lattice Boltzmann Method of which is the discretized form. The detail study on the characteristics of the Lattice Boltzmann Method for the free surface simulation was investigated. The developed code was validated with the traditional dam breaking problem by tracking the front position of the water. A basic roles of density functions in the Lattice Boltzmann Method is discussed. To have an engineering applications, the simulation is also conducted the free surface behavior with an arbitrary wall geometry.

• The Journal of the Korea Contents Association
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• v.10 no.10
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• pp.451-455
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• 2010

Hydraulics usually deals with flows with free surface. When the surface curvature is small, the assumption of hydrostatic pressure distribution is enough. However, in the case, when the curvature is big, the non-hydrostatic pressure distribution should be taken into account and the Navier-Stokes equations should be employed instead of the depth-averaged shallow water equations. For the simulation of two immiscible fluids with different characteristics (e.g. water and air, water and oil), the level set method is selected for this purpose. The developed model is applied to classical dam break problem and the computational results are compared with the experimental data. The effectiveness of the developed model is confirmed.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.1
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• pp.54-62
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• 2008

A new solution method was developed to solve the free surface flow around a hull and named as 'Variable Free Surface Panel Method'. In the method the non-linearity of the free surface boundary conditions was fully taken into account and the raised panel method was employed to effectively solve the problem. The transom stern flow was also considered and the panel on the hull was generated using the panel cutting method. Numerical calculations were performed for KCS(KRISO Container Ship) hull form and compared with the experimental data to confirm the validity of the method. The comparison with the conventional free surface panel method was also accomplished. It is confirmed that new method gives more reliable results than the conventional method.