• 대한조선학회논문집
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• 제50권2호
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• pp.79-87
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• 2013

In this paper, an Euler equation solver based on a Cartesian-grid method and non-uniform staggered grid system is applied to predict the ship motion response and added resistance in waves. Water, air, and solid domains are identified by a volume-fraction function for each phase and in each cell. For capturing the interface between air and water, the tangent of hyperbola for interface capturing (THINC) scheme is used with a weighed line interface calculation (WLIC) method. The volume fraction of solid body embedded in a Cartesian-grid system is calculated by a level-set based algorithm, and the body boundary condition is imposed by volume weighted formula. Added resistance is calculated by direct pressure integration on the ship surface. Numerical simulations for a Wigley III hull and an S175 containership in regular waves have been carried out to validate the newly developed code, and the ship motion responses and added resistances are compared with experimental data. For S175 containership, grid convergence test has been conducted to investigate the sensitivity of grid spacing on the motion responses and added resistances.

• International Journal of Naval Architecture and Ocean Engineering
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• 제9권6호
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• pp.641-654
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• 2017

The KVLCC2 and its modified hull form were investigated in regular head waves using Unsteady Reynolds Averaged Navier-Stokes (URANS) methods. The modified KVLCC2 (named KWP-bow KVLCC2) is designed for reducing wave reflection from the bow. Firstly, the original KVLCC2 is studied for verification of the present code and methodology and the computed time history of total resistance and 2DOF motions (heave and pitch) for the selected two wave length conditions are directly compared with the results obtained from KRISO towing tank experiment under the identical condition. The predicted added resistance, heave and pitch motion RAOs show relatively good agreement with the experimental results. Secondly, the comparison of performance in waves between KVLCC2 and KWP-bow KVLCC2 is carried out. We confirmed that newly designed hull form shows better performances in all the range of wave length conditions through both the computation and the experiment. The present URANS method can capture the difference of performance in waves of the two hull forms without any special treatment for short wave length conditions. It can be identified that KWP-bow KVLCC2 gives about 8% of energy saving in sea state 5 condition.

• International Journal of Ocean System Engineering
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• 제2권2호
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• pp.116-138
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• 2012

As in the other fields of mechanics, analytical methods represent an important analysis tool in marine hydrodynamics. The analytical approach is interesting for different reasons : it gives reference results for numerical codes verification, it gives physical insight into some complicated problems, it can be used as a simplified predesign tool, etc. This approach is of course limited to some simplified geometries (cylinders, spheres, ...), and only the case of one or more cylinders, truncated or not, will be considered here. Presented methods are basically eigenfunction expansions whose complexity depends on the boundary conditions. The hydrodynamic boundary value problem (BVP) is formulated within the usual assumptions of potential flow and is additionally simplified by the perturbation method. By using this approach, the highly nonlinear problem decomposes into its linear part and the higher order (second, third, ...) corrections. Also, periodicity is assumed so that the time dependence can be factorized i.e. the frequency domain formulation is adopted. As far as free surface flows are concerned, only cases without or with small forward speed are sufficiently simple to be solved semi-analytically. The problem of the floating body advancing in waves with arbitrary forward speed is far more complicated. These remarks are also valid for the general numerical methods where the case of arbitrary forward speed, even linearized, is still too difficult from numerical point of view, and "it is fair to say that there exists at present no general practical numerical method for the wave resistance problem" [9], and even less for the general seakeeping problem. We note also that, in the case of bluff bodies like cylinders, the assumptions of the potential flow are justified only if the forward speed is less than the product of wave amplitude with wave frequency.

• 해양환경안전학회지
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• 제18권2호
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• pp.153-159
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• 2012

본 연구에서는 실습선의 다방향 불규칙파중 종방향 운동응답특성을 선형 스트립이론에 기초한 상용코드(MAXSURF v.16)를 이용하여 해석하였다. 해석에 앞서 상용코드의 검증을 위해 파나막스급 컨테이너선에 대해 실험조건과 동일한 선형과 해석조건을 적용하여 계산한 결과와 기 계산된 결과(Flokstra, 1974)가 상호 유사한 경향을 얻어 해석의 신뢰성을 확보하였다. 계산조건으로는 Fn=0.257에서 파랑외력을 ITTC 파스펙트럼에 기초한 뷰포트 스케일 5($\bar{T}=5.46$, $H_{1/3}=2m$)의 파스펙트럼을 산출하였고, 조우각은 선수사파(Head & bow seas, $150^{\circ}$)를 적용하여 상하동요(Heave)와 종동요(Pitch)의 선체운동응답스펙트럼을 해석하였다. 다방향 불규칙파에 대한 운동응답스펙트럼은 선수사파에서 상하동요의 경우는 미소하게 단파정파에서 높은 스펙트럼 분포를 보이고 종동요의 경우는 장파정파에서 높게 나타났다.

• 해양환경안전학회지
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• 제28권4호
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• pp.667-679
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• 2022

선박의 피로 손상 해석에는 운항적인 요소를 고려한 매개 변수들을 포함하고 있다. 이러한 운항적인 변수들 때문에 설계 단계에서 예측하는 피로 손상도와 실제 운항 조건을 고려한 피로 손상도간의 차이가 발생한다. 마찬가지로 피로 해석에서 적재 하중 조건을 고려할 때 실제 컨테이너선은 다양한 적재 상태가 존재하지만 설계 단계에서 대표 하중 조건을 선택하여 피로 손상도를 계산한다. 실제 하중 조건과 설계시 하중 조건을 적용하였을 때 피로 손상 계산 결과의 차이가 예상됨에도 불구하고 컨테이너선의 하중 조건에 따른 피로 손상 기여도에 관한 연구는 거의 이루어지지 않은 실정이다. 본 연구에서는 컨테이너선의 화물 중량 분포를 변화시켰을 때 피로 손상기여도를 분석하고자 하였다. 일반적으로 설계 단계에서 적용하는 하중 조건뿐만 아니라 다양한 하중 조건을 생성하고 유체동역학 계산으로 얻을 수 있는 선체 거더 하중 및 스펙트럴 피로 해석을 수행하여 얻은 피로 손상도를 확인하였다. 그 결과, 컨테이너선에서 화물 중량 분포 변화는 선체 거더 하중을 변화시켰으며 선체 거더 응력에 영향을 주어 피로 손상의 변화를 야기시키는 것을 알 수 있었다.