• 대한조선학회논문집
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• 제47권3호
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• pp.377-387
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• 2010

In this study, the turbulent free surface around KVLCC1 employed in the circular motion test simulation is numerically calculated using a commercial CFD(Computational Fluid Dynamics) code, FLUENT. Also, hydrodynamic forces and yaw moments around a ship model are calculated during the steady turning. Numerical simulations of the turbulent flows with free surface around KVLCC1 have been carried out by use of RANS equation based on calculation of hydrodynamic forces and yaw moments exerted upon the ship hull. Wave elevation is simulated by using the VOF method. VOF method is known as one of the most effective numerical techniques handling two-fluid domains of different density simultaneously. Boundary layer thickness and wake field are changed various yaw velocities of ship model during the steady turning. The calculated hydrodynamic forces are compared with those obtained by model tests.

• 한국항해항만학회지
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• 제30권8호
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• pp.631-636
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• 2006

본 연구에서는 자유수면 위를 고속으로 항주하는 트랜섬 선미를 채택한 선박에 의하여 발생되는 선박주위 및 트랜섬 선미 끝단에서의 비선형 자유수면 경계조건식을 만족하는 자유 수면에서의 파형을 해석하는 수치해석 기법에 대하여 연구, 선체주위 유동해석프로그램을 개발하였다. 개발된 수치해석 프로그램의 타당성을 검증하기 위하여 고속선인 Athena선형, KCS(KRISO container ship)선형에 대하여 수치해석을 실시하였으며, 그 결과를 모형시험에 의하여 계측된 실험결과와 서로 비교하였다.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2004년도 학술대회지
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• pp.188-192
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• 2004

A Numerical analysis method is developed in order to compute the flaw and wave field for 2-dimensional floating body in the free roll motion with 3 degrees of freedom. Navier-Stokes and continuity equations are gaverning equations in tire present study. Finite Difference method is introduced to discretize the governing equation. The free surface is traced by the interface tracking method and the grid system is fitted to boundaries including free surface and body surface, which is moving in the flow field. The numerical scheme is based on Maker and Cell method. For the sake of validation of the numerical method, the computed roll decay factors according to tire midship section shapes are compared with measured results. The numerical results are discussed in order to understand the effect of midship section shape on roll motion.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제34회 춘계학술대회논문집
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• pp.217-225
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• 2010

격벽 착화 모듈은 도우너 화약이 폭발하면서 발생한 충격파가 격벽을 통해 억셉터 화약에 전달되었을 때 동작한다. 격벽 착화 모듈의 가장 중요한 설계 요소인 격벽의 최소 두께를 결정하기 위하여 구조해석을 수행한 결과 격벽의 두께가 0.1 mm 이상인 경우 구조적으로 충분한 마진이 있음을 확인하였다. 격벽의 적정 두께를 결정하기 위하여 VISAR 간섭계를 이용하여 억셉터 화약 충전면에서 자유 표면 속도를 계측하였다. 이 속도를 이용하여 충격 압력으로 환산하고 그 결과를 억셉터 화약의 반응 민감도와 비교함으로서 격벽 두께에 따른 격벽 착화 모듈의 작동 신뢰도를 계산하였다.

• 한국추진공학회지
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• 제14권4호
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• pp.16-24
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• 2010

격벽 착화 모듈은 도우너 화약이 폭발하면서 발생한 충격파가 격벽을 통해 억셉터 화약에 전달되었을 때 동작한다. 격벽 착화 모듈의 가장 중요한 설계 요소인 격벽의 최소 두께를 결정하기 위하여 구조해석을 수행한 결과 격벽의 두께가 0.1 mm 이상인 경우 구조적으로 충분한 마진이 있음을 확인하였다. 격벽의 적정 두께를 결정하기 위하여 VISAR 간섭계를 이용하여 억셉터 화약 충전면에서 자유 표면 속도를 계측하였다. 이 속도를 이용하여 충격 압력으로 환산하고 그 결과를 억셉터 화약의 반응 민감도와 비교함으로서 격벽 두께에 따른 격벽 착화 모듈의 작동 신뢰도를 계산하였다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제13권1호
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• pp.260-277
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• 2021

The appropriate radiation conditions of ship motion problem with advancing speed in frequency domain are investigated from a theoretical and practical point of view. From extensive numerical experiments that have been conducted for evaluation of the relevant radiation conditions, a hybrid radiation technique is proposed in which the Sommerfeld radiation condition and the free surface damping are mixed. Based on the comparison with the results of the translating and pulsating Green function method, the optimal damping factor of the hybrid radiation technique is selected, and the observed limitations of the proposed hybrid radiation technique are discussed, along with its accuracy obtained from the numerical solutions. Comparative studies of the forward-speed seakeeping prediction methods available confirm that the results of applying the hybrid radiation technique are relatively similar to those obtained from the translating and pulsating Green function method. This confirmation is made in comparisons with the results of solely applying either the free surface damping, or the Sommerfeld radiation condition. By applying the proposed hybrid radiation technique, the wave patterns, hydrodynamic coefficients, and motion responses of the Wigley III hull are finally calculated, and compared with those of model tests. It is found that, in comparison with the model test results, the three-dimensional Rankine source method adopting the proposed hybrid radiation technique is more robust in terms of accuracy and numerical stability, as well as in obtaining the forward speed seakeeping solution.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권2호
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• pp.736-749
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• 2019

This paper employs computational tools to investigate the diffraction effects in regular head waves on the added resistance and wake on the propeller plane. The objective ships are a 66,000 DWT bulk carrier and a 3,600 TEU container ship. Fixed and free to heave and pitch conditions at design speed have been taken into account. Two-phase unsteady Reynolds averaged Navier-Stokes equations have been solved using the finite volume method; and a realizable k-ε model has been applied for the turbulent closure. The free surface is obtained by solving a VOF equation. The computations are carried out at the same scale of the model tests. Grid and numerical wave damping zones are applied to remove unwanted wave reflection at the boundaries. The computational results are analyzed using the Fourier series. The added resistances in waves at the free condition are higher than those at the fixed condition, which are nearly constant for all wavelengths. The wake velocity in waves is higher than that in calm water, and is accelerated where the wave crest locates on the propeller plane. When the vertical motion at the stern goes upward, the wake velocity also accelerated.

• 한국해양공학회지
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• 제33권2호
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• pp.131-138
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• 2019

This study focused on the roll motion characteristics of a two-dimensional (2D) rectangular floating structure under regular beam sea conditions. An experiment was conducted in a 2D wave tank for a roll free decay test in calm water and the roll motion in a range of regular waves with and without heave motion to investigate the motion response and heave influence on the roll motion. A numerical study was carried out using Reynolds-averaged Navier Stokes (RANS)-based CFD simulations. A grid convergence test was conducted to accurately capture the wave condition on the free surface based on the overset mesh and wave forcing method. It was found in the roll free decay test that the numerical results agreed well with the experimental results for the natural roll period and roll damping coefficient. It was also observed that the heave motion had an impact on the roll motion, and the responses of the heave and roll motion from the CFD simulations were in reasonable agreement with those from the experiment.

• Structural Engineering and Mechanics
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• 제77권5호
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• pp.571-586
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• 2021

The present paper studies the influence of the inhomogeneous initial stresses in the bi-layered hollow cylinder and it is assumed that these stresses are caused by the hydrostatic pressures acting on the interior and outer free surfaces of the cylinder. The study is made by utilizing the version of the three-dimensional linearized theory of elastic waves in bodies with initial stresses for which the initial stress-strain state in bodies is determined within the scope of the classical linear theory of elasticity. For the solution to the corresponding eigenvalue problem, the discrete-analytical method is employed. Numerical results are presented and analyzed for concrete selected pairs of materials. According to these results and their analyses, it is established that, unlike homogeneous initial stresses, the influence of the inhomogeneous initial stresses on the torsional wave dispersion has not only quantitative but also qualitative character. For instance, in particular, it is established that as a result of the initial stresses caused by the hydrostatic pressure acting in the interior free surface of the cylinder, the cut-off frequency appears for the fundamental dispersive mode and the values of this frequency increase with the intensity of this pressure.

• 대한조선학회지
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• 제22권2호
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• pp.27-34
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• 1985

In this paper, the second order time mean forces acting on the circular cylinder floating on the free surface of a finite water depth are calculated. Under the assumption that fluid is idea and the wave the linear gravity wave, the velocity potential is calculated by the source distribution method, and the second order time mean lateral and vertical drifting forces are calculated by the direct integration of fluid pressures over the immersed body surface. The comparison of the lateral drifting forces with Rhee's results by momentum theorem shows good agreements. And it is shown that the second order time sinkage forces of a floating circular cylinder cross zero for all water depths.