Search

In this study, the free motion of a riser due to vortex shedding was numerically simulated with Large Eddy Simulation (LES) and Detached Eddy Simulation (DES) turbulence models. A numerical simulation program was developed by applying the Rhie-Chow interpolation method to the pressure correction of the OpenFOAM standard solver pimpleDyMFoam. To verify the developed program, the vortex shedding around the fixed riser at Re = 3900 was calculated, and the results were compared with the existing experimental and numerical data. Moreover, the vortex-induced vibration of a riser supported by a linear spring was numerically simulated while varying the spring constant. The results are compared with published direct numerical simulation (DNS) results. The present calculation results show that the numerical method is appropriate for simulating the vortex-induced motion of a riser, including lock-in phenomena.

A container ship has large flare on the bow flare region to accommodate more container recently. This flare region experiences the impact pressure due to slamming phenomenon under rough sea conditions. The impact pressure is transferred to the hull structure and the impact pressure causes structural damage. A strength assessment of the bow region is evaluated based on the empirical formulas according to various classifications. In this study, the numerical simulations were performed to compare with empirical method, and predict the bow flare slamming pressure on the container ship. It is found that the bow flare slamming pressure generated up to 625kPa near 0.975 station and the bow flare slamming pressure obtained from the formulas of the CSR and ABS tend to be similar to the CFD results.

Structure Using the Modified Marker-density Method Yoon-Jin Ha . Young-Gill Lee .Kwang-Leol Jeong . In-Jun Yang Korea Research Institute of Ships and Ocean Engineering, KRISO, Daejeon, Korea Dept. of Naval Architecture and Ocean Engineering, Inha University, Incheon, Korea Research Center, NEXTfoam Co., Ltd., Seoul, Korea Dept. of Naval Architecture and Ocean Engineering, Graduate School, Inha University, Incheon, Korea

This paper presents a numerical simulation method for the flow around advancing ships in regular waves by using a rectilinear grid system. Because the grid lines do not consist with body surface in the rectilinear grid system, the body geometries are defined by the interaction points of those grid lines and the body surface. For the satisfaction of body boundary conditions, no-slip and divergence free conditions are imposed on the body surface and body boundary cells, respectively. Meanwhile, free surface is defined with the modified marker density method. The pressure on the free surface is determined to make the pressure gradient terms of the governing equations continuous, and the velocity around the free surface is calculated with the pressure on the free surface. To validate the present numerical method, a vortex induced vibration (VIV) phenomenon and flows around an advancing Wigley III ship model in various regular waves are simulated, and the results are compared with existing and corresponding research data. Also, to check the applicability to practical ship model, flows around KRISO Container Ship (KCS) model advancing in calm water are numerically simulated. On the simulations, the trim and the sinkage are set free to compare the running attitude with some other experimental data. Moreover, flows around the KCS model in regular waves are also simulated.

In this paper, the effects of bow deck shape on the green water are studied by numerical and experimental method. Varying the deck shapes to triangular, elliptic and circular, the thickness and advancing velocity of green water leading edge are compared using numerical method. Also the motion, the pressure on the vertical wall and the height on the deck of green water are compared among the three bow deck shapes in the heave and pitch motion free condition by experimental method. To remove the effects of the difference of motions among the deck shapes, numerical simulations are performed varying the deck shape with the same motion. In the same motion condition, smallest impulsive pressure occurred in the condition of elliptic deck shape.

A numerical simulation method is developed for the description of a two-dimensional body moving in free surface flows using a fixed rectangular grid system. The nonlinear free surface is determined by the modified Marker-density method. The body boundary is defined by the line segments connecting the points where the body surface and grid lines meet. The Navier–Stokes equations and the continuity equation are used as the governing equations, which are coupled with a two-step projection method described in detail in this research. The velocities and pressures in the body boundary cells as well as the free surface cells are calculated using a simultaneous iterative method. For the verification of the present numerical method, four kinds of simulations have been conducted. The first case is to investigate the vortex shedding of an advancing cylinder, the second case is about the forced oscillation of a box, the third case is to clarify the sloshing phenomenon in a horizontally excited tank, and the last case is waves generation by a plunging-type wave maker. The simulation results are confirmed with corresponding experimental results or analytical solutions.

In this research, the relationship between the bow shape and green water phenomenon on the bow deck of an FPSO was studied using an experimental method. A 140,000 DWT FPSO was used as the objective hull form in the present research. The incident waves were regular types. The heights were 1.0 and 1.5 times the freeboard, and the length was equal in size to LBP. The wave heights and pressures on the deck were measured in experiments. Model tests were performed to determine the effects of bow flare angles, bow shapes, and a forecastle deck. The free heave and pitch conditions were applied to the models in these experiments. From the results of the model tests, an optimized bow shape was designed, which was found to decrease the green water impact loading. The results of this research could be used as fundamental data in the design of a bow shape.

A numerical simulation method is presented for nonlinear waves generated by advancing ships. The nonlinear free surface is determined by a modified Marker-density method. Pressures and velocities in body boundary cells and free surface cells are calculated through a simultaneous iterative method. The filtered Navier–Stokes equations and filtered continuity equation are used as governing equations. The equations are solved by using a finite difference method in a Cartesian grid system. The body boundary is defined by the line segments connecting the points where grid lines and body surface meet. Pressures are coupled with velocities through two-step projection method in the present approach. The governing equations are approximated in finite difference form using a forward time centered space (FTCS) scheme except convection terms. The convection terms are approximated in finite difference form employing third order upwind scheme in space and Adams–Bashforth scheme in time. For the verification of the present numerical simulation, a numerical computation is carried out with Series-60 cargo ship. For the grid convergence test, three grid levels are selected with a constant grid refinement ratio. For the purpose of understanding spilling type breaking waves near a ship bow, a wedge shape model is selected, and its numerical simulation is performed using the computational fluid dynamics program developed during the present research. For a specific case, plunging type breaking bow waves with scars which are frequently generated by a planing hull type patrol ship, are numerically simulated at several different speeds. In addition, the pressure resistance coefficients from the numerical computations are investigated in detail with respect to the residual resistance coefficients from the corresponding ship model experiments.

It is very important to investigate and understand the motion of a FPSO on waves because green water phenomenon occurs owing to the relative motions between incident waves and a ship on them. In this research, both experimental and some numerical approaches have been performed in head sea conditions with regular waves. As an object model of this research, a FPSO model is set free to heave and pitch during the experiments. Also, the motions of the FPSO model which are the results of the experiments are used for the corresponding numerical computations. The purpose of this study is to clarify the effect of bow flare on green water load. In this research, it is found that the amount of green water entered from the side of bow is decreased by the increase of bow flare angle. Moreover, the relation between the green water on the bow upper deck and the impact load on the vertical wall located at turrethead is investigated. The results of this research could be used as one of the fundamental data to design bow flares. Also, an optimized bow flare angle is proposed in this study.

The internal flows of moonpool usually causes huge added resistance on drillships, and those are very complex to analyze. Therefore, not only experimental approaches but also numerical simulations are required for better investigations when dealing with the hydrodynamic problems of moonpool. In the present research, numerical simulations are used to find out why the resistance increases by moonpool on a running drillship. That is, the three-dimensional numerical simulations and model tests are carried out to examine the characteristics of internal flow and added resistance by changing the section of the moonpool in both longitudinal and transverse directions. Finally, based on the present studies, an optimized shape of the moonpool is suggested, which effectively reduces added resistance, and that is confirmed with three-dimensional numerical simulations and model tests.

In the present study, three-dimensional sloshing phenomena occurring in liquid cargo tanks are numerically simulated. The Navier–Stokes equations and continuity equation are used for the governing equations, and solved with a finite difference method in a rectangular fixed staggered mesh system. The positions of free surface are defined by the Marker density method satisfying the free-surface boundary conditions, and the flows of the gas and liquid regions are simulated simultaneously. The irregular leg length and star method is employed on the cells near the free surface for the computations of pressure. The computation results are compared with other experimental results to verify the consistency of the present numerical method, and the agreements are reasonably good. Furthermore, the flow characteristics inside a partially filled liquid tank of a real sized ship oscillating regularly and irregularly are computed to verify the possibility of practical application of the present method.

Bulbous bow is one of the important design factors on the design of fore-body hull form. Using the interference technique of ship waves, the bulbous bow can decrease the wave resistance of ship. Recently, the goose neck bulb is applied mainly for high speed vessels like passenger ships and ferries etc.. Also, the goose neck bulb is applied for relatively high speed merchant vessels like container ships and LNG carriers. However, existing research papers about the goose neck bulb are not enough as reference data for the design of bow hull form. In this study, numerical calculations are carried out to investigate the bow wave characteristics of a high speed ferry with a normal high nose bulb or a goose neck bulb. By comparing the pressure distributions on the hull surface and the wave systems near the bow, the features of wave resistance reduction are discussed. Also, Numerical calculations were carried out for a series of goose neck bulbs to figure out the optimum bulb size. The maximum reduction rate of pressure resistance for the fore-body is achievable up to 8% by adopting the goose neck bulb in the present calculation.

2 Abstract This paper introduces a new hull form design method for the bow of a full ship, by actively applying the relation between the fore-body hull form and its wave resistance characteristics. For the hull form design, the Series 60(CB=0.8) hull is chosen as the parent ship, and Kracht's charts are used to determine the parameters of the bulbous bow in the early stages of hull form design. Several hull forms have been tested in order to obtain enough hull form variations with various bow shapes and design parameters in the search of the best design. In order to investigate the resistance characteristics of the designed hull forms, numerical simulations with corresponding model tests have been rigorously performed. For the numerical simulations, the Marker-density method is employed to track the nonlinear phenomena of the free surface(program IUBW). Model tests have also been performed to achieve an improved research performance using the designed hulls. Both numerical and experimental results show that the wave resistance of the hull forms can be effectively diminished if the bows are designed using the method introduced in this research. It is also expected that this research can facilitate better productivity in hull form design, especially at the preliminary design stage of a full ship type vessel.

In this paper, wave breakers which occur in two dimensional coasts are simulated using a SPH(Smoothed Particle Hydrodynamics) method which represents the movement of fluidic physical volume with particles. As continuative fluid is approximated to the particles, the simulations are performed using fully Lagrangian method without any grid system. Two-dimensional Navier-Stokes equations and continuity equation are used for the numerical simulations. To generate incident waves, a piston type wavemaker is employed. The accuracy of the wave which is numerically generated by the wavemaker is verified by comparing with analytical results. The computations are carried out with various wave heights and slopes. The wave patterns generated through the numerical simulations are compared with several existing experimental and computational results. Agreement between the experimental data and the computation results is comparatively good. Also, the breaker depth index and the breaker height index from the present calculations are compared with the existing experimental results, and the tendency is very similar.

Green water load is an important parameter to be considered in designing a modern ship or offshore structures like FPSO and FSRU. In this research, a numerical simulation method for green water phenomenon is introduced. The Navier-Stokes equ ations and the continuity equation are used as governing equations. The equations are calculated using Finite Difference Method(FDM) in rectangular staggered grid system. To increase the numerical accuracy near the body, the Cartesian cut cell method is employ ed. The nonlinear free-surface during green water incident is defined by Marker-d ensity method. The green waters on a box in regular waves are simulated. The simulation results are compared with other experimental and computational results for verification. To check the applicability to moving ship, the green water of the ship which is towed by uniform force in regular wave, is simulated. The ship is set free to heave and to surge. ※Keywords: Green water(갑판침입수), Non-linear wave(비선형 파도), Marker-density method(밀도함수법), Cartesian cut cell(잘린 직사각형 격자계)접수일: 2009년 12월 21일, 승인일: 2010년 3월 11일✝교신저자: younglee@inha.ac.kr, 032-860-7340

Two dimensional sloshing phenomena in regularly excited liquid cargo tank are numerically simulated with finite difference method. Navier-Sto kes equations and continuity equation are computed for this study. The free-surface is deter mined every time step satisfying kinematic boundary condition using marker-density me thod. And the exciting force is treated by adding the acceleration of the tank to source term. The results are compared with other existing experiment results. And the comparison resu lts show a good agreement. The sloshing phenomena in the tank of the 138K LNG carrier in s way motion is simulated with present calculation methods in low filling level. To find the relations between impact pressure and excitation condition, the calculations are performed in various amplitudes and periods. The averaged maximum pressures are compared each other . ※Keywords: Sloshing(슬로싱), LNG carrier(천연가스 운반선), Marker-density method(밀도함수법), Free-surface(자유수면), Liquid cargo tank(액체화물창)

According to the existing research result on the seabed organic sediment, pollutants from the land and the sea contaminate the coastal water and sediment on the seabed. To tackle this problem, we need to dredge organic sediment. In the presen t paper, the development of removing system of seabed sediment by the difference of water head is researched by experimental method. For the validation of the decompression system, computations for validation are carried out for sediment removing equipment. The performance of inhalation equipment is analysed by some model tests. ※Keywords: Water head(수두), decompression(감압), Inhalation equipment(흡입장비), Sediment(퇴적물), Model test(모형시험) 1. 서론 연안 해역 특히 음식점과 어시장이 들어서 있는 어항 내에서는 생선 세척수와 어패류 사체로 오염 접수일: 2006년 12월 29일, 승인일: 2008년 1월 28일✝교신저자: younglee@inha.ac.kr, 032-860-7340 은 점점 심해지고 있다. 해저 유기퇴적물에 관한 기존의 연구결과에 의하면 육상과 해상에서 유입된 오염물이 연안 해역에 퇴적되어 수온상승과 무산소환경의 확산으로 인해 적조현상의 주원인인 인(P)성분이 다량 용출되는 것으로 밝혀졌다(Hakanson and Jansson 1983, Lee and Lee 2004, Lennox 1984). 이를 개선하기 위해서는 해