Il-Ryong Park

Development of a Numerical Method for the Evaluation of Ship Resistance and Self-Propulsion Performances

A RANS(Reynolds averaged Navier-Stokes) based numerical method is developed for the evaluation of ship resistance and self-propulsion performances. In the usability aspect of CFD for the hull form design, the field grid around practical hull forms is generated by solving a grid Poisson equation based on the hull surface grid generated from station offsets and centerline profile. A body force technique is introduced to model the effects of the propeller in which the propeller loads are obtained from potential flow analysis using an unsteady lifting surface method. The free surface is captured by using a two-phase level-set method and the realizable model is used for turbulence closure. The hull attitude in vertical plane, i.e., trim and sinkage, is calculated by using a quasi-steady method and then considered in the computation by translating and rotating the grid system according to the values. For the validation of the proposed method, the numerical results of resistance tests for KCS, KLNG, and KVLCC1 and of self-propulsion test for KCS are compared with experimental data.

RANS Computation of Turbulent free Surface Flow around a Self Propelled KLNG Carrier

The turbulent free surface flow around a self-propelled KRISO 138K LNG Carrier is numerically simulated using the finite volume based multi-block RANS code, WAVIS developed at HRISO. The realizable k- turbulence model with a wail function is employed for the turbulence closure. The free surface is captured with the Level-Set method and body forces are used to model the effects of a propeller without resolving the detail blade flow. In order to obtain an accurate free surface solution and stable convergence, the computations are executed with a proper fine grid refinement around the free surface and with an adoption of implicit discretization scheme for the Level-Set formulation. The computed velocity vectors at the several stations and wave patterns show a good agreement with the experimental results measured at the KRISO towing tank.

Calculations on the Interactions between Main and Jib Sails

It is important to understand the flow characteristics around two sails of a sloop yacht. In this paper a computational aerodynamic investigation is performed over sail-like airfoils similar to the main and iIb sails of a 30 feet sailing yacht. Lift and drag are calculated for various conditions of slit distance between the two sails and overlapped length of the jib sail. The thrust and CE(center of effort) of the sail system are obtained. It is found that the combination of two sails produces the thrust force larger than the sum of the thrust force of each sail standing separately and the slit distance of the two sails are important factor to increase lift force.

A Study on a VOF Method for the Improvement of Free Surface Capturing

A new numerical scheme solving two-phase flow, the Hybrid VOF method for improved free surface capturing has been developed by combining a volume capturing VOF method with the Level-Set reinitialization procedure. For validation, the proposed method is applied to 3-D bubble rising problem, dam breaking and the free surface flow around a commercial container ship. The calculated results by using the Hybrid VOF method with the two previously applied VOF formulations are compared with available numerical and experimental data. It is found that the new method provides more reasonable results than the two previous ones.

RANS Simulations for KRISO Container Ship and VLCC Tanker

The finite volume based multi-block RANS code, WAVIS developed at KRISO, is used to simulate the turbulent flow field around the KRISO container ship (KCS) and the modified KRISO tanker (KVLCC2M). The realizable k- turbulence model with a wall function is employed for the turbulence closure. The free surface flow with and without propeller is mainly investigated for the KCS and the double model flow is concerned for the KVLCC2M which is obliquely towed in still water. The computed results are compared with the experimental data provided by CFD Tokyo Workshop 2005 in terms of wave profiles, hull surface pressure and wake distribution with and without propeller for the HCS and wake distribution and hydrodynamic forces and moments with various drift angles for the KVLCC2M.⨍怀܀㔵ㄮ㐶㬙E慲瑨⁳捩湥捥猠☠来潬潧礠

The Comparison of Flow Simulation Results around a KLNG Model Ship

AbstractNumerical simulations have been carried out for a 138K LNG Carrier (KLNG) model ship with free surface, using WAVIS 2.0 and Fluent 6.3.26 with various   values and different grid densities. Level-set method for free surface capturing was adopted in WAVIS, while VOF has been used in Fluent. The calculated results were compar ed with the experiment data. Resistance coefficient, wave pattern, wave profile along the hull surface, axial velocity contours and transverse vectors had been analyzed. When the first   value was fixed at 60, the simulation results from both WAVIS and Fluent were impr oved as the number of grids increased. The convergence time of WAVIS was much shorter than that of Fluent. Furthermore, WAVIS predicted the velocity field and the wave pr ofile along the hull surface better than Fluent. However, Fluent gave better wave patterns. ※Keywords: WAVIS, Fluent, Level-set method, VOF, Wave pattern(파형), Velocity field(속도장) 1. 서 언 수치계산용 컴퓨터와 전산유체역학(Computational Fluid Dynamics, CFD) 기술의발달에 힘입어 많은시간과 비용이 드는 수조시험

Numerical Prediction of Ship Motions in Wave using RANS Method

This paper provides the structure of a Reynolds Averaged Navier-Stokes(RANS) based simulation method and its validation results for the ship motion problem. The motion information of the hull computed from the equations of motion is considered in the momentum equations as the relative fluid motions with respect to a non-inertial coordinates system. A finite volume method is used to solve the governing equations, while the free surface is captured by using a two-phase level-set method and the realizable k- model is used for turbulence closure. For the validation of the present numerical approach, the numerical results of the resistance and motion tests for DTMB 5415 at two ship speeds are compared against available experimental data.

A Numerical Study on the Coupled Dynamics of Ship and Flooding Water

This paper presents a numerical method to solve the ship motion coupled with internal fluid flow. Physically the internal fluid motion is coupled with the ship motion. Hitherto the previous numerical results of the coupled motion predict only the general tendency with experiments. The main reason of inaccuracy is that the coupled dynamics of ship motion and internal water motion is not accurately accounted. In this study CFD technique based on VOF is employed for the accurate analysis of flooding water motion. Some cases of the 24th ITTC stability committee`s benchmark.study for tanker with internal fluid are analyzed by coupling the ship motion and sloshing dynamics. The calculated ship motion is compared with the experimental result to validate the coupled scheme and is in agreement with the experimental result.

Study on the Effects of Surface Roughness and Turbulence Intensity on Dam-break Flows

Dam-break flows, a type of very shallow gravity-driven flow, are substantially influenced by resistance forces due to viscous friction and turbulence. Assuming turbulent flow, the main focus of this study is to validate the increase of drag forces caused by surface roughness and especially turbulence intensity. A Reynolds Averaged Navier-Stokes(RANS) approach with the standard k-ɛ turbulence model is used for this study, where the free surface motion is captured by using a volume of fluid(VOF) method. Surface roughness effects are considered through the law of the wall modified for roughness, while the initial turbulence intensity which determines the lowest level of turbulence in the flow domain of interest is used for the variation of turbulence intensity. It has been found that the numerical results at higher turbulence intensities show a reasonably good agreement with the physical aspects shown by two different dam-break experiments without and with the impact of water.

Numerical Analysis of Ship Motions in Beam Sea Using Unsteady RANS and Overset Grid Methods

Abstract The present paper presents the CFD result for a beam wave test case. An ONR tumblehome ship model with bilge keels is used. The beam wave test is for zero forward speed and roll and heave 2DOF with wave slope a k =0.156 and wavelength λ =1. 12 L PP , with L PP the ship length. The problems is solved numerically with an unsteady Reynolds averaged Navier-Stokes approach. The free surface flow is computed using a single-phase level-set method and the motions in each time step are integrated using a predictor-corrector iteration approach which uses dynamic overs et grids moving with relative ship motion. The predicted CFD results for motions and forces are compared with experimental data, showing a reasonable agreement. ※Keywords: Roll motion(횡동요), Heave motion(상하동요), Beam sea(횡파), CFD(계산유체역학), URANS approach (비정상 RANS법), Overset grid(중첩격자), Level-set method(레벨셋법) 1. 서 론 일반적으로 선형설계 단계에서 파랑중 선박운동 응답은 주로 선형이론(linear theory)을 바탕으로 접수일: 2007년 9월 18일, 승인일: 2008년2월 21일 g교신저자, irpark@moeri.re.kr, 042-868-7267