• Journal of Ocean Engineering and Technology
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• v.11 no.2
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• pp.100-106
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• 1997

Viscous flow around an actual ship is calculated by an use of RANS(Reynolds-averaged Navier-Stokes) solver. Reynolds stress is modelled by using k-$\varepsilon$ turbulence model and the law of wall is applied near the body. Body fitted coordinates are introduced for the treatment of the complex boundary of the ship hull form. The transformed equations in the computational domain are numerically solved by an employment of FVM(Finite Volume Method). SIMPLE(Semi-Implcit Pressure Linked Equation) method is adopted in the calculation of pressure and the solution of the disssssssscretized equation is obtained by the line-by-line method with the use of TDMA(Tri-Diagonal Matrix Algorithme). The subject ship model of actual calculation is 4,410 TEU class container carrier. For 4 geosim models the calculated viscous resistancce values are compared with the model test results and analyzed on their componentss. The resistance performance of an actual ship is predicted very resonably, so this mothod may be utilized as a design tool of hull form.

• Journal of computational fluids engineering
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• v.19 no.4
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• pp.20-28
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• 2014

An efficient solution algorithm for simulating free surface problem is presented. Navier-Stokes equations for variable density incompressible flow are employed as the governing equation on Cartesian meshes. In order to describe the free surface motion efficiently, VOF(Volume Of Fluid) method utilizing THINC(Tangent of Hyperbola for Interface Capturing) scheme is employed. The most time-consuming part of the current free surface flow simulations is the solution step of the linear system, derived by the pressure Poisson equation. To solve a pressure Poisson equation efficiently, the PCG(Preconditioned Conjugate Gradient) method is utilized. This study showed that the proper application of the preconditioner is the key for the efficient solution of the free surface flow when its pressure Poisson equation is solved by the CG method. To demonstrate the efficiency of the current approach, we compared the convergence histories of different algorithms for solving the pressure Poisson equation.

• Journal of computational fluids engineering
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• v.15 no.1
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• pp.71-80
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• 2010

The violent free-surface motions and the corresponding impact loads are numerically simulated by using the Moving Particle Semi-implicit (MPS) method, which was originally proposed by Koshizuka and Oka (1996) for incompressible flows. In the original MPS method, there were several shortcoming including non-optimal source term, gradient and collision models, and search of free-surface particles, which led to less-accurate fluid motions and non-physical pressure fluctuations. In the present study, how those defects can be remedied is illustrated by step-by-step improvements in respective processes of the revised MPS method. The improvement of each step is explained and numerically demonstrated. The numerical results are also compared with the experimental results of Martin and Moyce (1952) for dam-breaking problem. The current numerical results for violent free-surface motions and impact pressures are in good agreement with their experimental data.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.10
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• pp.1971-1978
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• 1992

A turbulent flow in a conical diffuser with total divergence angle of 8.deg. was numerically studied. The low Reynolds number k-.epsilon. model(Launder-Sharma model) was adopted to simulate the turbulence. The continuity and time averaged Navier-Stokes equations in a nonorthogonal coordinate system were solved by a finite volume method based on the fully elliptic formulation. The low Reynolds number k-.epsilon. model reasonably simulates the pressure recovery and the mean velocity components. However, there are also considerable discrepancies between predicted and measured shear stress distribution on the wall and turbulent kinetic energy distributions. It is necessary to investigate the flow structure at the entry of the diffuser, numerically as well as experimentally.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.8
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• pp.677-684
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• 2007

In the Present Study, a 3-D viscous flow solver, based on unstructured hybrid meshses containing tetrahedra, prisms and pyramids, has been developed. A finite-volume discretization scheme is used for solving the compressible Navier-Stokes equations. A cell-vertex median dual volume is used for spatial discretization. The one-equation Spalart-Allmaras turbulence model has been adopted to evaluate the eddy viscosity. Validation were made by computing laminar and turbulent flows around a 3-D wing for steady flows and turbulent flows around an oscillating 3-D wing in harmonic motion for unsteady flows.

• The KSFM Journal of Fluid Machinery
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• v.2 no.2 s.3
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• pp.64-73
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• 1999

The three-dimensional numerical study of a water jet pump was carried out to investigate the relationship between performance and the geometric variables of nozzle space, area ratio, and throat length. Because of the complex geometry, the multiblock technique was adopted for numerical analysis and a special treatment for transferring data from each of the block interfaces was implemented in order to maintain the conserved properties. To validate the present code, flow passing through a square duct with a 90-deg bend was computed, our results show good accordance with other experimental and computational results. The numerical simulation was done with the flow of the water jet pump having a 180-deg bend in order to calculate the performance at different operating conditions. The performance of the water jet pump can be improved by study of parameters which clarify the relations between the geometric variables and the flow characteristics of vortex strength and location.

• Journal of Ocean Engineering and Technology
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• v.24 no.5
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• pp.31-38
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• 2010

The Floating storage and re-gasification unit (FSRU), which has large cargo storage tanks, is a floating liquefied natural gas (LNG) import terminal. The sloshing motion in tanks that are partially filled with LNG can cause impact pressure on the containment system and affect the global motion of the FSRU. Therefore, the accurate prediction of sloshing motion has been a significant issue in the offshore gas production industry. In this paper, a particle method based on the moving particle semi-implicit (MPS) method proposed by Koshizuka and Oka (1996) has been modified to predict sloshing motion accurately in a rectangular tank with the filling ratio of water. The simulation results, including the violent sloshing of the fluid, were validated by comparison with the original MPS method.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.4
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• pp.223-233
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• 2002

The air distribution duct with multiple outlets is an essential part of automotive air-conditioning system In a bus. The estimation of airflow rate in an automotive air-conditioning duct is typically very complicate due to large variations in cross-sectional area and abrupt changes in flow direction, as well as unbalanced distribution of the flow. In this paper, the flow characteristic in a duct with multiple outlets is investigated through experiment, CFD simulation and a one-dimensional simulation. Numerical simulations have been performed for two simplified air conditioning ducts with multiple outlets used in a medium bus. The three dimensional Navier-Stokes code was used to evaluate the overall pressure, velocity Held, and distribution rate at each diffuser according to the change of various design parameters such as ratio of cross-sectional area and radius of bifurcated region. In addition, a one-dimensional program based on Bernoulli equation was developed to obtain optimized diffuser area required to equalize discharge flow rate at each outlet. As a result of this study, optimized diffuser area of design variable by one-dimensional program was very reasonable as compared to the trend deduced from CFD Simulation. Therefore, the simple and convenient one-dimensional analysis developed in this study can be applied in practical design procedure for air-conditioning duct.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.6
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• pp.8-14
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• 2005

Understanding of the flow past a bluff body close to a moving ground is very important in automobile and aeronautical fields because of aerodynamic characteristic and instability induced by unsteady vortex shedding. The passive control method that mounted the vertical and horizontal plates at the lower surface of the cylinder is studied to suppress the unsteady oscillation motion. When the grounds moves, the diminish of the shear layer on the ground promotes the interaction between the lower and the upper separated shear layers of the cylinder, hence vortex shedding occurs at the lower gap height than the stationary ground.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.2
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• pp.267-278
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• 1996

Steady, laminar, forced convection flow and heat transfer in the entrance region of an internally finned circular duct with a finite thermal conductivity has been analyzed numerically. The problem under investigation is a three-dimensional boundary layer problem, and is solved by employing a marching-type procedure which involves solution of a series of 2-dimensional elliptic problems in the cross-stream plane. Two types of inlet hydrodynamic conditions are considered : (a) uniform velocity flow and (b) fully developed flow. From the above inlet conditions, the effects of the fin height(h), fin number(N) and conductivity ratio($k_r$) on the flow and thermal characteristics are investigated. The numerical results show that the height and number of fins, and ratio of the solid to fluid thermal conductivity have pronounced effect on the solution. Considering pressure drop, optimized dimensionless fin height is 0.4.