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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of the Society of Naval Architects of Korea
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Journal DOI :
The Society of Naval Architects of Korea
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Volume & Issues
Volume 41, Issue 6 - Dec 2004
Volume 41, Issue 5 - Oct 2004
Volume 41, Issue 4 - Aug 2004
Volume 41, Issue 3 - Jun 2004
Volume 41, Issue 2 - Apr 2004
Volume 41, Issue 1 - Feb 2004
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Turbulent Flow Analysis around Circular Cylinder and Airfoil by Large Eddy Simulation with Smagorinsky Model
Journal of the Society of Naval Architects of Korea, volume 41, issue 4, 2004, Pages 1~8
DOI : 10.3744/SNAK.2004.41.4.001
As a computer has been continuously progressed to reduce R&D time and cost, the study of the flow physics has been significantly relied on the numerical method. Recently, Large Eddy Simulation(LES) has been widely used in CFD community to accurately capture the turbulent flows. The LES code requires high accuracy in time, as well as in space. Also, it should have strong robustness to ensure the convergence in various complicated flows. The objective of the present work is to develop a base code for LES simulation, having 2
order accuracy in time and 4
order accuracy in space. To achieve the present objective, the four-step fractional step method was enhanced by adopting compact Pade'scheme. The standard Smagorinsky model was implemented for the first stage of the present code development. The flows over a cylinder and an airfoil were successfully simulated. and an airfoil were successfully simulated.
First Elbow Design for the Improvement of Tunnel Performance
Journal of the Society of Naval Architects of Korea, volume 41, issue 4, 2004, Pages 9~16
DOI : 10.3744/SNAK.2004.41.4.009
In the cavitation tunnel, the first corner playes role for the flow direction to execute 90-degree turn. So, energy loss is serious, and the cavitation phenomena well occur in the guide vane surface. In this paper, the flow in the first corner was numerically calculated. From the calculation result, cavitation phenomena mainly occurred in the suction side of the last guide vane and vicinity that vane and tunnel wall adjoin each other. And bubbles occurred from all guide vanes if the flow velocity in the test section reaches the any critical value. We could analogize with our experience in the water tunnel that bubbles that occurred in time not vanish, and become miniature in the flow although the pressure recover. So, they circulate with flow in the tunnel, and come into view in the test section. Therefore, first corner must be designed for bubbles not to appear in the test section according to the flow condition like velocity and pressure demanded by the experiment. We analyzed flow in case that the first elbow configuration was redesigned and some of the existing guides vanes were eliminated. And we presented that first elbow can be easely designed for the improvement of tunnel performance through the computational analysis.
Internal Wave Computations based on a Discontinuity in Dynamic Pressure
Journal of the Society of Naval Architects of Korea, volume 41, issue 4, 2004, Pages 17~29
DOI : 10.3744/SNAK.2004.41.4.017
Internal waves are computed using a ghost fluid method on an unstructured grid. Discontinuities in density and dynamic pressure are captured in one cell without smearing or oscillations along a multimaterial interface. A time-accurate incompressible Navier-Stokes/Euler solver is developed based on a three-point backward difference formula for the physical time marching. Artificial compressibility is introduced with respect to pseudotime and an implicit method is used for the pseudotime iteration. To track evolution of an interface, a level set function is coupled with the governing equations. Roe's flux difference splitting method is used to calculate numerical fluxes of the coupled equations. To get higher order accuracy, dependent variables are reconstructed based on gradients which are calculated using Gauss theorem. For each edge crossing an interface, dynamic pressure is assigned for a ghost node to enforce the continuity of total pressure along the interface. Solitary internal waves are computed and the results are compared with other computational and experimental results.
PIV Velocity Field Analysis of Inflow ahead of a Rotating Marine Propeller
Journal of the Society of Naval Architects of Korea, volume 41, issue 4, 2004, Pages 30~37
DOI : 10.3744/SNAK.2004.41.4.030
Flow characteristics of the inflow ahead of a rotating propeller attached to a container ship model were investigated using a two-frame PIV (Particle Image Velocimetry) technique. Ensemble-averaged mean velocity fields were measured at four different blade phases. The mean velocity fields show the acceleration of inflow due to the rotating propeller and the velocity deficit in the near-wake region. The axial velocity distribution of inflow in the upper plane of propeller is quite different from that in the lower plane due to the thick hull boundary layer. The propeller inflow also shows asymmetric axial velocity distribution in the port and starboard side. As the inflow moves toward the propeller, the effect of phase angle variation of propeller blade on the inflow becomes dominant. In the upper plane above the propeller axis the inflow has very low axial velocity and large turbulent kinetic energy, compared with the lower plane. The boundary layer developed along the bottom surface of stern hull forms a strong shear layer affecting vortex structure of the propeller near-wake.
Nonlinear Motion for an Elliptic Cylinder under Free Surface
Journal of the Society of Naval Architects of Korea, volume 41, issue 4, 2004, Pages 38~44
DOI : 10.3744/SNAK.2004.41.4.038
The motion response analysis of a submerged elliptic cylinder in waves is presented and the elliptic cylinder is a simplification of the section of submarine in this paper. The method is based on boundary integral method and two-dimensional 3 degree motions are calculated in regular harmonic waves. The fully nonlinear free surface boundary condition is assumed in an numerical domain and this solution is matched along an assumed boundary as a linear solution composed of transient Green function, The large amplitude motions of an elliptic cylinder are directly simulated and effects of wave frequency, wave amplitude and the distance from buoyancy center to gravity center are discussed.
Exact Solution on the Anti-symmetric Responses of Ships having Uniform Sectional Properties with Hydro-elasticity
Journal of the Society of Naval Architects of Korea, volume 41, issue 4, 2004, Pages 45~52
DOI : 10.3744/SNAK.2004.41.4.045
Exact solution on the anti-symmetric response of ships having uniform sectional properties in waves is derived. Boundary value problem consisted of Timoshenko beam equation and free-free end condition is solved analytically. The responses are assumed as linear and wave loads are calculated by using strip method. Horizontal bending moment, shear force and torsional moment are calculated. The developed analysis model is used for the benchmark test of the numerical codes in this problem. Also the application on the preliminary design of barge-like ships and VLFS (Very Large Floating Structure) is expected
Estimation of Roll Related Coefficients of a Ship by Using the System Identification Method
Journal of the Society of Naval Architects of Korea, volume 41, issue 4, 2004, Pages 53~58
DOI : 10.3744/SNAK.2004.41.4.053
When a fast container ship or a naval vessel is turning, comparable roll motions occur. Therefore, roll effect has to be considered in the horizontal equations of motion of the ship to predict the maneuverability well. In this thesis, a new method to determine a roll model structure and estimate its coefficients by applying the system identification technique to the data of sea trial tests was proposed. The simulation results from the estimated roll model were well consistent with the true one in spite of the difference between the estimated and the true model structures of roll hydrodynamic moment.
Turbulent Flow Analysis and Drag Reduction by Riblet Surfaces
Journal of the Society of Naval Architects of Korea, volume 41, issue 4, 2004, Pages 59~67
DOI : 10.3744/SNAK.2004.41.4.059
Direct numerical simulations of turbulent flows over riblet-mounted surfaces are performed to educe the mechanism of drag reduction by riblets. Numerical simulations are performed for flow fields with R
/=180. For riblet ridge angle
, two different riblet spacings of
+/=20 and 40 are used in this study. The computed drag on the riblet surfaces is in good agreement with existing computational and experimental data. The mean velocity profiles show upward and downward shifts in the log-law for drag-decreasing and drag-increasing cases, respectively Turbulence statistics above the riblets are computed and compared with those above a flat plate. The purpose of this study is in two categories: first, to understand the drag reduction mechanism on riblet surface, second, to verify our own code by comparison of the present results with those from previous studies.udies.
The Effectiveness of Weaving Motion and Determination of Optimal Heating Condition in Line-heating
Journal of the Society of Naval Architects of Korea, volume 41, issue 4, 2004, Pages 68~76
DOI : 10.3744/SNAK.2004.41.4.068
Inherent strain method for analyzing deformation of line-heating is substituting experiments of high cost, because of its high accuracy and quickness. Nowadays, the progressing forms of line-heating are not straight moving motions used to traditional studies, but weaving motions which can diversely input heat source. In shipyard, reasons of weaving motions are induction of a special characteristic by water cooling, maximum temperature limitation for keeping plates from melting, and rhythm for workman's maintaining velocity. On this study, a method which can obtain optimal weaving heating condition was presented, some examples were introduced, and the results corresponded to works of shipyard. Lastly, what the specifications of plates on efficiency are is presented, through the quality standard of shipyard and FEM heat transfer simulation. The ultimate purpose of line heating is the automation, so in case of plates which need weaving heating, the optimal heating condition suggested by this study can be used well in designing coil specifications of induction heaters which are heat input sources of new generation.
A Study on the Practical Use of an Active Control System to Reduce Ship Superstructure Vibration
Journal of the Society of Naval Architects of Korea, volume 41, issue 4, 2004, Pages 77~84
DOI : 10.3744/SNAK.2004.41.4.077
Active control is regarded as one of the most efficient and economic countermeasures to reduce excessive vibration of ship superstructure. However, it is difficult to find its practical application in real ships in spite that many studies on such systems have been done. In this study, for the practical use of an active control system to reduce ship superstructure vibration, we have developed an active vibration compensator consisting of a mechanical actuator having compact size and expected lifetime over 20 years, its control panel including exclusive signal processing and computing board, sensors to detect phase and vibration, and its operation software providing various user-interface functions. From the performance verification test of the system at a 5,500 TEU container carrier, we have confirmed the system could reduce ship superstructure vibration of a harmonic component of main engine rotating frequency up to 0.1 mm/s.
Analysis of Correction of Welding Deformation of Stiffened Plate by Heating Using Equivalent Loading Method based on Inherent Strain
Journal of the Society of Naval Architects of Korea, volume 41, issue 4, 2004, Pages 85~91
DOI : 10.3744/SNAK.2004.41.4.085
The objective of the present paper is to develop an analysis method for the correction of welding deformation of stiffened plate by line heating. In this paper, the equivalent loading method, based on the inherent strain theory, was used to analyze the heat-straightening of a stiffened plate. Equivalent loads were obtained by integrating the inherent strains which were determined from the highest temperature and the degree of restraint. Finally, the obtained equivalent loads were imposed, as applied loads, on the elastic analysis for the prediction of correction of welding deformation in stiffened plate. The proposed method is expected as a basic study in heat-straightening analysis of welding deformation in large scale block.