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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 40, Issue 6 - Dec 2003
Volume 40, Issue 5 - Oct 2003
Volume 40, Issue 4 - Aug 2003
Volume 40, Issue 3 - Jun 2003
Volume 40, Issue 2 - Apr 2003
Volume 40, Issue 1 - Feb 2003
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Uncertainty Analysis for the Resistance and Self-Propulsion Test of Ship Model
Journal of the Society of Naval Architects of Korea, volume 40, issue 5, 2003, Pages 1~9
DOI : 10.3744/SNAK.2003.40.5.001
To predict the powering performance of full scale ships from the towing tank tests, resistance, propeller open water and self-propulsion tests are conducted. Model tests inevitably include the experimental error defined as the sum of two types of uncertainties, bias and precision errors. The induced errors in each element of model test are propagated through various routes and correlated with one another. The correlation coefficients are very important in the uncertainty analysis. The coefficient gives a direction(increase or decrease) for a value of error in individual elements. If the coefficient is not used accurately, the error bounds of the individual elements are overestimated or underestimated. In this study, the new methodology is applied to the uncertainty analysis of HMRI's towing tank tests, thus error bounds of each element is suggested and verified by several repetitive experiments.
An Experimental Study of Coanda Effect on the Flapped Control Surfaces
Journal of the Society of Naval Architects of Korea, volume 40, issue 5, 2003, Pages 10~16
DOI : 10.3744/SNAK.2003.40.5.010
To investigate the jet effect on circulation control, a segment of model was prepared and inserted horizontally across the test section of the cavitation tunnel. The hydrodynamic forces acting on the model were measured under the 2 dimensional flow behavior. Circulation flow control requires higher flow rate of water jet than boundary layer control does. Jet injection is effective in increasing lift coefficient and the increments reach to 160% in a certain combination of parameters such as an angle of attack, jet flow rate and flap angle. The blown water jet not only reduces form drag but also thrust effect, which is sometimes greater than the form drag in specific conditions.
PIV Velocity Field Measurements of Flow around a Ship with Rotating Propeller
Journal of the Society of Naval Architects of Korea, volume 40, issue 5, 2003, Pages 17~25
DOI : 10.3744/SNAK.2003.40.5.017
Velocity field behind a container ship model with a rotating propeller has been investigated using PIV (particle image velocimetry) system. Four hundred instantaneous velocity fields were measured at 4 different blade phases and ensemble-averaged to investigate the spatial evolution of vortical structure of near wake within one propeller diameter downstream. The phase-averaged mean velocity fields show the potential wake and the viscous wake formed due to the boundary layers developed on the blade surfaces. The interaction between bilge vortex developed along the hull surface and the tangential velocity component of incoming flow causes to have asymmetric flow structure in the transverse plane.
Propeller Skew Optimization Considering Varying Wake Field
Journal of the Society of Naval Architects of Korea, volume 40, issue 5, 2003, Pages 26~35
DOI : 10.3744/SNAK.2003.40.5.026
Propellers operating in a given nonuniform ship wake generate unsteady loads leading to undesirable stern vibration problems. The skew is known to be the most proper and effective geometric parameter to control or reduce the fluctuating forces on the shaft. This paper assumes the skew profile as either a quadratic or a cubic function of the radius and determines the coefficients of the polynomial function by applying the simplex method. The method uses the converted unconstrained algorithm to solve the constrained minimization problem of 6-component shaft excitation forces. The propeller excitation was computed either by applying the two-dimensional gust theory for quick estimation or by the fully three-dimensional unsteady lifting surface theory in time domain for an accurate solution. A sample result demonstrates that the shaft forces can be further reduced through optimization from the original design.
Numerical Simulation of Body Motion Using a Composite Grid System
Journal of the Society of Naval Architects of Korea, volume 40, issue 5, 2003, Pages 36~42
DOI : 10.3744/SNAK.2003.40.5.036
A CFD simulation technique has been developed to handle the unsteady body motion with large amplitude by use of overlapping multi-block grid system. The three-dimensional, viscous and incompressible flow around body is investigated by solving the Navier-Stokes equations, and the motion of body is represented by moving effect of the grid system. Composite grid system is employed in order to deal with both the body motion with large amplitude and the condition of numerical wave maker in convenience at the same time. The governing equations, Navier-Stokes (N-S) and continuity equations, are discretized by a finite volume method, in the framework of an O-H type boundary-fitted grid system (inner grid system including test model) and a rectangular grid system (outer grid system including simulation equipments for generation of wave environments). If this study, several flow configurations, such as an oscillating cylinder with large KC number, are studied in order to predict and evaluate the hydrodynamic forces. Furthermore, the motion simulation of a Series 60 model advancing in a uniform flow under the condition of enforced roll motion of angle 20
is performed in the developed numerical wave tank.
Comparison of the Estimation-Before-Modeling Technique with the Parameter Estimation Method Using the Extended Kalman Filter in the Estimation of Manoeuvring Derivatives of a Ship
Journal of the Society of Naval Architects of Korea, volume 40, issue 5, 2003, Pages 43~52
DOI : 10.3744/SNAK.2003.40.5.043
Two methods which estimate manoeuvring derivatives in the model of hydrodynamic force and moment acting on a manoeuvring ship using sea trial data were compared. One is the widely used parameter estimation method by using the Extended Kalman Filter (EKF), which estimates state variables of linearized state space model at every instant after dealing with the coefficients as the augmented state variables. The other one is the Estimation-Before-Modeling (EBM) technique, so called the two-step method. In the first step, hydrodynamic force of which dynamic model is assumed the third-order Gauss-Markov process is estimated along with motion variables by the EKF and the modified Bryson-Frazier smoother. Then, in the next step, manoeuvring derivatives are identified through the regression analysis. If the exact structure of hydrodynamic force could be known, which was an ideal case, the EKF method would be regarded as being more superior compared to the EBM technique. However the EBM technique was more robust than the EKF method from a realistic point of view where the assumed model structure was slightly different from the real one.
Analysis of Hydroelastic Response of a Pontoon-type Structure Considering Effect of Wave Breaker with Underwater Opening
Journal of the Society of Naval Architects of Korea, volume 40, issue 5, 2003, Pages 53~59
DOI : 10.3744/SNAK.2003.40.5.053
Ocean space utilization using VLFS(Very Large Floating Structures) can provide environmental impact free space by allowing sea water flow freely through the floating structure. Use of Pontoon type VLFS for that purpose needs employment of breakwaters for reduction of wave effects. Therefore, in order to maximize advantage of environmental impact free structure, the breakwater should be the one that can allow water flow freely through it, too. In this paper hydroelastic response of a pontoon type structure is analyzed considering breakwaters which allow water flow through its opening at bottom of the breakwaters. Mode superposition technique is used for solving equation of flexible body while interactions between the pontoon and breakwaters is considered based on generalized mode concept. Bi-quadratic nine node higher-order boundary element method is adopted for more accurate numerical treatment near sharp edged body shape. Performance of various combinations of breakwaters is investigated.
Effects of Operational Condition and Sea States on Wave-Induced Bending Moments of Large Merchant Vessels
Journal of the Society of Naval Architects of Korea, volume 40, issue 5, 2003, Pages 60~67
DOI : 10.3744/SNAK.2003.40.5.060
For risk or reliability assessment of ship structures against particular hazardous situations such as total loss or sinking due to hull girder collapse, the short-term based response analysis rather than the long-term response analysis is required to determine wave-induced bending moments when the ship encounters a storm of specific duration and with a specified small encounter probability. In the present study, the effects of operational condition and sea states on wave-induced bending moments of large merchant vessels are investigated. A series of the short-term response analyses for a hypothetical VLCC and a Capesize bulk carrier (CSBC) are carried out with varying operational condition and sea states which include ship speed, significant wave height and wave persistence time, using the linear-strip theory based program ABS/SHIPMOTION and the MIT sea-keeping tables. The computed results are also compared with the IACS design formula predictions. The results and insights developed from the present study are summarized.