• Journal of the Society of Naval Architects of Korea
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• v.49 no.1
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• pp.60-67
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• 2012

This study considers the numerical analysis on parametric roll for container ships. As a method of numerical simulation, an impulse-response-function approach is applied in time domain. A systematic study is carried out for the parametric roll of two container ships, particularly observing the sensitivity of computational results to some parameters which can affect the analysis of parametric roll. The parameters to be considered are metacentric height (GM), simulation time window, and the discretization of wave spectrum. Based on the result of parametric roll simulation, numerical sensitivity and uncertainty in computational analysis are discussed.

• Journal of Korea Multimedia Society
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• v.23 no.8
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• pp.1066-1074
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• 2020

High Level Architecture/Run-Time Infrastructure (HLA/RTI) is used to connect individual simulators on networks in order to interoperate heterogeneous simulators. In defense domain, Ship Air Defense Model (SADM) and Extended Air Defense Simulation (EADSIM) are two of most advanced simulation tools. To interoperate these SADM and EADSIM, this paper attempts to use HLA/RTI that helps to support a Composite Combat Mission Planning Simulation Environment (CCMPSE). The CCMPSE allows us to analyze a group of simulations for comprehensive and accurate experiments. For the first time, this paper analyzes guided missile simulations in EADSIM and SADM by comparing related simulation models in their parameters and considerations. It presents characteristics of these models in view of guided missile simulation perspectives. For the contributions of this paper, it provides insights to select guided missiles between SADM and EADSIM on the CCMPSE according to specific simulation purposes.

• Journal of the Society of Naval Architects of Korea
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• v.40 no.5
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• pp.26-35
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• 2003

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.

• Journal of the Society of Naval Architects of Korea
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• v.32 no.2
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• pp.56-67
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• 1995

In this paper, a ship-cable-vehicle system's static configuration is shown obtained by solving cable nonlinear statics. Eigenfrequencies of the cable were calculated by the frequency domain analysis application of the linearized cable dynamic equations. Also extreme tensions in a slack-and-snapping long vertical cable were calculated by the clip-ping-off model.

• Journal of Ship and Ocean Technology
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• v.6 no.1
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• pp.34-53
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• 2002

Numerical solution of the forward-speed radiation problem for a half-immersed cylinder advancing in regular waves is presented by making use of the improved Green integral equation in the frequency domain. The B-spline higher order panel method is employed stance the potential and its derivative are unknown at the same time. The present numerical solution of the improved Green integral equation by the B-spline higher order Kelvin panel method is shown to be free of irregular frequencies which are present in the Green integral equation using the forward-speed Kelvin-type Green function.

• The Journal of the Acoustical Society of Korea
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• v.21 no.5
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• pp.485-493
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• 2002

Broadband interference patterns are studied using ship as an acoustic source in shallow waters with varying bathymetry. Waveguide invariant index (β) indicating the pattern of constructive (or destructive) interference in range-frequency domain is derived in a waveguide with constant bottom slope based on adiabatic mode theory. Using this invariant, changes of the interference patterns resulting from the variation of bottom bathymetry are analyzed. Results of the analytic interpretation is compared with those from sea experiments and numerical simulations.

• Journal of Ocean Engineering and Technology
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• v.8 no.2
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• pp.93-104
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• 1994

Recently in the design of super tankers or LNG carriers which transport a large amount of liquid in the cargo holds, the structural damage due to liquid sloshing becomes an important problem. The impact pressure from sloshing is most violent when the liquid motion of a partially filled tank is in resonance with the motion of a ship. In this paper the sloshing natural periods in liquid cargo tanks are estimated for partially filled tanks with various geometries. Especially the sloshing periods of baffled tanks which are often installed to reduce liquid motion and sloshing forces are calculated. A variational method is adopted to analyze the baffled tank of arbitrary filling depth of liquid. In this approach the liquid domain is divided into several subdomains in which the analytic solutions are potential energy are calculated from the velocity potentials in eachsubdomain. By minimizing the Hamilton's functional, the sloshing natural periods are estimated and the results are compared with experimental and numerical results.

• Journal of Ship and Ocean Technology
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• v.8 no.3
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• pp.50-60
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• 2004

In this paper, a continuum-based design sensitivity analysis (DSA) method is developed for the weakly coupled thermo-elasticity problems. The temperature and displacement fields are described in a common domain. Boundary value problems such as an equilibrium equation and a heat conduction equation in steady state are considered. The direct differentiation method of continuum-based DSA is employed to enhance the efficiency and accuracy of sensitivity computation. We derive design sensitivity expressions with respect to thermal conductivity in heat conduction problem and Young's modulus in equilibrium equation. The sensitivities are evaluated using the finite element method. The obtained analytical sensitivities are compared with the finite differencing to yield very accurate results. Extensive developments of this method are useful and applicable for the optimal design problems incorporating welding and thermal deformation problems.

• Journal of Ship and Ocean Technology
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• v.12 no.2
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• pp.32-40
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• 2008

This paper deals with the pressure fluctuation induced by propeller cavitation. The main objective of this study is to analyze the source mechanism of the pressure fluctuation induced by propeller cavitation. To analyze the source mechanism of the pressure fluctuation, modem acoustic theory is applied. The governing equation of the pressure fluctuation induced by propeller is derived using Ffowcs Williams-Hawkings proposed time domain acoustic method. The physical mechanism of pressure fluctuation at the blade rate frequency is analyzed using numerically generated cavitation volume variation. Finally the characteristics of the pressure fluctuation induced by a propeller are presented.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.6
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• pp.1044-1053
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• 2022

Time domain reflectometry (TDR) is a diagnostic technique to evaluate the physical integrity of cable and finds application in leak detection and localization of piping system. In this study, a cable-shaped leak detection sensor was proposed using the TDR technique for monitoring leakage detection of ship's engine room seawater piping system. The cable sensor was developed using a twisted pair arrangement and wound by an absorbent material. The availability and performance of the sensor for leak detection and localization were evaluated on a lab-scale pipeline set up. The developed sensor was installed onto the pipes and flanges of the lab-scale set up and various TDR waveforms were acquired and analyzed according to the dif erent variables including the number of twists and sheath thickness. The result indicated that the twisted cable sensor was able to produce clear and smooth signal as compared to the TDR sensor with a parallel arrangement. The optimal number of twist was determined to be above 10 per the unit length. The optimal diameter of sheath thickness that results in the desired sensitivity was determined to be ranging from 80% up to 120% of the diameter of the conductor. The linear regression analysis for estimation of leak localization was carried out to estimate the location of the leakage, and the result was a determination coefficient of 0.9998, indicating a positive relationship with the actual leakage point. The proposed TDR based leak detection method appears to be an effective method for monitoring leakage of ship's seawater piping system.