• Journal of the Institute of Convergence Signal Processing
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• v.24 no.2
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• pp.97-102
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• 2023

Numerical simulations have been performed to investigate the hydrodynamic characteristics of the rudder since they play an important role in naval architecture fields. Although some values such as hydrodynamics forces can be measured easily in the towing tanks, it is difficult to obtain the detailed information of the flow fields such as pressure distribution, velocity distribution, vortex generation from experiments. In the present study, the effects of hydrodynamic coefficients and Reynolds number acting on the rudder were studied by using Computational Fluid Dynamics(CFD). Ansys fluent, one of commercial CFD solvers, solves the Navier-Stokes equations and the k-epsilon turbulence model is selected for the viscous model to solve RANS equations. At first, drag coefficients and lift coefficient for different angle of attack are obtained by using a CFD commercial code for KCS rudder. Secondly, the 2-D lift coefficients and drag coefficients are compared with 3-D coefficients at the same conditions. Thirdly, the effects of Reynolds number on the hydrodynamic forces are investigated.

• Journal of Ocean Engineering and Technology
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• v.33 no.5
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• pp.400-410
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• 2019

In this study, the numerical code for the 3D nonlinear dynamic analysis of an SLWR (Steel Lazy Wave Riser) was developed using the lumped mass line model in a FORTRAN environment. Because the lumped mass line model is an explicit method, there is no matrix operation. Thus, the numerical algorithm is simple and fast. In the lumped mass line model, the equations of motion for the riser were derived by applying the various forces acting on each node of the line. The applied forces at the node of the riser consisted of the tension, shear force due to the bending moment, gravitational force, buoyancy force, riser/ground contact force, and hydrodynamic force based on the Morison equation. Time integration was carried out using a Runge-Kutta fourth-order method, which is known to be stable and accurate. To validate the accuracy of the developed numerical code, simulations using the commercial software OrcaFlex were carried out simultaneously and compared with the results of the developed numerical code. To understand the nonlinear dynamic characteristics of an SLWR, dynamic simulations of SLWRs excited at the hang-off point and of SLWRs in regular waves were carried out. From the results of these dynamic simulations, the displacements at the maximum bending moments at important points of the design, like the hang-off point, sagging point, hogging points, and touch-down point, were observed and analyzed.

• Journal of Ocean Engineering and Technology
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• v.6 no.1
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• pp.43-51
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• 1992

The hydrodynamic performance of a floating-type OWC (Oscillating Water Column) chamber is studied numerically and experimentally in this study. The numerical approach based on two-dimensional linear theory of floating wave absorber was attempted to design an efficient wave energy absorber, while model test was performed in a wave basin to test a performance of designed model and validate the reliability of developed numerical code. The focus of study is placed mainly on the experimental study to evaluate the principal characteristics of the designed OWC chamber in regular waves. The effects of the variation of wave height on OWC device and of air pressure inside chamber are also presented. Finally, the measured results were compared with computed ones, and it was shown that the designed chamber works with high efficiency $(\eta_H>1$ over most of wave lengths covered by present study. It is therefore concluded that the developed code is capable of being successfully employed to design OWC chambers at various ocean environments, even though there exist some minor discrepancies between measured and computed results.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.6
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• pp.795-804
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• 2002

The optimal design code of an axial flow pump has been developed to determine geometric and fluid dynamic variables under hydrodynamic as well as mechanical design constraints. The design code includes the optimization of the complete radial distribution of the geometry by determining the coefficients of 2$^{nd}$ order polynomials to represent the three-dimensional geometry. The optimization problem has been formulated with a nonlinear multivariable objective function, maximizing the efficiency and stall margin, while minimizing the net positive suction head required. Calculation of the objective function is based on the mean streamline analysis and through-flow analysis using the present state-of-the-art model. The optimal solution is calculated using the penalty function method in which the genetic optimizer is employed. The optimized efficiency and design variables are presented in this paper as a function of non-dimensional specific speed in the range, 2$\leq$ $n_{s}$ $\leq$10. The results can be used in preliminary design of axial flow pumps.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.5
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• pp.407-417
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• 2015

For the more accurate prediction on manoeuvring performance of a ship at initial design phase, bare hull manoeuvring coefficients were estimated by RANS(Reynolds Averaged Navier-Stokes) based virtual captive model tests. Hydrodynamic forces and moment acting on the hull during static drift and harmonic oscillatory motions were computed with a commercial RANS code STAR-CCM+. Automatic and consistent mesh generation could be implemented by using macro functions of the code and user dependency could be greatly reduced. Computed forces and moments on KCS and KVLCC 1&2 were compared with the corresponding measurements from PMM(Planar Motion Mechanism) tests. Quite good agreement can be observed between the CFD and EFD results. Manoeuvring coefficients and IMO standard manoeuvres estimated from the computed data also showed reasonable agreement with those from the experimental data. Based on these results, we could confirm that the developed virtual captive manoeuvring model test process could be applied to evaluate manoeuvrability of a ship at the initial hull design phase.

• Journal of Fisheries and Marine Sciences Education
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• v.28 no.1
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• pp.172-179
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• 2016

The study of Mobile MGIS (Marine Geographic Information System) based on the Android Mobile Platform is mainly performed on effective methodologies which transform real world data to computing world data. Mobile GUI system has its own target on reliable data service by acquisition of geometric information using EFDC (Environmental Fluid Dynamics Code) Model, accurate measurement and graphical visualization. Even simple visualizations can aid in the interpretation of complex hydrodynamic relationships that are frequently encountered in the marine environment. The Mobile MGIS provides an easy way for hydrodynamics geoscientists to construct complex visualizations that can be viewed with free software. This study proposes a Mobile GUI MGIS using EFDC Model result of Seomjin River estuary. Finally, we design a Seomjin River estuarine Coastal Waters Mobile MGIS integrating above data models. It must adds more ecological information and the various service item for approach more easily in order to user.

• 한국전산유체공학회:학술대회논문집
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• 1998.05a
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• pp.1-14
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• 1998

Underwater explosion properties for TNT, an ideal explosive, and DXD-04, a nonideal explosive, were numerically modeled with a one-dimensional Lagrangian hydrodynamic code. The equation of state parameters for detonation products for TNT and DXD-04 were obtained from the BKW code, assuming complete reaction. Burn of TNT was modeled by using the Chapman-Jouguet(CJ) volume burn technique, a programmed-burn technique, assuming instantaneous detonation reaction. Burn of DXD-04 was modeled by using the same technique and by using the reaction rate calibrated from two-dimensional steady-state detonation experiments. The calculations for TNT reproduced the experimental peak pressure of the shock wave propagating through water with an error of $3.0\%$ and the experimental oscillation period of the bubble formed of detonation products with an error of $2.3\%$. For DXD-04, the CJ volume burn technique could not reproduce the experimental observations. When the reaction rate calibrated from two-dimensional steady-state detonation experimental data, the calculated peak pressure was slightly higher by $7.3\%$ than the experimental data, but the calculated shock profile was in good agreement. The bubble period was reproduced with an error of $1.8\%$. These results demonstrated that underwater explosion properties for an ideal explosive can be predicted by using a programmed burn technique, and that, however, those for a nonideal explosive can be predicted only when a well-calibrated reaction rate is used.

• Journal of Korean Society on Water Environment
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• v.28 no.3
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• pp.384-393
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• 2012

Saemangeum lake is an artificial lake created by reclamation works and an estuary embankment since 2006. The sea water flows into the lake by the operation of two sluice gates, and the freshwater enters into the lake by the upper streams. For the reflection of hydrology and hydrodynamics effects in Saemangeum area, a hydrodynamics model was developed by connecting Hydrological Simulation Program with Fortran (HSPF) and Environmental Fluid Dynamic Code (EFDC). The HSPF was applied to simulate the freshwater discharge from the upper steam watershed, and the EFDC was performed to compute water flow, water temperature, and salinity based on time series from 2008 to 2009. The calibration and validation are performed to analyze horizontal and vertical gradients. The horizontal trend of model simulation results is reflected in the trend of observed data tolerably. The vertical trend is conducted an analysis of seasonal comparisons because of the limitation of vertically observed data. Water temperature reflects on the seasonal changes. Salinity has an effect on the near river input spots. The impact area of salinity is depending on the sea water distribution by gate operation, mainly.

• Journal of the Society of Naval Architects of Korea
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• v.36 no.2
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• pp.22-28
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• 1999

Small amplitude in-phase oscillations of multi-cylinders are considered both numerically and experimentally. Flow field is separated into inner and outer regions. The basic unsteady solution is obtained analytically and the secondary flow, termed as steady streaming flow, can be obtained numerically by using Finite Volume Code with Panel Method. The Particle Induced Velocimetry, one of whole field measurements, is introduced for comparison with numerical flow visualization quantitatively. Among the algorithms for PIV, the Three Step Vector Searching Technique is applied to reduce CPU time. Small but non-zero damping coefficient, that is important in lightly damped system can be obtained with varying number of bodies and distances.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.1
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• pp.43-51
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• 2015

This paper presents effect of aerodynamic loads on mooring line responses of a floating offshore wind turbine. A Matlab code based on blade element momentum (BEM) theory is developed to consider aerodynamic loads acting on NREL 5MW wind turbine. The aerodynamic loads are coupled with time-domain hydrodynamic analyses using one-way interaction scheme of the wave and wind loads. A semi-submersible floating platform which is from Offshore Code Comparison Collaborative Continuation(OC4) DeepCWind platform is used with catenary mooring lines simply composed of studless chain links. Average values of mooring peak tensions obtained from aerodynamic load consideration are significantly increased compared to those from simple wind drag force consideration. Consideration of aerodynamic loads also yield larger tension ranges which can be important factor to reduce fatigue life of the mooring lines.