• Journal of the Society of Naval Architects of Korea
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• v.37 no.4
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• pp.19-30
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• 2000

A finite-volume method is developed to solve turbulent flows around modern commercial hull forms with bow and stern bulbs. The RANS equations are solved. The cell-centered finite-volume method employs QUICK and central difference scheme for convective and diffusive flux discretization, respectively. The SIMPLEC method is adopted for the velocity-pressure coupling. The developed numerical methods are applied to calculate turbulent flow around KRISO 3600TEU container ship. Surface meshes are generated into five blocks: bow and stern bulbs, overhang, fore and afterbody. 3-D field grid system with O-H topology is generated using elliptic grid generation method. Surface friction lines and wake distribution at propeller plane is compared with experiment. The calculated results show that the present method can be used to predict flow around a modern commercial hull forms with bulbs.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.3
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• pp.595-609
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• 2015

The wake characteristics of Contra-Rotating Propeller (CRP) were investigated using numerical simulation and flow measurement. The numerical simulation was carried out with a commercial CFD code based on a Reynolds Averaged Navier-Stokes (RANS) equations solver, and the flow measurement was performed with Stereoscopic Particle Image Velocimetry (SPIV) system. The simulation results were validated through the comparison with the experiment results measured around the leading edge of rudder to investigate the effect of propeller operation under the conditions without propeller, with forward propeller alone, and with both forward and aft propellers. The evolution of CRP wake was analyzed through velocity and vorticity contours on three transverse planes and one longitudinal plane based on CFD results. The trajectories of propeller tip vortex core in the cases with and without aft propeller were also compared, and larger wake contraction with CRP was confirmed.

• Journal of Internet of Things and Convergence
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• v.7 no.3
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• pp.75-80
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• 2021

Since the optimization of the diesel engine for the ship cannot satisfy the NOx emission limit by the method of reducing the NOx emission, it is necessary to reduce the NOx by post-processing the exhaust gas. In this study, we will review the feasibility of designing a binary nozzle and mixing chamber duct for effectively converting the number of elements into NH3 in the oil burner for the SCR catalyst unit integrated duct in the ship under development through the computational heat flow analysis for the velocity distribution and temperature distribution.

• Journal of Ocean Engineering and Technology
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• v.33 no.5
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• pp.387-393
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• 2019

In this study, the free motion of a riser due to vortex shedding was numerically simulated with Large Eddy Simulation (LES) and Detached Eddy Simulation (DES) turbulence models. A numerical simulation program was developed by applying the Rhie-Chow interpolation method to the pressure correction of the OpenFOAM standard solver pimpleDyMFoam. To verify the developed program, the vortex shedding around the fixed riser at Re = 3900 was calculated, and the results were compared with the existing experimental and numerical data. Moreover, the vortex-induced vibration of a riser supported by a linear spring was numerically simulated while varying the spring constant. The results are compared with published direct numerical simulation (DNS) results. The present calculation results show that the numerical method is appropriate for simulating the vortex-induced motion of a riser, including lock-in phenomena.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.3
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• pp.88-93
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• 2019

This study concerns the distributions of flow in an air conditioning duct used for a marine and oil drilling ship. From the results of carrying out flow analysis and structural analysis of a ventilation duct applied to a marine structure, the following conclusion could be gained. The pressure tended to increase as the flow velocity at the inlet increased and the pressure at the inlet increased. It was recognized that the pressure decreased due to the influence of a corrugated tube when it entered and exited from the duct. As a result of structural analysis, a higher train was generated at the corrugated tube compared with the duct. In addition, in the case of the internal pressure of 0.7MPa, which was the designed load, it was found that there was almost no influence as it was within 0.1mm.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.918-927
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• 2020

Flows induced by hybrid CRP pod propulsion systems (CRP-POD) are fundamentally characterized by unsteadiness. This work presents a numerical study on the unsteady flow of a CRP-POD at behind-hull condition based on CFD (Computational Fluid Dynamics). Unsteady RANS method is adopted, coupled with SST k-u turbulence model and sliding mesh method. The propeller thrusts and torques obtained by CFD is validated by model tests and acceptable agreements are obtained. The time histories of shingle-blade loads and pressures near the hull surface are recorded for the analysis of unsteady flow features. The cases of forward propeller alone and aft propeller alone are also computed to distinguish the hull-propeller interaction and propeller-propeller interaction. The results show the blade loads of both forward and aft propellers strongly fluctuate with phase angles. For the forward propeller, the blade load fluctuation is mainly governed by the hull-propeller interaction, while the aft blade load is remarkably affected by the propeller-propeller interaction in terms of the load average and fluctuation pattern. The fields of pressure, vorticity and velocity are also analyzed to reveal the unsteady flow features.

• Journal of Ocean Engineering and Technology
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• v.36 no.3
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• pp.161-167
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• 2022

Three-dimensional finite element analysis (3D-FEA) models have been used to evaluate the shock-resistance responses of various equipments, including armaments mounted on a warship caused by underwater explosion (UNDEX). This paper aims to check the possibility of using one-dimensional (1D) FEA models for the shock-resistance responses. A frigate was chosen for the evaluation of the shock-resistance responses by the UNDEX. The frigate was divided into the thirteen discrete segments along the length of the ship. The 1D Timoshenko beam elements were used to model the frigate. The explosive charge mass and the stand-off distance were determined based on the ship length and the keel shock factor (KSF), respectively. The UNDEX pressure fields were generated using the Geers-Hunter doubly asymptotic model. The pseudo-velocity shock response spectrum (PVSS) for the 1D-FEA model (1D-PVSS) was calculated using the acceleration history at a concerned equipment position where the digital recursive filtering algorithm was used. The 1D-PVSS was compared with the 3D-PVSS that was taken from a reference, and a relatively good agreement was found. In addition, the 1D-PVSS was compared with the design criteria specified by the German Federal Armed forces, which is called the BV043. The 1D-PVSS was proven to be relatively reasonable, reducing the computing cost dramatically.

• Ocean Systems Engineering
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• v.13 no.4
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• pp.367-384
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• 2023

Herein, we present the design and development of an efficient finite element analysis model for thermal plate forming in shipbuilding. Double curvature shells in the ship building industries are primarily formed through the thermal forming technique. Thermal forming involves heating of steel plates using heat sources like oxy-acetylene gas torch, laser, and induction heating, etc. The differential expansion and contraction across the plate thickness cause plastic deformation and bending of plates. Thermal forming is a complex forming technique as the plastic deformation and bending depends on many factors such as peak temperature, heating and cooling rate, depth of heated zone and many other secondary factors. In this work, we develop an efficient finite element analysis model for the thermo-mechanical analysis of thermal forming. Different simulations are reported to study the effect of various parameters affecting the process. Temperature dependent properties are used in the analysis and the finite element analysis model is used to identify the critical flame velocity to avoid recrystallization of plate material. A spring connected plate is modeled for structural analysis using spring elements and that helps in identifying the resultant shapes of various thermal forming patterns. Finally, detailed simulation results are reported to establish the efficacy, applicability and efficiency of the designed and developed finite element analysis model.

• Corrosion Science and Technology
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• v.11 no.6
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• pp.263-269
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• 2012

Copper alloys are commonly applied to ship's propellers, pumps and valves which are serviced in seawater due to their good castability and corrosion resistance. In the environment of high flow velocity, however, erosion damage predominates over corrosion damage. In particular, the cavitation in seawater environment accelerates surface damage to copper alloys, resulting in degradation of products and economic losses and also threatening safety. The surface was coated with WC-27NiCr by high velocity oxygen fuel(HVOF) spraying technique to attain durability and cavitation resistance of copper alloys under high velocity/pressure flow. The cavitation test was performed for the WC-27NiCr coating deposited by HVOF in seawater at the amplitude of $30{\mu}m$ with seawater temperature. The cavitation at $15^{\circ}C$ caused exfoliation of the coating layer in 17.5 hours while that of $25^{\circ}C$ caused the exfoliation in 12.5 hours. When the temperature of seawater was elevated to $25^{\circ}C$ from $15^{\circ}C$, more damage was induced by over 160%. Although WC-27NiCr has good durability, corrosion resistance and eletrochemical stability, the cavitation damage rate of the coating layer could remarkably increase at the elevated temperatures under cavitation environments.

• Journal of Korea Water Resources Association
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• v.30 no.6
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• pp.671-678
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• 1997

Water surface velocity meters with microwave were applied to stream discharge measurements and its practical aspects were evaluted. The rating of the surface velocity meters was performed through a carriage and a water tank for the ship model test. It gave5.5% or less errors of average measured velocities under the vertical tilt ang1e of 20$^{\circ}$, 35$^{\circ}$, or 45$^{\circ}$ . A surface velocity meter was used to measure flood velocities at Yoju bridge from 8:00 a.m. to 10:00 a.m. on August 26, 1995. The results showed that surface velocities ranged from 2 to 4 m/s. With the measured surface velocities multiplied by 0.85, the discharge was computed as 10,500 m$^3$/s. It differed $\pm$2% or less from the value of a stage-discharge curve and that of an unsteady flow simulation. Although the measured data are used sparsely per 40 or 60 meters, the computed discharges do not give large variation. Stream discharge measurements were also performed under the normal condition without floods. With the known values of Taechong Dam releases. the depth averaging factors of velocity were calculated by 0.83~0.87. Although there are errors from wind action and inherent ones in the velocity meters, the research showed that surface velocity meters could be an simple and practical alternative for flood discharge measurements.