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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of Ocean Engineering and Technology
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Journal DOI :
Korean Society of Ocean Engineers
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Volume & Issues
Volume 28, Issue 6 - Dec 2014
Volume 28, Issue 5 - Oct 2014
Volume 28, Issue 4 - Aug 2014
Volume 28, Issue 3 - Jun 2014
Volume 28, Issue 2 - Apr 2014
Volume 28, Issue 1 - Feb 2014
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Changes in Dynamic Characteristics of Monopile-Type Offshore Structures According to Tidal Environments and Boundary Conditions
Jung, Byung-Jin ; Park, Jong-Woong ; Yi, Jin-Hak ; Park, Jin-Soon ;
Journal of Ocean Engineering and Technology, volume 28, issue 4, 2014, Pages 261~267
DOI : 10.5574/KSOE.2014.28.4.261
Because a change in the natural frequencies of a structure indicates structural health problems, monitoring the natural frequencies crucial. Long-term measurement for the Uldolmok tidal current power plant structure has shown that its natural frequencies fluctuate with a constant cycle twice a day. In this study, lab-scale tests to investigate the causes of these natural frequency fluctuations were carried out in a circulating water channel. Three independent variables in the tests that could affect the fluctuation of the natural frequencies were the water level, current velocity, and boundary condition between the specimen and the bottom of the circulating water channel. The experimental results were verified with numerical ones using ABAQUS. It was found that the fluctuation of the natural frequencies was governed by a decrease in stiffness due to the boundary condition much more than the effect of added mass. In addition, it was found that the natural frequency would decrease with an increase in the tidal current velocity because of its nonlinearity when the boundary condition was severely deteriorated due to damage.
Investigation of Turbulence Characteristics of Defect Law Region over Flat plate
Suh, Sung-Bu ; Park, Il-Ryong ; Jung, Kwang-Hyo ; Lim, Jung-Gwan ; Kim, Kwang-Soo ; Kim, Jin ;
Journal of Ocean Engineering and Technology, volume 28, issue 4, 2014, Pages 268~273
DOI : 10.5574/KSOE.2014.28.4.268
To investigate the turbulence characteristics within the boundary layer over a flat plate, an experimental study was performed using a PIV technique in a circular water channel. For two water velocities, 0.92 and 1.99 m/s, the water velocity profiles were taken and analyzed to determine turbulent characteristics such as the Reynolds stress, Taylor micro-length scale, and Kolmogorov length scale within the defect law region of the boundary layer. These analysis methods may be applied to research on the friction drag reduction technology using micro-bubbles or an air sheet over the surface of a ship's hull, because the physical reason for the friction drag reduction could be found by understanding the variation of the turbulence characteristics and structures in the boundary layer.
Parameter Study of Position Keeping for Semi-submersible Offshore Structure by Tugs
Lee, Jin Ho ; Park, Jun Heum ; Jang, Hag Soo ;
Journal of Ocean Engineering and Technology, volume 28, issue 4, 2014, Pages 274~279
DOI : 10.5574/KSOE.2014.28.4.274
This paper investigates the line dynamic forces connecting tugs and a floater, where the planar motion of the floater is due to the weather criteria during the position keeping of the offshore structure by tugs. The analysis situation consists of the position keeping states for the seabed mooring line connection work of the offshore structure at the offshore site. Specifically, the decision about the tug power capacity for the position keeping is essential and depends on the weather criteria, line characteristics, length of line, etc. The planar motion of the structure is constrained by the interference of the installation vessel's operational range, behavior of the underwater fairlead, and other surrounding structures. In this paper, the tug line forces and planar motion of an offshore structure are summarized dependent on the tug line length and line material characteristics in the states fora given floater draft and weather criteria. The tug line dynamic forces and planar motion evaluated here will be used to determine the proper tug power and clearance of an offshore structure.
CFD Simulation to Study Flow Characteristics in Cylindrical Gas-Liquid Cyclone Separator
Park, Gyung-Do ; Park, Jong-Chun ; Kim, Kyung-Mi ;
Journal of Ocean Engineering and Technology, volume 28, issue 4, 2014, Pages 280~287
DOI : 10.5574/KSOE.2014.28.4.280
In this paper, the numerical simulation of the gas-liquid flow in a cylinder cyclone separator is performed to investigate the flow characteristics using a commercial software, FLUENT, which solves the Reynolds-averaged Navier-Stokes(RaNS) equations. First, a single-phase flow with water in a gas-liquid cylinder cyclone(GLCC) separator is simulated and compared with the experiments(Farchi, 1990) and numerical simulations(Erdal, 1997). Then, the characteristics of the multi-phase flow for water-air, mud-only, and mud-air cases are discussed in the view point of the feasibilities for a mud handling system.
Effects of Initial Conditions on Transient Responses in Dynamic Simulation of FOWT
Song, Jin-Seop ; Rim, Chae-Whan ; Moon, Seok-Jun ; Nam, Yong-Yun ;
Journal of Ocean Engineering and Technology, volume 28, issue 4, 2014, Pages 288~293
DOI : 10.5574/KSOE.2014.28.4.288
The IEC standard for onshore or offshore wind turbines requires additional dummy simulations (at least 5 s) for the transient responses due to initial conditions. An increase in the dummy time causes a considerable increase in the computational cost considering multiple design spirals with several thousand design load analysis cases. A time of 30 s is typically used in practical simulations for a wind turbine design with a fixed platform. However, 30 s may be insufficient for floating offshore wind turbines (FOWT) because the platforms have lower natural frequencies, and the transient responses will last much longer. In this paper, an initial condition application algorithm is implemented for WindHydro, and the appropriate dummy simulation time is investigated based on a series of dynamic simulations of a FOWT. As a result, it is found that more than 300 s is required for the platform to have stationary motion after the initial transient responses for the FOWT under the conditions considered.
Methods for Nonlinear Structural Response Analysis of Offshore Structures with Passive Fire Protection under Fires
Kim, Jeong Hwan ; Lee, Dong Hun ; Ha, Yeon Chul ; Kim, Bong Ju ; Seo, Jung Kwan ; Paik, Jeom Kee ;
Journal of Ocean Engineering and Technology, volume 28, issue 4, 2014, Pages 294~305
DOI : 10.5574/KSOE.2014.28.4.294
In offshore structures, fire is one of the most important hazardous events. The concern of fires has recently been reflected in the rules and quantified risk assessment based design practice. Within the framework of quantified risk assessment and the management of offshore installations, therefore, more refined computations of the consequences or hazardous action effects due to fire are required. To mitigate fire risk, passive fire protection(PFP) is widely used on offshore structures. This study presents methods for a nonlinear structural response analysis considering the PFP effects under fires. It is found that a structural response analysis is most likely to use valuable technology for the optimization and design of offshore structures with PFP. Thermal and structural response analyses have been performed using LS-DYNA and FAHTS/USFOS. The results of these structural response analyses are compared with each other.
Low-temperature Mechanical Behavior of Super Duplex Stainless Steel Considering High Temperature Environment
Kim, Myung-Soo ; Jung, Won-Do ; Kim, Jeong-Hyeon ; Lee, Jae-Myung ;
Journal of Ocean Engineering and Technology, volume 28, issue 4, 2014, Pages 306~313
DOI : 10.5574/KSOE.2014.28.4.306
Super duplex stainless steels (sDSS) are excellent for use under severely corrosive conditions such as offshore and marine applications like pipelines and flanges. sDSS has better mechanical properties and corrosion resistance than the standard duplex stainless steel (DSS) but it is easier for a sigma phase to appear, which depresses the mechanical property and corrosion resistance, compared to DSS, because sDSS has a higher alloy element than DSS. In addition, sDSS has a feeble ductile-brittle transition temperature (DBTT) because it has a 50% ferrite microstructure. In the actual operating environment, sDSS would be thermally affected by welding and a sub-zero temperature environment. This study analyzed how precipitated sDSS behaves at a sub-zero temperature through annealing heat treatment and a sub-zero tensile test. Six types of specimens with annealing times of up to 60 min were tested in a sub-zero chamber. According to the experimental results, an increase in the annealing time reduced the elongation of sDSS, and a decrease in the tensile test temperature raises the flow stress and tensile stress. In particular, the elongation of specimens annealed for 15 min and 30 min was clearly lowered with a decrease in the tensile test temperature because of the increasing sigma phase fraction ratio.
Study of Dynamic Characteristics of 2.5-MW Wind Turbine Gearbox
Kimg, Jung-Su ; Park, No-Gill ; Han, Ki-Bong ; Lee, Hyoung-Woo ;
Journal of Ocean Engineering and Technology, volume 28, issue 4, 2014, Pages 314~323
DOI : 10.5574/KSOE.2014.28.4.314
In this study, a gearbox and blade were modeled in the MASTA program, and the housing and carrier components were modeled using a finite element method. Using substructure synthesis, all the components were combined and used to establish a vibration model of a 2.5-MW wind turbine gearbox. In addition, the safety displacement factor was evaluated using an AGMA data sheet about bearing's outer race for the input shaft and output shaft. As a result, the bearing's outer race for the input shaft, and the radial and axial responses were satisfied by the
planetary gears and the
helical gear transmission error(TE), respectively. However, the output shaft support bearing's outer race responses were not satisfied with the radial response by the
TE and axial response by the
TE. To reduce the vibration, tooth modification was needed. After profile tooth modification, at the outer race of the output shaft support bearing, the radial response was reduced by approximately
, and the axial response was reduced by approximately
Effective Analysis for Rapidly Varying Flows through Improvement in Spatial Discretization of Horizontal Advection Terms
Hong, Namseeg ;
Journal of Ocean Engineering and Technology, volume 28, issue 4, 2014, Pages 324~330
DOI : 10.5574/KSOE.2014.28.4.324
In this study, the numerical model developed by Hong et al.(2008) was improved to be applied to rapidly varying flows such as the inundation of dry land or flow transitions due to large gradients of the bathymetry. A numerical approximation was applied that was consistent with the conservation of momentum in flow expansions and with the Bernoulli equation in flow contractions. The approximation was second order, but the accuracy reduced to first order near extreme values by the use of a minmod limiter. The modified model was verified by acomparison with the theoretical critical depth of weir, and for sufficiently smooth conditions and a fine grid size, both approximations converged to the same solution. In terms of the grid size, it was more effective at obtaining solutions than the previous model and reproduced the inundation of dry land.
3D Characteristics of Dynamic Response of Seabed around Submerged Breakwater Due to Wave Loading
Hur, Dong-Soo ; Park, Jong-Ryul ; Lee, Woo-Dong ;
Journal of Ocean Engineering and Technology, volume 28, issue 4, 2014, Pages 331~337
DOI : 10.5574/KSOE.2014.28.4.331
We analyzed the 3-D characteristics of the dynamic response of seabed around a submerged breakwater due to wave loading using a 3-D numerical scheme (LES-WASS-3D). Using our model, which considers the wave-structure-sandy seabed interactions in a 3-D wave field, we were able to investigate the 3-D characteristics of the pore-water pressure in the seabed around the submerged breakwater under various incident wave conditions. To verify the 3-D numerical analysis method suggested in this study, we compared the numerical results with the existing experimental results and found good agreement between them. The numerical analysis reveals that high pore-water pressure in the seabed is generated below a large wave height at the front slope of the submerged breakwater. It was also shown that the non-dimensional pore-water pressure in the seabed increases as the wave period increases because the wave energy dissipation decreases on the submerged breakwater and seabed as the wave period increases.
Evaluation of dispersion degree of nanoparticles in TiO
/epoxy resin nanocomposites
Nam, Ki-Woo ; Moon, Chang-Kwon ;
Journal of Ocean Engineering and Technology, volume 28, issue 4, 2014, Pages 338~344
DOI : 10.5574/KSOE.2014.28.4.338
The purpose of this study was to evaluate the dispersion degree of particles using a nanoindentation test for titanium oxide nanoparticles/epoxy resin nanocomposites. Thus, the effects of the particle size and weight fraction, dispersion agent, and position of the sample on the modulus and degree of particle dispersion in the nanocomposites were investigated. As a result, the dispersion degree of large particles was found to be better than that of smaller particles in composites. It could be found that the aggregation or agglomeration of small particles with large surface energy occurred more easily in nanocomposites because of the large specific surface area. The moduli of the upper side of the film-shaped sample obtained from a nanoindentation test were low scattering, while the values for the bottom side were high scattering. Thus, the dispersion situation of the nanoparticles on the upper side of film-shaped samples could be considered to be better than that for the bottom side. This could be concluded due to the non-uniform nanoparticle dispersion in the same sample. The modulus obtained from nanoindentation test increased slightly with the content of nanoparticles and increased with the indented depth for the same sample. The latter is presumably due to the increase in the accumulated particles facing the indenter with the indented depth. The nanoindentation test was found to be a useful method to evaluate the dispersion status of nanoparticles in nanocomposites.
Evaluation of Performance in Semi-Open Type Impeller by Duplex Stainless Material for Ballast Water Centrifugal Pump
Lee, Jin-Woo ; Kim, Yun-Hae ; Gang, Young-Gwan ; Lee, Sang-Hoon ;
Journal of Ocean Engineering and Technology, volume 28, issue 4, 2014, Pages 345~350
DOI : 10.5574/KSOE.2014.28.4.345
A special usage impeller pump for ballast water treatment is part of an offshore plant's structure. It has to maintain a high corrosion resistance in an extreme environment, in which it can contact several kinds of aqueous solutions. The duplex stainless steel used in such severe environments is known to have corrosion resistance and excellent mechanical properties. This study estimated the performance of an impeller pump system designed using duplex stainless steel through a computational fluid dynamics analysis. As a result, it was determined that the pressure drop increases and the impeller performance is lowered if the equivalent roughness is enlarged. The surface precision of the duplex stainless steel must be consistently maintained. If thisis the case, it was determined that the existing STS steel can be substituted for the Duplex stainless steel.
Thermal Characteristics of Hybrid Composites for Application to Surfboard
Kim, Yun-Hae ; Lee, Jin-Woo ; Park, Chang-Wook ; Park, Soo-Jeong ;
Journal of Ocean Engineering and Technology, volume 28, issue 4, 2014, Pages 351~355
DOI : 10.5574/KSOE.2014.28.4.351
Today, carbon fibers are used as heating elements. Carbon fibers are generally used to reinforce composite materials because they are lightweight and have a high strength and modulus. Carbon fiber reinforced composite materials are used for aerospace, automobile, and wind turbine blade applications. This work explored the possibility of using carbon fiber reinforced composite materials as self heating materials. The temperatures of the carbon fiber reinforced composites were measured. These results verified that the carbon fiber reinforced composite materials could be used as heating elements. A glass fiber was laminated using various methods. The thermal characteristics of the composites were evaluated. This confirmed that the generation of heat varied according to the lamination thicknesses of the carbon fiber and glass fiber. As the number of carbon fiber laminations increased, the heat-generating temperature increased. In contrast, as the number of glass fiber laminations increased, the amount of heat decreased. The generation of heat and ability to remain warm could be controlled by controlling the carbon fiber and glass fiber laminations.
Evaluation of the Corrosion Property on the Welded Zone of Cast Steel Piston Crown with Types of Electrode
Moon, Kyung-Man ; Kim, Yun-Hae ; Lee, Myeong-Hoon ; Baek, Tae-Sil ; Kim, Jin-Gyeong ;
Journal of Ocean Engineering and Technology, volume 28, issue 4, 2014, Pages 356~362
DOI : 10.5574/KSOE.2014.28.4.356
Wear and corrosion of the engine parts surrounded with combustion chamber is more serious compared to the other parts of the engine because temperature of the exhaust gas in a combustion chamber is getting higher and higher with increasing of using the heavy oil of low quality. Therefore, an optimum repair weldment as well as an available choice of the base metal for these parts are very important to prolong their lifetime in a economical point of view. It reported that there was an experimental result for repair weldment on the forged steel which would be generally used with piston crown material, however, it is considered that there is no study for the repair weldment on the cast steel of piston crown material. In this study, four types of electrodes such as 1.25Cr-0.5Mo, 0.5Mo Inconel 625 and 718 were welded with SMAW and GTAW methods on the cast steel which would be generally used with piston crown material. And the corrosion properties of weld metal, heat affected zone and base metal were investigated using electrochemical methods such as measurement of corrosion potential, anodic polarization curves, cyclic voltammogram and impedance etc. in 35%
solution. In the cases of Inconel 625, 718, the weld metals and base metals exhibited the best and worst corrosion resistance respectively, however, 1.25Cr-0.5Mo and 0.5Mo indicated that corrosion resistance of the base metal was better than the weld metal. And the weld metal welded with electrodes of Inconel 625 revealed the best corrosion resistance among the electrodes, and Inconel 718 followed the Inconel 625. Hardness relatively also indicated higher value in the weld metal compared to heat affected zone and base metal. In particular, Inconel 718 indicated the highest value of hardness compared to other electrodes in the heat affected zone.
Formation Control for Unmanned Surface Vessels Using Lyapunov Redesign Method
Woo, Sangbum ; Lee, Jaeyong ;
Journal of Ocean Engineering and Technology, volume 28, issue 4, 2014, Pages 363~369
DOI : 10.5574/KSOE.2014.28.4.363
In this paper, a practical controller for a group of USVs is proposed in order to avoid matrix inversion problems in computation. Using nonlinear mapping, a formation composed of nonholonomic agents can be stabilized even when the formation is stationary. Since there is no matrix inversion in computing the control law, the computation complexity can be resolved. A controller for stabilizing the formation errors in the presence of model uncertainty is considered using the Lyapunov redesign method. The asymptotic stability of the formation errors is shown. It is also shown that the proposed controller can be applied to guide a formation to a different shape without modification.