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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 25, Issue 6 - Dec 2011
Volume 25, Issue 5 - Oct 2011
Volume 25, Issue 4 - Aug 2011
Volume 25, Issue 3 - Jun 2011
Volume 25, Issue 2 - Apr 2011
Volume 25, Issue 1 - Feb 2011
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Implementation of Noise Reduction Methodology to Modal Distribution Method
Choi, Myoung-Keun ;
Journal of Ocean Engineering and Technology, volume 25, issue 2, 2011, Pages 1~6
DOI : 10.5574/KSOE.2011.25.2.001
Vibration-based Structural Health Monitoring (SHM) systems use field measurements of operational signals, which are distorted by noise from many sources. Reducing this noise allows a more accurate assessment of the original "clean" signal and improves analysis results. The implementation of a noise reduction methodology for the Modal Distribution Method (MDM) is reported here. The spectral subtraction method is a popular broadband noise reduction technique used in speech signal processing. Its basic principle is to subtract the magnitude of the noise from the total noisy signal in the frequency domain. The underlying assumption of the method is that noise is additive and uncorrelated with the signal. In speech signal processing, noise can be measured when there is no signal. In the MDM, however, the magnitude of the noise profile can be estimated only from the magnitude of the Power Spectral Density (PSD) at higher frequencies than the frequency range of the true signal associated with structural vibrations under the additional assumption of white noise. The implementation of the spectral subtraction method to MDM may decrease the energy of the individual mode. In this work, a modification of the spectral subtraction method is introduced that enables the conservation of the energies of individual modes. The main difference is that any (negative) bars with a height below zero after subtraction are set to the absolute value of their height. Both noise reduction methods are implemented in the MDM, and an application example is presented that demonstrates its effectiveness when used with a signal corrupted by noise.
CFD Application to Evaluation of Wave and Current Loads on Fixed Cylindrical Substructure for Ocean Wind Turbine
Park, Yeon-Seok ; Chen, Zheng-Shou ; Kim, Wu-Joan ;
Journal of Ocean Engineering and Technology, volume 25, issue 2, 2011, Pages 7~14
DOI : 10.5574/KSOE.2011.25.2.007
Numerical simulations were performed for the evaluation of wave and current loads on a fixed cylindrical substructure model for an ocean wind turbine using the ANSYS-CFX package. The numerical wave tank was actualized by specifying the velocity at the inlet and applying momentum loss as a wave damper at the end of the wave tank. The Volume-Of-Fluid (VOF) scheme was adopted to capture the air-water interface. An accuracy validation of the numerical wave tank with a truncated vertical circular cylinder was accomplished by comparing the CFD results with Morison's formula, experimental results, and potential flow solutions using the higher-order boundary element method (HOBEM). A parametric study was carried out by alternately varying the length and amplitude of the wave. As a meaningful engineering application, in the present study, three kinds of conditions were considered, i.e., cases with current, waves, and a combination of current and progressive waves, passing through a cylindrical substructure model. It was found that the CFD results showed reasonable agreement with the results of the HOBEM and Morison's formula when only progressive waves were considered. However, when a current was included, CFD gave a smaller load than Morison's formula.
Numerical Simulation of Flow around Free-rolling Rectangular Barge in Regular Waves
Jung, Jae-Hwan ; Yoon, Hyun-Sik ; Kwon, Ki-Jo ; Cho, Sung-Joon ;
Journal of Ocean Engineering and Technology, volume 25, issue 2, 2011, Pages 15~20
DOI : 10.5574/KSOE.2011.25.2.015
This study aimed at validating the adopted numerical methods to solve two-phase flow around a two-dimensional (2D) rectangular floating structure in regular waves. A structure with a draft equal to one half of its height was hinged at the center of gravity and free to roll with waves that had the same period as the natural roll period of a rectangular barge. In order to simulate the 2D incompressible viscous two-phase flow in a wave tank with the rectangular barge, the present study used the volume of fluid (VOF) method based on the finite volume method with a standard turbulence model. In addition, the sliding mesh technique was used to handle the motion of the rectangular barge induced by the fluid-structure interaction. Consequently, the present results for the flow field and roll motion of the structure had good agreement with those of the relevant previous experiment.
Comparison of Local Scour around Pipeline Caused by Waves and Steady Currents
Kim, Kyoung-Ho ; Oh, Hyoun-Sik ;
Journal of Ocean Engineering and Technology, volume 25, issue 2, 2011, Pages 21~28
DOI : 10.5574/KSOE.2011.25.2.021
The primary purpose of the present study was to investigate the mechanism causing scour around a pipeline placed on the seabed in a shallow water zone. Such submarine pipelines are usually exposed to currents and waves. The present experiments made estimates for each different flow type. The scour width and depth in the equilibrium scour phase were analyzed by non-dimensional parameters. The experiment in this study considered various parameters: pipe diameters, wave periods, wave heights, and current velocities. Using the experimental results, the correlations of scour width, scour depth, and main non-dimensional parameters such as the Fr number and KC number were analyzed. In the case of steady currents, the scour hole was closely related to the bottom velocity, while the scour hole in waves showed a relatively low correlation to the bottom velocity because when exposed to waves the scour hole was restricted according to the movement distance of the water particles during a wave period. However, the scour width under a steady current was not limited because vortex shedding was well developed from having enough time and distance.
Study on Effect of Wave Control by Multi-Cylinder Piles Using Delft-3D Hydrodynamic Model
Lee, Snag-Hwa ; Jang, Ean-Chul ; Lee, Han-Seung ; Jeong, Seok-Jae ;
Journal of Ocean Engineering and Technology, volume 25, issue 2, 2011, Pages 29~35
DOI : 10.5574/KSOE.2011.25.2.029
In order to effectively control waves in a coastal zone, Multi-Cylinder Piles have been suggested as economic structures. A numerical analysis was conducted using the Delft-3D: WAVE module based on SWAN, which considered wave shoaling and refraction. Moreover, irregular waves were used to investigate the hydrodynamic characteristics of the wave interaction with the structure. In this paper, a numerical analysis was carried out to research the effect of wave control through a wave height analysis concerning an existing, concrete wave breaker and multi-cylinder piles placed at the same location. As a result, the effect of the wave control is shown using the wave breaker, multi-cylinder piles, and existing data.
CFD Analysis of Two-Dimensional Floating Body with Moon Pool under Forced Heave Motion
Heo, Jae-Kyung ; Park, Jong-Chun ; Kim, Moo-Hyun ;
Journal of Ocean Engineering and Technology, volume 25, issue 2, 2011, Pages 36~46
DOI : 10.5574/KSOE.2011.25.2.036
A two-dimensional floating body with a moon pool under forced heave motion, including a piston mode, is numerically simulated. A dynamic CFD simulation is carried out to thoroughly investigate the flow field around a two-dimensional moon pool over various heaving frequencies. The numerical results are compared with experimental results and a linear potential program by Faltinsen et al. (2007). The effects of vortex shedding and viscosity are investigated by changing the corner shapes of the floating body and solving the Euler equation, respectively. The flow fields, including the velocity, vorticity, and pressure fields, are discussed to understand and determine the mechanisms of wave elevation, damping, and sway force.
Laboratory Test of Piled-Raft Foundation Improved by Gravel Mat
Seo, Young-Kyo ; Lee, Jeong-Hoon ;
Journal of Ocean Engineering and Technology, volume 25, issue 2, 2011, Pages 47~54
DOI : 10.5574/KSOE.2011.25.2.047
A piled raft foundation is one of the systems used to reduce the settlement of structures. However, the general design method for a piled raft foundation system assumes that the piles only support external loads, which exclude the bearing capacity of the raft itself. In this study, an experimental model test was performed to evaluate the raft capacity for the external load on the sand. Additionally, a part of the sandy ground under the raft was replaced with a gravel mat to reinforce the piled raft foundation system and increase the bearing capacity. Then, parametric studies of the reinforced ground were performed to determine the displacement and load-sharing ratio of the piled raft foundation system.
Material Properties of Arctic Sea Ice during 2010 Arctic Voyage of Icebreaking Research Vessel ARAON: Part 1 - Sea Ice Thickness, Temperature, Salinity, and Density -
Park, Young-Jin ; Kim, Dae-Hwan ; Choi, Kyung-Sik ;
Journal of Ocean Engineering and Technology, volume 25, issue 2, 2011, Pages 55~61
DOI : 10.5574/KSOE.2011.25.2.055
A field trial in an ice-covered sea is one of the most important tasks in the design of icebreaking ships and offshore structures. To correctly estimate the ice load and ice resistance of a ship's hull, it is essential to understand the material properties of sea ice during ice field trials and to use the proper experimental procedure for gathering effective ice data. The first Korean-made icebreaking research vessel, "ARAON," had her second sea ice trial in the Arctic Ocean during the summer season of 2010. This paper describes the test procedures used to obtain proper sea ice data, which provides the basic information for the ship's performance in an ice-covered sea and is used to estimate the correct ice load and ice resistance of the IBRV ARAON. The data gathered from the sea ice in the Chukchi Sea and Beaufort Sea during the Arctic voyage of the ARAON includes the temperature, density, and salinity of the sea ice, which was believed to be from two-year old ice floes. This paper analyses the gathered sea ice data in comparison with data from the first voyage of the ARAON during her Antarctic Sea ice trial.
Analytic Analysis of Liquid-Filled Membrane Container Resting on Horizontal Foundation with Given Cross-Sectional Volume
Choi, Yoon-Rak ;
Journal of Ocean Engineering and Technology, volume 25, issue 2, 2011, Pages 62~66
DOI : 10.5574/KSOE.2011.25.2.062
In this paper, a liquid-filled long membrane container resting on a horizontal foundation is considered. All of the quantities are normalized to obtain similarity solutions. A system of nonlinear ordinary differential equations with undetermined boundary conditions is solved analytically. The integration of the curvature gives the solutions, which are expressed in terms of the elliptic integrals. A method for finding the shape and characteristic values is proposed for a given cross-sectional volume. The validity of these solutions is confirmed, and some results are shown for characteristic values and shapes.
Effect of Curvature on Deformation caused by Thermal Plate Forming
Lee, Joo-Sung ;
Journal of Ocean Engineering and Technology, volume 25, issue 2, 2011, Pages 67~72
DOI : 10.5574/KSOE.2011.25.2.067
This study had the goal of investigating the effect of the curvature along the heating line on the transverse angular distortion of plates having an initial curvature from line heating. A thermo-elasto-plastic analysis was carried out using 54 models with various radii of curvature, plate thicknesses, and heating speeds. The results show the effect of the curvature along the heating line on the angular distortion in relation to changes in the magnitudes of the curvature, heating speed, and plate thickness. The present numerical results show that the time history of the angular distortion after cooling and reaching the final deformed shape for a plate having an initial curvature is quite different from that of a flat plate. This emphasized the importance of considering the curvature effect on the transverse angular distortion. From the viewpoint of the curvature effect on the deformation, it has been seen that the curvature does not affect the transverse shrinkage. In this study the predicting formula for the transverse angular distortion was derived through a regression analysis. It showed that as the curvature increased, the angular distortion was reduced because of the higher bending rigidity at the same heat input parameter, and the peak points moved toward the origin as the curvature increased.
Modal Analysis of Filament-wound Composite Towers for Large Scale Wind-Turbine
Hong, Gheol-Hyun ;
Journal of Ocean Engineering and Technology, volume 25, issue 2, 2011, Pages 73~78
DOI : 10.5574/KSOE.2011.25.2.073
The purpose of this study was to investigate the natural frequency of filament-wound composite towers for large scale wind-turbines using the finite element method (FEM). To define the material properties, we used both the effective property method and the stacking properties method. The effective properties method assumes that a composite consists of one ply. The stacking properties method assumes that a composite consists of several stacked plies. First, a modal analysis of the tower, filament-wound with angles of
, was carried out using the two methods for composite material properties, the stacking method and effective method. Then, an FE analysis was performed for composite towers using filament winding angles of
. The FE analysis results using the stacking properties of the composite were in good agreement with the results from the effective properties method. The difference between the FEM and material properties methods was approximately 0~0.6%
Buckling Analysis of Filament-wound Composite Towers for Large Scale Wind-Turbine
Han, Jeong-Young ; Hong, Cheol-Hyun ;
Journal of Ocean Engineering and Technology, volume 25, issue 2, 2011, Pages 79~84
DOI : 10.5574/KSOE.2011.25.2.079
The purpose of this study was to investigate the buckling load of filament-wound composite towers for large scale wind-turbines using the finite element method (FEM). To define the material properties, we used both the effective property method and stacking properties method. The effective properties method assumes that a composite consists of one ply. The stacking properties method assumes that a composite consists of several stacked plies. First, a linear buckling analysis of the tower, filament-wound with angles of
, was carried out using the two methods for composite material properties: the stacking method and effective method. An FE analysis was also performed for the composite towers using the filament winding angles of
. The FE analysis results using the stacking properties of the composite were in good agreement with the results from the effective properties method. The difference between the FEM results and material properties method was approximately 0~2.3%. Above the angle of
, there was little change in the buckling load.
Evaluation of Corrosion Characteristics of Underwater Hardening Paint
Moon, Kyung-Man ; Oh, Min-Seok ; Lee, Myung-Hoon ; Lee, Syung-Yul ; Kim, Yun-Hae ;
Journal of Ocean Engineering and Technology, volume 25, issue 2, 2011, Pages 85~91
DOI : 10.5574/KSOE.2011.25.2.085
Many protection methods such as surface coating, electric protection, or other methods have been applied to the numerous steel structures widely used in continental and marine areas to control their corrosion, which is done from an economic point of view. Most of these steel structures are primarily protected by coating methods. However, some steel piles under seawater are protected by the electric protection method, that is, either using an impressed current or a sacrificial anode method. Furthermore, environmental contamination may cause a severely corrosive environment, which, in turn, causes the accelerated corrosion of steel structures. Subsequently, coated steel structures could deteriorate more rapidly than the designed lifetime because of the acid rain caused by air pollution, etc. Therefore, a coating of marine paint exposed to seawater, that is, underwater hardening painting, is increasingly required to be fast drying as well as highly corrosion resistant. In this study, five types of underwater hardening paints were prepared with different resin series and additives. Their corrosion and water resistances were investigated using electrochemical methods such as corrosion potential, polarization curves, impedance and cyclic voltammogram measurements, etc. Even though it is generally accepted that the corrosion resistance of bare steel tends to increase with a shift of the corrosion potential in the noble direction, the corrosion resistance of a sample with a coating exhibited a relatively better tendency when it had a lower corrosion potential in this study. The corrosion current density was also decreased with a decrease in the diffusion limiting current density, which may mean that there is some relationship between corrosion and water resistance. The S sample of the ceramic resin series showed the relatively best corrosion and water resistance among those of samples, while the worst corrosion and water resistance were observed for the R sample of the epoxy resin series. The corrosion and water resistance of those samples tended to deteriorate with an increase in the immersion days, and their corrosion and water resistances were considered to be apparently improved by the types of resin and additives.
Plasticity and Fracture Behaviors of Marine Structural Steel, Part II: Theoretical Backgrounds of Fracture
Choung, Joon-Mo ; Shim, Chun-Sik ; Kim, Kyung-Su ;
Journal of Ocean Engineering and Technology, volume 25, issue 2, 2011, Pages 92~100
DOI : 10.5574/KSOE.2011.25.2.092
The main goal of this paper is to provide the theoretical background for the fracture phenomena in marine structural steels. In this paper, various fracture criteria are theoretically investigated: shear failure criteria with constant failure strain and stress triaxiality-dependent failure strain (piecewise failure and Johnson-Cook criteria), forming limit curve failure criterion, micromechanical porosity failure criterion, and continuum damage mechanics failure criterion. It is obvious that stress triaxiality is a very important index to determine the failure phenomenon for ductile materials. Assuming a piecewise failure strain curve as a function of stress triaxiality, the numerical results coincide well with the test results for smooth and notched specimens, where low and high stress triaxialities are observed. Therefore, it is proved that a failure criterion with reliable material constants presents a plastic deformation process, as well as fracture initiation and evolution.
Parametric Design Considerations for Lifting Lug Structure on Ship Block
Ham, Juh-Hyeok ;
Journal of Ocean Engineering and Technology, volume 25, issue 2, 2011, Pages 101~107
DOI : 10.5574/KSOE.2011.25.2.101
In view of the importance of material reduction because of the jump in oil and steel prices, structural design studies for lifting lugs were performed. Hundreds of thousands of such lifting lug structures are needed every year for ship construction. A direct design study was reviewed using the developed design system to increase the design efficiency and provide a way of directly inserting a designer's decisions into the design system process. In order to understand the design efficiency and convenience of a lug structure, parametric studies for prototype lug shapes were performed using the developed design system. From these design studies, various patterns of design parameters for the lug structure according to changes in the main plate length were examined. Based on these parametric study results, design guides were developed for more efficiently suggesting structural data for enormous lug structures. Additionally, a more detailed structural analysis through local strength evaluations will be performed to verify the efficiency of the optimum structural design for a lug structure.
Study on Prediction for Prompt Countermeasures to Oil Spread in Ocean
Kim, Young-Bok ;
Journal of Ocean Engineering and Technology, volume 25, issue 2, 2011, Pages 108~112
DOI : 10.5574/KSOE.2011.25.2.108
When oil spills occur in the ocean because of a ship collision or grounding, the oil in the sea will spread to the coastline. To effectively and promptly prevent such an oil spread, the prediction of the direction and speed of the spreading oil must be made. By applying the coastal wave diffusion theory with a consideration of the effects of wind and current, the oil spreading direction and speed can be predicted promptly so that the National Disaster Prevention System can effectively and promptly take countermeasures against the attack and contamination of the coastline by such oil bands.
Feasibility Study on High Speed Craft Considering Environment in South Korea
Lee, Soon-Sup ; Kang, Dong-Hoon ; Shin, Sung-Chul ;
Journal of Ocean Engineering and Technology, volume 25, issue 2, 2011, Pages 113~119
DOI : 10.5574/KSOE.2011.25.2.113
The Korea navy has a vital national interest in maritime security. The national strategy for maritime security focuses on preventing terrorism, crime, and hostile acts in the maritime domain. This requires the development of high speed crafts for maritime security in the South Korea domain. This paper reviews the state of the art on the development of high speed craft internationally, including efforts by the U.S. navy, and analyses the riverine environment to operate high speed crafts in South Korea. This paper makes specific proposals for high speed craft such as their main dimensions, speed, endurance, hull structure material, propulsion system, and general arrangement and 3D shape. This paper was used in the generation of basic resources for future ROC (requirement of capability) of high speed crafts using an engineering methodology.
Data Acquisition of Time Series from Stationary Ergodic Random Process Spectrums
Park, Jun-Bum ; Kim, Kyung-Su ; Choung, Joon-Mo ; Kim, Jae-Woo ; Yoo, Chang-Hyuk ; Ha, Yeong-Su ;
Journal of Ocean Engineering and Technology, volume 25, issue 2, 2011, Pages 120~126
DOI : 10.5574/KSOE.2011.25.2.120
The fatigue damages in structural details of offshore plants can be accumulated due to various environmental loadings such as swell, wave, wind and current. It is known that load histories acting on mooring and riser systems show stationary and ergodic bimodal wide-banded process. This paper provides refined approach to obtain time signals representing stress range histories from wide-banded bimodal spectrum which consists of ideally narrow-banded and fully separated two spectrums. Variations of the probabilistic characteristics for time signals according to frequency and sampling time increments are compared with the reference data to be the probabilistic characteristics such as zero-crossing period, peak period, and irregularity factor obtained from an assumed ideal spectrum. It is proved that the sampling time increment more affects on the probabilistic characteristics than frequency increment. The fatigue damages according to the frequency and sampling time increments are also compared with the ones with minimum increment condition which are thought to be exact fatigue damage. It is concluded that the maximum sampling time increment to obtain reliable time signals should be determined that ratio of applied maximum sampling time increment and minimum period is less than approximately 0.08.
Future Vision through NL Tensioner Technology Development and Domestic Equipment Fabrication
Lee, Ki-Yeol ; Choi, Hae-Soo ; Lee, Eun-Jin ; Yoon, Tae-Sam ;
Journal of Ocean Engineering and Technology, volume 25, issue 2, 2011, Pages 127~133
DOI : 10.5574/KSOE.2011.25.2.127
The following Technology Report was written with respect to recent offshore technology development. This report was prepared with the purpose of suggesting recent offshore technology and upcoming visions by describing the principles of an offshore drilling operation, the NL Tensioner Cylinder Package R & D, and the general technology related to three offshore patent areas, as major contents.
Plasticity and Fracture Behaviors of Marine Structural Steel, Part I: Theoretical Backgrounds of Strain Hardening and Rate Hardening
Choung, Joon-Mo ; Shim, Chun-Sik ; Kim, Kyung-Su ;
Journal of Ocean Engineering and Technology, volume 25, issue 2, 2011, Pages 134~144
DOI : 10.5574/KSOE.2011.25.2.134
In this paper, the global study trends for material behaviors are investigated regarding the static and dynamic hardenings and final fractures of marine structural steels. In particular, after reviewing all of the papers published at the 4th and 5th ICCGS (International Conference on Collision and Grounding of Ship), the used hardening and fracture properties are summarized, explicitly presenting the material properties. Although some studies have attempted to employ new plasticity and fracture models, it is obvious that most still employed an ideal hardening rule such as perfect plastic or linear hardening and a simple shear fracture criterion with an assumed value of failure strain. HSE (2001) presented pioneering study results regarding the temperature dependency of material strain hardening at various levels of temperature, but did not show strain rate hardening at intermediate or high strain rate ranges. Nemat-Nasser and Guo (2003) carried out fully coupled tests for DH-36 steel: strain hardening, strain rate hardening, and temperature hardening and softening at multiple steps of strain rates and temperatures. The main goal of this paper is to provide the theoretical background for strain and strain rate hardening. In addition, it presents the procedure and methodology needed to derive the material constants for the static hardening constitutive equations of Ludwik, Hollomon, Swift, and Ramberg-Osgood and for the dynamic hardening constitutive equations of power from Cowper-Symonds and Johnson-Cook.