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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 22, Issue 6 - Dec 2008
Volume 22, Issue 5 - Oct 2008
Volume 22, Issue 4 - Aug 2008
Volume 22, Issue 3 - Jun 2008
Volume 22, Issue 2 - Apr 2008
Volume 22, Issue 1 - Feb 2008
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The Application of FBNWT in Wave Overtopping Analysis
Liu, Zhen ; Jin, Ji-Yuan ; Hyun, Beom-Soo ;
Journal of Ocean Engineering and Technology, volume 22, issue 1, 2008, Pages 1~5
A 2-D Fluent-based numerical wave tank(FBNWT) capable of simulating wave propagating and overtopping is presented. The FBNWT model is based on the Reynolds averaged Naiver-Stokes equations and VOF free surface tracking method. The piston wave maker system is realized by dynamic mesh technology(DMT) and user defined function(UDF). The non-iteration time advancement(NITA) PISO algorithm is employed for the velocity and pressure coupling. The FBNWT numerical solutions of linear wave propagation have been validated by analytical solutions. Several overtopping problems are simulated and the prediction results show good agreements with the experimental data, which demonstrates that the present model can be utilized in the corresponding analysis.
Mode Selection of Leaky Lamb Waves in Steel Plate
Lee, Ju-Won ; Kim, Jeong-Tae ; Cho, Hyun-Man ; Na, Won-Bae ;
Journal of Ocean Engineering and Technology, volume 22, issue 1, 2008, Pages 6~12
The dispersion and attenuation of Lamb and Leaky Lamb waves propagating in a 1 mm-thick steel plate were investigated. For acquiring a long(or large) range inspection capability, the fundamental symmetric and anti-symmetric wave modes(S0 and A0) over law frequencies were studied. Based on the dispersion curves, as well as pitch-catch and multi-mode simulations, it was shown that the S0 mode over law frequencies is the proper mode to minimize the dispersion and attenuation. In addition, it was shown that the S0 mode couldbe easily distinguished under multi-mode simulation since it has a larger group velocity than the A0 mode.
A Method for Critical Heat Flux Prediction in Vertical Round Tubes with Axially Non-uniform Heat Flux Profile
Shim, Jae-Woo ;
Journal of Ocean Engineering and Technology, volume 22, issue 1, 2008, Pages 13~21
In this study a method to predict CHF(Critical heat flux) in vertical round tubes with axially non-uniform cosine heat flux distribution for water was examined. For this purpose a local condition hypothesis based CHF prediction correlation for uniform heat flux in vertical round tubes for water was developed from 9,366 CHF data points. The local correlation consisted of 4 local condition variables: the system pressure(P), tube diameter(D), mass flux of water(G), and 'true mass quality' of vapor(
). The CHF data points used were collected from 13 different published sources having the following operation ranges: 1.01
206.79 bar, 9.92
G (mass flux)
0.04468 m, 0.0254
4.966 m, 0.11
, and -0.87
1.58. The result of this work showed that a uniform CHF correlation can be easily extended to predict CHF in axially non-uniform heat flux heater. In addition, the location of the CHF in axially non-uniform tube can also be determined. The local uniform correlation predicted CHF in tubes with axially cosine heat flux profile within the root mean square error of 12.42% and average error of 1.06% for 297 CHF data points collected from 5 different published sources.
Hydroelastic Analysis of Pontoon Type VLFS Considering the Location and Shape of OWC Chamber
Hong, Sa-Young ; Kyoung, Jo-Hyun ; Kim, Byoung-Wan ;
Journal of Ocean Engineering and Technology, volume 22, issue 1, 2008, Pages 22~29
A numerical investigation is made on the effects of the location and shape of the front wall of an OWC(Oscillating Water Column) chamber on the hydroelastic response of a VLFS. Most of the studies on the effects of an OWC chamber on the response of a VLFS have assumed the location of the OWC chamber to be at the front of the VLFS. In the present study, an OWC-chamber is introduced at an arbitrary position in relation to a VLFS to determine the influence of the location and shape of the OWC chamber on the hydroelastic response of the VLFS. A finite element method is adopted as a numerical scheme for the fluid domain. or the finite element method, combined with a mode superposition method, is applied in order to consider the change of mass and stiffness The OWC chamber in a piecewise constant manner. or the facilitated anefficient analysis of The hydroelastic response of the VLFS, as well as the easy modeling of different shape and material properties for the structure. Reduction of hydroelastic response of the VLFS is investigated for various locations and front wall shapes of the owe chamber.
Identification of Underwater Ambient Noise Sources Using Hilbert-Huang Transfer
Hwang, Do-Jin ; Kim, Jea-Soo ;
Journal of Ocean Engineering and Technology, volume 22, issue 1, 2008, Pages 30~36
Underwater ambient noise originating from geophysical, biological, and man-made acoustic sources contains information on the source and the ocean environment. Such noise affectsthe performance of sonar equipment. In this paper, three steps are used to identify the ambient noise source, detection, feature extraction, and similarity measurement. First, we use the zero-crossing rate to detect the ambient noisesource from background noise. Then, a set of feature vectors is proposed forthe ambient noise source using the Hilbert-Huang transform and the Karhunen-Loeve transform. Finally, the Euclidean distance is used to measure the similarity between the standard feature vector and the feature vector of the unknown ambient noise source. The developed algorithm is applied to the observed ocean data, and the results are presented and discussed.
Local/Spatial Variation of Settling Velocities of Cohesive Sediments from Han Estuary
Seo, Young-Deok ; Jin, Jae-Youll ; Hwang, Kyu-Nam ;
Journal of Ocean Engineering and Technology, volume 22, issue 1, 2008, Pages 37~45
The purpose of this study is to quantify the settling velocities of cohesive sediments from Han estuary and to evaluate their local variation within Han estuary. This study also includes an estimation of their spatial variation, for which the settling velocities of cohesive sediments from Han estuary arecompared with those for sediments from other regions. At the same time, physical-chemical properties, such as grain size distribution, the percentage of organic contents, mineralogical composition etc are measured in this study in order to examine their correlation with settling velocities and their effect on settling velocities. Results from settling tests shaw that the settling velocities of Han estuary mud varies in the range of two orders of magnitude(from 0.01 to 1.5 mm/sec) over the corresponding concentration range of 0.1 to 80 g/L, and a feature of the settling velocity profile is quite different in quantity as compared to those of previous studies for muds from other regions. Particularly in the flocculated settling region, the settling velocity for Han estuary muds is shown to be larger than that of Saemankeum and Keum estuary sediments, while in the hindered settling region all three sediments are shown to have a similar settling velocity. However, local variability of the settling velocities within Han estuary is shown to be insignificant.
Seiche Characteristics of Gun-Jang Harbor
Cho, Yong-Jun ; Park, Hyung-Soo ;
Journal of Ocean Engineering and Technology, volume 22, issue 1, 2008, Pages 46~52
Lately Gun-Jang Harbor has undergone a drastic change in hydraulic characteristics due to newly added harbor protection measures, like a wharf and breakwater. The wharf and breakwater, with a training dike, were constructed to keep enough depth far navigation. They make the plan view of Gun-Jang Harbor semi closed and very elongated, which makes it very vulnerable to seiche. Hence it is an urgent task to unveil the hydraulic characteristics, like seiche, for the optimal operation of the new harbor system. In this study, we numerically analyze the seiche characteristics of Gun-Jang Harbor over the
Hz frequency range, considering that wind waves due to seasonal winds are the most prevailing during winter in the West sea. As a wave driver, we use Mild Slope Eqs. and numerically integrate these using FEM based on Galerkin weak formulation. It turns out that the 1st, 2nd, 3rd and 4th eigen models are over 0.0009 Hz, 0.0013 Hz, 0.0017 Hz and 0.002 Hz.
Optimization of Friction Welded Joint Conditions in Alloy718 and the Nondestructive Evaluation
Kwon, Sang-Woo ; Kong, Yu-Sik ; Kim, Seon-Jin ;
Journal of Ocean Engineering and Technology, volume 22, issue 1, 2008, Pages 53~57
Friction welding was performed to investigate mechanical properties for Ni-base superalloy with 15 mm diameter solid bar. The main friction welding parameters were selected to endure good quality welds on the basis of visual examination, tensile tests, impact energy test, Vickers hardness surveys of the bond of area and heat affected zone. And then, the nondestructive technique to evaluate the weld quality was carried out by acoustic emission(AE) and ultrasonic attenuation coefficient. The tensile strength of the friction welded joint was shown up to 90 % of the Alloy718 base metal under the condition of the heating time over 5 sec. The optimal welding conditions were n=2,000 rpm,
sec when the total upset length was 4.4 mm.
Study on the Durability of GFRP Composites in Alkaline Environment(1)
Moon, Yong-Jae ; Park, Chang-Ho ; Moon, Chang-Kwon ;
Journal of Ocean Engineering and Technology, volume 22, issue 1, 2008, Pages 58~63
The effect of alkaline environmental condition on durability of GFRP composites according to additives was investigated. Additives used were polyvinyl alcohol(PVA), kaolin and alumina powder. Weight gains increased with immersion time in all GFRP composites at
. But weight gain of specimen added PVA did not differ through the wlwle immersion time in both tap water and alkaline solution at 20 and
. Tensile strength decreased with immersion time in all environment conditions. Tensile strength of GFRP composites regardless of additives decreased rapidly up to 5 days of immersion and then decreased slowly up to 30 days in alkaline solution environment at
. Weight gains had not. much difference in both tap water and alkaline solution at
. And weight gain of GFRP composites added polyvinyl alcohol had smaller than the others through the whole immersion time in both tap water and alkaline solution at
. Tensile strength of GFRP composites added polyvinyl alcohol had higher than the others through the whole immersion time in both tap water and alkaline solution at
Application of Tensioning Method to Deformation Control of Thin Plate Fillet Weld
Lee, Joo-Sung ; Park, Jae-Woo ;
Journal of Ocean Engineering and Technology, volume 22, issue 1, 2008, Pages 64~69
As it has been well appreciated from the viewpoint of efficiency, The weld-induced deformation control is one of the most important issues in marine structure production. In the case of thin plate block, weld-induced deformation is more serious than in the case of relatively thick plate block. The heat affect zone of thin plates is wider than that of thick plates with the same heat input. Among weld-induced deformations, the buckling deformation by the shrinkage and residual stress in the weld line direction is one of the most serious deformation types. This paper is concerned with controlling buckling deformations for the thin plate fillet welds, by using the tensioning method. A numerical analysis was carried out to illustrate several dominant buckling modes due to compressive residual stress in the fillet weldsof thin plates. Then, weld tests were carried out for 20 specimens with varying plate thickness, and with different magnitudes and directions for the tension load. The results graphically represented to shaw the effect of the tensioning method in reducing the weld-induced deformation. From the present findings, it was seen that the tensioning method is a useful way to control weld-induced deformations in the fillet welds of thin plates.
Experimental Vibration Analysis of Damped Beam Model Using Multi-degree Curve Fitting Method
Min, Cheon-Hong ; Bae, Soo-Ryong ; Park, Han-Il ;
Journal of Ocean Engineering and Technology, volume 22, issue 1, 2008, Pages 70~74
It is important to reduce the vibration and noise of submarines and ships. For the purpose of noise reduction, various researches are actively being conducted on the employment of complex structures. However, in the case of numerical analysis for complex structures with damping materials, substantial errors can be generated by the absence of an exact damping model. Thus experimental model analysis is necessary for the verification of a numerical analysis for complex structures. In this research, vibration experiments are conducted in order to ascertain the vibration properties of cantilever beam attached damping materials. First, an initial value is obtained by using a direct linear method. Next, based on this initial value, the exact modal parameters of the cantilever beam are obtained by using the Newton-Raphson method.
Vibration-Based Damage Monitoring in Model Plate-Girder Bridges under Uncertain Temperature Conditions
Park, Jae-Hyung ; Hong, Dong-Soo ; Cho, Hyun-Man ; Kim, Jeong-Tae ;
Journal of Ocean Engineering and Technology, volume 22, issue 1, 2008, Pages 75~82
A vibration-based damage-monitoring scheme is proposed that would generate an alarm showing the occurrence and location of damage under temperature-induced uncertainty conditions. Experiments on a model plate-girder bridge are described, for which a set of modal parameters was measured under uncertain temperature conditions. A damage-alarming model is formulated to statistically identify the occurrence of damage by recognizing the patterns of damage-driven changes in the natural frequencies of the test structure and by distinguishing temperature-induced off-limits. A damage index method based on the concept of modal strain energy is implemented in the test structure to predict the location of damage. In order to adjust for the temperature-induced changes in the natural frequencies that are used for damage detection, a set of empirical frequency correction formulas is analyzed from the relationship between the temperature and frequency ratio.