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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 29, Issue 6 - Dec 2015
Volume 29, Issue 5 - Oct 2015
Volume 29, Issue 4 - Aug 2015
Volume 29, Issue 3 - Jun 2015
Volume 29, Issue 2 - Apr 2015
Volume 29, Issue 1 - Feb 2015
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Sloshing Analysis in Rectangular Tank with Porous Baffle
Cho, IL-Hyoung ;
Journal of Ocean Engineering and Technology, volume 29, issue 1, 2015, Pages 1~8
DOI : 10.5574/KSOE.2015.29.1.001
An analytical model of liquid sloshing is developed to consider the energy-loss effect through a partially submerged porous baffle in a horizontally oscillating rectangular tank. The nonlinear boundary condition at the porous baffle is derived to accurately capture both the added inertia effects and the energy-loss effects from an equivalent non-linear drag law. Using the eigenfunction expansion method, the horizontal hydrodynamic force (added mass, damping coefficient) on both the wall and baffle induced by the fluid motion is assessed for various combinations of porosity, submergence depth, and the tank`s motion amplitude. It is found that a negative value for the added mass and a sharp peak in the damping curve occur near the resonant frequencies. In particular, the hydrodynamic force and free surface amplitude can be largely reduced by installing the proper porous baffle in a tank. The optimal porosity of a porous baffle is near P
Reynolds number effects on flow over twisted offshore structure with drag reduction and vortex suppression
Jung, Jae-Hwan ; Yoon, Hyun-Sik ;
Journal of Ocean Engineering and Technology, volume 29, issue 1, 2015, Pages 9~15
DOI : 10.5574/KSOE.2015.29.1.009
We investigated the Reynolds number effects on the flow over a twisted offshore structure in the range of 3×10
≤ Re ≤ 1 × 10
. To analyze the effect of the twisted surface treatment, a large eddy simulation (LES) with a dynamic subgrid model was employed. A simulation of the cylindrical structure was also carried out to compare the results with those of the twisted offshore structure. As Re increased, the mean drag and lift coefficient of the twisted offshore structure increased with the same tendency as those of the cylindrical structure. However, the increases in the mean drag and lift coefficient of the twisted offshore structure were much smaller than those of the cylindrical structure. Furthermore, elongated shear layer and suppressed vortex shedding from the twisted offshore structure occurred compared to those of the cylindrical cylinder, resulting in a drag reduction and suppression of the vortex-induced vibration (VIV). In particular, the twisted offshore structure achieved a significant reduction of over 96% in VIV compared with that of the cylindrical structure, regardless of increasing Re. As a result, we concluded that the twisted offshore structure effectively controlled the flow structures with reductions in the drag and VIV compared with the cylindrical structure, irrespective of increasing Re.
Structural Analysis of Deepwater Steel Catenary Riser using OrcaFlex
Park, Kyu-Sik ; Choi, Han-Suk ; Kim, Do-Kyun ; Yu, Su-Young ; Kang, Soo-Chang ;
Journal of Ocean Engineering and Technology, volume 29, issue 1, 2015, Pages 16~27
DOI : 10.5574/KSOE.2015.29.1.016
The design challenges when attempting to obtain sufficient strength for a deepwater steel catenary riser (SCR) include high stress near the hang-off location, an elevated beam-column buckling load due to the effective compression in the touchdown zone (TDZ), and increased stress and low-cycle fatigue damage in the TDZ. Therefore, a systematic strength analysis is required for the proper design of an SCR. However, deepwater SCR analysis is a new research area. Thus, the objective of this study was to develop an overall analysis procedure for a deepwater SCR. The structural behavior of a deepwater SCR under various environmental loading conditions was investigated, and a sensitivity analysis was conducted with respect to various parameters such as the SCR weight, weight of the internal contents, hang-off angle (HOA), and vertical soil stiffness. Based on a deepwater SCR design example, it was found that the maximum stress of an SCR occurred at a hang-off location under parallel loading direction with respect to the riser plane, except for a wave dominant dynamic survival loading condition. Furthermore, the tensile stress governed the total stress of the SCRs, whereas the bending stress governed the total stress at the TDZ. The weight of the SCR and internal contents affected the maximum stress of the SCR more than the HOA and vertical soil stiffness, because the weight of the SCR, including the internal contents, was directly related to its tensile stress.
A Comparative Study on Ice Load Characteristics between General and Ice-breaking Operations in Ice-covered Waters
Lee, Min-Woo ; Kwon, Yong-Hyeon ; Rim, Chae-Whan ; Lee, Tak-Kee ;
Journal of Ocean Engineering and Technology, volume 29, issue 1, 2015, Pages 28~33
DOI : 10.5574/KSOE.2015.29.1.028
The icebreaking research vessel ARAON had her second ice trial in the Arctic Ocean from July 16 to August 12, 2010. In this study, the ice loads measured during the “general” operation and “ice breaking” operation in ice-covered waters were analyzed and compared. Whereas the “general” operation stands for the voyage in the water partially covered by ice, the “ice breaking” operation involved substantial ice floes for the ice breaking performance test. Based on the measured data, comparisons of the relationship between the ship speed and ice load, and between the locations of strain gauges and ice loads were investigated. Peak stresses higher than 20 MPa were found. The longitudinal and vertical correlations between the measurement location and ice load were analyzed, and the probability of peak stress was calculated. As a result, the probability function for higher ice loads during both operation modes was expressed in an exponential and power forms.
Design of High Speed Tensile Test Machine for Flow Stress under Intermediate Strain Rate Condition
Choung, Joonmo ; Yoon, Sung-Won ; Park, Sung-Ju ; Kim, Younghun ;
Journal of Ocean Engineering and Technology, volume 29, issue 1, 2015, Pages 34~44
DOI : 10.5574/KSOE.2015.29.1.034
A hydraulic tensile test machine (HSTM) is one of the devices used to obtain the flow stress of a material during high-speed elongation. This paper first describes some features of a newly built HSTM. The improvement histories of the upper and lower jigs, which are the most vital parts of the HSTM, are also presented. We have frequently witnessed test failures with 1st generation jigs and specimens due to slip between the jig and specimen. 2nd generation jigs provide more stable test results, but the use of a longer upper jig induces excessive vibration and consequently makes it difficult to attach an environment chamber. 3rd generation jigs have some advances in terms of the symmetric fastening between the upper jig and specimen, as well as an exemption from direct contact between the lower jig and specimen. The performance of an environment chamber is verified by high and low temperature tests. A high-speed displacement measurement system is introduced based on a high-speed camera and motion-tracking software with aid of a surface grid device for the specimen.
Study on Hot Spot Stress Calculation for Welded Joints using 3D Solid Finite Elements
Oh, Jung-Sik ; Kim, Yooil ; Jeon, Seok-Hee ;
Journal of Ocean Engineering and Technology, volume 29, issue 1, 2015, Pages 45~55
DOI : 10.5574/KSOE.2015.29.1.045
Because of the high stress concentration near the toe of a welded joint, the calculation of local stress using the finite element method which is relevant to the fatigue strength of the weld toe crack, is a challenging task. This is mainly caused by the sensitivity of finite element analysis, which usually occurs near the area of a dramatically changing stress field. This paper presents a novel numerical method through which a less mesh-sensitive local stress calculation can be achieved based on the 3D solid finite element, strictly sticking to the original definition of hot spot stress. In order to achieve the goal, a traction stress, defined at 0.5t and 1.5t away from the weld toe, was calculated using either a force-equivalent or work-equivalent approach, both of which are based on the internal nodal forces on the imaginary cut planes. In the force-equivalent approach, the traction stress on the imaginary cut plane was calculated using the simple force and moment equilibrium, whereas the equivalence of the work done by both the nodal forces and linearized traction stress was employed in the work-equivalent approach. In order to confirm the validity of the proposed method, five typical welded joints widely used in ships and offshore structures were analyzed using five different solid element types and four different mesh sizes. Finally, the performance of the proposed method was compared with that of the traditionally used surface stress extrapolation method. It turned out that the sensitivity of the hot spot stress for the analyzed typical welded joints obtained from the proposed method outperformed the traditional extrapolation method by far.
Shape Optimization of Grinding Spindle using Response Surface Analysis
Bae, Gyeong-Tae ; Kim, Gwi-Nam ; Choi, Boo-Young ; Moon, Hong-Man ; Noh, Jung-Pil ; Huh, Sun-Chul ;
Journal of Ocean Engineering and Technology, volume 29, issue 1, 2015, Pages 56~61
DOI : 10.5574/KSOE.2015.29.1.056
To improve the accuracy of a machine, research needs to be conducted on the relationship between the output variables and design variables of a spindle-shaped part from the thermal and static viewpoints. Therefore, research was carried out by examining the correlation of each variable to find the optimum conditions. Moreover, DOE (design of experiments) was extensively used. The model used in this study was a grinding spindle to which a hydrostatic bearing was applied. This model was used in a preliminary analysis based on the experimental results of the previous studies. The influences of the output variables and design variables were compared through a main effect analysis. Generated response surfaces were applied to the Kriging model. To optimize the model, a screening method was selected. In comparison with the initial model, the deformation of the optimized model designed by DOE decreased by 4.1 μm, while the thermal deformation decreased by 1.2 μm. Therefore, it was efficient to design a spindle-shaped part through DOE to improve the accuracy of the machine.
Effects of Roughness and Vertical Wall Factors on Wave Overtopping in Rubble Mound Breakwaters in Busan Yacht Harbor
Dodaran, Asgar Ahadpour ; Park, Sang Kil ; Kim, Kook Hyun ; Shahmirzadi, Mohammad Ebrahim Meshkati ; Park, Hong Bum ;
Journal of Ocean Engineering and Technology, volume 29, issue 1, 2015, Pages 62~69
DOI : 10.5574/KSOE.2015.29.1.062
Coastlines are protected by breakwater structures against the erosion of sand or other materials along beaches due to wave action. This research examined the use of physical modeling to determine the effects of the tetrapod size and vertical walls of a rubble mound on the volume of wave overtopping under irregular wave conditions in coastal areas in Busan Yacht Harbor. In this analysis model, the structures were studied using irregular waves and the JONSWAP wave energy spectrum. To understand the effects of the tetrapod size and heights of the vertical wall, the study considered vertical walls of 0, 1.78, 6.83, and 9.33 cm with armor double layered material tetrapods of 8, 12, 16, and 20 tons. An extensive number of experiments covering a relatively large range of variables enabled a comprehensive discussion. First, in the presence of a short vertical wall, the water level played a key role in the overtopping discharge. In such circumstances, the values of the wave overtopping discharge decreased with increasing freeboard size. In the presence of a tall freeboard and middle, the value of the wave overtopping discharge was equally influenced by the vertical wall factor. Moreover, the tetrapod size decreased by an increase in the vertical wall factor, and relationship between them resulted in a short wall height. From an engineering point of view, considering a small water level may allow the choice of a shorter vertical wall, which would ultimately provide a more economical design.
Collision Behavior Evaluation of Flexible Concrete Mattress Depending on Material Models
Ryu, Yeon-Sun ; Cho, Hyun-Man ; Kim, Seo-Hyun ;
Journal of Ocean Engineering and Technology, volume 29, issue 1, 2015, Pages 70~77
DOI : 10.5574/KSOE.2015.29.1.070
The purpose of this study was to provide fundamental data for an anchor collision simulation of an FCM (flexible concrete mattress). Numerical material models (elastic-perfectly plastic model, Drucker-Prager model, and RHT concrete model) were compared. ANSYS Explicit Dynamics was used for collision analyses. An FE model was used for the anchor, FCM, andreinforcement bars. The results showed that the behavior of the FCM was verydifferent that those ofthe material models. In particular, the effect of the pressure dependent strength was most noticeable among the properties of concrete.
Bearing Characteristics of Waste Fishing Net - Reinforced Sand With Different Embedded Depths
Ha, Yong-Soo ; Kim, Yun-Tae ;
Journal of Ocean Engineering and Technology, volume 29, issue 1, 2015, Pages 78~84
DOI : 10.5574/KSOE.2015.29.1.078
Geosynthetics such as geogrids or geotextiles have been widely used to improve the bearing capacity of soft ground. This study investigated the California bearing ratio (CBR) of waste fishing net (WFN)-reinforced sand. CBR tests were carried out to evaluate the improvement in the bearing capacity of WFN-reinforced sand with different embedded depths. The experimental results indicated that the CBR increased as the embedded depth of the WFN decreased. The bearing capacity ratio (BCR) is the ratio of the bearing capacity of reinforced ground to that of unreinforced ground. The BCR at the penetration depths of 2.5 mm, 5 mm, and the peak point decreased with an increase in the embedded depth.
Study on Cryogenic Mechanical Behavior of 6000 Series Aluminum Alloys
Park, Doo-Hwan ; Kim, Jeong-Hyeon ; Choi, Sung-Woong ; Lee, Jae-Myung ;
Journal of Ocean Engineering and Technology, volume 29, issue 1, 2015, Pages 85~93
DOI : 10.5574/KSOE.2015.29.1.085
In this study, tensile tests were performed on aluminum alloys (AA6061 and AA6082) to investigate their mechanical behaviors at cryogenic temperatures. The temperature was varied from 110 K up to 293 K, and quasi-static strain rates of 10
were taken into account for the tests. The experimental results were analyzed to find the dependence on the temperature, strain rate, and fractured surfaces. As a result, it was found that the strength and elongation of the aluminum alloys were improved when the temperature was decreased. In addition, it was confirmed that the mechanical behaviors of the aluminum alloys were not dependant on the strain rate. Under a tensile load, two types of fractures were seen in the aluminum alloys: cup-cone (AA6061) and shear (AA6082).
Fabrication of Piezoelectric PZT Thick Film by Sol-gel Process
Park, Jong-whan ; Bang, Kook-soo ; Park, Chan ;
Journal of Ocean Engineering and Technology, volume 29, issue 1, 2015, Pages 94~99
DOI : 10.5574/KSOE.2015.29.1.094
Lead zirconate titanate (PZT) thick films with thicknesses of ㎛ were fabricated on silicon substrates using an aerosol deposition method. A PZT powder solution was prepared using a sol-gel process. The average diameters (d50) obtained were 1.67, 1.98, and 2.40μm when the pyrolysis temperatures were 300℃, 350℃, and 450℃ respectively. The as-deposited film had a uniform microstructure without any cracks or pores. The as-deposited films on silicon were annealed at a temperature of 700℃. The 20-㎛-thick PZT film showed good adherence between the PZT film and substrate, with no tearing observed in the conventional solid phase process. This was probably because the presence of pores produced from organic residue during annealing relieved the residual stresses in the deposited film.
Computational Analysis of Structural Behavior of Subsea Pipelines with Local Corrosion
Choi, Kwang-Ho ; Lee, Chi-Seung ; Ryu, Dong-Man ; Koo, Bon-Yong ; Song, Joon-Kyu ; Lee, Jae-Myung ;
Journal of Ocean Engineering and Technology, volume 29, issue 1, 2015, Pages 100~110
DOI : 10.5574/KSOE.2015.29.1.100
To meet the increasing demand for energy around the world, offshore and subsea energy development is constantly being conducted. This trend is accompanied by an increasing demand for pipeline installation, which brings numerous problems, including those related to accessibility, high pressure, and corrosion. Among these, corrosion is a primary factor in pipeline fractures, and can cause severe environmental and industrial damage. Hence, accurate corrosion assessment for corroded pipelines is very important. For this reason, the present study investigated the mechanical behavior of an idealized corroded subsea pipeline with an internal/external pressure load using the commercial FEA code ABAQUS. Then, the analysis result was compared with corrosion assessment codes such as ASME B31G, DNV RP F101, ABS. Finally, a fitness-for-service assessment was conducted.