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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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Numerical Analysis of Hydrodynamic Characteristics for Various Types of Jack-up Legs
Kim, Ji-Seok ; Park, Min-Su ; Koo, Weoncheol ;
Journal of Ocean Engineering and Technology, volume 28, issue 5, 2014, Pages 371~377
DOI : 10.5574/KSOE.2014.28.5.371
In this study, the hydrodynamic characteristics of various types of jack-up legs for a wind turbine installation vessel were analyzed. Using the modified Morison equation, the wave and current excitation forces on the jack-up legs were calculated. A modal analysis was performed to predict the dynamic responses for various types of jack-up legs. The Newmark-beta time integration scheme was used to solve the equation of motion in waves in the time domain. The maximum displacement and maximum bending stress were computed for four different types of legs, and their results were compared to select an optimum leg type. Finally, a six-leg jack-up rig with the selected optimal legs was modeled, and its natural period and hydrodynamic behaviors were evaluated.
Numerical Study of Current and Wind Forces Acting on Two Floating Bodies in Tandem Configuration
Hong, Jang-Pyo ; Nam, Bo Woo ; Yoon, Kyoung-Won ; Kim, Young-Sik ; Sung, Hong-Gun ;
Journal of Ocean Engineering and Technology, volume 28, issue 5, 2014, Pages 378~386
DOI : 10.5574/KSOE.2014.28.5.378
In this study, the characteristics of the current and wind forces acting on two floating bodies were numerically investigated using a commercial CFD software, STAR-CCM+. In the numerical analyses, LNGC was located right behind FSRU under uniform current or wind conditions. Steady calculations were carried out using a Reynolds averaged Navier-Stokes (RANS) solver and the realized k-epsilon model. First, the current coefficients of FSRU based only the CFD were compared with the model test data. Through this comparison, the present numerical models and mesh systems were indirectly verified. Next, computations for FSRU and LNGC in a uniform current were performed using different relative positions. It was found that the current coefficients were great affected by the longitudinal positions. Finally, the wind forces acting on FSRU and LNGC in tandem configurations were studied. The focus was on the shielding effects due to the aerodynamic interactions between FSRU and LNGC.
Numerical Study on Designing Truncated Mooring Lines for FPSO Stability Analysis
Kim, Yun-Ho ; Cho, Seok-Kyu ; Sung, Hong-Gun ; Seo, Jang-Hoon ; Suh, Yong-Suk ;
Journal of Ocean Engineering and Technology, volume 28, issue 5, 2014, Pages 387~395
DOI : 10.5574/KSOE.2014.28.5.387
In this paper, a numerical analysis for an internal turret moored vessel located at a 400-m water depth is conducted. The target vessel has an internal turret that is located at the 0.2 Lpp position from the fore-side, with
complex mooring lines installed around the turret circumference. To investigate the motion response of the vessel and the structural reliability of the lines, model tests were conducted. The KRISO ocean basin has a water depth of 3.2 m, which represents 192m using a scaling of 1:60. In order to precisely represent the real-scale condition, equivalent mooring lines needed to be designed. Truncated mooring lines were designed to supplement the restriction of the flume's water depth and increase the reliability of the model testing. These truncated mooring lines were composed of two different chains in order to match the pre-tension, simultaneously restoring the curve and variation in the effective line tension. The static similarities were compared using a static pull-out test and free decaying test, and the dynamic similarities were matched via a regular wave test and combined environments test. Consequently, the designed truncated mooring system could represent the prototype mooring system relatively well in the aspects of kinematics and dynamics.
Study on Prediction Method for Spring-Induced Tension Responses of TLP
Kim, Taeyoung ; Kim, Yonghwan ;
Journal of Ocean Engineering and Technology, volume 28, issue 5, 2014, Pages 396~403
DOI : 10.5574/KSOE.2014.28.5.396
This paper considered the prediction of the tension force in the design of a TLP tendon, particularly focusing on the springing problem. Springing is an important parameter that exerts a large tension in special cases. It is a nonlinear phenomenon and requires the 2nd-order wave loads to solve. In this paper, a new prediction method for springing and the resultant extreme tension on the tendon of a TLP is introduced. Using the 2nd-order response function computed using the commercial program WADAM, the probability density function of the 2nd-order tension is obtained from an eigenvalue analysis using a quadratic transfer function and sea spectra. A new method is then suggested to predict the extreme tension loads with respect to the number of occurrences. It is shown that the PDF suggested in this study properly predicts the extreme tension in comparison with the time histories of the 2nd-order tension. The expected tension force is larger than that from a linear analysis in the same time windows. This supports the use of the present method to predict the tension due to springing.
Layout Optimization of FPSO Topside High Pressure Equipment Considering Fire Accidents with Wind Direction
Bae, Jeong-Hoon ; Jeong, Yeon-Uk ; Shin, Sung-Chul ; Kim, Soo-Young ;
Journal of Ocean Engineering and Technology, volume 28, issue 5, 2014, Pages 404~410
DOI : 10.5574/KSOE.2014.28.5.404
The purpose of this study was to find the optimal arrangement of FPSO equipment in a module while considering the economic value and fire risk. We estimated the economic value using the pipe connections and pump installation cost in an HP (high pressure) gas compression module. The equipment risks were also analyzed using fire scenarios based on historical data. To consider the wind effect during a fire accident, fuzzy modeling was applied to improve the accuracy of the analysis. The objective functions consisted of the economic value and fire risk, and the constraints were the equipment maintenance and weight balance of the module. We generated a Pareto-optimal front group using a multi-objective GA (genetic algorithm) and suggested an equipment arrangement method that included the opinions of the designer.
Parametric Study for Helideck Design using Finite Element Analysis
Park, Doo-Hwan ; Park, Yong-Jun ; Park, Joo-Sin ; Kim, Jeong-Hyeon ; Kweon, Byoung-Cheol ; Lee, Jae-Myung ;
Journal of Ocean Engineering and Technology, volume 28, issue 5, 2014, Pages 411~422
DOI : 10.5574/KSOE.2014.28.5.411
A helideck is a very valuable offshore structure for the take-off and landing of a helicopter. In order to design a helideck, the design parameters and various loads defined by the regulations related to the design of a helideck should be applied. In this study, a risk analysis was performed based on the helicopter accidents for seven years, and the frequency and possible reasons for accidents involving helidecks were investigated. In addition, a finite element analysis of a steel helideck mounted on the upper deck of a ship (shuttle tanker) was performed with the load that should be considered when designing a helideck. Based on the results, a parametric study of helideck was carried out by applying a variety of design parameters, and an improved helideck design was presented. This improved helideck reduced the steel used by up to 24% compared to the initial helideck design, and the results of a finite element analysis were analyzed and compared with those of the initial analysis.
Study on Estimation of Local Ice Pressures Considering Contact Area with Sea Ice
Kim, Tae-Wook ; Lee, Tak-Kee ;
Journal of Ocean Engineering and Technology, volume 28, issue 5, 2014, Pages 423~428
DOI : 10.5574/KSOE.2014.28.5.423
Ice loads may be conveniently categorized as local ice loads and global ice loads. Local ice loads are often defined as ice pressures acting on local areas of shell plates and stiffeners. Therefore, local ice loads are defined in all ice class rules. However, directly measuring the local ice pressure using the actual ice class vessel is a very difficult task because appropriate instruments for direct measurement must be installed on the outer hull, and they are easily damaged by direct ice contacts/impacts. This paper focuses on the estimation of the local ice pressure using the data obtained from icebreaking tests in the Arctic sea in 2010 using the Korean icebreaking research vessel (IBRV) ARAON. When she contacted the sea ice, the local deformation of the side shell was measured by the strain gauges attached to the inside of the shell. Simultaneously, the contact area between the side shell and sea ice is investigated by analyzing the distribution of the measured strain data. Finally, the ice pressures for different contact areas are estimated by performing a structural analysis.
Investigation of Target Echoes in Multi-static SONAR System - Part I : Design for Acoustic Measuring System
Bae, Ho Seuk ; Ji, Yoon Hee ; Kim, Wan-Jin ; Kim, Woo-Shik ; Kim, Jea Soo ; Yun, Sung-Ung ;
Journal of Ocean Engineering and Technology, volume 28, issue 5, 2014, Pages 429~439
DOI : 10.5574/KSOE.2014.28.5.429
The target echoes contain information on the target such as the orientation, kinematics, and internal structure, as well as the external geometrical shape of the target. In addition, the pattern of the target echoes depends on the arrangement of the transmitters and receivers in space. Therefore, the study of the target echoes in a multi-static SONAR system can be useful for detecting and tracking submerged objects using an underwater surveillance system. For this purpose, an acoustic measuring system for multi-static target echoes was designed and tested in an acoustic water tank. Some preliminary data are presented and discussed.
Investigation of Target Echoes in Multi-static SONAR system - Part II : Numerical Modeling with Experimental Verification
Ji, Yoon Hee ; Bae, Ho Seuk ; Byun, Gi-Hoon ; Kim, Jea Soo ; Kim, Woo-Shik ; Park, Sang-Yoon ;
Journal of Ocean Engineering and Technology, volume 28, issue 5, 2014, Pages 440~451
DOI : 10.5574/KSOE.2014.28.5.440
A multi-static SONAR system consists of the transmitters and receivers separately in space. The active target echoes are received along the transmitter-target-receiver path and depend on the shape and aspect angle of the submerged objects at each receiver. Thus, the target echo algorithm used with a mono-static system, in which the transmitter and receiver are located at the same position, has limits in simulating the target echoes for a multi-static SONAR system. In this paper, a target echo modeling procedure for a 3D submerged object in space is described based on the Kirchhoff approximation, and the SONAR system is extended to a multi-static SONAR system. The scattered field from external structures is calculated on the visible surfaces, which is determined based on the locations of the transmitter and receiver. A series of experiments in an acoustic water tank was conducted to measure the target echoes from scaled targets with a single transmitter and 16 receivers. Finally, the numerical results were compared with experimental results and shown to be useful for simulating the target echoes/target strength in a multi-static SONAR system.
Friction Stir Welding Analysis Based on Equivalent Strain Method using Neural Networks
Kang, Sung-Wook ; Jang, Beom-Seon ;
Journal of Ocean Engineering and Technology, volume 28, issue 5, 2014, Pages 452~465
DOI : 10.5574/KSOE.2014.28.5.452
The application of friction stir welding (FSW) technology has been extended to all industries, including shipbuilding. A heat transfer analysis evaluates the weldability of a welded work piece, and elasto-plastic analysis predicts the residual stress and deformation after welding. A thermal elasto-plastic analysis based on the heat transfer analysis results is most frequently used today. However, its application to large objects such as offshore structures and hulls is impractical owing to its long computational time. This paper proposes a new method, namely an equivalent strain method using the inherent strain, to overcome the disadvantages of the extended analysis time. In the present study, a residual stress analysis of FSW was performed using this equivalent strain method. Additionally, in order to reflect the external constraints in FSW, the reaction force was predicted using a neural network, Finally, the approach was verified by comparing the experimental results and thermal elasto-plastic analysis results for the calculated residual stress distribution.
Dynamic Modeling and Motion Analysis of Unmanned Underwater Gliders with Mass Shifter Unit and Buoyancy Engine
Kim, Donghee ; Lee, Sang Seob ; Choi, Hyeung Sik ; Kim, Joon Young ; Lee, Shinje ; Lee, Yong Kuk ;
Journal of Ocean Engineering and Technology, volume 28, issue 5, 2014, Pages 466~473
DOI : 10.5574/KSOE.2014.28.5.466
Underwater gliders do not have any external propulsion systems that can generate and control their motion. Generally, underwater gliders would obtain a propulsive force through the lift force generated on the body by a fluid. Underwater gliders should be equipped with mechanisms that can induce heave and pitch motions. In this study, an inner movable and rotatable mass mechanism was proposed to generate the pitch and roll motions of an underwater glider. In addition, a buoyancy control unit was presented to adjust the displacement of the underwater glider. The buoyancy control unit could generate the heave motion of the underwater glider. In order to analyze the underwater dynamic behavior of this system, nonlinear 6-DOF dynamic equations that included mathematical models of the inner movable mass and buoyancy control unit were derived. Only kinematic characteristics such as the location of the inner movable mass and the piston position of the buoyancy control unit were considered because the velocities of these systems are very slow. The effectiveness of the proposed dynamic modeling was verified through sawtooth and spiraling motion simulations.
Wave Power Extraction by Strip Array of Multiple Buoys
Cho, Il-Hyoung ;
Journal of Ocean Engineering and Technology, volume 28, issue 5, 2014, Pages 474~483
DOI : 10.5574/KSOE.2014.28.5.474
The majority of existing WECs (wave energy converters) are designed to achieve maximum power at a resonance condition. In the case of a single WEC, its size must be large enough for tuning, and it has high efficiency only within a limited frequency band. Recently, wave power extraction by deploying many small buoys in a compact array has been studied under the assumption that the buoy's size and separation distance are much smaller than the water depth, wave length, and size of the array. A boundary value problem involving the macro-scale boundary condition on the mean surface covered by an infinite strip of buoys is solved using the eigenfunction expansion method. The energy extraction efficiency (
are the reflection and transmission coefficients for a strip array of buoys, is assessed for various combinations of packing ratio, strip width, and PTO damping coefficient.