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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 20, Issue 6 - Dec 2006
Volume 20, Issue 5 - Oct 2006
Volume 20, Issue 4 - Aug 2006
Volume 20, Issue 3 - Jun 2006
Volume 20, Issue 2 - Apr 2006
Volume 20, Issue 1 - Feb 2006
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Effect of Surface Condition and Corrosion-Induced Defect on Guided Wave Propagation in Reinforced Concrete
Na, Won-Bae ; Kang, Dong-Baek ;
Journal of Ocean Engineering and Technology, volume 20, issue 6, 2006, Pages 1~6
Corrosion of reinforcing steel bars is a major concern for ocean engineers when reinforced concrete structures are exposed to marine environments. Evaluating the degree of corrosion and corrosion-induced defects is extremely necessary to pursue a proper retrofit or rehabilitation plan for reinforced concrete structures. A promising inspection should be carried out for the evaluation, otherwise the retrofit or rehabilitation process would be useless. Nowadays, ultrasonic guided wave-based inspection techniques become quite promising for the inspection, mainly because of their long-range propagation capability and their sensitivity to different types of defects or conditions. Evaluating haw the guided waves response to the different types of defects or conditions is quite challenging and important. This study shows how surface conditions of reinforcing bars and a corrosion-induced defect, separation, affect guided wave propagation in reinforced concrete. Experiments and associated signal analysis show the sensitivity of guided waves to the surface conditions, as well as the amounts of separation at the interface between. concrete and steel bar.
Controller Design for an Autonomous Underwater Vehicle Using Estimated Hydrodynamic Coefficients
Kim, Joon-Young ;
Journal of Ocean Engineering and Technology, volume 20, issue 6, 2006, Pages 7~17
Depth and heading control of an AUV are considered to follow the predetermined depth and heading angle. The proposed control algorithm is designed. based on a sliding mode control using estimated hydrodynamic coefficients. The hydrodynamic coefficients are estimated with conventional nonlinear observer techniques, such as sliding mode observer and extended Kalman filter. By using the estimated coefficients, a sliding mode controller is constructed for the combined diving and steering maneuver. The simulation results of the proposed control system are compared with those of control system with true coefficients. This paper demonstrates the proposed control system, discusses the mechanisms that make the system stable and follows the desired depth and heading angle, accurately, in the presence of parameter uncertainty.
Development of Digital DC-ARC Welding Machine
Kim, Hak-Kyeong ; Park, Ba-Da ;
Journal of Ocean Engineering and Technology, volume 20, issue 6, 2006, Pages 18~23
This paper introduces the results of the development of a new mobile digital DC-arc welding machine (DDWM). A simple PI controller is applied to the DDWM to control the output welding current that is tracking the constant setting current. Furthermore, a hot-start function, an anti-stuck function, a standby mode and an intelligential circuit breaker (ICB) are included in the DDWM. The DDWM increases welding quality and saves more power energy than a conventional welding machine. The DDWM is changed from ready mode into the standby mode, automatically, after 2-minute intervals from this unload start. Then, the DDWM is changed into ready mode, automatically, since it is reused for welding. Moreover, the DDWM increases welding quality, productivity and reduces costs of welding. So, the DDWM can make a considerable contribution to the mobile welding industries. The effectiveness of the DDWM was proven by the experimental results.
Estimation of Hydrodynamic Coefficients for an AUV Using Nonlinear Observers
Kim, Joon-Young ;
Journal of Ocean Engineering and Technology, volume 20, issue 6, 2006, Pages 24~34
Hydrodynamic coefficients strongly affect the dynamic performance of an AUV. Thus, it is important to know the true values of these coefficients, in order to accurately simulate the AUV's dynamic performance. Although these coefficients are generally obtained experimentally, such as through the PMM test, the measured values are not completely reliable because of experimental difficulties and errors. Another approach, by which these coefficients can be obtained, is the observer method, in which a model-based estimation algorithm estimates the coefficients. In this paper, the hydrodynamic coefficients are estimated using two nonlinear observers: a sliding mode observer and an extended Kalman filter. Their performances are evaluated in Matlab simulations, by comparing the estimated coefficients obtained from the two observer methods, with the experimental values as determined from the PMM test. A sliding mode controller is constructed for the diving and steering maneuver by using the estimated coefficients. It is demonstrated that the controller, applied with the estimated values, maintains the desired depth and path with sufficient accuracy.
A Numerical Study of Wave Transformation on a Permeable Structure Considering Porous Media Flow
Kim, In-Chul ;
Journal of Ocean Engineering and Technology, volume 20, issue 6, 2006, Pages 35~40
In recent years, there's been strong demand for seawalls that havea gentle slope and permeability that serveswater affinity and disaster prevention from wave attack. The aim of this study is to examine wave transformation, including wave run-up that propagates on the coastal structures. A numerical model based on the weak nonlinear dispersive Boussinesq equation, together with the unsteady nonlinear Darcy law for fluid motion in permeable layer, is developed. The applicability of this numerical model is examined through Deguchi and Moriwaki's hydraulic model test on the permeable slopes. From this study, it is found that the proposed numerical model can predict wave transformation and run-up on the gentle slope with a permeable layer, but can't show accurate results for slopes steeper than about 1:10.
Experimental Study on Flow Characteristics of Regular Wave Interacting with Rectangular Floating Structure Using PIV Technique
Jung, Kwang-Hyo ; Chun, Ho-Hwan ;
Journal of Ocean Engineering and Technology, volume 20, issue 6, 2006, Pages 41~53
This experimental study investigated the flow characteristics for regular waves passing a rectangular floating structure in a two-dimensional wave tank. The particle image velocimetry (PIV) was employed to obtain the velocity field in the vicinity of the structure. The phase average was used to extract the mean flow and turbulence property from repeated instantaneous PIV velocity profiles. The mean velocity field represented the vortex generation and evolution on both sides of the structure. The turbulence properties, including the turbulence length scale and the turbulent kinetic energy budget were investigated to characterize the flow interaction between the regular wave and the structure. The results shaw the vortex generated near the structure corners, which are known as the eddy-making damping or viscous damping. However, the vortex induced by the wave is longer than the roll natural period of the structure, which presents the phenomena opposing the roll damping effect; that is, the vortex may increase the roll motion under the wave condition longer than the roll natural period.
Spatiotemporal Changes of the Sand Barrier using Marine Charts Analysis in the Nakdong River Estuarine
Yoo, Chang-Ill ; Yoon, Han-Sam ; Ryu, Cheong-Ro ; Lee, In-Cheol ;
Journal of Ocean Engineering and Technology, volume 20, issue 6, 2006, Pages 54~60
This study discusses characteristic of spatiotemporal changes of the sand barrier in the Nakdong estuarine for the last century, focusing on geomarphologic evolution and mobility of sand barriers in the view of coastal engineering. The Nakdong estuarine, the research subject, has a complexly changing natural environment by interaction between ground and marine elements such as ocean wave, tidal current, sediment, etc. Moreover, recently, unnatural geomorphologic changes (e.g., seaside reclamation, new harbor construction, etc.) has been radically increased in this area with increasing desire for coastal development. Because of this, its sand barrier has developed quite unstable condition. Therefore, to identify the development process of geomorphologic changes in this area, required is a close examination on historical characteristics of spatiotemporal changes of the sand barrier in relation to surrounding seaside reclamation and physical environmental changes. This study, based on the marine charts published in between 1927 and 1995 year, analyzes the length and area of the sand barrier for the last hundred years, and investigates the cause of the changes by looking into the change of water depth for the last two years and doing ocean-physical site observations. In conclusion, the sand barrier of the Nakdong estuarine expands toward the open sea by
in annual average, maintaining a fixed distance of
, and its area is expected to increase about
annually. This is characterized by the wocean wave from the open sea and the discharge of Nakdong River.
Efficient Iterative Solvers for Modified Mild Slope Equation
Yoon, Jong-Tae ; Park, Seung-Min ;
Journal of Ocean Engineering and Technology, volume 20, issue 6, 2006, Pages 61~66
Two iterative solvers are applied to solve the modified mild slope equation. The elliptic formulation of the governing equation is selected for numerical treatment because it is partly suited for complex wave fields, like those encountered inside harbors. The requirement that the computational model should be capable of dealing with a large problem domain is addressed by implementing and testing two iterative solvers, which are based on the Stabilized Bi-Conjugate Gradient Method (BiCGSTAB) and Generalized Conjugate Gradient Method (GCGM). The characteristics of the solvers are compared, using the results for Berkhoff's shoal test, used widely as a benchmark in coastal modeling. It is shown that the GCGM algorithm has a better convergence rate than BiCGSTAB, and preconditioning of these algorithms gives more than half a reduction of computational cost.
Time-Domain Analysis of Nonlinear Wave-Making Problems by a Submerged Sphere Oscillating with Large Amplitude
Kim, Yong-Jig ; Ha, Young-Rok ;
Journal of Ocean Engineering and Technology, volume 20, issue 6, 2006, Pages 67~74
A high-order spectral/boundary-element method is newly adapted as an efficient numerical tool. This method is one of the most efficient numerical methods by which the nonlinear gravity waves can be simulated and hydrodynamic forces also can be calculated in time-domain. In this method, the velocity potential is expressed as the sum of surface potential and body potential. Then, surface potential is solved by using the high-order spectral method and body potential is solved by using the high-order boundary element method. By the combination of these two methods, the wave-making problems by a submerged sphere oscillating with large amplitude under the free~surface are solved in time-domain. Through the example calculations, nonlinear effects on free-surface profiles and hydrodynamic forces are shown and discussed.
The Safety Assessment of the Connecting Cable in Deep Water Unmanned Underwater Vehicle
Nho, In-Sik ; Choi, Byoung-Gy ; Lee, Jong-Moo ;
Journal of Ocean Engineering and Technology, volume 20, issue 6, 2006, Pages 75~81
In this study, the dynamic response of the umbilical cable in a deep-water unmanned underwater vehicle system was analyzed. In order to analyze the forces acting on the cable, the launcher and umbilical cable were modeled by the simple 1-D mass-spring system. Damping and dynamic analysis was carried out by a direct time integration scheme using the
method with inverse iteration procedure, considering the nonlinear drag forces acting on the launcher. The obtained results of the present study can be used for the design of connecting the structure of the launcher and cable of the UUV system.
Optimum Distance between Multiple Submerged Breakwaters for Wave Screening Performance Enhancement
Cho, Won-Chul ;
Journal of Ocean Engineering and Technology, volume 20, issue 6, 2006, Pages 82~87
Numerical analysis is performed on the wave transmission coefficient of various crown widths of the double-submerged breakwater and the triple-submerged breakwater, varying the distance between submerged breakwaters. The finite element method is used, and the fluid motion is considered as linearized two-dimensional potential flow. In case of the double- and triple-submerged breakwaters, as the width of submerged breakwater increases, the minimum wave transmission coefficient decreases and the wave period at which the minimum wave transmission coefficient occurs moves to a longer wave period the distance between submerged breakwaters at which the minimum wave transmission coefficient occurs becomes larger.
Fatigue Behavior of Offshore Topside Structure
Im, Sung-Woo ; Park, Kwan-Kyu ; Park, Ro-Sik ; Cho, Won-Chul ; Jo, Chul-Hee ;
Journal of Ocean Engineering and Technology, volume 20, issue 6, 2006, Pages 88~92
Large-scale model tests of welded topside joints were carried out to observe the fatigue behavior of API 2W Gr.50 steel produced by POSCO. The fatigue crack behaviors for various loading conditions were measured and investigated around the critical joint sections. The experimental results have been verified with numerical approaches and also compared with the AWS D1.1 and DnV RP-C203 design curves. The large-scale experiment models were fabricated, based on the actual operating east area fixed platform. The dimensions of the models were slightly modified to accommodate the test facilities and capacities. The fatigue test was carried out having
of T1=705.6kN, T2=749.7kN and T3=793.8kN. The three specimens were statically loaded 20 times, with various loadings of about 50kN intervalsbetween the maximum and minimum loads required in the fatigue tests. This loading removed the residual stress in the specimen before the fatigue tests. The topside joint crack was initiated from the brace heel, where the maximum tensile stress occurred. The API 2W Gr.50 steel satisfied the AWS D1.1 detail category C and DnV RP-C203 detail category F
Dynamic Analysis of Underwater Tracked Vehicle on Extremely Soft Soil by Using Euler Parameters
Kim, Hyung-Woo ; Hong, Sup ; Choi, Jong-Su ; Yeu, Tae-Kyeong ;
Journal of Ocean Engineering and Technology, volume 20, issue 6, 2006, Pages 93~100
This paper is concerned with the dynamic analysis of an underwater tracked vehicle, operating on extremely soft soil of the deep-seafloor. The vehicle is assumed as a rigid-body with 6-dof. The orientation of the vehicle is defined by four Euler parameters. To solve the motion equations of the vehicle, the Newmark numerical integrator is used in the incremental-iterative algorithm. The normalization constraint of Euler parameters is satisfied by using of a sequential updating method. The hydrodynamic force and moment are included in the tracked vehicle's dynamics. The hydrodynamic effects on the performance of tracked vehicles are investigated through numerical simulations.
Hydroelastic Response Analysis of Very Large Floating Structures Including the Hydrodynamic Forces due to Elastic Motions in Waves
Kim, Chuel-Hyun ; Lee, Chang-Ho ; Lee, Seung-Chul ; Goo, Ja-Sam ;
Journal of Ocean Engineering and Technology, volume 20, issue 6, 2006, Pages 101~107
Recently, with the increase in requirements for marine development, a marine urbanism is being visualized, with more and more huge-scale structures at the scope of the ocean space utilization. In particular, a pontoon-type structure has attracted attention, since The Floating Structures Association of Japan proposed a new concept as the most suitable one of floating airports. The Very Lage Floating Structure (VLFS) is considered a flexible structure, for a quite large length-to-breadth ratio and its geometrical flexibility. The main objective of this study is to makean exact and convenient prediction about the hydro-elastic response on very large offshore structures in waves. The numerical approach for the hydro-elastic responses is based on the combination of the three dimensional source distribution method and the dynamic response analysis method, which assumed a dividing pontoon type structure, as many rigid bodies connected elastic beam elements. The established hydo-elastic theory was applied to the radiation forces caused by motions of a whole structure, formulated using the global coordinate system, which has the origin at the center of the structure. However, in this paper, we took radiation forces, occurred by individual motions of floating bodies, into consideration. The calculated results show good agreement with the experimental and calculated results by Yago.
Benefit Cost Analysis on Beach Restoration Work Using the Contingent Valuation Method
Kim, Kyu-Han ; Park, Chan-Ik ; Park, Jung-Wook ;
Journal of Ocean Engineering and Technology, volume 20, issue 6, 2006, Pages 108~113
For the past scores of years, our country has driven its land development toward economic growth as its top priority. ut, as a result that almost all developments been promoted excepting environmental values, in fact, they've incurred some bad environmental effects desirable. Especially, as representative examples, we can raise some issues such as damages of the foreshore or coast wet lands by seas reclamation, and coast corrosion by building up of rivers or coast constructions. Recently, many people started to have great interests in businesses of environment preservation or recycling to minimize effects of these environmental matters. However, before beginning public businesses of non-commercial goods relevant to the seas environments, there seemed to be some limitations that can not accomplish under consideration of environmental sides at the same time while performing economic validities and efficiencies with environmental economic analysis, which is already effective in countries advanced in environment, it's a very meaningful course in that citizens' opinions are being influenced in seas environmental policies for their efficient execution. In this research, after modeling coast corrosion preventives with Jeong-am coast of Gangwon Province, and using Contingent Valuation Method being widely used of value measuring methods on Non-commercial goods, we've appreciated environmental economy's validity of construction works and the scale of environmental economic value of beach restoration work.
Modelling and Accurate Tracking Controller Design of A Transfer Crane
Kim, Young-Bok ; Suh, Jin-Ho ; Lee, Kwon-Soon ;
Journal of Ocean Engineering and Technology, volume 20, issue 6, 2006, Pages 114~122
The most important thing in the container terminal is to handle the cargo effectively in a limited time. To achieve this objective, many strategies have been introduced and applied. If we consider the automated container terminal, it is necessary that the cargo handling equipment is equipped with more intelligent control systems. From the middle of the 1990s, an automated rail-mounted gantry crane (RMGC) and rubber-tired gantry crane (RTG) have been developed and widely used to handle containers in the yards. Recently, in these cranes, equipment like CCD cameras and sensors have been mounted to cope with the automated terminal environment. In this paper, we try to support the development of more intelligent automated cranes that make the cargo handling be performed effectively in the yards. For this plant, we ought to consider modeling, tracking control, anti-sway system design, skew motion suppressionand complicated motion control and suppressing problems. In this paper, the system modeling and a tracking control approach are discussed, based on a two-degree-of-freedom (2DOF) servo-system design. From the simulation results, the good control performance of the designed control system is evaluated.
Shape Optimization for Performance Improvement of Ship's U-type Bellows
Kim, Hyoung-Jun ; Kim, Hyun-Su ; Kim, Jong-Pil ; Park, Jun-Hong ; Kim, Myoung-Jin ;
Journal of Ocean Engineering and Technology, volume 20, issue 6, 2006, Pages 123~129
The mechanical properties of bellows, such as the extensibility and the strength can be changed depending on the shape. For the shipbuilding material, it is desirable that the fatigue life is long due to the elastic property and the reduction of thermal stress in piping system. Nowadays, the domestic production and design of bellows are based on the E.J.M.A. Code. Therefore, the design standard is in need because of much errors and lack of detailed analysis. In this study, it is attempted to find out the optimal shape of U-type bellows using the finite element analysis. The design factors, mountain height, length, thickness, and the number of convolutions are considered and the proper values are chosen for the simulation. The results shaw that as the number of convolutions reduces, the volume decreases while the stress increases. However, as the number of convolutions increases, the volume increases above the standard volume and the stress obviously increases. In addition, the effect of the thickness of bellows on the stress is very large. Both of the mass and stress are decreasing at a certain lower value region. Also, we investigated shape optimization with considering maximum stress distribution tendency.