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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 30, Issue 3 - Jun 2016
Volume 30, Issue 2 - Apr 2016
Volume 30, Issue 1 - Feb 2016
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Diffraction and Radiation of Waves by Array of Multiple Buoys
Cho, Il-Hyoung ;
Journal of Ocean Engineering and Technology, volume 30, issue 3, 2016, Pages 151~160
DOI : 10.5574/KSOE.2016.30.3.151
The diffraction and radiation of linear waves by an array of truncated floating multiple buoys are solved using the interaction theory based on a matched eigenfunction expansion method (MEEM). The interaction processes between multiple buoys are very complex and numerous, because the scattered and radiated waves from each buoy affect the others in the array. Our primary aim is therefore to construct the rigorous wave exciting forces and hydrodynamic forces to deal with the problem of multiple interactions. This present method is applied to a square array of four buoys with two incidence angles, and the results are given for the wave excitation forces on each buoy, heave RAO for each buoy heaving independently, and wave elevations around the buoys and wave run-up. The analytical solutions are in good agreement with the numerical solutions obtained from commercial code (WAMIT).
Fatigue Damage Estimation for Mooring lines of Spar Platform Using System Identification Method
Kim, Yong-Gyun ; Kim, Yooil ; Kim, Byoung-Hoon ;
Journal of Ocean Engineering and Technology, volume 30, issue 3, 2016, Pages 161~168
DOI : 10.5574/KSOE.2016.30.3.161
This paper presents a methodology through which the time series of the dynamic response of mooring line tension can be predicted without relying on a time-consuming nonlinear time-domain analysis. The mooring line tension for the target short-term sea states was predicted using a Hammerstein-Wiener model, a popular system identification scheme, based upon the pre-calculated motion-tension time history data for some selected short-term sea states that do not overlap with the targeted ones. The obtained mooring line tension was further processed, and a fatigue damage comparison was made between the predicted and calculated values. The results showed that the predicted time series of the mooring line tension matched the calculated one fairly well. Thus, it is expected that the methodology may be employed to enhance the efficiency of mooring line tension analysis.
Wake Volume Characteristics Considering Artificial Reef Canyon Intervals Constructed by Flatly Distributed Artificial Reef Set
Jung, Somi ; Kim, Dongha ; Na, Won-Bae ;
Journal of Ocean Engineering and Technology, volume 30, issue 3, 2016, Pages 169~176
DOI : 10.5574/KSOE.2016.30.3.169
Considering the artificial reef (AR) canyon intervals facilitated by flatly distributed placement models, the wake volumes of 25 AR sets were characterized through the following works. First, twenty-five different canyon intervals were established to investigate how the intervals affect the wake volumes of the AR placement models, each with nine cube-type ARs. Second, the element-based finite-volume method was used to facilitate flow analyses. Third, the so-called wake volume concept was adopted, and finally a reasonable placement interval was found based on the size of the wake volumes and the associated unit propagation indices. From the analysis results, it was found that a maximum wake volume of 25.18 m
was generated when the longitudinal and transverse intervals were fixed at 6 m and 0 m, respectively. Thus, to magnify the wake volume, it is recommended that artificial reefs be placed at intervals of 6 m (3 times the reef length) in the flow direction, with no intervals in the normal direction, implicitly indicating that an intensively stacked placement model is a better option to efficiently secure a larger wake volume for the cube-type ARs.
Effect of Consecutive Ship Docking and Undocking on Seawater Circulation in Harbor
Hong, Namseeg ;
Journal of Ocean Engineering and Technology, volume 30, issue 3, 2016, Pages 177~185
DOI : 10.5574/KSOE.2016.30.3.177
In this study, the model developed by Hong (2012) was modified to describe the consecutive docking/undocking situation and was also applied to investigate the effect on seawater circulation in Busan port by consecutive docking/undocking at the connecting bridge of Busan port. Numerical experiments for various docking/undocking cases were performed by dumping the initial concentration within Busan Port and indicated that the concentration in Busan port becomes steady state without numerical wiggles after sufficient time (at least 20 or 30 days). In addition, it was found that the seawater circulation under ship docking was slightly reduced in comparison with that under ship undocking, and the approach time to the target concentration under all the docking cases increased in comparison with the undocking case.
Settlement and Scour Characteristics of Artificial Reef according to Reinforced Ground
Yun, Dae-Ho ; Suh, Sung-Ho ; Kim, Yun-Tae ;
Journal of Ocean Engineering and Technology, volume 30, issue 3, 2016, Pages 186~193
DOI : 10.5574/KSOE.2016.30.3.186
Recently in Korea, a marine ranching project has continued to grow with the increasing needs of sea development. Management techniques, including settlement reduction and scour protection, have been required for constructing and maintaining the artificial reefs of this marine ranching project. The generation of settlement and scour can be influenced by ground characteristics. In this study, various laboratory tests (penetration test, two-dimensional water tank test) were performed to determine the settlement and scour characteristics of artificial reefs under various ground conditions. Three kinds of ground reinforcement were prepared: unreinforced, geogrid, and hybrid bamboo mat. Penetration test results showed that the normalized settlement ratio of ground reinforced with a hybrid bamboo mat was smaller than those of unreinforced ground and geogrid-reinforced ground. Two-dimensional water tank test results showed that the scour characteristics of ground reinforced with a geogrid were more reduced and stable than unreinforced ground. The amount of scour and ground settlement also decreased with increasing reinforced area.
Development of a Hover-capable AUV System for In-water Visual Inspection via Image Mosaicking
Hong, Seonghun ; Park, Jeonghong ; Kim, Taeyun ; Yoon, Sukmin ; Kim, Jinwhan ;
Journal of Ocean Engineering and Technology, volume 30, issue 3, 2016, Pages 194~200
DOI : 10.5574/KSOE.2016.30.3.194
Recently, UUVs (unmanned underwater vehicles) have increasingly been applied in various science and engineering applications. In-water inspection, which used to be performed by human divers, is a potential application for UUVs. In particular, the operational safety and performance of in-water inspection missions can be greatly improved by using an underwater robotic vehicle. The capabilities of hovering maneuvers and automatic image mosaicking are essential for autonomous underwater visual inspection. This paper presents the development of a hover-capable autonomous underwater vehicle system for autonomous in-water inspection, which includes both a hardware platform and operational software algorithms. Some results from an experiment in a model basin are presented to demonstrate the feasibility of the developed system and algorithms.
Process of Structural Design and Analysis of Thin Pressure Cylinder for Shallow Sea Usage
Lee, Jae-Hwan ; Maring, Kothilngam ; Kim, So-Ul ; Oh, Taek-Chan ; Park, Byoung-Jae ;
Journal of Ocean Engineering and Technology, volume 30, issue 3, 2016, Pages 201~207
DOI : 10.5574/KSOE.2016.30.3.201
In this paper, an aluminum pressure vessel (cylinder) for a 200 m water depth is designed and analyzed. Because of their lack of usage in the deep sea, only a few papers about pressure vessels subjected to external pressures have previously been published. Moreover, the high level of imported external-pressure-vessel products limits the academic pursuit. Yet, research on internal pressure vessels is widely available because of their broad usage at onshore. This paper presents the process of basic designing and modelling of pressure vessels using the design rules of American Standard of Mechanical Engineering (ASME) Section VIII Division 1. To promote understanding, finite element analysis (FEA) result of an existing sample cylinder which was not designed by ASME code is compared with the design obtained in this paper. Several methodologies are used for the finite element analysis, including rectangular, cylindrical, and axisymmetric coordinate, to attain an accurate stress result. Same dimensions except the thickness of the cylinder and loading condition of 0.200 MPa was given for the current study. Finally, a rigorous design procedure is added for the bolt and boundary conditions of the cylindrical body and its ends. The obtained stress level satisfies the allowable design stress value specified in the ASME code.
Design of Guidance Law for Docking of Unmanned Surface Vehicle
Woo, Joohyun ; Kim, Nakwan ;
Journal of Ocean Engineering and Technology, volume 30, issue 3, 2016, Pages 208~213
DOI : 10.5574/KSOE.2016.30.3.208
This paper proposes a potential field-based guidance law for docking a USV (unmanned surface vehicle). In most cases, a USV without side thrusters is an under-actuated system. Thus, there are undockable regions near docking stations where a USV cannot dock to a docking station without causing a collision or backward motion. This paper suggest a guidance law that prevents a USV from enter such a region by decreasing the lateral error to the docking station at the initial stage of the docking process. A Monte-carlo simulation was performed to validate the performance of the proposed method. The proposed method was compared to conventional guidance laws such as pure pursuit guidance and pure/lead pursuit guidance. As a result, the collision angle and lateral distance error of proposed method tended to have lower values compared to conventional methods.
Comparative Study of Sonar Image Processing for Underwater Navigation
Shin, Young-Sik ; Cho, Younggun ; Lee, Yeongjun ; Choi, Hyun-Taek ; Kim, Ayoung ;
Journal of Ocean Engineering and Technology, volume 30, issue 3, 2016, Pages 214~220
DOI : 10.5574/KSOE.2016.30.3.214
Imaging sonars such as side-scanning sonar or forward-looking sonar are becoming fundamental sensors in the underwater robotics field. However, using sonar images for underwater perception presents many challenges. Sonar images are usually low resolution with inherent speckled noise. To overcome the limited sensor information for underwater perception, we investigated preprocessing methods for sonar images and feature detection methods for a nonlinear scale space. In this paper, we focus on a comparative analysis of (1) preprocessing for sonar images and (2) the feature detection performance in relation to the scale space composition.
Implementation of Hovering AUV and Its Attitude Control Using PID Controller
Kim, Min-Ji ; Baek, Woon-Kyung ; Ha, Kyoung-Nam ; Joo, Moon-Gab ;
Journal of Ocean Engineering and Technology, volume 30, issue 3, 2016, Pages 221~226
DOI : 10.5574/KSOE.2016.30.3.221
An attitude controller for a 6-DOF hovering autonomous underwater vehicle (HAUV) is implemented. We add a vertical thruster, an underwater camera, a wireless communication device, and a DVL to the HAUV that was developed a year ago. The HAUV is composed of 5 thrusters, 2 servo-motors, and 4 apparatus parts. Two rotating thrusters control the surge, heave, and roll of the vehicle. The vertical thruster controls the pitch, and two horizontal thrusters control the sway and yaw of the vehicle. The HAUV’s movement in each direction is controlled by 6 PID controllers. Each PID controller controls the propulsive force and angle of a thruster. In a horizontal and vertical movement experiment, we showed the feasibility of the proposed controller by maintaining a given depth and heading angle of the HAUV.
Underwater 3D Reconstruction for Underwater Construction Robot Based on 2D Multibeam Imaging Sonar
Song, Young-eun ; Choi, Seung-Joon ;
Journal of Ocean Engineering and Technology, volume 30, issue 3, 2016, Pages 227~233
DOI : 10.5574/KSOE.2016.30.3.227
This paper presents an underwater structure 3D reconstruction method using a 2D multibeam imaging sonar. Compared with other underwater environmental recognition sensors, the 2D multibeam imaging sonar offers high resolution images in water with a high turbidity level by showing the reflection intensity data in real-time. With such advantages, almost all underwater applications, including ROVs, have applied this 2D multibeam imaging sonar. However, the elevation data are missing in sonar images, which causes difficulties with correctly understanding the underwater topography. To solve this problem, this paper concentrates on the physical relationship between the sonar image and the scene topography to find the elevation information. First, the modeling of the sonar reflection intensity data is studied using the distances and angles of the sonar beams and underwater objects. Second, the elevation data are determined based on parameters like the reflection intensity and shadow length. Then, the elevation information is applied to the 3D underwater reconstruction. This paper evaluates the presented real-time 3D reconstruction method using real underwater environments. Experimental results are shown to appraise the performance of the method. Additionally, with the utilization of ROVs, the contour and texture image mapping results from the obtained 3D reconstruction results are presented as applications.