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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 25, Issue 6 - Dec 2011
Volume 25, Issue 5 - Oct 2011
Volume 25, Issue 4 - Aug 2011
Volume 25, Issue 3 - Jun 2011
Volume 25, Issue 2 - Apr 2011
Volume 25, Issue 1 - Feb 2011
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Motion Control of Omnidirectional Mobile Platform for Path Following Using Backstepping Technique
Dinh, Viet-Tuan ; Thinh, Doan-Phuc ; Hoang, Giang ; Kim, Hak-Kyeong ; Oh, Sea-June ; Kim, Sang-Bong ;
Journal of Ocean Engineering and Technology, volume 25, issue 5, 2011, Pages 1~8
DOI : 10.5574/KSOE.2011.25.5.001
This paper proposes a controller design for an omnidirectional mobile platform (OMP) with three wheels using backstepping control. A kinematic model and dynamic model of the system are presented. Based on the dynamic modeling, a backstepping controller is designed to stabilize the OMP when following a desired path. The controller is designed based on a backstepping control theory. It includes two steps: first, a virtual state and a stability function are introduced. Second, Lyapunov functions for the system are chosen and an equation for the virtual control that makes the system stabile is obtained. The system stability is guaranteed by the Lyapunov stability theory. The simulation and experimental results are presented to demonstrate the effectiveness of the proposed controller.
Computation of Incompressible Flows Using Higher Order Divergence-free Elements
Kim, Jin-Whan ;
Journal of Ocean Engineering and Technology, volume 25, issue 5, 2011, Pages 9~14
DOI : 10.5574/KSOE.2011.25.5.009
The divergence-free finite elements introduced in this paper are derived from Hermite functions, which interpolate stream functions. Velocity bases are derived from the curl of the Hermite functions. These velocity basis functions constitute a solenoidal function space, and the gradient of the Hermite functions constitute an irrotational function space. The incompressible Navier-Stokes equation is orthogonally decomposed into its solenoidal and irrotational parts, and the decoupled Navier-Stokes equations are then projected onto their corresponding spaces to form appropriate variational formulations. The degrees of the Hermite functions we introduce in this paper are bi-cubis, quartic, and quintic. To verify the accuracy and convergence of the present method, three well-known benchmark problems are chosen. These are lid-driven cavity flow, flow over a backward facing step, and buoyancy-driven flow within a square enclosure. The numerical results show good agreement with the previously published results in all cases.
Study on Solid-liquid Mixture Flow in Inclined Annulus
Kim, Young-Ju ; Kim, Young-Hun ; Woo, Nam-Sub ;
Journal of Ocean Engineering and Technology, volume 25, issue 5, 2011, Pages 15~20
DOI : 10.5574/KSOE.2011.25.5.015
This study carried out a series of experiments involving impact tests (Drop Weight type & Charpy type with a standard specimen and newly designed I-type specimen), hardness tests, and fracture surface observations of French-made roll shell steel (F), abnormal roll shell steel (M), reheated roll shell steel (R), and S25C steel under heat treatment conditiAn experimental study was carried out to study the solid-liquid mixture upward hydraulic transport of solid particles in vertical and inclined annuli with a rotating inner cylinder. The lift forces acting on a fluidized particle play a central role in many important applications such as the removal of drill cuttings in horizontal drill holes, sand transport in fractured reservoirs, sediment transport, the cleaning of particles from surfaces, etc. In this study a clear acrylic pipe was used to observe the movement of solid particles. Annular velocities varied from 0.4 to 1.2 m/s. The effect of the annulus inclination and drill pipe rotation on the carrying capacity of a drilling fluid, particle rising velocity, and pressure drop in a slim hole annulus were measured for fully-developed flows of water and aqueous solutions of CMC (sodium carboxymethyl cellulose) and bentonite. The rotation of the inner cylinder was efficient at carrying particles to some degree. For a higher particle volume concentration, the hydraulic pressure loss of the mixture flow increased because of the friction between the wall and solids or between solids.
Numerical Study for Development of Submerged Seawater Lift Pump
Kim, Young-Ju ; Kim, Young-Hun ; Woo, Nam-Sub ; Kwon, Jae-Ki ;
Journal of Ocean Engineering and Technology, volume 25, issue 5, 2011, Pages 21~26
DOI : 10.5574/KSOE.2011.25.5.021
Seawater lift pump systems are responsible for maintaining open canal levels to provide the suction flow of circulating water pumps at the set point. The objective of this paper is to design a 2-stage mixed flow pump (for seawater lifting), investigate the new impeller modeling method, and performance improvements of the impeller by using a commercial CFD code. The rotating speed of the impeller is 1,750 rpm with a flow rate of 2,700 m3/h. A finite volume method with a structured mesh and realized k-
turbulent model is used to guarantee a more accurate prediction of turbulent flow in the pump impeller. The performance variables such as the static head, brake horsepower, and efficiency of the mixed flow pump are compared based on changes in the impeller blade shape.
Correlation Study on Course Keeping Stability of Barges according to Variations in Dimensions and Hull Coefficient
Chun, Jang-Ho ; Kim, Moon-Chan ; Chun, Ho-Hwan ; Do, In-Rok ; Koo, Ja-Kyun ;
Journal of Ocean Engineering and Technology, volume 25, issue 5, 2011, Pages 27~32
DOI : 10.5574/KSOE.2011.25.5.027
Recently, a ship-shaped barge has been developed to improve the resistance performance, as well as course-keeping capability. However, the stern of the barge is still similar to a box shape, and the vortex generated at the side of the barge creates drag and yaw instability. In order to solve this problem, stern skegs are normally used. The present paper deals with the correlation between the size of the stern skegs and the barge dimensions and hull coefficient. A stern skeg was designed to prevent yaw instability and minimize any additional resistance. The resistance test and course keeping test were performed in the towing tank at Pusan National University. To determine the correlation parameters between the designed stern skeg size and barge dimensions, a parametric study was also performed. Based on the experimental data from five barges, the optimum skeg dimensions were successfully derived. It is expected that the validation of the present study will be carried out by further experiments and computational comparisons in the near future.
Variation of Impact Values by Heat Treatment Temperature to Prevent Brittle Fracture of Roll Shell Steel
Suh, Chang-Min ; Suh, Min-Soo ; Cho, Hae-Yong ;
Journal of Ocean Engineering and Technology, volume 25, issue 5, 2011, Pages 33~39
DOI : 10.5574/KSOE.2011.25.5.033
This study involved a series of experiments, which included impact tests (drop weight & Charpy) and hardness tests under various heat treatment conditions, followed by fractography observations of Normal Roll Shell steel (NRS), Abnormal Roll Shell steel (ARS), and S25C steel, in order to analyze the cause of brittle fracture and damages in Roll Shell steel. The optimal tempering temperature was characterized for ARS and NRS.
Variation of Impact Values by Heat Treatment Temperature to Prevent Brittle Fracture of Roll Shell Steel (II) -Comparison of properties between domestic and French-made products-
Suh, Chang-Min ; Suh, Min-Soo ; Oh, Sang-Yeob ;
Journal of Ocean Engineering and Technology, volume 25, issue 5, 2011, Pages 40~46
DOI : 10.5574/KSOE.2011.25.5.040
This study carried out a series of experiments involving impact tests (Drop weight type & Charpy type with a standard specimen and newly designed I-type specimen), hardness tests, and fracture surface observations of French-made roll shell steel (F), abnormal roll shell steel (M), reheated roll shell steel (R), and S25C steel under heat treatment conditions (
) to analyze the cause and prevent the roll shell steel's brittle fracture and its damage.
Estimation Fatigue Life of Weldments by Notch Stress Approaches
Yang, Park-Dal-Chi ; Song, Joon-Kyu ;
Journal of Ocean Engineering and Technology, volume 25, issue 5, 2011, Pages 47~51
DOI : 10.5574/KSOE.2011.25.5.047
This paper analyzes the fatigue-life of welded joints using the notch stress approach. In the notch stress approach, the notch effects are usually approximated by introducing weld-bead parameters for the local detailed weld joints. The actual bead shape is complex and 3-dimensional. It may also greatly influence the fatigue strength. In this study, the welded shape was modeled using a 3D-scanner. The critical distance method was adopted in the evaluation of the fatigue effective notch stress for the weldments. Fatigue life tests were performed to verify the present method of fatigue life estimation for two types of welded plates with longitudinal attachments. The estimated results of the present methods were applied to the results of the experiment. The results of the analysis showed that the scatter of fatigue-life for the experimental data expressed in the nominal stress was significantly reduced by applying the effective fatigue stress of the present study.
Stress Analysis of Curved Portions of Pipe Loops Used in Ships and Offshore Structures
Park, Chi-Mo ; Bae, Byoung-Il ;
Journal of Ocean Engineering and Technology, volume 25, issue 5, 2011, Pages 52~57
DOI : 10.5574/KSOE.2011.25.5.052
Most ships and offshore structures are equipped with a variety of pipes, which inevitably contain curved portions. While it has been a usual practice to conduct bending stress analyses of these curved pipes using the straight-beam theory, this paper adopts two different types of finite elements, straight-beam elements and two-dimensional shell elements, for finite element analyses of a variety of curved pipes. It then compares the analysis results for two different types of elements to determine correction factors, which can be used to transform the bending displacements and bending stresses obtained by straight-beam elements to those obtainable by two-dimensional shell elements. The paper ends with a practical suggestion on how to efficiently use these correction factors to estimate the combined axial and normal stresses in a curved portion of a pipe.
Experimental Study on High Frequency Vibration Transfer Characteristic of Underwater Cylindrical Shell
Jung, Hyung-Gi ; Min, Cheon-Hong ; Park, Han-Il ;
Journal of Ocean Engineering and Technology, volume 25, issue 5, 2011, Pages 58~63
DOI : 10.5574/KSOE.2011.25.5.058
Underwater vehicles such as UUVs (Unmanned Underwater Vehicles) and ROVs (Remotely Operated Vehicles) use sonar to detect their underwater environment or other underwater vehicles. The underwater vehicles designed recently have an electrical power system with high rotational speed. This system can generate high frequency vibrations above 10 kHz, and these vibrations can cause bad (negative) effects on the performance of the sonar. In many previous investigations, numerical analyses have been used for high frequency vibration problems. In this study, an experimental analysis was carried out, and a circular cylindrical shell was considered as the hull structure of an underwater vehicle. Frequency transfer functions for the circular cylindrical shell were identified using an experimental vibration analysis in the air and in a fully-submerged condition. We compare the frequency transfer functions in the air and water to obtain hydro-elastic effects. It is found that the dynamic characteristics of the circular cylindrical shell are changed by varying the response position.
Motion Analysis of 5-MW Floating Offshore Wind Turbine
Shin, Hyun-Kyoung ; Kim, Kyoung-Man ;
Journal of Ocean Engineering and Technology, volume 25, issue 5, 2011, Pages 64~68
DOI : 10.5574/KSOE.2011.25.5.064
The motion responses of a 5-MW floating offshore wind turbine were simulated in regular and irregular waves and its RAOs and significant motion responses were calculated, respectively. The floating offshore wind turbine employed in this simulation was the OC3-Hywind designed by the National Renewable Research Laboratory, USA. The numerical simulation was carried out using MOSES (Multi-Operational Structural Engineering Simulator), which is widely used to analyze and design floating offshore structures in the gas and oil industry.
Study on Numerical-analysis Technique for Windpower System Structure under Environmental Loadings
Jung, Hae-Young ; Hong, Cheol-Hyun ;
Journal of Ocean Engineering and Technology, volume 25, issue 5, 2011, Pages 69~75
DOI : 10.5574/KSOE.2011.25.5.069
The purpose of this study was to develop a buckling analysis technique for a windpower system structure under environmental loadings (hydrostatic pressure) using FEM. We analyzed an isotropic material and composite material and made a comparison using buckling pressure formulas. First, finite element analyses for an isotropic material (SC410) were performed to obtain the variation of buckling pressure for the number of elements and boundary conditions in a pressure-shell model, and the numerical results were compared with those of existing empirical formulas. Then, additional finite element analyses based on the results of the isotropic material (SC410) were performed to determine the optimum lamination angle and pattern for a composite material (URN300). The results of the FE analyses for the composite material were also compared with those of existing empirical formulas. The ply orientations (lamination angles) used in the FE analyses were
, and. The lamination patterns in the FE analyses were and. The lamination pattern was assumed to be the equivalent model of. The results of the FE analyses for the isotropic material (SC410) indicated that the optimal values for the number of elements and the boundary conditions were 6000 and both simply supported, respectively. The results of the FE analyses for the composite material (URN300) showed that the optimal ply orientation was
Study on Erection Block Positioning Using Genetic Algorithm
Shin, Sung-Chul ; Lee, Jae-Chul ; Kim, Soo-Young ;
Journal of Ocean Engineering and Technology, volume 25, issue 5, 2011, Pages 76~81
DOI : 10.5574/KSOE.2011.25.5.076
In the shipbuilding industry, accuracy management is one of the keys for strengthening competitiveness. However, ship block errors are unavoidable in the block erection stage because of the deformation of the blocks. Currently, accuracy managers decide whether or not block corrections are needed, based on measured and designed point data. They adjust the locations of hull blocks so that the blocks are aligned with other assembly blocks based upon the experience of production engineers. This paper proposes an optimization process that can adjust the locations of ship blocks during the erection stage. A genetic algorithm is used for this optimization scheme. Finally, the feasibility of the proposed method is discussed using several case studies. We found that the proposed method can find the optimized re-alignment of erection blocks, as well as improve the productivity of the erection stage.