• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.5
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• pp.411-420
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• 2009

This study presents an extended finite difference method based on moving least squares(MLS) method for solving potential problems with interfacial boundary. The approximation constructed from the MLS Taylor polynomial is modified by inserting of wedge functions for the interface modeling. Governing equations are node-wisely discretized without involving element or grid; immersion of interfacial condition into the approximation circumvents numerical difficulties owing to geometrical modeling of interface. Interface modeling introduces no additional unknowns in the system of equations but makes the system overdetermined. So, the numbers of unknowns and equations are equalized by the symmetrization of the stiffness matrix. Increase in computational effort is the trade-off for ease of interface modeling. Numerical results clearly show that the developed numerical scheme sharply describes the wedge behavior as well as jumps and efficiently and accurately solves potential problems with interface.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.2
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• pp.132-139
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• 1992

This paper presents geometrically nonlinear formulation of shell problems using the three-dimensional curved shell element, which includs large displacements and large rotations. Formulations of the geometrically nonlinear problems can be derived in a variety of ways, but most of them have been obtained by assuming that nodal rotations are small. Hence, the tangent stiffness matrix is derived under the assumptions that rotational increments are infinitesimal and the effect of finite rotational increments have to be considered during the equilibrium iterations. To study the large displacement and large rotation problems, the restrictions are removed and the formulations of the curved shell element including the effect of large rotational increments are developed in this paper. The displacement based finite element method using this improved formulation are applied to the analyses of the geometrically nonlinear behaviors of the single and double curved shells, which are compared with the results by others.

• Journal of the Society of Naval Architects of Korea
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• v.31 no.1
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• pp.94-101
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• 1994

This paper describes a short-term prediction model for the movement of an oil slick in shallow waters. Under the assumption that the initial movement of the oil slick is governed by spreading and advection, the model has been developed and applied to Kyungki-Bay near Incheon Harbor. The initial spreading is estimated by using an empirical formula. The depth-averaged momentum equations are solved numerically for the volume transport velocities, in which the $M_2$ tide is the main driving source. A staggered grid system is adopted fur spatial discretization and the half-time method is implemented for time marching. The numerical result is visualized with the help of animation and thus the contaminated area is displayed on a monitor in time sequence. The input data are the time, the location and the volume of spill accident as well as environmental data such as md and $M_2$ tide.

• Geotechnical Engineering
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• v.11 no.3
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• pp.81-90
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• 1995

Based on the close investigation of Lade elasto -plastic model, this study proposes a new elasto -plastic constitutive model for foundation composed of granular soils. The new model contains 1st stress invariant in plastic potential function as well as yield function, which is different from Lade original model. Both these functions called a correction function include a correction term. To validate the new analytical model, it was compered with some previous models. Comparison between the test results and numerical results using Lade and new model was carried out concerning Sacramento River sand, U.S.A and Backma River sand. The conclusion was obtained that more refined model well be deft.eloped throughout this research.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.3 no.2
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• pp.81-91
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• 1991

A k-$\varepsilon$ equation model was established to investigate the behaviours of two-dimensional surface buoyant jets. Its computational results were compared with experimental data on the mean flow and the turbulent transport. The model was proved to predict the flow characteristics reasonably. The influence of the values of k and $\varepsilon$ given in the inlet on the evaluation of surface buoyant jets was examined to determine them quantitatively. Computations for several values of buoyancy production coefficient $C\varepsilon$$_3$ in the $\varepsilon$ equation, which has been neglected by many researchers. were carried out to evaluate its effect on the flow development. Computational results of the two-dimensional surface buoyant jets were presented and briefly discussed.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.23 no.3
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• pp.111-116
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• 1987

The accurate prediction of the ship wave resistance is very important to design ships which operate satisfactorily in a wave environment. Thus, work should continue on development and validation of methods to compute ship wave patterns and wave resistance. Research efforts to improve the prediction of ship waves and wavemaking resistance are categorized in two major areas. First is the development of higher-order theories to take account of the nonlinear effect of the free surface condition and improved analytical treatment of the body boundary condition. Second is the development of direct numerical methods aimed at solving body and free-surface boundary conditions as accurately as possible. A new formulation of the slender body theory for a ship with constant speed is developed by Maruo. It is quite different from the existing slender ship theory by Vossers, Maruo and Tuck. It may be regarded as a substitute for the Neumann-Kelvin approximation. In present work, the method of asymptotic expansion of the Kelvin source is applied to obtain a new wave resistance formulation in fluid of finite depth. It takes a simple form than existing theory.

• Journal of the Korean Society for Railway
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• v.12 no.6
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• pp.944-952
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• 2009

This paper presents an analytical model for calculation of crack widths in reinforced concrete structures. The model is mathematically derived from the actual bond stress-slip relationships between the reinforcement and the surrounding concrete, and the relationships summarized in CEB-FIP Model Code 1990 and Eurocode 2 are employed in this study together with the numerical analysis result of a linear slip distribution along the interface at the stabilized cracking stage. With these, the actual strains of the steel and the concrete are integrated respectively along the embedment length between the adjacent cracks so as to obtain the difference in the axial elongation. The model is applied to the test results available in literatures, and the predicted values are shown to be in good agreement with the experimentally measured data.

• Journal of Korean Society of Transportation
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• v.21 no.2
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• pp.7-16
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• 2003

To minimize the death and injury by a collision, the installation of an air bag is recommended as a mandatory practice together with the wearing of the seat belt. By using simulated collision experiments, this research focused on the effect of an air bag and seat belt on the driver safety. The vehicle deceleration characteristics were obtained from impact experiment. LSDYNA, a software program for vehicle collision analysis, and MADYMO. a software program for driver motion after collision, were used for simulated experiment. Four cases such as air bag installed and seat belt wearing (case A), air bag installed but seat belt not wearing (case B), air bag not installed but seat belt wearing (case C), air bag not installed and seat belt not wearing (case D) were analyzed. The impact of acceleration on the injury of driver's head was analyzed by Head Injury Criterion (HIC) as well. It was found that having air bag and wearing seat belt effectively reduced driver's head injury about 52.9% to 70.5% compared with the case of having neither air bag nor wearing seat belt.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.3
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• pp.57-63
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• 2002

This paper describes a control algorithm for the buffer of a deep-sea mining system, in which the buffer is connected to a long slender pipe and then to a surface ship on one end, and to a collector on sea floor through a flexible hose on the other end. A mathematical modeling is established for designing the controller for buffer thrusters, in which the dynamic response of the long pipe is taken into account based on the mode superposition method. The fluid loading acting on the pipe is estimated by using Morison's formula. For simplicity, the surface ship is assumed to be kept stationary, the reaction from the flexible hose is ignored and only the lateral motions are considered. In order to guide the buffer to react only to the low-frequency motion of the surface vessel, the FIR digital filter is introduced to a PID-based controller It can be shown numerically that the high frequency component of the ship's motion can be effectively filtered out by using the FIR low pass filter.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.1
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• pp.34-42
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• 2011

It's been reported that the global warming effect has invoked the ever increasing typhoon intensity and long-term sea level rise which jointly cause severe wave overtopping over breakwaters or shore dykes. A simple measure to cope with this undesirable change may be just to increase the crest height of the dykes and breakwaters. This is surely effective to prevent wave overtopping, but it also decreases the seaward visibility of coastal waterfront. In this paper, a dynamic deformable rubber membrane parapet which not only reduces wave overtopping in storm period but also secures seascapes in normal days is presented. Several optimal configurations of the parapet are proposed. Through numerical analyses using a nonlinear finite element model and hydraulic experiments, the air controlled expansion and contraction of the parapets, their behavior against wave overtopping and structural stability are investigated.