• 한국해양공학회지
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• 제25권2호
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• pp.127-133
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• 2011

The following Technology Report was written with respect to recent offshore technology development. This report was prepared with the purpose of suggesting recent offshore technology and upcoming visions by describing the principles of an offshore drilling operation, the NL Tensioner Cylinder Package R & D, and the general technology related to three offshore patent areas, as major contents.

• 한국해양공학회지
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• 제25권2호
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• pp.62-66
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• 2011

In this paper, a liquid-filled long membrane container resting on a horizontal foundation is considered. All of the quantities are normalized to obtain similarity solutions. A system of nonlinear ordinary differential equations with undetermined boundary conditions is solved analytically. The integration of the curvature gives the solutions, which are expressed in terms of the elliptic integrals. A method for finding the shape and characteristic values is proposed for a given cross-sectional volume. The validity of these solutions is confirmed, and some results are shown for characteristic values and shapes.

• 한국해양공학회지
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• 제25권2호
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• pp.47-54
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• 2011

A piled raft foundation is one of the systems used to reduce the settlement of structures. However, the general design method for a piled raft foundation system assumes that the piles only support external loads, which exclude the bearing capacity of the raft itself. In this study, an experimental model test was performed to evaluate the raft capacity for the external load on the sand. Additionally, a part of the sandy ground under the raft was replaced with a gravel mat to reinforce the piled raft foundation system and increase the bearing capacity. Then, parametric studies of the reinforced ground were performed to determine the displacement and load-sharing ratio of the piled raft foundation system.

• 한국해양공학회지
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• 제25권2호
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• pp.36-46
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• 2011

A two-dimensional floating body with a moon pool under forced heave motion, including a piston mode, is numerically simulated. A dynamic CFD simulation is carried out to thoroughly investigate the flow field around a two-dimensional moon pool over various heaving frequencies. The numerical results are compared with experimental results and a linear potential program by Faltinsen et al. (2007). The effects of vortex shedding and viscosity are investigated by changing the corner shapes of the floating body and solving the Euler equation, respectively. The flow fields, including the velocity, vorticity, and pressure fields, are discussed to understand and determine the mechanisms of wave elevation, damping, and sway force.

• 한국해양공학회지
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• 제25권2호
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• pp.108-112
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• 2011

When oil spills occur in the ocean because of a ship collision or grounding, the oil in the sea will spread to the coastline. To effectively and promptly prevent such an oil spread, the prediction of the direction and speed of the spreading oil must be made. By applying the coastal wave diffusion theory with a consideration of the effects of wind and current, the oil spreading direction and speed can be predicted promptly so that the National Disaster Prevention System can effectively and promptly take countermeasures against the attack and contamination of the coastline by such oil bands.

• 한국해양공학회지
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• 제28권4호
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• pp.363-369
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• 2014

In this paper, a practical controller for a group of USVs is proposed in order to avoid matrix inversion problems in computation. Using nonlinear mapping, a formation composed of nonholonomic agents can be stabilized even when the formation is stationary. Since there is no matrix inversion in computing the control law, the computation complexity can be resolved. A controller for stabilizing the formation errors in the presence of model uncertainty is considered using the Lyapunov redesign method. The asymptotic stability of the formation errors is shown. It is also shown that the proposed controller can be applied to guide a formation to a different shape without modification.

• 한국해양공학회지
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• 제28권4호
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• pp.324-330
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• 2014

In this study, the numerical model developed by Hong et al.(2008) was improved to be applied to rapidly varying flows such as the inundation of dry land or flow transitions due to large gradients of the bathymetry. A numerical approximation was applied that was consistent with the conservation of momentum in flow expansions and with the Bernoulli equation in flow contractions. The approximation was second order, but the accuracy reduced to first order near extreme values by the use of a minmod limiter. The modified model was verified by acomparison with the theoretical critical depth of weir, and for sufficiently smooth conditions and a fine grid size, both approximations converged to the same solution. In terms of the grid size, it was more effective at obtaining solutions than the previous model and reproduced the inundation of dry land.

• 한국해양공학회지
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• 제28권4호
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• pp.280-287
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• 2014

In this paper, the numerical simulation of the gas-liquid flow in a cylinder cyclone separator is performed to investigate the flow characteristics using a commercial software, FLUENT, which solves the Reynolds-averaged Navier-Stokes(RaNS) equations. First, a single-phase flow with water in a gas-liquid cylinder cyclone(GLCC) separator is simulated and compared with the experiments(Farchi, 1990) and numerical simulations(Erdal, 1997). Then, the characteristics of the multi-phase flow for water-air, mud-only, and mud-air cases are discussed in the view point of the feasibilities for a mud handling system.

• 한국해양공학회지
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• 제32권2호
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• pp.123-130
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• 2018

The present study investigated the validity of an equilibrium shoreline empirical formula for real phenomena. Among three types of equilibrium shoreline formulas, Hsu's parabolic type static formula was employed, which is well-known and the most practical for shoreline estimation after coastal or harbor structure construction. The wave data observed at Maengbang beach and the CERC formula on longshore sediment transport were used in the present investigation. A comparison study was only conducted for the case of a shoreline change after the construction of a groyne. Reasonable agreement was seen between the observed wave data and the data obtained under a wave angle spreading function S = 3.5. However, significant changes were observed when S increased. Thus, careful application is required when using Hsu's formula.

• 한국해양공학회지
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• 제32권2호
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• pp.143-150
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• 2018

In this study, we designed and developed an underwater LED communication system composed of an LED and a photo sensor. In addition, we experimented with video data transmission in a water tank. Two communication modules were installed in the 3 m water tank, and the image data transmission test was successfully performed at a rate of 20 frames per second(FPS), image resolution of $480{\times}272$, and data communication speed of 4 Mbps.