• Korean Journal of Fisheries and Aquatic Sciences
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• v.47 no.6
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• pp.978-982
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• 2014

A mass mortality of 249 finless porpoises Neophocaena asiaeorientalis occurred in the Saemangeum Dyke in February 2011. It was an extraordinary event, notable due to the death toll and the location of the occurrence, a semi-isolated lake enclosed by a man-made structure. We conducted sighting surveys that consisted of a land-based sighting survey recorded from three different platforms, and a ship-based sighting survey in the lake. The land-based survey was dedicated to clarifying the distribution of finless porpoises and whether they passed through two water gates (Shinsi and Garyek) of the dyke from 2011 to 2013. No finless porpoises were observed in the 2011 or January 2012 surveys. In April 2012, two months and one year after the mass mortality, one finless porpoise, swimming 400 m from the Shinsi water gate, was observed by a land-based survey. The number of observed individuals increased to nine in 2012 and reached 10 by May 2013 at the time of the surveys. Most of the porpoises were detected near the Garyek water gate. The density of the animals was $0.075/km^2$ in 2012 and $0.083/km^2$ in 2013. The density of porpoises was $2.063/km^2$ at the time of the mass mortality.

• Journal of the Society of Naval Architects of Korea
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• v.33 no.3
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• pp.66-80
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• 1996

Recently, HT steel has been widely used in structure, and this enables to reduce the plate thickness. To use the HT steel effectively for a ship hull, the plate thickness becomes thin so that plate buckling may take place. Therefore, precise assessment of the behaviour of plat above primary buckling load is important. The plate under the load, that is called, secondary buckling load may undergo abrupt changes in wave form after primary buckling. This is very important when the collapse strength of the whole structures is considered. From this point of view, this paper discusses secondary buckling behaviour of thin plate under inplane compressive loading. A elastic large deflection analysis of plates with initial imperfection is performed assuming uniaxial compression, respectively, and the influence of secondary buckling is investigated. It is known that square plate is not influenced by non-symmetrical deflection coefficient but influenced by symmetrical deflection coefficient. Also, it has been found that rectangular plate($\alpha$=a/b) is influenced by all deflection coefficient, and the reduction of inplane stiffness of the plate after primary buckling is continued.

• International Journal of Naval Architecture and Ocean Engineering
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• v.5 no.3
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• pp.348-363
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• 2013

The use of I-Core sandwich panel has increased in cruise ship deck structure since it can provide similar bending strength with conventional stiffened plate while keeping lighter weight and lower web height. However, due to its thin plate thickness, i.e. about 4~6 mm at most, it is assembled by high power $CO_2$ laser welding to minimize the welding deformation. This research proposes a volumetric heat source model for T-joint of the I-Core sandwich panel and a method to use shell element model for a thermal elasto-plastic analysis to predict welding deformation. This paper, Part I, focuses on the heat source model. A circular cone type heat source model is newly suggested in heat transfer analysis to realize similar melting zone with that observed in experiment. An additional suggestion is made to consider negative defocus, which is commonly applied in T-joint laser welding since it can provide deeper penetration than zero defocus. The proposed heat source is also verified through 3D thermal elasto-plastic analysis to compare welding deformation with experimental results. A parametric study for different welding speeds, defocus values, and welding powers is performed to investigate the effect on the melting zone and welding deformation. In Part II, focuses on the proposed method to employ shell element model to predict welding deformation in thermal elasto-plastic analysis instead of solid element model.

• 한국지구물리탐사학회:학술대회논문집
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• 2008.10a
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• pp.79-84
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• 2008

Compared to conventional high resolution acoustic profiling, ultra high resolution shallow acoustic profiling is limited in penetration, yet it provides resolution suitable for detailed seabed investigation in the shallow waters. Possible applications include search of buried pipeline, ship wrecks, and other artificial objects through the detailed mapping of thickness and structure of the upper sedimentary layers. In this study, contaminated sediments were discriminated by the correlation of ultra high resolution profiles with geologic data. In addition, the burial depth of submarine cable was measured by the interpretation of acoustic anomalies in the profiles.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.1
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• pp.27-36
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• 2012

The mobile harbor is a new concept system to solve the problems of a port. These problems are that container ships cannot be anchored at the dock because they have become larger or the waiting times of anchoring the ships are increased due to heavy container traffic. A new system is designed to carry out the loading and unloading of containers between the mobile harbor and the container ship using the mobile harbor crane at sea. The crane plays an important role when transferring the containers. In this research, various types of the mobile harbor crane are proposed and structural optimization for each type of the crane is carried out. The loading conditions consider the rolling and pitching conditions of the unstable sea state and the wind force are considered. The constraints are mainly the regulations made by the Korean Register of Shipping. The structure of the crane is optimized to minimize the mass while various constraints are satisfied.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.5
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• pp.331-338
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• 2020

In this study, the characteristic of a 3-D micro-woven material, which is one of the newly developed periodic open-cell structure, is analyzed through various computational simulations. To increase the accuracy of the numerical simulations, the distance between each directional wire is parameterized using six design variables, and its model geometry is precisely discretized using tetrahedron elements. Using the improved computational model, the material properties of the mechanical, thermal, and fluidic behavior are investigated using commercial software and compared with the previous experimental results. By changing the space between the x- and y-directional wires, a parametric test is performed to determine the tendency of the change in the material properties. In addition, the correlation between two different material properties is investigated using the Ashby chart. The result can further be used in determining the optimal pattern and wire spacing in 3-D micro-woven materials.

• Journal of Welding and Joining
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• v.34 no.2
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• pp.22-29
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• 2016

Recently, Application of composite materials are increased in transport area for weight reduction. Also, Related technical developments have been implemented actively at domestic and abroad. In particular, The carbon fiber has high strength and ultra light property higher than stainless steel, aluminum, GFRP as Eco-friendly material. Carbon fiber contribute to improving the environmental effect such as fuel saving, expansion of loadage, reducing the exhaustion of carbon dioxide through the weight reduction of transport area. In addition, The carbon fiber is applied to the ship in the area of race yacht, luxury cruise boat as weight reduction and high added-value materials, but there is limited application for general boat because price of carbon fiber is very expensive. For the weight reduction of general boat hull, being used as structure materials, glass fiber and carbon fiber are applied to hull with form of hybrid composite materials, but application of domestic and research for development are incomlete. In this study, An evaluations of mechanical strength property and fatigue strength are performed on composite materials by hybrid weaving of glass fiber and carbon fiber and composite materials forming method by hybrid forming.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.05a
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• pp.119-126
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• 2001

The potential pollution problems resulting from tanker collision necessitate the requirement for an effective structural design and the development of relevant safety regulation. During a few decades, the great effort has been made by International Maritime Organization and the Administration, etc, to reduce oil spillage from collision accidents. However there is still a need for investigation in the light of structural evaluation method for the experiments and rational analysis, and design development for an operational purpose of ships. This study is aimed at investigating a complicated structural response of bow structures of oil carriers for assessing the energy dissipation and crushing mechanics of striking vessel through a methodology of the numerical analysts for the various models and its design changes. Through this study an optimal bow construction absorbing great portion of kinetic energy in the least penetration depth prior to reach to the cargo area and an effective location of collision bulkhead are investigated. In order to obtain a rational results in this study, three stages of response analysis procedures are performed as follows; 1). 16 simplified ship models are used to investigate the structural response against bow collision with variation of primary and secondary members. Mass and speed are also varied in two conditions. 2). 21 models conisted of 5 size of full scaled oil carriers are used to perform the collision simulation with the various sizes and deadweight delivered in a recent which are complied with SOLAS and MARPOL. 3). 36 models of 100k oil carrier are used to investigate the structural response and its influence to the collision bulkhead against bow collision in variation with location of collision bulkhead, primary mombers, framing system and colliding conditions, etc.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.4
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• pp.456-462
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• 2014

In this paper, we develop a facility management system which provides fault effect and replacement alarm function of each component for supporting effective maintenance of facility. To do this, we use weighting method to each component, calculate importance of each component, and make them to hierarchy structure using bill of materials of facility. Also, we draw fault cause and fault effect of components based on failure modes effects and criticality analysis, and define criteria of severity, occurrence and detection to get risk priority number. To apply these concepts, we develop and test the facility management system to verify its practicality. In the future, we expect the developed system to apply many domains such as maintenance of ship and offshore plant.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.3
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• pp.296-302
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• 2008

Recently, a mesh-size insensitive structural stress definition (structural stress method) is proposed that gives a stress state at weld toe with a relatively large mesh size. The structural stress definition is based on the elementary structural mechanics theory and provides an effective measure of a stress state in front of weld toe. In this study, a fatigue strength assessment for a side shell connection of a container vessel using both the hot spot stress and the Battelle structural stress method was carried out. A consistent approach to compute the extrapolated hot spot stress for design purpose is described and current fatigue guidance is evaluated. Fatigue strength predicted by the two methodologies, e.g. hot spot stress and structural stress approaches, at hot spot locations of a typical ship structure are compared and discussed.