• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.47 no.3
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• pp.248-256
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• 2011

The inherent efficiency of a ship would be prior to any other quality factors in ship's safety, because lack of it may give rise to a serious sea casuality even if it were a light mistake in operation. And the representative casualty comes from a deficiency of stability and an operating error combined would be capsizing. The Korean offshore large purseiner looks to have a structural weak point with small range of stability in spite of her big initial metacentric height, and have various type of roll reduction devices in order to cover up the defect. The aim of this study is to grasp for the roll reduction characteristics of the purseiner with bilge keel only and a stern keel additionally attached. The results are summarized as follows; The rolling angle of the model ship was increased in accordance with increase of the wave period and height, especially at close to the natural wave period of her, and the trends were more distinguished in the situation of bilge keel only installation than in the stern keel additionally installed. And stern keel has not noticeable effect on the reduction of the roll in the light ship condition, but has a little effect in full load condition.

• Proceedings of the KSR Conference
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• 2008.06a
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• pp.2163-2172
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• 2008

The noise to be considered as the most important in railway systems is the noise generated from the wheel/rail interaction. Such noise can be divided into three categories; that is, the rolling noise, the squeal noise and the wheel howling noise. Especially in metro systems, this type of noise has been considered seriously in recent years, and the diversified studies on the mechanism and solutions of such noise are in progress by many railways and researching bodies. In this study, a specially designed wheel absorber is installed in the wheel, and FEM analysis and laboratory tests are executed for the two cases, i.e. with wheel absorber and without wheel absorber, to check the effect of the wheel absorber in noise reduction. For the FEM analysis, the frequency response functions for respective cases are compared. And, for the laboratory test, following four cases are tested and compared; that is, i) with wheel only, ii) installation of ring damper only, iii) installation of damping material and cover, iv) installation of complete absorber system.

• Proceedings of the KSR Conference
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• 2009.05a
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• pp.659-666
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• 2009

As the density and height of the buildings nearby subway lines get higher, the unprecedented residents' appeals for noise are on the rise. Furthermore, in accordance with the revision of enforcement regulations on the Noise and Vibration Control Act, the night time noise standards have been reinforced by 5dB effective on January 1st 2010 and the appropriate measures shall be taken accordingly. For the settlement of the public grievances against noise and vibration generated on tracks in at-grade and elevated section, the installation of continuously-welded-rail, rail lubrication system, improved fastening system and higher noise barrier is currently executed. Nevertheless, the noise and vibration levels in some areas are still exceeding the limits required in the regulation. Among the measures, an installation of higher noise barrier or noise tunnel seems to be the most effective way; however, it has limitations owing to the structural stability of existing elevated structures. The paper in consideration of the local conditions and foreign practices discusses the installation of fairing system under the train body as an noise insulation panel in order to reduce the rolling noise and under-carriage noise. Based on the result of this study, a performance verification test during actual train operation is in progress for further study.

• Journal of Ocean Engineering and Technology
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• v.33 no.2
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• pp.106-115
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• 2019

The interaction between a sloshing liquid damper (SLD) tank and a rectangular pontoon was investigated under the assumption of the linear potential theory. The eigenfunction expansion method was used not only for the sloshing problem in the SLD tank but also for analyzing the motion responses of a rectangular pontoon in waves. If the frictional damping due to the viscosity of the SLD tank was ignored, the effect of the SLD appeared to be an added mass in the coupled equation of motion. The installation of the SLD tank had a greater effect on the roll motion response than the sway and heave motion of the pontoon. One resonance peak for rolling motion showed up in the case of a frozen liquid in the SLD tank. However, if liquid motion in the SLD tank was allowed, two peaks appeared around the first natural frequency of the fluid in the SLD tank. In particular, the peak value located in the low-frequency region had a relatively large value, and the peak frequency located in the high-frequency region moved into the high-frequency region as the depth of the liquid in the tank increased.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.499-504
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• 2012

The high-speed train enjoys widespread acceptance as environment-friendly means of medium- to long-distance transportation. The pursuit of higher speed and lighter weight in railroad vehicles has engendered higher noise level. In particular, the environmental noise places many restrictions in the operation of high-speed railroad vehicles. This research investigates the effect of installing a skirt onto a high-speed train bogie with the top speed of 400 km/hr and using High Speed EMU for the purpose of reducing the environmental noise. In order to analyze the effect of the interior noise and environmental noise due to installation of the skirt, sound level is calculated using the Ray method and Statical Energy Analysis method. The numerical calculation predicts a reduction of approximately 2 dB in the environmental noise level, but at the cost of increase of approximately 2.5 dB in the interior noise level of the vehicle.

• The Journal of Engineering Geology
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• v.12 no.1
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• pp.53-61
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• 2002

Cut-slope due to the road construction is one of the most significant problems in the domestic case, that is, 70% of the land is covered by mountain. Moreover, typhoons or heavy rains concentrated in summer season causes the failure of cut-slope. Rock-fall and soil slope failure take 40.8% and 29.5% out of the entire domestic cut-slope failure, respectively. Rock-fall is quickly occurred by the free fall or rolling of rock fragments generally in the upper slope. Soil slope failure produces a clastics-flow and increases casualty especially when caused by heave rainfall because the velocity of the movement is verb high. Considering the car speed and rock-fall velocity, it will take a life in a moment. This study analyzes a set of field data of most recently collapsed domestic road cut-slopes to characterize these cut-slopes and the nature of rock-falls and clastics flows at each site. Based on the results, design criteria for a road alarm system are proposed, considering the relationship between the time required for clastics-flow and the velocity and braking distance of a cat at the incidence. The road alarm system proposed herein would operate instantly after a rock-fall and it will minimize damages, by warning drivels approaching to the collapse or collapsing location in advance.