• Fire Science and Engineering
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• v.20 no.2 s.62
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• pp.44-53
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• 2006

We have conducted a numerical simulation under two-dimensional unsteady conditions in order to analyze the effect according to the injection angle and velocity of the $CO_2$ agent nozzle which is one of the elements for the fixed type $CO_2$ fire extinguishing system installed in a ship on the characteristics of flow and $CO_2$ concentration distribution. The flow fields and concentration fields were measured and analyzed. We can found that the difference of flow patterns according to the conditions of $CO_2$ agent injection nozzle, and in all the conditions of $CO_2$ agent injection nozzle, the iso-concentration line was expanded from the region at which vortex was generated to the surroundings. We can expected that the intensity of the wall jet on the bottom floor was generated differently and the iso-concentration lines were expanded or shrunk according to the angle of $CO_2$ agent injection nozzle. In case of increasing $CO_2$ agent injection velocity maintaining the flow quantity of the $CO_2$ agent injection equally, the iso-concentration line of $CO_2$ agent on bottom floor can be formed more higher than in case of decreasing $CO_2$ agent injection velocity.

• Journal of Navigation and Port Research
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• v.42 no.1
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• pp.25-30
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• 2018

This study was carried out to analyze the risk attitude based on situation awareness of the Vessel Traffic Service Operator (VTSO) on the risk of collision between vessels during the monitoring of vessel traffic through the use of the VTS system. In general, when two vessels are in the close quarters situation, we analyzed the degree of risk of collision from the subjective viewpoint of the VTSOs through an administered survey. Chiefly, we analyzed the risk attitudes of each VTSO in the close quarters situation, by comparing it with the calculated value by the CoRi, which is the ship collision risk model from the VTSO's viewpoint. As a result, it was confirmed that more than 40% of the total VTSO was noted as being in a weak risk aversion type of category. Through a review of the results of analyzing the risk attitude of VTSO according to gender, age, VTS career, VTS center position, accident experience, and boarded career, it was found that there was a significant difference in the VTS career, VTS center position and accident experience. In addition, a regression model that is able to further explain the risk attitude of VTSO was derived as a factor that confirmed the significant difference and applied to CoRi to predict the collision risk according to the individual VTSO to be used as a fundamental information gathering tool for providing more accurate and safe VTS service at sea.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.2
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• pp.93-100
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• 2022

The collision behaviors of the tripod and jacket structures, which are considered as support structures for offshore wind towers at the Southwest sea of Korea, were compared by nonlinear dynamic analysis. These structures, designed for the 3 MW capacity of the wind towers, were modeled using shell elements with nonlinear behaviors, and the tower structure including the nacelle, was modeled by beam and mass elements with elastic materials. The mass of the tripod structure was approximately 1.66 times that of the jacket structure. A barge and commercial ship were modeled as the collision vessel. To consider the tidal conditions in the region, the collision levels were varied from -3.5 m to 3.5 m of the mean sea level. In addition, the collision behaviors were evaluated as increasing the minimum collision energy at the collision speed (=2.6 m/s) of each vessel by four times, respectively. Accordingly, the plastic energy dissipation ratios of the vessel were increased as the stiffness of collision region. The deformations in the wind tower occurred from vibration to collapse of conditions. The tripod structure demonstrated more collision resistance than the jacket structure. This is considered to be due to the concentrated centralized rigidity and amount of steel utilized.

• The Journal of Engineering Geology
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• v.18 no.2
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• pp.227-232
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• 2008

In this study, the pull out resistance characteristics of an anchor bar to support a spillway installed in a slope are investigated by field tests. The injection materials were a cement mortar and cement milk. Unconfined compression strengths of those materials under several conditions were measured. As the result of compression test, the unconfined compression strengths of the cement mortar and the cement milk have positive proportional relation-ship with the water-cement ratio. They also have negative proportional relationship with increasing the curing time. In the same condition of water-cement ratio and curing time, the unconfined compression strength of cement milk is larger than that of cement mortar. In order to reduce the eccentricity in anchor bar during pull-out test in the field, the installation apparatus was improved by inserting a nut type of steel fixing coupling into the anchor bar. As the result of the pull-out test, the strength modification of cement milk was increased steeply at the early curing time. However, that of cement mortar was increased gradually with passing the curing time. Therefore, the cement milk has to use as the injection material for a prompt construction of anchor bar because the strength modification of cement milk is occurred at the early curing time.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.5
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• pp.576-585
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• 2020

This study quantitatively investigated the increase in ballasting time through numerical calculations when an ultraviolet (UV) ballast water management system (BWMS) is installed on an existing vessel. The calculation results indicate that the ballasting time of a gas carrier having 55,000 dead weight tonnage was 2.152 hours without installation of the UV BWMS and implementation of a flow control function. Ballasting time increased by 14.2% after installing the UV BWMS, and it increased by 20.4% with both its installation and implementation of a flow control function. If actual conditions are taken into account, ballasting time after installing the UV BWMS is estimated to increase by at least 30% compared with current ballasting time. Therefore, when concerned parties select a UV type BWMS, it is advisable for them to minimize ship operation losses from an increase in ballasting time by considering the capacity of the actual ballast pumps on board and the flow energy loss of the UV BWMS. Additionally, it is recommended that a BWMS with larger capacity, larger pipes, and pipes with inside coatings be used to minimize the increase in ballasting time after installation of the BWMS.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.3
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• pp.51-57
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• 2021

The seawater cooling system of naval ships is installed to remove the toxic substances generated by CBR (Chemical, Biological, and Radiological) warfare and reduce the infrared signature of naval ships from outside the hull. The dispersion range of the nozzle is determined according to the injection pressure of seawater and the nozzle type. Therefore, it is necessary to select the appropriate injection pressure and design the optimal nozzles to increase the seawater dispersion area and maximize the efficiency of the cooling system. In this study, the applying feasibility of 3D printing technology to produce an injection nozzle for the seawater cooling system was examined. To this end, the extruded plastic specimens were fabricated by 3D printing, and the physical properties of the specimens were estimated through tensile testing. After this, the strain and stress of the nozzle as a function of the pressure were simulated by applying the estimated results to the finite element analysis. The finite element analysis results showed that the nozzle remained within the elastic range at the optimal pressure. The nozzle was estimated to be structurally stable, and the possibility of this study was confirmed.

• Journal of Navigation and Port Research
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• v.39 no.4
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• pp.285-291
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• 2015

Exposure to cold sea water can be life-threatening to the drowned individual. Although appropriate life jacket can be usually be provided for the buoyance at the drowning accident, heat loss can make the drowned individual experience the hypothermia. Inflatable life jackets filled with inflatable air pocket can increase the thermal protection as well as the buoyancy force. Because it is important to know how the human body behaves unde the different life jacket, present study compares the thermal insulation capacity of solid type life jacket with that of inflatable life jacket. In order to represent the insulation capacity of life jacket, thermal resistance is estimated based on the assumption of steady-state. Also, a transient three-dimensional thermal distribution of the thigh is analyzed by using finite element method implementing the Pennes bioheat equation. The finite element model is a segmental, multi-layered representation of the body section which considers the heat conduction within tissue, bone, fat and local blood flow rate.

• Journal of Navigation and Port Research
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• v.27 no.4
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• pp.437-441
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• 2003

In this paper, the 30 W power amplifier for an IMT-2000 repeater was developed a gain flatness and the third IMD (Intermodulation distortion) by microwave absorber. The absorption ability of the absorber is shown up to -10 dB and -4 dB at 3.6 GHz, 2.3 GHz band, respectively. The power amplifier without absorber has the gain over 57 dB, the gain flatness of $\pm$0.33 dB and the third IMD of 27 dBc at 33.3 W output. Otherwise, the power amplifier with absorber has the gain over 58 dB, the gain flatness of less than $\pm$0.9, the third IMD over 29 dBc at the same output power. As a result, the characteristic of the different type shows improvement of 1 dB in gain, 0.3 dB in gain flatness and 1.77 dBc in IMD.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.7
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• pp.967-976
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• 2021

Over the last ten years, the number of entanglement marine accidents has increased more than other accident types. This study analyzed the annual statistical report of marine accidents from the Korea Maritime Safety Tribunal and Korea Coast Guard. Despite some discrepancies between data of the two organizations, it was found that marine accidents involving fishing vessels were more prevalent than those involving non-fishing vessels. In addition, the main floating materials that caused wounded entanglement accidents were fishing nets, fishing gear, and ropes, and the proportion of them was high. Foreign and domestic policies on marine plastics recognize most marine plastics as marine environmental hazards and focus on marine litter recovery and the prevention of marine pollution. The representative Acts related to the marine environment and marine litter, the Marine Environment Management Act and the Marine Waste and Sediments Management Act, recognize marine litter as a type of marine waste, and deal with the types and definition of this waste. However, clearly defining marine waste is difficult. Therefore, this study tried to examine the relevant legal system of marine litter on ship operation and suggested improvement measures. Moreover, the definition of marine litter for the safe navigation and operation of ships was clearly proposed.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.7
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• pp.1038-1043
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• 2021

Guaranteed seafarer wage payment is essential to ensure a stable supply of seafarers. However, disputes over non-payment of wages to seafarers often occur. In this study, an automatic wage payment system was designed using a blockchain-based smart contract to resolve the problem of seafarers' wage arrears. The designed system consists of an information register, a matching processing unit, a review rating management unit, and wage remittance before deploying smart contracts. The matching process was designed to send an automatic notification to seafarers and shipowners if the sum of the weight of the four variables, namely wages, ship type/fishery, position, and license, exceeded a pre-defined threshold. In addition, a review rating management system, based on a combination of mean and median, was presented to serve as a medium to mutually fulfill the normal working conditions. The smart contract automatically fulfills the labor contract between the parties without an intermediary. This system will naturally resolve problems such as fraudulent advance payment to seafarers, embezzlement by unregistered employment agencies, overdue wages, and forgery of seafarers' books. If this system design is commercialized and institutionally activated, it is expected that stable wages will be guaranteed to seafarers, and in turn, the difficulties in human resources supply will be solved. We plan to test it in a local environment for further developing this system.