• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.4
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• pp.637-645
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• 2017

Jeju Island is composed of irregular volcanic rock layers formed by several volcanic activities. Since structure such as the offshore wind turbine has to support considerably large over turning moment due to long distance from foundation to load point and relatively large horizontal load. Pile foundations are needed to economically support such structure even in the case of rock layer. Therefore, in this study, mechanical performances are estimated by mixing ratio of water, cement, and sand to figure out optimal mixing ration of filling material for pile penetrated to rocky layers, and outcomes of this study are compared and analyzed with results of other researches. In the same conditions, mechanical performances of the mortar (S/(S+C)=20~40%) are better than those of cement paste and soil cement. On the basis of major outcome of this study, appropriate range of mixing and a strengthening model are suggested.

• International Journal of Naval Architecture and Ocean Engineering
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• v.9 no.2
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• pp.160-176
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• 2017

The interaction of focused wave groups with a vertical wall is investigated based on the second order potential theory. The NewWave theory, which represents the most probable surface elevation under a large crest, is adopted. The analytical solutions of the surface elevation, velocity potential and wave force exerted on the vertical wall are derived, up to the second order. Then, a parametric study is made on the interaction between nonlinear focused wave groups and a vertical wall by considering the effects of angles of incidence, wave steepness, focal positions, water depth, frequency bandwidth and the peak lifting factor. Results show that the wave force on the vertical wall for obliquely-incident wave groups is larger than that for normally-incident waves. The normalized peak crest of wave forces reduces with the increase of wave steepness. With the increase of the distance of focal positions from the vertical wall, the peak crest of surface elevation, although fluctuates, decreases gradually. Both the normalized peak crest and adjacent crest and trough of wave forces become larger for shallower water depth. For focused wave groups reflected by a vertical wall, the frequency bandwidth has little effects on the peak crest of wave elevation or forces, but the adjacent crest and trough become smaller for larger frequency bandwidth. There is no significant change of the peak crest and adjacent trough of surface elevation and wave forces for variation of the peak lifting factor. However, the adjacent crest increases with the increase of the peak lifting factor.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.6
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• pp.637-644
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• 2019

In recent years, many public safety systems in the smart city are developed. These systems are taking responsibility to make a safe and comfortable city. In this paper, we propose vehicle tracking systems include a public safety system that enables the policeman to track the stolen vehicles more efficiently by providing the vehicle information in real time. When a vehicle is stolen, the vehicle owner can send a user emergency request. Then, the public safety server which supported by a geospatial query technique will give information such as time, distance, and routes to a policeman who is closest to the location of the vehicle to catch the thief. 300 simulations were performed to evaluate the performance of the system. We found that the average of times required when vehicle owner send a user emergency message on user application until policeman obtain a vehicle tracking request on police application below 1.2 seconds.

• Ocean Systems Engineering
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• v.8 no.4
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• pp.427-439
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• 2018

Floating Production Storage and Offloading (FPSO) units have the advantages of their ability to provide storage and offloading capabilities which are not available in other types of floating production systems. In addition, FPSOs also provide a large deck area and substantial topsides payload capacity. They are in use in a variety of water depths and environments around the world. It is a good solution for offshore oil and gas development in fields where there is lack of an export pipeline system to shore. However due to their inherently high motions in waves, they are limited in the types of risers they can host. The Low Motion FPSO (LM-FPSO) is a novel design that is developed to maintain the advantages of the conventional FPSOs while offering significantly lower motion responses. The LM-FPSO design generally consists of a box-shape hull with large storage capacity, a free-hanging solid ballast tank (SBT) located certain distance below the hull keel, a few groups of tendons arranged to connect the SBT to the hull, a mooring system for station keeping, and a riser system. The addition of SBT to the floater results in a significant increase in heave, roll and pitch natural periods, mainly through the mass and added mass of the SBT, which significantly reduces motions in the wave frequency range. Model tests were performed at the Korea Research Institute of Ships & Ocean Engineering (KRISO) in the fall of 2016. An analytical model of the basin model (MOM) was created in Orcaflex and calibrated against the basin-model. Good agreement is achieved between global performance results from MOM's predictions and basin model measurements. The model test measurements have further verified the superior motion response of LM-FPSO. In this paper, numerical results are presented to demonstrate the comparison and correlation of the MOM results with model test measurements. The verification of the superior motion response through model test measurements is also presented in this paper.

• Journal of Ocean Engineering and Technology
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• v.35 no.3
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• pp.173-182
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• 2021

The maneuvering performance of a ship on the actual sea is very different from that in calm water due to wave-induced motion. Enhancement of a ship's maneuverability in waves at the design stage is an important way to ensure that the ship navigates safely. This paper focuses on the maneuvering prediction of a Russian trawler in wind and irregular waves. First, a unified seakeeping and maneuvering analysis of a Russian trawler is proposed. The hydrodynamic forces acting on the hull in calm water were estimated using empirical formulas based on a database containing information on several fishing vessels. A simulation of the standard maneuvering of the Russian trawler was conducted in calm water, which was checked using the International Maritime Organization (IMO) standards for ship maneuvering. Second, a unified model of seakeeping and maneuvering that considers the effect of wind and waves is proposed. The wave forces were estimated by a three-dimensional (3D) panel program (ANSYS-AQWA) and used as a database when simulating the ship maneuvering in wind and irregular waves. The wind forces and moments acting on the Russian trawler are estimated using empirical formulas based on a database of wind-tunnel test results. Third, standard maneuvering of a Russian trawler was conducted in various directions under wind and irregular wave conditions. Finally, the influence of wind and wave directions on the drifting distance and drifting angle of the ship as it turns in a circle was found. North wind has a dominant influence on the turning trajectory of the trawler.

• Progress in Superconductivity and Cryogenics
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• v.12 no.4
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• pp.24-30
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• 2010

The renewable energy source is considered as a good measure to cope with the global warming problem and the fossil energy exhaustion. The construction of electric power plant such as an offshore wind farm is rapidly increasing and this trend is expected to be continued during this century. The bulky and long distance power transmission media is essential to support and promote the sustainable expansion of renewable energy source. DC power cable is generally considered as the best solution and the demand for DC electric power has been rapidly increasing. Especially, the high temperature superconducting (HTS) DC cable system begins to make a mark because of its advantages of huge power transmission capacity, low transmission loss and other environmental friendly aspects. Technical contents of DC HTS cable system are very similar to those of AC HTS cable system. However the DC HTS cable can be operated near its critical current if the heat generation is insignificant, while the operating current of AC HTS cable is generally selected at about 50~70% of the critical current because of AC loss. We chose the specifications of the cable core of 'Tres Amigas' project as an example for our study and investigated the heat generation when the DC HTS cable operated near the critical current by some electric and thermal analyses. In this paper, we listed some technical issues on the design of the DC HTS cable core and described the process of the cable core design. And the results of examination on the current capacity, heat generation, harmonic loss and current distribution properties of the DC HTS cable are introduced.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2021.05a
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• pp.589-591
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• 2021

In the offshore plant industry, the Access service basket for aerial work is used of for various business purposes. However, various types of safety accidents continue to occur in operating these system. In the case of high-capacity workstations currently in use, workers are exposed to various risks in determining and operating the load capacity, proximity distance, and direction of operation. In this paper, to solve this problem, we develop a device that incorporates IoT-based monitoring and crash alarm systems into aerial work systems. The developed device was tested in the presence of experts to ensure reliability of the device, which allows workers and managers to easily check the operation status and thereby prevent safety accidents in advance.

• Journal of the Korean GEO-environmental Society
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• v.13 no.6
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• pp.91-100
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• 2012

Wireless monitoring system for the structural health evaluation has a limit to the reliability of measured response. The objective of this study is to evaluate an effective measurement range of the wireless monitoring system on the analyzed data. For the wireless monitoring system, Bluetooth and Wi-Fi are applied to datalogger-receiver and receiver-personal computer, respectively. For the model of the monopile structure response, a laboratory-scale monopile is manufactured with Mono Cast Nylon and a lateral loading is applied by hammer impacting. Strain gauges attached on the model monopile are connected with the datalogger. The distances of datalogger-receiver and receiver-personal computer are changed for the evaluation of the measurement range. Experimental results show that the receiving rates of the response remain almost constant within limited distance, while the receiving rates dramatically decrease out of effective range. In addition, the receiving rates affect on the measured natural frequencies of the model monopile. This study suggests that the effective range evaluation of the wireless monitoring system may be used for the determination of a monitoring distance to the monopile installed in the offshore wind farm.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.36 no.3
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• pp.175-185
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• 2000

This paper described on a basic study to organize fishing vessel control system in order to control efficiently fishing vessel in Korean offshore. It was digitalized ARPA image on the fishing processing of a fleet of purse seiner in conducting fishing operation at Cheju offshore in Korea as a digital camera and then simulated by used VTMS. Futhermore, it was investigated on the application of FVTMS which can control efficiently fishing vessels in fishing ground. The results obtained were as follows ; (1) It was taken 16 minutes and 35 minutes to casting and hauling net in fishing processing respectively. The length of rope pulled by scout boat was 200m, tactical diameter in casting net was 340.8m, turning speed was 6kts as well. (2) The processing of casting and hauling net was moved to SW, NE as results of simulation when the current direction and speed set into NE, 2kts and SW, 2kts respectively. Such as these results suggest that can predict to control the fishing vessel previously with information of fishing ground, fishery and ship's maneuvering, etc. (3) The control range of VTMS radar used in simulation was about 16 miles. Although converting from a radar of the control vessel to another one, it was continuously acquired for the vector and the target data. The optimum control position could be determined by measuring and analyzing to distance and direction between the control vessel and the fleet of fishing vessel. (4) The FVTMS(fishing vessel traffic management services) model was suggested that fishing vessels received fishing conditions and safety navigation information can operate safely and efficiently.

• Journal of Navigation and Port Research
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• v.34 no.10
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• pp.781-786
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• 2010

In this study, a new concept of ocean transport system, called the mobile harbor serving for a short distance transport of containers with cargo handling cranes between mother containerships and coastal ports, is introduced. Instead of direct berthing a very large containership at the coastal port, Mobile Harbor is moving to the offshore mooring basin with enough water depth condition. Therefore, investigation of the coastal environment, technical condition and limitation of the domestic trade ports for the application of Mobile Harbor, is essential process. To figure out the accessibility of mobile harbor, the environmental conditions, the cargo handling capacity and marine traffic volume and flow pattern has been analyzed with the tools for marine traffic simulation and virtual navigation aids system. The most proper Mobile Harbor mooring areas among trade ports of the south and east coast are selected by analyzing the obtained information and evaluating its application: (1) Under natural environmental conditions such as air and sea weather, three candidate areas are selected such as Masan port, Ulsan port, and Busan(New port) port. (2) Under marine traffic and appropriateness of water facilities, three candidate areas are selected as Mokpo port, Busan(New port) port, and Donghae & Mookho port (3) For a region-based analysis considering handling capacity and the local managed trade ports in vicinity, three candidate areas are selected as Busan region, Yosu & KwangYang region, and Mokpo region. Through this study, the basic guideline for selection of optimum trade port and offshore mooring basin for mothership and Mobile Harbor is recommended. In order to apply the Mobile Harbor to the real water, navigaton aids as the virtual route identification with AIS must be introduced for maritime safety in the vicinity of Mobile Harbor area which berthing and cargo handling is being conducted.