• Journal of Ocean Engineering and Technology
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• v.32 no.5
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• pp.297-309
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• 2018

After an accident involving mooring link failures in an offloading buoy, verification of the fatigue safety in terms of the out-of-plane bending (OPB) and in-plane bending (IPB) moments has become a key engineering item in the design of various floating offshore units. The mooring links for an 8 MW floating offshore wind turbine were selected for this study. To identify the OPB stiffness (OPB moment versus interlink angle), a numerical simulation model, called the 3-link model, is usually composed of three successive chain links closest to the fairlead or chain hawse. This paper introduces two numerical simulation techniques for the 3-link analyses. The conventional and advanced approaches are both based on the prescribed rotation approach (PRA) and direct tension approach (DTA). Comparisons of the nominal stress distributions, OPB stiffnesses, hotspot stress curves, and stress concentration curves are presented. The multiple link analyses used to identify the tension angle versus interlink angle require the OPB stiffness data from the 3-link analyses. A convergence study was conducted to determine the minimum number of links for a multi-link analysis. It was proven that 10 links were sufficient for the multi-link analysis. The tension angle versus interlink angle relations are presented based on multi-link analyses with 10 links. It was found that the subsequent results varied significantly according to the 3-link analysis techniques.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.27 no.6
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• pp.391-405
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• 2015

A global tsunami prediction system was suggested for a distant tsunami using a finite fault model and a cyclic boundary condition. The possibility of the suggested system as a distant tsunami response system was checked by applying it into the case of 2014 Chile tsunami. A comparison between the numerical results(tsunami height and arrival time) with different conditions (boundary condition, governing equation, grid size and fault model) and measured data (DART buoy, tide station) showed the importance of the finite fault model and the cyclic boundary condition.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.30 no.1
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• pp.29-38
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• 2018

In order to evaluate the performance of the floating wave power, which is an axisymmetric oscillating water column type, linearized free surface boundary condition considering the influence of PTO (power takeoff) was derived and a finite element numerical model was established. Numerical experiments were carried out by varying cylinder length, skirt length, and depth of water, which are design parameters that can change the resonance of water column in cylinder and heave resonance of the float, which is considered to affect the power generation efficiency. Finally, the basic data necessary for the optimum design of the power generation system were obtained. As a result, the efficiency of the power generation system is dominated by the heave motion resonance of the float rather than the water column resonance in the cylinder, and the resonance condition for the heave motion can be changed efficiently by attaching the skirt to the outside of the buoy.

• Smart Media Journal
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• v.5 no.3
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• pp.74-80
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• 2016

In this paper, we propose an accident-prevention smart monitoring system for Haenyeo(Woman diver) using Zigbee module and GPS sensor. This system can collect such information as the diving location, the body temperature, the depth of diving, and the diving time of a Woman diver working under the water and then respond immediately to an accident occurring. The research developed a smart Teawak and smart swimming goggles which can measure the state of a Woman diver and her diving activities. Smart Teawak, the buoy tool while a Woman diver is collecting seafoods under water, is able to receive GPS and transmit the data from smart swimming goggles and Zigbee Module to IHSS(IoT based Haenyeo Safety service Software) server. In addition, IHSS, a responsive web, provides the diving location and the state of a Woman diver on the smart phone. As a result, the system will be useful in the aspects of Woman diver' health care and the safety, furthermore, which will significantly contribute to global marketing of Woman diver with its being designated as a UNESCO intangible cultural asset.

• Journal of Ocean Engineering and Technology
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• v.34 no.6
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• pp.454-460
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• 2020

In 2019, the Korean government announced the 3rd Basic Plan for Energy, which included expanding the rate of renewable energy generation by 30-40% by 2040. Hence, offshore wind power generation, which is relatively easy to construct in large areas, should be considered. The East Sea coast of Korea is a sea area where the depth reaches 50 m, which is deeper than the west coast, even though it is only 2.5 km away from the coastline. Therefore, for offshore wind power projects on the East Sea coast, a floating offshore wind power should be considered instead of a fixed one. In this study, a response analysis was performed by applying the analytical conditions of IEC61400-3-2 for the design of floating offshore wind power generation systems. In the newly revised IEC61400-3-2 international standard, design load cases to be considered in floating offshore wind power systems are specified. The upper structure applied to the numerical analysis was a 5-MW-class wind generator developed by the National Renewable Energy Laboratory (NREL), and the marine environment conditions required for the analysis were based on the Ulsan Meteorological Buoy data from the Korea Meteorological Administration. The FAST v8 developed by NREL was used in the coupled analysis. From the simulation, the maximum response of the six degrees-of-freedom motion and the maximum load response of the joint part were compared. Additionally, redundancy was verified under abnormal conditions. The results indicate that the platform has a maximum displacement radius of approximately 40 m under an extreme sea state, and when one mooring line is broken, this distance increased to approximately 565 m. In conclusion, redundancy should be verified to determine the design of floating offshore wind farms or the arrangement of mooring systems.

• Journal of Ocean Engineering and Technology
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• v.36 no.6
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• pp.380-389
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• 2022

In the Haeundae area of Busan, South Korea, damage has continued to occur recently from building wind from caused by dense skyscrapers. Five wind observation stations were installed near LCT residential towers in Haeundae to analyze the effect of building winds during typhoon Omais. The impact of building wind was analyzed through relative and absolute evaluations. At an intersection located southeast of LCT (L-2), the strongest wind speed was measured during the monitoring. The maximum average wind speed for one minute was observed to be 38.93 m/s, which is about three times stronger than at an ocean observation buoy (12.7 m/s) at the same time. It is expected that 3 to 4 times stronger wind can be induced under certain conditions compared to the surrounding areas due to the building wind effect. In a Beaufort wind scale analysis, the wind speed at an ocean observatory was mostly distributed at Beaufort number 4, and the maximum was 8. At L-2, more than 50% of the wind speed exceeded Beaufort number 4, and numbers up to 12 were observed. However, since actual measurement has a limitation in analyzing the entire range, cross-validation with computational fluid dynamics simulation data is required to understand the characteristics of building winds.

• Journal of the Korean Geotechnical Society
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• v.22 no.3
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• pp.37-43
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• 2006

An analytical solution method capable of determining the geometric configuration and developed tensile forces of mooring lines associated with fixed plate/pile or drag anchors has been developed. The solution method, satisfying complete equilibrium conditions, is capable of analyzing multi-segmented mooring lines that can consist of either chains, cables, or synthetic wires embedded in layered seafloor soils. The solution method utilizes a systematic iterative search method based on specific boundary conditions. This paper describes the principles associated with the development of the solution for the mooring line analysis. Comparisons of predictions with results from a series of field tests of mooring lines on various types of drag anchors are also described. Comparisons include the tension in anchor, the length of mooring line on the bottom, and the angle of mooring line at the water surface buoy. The results indicate that the analytical solution method is capable of predicting the behavior of mooring lines with high degree of accuracy.

• The Journal of the Acoustical Society of Korea
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• v.28 no.4
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• pp.328-335
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• 2009

Phase variance of the acoustic signals has to be investigated with the research of the medium, because the phase of the acoustic signals carries the information of the medium. The phase compensation of the received signals is required for the signal processing of SAS (Synthetic Aperture Sonar) and underwater communication. In this paper, the phase variance of the acoustic signals was studied depending on the micro-scale-turbulence of ocean. The turbulence strength of the locally isotropic and homogeneous turbulence was calculated, and the phase variance affected by the turbulence strength was computed along the ray paths. The CTD and ADCP data were acquired from a buoy system near the Mukho port in the East Sea of Korea and the ray paths were calculated by the Bellhop algorithm. As a result, the turbulence strength was mainly determined by the variation of temperature and flow speed, changing the phase variance of the received signals. Hence, we thought the phase variance should be considered in the sonar operating system.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.4
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• pp.409-417
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• 2013

Mu-communication board supported by multi-communication is designed with Atxmega 128A1 which is a low power energy consuming of 8-bit microcontroller. ATxmega128A1 microcontroller consists of 8 UART(Universal asynchronous receiver/transmitter) ports which can be setting appropriate user interface having command line interpreter(CLI) program with each port, 2 kbytes EEPROM, 128 kbytes flash memory, 8 kbytes SRAM. 8 URAT ports are used for the multi communication modem, GPS module, etc. and EEPROM is used for saving a configuration for program running, and flash memory of 128 kbytes is used for storing a Firm Ware, and 8 kbytes SRAM is used for stack, storing memory of global variables while program running. If we uses the hybrid communication of path optimization of VHF, TRS and CDMA to remote control AtoN(aid to navigation), it is able to remove the communication shadow area. Even though there is a shadow area for individual communication method, we can select an optimum communication method. The compatibility of data has been enhanced as using of same data frame per communication devices. For the test, 8640 of data has been collected from the each buoy during 30 days in every 5 minutes and the receiving rate of the data has shown more than 99.4 %.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.26 no.2
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• pp.65-71
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• 2014

In recent years, strong typhoons have passed South Korea almost every year and severe damages were incurred directly and indirectly. However, instances where wave and wind data were procured from the offshore approach path of the typhoon are very rare and thus researchers are experiencing difficulties in obtaining calibration and verification data of typhoon-generated wave modeling. This paper provides a synthesis of records of observations by the Korea Meteorological Administration and Korea Institute of Ocean Science and Technology on storm waves generated by the typhoons SONGDA, NABI, and SHANSHAN that passed from 2004 to 2006 in order to help researchers interested in typhoon-generated wave numerical modeling. Although the trajectories of typhoon NABI and SHANSHAN were east of the Korea Strait, a significant wave height of 8.3 m was measured at Namhyeongjedo located east of Geojedo. Moreover, an unprecedented significant wave height of 12.2 m was measured for both typhoons at a station 1.4 km away from Yeongil Bay breakwater. Meanwhile, a comparative analysis of data obtained with a ocean data buoy at Geojedo and a Directional Waverider at Namhyeongjedo showed maximum wave heights that were similar but considerably different significant wave heights.