• 한국해양공학회지
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• 제30권2호
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• pp.91-99
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• 2016

The global demand for oil and natural gas has increased, and resource development is moving to the deep sea. Floating and flexible offshore structures such as semi-submersible, spar, and FPSO structures have been widely used. The major equipment of floating structures is always exposed to waves, currents, and other marine environmental factors, which cause structural damage. Moreover, flexible risers are susceptible to an exciting force due to the motion of the floating body. The inline and transverse responses from the three-dimensional behavior of a floating structure occur because of various forces. Typical risers are made of steel pipe and applied in the oil and gas development field, but flexible materials such as polyethylene are suitable for OTEC risers. Consequently, the optimal design of a flexible offshore plant requires a dynamic behavior analysis of slender bodies made of the different materials commonly used for offshore flexible risers. In this study, a three-dimensional motion measurement device was used to analyze the displacements of riser models induced by external force factors, and forced oscillation of a riser was linked to forced oscillation under a steady flow and regular wave condition.

• Journal of Advanced Marine Engineering and Technology
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• 제40권1호
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• pp.39-44
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• 2016

선박 및 해양플랜트용 자동전압조정기(AVR)는 발전기의 출력전압을 실시간 검출하여 기준 전압으로 조정하는 장치로서 기존에는 아날로그 타입의 자동전압조정기가 주로 사용되었지만 목표값에 대한 응답성과 신속성의 개선이 요구됨으로써 디지털 방식의 전압조정기로 대체되는 추세이다. 본 논문에서는 부하변동이 심하고 운전 환경이 열악한 해양플랜트 발전기용 자동전압조정기의 특성에 적합한 디지털 자동전압조정기 시스템을 새롭게 구성하였으며 부하변동 및 임의의 출력전압 변동 실험을 통해 안정성과 속응성을 비교하여 우수성을 입증하였다. 또한, 실시간으로 발전기의 출력 전압과 여자기의 계자전류를 감시하고 자동전압조정기의 게인 값을 편리하게 조정할 수 있는 통합제어시스템을 개발하였다.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2005년도 춘계학술대회 논문집
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• pp.285-290
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• 2005

지금까지 우리나라의 양식 산업은 양적인 측면에서 괄목할 만한 성장을 하였으나, 양적인 성장의 이면에 많은 문제를 파생시켜 최근에는 여러 가지 형태로 그 부작용이 나타나고 있다. 특히, 우리나라 양식 시설의 약 82%가 남해안의 내만에 집중 시설되어 있어 생활오수와 공장폐수의 유입 및 한정된 영역에서 장기간의 고밀도 양식으로 양식장들의 자가 오염등으로 어장환경이 악화되고 있다. 이같은 문제를 해소하기 위한 방안으로는 수질이 양호하며 해수유동이 많아 환경 피해가 적은 외해를 이용하는 것이 점차 대두되고 있다. 그러나 외해는 수질히 비교적 양호하나, 양식시설에 직접 피해를 줄 수 있는 높은 파도와 강한 흐름이 존재하고 있어 기존 내해용 양식시설로 외해로 진출하는 것이 곤란하므로 외해의 해양조건에 알맞은 양식 시설물의 개발이 필요하다. 본 연구는 이러한 필요성을 염두에 두고 외해양식에서 사용가능한 양식구조물의 설계에 필요한 이론적 연구와 실험적 해석을 수행하였다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제8권5호
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• pp.487-495
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• 2016

In the offshore project such as semi-submersible FPU and FPSO, the free fall type life boat called TEMPSC (Totally Enclosed Motor Propelled Survival Craft) has been installed for the use of an emergency evacuation of POB (People on Board) from the topside platform. For the design of life boat arrangement for semi-submersible FPU in the initial design stage, the drop height and launch angle are required fulfill with the limitation of classification society rule and Company requirement, including type of approval as applicable when intact and damage condition of the platform. In this paper, we have been performed the numerical studies to find proper arrangement for the life boats consider drop height in various environmental conditions such as wave, wind and current. In the calculations, the contributions from static and low frequency (LF) motions are considered from the hydrodynamic and mooring analysis as well as damage angle from the intact and damage stability analysis. Also, Air-gap calculation at the life boat positions has been carried out to check the effect on the life boat arrangement. The air-gap assessment is based on the extreme air-gap method includes the effect of 1st order wave frequency (WF) motions, 2nd order low frequency roll/pitch motion, static trim/heel and set down.

• 풍력에너지저널
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• 제14권2호
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• pp.26-33
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• 2023

In this study, the global response characteristics of floater and mooring for floating offshore wind turbine with a detachable mooring system are performed. Global motion and structural response result extracted from the coupled motion analysis of 10MW DTU floating offshore wind turbine with detachable mooring system modeled by high-order boundary element model and finite element mesh, were used to study the characteristics of tension on mooring lines subjected to three different types of ocean loads. Breaking limit of mooring line characterized by wind, current and wave load has a major effect on the distribution of mooring tension found in time domain analysis. Based on the numerical results of coupled motion analysis, governing equation for calculating the motion response of a floater under ocean loads, and excitation force and surge motion and tension respectively are presented using excursion curve. It is found that the response of floater is reliable and accurate for calculating the tension distributions along the mooring lines under complex loadings. This means that the minimun breaking limit of mooring system satisfied a design criteria at ultimate ocean environmental loading condtions.

• 한국표면공학회지
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• 제48권2호
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• pp.68-72
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• 2015

The corrosion behavior of metals and alloys for the safety of offshore structures in seawater was investigated for the application of sacrificial anodes. The experiments were focused on the polarization behaviors and the surface morphology of each metal after experiments. Pure Zn, pure Al (Al1050), Al alloys (Al5052, Al6061), Mg alloys (AZ31, AZ91D) and steel (SCM440) were assessed in 3.5% sodium chloride solution by means of potentiodynamic polarization to verify the galvanic corrosion potential ($E_{couple}$). Potentiostat plots were plotted to compare the surface and corrosion current density ($i_{couple}$) of metals as sacrificial anodes in seawater to protect steel alloy as a cathode. Al alloys showed the best performance as a sacrificial anode, on the other hand, Mg alloys showed overprotection behavior. The surface morphologies of sacrificial anodes were observed by FESEM and compared.

• 수산경영론집
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• 제37권1호
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• pp.1-24
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• 2006

Reducing fishing capacity is one of current issues in the international fisheries. This is because that increased fishing capacity has caused not only fish stocks to be depleted, but also additional fishing costs to be incurred, which resulted in reduction of economically viability of fisheries. For this reason, FAO adopted the International Plan of Action for the Management of Fishing Capacity' in 1999 and recommended member countries to estimate fishing capacity and to implement the policy to reduce fishing capacity. This study is aimed to measure fishing capacity of the Large Purse Seines Fishery that is one of offshore fisheries in Korea using both Peak - to - Peak Analysis and Data Envelopment Analysis in order to provide a policy information for preparation of domestic plan of action for the management of fishing capacity. The results of PTP Analysis were almost similar to those of DEA Analysis. The DEA results showed that the capacity utilization in 2004 was about 75%, it was obvious the capacity did not utilize enough. The sensitivity analysis on DEA results indicated that 24% of the number of ships, 26% of the tonnages, or 29% of the horse powers should be reduced if the present catch remained. In addition, if the catch remains at the MSY base level of large purse seines, the analysis suggested that the number of ships, tonnages and horse powers should be reduced by 15%, 18%, and 21% respectively.

• 한국해양공학회지
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• 제31권6호
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• pp.379-387
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• 2017

In this study, a pile-guide mooring system (PGMS) was designed for an offshore liquefied natural gas bunkering terminal (LNG-BT), which is an essential infrastructure for large LNG-fuelled ships. The PGMS consisted of guide piles to restrict five motions of the floater, except for heave, as well as a seabed truss structure to support the guide piles and foundation piles to fix the system to the seabed. Singapore port was considered for a case study because it is a highly probable ports for LNG bunkering projects. The wave height, current speed, and wind speed in Singapore port were investigated to calculate the environmental loads acting on the hull and PGMS. A load and resistance factor approach was used for the structural design, and a finite element analysis was performed for design verification. The steel usage of the PGMS was analyzed and compared with the material usage of a gravity-based structure under similar LNG capacity and water depth criteria. This paper also describes the water depth limit and wave conditions of the PGMS based on estimation of the initial investment and the present value profit difference. It suggests a suitable LNG-BT support system for various design conditions.

• 한국해안·해양공학회논문집
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• 제21권6호
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• pp.462-469
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• 2009

파랑과 흐름이 공존하는 해안에서의 비점착성 퇴적물이동에 대하여 육지-외해방향 총 퇴적물 이동률을 산정할 수 있는 경험식을 제안한다. 본 경험식은 파랑만 존재하는 경우와 흐름만 존재하는 경우에도 범용적으로 사용할 수 있다. 해수면 기준 비대칭인 파랑을 이용하여 퇴적물의 부상률과 이동거리의 곱으로 단위면적당 총 퇴적물 이동률을 계산할 수 있다. 대체로 파고가 큰 파랑이 입사하는 경우 퇴적물은 외해방향으로 이동하는 반면 파고가 작은 파랑의 경우 육지방향으로 퇴적물을 이동시키는 경향을 본 예측식이 잘 재현하고 있다. 또한 장주기 파랑의 경우 퇴적물을 육지방향으로 이동시키려는 경향을 본 예측식이 잘 보여준다.

• ALGAE
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• 제26권1호
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• pp.41-50
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• 2011

Yellow Sea surface sediment samples collected on October 15-31, 2003 were analyzed using the palynological process to investigate the spatial distribution of dinoflagellate resting cysts. The sampling areas comprised four latitudinal transects, the northernmost of which was located off the Shandong Peninsula, China and the southernmost off Jeju Island, Korea. Each transect line was composed of six to nine stations, spanning the distance between the Chinese and Korean coasts. Twenty-five different types of dinoflagellate cysts were identified. Gonyaulax scrippsae, Alexandrium spp. (ellipsoidal type), and G. spinifera were the most dominant at all stations surveyed. Dinoflagellate cysts belonging to the Gonyaulacales comprised over 50% of all cysts collected. The latitudinal distribution trend showed that cyst concentrations along the two middle transects were much higher than those along the two northern and southern transects. Cyst concentrations in the offshore central areas reached their highest values within each transect and gradually decreased toward the Chinese and Korean coasts. Overall, cyst concentrations were markedly elevated in the offshore central Yellow Sea areas and gradually decreased outward in all four directions. This concentric cyst distribution pattern was consistent with the hydrographic features of the Yellow Sea, such as circular current systems, sedimentary properties, and water depth.