• Ocean Systems Engineering
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• 제7권3호
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• pp.179-193
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• 2017

Dynamic response analysis of offshore triceratops with stiffened buoyant legs under impact and non-impact waves is presented. Triceratops is relatively new-generation complaint platform being explored in the recent past for its suitability in ultra-deep waters. Buoyant legs support the deck through ball joints, which partially isolate the deck by not transferring rotation from legs to the deck. Buoyant legs are interconnected using equally spaced stiffeners, inducing more integral action in dispersing the encountered wave loads. Two typical nonlinear waves under very high sea state are used to simulate impact and non-impact waves. Parameters of JONSWAP spectrum are chosen to produce waves with high vertical and horizontal asymmetries. Impact waves are simulated by steep, front asymmetric waves while non-impact waves are simulated using Stokes nonlinear irregular waves. Based on the numerical analyses presented, it is seen that the platform experiences both steady state (springing) and transient response (ringing) of high amplitudes. Response of the deck shows significant reduction in rotational degrees-of-freedom due to isolation offered by ball joints. Weak-asymmetric waves, resulting in non-impact waves cause steady state response. Beat phenomenon is noticed in almost all degrees-of-freedom but values in sway, roll and yaw are considerably low as angle of incidence is zero degrees. Impact waves cause response in higher frequencies; bursting nature of pitch response is a clear manifestation of the effect of impact waves on buoyant legs. Non-impact waves cause response similar to that of a beating phenomenon in all active degrees-of-freedom, which otherwise would not be present under normal loading. Power spectral density plots show energy content of response for a wide bandwidth of frequencies, indicating an alarming behaviour apart from being highly nonlinear. Heave, being one of the stiff degrees-of-freedom is triggered under non-impact waves, which resulted in tether tension variation under non-impact waves as well. Reduced deck response aids functional requirements of triceratops even under impact and non-impact waves. Stiffened group of buoyant legs enable a monolithic behaviour, enhancing stiffness in vertical plane.

• 대한조선학회논문집
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• 제54권1호
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• pp.34-42
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• 2017

In rough seas, green water shipped on board may impose quite large impact loads on the structures on deck and sometimes result in structure damages. One of the essential tasks of the naval fluid engineers is to provide the design impact loads which are needed for proper design of the structure strength against the green water impacts. Computation of the design impact load due to green water needs first a process to find the sea condition and the ship cruising condition which cause maximum green water impacts on structures as well as other succeeding processes to compute ship motion responses, green water flows and impact loads. Also, as a bold and practical process, it is needed that the irregular real seas are to be substituted by design regular waves which are equivalent in view points of green water impacts. In this paper, the whole processes to compute the design green water loads acting on bow structure are set up creatively. And the green water design impact loads acting on the box-type structure of a high-speed ship's bow are computed and discussed.

• 한국어류학회지
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• 제28권3호
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• pp.147-155
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• 2016

This study describes the cell type, ultrastructure and histochemical characteristics as a preliminary study for the research on integument of the smooth lumpsucker, Aptocyclus ventricosus in accordance with the physiological and environmental changes using light and electron microscopes. The SEM revealed the presence of well-developed finger printing structure in the skin surface. The skin surface of the smooth lumpsucker showed an irregular folds in cross section of light microscope. Integument is composed of outer epidermal and inner dermal layer. The epidermal layer is a stratified layer composed of epithelial cells, mucous cells, vacuolar cells, and granular cells. Epithelial cells are classified into superficial, intermediated, and basal cell. The superficial cells were the squamous with well-developed microridges on the free surface, and the microridges were covered with glycocalyx. The mucous cells of unicellular gland were mainly distributed in the apical layer of epidermis and contained mucosal materials of neutral glycoprotein. The vacuolar cells of unicellular gland were mainly distributed in the mid and basal layer of epidermis. The proportion of mucous cells and vacuolar cells were $7.0({\pm}1.07)%$ and $40.6({\pm}3.31)%$ of epidermal area, respectively. The granular cells contained membrane bounded secretory granules with high electron density and developed cell organelles in the cytoplasm. The dermal layer was loose connective tissue layer and composed of mainly collagen fibers. It also contained blood vessels and chromatophores of melanophores and reflecting platelets.

• 한국수산과학회지
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• 제36권2호
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• pp.129-135
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• 2003

2001년 9월부터 2002년 7월 사이 낙동강 하구역에서 otter trawl을 이용하여 계절별로 어류를 채집하여 종조성 및 양적변동을 파악하고, 하구둑 건설이전 어류 조사와 비교하였다. 본 조사에서는 총 21과 30종의 어류가 채집되었으며, 문절망둑과 주둥치가 최우점종이었는데, 이들 어종이 전체 채집 개체수와 성체량의 $71.2\%$와 $67.8\%$를 차지하였다. 그 외 양태, 꼼치 등이 우점하였다. 채집종수는 봄과 가을에, 개체수 및 생체량은 봄과 여름에 높았으나, 겨울에는 모두 낮았다. 하구둑이 완공되기 직전에 실시된 어류 조사와 비교한 결과 어류 종조성의 변화가 뚜렷하였다. 과거의 우점종인 흰베도라치, 실양태, 밴댕이 및 고등어 등은 채집량이 크게 감소한 반명, 문절망둑, 양태, 꼼치, 두줄망둑 및 농어 등은 채집량이 크게 증가하였다. 하구둑 건설 이후 강 상류로부터 내려오는 담수의 유입이 수시로 차단됨에 따라 하구역에서의 해수 유동 변동이 초래되었으며, 그 결과 하구역에 각종 부유물이 축척되는 등의 저질 환경이 변화가 일어나 어류상에 영향을 준 것으로 보인다.

• 수산해양기술연구
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• 제21권2호
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• pp.123-130
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• 1985

Loran-C 위치의 정도를 높이기 위하여 제주지역을 대상으로 북동태평양 Chain (GRI 5970)에 대한 시간차를 관측하여 그 전파경로와 측지계 및 전파속도에 따른 시간차오차 등을 분석 검토한 결과는 다음과 같다. 1. Loran-C 전파는 M-X 조국, M-Y조국 모두 주국, X, Y 종국과 관측점 사이에 높이 500m 이상 되는 한라산을 통과하여 전파될 때 시간차 오차가 커짐을 알 수 있었다. 2. 측지계 및 전파속도의 보정에 따른 시간차오차는 M-X 조국에서는 측지계변환과 속도보정을 행할수록 적어지고, M-Y조국에서는 M-X조국과는 달리 해상 및 육상의 전파경로에 따라 시간차오차가 불규칙적으로 변함을 알 수 있었다. 3. 보정요소별 측위의 정도는 측지계를 변화하고 속도보정을 행한 것이 가장 높고, WGS-72 측지계를 변환시키지 않은 것이 가장 낮았다. 4. 측정위치의 정도를 향상시키기 위해서는 굴절율에 의한 속도보정과 측지계변환 및 육상전파속도보정을 행하여야 함을 알 수 있었다.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2016년도 추계학술대회 논문집
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• pp.153-153
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• 2016

Aluminum alloys have poor corrosion resistance compared to the pure aluminum due to the additive elements. Thus, anodizing technology artificially generating thick oxide films are widely applied nowadays in order to improve corrosion resistance. Anodizing is one of the surface modification techniques, which is commercially applicable to a large surface at a low price. However, most studies up to now have focused on its commercialization with hardly any research on the assessment and improvement of the physical characteristics of the anodized films. Therefore, this study aims to select the optimum temperature of sulfuric electrolyte to perform excellent corrosion resistance in the harsh marine environment through electrochemical experiment in the sea water upon generating porous films by variating the temperatures of sulfuric electrolyte. To fabricate uniform porous film of 5083 aluminum alloy, we conducted electro-polishing under the 25 V at $5^{\circ}C$ condition for three minutes using mixed solution of ethanol (95 %) and perchloric (70 %) acid with volume ratio of 4:1. Afterward, the first step surface modification was performed using sulfuric acid as an electrolyte where the electrolyte concentration was maintained at 10 vol.% by using a jacketed beaker. For anode, 5083 aluminum alloy with thickness of 5 mm and size of $2cm{\times}2cm$ was used, while platinum electrode was used for cathode. The distance between the two was maintained at 3 cm. Afterward, the irregular oxide film that was created in the first step surface modification was removed. For the second step surface modification process (identical to the step 1), etching was performed using mixture of chromic acid (1.8 wt.%) and phosphoric acid (6 wt.%) at $60^{\circ}C$ temperature for 30 minutes. Anodic polarization test was performed at scan rate of 2 mV/s up to +3.0 V vs open circuit potential in natural seawater. Surface morphology was compared using 3D analysis microscope to observe the damage behavior. As a result, the case of surface modification presented a significantly lower corrosion current density than that without modification, indicating excellent corrosion resistance.

• International Journal of Naval Architecture and Ocean Engineering
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• 제9권1호
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• pp.1-10
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• 2017

Various offshore structures such as FPSO, FSO, Semi-submersible, TLP and Spar are operated to develop offshore oil and gas fields. Most of the offshore structures shall be operated over 20 years under the harsh environments at sites so that the offshore structures should be designed to endure the harsh environments. In this study, the effect of the impact load (so called slapping load) by the steep waves acting on the FPSO bow is investigated through the model test. For measurement of the impact pressures on the frontal area, a bow-shaped panel was fabricated, and installed the pressure sensors on the bow starboard side of the model FPSO. During the model test campaign, the impact load was investigated using the steep waves with $Hs/{\lambda}$ greater than 1/16 of the representative wave condition. Consequently, it is confirmed through the model test that the impact loads acting on the FPSO bow are significantly increased with the steep waves ($Hs/{\lambda}$ > 1/16) than the representative wave conditions of a maximum significant wave height and a pitch forcing period. Therefore, for safe design of North Sea FPSO, it is necessary to consider the steep waves in addition to the representative wave conditions and to be applied as proper structural load. Also, the effect of random seeds in irregular waves should be considered to build the safe FPSO.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 춘계학술대회 논문집
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• pp.208-213
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• 2003

Recently, Side-by-side mooring system of LNG FPSO and shuttle tanker is one of hot issues in offshore floating body dynamics, which requires accurate analysis of hydrodynamic interactions between side by side moored LNG FPSO and shuttle tanker than tandem moored vessels. This paper aims to investigate basic interaction characteristics of side-by-side moored multiple vessels both numerically and experimentally. A higher-order boundary element method combined with generalized nwde approach will be applied to analysis of motion and drift force of side by side moored multiple-body. Model tests were carried out for the same multiple floating bodies in regular and irregular waves. Motion responses and drift forces of vessels for two mooring situation(coupled & uncoupled) were compared with those of calculations. Discussions will be highlighted on applicability of numerical method to prediction of sophisticated multi-body interaction problem of which motion behavior is very important to analysis of mooring dynamics of deep sea floating bodies.

• 한국해안해양공학회지
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• 제14권1호
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• pp.76-85
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• 2002

부유식 방파제는 고정식 방파제에 비하여 항 내·외 해수교환성은 우수한 반면, 항내 정은도가 다소 저하되는 특징이 있다. 따라서, 설계초기단계에서 부유식 방파제의 여러 평면배치 대안에 대하여 항내 정온도를 적절히 평가할 필요가 있다. 본 연구에서는 기존의 시간의존완경사 방정식을 부유식 방파제 설치안에 대해서도 적용할 수 있도록 하기 위하여 부유식 방파제의 반사와 투과를 동시에 반영할 수 있는 일종의 반사-투과 경계조건을 정식화하였다. 본 경계조건의 성능을 검토하기 위하여 이차원 및 삼차원 해석을 수행한 결과, 수치해석에 입력된 반사 및 투과율이 수치적으로 잘 구현됨을 확인하였다. 마지막으로 본 반사-투과 경계조건을 부유식 방파제가 설치되어 있는 가상적 항만에 적용하였으며, 본 수치해석이 부유식 방파제의 실해역 설치를 위한 실무에서도 충분히 효과적으로 이용될 수 있음을 예시하였다.

• 한국해안해양공학회지
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• 제8권2호
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• pp.193-203
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• 1996

죽변항 내외의 2개 정점에 수압식 파고계를 설치하여 동계의 악천후시 현장관측을 실시하고 장주기 부진동 특성을 파악하였다. 관측자료 분석에 의한 공진주기 해석시 기존의 항내 정점에서 스펙트럼 에너지가 최대인 주기 및 그 분포 형태를 기준한 방법외에 항외에 대한 항내 정점에서의 상대 증폭비를 기준한 방법을 도입하였다. 자료 분석과 수치실험 결과 죽변항 수역의 제1 공진 모드는 약 12분에서 약 7배의 증폭비를 가지며 제2 공진 모드는 약 6분인 것으로 나타났다. 관측기간중 항내에서의 수면진동폭은 약 10-20 cm로 나타났으며 황천시 항내 정점에서 단주기파의 군파 효과 또는 이 성분이 장주기파에 중첩된 영향에 의한 것으로 생각되는 2-3분 부근의 부진동이 출현하였다. 단주기파와 장주기파에서 통상적으로 사용되는 반사율을 선형적으로 연결시킨 수치실험을 통하여 3분 이하 부진동에서의 증폭비를 비교적 잘 재현하였다.