• Journal of the Earthquake Engineering Society of Korea
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• v.16 no.3
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• pp.1-12
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• 2012

In this study, an analysis method for the earthquake response of an offshore wind turbine model is developed, considering the effects of the fluid-structure-soil interaction. The turbine is modeled as a tower with a lumped mass at the top of it. The tower is idealized as a tubular cantilever founded on flexible seabed. Substructure and Rayleigh-Ritz methods are used to derive the governing equation of a coupled structure-fluid-soil system incorporating interactions between the tower and sea water and between the foundation and the flexible seabed. The sea water is assumed to be a compressible but non-viscous ideal fluid. The impedance functions of a rigid footing in water-saturated soil strata are obtained from the Thin-Layer Method (TLM) and combined with the superstructure model. The developed method is applied to the earthquake response analysis of an offshore wind turbine model. The method is verified by comparing the results with reference solutions. The effects of several factors, such as the flexibility of the tower, the depth of the sea water, and the stiffness of the soil, are examined and discussed. The relative significance of the fluid-structure interaction over the soil-structure interaction is evaluated and vice versa.

• Journal of Navigation and Port Research
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• v.44 no.3
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• pp.264-274
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• 2020

The Ro-Ro ferry ship capsized and sank to the bottom of the sea because of the rapid turning for several reasons, such as lack of stability due to the center of gravity rise from the extension and rebuilding of the stern cabin, excessive cargo loading, and shortage ballast, poor lashing, etc. The purpose of this study was to investigate and analyze the cause of the ship's rapid flooding, capsizing, and sinking accident according to rapid turning scientifically and accurately using the Fluid-Structure Interaction( FSI) analysis technique. Several tests were conducted for this cause investigation of the flooding and sinking accident correctly and objectively, such as the realization of the accurate ship posture tracks according to the accident time using several accident movies and photos, the validation of cargo moving track, and sea water inflow amount through the exterior openings and interior paths compared with the ship's posture according to the accident time using the floating simulation and hydrostatic characteristics program calculation, and the performance of a full-scale ship flooding·sinking simulation.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.8
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• pp.1030-1035
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• 2012

In this research, we analysed design and CFD analysis of an inflow radial turbine for OTEC with an output power of 8kW using an working fluid of ammonia. The inflow radial turbine consists of scroll casing, vain nozzle with 18 blade numbers and rotor blade with 13 blade numbers. Mass flow rate, and inlet temperature are 0.5kg/s and $25^{\circ}C$ respectively, and variable rotational speeds were applied between 12,000 and 36,000 with 3,000 rpm intervals. As the results according to the rotational speeds, the designed speed is 24,000 rpm where maximum efficiency exists. The maximum efficiency and output power are 88.66% and 8.52kW, respectively. Through this study, we expect that the analysed results will be used as the design material for the composition of the turbine optimal design parameters corresponding to the target output power under various working material conditions.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.4
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• pp.50-60
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• 2014

Many countries are paying efforts to the research and development of water-breathing ramjet propulsion for submersible vehicle with the super-cavitation which makes traveling at high speed in underwater possible. In this study, a conceptual design of an underwater vehicle with water-breathing ramjet was carried out. Mission profiles and operating conditions are determined by examining the operation environment. Drag is estimated based on the theories of super-cavitation and fluid mechanics. The sizing and performance analysis of the components were performed using thrust required, thrust and specific impulse of designed engine were verified.

• The Korean Journal of Malacology
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• v.30 no.1
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• pp.9-15
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• 2014

This study is aimed at figuring out the reasons of the mass mortality of abalone and the increase in its mortality rate in the sea cage. The study suggests that lack seawater circulation in an abalone aquaculture cage is an important culprit for it. We analyzed the current distribution around a 1/20 scaled-down abalone unit cage of 4 rows and 10 columns by fluid flow visualization technique (PIV : Particle Image Velocimetry). The speed of current in the model cage definitely slowed down in the first column of a unit cage. We also observed currents going down to the bottom of a water tank from the unit cages placed in the middle. The speed of wakes behind inside the row in the middle was slower than that outside the row. Water velocity inside and outside a real abalone cage at Nowha Island adjacent to Wan Island was measured to verify results from the tank test. The speed of current in front of the cage by 2 m was 0.11 m/sec while it was only 0.0009 m/sec inside the cage. It had similar findings with those of a tank test.

• Journal of Energy Engineering
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• v.4 no.3
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• pp.420-428
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• 1995

현재 사용하고 있는 액화천연가스 기화기는 관내부로 -162$^{\circ}C$의 액화가스가 흐르고, 관외부로 발전소 증기응축기 출구에서 배출된 20~3$0^{\circ}C$의 해수를 흐르도록 하여, 두 유체사이의 온도차로 기화시키는 간접접촉방식 열교환기가 사용되고 있다. 그러나 간접접촉방식 열교환기는 두 유체사이의 큰 온도차로 인한 금속재료의 피로현상과 해수의 염분에 의한 재질의 부식 및 미생물 부착 등의 원인으로 열전달효율이 저하되고 있다. 따라서 본 연구는 관을 중간매체로 하는 간접접촉식 열교환기대신 액화천연가스와 기화용수인 물을 직접접촉시키는 방법으로 이용하여, 위와 같은 문제점들을 근본적으로 해결하려 한다. 본 실험에서는 기화기내의 수위 500 mm와 물의 유량 10 l/min을 일정하게 고정시키고, 액화천연가스의 유량 0.12 ㅣ/min, 0.36 l/min, 0.6 l/min, 기화기내의 압력을 100 kPa, 300 kPa, 500kPa로 변화시키면서 기화기내의 기포, 온도분포, 급팽창현상, 동결현상 및 기화후 수분함유량등의 비등특성을 규명하였다. 실험결과 기화기내의 압력이 증가할수록 기포는 작고 균일한 분포를 이루고, 폭발적인 급팽창현상은 일어나지 않았다. 또한 동결현상은 액화천연가스의 기화를 방지하지 못하였으며, 기화된 천연가스내의 수분함유량 몰%는 압력과 유량이 증가함에 따라 감소하는 경향을 보이고 있다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.15 no.4
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• pp.232-241
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• 2003

The interaction of incident monochromiatic waves with N bottom-mounted porous circular cylinders is investigated in the frame of three-dimensional linear potential theory. The fluid domain is divided into N+l regions i.e. a single exterior region and N interior regions, and the diffraction potential in each fluid region is expressed by an eigenfunction expansion method (Williams and Li,2000). The analytic results show that the porous structure reduces both the wave forces and the run-up wave around the cylinder. To verify the developed model, the systematic model test with a line array of porous cylinders is conducted at the wave tank (30m$\times$7m$\times$1.5m). The analytic results are in good agreement with the experimental results within measured frequency range. It is concluded that the breakwater constructed with an array of porous circular cylinders shows the performance of an effective wave barrier together with the seawater-exchange effect and is considered to have vast potentials for the use of seawater-exchanging breakwater in the future.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.7
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• pp.883-889
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• 2014

It is generated for cavitation erosion due to the local static boiling by pressure differentials in high speed rotating fluid environment. The cavitation is influenced by various elements such as pressure, velocity, temperature, pH of fluid and medium. In particular, the damage of material is accelerated due to the electrochemical corrosion by $C1^-$ and cavitation erosion due to cavities in seawater. In this paper, hence, it investigated for martensite stainless steel the damage behavior with applied current density and cavitation time in natural seawater solution. Less damage depth at the cavitation condition was observed than static condition as a result of galvanostatic experiment. Furthermore, it was shown that dramatic increase of weightloss, damage rate and damage depth after 3 hour of cavitation test.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.4
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• pp.432-436
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• 2015

This study computationally explored the thermal performance of passively-cooled polymer heat sinks utilizing seawater. Polymer heat sinks are proposed as cooling modules of the cold sides of thermoelectric generators for waste heat recovery. 3-D Computational Fluid Dynamics (CFD) modelling was conducted for a detailed numerical study. Polyphenylene sulfide (PPS) and pyrolytic graphite (PG) were selected for the base materials of polymer heat sinks. The computational study evaluated the performance of the PPS and PG heat sinks at various fin numbers and fin thicknesses. Their performances were compared with those of aluminum (Al) and titanium (Ti) heat sinks. The study results showed that the thermal performance of the PG heat sink was 3~4 times better than that of the Ti heat sink. This might be due mainly to the better heat spreading of the PG heat sink than the Ti heat sink. The effect of the number of fins on the performance of the PG heat sink was dissimilar to the cases of the PPS and Ti heat sinks. This result can be explained by the interrelationships among heat spreading, surface area enhancement, and fluidic resistance incorporating with an increase in the number of fins.

• Journal of the Society of Naval Architects of Korea
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• v.59 no.1
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• pp.46-54
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• 2022

A magnetohydrodynamic (MHD) seawater propulsion thruster has been proposed to reduce propeller noise, propeller pitting, and vessel vibration originated from the propeller cavitation. The MHD thruster was also focused to overcome the limitation of propulsion velocity for the special purpose of marine ships. The research trends and key technologies in the worldwide leading countries are reviewed for the development of MHD propulsion thrusters in Korea. A small performance test device was developed firstly with a conventional solenoid magnet of ≤0.6 Tesla and a helical-type cylindrical duct(inner diameter of 5 cm) of thruster. The artificial seawater was fabricated by a salt solution including a conductivity of 5~6 S/m. The measured flow velocity of artificial seawater in the test device was 0.03~0.42 m/s (0.06~0.84 Knot) with a magnetic field strength of 0.6 Tesla and the applied currents of 10~80 A including the change of anode materials. It was found that the flow direction of seawater was reversed by the directional change of applied current in the solenoid magnet.