• Journal of the Society of Naval Architects of Korea
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• v.48 no.4
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• pp.299-307
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• 2011

The offshore plants such as FPSO are subjected to combination loading of environmental conditions (swell, wave, wind and current). Therefore the fatigue damage is occurred in the operation time because the units encounter the environmental phenomena and the structural configurations are complicated. This paper is a research for frequency domain fatigue analysis of wide-band random loading focused on accuracy of fatigue damage estimation regarding the proposed methods. We selected ideal bi-modal spectrum. And comparison between time-domain fatigue analysis and frequency-domain fatigue analyses are conducted through the fatigue damage ratio. Fatigue damage ratios according to Vanmarcke's bandwidth parameter are founded for wide-band. Considering safety, we recommend that Jiao-Moan and Tovo-Benasciutti methods are optimal way at the fatigue design for wide-band response. But, it is important that these methods based on frequency-domain unstably change the accuracy according to the material parameter of S-N curve. This study will be background and guidance for the new frequency-domain fatigue analysis development in the future.

• 한국해양학회지
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• v.25 no.4
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• pp.182-188
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• 1990

The sedimentation processes and heavy metal distributions at the Nakdong estuary were investigated during October 1987 and September 1988. The depositional sedimentary environment of the studied area was estuarine environments and was divided into three provinces depending on its textural parameters such as barrier, tidal falt, and water passes. The relationship between the textural parameters showed that the barrier was under strong wave action, that the tidal flat was under relatively weak wind-driven currents, and that the water passes were under strong and continuous tidal currents. Each environments was resulted from different transport mechanism. the sand barrier sediments were transported by all three populations including suspension, saltation, and bed load, and water pass-deposited sediments were by the bad load with some suspension population. In water mass over the studied area, the concentrations of heavy metals including Cu, Cd, $Cr^{+6}$, Pb and Zn were recorded to be 27.8, 6.7, 20.4, 16.3, and 37.3 ppb in their highest concentrations, respectively. and those in sediments were 20.0, 1.65, 25.4, 15.4, and 132.0 ppm, respectively. The total up take factored of Cu, Cd, $Cr^{+6}$, Pb, and Zn by V. Muller (corbicula fluminea) were 1600, 310, 310, 490 and 7900, respectively.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.1 no.1
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• pp.19-30
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• 1968

An experiment on the culture of laver, Porphyra tenera, was carried out from September 26, 1965 to February 12, 1966 at a laver farm on the coast of Gae-do, Hwacheong-myeon, Yeocheon-gun, Jeonranam-do, using 'Sae-ol-bal' (triple-knotted blind) laver bed, resulting in the following data: 1. 'Sae-ol-bal' laver, bed was less destroyed compared to ordinary (dual knotted blind) laver bed, the destruction rate being $9.8\%$ in 'Sae-ol-bal' laver bed, while $35.3\%$ in ordinary laver bed (Table 5). 2. The quantity of laver yield is the greatest on the edge-part, the next on the basal part, and the smallest on the middle part of the 'Sae-ol-bal' laver bed (Table 6, Figs. $7\~8$). 3. The ordinary laver bed may yield better harvest on the calm farm but 'Sae-ol-bal' laver bed yields better harvest at a farm where the destruction of bed is remarkable by wind and wave action.

• KEPCO Journal on Electric Power and Energy
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• v.6 no.2
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• pp.163-171
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• 2020

A model test for assessment of towing stability and seakeeping of a multi-purpose mobile base (MMB) was performed in calm water and wave conditions. Scale ratio of the MMB was 1/48. Tension of the towing line was measured during tests to estimate effective power to tow the full scale MMB. The tests were repeated with towing speed. In addition, an inertial measurement unit was used to measure six DOF motion of the model. Seakeeping performance was assessed through the captive model test.

• Journal of Aerospace System Engineering
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• v.11 no.2
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• pp.43-50
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• 2017

The sea of the Korean peninsula has undergone various marine changes, including naval vessels, naval operational aircrafts, air force fighters, coastal airports and airfields. In particular, salt directly affected by the marine environment, equipment operating under a high temperature / high speed as the gas turbine is the high temperature corrosion (Hot Corrosion) caused by sulfur components and salinity of the fuel used. When the height of the demister (air intake) is less than 7 m, the salinity of the salt entering the sea increases and the corrosion increases rapidly. In addition, the weapon systems operating in the East Sea than in the West Sea showed a 17% increase in the corrosion rate due to the relatively high salinity scattered by saline, wind, and wave. In order to minimize the salinity inflow, it should be operated at more than 13 m from the sea to minimize rapid hot corrosion.

• Journal of Ocean Engineering and Technology
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• v.29 no.3
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• pp.231-240
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• 2015

FPSO model tests of mooring line failure were carried out in the ocean basin at KRISO. The characteristics of the motions and mooring lines were investigated. The FPSO ship was moored using an internal turret and catenary mooring. The test model was 1/60 scale. The mooring lines were designed to satisfy the characteristics of the original mooring lines using the truncation method. The experiments were conducted under various environments: a safe wave, current and wind condition; single broken mooring line condition; and transient mode condition. The moment of the break was determined based on experimental test results. The results showed that the FPSO behavior and mooring line tensions were acceptable under the failure condition.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2011.06a
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• pp.85-86
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• 2011

On 7 December 2007, the Hebei Spirit, a 260,000 dwt VLCC, anchored near Korea's Daesan Port, was collided with a passing crane-carrying barge Samsung1, which was under tow of two tugs Samsung T5 and Samho T3. In this study, the behaviour of Hebei Spirit at the time of the accident has been reproduced and analyzed by simulation. This study precedes the study for the investigation of any available countermeasures for Hebei Spirit to prevent the accident. The simulation has been done only for Hebei Spiri and the motion of Samsung barge is just given with recorded AIS data. Dynamic characteristics of Hebei Spirit have been modeled based on empirical data and her sea trial data. Effects of current, wave and wind are also estimateed using empirical formula. Considering uncertainty of environmental condition and control of Hebei Spirit, simulation has been done by varying engine control method and holding power coefficients of the anchor. Finally, based on simulations, the most plausible scenario on the state of anchor and engine control could cause real accidents.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.48 no.4
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• pp.86-93
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• 2011

The ship movement implies current position, wave, wind, and its other factors. We need to know exactly the location and the shape of the ship and control its motion because of these effects. In order to control the small ship according to the movement of the large ship, the position and shape of the ship should be given first. In this paper we propose the method with which we know the current status of the ship without dynamic equations of the ship. There are several methods to track the system such as optical, radio frequency, radar, camera, and infrared light. We propose the movement of the ship using the GPS absolute axis. But, the genuine error by the GPS itself and the movement of the ship cause the result of the GPS of not being accurate. This paper reduces the error of the location and the shape of the ship and gives the exact values of the ship movements even if the GPS implies some error itself.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.115.2-115.2
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• 2012

In this study we have used the data of various instruments onboard the THEMIS spacecraft to study the characteristics of the outer radiation belt during the ascending phase of solar cycle 24. The most astonishing result is that we discovered four long-term (a month or so) periods during which the belt has nearly disappeared. The first disappearance started late 2008, followed by reappearance in ~a month, and three more similar events repeated until early 2010 when the belt has reappeared. This is well revealed at 719 keV electrons, which is the currently available uppermost energy channel from the THEMIS SST observation, but also seen at even lower energies. Overall consistent features were confirmed using the NOAA-POES observations. The vanished belt periods are associated with extremely weak solar wind conditions, low geomagnetic disturbances (in terms of Kp and AE/AL), greatly suppressed wave (ULF and chorus) activities, greatly reduced storm and substorm activities (little source particle supply), and expanded plasmapause locations. The direct observations of such events shed light on the fundamental question of the origin of the radiation belt, which is the main focus of our presentation.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.101.2-101.2
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• 2012

Shocks are ubiquitous in astrophysical plasmas: bow shocks are formed by the interaction of solar wind with planetary magnetic fields, and supernova explosions and jets produce shocks in interstellar and intergalactic spaces. The global morphologies of these shocks are usually described by a set of magnetohydrodynamic (MHD) equations which tacitly assumes local thermal equilibrium, and the resulting Rankine-Hugoniot shock jump conditions are applied to obtain the relationship between the upstream and downstream physical quantities. While thermal equilibrium can be achieved easily in collisional fluids, it is generally believed that collisions are infrequent in astrophysical settings. In fact, shock widths are much smaller than collisional mean free paths and a variety of kinetic phenomena are seen at the shock fronts according to in situ observations of planetary shocks. Hence, both the MHD and kinetic equations have been adopted in theoretical and numerical studies to describe different aspects of the physical phenomena associated with astrophysical shocks. In this paper, we present the results of 3D relativistic particle-in-cell (PIC) simulations for ion-electron plasmas, with focus on the shock structures: when a jet propagates into an unmagnetized ambient plasma, a shock forms in the nonlinear stage of the Weibel instability. As the shock shows the structures that resemble those predicted in MHD systems, we compare the results with those predicted in the MHD shocks. We also discuss the thermalization processes of the upstream flows based on the time evolutions of the phase space and the velocity distribution, as well as the wave spectra analyses.