• Journal of Wetlands Research
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• v.8 no.3
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• pp.67-77
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• 2006

Sedimentological investigations on surface and suspended sediments were performed in Masan Bay of the South Sea in order to reveal recent changes in depositional environments concerning anthropogenic influence. Surface sediments had been classified as 3 sediment facies: mud, slightly gravelly mud, and gravelly mud. In general, mud facies with more than 60% of silt is predominant and slightly gravelly mud facies occurs at the watercourse of bay's central area. The silt-dominant mud faices appears to be predominant before and after dredging. Temperature and salinity changes during one tidal cycle for each season suggest that water columns were stratified without vertical mixing regardless of the season due to weak intensity of tide from the effect of geographical features. The effect of freshwater discharge from the land seems to be insignificant. The strongest current was observed during ebb tide in spring and autumn while observed during flood tide in summer and winter. Net sediment flux (fs) and net suspended sediment transport (Qs) for suspended sediment were determined by remaining drift developed here. Net suspended sediment transport loads were seaward with $62.02{\times}10^3kgm^{-1}$, $31.84{\times}10^3kgm^{-1}$ in spring and fall, respectively, and landward with $18.23{\times}10^3kgm^{-1}$, $3.22{\times}10^3kgm^{-1}$ in summer and winter, respectively.

• Journal of the Korean Society for Marine Environment & Energy
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• v.13 no.4
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• pp.296-304
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• 2010

The shoreline change caused by the construction of shore protection structures are discussed based on the example of Youngrang coast, Sokcho where the coastal erosion control system(CECS), three artificial headlands and two submerged breakwaters are being constructed. The study qualitatively analyzed the shoreline changes of Youngrang coast using available satellite/aerial photographs and camera photographs taken during the construction period of 6 years since 2002 for the artificial headlands construction. The main results from the study are as following. (1) Before the installation of the middle artificial headland, longshore drifts along Youngrang coast are transported in the NW-SE direction according to the seasonally different wave characteristics. (2) During the CECS construction the shoreline is continuously changed by altering the local longshore drift budget. Especially, the middle artificial headland induces considerable change of shoreline by blocking the sediment supply from the southern pocket beach to the northern pocket beach and by accelerating the sediment accretion at the wave shadow zone behind its head. It induces the asymmetry on the net longshore drift causing the significant erosion at the center of the southern pocket beach. (3) The study demonstrates that serious unintended erosion/accretion problem are possibly occurred due to local changes on the wave transformation and the sediment transport by the construction of coastal erosion control system.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.46 no.4
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• pp.445-453
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• 2013

Walleye pollock Theragra chalcogramma fisheries in Korean waters have changed dramatically during the last three decades: the highest catches occurred in 1981, followed by continuous decreases through the 1990s, ending with a complete collapse of the population in the 2000s. The major spawning ground of walleye pollock is located in North Korean waters, and some juveniles (called nogari in Korean, <300 mm) migrate to the south for feeding and growth. Since the 1960s, Korean fishermen have often caught juveniles, and the weight (metric tons) of juvenile catch was recorded from 1975-1997. However, because the walleye pollock were not aged, the population age structure was not delineated. We developed a model to estimate the number of walleye pollock of each size class based on catch statistics of adults and juveniles, the catch proportion of each size class, and length and weight information on specimens collected by Danish-seine and drift-gill-net fisheries. The model results demonstrated that the recruitment size of walleye pollock was consistently within the 200-250mm size class, and the highest number of this size class occurred in 1981, although values greatly fluctuated interannually. The number of juvenile pollock was 10.4 times higher than that of adult pollock during 1975-1997. The total yield of juvenile pollock was 0.95 million tons, which was equivalent to about 68.2% of total pollock production. The number of juvenile pollock caught during the same period, however, was 16 billion, comprising about 91.2% of the total number caught. Such high fishing pressure on juvenile pollock is considered one of the main factors causing the collapse of the pollock population.

• Nuclear Engineering and Technology
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• v.42 no.2
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• pp.219-230
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• 2010

In nuclear power plants (NPPs), periodic sensor calibrations are required to assure that sensors are operating correctly. By checking the sensor's operating status at every fuel outage, faulty sensors may remain undetected for periods of up to 24 months. Moreover, typically, only a few faulty sensors are found to be calibrated. For the safe operation of NPP and the reduction of unnecessary calibration, on-line instrument calibration monitoring is needed. In this study, principal component-based auto-associative support vector regression (PCSVR) using response surface methodology (RSM) is proposed for the sensor signal validation of NPPs. This paper describes the design of a PCSVR-based sensor validation system for a power generation system. RSM is employed to determine the optimal values of SVR hyperparameters and is compared to the genetic algorithm (GA). The proposed PCSVR model is confirmed with the actual plant data of Kori Nuclear Power Plant Unit 3 and is compared with the Auto-Associative support vector regression (AASVR) and the auto-associative neural network (AANN) model. The auto-sensitivity of AASVR is improved by around six times by using a PCA, resulting in good detection of sensor drift. Compared to AANN, accuracy and cross-sensitivity are better while the auto-sensitivity is almost the same. Meanwhile, the proposed RSM for the optimization of the PCSVR algorithm performs even better in terms of accuracy, auto-sensitivity, and averaged maximum error, except in averaged RMS error, and this method is much more time efficient compared to the conventional GA method.

• Korean Journal of Ichthyology
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• v.30 no.2
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• pp.114-118
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• 2018

A single specimen (1,058 mm TL) of Pteroplatytrygon violacea, belonging to the family Dasyatidae, was firstly collected by using drift gill net in the north-western coastal waters of Jejudo Island, Korea on 6 July, 2017. This species was characterized by having a broadly rounded snout, five pairs of gill openings, tail with a large spine, ventral tail fold not reaching to the tip of tail, no dorsal fold, and ventral surface of disc dark purple. Based on such morphological characters, the specimen was identified as P. violacea and confirmed with the nucleotide sequence of the mitochondrial cytochrome c oxidase subunit I gene. We added P. violacea to the Korean fish fauna and propose the new Korean names, "Bo-ra-saek-ga-o-ri-sok" and "Bo-ra-saek-ga-o-ri" for the genus and species, respectively.

• Korean Journal of Ichthyology
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• v.31 no.3
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• pp.178-182
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• 2019

This is the first report of Brachirus annularis (Pleuronectiformes: Soleidae) from Korea. A specimen of B. annularis (229.0 mm standard length) was firstly collected by drift gill net at a fishing ground locating between Jejudo and Geomundo Islands, the southern coast of Korea on 31 March, 2019. This species was characterized by having five large, deep colored patches on the ocular side of body, each patch outlined by dark brown ring, united dorsal and anal fins jointed with caudal fin, and short pectoral fin. We add this species to the Korean fish fauna and propose its new Korean names, "Eol-luk-seo-dae-sok" and "Eol-luk-seo-dae" for the genus and species, respectively.

• ALGAE
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• v.34 no.2
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• pp.71-90
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• 2019

A new encrusting red alga was found growing abundantly on glass debris items that drifted ashore along the coasts of Oregon and Washington. These included discarded fluorescent tubes, incandescent light bulbs, capped liquor bottles, and ball-shaped fishing-net floats. Field collections and unialgal cultures of the alga revealed that it consisted of two morphological phases: a young loosely aggregated turf and a mature consolidated mucilaginous crust. The turf phase consisted of a basal layer of globose cells that produced erect, rarely branched, uniseriate to multiseriate filaments up to $500{\mu}m$ long with closely spaced cells lacking pit-plugs. These filaments expanded in size from their bases to their tips and released single cells as spores. At maturity, a second phase of growth occurred that produced a consolidated crust, up to $370{\mu}m$ thick. It consisted of a basal layer of small, tightly appressed ellipsoidal-to-elongate cells that generated a mucilaginous perithallial matrix containing a second type of filament with irregularly spaced cells often undergoing binary division. At the matrix surface, the original filaments continued to grow and release spores but often also eroded. Individual cells, examined using confocal microscopy and SYBR Green staining, were found to contain a central nucleus, a single highly lobed peripheral chloroplast without a pyrenoid, and numerous chloroplast nucleoids. Morphological data from field and culture isolates and molecular data (rbcL, psbA, and SSU) show that this alga is a new genus and species which we name Viator vitreocola, "a traveller on glass."

• Journal of the Korean earth science society
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• v.43 no.6
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• pp.661-679
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• 2022

Plate tectonics, with the continental drift theory and later strongly supported by the sea-floor spreading theory with evidence of paleo-geomagnetic fields, ocean floor sediments, successfully explained the slow but continuous movements of rigid lithospheres in geological time. Initially, plate motions were described as relative movements between adjacent plates, mainly based on paleo-geomagnetic reversal data. The advent of space geodetic techniques in the 1980s enabled direct measurements of plate velocities and assessment of deformations within certain regions. In this review, early relative plate motion models are briefly summarized, the no-net-rotation frame theory and corresponding models are explained, and the characteristics of the most recent models that incorporate intraplate deformation are described. Additionally, the plate motion section of the International Terrestrial Reference Frame is introduced, and a few recent case studies of local plate motion are briefly described; for example, in South America, Europe, Antarctica, and Turkey. Finally, studies of plate motion in northeastern Asia focusing on the Korean Peninsula are introduced.

• Smart Structures and Systems
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• v.31 no.2
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• pp.101-111
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• 2023

Structural health monitoring (SHM) covers a range of damage detection strategies for buildings. In real-time, SHM provides a basis for rapid decision making to optimise the speed and economic efficiency of post-event response. Previous work introduced an SHM method based on identifying structural nonlinear hysteretic parameters and their evolution from structural force-deformation hysteresis loops in real-time. This research extends and generalises this method to investigate the impact of a wide range of flag-shaped or pinching shape nonlinear hysteretic response and its impact on the SHM accuracy. A particular focus is plastic stiffness (K_p), where accurate identification of this parameter enables accurate identification of net and total plastic deformation and plastic energy dissipated, all of which are directly related to damage and infrequently assessed in SHM. A sensitivity study using a realistic seismic case study with known ground truth values investigates the impact of hysteresis loop shape, as well as added noise, on SHM accuracy using a suite of 20 ground motions from the PEER database. Monte Carlo analysis over 22,000 simulations with different hysteresis loops and added noise resulted in absolute percentage identification error (median, (IQR)) in K_p of 1.88% (0.79, 4.94)%. Errors were larger where five events (Earthquakes #1, 6, 9, 14) have very large errors over 100% for resulted K_p as an almost entirely linear response yielded only negligible plastic response, increasing identification error. The sensitivity analysis shows accuracy is reduces to within 3% when plastic drift is induced. This method shows clear potential to provide accurate, real-time metrics of non-linear stiffness and deformation to assist rapid damage assessment and decision making, utilising algorithms significantly simpler than previous non-linear structural model-based parameter identification SHM methods.

• Nuclear Engineering and Technology
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• v.54 no.11
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• pp.4134-4145
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• 2022

The collimator is one of the high-heat-flux components used to avoid a series of vacuum and thermal problems. In this paper, the heat load distribution throughout the collimator is first calculated through experimental data, and a transient thermodynamic simulation analysis of the original model is carried out. The error of the pipe outlet temperature between the simulated and experimental values is 1.632%, indicating that the simulation result is reliable. Second, the model is optimized to improve the heat transfer performance of the collimator, including the contact mode between the pipe and the flange, the pipe material and the addition of a twisted tape in the pipe. It is concluded that the convective heat transfer coefficient of the optimized model is increased by 15.381% and the maximum wall temperature is reduced by 16.415%; thus, the heat transfer capacity of the optimized model is effectively improved. Third, to adapt the long-pulse steady-state operation of the experimental advanced superconducting Tokamak (EAST) in the future, steady-state simulations of the original and optimized collimators are carried out. The results show that the maximum temperature of the optimized model is reduced by 37.864% compared with that of the original model. The optimized model was changed as little as possible to obtain a better heat exchange structure on the premise of ensuring the consumption of the same mass flow rate of water so that the collimator can adapt to operational environments with higher heat fluxes and long pulses in the future. These research methods also provide a reference for the future design of components under high-energy and long-pulse operational conditions.