• Journal of Ocean Engineering and Technology
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• v.32 no.5
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• pp.361-366
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• 2018

The present study analyzed the variation factors in inducing a salinity change using the existing observation network in the section between the Nakdong River Estuary Barrage and Changnyeong-Haman Weir, and also examined the seasonal changes in precipitation, salinity, and discharge. Furthermore, this study analyzed the causes of a salinity increase by collecting observational data during a period when abnormal salinity occurred, and further investigated the salinity transfer time in a section of approximately 5.3 km from the Nakdong River Estuary Barrage to Nakdong River Bridge to understand the behavioral characteristics of the salinity moving upstream. The study results would make it possible to control the increase in salinity and block salt water from moving upstream by understanding the salinity variation characteristics according to the discharge amount. This will provide stability in collecting water from various residential, agricultural, and industrial sources through water intake facilities scattered near the Nakdong River Estuary Barrage.

• Proceedings of the KSRS Conference
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• 2002.10a
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• pp.428-428
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• 2002

The scientific objectives of PACRIM (Pacific Rim) are to advance the understanding of polarimetric and interferometric radar and to promote its application in environmental research designed to detect and quantify changes found in both the physical and humanly dominated ecosystems on the earth's surface. The information derived is used to more readily identify environments at risk; improve environmental decision making and the management of resources and thereby lead to the implementation of more effective and sustainable land use practices. PACRIM is a collaborative research project was organized by NASA's Mission to Planet Earth, Airborne Sciences Program; the Jet Propulsion Laboratory; CSIRO-COSSA and the Centre for Remote Sensing and GIS at the University of New South Wales. A decade of working with AIRSAR data (1993-2003) in the Australia-Asian-Pacific region has provided the opportunity for more than 400 investigators from 20 countries to collect, analyse, interpret and apply state-of-the-art radar data to earth-science studies. This has been achieved by scientists working within seven broad research themes; o Forestry and vegetation o Geology and tectonic processes o Interferometry o Disaster management o Coastal analysis o Agriculture o Urban and regional development. This paper presents an overview of the three data acquisition missions (1993,1996 and 2000) and the science research outcomes achieved from analyzing high quality radar data.

• Korean Journal of Remote Sensing
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• v.36 no.6_1
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• pp.1303-1322
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• 2020

Indonesia is more prone to natural disasters due to its geological condition under the three main plates, making Indonesia experience frequent seismic activity, causing earthquakes, volcanic eruption, and tsunami. Those disasters could lead to other disasters such as landslides, floods, land subsidence, and coastal inundation. Monitoring those disasters could be essential to predict and prevent damage to the environment. We reviewed the application of remote sensing and Geographic Information System (GIS) for detecting natural disasters in the case of Indonesia, based on 43 articles. The remote sensing and GIS method will be focused on InSAR techniques, image classification, and susceptibility mapping. InSAR method has been used to monitor natural disasters affecting the deformation of the earth's surface in Indonesia, such as earthquakes, volcanic activity, and land subsidence. Monitoring landslides in Indonesia using InSAR techniques has not been found in many studies; hence it is crucial to monitor the unstable slope that leads to a landslide. Image classification techniques have been used to monitor pre-and post-natural disasters in Indonesia, such as earthquakes, tsunami, forest fires, and volcano eruptions. It has a lack of studies about the classification of flood damage in Indonesia. However, flood mapping was found in susceptibility maps, as many studies about the landslide susceptibility map in Indonesia have been conducted. However, a land subsidence susceptibility map was the one subject to be studied more to decrease land subsidence damage, considering many reported cases found about land subsidence frequently occur in several cities in Indonesia.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.171-171
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• 2023

This study investigates the capability of Physics-Informed Neural Networks (PINNs) for solving the solution of partial differential equations. Particularly, the 1D Saint-Venant Equations (SVEs) were considered, which describe the movement of water in a domain with shallow depth compared to its horizontal extent, and are widely adopted in hydrodynamics, river, and coastal engineering. The core contribution of this work is to combine the robustness of neural networks with the physical constraints of the SVEs. The PINNs method utilized a neural network to approximate the solutions of SVEs, while also enforcing the underlying physical principles of the equations. This allows for a more effective and reliable solution, especially in areas with complex geometry and varying bathymetry. To validate the robustness of the PINNs method, numerical experiments were conducted on several benchmark problems. The results show that the PINNs could be achieved high accuracy when compared with the solution from the numerical solution. Overall, this study demonstrates the potential of using PINNs and highlights the benefits of integrating neural network and physics information for improved efficiency and accuracy in solving SVEs.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.293-293
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• 2020

기후변화로 인해 다양한 재난이 복합적으로 발생하고 있으며, 특히 해안과 인접해 있는 지역은 풍랑, 지진해일 등으로 인해 다양한 위험에 노출되어 있는 실정이다. 이에 따라 각 지자체는 자연재해대책법에 의거하여 자연재해저감종합계획을 수립하고 저감대책을 마련하고 있으나, 수립 절차에 따른 비용과 시간이 많이 소요되고 있다. 따라서 위험지역의 지리적·사회적 조건을 고려한 맞춤형 재해예방기법 도출방안이 필요하다. 이에 본 연구에서는 과거 피해이력과 침수예상도 정보가 반영된 위험성평가 지도를 활용하여 위험지역 유형을 4단계(관심, 주의, 경계, 위험)로 구분하고, 단계별 구조물적 대책과 비구조물 대책의 적용방안을 제시하였으며, 구조물적 대책과 비구조물적 대책의 도출에는 지역맞춤형 요소와 특성요소를 활용하였다. 지역맞춤형 요소는 자연인자, 재해영향인자, 재해원인인자, 지형인자, 사회인자로 구분하였으며, 각 인자별로 세부인자를 선택하여 논리연산에 따라 재해예방기법을 도출하였다. 특성요소는 효율성, 시공성, 공공성으로 구분하였고, 각 구분별 세부요소를 평가하여 재해예방기법의 우선순위를 도출하였다. 본 연구를 통해 향후 해안가 복합재난이 예상되는 지역을 대상으로 지역맞춤형 재해예방기법을 도출할 수 있을 것이며, 자연재해저감종합계획 수립 시에도 활용할 수 있을 것으로 기대된다.

• Geomechanics and Engineering
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• v.32 no.4
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• pp.411-426
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• 2023

Soft clay is widely distributed in the southeast coastal areas of China. Many large underground structures, such as subway stations and underground pipe corridors, are shallow buried in the soft clay foundation, so the dynamic characteristics of the soft clay must be considered to the seismic design of underground structures. In this paper, the dynamic characteristics of saturated soft clay in Shanghai under the bidirectional excitation for earthquake loading are studied by dynamic triaxial tests, comparing the backbone curve and hysteretic curve of the saturated soft clay under different confining pressures with those under different vibration frequencies. Considering the coupling effects of the confining pressure and the vibration frequency, a fitting model of the maximum dynamic shear modulus was proposed by the multiple linear regression method. The M-D model was used to fit the variations of the dynamic shear modulus ratio with the shear strain. Based on the Chen model and the Park model, the effects of the consolidation confining pressure and the vibration frequency on the damping ratio were studied. The results can provide a reference to the earthquake prevention and disaster reduction in soft clay area.

• Journal of the Korean Society for Marine Environment & Energy
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• v.12 no.4
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• pp.227-234
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• 2009

Using a finite volume ocean circulation model based on an unstructured grid (FVCOM), we studied the structure of a fresh water bulge that influences on the Region Of Freshwater Influence. Fresh water discharged a river forms a coastal boundary current to the righthand side and a cyclonically circulation freshwater bulge that grows with time. In the middle of the bulge, vertical motions bring fresh water to the bottom. When tidal motions are included, the bulge disappears while the boundary currents becomes wider. Through a simple comparison of areas occupied low salinity water we quantified vertical and horizontal mixing due to the tide and showed that the tidal motion enhances the vertical mixing. During the first few tidal cycles right after the onset of the river discharge, due to tidal excursion the horizontal mixing becomes stronger. The vertical mixing by the tide mixes the fresh water After a certain time the water around the river mouth is well mixed and the horizontal excursion of the fresh water near the river mouth does not have much effect on the horizontal mixing. When there is no tidal motion horizontal mixing is mainly by the inertial instability at the surface and the horizontal mixing becomes stronger over time.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.6
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• pp.737-743
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• 2016

Coastal hazards such as high waves are expected to increase due to global climate change. Therefore, we investigated new armor unit structures for disaster prevention. Recently, a concrete caisson has been used in many breakwaters against high waves in South Korea, but the demand for concrete armor unit has increased due to the high cost and many installation requirements. Though many new armor units have been developed over the world since Tetrapod in 1950, few have been used due to lack of systematical development. The representative armor units in current use have many advantages, but they cannot be applied to waves higher than 8 m. One of the new armor units developed by the design guide based on recent trend and hydraulic model experiments were conducted. The new armor unit was developed as a single layer due to cost effectiveness. However, the thickness is close to 1.5 times by overlapping the alphabet A and V. It showed higher overtopping compared to a double layer because of the thickness and the high packing density. It has a high interlocking vertically but low horizontally. It shows good stability at 9 m in model testing.

• Journal of the Korean Society for Marine Environment & Energy
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• v.7 no.1
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• pp.35-41
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• 2004

The yeongok stream originates at the natural park, Mt. O-dae and flows to the East Sea of korea, normally maintaining I or II grade of water quality and its average water flux is 352,100 ㎥/d. However, the typhoon 'Rusa', which occured on 31 August 2002, changed its watercourse and configuration, and the ecosystem was deeply damaged. Moreover, the hydrological characteristics were once more transformed, and the ecosystem was secondarily damaged during repair-work of destroyed bridges and elevations. After the flood disaster, the species diversity diminished 17% for attached diatom and 44% for aquatic animals. However, the earth and sand, dug from river bed during intensive repair-work throughout the entire stream, made diversity drop to 32% for the diatom and the aquatic animals were wiped out. Especially, fishes were totally destroyed except for some species such as Moroco oxycephalus in the upper stream. The yeongok stream has little contamination source and short water residence time due to the short length and rapid slope, and consequently a temporary deterioration of water quality caused by repair-work may be rapidly recovered, but it needs a long time to restore the damaged ecosystem.

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.6
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• pp.708-716
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• 2019

After the Sewol ferry disaster, the maritime safety supervisor system was introduced to strengthen maritime safety control for coastal vessels. If any critical defect is found in vessel facilities during periodical or occasional guidance and supervision on a vessel, a maritime safety supervisor takes an administrative measure: detention of the vessel until it has been completely corrected. The detention order is one of the most powerful regulations exercised by a maritime safety supervisor. It would not be an overstatement to say that the guidance and supervision conducted by a maritime safety supervisor is very important for the safety of a vessel and protection of the maritime environment. However, the regulatory level of each Regional Office of Oceans and Fisheries toward vessels may vary with the enforcers, and an individual's intentional act or negligence might occur during the execution process. Detention of a coastal vessel by the Regional Office of Ocean and Fisheries can easily lead to delayed navigation, and a vessel owner may suffer economic loss from suspension of a charter party. Nevertheless, the Maritime Safety Act does not prescribe filing a petition for objection to the measure of detention order by a maritime safety supervisor. To overcome this problem, therefore, the objection procedure under the Maritime Safety Act has to be reformed to reclaim a right against an inappropriate detention order measure caused by an individual's intentional act or negligence through a formal objection.