• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.3
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• pp.229-239
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• 2015

In light of the significant increase in the quantities of goods transported and the development of the shipping industry, the frequency of usage of port structures has increased; yet, the government's budget for the shipping & port of SOC has been reduced. Port structures require systematically effective maintenance and management trends that address their growing frequency of usage. In order to construct a productive maintenance system, it is essential to develop deterioration models of port structures that consider various characteristics, such as location, type, use, constructed level, and state of maintenance. Processes for developing such deterioration models include examining factors that cause the structures to deteriorate, collecting data on deteriorating structures, and deciding methods of estimation. The techniques used for developing the deterioration models are multiple regression analysis and Markov chain theory. Multiple regression analysis can reflect changes over time and Markov chain theory can apply status changes based on a probabilistic method. Along with these processes, the deterioration models of open-type and gravity-type wharfs were suggested.

• Economic and Environmental Geology
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• v.53 no.2
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• pp.147-157
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• 2020

Mass change in the Antarctic Ice Sheet(AIS) is the most important indicator of changes in Earth's climate system including global mean sea level rise that are largely affected by ongoing global warming. In this study, AIS mass variations are examined with satellite gravity data and outputs from a regional climate model. The analysis of gravity data shows that along the coastal region the Western AIS has experienced a continuous and significant ice loss while a slight increasing in the Eastern AIS during the study period (2002.08-2016.08). The temporal and spatial variations in ice mass changes are recovered by a regional climate model, but the recovered amplitudes are much smaller than those of observations. This under-estimation is remarkably resolved by modifying a base flow field for the ice discharge. The recovered estimates based on the ice-flow field can explain about 97% of the rate of mass change in observations before 2009. This implies that changes in ice flow dynamics along the coast line plays a pivotal role in regulating long-term budget of ice mass in AIS.

• Journal of the Korean Geotechnical Society
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• v.31 no.10
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• pp.5-16
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• 2015

Considering the conversion of the Korea Construction Standards to Limit State Design (LSD), we analyzed the resistance bias factor for pullout resistance, as a part of the development of the Load and Resistance Factor Design (LRFD) for soil nailing; very few studies have been conducted on soil nailing. In order to reflect the local characteristics of soil nailing, such as the design and construction level, we collected statistics on pullout tests conducted on slopes and excavation construction sites around the country. In this study a database was built based on the geotechnical properties, soil nailing specifications, and pullout test results. The resistance bias factors are calculated to determine the resistance factor of the pullout resistance for gravity and pressurized grouting method, which are the most commonly used methods in Korea; moreover, we have relatively sufficient data on these methods. We found the resistance bias factors to be 1.144 and 1.325, which are relatively conservative values for predicting the actual ultimate pullout resistance. It showed that our designs are safer than those found in a research case in the United States (NCHRP Report); however, there was an uncertainty, $COV_R$, of 0.27-0.43 in the pullout resistance, which is relatively high. In addition, the pressurized grouting method has a greater margin of safety than the gravity grouting method, and the actual ultimate pullout resistance determined using the pressurized grouting method has low uncertainty.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.6
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• pp.169-177
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• 2017

Recently, as the size of transportation vessels has increased, there is a growing need for securing the front-water depths of existing port facilities. The method of deepening front-water depth is securing the depth of the port facility, and it is reinforced by grouting after excavating the rubble-mound to the required depth. The purpose of this study is to investigate the reinforcing performance and filling performance of thixotropic grout as a grouting material for reinforcing rubble-mound. Compressive strength tests were carried out for two types of thixotropic grout, and 5 specimens with a diameter of 400 mm and a height of 530 mm were manufactured and evaluated for filling performance. The required strength of reinforced rubble-mound required to ensure the safety of the structure is 6 MPa. All the thixotropic grouts used in this study were found to satisfy the required strength over 9 MPa at 7 days of age. As a result of visual observation of filling state of the filling performance test specimens, it was confirmed that the thixotropic grout was well filled up to the desired fillet height.

• Korean Journal of Remote Sensing
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• v.37 no.5_1
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• pp.927-938
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• 2021

A similar magnitude of non-gravitational perturbations are act on the formation flying low earth orbit satellites with a certain time difference. Using this temporal correlation, the non-gravity acceleration of the low earth orbiting satellites can be transferred for the othersatellites. There is a period in which the accelerometer data of one satellite is unavailable for GRACE and GRACE-FO satellites. In this case, the accelerometer data transplant method described above is officially used to recover the accelerometer data at the Jet Propulsion Laboratory (JPL). In this paper, we proposed a model for predicting accelerometer data of formation flying low earth orbit satellites using a neural network (NN) model to improve the estimation accuracy of the transplant method. Although the transplant method cannot reflect the satellite's position and space environmental factors, the NN model can use them as model inputs to increase the prediction accuracy. A prediction test of an accelerometer data using NN model was performed for one month, and the prediction accuracy was compared with the transplant method. The NN model outperformsthe transplant method with 55.0% and 40.1% error reduction in the along-track and radial directions, respectively.

• Journal of Technology Innovation
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• v.27 no.2
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• pp.99-122
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• 2019

ODA (Official Development Assistance) aims for practicing international humanitarianism in developing countries. However, ODA donors also seek to find convincing evidence meeting the national economic & political interests in the international community. In this regards, precise & unbiased estimation of the policy effects of ODA aid on the donors' exports to the recipient countries has recently become one of the primary concerns of the ODA donors, especially developing countries including Korea of which economy structure heavily relies on exports for economic growth. Based on the basic gravity model, this study empirically analyzes the effects of technical cooperation ODA delivering skills, knowledge and technical know-how on Korea's exports to the ODA recipient countries using 10-year panel data from 2007 to 2016. Specifically, by incorporating major variables affecting trade such as GDP, distance, FDI etc, the effect of technical cooperation ODA on Korea's exports to the ODA recipient countries is estimated with various kinds of panel models. As a result, technical cooperation ODA has a statistically significant impact on Korea's exports to ODA recipient countries, especially in the exports of intermediate goods. And the detail process of this black-boxed mechanism is scrutinized through case studies on Uzbekistan, The Philippines, and Morocco.

• The Journal of the Convergence on Culture Technology
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• v.9 no.6
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• pp.123-130
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• 2023

As part of the research on cultural factors that determine international tourism demand, this study was conducted based on regional interest and the need for understanding religion. The purpose of this study is to empirically test how religious factors affect tourism demand in Korea to find out that religious factors are important considerations in establishing tourism policies and strategies. To achieve the purpose of this study, the research target areas were selected as Thailand, Indonesia, and the Philippines, which have relatively many tourists visiting Korea among Southeast Asian countries and are well known for their religious characteristics. GDP and nominal exchange rate, which are economic factors, were selected as explanatory variables. And religious diversity was selected as a characteristic factor variable of the tourism demand model based on the characteristic theory. An empirical analysis was conducted through a gravity model. As a result of the estimation, it was found that GDP has a positive effect on tourism demand in Korea. Nominal exchange rate variables and religious diversity variables were found to have a negative effect on tourism demand in Korea. We have confirmed that religion is an important factor in choosing tourist destinations for Filipino, Thai, and Malaysian tourists visiting Korea, and they choose religiously similar destinations.

• Environmental and Resource Economics Review
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• v.22 no.4
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• pp.785-815
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• 2013

This paper analyzes the three issues related to the effect of environmental regulations on the Korean trades with gravity equation model: the effect on the Korean exports, the bilateral trade flows between the Korea and the trade partners, and the Korean international competitiveness. For all three issues we carried the empirical tests with fixed effect estimation methods for total industries, non-pollution industries, pollution industries, and also 16 individual pollution industries. We use industry panel data for the 120 largest trading countries with Korea for the years 2000-2010. The Environmental Performance Index (EPI) is used as the proxy variable for the environmental regulation. The empirical result shows that while GDPs of both Korea and its trading partners are very important factors affecting positively the Korean trades for all industries, the environmental regulation of the importing country would be a definite trade barrier to the Korean pollution industries, but not a definite one for the non-pollution industries. In addition, the stricter environmental regulations of Korea's trade partners would weaken the Korean international competitiveness of Korean pollution industries. In this regard, the Porter Hypothesis would have not appeared in the Korean trades of pollution industries during the period observed in this study.

• Journal of Korean Society of Water and Wastewater
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• v.26 no.2
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• pp.177-189
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• 2012

Sediment load deposited in sewers and manholes reduces not only the capacity of pipes but also the efficiency of the whole sewer system. This causes the inundations of the low places and overflows at manholes, Moreover, sulfides and bad odor can occur due to deposited sediment with organic loads in manholes. Movements of sediment load in manholes are complicated depending on manhole size, location, inside structure, sediment load type, and time. Therefore, it is necessary to understand the movements of sediment load in manholes by experiments. In this study, experiments were implemented by a square manhole with straight path to measure deposited sedimentation quantity. The experimental apparatus was consisted of a high water tank, an upstream tank, test pipes, a sediment supplier, a manhole, and a downstream tank to measure the experimental discharge. The quantity of deposited sediment load was measured by different conditions, such as the inflow condition of sediment(continuous and certain period), the amount of inflow sediment, discharge, and the type of sediment. Jumoonjin sand(S=2.63, D50=0.55mm), general sand(GS, S=2.65, D50=1.83mm) and anthracite (S=1.45, D50=0.80mm) were employed for the experiment. The velocities in inflow pipe were 0.45 m/s, 0.67 m/s, and 0.9 m/s. Sediment load movement and sedimentation quantity in manhole were influenced by many factors such as velocity, shear stress, viscosity, amount of sediment, sediment size, and specific gravity. Suggested regression equations can estimated the quantity of deposited sediment in the straight path square manholes. The connoted equations that were evaluated through the experimental study have velocity range from 0.45 to 0.9m/sec. The study results illustrates that appropriation of design velocity ragne between 1.0 and 2.0m/sec could implement to maintain and manage manholes.

• Journal of the Korea Society for Simulation
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• v.29 no.1
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• pp.1-9
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• 2020

The ballistic missile threat continues to increase with the proliferation of missile technology. In response to this threat, many kinds of interceptors have been emphasized over the years. For development of interceptor, systematic flight tests are essential. Flight tests provide valuable data that can be used to verify performance and confirm the technological progress of ballistic missile defense system including interceptor. However, during flight tests, civilians near the test region could be risk due to a lot of intercept debris. For this reason, reliable estimate of safety area for the flight tests should be preceded. In this study, prediction of safety area is performed through modeling and simulation. Firstly, behaviors of ballistic missile and interceptor are simulated for those entire phase including interception to obtain the relative intercept velocity and the relative impact angle. By using obtained data of kinetic energy, the fragment ejection velocity is calculated and fragment trajectories are simulated by considering drag, gravity and wind effects. Based on the debris field formation and hazard evaluation of debris, final safety area is calculated.