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Kim Y.,National Disaster Management Institute | Eo Y.D.,Konkuk University
KSCE Journal of Civil Engineering

Given that the distribution of trees is irregular and individual trees differ from one another, applying a Digital Terrain Model (DTM) for cityscapes to a forest inventory causes many errors. In this study, a new DTM-generating technique that utilizes airborne Light Detection And Ranging (LiDAR), with iterative labeling for recovery of ground points, is proposed to solve the inaccuracy problem that occurs when DTMs are generated in forested areas. The proposed method consists of three steps: (1) generation of the initial DTM by a process that performs mean planar filtering and multireturn filtering, (2) recovery of ground points by iterative labeling through application of a ground extraction filter and limitation conditions, and (3) refinement to create the final DTM. The proposed method was tested at the experimental site with morphological and TerraScan DTM-generating techniques, followed by a visual assessment and a quantitative accuracy assessment through comparison with in-situ data. In the visual assessment, the proposed method exhibits such advantages as less noise and more precise representation of topographic features. Also, the method shows excellent performance in improving the average absolute deviation values of 110.3 cm and 50.4 cm over the morphological method and the TerraScan method, respectively, in the quantitative assessment. Thus, the proposed method is judged to have successfully solved the inaccuracy problem that often occurs with generation of DTMs for a forested area. © 2015 Korean Society of Civil Engineers and Springer-Verlag Berlin Heidelberg Source

Cheong T.S.,National Disaster Management Institute | Felix M.L.A.,Kongju National University | Jeong S.M.,Kongju National University
Desalination and Water Treatment

This study developed a disaster assessment system, which integrated flood inundation, risk analysis system, and a decision support system. The parameter representation of the model was selected through sensitivity analysis, used for automated parameter optimization of the model. The Bocheong watershed in South Korea was selected for this study. The results of the simulation were used for disaster assessments; estimated results were calculated basing from flood damages from historical flood disasters, GIS, population, and inundation results. Lastly, this study developed a user-support system to provide real-time meteorological and hydrological data to local government and disaster situation room in South Korea. From the results of the evaluation, the developed model in this study was proven to be more excellent than ModClark model. The application of this model was found superior for ungaged basin such as mountainous area and small creek basins. © 2014 Balaban Desalination Publications. All rights reserved. Source

Seong J.-Y.,National Disaster Management Institute | Min K.-W.,Dankook University | Kim J.-C.,Hyundai Engineering
Nonlinear Dynamics

The purpose of this study is to investigate analytically a single-degree-of-freedom (SDOF) building structure equipped with a friction damper for assessing its vibration control effect. Friction dampers are installed between stories to reduce inter-story displacements of building structures subjected to external loading. They are in general regarded to generate damping forces characterized by Coulomb damping, of which the directions are opposite to the inter-story velocities of building structures. Hence, the building structure model with friction dampers can be represented by a mass-spring-viscous-Coulomb damping system. The building response reduction as a result of damper installation can be provided by observing the damping ratio rather than the friction force contributed by the dampers. Since a large friction damper force is required to attenuate the response of the building due to strong excitation, friction force ratio is directly related to building response reduction, which is the friction force of the damper versus external force. Therefore, damping and friction force ratios are key parameters, playing a main role in selecting an optimal friction damper, which satisfies target response reduction. This study first identifies an SDOF building structure installed with a friction damper for free vibration with initial conditions. A closed-form expression of normalized displacement is derived in terms of friction force ratio in the time domain. Peak and valley of displacements are also found and then the time when the structure stops is derived with recursive interval number. This study is extended to identify steady-state vibration of the structure by deriving closed-form solution in case of resonance in terms of friction force ratio. Then, the dissipated energy balance is identified for both free and steady-state vibrations. Finally, equivalent viscous damping ratios are derived by using friction force ratio based on dissipated energy balance equation. The derived equations in terms of viscous damping ratio and friction force ratio can provide insight to design a friction damper for reducing structural displacement under external loadings. © 2012 Springer Science+Business Media B.V. Source

Song K.-Y.,Korea Institute of Geoscience and Mineral Resources | Oh H.-J.,Korea Institute of Geoscience and Mineral Resources | Choi J.,National Disaster Management Institute | Park I.,University of Seoul | And 2 more authors.
Advances in Space Research

The aim of this study was to identify landslide-related factors using only remotely sensed data and to present landslide susceptibility maps using a geographic information system, data-mining models, an artificial neural network (ANN), and an adaptive neuro-fuzzy interface system (ANFIS). Landslide-related factors were identified in Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite imagery. The slope, aspect, and curvature of topographic features were calculated from a digital elevation model that was made using the ASTER imagery. Lineaments, land-cover, and normalized difference vegetative index layers were also extracted from the imagery. Landslide-susceptible areas were analyzed and mapped based on occurrence factors using the ANN and ANFIS. The generalized bell-shaped built-in membership function of the ANFIS was applied to landslide susceptibility mapping. Analytical results were validated using landslide test location data. In the validation results, the ANN model showed 80.42% prediction accuracy and the ANFIS model showed 86.55% prediction accuracy. These results suggest that the ANFIS model has a better performance than does the ANN in predicting landslide susceptibility. © 2011 COSPAR. Published by Elsevier Ltd. All rights reserved. Source

Park I.,University of Seoul | Choi J.,National Disaster Management Institute | Jin Lee M.,Yonsei University | Jin Lee M.,Korea Environment Institute | Lee S.,Korea Institute of Geoscience and Mineral Resources
Computers and Geosciences

We constructed hazard maps of ground subsidence around abandoned underground coal mines (AUCMs) in Samcheok City, Korea, using an adaptive neuro-fuzzy inference system (ANFIS) and a geographical information system (GIS). To evaluate the factors related to ground subsidence, a spatial database was constructed from topographic, geologic, mine tunnel, land use, and ground subsidence maps. An attribute database was also constructed from field investigations and reports on existing ground subsidence areas at the study site. Five major factors causing ground subsidence were extracted: (1) depth of drift; (2) distance from drift; (3) slope gradient; (4) geology; and (5) land use. The adaptive ANFIS model with different types of membership functions (MFs) was then applied for ground subsidence hazard mapping in the study area. Two ground subsidence hazard maps were prepared using the different MFs. Finally, the resulting ground subsidence hazard maps were validated using the ground subsidence test data which were not used for training the ANFIS. The validation results showed 95.12% accuracy using the generalized bell-shaped MF model and 94.94% accuracy using the Sigmoidal2 MF model. These accuracy results show that an ANFIS can be an effective tool in ground subsidence hazard mapping. Analysis of ground subsidence with the ANFIS model suggests that quantitative analysis of ground subsidence near AUCMs is possible. © 2012 Elsevier Ltd. Source

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