• Geomechanics and Engineering
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• v.7 no.3
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• pp.317-333
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• 2014

The study of the mechanical behavior of rockfill materials under three-dimensional loading conditions is a current research focus area. This paper presents a microscale numerical study of rockfill deformation and strength characteristics using the Combined Finite-Discrete Element Method (FDEM). Two features unique to this study are the consideration of irregular particle shapes and particle crushability. A polydisperse assembly of irregular polyhedra was prepared to reproduce the mechanical behavior of rockfill materials subjected to axial compression at a constant mean stress for a range of intermediate principal stress ratios in the interval [0, 1]. The simulation results, including the stress-strain characteristics, relationship between principal strains, and principal deviator strains are discussed. The stress-dilatancy behavior is described using a linear dilatancy equation with its material constants varying with the intermediate principal stress ratio. The failure surface in the principal stress space and its traces in the deviatoric and meridian plane are also presented. The modified Lade-Duncan criterion most closely describes the stress points at failure.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.1
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• pp.151-158
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• 2009

Many people have been suffering and loosing their property from inundation due to concentrated rain and massive storm. Although, river banks are strengthened and pumping stations are constructed to protect the life and property of people, the flood damages (disaster)could not be controlled, in fact it is increasing. In USA, CWMS (Corps Water Management System) has very good system of integration of study of rainfall data, computation of stream stage and simulation of flood damages, but there is lack of this type of study and analysis in the domestic context, so we have been facing many difficulties in simulation of flood damages. Therefore, a systematic collecting of data analysis and evaluation of flood damages is necessary. The main objective of this study is to suggest a systematic data collection and evaluation method, which could be useful to prevent the life and property from unusual damages. In this study, the system (Flood Damage Evaluation Model; K-FDEM) is proposed to evaluate the flood damages from rainfall with considering many field parameters.

• Structural Engineering and Mechanics
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• v.58 no.2
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• pp.243-257
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• 2016

The aim of this study is to investigate the seismic resistance of dry stone arches under in-plane seismic loading. For that purpose, several numerical analyses were performed using the combined finite-discrete element method (FDEM). Twelve types of arches with different ratios of a rise at the mid-span to the span, different thicknesses of stone blocks and different numbers of stone blocks in the arch were subjected to an incremental dynamic analysis based on excitation from three real horizontal and vertical ground motions. The minimum value of the failure peak ground acceleration that caused the collapse of the arch was adopted as a measure of the seismic resistance. In this study, the collapse mechanisms of each type of stone arch, as well as the influence of the geometry of stone blocks and stone arches on the seismic resistance of structures were observed. The conclusions obtained on the basis of the performed numerical analyses can be used as guidelines for the design of dry stone arches.

• Geophysics and Geophysical Exploration
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• v.17 no.3
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• pp.129-136
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• 2014

Electromagnetic (EM) methods are generally divided into frequency-domain EM (FDEM) and time-domain EM (TDEM) methods, depending on the source waveform. The FDEM and TDEM fields are mathematically related by the Fourier transformation, and the TDEM field can thus be obtained as the Fourier transformation of FDEM data. For modeling in time-domain, we can use fast frequency-domain modeling codes and then convert the results to the time domain with a suitable numerical method. Thus, frequency-to-time transformations are of interest to EM methods, which is generally attained through fast Fourier transform. However, faster frequency-to-time transformation is required for the 3D inversion of TDEM data or for the processing of vast air-borne TDEM data. The diffusion expansion method (DEM) is one of smart frequency-to-time transformation methods. In DEM, the EM field is expanded into a sequence of diffusion functions with a known frequency dependence, but with unknown diffusion-times that must be chosen based on the data to be transformed. Especially, accuracy of DEM is sensitive to the diffusion-time. In this study, we developed a method to determine the optimum range of diffusion-time values, minimizing the RMS error of the frequency-domain data approximated by the diffusion expansion. We confirmed that this method produces accurate results over a wider time range for a homogeneous half-space and two-layered model.