• East Asian mathematical journal
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• v.17 no.1
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• pp.93-101
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• 2001

We give an equivalent formulation to the $Erd\"{o}s'$ conjecture on the lower bound of the greatest element in a set having distinct subset sums. On this basis we suggest a possible approach towards $ERD\"{O}S'$ conjecture. Also we reproduce L. Moser's result by means of an analytic method.

• Journal of the Korean Geotechnical Society
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• v.22 no.10
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• pp.111-120
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• 2006

In this research, numerical simulations by PFC considering discrete element method are conducted to predict experimental results of large triaxial compression test with rockfill material for dam construction. For generation of compacted assembly with specific grain size distribution and initial material porosity, the clump logic method and expansion of generated particles are adapted. To predict stress-stain behavior of large triaxial test, discrete particle modelling is applied with micro parameters which are chosen by calibration process. It is expected that distinct particle modelling method could be used as a useful tool to investigate micro and macro behavior associated with geotechnical problems and develop a numerical laboratory.

• Tunnel and Underground Space
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• v.30 no.1
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• pp.15-28
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• 2020

In this study, a procedure was introduced to estimate strength and deformation modulus of the 3-D discrete fracture network(DFN) systems using the distinct element method(DEM). Fracture entities were treated as non-persistent square planes in the DFN systems. Systematically generated fictitious fractures having similar mechanical characteristics of intact rock were combined with non-persistent real fractures to create polyhedral blocks in the analysis domain. Strength and deformation modulus for 10 m cube domain of various deterministic and stochastic 3-D DFN systems were estimated using the DEM to explore the applicability of suggested method and to examine the effect of fracture geometry on strength and deformability of DFN systems. The suggested procedures were found to effective in estimating anisotropic strength and deformability of the 3-D DFN systems.

• Journal of Industrial Technology
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• v.21 no.B
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• pp.51-58
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• 2001

The Distinct Element Method (DEM) was used to analyze the stability of jointed rock slope, of which dimension are about 200m(length), 60m(height), $55^{\circ}$ dip. The Barton-Bandis joint model was used, as a constitutive model. The parameters such as JRC and spatial distribution characteristics of discontinuities were acquired through field investigation. Three different cases such as $51^{\circ}$, $45^{\circ}$ and $38^{\circ}$ in angle of rock slope were analyzed to decide a stable slope. To keep the jointed rock slope safely, it is proposed to reduce the height of slope from 60m to 48m and to reduce the angle of the from $55^{\circ}$ to $38^{\circ}$ too.

• Journal of the Earthquake Engineering Society of Korea
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• v.4 no.4
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• pp.93-104
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• 2000

적충되어 있는 다중 블록 시스템은 역사적 건물이나 문화재등에 자주 사용되고 있다. 이러한 구조시스템은 지진에 매우 취약하고, 특히 세장한 구조물인 경우에는 낮은 수준의 지반가속도에 대해서도 전도가 일어날 수 있다. 지진으로부터 이러한 구조물을 보호할 수 있는 방법중의 하나로써 지진격기받침의 사용을 들 수 있으나, 아직 격리받침이 설치되어 있는 다중블록의 거동에 대해서는 잘 알려지지 않는 실정이다. 이 논문에서는 각각 P-F 시스템, FPS, LRB 시스템이 설치되어 있을때의 세장한 강체 블록의 동적거동에 대해 살펴보았다. P-F 시스템과 FPS에서의 마찰모델은 Coulomb의 마찰법칙을 이용하였도, 상부구조물은 붙음(stick)모드와 록킹(rocking) 모드만이 존재하도록 가정하였다. 충격은 개별요소법(distinct element method, DEM)을 이용해 기술하였고, 조화입력운동에 대한 응답을 조사하였다.

• Tunnel and Underground Space
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• v.31 no.6
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• pp.593-609
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• 2021

We proposed a numerical method for the thermo-mechanical behavior of rock fracture using a grain-based distinct element model (GBDEM) and simulated thermally induced fracture slip. The present study is the benchmark simulation performed as part of DECOVALEX-2023 Task G, which aims to develop a numerical method to estimate the coupled thermo-hydro-mechanical processes within the crystalline rock fracture network. We represented the rock sample as an assembly of Voronoi grains and calculated the interaction of the grains (blocks) and their interfaces (contacts) using a distinct element code, 3DEC. Based on an equivalent continuum approach, the micro-parameters of grains and contacts were determined to reproduce rock as an elastic material. Then, the behavior of the fracture embedded in the rock was characterized by the contacts with Coulomb shear strength and tensile strength. In the benchmark simulation, we quantitatively examined the effects of the boundary stress and thermal stress due to heat conduction on fracture behavior, focusing on the mechanism of thermally induced fracture slip. The simulation results showed that the developed numerical model reasonably reproduced the thermal expansion and thermal stress increment, the fracture stress and displacement and the effect of boundary condition. We expect the numerical model to be enhanced by continuing collaboration and interaction with other research teams of DECOVALEX-2023 Task G and validated in further study experiments.

• Structural Engineering and Mechanics
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• v.68 no.4
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• pp.399-408
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• 2018

Cable supported structures have been widely used in civil engineering. Cable tension estimation has great importance in cable supported structures' analysis, ranging from design to construction and from inspection to maintenance. Even though the Bernoulli-Euler beam element is commonly used in the traditional finite element method for calculation of frequency and cable tension estimation, many elements must be meshed to achieve accurate results, leading to expensive computation. To improve the accuracy and efficiency, a dynamic finite element method for estimation of cable tension is proposed. In this method, following the dynamic stiffness matrix method, frequency-dependent shape functions are adopted to derive the stiffness and mass matrices of an exact beam element that can be used for natural frequency calculation and cable tension estimation. An iterative algorithm is used for the exact beam element to determine both the exact natural frequencies and the cable tension. Illustrative examples show that, compared with the cable tension estimation method using the conventional beam element, the proposed method has a distinct advantage regarding the accuracy and the computational time.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.09a
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• pp.733-734
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• 2005

• Journal of the Korean GEO-environmental Society
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• v.15 no.8
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• pp.51-58
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• 2014

In this research, the composite grounds including original clay and soil-cement were constructed for conducting uniaxial compression test. Strength and deformation properties were analysed using results of laboratory tests with variations of water content of clay, replacement ratio and cement content. Numerical simulation using 3D distinct element method was conducted for soil cement. For strength of composite ground that contains more than cement contents of 15 %, it is more effective to increase cement content than increase of replacement ratio. Strength and elastic modulus of composite ground could be predicted by regression equations using uniaxial compression strength of clay, cement content of soil cement and replacement ratio. For strength and elastic modulus of soil cement, which is most important things for predicting final strength and elastic modulus of composite ground, numerical simulation using the distinct element method adapted bonding model could be used to verify laboratory test, and predict strength and elastic modulus.

• Tunnel and Underground Space
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• v.24 no.1
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• pp.46-54
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• 2014

Direct shear tests have been initiated to understand the characteristics of joints which crucially affect the stability of rock mass. In this research, numerical approach in direct shear tests has been initiated using 3DEC on the basis of 3D distinct element method. Normal loads were altered in four different levels on artificial joint tests depending on the sawtooth angle and strengths on constant normal stress conditions, measuring the peak shear strength according to the direct shear tests under laboratory condition. Also results obtained from mechanical properties through laboratory test were used to perform numerical modeling, and shear strength obtained from the modeling was used to compare with laboratory direct shear test. As a result numerical analysis from distinct element method can simulate well on the shear behavior of rockmass.