• 한국지진공학회논문집
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• 제4권4호
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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.

• 한국항해항만학회지
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• 제31권7호
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• pp.589-595
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• 2007

In the majority of previous studies on deformation of seabed structures using DEM, elements of structures have been assumed that it is composed with uniform materials or received fixed wave force, despite that actual submerged structures are composed with various size materials and influenced by complicated fluid field. The goal of this study is to develop a new model for analysis of seabed structure deformation using discontinuous structures composed with various size materials. As the first phase, a model using DEM and VOF, which can compute the deformation of submerged structures composed with various size materials, such as rubble mound structures, is proposed. A model test is carried out and then the validity of the model is discussed.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2005년도 추계 학술대회논문집
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• pp.11-19
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• 2005

First, methods of numerical analysis of gas-particle flows is classified into micro, meso and macro scale approaches based on the concept of multi-scale mechanics. Next, the explanation moves on to discrete particle simulation where motion of individual particles is calculated numerically using the Newtonian equations of motion. The author focuses on the cases where particle-to-particle interaction has significant effects on the phenomena. Concerning the particle-to-particle interaction, two cases are considered: the one is collision-dominated flows and the other is the contact-dominated flows. To treat this interaction mathematically, techniques named DEM(Distinct Element Method) or DSMC (Direct Simulation Monte Carlo) have been developed DEM, which has been developed in the field of soil mechanics, is useful for the contact -dominated flows and DSMC method, developed in molecular gas flows, is for the collision-dominated flows. Combining DEM or DSMC with CFD (computer fluid dynamics), the discrete particle simulation becomes a more practical tool for industrial flows because not only the particle-particle interaction but particle-fluid interaction can be handled. As examples of simulations, various results are shown, such as hopper flows, particle segregation phenomena, particle mixing in a rotating drum, dense phase pneumatic conveying, spouted bed, dense phase fluidized bed, fast circulating fluidized bed and so on.

• 한국터널지하공간학회 논문집
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• 제9권2호
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• pp.133-141
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• 2007

굴착손상영역(EDZ)은 굴착으로 인해 현지 암반이 역학적으로 손상을 입게 되어 응력상태, 변위상태, 암반의 안정성, 지하수의 흐름상태 등에 변화가 일어나는 영역을 의미한다. EDZ의 역학적 특성과 관련한 많은 연구들이 수행되었지만, EDZ에서의 지하수 유동 특성에 관한 연구는 아직 부족한 수준이다. 따라서 본 연구에서는 굴착으로 인해 굴착면 주변의 수리적 간극이 늘어나는 영역을 산정하여 '수리적 굴착손상영역'이라 정의하고 이를 위해 수리-역학적 상호작용(coupling)해석을 수행하였다. 이는 개별 불연속면 망의 생성을 통한 역학적, 수리적 변화의 모사가 가능한 개별요소법(discrete element method; DEM)을 이용하여 수행하였다. 이를 통해 EDZ에서 지하수의 흐름에 영향을 미치는 각종 조건들(불연속면의 간극, 불연속면 군의 방향, 불연속면 군의 길이, 불연속면의 각도 등)의 변화와, 응력분포, 지하수의 유동 등으로 인해 수리적 간극 값이 어떻게 변화하는지를 파악하였다. 이 결과를 토대로 수리적 간극이 커지는 영역, 수리적 EDZ를 공동 주변의 불연속면 방향에 수직 방향으로 존재하는 타원형의 형태로 모델링 하였다.

• 한국철도학회논문집
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• 제8권1호
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• pp.82-86
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• 2005

Numerical methods to estimate behaviors of jointed rock mass can be roughly divided into two methods : continuous and discontinuous model. Generally, distinct element method(DEM) is applied in discontinuous model, and finite element method(FDM) or finite difference method(FDM) is utilized in continuum model. To predict a behavior of discontinuous model by DEM, it is essential to understand characteristics of joints developed in rock mass through field tests. However, results of field tests can not provide full information about rock mass because field tests are conducted in limited area. In this paper, discontinuous analysis by UDEC and continuous analysis by FLAC are utilized to estimate a behavior of a tunnel in jointed rock mass. For including discontinuous analysis in continuous analysis, joints in rock mass is considered by reducing rock mass properties obtained by RMR and decreasing shear strength of rock mass. By comparing and revising two analysis results, analysis results similar with practical behavior of a tunnel can be induced and appropriate support system is decided.

• Structural Engineering and Mechanics
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• 제80권5호
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• pp.523-538
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• 2021

The mechanical behaviour and stability of coal mining engineering underground is significantly affected by ground water. In this study, nuclear magnetic resonance imaging (NMRI) technique was employed to determine the water distribution characteristics in coal specimens during saturation process, based on which the functional rule for water distribution was proposed. Then, using discrete element method (DEM), an innovative numerical modelling method was developed to simulate water-weakening effect on coal behaviour considering moisture content and water distribution. Three water distribution numerical models, namely surface-wetting model, core-wetting model and uniform-wetting model, were established to explore the water distribution influences. The feasibility and validity of the surface-wetting model were further demonstrated by comparing the simulation results with laboratory results. The investigation reveals that coal mechanical properties are affected by both water saturation coefficient and water distribution condition. For all water distribution models, micro-cracks always initiate and nucleate in the water-rich area and thus lead to distinct macro fracture characteristics. With the increase of water saturation coefficient, the failure of coal tends to be less violent with less cracks and ejected fragments. In addition, the core-wetting specimen is more sensitive to water than specimens with other water distribution models.

• 터널과지하공간
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• 제2권2호
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• pp.212-223
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• 1992

The distinct element method(DEM) si well suited to the kinematic analysis of blocky rock masses. Two distinctive problems, a rock avalache and tunnel in jointed rock masses, are chosen to apply the DEM which is based on perfectly rigid behaviour of blocks. Investigated for both problems are the effects of the input parameters such as contact stiffnesses, friction coefficient and damping property. Using various types of models of the avalanche and tunne, an extensive parametric study is done to gain experiences in the method, and then to alleviate difficulties in determining parameter values suitable for a given problem. The coefficient of frictio has significant effects on all aspects of avalanche motion(travel distance, velocity and travel time), while the stiffnesses affect the rebounding and jumping motions after collision. The motion predicted by the models having single and mutiple blocks agrees well to the observations reported on the actual avalache. For the tunnel problem, the behaviour of the key block in an example tunnel is compared by testing values of the input parameters. The stability of the tunnel is dependent primarily on the friction coefficient, while the stiffness and damping properties influence the block velocity. The kinematic stability of a tunnel for underground unclear waste repository is analyzed using the joint geometry data(orientation, spacing and persistence) occurred in a tailrace tunnel. Allowing a small deviation to the mean orientation results in different modes of failure of the rock blocks around the tunnel. Of all parameters tested, the most important to the stability of the tunnel in blocky rock masses are the geometry of the blocks generated by mapping the joint and tunnel surfaces in 3-dimensions and also the friction coefficient of the joints particularly for the stability of the side walls.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2002년도 춘계 학술발표회 논문집
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• pp.275-283
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• 2002

In this study, the shaking table tests of block systems on the rigid base have been performed to identify the seismic response and the dynamic behavior of the piled multi-block systems. To understand the characteristics of seismic response of piled multi-block systems, it is necessary to understand the dynamic behavior of single block system. Therefore, the skating table test of the single block system has been performed first. Moreover, by performing the shaking table tests of multi-block systems, the characteristics of dynamic behavior of piled multi-block systems have been analyzed. Also in this study, the distinct element method(DEM) has been used to analyze the nonlinear behavior of the piled multi-block systems. The results of the shaking table tests show that the response of the multi-block systems is very complicated. But by using DEM, the behavior of piled multi-block systems has been predicted and described well.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2001년도 봄 학술발표회 논문집
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• pp.241-247
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• 2001

A Fire Safety Evaluation Module(FSEM), which quantitatively evaluates the risk of evacuees when fire occurs in buildings or ships, is presented in this paper. The developed FSEM can be applied to multi-room structure. Basic input data for the FSEM are prepared by fire model and evacuation model. CFAST which is one of the existing fire models is used as fire model and MonteDEM evacuation model was developed for evacuation model, respectively. MonteDEM evacuation model makes use of distinct element method and Monte-Carlo simulation, and it can also take into consideration ground inclination by ship motions in order to simulate the real situation of evacuation. Some typical situations are modelled for illustrative examples and quantitative assessment of evacuee's risk under fire accident is carried out.

• 산업기술연구
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• 제23권A호
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• pp.69-81
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• 2003

Numerical analysis is important for the design, construction and maintenance of large caverns. The rock mass contains generally discontinuities such as faults, joints and fissures. The mechanical behavior and geometric characteristics of these discontinuities would have a significant impact on the stability of the caverns. In this research the Distinct Element Method(DEM) was used to analyze the structural stability of the large cavern. The Barton-Bandis Joint Model (B-B J.M) was used as a constitutive model for the joint. In addition, two different cases 1) analysis with a support system and 2) analysis with no support system, were analyzed to optimize a support system and to investigate reinforcing effects of a support system. The most significant parameters of in-situ stress, JRC of in-situ natural joints, and spatial distribution characteristics of discontinuities were acquired through field investigation. Displacement (horizontal, joint shear), maximum joint opening, maximum and minimum principal stresses, range of relaxed zone, rockbolt axial forces and shotcrete stresses were calculated at each excavation stage. As a result of analysis the calculated values proved to be under the allowable value Rockbolts also proved to be an efficient support measure to control joint shear displacement which had significant effects on extending the relaxed zone. As a consequence, the structural stability of the cavern was assured with an appropriate support system.