• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2001년도 추계학술발표회
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• pp.231-234
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• 2001

When constructing subsurface structures and/or wells, the precise estimates of hydraulic parameters must be obtained for operating safety and/or for developing necessary quantity of groundwater. Hydraulic conductivity is mainly subjected to the characteristics of fracture network in the fractured media such as fracture orientation and angle, fracture aperture and frequency, fracture length, interconnectivity of fractures, and filling material, feature of fracture plane. In this study we conducted water injection test at afferent depths on six boreholes drilled in granite of Mt. Geumjeong. hydraulic conductivity was calculated using Moye and Hvorslev methods. The relation between hydraulic conductivity and fracture frequency data obtained from acoustic televiewer and core log were analyzed. The result shows that the correlation between the hydraulic conductivity and the fracture frequency data obtained from acoustic televiewer is better than that with the core log.

• Interaction and multiscale mechanics
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• 제1권1호
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• pp.83-101
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• 2008

A derivation is given of two-scale models that are able to describe deformation and flow in a fluid-saturated and progressively fracturing porous medium. From the micromechanics of the flow in the cavity, identities are derived that couple the local momentum and the mass balances to the governing equations for a fluid-saturated porous medium, which are assumed to hold on the macroscopic scale. By exploiting the partition-of-unity property of the finite element shape functions, the position and direction of the fractures are independent from the underlying discretization. The finite element equations are derived for this two-scale approach and integrated over time. The resulting discrete equations are nonlinear due to the cohesive crack model and the nonlinearity of the coupling terms. A consistent linearization is given for use within a Newton-Raphson iterative procedure. Finally, examples are given to show the versatility and the efficiency of the approach.

• 대한기계학회논문집A
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• 제33권6호
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• pp.552-559
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• 2009

The effect of porosity on the crack propagation is studied by using the cohesive zone model. Standard mode I fracture test were done by using compact tension specimens with various porosities. Load-load line displacement curves and ${\delta}_5$-crack resistance curves for various porosities were obtained from experiments. The cohesive zone model proposed by Xu and Needleman was employed to describe the crack propagation in porous media, and the Gurson model is used for constitutive relation of porous materials. These models were implemented into user subroutines of a finite element program ABAQUS. The fracture mode changes from ductile fracture to brittle fracture as the porosity increases. Numerical calculations agree well with experimental results.

• 지질공학
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• 제5권2호
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• pp.201-213
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• 1995

열극암반(Fractured rockmass)의 지하수유동해석을 위해서는 열극현상에 대한 전반적인 이해를 필요로 한다. 열극현상과 관련된 분야는 열극(Fracture)의 생성과 역학이론, 전파, 종식, 분포체계와 구조 및 열극체계 모델링등 다양한 분야가 이에 속한다. 그러나 이러한 분야의 연구는 일부 분야를 제외하고 외국에서도 그 역사가 깊지 못하며, 우리나라의 경우 근래에 일부 학계와 업계에서 관심을 보이고 있을 뿐이다.산업사회의 발달과 함께 다양한 목적으로 지하공간의 이용을 필요로 하게 되었고, 지하공동의 성능평가에 대한 적용방법 또한 복잡하고 다양한 접근방법을 요구하고 있다. 열극현상에 대한 정확한 이해가 지질학과 같은 어느 한 분야의 지식만으로 접근할 수가 없으므로, 열극의 정확한 분포 특성과 열극생선과정의 이론을 근간으로 열극체계 및 유동해석모델의 적절한 연관성을 도출하도록 조화를 이루므로써 신뢰성 높은 성능평가의 목표를 달성할 수 있을 것으로 기대된다.

• Structural Engineering and Mechanics
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• 제24권4호
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• pp.411-427
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• 2006

The Discrete Element Method, DEM, is increasingly used in fracture studies of non-homogeneous continuous media, such as rock and concrete. A 2D circular rigid DEM formulation, developed to model concrete, has been adopted. A procedure developed to generate aggregate particles with a given aspect ratio and shape is presented. The aggregate particles are modelled with macroparticles formed by a group of circular particles that behave as a rigid body. Uniaxial tensile and compression tests performed with circular and non-circular aggregates, with a given aspect ratio, have shown similar values of fracture toughness when adopting uniform strength and elastic properties for all the contacts. Non-circular aggregate assemblies are shown to have higher fracture toughness when different strength and elastic properties are set for the matrix and for the aggregate/matrix contacts.

• Maxillofacial Plastic and Reconstructive Surgery
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• 제16권1호
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• pp.72-78
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• 1994

A naso-orbito-ethmoid(NOE) fracture is very complex diagnostically and therapeutically. The diagnosis of this fractures is usually made by physical findings aided by a CT scan. The primary treatment of NOE fracture must be directed toward the reconstruction of medial canthal ligament and bony skeleton. We prefer to correct lacrimal system abnormalities secondarily A 32-year old male patient visited emergency room of our hospital with NOE fracture. After emergency treatment and consultation with neurosurgery and ophthalmology, we treated this patient by performing reconstruction of medial canthal ligament, bone graft of media orbital rim blowout fracture, and dorsal nasal cantilever bone graft with calvarial bone. The authors present a case report with literature review.

• International Journal of Aeronautical and Space Sciences
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• 제2권2호
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• pp.65-72
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• 2001

This paper demonstrates an explicit-implicit, finite element analysis for linear as well as nonlinear hygrothermal stress problems. Additional features, such as moisture diffusion equation, crack element and virtual crack extension(VCE) method for evaluating J-integral are implemented in this program. The Linear Elastic Fracture Mechanics(LEFM) Theory is employed to estimate the crack driving force under the transient condition for an existing crack. Pores in materials are assumed to be saturated with moisture in the liquid form at the room temperature, which may vaporize as the temperature increases. The vaporization effects on the crack driving force are also studied. The ideal gas equation is employed to estimate the thermodynamic pressure due to vaporization at each time step after solving basic nodal values. A set of field equations governing the time dependent response of porous media are derived from balance laws based on the mixture theory. Darcy's law is assumed for the fluid flow through the porous media. Perzyna's viscoplastic model incorporating the Von-Mises yield criterion are implemented. The Green-Naghdi stress rate is used for the invariant of stress tensor under superposed rigid body motion. Isotropic elements are used for the spatial discretization and an iterative scheme based on the full Newton-Raphson method is used for solving the nonlinear governing equations.

• 자원환경지질
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• 제28권5호
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• pp.503-512
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• 1995

2차원 불연속 절리 모델 (Discrete Fracture Model)을 사용하여 절리망 내에서 지하수 흐름을 시뮬레이션하였다. 불연속 절리 모델에서는 지하수가 오직 절리망을 통해서 흐른다고 가정한다. 이와 같은 분석은 결정질암 같이 지질 매체의 투수율이 매우 낮은 경우에 유용하다. 하지만 불연속 절리망을 완벽하게 구현하는 것이 불가능하므로, 이에 접근하는 방법으로 확률 통계적 모델이 제안되었다. 확률-통계적 모텔은 특성인자(밀도, 방향, 길이, 틈새두께 등)가 특별한 분포 유형을 갖는다고 가정한다. 확률-통계적 모델은 가정된 분포를 따르도록 특성인자를 생성한다. 이 후 본 모델을 통해 분석된 몇몇 특성인자를 가지고 절리망을 생성한다. 절리망을 생성한 이 후 지하수의 유통을 계산하기 위해 유한요소법을 적용하였다. 이 때 일차원 선요소가 유한요소망의 주요 요소이다. 시뮬레이션 결과는 절리망 내의 주요 흐름 경로를 통해 보여진다. 절리망 내의 지하수 속도를 비교하여 주요 흐름 경로를 찾아낸다. 본 연구에서 개발된 모델은 절리망 내의 지하수 흐름에 특성인자들이 미치는 영향을 평가할 수 있는 방법을 제공한다. 이를 위하여 30번의 생성을 하는 몬테카를로 시뮬레이션을 통해서 여러 특성 인자들이 지하수 흐름에 미치는 영향을 평가하였다.

• Steel and Composite Structures
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• 제44권6호
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• pp.817-828
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• 2022

In this study, considering dissipated energy in fracture process zone (FPZ), a novel criterion based on maximum strain energy release rate (SER) for orthotropic materials is presented. General case of in-plane loading for cracks along the fibers is assumed. According to the experimental observations, crack propagation is supposed along the fibers and the reinforcement isotropic solid (RIS) concept is employed as a superior model for orthotropic materials. SER in crack initiation and propagation phases is investigated. Elastic properties of FPZ are extracted as a function of undamaged matrix media and micro-crack density. This criterion meaningfully links between dissipated energy due to toughening mechanisms of FPZ and the macroscopic fracture by defining stress intensity factors of the damaged zone. These coefficients are used in equations of maximum SER criterion. The effect of crack initiation angle and the damaged zone is considered simultaneously in this criterion and mode II stress intensity factor is extracted in terms of stress intensity factors of damage zone and crack initiation angle. This criterion can evaluate the effects of FPZ on the fracture behavior of orthotropic material. Good agreement between extracted fracture limit curves (FLC's) and available experimental data proves the ability of the new proposed criterion.

• 터널과지하공간
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• 제13권6호
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• pp.465-475
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• 2003

본 논문은 지하공동이 건설되는 지역을 대상으로 공동내 지하수 유입량을 계산하기 위하여 영국의 AEA Technology에서 개발한 NAPSAC과 NAMMU를 이용하여 수치 모델링을 실시하였다. 이것은 3차원의 파쇄된 매질에서 지하수 유동에 대하여 아주 유효한 유한요소 소프트웨어 패키지이다. 모델링에 사용된 입력자료는 지표조사, 시추조사, 단일공 수리시험 자료 등을 이용하여 산출하였다. 공동내 지하수 유입량을 보다 정확히 산출하기 위하여 이방성 수리전도도를 고려하였으며 이방성 수리전도도값은 연구지역에 분포하는 균열체계의 확률적 분포특성이 반영된 균열망에서 역산되었다. 연속체 개념의 수치모델링을 통하여 평수기, 갈수기와 풍수기시의 지하 공동내 유입량, 유동시간, 유동경로의 변화를 계산하였다.