• Tunnel and Underground Space
• /
• v.29 no.4
• /
• pp.262-279
• /
• 2019

In the engineering barriers of high-level radioactive waste disposal, gases could be generated through a number of processes. If the gas production rate exceeds the gas diffusion rate, the pressure of the gas increases and gases could migrate through the bentonite buffer. Because people and the environment can be exposed to radioactivity, it is very important to clarify gas migration in terms of long-term integrity of the engineered barrier system. In particular, it is necessary to identify the hydro-mechanical mechanism for the dilation flow, which is a very important gas flow phenomenon only in medium containing large amounts of clay materials such as bentonite buffer, and to develop and validate new numerical approach for the quantitative evaluation of the gas migration phenomenon. Therefore, in this study, we developed a two-phase flow model considering the mechanical damage model in order to simulate the gas migration in the engineered barrier system, and validated with 1D gas flow modelling through saturated bentonite under constant volume boundary conditions. As a result of numerical analysis, the rapid increase in pore water pressure, stress, and gas outflow could be simulated when the dilation flow was occurred.

• Journal of the Korean Geosynthetics Society
• /
• v.3 no.4
• /
• pp.3-12
• /
• 2004

In this paper, a mechanism of the soil structure reinforced by geosynthetics is discussed. The reinforcing mechanism is interpreted an effect arising from the reinforcement works so as to prevent the dilative deformation (negative dilatancy) of soil under shearing. A full-scale in-situ model test was carried out in Kanazawa of Japan(1994) and in the laboratory test the strength and the characteristics of deformation conducting a constant volume shear test are examined. The parameters needed in the FEM are also applied by using the experimental data. The elasto-plastic finite element simulation is carried out, and the results are quantitatively compared with that of experiment. As a results, it is known that the theoretical predictions could be explained effectively the experimental results which are obtained by a full-scale in-situ model test.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.17 no.2
• /
• pp.89-99
• /
• 1997

Although discontinuously reinforced metal matrix composite(MMC) is one of the most promising materials for applications of aerospace, automotive industries, the thermal residual stresses developed in the MMC due to the mismatch in coefficients of thermal expansion between the matrix and the fiber under a temperature change has been pointed out as one of the serious problem in practical applications. There are very limited nondestructive techniques to measure the residual stress of composite materials. However, many difficulties have been reported in their applications. Therefore it is important to establish analytical model to evaluate the thermal residual stress of MMC for practical engineering application. In this study, an elastic model is developed to predict the average thermal residual stresses in the matrix and fiber of a misoriented short fiber composite. The thermal residual stresses are induced by the mismatch in the coefficient of the thermal expansion of the matrix and fiber when the composite is subjected to a uniform temperature change. The model considers two-dimensional in-plane fiber misorientation. The analytical formulation of the model is based on Eshelby's equivalent inclusion method and is unique in that it is able to account for interactions among fibers. This model is more general than past models to investigate the effect of parameters which might influence thermal residual stress in composites. The present model is to investigate the effects of fiber volume fraction, distribution type, distribution cut-off angle, and aspect ratio on thermal residual stress for in-plane fiber misorientation. Fiber volume fraction, aspect ratio, and distribution cut-off angle are shown to have more significant effects on the magnitude of the thermal residual stresses than fiber distribution type for in-plane misorientation.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.38 no.5
• /
• pp.527-534
• /
• 2014

Poroelastic analyses of fiber-reinforced composites were performed using image-based computational models. The section image of a porous matrix was analyzed in order to investigate the porosity, number of pores, and distribution of pores. The resolution, location, and size of the section image were considered to quantify the effective elastic modulus, poroelastic parameter, and strain energy density using the image-based computational models. The poroelastic parameter was calculated from the effective elastic modulus and pore pressure-induced strain. In addition, the results of the poroelastic analyses were verified through representative volume elements by simplifying various pore configurations and arrangements.

• Composites Research
• /
• v.25 no.1
• /
• pp.1-8
• /
• 2012

In order to predict the thermoelastic behavior of porous composites, poroelastic parameters are measured by using micromechanics-based finite element models. The expanding deformation caused by pore pressure, and the degradation of homogenized elastic moduli with pores are calculated for the assessment of the poroelastic parameters. Various representative volume elements considering the shape, size, and array pattern of pores are modeled and analyzed by a finite element method. The effects of porosity and material anisotropy, and the distribution of stain energy density are investigated carefully. In addition, the measured poroelastic parameters are verified by predicting the thermo-pore-elastic behavior of carbon/phenolic composites.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2004.03b
• /
• pp.348-355
• /
• 2004

본 연구에서는 geosynthetics로 보강된 다짐토의 보강 메카니즘을 파악하기 위한 목적으로 실내시험 및 수치계산 수행하였다. 본 연구에서 고려하는 보강 메카니즘은 전단에 의한 다짐토의 체적 팽창(부의 다일렌탄시)을 geosynthetics에 의해 구속 억제하는 과정에서 생성되는 효과로 생각한다. 먼저, 실내실험을 위한 구제직인 방법으로서, geosynthetics의 보강효과를 정량직으로 파악하기 위하여 사질토를 다짐하여 공시체를 만들어 그 주위에 geosynthetics를 설치하여 전체적으로 압축전단 시험을 실시하였다. 또한, 다짐토의 다짐도를 달리 하고 한 가지 종류만의 geosynthetics를 이용하여, 다짐토와 geosynthetics의 상호작용에 따른 압축력 변화, geosynthetics의 인장력 변화 및 공시체의 파괴 진행상황 등을 살펴보았다. 수치계산에서는 다짐토의 다일렌탄시 특성에 대하여 표현 가능한 탄소성 구성모델을 이용하였다. 또한, 탄소성 구성 모델에서의 항복 이전의 탄성영역의 거동을 묘사하기 위하여 Hashiguchi(1989)가 제안한 subloading surface의 개념을 도입하였고, 유한요소(FEM)해석을 통해 얻어진 결과들을 실내시험의 결과와 비교 분석하였으며, 그 결과 양자 양호한 결과를 얻었다.

• Geotechnical Engineering
• /
• v.8 no.2
• /
• pp.81-96
• /
• 1992

This paper dealt with the influence of experimental error generated inevitably during performing experiments on the granular soil behaviour analysis selecting Lade's Single Work-Hardening constitutive model. Several isotropic compression-expansion tests and a series of drained conventional triaxial tests with various confining pressures for Baekma river sands were performed and the values of parameters for the above model were determined using computer program developed for this study based on regression analysis. By finding the range of the upper and lower bound for deviator stress and volumetric strain versus axial strain dependant on the increase and decrease of the standard deviation from mean value of parameters, sensitivities of all the parameters were examined. Practical use of program to determine the parameters and capability to predict the behaviour of granular soil by Lade's Single Work -Hardening model verified.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2011.04a
• /
• pp.211-214
• /
• 2011

In the present work, a computational study was conducted to investigate characteristic of lateral force on the flow fields inside the propulsion nozzle with step. The unsteady, compressible, axisymmetric, Navier-Stocks equations with SST k-${\omega}$ turbulence model are solved using a fully implicit finite volume scheme. In order to simulate the shut-down process of the engine, NPR is varied from 100.0 to 10.0. It is observed that the separation point and Mach-disk strongly depend on the variation of NPR, and adjusting the step lead to significantly different characteristics in the lateral forces.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.29 no.5
• /
• pp.483-490
• /
• 2016

In plant industry, sulfur storage tank is made of steel and annular plate is connected with concrete foundation of ring wall type by anchor bolt. Due to keep sulfur at high temperature in tank by coil, sulfur storage tank is expanded larger than another tank stores fluid at room temperature. Generally, structural design of tank foundation is performed analysis with loading of temperature gradient between inner and outer surface, this method can't consider the phenomenon that load is intensively transferred to concrete foundation at anchor bolt. This means that temperature load is underestimated and causes crack of concrete near anchor bolt. In this study, evaluation formula considering temperature load transfer mechanism through anchor bolt is proposed and load acting on concrete foundation is rationally decided. For this purpose, it is analyzed variation of thermal load per various anchor bolt number using finite element model including tank annular plate and anchor bolt. Solution is proposed as specified term combining result of analysis and theoretical solution for evaluating load transferred by anchor bolt. For confirmation of validation of proposed formula, it is applied in design of sulfur storage tank at plant site, it shows that the formula can be practically applied.

• Journal of the Korean GEO-environmental Society
• /
• v.13 no.1
• /
• pp.21-29
• /
• 2012

Ground failure by liquefaction can occur not only during shaking but also as the result of the post-liquefaction process after an earthquake. During the process of ground deformation and failure, excess pore water pressure in soil is redistributed, which can then lead to changes in the effective stress of soils. Therefore, in order to provide a further understanding of the phenomenon, we have to estimate the properties of effective stress during the recompression process in post-liquefaction as well, not only the total amount of pore water drained. The primary objectives of this study are to determine and compare the recompression properties in the post-liquefaction process in terms of the relationship between volumetric strains and mean effective stresses under the various conditions of relative density and shear stress history. In all experimental cases, the volumetric strains increase greatly in the low effective stress level, almost to the zero zone, and granite soil, which has fine grains, undergoes gradual changes in the relationship between volumetric strains and mean effective stresses compared with fine sand. And, we can also find that recompression properties in the post-liquefaction process by cyclic loading depend highly on the dissipation energy and maximum shear strain, and this fact can be obtained in all cases regardless of the existence of fine content, relative density, and loading history. Especially, granite soil having fine grains can be defined uniformly in the relationship between dissipation energy and maximum volumetric strain, while fine sand cannot be so uniformly defined.