• Magazine of the Korea Concrete Institute
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• v.7 no.5
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• pp.172-178
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• 1995

Concrete contains numerous microcracks at initially poured. The growth and propagation of nicrockacsk are believed tc finally incur the faiure of concrete. These processings are understood as a damage. Damage IS represented as a second-order tensor and crack is treated as a con tinuum phenomenon. In this paper, damage is characterized through the effective stress concept together with the hypothesis of elastic energy equivalence, and damage evolution law and constitutive equation of a damage model are derived by using the Helmholtz frte eriergy and the dissipation potential by means of the thermodynamic principles. The constitutive equation of the model includes the effects of elasticity, anisotropic damage and plasticity of concrete. There are two effective tangent stiffness tensors in this model : one is for elastic-darnage and the other for plastic damage. For the verification of the model, finite element analysis was performed for the analysis of concrete subjec:t to uniaxial and biaxial loading and the results obtained were compared with test results.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.4C
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• pp.221-230
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• 2008

The George Massey immersed tunnel passes the Fraser River near Vancouver, Western Canada. The tunnel was founded on sandy soils and its behavior during earthquake was analyzed by an effective stress constitutive model called UBCSAND. This model is able to calculate pore pressure rise and resulting tunnel movements due to cyclic loading. Centrifuge tests conducted at Rensselaer Polytechnic Institute (RPI) were used to verify the model performance. The centrifuge tests consisted of 2 models: Model 1 was designed for an original ground condition, Model 2 for a ground improvement by densification. In Model 1, large deformation of the tunnel was observed due to liquefaction of surrounding soil. Because of the densified zones around the tunnel the vertical and horizontal displacements of the tunnel in Model 2 was 50% less than Model 1. Measured excess pore pressures, accelerations, and displacements from centrifuge tests were in close agreement with the predictions of UBCSAND model. Therefore, the model can be used to predict seismic behavior of immersed tunnels on sandy soils and optimize liquefaction remediation methods.

• The Journal of Engineering Geology
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• v.22 no.2
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• pp.145-155
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• 2012

The matric suction and volumetric water content of Jumunin standard sand with a relative density of 60% were measured using an Automated Soil-Water Characteristic Curve (SWCC) apparatus during both drying and wetting processes. The test time for the drying process was longer than that for the wetting process, because the flow of water is likely to be protected by air trapped in voids within the soils during the drying process. Based on the matric suction and volumetric water content, the SWCC was estimated using the model proposed by van Genuchten (1980). For the drying process, the unsaturated fitting parameters ${\alpha}$, n, and m were 0.399, 8.586, and 0.884, respectively; for the wetting process, the values were 0.548, 5.625, and 8.220, respectively. The hysteresis phenomenon occurred in the SWCCs, which means the SWCC of the drying process is not matched with the SWCC of the wetting process. Using these unsaturated parameters, we estimated the Suction Stress Characteristic Curve (SSCC), based on the relationship between suction stress and the effective degree of saturation. The suction stress showed a rapid decrease when the matric suction exceeds the Air Entry Value (AEV). Therefore, the effective stress of unsaturated soils is different from that of saturated soils when the matric suction exceeds the AEV. The suction stress of the drying process exceeds that of the wetting process for a given effective degree of saturation. The hysteresis phenomenon was also recognized in SSCCs. The hysteresis phenomenon of SSCCs arises from that of SWCCs, which is induced by the ink bottle effect and the contact angle effect. In the case of a sandy slope, the suction stress is positive and acts to enhance the slope stability as the water infiltrates the ground, but is negative when the suction stress exceeds the AEV. The results obtained for the wetting process should be applied in analyses of slope stability, because the process of water infiltration into ground is similar to the wetting process.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.9
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• pp.1452-1461
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• 1997

The hot press apparatus to obtain the solidified rocks with 60mm of diameter against rock waste was developed, and the optimum conditions for solidification were founded out, of which were 300.deg. C of temperature and 1hr of holding time. The solidified rocks reinforced with the fibers (carbon, steel) were made by means of a hydrothermal hot press method. Fracture toughness of those was obtained using the round compact tension(RCT) specimens. Load and displacement behaviours of the solidified rocks reinforced with the fibers were dependent upon the fiber volume fraction and kind of the fibers. Strength and fracture energy of the solidified rocks with steel were much larger than those of the solidified ones with carbon because of the Bridge's effect, multiple cracking and crack branching phenomena.

• Journal of the Korean Institute of Gas
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• v.20 no.3
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• pp.59-65
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• 2016

It is imperative to use suitable explosion proof equipments to prevent explosion in different gas facilities. There is no technical standard for the classification of hazardous areas though standard of explosion proof is regulated. In this study, we have adopted Industrial Standard KS to develop the methodology for the prediction of the explosion risk in the natural gas facility with low pressure using the important factors including hole size, hypothetical volume, validation of ventilation effectiveness. The applicability of the developed methodology was evaluated by the comparison with the data obtained from experiments of natural gas explosion.

• Journal of rehabilitation welfare engineering & assistive technology
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• v.10 no.4
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• pp.259-265
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• 2016

In this paper, new method was proposed to classify lung tissues such as Broncho vascular, Emphysema, Ground Glass Reticular, Ground Glass, Honeycomb, Normal for early lung disease detection. 459 Statistical features was extraced from joint histogram matrix based on multi resolution analysis, volumetric LBP, and CT intensity, then dominant features was selected by using adaboost learning. Accuracy of proposed features and 3D AMFM was 90.1% and 85.3%, respectively. Proposed joint histogram based features shows better classification result than 3D AMFM in terms of accuracy, sensitivity, and specificity.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1378_1380
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• 2009

절연파괴 강도에대한 특성분석을 위해 와이블 plot을 이용하였다. ENMMC에서 실란처리와 미처리특성에서 실란처리된 결과 형상파라미터가 상대적으로 높은 값을 나타내었다. 이는 절연파괴결과가 균질함을 분명하게 나타낸 결과이다. 또한 스케일파리미터에서도 처리된 결과가 상대적으로 높은 결과를 보이고 있다. 나노입자 충진함량에 대한 효과에서도 체적비로 6.2vol%가 24.87vol%보다 월등하게 높은 형상파리미터와 스케일 파리미터를 나타내었다. 현장에서는 B10의 수명이 누적확률(63.2%)보다 오히려 유효한 평가자료 라고 사료된다. 역시 실란처리 된 결과가 미처리된 것에 비하여 그리고 나노입자 충진함량이 적을수록 높은 결과를 나타내었다. 이로서 중전기기 산업절연재료로서 향후 전망을 크게 할 것으로 본다.

• Journal of the Korean Society for Precision Engineering
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• v.30 no.9
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• pp.943-950
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• 2013

This paper describes the thermal contact resistance and its effect on the performance of thermal interface material. An ASTM D 5470 based apparatus is used to measure the thermal interface resistance. Bulk thermal conductivity of different interface material is measured and compared with manufacturers' data. Also, the effect of grease void in the contact surface is investigated using the same apparatus. The flat type thermal interface tester is proposed and compared with conventional one to consider the effect of lateral heat flow. The results show that bulk thermal conductivity alone is not the basis to select the interface material because high bulk thermal conductivity interface material can have high thermal contact resistance, and that the center voiding affects the thermal interface resistance seriously. On the aspect of heat flow direction, thermal impedance of the lateral heat flow shows higher than that of the longitudinal heat flow by sixteen percent.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.4
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• pp.1-7
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• 1997

This paper presents an analysis of the wave propagation in cross-type tunnels using the finite volume time domain (FVTD) method. Because the FVTD method is based on the volume intergrations of themaxwell's equations with respected to arbitrary shaped small polyhedron cells and the fields at every center point of the cells ar eassigned in a average fashion, the method can handle arbitrary boundary problems with inhomogeneous media. In this paper, the wave propagation in cross-type tunnels has been analyzed using the fVTD method with the PML (perfectly matched layer) absorbing bundary conditons, and the numerical results are verified with a set of experimental data.

• Nuclear Engineering and Technology
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• v.27 no.6
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• pp.870-876
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• 1995

In this paper, a new three-dimensional nodal diffusion code which is based on the AFEN methodology is described and tested. The method expands the homogeneous flux within a node in ter-ms of eighteen analytic basis functions satisfying the diffusion equation at any point of the node. And the nodal coupling equations are derived such that nodal balance, current continuity and leakage balance within an infinitesimally small box around the edge are satisfied. To verify its accuracy, the code was applied to the well-known static LMW benchmark problem and a small core benchmark problem that has the same material properties as the three-dimensional IAEA benchmark problem and compared with two other codes (QUANDRY, VENTURE). The results show that the code provides good accuracy both in the power distribution and in the effective multiplication factor.