• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.03a
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• pp.187-194
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• 2002

Bridge dynamic behaviors and the failure of the foundation are examined in this study under seismic excitations including the local scour effect. The simplified mechanical model, which can consider the effect of various influence elements, is proposed to simulate the bridge motions. The scour depths around the foundations are estimated by the CSU equation recommended by the HEC-18 and the local scour effect upon global bridge motions is then considered by applying various foundation stiffness based upon the reduced embedded depths. From the simulation results, it is found that seismic responses of a bridge with the same scour depth for both foundations increase due to the local scour effect. The bridge scour is found to be significant under weak and moderate seismic intensity. The recovery durations of the foundation stiffness after local scour are found to be critical in the estimation of the probability of foundation failure under earthquakes. Therefore, the safety of the whole bridge system should be conducted with the consideration of the scour effect upon the foundations and the recovery duration of stiffness should be determined rationally.

• Journal of the korean Society of Automotive Engineers
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• v.14 no.2
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• pp.65-75
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• 1992

An analytical scheme for predicting the crack aspect pattern of materials which contain twin surface cracks was developed. Fatigue tests were performed on twin surface cracked PMMA plate specimens to obtain the interaction factor accounting for the interference effect of adjacent cracks. Here, the interaction factor is defined as the ratio of the stress intensity factor for twin surface cracks to that for a single surface crack. From the analysis of the fatigue test result, the interaction factor was presented as the ninth-order polynomial expression having a function of dimensionless crack spacing ratio. Then the polynomial expression was incorporated into the prediction program of the crack aspect pattern for twin surface cracked materials. And, the interaction effect and the coalescence condition of adjacent cracks were simplified in the newly developed prediction scheme of the crack aspect pattern. The predicted crack growth pattern using the prediction scheme was compared with test data from PMMA specimen. The predicted pattern agreed well with the test data.

• Wind and Structures
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• v.9 no.2
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• pp.147-158
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• 2006

The purpose of this paper is to find a more accurate method to evaluate pedestrian wind by computational fluid dynamics approach. Previous computational fluid dynamics studies of wind environmental problems were mostly performed by simplified models, which only use simple geometric shapes, such as cubes and cylinders, to represent buildings and structures. However, to have more accurate and complete evaluation results, various shapes of blocking objects, such as trees, should also be taken into consideration. The aerodynamic effects of these various shapes of objects can decrease wind velocity and increase turbulence intensity. Previous studies simply omitted the errors generated from these various shapes of blocking objects. Adding real geometrical trees to the numerical models makes the calculating domain of CFD very complicated due to geometry generation and grid meshing problems. In this case the function of Porous Media Condition can solve the problem by adding trees into numerical models without increasing the mesh grids. The comparison results between numerical and wind tunnel model are close if the parameters of porous media condition are well adjusted.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.480-485
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• 2004

If a wall separates the bounded and unbounded spaces, then the wall's role in transporting the acoustic characteristics of the two spaces is not well defined. In this paper, we attempted to see how the acoustic characteristical of two spaces are really affected by the spatial characteristics of the wall. In order to understand coupling mechanism, we choose a finite space and a semi-infinite space separated by the flexible or rigid wall and an opening. A volume interaction can be occurred in structure boundary and a pressure interaction can be happened in the opening boundary. For its simplicity, without loosing generality, we use rather simplified rectangle model instead of generally shaped model. The source impedance is presented to the various types of boundaries. The distributions of pressure and active intensity are also presented at the cavity and structure-dominated modes. The resulting modification, shifts of mode1 frequencies and changing of standing wave patterns to satisfy both coupled boundary conditions and governing equations, are presented.

• Proceedings of the KSR Conference
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• 2004.10a
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• pp.1101-1106
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• 2004

Rainfall induced landslides are disasters causing sever damage on the human life and the infrastructures. In this paper, a simplified procedure to evaluate the slope stability problems induced by rainfall by modifying the Iverson's pressure head dispersion model. The proposed approach extends the applicability of the Iverson's model in to the cases of higher rainfall intensity than the permeability of the soil by incorporating the existence of overland flow. In addition, the Manning equation is applied to calculated the depth of overland flow. From the calculated depth of overland flow, shear stress acting on the surface is included for the driving component triggering the landslides. From the analysis of a case study, the long term rainfall alters the stability of slope.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2002.04a
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• pp.166-173
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• 2002

Seismic bridge failure due to the combined effects of earthquake and local scour are examined in probabilistic perspectives. The seismic responses of multi-span continuous bridge with deep foundations are evaluated with a simplified mechanical model. The probabilistic local scour depths around the deep foundations are estimated by using the Monte Carlo simulation. From the simulation results, it is found that seismic responses of a bridge slightly increase due to the local scour effect. The effect of local scour on the global motion of the continuous bridge is found to be significant under weak seismic intensity. In addition, the duration to regain its original foundation stiffness is critical in estimating the probability of foundation failure under earthquake. Therefore, the duration in recovering the foundation stiffness should be determined reasonably and the safely of the whole bridge system should be evaluated by considering the scour effect.

• 연구논문집
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• s.22
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• pp.65-74
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• 1992

This paper aims at calculating optimum design dimensions to minimize the weight satisfied strain and stress intensity of the frame while loading maximum weight into a mechanical press in the static condition. Analysis of the frame was carried out by using the FEM, then the optimum condition was obtained by using these data. As modeling in the finite element analysis has great impact on the reliablity of analysis results, the analyzed object was selected a 150-ton mechanical press of J Company, the part little affected to structural rigidity was simplified, the load condition was considered in the only maximum load, the boundary condition was used by giving symmetric displacement due to symmetric boundary condition, the finite element was applied a linear membrane element. An intermediate processor program applied the normal ANSYS to analyze finite elements was developed, and the design sensitivity was calculated. This program was applied to the optimum design.

• Journal of the Korean GEO-environmental Society
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• v.20 no.9
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• pp.13-19
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• 2019

Dynamic earth pressure is considered an important parameter in the design of embedded structures. In current engineering design simplified methods developed either for yielding or non-yielding structures are utilized to predict resultant dynamic pressure. The applicability of these equations to embedded structures have not yet been reported. In this study we perform a suite of equivalent linear time history analysis for a range of embedded structure configurations. Numerically calculated dynamic pressure is shown to depend on the flexibility ratio (F), aspect ratio (L/H) of the embedded structure, and ground motion. Increase in L/H and intensity increases the magnitude of dynamic pressure. An increase in F decreases the dynamic pressure. Overall, the trends highlight the need for development of new method that accounts for F and L/H to calculate the dynamic pressure for the performance-based design of embedded structures.

• Journal of the Korean Society for Precision Engineering
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• v.11 no.4
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• pp.148-157
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• 1994

A multi-cylindrical hydraulic valve incorporating with an electro-rheological(ER) fluid is developed in this study. Field-dependent Bingham properties of the ER fluid are exploited to devise the valve system which features fast system response as well as simple mechanism. The fast response is accrued from almost instant response characteristics of the ER fluid itself, and the mechanism configuration is simplified since no nechanically moving parts are required. The material properties of the ER fluids to be utilized for modeling of the proposed valve system are firstly tested with a couette-type electroviscometer. The design and manufacturing processes are then undertaken on the basis of model parameters. The performance characteristics of the valve system are evaluated in terms of pressure variations with respect to the intensity of employed electric fields and flow rates.

• Clinical and Experimental Pediatrics
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• v.53 no.11
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• pp.957-964
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• 2010

Purpose: Our study attempted to determine the prognostic significance of minimal residual disease (MRD) detected by a simplified flow cytometric assay during induction chemotherapy in children with B-cell acute lymphoblastic leukemia (B-ALL). Methods: A total of 98 patients were newly diagnosed with precursor B-ALL from June 2004 to December 2008 at the Asan Medical Center (Seoul, Korea). Of those, 37 were eligible for flow cytometric MRD study analysis on day 14 of their induction treatment. The flow cytometric MRD assay was based on the expression intensity of CD19/CD10/CD34 or aberrant expression of myeloid antigens by bone marrow nucleated cells. Results: Thirty-five patients (94.6%) had CD19-positive leukemic cells that also expressed CD10 and/or CD34, and 18 (48.6%) had leukemic cells with aberrant expression of myeloid antigens. Seven patients with ${\geq}1%$ leukemic cells on day 14 had a significantly lower relapse-free survival (RFS) compared to the 30 patients with lower levels (42.9 % [18.7%] vs. 92.0% [5.4%], $P$=0.004). Stratification into 3 MRD groups (${\geq}1%$, 0.1-1%, and <0.1%) also showed a statistically significant difference in RFS (42.9% [18.7%] vs. 86.9% [8.7%] vs. 100%, $P$=0.013). However, the MRD status had no significant influence on overall survival. Multivariate analysis demonstrated that the MRD level on day 14 was an independent prognostic factor with borderline significance. Conclusion: An MRD assay using simplified flow cytometry during induction chemotherapy may help to identify patients with B-ALL who have an excellent outcome and patients who are at higher risk for relapse.