• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.980-987
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• 2006

Recently, twin-tunnel is often designed considering the aspects of disaster prevention and economic reasons. However, the design cases and the studies are relatively insufficient. By the twin-tunnel excavation, deviate stresses of pillar between tunnels are increased and the increased stresses induce the instability of the twin-tunnel. In this study, numerical analyses about the twin-tunnel behaviour are conducted while varying ground strength, width of pillar and depth of earth cover and a series of regression analyses are carried out by using the results of numerical analyses for the twin-tunnel. Based on the numerical analyses, an estimation method of derived stresses is suggested though the regression analyses. Also, based on the results of regression analyses, an quantitative estimation method considering the reinforcement effects is also suggested. Then various parametric studies are conducted to be considered the reinforcement type and various design parameters. Finally, the efficiency of the suggested method is verified through the results of parametric studies.

• Journal of Korean Society for Quality Management
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• v.25 no.3
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• pp.96-107
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• 1997

The recent stream to reliability prediction is that it is totally inclusive in depth to consider even the operating and environmental condition at the level of finished goods as well as component itselves. In this study, firstly we present the reliability prediction methods by entire failure rate model which failure rate at the system level is added to the failure rate model at the component level. Secondly we build up the improved bases of reliability demonstration through a, pp.ication of Kaplan-Meier, Cumulative hazard, Johnson's methods as non-parametric and Maximum Likelihood Estimator under exponential & Weibull distribution as parametric. And also present the methods of curve fitting to piecewise failure rate under Weibull distribution, PRST (Probability Ratio Sequential Test), curve fitting to S-shaped reliability growth curve, computer programs of each methods. Lastly we show the practical for determination of optimal burn-in time as a method of reliability enhancement, and also verify the practical usefulness of the above study through the a, pp.ication of failure and test data during 1 year.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.10a
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• pp.185-192
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• 1999

This paper presents the results of a parametric study on the behavior of tunnel face reinforced with horizontal pipes. A three-dimensional finite element model was adopted in this study to capture the three-dimensional nature of tunnel face behavior under various boundary conditions. A parametric study was peformed on a wide range of boundary conditions with emphasis on the effect of reinforcing layouts on the deformation behavior of tunnel face. The results of analysis such as tunnel face deformation behavior under various conditions were thoroughly analyzed, and a database for the behavior of tunnel face under different reinforcing conditions was established for future development of a semi-empirical design/analysis method for the tunnel face reinforcing technique. The results indicated that there exits an optimum reinforcing layout for a given tunnel condition, which must be selected with due consideration of tunnel geometry and ground condition.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.6
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• pp.169-175
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• 2000

In this study, the hydraulic vibro-hammer system was analyzed and the analysis tool using GUI was developed. From the parametric analysis, the effects of each factor were revealed. Through the simulation with varying parameters, the method to improve the performance of the hydraulic vibro-hammer system was presented. The analysis tool will help an unskilled programmer analyze the hydraulic vibro-hammer system. The result of this study will help improve the performance of the hydraulic vibro-hammer systems.

• Tribology and Lubricants
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• v.19 no.2
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• pp.59-64
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• 2003

In this study, the hydraulic breaker system was analyzed and the analysis tool using GUI was developed. The analysis on the system with the accumulator was included. From the parametric analysis, the effects of each factor were revealed. Through the simulation with varying parameters, the method to improve the performance of the hydraulic breaker system was presented. The analysis tool will help a man without special knowledge about programming analyze the hydraulic breaker system. The result of this study will help improve the hydraulic breaker system in sight of Blow energy and Blows per minute.

• The KSFM Journal of Fluid Machinery
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• v.19 no.5
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• pp.12-19
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• 2016

In present study, a parametric study of a centrifugal compressor with inlet treatment has been performed numerically using three-dimensional Reynolds-averaged Navier-Stokes equations. The shear stress transport turbulence model was used for analysis of turbulence. The finite volume method and unstructured grid system were used for the numerical solution. Tested parameters were related to the geometry of the inlet duct. It was found that the application of circumferentially distributed holes in the inlet duct improves operational stability of the compressor compared to that with conventional inlet duct.

• Proceedings of the KIEE Conference
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• 2002.11d
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• pp.39-42
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• 2002

In this study, the computational heat transfer of the high-voltage vacuum circuit breaker was investigated. Higher normal current-ratings and stabilized thermal characteristics become more important in existing circuit breakers in order to satisfy market needs. Increases in current-ratings have an even greater effect on the Joule heating in the main circuit of the breakers. The thermal design must account for this increase in heat produced for the breaker to meet various temperature-rise limits set by industry standards. We are studying to enhance the normal current-ratings without major frame change of our present production models. As the method used in this research, we performed the computational analysis using the commercial Package, ICEPAK. We could get optimized thermal design suitable for 25% upgraded normal current-ratings through parametric study.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.453-456
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• 2008

This study is underway to develop a prediction model for formwork pressure exerted by self-compacting concrete(SCC). Three major mechanisms related to formwork evolution over time were found, and mathematical modelling of each mechanism was made. A calculation method for real formwork pressure by using the mathematical formulae was also established. To verify predictive capability of the prediction model, a parametric study on parameters used in the model was performed. It was confirmed that the proposed model include the essential parameters that can simulate the real formwork pressure evolution over time.

• Steel and Composite Structures
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• v.48 no.1
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• pp.89-102
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• 2023

This study investigates the eccentric performance of concrete-filled steel tubular (CFST) stub columns strengthened with steel tube and sandwiched concrete (STSC) jackets. It was revealed that the STSC jacketing method effectively weakened the cracking of concrete in CFST columns on the convex side and the crash on the concave side. Substantial increases in the eccentric bearing capacities were demonstrated after strengthening. A numerical study was further conducted. The decrease in diameter-to-thickness ratio and increase in strength of outer tube contributed to increase in peak load of all components, whereas the increase in sandwiched concrete strength resulted in load increase on itself and had negligible effects on other components. The parametric study showed the effect of inner concrete strength on columns' bearing capacity was magnified after strengthening, whereas that of inner tube thickness was reduced. Within the parameters investigated, high-strength concrete and high-strength steel can be applied without the concern of early abrupt failure of inner low-strength concrete or steel tube.

• Structural Engineering and Mechanics
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• v.33 no.3
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• pp.373-385
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• 2009

The purpose of this paper is to study shear locking-free parametric earthquake analysis of thick and thin plates using Mindlin's theory, to determine the effects of the thickness/span ratio, the aspect ratio and the boundary conditions on the linear responses of thick and thin plates subjected to earthquake excitations. In the analysis, finite element method is used for spatial integration and the Newmark-${\beta}$ method is used for the time integration. Finite element formulation of the equations of the thick plate theory is derived by using higher order displacement shape functions. A computer program using finite element method is coded in C++ to analyze the plates clamped or simply supported along all four edges. In the analysis, 17-noded finite element is used. Graphs are presented that should help engineers in the design of thick plates subjected to earthquake excitations. It is concluded that 17-noded finite element can be effectively used in the earthquake analysis of thick and thin plates. It is also concluded that, in general, the changes in the thickness/span ratio are more effective on the maximum responses considered in this study than the changes in the aspect ratio.