• Journal of Korean Association for Spatial Structures
• /
• v.7 no.5
• /
• pp.83-87
• /
• 2007

Elastic critical loads of sinusoidally tapered bars with simply supported ends are determined by finite element method. The parameters considered in the analysis are taper parameter (=a) and section property parameter (=m). The analysis result for the special case of porismatic bar (a=0) shows good agreement with the existing value. The changes of the critical load coefficients are expressed by an algebraic equation. The coefficients appearing in the equations are determined by regression technique. The critical loads coefficients estimated by the proposed equations reveal little errors when they are compared with those determined by finite element method.

• Journal of the Korean Society for Railway
• /
• v.7 no.3
• /
• pp.200-207
• /
• 2004

Theoretical study has been conducted to clarify pressure characteristics of KTX (Korea Train eXpress) in tunnel. The severe pressure change in tunnel may give rise to the ear-discomfort for passenger and fatigue for car body. Critical tunnel lengths which are induced by x-t diagram analysis can be applied to the experimental results measured by using the running test with atmospheric pressure sensors and portable data acquisition system in previous study. In this study, the tunnels from 200m to 4000m in length have been chosen for the investigation of tunnel length effects. We found that there are similar patterns of external pressure change for each critical tunnel length. The critical tunnel lengths are governed by train speed, train length and sonic velocity. And, the patterns of pressure wave in tunnel are classified into eight groups.

• Steel and Composite Structures
• /
• v.33 no.1
• /
• pp.133-142
• /
• 2019

In the present study, microstructure-dependent static stability analysis of inhomogeneous tapered micro-columns is performed. It is considered that the micro column is made of functionally graded materials and has a variable cross-section. The material and geometrical properties of micro column vary continuously throughout the axial direction. Euler-Bernoulli beam and modified couple stress theories are used to model the nonhomogeneous micro column with variable cross section. Rayleigh-Ritz solution method is implemented to obtain the critical buckling loads for various parameters. A detailed parametric study is performed to examine the influences of taper ratio, material gradation, length scale parameter, and boundary conditions. The validity of the present results is demonstrated by comparing them with some related results available in the literature. It can be emphasized that the size-dependency on the critical buckling loads is more prominent for bigger length scale parameter-to-thickness ratio and changes in the material gradation and taper ratio affect significantly the values of critical buckling loads.

• Journal of the Korean Mathematical Society
• /
• v.58 no.3
• /
• pp.723-740
• /
• 2021

Design and maintenance of large span roof structures require an analysis of their static and dynamic behavior depending on the physical parameters defining the structures. Therefore, it is highly desirable to estimate the parameters from observations of the system. In this paper we study the parameter estimation problem for damped shallow arches. We discuss both symmetric and non-symmetric shapes and loads, and provide theoretical and numerical studies of the model behavior. Our study of the behavior of such structures shows that it is greatly affected by the existence of critical parameters. A small change in such parameters causes a significant change in the model behavior. The presence of the critical parameters makes it challenging to obtain good estimation. We overcome this difficulty by presenting the Parameter Estimation Algorithm that identifies the unknown parameters sequentially. It is shown numerically that the algorithm achieves a successful parameter estimation for models defined by arbitrary parameters, including the critical ones.

• Nuclear Engineering and Technology
• /
• v.53 no.1
• /
• pp.19-29
• /
• 2021

This paper presents the validation of the MCS code for critical safety analysis with burnup credit for the spent fuel casks. The validation process in this work considers five critical benchmark problem sets, which consist of total 80 critical experiments having MOX fuels from the International Criticality Safety Benchmark Evaluation Project (ICSBEP). The similarity analysis with the use of sensitivity and uncertainty tool TSUNAMI in SCALE was used to determine the applicable benchmark experiments corresponding to each spent fuel cask model and then the Upper Safety Limits (USLs) except for the isotopic validation were evaluated following the guidance from NUREG/CR-6698. The validation process in this work was also performed with the MCNP6 for comparison with the results using MCS calculations. The results of this work showed the consistence between MCS and MCNP6 for the MOX fueled criticality benchmarks, thus proving the reliability of the MCS calculations.

• Structural Engineering and Mechanics
• /
• v.87 no.1
• /
• pp.29-46
• /
• 2023

Critical thermal buckling of functionally graded porous (FGP) sandwich plates under various types of thermal loading is considered. It is assumed that the mechanical and thermal nonhomogeneous properties of FGP sandwich plate vary smoothly by distribution of power law across the thickness of sandwich plate. In this paper, porosity defects are modeled as stiffness reduction criteria and included in the rule of mixture. The thermal environments are considered as uniform, linear and nonlinear temperature rises. The critical buckling temperature response of FGM sandwich plates has been analyzed under various boundary conditions. By comparing several numerical examples with the reference solutions, the results indicate that the present analysis has good accuracy and rapid convergence. Further, the effects of various parameters like distribution shape of porosity, sandwich combinations, aspect ratio, thickness ratio, boundary conditions on critical buckling temperature of FGP sandwich plate have been studied in this paper.

• Quality Improvement in Health Care
• /
• v.7 no.2
• /
• pp.156-167
• /
• 2000

Background: Emphasis in healthcare during the 1990s has been to provide both optimal wellness and function with quality in a Cost-effective manner. Critical pathway was developed to meet the need to guide clients along the continunm of care and to achieve continuity of care. The purpose of this study is to review and analyze articles related to the critical pathway that had developed and applied in Korea and abroad from 1995 to 1999. Methods: Total 39 studies were analyzed in terms of group of application, need of development, horizontal axis: time frame, vertical axis : items of care, task force team, identification of preliminary critical pathway, validation of preliminary critical pathway, types of final critical pathway, a person who coordinates and effects on critical pathway. Results: In the aspect of group of application, there were various diseases in the overseas than in Korea. In domestic and overseas, the horizontal axis included mainly the time from the start of hospitalization to discharge and vertical axis of the critical pathway included commonly the following nine items : tests, diet, medications, consultations, activity, assessments, treatments, education, discharge planning. Preliminary critical pathway was mainly drawn up through chart review in both. Types of final critical pathway were mostly for medical team use in Korea and were for medical team and patient use in abroad. A person who coordinates critical pathway was mostly nurse in abroad. There was positive effects on critical pathway in both. Conclusion: Staff education and information about critical pathway are needed to use it effectively.

• The Journal of Korean Academic Society of Nursing Education
• /
• v.23 no.2
• /
• pp.214-223
• /
• 2017

Purpose: This study was conducted to investigate the factors influencing the competence in intensive and critical care nursing of senior nursing students. Methods: A descriptive survey was used to examine the factors that influence competence in intensive and critical care nursing. The data were collected using self-administered questionnaires; 237 senior nursing students were asked about general characteristics, critical thinking, communication competence, self-esteem, self-resilience, and self-leadership. Results: Multiple regression analysis indicated that self-leadership, self-esteem, and confidence in intensive care unit practice predicted the competence in intensive and critical care nursing (37.8% of explanatory power). Critical thinking, communication competence, and self-resilience were not shown to be significant predictors of, but were positively correlated with, the competence in intensive and critical care nursing. Conclusion: Based on the results, it is suggested that self-leadership, self-esteem, and confidence in intensive care unit practice should be considered in nursing education in order to improve nursing students' level of competence in intensive and critical care nursing.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2010.09a
• /
• pp.687-697
• /
• 2010

This study was designed to carry out studies on critical seepage velocity and critical hydraulic gradient using a piping test targeting SM and ML which are widely distributed ahead of and behind the depth of E.L(-)10m in Saemangeum area in order to examine stability of embankment built on the ground vulnerable to piping. The effects of relative densities on critical hydraulic gradient and critical velocity were also compared and analyzed using empirical formula and theoretical formula, and relative densities were set up as respectively 9%, 25%, 50%, and 75% for this experiment. As a result, for critical hydraulic gradient, most of specimens detected piping at lower values than the empirical formula of Terzaghi(1922). It is, therefore, considered that the empirical formula devised by Kalin(1977) or Hayashi(1978) is more reasonable to be conservative. It was also found that critical velocity decreased as relative density increased, and critical velocity predicted was mostly lower than the theoretical formula.

• Journal of Mechanical Science and Technology
• /
• v.17 no.1
• /
• pp.57-63
• /
• 2003

An eigenvalue design sensitivity formulation of a general nonsymmetric-matrix rotor-bearing system is devised. using the DDM (direct differential method). Then, investigations on the design sensitivities of critical speeds are carried out for an APU turbogenerator with a spline shaft connection. Results show that the dependence of the rate of change of the critical speed on the stiffness changes of bearing models of spline shaft connection points is negligible, and thereby their modeling uncertainty does not present any problem. And the passing critical speeds up to the 4th critical speed are not sensitive to the design stiffness coefficients of four main bearings. Further, the dependence of the rate of change of the critical speed on the shaft-element length changes shows quantitatively that the spline shaft has some limited influence on the 4th critical speed but no influence on the 1st to 3rd critical speeds. With no adverse effect from the spline shaft, the APU system achieves a critical speed separation margin of more than 40% at a rated speed of 60,000 rpm.