• Earthquakes and Structures
• /
• v.19 no.6
• /
• pp.427-444
• /
• 2020

The performance of an isolated horizontally curved continuous bridge with High Damping Rubber (HDR) Bearings has been investigated under seismic loading conditions. The effectiveness of response controls of the bridge by HDR bearings for various aspects viz. variation in ground motion characteristics, multi-directional effect, level of earthquake shaking, varying incidence angle, have been determined. Three recorded ground motions, representative of historical earthquakes along with near-field, far-field and forward directivity effects, have been considered in the study. The efficacy of the bearings with bidirectional effect considering interaction behavior of bearing and pier has also been investigated. Modeling and analysis of the bridge have been done by finite element approach. Sensitivity studies of the bridge response with respect to design parameters of the bearings for the considered ground motions have been performed. The importance of the nonlinearity of HDR bearings along with crucial design parameters has been identified. It has been observed that the HDR bearings performed well in different variations of ground motions, especially for controlling torsional moment. However, the deck displacement has been found to be increased significantly in case of Turkey ground motions, considering forward directivity effect, which needs to be paid more attention from designer point of view.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.17 no.2
• /
• pp.137-146
• /
• 2016

An increase in EGR rate can reduce NOx emissions. On the other hand, an excessive EGR rate is a major cause of incomplete combustion. Precise position control of the EGR valve that is optimized for the operating conditions of the engine should be supported to meet the strict emission regulations. Accordingly, this study performed mathematical modeling and control theory for characteristic analysis of an EGR valve motor. Because it is a step for controlling the position of the EGR valve motor using the Microchip development tool, this study analyzed the characteristics of the motor for each opening and closing section according to the input value of the duty ratio of PWM (Pulse Width Modulation).

• Korean Journal of Social Welfare
• /
• v.61 no.4
• /
• pp.287-306
• /
• 2009

This study examines the effect of children's school satisfaction on academic achievement using the Seoul Children Panel Study data. More specifically, this study aims to add new knowledge to understaning the causal relationship between school satisfaction and academic achievement by taking into account of temporal order of the events of interest. In the analysis, we examine the effect of school satisfaction at the 4th- and 5th- grades on academic achievement at the 6th grade while controlling for the other factors including the level of academic achievement at the 4th grade. The results show that children's school satisfaction significantly affects their academic achievement. The findings of this study have implications for the school social welfare programs that attempt to improve academic achievement of children by raising the level of school satisfaction among children.

• Proceedings of the KSME Conference
• /
• 2001.11a
• /
• pp.568-572
• /
• 2001

An industrial vibratory conveyor system is devised for large-scale feeding by the low-power, using natural frequency of the system. The important thing in this system is to determine the natural frequency and to drive by it. The purpose of this study is to build up reliance on the system with changing of element parameters for vibration characteristics of balancing type vibratory conveyor by using F.E.M. modeling. For investigating the natural frequency, modal testing is performed by using impact hammer, accelerometer and LMS/Vibration Analysis System. Experimental results are compared with F.E.M results. The results of the comparisons within the errors of less than 2 percent can verify the reliability of the F.E.M. analysis of the system. Also we can verify that the characteristics of natural frequency have linearly decreased(-6%) as adding the mass($50{\sim}600kg$). We can find that controlling driving frequency is necessary for triggering the natural frequency, but natural frequency is less affected by adding the mass on the balancing weight.

• 한국노년학
• /
• v.39 no.4
• /
• pp.977-996
• /
• 2019

The current study aimed to examine the gender differences in trajectories of nine successful aging indicators (chronic disease, depression, activities of daily living, instrumental activities of daily living, mini mental state examination, social activity, personal contact, health satisfaction, and general life satisfaction) with age, controlling the effect of education. The data were from the Korean Longitudinal Study of Aging, which had been conducted biennially from 2006 to 2016. The sample included 822 men and 1,236 women who responded to all of the panel surveys and were 65 years old or above in 2006. Multilevel modeling analyses showed that older men had fewer chronic diseases; lower levels of depression; higher levels of activities of daily living, cognitive function, and social activity; and better perceived health satisfaction and general life satisfaction at age 65 years compared to women. However, both men and women showed increase in the number of chronic diseases and depression level, and decrease in physical, cognitive, and social functions with age. In addition, perceived health and life satisfaction also decreased after the age of 65. The trajectories of most of the indicators were non-linear, and markedly increased or decreased around mid-70s. Study limitations and implications were further discussed.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.17 no.6
• /
• pp.61-69
• /
• 2013

This research is aimed to evaluate characteristics and dynamic modeling of MR damper for semi-active vibration control. A MR damper of semi-active type was designed and made for the purpose of controlling the vibration of a real-size model structure. Usually a semi-active control system equipped with a MR damper requires a dynamic model which expresses numerical data about the damping capacity and dynamic characteristics generated by a MR damper. To fulfil the requirement, a Power model and a Bingham model were particularly employed among many dynamic models of MR damper. Those models being contrasted with other ones, a dynamic test was carried out on the developed MR damper. In the test, excitation frequencies were conditioned to be 0.15 Hz, 1.0 Hz, and 2.0 Hz, and three different currents were adopted for each frequency. From these test results, it was found that displacement affected control capacity of the MR damper. The test results led to the identification of model variables for each dynamic model, on the basis of which a force-speed relation curve and expected damping force were derived and contrasted to those of the developed MR damper. Therefore, it was proven that the MR damper designed and made in this research was effective as a semi-active controller, and also that displacement of 2mm at minimum was found to be secured for vibration control, through the test using various displacements.

• Clean Technology
• /
• v.20 no.4
• /
• pp.398-405
• /
• 2014

In the treatment of spent high energetic materials, the issues such as environmental pollution, safety as well as working capacity should be carefully considered and well examined. In this regard, incineration has been recommended as one of the most promising processes for the disposal of such explosives. Due to the fact that high energetic materials encompass various types and their different characteristics, the technology development dealing with various materials is not an easy task. In this study, rigorous modeling and dynamic simulation was carried out to predict dynamic physico-chemical phenomena for research department explosive (RDX). Plug flow reactor was employed to describe the incinerator with 263 elementary reactions and 43 chemical species. Simulation results showed that safe operations can be achieved mainly by controlling the reactor temperature. At 1,200 K, only thermal decomposition (combustion) occurred, whereas increasing temperature to 1,300 K, caused the reaction rates to increase drastically, which led to ignition. The temperature further increased to 3,000 K which was the maximum temperature recorded for the entire process. Case studies for different operating temperatures were also executed and it was concluded that the modeling approach and simulation results will serve as a basis for the effective design and operation of RDX incinerator.

• 한국노년학
• /
• v.38 no.4
• /
• pp.999-1013
• /
• 2018

This study examined the effect of the perception of age-friendly environment on perceived social bonding. In particular, this study focused on the mediating effects of perception of age-integration between perception of age-friendly environment and perceived social bonding. The data were analyzed using the '2017 Ages Integration Survey' conducted by the Korea Research Foundation(SSK). A total of 997 adults from 20 to 86 ears of age were participated in this study. The perception of age-friendly environment was measured using the age-friendly city guidelines set out by WHO and perception of age-integration was measured using questions that asked about age flexibility and age diversity. Also, the social capital scale was used to measure perception of social bonding. In order to increase the reliability of the analysis results, age, gender, educational achievement and residential area were controlled. Structural Equation Modeling approach was employed to answer the research questions. The results are following. First, perception of age-friendly environment was significantly associated with perceived social bonding in a positive direction, controlling for age, gender, educational achievement and residential area. Second, perception of age-integration partially mediated the relationship between perception age-friendly environment and perceived social bonding controlling for covariates. Based on these findings, this study proposes political and practical intervention strategies to promote age-friendly environment and age-integration.

• Korean Journal of School Psychology
• /
• v.9 no.2
• /
• pp.289-309
• /
• 2012

This is a longitudinal study which analyzed suppression effects of active/passive coping strategies on academic burnout, using a structural equation modeling. A total of 357 middle school students participated in this study for two waves. In order to measure the levels of students' coping strategies and academic burnout, the Ways of Coping Checklist and the Korean version of Maslach Burnout InventoryStudent Survey(MBI-SS) were used. Latent variables were constructed with standardized residuals computed from a simple linear regression in order to capture the intra-individual changes between two time points. The results of this study are like below. First, the relationship between the change of active coping strategy and the change of passive coping strategy is positively and significantly related with each other. This result indicates that students under stress use various coping strategies simultaneously. Second, significant suppression effects were revealed between the change of active coping strategy and the change of passive coping strategy. That is, when controlling passive coping strategy, the negative relationship between the change of active coping strategy and the change of academic burnout increased. On the other hand, when controlling active coping strategy, the positive relationship between the change of passive coping strategy and the change of academic burnout increased. Based on these results, the value of this study and implications for counseling were discussed.

• Wind and Structures
• /
• v.31 no.2
• /
• pp.103-142
• /
• 2020

One of the next frontiers in structural wind engineering is the design of tall buildings using performance-based approaches. Currently, tall buildings are being designed using provisions in the building codes and standards to meet an acceptable level of public safety and serviceability. However, recent studies in wind and earthquake engineering have highlighted the conceptual and practical limitations of the code-oriented design methods. Performance-based wind design (PBWD) is the logical extension of the current wind design approaches to overcome these limitations. Towards the development of PBWD, in this paper, we systematically review the advances made in this field, highlight the research gaps, and provide a basis for future research. Initially, the anatomy of the Wind Loading Chain is presented, in which emphasis was given to the early works of Alan G. Davenport. Next, the current state of practice to design tall buildings for wind load is presented, and its limitations are highlighted. Following this, we critically review the state of development of PBWD. Our review on PBWD covers the existing design frameworks and studies conducted on the nonlinear response of structures under wind loads. Thereafter, to provide a basis for future research, the nonlinear response of simple yielding systems under long-duration turbulent wind loads is studied in two phases. The first phase investigates the issue of damage accumulation in conventional structural systems characterized by elastic-plastic, bilinear, pinching, degrading, and deteriorating hysteretic models. The second phase introduces methods to develop new performance objectives for PBWD based on joint peak and residual deformation demands. In this context, the utility of multi-variate demand modeling using copulas and kernel density estimation techniques is presented. This paper also presents joined fragility curves based on the results of incremental dynamic analysis. Subsequently, the efficiency of tuned mass dampers and self-centering systems in controlling the accumulation of damage in wind-excited structural systems are investigated. The role and the need for explicit modeling of uncertainties in PBWD are also discussed with a case study example. Lastly, two unified PBWD frameworks are proposed by adapting and revisiting the Wind Loading Chain. This paper concludes with a summary and a proposal for future research.