• 한국터널공학회:학술대회논문집
• /
• 2005.04a
• /
• pp.348-358
• /
• 2005

Although the evaluation of the mechanical properties and behavior of discontinuous rock masses is very important for the design of underground openings, it has always been considered the most difficult problem. One of the difficulties in describing the rock mass behavior is assigning the appropriate constitutive model. This limitation may be overcome with the progress in discrete element software such as PFC, which does not need the user to prescribe a constitutive model for rock mass. Instead, the micro-scale properties of the intact rock and joints are defined and the macro-scale response results from those properties and the geometry of the problem. In this paper, a $30m{\times}30m{\times}30m$ jointed rock mass of road tunnel site was analyzed. A discrete fracture network was developed from the joint geometry obtained from core logging and surface survey. Using the discontinuities geometry from the DFN model, PFC simulations were carried out, starting with the intact rock and systematically adding the joints and the stress-strain response was recorded for each case. With the stress-strain response curves, the mechanical properties of discontinuous rock masses were determined and compared to the results of empirical methods such as RMR, Q and GSI. The values of Young's modulus, Poisson's ratio and peak strength are almost similar from PFC model and Empirical methods. As expected, the presence of joints had a pronounced effect on mechanical properties of the rock mass. More importantly, the mechanical response of the PFC model was not determined by a user specified constitutive model.

• Journal of the Korean Institute of Landscape Architecture
• /
• v.30 no.2
• /
• pp.39-49
• /
• 2002

The purpose of this study is to propose an objective and rational methodology for the selection of proposed sites far the National Trust(NT), which is the new alterative proposal far the conservation of natural environments destroyed by injudicious land development and economic growth. That is to enforce many analysis for the effective estimation of rare ecological and landscape resources and to propose a model based on estimation and united indicators. Using the estimative model, we apply it to the selection of the proposed site in micro scale and simultaneously offer the basic methodology of effective and systematic land conservation in macro scale. The results of this study are as follows: 1) The results of analysis for the reliability of estimative items and indicators, presented no problem in that the coefficient of reliability was over 0.7. 2) The correlation measure of the estimative indicator indicated that 'succession'and 'regenerating restorability' were highly correlative in the item of plants. Another three items showed a tendency to be alike. 3) The results of factor analysis on the characteristics of indicators, classified plants into four categories including a stable factor. The item of animals was classified as a stable and rare factor. The item of landscape was classified as a physical and mental factor and the environment as a pollutional and conditional factor. 4) The model of estimation created through factor analysis was valid for the approval of the regression model because significant probability was 0.00. When we consider the NT proposed site as a complex body that is composed of diverse natural and manmade resources, certainly the synthetic methodology of estimation is needed. If these studies are carried out, NT sites will be selected more rationally and effectively than at present. Consequently, they have the potential to play a core role of natural ecosystem conservation in Korea.

• Journal of Korean Library and Information Science Society
• /
• v.50 no.1
• /
• pp.125-155
• /
• 2019

The purpose of this study is to design an organizational model to improve the operation of the Gimhae Municipal Library through diagnosis and analysis of its organization. For this purpose, a new organizational model for the Library was designed while reconstruction of the human resource of each unit library was proposed according to the reorganization through research methods such as literature research, case study, FGI survey, etc. The organizational model was eventually designed with three alternatives: an organization for integration of related tasks, one for enhancement of policy function and finally one for improvement of administrative efficiency. We have found that it is the most empirical to measure required number of personnel by 'comparison of benchmarked local governments' method as a result of calculating the required number of staffs of the Library based on macro and micro approach; thus the appropriate number of staff of each unit library was worked out.

• Composites Research
• /
• v.19 no.1
• /
• pp.1-8
• /
• 2006

Prediction of damage caused by low-velocity impact in laminated composite plate is an important problem faced by designers using composites. Not only the inplane stresses but also the interlaminar normal and shear stresses playa role in estimating the damage caused. But it is well known that the conventional approach based on the homogenization has the limit in description of damage. The work reported here is an effort in getting better predictions of dynamic behavior and damage in composite plate using DNS approach. In the DNS model, we discretize the composite plates through separate modeling of fiber and matrix for the local microscopic analysis. In the view of microscopic mechanics with DNS model, interlaminar stress behaviors in the inside of composite materials are investigated and compared with the results of the homogenized model which has been used in the conventional approach to impact analysis. Also the multiscale model based on DNS concept is developed in order to enhance the effectiveness of impact analysis, and we present the results of multiscale analysis considering micro and macro structures simultaneously.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.11 no.9
• /
• pp.3176-3183
• /
• 2010

A multi-scale fatigue life prediction methodology of composite pressure vessels subjected to multi-axial loading has been proposed in this paper. The multi-scale approach starts from the constituents, fiber, matrix and interface, leading to predict behavior of ply, laminates and eventually the composite structures. The multi-scale fatigue life prediction methodology is composed of two steps: macro stress analysis and micro mechanics of failure based on fatigue analysis. In the macro stress analysis, multi-axial fatigue loading acting at laminate is determined from finite element analysis of composite pressure vessel, and ply stresses are computed using a classical laminate theory. The micro stresses are calculated in each constituent from ply stresses using a micromechanical model. Three methods are employed in predicting fatigue life of each constituent, i.e. a maximum stress method for fiber, an equivalent stress method for multi-axially loaded matrix, and a critical plane method for the interface. A modified Goodman diagram is used to take into account the generic mean stresses. Damages from each loading cycle are accumulated using Miner's rule. Monte Carlo simulation has been performed to predict the overall fatigue life of a composite pressure vessel considering statistical distribution of material properties of each constituent, fiber volume fraction and manufacturing winding angle.

• Journal of Labour Economics
• /
• v.26 no.3
• /
• pp.149-179
• /
• 2003

This study is analysing the factors determining individuals' behavior of selecting self-employment not only at the micro-level but also at the macro-level to put a particular emphasis on the financial constraint and unemployment rate representing business cycle. The data used in this study are "Korean Labor and Income Panal Study" of the Korea Labor Institute and "Economically Active Population Survey" of National Statistical Office. The main findings are as follows. First, human capital such as educational attainment and job experience has positive effects on male's selection of self-employment. The effects of job experience, however, changed negative for female's selection of self-employment. Second, real estate is significantly enhancing the selection probabilities of employer selection while the income from financial assets has negative effects. Third, entrepreneurial culture and environment are also raising the self-employment selection probability. Lastly, the regional unemployment rate representing the business cycle has positive effects on the self-employment selection after the financial crisis in 1997 both at the micro and macro level. Moreover, the coefficient of regional unemployment rate has changed positive in the structural model of self-employment selection controlling for selection bias and income opportunities, which means that individual's behavior of self-employment selection is rather complex when accounting for the uncertainties of income opportunities and diverse characteristics of self-employment workforce.

• Journal of the Korean association of regional geographers
• /
• v.9 no.4
• /
• pp.559-575
• /
• 2003

The purpose of this study is to systematically explain and discuss the return migration of Koreans in Central Asia to the Russian Far East. The Koreans' return migration is explained by the combination of push and pull factors inherent in the host and home countries. The structural or institutional push factors in Central Asia include the linguistic policy of a country, civil war, ethnic conflicts, while the micro ones are the Koreans' high concern of their children's education and the improvement of a socio-economic status. The macro pull factors operated in the Russian Far East are the permission to use the housing facilities and land previously controlled by military authorities and the laws of recovering the koreans' basic right and honor, while the micro ones are the networks of relatives and friends living in Central Asia and the Russian Far East. The two aspects related to the Koreans' return migration are also discussed. Firstly, the return migration of Koreans in Central Asia is interpreted as a migration of ethnic affinity. Secondly, the establishment of an autonomous district of Koreans in the Russian Far East is discussed.

• Korea Trade Review
• /
• v.45 no.2
• /
• pp.229-262
• /
• 2020

The price-to-earnings ratio (PER) is an important indicator to measure the stock price and profitability of a firm; it is also the most used valuation indicator among investors. When using the PER to compare the investment values of different stocks, these stocks must come from the same sector. This study mainly focuses on the China's listed manufacturing firms. By learning from previous research results and analyzing the current situation, we studied the correlation between the manufacturing sector's PER and its influencing factors from both macro and micro perspectives, the combination of which eventually sheds light on such correlation. Analyzing GDP growth rate data, Manufacturing Purchasing Managers' Index, and other macroeconomic variables from 2008 to 2018, we conclude that these variables jointly have a certain impact on the average PER of the manufacturing sector. We then form panel data based on relevant (2014-2018) data gathered from 317 of China's A-listed manufacturing firms to study the impact of micro-variables on PER. By using Stata and other software to analyze the panel data, we reach the conclusion that the Debt to Asset Ratio, Return on Equity, EPS growth rate, Operating Profit Ratio, Dividend Payout Ratio, and firm size have a significant impact on PER. The Current Ratio, Treasury Stock ratio and Ownership Concentration have no distinct effect on PER. Based on our empirical findings, we design a theoretical model that affects the PER.

• Advances in nano research
• /
• v.17 no.1
• /
• pp.33-49
• /
• 2024

Using the mechanical treatments for mechanical properties improvement was rarely in the development scope before. This research approves through analytical ways that surface impacts can improve the quality of the surface significantly. This fact is approved for deposited titanium on silicone substrate. The new algorithm called minimum resultant error method (MREM) which is a direct combination of nanoindentation, FEM and dimensional analysis through a reverse method is utilized to extract the mechanical characteristics of the coating surface before and after impact. This method is extended to the time dependent behavior of the material to obtain strain rate coefficient. To implement this new approach, a new analysis technic is developed to define the residual stress field caused by surface impact as initial condition for nanoindentation. Analyzing the model in micro and macro scale at the same time was one of the main resolved challenges in this study. The result was obtaining of the constants of Johnson-Cook constitutive equation. Comparing the characteristics of the coating surface before and after impact shows high improvement in yield stress (34%), Elastic modulus (7.75%) and strain hardening coefficient (2.8%). The main achievement is that the strength improvement in titanium thin layer is much higher than bulk titanium. The yield strength shows 41.7% improvement for coated titanium comparing with 24% for bulk material. The rate of enhancement is about 6 times when it comes to the Young's modulus.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2008.11a
• /
• pp.466-471
• /
• 2008

Structural vibration and noise are hot issues in underwater vehicles such as submarines for their survivability. Therefore, active vibration and noise control of submarine, which can be modeled as hull structure, have been conducted by the use of piezoelectric materials. Traditional piezoelectric materials are too brittle and not suitable to curved geometry such as hull structures. Therefore, advanced anisotropic piezoceramic actuator named as Macro-Fiber Composite (MFC), which can provide great flexibility, large induced strain and directional actuating force is adopted for this research. In this study, dynamic model of the smart hull structure is established and active vibration control performance of the smart hull structure is evaluated using optimally placed MFC. Actuating performance of MFC is evaluated by finite element analysis and dynamic modeling of the smart hull structure is derived by finite element method considering underwater condition. In order to suppress the vibration of hull structure, Linear-Quadratic-Gaussian (LQG) algorithm is adopted. After then active vibration control performance of the proposed smart hull structure is evaluated with computer simulation and experimental investigation in underwater. Structural vibration of the hull structure is decreased effectively by applying proper control voltages to the MFC actuators.