• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.2
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• pp.138-149
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• 2000

Various modeling techniques for ultrasonic wave propagation and scattering problems in finite solid media are presented. Elastodynamic boundary value problems in inhomogeneous multi-layered plate-like structures are set up for modal analysis of guided wave propagation and numerically solved to obtain dispersion curves which show propagation characteristics of guided waves. As a powerful modeling tool to overcome such numerical difficulties in wave scattering problems as the geometrical complexity and mode conversion, the Boundary Element Method(BEM) is introduced and is combined with the normal mode expansion technique to develop the hybrid BEM, an efficient technique for modeling multi mode conversion of guided wave scattering problems. Time dependent wave forms are obtained through the inverse Fourier transformation of the numerical solutions in the frequency domain. 3D BEM program development is underway to model more practical ultrasonic wave signals. Some encouraging numerical results have recently been obtained in comparison with the analytical solutions for wave propagation in a bar subjected to time harmonic longitudinal excitation. It is expected that the presented modeling techniques for elastic wave propagation and scattering can be applied to establish quantitative nondestructive evaluation techniques in various ways.

• Journal of Korean Society of Steel Construction
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• v.21 no.6
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• pp.597-608
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• 2009

In this paper, large-deformation elasto-plastic analysis of space frames that considersjoint connection properties is presented. This method is based on the large-deformation formula with finite rotation, which was developed initially for elastic systems, and is extended herein to include the elasto-plastic effect and the member joint connection properties of semi-rigid what?. The analytical method was derived from the Eulerian concept, which takes into consideration the effects of large joint translations and rotations. The localmember force-deformation relationships were obtained from the beam-column approach, and the change caused by the axial strain in the member chord lengths and flexural bowing were taken into account. The effect of the axial force of the member on bending and torsional stiffness, and on the plastic moment capacity, is included in the analysis. The material is assumed to be ideally elasto-plastic, and yielding is considered concentrated at the member ends in the form of plastic hinges. The semi-rigid properties of the member joint connection are considered based on the power or linear model. The arc length method is usedto trace the post-buckling range of the elastic and elasto-plastic problems with the semi-rigid connection. A sample non-linear buckling analysis was carried out with the proposed space frame formulations to demonstrate the potential of the developed method in terms of its accuracy and efficiency.

• Journal of Technology Innovation
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• v.20 no.2
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• pp.161-187
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• 2012

Recently, environmentally friendly technology are becoming important due to reconsideration about climate change and environmental pollution. In addition, as well as technical skills and social interaction through an analysis of the nonlinear transition management and policy implementation are emerging. This study of the development of photovoltaic industry in Korea 10 years analyze with strategic niche management (SNM) based on the theoretical and multi-layered perspective (MLP) is used as the analytical framework. Choose the gerverment-support project for niche technology, through a process of quantifying and alnalyze the phase transition to Regime with the numerical method and policy vision, learning effects, and network that key elements of SNM, MLP. Through the analysis of the photovoltaic industry technology-commercialization phase was investigated. This conventional overall and step-by-step model for technical management is proposed to replace exiting linear and narrow method and through the case study its validity was confirmed.

• Journal of The Korean Society of Grassland and Forage Science
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• v.29 no.1
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• pp.31-36
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• 2009

This study was conducted to find out an alternative way of rapid and accurate analysis of forage quality. Near reflectance infrared spectroscopy (NIRS) was used to evaluate the possibility of forage analysis and collect 258 samples such as barley for whole crop silage, forage corn and sudangrass from 2002 to 2007. The samples were analyzed for CP (crude protein), CF (crude fiber), ADF (acid detergent fiber), NDF (neutral detergent fiber) and IVTD (in vitro true digestibility), and also scanned using NIRSystem with wavelength from $400{\sim}2,400nm$. Multiple linear regression was used with wet analysis data for developing the calibration model and validate unknown samples. The important index In this experiment was SEC and SEP $r^2$ for CF, CP, NDF, ADF and IVTD in calibration set were 0.70, 0.86, 0.94, 0.94 and 0.89, also 0.47, 0.39, 0.89, 0.90 and 0.61 in validation sample, respectively. The results of this experiment indicates that NIRS was reliable analytical method to assess forage quality, specially in CF, ADF and IVTD, sample should be included for respective forage samples to get accurate result. More robust calibrations can be made to cover every forage samples if added representative sample set.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.4
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• pp.22-32
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• 2014

Durability is one of the most important and attractive subjects in concrete research field because not only durability of concrete is reduced by various degradation factors but also its reduction adversely influences the structural performance and service life of concrete structure. For this reason, a considerable amount of papers associated with concrete durability have been published and those researches were mainly focused on the changes of intrinsic properties of concrete due to chemicophysical degradations. However, the relationship between durability of concrete and structural behavior of concrete member has not been well established yet. In this study, calcium leaching degradation, a cause of concrete strength reduction, was dealt with. The experiments of compressive and flexural behavior of degraded concrete member were performed to evaluate the characteristics of structural behavior according to degradation level. Finally, the results from the experiments were compared with those obtained from nonlinear FEM analysis. The results from this study clearly showed that leaching degradation leads to decrease in compressive strength and compressive behavior evolves from brittle to ductile failure pattern during the degradation process. Load capacity and flexible rigidity of the degraded RC member decreased when the degradation level increased, in compressive zone. Additionally, it was found that the values from nonlinear FEM analysis, CDP model in ABAQUS, coincided well with the experimental results.

• Korean Journal of Social Welfare
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• v.35
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• pp.85-105
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• 1998

This article examined the trend of 125 empirical researches which were published in Jr. of Korean Social Welfare from the first issue to no. 33. in terms of theoretical and methodological orientations. The content analysis was employed for the purpose of the study. Since 1979, the number of empirical researches was in the trend of increasing. The findings from this research were as follows. 1) Among 166 authors, 96.4% were majored in social welfare. Also 6.0% were practitioners and the rest of them were in the position of professors or researchers. The outcome of lack of interdisciplinary co-work and researcher-practitioner co-work led the article to conclude that the nature of applied social science of social welfare was not so actively pursued in Korea. 2) It was almost impossible to find researches which studied same theme or employed same analytical framework. This meant that the work of re-verifying and proving the contray could not be done although it was essential for theory-building. In other words, the disciplinary of social welfare was far behind in the process of theory-building. 3) The methodology upon which most of researches were relied was quantitative methodology(92.8%). The article concluded 'paradigm shift' was not begun in the disciplinary of social welfare yet. 4) The study concluded that the particularity of empirical researches of social welfare in Korea was descriptive-configurative study. Whereas 65.5% of 125 empirical studies were descriptive-configurative, 25% were hypothesis - model test and only 6% causal analysis. 5) The most applied statistic models through the period from 1979 to 1997 were descriptive statistics such as frequency, chi square test, Pearson's r. More advanced statistics such as logit regression, probit regression, path analysis, covariance structure analysis were shown since 1990.

• Korean Journal of Plant Resources
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• v.27 no.4
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• pp.286-292
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• 2014

Near infrared reflectance spectroscopy (NIRS) is a rapid and accurate analytical method for determining the composition of agricultural products and feeds. This study was conducted to measure baicalin, baicalein, and wogonin contents in Scutellaria baicalensis by using NIRS system. Total 63 samples previously were analyzed by HPLC, which showed baicalin, baicalein, and wogonin contents ranging 4.56 to 13.59%, 0.28 to 5.54%, and 0.50 to 1.63% with an average of 9.66%, 2.09% and 0.52%, respectively. Each sample was scanned by NIRS and calculated for calibration and validation equation. A calibration equation calculated by modified partial least squares(MPLS) regression technique was developed in which the coefficient of determination for baicalin, baicalein, and wogonin content was 0.958, 0.944, and 0.709, respectively. Each calibration equation was applied to validation set that was performed with the remaining samples not included in the calibration set, which showed high positive correlation both in baicalin and baicalein content file. In case of wogonin, the prediction model was needed more accuracy because of low $R^2$ value in validation set. These results demonstrate that the developed NIRS equation can be practically used as a rapid screening method for quantification of baicalin and baicalein contents in Scutellaria baicalensis.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.3
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• pp.147-154
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• 2014

In the context of an increasing need for safety in concrete structures under blast and impact loading condition, the behavior of concrete under high strain rate condition has been an important issue. Since concrete subjected to impact loading associated with high strain rate shows quite different material behavior from that in the static state, several material models are proposed and used to describe the high strain rate behavior under blast and impact loading. In the process of modelling high strain rate conditions with these material models, mesh dependency in the used finite element(FE) is the key problem because simulation results under high strain-rate condition are quite sensitive to applied FE mesh size. This paper introduces an criterion which can minimize the mesh-dependency of simulation results on the basis of the fracture energy concept, and HJC(Holmquist Johnson Cook) model is examined to trace sensitivity to the used FE mesh size. To coincide with the purpose of the perforation simulation with a concrete plate under a projectile(bullet), the residual velocities of projectile after perforation are compared. The analytical results show that the variation of residual velocity with the used FE mesh size is quite reduced and accuracy of simulation results are improved by applying a unique failure strain value determined according to the proposed criterion.

• Nuclear Engineering and Technology
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• v.27 no.3
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• pp.301-316
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• 1995

experimental and computational studies ore carried out to investigate the natural convection of the single phase flow in a tank with a heated horizontal plate facing downward. This is a simplified model for investigations of the influence of a core melt at the bottom of a reactor vessel on the thermal hydraulic behavior in a oater filled cavity surrounding the vessel. In this case the vessel is simulated by a hexahedron insulated box with a heated plate Horizontally mounted at the bottom of the box. The box with the heated plate is installed in a water filled hexahedron tank. Coolers are immersed in the U-type water volume between the box and the tank. Although the multicomponent flows exist more probably below the heated plate in reality, present study concentrates on the single phase flow in a first step prior to investigating the complicated multicomponent thermal hydraulic phenomena. In the present study, in order to get a better understanding for the natural convection characteristics below the heated plate, the velocity and temperature are measured by LDA(Laser Doppler Anemometry) and thermocouples, respectively. And How fields are visualized by taking pictures of the How region with suspended particles. The results show the occurrence of a very effective circulation of the fluid in the whole How area as the heater and coolers are put into operation. In the remote region below the heated plate the new is nearly stagnant, and a remarkable temperature stratification can be observed with very thin thermal boundary. Analytical predictions using the FLUTAN code show a reasonable matching of the measured velocity fields.

• Journal of Korea Technology Innovation Society
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• v.14 no.1
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• pp.22-39
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• 2011

This study examines the wage level from a viewpoint of major-job match as part of an analysis on the skill mismatch problem in 4-year college graduates. The empirical analysis explicitly incorporate the sample selection bias as an econometric problem not only suggested but merely introduced in the earlier studies. This study also set up a major-job match variable, which was usually handled as a binary variable for analytical convenience, as a polychotomous choice variable in selection equation as provided by the survey. In particular, it considered multi-cohort survey on graduates of the years 1982, 1992, and 2002 for the empirical analysis. As a result of empirical analysis, the wage premium of a major-job match was identified. This result was consistent after the consideration of a sample selection bias and also after modeling the major-job match variable as polychotomously selective. Through an analysis classified by the major, this study identified a relatively high wage premium among Social Science, Engineering, and Science majors. However, there was a difference in the effect of selection among these majors. Also, by assessing cohort effects this study found that the skill mismatch had rapidly progressed in 1992, while difference between 1992 and 2002 cohorts are insignificant. The analysis suggests that wage level is better understood within the context of both sample selection and major-job match, and regardless of model specification the major-job match affects wage strongly.