• Structural Engineering and Mechanics
• /
• v.17 no.3_4
• /
• pp.379-391
• /
• 2004

This paper deals with the development of h-version adaptive mesh refinement and recovery strategy using variable-node elements and its application to various engineering field problems with 2D quadrilateral and 3D hexahedral models. The variable-node elements which have variable mid-side nodes on edges or faces are effectively used in overcoming some problems in connecting the different layer patterns of the transition zone between the refined and coarse mesh. A modified recovery technique of gradients adequate for variable-node elements and proper selection of error norms for each engineering field problems are proposed. In the region in which the error is greater than the permissible refinement error, the mesh is locally refined by subdivision. Reversely, in some parts of the domain having the error smaller than the permissible recovery error, the mesh is locally recovered (coarsened) by combination. Hierarchical structures (e.g. quadtrees and octrees) and element-based storage structures are composed to perform this adaptive process of refinement and recovery. Some numerical examples of a 3D heat conduction analysis of the concrete with hydration heat and a 2D flow analysis of vortex shedding show effectiveness and validity of the proposed scheme.

• Journal of ILASS-Korea
• /
• v.25 no.2
• /
• pp.45-50
• /
• 2020

Recently, global warming and environmental pollution are becoming more important, and fuel economy is becoming important. Each automobile company is actively developing various new technologies to increase fuel efficiency. CVVD(Continuously Variable Valve Duration) system means a device that continuously changes the rotational speed of the camshaft to change the valve duration according to the state of the engine. In this paper, VVT(Variable Valve Timing) and CVVD were applied to a single-cylinder diesel engine, and the characteristics of intake and exhaust flow rate and in-cylinder pressure characteristics were analyzed by numerical analysis. In order to analyze the effect of CVVD on the actual engine operation, the study was performed by setting the valve control and injection pressure as variables in two sections of the engine operating region. As a result, In the case of applying CVVD, the positive overlap with the exhaust valve is maintained, thus it is possible to secure the flow smoothness of air and increase the volumetric efficiency by improving the flow rate. The section 2 condition showed the highest peak pressure, but the pressure rise rate was similar to that of the VVT 20 and CVCD 20 conditions up to 40 bar due to the occurrence of ignition delay.

• Journal of Navigation and Port Research
• /
• v.35 no.1
• /
• pp.45-49
• /
• 2011

The recent trend for numerical experiment requires more higher resolution and accuracy. Generally, in the wave field calculation, it starts with a large region formulation first and follows by a separated detailed region formulation by more denser grids for the main interest area considering the geographical and bathymetrical variation. The wave fields resulted from the large region calculation is being introduced into the detail region calculation as the incident waves. In this process there exists a problem of continuity. In order to get over such problem, method of variable gridding system or spectrum sampling, etc., is being used. However, it seems not enough to examine and analyze the related numerical errors. Therefore, it is investigated in this study the field applicability of the most pervasive use of wave model, the nested SWAN model. For this purpose, we made model experiment for two coastal harbours with different tidal environment, and compared and analyzed the result. From the analysis, it was found that both the extracted values, near the boundaries of the large and detail region and the nested formulation of SWAN model, show almost the same and no different between those with different tidal environment conditions. However it is necessary for reducing the numerical errors to set the boundaries for the detailed region outside of the rapid bathymetric change and deeper region.

• East Asian Journal of Business Economics (EAJBE)
• /
• v.6 no.3
• /
• pp.1-15
• /
• 2018

Purpose - This study investigates the effect of MNEs' characteristics on the use of foreign currency denominated debt in the context of Korean firms. This study examines the relationship between MNEs and the use of foreign debt focusing on the accessibility to the capital market in addition to the motive of hedging against foreign exchange exposure. Research design and methodology - Probit estimation is employed for estimating significant factors in determination of the use of foreign debt by firms. The dependent variable is a dummy variable to indicate whether a firm uses foreign debt or not at the end of 2004. Independent variables include foreign subsidiaries ratio, export to sale, R&D expenditure to sale, and credit rating. Results - The results show that the interaction between the level of internationalization represented by intra-regional diversification and the strategic characteristics embedded in the region of entry affects the use of foreign debt. In case of a high level of diversification within the developing region with a strong pursuit of asset exploitation, MNEs are more likely to use foreign debt, whereas a high level of diversification within the developed region with a strong pursuit of asset seeking, MNEs are less likely to use foreign debt. Conclusions - The differences between MNEs in terms of intra-regional diversification, strategic orientation, and the accessibility to capital markets as well as the hedging motive affect the use of foreign debt.

• MALSORI
• /
• no.31_32
• /
• pp.9-22
• /
• 1996

This study aims to describe the acoustic characteristics of Korean nasal sounds making use of the notion of pole and zero. In case of [m], the 1st and 4th formant almost remains as the original shape respectively, on the contrary, the 2nd and 3rd formant were observed as a variable cluster together. Alveolar [n] shows that the 3rd and 4th formant make a variable cluster with their antiformant(zero), however, the 1st and 2nd formant keep the static shape of their on. Velar [$\eta$] has 4 formants below 2900 Hz and the 3rd and 4th formant constitute a variable cluster together as does the case [n]. With respect to the energy distribution in case of [n] and [$\eta$], the energy value diminishes from Fl up to F3 continuously but augments in F4. The [m] shows that in the region of Fl-F2 does the energy fall down and rise from F3 to above.

• Journal of the Optical Society of Korea
• /
• v.13 no.3
• /
• pp.349-353
• /
• 2009

We propose a simple in-line variable optical attenuator (VOA) based on the bending effect of tapered single mode fibers. The influence of the taper structure and the reflective index of the external medium surrounding the taper region on the bending loss of the tapered fiber have been investigated experimentally. An attenuation range exceeding 35 dB and a very low excess loss of < 0.2 dB at 1550 nm were achieved. The measured polarization dependent loss of the present VOA at the attenuation level of 10 dB, 20 dB, and 30 dB were 0.1 dB, 0.2 dB, and 0.5 dB, respectively.

• Journal of the Korean Institute of Telematics and Electronics B
• /
• v.29B no.1
• /
• pp.94-101
• /
• 1992

The multilayer perceptron, trained by the error back-propagation learning rule, has been known as a mapping network which can represent arbitrary functions. However depending on the complexity of a function and the initial weights of the multilayer perceptron, the error back-propagation learning may fall into a local minimum or a flat area which may require a long learning time or lead to unsuccessful learning. To solve such difficulties in training the multilayer perceptron by standard error back-propagation learning rule, the paper proposes a learning method which progressively enlarges the learning domain from a small area to the entire region. The proposed method is devised from the investigation on the roles of hidden nodes and connection weights in the multilayer perceptron which approximates a function of one variable. The validity of the proposed method was illustrated through simulations for a function of one variable and a function of two variable with many extremal points.

• Asian Journal of Innovation and Policy
• /
• v.12 no.1
• /
• pp.101-130
• /
• 2023

The increasing cost, and demand for, household energy has increased attention to the phenomena of energy burdens. Despite this increased attention, a lack of consensus remains in pinpointing the strongest predictors, and geographic differences, that exist within the energy ecosystem. This study addresses this gap by utilizing a series of dummy variable regressions across cities, suburbs, and rural areas within Erie County, New York-a county noted to have particularly high energy burdens. Specifically, three types of predictor sets were incorporated into the methodology: a set of socioeconomic variables, physical variables, and a combination of both variable sets. The results of this study suggest that cities tend to have the highest electricity burdens. Despite the aging infrastructure in Erie County, high energy burdens were driven primarily by socioeconomic factors such as housing cost burden and poverty status. Lastly, this study explores various planning and policy implications Erie County can utilize to reduce energy burdens. In turn, this study highlights the importance of focusing policy efforts on existing social service programs to provide support to the region's neediest households.

• The Bulletin of The Korean Astronomical Society
• /
• v.34 no.2
• /
• pp.40.1-40.1
• /
• 2009

• Kyungpook Mathematical Journal
• /
• v.20 no.1
• /
• pp.121-127
• /
• 1980

In the present paper the multiple generalized prolate spheroidal wave transform has been developed and its useful operational property has been discussed. As an application of this new transform we have considered the non-homogeneous cubical region. The source of heat generation lies inside it and is dependent upon temperature, and the conductivity is variable.