• Journal of applied mathematics & informatics
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• v.28 no.1_2
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• pp.383-395
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• 2010

In the present paper, we construct the traveling wave solutions involving parameters of nonlinear evolution equations in the mathematical physics via the (3+1)- dimensional potential- YTSF equation, the (3+1)- dimensional generalized shallow water equation, the (3+1)- dimensional Kadomtsev- Petviashvili equation, the (3+1)- dimensional modified KdV-Zakharov- Kuznetsev equation and the (3+1)- dimensional Jimbo-Miwa equation by using a simple method which is called the ($\frac{G'}{G}$)- expansion method, where $G\;=\;G(\xi)$ satisfies a second order linear ordinary differential equation. When the parameters are taken special values, the solitary waves are derived from the travelling waves. The travelling wave solutions are expressed by hyperbolic, trigonometric and rational functions.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.11
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• pp.1083-1090
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• 2004

Two noise reduction systems are proposed in order to overcome the geometric restriction of the reactive muffler such as an expansion chamber. First, membrane is installed as a part of a duct wall and an air cavity is covered outside membrane. Second, membrane is installed inside a duct, which gives no volume change of the duct. Structural-acoustic coupling between membrane and fluid inside the cavity and duct causes rapid impedance mismatching and thereby reflected wave. Theoretical prediction is conducted by using modal expansion approach. The results are compared with the experimental results, which show better noise reduction performance than an expansion chamber.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.474-479
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• 2004

Two noise reduction systems are proposed in order to overcome the geometric restriction of the reactive muffler such as an expansion chamber. First, membrane is installed as a part of a duct wall and an air cavity is covered outside membrane. Second, membrane is installed inside a duct, which gives no volume change of the duct. Structural-acoustic coupling between membrane and fluid inside the cavity and duct causes rapid impedance mismatching and thereby reflected wave. Theoretical prediction is conducted by using modal expansion approach. The results are compared with the experimental results, which show better noise reduction performance than an expansion chamber.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.1
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• pp.23-32
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• 1997

Swirling turbulent flows downstream of an abrupt axisymmetric expansion in a pipe are analyzed numerically by a second-order turbulence closure. Predictions for the flows without swirl and with strong swirl are obtained. The governing differential equations are discretized by finite volume approach. The results show that the on-axis recirculation induced by the strong swirl is correctly reproduced. The predictions for mean velocity components and turbulent normal stresses agree well with experimental data far downstream of expansion, but show large discrepancies in wall-bounded recirculation zone.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05a
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• pp.131-136
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• 1996

An analytic nodal expansion method has been derived for the multigroup neutron diffusion equation in 2-D cylindrical(R-Z) coordinate. In this method we used the second order Legendre polynomials for source, and transverse leakage, and then the diffusion eqaution was solved analytically. This formalism has been applied to 2-D LWR model. $textsc{k}$$_{eff}$, power distribution, and computing time have been compared with those of ADEP code(finite difference method). The benchmark showed that the analytic nodal expansion method in R-Z coordinate has good accuracy and quite faster than the finite difference method. This is another merit of using R-Z coordinate in that the transverse integration over surfaces is better than the linear integration over length. This makes the discontinuity factor useless.s.

• International conference on construction engineering and project management
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• 2015.10a
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• pp.472-476
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• 2015

The purpose of this study is to fully understand the present state of the domestic construction companies, and to analyze phased business types and construction management techniques in order to initiate overseas expansion. Because of the recession in the domestic construction market, a thorough and strategic perspective to constantly develop inroads into overseas market is required. So we carried out a questionnaire survey targeting the experts of the overseas construction and researcher, and consulted them in depth. The questionnaire survey was divided into three sections. The first section is the necessity of overseas construction and the reason. The second is the overseas business types classified into the way of advance in short-term and long-term phase possibility of expansion. Lastly, the importance of the phased construction management techniques and the current capacity of the domestic and the foreign business trends were scrutinized. On the basis of the consultation and surveys, we analyzed the overseas business types and the construction management types in the short-term and long-term phase.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.33-38
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• 2001

Bifurcation of unstable symmetric flow patterns to stable asymmetric ones in laminar sudden-expansion flow has been numerically investigated. Computations were carried out for an expansion ratio of 3 and over a range of the flow Reynolds numbers by using numerical methods of second-order time accuracy and a fractional-step method that guarantees divergence-free flowfields at all times. The critical Reynolds number above which bifurcation of pitchfork type to asymmetric flow pattern takes place is lower in a flow with a higher expansion ratio, in agreement with the previously reported results. The bifurcation diagrams show that the bifurcation takes place at a Reynolds number, $Re_c = 86.3$, higher than the value that has been reported. The lower critical Reynolds number may be due to deficiencies in their computations which employed SIMPLE-type relaxation methods rather than the initial-value approach of the present study. Characteristics of the flow development during the transition to asymmetric stable flow have been investigated by using spectral analysis of the velocity signals obtained by the simulations.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.1 s.256
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• pp.40-50
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• 2007

The present contribution describes the application of elliptic-blending second moment closure to predict the gas cooling process of turbulent super-critical carbon dioxide flow in a square cross-sectioned duct. The gas cooling process under super-critical state experiences a drastic change in thermodynamic and transport properties. Redistributive terms in the Reynolds stress and turbulent heat flux equations are modeled by an elliptic-blending second moment closure in order to represent strongly non-homogeneous effects produced by the presence of walls. The main feature of Durbin's elliptic relaxation second moment closure that accounts for the nonlocal character of pressure-velocity gradient correlation and the near-wall inhomogeneity guaranteed by the elliptic blending second moment closure.

• Journal of Convergence for Information Technology
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• v.11 no.11
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• pp.51-56
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• 2021

In this paper, performance degradation in the cross-eye jamming due to amplitude mismatch of two jamming antennas is considered. The mismatch of the amplitude ratio is modeled as a random variable with a normal distribution of the difference between the actual amplitude ratio and the nominal amplitude ratio due to mechanical defects. In the proposed analytic performance analysis, the first-order Taylor series expansion and the second-order Taylor series expansion is adopted. Performance measure of the cross-eye jamming is the mean square difference (MSD). The analytically derived MSD is validated by comparing the analytically derived MSD with the first-order Taylor series-based simulation-based MSD and the second-order Taylor series-based simulation-based MSD. It shows that the analysis-based MSD is superior to the Monte-Carlo-based MSD, which has a high calculation cost.

• Journal of the Korea Society of Computer and Information
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• v.21 no.5
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• pp.193-200
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• 2016

This study was conducted in order to assess the effect of variables influencing Korean baby-boomers' welfare consciousness. For this purpose, data from the $8^{th}$ supplementary survey of the Korea Welfare Panel in 2013 were analyzed. The subjects of analysis were 2,035 people who were born between 1955 and 1965 whose welfare panel data did not have missing values for the variables of the research model. According to the results of analysis, first, when the descriptive statistics of the major variables were analyzed, those showing a relatively high mean score among the sub-factors of the baby-boomers' welfare consciousness were 'expansion of expenditure for public assistance' (mean 3.65, SD .557), 'expansion of expenditure for social insurance' (mean 3.53, SD .646), and 'expansion of expenditure for social services' (mean 3.26, SD .424). The mean score of the baby-boomers' overall welfare consciousness was relatively high as 3.45 (SD .428), advocating the expansion of welfare expenditure. Second, the independent variables influencing the baby-boomers' welfare consciousness was found to have explanatory power of 12.9%. In the results of regression analysis, variables found to have a significant effect were gender (B=.100, t=2.573, p<.01), personal responsibility for poverty (B=-.151, t=-3.635, p<.01), social responsibility for poverty (B=.149, t=3.437, p<.001), and recipient's laziness (B=.251, t=6.578, p<.001). Based on these results were discussed major relevant policies.