• Journal of the Korean Society of Combustion
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• v.18 no.1
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• pp.1-6
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• 2013

Authors' previous works on thermoacoustic(TA) model development showed good results in predicting combustion instability characteristics in a gas turbine combustor. However, they also suggested there were some limitations in growth rate estimation, which might be related with over-simplification of flame structure. As a first trial for improving the model accuracy, the current paper introduces the modified TA model considering the actual flame location in the combustor. The combustor is divided into the unburned and the burned area before and after the flame location, and then acoustic equations are re-organized. The modified TA model results show a better accuracy in predicting the growth rate of instabilities comparing with the previous results. However, obtained results still overestimate the conditions where the combustor goes unstable. Further researches considering heat release distribution through flames are required.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.26 no.1
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• pp.1-9
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• 2018

Ground effect includes a reduction of induced drag, increase of lift, and nose-down moment during landing. These phenomena, occurring late in the landing maneuver, are considered to be of little significance because they tend to counteract and/or compensate in this respect. Even though it is unlikely to affect any flare profile variations appreciably, some pilots have reversed perception about such phenomenon and overestimate during landing. It is becoming a negative factor and is making an adverse effect on landing maneuver. This study examines the perception of ground effect of large aircraft pilots, reviews literature regarding ground effect, and makes suggestions that pilots can correctly recognize and respond to the effect during landing flare maneuvers.

• International Journal of Concrete Structures and Materials
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• v.18 no.2E
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• pp.133-142
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• 2006

An experimental study was conducted to investigate the effectiveness of transverse steel in reinforced concrete tied columns subjected to monotonically increasing axial compression. Eighteen large-scale columns($260{\times}260{\times}1,200mm$) were tested. Effects of such main variables as concrete compressive strength, configurations of transverse steel, transverse reinforcement ratio, spacing of transverse steel, and spalling of concrete cover were investigated. High-strength concrete columns under concentric axial loads show extremely brittle behavior unless the columns are confined with transverse steel that can provide sufficiently high lateral confinement pressure. A consistent decrease in the deformability of the column test specimens was observed with increasing concrete strength. Test results of this study were compared with existing confinement models of modified Kent-Park, Sheikh-Uzumeri, Mander, and Saatcioglu-Razvi. The comparison indicates many existing models to predict the behavior of confined concrete overestimate or underestimate the ductility of confined concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.271-276
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• 2002

Existing design equations generally overestimate the shear strength of the circular transverse reinforcement. This is due to the simplification of the discrete distribution of the reinforcement to the continuous one and the inappropriate application of the classical truss model to the circular section, which is different in shear-resisting component from the rectangular section. The present study introduces a new model considering the starting point of the diagonal crack, the number of transverse reinforcing bars crossing the crack and the effective strength component of the transverse resistance. This model leads to a simple design equation which is derived using the linear regression method and is in agreement with the lower bound of exact strength curve.

• Atmosphere
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• v.21 no.4
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• pp.471-480
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• 2011

This study investigates the characteristics of surface wind in North Korea using mesoscale model WRF. Hourly wind fields were simulated for one year representing mean characteristics of an 11-years period from 1998 to 2008. The simulations were performed on a nested grid from 27 km to 1 km horizontal resolution. The simulated wind map at 10 m above ground level is verified with 27 surface observations. Statistical verification skill score indicates that wind speed tends to overestimate in surface layer. The average RMSE value of the simulated wind speed is around $2.8ms^{-1}$. Wind map in North Korea showed that strong wind speed is distributed in the mountainous and western coastal region. The results of this wind mapping study contribute for the founding of wind energy potential location.

• Industrial Engineering and Management Systems
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• v.16 no.1
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• pp.52-63
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• 2017

The inventory level of concurrent spare parts (CSP) has a significant impact on the availability of a weapon system. A failure rate function might be of particular importance in deciding the CSP inventory level. We developed a CSP optimization model which provides a compromise between purchase costs and shortage costs on the basis of the Weibull and the exponential failure rate functions, assuming that a failure occurs according to the (non-) homogeneous Poisson process. Computational experiments using the data obtained from the Korean Navy identified that, throughout the initial provisioning period, the optimization model using the exponential failure rate tended to overestimate the optimal CSP level, leading to higher purchase costs than the one using the Weibull failure rate. A Pareto optimality was conducted to find an optimal combination of these two failure rate functions as input parameters to the model, and this provides a practical solution for logistics managers.

• Journal of the Korean Society of Combustion
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• v.10 no.2
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• pp.9-17
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• 2005

WSGGM with gray gas regrouping is successfully applied to study the flame structure of opposed flow flames including effect of radiative transfer. The statistical narrow band model is used to obtain the benchmark solutions. Results obtained by using the optically thin model are shown to overestimate the emission and to predict the flame structures inadequately especially for optically thick and low stretch rate flames. Computed results by using the WSGGM with 10 gray gases and SNB model show reasonable agreements with each other, and the required calculation time for the WSGGM is acceptable for engineering applications.

• Computers and Concrete
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• v.10 no.2
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• pp.173-196
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• 2012

Experimental results of cyclic reversed lateral force test on a two-story reinforced concrete shear wall sub-assemblage are simulated analytically by using the PERFORM-3D program. A comparison of experimental and analytical results leads to the following conclusions: (1) "Shear Wall" and "General Wall" models with "Concrete shear" cannot simulate the pinching phenomena due to shear and show larger amounts of inelastic energy absorption than those in the experiment. (2) Modeling a story-height wall by using two or more "General Wall" elements with "Diagonal shear" in the vertical direction induces the phenomenon of swelling-out at the belly, leading to the erroneous simulation of shear behaviors. In application to tall building structures, it is recommended to use one element of "General Wall" with "Diagonal shear" for the full height of a story. (3) In the plastic hinge area, concrete deformations of analytical models overestimate elongation and underestimate shortening when compared with experimental results.

• International Commerce and Information Review
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• v.6 no.3
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• pp.81-99
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• 2004

Research relevant to the electronic commerce tends to either overestimate or underrate the role of Information and Communication Technology (lCT). There is both technological skepticism within the social science circles and technical optimism within the engineering and computing field. Each perspective seems to have a limitation in adequately explaining the phenomenon of electronic commerce diffusion. Therefore, this research attempts to explore major characteristics of Web-based shopping systems as enablers of new business, concerning both the technical and business aspects in contemporary electronic commerce settings. On this basis, this paper addresses a configuration model of WBSS on the harmonious perspective concerning both the technical and business issues. It is our hope that both technical perspective and business perspective for exploring WBSS's configuration model presented in this paper can be an initial step towards a more balanced debate of ICT role, for electronic commerce.

• The KSFM Journal of Fluid Machinery
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• v.13 no.3
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• pp.49-53
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• 2010

The computational studies on the cavitating flow around a turbopump inducer were performed to see the effect of the cavitation on the performance of the inducer. The development of cavities around the inducer blades and the head drop of the inducer are observed as the inlet pressure reduces. The change of the backflow at the inducer inlet is also observed with the development of the cavities. The size of the backflow reduces as the inlet pressure is reduced due to the development of the cavities around the blades. The predicted suction performances of the inducer were compared with the experimental results. The results show that the computations overestimate the suction performances of the inducer than the experiments.