• Journal of the Korean Society for Railway
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• v.19 no.2
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• pp.135-144
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• 2016

It is essential to lighten the weight of switch girders in order to reduce their costs of manufacturing and make it easier to use them in construction. Lightening the weight of switch is also important to the Maglev 3-way switches system, however, the design variables should be considered very carefully if lightening is to be applied to the system, because these variables are vitally related to the levitation stability. Because Urban Maglev trains have a structure in which train bogie wraps around the guiderail, the adjustment of a girder's height is a possible way to reduce the weight. The safety of the application of this concept is ensured by repeated experiments in a test bed, however, due to a lack of space and budget limits, the design parametric study for the system model can substitute for actual application. The purpose of this paper is to study the design parameters that are concerned with levitation stability while a Maglev train is running on the Maglev 3-way system depending on the weight of the switch girders. In this study, switch girder weight is reduced by adjustment of girder height and girders are and modeled as a flexible body. The effect of the adjustment of girder height on the levitation stability can be analyzed by comparing the velocity of the train when it passes the switch girders, with the lateral gap, and the levitation gap which are obtained from the co-simulation of the Maglev train's dynamics model and flexible switching system. The results of this research will be used to design a Maglev switch.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.5
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• pp.107-114
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• 2019

In many military aircraft, s-shaped diffusers are used to prevent the fan blades of the turbofan engine from being exposed to the outside. The inlet configurations of the air intakes for military aircraft vary, such as the rectangular intake of the F-22, the crescent-like intake of the F-16, elliptical intake of the MQ-25. In this study, the aerodynamic performance of s-shaped diffusers with various inlet configurations was evaluated using numerical analysis. In addition, the configuration of the middle section of an s-shape duct was changed to the crescent shape, and the effects on its aerodynamic performance were investigated. As a result, there was a slight difference in total pressure recovery according to various inlet configurations with ellipse-shaped middle sections. Also, the total pressure distortion was the lowest in the rectangular inlet shape. When the configuration of the middle section was changed from an ellipse to a crescent shape, the total pressure recovery remained at a high level, except for the ellipse-shaped inlet configuration. In terms of total pressure distortion, the duct with the crescent-shaped middle section showed a significantly more uniform pressure distribution than that with the ellipse-shaped middle section.

• Korean Journal of Clinical Laboratory Science
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• v.54 no.4
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• pp.239-248
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• 2022

The taxonomy of bacteria in the field of clinical microbiology is in a state of constant flux. A large-scale revamping of the classification and nomenclature of anaerobic bacteria has taken place over the past few decades, mainly due to advances in molecular techniques such as 16S rRNA and whole genome sequencing (WGS). New genera and species have been added, and existing genera and species have been reclassified or renamed. A major role of the clinical microbiological laboratories (CMLs) is the accurate identification (ID) and appropriate antimicrobial susceptibility testing (AST) for clinically important bacteria, and rapid reporting and communication of the same to the clinician. Taxonomic changes in anaerobic bacteria could potentially affect the choice of appropriate antimicrobial agents and the antimicrobial breakpoints to use. Furthermore, current taxonomy is important to prevent treatment failures of emerging pathogenic anaerobes with antimicrobial resistance. Therefore, CMLs should periodically update themselves on the changes in the taxonomy of anaerobic bacteria and suitably inform clinicians of these changes for optimum patient care. This article presents an update on the taxonomy of clinically important anaerobic bacteria, together with the previous names or synonyms. This taxonomy update can help guide antimicrobial therapy for anaerobic bacterial infections and prevent treatment failure and can be a useful tool for both CMLs and clinicians.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.6
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• pp.688-696
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• 2023

In the present study, free roll decay and resistance performances of fishing vessels were evaluated with the combinations and variations of in the parameters of appendages which are attached to improve motion performance of fishing vessels. Computational Ffluid Ddynamics was used to perform free roll decay and resistance analysis. The roll period and decay coefficient were derived by the variations in the combination and dimensions of the primary appendages of the bilge keel and the under keel. It was observed thatThe variations of in the length of the under keel did not significantly impact to the roll damping coefficient. Conversely, for the bilge keel, an increase in the length and angle resulted in an increase in the roll damping coefficient. Comparison of resistance performance was additionally assessed among the selected hulls with the appendages and bare hull. The resistance of the hull with the appendages was higher than that of the bare hull due owing to the changes of in the pressure on the surface of the hull and trim angle. Throughout the present study, the impact of appendage parameter and arrangement on the free roll decay and resistance performance of fishing vessels were was assessed,. which This will be beneficial for the application of appendages to fishing vessels.

• Composites Research
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• v.13 no.2
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• pp.30-39
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• 2000

It is difficult for civil engineer to apply composite materials of laminated type to structure for civil construction because of complicated theory although those have much merit. A simple method by which one can predict "exact" values of the natural frequency of vibration of laminated plates is presented. Many laminates with particular orientations have negligible values of $B_{16}$ and $B_{26}$ as the number of plies increases. Such laminates, with $D_{16}$ = $D_{26}$ ->0 can be solved by the same equation as for the special orthotropic laminates(1991,1995). If the quasi-isotrpic constants are used, It is possible to simplify analysis procedure since the equations for isotropic plates can be used. Use of some coefficients can produce "exact" values for laminates with such configuration. This coefficient, in fact, represents the effect of the anisotropy of the laminate. D. H. Kim proposed to use a correction factor, he developed, to produce "exact" solution out of the approximate solution obtained by using the quasi-isotropic constants(1995). In this paper, the fiber orienation studied is [$\alpha$/$\beta$/$\beta$/$\gamma$/$\alpha$/$\alpha$/$\beta$]r, with $\alpha$=-$\beta$, and $\gamma$${\gamma}$=$0^{\circ}$ or $90^{\circ}$ and the above-mentioned method is used to obtain the natural frequencies of plates with such orientations, and detailed result is presented for the use of engineers.nted for the use of engineers.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.1
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• pp.17-24
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• 2012

There has been little study on the performance characteristics of the effective heat pump systems in the cooling mode using the two-stage compression cycles have hardly performed. In this study, the performance of the two-stage compression $CO_2$ cycle with an FI (flash intercooler) and the FGB (flash gas bypass) was investigated by using a theoretical method. The performance analysis was carried out with aby varyingiation (the indoor temperature, outdoor temperature, and 1st- and 2nd-stage EEV openings. As of a result, the coefficients of performance (COPs) of the Bbasic, FI, and FGB cycles were decreased by 28.5%, 22.1%, and 24.5%, respectively, for various outdoor temperature conditions. In addition to, the performance variation of the two-stage compression cycle was smaller than that of the single-stage compression cycle. The performance of the FI and FGB cycles was improved by 13.5%, and 6.9%, respectively, when the 1st-stage EEV opening was increased from 32% to 48%, and by 0.9%, and 2.6%, respectively, when the 1st- andthe 2nd-stage EEV opening was increased from 32% to 48%, andwas increased from 42% to 58%, respectively. The FI cycle showed anthe most improved performance for any given operating conditions.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.6
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• pp.134-141
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• 2019

This paper is a study on design improvement of rotorcraft horizontal stabilizer. The rotorcraft horizontal stabilizer stabilizes the behavior of the pitch, yaw, etc. from the aircraft. Because of this role, horizontal stabilizers are a major component (Flight Safety Part) that affects flight safety on rotorcraft. However, when the rotorcraft was operated in domestic, cracks were found in the inner structure of the horizontal stabilizer and design improvement was needed. In this paper, we identified the two causes of the horizontal stabilizer crack defects through fracture analysis and structural analysis. The first is the tightening torque when the bolt is tightened, and the second is the lead-lag behavior of aircraft. In order to improve these two causes, bolt fastening method, flange structure and thickness were changed and composite ring was applied. In order to verify the design improvement, the structural analysis was performed and the structural strength was improved. Also Fatigue analysis of the internal structure (Rib 1) was performed and it was confirmed that the requirements were satisfied.

• Journal of Bio-Environment Control
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• v.30 no.4
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• pp.278-286
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• 2021

In this study, based on the Computational Fluid Dynamics (CFD) simulation model developed through previous study, inner environmenct of the modified glass greenhouse was predicted. Also, suggested the optimal shape of the greenhouse and location of the heat exchangers for heat energy management of the greenhouse using the developed model. For efficient heating energy management, the glass greenhouse was modified by changing the cross-section design and the location of the heat exchanger. The optimal cross-section design was selected based on the cross-section design standard of Republic of Korea's glass greenhouse, and the Fan Coil Unit(FCU) and the radiating pipe were re-positioned based on "Standard of greenhouse environment design" to enhance energy saving efficiency. The simulation analysis was performed to predict the inner temperature distribution and heat transfer with the modified greenhouse structure using the developed inner environment prediction model. As a result of simulation, the mean temperature and uniformity of the modified greenhouse were 0.65℃, 0.75%p higher than those of the control greenhouse, respectively. Also, the maximum deviation decreased by an average of 0.25℃. And the mean age of air was 18 sec. lower than that of the control greenhouse. It was confirmed that efficient heating energy management was possible in the modified greenhouse, when considered the temperature uniformity and the ventilation performance.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.11
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• pp.42-47
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• 2007

In this paper, influence of lossy ground and gap variation between lossy ground and UWB antenna on impulse propagation in time domain for impulse ground penetrating radar (GPR) is numerically and experimentally investigated. For this study, a novel planar UWB fat dipole antenna is developed. First, influence of lossy ground and gap variation between lossy ground and UWB antenna is simulated. For verification, a test field of sand and wet clay soil is built and using the developed dipole antenna, transmission behavior is investigated at the test field. With an aid of IDFT (inverse discrete Fourier transform), time domain impulse response for transmission coefficient measured and simulated in frequency domain is obtained. Measurement and simulation show that the frequency of maximum transmission coefficient and transmission coefficient are increased with higher dielectric constant and larger gap distance. In time domain, it is shown that for higher dielectric constant, the amplitude of the received signal in time domain is higher and reflected signals are seriously modified. Also, it is found that variation of gap between antenna and ground surface makes timing of peak value changed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.2
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• pp.291-298
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• 1994

This paper presents a new stiffness matrix for the analysis of arbitrary thin-walled open beams in warp-restrained torsion. The element accounts for both flexural and warping torsional effects. To eliminate the ad hoc introduction of St. Venant stiffness in this $C^0$ element, the virtual work equation based on an orthogonal Cartesian coordinate system is used. The effectiveness of the derived block stiffness is addressed. The transformation matrix between two different reference systems is also shown. Numerical examples using the proposed matrix are compared with the classical solutions or other previous results in the literature.