• Tribology and Lubricants
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• 제17권6호
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• pp.476-481
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• 2001

This paper has been presented the hydrodynamic effect by the journal speed, eccentricity and source positions in order to overcome the defects of air bearing such as low stiffness and damping coefficient. Choosing the two row source position of air bearing is different from existed investigations in the side of pressure distribution of air film because of the high speed of journal and the wedge effects by the eccentricity. These optimal chooses of the two row source positions enable us to improve the performance of the film reaction force and loading force as making the high speed spindle. In this paper, The pressure behavior in theory of air film according to the eccentricity of journal and the source positions analyzed. The theoretical analysis have been identified by experiments. The results of investigated characteristics may be applied to precision devices like ultra-precision grinding machine and ultra high speed milling.

• 한국기계가공학회지
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• 제10권3호
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• pp.39-46
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• 2011

The automotive air conditioning hose is used for connecting the components of air conditioner in a vehicle. The hose is usually manufactured by the swaging process to connect the rubber hose with the metal fitting at the end of the hose. In case that the clamping force is small, the refrigerant gas in the hose can leak locally under the severe operating circumstances. The practical test of clamping force is performed by means of the measurement of separation force. In this study, the swaging process of a hose is simulated with the finite element method, to investigate the effect of friction coefficient on the clamping force. The contact condition is used in consideration of real manufacturing process, and the material properties for the Mooney-Rivlin model is obtained by the experimental results. The result interpretations are focused on the contact forces, which is displayed graphically with respect to friction coefficient, on the surfaces between the hose and the metal fittings.

• 전기학회논문지
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• 제56권6호
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• pp.1039-1046
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• 2007

This paper presents the analysis for power consumption, mechanical vibration and acoustic noise characteristics of the Coreless and Slotless Brushless DC motor in Digital Lightening Processor(DLP) Motor with the Air-Dynamic Bearing. The Coreless BLDC motor has not the stator yoke as well as the stator slot to remove the unbalance force by the interaction between the stator yoke and Air-Dynamic Bearing clearance. The assembling tolerance and the processing error make the air-gap difference between the magnet and the stator yoke .which occurs the unbalanced electro-magnetic force in the Slotless BLDC motor. It imposes the air-dynamic bearing on the disturbance force and makes the Air-Dynamic Bearing vibrated and noised. Also, The attractive force between the magnet and the silicon steel stator yoke increases the power consumption. In this paper, the power consumption, mechanical vibration and acoustic noise of the Coreless BLDC motor and the Slotless BLDC motor with the silicon steel stator yoke are simulated, analyzed, and tested using the manufactured proto-type motors with Air-Dynamic bearing. The simulated and tested results present that the Coreless BLDC motor without the silicon steel stator yoke has the lower mechanical vibration and noise ,and lower power consumption than the Slotless BLDC motor with the silicon steel stator yoke in Digital Lightening Processor Motor with Air-Dynamic Bearing.

• 한국군사과학기술학회지
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• 제21권3호
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• pp.403-412
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• 2018

In this study, a three-dimensional variational(3DVAR) data assimilation system was developed for the operational numerical weather prediction(NWP) system at the Republic of Korea Air Force Weather Group. The Air Force NWP system utilizes the Weather Research and Forecasting(WRF) meso-scale regional model to provide weather information for the military service. Thus, the data assimilation system was developed based on the WRF model. Experiments were conducted to identify the nested model domain to assimilate observations and the period appropriate in estimating the background error covariance(BEC) in 3DVAR. The assimilation of observations in domain 2 is beneficial to improve 24-h forecasts in domain 3. The 24-h forecast performance does not change much depending on the estimation period of the BEC in 3DVAR. The results of this study provide a basis to establish the operational data assimilation system for the Republic of Korea Air Force Weather Group.

• International Journal of Aeronautical and Space Sciences
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• 제11권4호
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• pp.345-350
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• 2010

The repetitive vibrating action of an aerodynamic load causes an external fuel tank's horizontal fin to experience a shorter life cycle than its originally predicted one. Store separation analysis is needed to redesign the fin of an external fuel tank. In this research, free-drop tests were conducted using 15% scaled models in a subsonic wind tunnel in order to analyze the store separation characteristics of an external fuel tank. The store separation trajectory based on grid tests was also obtained to verify the results of the free-drop tests. The results acquired from the free-drop tests correlated well with the grid tests in regards to the trajectories and behavior of the stores separated from the aircraft. This agreement was especially noted in the early stages of the store separation.

• 대한안전경영과학회지
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• 제17권4호
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• pp.57-66
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• 2015

This paper reviewed the effect of job burnout on safety outcomes, and the moderating effect of safety climate in Korean Air Force. The prevalence of burnout in air force pilots has not been determined and reviewed. It is also unknown whether pilots' burnout may affect their safety outcomes(safety action & compliance). The primary objective of this study was to determine the prevalence of burnout and it's effect on safety outcomes. For cross-sectional survey, 910 questionnaires were sent to pilots in air force, and 722 questionnaires among them were returned effectively. The questionnaire was divided into 4 parts examining pilots' demographic factors, job burnout, safety outcomes, and safety climates. To test and review proposed hypotheses, hierarchical multiple regression analysis was used. The results of statistical analysis appeared as follow; 1) EE(emotional exhaustion) and RPA(reduced personal accomplishment) effected negatively on safety action. 2) EE and RPA effected negatively on safety compliance. 3) EE effected more positively on safety action in higher SS(superior support) group than in lower SS group. 4) RPA effected more positively on safety compliance in higher SS(superior support) group than in lower SS group. 5) RPA effected more positively on safety action in higher CW(coworker support) group than in lower CW group.

• Journal of Power Electronics
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• 제16권1호
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• pp.182-189
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• 2016

Fault detection is the research focus and priority in this study to ensure the high reliability of a proposed three-level inverter. Kernel principal component analysis (KPCA) has been widely used for feature extraction because of its simplicity. However, highlighting useful information that may be hidden under retained KPCs remains a problem. A weighted KPCA is proposed to overcome this shortcoming. Variable contribution plots are constructed to evaluate the importance of each KPC on the basis of sensitivity analysis theory. Then, different weighting values of KPCs are set to highlight the useful information. The weighted statistics are evaluated comprehensively by using the improved feature eigenvectors. The effectiveness of the proposed method is validated. The diagnosis results of the inverter indicate that the proposed method is superior to conventional KPCA.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제15권1호
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• pp.216-239
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• 2021

The present work addresses the challenging problem of coordinating power allocation with interference management in multi-robot networks by applying the promising expansion capabilities of multiple-input multiple-output (MIMO) and full duplex systems, which achieves it for maximizing the throughput of networks under the impacts of Doppler frequency shifts and external jamming. The proposed power allocation with interference coordination formulation accounts for three types of the interference, including cross-tier, co-tier, and mixed-tier interference signals with cluster head nodes operating in different full-duplex modes, and their signal-to-noise-ratios are respectively derived under the impacts of Doppler frequency shifts and external jamming. In addition, various optimization algorithms, including two centralized iterative optimization algorithms and three decentralized optimization algorithms, are applied for solving the complex and non-convex combinatorial optimization problem associated with the power allocation and interference coordination. Simulation results demonstrate that the overall network throughput increases gradually to some degree with increasing numbers of MIMO antennas. In addition, increasing the number of clusters to a certain extent increases the overall network throughput, although internal interference becomes a severe problem for further increases in the number of clusters. Accordingly, applications of multi-robot networks require that a balance should be preserved between robot deployment density and communication capacity.

• 한국항공운항학회지
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• 제29권2호
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• pp.36-46
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• 2021

The purpose of this study is to ensure safety by proactively identifying hazards that could be derived from changes in mission form and environment as the advanced aircraft such as F-35A stealth fighter, KC-330 Multi-role transport and tanker, RQ-4B high altitude unmanned reconnaissance aircraft, etc are introduced that the Republic of Korea Air Force(ROKAF) has never been operated so far. To this end, the safety management methods based on proactive and predictive approaches used in advanced countries(US Air Force, UK Royal Air Force, Royal Australian Air Force) operating aircraft types same or similar things being newly powered by the ROKAF were reviewed. In addition, the direction for improvement of the safety management methods operating in the ROKAF and the measures necessary for establishment of the new safety management techniques to be applied were suggested.

• International Journal of Computer Science & Network Security
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• 제22권11호
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• pp.184-188
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• 2022

The article considers the improved method and model of automated air situation assessment using a decision support system based on fuzzy networks of target installations. The advanced method of automated assessment of the air situation using the decision support system is based on the methodology of reflexive control of the first rank. With this approach, the process of assessing the air situation in the framework of the formulated task can be reduced to determining the purpose, probabilistic nature of actions and capabilities of the air target. The use of a homogeneous functional network for the formal presentation of air situation assessment processes will formally describe the process of determining classes of events during air situation assessment and the process of determining quantitative and qualitative characteristics of recognized air situation situations. To formalize the patterns of manifestation of the values of quantitative and symbolic information, it is proposed to use the mathematical apparatus of fuzzy sets.