• Journal of the Korean Society for Precision Engineering
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• v.21 no.7
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• pp.185-194
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• 2004

In order to analyze the motion errors of the aerostatic stage, it is necessary to consider the influence of the moment variation occurred inside the pads. In this paper, a motion error analysis method utilizing the transfer functions on the reaction force and moment is proposed, and general characteristics of the transfer functions are discussed. Calculated motion errors by the proposed method show good agreement with the ones calculated by Multi fad Method, which is considered the entire table as an analysis object. Also, by the introduction of the transfer function of motion errors, which represent the relationship between the spatial frequency components of the rail form error and motion errors, motional characteristics of the porous aerostatic stage can be generalized. In detail, the influence of the spatial frequencies is analyzed qualitatively, and the patterns of the insensitive frequencies which almost do not affect the linear motion error or angular motion error according to the rail length ratio and the number of the pad are verified. The relationship between the moment variation occurred inside the pads and the motion errors is also verified together.

• Journal of Power Electronics
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• v.19 no.5
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• pp.1303-1314
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• 2019

This paper studies the harmonic characteristics of ship electric propulsion systems and their treatment methods. It also adopts effective measures to suppress and prevent ship power systems from affecting ship operation due to the serious damage caused by harmonics. Firstly, the harmonic characteristics of a ship electric propulsion system are reviewed and discussed. Secondly, aiming at problems such as resonant frequency and filter characteristics variations, resonance point migration, and unstable filtering performances in conventional passive filters, a method for fully tuning of a passive dynamic tunable filter (PDTF) is proposed to realize harmonic suppression. Thirdly, to address the problems of the uncontrollable inductance L of traditional air gap iron core reactors and the harmonics of power electronic impedance converters (PEICs), this paper proposes an electromagnetic coupling reactor with impedance transformation and harmonic suppression characteristics (ECRITHS), with the internal filter (IF) designed to suppress the harmonics generated by PEICs. The ECRITHS is characterized by both harmonic suppression and impedance change. Fourthly, the ECRITHS is investigated. This investigation includes the harmonic suppression characteristics and impedance transformation characteristics of the ECRITHS at the fundamental frequency, which shows the good performance of the ECRITHS. Simulation and experimental evaluations of the PDTF are carried out. Multiple PDTFs can be configured to realize multi-order simultaneous dynamic filtering, and can effectively eliminate the current harmonics of ship electric propulsion systems. This is done to reduce the total harmonic distortion (THD) of the supply currents to well below the 5% limit imposed by the IEEE-519 standard. The PDTF also can eliminate harmonic currents in different geographic places by using a low voltage distribution system. Finally, a detailed discussion is presented, with challenges and future implications discussed. The research results are intended to effectively eliminate the harmonics of ship electric power propulsion systems and to improve the power quality of ship power systems. This is of theoretical and practical significance for improving the power quality and power savings of ship power systems.

• Journal of the Korean Society of Safety
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• v.14 no.3
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• pp.101-109
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• 1999

This study attempts to analyse the solid mixing in the feeder and the packing effect for pressure fluctuations in the fluidized bed. To study the mixing characteristics of solid in vibrating feeder for the stable operations of fluidized combustion, the system consisted of two groups of particles such that fine particles were located on the top of the coarse particles before vibratory mixing had started. The effects of packing materials on the pressure fluctuations in a fluidized bed were analysed by using a statistical method to interpret the behavior of fluidized bed. The experiments were carried out in a fluidized bed of 6.7cm-ID, and the experimental variables were particle sizes, of 115 to 1,015$\mu\textrm{m}$ in diameter and the multi-sized particles haying Rosin-Rammler and Gaussian distributions. The settled bed heights of particles to diameter ratios (L/D) were ranged from 0.5 to 2.0. And fluidizing of particles was carried out by air. The packing materials used were screen packing, and the properties of the pressure fluctuations in the fluidized bed were measured by a differential pressure transducer. The properties of the pressure fluctuations calculated were the mean, the standard deviation, and the major frequency of the power spectral density functions. From the characteristics of fluidizing, it was found that the standard deviation of pressure fluctuations could be effectively used to explain the fluidized phenomena, and the packing materials affected severely the properties of the pressure fluctuations. As a result, from the interpretation by spectral analysis, the effects of measuring radius of pressure fluctuations on standard deviation were constant in the case of the fluidized bed with and without packing materials. However, the effects of measuring the height of pressure fluctuations on standard deviations were linear increasing for the fluidized bed with packing materials, but were constant for the fluidized bed without packing materials at 4.5cm above the gas distributor. The major frequency of pressure fluctuations was found to be nearly independent of fluidized system. Also, the major frequency of pressure fluctuations decreased with increasing packing size, and it had maximum value at 10% of the packing amount.

• Journal of IKEEE
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• v.26 no.3
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• pp.456-461
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• 2022

In this paper, a two-stage single-ended power amplifier (PA) with broadband gain characteristics was presented by utilizing a radio frequency (RF) transformer (TF), which is essential for a differential amplifier. The bandwidth of a PA can be improved by designing TF to have broadband characteristics and then applying it to the inter-stage matching network (IMN) of a PA. For broadband gain characteristics while maintaining the performance and area of the existing PA, an IMN was implemented on an monolithic microwave integrated circuit (MMIC) and a multi-layer printed circuit board (PCB), and the simulation results were compared. As a result of simulating the PA module designed using InGaP/GaAs HBT model, it has been confirmed that the PA employing the proposed design method has an improved fractional bandwidth of 19.8% at a center frequency of 3.3GHz, while the conventional PA showed that of 11.2%.

• The Journal of the Acoustical Society of Korea
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• v.24 no.2
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• pp.97-102
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• 2005

Acoustic experiments were performed with Zostera marina to study the characteristics of backscattering of seagrass living in the bottom interface. Field experiments were conducted in the Dongdae man, Namhae for day and night to consider the effects of air-bubble from photosynthesis of seagrass. The multi-frequency (30$\~$120 kHz) responses were measured and the distributions of back scattering strength due to the movement of seagrass were Presented by PDF (probability density function) at 120 120 kHz. The results were shown both the frequency dependence and diurnal variation of the backscattering strength between day and night. This diurnal variation may be caused by the amount of oxygen in dissolved bubbles formed by Photosynthesis of seagrass.

• Tuberculosis and Respiratory Diseases
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• v.64 no.6
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• pp.414-421
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• 2008

Background: Recently, in addition to multi-drug resistant tuberculosis (MDR-TB), extensively drug-resistant tuberculosis (XDR-TB) has become rapidly growing public health threat. This study examined the clinical differences between pulmonary TB patients with extensively drug resistance (XDR) and multi-drug resistance (MDR) at the National Medical Center in Korea in order to determine the clinical characteristics associated more with XDR-TB than MDR-TB. Methods: Patients who received a diagnosis of culture-confirmed pulmonary TB and a drug sensitivity test (DST) for anti-TB drugs at the National Medical Center between January 2000 and August 2007 were enrolled in this study. The patients were identified into the XDR-TB or MDR-TB group according to the DST results. The clinical characteristics were reviewed retrospectively from the medical records. Statistical analysis for the comparisons was performed using a ${\chi}^2$-test, independent samples t-test or binary logistic regression where appropriate. Results: A total 314 patients with culture-confirmed pulmonary TB were included. Among them, 18 patients (5.7%) had XDR-TB and 69 patients (22%) had MDR-TB excluding XDR-TB. A comparison of the clinical characteristics, revealed the XDR-TB group to have a higher frequency of a prior pulmonary resection for the treatment of TB (odds ratio [OR], 3.974; 95% confidence interval [CI], 1.052~15.011; P value 0.032) and longer average previous treatment duration with anti-TB drugs, including a treatment interruption period prior to the diagnosis of XDR, than the MDR-TB group (XDR-TB group, 72.67 months; MDR-TB group, 13.09 months; average treatment duration difference between two groups, 59.582 months; 95% CI, 31.743~87.420; P value, 0.000). In addition, a longer previous treatment duration with anti-TB drugs was significantly associated with XDR-TB (OR, 1.076; 95% CI, 1.038~1.117; P value, 0.000). A comparison of the other clinical characteristics revealed the XDR-TB group to have a higher frequency of male gender, diabetes mellitus (DM), age under 45, treatment interruption history, cavitations on simple chest radiograph and positive result of sputum AFB staining at the time of diagnosis of XDR. However, the association was not statistically significant. Conclusion: Pulmonary TB patients with XDR have a higher frequency of a prior pulmonary resection and longer previous treatment duration with anti-TB drugs than those with MDR. In addition, a longer previous treatment duration with anti-TB drugs is significantly associated with XDR-TB.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.13 no.2
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• pp.123-128
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• 2020

A low phase noise phase locked loop (PLL) with negative feedback loop including frequency variation sensing circuit (FVSC) has been proposed. The FVSC senses the frequency variation of voltage controlled oscillator output signal and controls the volume of electric charge in loop filter capacitance. As the output frequency of the phase locked loop increases, the FVSC reduces the loop filter capacitor charge. This causes the loop filter output voltage to decrease, resulting in a phase locked loop output frequency decrease. The added negative feedback loop improves the phase noise characteristics of the proposed phase locked loop. The size of capacitance used in FVSC is much smaller than that of loop filter capacitance resulting in no effect in the size of the proposed PLL. The proposed low phase noise PLL with FVSC is designed with a supply voltage of 1.8V in a 0.18㎛ CMOS process. Simulation results show the jitter of 273fs and the locking time of 1.5㎲.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.4
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• pp.1-10
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• 2023

In the seismic design of structures, seismic forces are calculated based on structural models and analysis. In order to accurately address the dynamic characteristics of the actual structure in the structural model, calibration based on actual measurements is required. In this study, a 4-story frame test specimen was manufactured to simulate frame building, accelerometers were attached at each floor, and 1-axis shaking table test was performed. The natural period of the specimen was similar to that of the actual 4 story frame building, and the columns were designed to behave with double-curvature having the infinite stiffness of the horizontal members. To investigate the effects seismic waves characteristics, historical and artificial excitations with various frequencies and acceleration magnitudes were applied. The natural frequencies, damping ratios, and mode shapes were obtained using frequency response functions obtained from dynamic response signals, and the mode vector deviations according to the input seismic waves were verified using the Mode assurance criterion (MAC). In addition, the damping ratios obtained from the vibration tests were applied to the structural model, and the method with refined dynamic characteristics was validated by comparing the analysis results with the experimental data.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.5
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• pp.375-380
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• 2007

The nonlinear aerodynamic analysis of wing with control surface is performed using the frequency-domain panel method. To take into consideration the nonlinear aerodynamic characteristics of wing an iterative decambering approach is introduced. The iterative decambering approach uses the known aerodynamic characteristics of airfoil to calculate the aerodynamic characteristics of wing. The multi-dimensional Newton iteration is used to account for the coupling between the different sections of wing. The present method is verified by showing that it produces results that are in good agreement with experiments. The present method will be useful for the analysis of aircraft in the conceptual design because the present method can calculate promptly the nonlinear aerodynamic characteristics of wing with a few computing resources.

• Journal of the Korea Society of Computer and Information
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• v.28 no.2
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• pp.9-17
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• 2023

In this paper, we propose a one-class vibration anomaly detection system for bearing defect diagnosis. In order to reduce the economic and time loss caused by bearing failure, an accurate defect diagnosis system is essential, and deep learning-based defect diagnosis systems are widely studied to solve the problem. However, it is difficult to obtain abnormal data in the actual data collection environment for deep learning learning, which causes data bias. Therefore, a one-class classification method using only normal data is used. As a general method, the characteristics of vibration data are extracted by learning the compression and restoration process through AutoEncoder. Anomaly detection is performed by learning a one-class classifier with the extracted features. However, this method cannot efficiently extract the characteristics of the vibration data because it does not consider the frequency characteristics of the vibration data. To solve this problem, we propose an AutoEncoder model that considers the frequency characteristics of vibration data. As for classification performance, accuracy 0.910, precision 1.0, recall 0.820, and f1-score 0.901 were obtained. The network design considering the vibration characteristics confirmed better performance than existing methods.