• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.3
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• pp.325-331
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• 2013

In this study, a complex eigenvalue analysis is implemented to verify the unstable mode of a brake system using ABAQUS software. The component participation factors and component modal participation factors are used to analyze the total contributions from each component and each component mode to a particular unstable system mode. This study shows that the 1.4-kHz unstable system mode comes from mode coupling between the 2nd nodal diametric mode and 3rd lateral axial mode (LAM) in the baseline model. A sensitivity analysis with a linking index is performed to prevent the mode coupling of the component modes. This linking index analysis shows the optimum mass loading position to move away the natural frequency of the 3rd LAM, which contributes to the unstable mode. Finally, a complex eigenvalue analysis is implemented with mass loading in the tie bar position, and no unstable system mode is generated in the low-frequency range (below 2 kHz).

• Journal of the Korean Vacuum Society
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• v.15 no.4
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• pp.421-426
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• 2006

In examining particulate deposits in the pipes of a chemical vapor deposition (CVD) system, vibration diagnostics is compared and studied against ultrasonic diagnostics, The latter method involves pulsing the outer wall of pipes with an ultrasonic sensor and analyzing the resulting echo to observe particulate deposits inside pipes. Vibration diagnostics examines the existence of particulate deposits by analyzing the difference in the frequencies generated when a vibrator is adhered to the outer wall of pipes. With ultrasonic diagnostics, good test results were obtained only when particulate deposits were attached to the inner wall of the pipes, After some time, however, particulate deposits were not detected properly, as the ultrasonic wave failed to cross the fine gaps created between the inner wall of the pipe and the deposits. The ultrasonic wave bounced back because of the dried particulate deposits on the wall. Thus, it has been proven that the ultrasonic diagnostics is not an appropriate means of examining the particulate deposits in a vacuum, On the other hand, vibration diagnostics succeeded in detecting the particulate deposits regardless of the lapsed time. In conclusion, the vibration diagnostics is being expected as the effective method in monitoring the particulate deposits inside pipes in the CVD system where the desired behavior is reduced frequency along with the particulate deposits in comparison to the case where the pipe is clean.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.5
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• pp.673-678
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• 2013

Creep groan noise occurs at low frequencies immediately after releasing brake pressure or when a car stops. This noise can be used to predict problems in not only the brake system but also the vehicle system. Because of its complexity, it is difficult to determine its characteristics. Therefore, most improvements are conducted by changing the brake pad, and it still remains difficult to conduct a test using a vehicle. In this study, the characteristics of creep groan noise and the effects from a vehicle system are investigated by using vehicles and an NVH chassis-dynamometer through various tests. A new evaluation method for creep groan noise by using a vehicle is proposed, and the possibility of reduction schemes from the viewpoint of the vehicle system is confirmed from the results mentioned above.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.743-749
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• 2012

Grunt (Stick-slip) noise happens between rear lining and drum on braking condition while vehicle is returning to steady position after nose-dive. The study presents a new testing and analysis methods for improving brake grunt noise on vehicle. Grunt noise is called a kind of stick slip noise with below 1kHz frequency that is caused by the surfaces alternating between sticking to each other and sliding over each other with a corresponding change in friction force. This noise is typically come from that the static friction coefficient of surfaces is much higher than the kinetic friction coefficient. For the identification of the excitation mechanism and improvement of grunt noise, it is necessary to study variable parameters of rear drum brake systems on vehicle and to implement CAE analysis with stick slip model of drum brake. The aim of this study has been to find solution parameters throughout test result on vehicle and dynamo test. As a result of this study, it is generated from stick slip between rear lining and rear drum and it can be solved to reduce contact angle of lining with asymmetric and is effected not only brake drum strength but also rear brake size and brake factor.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.12 no.6
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• pp.57-63
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• 2012

Effective use of stethoscope is very important for primary clinical diagnosis for the increasing cardiovascular and respiratory disease. This study developed the contact vibration sensor using piezopolymer film which minimizes the ambient noise, and signal processing algorithm was applied for providing better auscultation sounds compare to the existing electronic stethoscopes. Especially, low frequency heart sounds were acquired without distortion, and the quality of lung sounds were improved. Also, auscultating sounds could be transmitted using bluetooth, which made possible to be used for the u-healthcare environment. Results of this study, auscultation of heart and lung sounds, could be applied to the convergence industry of medical and information communication technology through remote diagnosis.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.54 no.3
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• pp.122-132
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• 2005

This paper presents a novel approach based on Prony method to analysis of small signal stability in power system. Prony method is a valuable tool in identifying transfer function and estimating the modal parameter of power system oscillation from measured or computed discrete time signal. This paper define the relative residue of time signal and propose the condition to select low frequency oscillation in each generator. This paper describes the application results of proposed algorithm with respect to KEPCO systems. Simulation results show that the proposed algorithm can be used as another tools of power systems analysis.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.7
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• pp.875-882
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• 2014

In this paper, we propose a new parameter estimation method that can deal with the data of multiple time intervals simultaneously. If there are common modes in the multiple time intervals, it is possible to create a new polynomial by summing the coefficients of the prediction error polynomials of each time interval. By calculating the roots of the new polynomial, it is possible to estimate the common modes that exist in each time interval. The accuracy of the proposed parameter estimation method has been proven by using appropriate test signals.

• Journal of Power System Engineering
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• v.7 no.2
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• pp.36-43
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• 2003

In this paper, the strain-gauge type accelerometer is developed. This type of accelerometer has simple structure and cost for manufacturing is cheap, compared with other types of accelerometer such as piezoelectric, capacitance and servo, etc. Also it is very sensitive to the low frequency vibration which is the prominent characteristics of the vibration occurring by vehicles moving across a bridge. Two prototype accelerometers are designed and manufactured based upon the FE(Finite Element) method and static and dynamic calibration tests are performed to check out the linearity, sensitivity and cross sensitivity, etc. Experimental results designate that the proposed accelerometer show reasonable performances compared to the commercial one.

• Proceedings of the KIEE Conference
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• 1988.07a
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• pp.870-873
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• 1988

AESOPS computer program is designed to find those eigenvalues of a linear dynamic system model which most strongly characterize oscillations between generator rotors. The low frequency oscillation actually occurred in October, 1986 in Korean Electric Power Corporation (KEPCO) System. 28 oscillation modes are identified through computer runs and two of them are calculated unstable in the case of the start of a pumped-storage unit. This program is considered to complement the conventional PSS/E stability program for the stability study of KEPCO system.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.52 no.1
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• pp.1-8
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• 2003

This paper presents a novel application method of H$_{\infty}$ optimization method to the design of Power System Stabilizer(PSS) and experimental results through hardware simulator. The approach is focused on decision of performance index and selection strategy of weighting functions together with its tuning for direct design. As the Purpose of the PSS is to increase system damping at very narrow frequency band, weighting functions are determined differently from the case of general servo system control. The designed PSS was confirmed through experiments on a hardware simulator.