• Proceedings of the KSR Conference
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• 2007.11a
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• pp.784-791
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• 2007

Most operational organization and railway authority which conduct scheduled maintenance(SM) have carried out the preventive maintenance(PM) based on the information provided from supplier and manufacturer of railway system. However these activities are far away from reality and low the efficiency, it is because an appropriate methods for system selection didn't take into account for improving maintenance efficiency. Therefore, the current SM tasks and maintenance activities lead to lots of spend on the cost and time. To solve the above problem, this thesis presents new approach methodology. This proposes the criteria for reliability centered maintenance(RCM) system selection through level of quantification of each parameter, i.e, frequency, severity and maintenance cost, etc. To do this, the field operation data and information of maintenance cost are essential. As applying this methodology, we can look forward to improving efficiency of PM/SM, and reducing cost.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.12
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• pp.4872-4891
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• 2015

Orthogonal frequency division multiplexing (OFDM) signals suffer from the problem of high peak-to-average power ratio (PAPR), which complicates the design of analog front-end of the system. Companding is a well-known PAPR reduction technique that involves transforming signal amplitudes using a deterministic function. OFDM signal amplitude, on average, is Rayleigh distributed but the distribution can vary significantly from symbol to symbol, especially when constellation size increases. In this paper, a new adaptive companding scheme is proposed along with its design methodology aiming at optimizing the compander performance by accommodating this variation in its design. This is achieved by designing compander parameters separately for statistically dissimilar symbols in OFDM waveform and making the compander select from these parameters, during run-time, according to the features of input symbols.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.5
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• pp.1028-1048
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• 2011

The relation of multicast transmission and directional antennas is an open problem that has been debated for a long period of time. In this paper, we propose a group-aware multicast scheme of efficient multicast communication using the directional antennas for 60GHz millimeter wave wireless networks. For this purpose, we first derive the relation among beamwidth, distance between devices and most suitable data rate in the 60GHz frequency-based wireless network. In addition, for the dynamic beamforming of multicast communication, the x and y coordinates of any point with sender device at the center is generated, and a best-chosen group is deduced based on the Euclidean distance. Then the most suitable data rate for the group is obtained using the law of cosine. Using the Standard IEEE 802.11ad MAC protocol as an example, extensive simulation results demonstrate that the proposed scheme outperforms the existing multicast communication schemes with directional antennas under different situations.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11a
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• pp.409-412
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• 2001

Identification of systems operating in closed loop has long been of prime interest in industrial applications. The fundamental problem with closed-loop data is the correlation between the unmeasurable noise and the input. This is the reason why several methods that work in open loop fail when applied to closed-loop data. The prediction error based approaches to the closed-loop system are divided to direct method and indirect method. Both of direct and indirect methods are known to be applied to the closed-loop data without critical modification. But the direct method induces the bias error in the experimental frequency response function and this bias error may deteriorates the parameter estimation performance

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.206-211
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• 2004

Recently, the ride comfort problem becomes increasingly important because of today's needs for train speedup. The concept of ride comfort is equivocal. Generally, it is defined as the body vibration. The commercial high-speed train must be run the compound line in Korea which is composed of high-speed line and conventional line. In this paper, the ride comfort has been reviewed by the various experimental methods when the high-speed train is operated on both lines. The results show that the high-speed train has no problems from the viewpoint of the comfort ride during the operation on both lines.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.449-454
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• 2000

A three-parameter model of viscoelastic damper, which has a non-linear spring as an element is incorporated into an oscillator. The behavior of the damper model shows non-linear hysteresis curves which is qualitatively similar to those of real viscoelastic materials. The motion is governed by three-dimensional non-linear dynamical system of equations. The harmonic balance method is applied to get analytic solutions of the system. The frequency-response curves show that multiple solutions co-exist and that the jump phenomena can occur. In addition, it is shown that separate solution branch exists and that it can merge with the primary response curve. Saddle-node bifurcation sets explain the occurences of such non-linear phenomena. A direct time integration of the original equation of motion validifies the use of the harmonic balance method to this sort of problem.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.972-977
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• 2000

One of the major differences of Korean residential building compared with other countries is a rigid diaphragm of a floor due to the panel heating system. An increment of a gravity floor load might cause vibration problem when the composite floor system is introduced to the panel heating system. Since the noise criteria of a residential building is lower than that of an office building, the development of a noise absorbing system should be preceded. The response evaluation was performed for the finished floor, that is with panel heating and noise absorbing system. The natural frequency was obtained both from an experimental study and an analytical study. An appropriate vibration condition of a floor with panel heating and noise absorbing systems was evaluated from this study.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.955-960
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• 2000

This paper evaluates the serviceability of vibration that is induced by people's walking and running when the long span hollow core slab is used. The dynamic characteristics like a natural frequency and a ramping ratio are found by impact loading test on the mock-up structures. Also, the human induced loading test output is evaluated by the various serviceability criteria. As the various serviceability criteria satisfy with this result, the vibration problem of relevant slab caused by people's behavior does not matter.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.724-730
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• 2000

Although there have been many investigations employing the continuous wavelet transform for the analysis of dispersive waves, they seem to lack theoretical justifications for the effectiveness of the continuous wavelet transform over other time-frequency analysis tools such as the short-time Fourier transform. The goal of this paper is to answer this question by investigating theoretically the performance of the continuous wavelet transform and the short-time Fourier transform in tracing rapidly time-varying flexural waves. As a specific example, the performance of the two transforms is compared in a problem dealing with flexural waves generated by an impact in a solid circular cylinder.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.12
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• pp.165-172
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• 1995

Many algorithms to enhance a speed performance of a robot have been studied, but it's rare to consider disign aspect of a robot arm for time optimal problem. In this paper, section demensions of a robot arm and a velocity profile of an end-effector were optimally designed to minimize the cycle time. Capacity of actuators, deflections of end-effector, and a fundamental natural frequency of the robot arm were constrained in optimal design. For a given path with a trapezoidal velocity profile, torques of each joint were calculated using the inverse kinematics and dynamics. For the SCARA type robot which is mainly used for assembly tasks, the time optimal design of each robot arm id presented with the above constraints.