• The Transactions of the Korean Institute of Power Electronics
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• v.6 no.6
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• pp.474-480
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• 2001

In this paper a low signal reduction communication system that does not use the communication line but power line is presented It will be very useful for an information-oriented society with tele-metering and home automation. The conventional system has a difficulty in transmitting information due to decreasing communication voltage. The proposed system employs a special type switching amplifier system which has a low inner resistance and uses high efficient ferrite core in coupling circuit. This new system is proposed to reduce the loss of conductor load and coupling circuit in a PLC system.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.2
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• pp.255-264
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• 2015

Steel plate concrete (SC) structure has been developed as a new structural type. Rational damping value shall be determined for the seismic design of SC structure. This study evaluated damping ratio of SC structure through experiments. For the study, a SC shear wall specimen was constructed and dynamically tested on the shaking table. Acceleration time history responses measured from testing were converted to the transfer functions and analyzed by using experimental modal analysis technique. The structural damping ratio of the specimen was identified as 4% to critical. Considering the shaking table test was performed at the excitation level corresponding to the low stress level of the specimen, 4% could be suggested as a structural damping for design of SC structure for operating basis earthquake.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.8
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• pp.850-856
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• 2009

A new type bi-directional damper using a tuned liquid column damper(TLCD) and a tuned sloshing damper(TSD) is introduced in this study. Two dampers are usually needed to reduce wind-induced responses of tall buildings since they are along and across wind ones. The proposed damper has the advantage of controlling both responses with one damper. One of objectives of this study is to derive analytical dynamics to investigate coupled effects due to TLCD and TSD. Another objective is to address the effect of coupled control force due to TLCD and TSD on the dynamic characteristic of the damper based on analytical dynamics. Shaking table test is undertaken to experimentally grasp dynamic characteristics of the damper under white noise excitation. Its dynamic characteristic is expressed by the transfer function from the shaking table acceleration to the control force generated from the damper. Finally, its design parameters are identified based on the coupled dynamics, which include the mass ratio of horizontal liquid column to total liquid for a TLCD, the participation factor of the fundamental liquid sloshing for a TSD and damping ratio for both cases.

• The Journal of the Acoustical Society of Korea
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• v.21 no.1
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• pp.37-41
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• 2002

In this paper, we made shorter EDT(early decay time) of room reverberation curve using multiple-channel. The speech signal was processed inverse filtering with full-band and sub-band in the basis MINT, and then the multiple-channel adaptive filters were used LMS (Least Mean Square) and NLMS (Normalized Least Mean Square) algorithm. Experimental results, we could get 1/3 of time reduction at 20dB level in the reverberation curve using full-band NLMS when two microphones were used. Also, it is shown that the speech articulation was improved 80% from the test listeners with the speech, which was to shorten EDT by MINT in the subjective assessments using real room impulse response.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.4
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• pp.489-496
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• 2019

This paper is a study on the evaluation of loss factor of damping treatment materials to reduce the noise and vibration for panels of railway vehicles and automobiles. In order to determine the modal parameters of damping materials, beam excitation tests were carried out using different type PVC coated aluminum and steel base beam specimens. The specimens were excited from 10 Hz to 1000 Hz frequency range using sinusoidal force, and transfer mobility data were measured by using an accelerometer. The loss factors were determined by using integrated program, based on theories of Half Power Method, Minimum Tangent Error Method, Minimum Angle Error Method and Phase Change Method, which enable to evaluate the parameters using modal circle fit and least squares error method. In the case of lower loss factor and data of linear characteristics, any method could be applied for evaluation of parameters, however the case of higher loss factor or data including non-linear characteristics, the minimum angle error method could reduce the loss factor evaluation. The obtained dynamic properties of the coating material could be used for application of Finite Element Method analyzing the noise control effects of complex structures such as carbody or under-floor boxes of rolling stock. The damping material will be very useful to control the structural noise, because the obtained modal loss factors of each mode show very good effect on over $2^{nd}$ mode frequency range.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.7C
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• pp.658-666
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• 2007

In general, the earlier linear-phase MAXFLAT(maximally flat) lowpass FIR filters have the main disadvantage of a gain response in the half frequency band $(0{\leq}w{\leq}{\pi}/2)$ by the closed form transfer functions used in design techniques for realizing them. Moreover, most of them has existent problems as follows : ripple error in the stopband, gentle-cutoff attenuation, phase and group delay and inexact cutoff frequency response. It is due to the approximation algorithms such as Chebyshev norm and Remez exchange which are used to approach MAXFLAT and linear-phase characteristics in frequency domain. In this paper, a new mathematically closed-form transfer function is introduced for the design of MAXFLAT lowpass FIR filters which have the zero-phase and wideband-gain response. In addition, we verify that the closed-form transfer function is easily realized due to our generalized formulas derived newly by using MAXFLAT conditions including an arbitrary cutoff point. This method is, therefore, useful for "simple and quick designs". Conclusively, we propose a technique for the design of new zero-phase wideband MAXFLAT lowpass FIR filters which can achieve sharp-cutoff attenuation exceeding 250 dB almost everywhere.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.138-145
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• 2005

• Proceedings of the Korean Magnestics Society Conference
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• 2012.05a
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• pp.129-130
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• 2012

• Journal of the Earthquake Engineering Society of Korea
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• v.5 no.4
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• pp.27-38
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• 2001

A mechanical lumped parameter model is proposed for the dynamic modeling of a semi-infinite reservoir. A semi-analytic transmitting boundary is derived for a semi-infinite 2-D reservoir of constant depth. The characteristics of the solution are examined in both frequency and time domains. Mass, damping and spring coefficients of the mechanical model are obtained to preserve the major features of the solution such as eigenfrequencies and the shapes of Bessel functions that appear as kernels in the convolution integrals. The lumped parameter model in its final form consists of two masses, a spring and two dampers for each eigenfrequency. Application examples demonstrated that the new lumped parameter model could be used for the time domain analysis of dam-reservoir systems.

• Explosives and Blasting
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• v.21 no.4
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• pp.37-42
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• 2003

The source of rock breakage by explosive blasting is the energy released from an explosive. It is transmitted to the surrounding rock mass causing various types of fracture of rock material. The reaction of explosives and the resulting action on the surrounding rock mass are completed in very short tine, making it almost impossible to observe the processes occurring in the interior of the rock mass. In this study several input parameters are investigated by numerical modelling of blast source and dynamic response of rock mass. It is shown that damping coefficient and rising time are major parameters affecting dynamics response of rock mass.