• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.11
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• pp.5306-5313
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• 2011

Most previous studies for finding optimal design parameters of a tuned mass damper(TMD) have been focused on the harmonic excited single-degree-of freedom system. In this study, optimal values of damping ratio and tuning frequency ratio of a TMD applied to control a seismically excited structure are investigated through numerical analyses. Considering that the structural responses due to earthquake loads are strongly dependent on the soil condition, the site effects on the optimal parameters of the TMD are studied and compared to those presented by previous studies. Numerical analyses results indicate that better control performance can be obtained by using the parameters proposed by this study in the seismic application of the TMD.

• 대한방사선방어학회:학술대회논문집
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• 2011.11a
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• pp.98-99
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• 2011

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.6
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• pp.1149-1157
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• 1994

In this case of the mobile communication of vehicles with satellite, the signal at attenuation is due to roadside trees. To analyze this signal attenuation, a roadside tree was modeled as different obstacles of rectangular type and then using Fresnel and Kirchhoff diffraction theory, a formula was derived for signal intensity variation caused by the roadside tree model. The signal attenuation of a roadside tree model was obtained by numerical analysis with variation of the elevation angle, the position and distance between a receiver and a transmitter, and these were compared with experimental results. The results of comparison between theoretical and experimental values show, as expected, the good agreement of the signal attenuation trend.

• Journal of Advanced Navigation Technology
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• v.10 no.4
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• pp.356-363
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• 2006

The demand for digital multimedia service using Ka band satellite communication are growing rapidly. So, in this paper, we have analyzed rain attenuation with typical model, and proposed prediction model of rain attenuation in high frequency(20 GHz). This paper illustrates Korea rain attenuation characteristics at the Ka band Koreasat beacon frequency based on the theoretical and empirical approaches and seek for efficient techniques by rain attenuation estimate and analyzed performance of adaptive modulation system. Propose prediction model of rain attenuation and parameter of satellite link can be available for the Ka band satellite communication.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.11C
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• pp.1025-1028
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• 2009

This paper presents upper bounds of Maximum Likelihood (ML) decoding performance of a few irregular LDPC codes using the simple bound and ML input output weight distributions and it is shown that contrary to general opinion that as block length becomes longer, BP decoding performance becomes simply closer to ML decoding performance, before peak degradation, as block length becomes longer, BP decoding performance falls behind ML decoding performance more and after peak degradation, general opinion holds.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.2
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• pp.242-251
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• 2000

Design of wireless link in Ka and mm-wave bands is critically affected by rain attenuation. In this paper, we compared and analyzed the main distributions of rain drop size to estimate the rain attenuation which can be used in domestic environment. Mie scattering theory was checked to agree with Rayleigh theory in its low frequency limit and agree with optical scattering theory in its high frequency limit. We intended to provide more specific criteria to estimate rain attenuation with a generalized approach.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.7
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• pp.3197-3202
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• 2013

When car builder designs the large carbody structure of railway vehicles, it is necessary to optimize the damping characteristics through the analysis of structure borne noise such as sound pressure level(SPL). This paper is a study on the structure borne noise analysis by characterizing the damping of double skin aluminum extruded panels for rolling stock carbody. The normalized SPL was calculated based on the simple source theory using measured mechanical mobility parameters from vibration tests(i.e. point, transfer and modal mobility). The reduced SPL was predicted by using finite element method by applying loss factor of damping material into laminated shell elements. It was found out that the damping material coated on the panels like underframe, which part is seriously affected by vibration during train run, took effect to reduce noise level.

• Journal of Advanced Navigation Technology
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• v.13 no.3
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• pp.399-405
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• 2009

This paper proposes a design of attenuator based on meta-material structure and its application. The unit-cell attenuator based on the lossy transmission line consists of the CRLH(Composite Right/Left Handed) transmission line and PIN diodes to be controlled internal loss according to diode bias voltage to change resistance of diode. Also, to reduce the initial losses, there is used parallel connection of PIN diodes. To increase attenuations, it is connected a cascade unit-cell of attenuator with periodic structure. The attenuation quantities of unit-cell are about 10dB and phase variations are 15o maximum at 1.5 GHz ~ 2.5 GHz. Also, its application is represented a vector modulator.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.2C
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• pp.119-125
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• 2011

Start This paper analyzes the propagation characteristics of acoustic signals in indoor environments, which is applicable to indoor positioning system. Indoor stereo sound system is generally valid within $25m^2$. So it is not possible to apply prevalent sound propagation characteristic to indoor positioning system because the prevalent acoustic signals propagation characteristic is defined under free space condition. Therefore, in this paper, we present the propagation characteristics of acoustic signals in indoor environments considering the free space propagation characteristic as well as room characteristic such as humidity, temperature, absorption of atmosphere and so on. To verify the designed propagation model of indoor acoustic signals, this paper presents the propagation characteristics of decreasing sinusoidal signals whose frequencies ate from 1kHz to 20kHz in anechoic room. In addition, this paper also presents the propagation characteristics of decreasing sinusoidal signals which have multiple frequencies.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.5
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• pp.601-611
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• 2016

The research, development and use of seismic isolation systems have been increasing with the gradual development of structure safety assurance methods for earthquakes. The High Damping Rubber Bearing (HDRB), one type of seismic isolation system, is a Laminated Rubber Bearing using special High Damping Rubber. However, as its damping function is slightly lower than that of the Lead Rubber Bearing, a similar seismic isolation system, its utilization has not been high. However, the HDRB has a superior damping force to the Natural Rubber Bearing, which has similar materials and shapes, and the existing Lead Rubber Bearing has a maleficence problem in that it contains lead. Thus, studies on HDRBs that do not use lead have increased. In this study, a test targeting the HDRB was done to examine its various dependence properties, such as its compressive stress, frequency and repeated loading. To evaluate the HDRB's seismic performance in response to several earthquake waves, the shaking table test was performed and the results analyzed. The test used the downscaled bridge model and the HDRB was divided into seismic and non-seismic isolation. Consequently, when the HDRB was applied, the damping effect was higher in the non-seismic case. However, its responses on weak foundations, such as in Mexico City, represented increased shapes. Thus, its seismic isolator.