• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2001.10a
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• pp.319-323
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• 2001

In significant number of energy-related facilities for like thermal power plant or petro-chemical industry, CrMo steels are widely used energy conversion industries. However, these materials undergo precipitation of carbides or intermetallic compounds into grain boundary and change of internal microstructure such as coarsening of precipitation, decrease of solute elements and impurity segregation under more severe service conditions, which results in deterioration of inherent superior material characteristics. In this study, it was verified experimentally the feasibility of the aging degradation evaluation for degraded 2.25Cr-lMo steel specimens prepared by isothermal aging heat treatment at 63$0^{\circ}C$ by high frequency longitudinal ultrasonic and surface SH wave investigating the change of attenuation coefficient analyzed by spectral analysis. Attenuation coefficient had a tendency to increase as degradation proceeded.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.751-755
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• 2003

In this paper, We proposed compact multi-layer LTCC (Low Temperature Cofired Ceramic) bandpass filter for Bluetooth module. A ${\lambda}/4$ coupled stripline resonators are designed, which composed of coupled strip-line section and loading capacitance. This resonator with a loading capacitor has slow-wave characteristics. Due to the slow-wave effect of the proposed resonator, it is possible to design and fabricate a compact bandpass filter with a wide upper stop band. Attenuation poles in the lower stop band are achieved using controlling of electro-magnetic coupling between resonators. Using multi-layer LTCC technology, we designed and fabricated band pass filter with a finite attenuation pole and wide upper stopband. The overall size of the filter is $1.2{\times}2.0{\times}1.0mm^3$.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.5
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• pp.819-830
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• 2016

Hydrodynamic characteristics of wave propagation through density stratification have not been identified in details. So this study conducted a numerical simulation using LES-WASS-3D ver. 2.0 for analysis of density current due to water temperature and salinity in order to analyze hydraulic characteristics under wave action in a two-layer density stratified fluid. For the validity and effectiveness of numerical wave tank used, it was compared and analyzed with the experiment to show waveform based on $3^{rd}$-order Stoke wave theory at the internal of a density stratification. Using the results obtained from numerical simulation, the surface and internal wave heights are reduced as the wave propagates in a two-layer density stratified water. And the surface or internal wave attenuation became more serious as the vorticities were increased by the velocity difference of wave propagation due to the upper-lower density difference around the interface of a density stratification. As well, the surface and internal wave attenuations became more serious with higher density difference and depth ratio between upper and lower layers when the wave propagates through a density stratification.

• Earthquakes and Structures
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• v.15 no.4
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• pp.403-410
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• 2018

The choice of attenuation relationships is one of the most important parts of seismic hazard analysis as using a different attenuation relationship will cause significant differences in the final result, particularly in near distances. This problem is responsible for huge sensibilities of attenuation relationships which are used in seismic hazard analysis. For achieving this goal, attenuation relationships require a good compatibility with the target region. Many researchers have put substantial efforts in their studies of strong ground motion predictions, and each of them had an influence on the progress of attenuation relationships. In this study, two attenuation relationships are presented using seismic data of Mazandaran province in the north of Iran by Genetic Expression Programming (GEP) algorithm. Two site classifications of soil and rock were considered regarding the shear wave velocity of top 30 meters of site. The quantity of primary data was 93 records; 63 of them were recorded on rock and 30 of them recorded on soil. Due to the shortage of records, a regression technique had been used for increasing them. Through using this technique, 693 data had been created; 178 data for soil and 515 data for rock conditions. The Results of this study show the observed PGA values in the region have high correlation coefficients with the predicted values and can be used in seismic hazard analysis studies in the region.

• Journal of the Korean Society for Nondestructive Testing
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• v.14 no.1
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• pp.23-31
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• 1994

Sound scattering by cylindrical tubes submerged in water is numerically analyzed with material attenuation considered. Complex wave numbers is introduced to see the effects of material attenuation on resonance scattering Backscattering pressures from the shells immersed in water are calculated for air-filled aluminium and acryl tubes. In order to investigate the resonance characteristics in detail, numerical analysis program has been completed which enables us to evaluate the effects of material attenuation. The testing of the program by comparison with previous results is reported and calculation results are compared and discussed for both aluminium and acryl tubes with material attenuation considered. The resonance peak and width is strongly affected by attenuation and this becomes severe as the peak is sharp and narrow and $k_{1{\alpha}}$ is high.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.2
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• pp.149-154
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• 2002

An attempt was made to evaluate the changes of microstructures and mechanical properties with increasing aging time in 2.25Cr-1Mo steel. In this study, it was verified the feasibility of the evaluation for degraded 2.25Cr-1Mo steel by isothermal heat treatment at $630^{\circ}C$ up to 1,000 hours using surface SH wave and investigated the change of attenuation coefficient and propagation time. Attenuation coefficient had a tendency to increase according to degradation and propagation time drastically in the beginning of deterioration. A good correlation between ultrasonic attenuation coefficient and hardness was found, which made sure that attenuation coefficient is an potential parameter for evaluation of aging degradation. In addition, it has verified experimentally the frequency dependence of ultrasonic group velocity and attenuation coefficient using wavelet transform.

• Journal of KSNVE
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• v.4 no.2
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• pp.187-198
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• 1994

This study is to describe the effects of the duct termination conditions conditions upon the active noise attenuation system. The adaptive filtering algorithm using FIR filter is implemented for duct noise attenuation. To avoid the instability caused by the acoustic feedback, two methods are considered. One is to use a compensating FIR filter. The other is to utilize uni-directional detecting microphone and uni-directional control speaker. Experimental results show that the reflections of sound from duct terminations greatly reduce the performance of ANC system. The directionality of detecting microphone and control speaker is a major factor to decide ANC performance. When there are some reflections from both duct terminations, the noise attenuation using finite FIR filter is not enough to model the duct plant. Especially, the reflection from the upstream termination reduces the noise attenuation in the frequencies related to the distance between control speaker and upstream termination. The performance of the noise attenuation is found to be largely enhanced by using uni-directional coupler, both on detecting microphone and control speaker, even if the duct system has an arbitrary termination conditions.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.3
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• pp.245-253
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• 2008

A precise description of the material is a key point to obtain reliable results when using wave propagation codes. In the case of multipass welds, the material is very difficult to describe due to its anisotropic and heterogeneous properties. Two main advances are presented in the following. The first advance is a model which describes the anisotropy resulting from the metal solidification and thus the model reproduces an anisotropy that is correlated with the grain orientation. The model is called MINA for modelling anisotropy from Notebook of Arc welding. With this kind of material model1ing a good description of the behaviour of the wave propagation is obtained, such as beam deviation or even beam division. But another advance is also necessary to have a good amplitude prediction: a good quantification of the attenuation, particularly due to grain scattering, is also required as far as attenuation exhibits a strong anisotropic behaviour too. Measurement of attenuation is difficult to achieve in anisotropic materials. An experimental approach has been based both on the decomposition of experimental beams into plane waves angular spectra and on the propagation modelling through the anisotropic material via transmission coefficients computed in generally triclinic case. Various examples of results are showed and also some prospects to continue refining numerical simulation of wave propagation.

• Journal of the Korean earth science society
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• v.25 no.8
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• pp.774-783
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• 2004

The S wave velocity and Q$s^{-1}$ structure of the uppermost part of the soil in Nakdong Delta area have been obtained to determine the characteristics of the forementioned soil. The phase and attenuation coefficients of multichannel seismic records were inverted to obtain the S wave velocity and Q$s^{-1}$ structure of the soil. The inversion results have been compared with the borehole measurements of the area. The seismic signal of the nearest geophone from a seismic source was used as the source signal to obtain the attenuation coefficients. Amplitude ratios of the signal at each geophone to the source signal wave plotted as a function of distance for the frequency range between 10 Hz and 45 Hz. The slope of a linear regression line which fits amplitude ratio-distance relationship best for a given frequency was used as the attenuation coefficients for the frequency. The dispersion curve of Rayleigh waves and the attenuation coefficients were inverted to obtain the S-wave velocity and Q$s^{-1}$, respectively, in the uppermost 8 meter of soil layer. The borehole measurements of the area show that are two distinct layers; the upper 4 meter of silty-sand and the lower 4 meter of silty-clay. The inversion results indicate that the shear wave velocity of the upper layer is 80 m/sec and 40m/sec in the lower silty-clay layer. The spacial resolution of the shear wave velocity structure is very good down to a depth of 8 meter. The Q$s^{-1}$ in the upper silty-sand layer is 0.02 and increase to 0.03 in the lower silty-sand layer. The spacial resolution of quality factor is relatively good down to a depth of 5 meter, but very poor below the depth. In this study, the S-wave velocity is higher in the silty-clay and the Q$s^{-1}$ is smaller silty-sand than in the silty-clay. However, much more data should be analyzed and accumulated before making any generalization on the shear wave velocity and Q$s^{-1}$ of the sediments.

• Journal of electromagnetic engineering and science
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• v.17 no.3
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• pp.165-167
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• 2017

We predict the electromagnetic wave propagation in space environments using geometrical optics. The effective indices of the troposphere, stratosphere, and ionosphere are computed, and the reflection, refraction, and attenuation of electromagnetic waves in space environments are calculated based on the ray tracing technique and geometrical optics. The influence of the refractive index and loss of atmosphere and the incident angle of the antenna on electromagnetic wave propagation is discussed.