• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.2 s.54
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• pp.81-94
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• 2007

In most experimental researches on the liquefaction phenomenon, an earthquake as a random vibration has been regraded as a sinusoidal wave or a triangular wave with an equivalent amplitude. Together with the development in the part of signal control and data acquisition, dynamic experimental equipments in the soil dynamics have also developed rapidly and further more, several real earthquakes have been simulated in the large model test such as shaking table tests and centrifuge tests. In Korea, several elementary laboratory tests to simulate the real earthquake load were performed. From these test results, it was reported that the sinusoidal wave cannot reliably reflect the soil dynamic behavior under the real earthquake motion. In this study, 4 types of dynamic motions such as the sinusoidal wave, the triangular wave, the incremental triangular wave and several real earthquake motions which were classified with shock-type and vibration-type were loaded to find something new to explain the change of the excess pore water pressure under the real earthquake load. Through the detailed investigation and comparison on all test results, it is found that the dynamic flow is generated by the soil plastic deformation and the velocity head of dynamic flow is changed the pressure head in the un-drained condition. It can be concluded that the change of the excess pore water pressure is related to the pressure head of dynamic flow. Lastly, a new hypothesis to explain such a liquefaction initiation phenomenon under the real earthquake load is also proposed and verified.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.8 no.2
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• pp.177-186
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• 2003

The influences of horizontal and vertical flow components including the stratification of water column and the wind field on the formation of oxygen-deficient water in summer in Jindong Bay, northern part of Chinhae Bay, were examined. Temperature, salinity and dissolved oxygen in seawater, and direction and velocity of wind were observed in Jindong Bay from March 1998 to February 1999. Low concentration of 5 mg/L in dissolved oxygen (DO) appeared at the bottom layer from May to September. Extremely low DO concentration less than 3 mg/L was investigated in summer (July to August) when stratification was strongest due to abrupt vertical gradients of temperature and salinity in water column. Bottom waters with the extremely low DO concentration were observed even in spring (May to June) at the inner part of the bay. In summer (August to September), the bottom waters with the low DO concentration (less than 5 mg/L) existed at the water depth from 4 to 6 m, being moved upward to the surface layer compared to other seasons. Vertical components of residual flow, calculated by the direction and velocity of wind, in Jindong Bay in summer showed that locally prevailed northerly and westerly wind resulted in downwelling flow at the outer part of the bay and conversely, upwelling at the inner part of the bay. In addition, bottom current at the outer part corresponding to the downwelling area directed to the inner part, probably resulting in a transport of the particulate organic matter settled at the bottom waters to the inner part of the bay. The oxygen-deficient watermass, which was formed at the bottom layer of the inner part, was likely to transported to the surface layer by the upwelling flow.

• The Journal of the Acoustical Society of Korea
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• v.16 no.4
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• pp.21-28
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• 1997

In this study, comparison between Harris-theoretical values and experimental data of load-deflection characteristics in bearing was made. The experiments are conducted under the conditions of the various radial loads and speed of shaft. In the case of non-defective ball bearing, the experimental data agreed well with the Harris-theoretical values for the small steady radial load but not for the large steady radial load. For the radial load bearing, the experimental results show that the stiffness of bearing at the single and multiple defective bearing are bigger in the radial defectiion than in the axial deflection. Load-deflection characteristics for the bearing defect part make it possible to detect the presence of a defect in bearing.

• Journal of the Korean Geotechnical Society
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• v.18 no.1
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• pp.127-132
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• 2002

Shaking table tests are performed on model group piles to investigate the mechanics of dynamic pile-soil interaction, and to evaluate the dynamic group pile effect. Tests are executed on a single pile as well as group piles($3\times3$) by varying a pile spacing from 3D to 8D. A lumped mass is located on top of piles to simulate a superstructure. Dynamic p-y curves of the single pile and the group piles are obtained from the tests and compared with the backbone slopes of API cyclic p-y curves. From the comparisons, dynamic pile group effects are evaluated in terms of a pile spacing, a shaking frequency, and a shaking intensity.

• Journal of the Korea institute for structural maintenance and inspection
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• v.7 no.3
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• pp.167-174
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• 2003

Military facilities with masonry have a great portion in the whole military facilities. But lots of them have been used for more than 20 years, the degree of deterioration of the facilities are serious. Futhermore, as insufficient budget for the facilities maintenance and poor maintenance, the performance of the aged masonry facilities have continually decreased. We suggest a structural performance assessment criteria for the military facility through literature review, interview with experts and questionnaire. The major assessment factors for the structural performance include the inclining and sinking degree of the facilities, durability of materials and resisting force of the structural members.

• Journal of the Korea Society of Computer and Information
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• v.18 no.7
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• pp.23-35
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• 2013

This paper proposes an effective technique that is used to automatically extract feature vectors from vibration signals for fault classification systems. Conventional mel-frequency cepstral coefficients (MFCCs) are sensitive to noise of vibration signals, degrading classification accuracy. To solve this problem, this paper proposes spectral envelope cepstral coefficients (SECC) analysis, where a 4-step filter bank based on spectral envelopes of vibration signals is used: (1) a linear predictive coding (LPC) algorithm is used to specify spectral envelopes of all faulty vibration signals, (2) all envelopes are averaged to get general spectral shape, (3) a gradient descent method is used to find extremes of the average envelope and its frequencies, (4) a non-overlapped filter is used to have centers calculated from distances between valley frequencies of the envelope. This 4-step filter bank is then used in cepstral coefficients computation to extract feature vectors. Finally, a multi-layer support vector machine (MLSVM) with various sigma values uses these special parameters to identify faulty types of induction motors. Experimental results indicate that the proposed extraction method outperforms other feature extraction algorithms, yielding more than about 99.65% of classification accuracy.

• Journal of the Korean Geotechnical Society
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• v.25 no.11
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• pp.27-38
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• 2009

In this study, a series of 1 g shaking table model pile tests were carried out in saturated dense and loose sand to evaluate dynamic p-y curves for various conditions of flexural stiffness of a pile shaft, acceleration frequency and acceleration amplitude for input loads. Dynamic p-y backbone curve which can be applied to pseudo static analysis for saturated dense sand was proposed as a hyperbolic function by connecting the peak points of the experimental p-y curves, which corresponded to maximum soil resistances. In order to represent the backbone curve numerically, empirical equations were developed for the initial stiffness ($k_{ini}$) and the ultimate capacity ($p_u$) of soils as a function of a friction angle and a confining stress. The applicability of a p-y backbone curve was evaluated based on the centrifuge test results of other researchers cited in literature, and this suggested backbone curve was also compared with the currently available p-y curves. And also, the scaling factor ($S_F$) to account for the degradation of soil resistance according to the excess pore pressure was developed from the results of saturated loose sand.

• Journal of the Korean Magnetics Society
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• v.9 no.4
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• pp.190-195
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• 1999

The crystallographic and magnetic properties of the system of $Fe_{1-x}Co_x$(x=0.2 and 0.4) prepared by microwave arc-melting with the maximum power of 3.5 kW and a iron-foil with thickness of 25 ${\mu}{\textrm}{m}$ have been studied by the methods of X-ray diffraction and the measurement of the magnetic hysteresis using the vibrating sample magnetometer at room temperature. The samples were prepared in three different ways: First, pellet form pressed under the pressure of 9,000 N/$\textrm{cm}^2$. Second, the sheet cold rolled. Third, thin sheet treated with the temperature of 90$0^{\circ}C$. The X-ray diffraction pattern of the sample prepared by the first method shows that the crystal structure of the sample is bcc as same as that of Fe with a good uniformity. The iron-foil has the coercivity of 43 Oe and the initial slope of magnetization of 0.328 emu/gOe. The coervicity and magnetization of the sample prepared by the second method increased as the Co content increased. But the initial slop of the magnetization decreased as the Co content increased. This means that the displacement of domain wall is suppressed by the increases of coercivity as the Co content increased. The saturation magnetization of the samples made by the third method increased. On the other hand, the coercivity of these samples decreased. The increase of saturation magnetization of the samples seems to be related to the changes in X-ray intensity after heat treatment. Also some magnetic parameters of the samples were calculated by using a simple model and compared with other values.

• Applied Chemistry for Engineering
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• v.26 no.3
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• pp.336-340
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• 2015

Three different types of polycarbonate (PC)/graphene oxide (GO) composites using diphenyl carbonate as a monomer were fabricated by melt polymerization. Those were the PC/GO composite (PC/GO) using a twin extruder, in-situ PC/GO composite (PC/GO-cat.) using a catalyst, and in-situ PC/GO composite (PC/GO-COCl) using a GO-COCl treated by -COCl, Chemical structures of the composites were confirmed by C-H and C=O stretching peak at $3000cm^{-1}$ and $1750cm^{-1}$, respectively. The slope for the storage (G') versus loss (G") modulus plot decreased with an increase in the heterogeneous property of polymer melts. So we can check the GO dispersion of the PC/GO composites using by the slop for G'-G" plot. According to the G'- G" slopes for three different types of PC/GO composites, GO was well dispersed within PC matrix in case of PC/GO and PC/GO-cat.. It was also confirmed by atomic force microscope (AFM) photos. One of the reasons for the poor GO dispersion of PC/GO-COCl is branching and crosslinking processes occurred during polymerization, which was further confirmed by a plot for the complex modulus versus phase difference.

• Korean Journal of Optics and Photonics
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• v.13 no.2
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• pp.140-145
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• 2002

We measured the absorption rate of a Nd:YVO$_4$crystal with a thickness of 1 mm and the output power characteristics of a cw Nd:YVO$_4$/KTP laser with respect to the change of wavelength and the polarizations of a tunable Ti:sapphire pump laser with a linewidth of 0.2 nm. In the case of S-polarization (E┴$\pi$) and P-polarization (E∥$\pi$) of a pump laser, the maximum absorption rate of the crystal was 82% at 809.4 nm and 98% at 808.8 nm, and slope efficiencies for the output power of the Nd:YVO$_4$laser (1064 nm) were 43% and 52%, respectively. The maximum Nd:YYO$_4$laser output power of 516 mW was obtained from the P-polarization pump laser of 1000 mW. As a result of an intracavity frequency-doubling, slope efficiency for the output power of the Nd:YVO$_4$/KTP green laker (532nm) was 23% and the maximum output power of 205 mW with the beam quality (M$^2$) of 1.42 was obtained from the P-polarization pump laser of 1000 mW.