• Economic and Environmental Geology
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• v.36 no.3
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• pp.213-223
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• 2003

We estimated the Moho depth of Korean Peninsula from gravity anomalies and digital elevation model. The satellite radar altimetry-derived global free-air gravity model was used to ensure the homogeneity in both data and frequency domains of the original data. Two different methods were implemented to calculate the Moho depth; the wavenumber correlation analysis (Kim et al., 2000a) and the power spectrum analysis. The former method calculates depth-to-the-Moho by correlating topographic gravity effect with free-air gravity anomaly in the wavenumber domain under the assumption that the study area is not isostatically compensated. The latter one, on the other hand, considers the different density layers (i.e., Conrad and Moho), using complete Bouguer gravity anomaly in the Frequency domain of the Fourier transform. The correlation coefficient of the two Moho model is 0.53, and methodology and numerical error are mainly responsible for any mismatch between the two models. In order to integrate the two independentely-estimated models, we applied least-squares adjustment using the differenced depth. The resultant model has mean and standard deviation Moho depths of 32.0 km and 2.5 km with (min, max) depths of (20.3, 36.6) kms. Although this result does not include any topographic gravity effect, however, the validity of isostasy and the role of local stress field in the study area should be further studied.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.39-44
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• 2001

The thermocapillary flow in a differentially heated cylindrical liquid bridge under steady rotation of the hot disk is considered in the limit of zero capillary number. Steady flow states and their three-dimensional stability are calculated numerically. A linear stability analysis reveals that the most dangerous perturbations are oscillatory with azimuthal wavenumber m=1 or m=2 depending on the parameters.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.313-320
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• 2003

Synthetic seismograms recorded with a logging-while-drilling (LWD) tool in the presence of slow formation are computed by the discrete wavenumber method. Monopole, dipole, and quadrupole logging tools are simulated with a source center frequency of 4 kHz. The modes in the responses are identified and characterized with time and frequency semblance plots. Numerical results show that, to obtain the formation shear velocity, we need to correct the peak velocities of the multipole modes in the semblance plots by using analytical dispersion curves.

• The Journal of the Acoustical Society of Korea
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• v.34 no.5
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• pp.360-370
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• 2015

In case that an infinite length waveguide structure is connected with a finite length structure, it is required to combine a wave approach for the waveguide structure and a modal approach for the finite length structure to investigate the dynamic response of the connected target structure. In this study, the wavenumber finite element (WFE) analysis is adopted for the infinite length waveguide substructure and a finite element (FE) method is applied for the finite length substructure and then their results are coupled in terms of the impedance or mobility at the connected points between the substructures. As a structural model, an infinite length cylindrical shell with a rectangular plate inside is regarded. These two substructures are connected at the four corner points of the plate, rigidly or resiliently. From this investigation, it was confirmed that the wave approach (WFE method) and modal approach (FE method) can be combined by the impedance coupling.

• The Journal of the Acoustical Society of Korea
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• v.43 no.1
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• pp.131-137
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• 2024

Aerodynamic noise generated by the surrounding flow of a train traveling at high speed affects both outdoor and indoor noise. This study's goal is to develop a test method to measure and quantitatively evaluate aerodynamic noise through pressure perturbation data on the train surface. To accurately evaluate aerodynamic noise, it is important to separate and evaluate the compressive and incompressible pressure fluctuations mixed in the acquired surface pressure fluctuation data. This is because the noise transmission characteristics of the two pressure fluctuations are different. First, the installation length and interval of the microphone were determined to acquire surface pressure fluctuation data, and wavenumber-frequency analysis was performed to separate incompressible pressure fluctuation and compressible pressure fluctuation to obtain a sound pressure level spectrum. Finally, as a result of comparing the test results measured in the train head and trail, It was confirmed that the pressure fluctuation on the train head surface was greater than that on the tail.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.771-775
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• 2006

There has been much effort to find suitable methods for structural analysis in the mid-frequency region where traditional low frequency methods have increasing uncertainties whilst statistical energy analysis is not strictly applicable. Systems consisting of relatively stiff beams coupled to flexible plates have a particularly broad mid-frequency region where the beams support only a few modes whilst the plate has a high modal density and modal overlap. A system of two parallel beams coupled to a plate is investigated based on the wave method, which is an approximate method. The wave model is extended from a single-beam-plate system, to a plate with two identical beams which is modelled using a symmetric-anti symmetric technique. Experimental results such as powers and energy ratios show the validity of the analytical wave models.

• Atmosphere
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• v.16 no.4
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• pp.303-318
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• 2006

A parameterization of gravity wave drag induced by cumulus convection (GWDC) proposed by Chun and Baik is implemented in the KMA operational global NWP model (GDAPS), and effects of the GWDC on the forecast for July 2005 by GDAPS are investigated. The forecast result is compared with NCEP final analyses data (FNL) and model's own analysis data. Cloud-top gravity wave stresses are concentrated in the tropical region, and the resultant forcing by the GWDC is strong in the tropical upper troposphere and lower stratosphere. Nevertheless, the effect of the GWDC is strong in the mid- to high latitudes of Southern Hemisphere and high latitudes of Northern Hemisphere. By examining the effect of the GWDC on the amplitude of the geopotential height perturbation with zonal wavenumbers 1-3, it is found that impact of the GWDC is extended to the high latitudes through the change of planetary wave activity, which is maximum in the winter hemisphere. The GWDC reduces the amplitude of zonal wavenumber 1 but increases wavenumber 2 in the winter hemisphere. This change alleviates model biases in the zonal wind not only in the lower stratosphere where the GWDC is imposed, but also in the whole troposphere, especially in the mid- to high latitudes of Southern Hemisphere. By examining root mean square error, it is found that the GWDC parameterization improves GDAPS forecast skill in the Southern Hemisphere before 7 days and partially in the Northern Hemisphere after about 5 days.

• 보존과학연구
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• s.32
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• pp.89-98
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• 2011

It is quite difficult to identify its corrosion compound because they have a wide variety of crystal structures and they are mixed with two component. This study was conducted with the standard iron corrosion compounds through the analysis by Raman Micro-Spectroscopy, which aims to obtain standard Raman Data. To assess the reliability of standard iron corrosion compounds, SEM-EDS analysis and XRD analysis were conducted. Through SEM-EDS analysis, the elements of corrosion compound matched with those of standards iron corrosion compounds except Goethite. XRD analysis showed that the structures of corrosion compounds were identical to those of standard iron corrosion compounds, however, it was identified that Iron sulfate ($FeSO_4{\cdot}6H_2O$) is the Rozenite ($FeSO_4{\cdot}4H_2O$). Through Raman Micro-Spectroscopy analysis, the new peak was detected from the wavenumbers of hydroxide and iron oxide. It is considered that it is due to changes in the wavelength of the laser. As the wavenumbers of iron chloride and iron sulfate have been identified, eight kinds of Raman Data were obtained. It can be considered to contribute to cultral heritage for iron objects that Raman Micro-Spectroscopy analysis which is relatively easy to compare material properties and structures can be highly applicable to the research on cultural heritage with the limited amount of samples.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.10
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• pp.2426-2436
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• 1993

Vibration characteristics of a tire play an important role to judge a ride conformability and sound quality for a passenger car. In this study, the experimental investigation for the sound radiation of a radial tire has been examined. Based on the sound intensity techniques, the sound pressure field and the sound radiation are measured. It turns out that air pressure in tire, tread patterns, and aspect ratio of the tire govern the sound radiation characteristics. Then a numerical analysis for the tire element is conducted. During analysis, the tire element is modelled as an elastic ring. The comparison shows that the numerical output correlates to the experimental data.

• Structural Engineering and Mechanics
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• v.54 no.4
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• pp.623-648
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• 2015

A numerical approach is presented for the analysis of the forced vibration of a rigid surface foundation with arbitrary shape. In the analysis, the foundation is discretized into a number of sub squaree-lements. The dynamic response within each sub-element is described by the Green's function, which is obtained by the Fourier-Bessel transform and Precise Integration Method (PIM). Incorporating the displacement boundary condition and force equilibrium of the foundation, it obtains a system of linear algebraic equation in terms of the contact forces within each sub-element. Solving the equation leads to the desired dynamic impedance functions of the foundation. Numerical results are obtained for foundation not only with simple geometrical configurations, such as rectangular and circular foundation, but also the case of irregularly shaped foundation. Several comparisons between the proposed approach and other methods are made. Very good agreement is reached. Also, parametric studies are carried out on the dynamic response of foundation. Addressed in this study are the effects of Poisson's ratio, material damping and contact condition of soil-foundation interface. Several conclusions are drawn the significance of the factors.