• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.28 no.3
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• pp.361-367
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• 2010

We produced continuous vertical time series of 14 permanent GPS stations operated by National Geographic Information Institute by processing about five years of data. Then we computed the height velocities by using a linear regression fitting of those time series, and did principal component analysis to understand the overall characteristics of the series. The prominent signal obtained as the first mode of PCA results showed an average of 4.2 mm/yr vertical velocity. The values of the first mode eigenvectors were consistent at all sites. Thus, we concluded that all the 14 stations are uplifting nearly at the same velocity for the test period. Then changes of precision before and after removing the first mode signal from the 14 height time series were analyzed. As a result, the precision improved 34.8% on average.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.3 no.1
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• pp.3-10
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• 1992

Flux-drive waveguide phase shifter is designed by twin-slab model. Measured differential phase shifts are smaller than the theoretical values by 8-9 percents. Measured insertion loss and VSWR of the phase shifter using TT73-2200 ferite are less than 0.45dB and 1.25 respectively, within pass band. The phase shifter using double-setup transformer shows wider bandwidth characteristics. Finally the reduced-height waveguide phase shifter using TT3-2900 ferrite shows very efficient suppression of higher-oreder modes.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.3 no.3
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• pp.73-80
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• 2010

Complex-valued blind algorithms which are based on constant modulus error and Euclidian distance (ED) between two probability density functions show relatively poor performance in spite of the advantages of information theoretic learning since the inherent characteristics of the constant modulus error prevent the algorithm from coping with the symbol phase rotation caused by the complex channels. In this paper, we show that the symbol phase rotation problem can be avoided and the advantages of information theoretic learning can be preserved by introducing decision-directed mode to the blind algorithm whenever the equalizer output power lies in the neighborhood of multi-modulus levels. Simulation results through MSE convergence and constellation comparison for severely distorted complex channels show significantly enhanced performance of symbol-point concentration and no phase rotation problems caused by the complex channel models.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.10
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• pp.1968-1976
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• 2007

This paper proposes a hybrid pseudo-noise (PN) code acquisition scheme for Multicarrier Direct Sequence - Code Division Multiple Access (MC DS-CDMA) mobile communication systems on the code acquisition performance for Nakagami-m fading channel. The hybrid acquisition scheme combines parallel search with serial search to cover the whole uncertainty region of the input code phase. It has a much simpler acquisition hardware structure than the total parallel acquisition and can achieve the mean acquisition time (MAT) slightly inferior to that of the total parallel acquisition. The closed-form expressions of the detection and false-alarm probabilities are derived.

• Journal of the Korean Geotechnical Society
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• v.33 no.1
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• pp.79-91
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• 2017

An experimental study has been conducted by using the Cyclic Direct Simple Shear apparatus to evaluate the influence of average and cyclic shear stresses on the undrained shear failure behavior of marine silty sand considering various relative densities. The obtained results show that despite using different relative densities, similar trends were gained in the cyclic shear deformation. Moreover, the cyclic shear deformation is affected mainly by the average and cyclic shear stresses. The number of cyclic loads for failure is significantly affected by the cyclic shear stress ratio and relative density, and is less affected by the average shear stress ratio. The proposed three-dimensional stress-dependent failure contour can be used effectively to assess the soil shear strength considering various relative densities in the design of foundation used for offshore structures.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.11
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• pp.1950-1956
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• 1997

An engineering goal in vibration and noise professionals is to develope quiet machines at the preliminary design stage, and various numerical techniques such as FEM, SEA or BEM are one of the schemes toward the goal. In this paper, the research has been focused on the sensitivity effect of mesh sizes for FEM application so that the optimum size of the mesh that leads to engineering solution within acceptable computing time could be generated. In order to evaluate the mesh size effect, three important parameters have been examined : natural frequencies, number of modes and driving point mobility. First, several lower modes including the fundamental frequency of a 2-D plate structure have been calculated as mesh size changes. Since theoretical values of natural frequencies for a simple structure are known, the deviation between the numerical and theoretical values is obtained as a function of mesh size. The result shows that the error is no longer decreased if the mesh size becomes a quarter wavelength or smaller than that. Second, the mesh size effect is also investigated for the number of modes. For the frequency band up to 1.4 kHz, the structure should have 38 modes in total. As the mesh size reaches to the quarter wavelength, the total count in modes approaches to the same values. Third, a mobility function at the driving point is compared between SEA and FEM result. In SEA application, the mobility function is determined by the modal density and the mass of the structure. It is independent of excitation frequencies. When the mobility function is calculated from a wavelength to one-tenth of it, the mobility becomes constant if the mesh becomes a quarter wavelength or smaller. We can conclude that dynamic parameters, such as eigenvalues, mode count, and mobility function, can be correctly estimated, while saving the computing burden, if a quarter wavelength (.lambda./4) mesh is used. Therefore, (.lambda./4) mesh is recommended in structural vibration analysis.

• The Journal of the Acoustical Society of Korea
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• v.19 no.6
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• pp.17-22
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• 2000

Statistical Energy Analysis(SEA) is an efficient tool to predict the broadband noise and vibration for the huge and complex structures such as aircraft and ships. To estimate the noise and vibration by using SEA accurately, the characteristics of SEA parameters associated with fluid loading have to be investigated. In this report, the fluid loaded coupling loss factors were calculated for an 'L' and 'T' type line connections and compared to the ones without fluid loading. Then, the vibration levels for steel box model with 'L' and 'T' type line connection were computed using the fluid loaded and no fluid loaded coupling loss factors, respectively. As a result, the calculated vibration levels of the model using the fluid loaded coupling loss factors were lower than those without fluid loading. As a conclusion, it is necessary to use the fluid loaded coupling loss factors for increasing the prediction accuracy on the noise and vibration of immersed structures.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.258-264
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• 2012

The overall aim of this paper is to determine coupling loss factor of welding point between shell and cylinder using loss factor and structural loss factor. For this purpose, two kinds of loss factor were adopted. One is loss factor of each sub structure, another is structural loss factor based on the complex welded or assembled structure. Using these two parameters, it is possible to derive the coupling loss factor which represents characteristic condition of SEA theory. Coupling loss factor of conjunction in complex structure was expressed as power balance equation. The derived equation for a coupling loss factor has been simplified on the assumption of one way (uni-directional) power flow between multi-sub structures. Using these conditions, it is possible to find the equation of coupling loss factor expressed as above two loss factors. To check the effectiveness of above equation, this paper used two-stage application. The first approach was application between simple cylinder and shell. The next was adopted rotary compressor. Rotary compressor has three main conjunctions between shell and internal vibration part. This equation was applied to find out the optimum welding point with respect to reduce the noise propagation. It shows the effective tool to evaluate the coupling loss factor in complex structure.

• Journal of the Korean Wood Science and Technology
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• v.27 no.3
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• pp.1-6
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• 1999

European spruce and maple were to be estimated as raw material of violin family instruments with linear modal analysis to provide the information data for the design of their bodies. Wood specimens cut in different direction were excited by impact hammer to measure the resonant frequency with typical vibrational modes. In spite of lower density than maple, European spruce showed the excellent acoustical properties with higher resonant frequency. And edge-grained spruce had more even frequencies than flat-grained ones to be more acceptable as front plate of violin. Resonant frequency was positively correlated with wood density of each specimen and the coefficients of edge-grained specimens were higher than those of flat-grained specimens of both wood species.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.4B
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• pp.183-190
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• 2007

The cdma2000 mobile network covers a wide area but its characteristics are high cost and low bandwidth. On the other hand, WLAN covers a small area like a hot spot area but its characteristics are large bandwidth and low cost. Thus we can provide efficient services when we employ an integration network between WLAN and cdma2000 mobile networks. In this paper, we propose an integration scheme between WLAN and cdma2000 mobile networks. In addition, we design and implement the dual mode terminal which receives seamless data services in the integrated network. The proposed dual mode terminal manages connections by monitoring the signal strength of WLAN and selecting a proper network. We validate the functions through the implementation of VOD and show the effectiveness through the performance measurement.