• Journal of information and communication convergence engineering
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• v.6 no.2
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• pp.129-133
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• 2008

In this paper, modified power control algorithms are proposed for a satellite mobile communications system with ATC (ancillary terrestrial component). In order to increase system capacity and reduce the transmitting power of the user's equipment, we propose the modified power control scheme consisting of the modified closed-loop and open-loop power control. The modified CLPC (closed-loop power control) algorithm, combining the delay compensation algorithms and pilot diversity, is mainly applied to the ATC link in urban areas because it is more suitable to the short RTD (round-trip delay). In the case of rural areas where ATCs are not deployed or a signal is not received from ATCs, combining monitoring transmitting power equipment and OLPC (open-loop power control) algorithms using an efficient pilot diversity is mainly applied to the link between the user's equipment and the satellite. Two power control algorithms are applied equally to the boundary areas where two kinds of signals are received in order to ensure coverage continuity. The simulation results show that the modified power control scheme has good performance compared to conventional power control schemes in a GEO (geostationary earth orbit) satellite system with ATC.

• Earthquakes and Structures
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• v.8 no.1
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• pp.275-304
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• 2015

The objective of this paper is to investigate the validity of transmitting boundaries in dynamic analysis of soil-structure interaction problems. As a case study, the proposed Baghdad metro line is considered. The information about the dimensions and the material properties of the concrete tunnel and surrounding soil were obtained from a previous study. A parametric study is carried out to investigate the effect of several parameters including the peak value of the horizontal component of earthquake displacement records and the frequency of the dynamic load. The computer program (Mod-MIXDYN) is used for the analysis. The numerical results are analyzed for three conditions; finite boundaries (traditional boundaries), infinite boundaries modelled by infinite elements (5-node mapped infinite element) presented by Selvadurai and Karpurapu, 1988), and infinite boundaries modelled by dashpot elements (viscous boundaries). It was found that the transmitting boundary absorbs most of the incident energy. The distinct reflections observed for the "fixed boundaries" disappear by using "transmitted boundaries". This is true for both cases of using viscous boundaries or mapped infinite elements. The type and location of the dynamic load represent two controlling factors in deciding the importance of using infinite boundaries. It was found that the results present significant differences when earthquake is applied as a base motion or a pressure load is applied at the surface ground. The peak value of the vertical displacement at nodes A, B, E and F (located at the tunnel's crown and side walls, and at the surface above the tunnel and at the surface 6.5 m away from tunnel's centre respectively) increases with the frequency of the surface pressure load for both cases 1 and 2 (traditional boundaries and mapped infinite elements respectively) while it decreases for case 3 (viscous boundaries). The modular ratio Ec/Es (modulus of elasticity of the concrete lining to that of the surrounding soil) has a considerable effect on the peak value of the horizontal displacement at node B (on the side wall of the tunnel lining) increase about (17.5) times, for the three cases (1, 2, and 3).

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.39 no.6
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• pp.623-629
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• 2002

In transmitting compressed video bit-stream over Internet, packet losses cause error propagations in both spatial and temporal domains, which in turn leads to severe degradation I image quality. In this paper, a new error concealment algorithm, called EBMA(Edge Detection based Boundary Matching Algorithm), is proposed to repair damaged portions of the video frames in the receiver. Conventional BMA(Boundary Matching Algorithm) assumes that the pixels on the boundary of the missing block and its neighboring blocks are very similar, but has no consideration of edges across the boundary. In our approach, the edges are detected across the boundary of the lost or erroneous block. Once the orientation of each edge is found, only the pixel difference along the expected edges across the boundary is measured instead of the calculation of difference along the expected edges across the boundary is measured instead of the calculation of differences between all adjacent pixels on the boundary Therefore, the proposed approach needs very few computations and the experiment shows and improvement of the performance over the conventional BMA in terms of both subjective and objective quality of video sequences.

• Journal of Korean Society for Atmospheric Environment
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• v.25 no.5
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• pp.450-458
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• 2009

The range-dependent overlap factor of a lidar system can be determined experimentally if a Raman backscatter signal by molecule is measured in addition to the usually observed elastic backscatter signal, which consists of a molecular component and a particle component. The direct determination of the overlap profile is presented and applied to a lidar measurement according to variation of telescope field-of-view and distance between telescope and transmitting laser. The retrieval of extinction coefficient by Raman method can generate high errors for heights below planetary boundary layer if the overlap effect is ignored. The overlap correction method presented here has been successfully applied to experimental data obtained in Gwangju, Korea.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2005.03a
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• pp.47-51
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• 2005

If a structure is founded on the ground saturated with pore water, then the ground should be modeled as a saturated two-phase porous medium for accurate earthquake response analysis. In this study, an axisymmetric transmitting boundary hyperelement is developed for modeling of far field of the ground using u-U formulation for water-saturated transversely isotropic layered stratum. The developed hyperelement is verified by comparing the dynamic stiffness of rigid circular foundation on water-saturated isotropic layered stratum with the case of using equivalent single-phase medium model.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.4
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• pp.355-361
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• 2012

This paper presents an experimental study on the detection and location of nonlinear scattering source due to the presence of fatigue crack in a laboratory specimen. The proposed technique is based on a combination of nonlinear elastic wave spectroscopy(NEWS) and time reversal(TR) focusing approach. In order to focus on the nonlinear scattering position due to the fatigue crack, we employed only one transmitting transducer and one receiving transducer, taking advantage of long duration of reception signal that includes multiple linear scattering such as mode conversion and boundary reflections. NEWS technique was then used as a pre-treatment of TR for spatial focusing of reemitted second harmonic signal. The robustness of this approach was demonstrated on a cracked specimen and the nonlinear TR focusing behavior is observed on the crack interface from which the second harmonic signal was originated.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.578-581
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• 2004

In this paper numerical and experimental studies are conducted to examine the wave screening effectiveness of wave barriers. The numerical study is based on a finite element model of a 'sandbox' with Lysmer-Kuhlemeyer-type absorbing boundaries. Using the model, the screening effectiveness of wave barriers is studied for different barrier dimensions and distances between the source/receiver and the wave barrier. The results of the numerical modeling are compared with those of the ultrasonic experiment which is performed on an acrylic block with a drilled rectangular cut. Finally, the problem of ground transmitting vibration from a traveling train is numerically treated as a real-world application and the results are discussed in some detail.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.6
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• pp.569-577
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• 2012

In this study, a theoretical investigation of optimized sleeper spacing which can suppress resonances of a railway track is attempted. To achieve this, we introduced a minimization problem in which the objective function is given by the wave transmittance and the design variable is defined by sleeper distribution. In the analysis the rail is modeled by a Timoshenko beam and the sleeper is represented by a mass. The infinite track analysis is realized by attaching the transmitting boundaries at both ends of the finite optimization region. Through numerical analyses the sleeper spacing effective in reduction of the transmittance is discussed. Furthermore, the feasibility of the proposed method is validated in the aspect of vibration reduction through response analyses for a harmonic load.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.2
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• pp.111-117
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• 2008

The effect of characteristics of ground and circular foundation on the dynamic behavior of the foundation in vertical motion are considered using an approximated analytical solution and a finite element analysis with absorbing (consistent transmitting) boundary. The shear wave velocity of homogeneous ground affects the resonant frequency of the foundation much but has nothing to do with the maximum response amplitude at resonant frequency. The density in this case affects both the resonant frequency and the maximum response. The size and the mass of the circular foundation are related both to the resonant frequency and the maximum response. However, Poisson's ratio has very little effect on dynamic behavior of the foundation. When the ground is not homogeneous but has the layers, different formations of shear wave velocities would also change the maximum response at resonant frequency.

• Journal of the Korean Geotechnical Society
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• v.22 no.9
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• pp.37-43
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• 2006

Dynamic numerical analysis of geotechnical problems requires a way to simulate the decrease of energy as the domain of interest gets larger. This phenomenon is usually referred to as radiation damping or geometric attenuation and it is distinguished from material damping in which elastic energy is actually dissipated by viscous, hysteretic, or other mechanism. The fact that the domain of analysis in numerical modeling must be chosen, however, causes a need for special attention at the boundary. This observation leads directly to the idea of determining the dynamic response of the interior region from a finite model consisting of the interior region subjected to a boundary condition which ensures that all energy arriving at the boundary is absorbed. This paper presents a simple methodology to simulate transmitting boundaries condition using viscoelastic infinite elements within the recently developed "OpenSees" finite element code. The methodology used here provides that the level of absorption for traveling waves is efficient enough for practical purposes, but unsatisfactory for the case of sharp incident angles. The effectiveness of the infinite elements for the absorption of incident waves at boundaries is evaluated via example analysis.