• ETRI Journal
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• v.20 no.1
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• pp.16-27
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• 1998

In this paper, we consider the acquisition performance of an IS-95 reverse link access channel slot as a function of system design parameters such as postdetection integration length and the number of access channel message block repetitons. The uncertainty region of the reverse link spreading codes compared to that of forward link is very small, since the uncertainty region of the reverse link is determined by a cell radius. Thus, the parallel acquisiton technique in the reverse link is more efficient than a serial acquisition technique in terms of implementation and of acquisition time. The parallel acquisition is achieved by a bank of N parallel I/Q noncoherent correlator are analyzed for band-limited noise and the Rayleigh fast fading channel. The detection probability is derived for multiple correct code-phase offsets and multipath fading. The probability of no message error is derived when rake combining, access channel message block combining, and Viterbi decoding are applied. Numerical results provide the acquisition performance for system design parameters such as postdetection integration length and number of access channel message block repetitions in case of a random access on a mobile station.

• Journal of Positioning, Navigation, and Timing
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• v.3 no.2
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• pp.37-44
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• 2014

The most effective method to overcome GPS jamming problem is to use an adaptive array antenna which has the capability of beamforming or nulling to a certain direction. In this paper, Space Time Adaptive Processing (STAP) beamforming algorithm of four elements array antenna will be designed and the anti-jamming performance will be analyzed. According to the analysis, the signal to noise ratio (SNR) and anti-jamming performance can be enhanced by beamforming algorithm. Also, the time tap effect of STAP algorithm will be analyzed theoretically and verified with array antenna modeling and simulation. Specially, the cautious selection of reference time tap in STAP can prevent the degradation of position accuracy performance.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.167-169
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• 2003

This paper presents a theoretical study concerning multibubble dynamics in a sound field and the numerical validation for it by employing our new CFD code MTS-DiCUP. In recent papers, the author has shown theoretically that an unknown characteristic frequency, named 'transition frequency,' exists in a multibubble system. For a N -bubble case, up to 2N -1 transition frequencies per bubble have been predicted, only N ones of them correspond to the natural frequencies of the system. The transition frequencies that do not correspond to the natural frequencies give rise to the phase reversal of bubbles' pulsation without resonant response. In this paper, it has been suggested theoretically that those transition frequencies may cause the sign reversal of the secondary Bjerknes force, which is an interaction force acting between acoustically coupled gas bubbles. This theoretical result has been validated by the direct numerical simulation, at least in a qualitative sense.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.233-234
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• 2003

Fly ash enters axial compressor when a turbomachinery is operated in an adverse environment. We have numerically investigated erosion of the blade and shroud in the turbulent compressor passage flow under the influence of gas-particle two-phase interaction. There have appeared quasi-three dimensional calculations on this subject but not the complete three-dimensional gas-particle interaction as done in the present work. Lagrangian particle tracing technique is used on the base of parallel processing for efficient calculation. Accuracy of the present code is tested using the benchmark lPL nozzle. In the DFVLR compressor blades, we have shown that a large number of particles passing through the tip clearance make impact on the blade tip and on the shroud. Higher degree of erosion is resulted by the heavier particles due to the centrifugal force.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.203-204
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• 2003

Fly ash enters axial compressor when a turbomachinery is operated in an adverse environment. We have numerically investigated erosion of the blade and shroud in the turbulent compressor passage flow under the influence of gas-particle two-phase interaction. There have appeared quasi-three dimensional calculations on this subject but not the complete three-dimensional gas-particle interaction as done in the present work. Lagrangian particle tracing technique is used on the base of parallel processing for efficient calculation. Accuracy of the present code is tested using the benchmark JPL nozzle. In the DFVLR compressor blades, we have shown that a large number of particles passing through the tip clearance make impact on the blade tip and on the shroud. Higher degree of erosion is resulted by the heavier particles due to the centrifugal force.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.479-486
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• 2010

Using the numerical code for the interior ballistics, the performance of the interior ballistics with the characteristics according to the position of the solid propellant in chamber has been investigated. In existing research, propellants have been evenly distributed in the chamber. In this study, however, several cases of the existence of empty space in the chamber at which the propellants are not evenly distributed are considered. The 7-perforated propellant configuration has been used in this research. The results have shown the change of performance of the interior ballistics according to solid propellant positions in the chamber.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.464-467
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• 2010

Ice accretion on aircraft surface in icing condition induces external shape changes that may result in a hazard factor for aircraft safety. In case of aircraft main wing with high lift equipment, ice accretion is observed around leading edge and flap. During the design phase, location of ice accretion and associated aerodynamic characteristics must be investigated. In this study, icing effects on aerodynamic characteristics of the main wing section of KC-100 aircraft are investigated using an Eulerian-based FENSAP-ICE code in various icing conditions.

• Journal of computational fluids engineering
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• v.15 no.4
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• pp.17-24
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• 2010

Using the numerical code for the interior ballistics, the performance of the interior ballistics with the characteristics according to the position of the solid propellant in chamber has been investigated. In existing research, propellants have been evenly distributed in the chamber. In this study, however, several cases of the existence of empty space in the chamber at which the propellants are not evenly distributed are considered. The 7-perforated propellant configuration has been used in this research. The results have shown the change of performance of the interior ballistics according to solid propellant positions in the chamber.

• Journal of computational fluids engineering
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• v.18 no.2
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• pp.41-48
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• 2013

Ice accretion on the solid surface is an importance factor in assessing the performance of aircraft and wind turbine blade. Changes in the external shape due to ice accretion can greatly deteriorate the aerodynamic performance. In this study, a three-dimensional upwind-type second-order positivity-preserving finite volume CFD scheme based on the unstructured mesh topology is developed to simulate two-phase flow in atmospheric icing condition. The code is then validated by comparing with NASA IRT experimental data on the sphere. The present results of the collection efficiency are found to be in close agreement with experimental data and show improvement near the stagnation region.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.11a
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• pp.219-222
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• 1999

A method for numerical simulation of the carbonization process in manufacturing of a carbon-carbon composite is developed. A general theory, which consists of analyses of heat and mass transfer together with stress and displacement predictions, is constructed. A homogeneous, single phase, isotropic material is selected and a computer program is developed for an arbitrary 2-dimensional geometry using FEM. Material properties are obtained through experiments and references, and are modeled effectively to serve the simulation purpose. The validity of the simulation is verified through several comparisons with experimental data, where close agreements are observed. Finally, examples of actual applications are considered to exhibit the capability and utilization of the code in process optimization.