• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.1
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• pp.24-31
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• 2006

In the present study, a strongly coupled analysis code is developed for transonic flutter analysis. For aerodynamic analysis, two dimensional Reynolds-Averaged Navier-Stokes equation was used for governing equation, and ε-SST for turbulence model, DP-SGS(Data Parallel Symmetric Gauss Seidel) Algorithm for parallelization algorithm. 2 degree-of-freedom pitch and plunge model was used for structural analysis. To obtain flutter response in the time domain, dual time stepping method was applied to both flow and structure solver. Strongly coupled method was implemented by successive iteration of fluid-structure interaction in pseudo time step. Computed results show flutter speed boundaries and limit cycle oscillation phenomena in addition to typical flutter responses - damped, divergent and neutral responses. It is also found that the accuracy of transonic flutter analysis is strongly dependent on the methodology of fluid-structure interaction as well as on the choice of turbulence model.

• Journal of Positioning, Navigation, and Timing
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• v.12 no.3
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• pp.215-228
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• 2023

The State Space Representation (SSR) method provides individual corrections for each Global Navigation Satellite System (GNSS) error components. This method can lead to less bandwidth for transmission and allows selective use of each correction. Precise Point Positioning (PPP) - Real-Time Kinematic (RTK) is one of the carrier-based precise positioning techniques using SSR correction. This technique enables high-precision positioning with a fast convergence time by providing atmospheric correction as well as satellite orbit and clock correction. Currently, the positioning service that supports PPP-RTK technology is the Quazi-Zenith Satellite System Centimeter Level Augmentation System (QZSS CLAS) in Japan. A system that provides correction for each GNSS error component, such as QZSS CLAS, requires monitoring of each error component to provide reliable correction and integrity information to the user. In this study, we conducted an analysis of the performance of residual error bounding for each error component. To assess this performance, we utilized the correction and quality indicators provided by QZSS CLAS. Performance analyses included the range domain, dispersive part, non-dispersive part, and satellite orbit/clock part. The residual root mean square (RMS) of CLAS correction for the range domain approximated 0.0369 m, and the residual RMS for both dispersive and non-dispersive components is around 0.0363 m. It has also been confirmed that the residual errors are properly bounded by the integrity parameters. However, the satellite orbit and clock part have a larger residual of about 0.6508 m, and it was confirmed that this residual was not bounded by the integrity parameters. Users who rely solely on satellite orbit and clock correction, particularly maritime users, thus should exercise caution when utilizing QZSS CLAS.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.5
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• pp.558-565
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• 2013

In this paper, modeling and simulation for performance analysis of high resolution SAR system has been carried out in the time, frequency and numeric domain using ADS Ptolemy simulation tool of Agilent corporation. SAR system consists of antenna, controller and transceiver. Error parameters affecting SAR system performances have been defined, modeled and simulated such as phase noise of frequency synthesizer, amplitude and phase characteristic of TWTA, sampling frequency of waveform generator and I/Q imbalance. Finally, the development requirements of SAR system based on the impulse response function have been derived.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.2
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• pp.313-321
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• 2000

This paper deals with a kind of the half-space interfacial problem in time domain, requiring the calculation of the horizontal electric field generated by a tiny impulsive current source located horizontally at the interface between an isotropic upper half-space and a uniaxially anisotropic lower half-space. With the Cagniard-de-Hoop method adapted for our interfacial case, we obtain the explicit-form solution for this electric field. We also investigate the impulse radiation in the radial direction. The impulse components of Dirac $\delta$-function type in transient waveforms are important for the understanding of the interfacial far-field characteristics. The uniaxial case is a generalization of the isotropic one, and the explicit solutions of the uniaxial problem in this paper reduce to the solutions of the isotropic problem if the anisotropy is removed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.8
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• pp.909-922
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• 2012

To fully utilize scarce spectrum resource, it's necessary to develop and evaluate promising business models prior to making technology R&D plan and industrial promotion policy. The purpose of this paper is to design potential business models, evaluate the propriety of commercializing the models, and discuss promotion policies after exploring promising sectors consuming spectrum resources. The research is based on TV white space, which is vacant TV channels in region or time domain and considered as core spectrum resource along with digital terrestrial television switchover. As the result, four kinds of business models were derived, including broadcasting and telecommunication types. Each model was discussed from four standpoints: customer value proposition, profit formula, key resources, and key processes, and the propriety for commercialization was evaluated by three dimensions: technological evaluations, business-oriented evaluations, and user-oriented evaluations. The promotion policies of government and market participants for the activation of TV White space-based business models were discussed as well.

• Journal of computational fluids engineering
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• v.15 no.2
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• pp.35-40
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• 2010

In the present work, LES with new variational multiscale method is conducted on the fully developed channel flow with Reynolds number, 180 based on the friction velocity and the channel half width. Incompressible Navier-Stokes equations are integrated using finite element method with the basis function of NURBS. To solve space-time equations, Newton's method with two stage predictor multicorrector algorithm is employed. The code is parallelized using MPI. The computational domain is a rectangular box of size $2{\pi}{\times}2{\times}4/3{\pi}$ in the streamwise, wall normal and spanwise direction. Mean velocity profiles and velocity fluctuations are compared with the data of DNS. The results agree well with those of DNS and other traditional LES.

• International Journal of Control, Automation, and Systems
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• v.1 no.1
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• pp.76-82
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• 2003

This paper establishes some integral equalities formulated by zeros located in the convergence region of a Laplace transformable function. Using the definition of the Laplace transform, it shows that Laplace transformable functions have to satisfy the integral equalities in the time-domain, which can be applied to the understanding of the fundamental limitations on the control system represented by the transfer function. In the unity-feedback control scheme, another integral equality is derived on the output response of the system with open-loop poles located in the convergence region of the output function. From these integral equalities, two sufficient conditions related to undershoot and overshoot phenomena in the step response, respectively, are investigated.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.1668-1671
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• 2003

A novel dual-frequency microstrip printed-dipole antenna operating at 5 GHz and 10 GHz is presented. This antenna is designed for wireless and mobile communication. The balance step coplanar strip is used to be a transmission line at the center of dipole with matching impedance at 50 ohm. Using the conductor strip align on the other side of antenna and adjust the width of step coplanar strip line to improved input impedance matching. By modification for matching impedance of dual frequency antenna are not affected to the radiation patterns. The Finite Difference Time Domain (FDTD) technique is applying to analyze the basic characteristic properties such as $S_{11}$ , input impedance , VSWR and radiation patterns. And these parameters are discussed. The analyze problem space are $51{\times}197{\times}175$ cells and cell dimension are ${\Delta}x=0.3\;mm$ and ${\Delta}y={\Delta}z=0.15\;mm$.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.1672-1675
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• 2003

Microstrip antennas have many applications in wireless communication system. This paper propose a analytical far-field pattern of radiation for application of the wireless communication. The triangular slot antenna fed by micorstrip line is proposed at resonance frequency 10 GHz. The simulation results of the electromagnetic field radiation pattern, S parameter, characteristic of input impedance are obtain by using the finite difference time domain (FDTD) method. The analytical space in FDTD analysis are $50{\times}171{\times}120$ cells with the cell dimension ${\Delta}x=0.152\;mm$, ${\Delta}y={\Delta}z=0.15\;mm$.