• Steel and Composite Structures
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• v.20 no.5
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• pp.1119-1131
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• 2016

As a first attempt, an inverse hybrid numerical method for small scale parameter estimation of functionally graded (FG) nanobeams using measured frequencies is presented. The governing equations are obtained with the Eringen's nonlocal elasticity assumptions and the first-order shear deformation theory (FSDT). The equations are discretized by using the differential quadrature method (DQM). The discretized equations are transferred from temporal domain to frequency domain and frequencies of the nanobeam are obtained. By applying random error to these frequencies, measured frequencies are generated. The measured frequencies are considered as input data and inversely, the small scale parameter of the beam is obtained by minimizing a defined functional. The functional is defined as root mean square error between the measured frequencies and calculated frequencies by the DQM. Then, the conjugate gradient (CG) optimization method is employed to minimize the functional and the small scale parameter is obtained. Efficiency, convergence and accuracy of the presented hybrid method for small scale parameter estimation of the beams for different applied random error, boundary conditions, length-to-thickness ratio and volume fraction coefficients are demonstrated.

• Journal of the Korea institute for structural maintenance and inspection
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• v.5 no.1
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• pp.169-175
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• 2001

Bridge load rating calculations provide a basis for determining the safe load capacity of bridge. Load rating requires engineering judgement in determining a rating value that is applicable to maintaining the safe use of the bridge and arriving at posting and permit decisions. Load testing is an effective means in calculating the rating value of bridge. In Korea, load carrying capacity of bridge is modified by response modification factor that is determined from comparisons of measured values and analysis results. The response modification factor may be corrupted by vehicle location error that is defined as the gap of test vehicle location between load testing and analysis. In this study, the effects of vehicle location error to structural response and response modification factor are investigated, and a new method for evaluating response modification factor is proposed. The random data analysis shows that the proposed method is less sensitive to vehicle location error than the present method.

• Journal of the Korean Institute of Telematics and Electronics
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• v.23 no.5
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• pp.605-615
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• 1986

The phase-locked loop(PLL) is a communication receiver which operates as a coherent detector by continuously correcting the phase error. In this paper analysis for the Phase-error behavior of analog phase-locked loop (APLL) in the presence of additive white gaussian noise has been done theoretically and experimentally. A close form solution of the first-order loop is obtained and approximate solutions are derived for the second-order loops with RC, leadlag and perfect integrator filters. The perdormance of APLL's and their characteristics are also thoroughly investigated through experiments. In order to analyze the effect of the stochastic nature on nonlinear dynamics characteristics of the second order APLL, the phase error distribution and its variance have been obtained by using the Fokker-Planck equation. Theoretical results agree closely with those of experiment.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.8
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• pp.3585-3601
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• 2016

The error rate performance of circularly distributed antenna system is studied over Nakagami-m fading channels, where a dual-channel receiver is employed for the quadrature phase shift keying signals detection. To mitigate the Co-Channel Interference (CCI) caused by the adjacent cells and to save the transmit power, this work presents remote antenna unit selection transmission based on the best channel quality and the maximized path-loss, respectively. The commonly used Gaussian and Q-function approximation method in which the CCI and the noise are assumed to be Gaussian distributed fails to depict the precise system performance according to the central limit theory. To this end, this work treats the CCI as a random variable with random variance. Since the in-phase and the quadrature components of the CCI are correlated over Nakagami-m fading channels, the dependency between the in-phase and the quadrature components is also considered for the error rate analysis. For the special case of Rayleigh fading in which the dependency between the in-phase and the quadrature components can be ignored, the closed-form error rate expressions are derived. Numerical results validate the accuracy of the theoretical analysis, and a comparison among different transmission schemes is also performed.

• Journal of the Korean Institute of Telematics and Electronics
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• v.22 no.5
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• pp.24-28
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• 1985

In this paper, the cyclic product codes which are capable of correcting random erros and burst errors simultaneously have been designed and constructed. First, the procedure for product of two cyclic codes is shown and thin the encoder and decoder system using the (7,4) cyclic Hamming code and the (3,1) cyclic code is implemented. The micro-computer is used for experiment and the system consists of encoder, decoder and interface circuits. The encoder of cyclic product code is implemented by interlacing encoders while the decoder is implemented by cascading decoders that interlace error trapping decoders. In conclusion, cyclic product codas are easily decodable and are capable of correcting four random errors and eight-burst errors. Better performance is obtained with low error rate.

• Aerospace Engineering and Technology
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• v.9 no.1
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• pp.151-157
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• 2010

The tracking radars in NARO space center are precious, long-range tracking systems for tracking the launch vehicle (KSLV-1) and transmitting TSPI (Time, Space and Position Information) data to MCC (Mission Control Center). Because TSPI data from tracking radars to MCC are important information for the launch mission and flight safety control, TSPI data are required to be more accurate. In this paper, we analyzed theoretically the required specification of the random noise error in tracking radar and verified the real random noise error. In this analysis, we evaluated the TSPI data of several flight tests performed in NARO space center.

• Journal of the Korean Society of Visualization
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• v.17 no.2
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• pp.48-57
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• 2019

A straightforward strategy for particle image velocimetry (PIV) interrogation and post-processing has been proposed, aiming at reducing errors and clarifying vortex structures. The interrogation window size should be kept small to reduce bias error and improve spatial resolution. A spatial filter is then applied to the velocity field to reduce random error and clarify flow structure. The performance of three popular spatial filters were assessed: box filter, median filter, and local quadratic polynomial regression filter. In order to quantify random uncertainty, the image matching (IM) method is applied to an experimental dataset of homogeneous and isotropic turbulence (HIT) obtained by 2D-PIV. We statistically analyze the uncertainty propagation through the spatial filters, and verify the reduction in random uncertainty. Moreover, we illustrate that the spatial filters help clarify vortex structures using vortex identification criteria. As a result, PIV random uncertainty was reduced and the vortex structures became clearer by spatial filtering.

• Journal of applied mathematics & informatics
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• v.20 no.1_2
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• pp.445-454
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• 2006

We describe a solution to the Ornstein-Uhlenbeck equation $\frac{dI}{dt}-\frac{1}{\tau}$I(t)=cV(t) where V(t) is a constant multiple of a Gaussian white noise. Our solution is based on a discrete set of Gaussian white noise obtained by taking sample points from a sum of single frequency harmonics that have random amplitudes, random frequencies, and random phases. Hence, it is different from the solution by the standard random walk using random numbers generated by the Box-Mueller algorithm. We prove that the power of the signal has the additive property, from which we derive that the Lyapunov characteristic exponent for our solution is positive. This compares with the solution by other methods where the noise is kept to be in an error range so that its Lyapunov exponent is negative.

• Journal of the Korean Statistical Society
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• v.29 no.2
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• pp.231-245
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• 2000

This paper considers a linear regression model with space and time data in where the disturbances follow spatially correlated error components. We provide the best linear unbiased predictor for the one way error components. We provide the best linear unbiased predictor for the one way error component model with spatial autocorrelation. Further, we derive two diagnostic test statistics for the assessment of model specification due to spatial dependence and random effects as an application of the Lagrange Multiplier principle.

• Proceedings of the KIEE Conference
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• 1988.07a
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• pp.198-202
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• 1988

In digital mobile communications received speech data are affected by burst errors as well as random errors. To overcome these errors we propose a bit-selective forward error correction scheme for the speech data which is sub-band coded at 13 kbps and transmitted over a 16 kbps channel. For a few error correcting codes the signal-to-noise ratio of error-corrected speech is obtained and compared through the simulation of mobile communication channels.