• Proceedings of the Korea Institute of Convergence Signal Processing
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• 2000.12a
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• pp.85-88
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• 2000

Signal splitting and perfect reconstruction in subband coding is based on the assumption that quantization errors are negligible. But if subband signal is quantized, 4 types of errors occurs thus it is not impossible to do perfect reconstruction. These errors are QMF design error, aliasing error, signal error and random error. By using the QMF for subband splitting, the QMF error does not present. and by using the Lloyd-Max quantizer for the quantization and by using an appropriate synthesis filter, all signal dependent errors can be cancelled and the remaining error is random error which is uncorrelated with the original image〔1〕. In this thesis, Lenna and Camera-Man image are devided into 10 subbands by using the D4 and D20 wavelet And the subband signals are quantized by using the Lloyd-Max quantizer and the quantization errors are compared. and evaluated.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.2
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• pp.407-416
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• 2000

Adaptive digital filtering and noise cancelling technique using a tree structured filter bank are presented to reduce a undesirable aliasing due to the decimation of filtered output and improve the performance in terms of mean-square error and the convergence speed using a aliasing canceller. A signal is split into two subband by analysis filter bank and decimated by decimator and reconstructed by interpolation technique and synthesis filter bank. A variable step-size LMS algorithm is used to improve the convergence speed in case of existing the measurement noise in desired input of filter. It is shown by computer simulation that the proposed subband structure in this paper is superior to conventional subband filter structure in terms of mean-square error and convergence speed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1993.04a
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• pp.123-127
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• 1993

소음방사의 이해 및 효과적인 소음제어를 위해서는 소음원의 특성, 음장의 공간상 방사 특성 등을 아는 것이 중요하며, 이를 위해 많은 연구가 진행되 어 왔다. 특히 다수의 마이크로폰 어레이를 이용한 음향 홀로그래피 방법에 의한 실험적 음장 예측 방법이 소개되었고 연구가 진행됨에 따라 많은 실용 가능성을 보여 주었다. 음향 홀로그래피 방법에는 측정상 제한이 필연적으로 존재할 수밖에 없는데, 이에 따른 오차가 존재하며 결국 예측음장의 신뢰도 를 떨어뜨리는 요인이 된다. 본 연구의 목적은 측정조건에 따른 오차의 요인 을 고찰하고 이를 정량적으로 표현함으로써 음향 홀로그래피 방법의 적용에 도움을 주고자 한다. 평면 음향 홀로그래피에 나타나는 오차는 둘러 싸기 오 차(wraparound error), 앨리애싱(aliasing), 창문영향(window effect)으로 나 눌 수 있는데, 오차는 측정구경의 크기와 마이크로폰 사이의 간격등의 측정 조건 뿐만 아니라 음원의 특성, 홀로그램 평면의 위치 등에 직접적인 영향을 받게 된다. 본 연구에서는 오차해석을 위한 기본 연구로써 점음원(monopole) 과 쌍극자(dipole)음장의 파수 스펙트럼을 해석적으로 구하고 이를 기본으로 평면 음향 홀로그래피 적용시 존재하는 앨리애싱에 대해 고찰하고 전산기 모의 실험 (computer simulation)을 통해 오차를 최소화하는 측정조건을 제 시하고자 한다.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.25 no.5
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• pp.393-399
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• 2016

In this study, an experiment was conducted using a 3D scanner, commonly used in reverse engineering techniques, and the newly introduced CT measuring machine. The hole, width, and angle of specimens having various shapes were designated, the error rates in dimensional modelling generated during scanning with each device were compared, and the models were printed using a 3D printer. A secondary comparative analysis of the two printed specimens was conducted; the causes of dimension errors that occur during the printing process after scanning with each device and the differences associated with variation in shape were also analyzed. Based on the analysis results, the featured shape for each scanning application method and issues to consider in reverse engineering were presented, and the use of the CT measuring machine was recommended as a method to minimize error rates in dimensions and ensure efficient reverse engineering.

• Journal of the Korea Institute of Military Science and Technology
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• v.24 no.6
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• pp.577-590
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• 2021

In this paper, we theoretically analyzed the self-alignment/navigation performance in the accelerometer resonance state generated by dither motion of ring laser gyroscope in LINS and verified it through simulation. As a result of analysis, it is confirmed that the amplitude of the accelerometer measurement amplified in the accelerometer resonance state is decreased in the process of sampling per the navigation calculation period and that frequency is changed by the aliasing effect too. It was also analysed that the attitude error in self-alignment is determined by the amplitude/frequency of the accelerometer measurement, the gain of the self-alignment loop, and the velocity and position error in the navigation is determined by the amplitude/frequency/phase error of the accelerometer measurement. This analysis and simulation results show that the self-alignment and navigation performance is not be degraded only when the amplification factor of the accelerometer measurement in the accelerometer resonance state is 3 or less

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.2193_2194
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• 2009

A digital over current relay(OCR) is realized by using TMS320C32 microprocessor. Fourier Transform is used to obtain the phasor of a current signal and a 2nd low pass filter is adopted to prevent aliasing error. H/W test shows almost same results with those of the S/W test. It could be possible that confirm simularity between H/W and S/W test in this paper.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1994.10a
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• pp.317-322
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• 1994

본 연구에서는 원통면 음향 홀로그래피 방법에 대한 세밀한 고찰을 통하여 이 방법을 이용한 음장예측의 실제 적용에 도움을 주고자 한다. 먼저 원통면 음향 홀로그래피 방법의 기본적인 이론에 대한 고찰을 하였고, 원통면 음향 홀로그래피 방법의 실제 적용시 나타나는 창문함수의 영향(window effect)이나 공간상의 엘리어싱(spatial aliasing), 둘러싸기 오차(wraparound error)와 같은 오차에 대하여 모의 실험을 통하여 살펴보았다. 이러한 오차해석을 통하여 가능한 한 오차를 줄이고 신뢰할 수 있는 예측결과를 얻을 수 있는 측정조건을 제시하였으며, 오차를 감소시킬수 있는 Tukey 창문함수의 사용과 제로패딩(zero padding) 방법을 제시하였다. 이러한 기본적인 이해를 바탕으로 원통형 구조물의 방사음장을 예측하는 실험을 하였다.

• 한국전산유체공학회:학술대회논문집
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• 2006.10a
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• pp.106-109
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• 2006

A large eddy simulation with explicit filters on unstructured mesh is presented. Two explicit filters are adopted for reducing the aliasing error of the nonlinear convective term and measuring the level of subgrid scale velocity fluctuation, respectively. The developed subgrid scale model is basically eddy viscosity model which depends on the explicitly filtered fields and needs no additional ad hoc wall treatment such as van Driest damping function. As a validation problem, the flows around a sphere at several Reynolds numbers, including laminar and turbulent regimes, are calculated and compared to experimental data and numerical results in the literature.

• The Journal of the Acoustical Society of Korea
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• v.19 no.2E
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• pp.14-19
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• 2000

The forward propagated ultrasonic fields resulting from a circular plane or a concave transducer in layered fluid media as well as in homogeneous water are theoretically estimated by the angular spectrum method(ASMJ) combined with Rayleigh-Sommerfeld diffraction theory(RSDT), and measured by a precision 3-D scanning system with a needle-point hydrophone. To make the aliasing error negligible on the 2-D FFT in the theoretical estimation, the spatial discretization in the ASM are carefully considered for optimal selection of spatial sampling intervals and the size of discretization area. It is shown that the estimated fields agree reasonably with the measured ones.

• 한국전산유체공학회:학술대회논문집
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• 2007.04a
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• pp.41-44
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• 2007

A large eddy simulation method with unstructured mesh is presented. Two explicit filtering procedures are adopted for reducing the aliasing error of the nonlinear convective term and measuring the level of subgrid scale velocity fluctuation, respectively. The developed subgrid scale model is basically an eddy viscosity model which depends on both local velocity fluctuation level and local grid scale. As a validation problem, the flows around a sphere of several Reynolds numbers are simulated and some characteristic quantities are compared to experimental data and numerical results in the literature.