• Structural Engineering and Mechanics
• /
• 제13권5호
• /
• pp.569-589
• /
• 2002

In performing the dynamic analysis, the step size used in a step-by-step integration method might be much smaller than that required by the accuracy consideration in order to capture the rapid chances of dynamic loading or to eliminate the linearization errors. It was first found by Chen and Robinson that these difficulties might be overcome by integrating the equations of motion with respect to time once. A further study of this technique is conducted herein. This include the theoretical evaluation and comparison of the capability to capture the rapid changes of dynamic loading if using the constant average acceleration method and its integral form and the exploration of the superiority of the time integration to reduce the linearization error. In addition, its advantage in the solution of the impact problems or the wave propagation problems is also numerically demonstrated. It seems that this time integration technique can be applicable to all the currently available direct integration methods.

• International Journal of Fuzzy Logic and Intelligent Systems
• /
• 제15권1호
• /
• pp.20-26
• /
• 2015

It is very difficult to design an underwater communication system because of multipath, Doppler effects, noise, and attenuation. These factors lead to errors in the communication performance and maximum propagation distance. In this study, we calculate the distance that can be realized using the direct-sequence code division multiple access (DS-CDMA) technique with direct-sequence spread spectrum (DSSS) in an underwater communication system considering only the attenuation and noise. We also compare the estimated and calculated propagation distances obtained for several different scenarios.

• 방송공학회논문지
• /
• 제10권4호통권29호
• /
• pp.540-547
• /
• 2005

ATSC DTV 수신기의 결정 궤환 등화기는 양자화기나 지연시간이 없는 트렐리스 복호기에서 에러가 발생하면, 발생된 에러는 후방 필터의 입력으로 사용되어 에러 전파 현상을 야기한다. 에러 전파 현상은 잔류 에러의 증가와 수렴 속도 저하라는 등화기의 성능 열화를 가져온다. 따라서 본 논문에서는 에러 전파 현상을 해결하기 위하여 이중 후방 필터 구조의 결정 궤환 등화기를 제안한다. 제안된 등화기의 후방 필터는 지연 시간이 없는 트렐리스 복호기의 출력을 입력으로 사용하는 결정 후방 필터와 등화기의 출력을 입력으로 사용하는 비결정 후방 필터로 구성되어 있다. 부가적으로 사용된 비결정 후방 필터는 에러 전파 현상이 발생하지 않고, 또한 결정 후방 필터에서 발생되는 에러 전파 현상을 보상한다. 따라서 제안된 등화기는 기존의 등화기에 비해서 수렴 속도는 빨라지고 잔류에러는 감소한다. 전산 모의 실험을 통하여 제안된 이중 후방필터 구조의 등화기의 성능 향상을 분석하였다.

• 한국광학회지
• /
• 제34권5호
• /
• pp.192-201
• /
• 2023

Band-limited angular spectrum method (BL-ASM)는 공간주파수 제어의 문제로 aliasing 오류가 발생한다. 본 논문에서는 위상 홀로그램에 대한 표본화 간격 조정 기법과 딥 러닝 기반의 U-net 모델을 사용한 스펙클 노이즈 감소 및 이미지 품질 향상 기법을 제안하였다. 제안한 기법에서는 넓은 전파 범위에서 aliasing 오류를 제거할 수 있도록 먼저 샘플링 팩터를 계산하여 표본화 간격 조절에 의한 공간주파수를 제어함으로써 스펙클 노이즈를 감소시킨다. 그 후 딥 러닝 모델을 적용한 위상 홀로그램을 학습시켜 복원 이미지의 품질을 향상시킨다. 다양한 샘플 이미지에 대한 S/W 시뮬레이션에서 기존의 BL-ASM과의 peak signal-to-noise ratio (PSNR), structural similarity index measure (SSIM)을 비교할 때 각각 평균 5%, 0.14% 정도 비율이 향상됨을 확인하였다.

• 한국수자원학회:학술대회논문집
• /
• 한국수자원학회 2001년도 학술발표회 논문집(I)
• /
• pp.7-14
• /
• 2001

In this study, we characterized the variation of sampling errors using the Waymire-Gupta-rodriguez-Iturbe multi-dimensional rainfall model (WGR model). The parameters used for this study are those derived by Jung et al. (2000) for the Han River Basin using a genetic algorithm technique. The sampling error problems considering in this study are those far using raingauge network, satellite observation and also for both combined. The characterization of sampling errors was done for each month and also for the downstream plain area and the upstream mountain area, separately. As results of the study we conclude: (1) The pattern of sampling errors estimated are obviously different from the seasonal pattern of mentally rainfall amounts. This result may be understood from the fact that the sampling error is estimated not simply by considering the rainfall amounts, but by considering all the mechanisms controlling the rainfall propagation along with its generation and decay. As the major mechanism of moisture source to the Korean Peninsula is obviously different each month, it seems rather norma1 to provide different pattern of sampling errors from that of monthly rainfall amounts. (2) The sampling errors estimated for the upstream mountain area is about twice higher than those for the down stream plain area. It is believed to be because of the higher variability of rainfall in the upstream mountain area than in the down stream plain area.

• Water Engineering Research
• /
• 제2권1호
• /
• pp.63-72
• /
• 2001

The variation of sampling errors was characterized using the Waymire-Gupta-Rodriguez-Iturbe multi-dimensional rainfall model(WGR model). The parameters used for this study are those derived by Jung et al. (2000) for the Han River Basin using a genetic algorithm technique. The sampling error problems considered are those for using raingauge network, satellite observation and also for both combined. The characterization of sampling errors was done for each month and also for the downstream plain area and the upstream mountain area, separately. As results of the study we conclude: (1) The pattern of sampling errors estimated are obviously different from the seasonal pattern of monthly rainfall amounts. This result may be understood from the fact that the sampling error is estimated not simply by considering the rainfall amounts, but by considering all the mechanisms controlling the rainfall propagation along with its generation and decay. As the major mechanism of moisture source to the Korean Peninsula is obviously different each month, it seems rather normal to provide different pattern of sampling errors from that of monthly rainfall amounts. (2) The sampling errors estimated for the upstream mountain area is about twice higher than those for the down stream plain area. It is believed to be because of the higher variability of rainfall in the upstream mountain arean than in the down stream plain area.

• International Journal of Naval Architecture and Ocean Engineering
• /
• 제10권2호
• /
• pp.225-234
• /
• 2018

A Multibeam Echo Sounder (MBES) is commonly used for rapid seafloor mapping. We herein present a time-domain integrated system simulation technique for MBES development. The Modeling and Simulation (M&S) modules consist of four parts: sensor array signal transmission, propagation and backscattering modeling in the ocean environment, beamforming of the received signals, and image processing. Also, the simulation employs a ray-theory-based algorithm to correct the reconstructed bathymetry, which has errors due to the refraction caused by the vertical sound velocity profile. The developed M&S technique enables design parameter verification and system parameter optimization for MBES. The framework of this technique can also be potentially used to characterize the seabed properties. Finally, typical seafloor images are presented and discussed.

• 한국방송∙미디어공학회:학술대회논문집
• /
• 한국방송공학회 1998년도 Proceedings of International Workshop on Advanced Image Technology
• /
• pp.5-9
• /
• 1998

In this paper, we propose an error-resilient transmission technique for the H.263 video data stream over wireless networks. The proposed algorithm employs bit rearrangement hierarchically, providing the robust and exact synchronization against the bit errors, without requiring extra redundant information. In addition, we propose the recovery algorithm for the lost or erroneous motion vectors. We implement the encoder and decoder, based on the H.263 standard, and evaluate the proposed algorithm through intensive computer simulation. The experimental results demonstrate that the proposed algorithm yields good image quality, in spite of the channel errors, and prevents the error propagation both in the spatial and the temporal domain efficiently.

• 한국콘텐츠학회논문지
• /
• 제7권12호
• /
• pp.303-310
• /
• 2007

영상을 통신망에서 실시간 전송하려면 압축된 비디오 비트열이 필요하다. 비디오 압축 알고리즘은 시간적, 공간적, 확률적 중복성을 제거하기 때문에 부호화된 비트열은 전송과정 중에 발생하는 전송에러에 매우 민감한 특성을 보인다. 본 논문에서는 저 전송률 비디오 코딩에서 에러의 확산을 막기 위한 에러 복원코딩 방식을 제안한다. 이런 에러 복원 코딩 기술의 성능은 전송에러를 얼마나 정확하게 탐지해 내느냐에 달려 있는데, 전송 에러를 검출하기위해 데이터 숨김이라는 방식을 제안한다. 그리고 에러가 발생한 매크로블록을 복원하기 위해 인트라 매크로블록 갱신 기술과, 움직임 벡터 예측을 이용한 움직임 보상 기술을 적용하여 성능을 비교 및 평가한다. 이 방식은 WCDMA와 같이 에러가 발생할 확률이 있는 비디오 전송망에서 사용할 경우 매우 효과적이다.

• The Journal of the Acoustical Society of Korea
• /
• 제25권2E호
• /
• pp.79-84
• /
• 2006

Acoustic characteristics of a sound absorbing material can be identified, if the characteristic impedance and propagation constants are known, which have generally been determined experimentally. One easy method determining these two essential parameters is to measure the one dimensional wave characteristics in the impedance tube. In th udy, the effects of backing conditions on the impedance tube measurement have been examined using several pairs of generally used end conditions. The results showed that the measured values are similar for most pairs of end conditions: however, it was observed that the measured characteristic impedance for different thickness did not agree well for some pairs. In this work, the multi termination method, using three or more known backing con ns, was suggested to reduce such random errors, which are mostly caused by the test procedure. Employing three terminations as a set, comprised of a rigid end, an end with porous material, and an end with a backing cavity, it was demonstrated that improved measured results could be obtained for an open cell PU foam varying widely with three different thicknesses.