• 한국멀티미디어학회:학술대회논문집
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• 한국멀티미디어학회 2003년도 춘계학술발표대회논문집
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• pp.49-52
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• 2003

OFDM(Orthogonal Frequency Division Multiplexing) scheme can compensate for distortions caused by multipath delay spread and reduce the burst errors caused by the Doppler effect since OFDM signals have long symbol durations. However, OFDM is required to be improved for high speed data transmission and large capacity. Therefore, coding schemes should be combined with OFDM. In this paper, it was studied that the performance of OFDM transmission scheme was improved in mobile communication channel by applying TCM, which has advantages of error correction and bandwidth efficiency. Simulation was carried out for two TCM models with different code efficient length. By mapping two models to square 16QAM, the model with the code efficient length of 2 achieved 3dB better than the other for the BER of 10/sub -3/. In conclusion, if we want to achieve a better performance with TCNA in OFDM applications, we should select a TCM with larger code efficient length.

• 전자공학회논문지SC
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• 제38권1호
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• pp.45-52
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• 2001

PISA 방법은 주로 승모판에서 역류하는 혈류량을 측정하기 위해 사용되고 있다. 이 방법은 PISA isotach의 기하학적 모양에 대한 모델링에 관한 것이다. PISA의 일반적인 유동모델은 isotach의 표면이 수식적으로 반구이거나 비반구임을 가정하여 계산된 것이지만, 본 논문에서는 영역기반방법으로 isotach를 추정한 후, 타원체의 높이에 기초한 실제적인 표면분할 유동모델을 이용하여 유체량을 추정하였다. 제안한 밥법을 평가하기 위해, $30cm^3/sec-60\;cm^3/sec$의 실제 유량을 가지는 동적인 180개의 유동영상에 대해서 기존 방법들과 비교하였다. 실험한 결과, 반구 유동모델의 유체량 평균이 $29\;cm^3/sec$로 실제 유체량 평균보다 35%정도 적게 추정을 하였고, 제안한 방법의 평균은 $45\;cm^3/sec$으로 비반구 유동모델의 평균과 같았고, 유체량 변화파형도 유사한 결과를 가짐을 알 수 있었다.

• International Journal of Air-Conditioning and Refrigeration
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• 제12권1호
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• pp.50-60
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• 2004

An experimental analysis using three-dimensional Laser Doppler Velocimetry(LDV) measurement and computational analysis using the Reynolds stress model in FLUENT are conducted to give a clear understanding of the effect of blade loading on the structure of tip leakage flow in a forward-swept axial-flow fan operating at the maximum efficiency condition ($\Phi$=0.25) and two off-design conditions ($\Phi$=0.21 and 0.30). As the blade loading increases, the onset position of the rolling-up of tip leakage flow moves upstream and the trajectory of tip leakage vortex center is more inclined toward the circumferential direction. Because the casing boundary layer becomes thicker and the mixing between the through-flow and the leakage jet with the different flow direction is enforced, the streamwise vorticity decays more fast with the blade loading increasing. A distinct tip leakage vortex is observed downstream of the blade trailing edge at $\Phi$=0.30, but it is not observed at $\Phi$=0.21 and 0.25.

• 수산해양기술연구
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• 제50권4호
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• pp.551-555
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• 2014

ADCPs have been widely used to estimate the dynamic characteristics and biomass of sound scattering layers (SSLs), and swimming speed of fish schools for analyzing SSLs spatial distribution and/or various behavior patterns. This result showed that the verification of the mean volume backscattering strength (MVBS or averaged SV, dB) acquired by the ADCP would be necessary for a quantitative analysis on the spatial distribution and the biomass estimation of the SSLs or fish school when ADCP is used for estimating their biomass. In addition, the calibrated sphere method was used to verify values of each MVBS obtained from 4 beams of ADCP (153.6 kHz) on the base of 3 frequencies (38, 120, 200 kHz) of Scientific echo sounder's split beam system. Then, the measured SV values were compared and analyzed in its Target Strength (TS, dB) values estimated by a theoretical acoustic scattering model.

• 설비공학논문집
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• 제15권4호
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• pp.294-304
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• 2003

An experimental analysis using three-dimensional laser Doppler velocimetry(LDV) measurement and computational analysis using the Reynolds stress model in FLUENT are conducted to give a clear understanding of the effect of blade loading on the structure of tip leakage flow in a forward-swept axial-flow fan operating at the maximum efficiency condition ($\Phi$=0.25) and two off-design conditions ($\Phi$=0.21 and 0.30). As the blade loading increases, the onset position of the rolling-up of tip leakage flow moves upstream and the trajectory of tip leakage vortex center is more inclined toward the circumferential direction. Because the casing boundary layer becomes thicker and the mixing between the through-flow and the leakage jet with the different flow direction is enforced, the streamwise vorticity decays more fast with the blade loading increasing. A distinct tip leakage vortex is observed downstream of the blade trailing edge at $\Phi$=0.30, but it is not observed at $\Phi$=0.21 and 0.25.

• International Journal of Ocean System Engineering
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• 제1권4호
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• pp.192-197
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• 2011

This paper describes the mathematical modeling, control algorithm, system design, hardware implementation and experimental test of a Manta-type Unmanned Underwater Vehicle (MUUV). The vehicle has one thruster for longitudinal propulsion, one rudder for heading angle control and two elevators for depth control. It is equipped with a pressure sensor for measuring water depth and Doppler Velocity Log for measuring position and angle. The vehicle is controlled by an on-board PC, which runs with the Windows XP operating system. The dynamic model of 6DOF is derived including the hydrodynamic forces and moments acting on the vehicle, while the hydrodynamic coefficients related to the forces and moments are obtained from experiments or estimated numerically. We also utilized the values obtained from PMM (Planar Motion Mechanism) tests found in the previous publications for numerical simulations. Various controllers such as PID, Sliding mode, Fuzzy and $H{\infty}$ are designed for depth and heading angle control in order to compare the performance of each controller based on simulation. In addition, experimental tests are carried out in a towing tank for depth keeping and heading angle tracking.

• Current Optics and Photonics
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• 제1권5호
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• pp.433-439
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• 2017

The rodent model has been used frequently to understand stroke pathophysiology, due to its low cost and the large spectrum of genetic strains available. Here, we present a diffuse speckle contrast analysis system (DSCA) with a $1{\times}2$ optical switch that was used to non-invasively assess cerebral blood flow (CBF) changes in the rat during intraluminal suturing for middle cerebral artery occlusion (MCAO) surgery. The blood flow index (BFI) in the left hemisphere was lower than that in the right hemisphere because the left middle cerebral artery was occluded. Furthermore, the performance of the DSCA system was compared with that of commercial laser Doppler flowmetry. The changes in the BFI measured by the two systems were correlated strongly. The DSCA system was less sensitive to motion artifacts and able to measure relatively deep tissue flow in the rat's brain. In conclusion, the DSCA system secured CBF monitoring during surgery in a rodent model without craniotomy.

• 한국전자파학회지:전자파기술
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• 제6권1호
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• pp.66-76
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• 1995

본 논문에서는 다경로 페이딩 채널에서 DA/SSMA 시스템의 오율특성을 컴퓨터시뮬레이션을 통하여 성능분석을 하였다. 먼저 다경로 페이딩 채널을 모델링 하였으며, 채널의 특성을 알아보기 위하여 도플러 주파수와 신호의 대역폭, 시간지연 등을 변화시키면서 그때의 주파수 응답특성과 여러 형태에 대하여 살펴보았다. 그리고 모델링한 태널을 블럭코드와 콤볼루션코드로 성능을 비교하였으며 DS/SSMA 시스템에 적용하여 성능을 비교 분석하였다. 그 결과를 보면 상관기를 사용하지 않은 코딩 시스템의 수신기[5]보다 1~3[dB] 향상됨을 나타내었다.

• 한국해양공학회지
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• 제19권5호
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• pp.71-77
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• 2005

This paper presents an integrated underwater navigational algorithm for unmanned underwater vehicles, using additional two-range transducers. This paper proposes a measurement model, using two range measurements, to improve the performance of an IMU-DVL (inertial measurement unit - Doppler velocity log) navigation system for long-time operation of underwater vehicles, excluding DVL measurement. Extended Kalman filter was adopted to propagate the error covariance, to update the measurement errors, and to correct the state equation when the external measurements are available. Simulation was conducted with the 6-d.o.f nonlinear numerical model of an AUV in lawn-mowing survey mode, at current flaw, where the velocity information is unavailable. Simulations illustrate the effectiveness of the integrated navigation system, assisted by the additional range measurements without DVL sensing.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2012년도 학술발표회
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• pp.36-36
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• 2012

Drainage water in lowland paddy fields is quantitatively influenced recycle and/or repeated irrigation by irrigation facilities, i.e. pumps, check gates, small reservoirs and so on. In those drainage channels, nutrients accumulation and increasing organic matters are considered to be occurred, and water quality would be degraded not only environmental aspect but irrigation purpose. In general, Total Nitrogen (T-N) is interested water quality index in irrigation water, because high nitrogen concentration sometimes caused decreasing rice production by excess growth and fallen or degrading quality of taste, then, farmers would like to clear water less than 1mg/L of T-N concentration. In drainage channel, it is known that the nitrogen concentration change is influenced by physical, chemical and biological properties, i.e, stream or river bed condition, water temperature, other water quality index, and plant cover condition. In this study, discharge data (velocity and level) in a drainage channel was monitored by an Acoustic Doppler system and water quality was sampled at same time in 2011. So those data was analyzed by multi regression model to realize hydrological and environmental factors to influence with nitrogen concentration. The results showed the difference tendency between irrigation and non-irrigation period, and those influenced factors would be considered in water quality model developing in future.