• 한국유체기계학회 논문집
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• 제13권2호
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• pp.48-53
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• 2010

A computerized design system of axial fan is developed for constructing 3-D blade geometry and predicting both aerodynamic performance and noise. The aerodynamic blading design of fan is conducted by blade angle distribution, camber line determination, airfoil thickness distribution and blade element stacking along spanwise distance. The internal flow and the aerodynamic performance of designed fan are predicted by the through-flow modeling technique with flow deviation and pressure loss correlations. Based on the predicted internal flow field and performance data, fan noise is predicted by two models for discrete frequency and broadband noise sources. The present predictions of the flow distribution, the performance and the noise level of actual fans are well agreed with measurement results.

• 한국수산과학회지
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• 제51권3호
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• pp.321-327
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• 2018

To classify seafloor sediments using a probabilistic neural network (PNN), the frequency-dependent characteristics of broadband acoustic scattering, which make it possible to qualitatively categorize seabed type, were collected from three different geographical areas in Korea. The echo data samples from three types of seafloor sediment were measured using a chirp sonar system operating over a frequency range of 20-220 kHz. The spectrum amplitudes for frequency responses of 35-75 kHz were fed into the PNN as input feature parameters. The PNN algorithm could successfully identify three seabed types: mud, mud/shell and concrete sediments. The percentage probabilities of the three seabed types being correctly classified were 86% for mud, 66% for mud/shell and 72% for concrete sediment.

• Structural Engineering and Mechanics
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• 제56권3호
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• pp.423-442
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• 2015

This study examines the wavelet transform for output-only system identification of ambient excited engineering structures with emphasis on its utilization for modal parameter estimation of high-order and closely-spaced modes. Sophisticated time-frequency resolution analysis has been carried out by employing the modified complex Morlet wavelet function for better adaption and flexibility of the time-frequency resolution to extract two closely-spaced frequencies. Furthermore, bandwidth refinement techniques such as a bandwidth resolution adaptation, a broadband filtering technique and a narrowband filtering one have been proposed in the study for the special treatments of high-order and closely-spaced modal parameter estimation. Ambient responses of a 5-story steel frame building have been used in the numerical example, using the proposed bandwidth refinement techniques, for estimating the modal parameters of the high-order and closely-spaced modes. The first five natural frequencies and damping ratios of the structure have been estimated; furthermore, the comparison among the various proposed bandwidth refinement techniques has also been examined.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권1호
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• pp.52-68
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• 2019

Aiming at the optimal placement of communication relay nodes (OPCRN) problem in manned/unmanned aerial vehicle cooperative engagement system, this paper designed a kind of fully connected broadband backbone communication topology. Firstly, problem description of OPCRN was given. Secondly, based on problem analysis, the element attributes and decision variables were defined, and a bi-level programming model including physical layer and logical layer was established. Thirdly, a hierarchical artificial bee colony (HABC) algorithm was adopted to solve the model. Finally, multiple sets of simulation experiments were carried out to prove the effectiveness and superiority of the algorithm.

• 한국지구과학회지
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• 제38권4호
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• pp.269-282
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• 2017

이 연구에서는 Earth Observing System Terra 위성에 탑재된 Moderate Resolution Imaging Spectroradiometer (MODIS) 협대역 방출율(채널 29, 30, 31) 자료와 다중선형회귀모형을 이용하여 지표면 광대역 방출율을 추정하였다. 다중선형회귀모형 도출 및 검증을 위한 분광 방출율 자료는 MODIS University of California, Santa Barbara와 Advanced Spaceborne Thermal Emission and Reflection Radiometer spectral library의 307종(토양 123종, 식생 32종, 물 19종, 인위적 재료 43종, 바위 90종)을 사용하였다. 도출된 다중선형회귀모형의 결정계수($R^2$)는 0.95 (p<.001)로 높게 나타났고 또한 이 모형 결과와 이론적 광대역 방출율 값의 평균제곱근오차(Root Mean Square Error)는 0.0070이었다. 그리고 이 연구 결과에 따라 계산된 지표면 광대역 방출율을 선행 연구 Wang et al. (2005)의 결과와 비교하였다. 그 결과 아시아, 아프리카, 오세아니아 지역에서 이 연구와 Wang et al. (2005)의 결과에 대한 1월 평균 지표면 광대역방출율의 평균제곱근오차는 0.0054이었고 최소와 최대 편차는 각각 0.0027과 0.0067이었으며 이러한 통계 값은 8월에도 유사하였다. 이 연구에서 다중선형회귀모형에 의하여 계산한 지표면 광대역 방출율은 Wang et al. (2005)의 값과 큰 차이가 없이 비교적 정확하게 산출되었으나 산출 정확성 향상을 위해서는 토지피복특성에 따른 차별화된 회귀모형 적용 필요성이 제기된다.

• 산업공학
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• 제17권spc호
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• pp.111-121
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• 2004

In this paper, we propose an urgency and efficiency based wireless packet scheduling (UEPS) algorithm that is able to schedule real time (RT) and non-real time (NRT) traffics at the same time. The proposed UEPS algorithm is designed to support wireless downlink packet scheduling in the OFDMA system which is a strong candidate wireless system for the next generation mobile communications. The UEPS algorithm uses the time-utility function as a scheduling urgency factor and the relative status of the current channel to the average one as an efficiency indicator of radio resource usage. The design goal of the UEPS algorithm is to maximize throughput of NRT traffics with satisfying QoS requirements of RT traffics. The simulation study shows that the proposed UEPS algorithm is able to give better throughput performance than existing wireless packet scheduling algorithms such as proportional fair (PF) and modified-largest weighted delay first (M-LWDF) while satisfying QoS requirements of RT traffics such as the average delay and the packet loss rate under various traffic loads.

• 한국통신학회논문지
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• 제32권1B호
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• pp.71-82
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• 2007

광 네트워크 기술의 발달로 인한 가용 대역폭의 증가는 고품질 협업환경 구축을 위한 비압축 인터넷 HDTV의 개발과 서비스를 촉진시키고 있다. 비압축 인터넷 HDTV는 고품질 갈무리 및 재생, 고성능 데이터 처리, 고속 전송 기술 등을 필요로 하는 첨단 광대역 응용이다. 하지만, 높은 장비 구축비용과 대용량 데이터의 전송을 위해 필요한 기가급 광대역 네트워크 요구는 비압축 인터넷 HDTV의 서비스 인프라를 확대하는데 있어 걸림돌로 작용하고 있다. 본 논문에서는 비압축 인터넷 HDTV 시스템의 저비용 구축을 위한 하드웨어 구성 및 시스템 구조를 제안하고 하드웨어의 제어와 데이터의 효과적인 전송 및 재생을 위해 개발된 소프트웨어를 소개한다. 개발 구축된 비압축 인터넷 HDTV 시스템의 성능 검증을 위해 연구망에 실험환경을 구축하고 종단 간 전송 및 재생 실험을 수행하여 효용성을 입증하였다.

• 한국수산과학회지
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• 제49권4호
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• pp.509-515
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• 2016

At the first time in South Korea, the state of the art acoustic systems were mounted on the R/V Tamgu 21. The acoustic systems are an EK80 broadband echosounder (18, 38, 70, 120, 200 and 333 kHz) which has two beam modes such as continuous wave (narrowband) and frequency modulation (broadband), an ME70 multibeam echosounder (70-120 kHz), and a SH90 sonar (111.5-115.5 kHz). Acoustic data from broadband mode have a very short range resolution, a large detection range, a high signal to noise ratio, and a wide and consecutive frequency response. In ME70, each individual beam consisted in a multibeam plays a role as a spilt beam. The first trial of the cutting edge acoustic system installed on the R/V Tamgu 21 was conducted from 15 Feb to 29 Feb 2016 in East Sea, South Sea and East China Sea. The properties of the acoustic systems were elucidated and exploratory results from three systems were exhibited. Lastly, issues which should be considered and future research plan are mentioned.

• 한국정보통신학회논문지
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• 제23권12호
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• pp.1618-1623
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• 2019

본 논문에서는 광대역 전력선통신을 실현할 수 있는 유도성 커플러를 Fe계 나노결정립 합금을 이용하여 제작하고 성능을 분석하였다. 배전자동화시스템의 주상 및 지상개폐기에 적용하여 현장시험을 수행한 결과, 광대역 전력선통신의 주요 주파수대역에서 제작된 커플러는 분기 유무에 따라 통신속도의 차이는 있으나 비교적 우수한 데이터통신을 달성하는 것으로 측정되었다. 또한, 배전선로에서 발생되는 대전류 환경에서도 통신거리에 따라 전송률의 차이는 있으나 실시간 데이터 전송이 가능한 통신속도를 유지하는 것으로 확인되었다. 따라서 제작된 유도성 커플러는 접근성이 낮은 지역에 위치한 배전자동화시스템의 배전설비 상시 감시 및 원격제어에 활용함으로써 지능형 전력망 실현을 위한 핵심소자로 사용할 수 있을 것으로 판단된다.

• 한국수산과학회지
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• 제53권2호
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• pp.218-230
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• 2020

The single anatomical attribute that has the greatest influence on acoustic scattering from fish is the presence or absence of a swimbladder. This study examined the effect of removing the gas from the swimbladder on the broadband backscattering characteristics of six species of swimbladdered fish: striped beakperch Oplegnathus fasciatus, black scraper Thamnaconus modestus, dark-banded rockfish Sebastes inermis, goldeye rockfish Sebastes thompsoni, black rockfish Sebastes schlegeli and panther puffer Takifugu pardalis. Before and after removing the gas from the swimbladder, the species-specific, frequency-dependent backscattered echo signals from anaesthetized individuals of each fish species were measured at approximately 1° intervals spanning a 90° aspect angle range from -45° (head down) to +45° (head up) using a broadband echo sounder operating at 100-200 kHz. The relationship between the wavelength-normalized backscattering cross section (σ/λ²) and fish length (L/λ) was calculated for each species. The average σ/λ² value for the six fish species at a L/λ range of 19.79-25.85, with a mean of 22.89, was reduced by approximately 52.3% when the gas was removed.