• 한국항행학회논문지
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• 제24권6호
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• pp.587-592
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• 2020

사물 인터넷 패러다임에 의해 가능해진 거대한 정보 교환은 즉시 사용 가능한 인프라로 전선을 이용할 가능성이 높아지고 있다. 사전에 설치된 배선 네트워크 인프라를 사용하는 이점은 전력선 통신을 광대역 통신을 위한 경쟁력있는 기술로 만들었다. 따라서 기존의 전력선 통신 채널을 고속 데이터 전송 및 인터넷 서비스를 위한 효과적인 수단으로 사용하는 것에 대한 관심이 높아지고 있다. 전력선 통신 시스템에 영향을 미치는 주요 잡음의 유형 중 하나는 임펄스 잡음이며 본 논문은 임펄스 잡음이 OFDM-QPSK 시스템의 성능에 미치는 영향을 해석하였다. 임펄스 잡음의 성능 분석을 위하여 3가지 환경에서 측정된 데이터를 사용하였다. 분석을 통해 OFDM-QPSK 시스템이 대부분의 임펄스 잡음 사례에서 QPSK 시스템보다 우수한 것으로 나타났다. 또한 RS 부호화된 OFDM-QPSK 시스템은 3 가지 경우의 임펄스 잡음 환경에서 우수한 BER 성능을 달성할 수 있었다.

• 대한기계학회논문집B
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• 제23권1호
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• pp.58-68
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• 1999

The entry compression wave, which forms at the entrance of a high-speed railway tunnel, is closely related to the pressure transients in the train/tunnel systems as well as an impulsive noise appearing at the exit of the tunnel. In order to alleviate such undesirable phenomena, some control strategies have been applied to the compression wave propagating inside the tunnel. The objective of the current work is to investigate the effect of tunnel entrance hoods on the entry compression wave at the vicinity of the tunnel entrance. Three types of entrance hoods were tested by the numerical method using the characteristics of method for a wide range of train speeds. The results show that the maximum pressure gradient of compression wave can be considerably reduced by the tunnel entrance hood. Optimum hood shape necessary to reduce the pressure transients and impulsive noise was found to be of an abrupt type hood with its cross-sectional area 2.5 times the tunnel area. It is believed that the current results are highly useful in predicting the effects of entrance hoods and in choosing the shape of proper hood.

• 대한기계학회논문집
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• 제19권8호
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• pp.1972-1981
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• 1995

As a railway train enters a tunnel at high speed, a compression wave is formed in front of the train and propagates along the tunnel. The compression wave subsequently emerges from the exit of the tunnel, which causes an impulsive noise. The impulsive noise is closely related to the pressure gradient of the compression wave propagating the tunnel. In order to investigate the characteristics of the compression waves, in the present study an experiment was made using a shock tube. The results show that the strength of a compression wave decreases with the distance from the tunnel entrance and the nonlinear effect of compression wave appears to be significant if strength of the initial compression wave is greater than 7 kPa. Furthermore if the wave pattern is known, attenuation of the compression wave propagating in a tunnel can be reasonably predicted by a theoretical equation considering viscous action and heat transfer in boundary layer.

• 대한기계학회논문집B
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• 제23권2호
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• pp.234-242
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• 1999

Flow phenomena such as the pressure transients Inside a high-speed railway tunnel and the Impulsive waves at the exit of the tunnel are closely associated with the characteristics of the entry compression wave, which is generated by a train entering the tunnel. Tunnel entrance hood may be an effective means for alleviating the Impulsive waves and pressure transients. The objective of the current work is to explore the effects of the train nose shape and the entrance hood on the characteristics of the entry compression wave. Numerical calculations using the method of characteristics were applied to one-dimensional, unsteady, compressible flow field with respect to high-speed railway/tunnel systems. Two types of the entrance hoods and various train nose shapes were employed to reveal their influences on the entry compression wave for a wide range of train speeds. The results showed that the entry compression wave length increases as the train nose becomes longer and the train speed becomes lower. The entry compression wave length in the tunnel with hood becomes longer than that of no hood. Maximum pressure gradient in the compression wavefront reduces by the entrance hood. The results of the current work provide useful data for the design of tunnel entrance hood.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제15권7호
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• pp.2356-2376
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• 2021

In this paper, we proposed a novel modulation recognition method based on quantum elephant herding algorithm (QEHA) evolving neural network under impulse noise environment. We use the adaptive weight myriad filter to preprocess the received digital modulation signals which passing through the impulsive noise channel, and then the instantaneous characteristics and high order cumulant features of digital modulation signals are extracted as classification feature set, finally, the BP neural network (BPNN) model as a classifier for automatic digital modulation recognition. Besides, based on the elephant herding optimization (EHO) algorithm and quantum computing mechanism, we design a quantum elephant herding algorithm (QEHA) to optimize the initial thresholds and weights of the BPNN, which solves the problem that traditional BPNN is easy into local minimum values and poor robustness. The experimental results prove that the adaptive weight myriad filter we used can remove the impulsive noise effectively, and the proposed QEHA-BPNN classifier has better recognition performance than other conventional pattern recognition classifiers. Compared with other global optimization algorithms, the QEHA designed in this paper has a faster convergence speed and higher convergence accuracy. Furthermore, the effect of symbol shape has been considered, which can satisfy the need for engineering.

• 대한기계학회논문집B
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• 제21권10호
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• pp.1294-1302
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• 1997

For the purpose of investigating the impulsive noise at the exit of high-speed railway tunnel and the pressure transients inside the tunnel, experiments were carried out using a shock tube with an open end. A great deal of experimental data were obtained and explored to analyze the peak pressures and maximum pressure gradients in the pressure waves. The effects of the distance and cross-sectional area ratio between two-continuous tunnels on the characteristics of the pressure waves were investigated. The peak pressure inside the second tunnel decreases for the distance and cross-sectional area ratio between two tunnels to increase. Also the peak pressure and maximum pressure gradient of the pressure wave inside the second tunnel increase as the maximum pressure gradient of initial compression wave increases.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1996년도 추계학술대회논문집; 한국과학기술회관, 8 Nov. 1996
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• pp.443-449
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• 1996

헬리콥터, 팬, 프로펠러, 터이빈같이 회전익에서 유체역학적 소음이 발생하는 장치의 설계에 있어서는 공기 역학적 성능 분석과 함께 소음에 대한 해석이 절대적으로 필요하다. 근래에 들어와서 소음에 대한 관심이 급격히 증가하고 공항 주변에서의 국제적인 규약들은 낮은 소음 수준(low noise level)을 규정하고 있으며, 이에 따라서 소음을 감소시키려는 연구가 매우 활발히 진행되고 있는 실정이다. 더욱이 컴퓨터의 냉각 팬을 비롯한 공조기기 및 산업기기에 사용되는 회전기계에서 발생되는 소음의 저감은 보다 더 쾌적한 환경을 요구하는 사회적 요구에 부합하면서 공력소음의 연구 분야가 더 넓어지고 있다. 본 논문에서는 소음예측 방법중의 하나인 음향상사(acoustic analogy)를 주파수 영역 방법(frequency domain method)을 이용하여 헬리콥터 블레이드의 고속 충격소음(High Speed Impulsive Noise)을 해석한다. 고속 충격소음은 블레이드-와류 상호작용 소음과 더불어 헬리콥터의 지배적인 소음원으로서 깃끝 속도가 큰 전진 수평비행(forward level flight)또는 제자리 비행(hovering flight)시 발생하는 소음으로 블레이드의 깃끝 마하수(critical Mach number)보다 크거나 비슷할 경우 충격파의 교란에 의해서 일어나는 충격적인 소음을 말한다. 고속 충격소음은 고주파수 스펙트럼 성분과 큰 소음강도를 가지고 있기 때문에 날카로운 금속성의 소리를 내며 먼 거리까지 전파되는 특징을 가지고 있다.

• 한국음향학회:학술대회논문집
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• 한국음향학회 1999년도 학술발표대회 논문집 제18권 2호
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• pp.427-432
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• 1999

When a high-speed train enters a tunnel, a compression wave is generated. This wave subsequently emerges from the exit portal of the tunnel, which causes an impulsive noise called 'Sonic boom' or 'micro-pressure wave'. In the present study, new method is presented for prediction of sonic boom noise, especially focusing on the effect of the nose shape of the train on the resultant noise. Acoustic theory for monopole source is used to represent a nose shape of the train in wave equation. Compression wave propagation in tunnel considering tunnel track condition and emission of sonic boom was calculated. The predicted compression waves and impulsive sound waves are compared with recent measurements, and show reasonable agreements.

• 한국항행학회논문지
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• 제27권6호
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• pp.835-840
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• 2023

RFID(Radio Frequency Identification) 시스템은 응용 서비스의 비용과 에너지 효율성으로 인해 사물인터넷 기술의 핵심 구성 요소로 각광받고 있다. RFID 기술을 사물인터넷 응용 서비스 분야에서 사용하기 위해서는 RFID 시스템의 리더와 태그 사이의 단순한 인식뿐만 아니라 다양한 정보를 장기간 저장하고 관리할 수 있어야 한다. 그리고 정보를 태그에 읽고 쓰기 위하여 열악한 무선 채널에 강하고 신뢰성 있는 성능 향상 기술이 필요하다. 특히, UHF(Ultra High Frequency) RFID 시스템에서는 다수의 태그가 밀집 환경에서 수동적인 방법으로 통신하기 때문에 개별 태그의 인식률과 전송속도 향상이 필수적이다. 본 논문에서는 임펄스 잡음 환경에서 RFID 시스템의 성능을 분석하기 위하여 Middleton의 A급 임펄스 잡음 모델을 선정하였고 태그에서는 FM0 인코딩과 Miller 인코딩을 적용하여 RFID 시스템의 오율 성능을 분석하였다. Middleton의 A급 임펄스 잡음 채널에서 RFID 시스템의 성능을 분석한 결과, 가우스 잡음 대 임펄스 잡음의 전력비 값과 임펄스 잡음 지수 값이 클수록 가우시안 잡음 채널과 유사함을 알 수 있었다.

• 연구논문집
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• 통권25호
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• pp.13-22
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• 1995

At the running speed higher than 250 km/h, several aerodynamic problems such as the increase of aerodynamic resistance, aerodynamic noise, pressure fluctuation at the tunnel entry, impulsive wave at the tunnel exit bring about the power consumption, deterioration of riding quality, and severe environmental noise. To solve these aerodynamic problems, the flow phenomena around the high speed train have to be analyzed in detail. In this study, the flow around the train is modelled as the 2-dimensional viscous compressible flow and the flow field is calculated numerically for the three different types of geometry and running speed. The aerodynamic drag coefficient and the pressure coefficient are evaluated each case.