• 한국음향학회지
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• 제12권1호
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• pp.47-54
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• 1993

Performance analysis is very important to transmit the high quality information and to construct the optimal system for the minimze the noise from the channel of spread spectrum system. In this paper the error rate performance is analyzed with computer simulation in noncoherent frequency hopping M-qry frequency shift keying(FH/MFSk) systems with regard to thermal noise under the partial band jamming environments. AS a result, in case the thermal noise is disregarded, bit error probability of system in jamming fraction ρ and Eb/Nj(bit energy to jamming power density) is reduced with the increase of K and in worst case 32FSK system is better than 2FSK system by 3.23dB with the variatio of Eb/Nj. In case thermal noise is considered, bit error probability of system by 3.23dB with the variation of Eb/Nj. In case thermal noise is considered, bit error probability of system are reduced with the increase of K and Eb/No(bit energy to thermal noise density). Bit error probability in connection with worst case ρ is not largely influenced form over the 14dB to K=1 and 8dB to K=5 accordingly thermal noise disregarding. These results may be useful for avoiding the common vulnerabilities when the spread spectrum system is designed.

• 한국음향학회지
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• 제14권6호
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• pp.48-53
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• 1995

대부분의 도로교통소음 예측 방법에서는 음파가 자유로이 전과된다고 가정하였다. 그러나 도시가노변의 건물들은 음파를 반재시켜 도로내에 음에너지를 증가시키고 있다 따라서 본 연구는 반사조건을 고려한 도로교통소음 예측 방법을 찾고자 한다. 이 방법은 예측식에 반재효과를 고려하여 $L_{10},\;L_{50},\;L_{90}$ 및 $L_{eq}$ 등의 소음레벨을 구하는 것이다. 제시된 예측 방법의 적합성을 파악하기 위해 측정조사된 교통 등의 특성을 예측식에 잠용하여 예측된 소음레벨과 실측된 소음레벨을 비교분석하였다. 전반적으로 예측 소음레벨과 실측 소음레벨이 일치하였다. 그러므로 본 연구에서 제시하고 있는 반사조건을 고려한 예측 방법이 도시가노에서 도로교통소음 예측에 적합한 것으로 사료된다.

• 환경영향평가
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• 제20권4호
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• pp.425-434
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• 2011

The energy produced by wind power generation is a clean energy product because it is acquired by using renewable resource. Wind power plants("wind farms), in Korea, have been built and operated as 345.6MW facilities from 2001 until now 2009. Nevertheless, environmental issues regarding construction of wind power plants have arisen. accordingly it is time to consider the environmental and social issues of wind power in accordance with the government's policy objectives of increased wind power production. In this study, we investigated the influence that noise and low frequency noise caused by Wind power plants have on neighborhood and residents. We also sought solutions to these issues. In order to analyze the issues of wind power facilities, we compared and examined precedents and the solutions for noise and low frequency noise in Europe, the United states and Japan. We intended to examine the influences of wind power facilities and propose alternative in dealing with these issues.

• Corrosion Science and Technology
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• 제16권4호
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• pp.194-200
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• 2017

Stress-corrosion cracking (SCC) of alloy 600 and alloy 800 in 0.5 mol/L thiosulfate solution during constant strain was investigated using electrochemical noise (EN) combined with 3-D microscope techniques. The in-situ morphology observation and EN results indicate that the SCC process could be divided into three stages: (1) passive film stabilization and growth, (2) crack initiation, (3) and crack growth. Power Spectral Density (PSD) and the probability distribution obtained from EN were used as the "fingerprint" to distinguish the different processes. During passive film stabilization and growth, the current noise signals resembled "white noise": when the crack initiated, many transient peaks could be seen in the current noise and the wavelet energy at low frequency as well as the noise resistance decreased. After crack propagation, the noise amplitudes increased, particularly the white noises at low and high frequencies ($W_L$ and $W_H$) in the PSDs. Finally, the detection of metal structure corrosion in a simulated sea splash zone and pipeline corrosion in the atmosphere are established.

• 한국정밀공학회지
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• 제17권1호
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• pp.83-92
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• 2000

Sound intensity method is well known as a visualization technique of sound field or sound propagation in noise control. Sound intensity or energy flux is a vector quantity which describes the amount and the direction of net flow of acoustic energy at a given position. Especially two dimensional sound intensity method is very useful in evaluating periodic characteristics and acoustic propagation mode of noise source. In this paper, we have studied the noise source Identification, acoustic sound field analysis, and characteristics of noise source of rotary compressor and scroll compressor for air conditioner using complex sound intensity method. Also we proposed a now method of time domain analysis which is used in evaluating of position of noise source in rotary and scroll compressor in this paper This paper presents the advantage, simplicity and economical efficiency of this method by analysing the characteristics of noise source with two dimensional complex sound intensity simultaneously.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.473-478
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• 2007

The energy efficiency and environment-friendly aspect of the railway system would be superior to other on-land transportation systems. In a preliminary feasibility study stage, the energy efficiency and problems related with environment are usually not considered. The railway noise and vibration which could be reasons of environmental problems are focused and studied in this paper. The investment for railway systems could be encouraged by the considering of main environmental elements evaluated with the modified noise and vibration standard for environment-friendly railway construction.

• Journal of applied mathematics & informatics
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• 제20권1_2호
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• pp.445-454
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• 2006

We describe a solution to the Ornstein-Uhlenbeck equation $\frac{dI}{dt}-\frac{1}{\tau}$I(t)=cV(t) where V(t) is a constant multiple of a Gaussian white noise. Our solution is based on a discrete set of Gaussian white noise obtained by taking sample points from a sum of single frequency harmonics that have random amplitudes, random frequencies, and random phases. Hence, it is different from the solution by the standard random walk using random numbers generated by the Box-Mueller algorithm. We prove that the power of the signal has the additive property, from which we derive that the Lyapunov characteristic exponent for our solution is positive. This compares with the solution by other methods where the noise is kept to be in an error range so that its Lyapunov exponent is negative.

• 신재생에너지
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• 제5권2호
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• pp.25-30
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• 2009

The wind tunnel test to identify the acoustic noise source position of the wind turbine blade was conducted in KARI low speed wind tunnel. Microphone array and time-domain beamforming methodology was applied to this study. To reduce the data processing time, a modified beamforming method with a criteria between calculation time step and grid size for rotating angle in the cylinderical coordinate system was proposed. The test results shows that the data processing time to identify the noise source position was reduced to 20% compared with conventional method. And the dominant noise source of the blade moves from inboard to blade tip as the frequency increases.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 춘계학술대회논문집
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• pp.1162-1167
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• 2001

Suction valve fluttering is generated by reciprocating motions of the piston inhaling and discharging process of gas in the hermetic compressor. A reactive type suction muffler, which produces high pressure-drop because of its complicated flow path, controls the impulsive noise radiated from the flutter of suction valve. The high-pressure drop in the muffler increases the transmission loss, but reduces the EER(Energy Efficiency Ratio) of the compressor. We consider how to design the high acoustic attenuation and low pressure-drop performance to take account of the acoustic and flow performances of the suction muffler. In this study, we identified the suction noise source of compressor from the measurement of the acoustic pulsation and flutter of suction valve. We analyzed the acoustic characteristics of muffler using the finite element method, and compared the experimental and analytical characteristics of flow path of suction muffler. Theoretical predictions and experimental results are compared from the viewpoint of the acoustic performance and energy efficiency of the compressor.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2012년도 춘계학술대회 논문집
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• pp.311-315
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• 2012

In these days, promising renewable energy, wind turbine is clean energy but has an environmental pollutant which is noise. Noise assessment is one of the major performance evaluations for wind turbine and nowadays, developing and research for measurement and method of the assessment considering environmental pollutants is being important. Object in this study is that figuring out sound power characteristic of the gearbox for wind turbine through measuring sound intensity. In back-to-back test, we can figure out the noise characteristic of the gearbox for wind turbine through comparing and measuring sound pressure level, sound power level in operating at the each load condition respectively.