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Reduction of Radiated Noise in a Reciprocating Compressor (왕복동식 압축기의 방사소음 저감)

  • Kim, Yong-Tae;Lee, Jin-Woo;Joo, Jae-Man
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.431-434
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    • 2005
  • Generally, noise in a reciprocating compressor is attributed to the driving force of a pump. However, close examination shows that the noise heard by customers finally results from radiation of a shell in a compressor, the noise caused by both transmission through a shell and resonance with the natural frequency of a shell. Therefore, the peak frequencies contributing to the overall level of a compressor' noise are closely concerned with vibration of a shell. That's why radiated noise by vibration can be reduced by changing the mode of a shell and by shifting the peak frequencies to other ranges, which are not globally related with the overall noise level. In this paper, the main peak frequencies are analyzed to reduce the radiated noise of a shell, and the vibration characteristics of a shell are examined through Frequency Response Function and Finite Element Analysis. Moreover, the Operational Deflection Shape for a shell is measured with consideration of real driving force of a pump. Finally, the optimum position on a shell, closely related to the main peak frequencies, is found, and the overall noise level caused by radiated noise of a shell is noticeably reduced by mass or stiffness modification of the position.

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TIME-DOMAIN TECHNIQUE FOR FRONT-END NOISE SIMULATION IN NUCLEAR SPECTROSCOPY

  • Neamintara, Hudsaleark;Mangclaviraj, Virul;Punnachaiya, Suvit
    • Nuclear Engineering and Technology
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    • v.39 no.6
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    • pp.717-724
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    • 2007
  • A measurement-based time-domain noise simulation of radiation detector-preamplifier (front-end) noise in nuclear spectroscopy is described. The time-domain noise simulation was performed by generating "noise random numbers" using Monte Carlo's inverse method. The probability of unpredictable noise was derived from the empirical cumulative distribution function via the sampled noise, which was measured from a preamplifier output. Results of the simulated noise were investigated as functions of time, frequency, and statistical domains. Noise behavior was evaluated using the signal wave-shaping function, and was compared with the actual noise. Similarities between the response characteristics of the simulated and the actual preamplifier output noises were found. The simulated noise and the computed nuclear pulse signal were also combined to generate a simulated preamplifier output signal. Such simulated output signals could be used in nuclear spectroscopy to determine energy resolution degradation from front-end noise effect.

Medium.Large Horizontal Axis Wind Turbine Noise Analysis Considering Blade Passing Frequency Noise and Retarded Time (블레이드 통과 주파수 소음과 지연시간을 고려한 중.대형 수평축 풍력발전기의 공력소음해석)

  • Kim, Hyun-Jung;Kim, Ho-Geon;Lee, Soo-Gab
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.1490-1493
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    • 2007
  • Aerodynamic noise generated from wind turbines is predicted by it's classified source mechanisms using computational method. BPF noise according to the blade passing motion, is modelled on monopole and dipole sources. They are predicted by Farassat 1A equation. Airfoil self noise and turbulence ingestion noise are modelled upon quadrupole sources and are predicted by semi-empirical formulas composed on the groundwork of Brooks et al. and Lowson. Retarded time is considered, not only in low frequency noise prediction but also in turbulence ingestion noise and airfoil self noise prediction. Wind turbine noise emission of a 3MW wind turbine and a 600 kW wind turbine, standing for large and middle sized wind turbines, is analyzed.

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Adaptive Active Noise Control of Single Sensor Method (단일 센서 방식의 적응 능동 소음제어)

  • 김영달;장석구
    • Journal of KSNVE
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    • v.10 no.6
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    • pp.941-948
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    • 2000
  • Active noise control is an approach to reduce the noise by utilizing a secondary noise source that destructively interferes with the unwanted noise. In general, active noise control systems rely on multiple sensors to measure the unwanted noise field and the effect of the cancellation. This paper develops an approach that utilizes a single sensor. The noise field is modeled as a stochastic process, and an adaptive algorithm is used to adaptively estimate the parameters of the process. Based on these parameter estimates, a canceling signal is generated. Oppenheim assumed that transfer function characteristics from the canceling source to the error sensor is only a propagation delay. This paper proposes a modified Oppenheim algorithm by considering transfer characteristics of speaker-path-sensor This transfer characteristics is adaptively cancelled by the proposed adaptive modeling technique. Feasibility of the proposed method is proved by computer simulations with artificially generated random noises and sine wave noise. The details of the proposed architecture. and theoretical simulation of the noise cancellation system for three dimension enclosure are presented in the Paper.

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Noise Reduction of a Range Hood using Micro-Perforated Panel (미세 다공판을 이용한 레인지 후드의 소음저감)

  • Kim, Deok-Han;Song, Hwa-Young;Lee, Dong-Hoon;Lee, Chang-Kun;Kim, Dong-Yun
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.1205-1208
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    • 2006
  • This paper introduces a study for the noise reduction of a range hood for household. Generally, range hoods have a built-in sirocco fan from which rumbling noise is generated. Though the rumbling noise has low noise level. this noise makes most of the users nervous due to the its low frequency characteristics. For the purpose of noise reduction, in this study, a micro-perforated panel system is installed in the fan housing of range hood. From the experimental results, it is confirmed that the noise level emitted from the range hood is decreased over 2dB(A) in all frequency regions due to the effect of noise reduction by micro-perforated panel system.

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A comparative Study of Noise Prediction Method for Road Traffic Noise Map -Focused on Foreign Traffic Noise Prediction Method- (소음지도 제작을 위한 도로교통 소음예측식 비교연구 -국외 예측식을 중심으로-)

  • Jang, Hwan;Bang, Min;Kim, Heung-Sik
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.709-714
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    • 2008
  • The various computer programs are used in computer simulation of the traffic noise prediction. But the difference or problem of calculation method used for road traffic noise prediction is not exactly investigated. In this paper, Road traffic noise is predicted on the specific regions by using four prediction methods such as XPS31-133 model(France), RLS-90 model(Germany), ASJ RTN model(Japan) and FHWA model(U.S.A.), which are operated by a program named SoundPLAN, a program to predict road traffic noise. Those prediction values are compared with a measurement value. The results show that four prediction values for taraffic noise are a little different, because of various input factors according to the prediction methods.

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Measurement Method of Noise Correlation Matrix Using Relative Noise Ratio (상대적인 잡음비를 이용한 잡음상관행렬 측정방법)

  • Lee, Dong-Hyun;Yeom, Kyung-Whan
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.27 no.5
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    • pp.430-437
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    • 2016
  • In general, noise measurement results show larger random ripple than those of the network analyzer. The reason for the lager random ripple of the noise measurements is considered that the general noise measurements uses absolute measured noise powers, while the network analyzer measures using a ratio of the measured powers. In this paper, a novel measurement method of noise correlation matrix using relative noise ratios is proposed. Proposed method measures the five noise powers of DUT for the five input impedance variations and the four relative noise ratios are formed using the five measured noise powers. The four noise ratios are used to compute the noise correlation matrix and noise parameters. The resulting noise parameters for a 0.5 dB attenuator show good agreements with theoretical values calculated by S-parameters. Also, the noise parameters of an active DUT with a noise figure of less than 1 dB are measured and the measured results show a small random ripple as expected and their values are physically acceptable. In conclusion, the proposed method can be applied to the noise parameter measurements for DUT with a noise figure below 1 dB.

Road Noise Prediction Based on Frequency Response Function of Tire Utilizing Cleat Excitation Method (크리트 가진법을 이용한 타이어특성에 따른 로드노이즈 예측 연구)

  • Park, Jong-Ho;Hwang, Sung-Wook;Lee, Sang-Kwon
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.22 no.8
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    • pp.720-728
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    • 2012
  • It is important for identification of noise and vibration problem of tire to consider influence of interaction between road and tire. A quantification of road noise is a challenging issue in vehicle NVH due to extremely complicated transfer paths of road noise as well as the difficulty in an experimental identification of input force from tire-road interaction. A noise caused by tire is divided into road noise(structure-borne noise) and pattern noise(air-borne noise). Pattern noise is caused by pattern shape of tire, which has larger than 500 Hz, but road noise is generated by the interactions between a tire and a vehicle body. In this paper, we define the quantitative analysis for road noise caused by interactions between tire and road parameters. For the identification of road noise, the chassis dynamometer that is equipped $10mm{\times}10mm $ square cleat in the semi-anechoic chamber is used, and the tire spindle forces are measured by load cell. The vibro-acoustic transfer function between ear position and wheel center was measured by the vibro-acoustic reciprocity method. In this study three tires with different type of mechanical are used for the experiment work.

A Study on the Conversion of Annoyance using the Noise Standard in Korea (국내 소음기준을 이용한 성가심(annoyance) 변환에 관한 연구)

  • Kim, Deuk-Sung;Chang, Seo-Il;Lee, Ki-Jung;Lee, Yeon-Soo
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.754-758
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    • 2006
  • The purpose of this study is to propose calculation and application method of a common factor from different noise source unit such as $L_{eq}$ and WECPNL, A calculation was conducted by method that propose TNO-PG. Also, An applied example is a noise environmental standard of Korea and Japan. After %HA of two country are calculated, noise standards of two countries were compared by using %HA. The result by a equation of %HA is to convert a noise level($L_{dn}$) into a %HA. To calculate a %HA, First $L_{eq}$ is converted into $L_{dn}$. Then, $L_{dn}$, has inputted into and %HA has deduced from a %HA equation of TNO-PG. If the same area is applied the same %HA value according to area categories, it can be applied the same %HA to different noise sources. As a results. a noise levels have computed different values because responses of human change in accordance with a noise sources. This results can be applied to the noise environmental assessment for a domestic railway and aircraft noise.

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A Case Study on Noise Reduction Effect of Two-layer Porous Asphalt Pavement in an Urban Area (도심지 내 복층 저소음포장 설치에 따른 소음저감 사례연구)

  • Jung, Jong-Seo;Sohn, Jeong-Rak;Lee, Soo-Hyoung;Yang, Hong-Seok
    • International Journal of Highway Engineering
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    • v.18 no.5
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    • pp.49-56
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    • 2016
  • PURPOSES : In this study, noise reduction effect of a two-layer porous asphalt pavement was investigated through site measurement and computer simulation. METHODS : To examine noise reduction effect, a 3 km long quiet pavement was installed by removing previous normal pavement, which had a rather low porosity. The studied site was a high-rise apartment building surrounded by the quiet pavement and Seoul ring road with heavy traffic volume, indicating relatively high background noise. RESULTS : The measurement result before and after installing the quiet pavement showed a noise reduction effect of 4.3 dB(A) at a distance of 7.5 m from the road. After validating the accuracy of simulation using SoundPLAN, the reduction in SPL(sound pressure level) at the facades by the quiet pavement was predicted by considering five different road conditions generating traffic noise from each road or in the combination of the quiet pavement and Seoul ring road. In the case of no noise from Seoul ring road, noise reduction at the facades was 4.2 dB(A) on average for 702 housing units. With background noise from Seoul ring road, however, the average SPL decreased to 2.0 dB(A). Regarding subjective response of noise, the number of housing units with a noise reduction of over 3 dB(A) was 229 out of 706 units (approximately 32%). For 77 housing units, the noise reduction was between 1~3 dB(A), while it was less than 1 dB(A) for 400 housing units. CONCLUSIONS : The overall result indicates that the quiet pavement is useful to reduce noise evenly at low and high floors compared to noise barriers, especially in the urban situation where background noise is low.