• International journal of advanced smart convergence
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• v.6 no.2
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• pp.16-23
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• 2017

In contemporary modern society, people are constantly exposed to many kinds of noise, such as that from machinery, aircraft, construction sites, or road traffic. Noise is considered one of the most indispensable and influential parts of human life. This study investigates the acoustic characteristics of noise transfer from external sources to the human ear. For this study, we measured and analyzed various types of noise environments, installed monitoring speakers in a semi-anechoic room, and conducted intentional noise-filled experiments. In this environment, the size of the sounds generated by use of a portable device was also measured and the SNR (signal to noise ratio) calculated to study the influence of the noise. As sound is transmitted to the ear and the human body, it affects not only auditory damage but also other parts of the body. In this paper, we propose a proper SNR for noise emitted by portable IT equipment to prevent hearing loss when IT equipment is used.

• Journal of the Korea Safety Management & Science
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• v.17 no.4
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• pp.97-103
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• 2015

The people who are in the noise factory are difficult to hear and recognize about fire and to evacuate quickly when a fire occurs. This study was conducted to analyze workplace's background noise of 31 factories in Incheon and to know the workplace noise level comparing to fire alarm sound level. The measured average noise level was 96.8dB(A). Noise level of measured result was exceeded as 6.8dB(A) comparing to NFSC (National Fire Safety Code) noise level of 90dB. NFPA suggests that when background noise exceeds 85dB or more than that, other methods should be considered to know alarm sound. Also fire alarm sound should exceed more than 15dB(A) comparing to background noise level. Therefore it was concluded that the design of the fire alarm systems should not be applied to the workplace without considering background noise and it needs to be improved with regulations and the systems.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.51 no.3
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• pp.120-125
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• 2002

The switching-mode power converter has been widely used because of its features of high efficiency and small weight and size. These features are brought by the ON-OFF operation of semiconductor switching devices. However, this switching operation causes the surge and EMI(Electromagnetic Interference) which deteriorate the reliability of the converter themselves and entire electronic systems. This problem on the surge and noise is one of the most serious difficulties in AC-to-DC converter. In the switching-mode power converter, the output voltage is generally controlled by varying the duty ratio of main switch. When a converter operates in steady state, duty ratio of the converter is kept constant. So the power of switching noise is concentrated in specific frequencies. Generally, to reduce the EMI and improve the immunity of converter system, the switching frequency of converter needs to be properly modulated during a rectified line period instead of being kept constant. Random Pulse Width Modulation (RPWM) is performed by adding a random perturbation to switching instant while output-voltage regulation of converter is performed. RPWM method for reducing conducted EMI in single switch three phase discontinuous conduction mode boost converter is presented. The more white noise is injected, the more conducted EMI is reduced. But output-voltage is not sufficiently regulated. This is the reason why carrier frequency selection topology is proposed. In the case of carrier frequency selection, output-voltage of steady state and transient state is fully regulated. A RPWM control method was proposed in order to smooth the switching noise spectrum and reduce it's level. Experimental results are verified by converter operating at 300V/1kW with 5%~30% white noise input. Spectrum analysis is performed on the Phase current and the CM noise voltage. The former is measured with Current Probe and the latter is achieved with LISN, which are connected to the spectrum analyzer respectively.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.6
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• pp.624-631
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• 2008

This study evaluates the impact of aircraft noise on people's health using the Todai health index(THI). A questionnaire survey was conducted in the vicinity of Gimpo International Airport in Seoul, South Korea, from August 8th to September 9th, 2005. The survey area was divided into three groups based on different aircraft noise levels : area (1) for $80{\sim}85$ WECPNL, area (2) for $75{\sim}80$ WECPNL and area (3) for less than 75 WECPNL. In each area, approximately 200 respondents were sampled. Twelve scale scores of THI are converted to dichotomous variables based on scale scores of 90 percentile value or 10 percentile value in the control group. Logistic regression analysis taking twelve scores converted as the dependent variables and WECPNL(area), age, gender as the independent variables is conducted. Significant dose-response relationships are found in the scale of MOUT, DEPR, NERV, LIFE. Factor analysis was carried out and 2 factors are extracted. Those two factors might be called the "somatic factor" and the "mental factor". The dose-response relationship between two factors and noise seems to be unclear. Unexpectedly the odds ratio of the menatl factor in area (2), where the noise exposure level is lower than that of the area (1), is the highest and the annoyance in this area is also higher than area (1).

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.365.2-365
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• 2002

The flow field around a symmetrical airfoil in a uniform flow under the generation of noise was studied by experiments and numerical simulation. The experiments are conducted by visualizing the surface flow over the airfoil with a shear-sensitive liquid-crystal coating and by measuring the instantaneous velocity field around the trailing edge of the airfoil. The numerical simulation was carried out by LES. (omitted)

• Journal of Power Electronics
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• v.10 no.3
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• pp.228-234
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• 2010

This paper investigates the conducted-noise characteristics of a digitally-controlled randomly-switched dc-dc converter. In order to investigate the effect of the suggested digital controller on the conducted-noise characteristics of a dc-dc converter, three factors have been studied: the field-programmable gate array (FPGA) clock speed, the randomization ratio percentage, and the effect of using a closed loop feedback controller. A field-programmable gate array is much more flexible than analog control circuits, has a lower cost, and can be used for power supply applications. A novel FPGA-based implementation has been suggested for obtaining the experimental validations and realizing the studied concepts. Furthermore, the experimental results have been discussed and design guidelines have been included.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2000.11a
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• pp.286-291
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• 2000

본 논문에서는 일반적인 EMI 노이즈 개요 및 SMPS(Switching Mode Power Supply)에서의 Noise 발생 메카니즘을 분석하고, 전도성 Noise를 측정하였으며, SMPS에서 발생되는 잡음행태를 분석하여 대책방법을 연구하였다.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.22 no.4
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• pp.723-729
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• 2013

The contraction and expansion noise of a refrigerator are investigated, and some effective methods are proposed to reduce the level and occurrence frequency of noise. First, the noise of a refrigerator is measured to estimate the frequency spectrum and occurrence frequency of noise. Second, a sound visualization was conducted using an acoustic camera to determine the location of the noise source. From the results, it was observed that the internal part mainly producing noise was the third shelf in the freezer room. A method to estimate the acceleration on the location of the noise source is introduced to analyze the contraction and expansion noise precisely and accommodate experimental convenience. Noise reduction methods such as the replacement of the existing shelf with glass shelves, adoption of rail slides, and increase of roughness on the contact surface of the shelf are proposed and tested.

• Journal of KSNVE
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• v.11 no.3
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• pp.471-476
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• 2001

This paper focuses on the numerical prediction of airflow-induced sound in DVD drives. As a first step, computational fluid dynamics (CFD) is conducted to evaluate flow field characteristics due to the high-speed disk rotation, and to support the acoustic analysis. Acoustic analogy based on Ffowcs Wi1liams-Hawkings (FW-H) equation is adopted to predict aeroacoustic noise patterns. The integral solution for quadrupole volume source is included to identify the turbulence noise generated inside the DVD tray. The strength of sound pressure revel with respect to rotating speed is discussed to meet upfront demand on the high fidelity product development. The present study also focuses on the noise directivity and examines how much the sound noise is sensitive to change in rotating speed. Near-field noise is strongly affected by the flow field characteristic, which is caused by the complex shape of the tray. For a mid-field, the quadrupole noise play as a counterpart of thickness noise or loading noise, so it generates different sound noise Patterns compared with those in the near field.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.733-738
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• 2012

This paper presents active noise control for the reduction of transmission noise passing through opening of enclosures. Enclosures are essential measure to protect noise propagation from operating machinery. Access openings of the enclosures are important path of noise leakage. First, we modeled and analyzed the noise characteristics passing through the openings of the enclosure generated by the operation of the machinery based on the finite element method. We then implemented a feedforward controller to actively control the acoustic power through the opening. Finally, we conducted optimization of placement of the reference sensors for several cases of the number of sensors. A good control performances were achieved using a minimum number of microphones arranged a optimal placement.