• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1997.10a
• /
• pp.391-395
• /
• 1997

The transmission of sound and vibration through structures is of interest in many noise control problems, including architectural acoustics, sound transmission through air craft, spacecraft and ship, and the transmission of noise through machinery and engine enclosures. Statistical Energy Analysis provides a simple and accurate method of approaching these problems. In this paper, comparing the measured coupling loss factor of plate-beam with measured coupling loss factor of mass on the junction will be inspected.

• 제어로봇시스템학회:학술대회논문집
• /
• 1993.10b
• /
• pp.550-553
• /
• 1993

Methods of Alternating Noise Canceling were previously developed for the optical instrumentation;one using a dual photo sensor and another using a single photo sensor that could cancel normal mode noise on a transmission line, even if the noise was of equal status noise. But the methods could not remove noise on sensor line. This paper discusses a new method of using a photo sensor with a resistance sensordummy, effectively canceling equal status normal mode noise not only on a sensor line but also on a transmission line of an optical instrumentation. The accuracy of this method has been verified by experiments using sinusoidal wave as an equal status noise on a sensor line and/or rectangular wave as an equal status wide band noise on a transmission line respectively.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2001.05a
• /
• pp.628-632
• /
• 2001

Experimental approach was investigated to improve gear rattle noise of a small car. During the development of a small car serious problem occurred inside the transmission gear units. The transmission was a carried over system from a less powered predecessor. Several components of suspicion were investigated, and applied to reduce rattle noise. In general, backlash, the assembly gaps, and the clutch disk rattle induce gear rattle noise. Above mentioned improvements were applied to reduce the noise, but still problem remained. Meanwhile, the temperature inside the gearbox was reported to be unusually high and the life of transmission oil quality deteriorated drastically, Temperature increment caused the large gap between the bearing outer diameter and the transmission housing. Large gap made the gear shaft assembly move intermittently and impact each other. The tighter control of the assembly gap allowed the rotating shafts smoothly and reduced the gear rattle noise even in the high temperature range.

• The Journal of the Acoustical Society of Korea
• /
• v.40 no.6
• /
• pp.607-614
• /
• 2021

Research on elevator noise has mainly focused on the cause of its occurrence and measures to reduce it. There is still insufficient research on how to accurately measure and evaluate elevator noise. There is a measurement method established as an international standard for the measurement method, but it is also difficult to apply to high-rise apartments, and there are many cases that do not closely reflect the characteristics of elevator noise. In order to solve this problem, a study was conducted to improve the elevator noise measurement method in the current standard. In this study, the characteristics of elevator noise were closely identified. Through frequency analysis of the elevator noise and other equipment, it was verified that the elevator noise is noise with different characteristics from other equipment. Elevator noise was compared with heavy floor impact noise, which is a representative structural transmission noise, as structural transmission noise. Elevator noise was compared with heavy floor impact noise, which is a representative structural transmission noise, as structural transmission noise. The correlation between bang machine and rubber ball was found to be very high at 0.9 level. As a result, it was verified that the mid-low frequency band of the elevator noise is the main structural transmission noise and cannot be evaluated together with other equipment.

• Journal of KSNVE
• /
• v.11 no.3
• /
• pp.401-409
• /
• 2001

Passive type mufflers installed on every car haute inherent problem of lowering engine power and fuel efficiency caused by backpressure which is byproduct of complex internal structure. Recent improvements like installing a calve to change exhaust gas path depending on power requirement and rpm have only marginally improved performance. Tremendous amount of recent research works on active exhaust noise control have failed to commercialize because of numerous physical and economical reasons. In this paper, a unique seal-active muffler using difference of transmission paths is presented. In this system exhaust pipe is divided into two and joined again downstream. Exhaust noise is reduced by destructive interference when two-divided noise join again with transmission paths'difference which is half of the wavelength of a main noise frequency. One divided path has a sliding mechanism to change length thereby transmission path length difference is adjusted to entwine rpm change. The proposed system has minimal backpressure and does not need a secondary sound source like a speaker so it can overcome many problems of failed active noise control methods. We have verified proposed system's superior performance by simulation and comparison experiment with passive mufflers.

• The Transactions of the Korean Institute of Electrical Engineers A
• /
• v.51 no.1
• /
• pp.23-28
• /
• 2002

In order to survey the radiation characteristics of pure line noise of unwanted noise from overhead high voltage AC transmission lines, a disk type gap noise generator was manufactured. Disk size which decides capacitance between the noise generator and earth was selected through preliminary indoor experiments and analysis by using surface charge method. The capacitance is one of principal parameters related to the injection of a proper noise current into lines. On the basis of the capacitance obtained from calculation, 5mm of space was given to the gap of the noise generator to be installed o test line and an aluminum disk of 60cm radius was made. The field experiments were performed with the noise generator hung on the Kochang 765 kV full scale test line. As the results, the useful data which can be used to analysis the radiation characteristics of noise from transmission lines were obtained. Those are the directivity of antenna toward the line, lateral profiles, frequency spectra, height pattern and so on.

• Journal of Mechanical Science and Technology
• /
• v.18 no.11
• /
• pp.1909-1915
• /
• 2004

The hermetic rotary compressor is one of the most important components of an air conditioning system since it has a great effect on both the performance and the noise and vibration of the system. Noise and vibration occurs due to gas pulsation during the compression process and to unbalanced dynamic force. In order to reduce noise and vibration, it is necessary to identify their sources and transmission path and effectively control them. Many approaches have been tried in order to identify the noise transmission path of a compressor. However, identification has proven to be difficult since the characteristics of compressor noise are complicated due to the interaction of the compressor parts and gas pulsation. In this study, the statistical energy analysis has been used to trace the energy flow in the compressor and to identify the transmission paths from the noise source to the exterior sound field.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.9 no.6
• /
• pp.9-18
• /
• 2000

This study includes noise automatic inspection system for washing machine auto-transmission one of modern home necessary. We effort to find and certificate sound noise source by sound power and sound intensity, and apply to frequency analysis in vibration related sound noise. still more we have been studying to data acquisition and programming for MS VisualBasic version 5.0. System component is below. 1) Pentium PC or data acquisition. 2) DSO for noise acquisition. 3)S/W for comparison and decision. 4) I/F Board for data communication. Wave form data through the DSO are converting to ASCII code data. The ASCII code through binary converting S/W. Finally we will making noise monitoring system and automatic inspection system.

• Proceedings of the KSR Conference
• /
• 1998.05a
• /
• pp.249-256
• /
• 1998

Design target values of transmission loss in a high-speed train wall are suggested by calculating the difference between interior and exterior noise levels of it. Exterior noise level distribution on the boundary of train wall is calculated by Sysnoise, with sound source input prepared by experiments. Two kinds of exterior sound sources are considered, the rolling noise of train wheels on the rail and the aerodynamic noise from the pantograph. Interior noise level is provided by high-speed design target. Transmission loss characteristics according to the frequency band are examined.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
• /
• v.4 no.3
• /
• pp.18-29
• /
• 1993

In single mode fiber optic transmission systems(FOT's) operated at high modulation rates over long fiber spans, chromatic dispersion can produce distortion in the demodulated waveforms, resulting in intersymbol interference(ISI) in the received signal and a reduction of transmission system performance. In this paper, chromatic dispersion limitations for intensity modulation and direct detection(IM-DD) systems are studied by considering the effect of phase modulation to amplitude modulation (PM-AM) conversion noise. Laser phase noise conversion to amplitude noise due to fiber chromatic dispersion is analyzed by deriving the noise power spectral density. We first derive the noise power spectral density of the laser phase noise to intensity noise conver- sion. Next, also evaluate the system power penalty and the transmitter laser linewidth required to avoid PM-AM conversion noise penalties in long-haul nonregenerative transmission system using an external modulator and optical amplifiers. For such system with optical amplifiers, transmission sys- tem length is limited due to fiber chromatic dispersion, even if an ideal external modulator is used.