• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.15 no.2 s.95
• /
• pp.176-183
• /
• 2005

The exhaust noise of auxiliary engine in ships is directly transmitted to bridge wing with only distance attenuation. It is not easy to find out practical treatment to be applied between exhaust pipe and bridge wing to reduce the transmission of the exhaust noise. In general, therefore, a silencer is fitted to reduce the exhaust noise and correspondingly noise of bridge wing. The silencer should be properly designed under the consideration of the frequency component of the exhaust noise and the required performance such as noise reduction or insertion loss. In general, the gas inside the exhaust pipe flows with high temperature and speed and thus onboard test condition is more adverse than the standard atmospheric condition. In this study, the test method to evaluate silencer performance using a probe microphone is introduced.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.16 no.8 s.113
• /
• pp.857-863
• /
• 2006

This paper described the performance test and sound characteristics of helicopter 'Tail-Fan' anti-torque system. In this research, Korea Aerospace Research Institute(KARI) developed 'Tail-Fan' anti-torque system for a helicopter and carried out performance and sound capturing tests of even and uneven tail fans. The performance test is carried out and the noise signals which are generated during the test are saved with microphones at the same time. The performance test's results meet the design requirements. Tone-corrected perceived noise level is reduced by replacing the even product with the uneven one.

• Journal of electromagnetic engineering and science
• /
• v.5 no.2
• /
• pp.49-60
• /
• 2005

In this paper, an efficient performance enhancement scheme for an adaptive antenna array under the flat and the frequency-selective Rayleigh fadings is proposed. The proposed signal enhancement scheme is the modified linear signal estimator which combines the rank N approximation by reducing noise eigenvalues(RANE) and Toeplitz matrix approximation(TMA) methods into the linear signal estimator. The proposed performance enhancement scheme is performed by not only reducing the noise component from the signal-plus-noise subspace using RANE but also having the theoretical property of noise-free signal using TMA. Consequently, the key idea of the proposed performance enhancement scheme is to greatly enhance the performance of an adaptive antenna array by removing all undesired noise effects from the post-correlation received signal. The proposed performance enhancement scheme applies at the Wiener maximal ratio combining(MRC) method which has been widely used as the conventional adaptive antenna array. It is shown through several simulation results that the performance of an adaptive antenna array using the proposed signal enhancement scheme is much superior to that of a system using the conventional method under several environments, i.e., a flat Rayleigh fading, a fast frequency-selective Rayleigh fading, a perfect/imperfect power control, a single cell, and a multicell.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2008.11a
• /
• pp.658-661
• /
• 2008

Vibrations transmitted through rolling tire are major sources of road noise in vehicle interior on the range of $0{\sim}500Hz$. Among various road noises, tire cavity noise makes many problems recently. Vehicle NVH performance has improved better and road surfaces are made well. But tires are changed to high inches and low series. So tire cavity noise becomes more serious. In this paper, a designed material for reducing tire cavity noise is proposed. On the surface inside tire, this material is attached at one position using double-tape. This material disperses the pressure variations inside the tire. So a spindle forces at wheel center are reduced. And tire cavity noise at vehicle interior is also reduced. Durability is verified by tire only test and vehicle test. Noise performance also compared with peak levels after attaching this material.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2011.10a
• /
• pp.301-306
• /
• 2011

In this paper, active noise barriers for attenuation of road noise are proposed. multi-channel audio systems, DAQ part and high performance DSP H/W were designed. Active noise control firmware programs were implemented for multi-channel off-line/on-line estimation methods for secondary path transfer functions and FIR/IIR filter structure are used main noise control algorithms. To evaluate performance of proposed systems, the experiments were performed in an active noise barrier test bed for various noise cases.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2014.10a
• /
• pp.710-711
• /
• 2014

In many cases, periodic noise occurs because most applications include motors, compressors and so on which have reciprocating motion. The noise usually contains tones at the fundamental frequency and at several higher harmonic frequencies in practice. For this type of noise, we developed a frequency-domain active noise control algorithm and determined that it's effective. However, the performance deteriorated for quasi-periodic noise. In this paper, we develop compensated frequency-domain active noise control algorithm for quasi-periodicity. And then, we implement computer simulation and compare the performance.

• Proceedings of the Acoustical Society of Korea Conference
• /
• 1985.10a
• /
• pp.87-94
• /
• 1985

In this paper, enhancement of speech corrupted by additive white or colored noise is stuided. The nuconstrained frequency-domain block least-mean-square (UFBLMS) adaptation algorithm and its frequency-weighted version are newly applied to speech enhancement. For enhancement of speech degraded by white noise, the performance of the UFBLMS algorithm is superior to the spectral subtraction method or Wiener filtering technique by more than 3 dB in segmented frequency-weighted signal-to-noise ratio(FWSNERSEG) when SNR of speech is in the range of 0 to 10 dB. As for enhancement of noisy speech corrupted by colored noise, the UFBLMS algorithm is superior to that of the spectral subtraction method by about 3 to 5 dB in FWSNRSEG. Also, it yields better performance by about 2 dB in FWSNR and FWSNRSEG than that of time-domain least-mean-square (TLMS) adaptive prediction filter(APF). In view of the computational complexity and performance improvement in speech quality and intelligibility, the frequency-weighted UFBLMS algorithm appears to yield the best performance among various algorithms in enhancing noisy speech corrupted by white or colored noise.

• The KSFM Journal of Fluid Machinery
• /
• v.2 no.4 s.5
• /
• pp.57-64
• /
• 1999

The prediction method of the performance and aerodynamic noise from a sirocco fan was developed and compared with measured data. To predict the performance of the sirocco fan, the well-known slip coefficients and various loss models were tested and applied to forward curved sirocco impellers. Using loss models proposed for both impeller and casing, the predicted performance characteristics were in good agreement with measured ones by an ANSI test plenum. Various scaling models for aerodynamic noise from the sirocco fan were evaluated and tested against measured power levels in terms of flow coefficient. It was shown that the turbulent broadband sound power from the sirocco fan can be modeled successfully by trailing edge noise.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.14 no.3
• /
• pp.214-223
• /
• 2004

This study aim to find an appropriate window for classrooms to provide proper sound insulation against aircraft noise and to achieve this goal, measurements were taken of the sound insulation performance of windows with various thicknesses of inner air space and sound absorption materials in the inner air spaces. As a result of this study the improvement of the sound insulation performance of windows(single, double and triple window) was shown through the analysis and the measuring of windows with these characteristics. These results may be applied to the manufacture of window frames and provide basic data for the improvement of the sound insulation performance of windows.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2003.11a
• /
• pp.710-717
• /
• 2003

This study aim to find an appropriate window for class rooms to provide proper sound insulation against aircraft noise and to achieve this, measurements were taken of the sound insulation performance of windows with varying thicknesses of inner air space and sound absorption materials in the inner air spaces. As a result of (his study the improvement of the sound insulation performance of windows(single , double and triple window) has been shown through the analysis and the measuring of windows with these characteristics. These results may be applied to the manufacture of window frames and provide data lot the improvement of the sound insulation performance of windows.