• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.491-495
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• 2008

The effects of vehicles and pavement surface types on noise have been investigated at the Korea Expressway Corporation's Test Road along the southbound side of the Jungbu Inland Expressway, South Korea. The study was conducted in 2005 and 2006 through field measurements at nine surface sections of asphalt concrete and Portland cement concrete pavements using eleven vehicles. For the road noise analysis, the sound power levels (PWLs) of combined noise (e.g., tire/pavement interaction noise and power-train noise together) and tire/pavement interaction noise using various vehicles were calculated based on the novel close proximity (NCPX) and pass-by methods. Then, the characteristics of the PWLs were evaluated according to surface type, vehicle type, and vehicle speed. The results show that the PWLs of vehicles are diversely affected by vehicle speed and the condition of the road surface.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 추계학술대회논문집
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• pp.763-766
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• 2006

The principal of a Maglev train is that floats on a magnetic field and is propelled by a linear induction motor. One of advantages is that it generates less noise compared to the wheel-on-rail train, because there are no wheels running along the rail. However, noises due to aero-dynamic disturbance and electrical system such as VVVF inverter and SLIM still occur. In this study, the Maglev cabin noises are measured during running and zero speed conditions. Pass-by noise measurements are performed to obtain outside noise during the operation of the train on the test tract. Data include a single microphone measurement as well as microphone array measurements. The array data are useful for sound source localization and more detailed noise reduction planning.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제48권1호
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• pp.45-50
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• 1999

This paper describes a partial discharge (PD) on-line monitoring system used for large turbine generators. The system consists of a broadband current transducer, a computer-aid PD measurement system. By using a programmable fabricate band pass filter and an adaptive digital filter, the system can suppress the noise and extract PD signal from the intense noise surroundings successfully. Two simulated PD sources, which often exist in the large generators, were simulated and detected. At the end of this paper, some field test results, obtained from a 200MW generating set, were presented and discussed.

• 조명전기설비학회논문지
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• 제25권2호
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• pp.143-149
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• 2011

In this paper, IIR structures are proposed to reduce the computation complexity of the secondary-pass estimation in active noise control(ANC) systems. However, there are stability problems of using IIR models to reduce the computation complexity in ANC systems. To overcome these problems, we propose a stabilizing procedure of recursive least mean squares (RLMS) algorithms for eatimating the parameters of IIR models of the secondary path transfer functions. The multichannel ANC systems are implemented by using the TMS320C6713 DSP board to test the performance of computation complexity and stability of the proposed methods. Comparing the IIR filters with the FIR filters, the IIR filters can reduce 50[%] of the computation and obtain similar noise reduction result.

• 대한음성학회지:말소리
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• 제62호
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• pp.85-96
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• 2007

In this paper, we carried out recognition experiments for noisy speech having various levels of car noise and output of an audio system using the speech interface. The speech interface consists of three parts: pre-processing, acoustic echo canceller, post-processing. First, a high pass filter is employed as a pre-processing part to remove some engine noises. Then, an echo canceller implemented by using an FIR-type filter with an NLMS adaptive algorithm is used to remove the music or speech coming from the audio system in a car. As a last part, the MMSE-STSA based speech enhancement method is applied to the out of the echo canceller to remove the residual noise further. For recognition experiments, we generated test signals by adding music to the car noisy speech from Aurora 2 database. The HTK-based continuous HMM system is constructed for a recognition system. Experimental results show that the proposed speech interface is very promising for robust speech recognition in a noisy car environment.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 추계학술대회 논문집
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• pp.265-267
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• 2013

Tire labeling is an important issue to reduce $CO_2$ and to secure the safety of tire/vehicle on wet road. A basic study on the effects of tire basic stiffness design on tire labeling performance has been done through experimental test. The pass-by noise is affected by tire structural design. The tire with lower side part stiffness and lower tread part stiffness has the lowest PBN level and the best wet grip. And the tire with higher tread part stiffness and higher side part stiffness has the better RR performance. Also it is observed that the trade-off between RR and wet grip exists for various tire stiffness design.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 춘계학술대회논문집
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• pp.919-924
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• 2004

A CFA(Cooling Fan Assembly) is composed of a fan, motor and shroud, which is at the back of the automotive radiator. By forcing the wind to pass, the CFA controls the cooling performance of the radiator. The noise and vibration of the CFA may be primarily due to the resonance between the CFA and engine. The Interference among the fan, shroud and radiator by deformation is considered when the CFA is designed. In this paper, in order to analyze the structural vibration of the CFA for automobiles, a finite element model of the CFA is established by using a commercial FEM code. After the finite element modeling, the natural frequencies and the mode shapes are obtained from the FE analysis. The natural frequencies are obtained from the vibration test as well. Then, the results of the vibration test are compared with those of the FE analysis. The natural frequencies obtained by experiment have a great similarity to the results from FE model. We have confirmed the validity of the FE model and verify the structural safety for the resonance. The stress and displacements are obtained from FE analysis. We have confirmed the safety for the interference and failure.

• 수산해양기술연구
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• 제30권2호
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• pp.125-131
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• 1994

This paper describes a method to measure the distortion level of loudspeaker using a LMS(Least Mean Square) adaptive filter. Conventional technique to measure the distortion level uses a band-pass filter with a sharp cut-off frequency characteristics. However. such the band-pass filter has a bed time response characteristics. On the other hand, the proposed method offers us an easy way to measure the specified harmonic distortion level with a small hardware. Moreover, our method is not affected by noise which has no correlation with the test signal, and the measurement can be carried out in a noisy environment. The effectiveness of the proposed method is confirmed by experiment using a loudspeaker in a noisy room.

• 한국군사과학기술학회지
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• 제13권4호
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• pp.528-533
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• 2010

This paper describes a calculation method of source level of a ship transient noise, which is one of the important elements for the ship detection. Aim of transient noise measurements is to evaluate of acoustic energy due to singular occurrence, which is therefore defined as non-periodic and short termed events like an attack periscope, a rudder and a torpedo door. In generally, in the case of randomly spaced impulse, the spectrum becomes a broadband random noise with no distinctive pattern. Therefore, frequency analysis is not particularly revealing for type of signal. In the paper, it is performed in time domain to analyze a transient noise. However, a source level of transient noise is required an investigation for multiple frequency band. So, in order to calculate a source level of transient noise, a design of exponential weighting function, convolution, band pass filtering, peak detection, root mean square, and parameter compensation are applied. The effectiveness of this calculation scheme is studied through computer simulations and a sea test. Furthermore, an application of the method is applied in a real case.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 춘계학술대회논문집
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• pp.991-996
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• 2001

It is well known that there are two experimental errors on acoustic decay measurements. One is due to the influence of the band pass filter the other one is that of an averaging device. In this paper the influence of the filter is in detail investigated. To minimize the influence of filter, the product of the filter bandwidth Β (3㏈ bandwidth) and the reverberation time T$\sub$60/ of the room under test is at least 16. Moreover, if the initial part of an acoustic decay curve is important, the strong requirement, i.e. BT$\sub$60/＞ 64, must be satisfied. In this paper, the wavelet filter bank instead of the band pass filter bank is applied to obtain an acoustic decay curve. As results, the influence of filter is reduced and then the value of BT$\sub$60/ required for obtaining an acceptable decay curve is at least 4. The strong requirement for the initial part of a decay curve is also replaced by the BT$\sub$60/＞ 16 instead of BT$\sub$60/＞ 64.