• 한국소음진동공학회논문집
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• 제12권5호
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• pp.374-379
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• 2002

A new active muffler system has been developed and its superior performance on both noise reduction and engine torque increase is demonstrated with experiment. Main characteristic of the proposed muffler system is the use of destructive interference by transmission path difference of divided exhaust pipes to reduce major exhaust noise components thereby overcoming problems of other active exhaust noise control methods. The exhaust pipe is divided into two sections and joined again downstream. One divided pipe has a sliding mechanism to vary its length, which is controlled to make half wavelength transmission path difference for the major engine rpm frequency. In this system one divided pipe is used to control major rpm frequency and its Harmonics and another pipe is used to control noise component double the frequency of rpm. An after-market tuning muffler, which has very simple internal structure and minimal back pressure, is also installed to remove remaining wideband noise. To make the system to be small enough to be practical, conventional muffler is also installed and used in low rpm range and active muffler is only employed in high rpm range. Noise reduction of the proposed system is comparable to conventional passive muffler. The engine dynamo test has proved the proposed system can recover almost all the torque lost by conventional muffler.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.812-817
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• 2005

The objective of the present work is to develop a time-domain numerical method of broadband noise in a cascade of airfoils. This paper focuses on dipole broadband noise sources, resulting from the interaction of turbulent inflows with the flat-plate airfoil cascade. The turbulence response of a two-dimensional cascade is studied by solving both of the linearised and full nonlinear Euler equations employing accurate higher order spatial differencing, time stepping techniques and non-reflecting inflow/outflow boundary condition. The time-domain result using the linearised Euler equations shows good agreement with the analytical solution using the modified LINSUB code. Through the comparison of the nonlinear time-domain result using the full nonlinear Euler equations with the linear, it is found that the acoustic mode amplitude of the nonlinear response is less than that of the linear response due to the energy cascade from low frequency components to the high frequency ones. Considering the merits of the time-domain methods over the typical time-linearised frequency-domain analysis, the current method is expected to be promising tools for analyzing the effects of the airfoil shapes, non-uniform background flow, linear-nonliear regimes on the broadband noise due to gust-cascade interaction.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2000년도 KIASC Conference 2000 / 2000년도 학술대회 논문집
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• pp.26-28
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• 2000

Generally high frequency electromagnetic waves can not penetrate into waveguide, and it is called skin effect. Since the shape of superconducting CICC (Cabel In Conduit Conductor) is similar to that of waveguide, the characteristics of waveguide can be applied to CICC. In this paper, we analyzed penetrated magnetic field in CICC according to external noise. From it, noise frequency bandwidth affecting voltage tap sensor in CICC was found.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 추계학술대회 논문집
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• pp.843-848
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• 2011

Planning and construction of railway for high speed trains up to 400 km/h are recently driven in Korea. High speed train is one of the environment-friendly fastest mass transportation means but its noise generated by rolling, traction and aerodynamic mechanism can cause public complaints of residents nearby railways. To cost-effectively prevent the troublesome noise in a railway planning stage, the rational railway noise prediction method considering the characteristics of trains as well as railway structures should be required but it is difficult to find authentic methods for Korean high speed trains such as KTX and KTX-II. In this study, we propose a framework of our own railway noise prediction model emitted by Korean high speed trains over 250 km/h based on the recent research results carried out in EU countries. The model considers railway sound power level using several point sources distributed in heights as well as tracks, whose detail speed- and frequency-dependent emission characteristics of Korean high speed trains should be determined in near future by measurement or numerical analysis. The attenuation during propagation outdoors is calculated by the well-known ISO 9613-2 and auxiliary methods to consider undulated terrain and wind effect.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.388-395
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• 2000

Axial fans are widely used in heavy machines due to their ability to produce high flow rate for cooling of engines. At the same time, the noise generated by these fans causes one of the most serious problems. This work is concerned with the low noise technique of discrete frequency noise. The prediction model, which allowed the calculation of acoustic pressure at the blade passing frequency and it's harmonics, has been developed by Farrasat. This theory is founded upon the acoustic radiation of unsteady forces acting on blade. To calculate the unsteady resultant force over the fan blade. Time-Marching Free-Wake Method are used. The ideas of low noise technique are obtained from Blade-Momentum Methods. In this paper, the discussion is confined to the performance and discrete noise of axial fan in heavy equipments.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 C
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• pp.1784-1786
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• 1996

It is necessary to eliminate the broad band noise which frequency is in a few kHz to MHz in the AC line to supply the power to electrical and electronic control equipments. Because this kind of noise could damage the device or could be a source of malfunction, many devices like a filter and surge suppressor are developed to cut off the noise. But those device could not disconnected from the power line, so it remain some problem and on be used in limited area, In this paper, we present performance test results NCT(noise Cut Transformer) with excellent performance for reducing the high frequency noise and surge existing in the power line.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 II
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• pp.1120-1125
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• 2001

A new concept of piezoelectric smart panels for noise reduction in wide band frequencies is proposed and their possibility is experimentally investigated. Multi-mode damping is studied by using a newly proposed tuning method. The proposed panels are based on passive shunt damping methods. This method is based on electrical impedance model and maximizing the dissipated energy at the shunt circuit. four PZT are attached on smart panel for improving performance of transmission noise reduction. 0 prove the concept of piezoelectric smart panels, an acoustic measurement experiment was performed. The smart panels exhibit a good noise reduction in middle and high frequency ranges due to the mass effects of absorbing materials or/and the air gap. The use of piezoelectric smart panel renders noise reduction at resonance frequency. Noise reduction at multiple resonance frequencies is experimentally investigaed.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 추계학술대회논문집
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• pp.106-112
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• 2000

Axial fans are widely used in heavy machines due to their ability to produce high flow rate for cooling of engines. At the same time. the noise generated by these fans causes one of the most serious problems. This work is concerned with the low noise technique of discrete frequency noise. The prediction model. which allowed the calculation of acoustic pressure at the blade passing frequency and it's harmonics. has been developed by Farrasat. This theory is founded upon the acoustic radiation of unsteady forces acting on blade. To calculate the unsteady resultant force over the fan blade. Time-Marching Free-Wake Method are used. The fan noise of fan system having unsymmetric engine-room is predicted. In this paper, the discussion is confined to the performance and discrete noise of axial fan and front part of engine room in heavy equipments.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2006년도 학술발표회 논문집
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• pp.49-55
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• 2006

The purpose of the present study is to analyse characteristics of the background noise for the broadband seismic stations in KMA. It is well known that the background noise arises continuously from long period microseism, sea waves, minute changes of atmospheric pressure, seasonal temperature change of the ground surface, culture activities, and etc. The background noise shows spatial and temporal changes and it has various characteristics such as its spectral amplitudes in frequency domain are not constant Such the background noise gives considerable influences on the quality of seismic record. To investigate annual variations, the background noise was separated into high frequency components of above 1Hz More larger average amplitude is found in winter than other seasons. The average amplitude for 12 seismic stations are compared. It is known that the background noise is considerably larger in stations located in island region such as Jeju, Ulleungdo, and Bagryeongdo seismic stations. However the noise is relatively small in inland stations such as Chuncheon, Chungju and Uljin seismic stations.

• Transactions on Electrical and Electronic Materials
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• 제7권1호
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• pp.42-50
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• 2006

Co-Fe-Al-O nano-granular thin films with high electrical resistivity, fabricated by radio frequency magnetron sputtering under an $Ar+O_2$ atmosphere, are found to show good soft magnetic properties in the GHz frequency range. The real part value of the relative permeability is 260 at low frequencies and this value is maintained up to the GHz frequency range. A non-integrated type noise filter on a coplanar waveguide transmission line is demonstrated by using the Co-Fe-Al-O nano-granular thin film with the dimensions of $4\;mm(l){\times}4\;mm(w){\times}0.1\;{\mu}m(t)$. The insertion loss is very low being less than 0.3 dB and this low value is maintained up to 2 GHz. At a ferromagnetic resonance frequency of 3.3 GHz, the degree of noise suppression is measured to be 3 dB. This level of noise attenuation is small for real applications, but there is much room for further improvement by increasing the magnetic volume and integrating the magnetic thin film into the CPW transmission line.