• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2006.05a
• /
• pp.114-117
• /
• 2006

The air filter in engine intake system has a function of filtrating the dirt in the scavenging air as well as attenuating the noise. The noise attenuation within the air cleaner filter, however, has been regarded as negligible by the field engineers. In this paper, for the analysis of the acoustical performance of air filter, an acoustical model was suggested and the characteristics of air filter system were investigated. Fibrous structure of the filter element was modeled as a micro-perforated panel using the flow resistivity and porosity. The pleated geometry of the filter element was modeled as two coupled ducts that have permeable walls, in which each duct area was assumed being constant. Using such simplified geometry, a mathematical model was developed for the sound propagation within a narrow duct system. Visco-thermal effect was considered in modeling the sound propagation through such tubes; the filter box was modeled as a rigid rectangular box. By combining two models, a four-pole transfer matrix was derived. For the validation purpose, transmission loss was measured for a plastic rectangular box containing an air filter. A noticeable effect of the air filter element was observed by including the filter into the box. Comparing the predicted and measured data, we found that the predicted TL agrees well with experimental results, in particular, in magnitude and frequency at TL troughs.

• Journal of Korea Water Resources Association
• /
• v.49 no.8
• /
• pp.707-717
• /
• 2016

In this study we carried out laboratory experiments to investigate the three-dimensional turbulent flows around a spur dike installed in a straight open channel flume. The experiments are conducted under the two different Froude numbers, 0.100 and 0.185. The three-dimensional instantaneous velocities are measured using the Acoustic Doppler Velocimetry (ADV) to obtain the time-averaged velocities and the turbulence stresses. The measured flow field reveal the existence of the recirculation zones downstream of the dike, which is characterized by high turbulence stresses near its boundaries. The results show that although the overall mean flow patterns between the low and high Froude number cases are very similar to each other, there exist moderate changes in the maximum dimensionless turbulence stresses and the maximum dimensionless bed shear stress with the increase of the Froude number.

• Journal of the Society of Naval Architects of Korea
• /
• v.45 no.4
• /
• pp.345-352
• /
• 2008

The motion of a projectile initiated by the release of highly pressurized air is simulated presuming the flow field as a two dimensional one. The effects of water compressibility on projectile movements are investigated, comparing results based on the Fluent VOF model where water is treated as an incompressible medium with those from the presently developed VOF scheme. The present model considers compressibility of both air and water. The Fluent results show that the body moves farther and at higher speeds than the present ones. As time proceeds, the relative difference of speed and displacement between the two results drops substantially, after acoustic waves in water traverse and return the full length of the tube several times. To estimate instantaneous accelerations, however, requires implementation of the water compressibility effect as discrepancies between them do not decrease even after several pressure wave cycles.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2003.05a
• /
• pp.1026-1031
• /
• 2003

Numbers of people living in high rise apartments are growing due to the overcrowding in urban area. Acoustic environment in those residential buildings has been seriously deteriorated by the increase of wheeled transports. Commonly used sound barriers have a limitation in controlling noise influencing higher part of a residential building. The use of noise barrier tunnels can be an alternative to supplement the defects of conventional noise barriers. But intensive measurements on noise levels at apartments vicinity of current noise barrier tunnels show that the tunnel now has a limited advantage on reducing the noise levels from arterial roads. The present work aims at providing an useful design tool In designing noise barrier tunnels for residential areas adjacent to roads. Number of field measurements, scale model measurements, and computer simulations were performed to ensure whether the prediction from scale model and computer simulation are appropriate. Result shows that the predictions from scale models and computer simulations could be valid prediction tools for designing sound barrier tunnels.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2005.05a
• /
• pp.162-167
• /
• 2005

Recently, the advanced industries using micro parts are rapidly growing. Micro endmilling is one of the prominent technology that has wide spectrum of application field ranging from macro to micro parts. Also, the method of micro-grooving using micro endmilling is used widely owing to many merit, but has problems of precision and quality of products due to tool wear and tool fracture. This study deals with condition monitoring using acoustic emission(AE) signal in the micro-grooving. First, the feature extraction of AE signal directly related to machining process is executed. Then, the distinctive micro endmill state according to the each tool condition is classified by using the fuzzy C-means algorithm, which is one of the methods to recognize data patterns. These result is effective monitoring method of micro endmill state by the AE sensing techniques which can be expected to be applicable to micro machining processes in the future.

• Proceedings of the Acoustical Society of Korea Conference
• /
• autumn
• /
• pp.231-234
• /
• 2000

In relation to a non-destructive evaluation of irradiation damage of micro-structure of interstitial, void and dislocation, the changes in the hysteresis loop and Barkhausen noise amplitude and the harmonics frequency due to neutron irradiation were measured and evaluated. The Mn-Mo-Ni low alloy steel of reactor pressure vessel was irradiated to a neutron fluence of $2.3\times10^{19}n/cm^2$ $(E\ge1MeV)$ at $288^{\circ}C.$The saturation magnetization of neutron irradiated metal did not change. Neutron irradiation caused the coercivity to increase, whereas susceptibility to decrease. The amplitude of Barkhausen noise parameters associated with the domain wall motion were decreased by neutron irradiation. The spectrum of Barkhausen noise was analyzed with an applied frequency of 4Hz and 8Hz, and a sampling time of 50 $\mu$ sec and 20 $\mu$ sec. The harmonic frequency of Joule effect shows 4Hz, 8Hz, 12Hz and 16Hz reflected from an unirradiated specimen. On the contrary, the harmonic frequency disappeared for the irradiated specimen. Harmonic frequency of induced voltage of sinusoidal magnetic field And Spectrum of Barkhausen noise on material is determined.

• Journal of the Korean Society for Railway
• /
• v.10 no.1 s.38
• /
• pp.1-6
• /
• 2007

Railway wheels in service are regularly checked by ultrasonic testing, acoustic emission and eddy current testing method and so on. However, ultrasonic testing is sometimes inadequate for sensitively detecting the cracks in railway wheel which is mainly because of the fact of crack closure. Recently, many researchers have actively fried to improve precision for defect detection of railway wheel. The development of a nondestructive measurement tool for wheel defects and its use for the maintenance of railway wheels would be useful to prevent wheel failure. The induced current focusing potential drop(ICFPD) technique is a new non-destructive tasting technique that can detect defects in railway wheels by applying on electro-magnetic field and potential drops variation. In the present paper, the ICFPD technique is applied to the detection of surface and internal defects for railway wheels. To defect the defects for railway wheels, the sensor for ICFPD is optimized and the tests are carried out with respect to 4 surface defects and 6 internal defects each other. The results show that the surface crack depth of 0.5 mm and internal crack depth of 0.7 mm in wheel tread could be detected by using this method. The ICFPB method is useful to detect the defect that initiated in the tread of railway wheels

• Journal of the Korea Institute of Military Science and Technology
• /
• v.18 no.4
• /
• pp.350-357
• /
• 2015

Many countries have been developing and operating an underwater surveillance system in order to protect their oceanic environment from infiltrating hostile marine forces which intend to lay mines, conduct reconnaissance and destroy friendly ships anchored at the harbor. One of the most efficient methods to detect unidentified submarine approaching harbor is sensing variation of magnetism of target by magnetic sensors. This measurement system has an advantage of high possibility of detection and low probability of false alarm, compared to acoustic sensors, although it has relatively decreased detection range. The contents of this paper mainly cover the analysis of possible effectiveness of magnetic sensors. First of all, environmental characteristics of surveillance area and magnetic information of simulated targets has been analyzed. Subsequently, a signal processing method of separating target from geomagnetic field and methods of estimating target location has been proposed.

• Journal of Electrical Engineering and Technology
• /
• v.9 no.2
• /
• pp.635-642
• /
• 2014

The space charge behaviors of oil-paper insulation affect the stability and security of oil-filled converter transformers of traditional and new energies. This paper presents the results of the electrical aging of oil-impregnated paper under AC-DC combined voltages by the pulsed electro-acoustic technique. Data mining and feature extractions were performed on the influence of electrical aging on charge dynamics based on the experiment results in the first stage. Characteristic parameters such as total charge injection and apparent charge mobility were calculated. The influences of electrical aging on the trap energy distribution of an oil-paper insulation system were analyzed and discussed. Longer electrical aging time would increase the depth and energy density of charge trap, which decelerates the apparent charge mobility and increases the probability of hot electron formation. This mechanism would accelerate damage to the cellulose and the formation of discharge channels, enhance the acceleration of the electric field distortion, and shorten insulation lifetime under AC-DC combined voltages.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2006.06a
• /
• pp.505-506
• /
• 2006

PD(partial discharge) occurred from variable PD sources in air may be the cause of breakdown in high voltage equipment which affect huge outage in power system. Identification and localization of PD sources is very important for engineer to cope with huge accident beforhand. PD phenomena can be detected by acoustic emission sensor or electromagnetic sensor like antenna. This paper has investigated the identification method using PCA(principal component analysis) for the PD signals from variable PD sources, for which the electric field distribution and PD inception voltages were simulated by using commercial FEM program. PD signals was detected by ultra wideband antenna. Their own features were extracted as the frequency coefficients transformed with FFT(fast fourier transform) and used to obtain independent pincipal components of each PD signals.