• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2000.06a
• /
• pp.413-418
• /
• 2000

The noise sources from a rotating cylinder were identified to describe the blunt trailing edge noise. Firstly, LES formulation was applied to a non-orthogonal grid system and was tested with three-dimensional cross-flow over a cylinder with a yaw angle. The computed far-field noise showed peaks at Strouhal numbers ranging from 0.135 to 0.165 for the yawed cylinder flow with end-plates placed at both extremes under the yaw angle of $30^{\circ}$ and Reynolds number of $1.15{\times}10^4$. It was observed that the slantwise shedding at angles other than the cylinder yaw angle is intrinsic to inclined cylinder, with the result of shedding angles between $15^{\circ}$ and $31^{\circ}$. To study the trailing-edge wake thickness and unsteady lift-coefficient distribution in the span-wise direction of a rotating fan blade, the flows around rotating cylinder with 1,000 rpm were simulated and the far-field noise was exactly computed using the Ffowcs-Williams and Hawkings equation with quadrupole source term. The incoming velocities and stagnant zones were continuously distributed along the cylinder, and their changes made the Strouhal sheddings to occur at different phases even at almost same Strouhal number.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2014.10a
• /
• pp.713-717
• /
• 2014

This paper presents a beamforming technique for locating impulsive sound source. The conventional frequency-domain beamformer is advantageous for localizing noise sources for a certain frequency band of concern, but the existence of many frequency components in the wide-band spectrum of impulsive noise makes the beamforming image less clear. In contrast to a frequency-domain beamformer, it has been reported that a time-domain beamformer can be better suited for transient signals. Although both frequency- and time-domain beamformers produce the same result for the beamforming power, which is defined as the RMS value of its output, we can use alternative directional estimators such as the peak value and crest factor to enhance the performance of a time-domain beamformer. In this study, the performance of three different directional estimators, the peak, crest factor and RMS output values, are investigated and compared with the incoherent interfering noise embedded in multiple microphone signals. The proposed formula is verified via experiments in an anechoic chamber using a uniformly spaced linear array. The results show that the peak estimation of beamformer output determines the location with better spatial resolution and a lower side lobe level than crest factor and RMS estimation in noise free condition, but it is possible to accurately estimate the direction of the impulsive sound source using crest factor estimation in noisy environment with stationary interfering noise.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.21 no.3
• /
• pp.553-563
• /
• 1996

Detecting edges is one of issues with essentialimprotance in the area of image analysis. An edge in an image is a boundary or contour at which a significant change occurs in image intensity. Edge detection has been studied in many addlications such as imagesegmentation, robot vision, and image compression. In this paper, we propose an automatic threshold selection scheme for edge detection and show its application to noise elimination. The scheme suggested here applied statistical properties of the noise estimated from a noisy image to threshold selection. Since a selected threshold value in the scheme depends on not the characgreistic of an orginal image but the statistical feature of added noise, we can remove ad-hoc manners used for selecting the threshold value as well as decide the value theoretically. Furthermore, that shceme can reduce the number of edge pixels either generated or lost by noise. an application of the scheme to noise elimination is shown here. Noise in the input image can be eliminated with considering the direction of each edge pixedl on the edge map obtained by applying the threshold selection scheme proposed in this paper. Achieving significantly improved results in terms of SNR as well as subjective quality, we can claim that the suggested method works well.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2014.10a
• /
• pp.795-797
• /
• 2014

Image treatment has grown in its necessity in many fields due to the development of display technology used in smart phones and tablet computers. In digital imaging technology, noise is created by many causes during the process of acquiring, transmitting and treating image data. Therefore, this paper suggests a median filter that is more competent in removing noise by taking into account the direction when restoring noisy images that have been damaged by impulse noise. In order to verify the noise removal characteristics, PSNR(peak signal to noise ratio) was used for comparison against existing methods.

• Journal of IKEEE
• /
• v.25 no.2
• /
• pp.234-242
• /
• 2021

In case implementation of microwave photonic (MWP) systems for phased array radars (PARs), noise and time delay error should be minimized to obtain accurate beam direction. Time delay error in MWP systems is generated from signal noise and timing jitter. In this paper, noise and timing jitter in MWP systems for PAR is researched, also according to the amplification of an erbium-doped fiber amplifier, noise and timing jitter variation is verified by an experiment. Timing jitter is decreased and SNR is increased if we amplify the signal by using an erbium-doped fiber amplifier, up to the amplification rate of signal and noise is similar.

• Journal of the Korea Convergence Society
• /
• v.9 no.12
• /
• pp.107-113
• /
• 2018

The purpose of this study was to evaluate the dose and image quality according to the rotation of the X-axis direction in the abdominal CT scan, and to find ways to reduce the exposure dose. The phantom was scanned by rotating in the X-axis direction at 0, 5, 10, and 15 degrees, respectively. The CTDIvol value, HU, noise, and signal-to-noise ratio were measured at each rotation. ANOVA analysis was performed using the SPSSWIN (ver 19.0) program. The radiation exposure dose was 5.44mGy, 5.70mGy, 5.98mGy and 6.38mGy at 0, 5, 10 and 15 degrees, respectively. HU, noise, and signal-to-noise ratio were not statistically significant. In the CT scan, if the patient is located in the isocenter of the gantry aperture and there is no rotation in the X-axis direction, the exposure dose is reduced.

• Proceedings of the KSR Conference
• /
• 2011.10a
• /
• pp.2269-2275
• /
• 2011

This paper deals with the design of a microphone array to measure location and spectral characteristics of railway noise sources. A microphone array estimates the direction of a noise source assumed as a point source using the delayed-sum beamforming method and its performance is determined in terms of resolution and side-lobe level. A 48 channel microphone array was already developed to measure noise sources of KTX trains and a new array with 96 microphones has been designed to enhance the performance. This paper simulates the performance the microphone arrays according to the configuration of microphones and verifies it through on-site tests.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.6 no.1
• /
• pp.122-133
• /
• 1998

This paper presents the static analysis, the modal analysis and the forced vibration analysis on engine structures to find out the structure-borne noise sources by finite element method. The deformation of engine structures under the maximum combu- stion gas force was calculated through the static analysis, and the resonance possibilities were predicted by the modal analysis which ascertains mode shapes and the corresponding frequencies of engine global and its major noise sources in engine surfaces were investigated with the forced vibration analysis by means of finding the transfer mobilities on engine surfaces due to the piston impact and the velocity levels due to the combustion in consideration of oil film stiffness and damping coefficients. Finally, the direction of engine structure-borne noise reduction can be estabilished by the above-mentioned analysis procedure and the reduction effect of cost on proto-type engine build-up is expected.

• Proceedings of the KSME Conference
• /
• 2003.11a
• /
• pp.798-803
• /
• 2003

The objective of the present study is to investigate the changes in the acoustic source characteristics and far-field noise propagation in an incompressible round jet at Re=10000 for single-frequency excitations using large eddy simulation and Lighthill acoustic analogy. We apply excitations at a frequency corresponding to the jet-column mode ($St_{D}=0.85$) or maximum growth rate in the shear layer ( $St_{\theta}=0.017$ ). The acoustic source derived from the Lighthill acoustic analogy is the second spatial derivative of the Reynolds stresses. In the case of $St_{D}=0.85$, vortex ring and large scale structures are dominant sources, whereas in the case of $St_{\theta}=0.017$, the main sources are located at an upstream position along the shear layer than in the uncontrolled case. Also, the far-field noise propagates along the axial direction due to excitation.

• 한국지구물리탐사학회:학술대회논문집
• /
• 2007.06a
• /
• pp.279-284
• /
• 2007

The cultural noise sources in magnetotellurics were localized using the source localization method. Conventional beamforming techniques are not applicable for electromagnetic source localization. In this study, the matched field processing and genetic algorithm are used to localize an electromagnetic source and estimate the polarization direction. The source localization using MT field data shows the characteristics of estimated source distribution related to the strength of cultural noise.