• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.26 no.2
• /
• pp.91-96
• /
• 2014

An acoustical model for detecting the leak location in a buried gas pipeline has been developed. This model is divided into an experimental model for sound diagnosis, and a theoretical model for sound prediction, which is based on the transfer matrix method, representing the sound pressure and the volume velocity as state variables. The power spectrum is measured by attaching only one microphone to the closed end pipe. It has been shown that the response magnitude of acoustic pressure signals calculated by the acoustical model depends upon the thickness and diameter of a pinhole. The validity for the acoustical model has been verified through a comparison between the measured and calculated results.

• The Journal of the Acoustical Society of Korea
• /
• v.24 no.3
• /
• pp.166-170
• /
• 2005

This paper describes the experimental study for the position estimation method of underwater sound source using the Nearfield Acoustic Holography. The result confirms that it can be used in the identification of underwater noise sources. The sound sources in the experimental work consists of 2 spherical projectors and the near-Held sound pressure is measured in the hologram plane. From the cross-power spectra of the measured data, the complex sound pressures on the hologram plane is derived and its spatial transformation gives sound fields in a source region. The obtained sound fields in a source region showed that the position of each sound source and their relative source strength are exactly estimated. In conclusion, this technique can be applied for estimation of each source position and its relative strength contribution for the underwater multiple sound sources.

• Publications of The Korean Astronomical Society
• /
• v.30 no.2
• /
• pp.321-325
• /
• 2015

Determining the absolute neutrino mass scale and the neutrino mass hierarchy are central goals in particle physics, with important implications for the Standard Model. However, the final answer may come from cosmology, as laboratory experiments provide measurements for two of the squared mass differences and a stringent lower bound on the total neutrino mass - but the upper bound is still poorly constrained, even when considering forecasted results from future probes. Cosmological tracers are very sensitive to neutrino properties and their total mass, because massive neutrinos produce a specific redshift-and scale-dependent signature in the power spectrum of the matter and galaxy distributions. Stringent upper limits on ${\sum}m_v$ will be essential for understanding the neutrino sector, and will nicely complement particle physics results. To this end, we describe here a series of cosmological hydrodynamical simulations which include massive neutrinos, specifically designed to meet the requirements of the Baryon Acoustic Spectroscopic Survey (BOSS) and focused on the Lyman-${\alpha}$ ($Ly{\alpha}$) forest - also a useful theoretical ground for upcoming surveys such as SDSS-IV/eBOSS and DESI. We then briefly highlight the remarkable constraining power of the $Ly{\alpha}$ forest in terms of the total neutrino mass, when combined with other state-of-the-art cosmological probes, leaving to a stringent upper bound on ${\sum}m_v$.

• The Journal of the Acoustical Society of Korea
• /
• v.28 no.8
• /
• pp.822-831
• /
• 2009

The porcelain insulators are important devices, that are used to isolate electrically and hold mechanically in the high-voltage power transmission systems. The faults of the insulators induce very serious problems to the power transmission line. In this paper, we introduce techniques for fault detections of insulators by acoustic radiation noises from them. We measured radiation noises from normal state insulators and fault state insulators. The used insulators were two different type porcelain insulators, a cut out switch, two different type line posters, and a lightning arrester. Each results was compared each other in time domain, frequency domain and filter banks' outputs. We found the possibility of detection of insulators' faults and also suggested techniques for fault detections.

• Proceedings of the KSPS conference
• /
• 2007.05a
• /
• pp.143-145
• /
• 2007

Muscle groups that are located in and around the vocal tract can produce audible changes in frequency and/or intensity of the voice. Vocal vibrato is a characteristic feature in the singing of performers trained in the western classical tradition and vibrato is generally considered to result from modulation in frequency amplitude and timbre. Vocal tremor is also characterized by periodic fluctuations in the voice frequency or intensity and vocal tremor is symptom of a neurological disease as Spasmodic dysphonia , Parkinson's disease. Vocal vibrato and Vocal tremor may have many of the same origins and mechanisms in the voice production systems. The purpose of this study is to find acostic character of Korean traditional song Pansori singer's vibrato and Spasmodic dysphonia patient's vocal tremor. twelve Pansori singers and seven Spasmodic dysponia patients participated to this study. Power spectrum and Real time Spectrogram are used to analyze the acoustic characteristics of Pansori singing and Spasmodic dysphonia patient's voice The results are as follows; First, vowel formant differences between Pansori singing and Spasmodic dysphonia patient's voice are higher F1, F3. Second, The vibrato rate show differences between Pansori singing and Spasmodic dysphonia patients;$4^{\sim}6/sec$ and $5{\sim}6/sec$ Vibrato rate of pitch is 5.7 Hz ${\sim}$ 42.4 Hz for Pansori singing , 3.8 Hz ${\sim}$ 27.9 Hz for Spasmodic dysphonia patients ;Vibrato rate of intensity range is 0.07 dB ${\sim}$ 8.26 dB for Pansori singing and 0.07 dB ${\sim}$ 4.81 dB for Spasmodic dysphonia patients

• The Journal of the Acoustical Society of Korea
• /
• v.32 no.2
• /
• pp.116-123
• /
• 2013

This paper represents generation of time-varying underwater acoustic channels by performing scattering simulation with time-varying ocean surface and Kirchhoff approximation. In order to estimate the time-varying ocean surface, 1D Pierson-Moskowitz ocean power spectrum and Gaussian correlation function were used. The computed scattering coefficients are applied to the amplitudes of each impulse of BELLHOP simulation result. The scattering coefficients are then compared with measured doppler spectral density of signal components which were scattered from ocean surface and the correlation time used in the Gaussian correlation function was estimated by the comparison. Finally, bit-error-rate and channel correlation simulations were performed with the generated time-varying channel based on passive time-reversal communication scenario.

• Journal of Clinical Otolaryngology Head and Neck Surgery
• /
• v.29 no.2
• /
• pp.212-222
• /
• 2018

Background and Objectives : The purpose of this study was to compare the measured values of acoustic and auditory perceptual assessments between normal and functional dysphonia (FD) groups. Materials and Methods : 102 subjects with FD and 59 normal voice groups were participated in this study. Mid-vowel portion of the sustained vowel /a/ and two sentences of 'Sanchaek' were edited, concatenated, and analyzed by Praat script. And then auditory-perceptual (AP) rating was completed by three listeners. Results : The FD group showed higher acoustic voice quality index version 2.02 and version 3.01 (AVQIv2 and AVQIv3), slope, Hammarberg index (HAM), grade (G) and overall severity (OS), values than normal group. Additionally, smoothed cepstral peak prominence in Praat (PraatCPPS), tilt, low-to high spectral band energies (L/H ratio), long-term average spectrum (LTAS) in FD group were lower than normal voice group. And the correlation among measured values ranged from -0.250 to 0.960. In ROC curve analysis, cutoff values of AVQIv2, AVQIv3, PraatCPPS, slope, tilt, L/H ratio, HAM, and LTAS were 3.270, 2.013, 13.838, -22.286, -9.754, 369.043, 27.912, and 34.523, respectively, and the AUC of each analysis was over .890 in AVQIv2, AVQIv3, and PraatCPPS, over 0.731 in HAM, tilt, and slope, over 0.605 in LTAS and L/H ratio. Conclusions : In conclusion, AVQI and CPPS showed the highest predictive power for distinguishing between normal and FD groups. Acoustic analyses and AP rating as noninvasive examination can reinforce the screening capability of FD and help to establish efficient diagnosis and treatment process plan for FD.

• International Journal of Aeronautical and Space Sciences
• /
• v.18 no.2
• /
• pp.197-205
• /
• 2017

We investigate the slat noise generation mechanism by using large-eddy simulation (LES) and simple source modeling based on linearized Euler equations. An incompressible LES of an MD 30P30N three-element airfoil in the high-lift configuration is conducted at $Re_c=1.7{\times}10^6$. Using the total derivative of the hydrodynamic pressure (DP/Dt) acquired from the incompressible LES, representative noise sources in the slat cove region are characterized in terms of simple sources such as frequency-specific monopoles and dipoles. Acoustic radiation around the 30P30N multi-element airfoil is effectively computed using the Brinkman penalization method incorporated with the linearized Euler equation. The directivity pattern of $p^{\prime}_{rms}$ at $r=20c_{slat}$ in the multiple sources is closely compared to that obtained by the application of the LES/Ffowcs-Williams and Hawking's methods to the entire flow field. The power spectrum of p' at ${\theta}=290^{\circ}$ is in good agreement with the data reported in BANC-III, especially the broadband part of the spectrum with a decaying slope ${\propto}f^{-3}$.

• The Bulletin of The Korean Astronomical Society
• /
• v.40 no.1
• /
• pp.44.1-44.1
• /
• 2015

We present joint constraints on the number of effective neutrino species $N_{eff}$ and the sum of neutrino masses ${\Sigma}m_{\nu}$, based on a technique which exploits the full information contained in the one-dimensional Lyman-${\alpha}$ forest flux power spectrum, complemented by additional cosmological probes. In particular, we obtain $N_{eff}=2.91{\pm}0.22$ (95% CL) and ${\Sigma}m_{\nu}$ < 0.15 eV (95% CL) when we combine BOSS Lyman-${\alpha}$ forest data with CMB (Planck+ACT+SPT+WMAP polarization) measurements, and $N_{eff}=2.88{\pm}0.20$ (95% CL) and ${Sigma}m_{\nu}$ < 0.14 eV (95% CL) when we further add baryon acoustic oscillations. Our results tend to favor the normal hierarchy scenario for the masses of the active neutrino species, provide strong evidence for the Cosmic Neutrino Background from $N_{eff}{\approx}3$($N_{eff}=0$ is rejected at more than $14{\sigma}$), and rule out the possibility of a sterile neutrino thermalized with active neutrinos (i.e., $N_{eff}=4$) - or more generally any decoupled relativistic relic with $${\Delta}N_{eff}{\sim_=}1$$ - at a significance of over $5{\sigma}$, the strongest bound to date, implying that there is no need for exotic neutrino physics in the concordance ${\Lambda}CDM$ model.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2012.10a
• /
• pp.388-393
• /
• 2012

Vibration condition monitoring at low rotational speeds is still a challenge. Acoustic emission (AE) is the most used technique when dealing with low speed bearings. At low rotational speeds, the energy induced from surface contact between raceway and rolling elements is very weak and sometimes buried by interference frequencies. This kind of issue is difficult to solve using vibration monitoring. Therefore some researchers utilize artificial damage on inner race or outer race to simplify the case. This paper presents vibration signal analysis of low speed slewing bearings running at a low rotational speed of 15 rpm. The natural damage data from industrial practice is used. The fault frequencies of bearings are difficult to identify using a power spectrum. Therefore the relatively improved method of empirical mode decomposition (EMD), ensemble EMD (EEMD) is employed. The result is can detect the fault frequencies when the FFT fail to do it.