• The Journal of the Acoustical Society of Korea
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• v.19 no.2E
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• pp.20-26
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• 2000

A conceptual simplified model of Hartmann-Sprenger tube is suggested and investigated to decouple the regurgitant mode in the present paper. In spite of high nonlinearity, the acoustic behavior of this resonant tube system is dependent on wavelength and depth of the tube. The effect of forcing frequency and tube geometry on jet regurgitant mode are studied and discussed. With a conventional axisymmetric Euler code, sensitive acoustic problems are solved and validated by comparison with analytic theories.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.177-182
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• 2003

This study is directed toward determining the number and characteristics of psychologically meaningful perceptual dimensions required for assessing the sound Ouaiity with respect to vehicle interior and/or exterior noises. and toward identifying the acoustical or psychoacoustical bases underlying the perception. By nonmetric MDS and clustring analysis of sound quality data sets on our own, of critical importance are two perceptual dimensions for which subjective verdicts can be interpreted as loudness and sharpness. The perceptual dimensions based upon similarity judgments could be accounted for 48% and 24% of the variance. each of which might be a match for the acoustic parameter "A-weighted maximum pressure level"(r= .85) and for the psychoacoustic parameter "sharpness" (r= .65), respectively. On the other hand, the perceptual dimensions based upon preference ratings could explain 66% and 10% of the variance. where the acoustic parameter "A-weighted maximum pressure leve"(r= .92) might be taken to be a best predictor, but sharpness appeared to be less suitable for the description of Preference behavior. Linked to the results, the problems of quantitative modelling of subjective sound quality evaluation and also of implementing corresponding cognitive combination rule for technical and industrial applications, say having "winner-sound qualify" according to preference criteria will be shortly in discussion.

• MALSORI
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• no.60
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• pp.13-28
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• 2006

This study focused on comparing the following acoustic changes according to age and sex in adulthood: Fo, Jitter, Shimmer, and NHR. One hundred twenty Korean adults were divided into three age groups (20's, 50's, and 70's) and two sex groups (male and female). The subjects of this study performed three tasks: (1) sustained three vowels; (2) read on paragraph of 'Taking a Walk' (3) explained a picture. The data was analyzed using the MDVP of Multi-Speech. In the parameter of Fo, sex and age were influential factors. In the parameters of Jitter, Shimmer and NHR, the effect of sex and age was different in all three parameters. When the groups organized by sex were analyzed by age, the 20's group showed a statistical difference in all four parameters (Fo, Jitter, Shimmer, and NKR), when compared to the other two age ranges of 50's and 70's. We need to consider our standard parameter for the normal voice in the Korean elderly because the 50's and 70's age normal groups in our study are out of the current range of normal in MDVP.

• Geomechanics and Engineering
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• v.39 no.2
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• pp.157-170
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• 2024

In the present study, the acoustic emission characteristics of hard sedimentary sandstone with varying bedding dip angles were examined through uniaxial compression tests using a rock mechanics creep apparatus combined with an acoustic emission system. The deformation and failure behavior of the sandstone was analyzed by correlating acoustic emission parameters with stress over time. A damage constitutive model was developed, incorporating cumulative acoustic emission ringing counts as a key parameter, with time acting as the intermediary. The findings indicate that, despite the differences in bedding dip angles, the stress-strain curves of the samples follow a similar pattern throughout the loading process, passing through four distinct phases: compaction, elastic deformation, yielding, and post-peak failure. The fracture patterns of the sandstone are influenced by the dip angle of the bedding. Acoustic emission parameters, including the ringing count, cumulative ringing count, and energy, align with these four stages of the stress-strain curve. During the compaction and elastic deformation phases, acoustic emissions remain in a quite state, with only brief spikes at points of rapid stress change. In the unstable fracture stage, acoustic emissions become highly active, while they return to a quite state in the post-fracture stage. The RA value of the acoustic emission displays a banded pattern as time progresses, with areas of dense clustering. When the stress curve declines, RA values enter an active period, mainly associated with the generation of shear cracks. Conversely, during periods of smooth stress progression, RA values remain in a quiet state, primarily linked to the formation of tensile cracks. The time-based damage constitutive model for layered sandstone effectively captures the entire process of rock fracture development.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.5
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• pp.436-442
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• 2013

Friction welding is a very useful joining process to weld metals which have axially symmetric cross section. In this paper, the feasibility of industry application was determined by analyzing the mechanical properties of weld region for a specimen of tube-to-tube shape for excavator hose nipple with friction welding, and optimized welding variables were suggested. In order to accomplish this object, friction heating pressure and friction heating time were selected as the major process variables and the experiment was performed in three levels of each parameter. An acoustic emission(AE) technique was applied to evaluate the optimal friction welding conditions nondestructively. AE parameters of accumulative count and event were analyzed in terms of generating trend of AE signals across the full range of friction weld. The typical waveform and frequency spectrum of AE signals which is generated by friction weld were discussed. From this study the optimal welding variables could be suggested as rotating speed of 1300 rpm, friction heating pressure of 15 MPa, and friction heating time of 10 sec. AE event was a useful parameter to estimate the tensile strength of tube-to tube specimen with friction weld.

• The Journal of the Acoustical Society of Korea
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• v.28 no.3
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• pp.165-173
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• 2009

The physical properties of a seafloor sediment have been used as a basic data for the ocean survey. Conventional methods such as a coring, a drilling, and a grabbing have been used to explore the physical properties but these methods have a number of shortcomings as it is time consuming, expensive and spatially limited. To overcome these limitations, seafloor sediment classification using acoustic signals has been studied actively. In this paper, we obtained the backscattered signal from the seafloor sediment using an echo sounder which is one kind of seafloor topography equipment. Nakagami probability density function of the backscattered signals from the seafloor sediment was computed and a Nakagami parameter was compared with the physical properties of the seafloor sediment. We have confirmed that Nakagami parameter, m is correlated with the physical properties of a seafloor sediment. This study will be utilized as a basic data of the seafloor sediment research.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1996.03a
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• pp.119-123
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• 1996

The demands for robotic and automatic system are continually increasing in manufacturing fields. There were so many studies to monitor and predict system, but it were mainly relied upon measuring of cutting force, current of motor spindle and using acoustic sensor, etc. In this study digital image of time series sequence was acquired taking advantage of optical technique. Then, mean square error was obtained from it and was available for useful observation data. The parameter was estimated using PAA(parameter adaptation algorithm) from observation data. AR model was selected for system model, fifth order was decided according to parameter estimation. Uncorrelation test was also carried out to verify convergence of parameter. Through the proceedings, we found there was a system stability.

• The KSFM Journal of Fluid Machinery
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• v.2 no.3 s.4
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• pp.45-51
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• 1999

Centrifugal fans are widely used and the noise generated by these machines causes one of the most serious problems. In general, the centrifugal fan noise is often dominated by tones at BPF(blade passage frequency) and its higher harmonics. This is a consequence of the strong interaction between the flow discharged from the impeller and the cutoff in the casing. However, only a few researches have been carried out on predicting the noise due to the difficulty in obtaining detailed information about the flow field and casing effects on noise radiation. The objective of this study is to develop a prediction method for the unsteady flow field and the acoustic pressure field of a centrifugal fan and to calculate the effects of rotating velocity, flow rate, cut-off distance and the number of blades and its effects on the noise of the fan. We assume that the impeller rotates with a constant angular velocity and the flow field around the impeller is incompressible and inviscid. So, a discrete vortex method (DVM) is used to model the centrifugal fan and to calculate the flow field. The force of each element on the blade is calculated with the unsteady Bernoulli equation. Lowson's method is used to predict the acoustic source. The cut-off distance is the most important factor effecting the noise generation. Acoustic pressure is proportional to 2.8, which shows the same scaling index as the experimental result. In this paper, the cut-off distance is found to be the dominant parameter offecting the acoustic pressure.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.3
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• pp.220-226
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• 2003

This paper presents the result of an investigation on the application of the acoustic emission method to the monitoring of fatigue crack initiation, growth and track location in welded joints. Fatigue test was carried out for a typical fillet welded joint of ship structure. AE parameter such as ring down count was analyzed in time domain and crack locations were examined by source location and cluster option which is one of the functions of AE signal processor The usability of AE mettled was confirmed for the detection of the initiation and location of through crack.

• The Journal of the Acoustical Society of Korea
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• v.24 no.2
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• pp.111-116
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• 2005

This study deals with a subjective assessment to investigate the preferred acoustic conditions and determine the important acoustical parameters in concert halls. A subjective test was carried out using dummy head recorded sounds made in actual halls in Australia (referred to as Hall A and Hall B) to evaluate the acoustic performance of two halls. The results of subjective tests were then correlated with measured acoustical parameters to investigate the significant determinants for the preference judgements. The listeners show a stronger Preference for seats in the Hall B than those in the Hall A. The low preferences for seats in the Hall A are in agreement with live performance ratings assessed by musicians. It is found that the sound level is the most significant acoustical parameter for evaluating the overall acoustic preference in the two halls.