• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.3
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• pp.233-239
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• 2004

Smart material is used in various applications such as for glass frame, for medical instruments and for a part of sensors. Smart composite materials ran be applied to a part of aircraft and to the on-line monitoring system for industrial structures, using the shape memory effect. However, it is very difficult to simulate and analyze the shape memory effect in smart composites. In this paper, a two dimensional axisymmetric model was proposed to analyze the smart composite of one fiber and matrix using the finite element method(FEM). The finite element analysis was carried out in two renditions of the room temperature(293K) and a higher temperature (363K). The results we.e compared with the experimental results to confirm the validity of the analysis. In addition, the acoustic emission(AE) technique was used to study the microscopic damage behavior and the effect of pre-strains on TiNi/A16061 shape memory alloy composite.

• Computers and Concrete
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• v.22 no.1
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• pp.93-100
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• 2018

It is seldom possible that geotechnical materials like rocks and concretes found without joints, cracks, or discontinuities. Thereby, the impact of micro-cracks on the mechanical properties of them is to be considered. In the present study, the effect of micro-crack on the failure mechanism of rock specimens under uniaxial compression was investigated experimentally. For this purpose, thermal stress was used to induce micro-cracks in the specimens. Several cylindrical and disk shape specimens were drilled from granite collected from Zanjan granite mine, Iran. Some of the prepared specimens were kept in room temperature and the others were heated by a laboratory furnace to different temperature levels (200, 400, 600, 800 and 1000 degree Celsius). During the experimental tests, Acoustic Emission (AE) sensors were used to monitor specimen failure at the different loading sequences. Also, Scanning Electron Microscope (SEM) was used to distinguish the induced micro-crack by heating in the specimens. The fractographic analysis revealed that the thin sections heated to $800^{\circ}C$ and $1000^{\circ}C$ contain some induced micro-fractures, but in the thin sections heated to $200^{\circ}C$, $400^{\circ}C$ and $600^{\circ}C$ have not been observed any micro-fracture. In the next, a comprehensive experimental investigation was made to evaluate mechanical properties of heated and unheated specimens. Results of experimental tests showed that induced micro-cracks significantly influence on the failure mode of specimens. The specimens kept at room temperature failed in the splitting mode, while the failure mode of specimens heated to $800^{\circ}C$ are shearing and the specimens heated to $1000^{\circ}C$ failed in the spalling mode. On the basis of AE monitoring, it is found that with increasing of the micro-crack density, the ratio of the number of shear cracks to the number of tensile cracks increases, under loading sequences.

• Journal of Power System Engineering
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• v.3 no.3
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• pp.60-69
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• 1999

The noise and vibration sources of rotary compressor for room air-conditioner are pressure pulsation of compression process, cavity resonance of inner space, structural radiation noise of shell and impact noise of discharge valve. Among them, pressure pulsation is very important noise and vibration source. Because it transferred various kinds of noise and vibration like as mentioned above. In this reason, muffler and resonator are used in order to absorb and remove these noises. But an analytical prediction using acoustic analysis does not coincident with the experimental result. The difference between analysis and actual state is due to the assumption of analysis. This paper covered with new concept of muffler design based on the turbulence kinetic energy of flow by using CFD. From this analysis, it is possible to decide the best position of discharge port of muffler. Therefore $2{\sim}3dB$ noise reduction effect is acquired in rotary compressor of 5000 BTU grade. Also new approach of resonator design is suggested. From this study, the characteristics of resonator and surge hole (a kind of resonator without pipe length) are identified. The former is useful for pure tone noise (narrow frequency band), and the latter is effective for broad frequency band. This paper shows that it is very available to use 3 dimensional analysis of resonator in order to predict more exact tuning frequency. The result is proved by a lot of experiments. From combination of fluid analysis and acoustic analysis, up stream position is effective location of resonator concerning turbulence motion of fluid.

• Fire Science and Engineering
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• v.33 no.1
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• pp.130-137
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• 2019

In this study, the acoustic characteristics of 13 types of emergency broadcasting speakers were tested under the test set-up of UL 2043 and compared. When the sound pressure level of 1 W speakers was compared with speakers with a 15 W output, the SPL of the 15 W speakers was approximately 20 dB higher in some frequency bands. Loudness analysis showed that people can recognize emergency sound from a 15 W speaker twice as loud as the emergency sound from 1 W speakers. The analysis results on the articulation index (room) had an opposite tendency with loudness results, meaning that small speakers can generate clearer sound. Therefore, it is necessary to improve emergency broadcasting speakers to generate louder and clearer sound. Moreover, a performance evaluation standard is needed based on the reasonable and quantitative measurements and evaluations of the acoustic characteristics of the emergency-broadcasting speakers so that a sufficient and clear sound can be generated in various spaces. In addition, it is necessary to establish standards for the clarity of emergency broadcasting in various spaces.

• The Journal of the Acoustical Society of Korea
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• v.40 no.5
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• pp.452-459
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• 2021

Estimating the mutual time delay between two acoustic sensors is used in various fields such as tracking and estimating the location of a target in room acoustics and sonar. In the time delay estimation methods, there are a non-parametric method, such as Generalized Cross Correlation (GCC), and a parametric method based on system identification. In this paper, we propose a time delay estimation method based on the parametric method. In particular, we propose a method that considers the noise in each receiving acoustic sensor. Simulation confirms that the proposed algorithm is superior to the existing generalized cross-correlation and adaptive eigenvalue analysis methods in white noise and reverberation environments.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.795-800
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• 2008

The sound transmission loss is a key index to evaluate the acoustic performance of a car-body structure at the high frequency range. From this paper, a new validation method for in-situ sound transmission loss is proposed. First, in-situ sound transmission loss is measured by using PU intensity probe on the condition of complete vehicle. Second, validation test, which is consisted of internal, external and total frequency response function test, is performed by using volume acceleration source and microphones. Then, these test results are compared to validate the accuracy of in-situ sound transmission loss. Finally, the test result of in-site method is compared with results of two reverberant room test method and SEA analytical method. The reliability of in-situ method is confirmed by these procedures.

• Journal of KSNVE
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• v.9 no.5
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• pp.991-997
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• 1999

It is getting higher the demand on a good sound in a car. Like some other sensory qualities, achieving a good sound is still treated as a black-box followed by the individual taste of tuning engineers. This study aims to define the attributes of a good car audio sound and the assessment factors affecting the sound quality. With a variety of surveys on professional listening groups and car audio installers, 26 most frequently used vocabularies are selected as typical presentations of car audio sound quality. After repetitions of listening tests with deliberately selected test CD, pre-recorded 15 different digital car-recordings, headphones replay system, and three different listening groups, it is proved that there are at least 5 different assessment factors which significantly affect the car audio sound quality. They are high fidelity, spectral balance, tonal accuracy, sound stage and acoustic fault.

• Speech Sciences
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• v.8 no.3
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• pp.43-50
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• 2001

This paper deals with voice similarities between sisters who are supposed to have common physiological characteristics from a single biological mother. Nine pairs of sisters who are believed to have similar voices participated in this experiment. The speech samples obtained from one pair of sisters were eliminated in the analysis because their perceptual score was relatively low. The words were measured in both isolation and context, and the subjects were asked to read the text five times with about three seconds of interval between readings. Recordings were made at natural speed in a quiet room. The data were analyzed in pitch and formant frequencies using CSL (Computerized Speech Lab) and PCQuirer. It was found that data of the initial vowels are much more similar and homogeneous than those of vowels in other positions. The acoustic data showed that voice similarities are strikingly high in both pitch and formant frequencies. It is assumed that statistical data obtained from this experiment can be used as a guideline for modelling speaker identification and speaker verification.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.6
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• pp.483-492
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• 2014

Uncomfortable feelings of occupants by indoor floor impact noise in a residential building are not accurately represented by the floor impact noise from a standard impact source. It is due to the characteristics of standard impact sources, which are different from the impact forces produced by occupants. It varies significantly by impact source, and it is not easy to be replicated for testing. As a result, the indoor floor impact noise under different acoustic conditions cannot be directly compared. Using frequency response function(FRF), which represents the input-output relationships of a dynamic system, it is possible to examine the characteristics of the system. Especially, FRF can predict the response of a linear dynamic system subjected to various excitation. To determine the relationship between impact force and the corresponding response of dynamic system in residential building, the acceleration response of a concrete slab and the floor impact noise in the living room, produced by bang-machine and rubber-ball excitation, were measured. The test results are compared to the estimates based on FRF and impact force spectrum.

• Journal of the Korean housing association
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• v.21 no.3
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• pp.11-21
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• 2010

The purpose of this study is to gather baseline data on perceived priority of residential choice and housing satisfaction rates among consumers with the aim of using this information for future planning. Self-administered questionnaires were provided to 196 studio-type multi-family housing dwellers in the City of Gwangju from 2009 Apri 5th to 29th. The collected data was used to conduct comparative and descriptive statistical analysis: factor analysis, t-test, one-way ANOVA, correlation analysis. The main findings obtained are as follows: Firstly, in relation to perceived priority of residential choice, dwellers identified seven factors as important. Secondly, in terms of housing satisfaction about a unit room, the respondents identified five factors as important. This study confirmed that there existed passive correlation between priority of residential choice and housing satisfaction among residents in studio-type multi-family housings in Gwangju. It is very necessary to project a studio-type multi-family housing close to transportation for easy access, avoiding commercial districts. Delicate interior and design will attract more female residents as well as fully-equipped parking lots for people who drive to their workplace. According to research on a degree of housing satisfaction, all respondents expressed dissatisfaction with "noise". Therefore, in dealing with construction plans of studio apartment units, from now on, sound proofing facilities are required to reduce the acoustic invasion of privacy, especially, for units with more than two people. In order to satisfy all the demand of residents in studio apartment units, we have to pursue systematic and succeeding research about a studio-type multi-family housing well-fitted for the actual circumstances of local area and suitable for longer stay. To sum up, more research and development will be required for high-class studio-type multiplex housing for sale in dealing with households with financial stability such as two-paycheck couples, so-called DINK, or a professional single person, in the future.