• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.21 no.11
• /
• pp.1527-1537
• /
• 1997

Extinction characteristics and acoustic response of hydrogen-air diffusion flames at various pressures are numerically studied by employing counterflow diffusion flame as a model flamelet in turbulent flames in combustion chambers. The numerical results show that extinction strain rate increases linearly with pressure and then decreases, and increases again at high pressures. Thus, flames are classified into three pressure regimes. Such nonmonotonic behavior is caused by the change in chemical kinetic behavior as pressure rises. The investigation of acoustic-pressure response in each regime, for better understanding of combustion instability, shows different characteristics depending on pressure. At low pressures, pressure-rise causes the increase in flame temperature and chain branching/recombination reaction rates, resulting in increased heat release. Therefore, amplification in pressure oscillation is predicted. Similar phenomena are predicted at high pressures. At moderate pressures, weak amplification is predicted since flame temperature and chain branching reaction rate decreases as pressure rises. This acoustic response can be predicted properly only with detailed chemistry or proper reduced chemistry.

• Journal of the Korean Society for Precision Engineering
• /
• v.28 no.10
• /
• pp.1196-1203
• /
• 2011

Statistical optimum methodology of table of orthogonal array, ANOM, ANOVA and RSM are applied to formulate optimum allocation design with design variables. It can be minimized average SPL of control volume, the objective function in closed system by optimal allocated positions of absorbing material. Structural natural frequency and acoustic natural frequency of cavity are analyzed by FEM and BEM in the closed system. Using BEM, average SPL of specific control volume is calculated according to the condition before using absorbing material and after using it. It is shown that noise is reduced by $5.02dB_{RMS}$ by absorbing material located at optimal position and minimum $1.83dB_{RMS}$ and maximum $3.47dB_{RMS}$ by the table of orthogonal array.

• The Journal of the Acoustical Society of Korea
• /
• v.40 no.4
• /
• pp.290-296
• /
• 2021

The purpose of this study was to examine the perceived emotion of music according to cognitive styles of music listening. A total of 91 music-related graduate students participated in this study. They were given a questionnaire about perceived emotions of music, musical elements, and Music Empathizing-Music Systemizing Inventory. To analyze statistically, Descriptive statistics, paired t-test, ANalysis Of VAriance (ANOVA), multi-variate analysis, and Pearson correlation analysis were conducted. Results showed that participants had relatively universal experience in perceived emotions of both types of music, and also showed that musical elements contributed to the experience differed by cognitive styles of music listening.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.3 no.3
• /
• pp.158-164
• /
• 1998

We introduce a statistical scheme to classify seabed from acoustic profiling data acquired using Chirp sonar system. The classification is based on grouping of signal traces by similarity index, which is computed using the K-L (Karhunen-Lo$\grave{e}$ve) transform of the Chirp profiling data. The similarity index represents the degree of coherence of bottom-reflected signals in consecutive traces, hence indicating the acoustic roughness of the seabed. The results of this study show that similarity index is a function of homogeneity, grain size of sediments and bottom hardness. The similarity index ranges from 0 to 1 for various types of seabed material. It increases in accordance with the homogeneity and softness of bottom sediments, whereas it is inversely proportional to the grain size of sediments. As a real data example, we classified the seabed off Cheju Island, Korea based on the similarity index and compared the result with side-scan sonar data and sediment samples. The comparison shows that the classification of seabed by the similarity index is in good agreement with the real sedimentary facies and can delineate acoustic response of the seabed in more detail. Therefore, this study presents an effective method for geoacoustic modeling to classify the seafloor directly from acoustic data.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.32 no.4
• /
• pp.331-339
• /
• 1996

It is most important to understand the behaviour of fish in case of the betterment of the current fishing gear and methods or the development of the conditioning by acoustic sound in marine ranching. This investigation has been attempted to provide for the prediction of the response action of fish to acoustic sound. The experimental fish was conditioned with sound and bait. As the acoustic sound for stimulus, the pure tone of sine waveform at the frequency of 200Hz was used. This pure tone was determined from previous investigation about hearing ability of walleye pollock Theragra chalcogramma. The fork length of walleye pollock used in this experiment was 385~450mm. The conditioning proceeding was recorded in the video tape recorder. Frequency of appearance in the feeding area was analyzed with computer and video tape recorder. The position of fish was tracked using the mouse cursor and picture mixed on the superimpose board. The response of conditioned fish to sound stimulus was appeared in the 8th day firstly. The conditioned fish remembered the stimulus sound for 4 days. Average frequency of appearance in the feeding area during the 30 seconds sound projection or 1 minute after the sound stimulus was 51%, and was higher than before it.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.31 no.8
• /
• pp.91-98
• /
• 2003

In the structural analysis of a launch vehicle, the construction of loading functions and the determination of responses to them are very important. Among many kinds of loads, acoustic load generated by exhaust is a random load that can be described in a statistical manner. In this study, loading functions corresponding to the acoustic loads are constructed and applied to the structural analysis of launch vehicle. Acoustic loading functions are constructed using source allocation method. Structural analyses are carried out by using finite element modelling and frequency response function of finite element model. The stresses resulting from acoustic loads and acceleration power spectral density functions at interfaces of each section are calculated. These analyses are essential for the development of environmental test specifications and associated dynamic design requirements which are necessary to ensure overall vehicle reliability.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.22 no.2
• /
• pp.170-176
• /
• 2002

Nonlinear acoustic effect has been considered as an effective tool for the evaluation of material degradation. In this paper, the applicability of nonlinear acoustic effect to the evaluation of degraded 2.25Cr-1Mo steel is investigated. Firstly, artificial aging was performed to simulate the microstructural degradation in 2.25Cr-1Mo steel arising from long time exposure at $540^{\circ}C$. Secondly, ultrasonic nonlinear parameter was quantitatively measured by bi-spectrum and power spectrum. Nonlinear acoustic parameter from bi-spectrum was found to be clearly sensitive to the aging time.

• Journal of Korean Association for Spatial Structures
• /
• v.10 no.3
• /
• pp.75-80
• /
• 2010

The present study tried to provide useful data for the acoustic design of sound amplification system with measuring and analyzing subjective preference and intelligibility by varying the number of speakers and their directivity. The results suggest that the room absorption plays a key role in subjective responses of listeners and the large sound absorption of ceiling contributes to the increase of intelligibility. Also, larger number of speakers with narrow directivity improves perceived intelligibility when speakers were installed at the lower height. However, the highest degree of intelligibility and preference were obtained when speakers were installed close enough to the sound absorptive ceiling. The highest intelligibility and preference were observed when 8 to 10 speakers with the directivity of 60 degree were used.

• Proceedings of the Korean Society of Computer Information Conference
• /
• 2016.07a
• /
• pp.43-44
• /
• 2016

본 논문에서는 사용자와의 실시간 상호작용을 활용하여 역사적 사실을 전달하는 반응형 미디어 아트 작품 을 보인다. 본 작품은 젊은 계층의 역사적 무관심을 김이 서리는 현상에 비유하고 사용자가 서린 김을 닦음으로써 잊고 있던 아픈 역사와 마주하게 되는 내용으로 구성된다. 김이 서리는 자연 현상과 서린 김을 닦는 행위를 영상으로 표현하였으며, 서려있는 정도와 사용자의 손 움직임에 따라 영상과 음향이 상이하게 반응한다. 이는 관객의 역사에 대한 무관심을 스스로 닦음으로서 역사적 본질과 마주할 수 있다는 의미를 극대화 한다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2011.11a
• /
• pp.415-418
• /
• 2011

It is critical to assess the characteristics of flame response to pressure perturbations for the understanding of nonlinear combustion instabilities. Previous studies can be grouped into flame response upon perturbed, fresh air and fuel mixture, and flame response directly perturbed from longitudinal waves. The present study presents experimental methodology for the understanding of the flame response exposed to transverse acoustic waves generated by loud speakers.