• Journal of KSNVE
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• 제6권6호
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• pp.755-762
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• 1996

An acoustic transmission loss analysis method for mufflers with complex geometry is developed using MSC/NASTRAN on the basis of acoustic-structural analogy and two-microphone method. In this study, mufflers with simple and complex shapes are analyzed using this method and compared with theoretical and experimental results to verify it. Applying this method to design of discharge muffler in a rotary compressor, we obtained 2dB(A) of noise reduction in the range of lower than 1300Hz. Futhermore, adopting this technique for a suction muffler in reciprocal compressor, more than 10dB(A) noise reduction at 500Hz, and in total, 3dB(A) noise reduction is achieved.

• Proceeding of Spring/Autumn Annual Conference of KHA
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• 한국주거학회 2003년도 정기총회 및 추계학술대회
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• pp.67-72
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• 2003

The present article evaluates a performance hall, which improves sound efficiency. In general, the sidewall of the music hall is plane circle. thus there happens a focus phenomenon. To overcome it. the music hall improves its sound efficiency by making its sidewall irregular. After measuring impulse response from the performance hall, evaluation indices on the temporal distribution of sound energy such as RT, EDT, D50, C80, RASTI and BR were obtained, and based on them, indoor acoustic characteristics and the generation of echoes were determined. According to the results, evaluation indices showed that the acoustic condition was satisfactory in general. This study is to provide fundamental data for acoustic design of music hall with round form by analyzing the room acoustic characteristics of music hall.

• Journal of the Korean Institute of Landscape Architecture
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• 제29권3호
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• pp.10-18
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• 2001

The purpose of this study is to research the influence of soundscape in the preference of landscape. Specifically, Standards types of communications are applied to the landscape such as artificial waterscapes and natural valley. The spatial image was analyzed by the variables of Kaplan´s information processing model. The level of visual preferences was measured by a type of acoustic information in landscape and media of communication, and these data were analyzed by multiple regression. The results of this study can be summarized as follows; The value of landscape preference was not different from all fluent of coherence, complexity, legibility ,mystery and preference utilized the communication media, but it was different by the type of acoustic information in landscape. These results clearly show the influence of sound affecting decisions of landscape preference. The factors determining the level of landscape preference were found to be coherence, complexity, legibility, mystery and dummy variables of acoustic information in landscape and media od communication. These variables amy be the major factors which must be considered on planning and designing as the functional basis for the quantitative analysis.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 한국소음진동공학회 2003년도 추계학술대회논문집
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• pp.183-188
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• 2003

This study is to make the fundamentals of sound quality evaluation in regard of acoustical characteristics of passenger compartment. The deviation of frequency response function level within audible frequency is evaluated at receiving point in the research of room acoustics. In this study, frequency response function is the one between speaker and driver's ear positions. The positions of driver and audio speakers are optimized by analysis of acoustic mode of acoustic cavity. The main reflection planes are determined by analysis sound ray path diffused at optimized speaker positions. Finally, designer selects acoustical material by analysis of absorption effect of acoustical materials on the main reflection planes in order to avoid to distortion and fluctuation of frequency response function..

• Proceedings of the Korean Geotechical Society Conference
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• 한국지반공학회 2009년도 세계 도시지반공학 심포지엄
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• pp.1346-1353
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• 2009

In this study, a numerical study was carried out to simulate the expansion of ground borehole by pulse discharge technology using finite element analysis. Considering the mortar in the borehole as an acoustic medium and the surrounding soil as an elasto-plastic material, the strong shock wave developed by the pulse discharge was modeled using the underwater explosion model. The ground expansion was simulated based on a coupled acoustic-structural analysis with varying properties of mortar and soil, and the behavior between acoustic-structural interface.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• 제46권2호
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• pp.106-113
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• 2018

The Intense acoustic wave generated by the jet flame at the lift-off causes the vehicle to vibrate in the form of acoustic loads. The DSM-II(Distributing Source Method-II), which is a representative empirical acoustic loads prediction method, is a method of distributing a noise source along a jet flame axis and has advantages in calculation cost and accuracy. However, due to the limitation of the distributing method, there is a limit to accurately reflect the various launch pad configurations. In this study, acoustic loads prediction method which can freely distribute noise sources is studied. by introducing NURBS(Non-Uniform Rational B-Spline) modeling into empirical prediction method. For the verification of the newly introduced analytical technique of the NURBS, the acoustic loads prediction for the Epsilon rocket's low-noise launch pad shape was performed and the results of the analysis were compared with the existing prediction methods and experimental results.

• Journal of the Korean Society for Nondestructive Testing
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• 제35권2호
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• pp.134-140
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• 2015

Traditional moxibustion therapy can cause severe pain and leave scarring burns at the moxibustion site as it relies on the practitioner's subjective and qualitative treatment. Recently, ultrasound therapy has received attention as an alternative to moxibustion therapy owing to its objectiveness and quantitative nature. However, in order to convert ultrasound energy into heat energy, there is a need to precisely understand the ultrasound-focusing characteristics of the acoustic lens. Therefore, in this study, an FEM simulation was performed for acoustic lenses with different geometries a concave lens and zone lens as the geometry critically influences ultrasound focusing. The acoustic pressure field, amplitude, and focal point were also calculated. Furthermore, the performance of the fabricated acoustic lens was verified by a sound pressure measurement experiment.

• Journal of Advanced Navigation Technology
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• 제9권2호
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• pp.131-139
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• 2005

On this study, I constructed the reflective acoustic signal detecting system using 15MHz acoustic transducer. The most difficult problems discriminating the characteristics of the metal substance are the discriminating the corrosion state and seeking hidden defects by using none destructive testing. For solving these problems, at first, theoretic analysis has been proceeded on the acoustic V(z) characteristics which is very important on discriminating the material characteristics. For application the V(z) theory to discriminating corrosion state, the 100 and 500 won metal coins which are issued on the different years are used as the test samples. The experimental results showed the distinct differences among the coin's acoustic signals accorded to its issued years. I catched the common regulation by analysing the acquisited acoustic signals and convinced this technique to be very useful on corrosion discrimination of the metal substances by none destructive testing and also can be used to inspect on the aeronautical materials for safety navigation.

• Journal of the Korea Convergence Society
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• 제10권3호
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• pp.73-79
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• 2019

This study simulated external ear canal modeling with different external ear canal lengths, vertical flexion angles, and inner/outer diameter ratios using digital imaging and communications in medicine(DICOM) of the head temporal region and measured the acoustic sensitivity. The experiment was performed by increasing the audible frequency for humans by 200 Hz and expressing the frequency constantly transmitted at 1 Pa as the eardrum acoustic volume and presented the measurements by linear and quadratic curve regression analysis. The results showed that the longer the external ear canal length and the higher the ratio of the outer/inner diameter, the faster the acoustic response at lower frequencies. The acoustic sensitivity correlation of the meta-model using regression analysis showed a 77% influence by the external ear canal length and 5% by the external/internal diameter ratio, while the vertical flexion angle did not show a significant relationship. This showed that auditory acoustic sensitivity of humans is a factor that reacts faster at a low frequency when the external ear canal length is longer and when the difference between the outer and inner diameter is higher.

• Journal of the Korea Institute of Information and Communication Engineering
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• 제24권3호
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• pp.405-411
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• 2020

Recently, studies on underwater communication, related to the development of underwater resources, disaster monitoring and defense, have been actively carried out. In the design of wireless communication systems, path loss is the most important information to derive a link budget that is required to guarantee communication reliability by calculating received power level for the given communication link. The underwater acoustic channel have different characteristics according to geographical location and relevant environmental factors such as water temperature, depth, wave height, algae, and turbidity. Subsequently, many research institutes aiming to develop underwater acoustic communication systems are researching actively on the underwater acoustic channels in various sea areas. In Korea, however, studies on the path loss of the acoustic channel are still insufficient. Therefore, in this study, the path loss of the acoustic channel are studied based on measurement data of the at-sea experiment conducted at Geohae-do, southern sea of Korea.