• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.196-199
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• 2005

Flow traveling over a cavity opening forms a vortex due to unstable shear layer and induces an aerodynamic pressure excitation from the diffusion of the vortex convecting out of the trailing edge of the opening. The interaction between the excitation force and the cavity response sustains resonance in the resonator(cavity) and locked-in vortex shedding at the leading edge of the opening. The aerodynamic excitation force can be described from the diffusion of the vortex over the trailing edge and the level of its diffusivity is related to the strength of vorticity seeded at the loading edge. In this study, the control scheme of the internal pressure oscillation was proposed from regulating the vorticity at the leading edge by use of an oscillating spoiler. It was found that the relative motion between the spoiler and the air mass at the cavity opening influenced vorticity strength and the control was achieved by direct feedback of the cavity pressure fluctuation to the actuator.

• KIEAE Journal
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• v.11 no.4
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• pp.37-45
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• 2011

In order to have better understanding of the concept and meaning of soundscape, it is very important to consider entirely the objectives, activities, historical development processes and accomplishments of world soundscape project leading by R. Murray Schafer. Therefore, the ultimate purpose of this study is to inquire into the concrete development processes and practical activities of the soundscape in order to correspond to Schafer's conception of a tuning of the world. The establishment of WSP is based on noise pollution, listening attitudes and noisy music. Schafer formulated 5 types of item as a target, and wrote down concrete activities to achieve the goals. Especially, he devised the conceptual, educational, political and social strategies as the practical strategies of WSP. It is obtained various products by the activities of WSP from the planning starting year in 1969 to the stagnation period in 1979. That is, there are the social survey on noise-vancouver 1969, the book of noise, Okeanos, a study of community noise by-laws in canada 1972, the music of the environment, the vancouver soundscape, european sound diary, five village soundscapes, handbook for acoustic ecology and so on. The research activities of WSP arouse inspiration in many people interested in sound. Specially, it is emphasized the importance of increasing for their social roles in order to more actively improve and create the quality of sound environment. Also, it shows us the directions on how to lead our furture sound.

• Journal of the Korea Convergence Society
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• v.4 no.4
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• pp.7-12
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• 2013

Presence of music in the modern game is getting bigger and bigger, and storytelling in the area of game play a leading role in many cases. Platform game is one type of action game genre. In its nature, the character and the object in a game are closely coupled, thus they have intermate relation with reactive sound system. In this study, we tried to build a effective and reactive sound system which is suitable for the storytelling of platform game. In addition, we speculated various aspects of game including psychological, musical and social aspects, finally investigating the future aspects of the game music.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.39.1-39.1
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• 2012

Nuclear rings in barred galaxies are sites of active star formation (SF). We investigate SF and its feedback effects occurring in barred galaxies, for the first time, using high-resolution grid-based hydrodynamic simulations. The gaseous medium is assumed to be infinitesimally thin, isothermal, and unmagnetized. The SF recipes include a density threshold corresponding to the Jeans condition, a SF efficiency of 1%, and momentum feedback via Type II supernova events together with stellar-wind mass loss. To investigate various environments, we vary the gas sound speed as well as the efficiency of momentum injection in the in-plane direction. We find that when the sound speed is small, the surface density of a ring becomes largely independent of the azimuthal angle, resulting in star-forming regions distributed over the whole length of the ring. When the sound speed is large, on the other hand, the ring achieves the largest density at the contact points between the dust lanes and the ring where SF occurs preferentially, leading to a clear age gradient of star clusters in the azimuthal direction. Since rings shrink with time, a radial age gradient of star clusters naturally develop regardless of sound speed, consistent with observations. SF persists over 200 Myr, with an average rate of ${\sim}1.3M_{\odot}/yr$ similar to observed values. Rings gradually become hostile to SF as they lose gas into stars and turbulent motions dominate.

• Trans-
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• v.8
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• pp.1-28
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• 2020

This study examines musical characteristics of so-called 'Hongdae Sound' as a historic musical trend by comparing with 'US 8^th Army Sound' and British 'London Punk'. Hongdae Sound refers to the musical trend that was formed with independent bands and musicians who mostly performed live in the club called 'Drug' in Hongdae area, and voluntarily adopted minor musical sensitivity and indie spirit of 'post-punk rock' genre. But as an industrial standpoint the superficial identity of 'indie' interferes with academic approach when analysing musical aspects of Hongdae Sound. Therefore it is necessary to rearrange its characteristics as the musical trend based on regional classification in order to fully appreciate its status in history of Korean popular music. US 8^th Army Sound refers to the musical trend that was played within the live stages in US military bases in Korea. Many hired Korean musicians for those shows were able to learn the current popular musical trend in the States, and to spread those to the general public outside the bases. The industrial system of the Army Sound was very similar to that of K-Pop, but when it comes to leading the newest musical trend of 'rock-n-roll', it had more resemblance to that of Hongdae Sound. London punk was the back-to-basic form of pure rock that was armed with social angst and rebel, indie spirit. Its primal motto was 'do-it-yourself', and Hongdae Sound mostly followed its industrial, musical and spiritual paths. London punk was short-lived because it abandoned its indie spirits and became absorbed to the mainstream. But Hongdae sound maintain its longevity by maintaining the spirit and truthfulness of indie, while endlessly experimenting with new trends.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.202-207
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• 2002

The soundness of honeycomb core sandwich and laminate structure used for commercial aircrafts is generally evaluated with ultrasonic inspection because the inspection is most sensitive to planar surfaces which are perpendicular to sound propagation pass and reflects sound almost 100％ to equipment. And most defects inherent in composite material curing process has good reflective surfaces. With all this advantage, unexpected obstruction to product and additional cost could be occurred when inappropriate accept/reject criteria is given. In this study the importance of inspection criteria will be discussed to show how inappropriate criteria cause unexpected results leading to high production cost and how much time must be spent to correct those improper criteria with an actual case occurred in Aerospace Division, Korean Air.

• Journal of computational fluids engineering
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• v.15 no.4
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• pp.60-66
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• 2010

Unsteady Reynolds Averaged Navier-Stokes(URANS) and Large Eddy Simulation(LES) simulation of an axial flow fan are calculated upon same conditions and computational grids in order to study aeroacoustic noise of an axial flow fan numerically. Results of computed performance and predicted noise are compared with those of measurement. Both performances show accurate results with a significant difference of less than 5%. However, noise of LES result is more close to measured noise qualitatively than URANS. Levels of tonal noises of both LES and URANS are quite similar with those of measured at BPF(Blade Passing Frequency) in sound spectrum. However, as leading edge separation and tip vortex shedding phenomena of LES are showed more clearly than those of URANS, sound level of broadband noise of LES corresponds better than that of URANS, especially.

• Journal of Mechanical Science and Technology
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• v.18 no.2
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• pp.272-285
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• 2004

The losses at off-design points from a compressor cascade occur due to the deviation from a design incidence angle at the inlet of the cascade. The self-noise from the blade cascade at off-design points comes from a separated boundary layer and vortex sheddings. If the incidence angle to the cascade increases, stalling in blades may occur and the noise level increases significantly. This study applied Large-Eddy Simulations (LES) using deductive and deductive dynamic SGS models to low Mach-number, turbulent flow with each incidence angle to the cascade ranging from -40$^{\circ}$ to +20$^{\circ}$ and compared numerical predictions with measured data. It was observed that the oscillating separation bubbles attached to the suction surface do not modify wake flows dynamically for cases of negative incidence angles. However, an incidence angle greater than 8$^{\circ}$ caused a separated vortex near the leading edge to be shed downstream and created stalling. The computed performance parameters such as drag coefficient and total pressure loss coefficient showed good agreement with experimental results. Noise from the cascade of the compressor is summarized as sound generated by a structure interacting with unsteady, turbulent flows. The hybrid method using acoustic analogy was observed to closely predict the measured overall sound powers and directivity patterns at design and off-design points of blade cascade.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.189-195
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• 2003

This paper represents an identification procedure for leading mechanism of a car A/V system which is composed of a DC motor and a set of plastic gears. In addition, we studied dominant noise source of rattle noise generated by external forced vibration as a car drives. we made a dynamometer to produce stationary operation on loading mechanism of A/V system because noise generated by actual loading mechanism is non-stationary signal. operating the dynamometer setup at various motor speeds, sound pressure spectra are measured and the results are analyzed. its dominant noise source is also identified by using a sound Intensity technique. we made use of multi-dimensional spectral analysis to rind a dominant rattle noise. this method is so useful to eliminate coherence between vibration sources and helps us obtain coherent output spectrum of individual vibration source which make a rattle noise.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.2
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• pp.179-186
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• 2012

The potential hazards resulting from a low-velocity impact(bird-strike, tool drop, runway debris, etc.) on aircraft structures, such as engine nacelle or leading edges has been a long-term concern to the aircraft industry. Certification authorities require that exposed aircraft components must be tested to prove their capability to withstand low-velocity impact without suffering critical damage. In most of the past research studies unloaded specimens have been used for impact tests, however, in reality it is much more likely that a composite structure is exposed to a certain stress state when it is being impacted, which can have a significant effect on the impact performance. And the radiated impact sound induced by impact is analyzed for the damage detection evaluation. In this study, an investigation was undertaken to evaluate the effect in-plane loading on the impact force and sound of composite laminates numerically.