• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2001.05a
• /
• pp.768-773
• /
• 2001

The self-noise from blade cascade at off-design points mainly comes from separated boundary layer and vortex sheddings, and is also dependent on blade shape. If the incidence angle to the cascade increases, the stalling in blades may occur and the noise level increases significantly. The hybrid method using acoustic analogy was employed to compute the far-field noise spectra and directivity patterns from the separated vortex shedding at off-design points of the cascade of impeller. This paper is compared with the experimental data of a stationary cascade in the same conditions. The simulated result is in excellent .agreement with the measured data except th slight under-prediction near the maximum radiation angle for a dipole sound.

• The Journal of the Acoustical Society of Korea
• /
• v.16 no.1E
• /
• pp.9-14
• /
• 1997

Check valves used in industrial and Nuclear Power Plant safety systems are susceptible to failure modes generally associated with wear of internal parts. Specifically, hinge pins, disc studs, pistons, and other mechanical parts may degrade over time, and in some cases, may which might produce a disabling event leading to plant or process shutdown. The primary diagnostic technique in the past has been to disassemble the valves. This procedure is costly, time consuming, and in the nuclear industry, it can lead to radiation exposure in some situations. Additionally repair and reassembly of a valve does not ensure proper operation. Non-intrusive diagnostic technologies including acoustics and magnetics with a digital signal analysis allow to evaluate check valve performance without a disassembly and is able to help the user detect degraded valve conditions.

• The Journal of the Acoustical Society of Korea
• /
• v.23 no.3E
• /
• pp.98-102
• /
• 2004

In 1896, Rayleigh was appointed as Scientific Advisor of the Trinity House. Rayleigh applied his knowledge of sound to developing effective fog signals during his IS-year tenure at the maritime organization. Rayleigh's expertise on acoustics met an appropriate field for its application during his improvement of the fog signal for the institution. Rayleigh's activities at the Trinity House were motivated by his desire to make contribution to the public. During his research on the fog signal, Rayleigh effectively employed his expertise acquired through his mathematical and experimental research on sound and vibration since the 1860s. Rayleigh developed effective horns for emitting fog signals and proposed various ways of overcoming the weaknesses of sound signals available at that time. While attempting to solve the problem of the attenuation of sound signals disseminating through the air, Rayleigh put foundations of atmospheric acoustics by developing new scientific theories about it.

• Proceedings of the Acoustical Society of Korea Conference
• /
• spring
• /
• pp.185-188
• /
• 1999

수중에서 기포의 강한 비선형성을 이용하여 기포막상의 두 입사 음파의 상호작용 영역으로부터 산란된 차주파수 성분 음파의 확인과 두 입사 음파의 전파방향으로 차주파수 음파가 분포하고 있음을 관측하였다 본 논문에서는 기포막을 이용하여 두 입사 음파의 상호작용 영역으로부터 산란된 차주파수 성분 음파의 지향특성을 예측할 수 있음을 제시하였다.

• The Journal of the Acoustical Society of Korea
• /
• v.30 no.7
• /
• pp.377-382
• /
• 2011

From 1860s to 1910s, Rayleigh's efforts to reveal the nature and various features of sound continued to achieve good success in theory and experiment. Although his concern with acoustics primarily originated from intellectual curiosity, he did not ignore its practicality. His efforts were made to develop public lectures with demonstration experiments during his professorship at the Royal Institution of Great Britain. Acoustics covered the second-most frequent subject in his public lectures and his acoustical experiments were designed for satisfying the needs of the audience by employing ingenious strategies.

• Journal of Sensor Science and Technology
• /
• v.19 no.2
• /
• pp.124-129
• /
• 2010

For the industrial printing applications, the stability of the piezo-driven inkjet printhead is a major requirement. In this paper, we focused on the failure modes of the inkjet printhead and realized a method to detect and repair them at high speed. The printhead monitoring is performed by detecting the residual vibration of the actuating plate using the self- sensing capability of the piezoelectric material. To measure the channel acoustics and to identify the malfunctioning nozzle, we devised the bridge sensing circuitry and failure detection algorithm. The residual vibration signals can be affected by the boundary conditions of the channel acoustics, so it is possible to identify the failure causes by analyzing the monitoring signals. Therefore it is also possible to apply a proper restoring process to the defective printhead. The experimental results show that this method is effective in improving the reliability of the industrial printing.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.11 no.4
• /
• pp.58-64
• /
• 2001

Sound absorbing materials are applied to the exposed surfaces of curvet subway tunnel for the reduction of curving noise level. Before the treatment, acoustical engineering simulation is performed to predict the noise level reduction for different kinds and amounts of absorbing material. The principle of geometrical acoustics is utilized to perform the simulation efficiently and accurately. The noise bevels of the inside and outside of running car body are measured to find the noise level reduction. The average noise level reduction of 8 dB has been attained. It has been shown that the simulated results are comparable to the measured ones.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2000.06a
• /
• pp.98-103
• /
• 2000

The cut-off is a unique feature associated with duct acoustics due to the presence of duct walls. Duct geometry effect on sound radiation is another issue of duct acoustics. The radiation of duct internal noise to ambient from duct open ends with various geometries is studied via numerical methods. The linearized Euler's equations in generalized curvilinear coordinates are solved by the DRP finite difference scheme. A number of accurate boundary conditions are used at boundaries for the computational domain to minimize the non-physical reflections. The far field sound pressure levels are computed by the Kirchhoff integration method. We investigate the cut off phenomana and duct geometry effects on sound radiation with numerical results.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2000.06a
• /
• pp.197-201
• /
• 2000

For building acoustics, the revision and establishment of ISO JIS were carried out actively in the direction of international harmonization recently. In this consideration, the trends of the ISO and JIS were reviewed and the establishment process of KS was introduced. As a result of this consideration, it is thought to be that 'International Harmonization' should be a base for KS and the speciality of domestic characteristics should be attached to annex.

• Proceeding of Spring/Autumn Annual Conference of KHA
• /
• 2003.11a
• /
• pp.67-72
• /
• 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.