• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.759-762
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• 2002

Automobile aeroacoustics Is a developing area of technology where experimental and theoretical tools are being continuously refined to understand, analyze and modify the noise-generating mechanisms in the vehicle flow. Main sources of ground vehicle exterior noise are the tires (tire/road interaction) and the unsteady flow field around the vehicle. In this study, the sound source localization of a rolling tire was applied to the measurement of radiated sound by using an acoustic mirror system. A possible flow pattern that develops is suggested based on detailed wind tunnel investigations with a rotating wheel in contact with a moving belt.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1998년도 춘계학술대회 논문집
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• pp.214-220
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• 1998

The determination of sound pressure radiated from periodic plate structures is fundamental in the estimation of noise levels in aircraft fuselages and ship hull structures. As a robust approach to this problem, here a very general and comprehensive analytical model for prediction the sound radiated by a vibration plate stiffened by periodically spaced orthogonal symmetric beams subjected to a sinusoidally time varying point load is developed. The plate is assumed to be infinite in extent, and the beams are considered to exert both line force and moment reactions on it. Structural damping is included in both plate and beam materials. From this theoretical model, the sound pressure levels on axis in a semi-infinite fluid(water) bounded by the plate with the variation in the loactions of an external using three numerical tools such as the Gauss-Jordan method, the LU decomposition method and the IMSL numerical package.

• 소음진동
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• 제6권6호
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• pp.781-790
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• 1996

The goal of current research is to suppress the acoustic noise radiated from vibration of composite plate structure. The induced noise can be reduced through the control of the corresponding structural vibration modes by using the piezoelectric materials as actuator. The acoustic fields are to be analyzed through the boundary element method (BEM) based on the Rayleigh intergral equation and structural system through the finite element method (FEM). The suppression of rediated sound is studied by adaping the piezoelectric material as the distributed actuator. Numerical results are presented on the sound radiation from composite plate of arbitrary boundary conditions, the noise reduction adapting the piezoelectric materials as distributed actuator. The results show the effectiveness and possibility of piezoelectric actuator in the control of sound radiation from composite structure.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문초록집
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• pp.348.2-348
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• 2002

ER mount is often used instead of rubber mount in cylindrical shell to improve the vibration and noise performanec. The noise radiated by cylindrical shell will be reduced by reducing the force transmitted to the cylindrical shell through ER mount. In this paper, LQ control theory is used to reduce the transmitted force to the cylindrical shell. The finite element method of cylindrical shell is formulated by NASTRAN and its vibrating shape is calculated in frequency domain. (omitted)

• 한국소음진동공학회논문집
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• 제25권11호
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• pp.747-752
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• 2015

Underwater radiated noise is an important characteristic in the naval weapon systems. It is difficult to measure the radiation efficiency of underwater vehicle, such as UUV(unmanned underwater vehicle) and underwater weapons in real operation environment. In this study, acoustic radiation efficiency of a circular cylindrical structure is measured in the laboratory-water tank. The radiation efficiency is compared with the numerical results and it is found that they are in a good agreement. Therefore, the measurement method can be applied effectively for predicting the underwater radiation noise and effectiveness of radiation reduction means.

• The Journal of the Acoustical Society of Korea
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• 제16권1E호
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• pp.29-34
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• 1997

Numerical prediction of aerodynamic noise radiated by subsonic rotors are carried out. A computer program has been developed which incorporates both the discrete frequency noise as well as the broadband noise arising from the ingestion of turbulence. Acoustic analogy is used in conjunction with Homicz's formulation of turbulence ingestion noise. Formulation 1A of Farassat is used to enhance the numerical analysis performance of Ffowcs-Williams Hawkings equation by eliminating the numericla time differentiation. Homicz's trubulence ingestion noise prediction technique is used to understand the characteristics of broadband noise radiated by isotropic trubulence in gestion. Numerical predictions are carried out for a number of rotor configurations and compared with experimental data. Monopole consideration of transonic rotor agrees well with both the experimental data and the linear theory. Noise radiation characteristics of rotor at lifting hover are investigated utilizing simple blade loading obtained by thin wing section theory. By incorporating discrete noise prediction of steady loading with broadband spectrum, much better agreement with experimental data is obtained in the low frequency region. The contributions from different noise mechanisms can also be analyzed through this method.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2010년도 춘계학술대회 논문집
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• pp.41-45
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• 2010

In this paper, we analyzed the frequency spectrum of radiated electromagnetic waves generated by series arc- and corona- discharges as a basic study to develop an online diagnostic technique for power facilities installed inside switchboards. To simulate corona and series arc discharges, an arc generator specified in UL1699 and a corona generator were fabricated. The experiment was carried out in an electromagnetic shielding room, and the measurement system consists of an Ultra Log Antenna and an EMI Test Receiver. The frequency spectrum exists in ranges from 30 to 500 [MHz] for series arc discharge and 30 [MHz] to 2 [GHz] depending on defects for corona discharge. The peak frequency of series arc discharge and corona were 40 [MHz], 80 [MHz] and 35 [MHz]~160 [MHz], respectively.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.346-350
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• 2000

In scroll compressors, there are two major noise sources. Sturctural path: excitation of the compressor housing by unbalance forces and forces generated by compression cycle. Gas cavity path: excitation of top cap by discharge gas pulsation. In this study, in order to analyze the radiated noise generated by the discharge gas pulsation, FEM/BEM model of the top cap is established. Measured pressure of discharge pulsation is introduced in the FEM model as the excitation and vibration response is calculated. Radiated sound pressure is then obtained by BEM method based on this vibration response. Results are compared with the measured data. It is shown that the trend of the noise radiation can be predicted in this approadch.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.104-109
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• 2000

The modes of oscillation and radiated acoustic fields of compressible flows over open cavities are investigated computationally. The compressible Navier-Stokes equations are solved for two-dimensional cavities with laminar boundary layers upstream. The high-order and high-resolution numerical schemes are used for the evaluation of spatial derivatives and the time integration. Physically correct numerical boundary conditions are implemented to produce time-accurate solutions in the whole computation domain. The computational domain is large enough to directly resolve a portion of the radiated acoutic field. The results show a transition from a shear layer mode, for shorter cavities and lower Mach numbers, to a wake mode for longer cavities and higher Mach numbers. The shear layer mode is well characterized by Rossiter modes and these oscillations lead to intense upstream acoustic radiation dominated by a single frequency. The wake mode is characterized instead by a large-scale vortex shedding. Acoustic radiation is more intense, with multiple frequencies present.

• 한국전문물리치료학회지
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• 제9권3호
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• pp.93-99
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• 2002

Traditionally, ultraviolet (UV) has been used for treating the pressure sore and skin wound. The effects of UVA and UVB radiation on disinfection have been reported. The purpose of this study was to examine the effectiveness of UVC radiation on disinfection of Escherichia coli, Staphylococcus aureus, Salmonella typhimurium in vitro. Three bacterium were radiated by UVC (250 nm, 20 seconds) and incubated at $37^{\circ}C$ for 24 hours at the agar culture medium. Kill rates of all three bacterium were 99.9%. UVC radiated on three kinds of bacterium for 30 or 60 seconds. Kill rates were 99.9% both 30 and 60 seconds. This data suggests that UV light at 250 nm could be a useful method to minimize infection and shorten healing time in pressure sore and skin wound condition.