• Journal of Advanced Marine Engineering and Technology
• /
• v.12 no.2
• /
• pp.21-34
• /
• 1988

Machinery enclosures are widely adopted to reduce the noise emission in various fields of application. Emitted noise, which is due to the vibration of enclosure's outer surface, is composed of two kinds of sound with different path of propagation. One is the "structure-borne sound", while the other is "air-borne sound". In order to get a most efficient machinery enclouser a prudent consideration upon the above structure-borne and air-borne sound is required, as the guiding principle of contermeasure for each noise is quite different. The controlling of input vibration and its isolation are major subjects for the structure-borne sound, and the specifications of absorbing members and damping panels are the major related matters for the air-borne sound. Hence, it seems very efficient to separate the total sounds into two categories with a great accuracy when one think of further reduction of noise from the existing enclosure, although its separating methods have not been made clear for many years. Author proposes an application method of experimental modal analysis to extract the structure-borne sound from the measured total radiation sound, as the air-borne sound is deduced by the vectorial difference between the measured total radiation sound and the calculated structure-borne sound. In order to calculate the correct structure-borne sound by the excitation at an arbitrary point on the enclosure structure, it is important to decide 1) how to estimate the enclosure's surface vibration velocity and 2) how to compute the radiation sound which is considered as the effect of vibration modes of enclosure surface. The former can be solved with total frequency response function calculated by the application of experimental modal analysis. The latter is to be solved by the author's new approaches for radiation sound computation by means of the Rayleigh's integral equation and the boundary-element method applied complex surface vibration velocity. As a first step, structure-borne sound by the excitation at an arbitry point on the rectangular plate with fixed edges, has been calculated to verified the reliability of the developed computation methods. The results of calculation show good agreements with those of the actual measurements.actual measurements.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.12 no.3
• /
• pp.34-40
• /
• 2008

Acoustic design parameters of a half-wave resonator are studied experimentally for acoustic stability in a model chamber. According to the standard acoustic-test procedures, acoustic-pressure signals are measured. Quantitative acoustic properties of damping factor and sound absorption coefficient are evaluated and thereby, the acoustic-damping capacity of the resonator is examined. The diameter and the number of a half-wave resonator, its distribution, and the diameter of an enclosure are selected as the design parameters for optimal tuning of the resonator. Aroustic-damping capacity of the resonator increases with its diameter. When the open-area ratio of the resonator exceeds the optimum value, over-damping appears, leading to the decrease in the peak absorption coefficient and the broadening of absorption bandwidth. As the resonator diameter increases, optimum open-area ratio decreases.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.2 no.2
• /
• pp.49-56
• /
• 2001

The possibility of a noise reduction of piezoelectric single Panels is experimentally studied. Piezoelectric single panel is basically a plate structure on which piezoelectric patch with shunt circuit is mounted. The use of piezoelectric shunt damping can reduce the transmission at resonance frequencies of the panel structure. Piezo-damping is implemented by using a newly proposed tuning method. This method is based on electrical impedance model and maximizing the dissipated energy at the shunt circuit. By measuring the electrical impedance at the piezoelectric patch bonded on a structure, an equivalent electrical model is constructed near the system resonance frequency. Resonant shunt circuit for piezoelectric shunt damping is composed of register and inductor in series, and they are determined by maximizing the dissipated energy throughout the circuit. The transmitted noise reduction performance of single Panel is tested on an acoustic tunnel. The tunnel is a tube with a square cross section and a loud speaker is mounted at one side of the tube as a sound source. Panels are mounted in the middle of the tunnel and the transmitted sound pressure across Panels is measured. By enabling the piezoelectric shunt damping noise reduction is achieved at the resonance frequencies as well. Piezoelectric single panel with piezoelectric shunt damping is a promising technology for noise reduction in a broadband frequency.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2001.11b
• /
• pp.1150-1155
• /
• 2001

Vehicle Manufacturers use asphalt deadener sheets for their passenger cars to reduce noise and vibration from engine and road surface. Since their shapes are limited to a few variations, it is very difficult to reduce unnecessary weight by changing the shape of the deadeners. There is also damping performance limit in the asphalt sheets. Therefore, a high damping material should be implemented into the vehicle noise and vibration reduction activities to overcome the disadvantage of asphalt sheets. In this study, measurement of the damping loss factor and sound transmission loss were made to compare the properties and vehicle test and analysis was followed to evaluate the NVH performance of each deadener type in the vehicle.

• Journal of the Korean Society for Railway
• /
• v.13 no.5
• /
• pp.476-480
• /
• 2010

In the corrugated steel panels used for railway vehicles, sound insulation performance is significantly deteriorated by local resonance effect. In this study, as a countermeasure, polyurethane foam is filled in the corrugated steel panel and glass wool layer is inserted in the layered floor panel, and then improvement effect of the sound insulation performance is experimentally estimated. Based on ASTM E2249-02, intensity transmission loss is measured and estimated on the corrugated panel and floor structure. The aim of the study is to identify how the foam filling and inserting glass wool layer improve the sound insulation performance of the train body structure in aspect of the weight increment.

• Journal of the Institute of Convergence Signal Processing
• /
• v.15 no.3
• /
• pp.91-96
• /
• 2014

For Sound source direction and separation method, Frequency Domain Binaural Model(FDBM) shows low computational cost and high performance for sound source separation. This method performs sound source orientation and separation by obtaining the Interaural Phase Difference(IPD) and Interaural Level Difference(ILD) in frequency domain. But the problem of reflection occurs in practical environment. To reduce this reflection, a method to simulate the sound localization of a direct sound, to detect the initial arriving sound, to check the direction of the sound, and to separate the sound is presented. Simulation results show that the direction is estimated to lie close within 10% from the sound source and, in the presence of the reflection, the level of the separation of the sound source is improved by higher Coherence and PESQ(Perceptual Evaluation of Speech Quality) and by lower directional damping than those of the existing FDBM. In case of no reflection, the degree of separation was low.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2011.04a
• /
• pp.646-647
• /
• 2011

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.20 no.12
• /
• pp.24-29
• /
• 2021

Recently, owing to the high demand for eco-friendly cars in the automotive industry, noise and vibrations have become major challenges. The use of laminated damping steel is increasing in response to these demands. Laminated damping steel is primarily used in sound insulation plates. The vibration energy is converted into thermal energy due to the viscoelastic resin being located between two steel sheets and being able to damp the vibrations when an external force, such as, noise or vibration is applied to the steel plate. Laminated damping steel is chiefly applied to dash panels in automotive body parts, and because of its structure, junction technology for bonding with other components is necessary. However, there has not been sufficient research conducted on junctions. In this study, regardless of the electrode shape, in the range of 4.0 ~ 8.0 kA welding current, the same welding force and welding time were applied which were 2.8 kN and 200 m/s (12 cycles) and the tensile shear load and nugget size were analyzed after the resistance spot welding between different materials of laminated damping steel with a thickness of 1.035 mm. The results show that in the range of 5 ~ 8 kA welding current, 1.035 mm laminated damping steel meets the MS181-15 standard, which is the technical standard of Hyundai-Kia Motors.

• 제어로봇시스템학회:학술대회논문집
• /
• 1996.10b
• /
• pp.399-402
• /
• 1996

The electrodynamic loudspeakers should have a wide dynamic range to reproduce various sound levels. When the input signal is small, the radiated sound from the loudspeaker is not so much distorted. However, for large input signal with low frequency component the radiated sound is significantly distorted due to the nonlinearities of the loudspeaker. The suspension, damping, and magnetic flux of loudspeaker are the main sources of the nonlinearity. Such electromechanical parameters related to harmonic distortion have been represented by a polynomial model for diaphragm displacement, while each of the polynomial coefficient is evaluated by using the principle of harmonic balance experimentally. Based on the polynomial model, we designed a compensator for nonlinear harmonic distortion of direct radiator loudspeaker. Than observer is used to estimate the displacement of the loudspeaker diaphragm, which is rather difficult to measure directly in the conventional setting. The usefulness of the designed compensator is demonstrated by numerical simulations. Simulation results show about 30db decrease at the second and third higher harmonic distortions. We carry out an experiment on speaker to verify designed controller and nonlinear observer.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 1998.03a
• /
• pp.214-220
• /
• 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.