• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.643-648
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• 2011

This paper deals with the ESM(equivalent source method) with the continuation of acoustic near-field for NAH(near-field acoustic holography) to overcome the finite measurement aperture effect and reconstruct the normal velocity on an arbitrarily shaped structure surface. The continuation method is an extension of the measured sound field into a region outside and is based on the Green's function relating acoustic quantities on the two conformal surfaces. This algorithm is not limited to planar surfaces and can be applied to arbitrarily shaped surfaces. The ESM is an alternative approach of BEM-based NAH for the reconstruction on a general structure. In ESM the acoustic field is represented by a set of point sources located over a surface that is close to the structure surface. The simulation results of this study shows that the reconstruction error of particle velocity on the source surface is 11% and 16% for planar and cylindrical sources separately.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.607-613
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• 2011

In this study, structural vibration analyses for a 5MW offshore wind wind-turbine model have been performed for different substructure models. The efficient equivalent modeling method based on computational multi-body dynamics are applied to the finite element models of the present offshore wind turbines. Monopile and tri-pod substructure types of the typical offshore wind-turbine are considered herein. Detailed finite element modeling concepts and boundary conditions are described and the comparison results for previous analyses are presented in order to show the verification of the present numerical approach. Campbell diagrams are also present to investigate the rotational resonance characteristics of the offshore wind-turbines with different substructures.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.772-777
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• 2013

This article presents the reduction of vibration generated by an automobile fuel pump. In order to analysis the vibration of the fuel pump, a simplified dynamic model is established, which is composed of a rigid rotor and a equivalent springs. The equivalent stiffnesses of the upper and lower assemblies are evaluated by the comparison of modal testing results and the finite element analysis. the stiffness for the oil film of the journal bearing is extracted by using Reynold's equation. In addition, the time responses for the vibration of the fuel pump are computed by using a commercial multi-body dynamics software, RecurDyn. Based on these results, some design suggestions are proposed to reduce the vibration of an automobile fuel pump.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.9 s.102
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• pp.1003-1008
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• 2005

The acoustic absorption of a multiple layer perforated plate system is very good near the resonance frequency region, while it has been regarded as a demerit that its frequency bandwidth is considerably narrow. In order to overcome such a demerit, the parallel perforated plates with different porosities are proposed. The sound absorption of such system composed of a parallel perforated plate is calculated by an equivalent electroatoustic circuit approach and validated by comparing the calculated absorption coefficients with those measured by the two-microphone impedance tube method. The sound absorptive characteristics and performance of parallel perforated plate systems are discussed from a standpoint of frequency bandwidth related with sound absorption.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.10
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• pp.936-945
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• 2007

We studied the influences of open cracks in free vibrating beam with rectangular section using a numerical model. The crack was assumed to be single and always open during the free vibration and equivalent bending stiffness of a cracked beam was calculated based on the strain energy balance. By Galerkin's method, the frequencies of cantilever beam could be obtained with respect to various crack depths and locations. Also, the experiments on the cracked beams were carried out to find natural frequencies. The cracks were initiated at five locations and the crack depths were increased by five steps at each location. The experimental results were compared with the numerical results and the comparison results were discussed.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.4
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• pp.355-360
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• 2010

In this study, a modeling process of a 3-axis planar alignment stage is suggested. Vibration tests using a laser vibro-meter is performed to find the modeling parameters of the stage. By analyzing the result of the test, the stiffness of prismatic joints and revolute joints, as well as the contact conditions of the thrust bearings, can be calculated. The modeling of the stage was validated by comparing six normal mode shapes, which are acquired from experiments and simulations.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.88-93
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• 2003

This paper presents an efficient dynamic modeling method for open cracked rotor-bearing systems. An equivalent bending spring model is introduced to represent the structural weakening effect in the presence of cracks. The proposed modeling method is validated through a series of simulations and experiments. First, the proposed method is rigorously compared with a commercial finite element code. Then, an experiment is performed to validate the proposed modeling method. Finally, a numerical example is introduced to demonstrate the possible application of the proposed method in the crack diagnosis fur rotor systems.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.617-621
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• 2003

Existing loudness models are specified only to diotic sounds in spite of the fact that normal human beings hear dichotic sounds. Approximately, the arithmetic mean of loudness values of both ear signals has been suggested for the resultant perceived loudness. In this study, the dependence of overall loudness perception on the interaural level differences was investigated by the subjective tests. It was found that the larger the interaural level difference, the louder the perception than the mean of calculated loudness values at both ears and the lower the critical band rate or the reference level, the louder the perception than the mean value. A modified loudness model was proposed to he applicable to dichotic sounds by using the equivalent diotic levels.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.123-126
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• 2005

This study provides a comprehensive experimental study on the dynamic characteristics of a flexible matrix composite(FMC) driveshaft. A primary objective is to verify the analytic results of the FMC drivetrain based on the equivalent complex modulus approach and the classical lamination theory. A testrig has been constructed, which consists of a FMC shaft, a foundation beam, bearings, external dampers and a driving motor. The frequency response functions and transient responses are obtained from the external excitation and the spinup testings. It turns out that the analytic results are in good agreement with the experimental ones.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.275-278
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• 2005

The dynamic characteristics of rotor shafts for electric motors were investigated through the modal tests. The natural frequencies and modal dampings in each manufacturing stage of rotor core assembly were analyzed from the frequency response functions fer all 6 motors of a product model. The deviation of the each individual modal feature was found dependent on the mode shapes as well as the rotor assembly stage. The core stacking itself is known to widen the deviation of modal properties but fellowing processes of rotor bar insertion and swaging are confirmed to reduce the deviation. Finally the equivalent diameter of core part was estimated from the comparison of measured and calculated results to include the stiffness of core part.