• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.10
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• pp.1326-1334
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• 2000

The oscillatory excitation with a Strouhal number of 2.65 ncar the stagnation zone of hemispherical nose model was employed to control the laminar separation bubble and the transition to turbulence. The effects of oscillatory excitation upon the separation bubble and the transition were addressed in terms of kurtosis/skewness and time-frequency analyses. The measured noise spectrum of radiated sound from the turbulent boundary layer on the axi-symmetric infinite cylinder is compared with that by Sevik's wave-number white approximations. The noise sources in TBL on axi-symmetric cylinder and the caling of their far-field sound are also discussed.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.11 no.5
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• pp.148-155
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• 2001

Hydraulic breaker is currently used for many civil engineering areas owing to the ease of changing the tooling mechanism. However, due to a high noise level, it has been one of notorious sources of environmental noise and the prevailing environmental concerns force the manufacturers to reduce the radiated noise levee during operations. To comply with such concerns, the present study is focused on designing and developing a low-noise hydraulic breaker For this purpose, sound sources are identified and relative contributions are rated. Acoustic enclosure. sealing systems, and low-nolle type chisel have been developed and applied to the actual machine. As a result, the radiated noise from the developed low-noose hydraulic breaker is reduced more than 13 dB(A) In comparison with the conventional hydraulic bleaker.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.891-896
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• 2007

Noise radiated from the powertrain is an important factor of the vehicle interior noise. In this paper, Finite Element(FE) model and Boundary Element(BE) models were created. The FE model was updated by doing a correlation between experimental modal analysis(EMA) values and finite element analysis(FEA) values. Main bearing forces were calculated using a running modal data. The forced vibration analysis was simulated using the software MSC/NASTRAN, and the radiated noise was predicted using the software LMS/VIRTUAL.LAB.

• Journal of the Korean Institute of Navigation
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• v.23 no.2
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• pp.61-66
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• 1999

It is being more and more difficult to suppress emissions from electronic products using PCB(Printed Circuit Board) to the limit. Therefore, the exact evaluation of the emission from PCB has been more important to reduce the required time and the cost at the design phase of the products, especially on board ship's equipments. This research has evaluated the emission radiated from PCB based on the theoretical approach of SDA(Spectral Domain Analysis), which is available to analyze microwave stripline, coplanar line, patch antenna, etc. According to the theoretical results, it has been clearly shown that the emission radiated from PCB is reduced as the thickness of PCB is thinner, the permittivity of PCB is higher, the length of stripline is shorter, and the frequency is lower.

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1774-1776
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• 2001

The most of faults in gas insulation of power facilities are caused by partial discharge. Therefore we simulated partial discharge and measured the radiated electromagnetic wave emitted from partial discharge in the $SF_6$ gas by biconical antenna. This paper describes time delay characteristics of radiated electromagnetic waves with distance between antenna and discharge source.

• Journal of Mechanical Science and Technology
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• v.17 no.12
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• pp.1949-1960
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• 2003

This paper presents vibration and noise control of flexible structures using squeeze mode electro-rheological mounts. After verifying that the damping force of the ER mount can be controlled by the intensity of the electric fild, two different types of ER squeeze mounts have been devised. Firstly, a small size ER mount to support 3 kg is manufactured and applied to the frame structure to control the vibration. An optimal controller which consists of the velocity and the transmitted force feedback signals is designed and implemented to attenuate both the vibration and the transmitted forces. Secondly, a large size of ER mount to support 200 kg is devised and applied to the shell structure to reduce the radiated noise. Dynamic modeling and controller design are undertaken in order to evaluate noise control performance as well as isolation performance of the transmitted force. The radiated noise from the cylindrical shell is calculated by SYSNOISE using forces which are transmitted to the cylindrical shell through two-stage mounting system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.138-142
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• 2001

A comparison between theoretical and measured transfer function, which relates structure-borne noise source level to underwater radiated noise, of a naval ship is presented in this study. Transfer functions are obtained by dividing far field underwater noise by the value of structure borne noise source levels below machinery mounts. In prediction, statistical energy analysis of the whole ship structure is used to get vibration levels of wetted hull plates below water line. Then, far field radiated noise is calculated by summing up contributions from each plates using vibration levels and radiation efficiencies. And 1/3-octave band underwater sound pressure at the distance of 1 m away from the hull were measured to get experimental transfer functions. The two transfer functions are compared to show resonable agreements in spite of the subtle physical differences between each other.

• Journal of KSNVE
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• v.8 no.5
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• pp.908-913
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• 1998

Analogous problem for a gear dynamics where helical gears excite logitudinal forces in the shaft is studied. These shaft forces excite the supporting gear housing through bearing, causing structural vibration. In this study, shaft is modeled as a rod, and bearing is modeled by a massless spring. A simple model for gear housing is a clamped circular plate. To model this force transmission, the transfer functions from the shaft to a clamped circular plate are analytically derived by using the spectral method and four-pole parameter. Finally, radiated noise is computed, using the acoustic relations due to plate surface vibration.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.334-339
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• 2000

In order to predict the noise of the spur gear system, a simplified model of spur system including the housing is studied. The spur gear is modeled as a single degree of freedom system. The shaft-housing system is modeled as a clamped circular plate connected with a beam. The moment components of the beam excited by the spur gear mesh force are considered in the calculation of plate vibration and radiated noise. The out-of-displacements of the clamped circular plate due to the r-direction moment and ${\theta}$-direction moment are calculated. Radiated noise from the plate in the air is also calculated using Rayleigh integral. Using the numerical example, the numerical validation of the analytical procedure on the noise prediction are given.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1386-1392
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• 2000

This paper presents a new prediction method of radiated noise from grille of the airconditioning appliance. Laminar vortex sheddings behind a circular cylinder are simulated by solving two dimensional unsteady incompressible Navier-Stokes equation. The Finite Elements Method(FEM) and unstructured grid generation technique are applied to solve, the unsteady lift/drag coefficients are obtained to compute far-field noise using Lighthill's acoustic analogy. Grille is divided into some cylinder segments, and radiated noise from grille is obtained by summing noise generated from each segment. The effects of changing cross section of cylinder and grille geometry are studied. And sound pressure levels radiated from typical H-type grille are measured in KAIST anechoic wind tunnel at various inflow conditions and compared with numerical predictions.