• Journal of KSNVE
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• v.9 no.4
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• pp.687-692
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• 1999

Digital holographic reconstruction method [W. A. Veronesi, et al, 1989, JASA, Vol. 85, pp. 588∼598] reconstructs a whole sound field by using measured sound pressure. This paper reports numerical errors of the method that occur at specific frequencies. The errors occur due to the truncation errors included in the calculation of transfer matrixes. The frequencies of the errors depend on the size of boundary element surfaces. Moreover, a modified calculation technique is proposed in the paper. The technique prevents the truncation errors by employing an indirect calculation procedure.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.783-786
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• 2002

The unsteady turbulent flow characteristics of NACA4406 airfoil at close proximity to the pound are numerically investigated, especially focused on the noise generation mechanism near the blunt trailing edge. The unsteady two-dimensional compressible Wavier-Stokes equations with a Spalart-Allmaras turbulence closure model are solved by the 6th-order compact scheme and the 4th-order Runge-Kutta scheme. The computation shows a noise generation by a feedback mechanism at the blunt tailing edge, where the acoustic-fluidic coupling occurs between the wall-reflected sound waves and the periodically disturbed turbulent shear layer.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.11
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• pp.1123-1128
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• 2004

An experimental study on firing noise of K2 rifle was performed. Firing noises of K2 rifle were measured at close distance to rifle. Firing noise of K2 rifle which made in Korea, has not measured before. The measurement of firing noise at close distance is not simple, because the amplitude of firing noise is much bigger than the measuring limit of ordinary sound level meter even though it uses a signal attenuator. The measurement of firing noise at close distance is necessary for noise source positioning and for obtaining the sound power of K2 rifle. By this experimental study, the firing noise levels of K2 rifle at different positions are obtained and these data can be used to Predict the sound pressure level at any distance from muzzle of the rifle. Also these data can be used to calculate the threshold shift of gunner's ear.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.874-875
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• 2008

Gap servo NFR (Near Field Recording) system is one of technologies to reduce beam spot size by increasing NA (Numerical Aperture) of lens. To achieve high NA, SIL (Solid Immersion Lens) is used. In case of using a blue LD (405 nm) as the light source the gap distance should be controlled under 100 nm with much tighter margin. To develop NFR disc drive with very small gap distance between SIL bottom and the surface of media, we need to research for the vibration characteristics and design considerations. This paper deals with a study on vibration characteristic of NFR disc drive.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.10a
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• pp.86-91
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• 1995

음원의 위치를 찾는 문제에 있어서 비독립 음원들이 존재하는 경우, 근접장에서는 음원으로부터 나오는 파형을 평면파로 가정할 수 없고 구면파로 가정해야 하며, 여러개의 비독립 음원이 존재한다고 가정하여 각각의 음원의 위치를 변화시켜 가면서 MUSIC파워를 계산하여야 한다. 실제 음원의 갯수보다 가정한 음원의 갯수가 작으면 정확한 음원의 위치를 가르키지 못하며 MUSIC 파워 값도 작다. 실제 음원의 갯수와 가정한 음원의 갯수가 같으면 정확한 음원의 위치를 가르치며 MUSIC 파워 값이 크게 얻어진다. 실제 음원의 갯수보다 가정한 음원의 갯수가 큰 경우 실제의 음원의 위치를 포함하여 다른 음원의 위치를 얻을 수 있으나 그 음원의 세기는 무시할 정도로 작다. 즉 실제 음원의 갯수보다 많은 수의 음원을 가정하여 음원을 탐지할 수 있다. 일반 음장 즉 독립 음원과 비독립 음원이 공존하는 경우 실제의 음원의 갯수만큼 가정한다면 음원이 위치를 찾을 수 있다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.10a
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• pp.74-79
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• 1995

모우드 밀도의 산정을 정확하게 구하기 위해 고주파수 영역에서 흔히 적용되는 3채널 측정법이 저주파수대 영역에서도 2채널법에 의한 방법보다 주파수 응답함수의 크기 및 공전주파수의 위치를 보다 더 잘 나타내 주고 있다는 것을 실험적으로 제시하였다. 2채널 측정법에 비하여 3채널 측정법이 모우드 밀도가 균일한 보의 경우에 있어서도 주파수 응답함수의 크기를 실제의 경우와 근접하게 추정해 줄 수 있을 뿐 아니라, 상대적으로 모우드 밀도가 높은 평판의 경우에 있어서도 공진주파수 대에서의 주파수 응답함수의 형태를 보다 분명히 나타내어 줄 수 있는 것으로 나타났다. 한편, 구조물과 가진기의 상호작용에 의한 고유진동수의 변동량 측정의 관점에서는 2채널 측정법과 3채널 측정법의 경우 모두 주파수 응답함수를 적절히 나타내어 주고 있는 것으로 나타났다.

• Journal of KSNVE
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• v.9 no.3
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• pp.621-628
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• 1999

The fundamental dynamic properties of the planar electric charged particle are investigated experimentally. The experiment is conducted using electric charged spheres(4 table tennis balls with conductive surfaces) suspended by insulating strings to cancel the gravitational force. The measurements of the equilibrium angles and the natural frequencies of oscillation agree well with the analytical predictions with some error, respectively.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.1165-1169
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• 2003

This paper presents an approach to optimally design the air-bearing surface (ABS) of the optical flying head for near-field recording technology (NFR). NFR is an optical recording technology using very small beam spot size by overcoming the limit of beam diffraction. One of the most Important problems in NFR is a head disk interface (HDI) issue over the recording band during the operation. A multi-criteria optimization problem is formulated to enhance the flying performances over the entire recording band during the steady state. The optimal solution of the slider, whose target flying height is 50 nm, is automatically obtained. The flying height during the steady state operation becomes closer to the target values than those fur the initial one. The pitch and roll angles are also kept within suitable ranges over the recording band. Especially, all of the air-bearing stiffness are drastically increased by the optimized geometry of the air bearing surface.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.592-596
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• 2001

Near field technology makes it possible to overcome the diffraction limit of laser beam and create the small spot. Because of the small spot size, the pit size and track pitch can be decreased. So the high performance actuator is needed for near field recording system. And the light mass and the small form factor are also important properties of the NFR actuator in order to be used for hand held device. The purpose of this paper is the optimal design of the NFR coarse actuator to maximize actuating force. The structure of NFR coarse actuator is the same as HDD VCM actuator. The permeance method is used for modeling of the coarse actuator. The optimal result and the FEM simulation result are presented.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.586-591
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• 2001

Dynamic analysis using impulse responses is formulated to estimate effect of slider rail shape on dynamic responses. Impulse responses are obtained on numerical nonlinear model including rigid motion of slider and fluid motion of air bearing under the slider. Dynamic characteristics of slider motion are evaluated by utilizing the decay ratio of impulse responses and modal frequencies from frequency response functions. The dynamic characteristics of the developed NFR(Near Field Recording) slider are checked by comparing those of HDD sider(Nutcracker). Also, sensitivities of slider position conditions and rotation speed on the dynamic characteristics are investigated. The researches show that the utilized method is a good indicator of designing the better slider.