• The Journal of the Acoustical Society of Korea
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• v.27 no.8
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• pp.411-417
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• 2008

An alternative formulation of the Helmholtz integral equation derived to express the pressure field explicitly in terms of the velocity vector of a radiating surface is used to solve acoustic radiation and fluid/structure interaction problems. This formulation, derived for arbitrary sources, is similar in form to the Rayleigh's formula for planar sources. Because the surface pressure field is expressed explicitly as a surface integral of the surface velocity, which can be implemented numerically using standard Gaussian quadratures, there is no need to use BEM to solve a set of simultaneous equations for the surface pressure at the discretized nodes. Furthermore the non-uniqueness problem inherent in methods based on Helmholtz integral equation is avoided. Validation of this formulation is demonstrated for some simple geometries.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.227-230
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• 2000

본 논문에서는 외부방사 문제에 널리 사용되는 음향경계 요소 법(Acoustic Boundary Element Method)을 확장하여 저주파수 대역은 기존의 방법을 이용하고 고주파수 대역에서는 경계요소의 특성길이에 의한 고주파수 상한을 극복할 수 있는 방법을 제시한다. 밴드를 대표하는 음압 레벨을 직접 계산하도록 상호상관도 가정을 통하여 간략화 하였다. 간단한 음향방사 모델인 배플이 있는 빔과 평판에 대하여 Rayleigh 적분식의 계산결과와 제안된 방법을 비교하여 적용효능성을 검토하였다. 적용을 위한 조건으로는 방사면 진동의 상호상관도가 작아야 하므로, 이를 만족시키기 위한 일반적인 조건식을 제시하여 이로부터 경계요소의 특성길이를 정하는 기준을 제시하였다.

• Proceedings of the Acoustical Society of Korea Conference
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• 1996.10a
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• pp.8-13
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• 1996

균질 매질내에 형성되는 근거리 음장의 해석에는 종래 회절 이론에서의 Rayleigh 적분식에 근거한 Lommel 근사식이 주로 이용되어져 왔다. 그러나, 불균질한 매질에서는 그 방법의 적용이 어렵고, 유한요소법등 새로운 방법이 적용되어야 한다. 본 연구에서는 불균질 매질에서의 음장을 해석하는 한 방법으로 Angular Spectrum법을 제안하고, 경계를 가상한 등수온의 물에 대하여 Lommel 근사식에 의해 직접 산출한 음장과 Angular Spectrum법을 적용하여 산출한 음장을 서로 비교함으로써 그 유효성을 검토하였다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.8
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• pp.1485-1492
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• 1992

While the vibration of circular plates were considered by many researchers, rather less attention is given to elliptical plates. In the present paper, the Rayleigh-Ritz mothod is used to obtain an eigenvalue equation for the free flexural vibration of thin elliptical plates having the classical free, simply suported or clmped boundary condition. Circular plates are included as a special case of the elliptical plates. Products of simple polynomials are used as the admissible functions and a recurrence relationship facilitates the evaluation of the necessary integrals. The analysis is developed for rectilinear orthotropic plates but the numerical results are given for isotropic plates with various aspect ratios.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.11
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• pp.1089-1095
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• 2009

The radiated sound pressure induced by tapping test is obtained by solving the Rayleigh integral equation. For structurally radiated sound, the sound field is directly coupled to the structural motion. Therefore the impact response should be analyzed. In this paper, the delamination model is used to analyze the impact response of delaminated composite laminates. And efficient spring-mass model has been proposed to model hammer shaped impactor. Predicted sound pressure histories are compared with test data. The influence of damage on the sound pressure and impacted force history of laminates were investigated. The results show that both radiated sound pressure and impact force history are strongly influenced by delamination on laminates. As a result, it is shown that the presented sound based tapping method was found to be reliable for detecting the damage in composite laminate.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.763-768
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• 2012

Active window system which can reduce the environmental noises, such as traffic noise and construction noise, from an open window into a room was proposed in the previous works. The key idea of the proposed active window system was that the control sources are approximately collocated with the primary noise source in terms of the acoustic power for global noise reduction throughout the interior room. Moreover, because it is important not to intrude into the living space in the building environment, no error sensors were used and an open-loop control method using control sources at the window frame and the reference sensors outside the room was used for the proposed system. The open-loop control gain was calculated by the interior room model assumed as the semi-infinite space, and the interior sound field was estimated by Rayleigh integral equation under the baffled window model assumption. However, windows with a finite thickness should were considered for the calculation of the open-loop control gain of the active window system since these are representative of most window cases. Therefore, the finite thickness window model based on the Sgard's model was derived and the open-loop control gain using the interior sound field estimated by that model was calculated for active window system. To compare the performance of these two models, a scale-model experiment was performed in an anechoic chamber according to noise source directions. Experimental results showed that the performance for the thickness window model is better than the baffled window model as the angle with respect to the perpendicular direction is larger.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.465-475
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• 2010

구조물의 손상을 평가하기 위한 적용되는 태핑 테스트를 효과적이고, 정확하게 사용하기 위하여 적층판의 충격 시 발생하는 현상을 수치적인 방법을 이용하여 해석하였다. 구조물의 진동에 의해 방사되는 음은 구조물의 거동과 직접적으로 연관되므로 충격응답해석이 수행되어야 한다. 본 논문에서는 층간분리가 존재하는 적층판의 해석을 위하여 층간분리 모델을 사용하였으며, 해머 형상의 충격체를 모사할 수 있는 효과적인 스프링-질량모델을 제시하였다. 또한 태핑 테스트 시 방사되는 음압을 Rayleigh 적분식을 이용하여 해석하였다. 예측된 음압이력과 시험결과와 비교하였으며, 음압이력과 충격하중이력에 손상이 주는 영향을 검토하였다. 방사되는 음압과 충격하중이력은 적층판에 존재하는 손상에 영향을 받는 것을 보였다. 결과적으로 제안된 음을 이용한 태핑실험은 복합재에 존재하는 손상을 검출하는데 신뢰성 있는 방법임을 알 수 있었다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.6
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• pp.583-590
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• 2016

This paper presents a dynamic crack propagation algorithm with Rayleigh damping effect based on the MLS(Moving Least Squares) Difference Method. Dynamic equilibrium equation and constitutive equation are derived by considering Rayliegh damping and governing equations are discretized by the MLS derivative approximation; the proportional damping, which has not been properly treated in the conventional strong formulations, was implemented in both the equilibrium equation and constitutive equation. Dynamic equilibrium equation including time relevant terms is integrated by the Central Difference Method and the discrete equations are simplified by lagging the velocity one step behind. A geometrical feature of crack is modeled by imposing the traction-free condition onto the nodes placed at crack surfaces and the effect of movement and addition of the nodes at every time step due to crack growth is appropriately reflected on the construction of total system. The robustness of the proposed numerical algorithm was proved by simulating single and multiple crack growth problems and the effect of proportional damping on the dynamic crack propagation analysis was effectively demonstrated.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.9
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• pp.820-827
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• 2011

Recently, noise has been regarded as one of the most notorious and frequent environmental pollutions which can be often encountered not only in the living space but also in the industrial site. Studies on physiological and psychological effects of long-term noise exposure to human being have commanded the public interest on noise issues. Since environmental noises such as traffic noise and construction noise is mainly flowed through the open window, it is necessary to develop the active noise control system to reduce it inside the building. Although control speakers and microphones for the noise signal measurement in the control region are essential for the conventional active noise control methods, it is impossible to implement them in the control region in the building environment because the control region is the living quarter and they may hinder activities of the residents. Therefore, we proposed the active window system to reduce the exterior noise flowed through the open window with microphones installed outside the window and control speakers installed at the frame of the window. To confirm the performance of the proposed active window, we carried out the simulation and experiment using active window system with 8 control speakers. Simulation results showed the noticeable noise reduction effect inside the control region within the frequency range without the spatial aliasing. Experimental result showed that the total acoustic potential energy inside the room of the scale model is reduced to about 10dB within the interest of frequency range.

• Korean Journal of Optics and Photonics
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• v.7 no.2
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• pp.89-95
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• 1996

Superresolution optics, employing Gaussian apodization, is rigorously treated at the soft X-ray wave-length(λ=0.013 ${\mu}{\textrm}{m}$) region. In the diffraction integral, the line integral along the imaginary axis is found small, and it is ignored, so that the diffraction integral consists of the integration along the real axis. The resolution of the diffracted image is not effected by the pupil angular frequency bandwidth $2{\omega}_0$, which is one of the most important the characteristic features of Gaussian apodization ($e^{-o^2x^2}$ optics. The superresolution optics has resolution ($\frac{1}{2}{\times}FWHM)$=$\Delta$x=0.008 $\mu$m which is smaller than the Rayleigh criterion of 2λ=0.026 ${\mu}{\textrm}{m}$ for NA=0.25. The optical system has ${\omega}_0{\ge}\frac{1}{2}{\sigma}$, which gives the peak intensity of the diffracted image larger than $e^{-2}$ times intensity obtainable by the infinite sperture.