• Journal of KSNVE
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• v.7 no.3
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• pp.401-409
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• 1997

This study observed the meterological influence on the excess attenuation with various flow resistivities. The flow resistivity is simulated up to 30, 000 cgs rayls. There is no significant differences among results from spherical wave analysis for excess attenuation, from plane wave analysis, and from locally reacting analysis. This is validated only when the flow resistivity is more than 100 cgs rayls. For the determination of effective flow resistivity of ground by measuring the excess attenuation experimentally, it is highly recommended that the distance between source and receiver is about 2.5m, and that the height of them is 0.3-0.4 m in case that they have the same height. Under this proposed conditions, the flow resistivity of 6-month-passed asphalt ground is estimated to 5, 000 cgs rayls by comparing the measured excess attenuation with the calculated.

• Journal of KSNVE
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• v.6 no.6
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• pp.835-842
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• 1996

To identify the locations and strengths of acoustic sources, one may use a microphone line array. Apparent advantage of the source identification method utilizing a line array is that it requires less measurement points than intensity method and holography. This method is based on the information of magnitude and phase difference between pressure signals at each microphone. Since those differences are dependent on the source model, we have to assume them such as plane, monopole, etc. In this paper the conventional source identification methods such as beamforming method and MUSIC method are briefly reviewed by modeling a source as plane and spherical wave, then a modified method is introduced. This can be applied to sound field which may by either coherent or incoherent. Typical simulations and experiment are performed to confirm this identification method.

• 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 Optical Society of Korea Conference
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• 2002.11a
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• pp.206-207
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• 2002

• Korean Journal of Optics and Photonics
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• v.14 no.2
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• pp.200-207
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• 2003

In this paper we present a new method of measuring the relative distance of two point objects in three-dimensional space by using phase-shifting digital holography. In our system the reference beam of a spherical wave is used instead of a plane wave. The system is computer simulated and built on an optical table for experiments. It is shown from computer simulations and experiments that the relative distance can be measured without the exact information on the reference beam used in the hologram record. It is shown from experiments that the relative distance between two point objects separated by 0.5 cm in the distance of about 300 cm from the CCD can be measured with an error less than 10％.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.2 s.233
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• pp.293-302
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• 2005

In this paper, the thick-walled laminated, orthotropic as well as bimaterial, composite hollow spheres under impact pressure are analyzed in detail by using the semi-discrete finite element method with the Houbolt time-integration scheme which results in unconditionally stable transient numerical results. Numerical results are obtained by using the self-constructed spherically symmetric (one-dimensional) and axially symmetric (two-dimensional) finite element programs, and compared with the previous solutions by other researchers, being shown some of which are incorrect. The finite element package Nastran is also adopted for numerical comparison.

• Proceedings of the KOSOMBE Conference
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• v.1998 no.11
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• pp.215-216
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• 1998

The ultrasonic imaging systems using synthetic aperture beamforming has been formed in the way that one element transmits and then receives a pulse. Because the amplitude of a pulse from one element is too small to propagate a long distance, the SNR(Signal to Noise Ratio)is low. This paper proposes the method to make a circular wave almost equal to one generated by one element using several elements. The amplitude of the wave made up of several elements is much larger than that of one element. And we can improve the SNR.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.208-211
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• 2005

The volumetric interferometer, which uses the interference of wavefronts emitted from two single mode fibers, measures the target position in 3-D. In this paper, we suggest a new calculation method which doesn't need a non-linear optimization and an initial guess. We find the relationship between the coefficients of the Zernike polynomials for a spherical wavefront and its center and reconstruct a spherical wavefront by using the Zernike polynomials from two interference fringes like a lateral shearing interferometer. The target position can be obtained from the coefficients of the Zernike polynomials of the reconstructed wavefront. We can get the target position in 3-D with $sub-{\mu}m$ errors in a simulation.

• Journal of the Korean earth science society
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• v.37 no.2
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• pp.107-116
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• 2016

Stability of the barotropic Rossby-Haurwitz wave is investigated using the numerical models on the global domain. The Rossby-Haurwitz wave under investigation is composed of the basic zonal flow of super-rotation and a finite amplitude spherical harmonic wave. The Rossby-Haurwitz wave is given as either steady or unsteady wave by adjusting the strength of the super-rotating zonal flow. Stability as well as the growth rate of the wave in the numerical simulation is determined by comparing the perturbation amplitude at two different time stages. Unstable modes of the Rossby-Haurwitz wave exhibited a horizontal structure composing of various zonal-wavenumber components. The vorticity perturbation for some modes showed a discontinuity around the area of weak flow, which was found robust regardless of the horizontal resolution of the model. Fourier finite element model was shown to generate the unstable mode in earlier stage of the time integration due to less accuracy compared to the spherical harmonic spectral model. Taking the overall accuracy of the models into consideration, the time by which the unstable mode begin to dominate over the spherical harmonic wave was estimated.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.5
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• pp.1-5
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• 2010

This paper deals with a method to measure the thickness of scale-layer, iron oxide formed on the surface of the rolling steel, using a dielectric lens antenna. The dielectric lens antenna has an independent characteristic with the frequency in the X-band and changes the spherical wave radiated from a horn antenna into a plane wave at the focusing point. Using this concept, we regard a scale-layer on the rolling steel as a dielectric-PEC(Perfect Electric Conductor) layer and apply a theoretical analysis of the normal-incident plane wave. To reduce the phase error arising from the use of the dielectric lens antenna, this paper utilizes a regression process algorithm. In comparison with the conventional iteration algorithm, the present algorithm led to a unique solution for the thickness of the scale-layer.