• Proceedings of the IEEK Conference
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• 2001.09a
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• pp.125-128
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• 2001

본 논문은 파동분할(Wave partitioning) 방식을 이용한 순차적(Sequential) 메쉬 부호화 방식을 제안한다. 파동분할 방식은 호수에 물방울이 퍼져 나가는 자연 원리를 이용하여 초기 삼각형의 주위에 삼각형을 덧붙여 가면서 하나의 SPB(Small Processing Block)을 만들어내는 방식이다. 이 방식을 이용하여 하나의 모델을 서로 독립적인 SPB로 분할하고, 각각의 SPB 내에서 초기 삼각형을 중심으로 그것에 덧붙여진 삼각형에 의해 만들어진 원 또는 반원을 찾는다. 또한 그 원주를 따라 순차적으로 꼭지점을 구하면 각각의 꼭지점들은 일정한 패턴으로 늘어서게 되고, 이를 이용하여 연결성 정보 없이 부가 정보만 이용하여 모델을 순차적으로 무손실 부호화한다.

• Geophysics and Geophysical Exploration
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• v.10 no.4
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• pp.377-382
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• 2007

Several prospecting methods have been used to detect deep seated small tunnel in Korea. Tunnel interpretation of seismic method has been performed mainly by wave traveltime inversion method. But it often gives inacurate solution for the exact tunnel position because of the short distance between two measuring boreholes and picking errors of first arrivals. In this study, "error tomogram" was proposed to detect tunnel position and applied to theoretical and field dat using multi-source amplitude data.

• Geophysics and Geophysical Exploration
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• v.3 no.2
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• pp.70-75
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• 2000

In the seismic migration, Kirchhoff and reverse time migration are used in general. In the reverse time migration using wave equation, two-way and one-way wave equation are applied. The approach of one-way wave equation uses approximately computed downward continuation extrapolator, it need tess amounts of calculations and core memory in compared to that of two-way wave equation. In this paper, we applied one-way wave equation to pre-stack reverse time migration. In the frequency-space domain, forward propagation of source wavefield and back propagration of measured wavefield were executed by using monochromatic one-way wave equation, and zero-lag cross correlation of two wavefield resulted in the image of subsurface. We had implemented prestack migration on a massively parallel processors (MPP) CRAYT3E, and knew the algorithm studied here is efficiently applied to the prestck migration due to its suitability for parallelization.

• Korean Journal of Optics and Photonics
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• v.7 no.3
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• pp.272-279
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• 1996

A simple transfer matrix algorithm to analyze the properties of 2 dimensional waveguides is introduced. We applied this algorithm to strained InGaAs/InGaAsP GINSCH MQW laser structures. We studied how optical confinement factor and effective refractive index, which are important in calculating the modal gain, depend on the structure parameters such as waveguide width, shape of GRIN, and number of quantum wells. Especially we suggested that the concept of effective waveguide width is very useful in understanding the GRINSCH waveguide.

• 한국지구물리탐사학회:학술대회논문집
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• 2006.06a
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• pp.181-186
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• 2006

An imaging method of seismic sources using time-reversal wave propagation is presented. The method is based on the time-reversal invariance and the spatial reciprocity of the wave equation. Time-reversal wave propagation has been used to image anomalous features of a midium in medical imaging, non destructive testing and waveform tomography. Seismogram is the record whose energy is propagated from the seismic source. If time-reversed seismogram propagates back into the medium, seismic energy is concentrated at the origin time of the event and at the source location. In this work, a staggered-grid finite-difference method of the elastic wave equation is parallelized for 3-D wave propagation simulation. With numerical experiments, we show that the time-reversal imaging will enable us to explore the spatio-temporal history of complex earthquake.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2001.11b
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• pp.213-218
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• 2001

본 논문에서는 파동분할(Wavepartitioning) 방식을 기반으로 꼭지점들간의 특징적인 관계(Vertex Pedigree)를 이용한 순차적(Sequential) 메쉬 부호화 방식을 제안한다. 파동분할 방식은 호수에 물방울이 퍼져 나가는 자연 원리를 이용하여 초기 삼각형의 주위에 삼각형을 덧붙여 가면서 하나의 SPB(Small Processing Block)을 만들어내는 방식이다. 이 방식을 이용하여 하나의 모델을 서로 독립적인 SPB로 분할하고, 각각의 SPB내에서 초기 삼각형을 중심으로 그것에 덧붙여진 삼각형에 의해 만들어진 원 또는 반원을 찾는다. 또한, 그 원주를 따라 순차적으로 꼭지점을 구하면 각각의 꼭지점들은 서로의 관계에 따라 일정한 패턴으로 늘어서게 되고, 이것을 이용하여 연결성 정보 없이 부가 정보만으로 모델을 순차적으로 무손실 부호화한다.

• Geophysics and Geophysical Exploration
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• v.15 no.3
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• pp.129-135
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• 2012

The simultaneous-source full waveform inversion improves the applicability of full waveform inversion by reducing the computational cost. Since this technique adopts simultaneous multi-source for forward modeling, unwanted events remain in the residual seismograms when the receiver geometry of field acquisition is different from that of numerical modeling. As a result, these events impede the convergence of the full waveform inversion. In particular, the streamer-type data with limited offsets is the most difficult data to apply the simultaneous-source technique. To overcome this problem, the global-correlation-based objective function was suggested and it was successfully applied to the simultaneous-source full waveform inversion in time domain. However, this method distorts residual wavefields due to the modified objective function and has a negative influence on the inversion result. In addition, this method has not been applied to the frequency-domain simultaneous-source full waveform inversion. In this paper, we apply a timedamping function to the observed and modeled data, which are used to compute global correlation, to minimize the distortion of residual wavefields. Since the damped wavefields optimize the performance of the global correlation, it mitigates the distortion of the residual wavefields and improves the inversion result. Our algorithm incorporates the globalcorrelation-based full waveform inversion into the frequency domain by back-propagating the time-domain residual wavefields in the frequency domain. Through the numerical examples using the streamer-type data, we show that our inversion algorithm better describes the velocity structure than the conventional global correlation approach does.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.758-759
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• 2010

In this study, it was experimentally confirmed that the phenomenon of resonance effect of wave drag in two wavy walls. The channel had saw-tooth type of relief surfaces when supersonic gas flows into this channel. Experiment was carried out on the differential apparatus by conducting the comparative test of two nozzles (round sonic nozzle and two-dimensional nozzle with wavy walls). The two-dimensional nozzle was joined alternately with flat walls which had saw-tooth type of symmetrical and asymmetric reliefs. Two-dimensional nozzle was designed for the M=3 and profiled parabolic contour.

• Proceedings of the Mineralogical Society of Korea Conference
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• 2002.05a
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• pp.34-34
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• 2002

• The Korean Journal of Petroleum Geology
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• v.1 no.1 s.1
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• pp.47-52
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• 1993

A method and results of computations are presented for the 2-D seismic migration process in the frequency-wavenumber domain for the laterally and vertically inhomogeneous medium. In order to take the intrinsic attenuation effect into account in the migration process the complex-valued wave velocity is used in the wavefield extrapolation operator, improving the generalized frequency-wavenumber migration technique. The imaginary part of the complex-valued wave velocity includes the seismic quality factor Q value. In derivation of the solution of the wave equation for the medium of inhomogeneous wave velocity and anelasticity, the inhomogeneous medium is mathematically converted to an equivalent system which consists of a homogeneous medium of averaged slowness and an inhomogeneous distribution of hypothetical wave source. The strength of the hypothetical wave source depends on the deviation of squared slowness from the averaged value of the medium. Results of numerical computation using the technique show more distinct geologic images than those using the convensional generalized frequency-wavenumber migration. Especially, the obscured images due to the wave attenuation by anelasticity are restored to show sharp boundaries of structures. The method will be useful in the imaging of the reflection data obtained in the regions of possible petroleum or natural gas reservoir and of fractured zone.