• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.4
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• pp.1-7
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• 1997

This paper presents an analysis of the wave propagation in cross-type tunnels using the finite volume time domain (FVTD) method. Because the FVTD method is based on the volume intergrations of themaxwell's equations with respected to arbitrary shaped small polyhedron cells and the fields at every center point of the cells ar eassigned in a average fashion, the method can handle arbitrary boundary problems with inhomogeneous media. In this paper, the wave propagation in cross-type tunnels has been analyzed using the fVTD method with the PML (perfectly matched layer) absorbing bundary conditons, and the numerical results are verified with a set of experimental data.

• Geophysics and Geophysical Exploration
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• v.16 no.2
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• pp.71-78
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• 2013

The one-way wave equation migration is much more computationally efficient comparing with reverse time migration and it can provide better image than the migration algorithm based on the ray theory. We have developed the prestack depth migration module adopting (GS) propagator designed for vertical transverse isotropic media. Since GS propagator considers the higher-order term by expanding the Taylor series of the vertical slowness in the thin slab of the phase-screen propagator, the GS migration can offer more correct image for the complex subsurface with large lateral velocity variation or steep dip. To verify the validity of the developed GS migration module, we analyzed the accuracy with the order of the GS propagator for VTI media (GSVTI propagator) and confirmed that the accuracy of the wavefield propagation with the wide angles increases as the order of the GS propagator increases. Using the synthetic seismic data, we compared the migration results obtained from the isotropic GS migration module with the anisotropic GS migration module. The results show that the anisotropic GS migration provides better images and the improvement is more evident on steeply dipping structures and in a strongly anisotropic medium.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.14 no.1
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• pp.161-167
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• 2014

This paper presents the results of permittivities of various materials by measurements of the dielectric properties for the materials in millimeter-wave band. Since the advantages of millimeter wave band include the miniaturization, weight reduction of component and a lot of information transfer, its study has received increasing attention of researches. Also, because of the characteristics of the band have the superior straightness and the small diffractive, in the band, the analysis for the reflection and transmission characteristics of the materials will be very important. Moreover, a low interference is one of characteristics of the band due to the fact that the millimeter wave is absorbed in the materials. Therefore, in this paper, the reflection and transmission characteristics of materials are measured in the band by using the free space method. Based on the presented result, the permittivities of the materials are derived by the calculation of Nicolson-Ross Weir method.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1992.06a
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• pp.347-350
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• 1992

• Journal of the Korean Geosynthetics Society
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• v.21 no.2
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• pp.57-65
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• 2022

This study simulated the shock wave propagation through the tamping material between explosives and hole wall at blasting works and verified the effect of tamping materials. The Arbitrary Lagrangian-Eulerian(ALE) method was selected to model the mixture of solid (Lagrangian) and fluid (Eulerian). The time series analysis was carried out during blasting process time. Explosives and tamping materials (air or water) were modeled with finite element mesh and the hole wall was assumed as a rigid body that can determine the propagation velocity and shock force hitting the hole wall from starting point (explosives). The numerical simulation results show that the propagation velocity and shock force in case of water were larger than those in case of air. In addition, the real site at blasting work was modeled and simulated. The rock was treated as elasto-plastic material. The results demonstrate that the instantaneous shock force was larger and the demolished block size was smaller in water than in air. On the contrary, the impact in the back side of explosives hole was smaller in water, because considerable amount of shock energy was used to demolish the rock, but the propagation of compression through solid becomes smaller due to the damping effect by rock demolition. Therefore, It can be proven that the water as the tamping media was more profitable than air.

• Journal of the KSME
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• v.34 no.7
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• pp.510-516
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• 1994

탄성파의 속도는 파동 전파 매질의 밀도와 탄선계수에 달려 있으므로, 박막이 입혀진 기판에서 전파하는 표면파에 대해서 기판과 박막의 밀도와 탄성계수 및 박막의 두께 등을 알면 전파 속 도를 계산할 수 있다. 박막의 탄성계수를 모르는 경우에는 표면파 속도를 측정하여 역으로 탄 성계수를 산출할 수 있다. 이러한 역산과정에는 일반적인 비선형 방정식의 curve-fitting에 이용될 수 있는 simplex법이 효율적으로 활용된다. 이 글에서는 표면파 속도를 측정하고 그 데이터로 부터 역산하여 박막의 탄성계수를 구하는 원리와 과정을 설명한다.

• Economic and Environmental Geology
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• v.23 no.4
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• pp.393-409
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• 1990

Synthetic seismograms and deduced characteristic properties of the non-geometrical $S^*$ and $P^*$ waves are presented. These waves are excited on the free surface or an interface between two different media by an inhomogeneous P wave from a point source nearby, and propagate as homogeneous waves in the media. Synthetic seismograms are computed using an extended reflectivity method designed for buried source and receiver. An efficient computational procedure for propagator matrices of layers is devised to reduce the computational time and the RAM memory size in the implementation of the reflectivity method. Radiation patterns are obtained from the particle motions of the four types of the "*" waves, i.e., the $S^*$ wave generated near the free surface, and the reflected $S^*$, transmitted $S^*$ and transmitted $P^*$ waves generated near an interface. Some patterns show polarity changes of displacements and others reveal monotonic or non-monotonic variation of amplitude depending on the velocity structure. The decaying trend of amplitude with increasing epicentral distance are also shown for the head wave type of the "*" waves.

• Geophysics and Geophysical Exploration
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• v.25 no.4
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• pp.214-216
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• 2022

Distributed acoustic sensing (DAS), an increasingly growing acquisition technique in the oil and gas exploration and seismology fields, has been used to record seismic signals using optical cables as receivers. With the development of imaging methods for DAS data, full waveform inversion (FWI) is been applied to DAS data to obtain high-resolution property models such as P- and S-velocity. However, because the DAS systems measure strain from the phase distortion between two points along optical cables, DAS data must be transformed from strain to particle velocity for FWI algorithms. In this study, a plane-wave FWI algorithm based on the relationship between strain and horizontal particle velocity in the plane-wave assumption is proposed to apply FWI to DAS data. Under the plane-wave assumption, strain equals the horizontal particle velocity, which is scaled by the velocity at the receiver position. This relationship was confirmed using a numerical experiment. Furthermore, 4-layer and modified Marmousi-2 velocity models were used to verify the applicability of the proposed FWI algorithm in various survey environments. The proposed FWI was implemented in land and marine survey environments and provided high-resolution P- and S-velocity models.

• Proceedings of the Korean Society of Computer Information Conference
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• 2023.07a
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• pp.585-586
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• 2023

본 논문에서는 바람의 이류(Advection)를 고려하여 사운드의 전파를 변형하는 방법을 제시한다. 사운드는 공기와 같은 매질의 진동을 통해 전파되는 파동이며, 이런 바람의 이동 방향은 사운드 에너지 전파에 직접적인 영향을 주며, 본 논문에서는 이를 광선추적법(Raytracing) 기반으로 모델링한다. 기존의 사운드 전파는 물리기반, 기하처리(Geometry processing), 혼합기법(Hybrid method) 등의 방법이 제안됐으며, 다양한 장면에서 좋은 결과를 만들어냈다. 하지만 바람의 움직임은 유체역학을 기반으로 한 나비에-스토크스 방정식(Navier-Stokes equation)에 의해 표현되기 때문에 사운드 전파만으로는 바람의 영향을 고려한 전파 형태를 모델링할 수 없다. 본 논문에서는 바람의 유동 중 이류를 고려하여 사운드 맵을 효율적으로 변형할 수 있는 방법을 제시한다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.9 no.1
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• pp.52-59
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• 1998

We calculated the wave attenuation due to rain using the effective permittivity of the air with raindrops. The effective permittivity depends on the complex permittivity of rain drop and the fractional volume occupied by the raindrops. We calculate the complex permittivity of rain drop and the raindrops' volume using Marshall-Palmer Rain drop size distribution. The rain attenuation calculated by effective permittivity is compared with the results of ITU rain attenuation model, and the two rain attenuation models have a very close agreement. The effetive permittivity model underestimates the rain attenuation under 50 GHz, and overestimate at the frequencies under 50 GHz copmpared with the ITU model.