• Title/Summary/Keyword: 파동속도

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Wave Propagation Characteristics in Saturated Porous Media II. Parametric Studies (포화된 다공성매체에서 파동의 전파특성 II. 파라미터 연구)

  • Kim, Sun-Hoon;Kim, Kwang-Jin
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.20 no.2
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    • pp.191-206
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    • 2007
  • The general theoretical solutions for the wavespeed and damping derived in Part 1 of this work, are incorporated into the computer code. In this paper the code is used in a parametric study of the influence of excitation frequency and variations in material properties on propagation velocity and damping. Compressional wave velocity for waves of the first kind is shown to vary as a function of the frequency-permeability product, with a zone where wavespeed transitions from a lower bound value to a higher bound value with increasing values of the product. Damping is seen to be a maximum where the rate of change in wavespeed is greatest. Waves of the second kind also show a transition in wavespeed from near zero at low values of the frequency-permeability product to an upper bound value at higher values of the product.

Deep-Learning Seismic Inversion using Laplace-domain wavefields (라플라스 영역 파동장을 이용한 딥러닝 탄성파 역산)

  • Jun Hyeon Jo;Wansoo Ha
    • Geophysics and Geophysical Exploration
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    • v.26 no.2
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    • pp.84-93
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    • 2023
  • The supervised learning-based deep-learning seismic inversion techniques have demonstrated successful performance in synthetic data examples targeting small-scale areas. The supervised learning-based deep-learning seismic inversion uses time-domain wavefields as input and subsurface velocity models as output. Because the time-domain wavefields contain various types of wave information, the data size is considerably large. Therefore, research applying supervised learning-based deep-learning seismic inversion trained with a significant amount of field-scale data has not yet been conducted. In this study, we predict subsurface velocity models using Laplace-domain wavefields as input instead of time-domain wavefields to apply a supervised learning-based deep-learning seismic inversion technique to field-scale data. Using Laplace-domain wavefields instead of time-domain wavefields significantly reduces the size of the input data, thereby accelerating the neural network training, although the resolution of the results is reduced. Additionally, a large grid interval can be used to efficiently predict the velocity model of the field data size, and the results obtained can be used as the initial model for subsequent inversions. The neural network is trained using only synthetic data by generating a massive synthetic velocity model and Laplace-domain wavefields of the same size as the field-scale data. In addition, we adopt a towed-streamer acquisition geometry to simulate a marine seismic survey. Testing the trained network on numerical examples using the test data and a benchmark model yielded appropriate background velocity models.

The Wave Propagation in transversely isotropic composite laminates (가로 등방성 복합재료의 파동전파에 관한 연구)

  • Kim Hyung-Won
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2005.11a
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    • pp.422-425
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    • 2005
  • In an transversely isotropic composite laminates, the velocities, the particle directions and the amplitudes of reflected and transmitted waves were obtained using the equation of motion, the constitutive equation, and the displacement equation expressed by wave number and frequency Eigenvalue problem involving a velocity was solved by Snell's law. Finally, the results were confirmed by T300 Carbon fiber/5208 Epoxy materials. This approach could be applied to the detection of flaws in a transversely isotropic composite laminates by the water immersion C-scan procedure.

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LCD 백라이트용 형광램프에서의 광 방출 광의 전파

  • Im, Yu-Ri;Han, Guk-Hui;Jeong, Jong-Yun;Im, Hyeon-Gyo;Jo, Yun-Hui;Kim, Hyeon-Cheol;Yu, Dong-Geun;Jo, Gwang-Seop
    • Proceedings of the Korean Vacuum Society Conference
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    • 2010.02a
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    • pp.417-417
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    • 2010
  • 작은 직경의 외부 전극 형광램프와 냉음극 형광램프는 LCD-TV의 광원으로 사용하고 있다. 교류 전압으로 구동되는 외부전극 형광램프와 교류 및 직류 전압으로 구동되는 냉음극 형광램프에서 광 방출 신호를 관측하였다. 이러한 빛은 양광주의 고전압부에서 접지부로 $10^5-10^6\;m/s$의 속도로 전파한다. 램프에서 방출된 광이 양광주를 따라 전파하는 현상은 일반 형광등과 네온싸인관에서도 동일하게 관측된다. 이러한 빛의 전파 현상은 지난 70년의 형광 램프 역사상 처음 관측되었다. 양광주 영역의 플라즈마는 높은 전압과 수 십 kHz가 인가되는 전극부에서 발생한 고밀도 플라즈마의 확산으로 생성된다. 고전압이 인가된 전극부에서 발생한 고밀도의 플라즈마는 인가되어지는 구동 주파수에 해당하는 섭동으로 작용하여 플라즈마 파동으로 양광주 영역으로 전파된다. 이러한 플라즈마 파동은 고밀도 전극부에서 저밀도 양광주 영역으로 플라즈마 밀도의 차이에 의하여 된다. 이때 파동의 전파 속도는 관 전류에 따라 달라진다. 타운젠트 방전 이전의 저 전류일 때는 ${\sim}10^5\;m/s$이며, 타운젠트 방전 이후 글로우 방전에서의 전파 속도는 ${\sim}10^6\;m/s$로 증가한다. 또한 타운젠트 방전 이전의 저 전류에서는 파동이 감쇠하는 경향을 보이며, 고 전류에서의 파동의 감쇠는 매우 작다. 관측된 광신호의 결과로부터 전파되는 파동의 원인은 플라즈마 확산에 의한 밀도의 차이에 의한 것으로 해석된다. 즉, 수 십 kHz의 구동 주파수를 갖는 플라즈마 파동이 양광주의 플라즈마 밀도 구배에 의하여 전파된다. 이러한 파동은 높은 전압이 인가되는 전극부에서 낮은 전압부로 향하는 조류의 흐름과 같이 나타난다.

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Study on the Drivers' Response Characteristics Using Spectral Analysis of Car Following Data (차량 추종자료의 파동해석을 통한 운전자 반응 특성 연구)

  • CHAE, Chandle;OH, Sei-Chang;KIM, Youngho;LEE, Jun
    • Journal of Korean Society of Transportation
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    • v.33 no.4
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    • pp.405-416
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    • 2015
  • This paper developed a method analyze drivers' response characteristics using spectral analysis with car following data. Cross-correlation function and cross spectrum are produced by Fourier transform from speed fluctuations of leading vehicle and following vehicle during the designated time ${\tau}$. Based on the analysis data, a process to calculate the reaction time and stimulus-adaption index of following vehicle was developed and 170 cases of field data was applied. It was reported average of 0.654 and 2.091 seconds of stimulus-adaption index and reaction time respectively. In conclusion, the developed indexes might contribute to enhance vehicle control of autonomous vehicle more efficient and safer.

Impact Response Behaviors of Laminated Composite Plates Subjected to the Transversely Impact of a Steel Ball (강구에 의한 횡방향 충격을 받는 적층복합판의 충격 응답 거동)

  • 김문생;김남식;박승범;백인환
    • Journal of Ocean Engineering and Technology
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    • v.7 no.2
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    • pp.44-56
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    • 1993
  • The purpose of this paper is to analyze the impact response behaviors of glass/epoxy laminated composite plates subjected to the transversely impact of a steel ball. For this purpose, dynamic finite element analysis based on the higher-order shear defomation plate theory is used to compute the contact forces, rebound velocity of a steel ball, and dynamic strain response histories. And low-velocity and high-velocity impact experiments were conducted to compare the results and compute the wave propagation velocities. The results obtained from impact experiments are in good agreement with those of dynamic finite element analysis. Also the wave propagation velocities obtained from high-velocity impact experiments and wave propagation theory agree well, and wave velocities were higher in the smaller radius of steel ball.

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The Wave Propagation in Transversely Isotropic Composite Laminates (가로 등방성 복합재료의 초음파에 관한 연구)

  • Kim Hyung-Won
    • Journal of the Korean Society of Propulsion Engineers
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    • v.10 no.2
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    • pp.62-69
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    • 2006
  • In transversely isotropic composite laminates, the velocities, the particle directions and the amplitudes of reflected and transmitted waves were obtained using the equation of motion, the constitutive equation, and the displacement equation expressed by wave number and frequency. Eigenvalue problem involving a velocity was solved by Snell's law. Finally, the results were confirmed by 7300 Carbon fiber/5208 Epoxy materials. This approach could be applied to the detection of flaws in transversely isotropic composite laminates by the water immersion C-scan procedure.

A Finite-difference Modeling of Love Channel Waves in Transversely Isotropic Medium (유한차분식을 이용한 Transverse 이방성(異方性) 매질내 Love채널파동 연구)

  • Cho, Dong-Heng;Lee, Sung-Soo
    • Economic and Environmental Geology
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    • v.27 no.3
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    • pp.281-287
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    • 1994
  • The present paper deals with numerical modeling of Love channel waves in transversely isotropic elastic medium. First, an explicit finite-difference scheme of second order approximation is formulated with the wave equation of SH particle displacement in transversely isotropic medium. Since it is a heterogeneous formulation, it should enable efficient modeling of complex model structures without additional treatment of the internal boundary matching. With a model of isotropic coal seam embedded in high velocity host rock, seismograms are synthesized and tutn out to be essentially identical with published ones of Korn and $St{\ddot{o}}ckl$. Next, anisotropic coal seams are investigated. It is found that the horizontal velocity of the seam appears to play a major role of determining the group velocity of Love channel waves. The group velocity increases with the increase of the horizontal velocity or vice versa. However, further study will be needed to exploit fully Love channel waves for the determination of lithology, stratification, fracture in sedimentary rocks, for instance, for hydrocarbon exploration and development.

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Computational and Experimental Analyses of the Wave Propagation Through a Bar Structure Including Liquid-Solid Interface (액체-고체 경계면이 존재하는 구조물에서의 파동 전파 해석 및 실험)

  • Park, Sangjin;Rhee, Huinam;Yoon, Doo Byung;Park, Jin Ho
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.39 no.8
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    • pp.793-799
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    • 2015
  • In this research, we study the propagation of longitudinal and transverse waves through a metal rod including a liquid layer using computational and experimental analyses. The propagation characteristics of longitudinal and transverse waves obtained by the computational and experimental analyses were consistent with the wave propagation theory for both cases, that is, the homogeneous metal rod and the metal rod including a liquid layer. The fluid-structure interaction modeling technique developed for the computational wave propagation analysis in this research can be applied to the more complex structures including solid-liquid interfaces.

Mode Characteristics of Longitudinal Guided Waves in Buried Steel Pipes (매립된 파이프에서 유도초음파의 종파 모드 특성)

  • Lee, Ju-Won;Shin, Sung-Woo;Na, Won-Bae;Kim, Jae-Min
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2010.04a
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    • pp.674-677
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    • 2010
  • 본 논문에서는 지반에 매립된 파이프에서 전파되는 유도초음파의 종파 모드 특성을 분석하였다. 지상 배관과는 달리 매립 배관에서는 주변 매질로 유도초음파의 누설이 발생할 수 있으며, 이로 인하여 유도초음파의 감쇠가 상대적으로 커질 수 있다. 따라서 본 연구에서는 유도초음파의 여러 특성들 중 종파 모드의 감쇠 특성을 중점적으로 분석하였다. 감쇠에 영향을 미치는 지반의 파동 특성(밀도, 체적종파속도, 체적횡파속도)을 결정하기 위하여 포화도와 다짐을 고려하였다. 포화도가 증가할수록 지반의 체적종파속도와 체적횡파속도는 감소하며, 다짐된 지반은 밀도와 체적종파속도, 체적횡파속도를 증가시킨다. 이와 같은 조건으로 결정된 지반의 파동 특성치와 배관의 물성치를 바탕으로 유도초음파 종파 모드의 감쇠 곡선을 계산하고, 특성을 분석하였다. 결과적으로 포화도가 증가할수록 종파 모드의 감쇠는 감소하는 경향을 나타내었고, 다짐이 증가할 경우 감쇠는 전반적으로 증가하는 경향을 나타냄을 알 수 있었다.

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