• Title/Summary/Keyword: Spherical wave

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Incoherent Inverse Scattering of 3-Dimensional Underground Cavity in Lossy Medium (손실 매질내에 있는 3차원 지하공동의 Incoherent 역산란)

  • 홍성용;강진섭
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.10 no.3
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    • pp.378-391
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    • 1999
  • When the time-harmonic plane wave is incident upon a high-contrast spherical cavity in a lossy medium, the incoherent shadow intensity pattern is acquired by averaging out the multi-frequency intensities of the co-polarized total electric field calculated at the measurement plane perpendicular to the propagating direction of the incident wave in the forward direction. In the spherical rotational measurement configuration, an incoherent imaging of the spherical cavity is obtained via the back-projections of the incoherent shadow intensity pattern. This imaging method is validated by imaging an air sphere in the lossy medium of ${\epsilon}_r$ = 2 and $\sigma$ = 0.001, 0.003 S/m and the conditions for obtaining better images are investigated.

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The Scattering Analysis for the Sphere in Water (수중에서 구형 산란체에 의한 음의 산란 해석)

  • 김관주;김재환;유상욱
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 1998.04a
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    • pp.622-628
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    • 1998
  • The SONAR(SOund NAvigation and Ranging) is the system that detects objects and finds their locations in water by using the echo ranging technique. In this paper, the scattering phenomena for a rigid spherical scatterer will be analyzed using closed form solution, Boundary Element Method and Finite Element Method. Scattering analysis for an elastic spherical scatterer will be analyzed, later. In oder to analyzing the sound wave scattering phenomena for an elastic scatterer in water coupled problem between acoustic and vibration must be considered.

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Performance Analysis of the reconstruction Algorithms in the Stripmap-mode SAR (Stripmap-mode SAR에서의 영상복원 알고리즘의 성능분석)

  • 박현복;김형주;최정희
    • Proceedings of the Korea Electromagnetic Engineering Society Conference
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    • 2000.11a
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    • pp.29-33
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    • 2000
  • The classical image reconstruction for stripmap SAR is based on the Fresnel approximation which utilizes deramping or chirp deconvolution in the synthetic aperture(slow-time) domain. Another approach in formulating stripmap SAR processing and imaging is based on the SAR wavefront reconsturction theory, and analysis of the SAR signal in the slow-time via the spherical wave Fourier decomposition of the radar radiation pattern. In this paper, we compare the Fresnel approximation and the wavefrong reconstruction methods using simulated stripmap SAR dada.

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Transient interactions between submerged elastic shells and acoustic shock waves from a moving source (움직이는 소스와 구형쉘의 상호작용 해석)

  • 이민형;이범헌;이승엽
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2001.05a
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    • pp.85-89
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    • 2001
  • The problem of the transient interaction of a plane acoustic shock wave which has an infinitely steep wave front with a cylindrical or spherical elastic shell has been studied analytically from early fifties based on the integral transform and series solution techniques. Huang adopted an inverse Laplace transform, and used a finite number of terms of the infinite series expansion of the equations for the shells. In the 1990s, the results have been used by many authors for validation of computer codes. The object of this paper is to discuss the interaction between a moving source and submerged spherical shells. Since the center of source is moving the first contact location between the waves and shell changes depending on the source velocity and distance. These are considered in the analysis. Furthermore, constant source strength and decreasing strength are considered in the analysis. Radial velocities at several locations on the structure are obtained and the results are discussed.

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Scour around spherical bodies due to long-crested and short-crested nonlinear random waves

  • Myrhaug, Dag;Ong, Muk Chen
    • Ocean Systems Engineering
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    • v.2 no.4
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    • pp.257-269
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    • 2012
  • This paper provides a practical stochastic method by which the maximum equilibrium scour depth around spherical bodies exposed to long-crested (2D) and short-crested (3D) nonlinear random waves can be derived. The approach is based on assuming the waves to be a stationary narrow-band random process, adopting the Forristall (2000) wave crest height distribution representing both 2D and 3D nonlinear random waves, and using the regular wave formulas for scour and self-burial depths by Truelsen et al. (2005). An example calculation is provided.

Optimization of extended holographic zone plate for f-$\Theta$lens (f-theta lens용 holographic zone plate(EHZP)의 설계)

  • 이상수
    • Proceedings of the Optical Society of Korea Conference
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    • 1989.02a
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    • pp.81-84
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    • 1989
  • EHZP is a kind of holographic optical element, which is generated by the interference of two divergent spherical waves from point sources on the same axis. It has the spherical aberration that the focal power increases as the radial distance r increases. By using this property, optimal design of EHZP was performed for f-$\theta$ lens. As the result of optimization, the f-$\theta$ condition and the field flattening condition were well satisfied when EHZP has f0=0.803f, faR=4.076f, 1=0.406f. It was assumed for calculation of field flattening condition that the incident wave was a plane wave with the diameter of 1mm.

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NEAR=FIELD DIFFRACTION PATTERN BY A SPHERICAL AIR CAVITY IN A DIELECTRIC MEDIUM (유전체 매질내에 있는 구형공동에 의한 근거리 회절패턴)

  • 강진섭;라정웅
    • Journal of the Korean Institute of Telematics and Electronics A
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    • v.32A no.2
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    • pp.19-30
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    • 1995
  • Diffraction patterns of the copolarized and the crosspolarized total electric fields by a spherical air cavity in a dielectric medium are analyzed in the forward near-field region when the wavelength of the incident plane wave is comparable to one half of the cavity radius. It is shown that double nulls and dips of the copolarized and the crosspolarized total electric fields exist in the measurement plane tansverse to the propagating direction of the incident field, and their dependences on the frequency, the distance of the measurement plane, and the measurement angle are analyzed.

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Analysis of Corneal Higher-order Aberrations after Myopic Refractive Surgery

  • Kim, Jeong-mee
    • Current Optics and Photonics
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    • v.3 no.1
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    • pp.72-77
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    • 2019
  • This study was performed to analyze the optical aberrations of the cornea induced by myopic refractive surgery. Corneal total higher-order aberrations, spherical aberration and coma for 4-mm and 6-mm pupils were measured using a wave-front analyzer. The amount of aberrations of the oblate corneal optics by the achieved correction was found to be larger than for the prolate corneal shape with complete eye, in an emmetropia control group. The change in corneal shape acts as an optical factor that degrades the quality of the retinal image; it seems to be one of the important factors related to quality of vision.

Study of the Weak Shock Wave Discharged from an Annular Tube (환형 관출구로부터 방출되는 약한 충격파에 관한 연구)

  • Kweon Yong-Hun;Lee Dong-Hoon;Kim Heuy-Dong
    • 한국가시화정보학회:학술대회논문집
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    • 2002.11a
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    • pp.113-116
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    • 2002
  • The shock wave discharged from an annular duct leads to very complicated flow features, such as Mach stem, spherical waves, and vortex rings. In the current study, the merging phenomenon and propagation characteristics of the shock wave are numerically investigated using a CFD method. The Harten-Yee's total variation diminishing (TVD) scheme is used to the unsteady, axisymmetric, two-dimensional, compressible Euler equations. The Mach number of incident shock wave $M_s$ is varied in the range below 2.0. The computational results are visualized to observe the major features of the annular shock waves discharged from the tube. On the symmetric axis, the peak pressure produced by the shock wave and its location depend upon strongly the radius of the annular tubes. A Mach stem is generated along the symmetric axis of the annular tubes.

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