• 한국소음진동공학회논문집
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• 제22권10호
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• pp.1010-1019
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• 2012

Non-contact detection of internal defects in a rail using ultrasonic waves is discussed in this paper. Cracks in a rail may be the cause of a serious railway accident such as derailment if left undetected. Concurrent rail inspection method based on ultrasonic testing using piezoelectric transducers has several limitations as it should keep physical contact with the rail. This work suggests a non-contact detection of internal defects in a rail using ElectroMagnetic Acoustic Transducers (EMAT) which can produce and measure ultrasonic waves in a rail without any couplant. The EMATs for rail inspection are designed and fabricated and their working performance is verified through a series of experiments on various types of internal defects in test rails. The effect of lift-off between the transducers and the rail on the generated signals is also discussed.

• 한국해양공학회지
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• 제16권3호
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• pp.34-39
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• 2002

본 논문에서는 수면파(Surface wave)와 수중파 (Internal wave)간의 동적 상관관계에 관하여 수행된 연구결과를 정리하였다. 표면파의 비선형 문제는 파의 경사매개변수를 2차원으로 가정하여 해석하였으며, Cauchy 문제는 불균일 조류상의 균일 수면중력파에 대하여 해석하였다. 또한, 파의 경사, 주기의 범위(Frequency range) 그리고 자유표면하의 조류의 분포들간의 조화에 대한 연구가 수행되었으며 해류 및 이동파와 연계되어 수중파의 최전 후방에 형성될 수 있는 정적 파형 (Steady wave pattern)이 수면파형에 포함되었다.

• Structural Engineering and Mechanics
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• 제57권4호
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• pp.703-716
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• 2016

In this paper, we have investigated shear horizontal wave propagation in a layered structure, consisting of granular macromorphic rock (Dionysos Marble) substrate underlying a viscoelastic layer of finite thickness. SH waves characteristics are affected by the material properties of both substrate and the coating. The effects of microstructural parameter "characteristic length" of the substrate, along with heterogeneity, internal friction and thickness of viscoelastic layer are studied on the dispersion curves. Dispersion equation for SH wave is derived. Real and damping phase velocities of SH waves are studied against dimensionless wave number, for different combinations of various parameters involved in the problem.

• 한국해안해양공학회지
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• 제17권1호
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• pp.21-31
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• 2005

본 연구에서 Nwogu(1993)의 확장형 Boussinesq 방정식에 대하여 한 격자의 조파 띠에 균일하게 분포하는 원천함수를 유도하였다. 원천함수를 포함하는 확장형 Boussinesq 방정식에 부분단계분리법을 적용하여, 에너지 전송속도를 사용하는 선 조파기법의 타당성을 해석적으로 증명하였다. 수평공간 1차원의 경우 선형파 뿐만 아니라 비선형파를 조파하여 원천함수기법에 의한 내부조파기법의 정확성을 검증하였다. 또한 원천함수기법에 의한 수치 결과가 선 내부조파기법에 의한 수치 결과와 동일함을 확인하였다.

• 한국해안해양공학회지
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• 제18권1호
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• pp.1-14
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• 2006

본 논문에서 직사각형 격자 체계에서 원호형 내부조파에 의한 선 조파기법을 개발하였다. 총 다섯 가지 조파형식의 수치실험이 다음의 조건에 수행되었다. 즉, 일정수심에서의 파랑의 전파, 일정경사를 가지는 평면에서의 굴절과 천수, 반무한 방파제에서 회절 실험을 수행하였다. 수치실험 수행 시 기본방정식으로 Suh et al. (1997)이 제안한 확장형 완경사방정식을 이용하였다. 두 개의 평행한 직선이 반원으로 연결된 제5형식 조파기법을 사용하면 가장 우수한 결과를 얻을 수 있었다. 특히, 격자간격이 작은 경우에 그 우수성이 확연히 드러났다.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2003년도 Proceedings of ACRS 2003 ISRS
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• pp.1246-1248
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• 2003

Internal wave with a soliton-like, large amplitudes within several kilometers, is frequently observed in the sea surface caused by tidal rectification due to sill or rough topographic changes. Internal waves can perturb current and density field, initiate bottom sediment re -suspension and mix nutrients to photic zone. Previous studies indicate that the appearance of internal wave in the Lombok Strait have been detected in SAR image data. This paper studies effect of internal wave in the Lombok Strait to chlorophyll distribution in the surrounded areas using SeaWiFS and ERS SAR images data during 1996-2001 periods. The preliminary result concludes that the internal waves presumably affect phytoplankton distribution spreading southeastward in the coast off Bali Island. The distribution of phytoplankton at southern coastline off Bali Island when internal wave occurred is elongated and distributed further to westward (from 8.8$^{\circ}$ to 10.7$^{\circ}$LS) than the area when internal wave did not occur on August 2000 (from 9.25$^{\circ}$ to 10.25$^{\circ}$LS) as shown in figure 3. It shown that the surface phytoplankton concentration near coastal area, i.e. from 8.8$^{\circ}$ to 9.25$^{\circ}$ LS, increased when internal wave is occurred.

• Structural Engineering and Mechanics
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• 제85권4호
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• pp.501-510
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• 2023

Horizontally polarized shear waves (SH) have numerous applications in various scientific, engineering, and medical fields. The study deals with an investigation of SH-waves in a thin microstructural plate. The plate has been mathematically modelled by employing size dependent consistent couple stress theory, which involves a length parameter, known as characteristic length. Characteristic length is assumed to be of the order of internal microstructures of the material. Dispersion relations have been calculated for the propagation of SH-waves using different set of boundary conditions. Group velocity of the SH-waves has been calculated by using an analytical approach. The mathematical results obtained in the problem are discussed in detail and the impacts of characteristic length parameter and thickness of plate are presented on phase velocity of SH-waves through graphical illustrations.

• 한국음향학회:학술대회논문집
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• 한국음향학회 1999년도 학술발표대회 논문집 제18권 1호
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• pp.189-197
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• 1999

To investigate internal waves (IW) effect on acoustic wave propagation, m analysis is conducted on mode travel time and model simulation. Based on the thermistor string data, it can be shown that the thermocline depth variation may cause travel time difference as much as 4-10 ms between mode 1 and 2 over range 10 km. This travel time difference causes interference among modes and thus fluctuation from range-independent stratified ocean structure. In real situations, however, there exist additionally spatial variation of IW. Model simulation with all modes and simple IW shows clear responses of acoustic signals to IW, amplitude and phase fluctuation.

• 한국해안해양공학회:학술대회논문집
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• 한국해안해양공학회 2000년도 한국해안해양공학발표논문집 Proceedings of Coastal and Ocean Engineering in Korea
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• pp.113-119
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• 2000

Internal waves, including all kinds of wave phenomena inside a stratified fluid system, have been a subject of interest for a long time in geophysics, coastal and ocean engineering, applied mathematics and hydrodynamics. The vast oceans on the earth are a complex stratified fluid system widely distributed with pycnoclines, which are horizontally layered regions with a large density variation, commonly located about 50-150 meters below the ocean surface. (omitted)

• 대한조선학회지
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• 제25권2호
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• pp.1-10
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• 1988

An axially marching numerical method is developed for the simulation of the internal waves produced by translation of a submersed vehicle in a density-stratified ocean. The method provides for the direct solution of the primitive variables [$\upsilon,\;p,\;\rho$] for the nonlinear and steady state three-dimensional Euler's equation with a non-constant density term in the vehicle-fixed cartesian co-ordinate system. By utilizing a known potential flow around the vehicle for an estimate of the axial velocity gradient, the present parabolic algorithm local upstreamwise disturbances and axial velocity variation.