• 한국광학회:학술대회논문집
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• 한국광학회 2007년도 하계학술발표회 논문집
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• pp.77-78
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• 2007

• Corrosion Science and Technology
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• 제4권3호
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• pp.108-113
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• 2005

One of the recent safety issues in the pressurized heavy water reactor (PHWR) is the cracking of the feeder pipe. Because of the limited accessibility to the cracked region and a high dose of radiation exposure, it is difficult to inspect all the pipes with the conventional ultrasonic method. In order to solve this problem, a long-range guided wave technique has been developed. A computer program to calculate the dispersion curves in the pipe was developed and the dispersion curves for the feeder pipes in PHWR plants were determined. Several longitudinal and/or flexural modes were selected from the review of the dispersion curves and an actual experiment has been carried out with the specific alignment of the piezoelectric ultrasonic transducers. They were confirmed as L(0,1)) and/or flexural modes(F(m,2)) by the short time Fourier transformation(STFT) and were sensitive to the circumferential cracks, but not to the axial cracks in the pipe. An electromagnetic acoustic transducers(EMAT) was designed and fabricated for the generation and reception of the torsional guided wave. The axial cracks were detected by a torsional mode(T(0,1)) generated by the EMAT.

• Nuclear Engineering and Technology
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• 제41권3호
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• pp.327-334
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• 2009

Elastic wave is one of the most useful tools for non-destructive tests in nuclear power plants. Since the elastic properties are indispensable for analyzing the behaviors of elastic waves, they should be predetermined within an acceptable accuracy. Nuclear power plants are exposed to harsh environmental conditions and hence the structures are degraded. It means that the Young's modulus becomes unreliable and in-situ measurement of Young's modulus is required from an engineering point of view. Young's modulus is estimated from the group velocity of propagating waves. Because the flexural wave of a plate is inherently dispersive, the group velocity is not clearly evaluated in temporal signal analysis. In order to overcome such ambiguity in estimation of group velocity, Wigner-Ville distribution as the time-frequency analysis technique was proposed and utilized. To verify the proposed method, experiments for steel and acryl plates were performed with accelerometers. The results show good estimation of the Young's modulus of two plates.

• 대한기계학회논문집A
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• 제24권8호
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• pp.1923-1930
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• 2000

A bar with periodically nonuniform material properties is selected as a one-dimensional model of a flat-panel speaker. This paper describes a theoretical approach to the bending waves propagating i n the nonuniform bar. The phase speed of the wave is obtained using perturbation techniques for small amplitude, sinusoidal modulation of the flexural rigidity and mass density. It is shown that the wave speed is decreased due to the nonuniformity of the material properties by the amount proportional to the square of the modulation amplitude. The resonance occurring when the wavelength is half of the period of the material properties is analyzed by the method of multiple scales. It is also shown that the wave speed at the resonance mode is decreased by the amount proportional to the modulation amplitude but the wave of this mode does not propagate far enough due to attenuation.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.353-356
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• 2008

초고성능 콘크리트(Ultra High Performance Concrete)는 압축강도 200MPa, 인장강도 15MPa 및 휨강도 35MPa 정도의 높은 강도 특성과 열화인자의 침투 및 확산 속도가 보통콘크리트에 비해 1/20에서 최대 1/10,000까지 낮은 고내구성을 나타내면서 동시에 슬럼프 플로우가 약 220mm 정도의 자기충전성 특성을 갖는 콘크리트이다. 또한 초고성능 콘크리트의 가장 큰 특징으로는 강섬유의 혼입함으로써 휨강도와 인성의 향상이다. 따라서 본 연구에서는 초고성능 콘크리트의 섬유 형상에 따라 휨거동특성에 미치는 효과를 평가하였다. 그 결과 섬유 형상에 따라 휨강도에 큰 영향을 미치는 것으로 나타났다. 또한 초기균열강도에는 큰 영향을 미치지 않고 물결타입의 강섬유 사용으로 최대 휨강도가 높게 나타났다.

• 한국소음진동공학회논문집
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• 제15권3호
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• pp.266-271
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• 2005

Although time-frequency analysis is useful for dispersive wave analysis, conventional methods such as the short-time Fourier transform do not take the dispersion phenomenon into consideration in the tiling of the time-frequency domain. The objective of this paper is to develop an adaptive time-frequency analysis method whose time-frequency tiling is determined with the consideration of signal dispersion characteristics. To achieve the adaptive time-frequency tiling, each of time-frequency atoms is rotated in the time-frequency plane depending on the local wave dispersion. To carry out this adaptive time-frequency transform, dispersion characteristics hidden in a signal are first estimated by an iterative scheme. To examine the effectiveness of the present method, the flexural wave signals measured in a plate were analyzed.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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• pp.606-610
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• 2004

Although time-frequency analysis is useful for dispersive wave analysis, conventional methods such as the short-time Fourier transform do not take the dispersion phenomenon into consideration in the tiling of the time-frequency domain. The objective of this paper is to develop an adaptive time-frequency analysis method whose time-frequency tiling is determined with the consideration of signal dispersion characteristics. To achieve the adaptive time-frequency tiling, each of time-frequency atoms is rotated in the time-frequency plane depending on the local wave dispersion. To carry out this adaptive time-frequency transform, dispersion characteristics hidden in a signal are first estimated by an iterative scheme. To examine the effectiveness of the proposed method, the flexural wave signals measured in a plate were analyzed.

• Geomechanics and Engineering
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• 제31권6호
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• pp.615-622
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• 2022

In this paper, considering the temperature dependence of material physical parameters as well as the effects of thermal effect and shear deformation, we have conducted an in-depth study on the wave propagation of functionally graded (FG) materials circular plate in thermal environment based on the physical neutral surface concept. The dynamic governing equations of functionally graded plates are established, and the dispersion relation of wave propagation is derived. The influence of different temperature fields on the propagation characteristics of flexural waves in FG circular plates is discussed in detail. It can be found that the phase velocity and group velocity of wave propagation in the plate decrease with the increase of temperature.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2009년도 춘계 학술대회 제21권1호
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• pp.533-534
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• 2009

연구에서는 초고성능 콘크리트의 섬유 형상에 따라 휨거동특성에 미치는 효과를 평가하였다. 그결과 섬유 형상에 따라 휨강도에 큰 영향을 미치는 것으로 나타났다. 또한 초기균열강도에는 큰 영향을 미치지 않고 물결타입의 강섬유 사용으로 최대 휨강도가 높게 나타났다.

• Structural Engineering and Mechanics
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• 제55권2호
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• pp.335-348
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• 2015

The influence of the interface imperfect bonding on the flexural wave dispersion in the bilayered hollow circular cylinder is studied with utilizing three-dimensional linear theory of elastodynamics. The shear-spring type model is used for describing the imperfect bonding on the interface between the layers and the degree of the imperfectness is estimated through the dimensionless shear-spring parameters which enter the mentioned model. The method for finding the analytical expressions for the sought values and dispersion equation are discussed and detailed. Numerical results on the lowest first and second modes are presented and analyzed. These results are obtained for various values of the shear-spring parameters. According to these results, in particular, it is established that as a results of the imperfection of the bonding between the layers the new branches of the dispersion related the first fundamental mode arise and the character of the dispersion curve related to the second mode becomes more complicated.