• 비파괴검사학회지
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• 제31권6호
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• pp.656-664
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• 2011

In this work, a numerical model is proposed for the relation between the magnitudes and the depth residual stress with the velocity of Rayleigh wave. Three cases, stress-free, uniform stress and layered stress, are investigated for the change tendency of the Rayleigh wave speed. Using the simulated signal with variation of residual stress magnitude and depth, investigation of the parameters for fitting residual stress and velocity change are performed. The speed change of Rayleigh wave shows a linear relation with the magnitude and an exponential relation with the depth of residual stress. The combination of these two effects could be used for the depth profile evaluation of the residual stress.

• 대한공업교육학회지
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• 제33권2호
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• pp.300-311
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• 2008

두 벽면이 서로 다른 평균 온도와 일정한 위상 차이 하에서 작은 파동수의 정현적인 온도 분포를 갖는 시스템에서의 자연 대류를 조사한다. 벽면 온도 분포의 파동수 k=0.5이고 위상차는 ㄱ/2 이며, 고려하는 유체는 Pr =0.7인 공기이다. 작은 Rayleigh 수의 전도 영역에서는 한 주기에 걸쳐 약간 기울어진 형태의 두 개의 큰 셀이 형성된다. 그러나 Rayleigh 수가 증가하면 열적으로 불안정한 영역에서 여러 개의 셀이 형성되는 다수 셀 유동이 일어난다. 다수 셀 영역에서 과도기적인 기간에서는 일시적으로 공간적인 점대칭성이 깨어지기도 하지만 정상 상태의 유동장은 언제나 대칭성을 만족한다. 유동 형태의 천이가 일어나는 임계 Rayleigh 수 부근에서는 Nusselt 수가 급격하게 증가한다.

• 한국지반공학회논문집
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• 제21권4호
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• pp.155-165
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• 2005

러브파와 레일리파는 표면파로서 각 파가 가지는 분산특성을 활용하여 지반의 강성주상도를 파악할 수 있는 특징을 가지고 있다. 이 중 러브파는 한 방향에 대한 응력-변위만 고려하기 때문에 수치적 모델링이 간단하고 전파시에는 이론적으로 체적파의 영향 및 밀도의 변화가 없어 각 각의 물성치를 갖는 다층구조지반에서 적용성이 높다고 할 수 있다. 이러한 장점을 활용하여 러브파와 레일리파의 분산정보를 같이 이용하여 동시역산해석을 할 수 있는 기법이 제안되었다. 동시역산해석기법은 본 논문을 통하여 수치해석, 이론모델, 그리고 현장시험을 통하여 검증되었다. 수치해석에서는 2, 3차원 유한요소해석과 전달행렬법의 결과를 비교하였고, 이론모델해석에서는 각 각의 역산해석에서의 결과를 서로 비교하여 검토하였다. 더불어, 현장에서 SASW시험을 수행하여 제안된 동시역산해석기법의 적용성을 검토하였다. 검토 결과, 각 표면파의 정보를 동시에 고려하는 것이 과도한 발산을 방지하고 해의 정확도를 향상시키는 것으로 확인되었다.

• Computers and Concrete
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• 제20권5호
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• pp.583-593
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• 2017

Applications of fibre-reinforced polymer (FRP) composites for retrofitting, strengthening and repairing concrete structures have been expanded dramatically in the last decade. FRPs have high specific strength and stiffness compared to conventional construction materials, e.g., steel. Ease of preparation and installation, resistance to corrosion, versatile fabrication and adjustable mechanical properties are other advantages of the FRPs. However, there are major concerns about long-term performance, serviceability and durability of FRP applications in concrete structures. Therefore, structural health monitoring (SHM) and damage detection in FRP-retrofitted concrete structures need to be implemented. This paper presents a study on investigating the application of Rayleigh wave for detecting debonding defect in FRP-retrofitted concrete structures. A time-of-flight (ToF) method is proposed to determine the location of a debonding between the FRP and concrete using Rayleigh wave. A series of numerical case studies are carried out to demonstrate the capability of the proposed debonding detection method. In the numerical case studies, a three-dimensional (3D) finite element (FE) model is developed to simulate the Rayleigh wave propagation and scattering at the debonding in the FRP-retrofitted concrete structure. Absorbing layers are employed in the 3D FE model to reduce computational cost in simulating the practical size of the FRP-retrofitted structure. Different debonding sizes and locations are considered in the case studies. The results show that the proposed ToF method is able to accurately determine the location of the debonding in the FRP-retrofitted concrete structure.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.338-345
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• 2005

Recently, surface-wave methods have been widely used for site investigation due to economic advantage and improved reliability. Specially, the Spectral-Analysis-of-Surface-Wave (SASW) method has been used to evaluate soil properties in geotechnical engineering. In determination of subgrade stiffness by SASW measurements, only the vertical Rayleigh waves have been used. This study proposed a framework to determine shear-wave velocity profiles by using vertical and horizontal Rayleigh waves and Love wave all together. In addition, the Common-Array-Profiling(CAP) SASW method was employed, which subgrade stiffness of profile the local material under two fixed receivers. The procedure proposed in this study was verified by comparing the shear-wave velocity profiles with the shear-wave velocity profiles of downhole testing at two geotechnical sites.

• Nuclear Engineering and Technology
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• 제54권9호
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• pp.3540-3550
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• 2022

The supercritical carbon dioxide (S-CO₂) Brayton cycle is an important energy conversion technology for the fourth generation of nuclear energy. Since the printed circuit heat exchanger (PCHE) used in the S-CO₂ Brayton cycle has narrow channels, Rayleigh-Bénard (RB) convection is likely to exist in the tiny channels. However, there are very few studies on RB convection in supercritical fluids. Current research on RB convection mainly focuses on conventional fluids such as water and air that meet the Boussinesq assumption. It is necessary to study non-Boussinesq fluids. PRB convection refers to RB convection that is affected by horizontal incoming flow. In this paper, the computational fluid dynamics simulation method is used to study the PRB convection phenomenon of non-Boussinesq fluid-supercritical carbon dioxide. The result shows that the inlet Reynolds number (Re) of the horizontal incoming flow significantly affects the PRB convection. When the inlet Re remains unchanged, with the increase of Rayleigh number (Ra), the steady-state convective pattern of the fluid layer is shown in order: horizontal flow, local traveling wave, traveling wave convection. If Ra remains unchanged, as the inlet Re increases, three convection patterns of traveling wave convection, local traveling wave, and horizontal flow will appear in sequence. To characterize the relationship between traveling wave convection and horizontal incoming flow, this paper proposes the relationship between critical Reynolds number and relative Rayleigh number (r).

• 지구물리와물리탐사
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• 제9권2호
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• pp.148-154
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• 2006

소규모 천부 불균질대가 레일리파의 전파 및 분산특성에 미치는 영향에 대해 알아보기 위해 반무한 균질 매질과 2층 층서구조상의 소규모 천부 불균질대를 상정하고 이 불균질대의 심도, 규모 등을 변화시키면서 레일리파의 전파양상과 분산특성에 대해 고찰하였다. 불균질대의 크기가 최소파장을 기준으로 한파장 이상의 경우 레일리파의 분산 현상이 확인되었으며 이러한 현상은 불균질대의 크기가 클수록 커지며 심도가 깊어질수록 작아지고 심도와 수직적 크기변화보다는 수평적 크기변화에 더 민감한 것을 확인하였다. 분산으로 인한 위상속도의 변화 양상은 불균질대의 크기가 일정정도 이하일 경우에는 탄성파 기록상에서는 확인하기 어려우나 분산된 레일리파의 반사 및 투과 이벤트와 그로 인한 진폭변화를 통해 불균질대 존재 여부를 확인하는 지시자로 사용될 수 있을 것으로 판단되며 이런 결과는 소규모 불균질대나 공동탐지를 위한 현장탐사나 새로운 해석방법 개발에 있어 한 지침을 제공할 것으로 기대된다.

• 한국전산유체공학회지
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• 제9권4호
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• pp.1-6
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• 2004

This study investigates the transition of flows in a natural convection problem with periodic wall temperatures of the form, T/sub L/=T₁＋δ Tsinκχ and T/sub L/=T₂＋δ Tsinκχ .The fluid considered is air with P/sub γ/=0.7. In the conduction-dominated regime with a small Rayleigh number, two large cells are formed over one wave length, for all wave numbers. When k≤1.8, the flow becomes unstable with increase of the Rayleigh number, and multicellular convection occurs above a critical Rayleigh number. The flow patterns are classified by the number of eddies over one wave length, and several kinds of transition phenomena, such as 2→3→4, 4→3→2, and 2→4 eddy flow, occur with increase( or decrease) of the Rayleigh number. Dual solutions are found above a critical Rayleigh number, and an anomalous bifurcation is observed.

• Advances in materials Research
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• 제12권3호
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• pp.211-226
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• 2023

The present work is considered to study the two-dimensional problem in an orthotropic magneto-thermoelastic media and examined the effect of thermal phase-lags and GN-theories on Rayleigh waves in the light of fractional order theory with combined effect of rotation and hall current. The boundary conditions are used to derive the secular equations of Rayleigh waves. The wave properties such as phase velocity, attenuation coefficient are computed numerically. The numerical simulated results are presented graphically to show the effect of phase-lags and GN-theories on the Rayleigh wave phase velocity, attenuation coefficient, stress components and temperature change. Some particular cases are also discussed in the present investigation.

• The Journal of the Acoustical Society of Korea
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• 제17권1E호
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• pp.44-53
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• 1998

Bolt degradation has become a major issue in the nuclear industry since the 1980's due to failure during operation. If small cracks in stud bolt are not detected early enough, they grow rapidly and cause catastrophic disasters. Their detection, despite its importance, is known to be a very difficult problem due to the complicated structures of the stud bolts. This paper presents a method of detecting and sizing a small crack in the root between two adjacent crests in threads. The key idea is from the fact that the Rayleigh wave propagates slowly along a crack from the tip to the opening and is reflected from the opening mouth. When there exists a crack, a small delayed pulse due to the Rayleigh wave is detected between large regularly spaced pulses from the thread. The delay time is the same as the propagation delay time of the slow Rayleigh wave and is proportional to the size of the crack. To efficiently detect the slow Rayleigh wave, three methods based on digital signal processing are proposed : modified wave shaping, dynamic predictive deconvolution, and dynamic predictive deconvolution combined with wave shaping.