• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.834-839
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• 2003

Previous research has been conducted on an ultrasonic wave reflection method that utilizes a steel plate embedded in the concrete to measure the reflection loss of shear waves at the steel-concrete interface. The reflection loss has been shown to have a linear relationship to compressive strength at early ages. The presented investigations continue this research by examining the fundamental relationship between the reflection loss, measured with shear waves, and the hydration kinetics of Portland cement mortar, represented by dynamic elastic moduli, compressive strength and degree of hydration. Dynamic elastic moduli are measured by fundamental resonant frequency and degree of hydration is determined by thermogravimetric analysis. The water/cement ratio was varied for the tested mixture compositions. The results presented herein show that compressive strength, dynamic shear modulus and degree of hydration have a linear relationship to the reflection loss for the tested mortars at early ages.

• Smart Structures and Systems
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• 제30권4호
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• pp.371-383
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• 2022

A novel impact localization method is presented based on impact induced elastic waves in sensorized composite structure subjected to temperature fluctuations. In real practices, environmental and operational conditions influence the acquired signals and consequently make the feature (particularly Time of Arrival (TOA)) extraction process, complicated and troublesome. To overcome this complication, a robust TOA estimation method is proposed based on the times in which the absolute amplitude of the signal reaches to a specific amplitude value. The presented method requires prior knowledge about the normalized wave velocity in different directions of propagation. To this aim, a finite element model of the plate was built in ABAQUS/CAE. The impact location is then highlighted by calculating an error value at different points of the structure. The efficiency of the developed impact localization technique is experimentally evaluated by dropping steel balls with different energies on a carbon fiber composite plate with different temperatures. It is demonstrated that the developed technique is able to localize impacts with different energies even in the presence of noise and temperature fluctuations.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권2호
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• pp.828-834
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• 2019

Researchers have previously proven that the flapping motion of the hydrofoil can convert wave energy into propulsive energy. However, the estimation of thrust forces generated by the flapping foil placed in waves remains a challenging task for ocean engineers owing to the complex dynamics and uncertainties involved. In this study, the flapping foil system consists of a rigid NACA0015 section undergoing harmonic flapping motion and a passively actuated elastic flat plate attached to the leading edge of the rigid foil. We have experimentally measured the thrust force generated due to the flapping motion of a rigid foil attached to an elastic plate in a wave flume, and the effects of the elastic plates have been discussed in detail. Furthermore, an empirical formula was introduced to predict the thrust force of a flapping foil based on our experimental results using multiple regression analysis.

• 한국공간구조학회논문집
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• 제8권6호
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• pp.75-83
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• 2008

철근 콘크리트 구조물에서 발생하는 균열에 의한 손상은 과도한 하중이나 사용성에 의해 발생한다. 이러한 손상을 검사하는 방법으로 육안으로 확인하거나 비파괴 시험법을 주로 이용하고 있다. 후자의 경우, 콘크리트 내부 철근의 배근 방향성에 의해 균열에 의한 손상인지 판별하기 어려운 문제가 발생하게 되며, 비파괴시험(Non-destructive Test)에 사용되는 대부분의 센서(Sensor)는 1축 가속도 센서이기 때문에 중첩된 전달파를 분석하기에는 어렵다. 따라서, 이를 해결하기 위해 중공 유리관을 이용하였고 콘크리트 보 내부에 매입하여 철근이 매입되어 있는 경우에 대하여 3축 가속도계를 이용하여 탄성파로 가진 하였을 경우에 발생하는 파(Wave)를 비교 분석하였다.

• 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.

• 한국음향학회지
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• 제11권4호
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• pp.22-30
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• 1992

섬유강화 복합재료의 동탄성계수와 감쇠특성을 규명하기 위하여 랜덤하게 분포된 무한 실린더 형상의 산란계를 가진 메질내에서, 축방향으로 분극되어 조화운동을 하는 탄성파의 전파에 관하여 연구하였다. 단일 실린더에 대한 산란계수로부터 Lax의 준결정근사법을 이용하여 다중산란에 관한 이론을 유도하였고, 매질내에서의 파동전파특성을 내포하는 분산관계식을 얻었다. 다중 산란에 의한 실린더간의 상호작용을 수식화하기 위하여 필요한 실린더의 쌍분포함수는 몬테카를로 모의실험을 이용하여 구하였다. 수치적으로 구한 감쇠계수 및 유효전단강성을 주파수와 면적밀도의 함수로 제시하였다.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2008년도 공동학술대회
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• pp.57-62
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• 2008

탄성파 수치 모형 계산에 있어서 널리 사용되는 엇갈린 격자 방법이 아니라 회전된 엇갈린 격자 방법을 사용하여 탄성파 수치 모사를 수행하였다. 표준 엇갈린 격자 방법에서는 자유 경계조건을 적용하여야 하는 단점이 있지만 회전된 격자 방법에서는 자유 경계조건을 적용할 필요 없이 물성을 부여함으로써 해결될 수 있다. 파동전파에 있어서 유한 경계 조건에서 발생하는 인공 반사파를 제거하기 위하여 최근에 뛰어난 성능을 보이는 PML(Perfectly Matched Layer)법이 많이 적용되고 있다. 이 연구에서는 PML보다 성능이 뛰어나기도 하지만 차분에 있어 파동식을 분리할 필요가 없는 CPML(Convolutional Perfectly Matched Layer)법을 회전된 엇갈린 격자법(RSG : Rotatged Staggered Grid)에 적용하고자 하였다. Cerjan법의 감쇠법과 비교한 결과 매우 효과적으로 인공 반사파를 제거할 수 있음을 알 수 있었다.

• Composites Research
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• 제20권1호
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• pp.15-22
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• 2007

이 논문에서는 섬유강화 복합재료에서의 초음파의 거동에 대해 파동의 모드, 방향, 자유표면에서의 반사파의 반사계수 등을 예측하는 해석적인 방법을 소개한다. 이 논문은 또한 복합재료의 자유표면에서 반사가 일어날 때의 특이한 현상을 새로이 고찰하였는데, 이는 완도면(slowness surface)만을 고려하면 존재할 것으로 예상되지만 실제로는 존재하지 않는 반사파에 대한 것이다. 이는 입사파가 유사횡파일 경우, 입사각이 이 논문에서 새로 정의된 제3임계각을 넘어설 경우 나타나는 현상이다. 본 논문의 내용은 초음파검사와 같은 해당 분야에 종사하는 연구자들에게 유용한 가이드라인을 제시할 것으로 기대된다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.833-838
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• 2003

The problem of elastic wave resonance scattering from elastic targets is studied in this paper. A new resonance formalism to extract the elastic resonance information of the target from scattered elastic waves is introduced. The proposed resonance formalism is an extension of the works developed for acoustic wave scattering problems by the author. The classical resonance scattering theory computes reasonable magnitude information of the resonances in each partial wave, but the phase behaves in somewhat irregular way, therefore, is not clearly explainable. The proposed method is developed to obtain physically meaningful magnitude and phase of the resonances. As an example problem, elastic wave scattering from an infinitely-long elastic cylinder was analyzed by the proposed method and compared to the results by RST. In case of no mode conversion, both methods generate identical magnitude. However, the new method computes exact $\pi$ radian phase shills through resonances and anti-resonances while RST produces physically unexplainable phases. In case of mode conversion, in addition to the phase even magnitudes are different. The phase shifts through resonances and antiresonances obtained by the proposed method are not exactly $\pi$ radians due to energy leak by mode conversion. But, the phases by the proposed method show reasonable and intuitively correct behavior compared to those by RST.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2009년도 춘계학술대회 논문집
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• pp.466-467
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• 2009