• 비파괴검사학회지
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• 제30권6호
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• pp.539-547
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• 2010

In this study, characteristics of the fundamental longitudinal guided wave mode, L(0,1), which is a usual mode employed in the inspection of the above-ground pipe, of the buried pipe were numerically investigated considering property changes in the surrounding soil. Results showed that soil conditions are significantly affecting the attenuation of L(0,1) mode in the pipe embedded in soil. Especially, if the soil is partially saturated, the attenuation of L(0,1) mode is larger and is very similar regardless of the degree of water saturation in the surrounding soil. However, when the soil is fully saturated, the attenuation of L(0,1) mode is less and show different trend with its partially saturated counterparts.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2002년도 추계 학술발표회 논문집
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• pp.3-10
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• 2002

The strong ground motion data recorded in the Sino-Korea Craton are analysed toobtain attenuation relations valid for 5 < M < 8, r < 400 km applicable to the Korean Peninsula. The result is logA : -1.83+0.386M- log${\gamma}$-0.0015${\gamma}$ where A is peak horizontal acceleration in g, M is surface-wave magnitude, and r is hypocentral distance in km. Our result is compared with the existing attenuation relations of Western North America and Eastern North America and the prior predictive equations for the Southern part of Korean Peninsula. Our result compares better with those of North America than those of the Southern part of the Korean Peninsula. More theoretical and empirical studies are required for better attenuation relations appropriate for the Korean Peninsula.

• 한국소음진동공학회논문집
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• 제26권5호
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• pp.594-601
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• 2016

Mass estimation analysis of loose-parts in pressure vessel is necessary for the structural integrity assessment of pressure boundary in nuclear power plants. Mass of loose-parts can be generally estimated from the peak values and the center frequency of impact signals. Magnitude of impact signals is, however, inevitably attenuated according to the traveling distance of the signals and depending on the frequencies. Attenuation rate must be therefore carefully compensated for the precise estimation of loose-part mass. This paper proposes a new compensation method for the attenuation rate based on Bessel function instead of Hankel function in conventional method which has a limitation of usage in near the impact location. It was verified that the suggested compensating equation based on the Bessel function can be applied to the attenuation rate calculation without any limitation.

• Structural Engineering and Mechanics
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• 제61권1호
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• pp.143-160
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• 2017

The paper studies the attenuation of the axisymmetric longitudinal waves propagating in the bi-layered hollow cylinder made of linear viscoelastic materials. Investigations are made by utilizing the exact equations of motion of the theory of viscoelasticity. The dispersion equation is obtained for an arbitrary type of hereditary operator of the materials of the constituents and a solution algorithm is developed for obtaining numerical results on the attenuation of the waves under consideration. Specific numerical results are presented and discussed for the case where the viscoelasticity of the materials is described through fractional-exponential operators by Rabotnov. In particular, how the rheological parameters influence the attenuation of the axisymmetric longitudinal waves propagating in the cylinder under consideration, is established.

• 지구물리와물리탐사
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• 제14권1호
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• pp.105-115
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• 2011

유체를 포함하는 혼합 매질에서의 탄성파 고유 감쇠에 대한 다양한 메커니즘 중, 탄성파 전파 시 고체와 유체 사이에서의 상대적 운동은 가장 중요한 감쇠 메커니즘 중의 하나이다. 선행 연구에서는 얼음의 미세 공극 안에 존재하는 소금물이 초음파의 전파에 미치는 영향을 분석하기 위하여 얼음과 소금물이 공존하는 매질에서 초음파 전파 실험하였다. 부분적으로 동결된 소금물에서 각기 다른 온도에서의 초음파 감쇠의 물리적인 메커니즘을 350 ~ 600 kHz의 주파수 대역에서 규명하기 위하여, Biot 이론에 입각한 다공성의 탄생 모델을 도입하여 초음파의 전파를 측정하였다. 고체상은 얼음으로, 액체상은 소금물로 가정한 뒤 펄스 핵자기공명기술로 측정한 유체의 성질을 이용하여 각각의 온도에서의 공극률을 계산한 결과, 실험으로 측정한 감쇠값은 500 kHz에서 계산된 고유 감쇠값과 다르게 나타났으며 이는 squirt -flow 메커니즘과 파의 산란 효과와 같은 다른 감쇠 메커니즘도 고려해야 한다는 것을 의미한다.

• 비파괴검사학회지
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• 제18권1호
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• pp.1-9
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• 1998

짧은 섬유로 강화된 열가소성수지의 복합재료를 대상 재료로 하여 AE의 발생위치(AE source location)를 구하고 AE신호의 진폭분포에 미치는 감쇠 손실(attenuation loss)의 영향을 정량적으로 검토했다. 모의 AE파를 이용하여 측정된 감쇠율은 시험편내의 섬유체적함유율의 증가에 따라 단순 선형관계식으로 예상되는 값보다 더 작았다. 시험편에서 계측된 AE진폭분포에 감쇠손실을 보정한 결과, 시험편의 게이지부에 설정된 각 구역에서 서로 유사한 수준의 진폭분포가 나타났다. 또한 보정된 AE진폭은 시험편의 변형이 진행됨에 따라 더욱 크게 되었다. 따라서, AE진폭을 이용한 고분자복합재료의 손상해석에서는 AE파의 감쇠효과를 보정해야 됨이 확인되었다.

• 한국해양공학회지
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• 제21권5호
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• pp.18-24
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• 2007

The environmental value of coastal vegetation has been widely recognized. Coastal vegetation such as reed forests and seaweed performs several useful functions, including maintaining water quality, supporting fish (and, thus, fisheries), protecting beaches and land from wave attack, stabilizing sea beds and providing scenic value. However, studies on the physical and numerical process of wave propagation, sediment transport and bathymetric change are few and far between compared to those on the hydrodynamic roles of coastal vegetation. In general, vegetation flourishing along the coastal areas attenuates the incident waves through momentum exchange between stagnated water mass in the vegetated area and rapid mass in the un-vegetated area. This study develops a numerical model for describing the wave attenuation and sediment transport in a wave channel in a vegetation area. By comparing these results, the effects of vegetation properties, wave properties and model parameters are clarified.

• 비파괴검사학회지
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• 제11권2호
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• pp.22-31
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• 1991

Various types of ultrasonic techniques have been used for the estimation of compressive strength of concrete structures. However, conventional ultrasonic velocity method using only longitudial wave cannot be determined the compressive strength of concrete structures with accuracy. In this paper, by using the introduction of multiple parameter, e. g. velocity of shear wave, velocity of longitudinal wave, attenuation coefficient of shear wave, attenuation coefficient of longitudinal wave, combination condition, age and preservation method, multiple regression analysis method was applied to the determination of compressive strength of concrete structures. The experimental results show that velocity of shear wave can be estimated compressive strength of concrete with more accuracy compared with the velocity of longitudinal wave, accuracy of estimated error range of compressive strength of concrete structures can be enhanced within the range of ${\pm}$10% approximately.

• Structural Engineering and Mechanics
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• 제41권5호
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• pp.605-615
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• 2012

In this paper, guided circumferential wave propagating in an orthotropic viscoelastic cylindrical curved plate subjected to traction-free conditions is investigated in the frame of the Kelvin-Voight viscoelastic theory. The obtained three wave equations are decoupled into two groups, Lamb-like wave and SH wave. They are separately solved by the Legendre polynomial series approach. The availability of the method is confirmed through the comparison with the published data of the SH wave for a viscoelastic flat plate. The dispersion curves and attenuation curves for the carbon fiber and prepreg cylindrical plates are illustrated and the viscous effect on dispersion curves is shown. The influences of the ratio of radius to thickness are analyzed.

• 비파괴검사학회지
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• 제32권3호
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• pp.241-262
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• 2012

Some applications require structural health monitoring in inaccessible components. This paper presents a technique useful for Structural Health Monitoring of double wall structures, such as double wall steam pipes and double wall pressure vessels separated from an ultrasonic transducer by three layers. Detection has been demonstrated at distances in excess of one meter for a fixed transducer. The case presented here is for one of the layers, the middle layer, being a fluid. For certain transducer configurations the wave propagating in the fluid is a wave with low velocity and attenuation. The paper presents a model based on wave theory and finite element simulation; the experimental set-up and observations, and comparison between theory and experiment. The results provide a description of the technique, understanding of the phenomenon and its possible applications in Structural Health Monitoring.