• 소음진동
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• 제9권6호
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• pp.1218-1226
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• 1999

In this paper, the extended Biot's semilinear model was developed. Combining the extended Biot model with the dynamic equation yields the nonlinear wave equation in poproelastic sound absorbing materials. Both perturbation and matching techniques are used to find solutions for nonlinear wave equations. By comparing results between linear and nonlinear wave solutions, characteristics of nonlinear waves in poroelastic sound abosrbing materials have been studied. Nonlinear waves were found to be attenuated faster than the linear ones. A maximum amplitude of the nonlinear wave occurred near its surface boundaries and decay quickly with distance from the surface. It has also been found that, if the amplitudes of linear waves are known at the surface boundaries, those of nonlinear ones can be determined. This will be the basis of finding effects of nonlinearity on the absorption coefficient and the transmission loss.

• 비파괴검사학회지
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• 제28권2호
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• pp.112-118
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• 2008

본 논문에서는 유체에 포화된 다공성 매질에 적용되는 Biot 모델 및 modified Biot-Attenborough (MBA) 모델을 이용하여 해면질골에서 다공율 및 주파수에 대한 초음파 위상속도의 의존성을 예측하였다. 또한 선행 연구자들에 의하여 사람 및 소의 해면질골에서 측정된 값과 비교하였다. 해면질골에서 위상속도는 다공율 및 주파수가 증가함에 따라 감소하는 것을 알 수 있었다. 또한 전파각 효과를 포함하도록 수정된 Biot 모델 및 MBA 모델뿐만 아니라 Schoenberg 모델을 이용하여 해면질골에서 전파각에 대한 위상속도의 의존성을 예측하였다. 본 논문에서 이용된 이론적인 모델들은 초음파와 해면질골의 상호작용에 대한 물리학적인 이해를 증진시키는데 기여할 뿐만 아니라 골다공증을 진단하기 위하여 유용하게 이용될 수 있을 것으로 기대된다.

• The Journal of the Acoustical Society of Korea
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• 제27권2E호
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• pp.45-50
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• 2008

In recent years, quantitative ultrasound (QUS) technologies have played a growing role in the diagnosis of osteoporosis. Most of the commercial bone somometers measure speed of sound (SOS) and/or broadband ultrasonic attenuation (EUA) at peripheral skeletal sites. However, the QUS parameters are purely empirical measures that have not yet been firmly linked to physical parameters such as bone strength or porosity. In the present study, the theoretical models for wave propagation in cancellous bone, such as the Biot model, the stratified model, and the modified Biot-Attenborough (MBA) model, were applied to predict the dependence of phase velocity on porosity in cancellous bone. The optimum values for the input parameters of the three models in cancellous bone were determined by comparing the predictions with the previously published measurements in human cancellous bone in vitro. This modeling effort is relevant to the use of QUS in the diagnosis of osteoporosis because SOS is negatively correlated to the fracture risk of bone, and also advances our understanding of the relationship between phase velocity and porosity in cancellous bone.

• The Journal of the Acoustical Society of Korea
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• 제25권1E호
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• pp.1-7
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• 2006

This study examines the reflection characteristic of a thin transition layer of the ocean bottom showing variability with respect to depth. In order to model the surficial sediment simply, we reduce the Biot model to the depth dependent wave equation for the pseudo fluid using the fluid approximation (weak frame approximation). From the reduced equation, the difference between the inherent frequency dependency of the reflection and the frequency dependency resulting from a thin transition layer is investigated. Using Tang's depth porosity profile model of the surficial sediment [D. Tang et al., IEEE J. Oceanic Eng., vol.27(3), 546-560(2002)], we numerically simulated the reflection loss and investigated the contribution from both frequency dependencies. In addition, the effects of different sediment type and varying depth structure of the sediment are discussed.

• 한국음향학회:학술대회논문집
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• 한국음향학회 2004년도 추계학술발표대회논문집 제23권 2호
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• pp.183-186
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• 2004

Biot's theory and a modified Biot-Attenborough (MBA) model are applied to predict the dependences of acoustic characteristics on frequency and porosity in cancellous bone. The phase velocity and the attenuation coefficient predicted by both theories are compared with previous in vitro experimental measurements in terms of the mixed, the fast, and the slow waves. Biot's theory successfully predicts the dependences of phase velocity on frequency and porosity in cancellous bone, whereas a significant discrepancy is observed between predicted and measured attenuation coefficients. The MBA model is consistent with reported measurements for both dependences of phase velocity and attenuation coefficient on frequency and porosity. Based on the theoretical predictions from the MBA model, it is suggested that the attenuation coefficient of the mixed wave is dominated by the fast wave in the low-porosity region while it is dominated by the slow wave in the high-porosity region. This provides a qualitative explanation for the nonlinear relationship of attenuation of the mixed wave with porosity in cancellous bone.

• The Journal of the Acoustical Society of Korea
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• 제29권2E호
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• pp.64-72
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• 2010

Osteoporosis is a skeletal disease characterized by two factors: reduced bone mass and microstructure disruption of bone tissue. These symptoms increase bone fragility and can contribute to eventual fracture. In recent years, quantitative ultrasound (QUS) technologies have played a growing role in the diagnosis of osteoporosis. Most of the commercial bone sonometers measure speed of sound and/or broadband ultrasound attenuation at peripheral skeletal sites. However, QUS parameters are purely empirical measures that have not yet been firmly linked to physical parameters, such as bone strength or porosity, and the underlying physics for their variations in cancellous bone is not well understood yet. This paper reviews the QUS technologies for the diagnosis of osteoporosis and also addresses several theoretical models, such as the Biot model, the scattering model, the stratified model, and the modified Biot-Attenborough model, for ultrasonic wave propagation in bone.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 추계학술대회논문집
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• pp.934-937
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• 2006

This investigation presents a topology formulation to design optimal poroelastic acoustic foams to maximize absorbing ability. For successful formulation, a single set of equations based on Biot's theory is adopted and an appropriate material interpolation strategy is newly developed. Because there was no earlier attempt to solve poroelastic acoustic foam design problems in topology optimization setting, many challenging issues including modeling and interpolation must be addressed. First, the simulation accuracy by a proposed unified model encompassing acoustic air and poroelastic material was checked against analytical and numerical results. Then a material interpolation scheme yielding a distinct acoustic air-poroelastic material distribution was developed. Using the proposed model and interpolation scheme, the topology optimization of a two-dimensional poroelastic acoustic foam for maximizing its absorption coefficient was carried out. Numerical results show that the absorption capacity of an optimized foam layout considerably increases in comparison with a nominal foam layout.

• 한국암반공학회:학술대회논문집
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• 한국암반공학회 2000년도 암반공학문제의 수치해석(Numerical Analysis in Rock Engineering Problems)
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• pp.105-115
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• 2000

방사성 폐기물지하처분이나 열수 및 축열 에너지저장, 지열에너지 개발 등과 같은 대규모 지하공간 프로젝트들이 대두됨에 따라 역학, 수리 및 열적 거동을 동시에 고려한 연구가 필요하게 되었다. 열-수리-역학 상호작용 해석은 열로 교란되고 지하수로 포화된 암반내의 거동을 열 수리, 역학 3가지 지배방정식의 결합을 통해 구현하는 상당히 복잡한 수치 해석 기법 중의 하나이다. 본 연구에서는 기존의 Biot의 압밀이론에 기초한 수식화들을 이용하여 연속체 암반의 열-수리-역학적 상호작용을 모사할 수 있는 유한요소 프로그램을 개발하였다. 개발된 프로그램의 검증을 위해 등온과 비등온 조건하의 일차원 압밀모델에 대한 해석을 실시하여 해석해와 비교하였다. 이타원 압밀에 대한 변수해석을 통하여 포아송비나 수리적 이방성과 같은 인자들이 매체 거동에 미치는 영향을 조사하였다. 앞으로 본 프로그램에 개별체 절리 모델을 통합시켜 보다 일반적인 불연속 암반의 상호작용 거동 해석에 이용할 수 있을 것이다.

• 터널과지하공간
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• 제10권3호
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• pp.355-365
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• 2000

방사성 폐기물지하처분이나 열수 및 축열 에너지저장, 지열에너지 개발 둥과 같은 대규모 지하공간 프로젝트들이 대두됨에 따라 역학, 수리 및 열적 거동을 동시에 고려한 연구가 필요하게 되었다. 열-수리-역학 상호작용 해석은 열로 교란되고 지하수로 포화된 암반내의 거동을 열, 수리, 역학 3 가지 지배방정식의 결합을 통해 구현하는 상당히 복잡한 수치 해석 기법 중의 하나이다. 본 연구에서는 기존의 Biot의 압밀이론에 기초한 수식화들을 이용하여 연속체 암반의 열-수리-역학적 상호작용을 모사할 수 있는 유한요소 프로그램을 개발하였다. 개발된 프로그램의 검증을 위해 등온과 비등온 조건하의 일차원 압밀모델에 대한 해석을 실시하여 해석해와 비교하였다. 이차원 압밀에 대한 변수해석을 통하여 포아송비나 수리적 이방성과 같은 인자들이 매체 거동에 미치는 영향을 조사하였다. 앞으로 본 프로그램에 개별체 절리 모델을 통합시켜 보다 일반적인 불연속 암반의 상호작용 거동 해석에 이용할 수 있을 것이다.

• Geomechanics and Engineering
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• 제5권6호
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• pp.595-611
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• 2013

This paper presents a three-dimensional (3D) integrated numerical model where the wave-induced pore pressures in a porous seabed around breakwater heads were investigated. Unlike previous research, the Navier-Stokes equation is solved with internal wave generation for the flow model, while Biot's dynamic seabed behaviour is considered in the seabed model. With the present model, a parametric study was conducted to examine the effects of wave and soil characteristics and breakwater configuration on the wave-induced pore pressure around breakwater heads. Based on numerical examples, it was found that the wave-induced pore pressures at breakwater heads are greater than that beneath a breakwater. The wave-induced seabed response around breakwater heads become more important with: (i) a longer wave period; (ii) a seabed with higher permeability and degree of saturation; and (iii) larger angle between the incident waves and breakwater. Furthermore, the relative difference of wave-induced pore pressure between fully-dynamic and quasi-static solutions are larger at breakwater heads than that beneath a breakwater.