• Coupled systems mechanics
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• 제13권3호
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• pp.247-275
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• 2024

The paper studies the influence of the fluid flow velocity and flow direction in the initial state on the dispersion of the axisymmetric waves propagating in the inhomogeneously pre-stressed hollow cylinder containing this fluid. The corresponding eigenvalue problem is formulated within the scope of the three-dimensional linearized theory of elastic waves in bodies with initial stresses, and with linearized Euler equations for the inviscid compressible fluid. The discrete-analytical solution method is employed, and analytical expressions of the sought values are derived from the solution to the corresponding field equations by employing the discrete-analytical method. The dispersion equation is obtained using these expressions and boundary and related compatibility conditions. Numerical results related to the action of the fluid flow velocity and flow direction on the influence of the inhomogeneous initial stresses on the dispersion curves in the zeroth and first modes are presented and discussed. As a result of the analyses of the numerical results, it is established how the fluid flow velocity and flow direction act on the magnitude of the influence of the initial inhomogeneous stresses on the wave propagation velocity in the cylinder containing the fluid.

• Structural Engineering and Mechanics
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• 제20권4호
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• pp.421-434
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• 2005

In this paper, the finite element method is applied to investigate the effect of the lateral boundary in homogenous soil on the seismic response of a superstructure. Some influencing factors are presented and discussed, and several parameters are identified to be important for conducting soil-structure interaction experiments on shaking tables. Numerical results show that the cross-section width L, thickness H, wave propagation velocity and lateral boundaries of soil layer have certain influences on the computational accuracy. The dimensionless parameter L/H is the most significant one among the influencing factors. In other words, a greater depth of soil layer near the foundation should be considered in shaking table tests as the thickness of the soil layer increases, which can be regarded as a linear relationship approximately. It is also found that the wave propagation velocity in soil layer affects the numerical accuracy and it is suggested to consider a greater depth of the soil layer as the wave propagation velocity increases. A numerical study on a soil-structure experimental model with a rubber ring surrounding the soil on a shaking table is also conducted. It is found the rubber ring has great effect on the soil-structure interaction experiments on shaking table. The experimental precision can be improved by reasonably choosing the elastic parameter and width of the rubber ring.

• Structural Engineering and Mechanics
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• 제59권6호
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• pp.951-972
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• 2016

The purpose of this study is to illustrate the propagation of the shear waves (SH-waves) in a prestressed hetrogeneous orthotropic media overlying a pre-stressed anisotropic porous half-space with self weight. It is considered that the compressive initial stress, mass density and moduli of rigidity of the upper layer are space dependent. The proposed model is solved to obtain the different dispersion relations for the SH-wave in the elastic-porous medium of different properties. The effects of compressive and tensile stresses along with the heterogeneity, porosity, Biot's gravity parameter on the dispersion of SH-wave are shown numerically. The wave analysis further indicates that the technical parameters of upper and lower half-space affect the wave velocity significantly. The results may be useful to understand the nature of seismic wave propagation in geophysical applications and in the field of earthquake and material science engineering.

• 전기학회논문지
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• 제60권3호
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• pp.594-599
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• 2011

A SAW strain sensor based on Shear Horizontal wave with an 92 MHz central frequency was developed. It consists of SAW sensor, PCB substrate and bonding material (Loctite 401). External force applied to PCB substrate bonded to a piezoelectric substrate induces strain at the substrate surface, which causes changes in the elastic constant and density of the substrate and hence the propagation velocity of the SAW. The change in the velocity of the SAW result in a frequency shift of the sensor and by measuring a frequency shift, we can extract the strain induced by the external force. The $41^{\circ}$ YX $LiNbO_3$ was used because it has a Leaky shear horizontal(SH) wave propagation mode and a high electromechanical coupling coefficient ($K^2$=17.2%). And to compare with Rayleigh wave mode, $128^{\circ}$ YX $LiNbO_3$ was used. And to make a stable and low insert loss, Split IDT structure was used. The obtained sensitivity and linearity of the SAW strain sensor in the case of Split IDT were measured to be 17.2 kHz / % and 0.99, respectively.

• Journal of Mechanical Science and Technology
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• 제14권7호
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• pp.705-714
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• 2000

The formulation of Smoothed Particle Hydrodynamics (SPH) and a shortcoming of traditional SPH in contact simulation are presented. A contact algorithm is proposed to treat contact phenomenon between two objects. We describe the boundary of the objects with non-mass artificial particles and set vectors normal to the contact surface. Contact criterion using non-mass particles is established in this study. In order to verify the contact algorithm, an algorithm is implemented in to an in-house program; elastic wave propagation is an analysed under low velocity axial impact of two rods. The results show that the contact algorithm eliminates the undesirable phenomena at the contact surface; numerical result with the contact algorithm is compared with theoretical one.

• 한국농업기계학회:학술대회논문집
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• 한국농업기계학회 1996년도 International Conference on Agricultural Machinery Engineering Proceedings
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• pp.344-353
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• 1996

A fundamental study was conducted to obtain the basic data involved in nondestructive quality evaluation of the fruit and vegetables. An experimental equipment for ultrasonic propagation characteristics of the fruit and vegetables such as radish , carrot , potato, and apple was set up and also power spectrum analysis system of an ultrasonic wave through the fruit and vegetables was set up. The velocity and attenuation of ultrasonic wave through the tissue specimens from the fruit and vegetables were measured and analyzed. The elastic modulus and density by the mechanical method currently used were compared with those using by ultrasonic method. The ultrasonic tranit time was almost linearly increased with the length of the specimens and attenuation of ultrasonic was mainly affected by the internal flbrous structure of the products. The regression equation was derived from the highly correlated experimental variables.

• Coupled systems mechanics
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• 제12권4호
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• pp.337-364
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• 2023

The Rayleigh wave propagation is considered in the structure of the functionally graded piezoelectric material (FGPM) layer over the elastic substrate. The elastic substrate loosely bonds the layer through a corrugated interface, whereas its upper boundary is also corrugated but stress-free. Additionally, the solutions for the FGPM layer and substrate are derived using the fundamental variable separable approach to convert the partial differential equation to an ordinary differential equation. The results with boundary conditions lead to dispersion relations for the electrically open and electrically short cases in the determinant form. The outcomes have been numerically analyzed using a specific model. The findings were presented in the form of graphs, which were created using Mathematica 7. Graphs are plotted for variations in wavenumber and phase velocity. The outcomes may help measure interface defects and design Surface Acoustic Wave (SAW) devices.

• 비파괴검사학회지
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• 제23권2호
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• pp.98-106
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• 2003

비파괴시험(NDT)은 구조물의 기능에 손상을 주지 않으면서 콘크리트에 대한 많은 정보를 준다. 여러 가지 NDT 방법들 중에서, 초음파 속도법과 충격반향기법과 같이 탄성파의 속도를 이용하는 방법은 콘크리트의 압축강도, 탄성계수, 포아송비의 추정뿐만 아니라, 내부 미세구조 변화 모니터링과 결함 탐지 등을 위해 이용되고 있다. 본 연구에서는 물-결합재비가 $0.27{\sim}0.50$이고 시멘트 중량의 20%를 플라이 애쉬로 대체 사용한 콘크리트를 제조한 후, 동일한 콘크리트에 대해 초음파 속도법과 충격반향기법을 이용하여 종파 속도를 각각 측정하여 서로 비교하였다. 실험 결과, 콘크리트 공시체로부터 측정된 초음파 속도가 충격반향기법에 의해 측정된 종파 속도, 즉 막대파 속도보다 큰 경향을 나타내었으며, 이들의 차이는 재령이 증가함에 따라 그리고 콘크리트의 강도가 커질수록 각각 감소하는 경향을 나타내었다. 또한, 동포아송비, 정탄성계수, 동탄성계수, 속도-강도의 상관관계 등을 실험적으로 결정하였다. 그 결과, 동적인 방법으로 결정되는 포아송비와 탄성계수가 정적인 시험에 의한 것보다 크게 나타났다. 따라서, 탄성파 속도를 이용하여 콘크리트의 성질들을 보다 정확하게 추정하기 위해서는 속도 특성에 대한 이해가 필요할 것으로 사료된다.

• Structural Engineering and Mechanics
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• 제53권2호
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• pp.277-296
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• 2015

The objective of this paper is to investigate the surface waves in fibre-reinforced anisotropic thermoelastic medium subjected to gravity field. The theory of generalized surface waves has firstly developed and then it has been employed to investigate particular cases of waves, viz., Stoneley waves, Rayleigh waves and Love waves. The analytical expressions for displacement components, force stress and temperature distribution are obtained in the physical domain by using the harmonic vibrations. The wave velocity equations have been obtained in different cases. The numerical results are given and presented graphically in Green-Lindsay and Lord-Shulman theory of thermoelasticity. Comparison was made with the results obtained in the presence and absence of gravity, anisotropy, relaxation times and parameters for fibrereinforced of the material medium. The results indicate that the effect of gravity, anisotropy, relaxation times and parameters for fibre-reinforced of the material medium are very pronounced.

• 한국음향학회지
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• 제25권3호
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• pp.107-112
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• 2006

판재를 따라 전파하는 Lamb wave (램파)는 주파수에 따라 속도가 변하는 분산특성을 갖는다. 일반적으로 등방성 재료에서는 파수 벡터 방향과 에너지 흐름 방향은 같아, 파면이 원형을 유지하면서 전파하지만, 복합재료와 같이 이방성재료에서는 파수 벡터와 에너지 흐름 방향이 서로 다르다. 따라서 이방성 재료에서 하나의 속도에서 다른 속도로 전환하려면 방향을 교정해야 하고 이에 따라 크기도 달라지게 된다. 본 연구에서는 복합재료 판재에서 전파하는 램파 분산방정식을 이용하여 대칭, 비대칭 모드의 분산선도를 작성하였고, 각도에 따라구한 위상속도 분산선도에서 얻어진 위상속도 값으로 slowness surface를 구한 후, 이로부터 군속도의 크기와 방향을 교정하였고, 이를 실험적으로 측정한 속도값과 비교하여 서로 일치함을 확인하였다.