Sharif Digital Repository

Phoxonic crystal as a means of guiding and confining electromagnetic and elastic waves has already attracted attentions. Lack of exact knowledge on how these two types of waves interact inside this crystal and how electromagnetic wave evolves through this interaction has increased this field complexity. Here we explain how an elastic wave affects an electromagnetic wave through photoelasticity and interface displacement mechanisms in a phoxonic crystal slab waveguide. We obtain a master equation which can describe electromagnetic wave evolution. In this equation we define a coupling parameter and calculate its value for different modes of electromagnetic and elastic waves and show it... 

We study localization of elastic waves in two-dimensional heterogeneous solids with randomly distributed Lamé coefficients, as well as those with long-range correlations with a power-law correlation function. The Matin-Siggia-Rose method is used, and the one-loop renormalization group (RG) equations for the coupling constants are derived in the limit of long wavelengths. The various phases of the coupling constants space, which depend on the value ρ, the exponent that characterizes the power-law correlation function, are determined and described. Qualitatively different behaviors emerge for ρ<1 and ρ>1. The Gaussian fixed point (FP) is stable (unstable) for ρ<1 (ρ>1). For ρ<1, there is a... 

We derive the exact dispersion relations for flexural elastic wave motion in a beam under finite deformation. We employ the Euler-Bernoulli kinematic hypothesis. Focusing on homogeneous waveguides with constant cross-section, we utilize the exact strain tensor and retain all high order terms. The results allow us to quantify the deviation in the dispersion curves when exact large deformation is considered compared to the small strain assumption. We show that incorporation of finite deformation shifts the frequency dispersion curves downwards. Furthermore, the group velocity increases with wavenumber but this trend reverses at high wavenumbers when the wave amplitude is sufficiently high. At... 

This paper is devoted to the study of scattering of plane harmonic waves by a piezoelectric sphere with spherical isotropy embedded in an unbounded isotropic polymer matrix. The scattered displacement field and the electric potential in the matrix are expressed in terms of spherical vector wave functions and spherical harmonic functions, respectively. For the field points inside the inhomogeneity, new displacement functions are introduced. Expansion of the new displacement functions and the electric potential in terms of spherical harmonic functions, the equations of motion and electrostatic lead to four second order ordinary differential equations (odes), where three of them are coupled.... 

Throughout this paper four locomotion mechanisms have been presented for underwater robo-sankes. In this respect; initially, two methods of locomotion including traveling and standing wave have been examined. Next, applications of these methods are described. Ultimately, assessing and comparison of those mechanisms have been studied and the best plan is determined. © 2009 WASET.ORG  

We derive exact dispersion relations for axial and flexural elastic wave motion in a rod and a beam under finite deformation. For axial motion we consider a simple rod model, and for flexural motion we employ the Euler-Bernoulli kinematic hypothesis and consider both a conventional transverse motion model and an inextensional planar motion model. The underlying formulation uses the Cauchy stress and the Green-Lagrange strain without omission of higher order terms. For all models, we consider linear constitutive relations in order to isolate the effect of finite motion. The proposed theory, however, is applicable to problems that also exhibit material nonlinearity. For the rod model, we... 

Incorporation of the first gradient of strain, in addition to the strain itself, into the strain energy density of an elastic solid leads to Mindlin's first strain gradient theory, which is useful for examination of size effect as well as other mechanical phenomena at the nano-scale. For isotropic elastic solids, the first strain gradient theory, in addition to the two independent Lamé constants, gives rise to five new material constants which in turn reduce to two material parameters, ℓ1 and ℓ2 with dimension of length. The evaluation of these parameters, however, has posed serious challenges, both experimentally and theoretically. In this work ab initio method is used to compute the... 

In this paper, the governing equations and boundary conditions of a functionally graded Euler-Bernoulli beam are developed based on the non-local theory of elasticity. Afterward, the free vibration is investigated and the effects of the axial load, the non-local parameter and the power index on the natural frequency of a hinged-hinged beam is assessed. The results indicate that the non-local parameter has a decreasing effect on the frequency while the power index has an increasing effect. It is also noted that the effect of the axial load is increasing too  

Till now, no mathematical model is presented to model the flow under sonic field be applied in fractured reservoirs. This will be more noticeable when we bear in mind that several reservoirs in Middle East region are fractured. In this work the effects of elastic waves on capillary trapping and mobility of Bingham plastic fluids in fractures have been investigated. Eventually, a model for predicting the influence range of the wave in fractured reservoirs is presented. The results of this study clarified that radiation of wave with low frequency and intensity extremely increases the flow rate and decreases the minimum pressure gradient required for flow of Bingham plastic fluids in fractured... 

This study presents the application of the Proposed Modified Reduced-Order Aerodynamics Modelling approach for aeroelastic analysis based on the boundary element method (BEM) as a novel approach. The used BEM has the capability to capture the thickness effect and geometric complexity of a general three-dimensional model. In this approach the reduced-order aerodynamic model is defined through the eigenvalue problem of unsteady flow based on the unknown wake singularities. Based on the used aerodynamic model an explicit algebraic form of the aeroelastic equations is derived that reduces computational efforts and complexity. This special feature enables us to determine the aeroelastic... 

In recent years, some numerical models have been proposed to investigate the effects of the elastic wave such as ultrasonic on fluid flow behavior in porous media. Nevertheless, none of these models are applicable to the fractured reservoirs, especially when the fluid is a Bingham plastic. In this work, the model proposed by P. P. Iassonov and I. A. Beresnev (2003) for flow under exposure of elastic wave in nonfractured porous media is considered and used for development of a new model of steady state flow of a Bingham plastic fluid in fractured reservoirs. The Kazemi's "block and fracture" model assuming negligible vertical permeability in blocks is considered for modeling. In addition,... 

Vertical vibration of structures due to strong near-field earthquakes could culminate in catastrophic consequences. In this article, the optimum patterns of two types of wave barriers with different geometry configurations, buried in the soil domain, are obtained in order to reduce the vertical acceleration of the top of a circular foundation placed on the soil surface. In order to look into the influence of various soil deposits, six soil deposits with diverse material properties and bedrock depths are examined. The topology optimization procedure for finding the optimum position of the wave barriers has been conducted using coupled finite element-genetic algorithm methodology. First, the... 

The scattering of in-plane P- and SV-waves by a multi-coated circular nanofiber with deformable interfaces is of interest. To this end, in the present work, after introducing two kinds of interface momenta defined as the derivative of the interface excess kinetic energy with respect to the average and relative velocities at the interface, we extend the elastostatic theory of Gurtin et al. (1998) on deformable interfaces to the elastodynamic theory and derive the interface equations of motion using Hamilton principle. The effects of the generalized interface properties including the interface inertial parameters and interface stiffness towards stretch and slip on the dynamic stress... 

Vertical vibration of structures due to strong near-field earthquakes could culminate in catastrophic consequences. In this article, the optimum patterns of two types of wave barriers with different geometry configurations, buried in the soil domain, are obtained in order to reduce the vertical acceleration of the top of a circular foundation placed on the soil surface. In order to look into the influence of various soil deposits, six soil deposits with diverse material properties and bedrock depths are examined. The topology optimization procedure for finding the optimum position of the wave barriers has been conducted using coupled finite element-genetic algorithm methodology. First, the... 

A fully analytical solution of the classic coupled thermoelasticity problem in a rotating disk subjected to thermal and mechanical shock loads is presented. Axisymmetric thermal and mechanical boundary conditions are considered in general forms of arbitrary heat transfer and traction, respectively, at the inner and outer radii of the disk. To solve the governing system of equations, an analytical procedure based on the Fourier-Bessel transform is employed. Closed form formulations are presented for temperature and displacement fields. The results of the present formulations are in good agreement with the numerical results available in the literature. The radial distribution and time history... 

The controllable flaps and interceptors in planing crafts not only may reduce the resistance, but also could be designed to make a boat run at or near optimum attitude in various environments, which results in a reduction in both resistance and vertical motion in waves. Planing vessels suffer from porpoising instability and violent vertical motion at high forward speeds. The controllable flaps and interceptors can be used to control and reduce the vertical motion of planing crafts. In the present study, the impact of controlled interceptors on a planing craft seakeeping quality is investigated through application of experimental and theoretical methods. In the experimental part of the study,... 

This paper deals with the coupling flexural-torsional vibration analysis of a grid formed by two members. A mass-spring system is attached to the grid at the intersecting joint. The members of the grid are assumed to resist torsion as well as bending and shear. Moreover, the mechanical and geometrical properties of each member are different. In order to analyze the problem, a closed-form solution is obtained. In doing so, the governing differential equations of the system along with the pertinent boundary and compatibility conditions of the system are introduced. Then, the frequency parameters of the mechanical system under study are derived and given for the first five modes of vibration.... 

A new resonance phenomenon is discussed and demonstrated by experiment in a dual-polarization cavity. The resonance is formed by waves bouncing between two anisotropic metasurfaces placed at the cavity ends. The simple metasurfaces are designed to preserve the handedness of circularly polarized waves upon reflection. The standing waves resulting from such reflections do not have nodes and antinodes. A theoretical solution to the resonance condition is discussed, both for plane-waves and equivalent guided waves. The concept is then experimentally applied to dual-mode guided waves, demonstrating a very short cavity at X-band. This brings new possibilities for resonator design and can...