Love wave propagation in heterogeneous micropolar media

The present paper framed to study the impact of heterogeneity on propagation of Love wave in a heterogeneous micropolar layer over an elastic inhomogeneous stratum, when both rigidity and density are assumed to vary linearly with depth. The equations of motion have been formulated separately for layer and half-space under suitable boundary conditions. Analytical solution for the dispersion equation has been obtained using method of separation of variables by means of the Airy function and Whittaker function. Some particular cases have also been investigated. Further, as a special case the velocity equation for isotropic layer over a homogeneous half-space coincides with the standard result of Love wave. Numerical calculations of frequency relation have been performed and depicted by means of graphs to exhibit the substantial impact of heterogeneity, micropolar parameters and wave number on the phase velocity of Love wave. The wave velocity is strongly influenced by these parameters.     

Acceleration waves and ellipticity in thermoelastic micropolar media

Acceleration waves in nonlinear thermoelastic micropolar media are considered. We establish the kinematic and dynamic compatibility relations for a singular surface of order 2 in the media. An analogy to the Fresnel–Hadamard–Duhem theorem and an expression for the acoustic tensor are derived. The condition for acceleration wave’s propagation is formulated as an algebraic spectral problem. It is shown that the condition coincides with the strong ellipticity of equilibrium equations. As an example, a quadratic form for the specific free energy is considered and the solutions of the corresponding spectral problem are presented.     

A micropolar mixture theory of multi-component porous media

A mixture theory is developed for multi-component micropolar porous media with a combination of the hybrid mixture theory and the micropolar continuum theory. The system is modeled as multi-component micropolar elastic solids saturated with multi- component micropolar viscous fluids. Balance equations are given through the mixture theory. Constitutive equations are developed based on the second law of thermodynamics and constitutive assumptions. Taking account of compressibility of solid phases, the volume fraction of fluid as an independent state variable is introduced in the free energy function, and the dynamic compatibility condition is obtained to restrict the change of pressure difference on the solid-fluid interface. The constructed constitutive equations are used to close the field equations. The linear field equations are obtained using a linearization procedure, and the micropolar thermo-hydro-mechanical component transport model is established. This model can be applied to practical problems, such as contaminant, drug, and pesticide transport. When the proposed model is supposed to be porous media, and both fluid and solid are single-component, it will almost agree with Eringen＇s model.     

Asymptotic partition of energy in micropolar mixture theory of porous media

The aim of this paper is to study the asymptotic partition of the energy associated with the solution of the initial-boundary value problem who describes the behavior of binary homogeneous micropolar mixtures of an isotropic micropolar elastic solid with an incompressible micropolar viscous fluid. Some Lagrange-Brun identities are established. Using the Cesáro means of various parts of total energy, the relations that describe the asymptotic behavior of mean energies are established. The author acknowledges support from the Romanian Ministry of Education and Research through CEEX program, contract CERES-2-CEx06-11-12/25.07.2006.     

Continuum theory of dislocations and disclinations in nonlinearly elastic micropolar media

A nonlinear theory of continuously distributed dislocation and disclination type defects in elastic media with intrinsic rotational degrees of freedom and couple stresses is proposed. The mediumstrains are assumed to be finite. The solving equations of the continuum theory of defects are obtained by passing to the limit from a discrete set of isolated dislocations and disclinations to their continuous distribution. The notions of dislocation and disclination densities in a micropolar body under large deformations are introduced. Incompatibility equations are obtained and a boundaryvalue problem of equilibriumis posed for an elastic micropolar body with a given density of distributed defects. A nonlinear problem of determining the intrinsic stresses in a hollow circular cylinder due to a given distribution of disclinations is solved.     

Interfacial imperfection on reflection and transmission of plane waves in anisotropic micropolar media

This study is concerned with the reflection and transmission of plane waves at an imperfectly bonded interface between two orthotropic micropolar elastic half-spaces with different elastic and micropolar properties. There exist three types of coupled waves in xy-plane. The reflection and transmission coefficients of quasi-longitudinal (QLD) wave, quasi-coupled transverse microrotational (QCTM) wave and quasi-coupled transverse displacement (QCTD) wave have been derived for different incidence waves and deduced for normal force stiffness, transverse force stiffness, transverse couple stiffness and perfect bonding. The numerical values of modules of the reflection and transmission coefficients are presented graphically with the angle of incidence for orthotropic micropolar medium (MOS) and isotropic micrpolar medium (MIS). Some particular cases of interest have been deduced from the present investigation.     

A micropolar formulation of the Desai hierarchical model for elastoplastic porous media

In this contribution, the Desai hierarchical model is extended to the case of 3D elasto-plastic two-phase micropolar continuum. An unconditionally stable implicit Euler backward algorithm for integration of the constitutive relations is developed and presented in detail. The regularizing effect of the introduction of a length parameter to the classical Desai model is demonstrated by means of several case studies of single phase and two-phase porous media.     

Wave propagation at interface of heat conducting micropolar solid and fluid media

The present investigation is concerned with the wave propagation at an interface of a micropolar generalized thermoelastic solid half space and a heat conducting micropolar fluid half space. Reflection and transmission phenomena of plane waves are investigated, which impinge obliquely at the plane interface between a micropolar generalized thermoelastic solid half space and a heat conducting micropolar fluid half space.The incident wave is assumed to be striking at the interface after propagating through the micropolar generalized thermoelastic solid. The amplitude ratios of various reflected and transmitted waves are obtained in a closed form. It is found that they are a function of the angle of incidence and frequency and are affected by the elastic properties of the media. Micropolarity and thermal relaxation effects are shown on the amplitude ratios for a specific model. The results of some earlier literatures are also deduced from the present investigation.     

The question of the uniform-pressure condition in bubble dynamics

Spherical gas bubbles which oscillate radially under the action of an acoustic field in a fluid are considered. It is shown that the results of [1] in which the problem was solved in the complete formulation (with the use of the momentum equation for the gas) are inconsistent. In [1], the pressure in the bubble was not assumed to be uniform but some inaccuracies were made.     

ONSET CONDITION OF STRAIN LOCALIZATION IN MATRIX OF SATURATED POROUS MEDIA

Introduction Strainlocalizationofgeomaterialsisoneofmostpopularfailuretypesinnature,which canbeshowedaslandslidesandmudflowsinmountainousareasunderincessantorheavy raining,especiallythevegetationisseverelydamagedbywoodsharvest;pipingeffect,a typeoflocalfa…     

Propagation dynamics of tripole breathers in nonlocal nonlinear media

Nonlinear Dynamics - We demonstrate the propagation dynamics of optical breathers in nonlinear media with a spatial nonlocality, which is governed by the nonlocal nonlinear Schrödinger...     

The computer simulations of polymer dynamics in porous media

We designed and developed a simple model of polymer chains. Three types of model chains with different internal macromolecular architecture were studied: linear, star-branched with f=3 arms of equal length and rings. The chains consisted of identical united atoms (segments) and were restricted to a simple cubic lattice with the excluded volume interactions only (the athermal system). The macromolecules were confined between two parallel impenetrable walls with a set of irregular obstacles that can be treated as a crude model of porous media. The properties of the model studied were determined by the Monte Carlo simulations. A Metropolis-like sampling algorithm with local changes of chains’ conformation was used. The short- and long-time dynamic properties of the model system were studied. The differences in the mobility of chains and their fragments for different internal polymer architectures were shown and discussed. The possible mechanisms of chain’s motion were discussed.This paper was presented at the 2nd Annual European Rheology Conference (AERC) held on April 21–23, 2005 in Grenoble, France.     

Electroosmotic oscillatory flow of micropolar fluid in microchannels: application to dynamics of blood flow in microfluidic devices

The electroosmotic flow of a micropolar fluid in a microchannel bounded by two parallel porous plates undergoing periodic vibration is studied. The equations for conservation of linear and angular momentums and Gauss' s law of charge distribution are solved within the framework of the Debye-H¨uckel approximation. The fluid velocity and microrotation are assumed to depend linearly on the Reynolds number. The study shows that the amplitude of microrotation is highly sensitive to the changes in the magnitude of the suction velocity and the width of the microchannel. An increase in the micropolar parameter gives rise to a decrease in the amplitude of microrotation. Numerical estimates reveal that the microrotation of the suspended microelements in blood also plays an important role in controlling the electro-osmotically actuated flow dynamics in microbio-fluidic devices.     

Peculiarities of wave dynamics in media with oscillating inclusions

The article is concerned with mathematical models for media with oscillating inclusions. These models consist of mutually connected equations, one of which is the wave equation for carrying medium and others are equations of motion for partial oscillators. To close these models, we use cubic and nonlocal equations of state for the carrying medium. Travelling wave solutions to these models are studied in detail. Using qualitative analysis methods, the phase space is shown to contain periodic, homo- and heteroclinic trajectories. Moreover, in the case of nonlocal models we observe the creation of quasiperiodic and chaotic regimes. Bifurcations of localized regimes are studied via the Poincaré section technique.     

Isotropic hardening in micropolar plasticity

Experimental evidence for length scale effects in plasticity has been provided, e.g., by Fleck et al. (Acta Metall. Mater. 42:475–487, 1994). Results from torsional loadings on copper wires, when appropriately displayed, indicated that, for the same shear at the outer radius, the normalized torque increased with decreasing specimen radius. Modeling of the constitutive behavior in the framework of micropolar plasticity is a possibility to account for length scale effects. The present paper is concerned with this possibility and deals with the theory developed by Grammenoudis and Tsakmakis (Contin. Mech. Thermodyn. 13:325–363, 2001; Int. J. Numer. Methods Eng. 62:1691–1720, 2005; Proc. R. Soc. 461:189–205, 2005). Both isotropic and kinematic hardening are present in that theory, with isotropic hardening being captured in a unified manner. Here, we discuss isotropic hardening composed of two parts, responsible for strain and gradient effects, respectively.     

Heat-conducting micropolar fluids

Summary In this paper heat-conducting micropolar fluids are introduced as an extension of the theory of micropolar fluids. Constitutive equations appropriate to describe the thermal and mechanical response of micropolar fluids are constructed. The heat conduction equation is derived and the field equations are obtained. The solution to the problem ofPoiseuille flow through a channel with flat walls is given.

---

Zusammenfassung In dieser Arbeit werden wärmeleitende mikropolare Flüssigkeiten als Erweiterung der Theorie mikropolarer Flüssigkeiten eingeführt. Es werden geeignete Zustandsgleichungen zur Beschreibung der thermischen und mechanischen Empfindlichkeit mikropolarer Flüssigkeiten abgeleitet. Die Wärmeleitungsgleichung und die Feldgleichungen werden ermittelt. Für das Problem derPoiseuille-Strömung durch einen Kanal mit glatten Wänden wird die Lösung angegeben.

     

Experimental studies of model porous media fluid dynamics

The three-dimensional, steady flow velocity components of a viscous, incompressible, Newtonian fluid in model porous media were measured. The model porous geometries were constructed from 3 mm glass rods. A laser Doppler anemometer was used to measure two of the velocity components and the third was calculated by integrating the continuity equation. The effects of viscous drag, inertial flow fields and eddy losses in the model were studied. The results showed that the measured flow was laminar and stable such that micromixing of the fluid was absent. Inertial flow effects were absent due to high viscous drag coefficients.