Peristaltic transport of viscoelastic bio-fluids with fractional derivative models

Peristaltic flow of viscoelastic fluid through a uniform channel is considered under the assumptions of long wavelength and low Reynolds number. The fractional Oldroyd-B constitutive viscoelastic law is employed. Based on models for peristaltic viscoelastic flows given in a series of papers by Tripathi et al. (e.g. Appl Math Comput. 215 (2010) 3645–3654; Math Biosci. 233 (2011) 90–97) we present a detailed analytical and numerical study of the evolution in time of the pressure gradient across one wavelength. An analytical expression for the pressure gradient is obtained in terms of Mittag-Leffler functions and its behavior is analyzed. For numerical computation the fractional Adams method is used. The influence of the different material parameters is discussed, as well as constraints on the parameters under which the model is physically meaningful

A Compact Alternating Direction Implicit Scheme for Two-Dimensional Fractional Oldroyd-B Fluids

[Vasileva Daniela; Василева Даниела]; [Bazhlekov Ivan; Бажлеков Иван]; [Bazhlekova Emilia; Бажлекова Емилия]The two-dimensional Rayleigh-Stokes problem for a generalized Oldroyd-B fluid is considered in the present work. The fractional time derivatives are discretized using L1 and L2 approximations. A fourth order compact approximation is implemented for the space derivatives and two variants of an alternating direction implicit finite difference scheme are numerically investigated. 2010 Mathematics Subject Classification: 26A33, 35R11, 65M06, 65M22, 74D05

Transition from Diffusion to Wave Propagation in Fractional Jeffreys-Type Heat Conduction Equation

The heat conduction equation with a fractional Jeffreys-type constitutive law is studied. Depending on the value of a characteristic parameter, two fundamentally different types of behavior are established: diffusion regime and propagation regime. In the first case, the considered equation is a generalized diffusion equation, while in the second it is a generalized wave equation. The corresponding memory kernels are expressed in both cases in terms of Mittag–Leffler functions. Explicit representations for the one-dimensional fundamental solution and the mean squared displacement are provided and analyzed analytically and numerically. The one-dimensional fundamental solution is shown to be a spatial probability density function evolving in time, which is unimodal in the diffusion regime and bimodal in the propagation regime. The multi-dimensional fundamental solutions are probability densities only in the diffusion case, while in the propagation case they can have negative values. In addition, two different types of subordination principles are formulated for the two regimes. The Bernstein functions technique is extensively employed in the theoretical proofs

Stokes’ First Problem for Viscoelastic Fluids with a Fractional Maxwell Model

Stokes’ first problem for a class of viscoelastic fluids with the generalized fractional Maxwell constitutive model is considered. The constitutive equation is obtained from the classical Maxwell stress–strain relation by substituting the first-order derivatives of stress and strain by derivatives of non-integer orders in the interval ( 0 , 1 ] . Explicit integral representation of the solution is derived and some of its characteristics are discussed: non-negativity and monotonicity, asymptotic behavior, analyticity, finite/infinite propagation speed, and absence of wave front. To illustrate analytical findings, numerical results for different values of the parameters are presented

Nonsingular boundary integral method for deformable drops in viscous flows

A three-dimensional boundary integral method for deformable drops in viscous flows at low Reynolds numbers is presented. The method is based on a new nonsingular contour-integral representation of the single and double layers of the free-space Green's function. The contour integration overcomes the main difficulty with boundary-integral calculations: the singularities of the kernels. It also improves the accuracy of the calculations as well as the numerical stability. A new element of the presented method is also a higher-order interface approximation, which improves the accuracy of the interface-to-interface distance calculations and in this way makes simulations of polydispersed foam dynamics possible. Moreover, a multiple time-step integration scheme, which improves the numerical stability and thus the performance of the method, is introduced. To demonstrate the advantages of the method presented here, a number of challenging flow problems is considered: drop deformation and breakup at high viscosity ratios for zero and finite surface tension; drop-to-drop interaction in close approach, including film formation and its drainage; and formation of a foam drop and its deformation in simple shear flow, including all structural and dynamic elements of polydispersed foams

Spreading of a wetting film under the action of van der Waals forces

The profiles of a spreading wetting film are computed using a variable grid implicit scheme. The form of Tanner's law is deduced from the scaling, and the dependence of its coefficient on ratio of the van der Waals to the capillary length and on the inclination angle is determined