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EN
In this paper, the steady two-dimensional stagnation-point flow of a viscoelastic Walters’ B’ fluid over a stretching surface is examined. It is assumed that the fluid impinges on the wall obliquely. Using similarity variables, the governing partial differential equations are transformed into a set of two non-dimensional ordinary differential equations. These equations are then solved numerically using the shooting method with a finite-difference technique.
EN
In this paper, we investigate the Dufour and Soret effects on MHD mixed convection of a chemically reacting fluid over a stretching surface in a porous medium with convective boundary condition. The similarity transformation is used to reduce the governing non-linear partial differential equations into ordinary differential equations. Then, they are solved analytically by using the homotopy analysis method (HAM) and are solved numerically by the Runge-Kutta fourth-order method. The analytical and numerical results for the velocity, temperature, concentration, skin friction, Nusselt number and Sherwood number are discussed.
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Content available remote A bi-phasic model for artificial replacement
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EN
Joint replacement is widely used for treatment when joints fail to support loads or normal functions due to some accidental force or diseases. The analytical models for artificial human knee joints introducing the concept of porous implants with bone in growth into the pores, may provide better implantation than using cement or rigid, plastic/metallic materials. The purpose of the present study is to determine theoretically the articular contact mechanics of an artificial knee joint containing biphasic cartilage layers under restricted motion during normal walking. The present work incorporates the effect of a viscoelastic fluid as a lubricant on the parameter related to the lubrication mechanism. It has been observed that the load carrying capacity increases with increasing values of viscoelastic parameters. The effect of an increase in the viscoelastic parameter of the lubricant in similar to that of an increase in concentration of hyaluronic acid molecules in the synovial fluid. This helps in sustaining the greater loads. Further, we also observe that as the slip velocity at the porous boundary increases, load carrying capacity decreases owing to the increased filtration of base fluid into the porous cartilage. Thus, the slip velocities existing at the porous boundary play on important role in the self-adjusting nature of the artificial joint.
EN
Boundary layer MHD flow of a viscoelastic fluid in a porous medium over a porous stretching sheet has been presented in this article. A typical choice of quadratic stretching of the boundary, having a quadratic part in velocity parallel to the boundary sheet and a linear mass flux in the velocity normal to the stretching sheet, constitutes the boundary conditions of the problem. The effect of various values of nondimensional physical parameters on streamline patterns and skin friction coefficient are discussed. Some of the important findings of the article are: (a) the flow is enhanced by the positive values of linear mass flux parameter and suppressed by the negative values of linear mass flux parameter; (b) the effect of permeability parameter is not significant when linear mass flux parameter takes zero or negative values; (c) the combined effect of reduction of the values of permeability parameter, Hartmann number and linear mass flux parameter is expected to reduce largely the values of skin friction coefficient.
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Content available remote Boundary layer viscoelastic fluid flow over an exponentially stretching sheet
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EN
In the present paper, a viscoelastic boundary layer fluid flow over an exponentially stretching continuous sheet has been examined. The flow is assumed to be generated solely by the application of two equal and opposite forces along the x-axis such that stretching of the boundary surface is of exponential order in x. Approximate analytical similarity solutions (zero and first order) of the highly non-linear boundary layer equation are obtained for the dimensionless stream function and velocity distribution function after transforming the boundary layer equation into Riccati type and solving that sequentially. The first-order solution is derived in the form of confluent hypergeometric Whittaker functions. The solutions are verified at the boundary sheet. These solutions (zero and first order) involve an exponential dependence of the similarity variable, the stretching velocity and the stream function on the axial coordinate. The accuracy of the analytical solutions is also verified by the numerical solutions obtained by employing the Runge-Kutta fourth order method with shooting. The effects of various physical parameters on the velocity profile and skin-friction coefficient are also discussed in this paper.
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Content available remote Tribology of stochastic phenomena on the hard tissue
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EN
The aim of this paper is to show analytical solutions of friction forces and the velocity component of viscoelastic nutrient fluid in the thin layer resting on the surface sample of tissue. Friction forces and stresses are caused by the perfusion in bioreactor. Stochastic Christensen model of rough surfaces of tissue sample is taking into account.
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Content available Metody pomiaru własności sprężystolepkich
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PL
Objawy sprężystolepkości płynu z reguły są szkodliwe w procesach technologicznych ze względu na generowanie dodatkowych naprężeń i związanych z nimi odkształceń, często obniżających jakość produktu. Te efekty mogą być zmniejszone przez odpowiedni dobór parametrów procesu technologicznego. Omówiono metody badania własności sprężystolepkich wykorzystujące przepływy ustalone (wiskozymetryczne), przepływy jednokierunkowe nieustalone i przepływy oscylacyjne. Przedstawiono test naprężeń normalnych, test pełzania, test relaksacyjny i badania oscylacyjne oraz wskazano, który z nich wybrać w celu uzyskania charakterystyki reologicznej płynu odpowiedniej dla danego procesu technologicznego.
EN
Manifestation of fluid viscoelasticity is usually a disadvantage in technological processes due to the generation of additional stresses and relevant deformations often decreasing product quality. These effects can be restricted via appropriate selection of technological process parameters. Testing methods of viscoelastic properties using steady-state (viscometry), one-directional unsteady-state and oscillatory flows are discussed. The creep, relaxation and normal stresses tests are presented. It was indicated which of these tests should be chosen to obtain the fluid rheological characteristics appropriate for a given technological process.
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Content available remote On the viscoelastic core of a line vortex embedded in a stagnation point flow
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EN
The viscoelastic core of a line vortex embedded in a radially inward axisymmetric stagnation point flow for a Maxwell fluid and an Oldroyd B fluid is considered. Velocity, vorticity and stress distributions are calculated and compared with those of the Newtonian fluid. It is found that there are pronounced effects of viscoelastic properties on these distributions with respect to those of the Newtonian fluid.
EN
The free convective magnetohydrodynamics (MHD) flow of a non-Newtonian fluid due to a semi-infinite vertical plate under the influence of radiation and viscous dissipation is investigated. The system of partial differential equations is derived and solved for the solutions of velocity and temperature profiles along with the Nusselt number and skin friction by using the perturbation technique. The related important dimensionless parameters of Eckert, Grashof, and Prandtl numbers, magnetic field, radiation and heat source are discussed and shown in graphs. Also, the Nusselt number and skin friction at the plate are obtained and presented in the tabular forms. Finally, the corresponding result of Newtonian fluid is obtained by setting viscoelastic parameter k1 = 0. It is worth mentioning that the obtained results coincide with the previously published results.
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Content available remote Simulation of the electrospinning process
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EN
The electrospinning process is modeled and the bending instability of a slender viscoelastic jet is simulated. This is accomplished by modifying the discrete bead model by Reneker et al. (2000). Specifically, the force due to surface tension is incorporated using the expression suggested by Kowalewski et al. (2005) (see Eq.(7)). The results obtained by the use of this modification seem to be in accord with the experimental observations reported in Reneker et al. (2000) (Fig.2). An attempt is also made to simulate the effect of a secondary electric field which could be used to control the electrospinning process and whipping instability. It is observed that the external secondary field considered here, unwinds the jet spirals, reduces the whipping instability and increases the tension in the fiber.
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EN
A mathematical analysis on the boundary layer MHD flow of a viscoelastic fluid over a porous stretching sheet has been presented in this paper. A typical choice of quadratic stretching of the boundary, which generates a quadratic part in velocity parallel to the boundary sheet and a linear mass flux part in the velocity normal to the stretching sheet, has been assumed. Streamline patterns and skin friction coefficients are discussed for various values of nondimensional physical parameters. The result of the analysis reveals that the combined effect of the non-dimensional viscoelastic parameter and Hartmann number is to increase significantly the values of skin friction coefficient, whereas, the combined effect of the nondimensional constant mass flux parameter and modified linear mass flux parameter is to reduce largely the values of skin friction coefficient. For positive values of the linear mass flux parameter the stream functions attain a positive slope away from the origin while they attain a negative slope everywhere for zero value. The limiting cases of our results yield the results of Andersson (1992) and Kumaran and Ramanaiah (1996).
EN
In the present paper, a viscoelastic boundary layer flow and heat transfer over an exponentially stretching continuous sheet in the presence of a heat source/sink has been examined. Loss of energy due to viscous dissipation of the non-Newtonian fluid has been taken into account in this study. Approximate analytical local similar solutions of the highly non-linear momentum equation are obtained for velocity distribution by transforming the equation into Riccati-type and then solving this sequentially. Accuracy of the zero-order analytical solutions for the stream function and velocity are verified by numerical solutions obtained by employing the Runge-Kutta fourth order method involving shooting. Similarity solutions of the temperature equation for non-isothermal boundary conditions are obtained in the form of confluent hypergeometric functions. The effect of various physical parameters on the local skin-friction coefficient and heat transfer characteristics are discussed in detail. It is seen that the rate of heat transfer from the stretching sheet to the fluid can be controlled by suitably choosing the values of the Prandtl number Pr and local Eckert number E, local viscioelastic parameter k1 and local heat source/ sink parameter β.
EN
The influence of elasticity and magnetic field on pulastile viscoelastic flow and heat transfer in a circular pipe is examined. By means of the perturbation method of the velocity and temperature fields, the analytical solution of the velocity and temperature are obtained in terms of Bessel and hypergeometric functions .The discharge and the rate of heat transfer are determined through the course of discussions.
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