Table of Content

01 October 2015, Volume 36 Issue 10

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Articles

Unsteady mixed convection flow over stretching sheet in presence of chemical reaction and heat generation or absorption with non-uniform slot suction or injection

R. RAVINDRAN, N. SAMYUKTHA

2015, 36(10):  1253-1272.  doi:10.1007/s10483-015-1982-9

Abstract ( 749 )   HTML   PDF (532KB) ( 476 )  

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The article examines the unsteady mixed convection flow over a vertical stretching sheet in the presence of chemical reaction and heat generation or absorption with non-uniform mass transfer. The unsteadiness is caused by the time dependent free stream velocity varying arbitrarily with time. Non-similar solutions are obtained numerically by solving the coupled nonlinear partial differential equations using the quasilinearization technique in combination with an implicit finite difference scheme. To reveal the tendency of the solutions, typical results for the local skin friction coefficient and the local Nusselt and Sherwood numbers are presented for different values of parameters. The effects of various parameters on the velocity, temperature, and concentration distributions are discussed here. The present numerical results are compared with the previously published work, and the results are found to be in excellent agreement.

Effect of slip velocity on Casson thin film flow and heat transfer due to unsteady stretching sheet in presence of variable heat flux and viscous dissipation

A. M. MEGAHED

2015, 36(10):  1273-1284.  doi:10.1007/s10483-015-1983-9

Abstract ( 648 )   HTML   PDF (315KB) ( 406 )  

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The aim of the present paper is to study flow and heat transfer characteristics of a viscous Casson thin film flow over an unsteady stretching sheet subject to variable heat flux in the presence of slip velocity condition and viscous dissipation. The governing equations are partial differential equations. They are reduced to a set of highly nonlinear ordinary differential equations by suitable similarity transformations. The resulting similarity equations are solved numerically with a shooting method. Comparisons with previous works are made, and the results are found to be in excellent agreement. In the present work, the effects of the unsteadiness parameter, the Casson parameter, the Eckert number, the slip velocity parameter, and the Prandtl number on flow and heat transfer characteristics are discussed. Also, the local skin-friction coefficient and the local Nusselt number at the stretching sheet are computed and discussed.

Throughflow and g-jitter effects on binary fluid saturated porous medium

P. KIRAN

2015, 36(10):  1285-1304.  doi:10.1007/s10483-015-1984-9

Abstract ( 965 )   HTML   PDF (647KB) ( 7819 )  

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A non-autonomous complex Ginzburg-Landau equation (CGLE) for the finite amplitude of convection is derived, and a method is presented here to determine the amplitude of this convection with a weakly nonlinear thermal instability for an oscillatory mode under throughflow and gravity modulation. Only infinitesimal disturbances are considered. The disturbances in velocity, temperature, and solutal fields are treated by a perturbation expansion in powers of the amplitude of the applied gravity field. Throughflow can stabilize or destabilize the system for stress free and isothermal boundary conditions. The Nusselt and Sherwood numbers are obtained numerically to present the results of heat and mass transfer. It is found that throughflow and gravity modulation can be used alternately to heat and mass transfer. Further, oscillatory flow, rather than stationary flow, enhances heat and mass transfer.

General investigation for longitudinal wave propagation under magnetic field effect via nonlocal elasticity

U. GÜVEN

2015, 36(10):  1305-1318.  doi:10.1007/s10483-015-1985-9

Abstract ( 529 )   HTML   PDF (274KB) ( 300 )  

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In this paper, the propagation of longitudinal stress waves under a longitudinal magnetic field is addressed using a unified nonlocal elasticity model with two scale coefficients. The analysis of wave motion is mainly based on the Love rod model. The effect of shear is also taken into account in the framework of Bishop's correction. This analysis shows that the classical theory is not sufficient for this subject. However, this unified nonlocal elasticity model solely used in the present study reflects in a manner fairly realistic for the effect of the longitudinal magnetic field on the longitudinal wave propagation.

Note on characteristics of homogeneous-heterogeneous reaction in flow of Jeffrey fluid

M. FAROOQ, A. ALSAEDI, T. HAYAT

2015, 36(10):  1319-1328.  doi:10.1007/s10483-015-1981-9

Abstract ( 550 )   HTML   PDF (223KB) ( 274 )  

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This letter describes the characteristics of homogeneous-heterogeneous reaction in the boundary layer flow of a Jeffrey fluid due to an impermeable horizontal stretching sheet. An analysis is carried out through the similar values of reactant and auto catalyst diffusion coefficients. Heat released by the reaction is not accounted. The exact solution for the flow of the Jeffrey fluid is constructed. The series solution for the concentration equation is derived. The velocity and concentration fields reflecting the impact of interesting parameters are plotted and examined.

Design optimization of unsteady airfoils with continuous adjoint method

Liang FANG, Xiaowei LI

2015, 36(10):  1329-1336.  doi:10.1007/s10483-015-2010-9

Abstract ( 511 )   HTML   PDF (510KB) ( 187 )  

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In this paper, a new unsteady aerodynamic design method is presented based on the Navier-Stokes equations and a continuous adjoint approach. A basic framework of time-accurate unsteady airfoil optimization which adopts time-averaged aerodynamic coefficients as objective functions is presented. The time-accurate continuous adjoint equation and its boundary conditions are derived. The flow field and the adjoint equation are simulated numerically by the finite volume method (FVM). Feasibility and accuracy of the approach are perfectly validated by the design optimization results of the plunging NACA0012 airfoil.

Optimal bounded control for maximizing reliability of Duhem hysteretic systems

Ming XU, Xiaoling JIN, Yong WANG, Zhilong HUANG

2015, 36(10):  1337-1346.  doi:10.1007/s10483-015-1986-9

Abstract ( 501 )   HTML   PDF (309KB) ( 219 )  

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The optimal bounded control of stochastic-excited systems with Duhem hysteretic components for maximizing system reliability is investigated. The Duhem hysteretic force is transformed to energy-depending damping and stiffness by the energy dissipation balance technique. The controlled system is transformed to the equivalent nonhysteretic system. Stochastic averaging is then implemented to obtain the Itô stochastic equation associated with the total energy of the vibrating system, appropriate for evaluating system responses. Dynamical programming equations for maximizing system reliability are formulated by the dynamical programming principle. The optimal bounded control is derived from the maximization condition in the dynamical programming equation. Finally, the conditional reliability function and mean time of first-passage failure of the optimal Duhem systems are numerically solved from the Kolmogorov equations. The proposed procedure is illustrated with a representative example.

Determination of elastic and plastic mechanical properties of dentin based on experimental and numerical studies

Xingguo LI, Bingbing AN, Dongsheng ZHANG

2015, 36(10):  1347-1358.  doi:10.1007/s10483-015-1987-9

Abstract ( 587 )   HTML   PDF (630KB) ( 260 )  

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The aim of this study is to investigate the change of mechanical properties of human dentin due to aging and spatial variation. Sections of coronal dentin are made from human molars in three groups: young, mid-aged, and old patients. A nanoindentation test is conducted from regions near the pulp to the dentin-enamel junction (DEJ) to evaluate the load-depth indentation response and determine Young's modulus and hardness. Based on the loading and unloading load-displacement curves in nanoindentation, a numerical model of plastic damage is used to study the plastic and the damage behaviors and the contribution to the degradation in the unloading stiffness. The experimental results show that Young's modulus of the inner dentin is significantly lower than that of outer dentin in each age group. Compared with the young dentin, the old dentin has greater hardness and Young's modulus with similar spatial variations. The magnitudes of the yield strength and the damage variable are also affected by aging and vary with spatial locations. In the same age group, the yield strength in inner dentin is lower than those in middle and outer dentin, more damage occurs with similar spatial variations, and the yield strength of young dentin is generally lower and causes more damage compared with those in both the mid-aged and old groups.

Relations between cubic equation, stress tensor decomposition, and von Mises yield criterion

Haoyuan GUO, Liyuan ZHANG, YajunYIN, Yongxin GAO

2015, 36(10):  1359-1370.  doi:10.1007/s10483-015-1988-9

Abstract ( 624 )   HTML   PDF (226KB) ( 322 )  

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Inspired by Cardano's method for solving cubic scalar equations, the additive decomposition of spherical/deviatoric tensor (DSDT) is revisited from a new viewpoint. This decomposition simplifies the cubic tensor equation, decouples the spherical/deviatoric strain energy density, and lays the foundation for the von Mises yield criterion. Besides, it is verified that under the precondition of energy decoupling and the simplest form, the DSDT is the only possible form of the additive decomposition with physical meanings.

Convergence analysis on Browder-Tikhonov regularization for second-order evolution hemivariational inequality

Yibin XIAO, Guoji TANG, Xianjun LONG, Nanjing HUANG

2015, 36(10):  1371-1382.  doi:10.1007/s10483-015-1989-9

Abstract ( 623 )   HTML   PDF (175KB) ( 267 )  

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This paper studies the Browder-Tikhonov regularization of a second-order evolution hemivariational inequality (SOEHVI) with non-coercive operators. With duality mapping, the regularized formulations and a derived first-order evolution hemivariational inequality (FOEHVI) for the problem considered are presented. By applying the Browder-Tikhonov regularization method to the derived FOEHVI, a sequence of regularized solutions to the regularized SOEHVI is constructed, and the strong convergence of the whole sequence of regularized solutions to a solution to the problem is proved.