Ahmed M. Elaiw

Conditions for MPC Based Stabilization of Sampled-Data Nonlinear Systems Via Discrete-Time Approximations

This paper is devoted to the stabilization problem of nonlinear continuous- time systems with piecewise constant control functions. The controller is to be computed by the receding horizon control method based on discrete-time approximate models. Multi-rate — multistep control is considered and both measurement and computational delays are allowed. It is shown that the same family of controllers that stabilizes the approximate discrete-time model also practically stabilizes the exact discrete-time model of the plant. The conditions are formulated in terms of the original continuoustime models and the design parameters so that they should be veri.able in advance.

Effect of variable viscosity on vortex instability of non-Darcy free convection boundary layer flow adjacent to a non-isothermal horizontal surface in a porous medium

In this article, we study the effect of variable viscosity on the flow and vortex instability of non-Darcian free convection boundary layer flow on a horizontal surface in a saturated porous medium. The wall temperature is a power function of the distance from the origin. The variation of viscosity is expressed as an exponential function of temperature. The transformed boundary layer equations, which are developed using a non similar solution approach, are solved by means of a finite difference method. The analysis of the disturbance flow is based on linear stability theory. The local Nusselt number, critical Rayleigh number and the associated wave number at the onset of vortex instability are presented over a wide range of wall to ambient viscosity ratio parameters μ*= μw/μ∞. The variable viscosity effect is found to enhance the heat transfer rate and destabilize the flow for liquid heating, while the opposite trend is true for gas heating.

Effect of Variable Viscosity on Vortex Instability of Non-Darcy Mixed Convection Boundary Layer Flow Adjacent to a Nonisothermal Horizontal Surface in a Porous Medium

We study the effect of variable viscosity on the flow and vortex instability for non-Darcy mixed convection boundary layer flow on a nonisothermal horizontal plat surface in a saturated porous medium. The variation of viscosity is expressed as an exponential function of temperature. The analysis of the disturbance flow is based on linear stability theory. The base flow equations and the resulting eigenvalue problem are solved using finite difference schemes. It is found that the variable viscosity effect enhances the heat transfer rate and destabilizes the flow for liquid heating, while the opposite trend is true for gas heating.