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Aerodynamic Instability Modeling of a High Speed Centrifugal Compressor
, M.Sc. Thesis Sharif University of Technology ; Ghorbanian, Kaveh (Supervisor)
Abstract
The present thesis investigates the surge phenomenon of high speed centrifugal compressors. Surge is a highly undesired condition and may cause severe damage to the machine and thus the plant. Traditionally, surge is avoided via a surge avoidance scheme wih recycle valve in discharge at the most common approach. A one dimensional technique is developed where the Greitzer lumped parameter model along with the Gravdahl one dimensional model is considered as the basis. Shaft dynamics, volume dynamics, losses, energy transfer and time lag are imbedded in the present model to improve the prediction of the compressor characteristics beyond the stability region. On the other hand, in order to...
Effects of surface elasticity on 3D micromechanical modeling of short fiber nanocomposites
, Article 2012 3rd International Conference on Manufacturing Science and Technology, ICMST 2012, New Delhi, 18 August 2012 through 19 August 2012 ; Volume 622 , 2013 , Pages 975-979 ; 10226680 (ISSN) ; 9783037855638 (ISBN) ; Naghdabadi, R ; Sharif University of Technology
2013
Abstract
Recent studies have shown that the surface/interface free energy plays an important role in the effective mechanical properties of solids with nanosized inhomogeneity. In the present study, an analytical model is developed for 3D axisymmetric analysis of short fiber nanocomposites including the fiber end region, subjected to an applied axial load considering surface effects. Closed form expressions are obtained for 3D stress filed in the fiber and matrix. Moreover, performing numerical examples, it is shown that the elastic stress field is size dependent in both the fiber and matrix especially for fiber radii less than 50 nm
Investigation of Mechanical Behavior of Short Carbon Nanotubes Reinforced Metal Matrix Nanocomposites Using Surface Elasticity Theory
, M.Sc. Thesis Sharif University of Technology ; Naghdabadi, Reza (Supervisor)
Abstract
In recent years, carbon nanotubes have been the focus of considerable researches. Numerous investigators have reported remarkable physical and mechanical properties for this new form of carbon. In particular, the exceptional mechanical properties of carbon nanotubes, combined with their low density, offer scope for the development of nanotube reinforced composite materials. The potential for nanocomposites reinforced with carbon tubes having extraordinary specific stiffness and strength represent tremendous opportunity for application in this century and recently metal matrix type of these nanocomposites, due to their advantages, have received great attention. Classical theories of...
Decentralized adaptive control of large-scale affine and nonaffine nonlinear systems
, Article IEEE Transactions on Instrumentation and Measurement ; Volume 58, Issue 8 , 2009 , Pages 2459-2467 ; 00189456 (ISSN) ; Menhaj, M. B ; Karimi Ghartemani, M ; Saboori, I ; Sharif University of Technology
2009
Abstract
This paper presents a decentralized adaptive control design for a class of large-scale nonlinear systems with unknown subsystems. When the subsystems are modeled by affine equations, a direct adaptive controller is devised based on the Lyapunov theory, so that the stability of the closed-loop system is guaranteed by introducing a suitably driven adaptive rule. A neuro-based structure is proposed when the subsystems are nonaffine, and the stability analysis is also performed based on the Lyapunov theory. Moreover, the unknown interactions among the subsystems are considered as having a nonlinear function against the simple form considered for the affine case. The proposed controllers are...