A full 3-D material stability analysis of a classical elasto-plastic medium through a linear perturbation approach

2006 ◽  
Vol 34 (2) ◽  
pp. 85-96
Author(s):  
N. G. Diouta ◽  
I. Shahrour
Keyword(s):  
Stability Analysis ◽  
Linear Perturbation ◽  
Perturbation Approach ◽  
Plastic Medium ◽  
Material Stability

Linear stability analysis of finite hydrodynamic journal bearing under turbulent lubrication with coupled-stress fluid

2016 ◽  
Vol 68 (3) ◽  
pp. 386-391 ◽  
Author(s):  
Abhishek Ghosh ◽  
Sisir Kumar Guha
Keyword(s):  
Stability Analysis ◽  
Newtonian Fluid ◽  
High Speed ◽  
Journal Bearing ◽  
Slenderness Ratio ◽  
Linear Perturbation ◽  
Content Type ◽  
Hydrodynamic Journal Bearing ◽  
The Stability ◽  
Coupled Stress

Purpose Several researchers have observed that to satisfy modern day’s need, it is essential to enhance the characteristics of journal bearing, which is used in numerous applications. Moreover, the use of Newtonian fluid as a lubricant is diminishing day by day, and the use of Non-Newtonian fluids is coming more into picture. Furthermore, if turbo-machinery applications are taken into account, then it can be seen that journal bearings are used for high speed applications as well. Thus, neglecting turbulent conditions may lead to erroneous results. Hence, this paper aims to present focuses on studying the stability characteristics of finite hydrodynamic journal bearing under turbulent coupled-stress lubrication. Design/methodology/approach First, the governing equation relevant to the problem is generated. Then, the dynamic analysis is carried out by linear perturbation technique, leading to three perturbed equations, which are again discretized by finite difference method. Finally, these discretized equations are solved with the help of Gauss-Seidel Iteration technique with successive over relaxation scheme. Consequently, the film response coefficients and the stability parameters are evaluated at different parametric conditions. Findings It has been concluded from the study that with increase in value of the coupled-stress parameter, the stability of the journal may increase. Whereas, with increase in Reynolds number, the stability of the journal decreases. On the other hand, stability increases with increasing values of slenderness ratio. Originality/value Researches have been performed to study the dynamic characteristics of journal bearing with non-Newtonian fluid as the lubricant. But in the class of non-Newtonian lubricants, the use of coupled-stress fluid has not yet been properly investigated. So, an attempt has been made to perform the stability analysis of bearings with coupled-stress fluid as the advanced lubricant.

scholarly journals Non-modal stability analysis of miscible viscous fingering with non-monotonic viscosity profiles

2018 ◽  
Vol 856 ◽  
pp. 552-579
Author(s):  
Tapan Kumar Hota ◽  
Manoranjan Mishra
Keyword(s):  
Stability Analysis ◽  
Viscous Fluid ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Physical Mechanism ◽  
Stable State ◽  
Viscous Fingering ◽  
Linear Perturbation ◽  
Optimal Perturbation ◽  
Nonlinear Simulations

A non-modal linear stability analysis (NMA) of the miscible viscous fingering in a porous medium is studied for a toy model of non-monotonic viscosity variation. The onset of instability and its physical mechanism are captured in terms of the singular values of the propagator matrix corresponding to the non-autonomous linear equations. We discuss two types of non-monotonic viscosity profiles, namely, with unfavourable (when a less viscous fluid displaces a high viscous fluid) and with favourable (when a more viscous fluid displaces a less viscous fluid) endpoint viscosities. A linear stability analysis yields instabilities for such viscosity variations. Using the optimal perturbation structure, we are able to show that an initially unconditional stable state becomes unstable corresponding to the most unstable initial disturbance. In addition, we also show that to understand the spatio-temporal evolution of the perturbations it is necessary to analyse the viscosity gradient with respect to the concentration and the location of the maximum concentration $c_{m}$. For the favourable endpoint viscosities, a weak transient instability is observed when the viscosity maximum moves close to the pure invading or defending fluid. This instability is attributed to an interplay between the sharp viscosity gradient and the favourable endpoint viscosity contrast. Further, the usefulness of the non-modal analysis demonstrating the physical mechanism of the quadruple structure of the perturbations from the optimal concentration disturbances is discussed. We demonstrate the dissimilarity between the quasi-steady-state approach and NMA in finding the correct perturbation structure and the onset, for both the favourable and unfavourable viscosity profiles. The correctness of the linear perturbation structure obtained from the non-modal stability analysis is validated through nonlinear simulations. We have found that the nonlinear simulations and NMA results are in good agreement. In summary, a non-monotonic variation of the viscosity of a miscible fluid pair is seen to have a larger influence on the onset of fingering instabilities than the corresponding Arrhenius type relationship.

An Eigenvalue Perturbation Approach to Stability Analysis, Part I: Eigenvalue Series of Matrix Operators

2010 ◽  
Vol 48 (8) ◽  
pp. 5564-5582 ◽  
Author(s):  
Jie Chen ◽  
Peilin Fu ◽  
Silviu-Iulian Niculescu ◽  
Zhihong Guan
Keyword(s):  
Stability Analysis ◽  
Perturbation Approach ◽  
Matrix Operators

Stability Analysis of Internal Model Based Gain Control System for Three-Level EDFA Model

2013 ◽  
Vol 339 ◽  
pp. 33-37
Author(s):  
Seong Ho Song ◽  
Chang Seop Kim ◽  
Jeom Keun Kim
Keyword(s):  
Control System ◽  
Stability Analysis ◽  
Singular Perturbation ◽  
Internal Model ◽  
Gain Control ◽  
Fiber Amplifier ◽  
Perturbation Approach ◽  
Optical Fiber Amplifier ◽  
Amplifier Gain ◽  
The Mathematical Model

In this paper, stability analysis of an optical fiber amplifier gain controller is presented. The mathematical model of an EDFA (Eribium-Doped Fiber Amplifier) control system is described by two-time scaled system and thus singular perturbation approach can be applied to the design and analysis of the control system. In order to handle the channel variations such as add/drop, we adopt an internal model. The performance of the control system is theoretically analyzed based on a novel singular-perturbation-like approach.

scholarly journals Material stability analysis of rock joints

2012 ◽  
Vol 37 (15) ◽  
pp. 2539-2562 ◽  
Author(s):  
Jérôme Duriez ◽  
Félix Darve ◽  
Frédéric-Victor Donzé ◽  
François Nicot
Keyword(s):  
Stability Analysis ◽  
Rock Joints ◽  
Material Stability
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