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Trace anomaly and backreaction of the dynamical Casimir effect
, Article General Relativity and Gravitation ; Volume 35, Issue 12 , 2003 , Pages 2279-2286 ; 00017701 (ISSN) ; Sharif University of Technology
2003
Abstract
The Casimir energy for massless scalar field which satisfies periodic boundary conditions in two-dimensional domain wall background is calculated by making use of general properties of renormalized stress-tensor. The line element of domain wall is time dependent, the trace anomaly which is the nonvanishing Tμμ for a conformally invariant field after renormalization, represent the back reaction of the dynamical Casimir effect
General derivations for conjugate strains of eshelby-like stress tensors
, Article Proceedings of the 7th Biennial Conference on Engineering Systems Design and Analysis - 2004, Manchester, 19 July 2004 through 22 July 2004 ; Volume 1 , 2004 , Pages 353-356 ; 0791841731 (ISBN); 9780791841730 (ISBN) ; Sheshmani, A ; Naghdabadi, R ; Sharif University of Technology
American Society of Mechanical Engineers
2004
Abstract
In this paper, a general type of Eshelby-like stress tensor is defined which is based on the right stretch tensor and is equal to the product of a general class of strain and the corresponding conjugate stress tensor. The Eshelby-like stress tensor depending on the fact that from which side the stress tensor is multiplied by, is categorized into the right-weighted and left-weighted ones. General relations for conjugate strains of Eshelby-like stress tensors are investigated using the method, based on the definition of energy conjugacy and Hill's principal axis method
Holography of Asymptotically Flat Spacetimes Using BMS/GCA Correspondence
, M.Sc. Thesis Sharif University of Technology ; Arfaei, Hessamaddin (Supervisor) ; Fareghbal, Reza (Co-Advisor)
Abstract
According to the AdS/CFT correspondance,Gravity in an asymptotically AdS spacetimes has a conformal field theory dual. One of the perplexing concepts in theoretical physics is obtaining a comprehensive understanding of holography. To this end, it is of interest to explore whether holography exists beyond the known example of the AdS/CFT correspondence and for spacetimes other than the AdS. asymptotically flat spacetimes are of great theoretical importance.A correspondence has recentlay been proposed,which is between asymptotically flat spacetimes and a field theory with Galilean conformal symmerty and it is known as BMS/GCA correspondance.In this thsis,we have reviewed this correspondence...
Intrinsic expressions for arbitrary stress tensors conjugate to general strain tensors
, Article Scientia Iranica ; Volume 14, Issue 5 , 2007 , Pages 486-493 ; 10263098 (ISSN) ; Naghdabadi, R ; Asghari, M ; Sharif University of Technology
Sharif University of Technology
2007
Abstract
In this paper, a unified explicit tensorial relation is sought between two stress tensors conjugate to arbitrary and general Hill strains. The approach used for deriving the tensorial relation is based on the eigenprojection method. The result is, indeed, a generalization of the relations that were derived by Farahani and Naghadabadi [1] in 2003 from a component to intrinsic form. The result is unified in the sense that it is valid for all cases of distinct and coalescent principal stretches. Also, in the case of three dimensional Euclidean inner product space, using the derived unified relation, some expressions for the conjugate stress tensors are presented. © Sharif University of...
Basis-free relations for conjugate strains of eshelby-like stress tensors
, Article Mechanics of Materials ; Volume 39, Issue 7 , 2007 , Pages 637-642 ; 01676636 (ISSN) ; Naghdabadi, R ; Arghavani, J ; Asghari, M ; Sharif University of Technology
2007
Abstract
In this paper, a general class of Eshelby-like or weighted stress tensors based on the right stretch tensor is defined as the product of a general type of Lagrangian stress tensor and a class of stretch measure. In addition, basis free relations for conjugate strains of Eshelby-like stress tensors are investigated, which are based on Hill's definition of energy conjugacy. The equations for strain tensors conjugate to Eshelby-like stress tensors are generally determined, but the case in which the conjugate strains are coaxial with the right stretch tensor is mostly investigated. © 2006 Elsevier Ltd. All rights reserved
A study on a grade-one type of hypo-elastic models
, Article ASME 2014 12th Biennial Conference on Engineering Systems Design and Analysis, ESDA 2014 ; Vol. 1 , 2014 ; Asghari, M ; Sharif University of Technology
Abstract
In Hypo-elastic constitutive models an objective rate of the Cauchy stress tensor is expressed in terms of the current state of the stress and the deformation rate tensor D in a way that the dependency on the latter is a homogeneously linear one. In this work, a type of grade-one hypo-elastic models (i.e. models with linear dependency of the hypo-elasticity tensor on the stress) is considered for isotropic materials based on the objective corotational rates of stress. A positive real parameter denoted by n is involved in the considered type. Different values can be selected for this parameter, each selection leads to a specific model within the class of grade-one hypo-elasticity. The spin of...
Basis free expressions for the stress rate of isotropic elastic materials in the cases of coalescent principal stretches
, Article International Journal of Solids and Structures ; Volume 47, Issue 5 , 2010 , Pages 611-613 ; 00207683 (ISSN) ; Sharif University of Technology
2010
Abstract
In this paper, some basis-free expressions for the material time derivative of Lagrangian stress tensors are presented which are generally valid in all cases of coalescent principal stretches. The material is assumed to be elastic and isotropic
Application of corotational rates of the logarithmic strain in constitutive modeling of hardening materials at finite deformations
, Article International Journal of Plasticity ; Volume 21, Issue 8 , 2005 , Pages 1546-1567 ; 07496419 (ISSN) ; Yeganeh, M ; Saidi, A. R ; Sharif University of Technology
2005
Abstract
In this paper a finite deformation constitutive model for rigid plastic hardening materials based on the logarithmic strain tensor is introduced. The flow rule of this constitutive model relates the corotational rate of the logarithmic strain tensor to the difference of the deviatoric Cauchy stress and the back stress tensors. The evolution equation for the kinematic hardening of this model relates the corotational rate of the back stress tensor to the corotational rate of the logarithmic strain tensor. Using Jaumann, Green-Naghdi, Eulerian and logarithmic corotational rates in the proposed constitutive model, stress-strain responses and subsequent yield surfaces are determined for rigid...
Parametric stability of symmetrically laminated composite super-elliptical plates
, Article Journal of Composite Materials ; Volume 50, Issue 28 , 2016 , Pages 3935-3951 ; 00219983 (ISSN) ; Nosier, A ; Keshmiri, A ; Sharif University of Technology
SAGE Publications Ltd
Abstract
Static and parametric stability of thin symmetrically laminated composite super-elliptical plates resting on Winkler-type foundation and subjected to uniform in-plane harmonic loads, under clamped, simply supported and free boundary conditions, are investigated based on the classical laminated plate theory. The governing equations are obtained from a variational approach and then the classical Ritz method is used to reduce the problem into a set of coupled Mathieu-Hill equations. Hsu's technique is utilized to determine the dynamic instability regions of principal and combination resonance frequencies. Extensive numerical data are provided to examine the effects of plate aspect ratio,...
Geometrically Nonlinear Random Vibration of Structures Using Finite Element Method
, M.Sc. Thesis Sharif University of Technology ; Hosseini Kordkheili, Ali (Supervisor)
Abstract
Indeterminate behavior of some forces in the aerospace industry due to flight at high speeds, gust, combustion, etc., has led to the exposure of structures to dynamic loads with random behavior in the nonlinear manner. To analyze problems in which the loading is random or the system parameters are random, the only possible way is to describe the system response in statistical values.Since most modern structures have complex geometry and the number of degrees of freedom is very high, advanced numerical solution methods are used to obtain the system response. In this study, the geometric nonlinear vibrations of structures under random loading are investigated by the finite element...
Kinematics and kinetics description of thermoelastic finite deformation from multiplicative decomposition of deformation gradient viewpoint
, Article Mechanics Research Communications ; Volume 37, Issue 6 , 2010 , Pages 515-519 ; 00936413 (ISSN) ; Kargarnovin, M. H ; Sharif University of Technology
Abstract
In this paper, using the multiplicative decomposition of the deformation gradient into mechanical and thermal parts, both kinematic and kinetic aspects of finite deformation thermoelasticity are considered. At first, the kinematics of the thermoelastic continua in the purely thermal process of nonisothermal deformation is investigated for finite deformation thermoelasticity. Also, a linear relation between the thermal expansion tensor and the rate of the thermal deformation tensor is presented. In order to model the mechanical behavior of thermoelastic continua in the stress-producing process of nonisothermal deformation, an isothermal effective stress-strain equation based on the...
Unidirectional surface waves in bi-anisotropic media
, Article IEEE Journal of Quantum Electronics ; Volume 54, Issue 6 , 2018 ; 00189197 (ISSN) ; Rejaei, B ; Khavasi, A ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2018
Abstract
We show theoretically that unidirectional surface waves can propagate on the surface of homogeneous bi-anisotropic layers with an anti-symmetric chirality tensor. These materials mimic the electromagnetic behavior of an anisotropic medium with gyrotropic permittivity and permeability tensors that operate on pseudo-electromagnetic fields. The unidirectional waves have transverse pseudo-electric or magnetic polarizations and pass through an obstacle without backscattering if the obstacle does not cause polarization change. The bi-anisotropic medium can be realized as a metamaterial comprising omega particles tailored to achieve the constitutive parameters desired. © 2018 IEEE
Material growth and remodeling formulation based on the finite couple stress theory
, Article International Journal of Non-Linear Mechanics ; Volume 121 , 2020 ; Asghari, M ; Sohrabpour, S ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
The mathematical formulation for material growth and remodeling processes in finite deformation is developed based on the couple stress theory. The generalized continuum mechanics of couple stress theory is capable of capturing small-scale cellular effects and of modeling mass flux in these processes. The frame-indifferent balance equations of mass, linear and angular momentums, as well as internal energy together with the entropy inequality are first introduced in the presence of the mass flux based on the finite couple-stress theory. Then, within the framework of material uniformity the Eshelby and Mandel stress tensors as driving or configurational forces for local rearrangement of the...
A plasticity model for metals with dependency on all the stress invariants
, Article Journal of Engineering Materials and Technology, Transactions of the ASME ; Volume 135, Issue 1 , 2013 ; 00944289 (ISSN) ; Hoseini, S. H ; Farrahi, G. H ; Sharif University of Technology
2013
Abstract
Recent experiments on metals have shown that all of the stress invariants should be involved in the constitutive description of the material in plasticity. In this paper, a plasticity model for metals is defined for isotropic materials, which is a function of the first stress invariant in addition to the second and the third invariants of the deviatoric stress tensor. For this purpose, the Drucker-Prager yield criterion is extended by addition of a new term containing the second and the third deviatoric stress invariants. Furthermore for estimating the cyclic behavior, new terms are incorporated into the Chaboche's hardening evolution equation. These modifications are applied by adding new...
An additive theory for finite elastic-plastic deformations of the micropolar continuous media
, Article Acta Mechanica ; Volume 206, Issue 1-2 , 2009 , Pages 81-93 ; 00015970 (ISSN) ; Naghdabadi, R ; Sohrabpour, S ; Sharif University of Technology
2009
Abstract
In this paper, the method of additive plasticity at finite deformations is generalized to the micropolar continuous media. It is shown that the non-symmetric rate of deformation tensor and gradient of gyration vector could be decomposed into elastic and plastic parts. For the finite elastic deformation, themicropolar hypo-elastic constitutive equations for isotropicmicropolar materials are considered.Concerning the additive decomposition and the micropolar hypo-elasticity as the basic tools, an elastic-plastic formulation consisting of an arbitrary number of internal variables and arbitrary form of plastic flow rule is derived. The localization conditions for the micropolar material obeying...
A compatible mixed finite element method for large deformation analysis of two-dimensional compressible solids in spatial configuration
, Article International Journal for Numerical Methods in Engineering ; Volume 123, Issue 15 , 2022 , Pages 3530-3566 ; 00295981 (ISSN) ; Sharif University of Technology
John Wiley and Sons Ltd
2022
Abstract
In this article, a new mixed finite element formulation is presented for the analysis of two-dimensional compressible solids in finite strain regime. A three-field Hu–Washizu functional, with displacement, displacement gradient and stress tensor considered as independent fields, is utilized to develop the formulation in spatial configuration. Certain constraints are imposed on displacement gradient and stress tensor so that they satisfy the required continuity conditions across the boundary of elements. From theoretical standpoint, simplex elements are best suited for the application of continuity constraints. The techniques that are proposed to implement the constraints facilitate their...
Analysis of concrete pressure vessels in the framework of continuum damage mechanics
, Article International Journal of Damage Mechanics ; Volume 21, Issue 6 , 2012 , Pages 843-870 ; 10567895 (ISSN) ; Naghdabadi, R ; Asghari, M ; Sharif University of Technology
SAGE
2012
Abstract
In this article, a constitutive model in the framework of continuum damage mechanics is proposed to simulate the elastic behavior of concrete in tension and compression states. We assume two parts for Gibbs potential energy function: elastic and damage parts. In order to obtain the elastic-damage constitutive relation with the internal variables, two damage thermodynamic release rates in tension and compression derived from the elastic part of Gibbs potential energy are introduced. Also, two anisotropic damage tensors (tension and compression) are defined which characterize the tensile and compressive behaviors of concrete. Furthermore, two different linear hardening rules for tension and...
Analysis of non-newtonian fluids in microchannels with different wall materials
, Article ASME 2009 7th International Conference on Nanochannels, Microchannels, and Minichannels ; 2009 , Pages 697-703 ; 9780791843499 (ISBN) ; Behshad Shafii, M ; Safari Mohsenabad, S ; Sharif University of Technology
Abstract
The behavior of non-Newtonian fluids is considered as an important subject in micro scale and microfluidic flow researches. Because of the complexity and cost in the numerical works and the experimental set-ups in some instances, the analytical approach can be taken into account as a robust alternative tool to solve the non-Newtonian microfluidic flows in some special cases benefiting from a few simplified assumptions. In this work, we analyze the flow of two non-Newtonian fluids including the power-law and grade-fluid models in microchannels. For the grade-fluid, the stress tensors are defined considering the Rivlin-Ericksen tensor definitions. To avoid the complexities in the entrance...