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elasticity
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An Appraisal of Trade and Transportation Trends in Asia-Europe-Africa
, M.Sc. Thesis Sharif University of Technology ; Vaziri, Manouchehr (Supervisor)
Abstract
In this research, trade and transportation trends of Asia-Europe-Africa, in the both intercontinental and intracontinental levels have been analyzed. With analyses which are done in this research, determinant factors for modeling and investigating international bilateral trade in these three continents have been recognized. The relevant time-series data were extracted from centralized and international databases. The examined database consists of 11 variables grouped in four categories: bilateral trade data, transportation, geographical and socio-economic characteristics. Transportation data is based on three different networks. The first network consisted of highway, rail and marine modes...
Dynamics of a Viscoelastic Plate on a Viscoelastic Foundation Subjected to a Moving Mass
, Ph.D. Dissertation Sharif University of Technology ; Esmaeil Purestekanchi, Homayoun (Supervisor) ; Mofid, Masoud (Co-Advisor)
Abstract
This thesis investigates the dynamic response of a viscoelastic plate resting on a viscoelastic Winkler foundation subjected to the excitation of a moving mass. Through application of the Laplace transform, the governing equation of the problem is derived for a general viscoelastic material. Thereafter, an analytical-numerical method is proposed in order to determine the dynamic response of the viscoelastic plate. The method is based on transforming the governing partial differential equation into a new solvable system of linear ordinary differential equations. To that extent, the proposed solution proves to be applicable to plates made of any viscoelastic material and with various boundary...
An Implicit Algorithm for Numerical Simulation of Large Deformation Structures with Incompressible Fluid Flow
, Ph.D. Dissertation Sharif University of Technology ; Darbandi, Masoud (Supervisor)
Abstract
The fluid structure interaction (FSI) problems are widely encountered in many industrial applications in mechanical, aerospace, biomedical, marine, and wind engineering. The main contributions of this research are focused on simulating flow with moving or deforming boundaries including FSI problems with large movement or deformations. In this regard, a hybrid finite-element-volume (FEV) method was used in an arbitrary Lagrangian-Eulerian (ALE) framework. In this research, a new layer-by-layer mesh movement strategy was developed to perform the unstructured grid movement more robustly. This strategy converts the complex data structure of an unstructured grid to a simple quasi-structured data...
Nonlinear Vibration Analysis of Circular Microplate Based on Strain Gradient Theory
, M.Sc. Thesis Sharif University of Technology ; Asghari, Mohsen (Supervisor)
Abstract
Nowadays the combination of mechanical and electronic systems in small scales is gaining attention. Micro electro-mechanical systems are widely used in various industries such as car manufacturing and electronic chips. In these devices, the most important and useful mechanical structures are beams and plates. Therefore, investigating the mechanical properties of these structures in very small scales (micro and nano) is of great importance. Decreasing the size to these scales leads to the dependence of the behavior of these structures to size. Accordingly, some theories for prediction of these behaviors have been presented, one of which is the strain gradient theory. This theory is used in...
Elastic Analysis of Brazilian Test of Transversely Isotropic Material
, M.Sc. Thesis Sharif University of Technology ; Eskandari, Morteza (Supervisor)
Abstract
In Former research we determinate elastic response of Brazilian Test of transversely Isotropic material . In Bio-mechanic science surveying mechanical properties and modeling biological organ such as bone , tooth and bio-material such as titanium, zirconium with application in joint replacement is very important . One of method to determine properties of bio-material which mostly has transversely Isotropic behavior is Brazilian Test. Also most rocks has transversely Isotropic behavior, so choosing efficient test is so important. In current issue , load apply in limited area and it is also considered friction in area of jaw loading area .By use of displacement potential function ...
Investigation of Mechanical Properties of Particulate Metal Matrix Nanocomposites Using Surface Elasticity Theory
, M.Sc. Thesis Sharif University of Technology ; Naghdabadi, Reza (Supervisor) ; Asghari, Mohsen (Supervisor)
Abstract
Excellent mechanical properties and high aspect ratio of carbon nanotubes have been the reason for extensive research on nanocomposites reinforced by this nanostructure, and recently metal matrix type of these nanocomposites, due to their advantages, have received great attention. Moreover, nanoporous materials are another type of nanostructured materials which due to their very high porosity have special applications in hydrogen storage, separating molecules, purification and energy absorption. Because of completely neglecting the details of nanoscale structure and not paying attention to the length scale, classical continuum mechanics methods are not precise enough for evaluating different...
Vibration and Stability Analysis of Multiwall Carbon Nanocones on Elastic Foundation Using Nonlocal Theorem
, Ph.D. Dissertation Sharif University of Technology ; Haddadpour, Hassan (Supervisor) ; Dehghani Firoozabadi, Rouhollah (Supervisor)
Abstract
Carbo nanocones are one of the nanostructures that are investigated and takes a large deal of attention in nanotechnology. In the present study the governing equilibrium equations of motion of carbon nanotubes under external pressure are derived using a nonlocal shell model and first order shear deformation theory. The natural frequency and buckling load are extracted using modal method along with Galerkin technique.Afterthis using both Winkler and Pasternak elastic foundation models, the governing equations of motion of nanocones embedded in the elastic medium extracted using a novel approach with the nonlocal shell model along with Hamilton’s principle. These equations solved using...
Modeling Online Taxi Drivers’ Decision Making in Accepting or Rejecting Ride Offers
, M.Sc. Thesis Sharif University of Technology ; Madanizadeh, Ali (Supervisor) ; Joshaghani, Hossein (Supervisor)
Abstract
Online ride-hailing platforms aim to match drivers and riders instantly by receiving ride requests from riders and sending them to drivers nearby. However, the low acceptance rate of offers by drivers leads to friction in the process of driver and rider matching. Various factors influence drivers' decisions to accept or reject offers. Specifically, drivers are more likely to turn down a ride offer when they know that by rejecting it, they can quickly receive another offer or find a passenger traditionally. To examine the factors influencing drivers' decisions in online ride-hailing markets, we focus on the behavior of drivers employed by Tapsi ride-hailing platform, and by specifying a...
Eigenfield Theory for Grade Two Flexoelectric Composites with Periodic or Arbitrary Nanostructure and General Anisotropy
, M.Sc. Thesis Sharif University of Technology ; Mohammadi Shodja, Hossein (Supervisor)
Abstract
Studying the behavior of electromechanical systems containing nanostructures, because of their widespread applications in the nanoscience and technology is of great interest. For this purpose, this work is devoted to analytical and exact determination of the electroelastic fields associated with periodic and arbitrary distributions of electromechanical nano inclusions and nano inhomogeneities of various shapes within electroelastic mediums of general anisotropy. Since classical continuum Theories are inadequate in accounting for size affects in nanostructures, a first strain gradient - first electric field gradient theory is applied. The present work considers Piezoelectric and Flexoelectric...
Surface/Interface Effect on the Scattering of Love Waves by a Surface-Breaking Crack Within an Ultra-Thin Layer Bonded to an Elastic Half-Space
, M.Sc. Thesis Sharif University of Technology ; Mohammadi Shoja, Hossein (Supervisor)
Abstract
In this study, an analytical solution is presented for anti-plane scattering of Love waves by a surface-breaking crack normal to the free surface of an ultra-thin layer bonded to a semi-infinte medium within the surface/interface elasticity theory. The Fourier transform techniques are used to formulate the corresponding mixed-boundary value problem as a singular integral equation of the Cauchy type which is solved numerically. Mode III dynamic stress intensity factor at the crack tip, crack face and crack mouth opening displacements, the reflection coefficient at large distances from the crack face, and the stress field on the interface are computed and plotted for different valued of...
Essays on Explaining the Household Consumption Smoothing
,
Ph.D. Dissertation
Sharif University of Technology
;
Nili, Masoud
(Supervisor)
Abstract
This dissertation studies the intertemporal decisions on private consumption and its relationship with financial markets. The main focus here is on using micro-data and heterogeneities. The first chapter gives a brief review on the literature. In the second chapter, we present estimates of the Elasticity of Intertemporal Substitution (EIS) for Iranian households using synthetic cohort panels based on household micro-data. Results show significant difference with the common values used in Dynamic Stochastic General Equilibrium (DSGE) models which are originally based on estimated values for developed countries. We show that this difference has important theoretical and practical implications....
Numerical Modeling of Cohesive Cracks in Functionally Graded Materials Using XFEM
, M.Sc. Thesis Sharif University of Technology ; Kazemi, Mohammad Taghi (Supervisor)
Abstract
Nowadays in high-tech industries there is a serious demand for using advanced materials. Functionally graded materials (FGMs) are in the last generations of these group of materials. FGMs have shown good behavior in special conditions. According to sensitive applications of FGMs , there is a large amount of effort to understand it’s behavior in the presence of crack. Finite element method and other numerical methods, in recent years are widely used in modeling fracture problems.Remeshing requirements and mesh sensitivity are among the disadvantages of analyzing crack growth using the conventional FEM. Recent finite element methods such as extended finite element method, are proposed to model...
Numerical Modeling of a Smooth Notched Tensile Specimen Via Gradient Elasticity Based RKPM
, M.Sc. Thesis Sharif University of Technology ; Mohammadi Shodja, Hosain (Supervisor)
Abstract
Recently, there has been a strong interest in the development of a new class of meshfree methods. As an alternative to the finite element method (FEM), mainly due to elimination of high cost mesh generation processes. In addition, the size effect is currently a subject of increasing interest since it is an important parameter in predicting, correctly, the mechanical behavior of materials with microstructure. It was well established that classical linear elastic continua which neglects the higher order terms is not able to describe size effects. In contrast, enhanced continuum theories such as nonlocal or gradient-dependent models do involve an internal length scale. Thorough this length...
Expressions for Objective Co-Rotational Rates of Eulerian Stress Tensors
, M.Sc. Thesis Sharif University of Technology ; Asghari, Mohsen (Supervisor)
Abstract
Stress tensors and their rates are fundamental quantities in modeling the behavior of materials in the field of nonlinear continuum mechanics. One of the most remarkable applications of stress rates is their presence in the rate type constitutive equations of materials.
Co-rotational rates are corresponding to the rates which are measured by an observer who is in a reference rotating coordinate system. In general, under some specific conditions for the spin of a co-rotational rate, the rate of an Eulerian tensor would be objective. In this thesis, the objective co-rotational rates of Eulerian stress tensors for isotropic elastic materials under large deformations are obtained for the...
Co-rotational rates are corresponding to the rates which are measured by an observer who is in a reference rotating coordinate system. In general, under some specific conditions for the spin of a co-rotational rate, the rate of an Eulerian tensor would be objective. In this thesis, the objective co-rotational rates of Eulerian stress tensors for isotropic elastic materials under large deformations are obtained for the...
Dynamic Buckling of Laminated Composite Beams Resting on Elastic Foundation under Thermal and Mechanical Load
,
M.Sc. Thesis
Sharif University of Technology
;
Kouchakzadeh, Mohammad Ali
(Supervisor)
Abstract
In this study, static and dynamic buckling of laminated composite beams resting on an elastic foundation under thermal and mechanical load is studied. Beam is resting on an elastic foundation with hardening/softening term. Nonlinear governing equations are obtained based on the energy method and are solved via the multi-term Galerkin method and the Newton-Raphson numerical method. Critical dynamic load is estimated by the Hoff Simitses criterion. The results are validated with the results of available articles in this field. In the following, the effects of different parameters of the problem on the results are examined. Results reveal that for a sufficiently stiff softening elastic...
Surface and Interface Effects on the Elastic Fields of an Edge Dislocation Inside a Silicon Nanotube with Thin Siox Coating
, M.Sc. Thesis Sharif University of Technology ; Mohammadi Shodja, Hossein (Supervisor)
Abstract
The exact analytical elastic fields within a double-walled silicon nano-tube with a thin layer of SiOx coating associated with surface/ interface effects as well as the classical theory of elasticity due to the presence of an edge dislocation with an arbitrary Burger’s vector and position inside of the silicon is determined via complex potential function method. Stress contours within surface elasticity and classical theory are given, and both theory results are compared. Then, the effects of surface Lamé Constants, magnitude and direction of Burger’s vector, shear modulus, nano-tube size, and position of the edge dislocation on the distribution of stress components are illustrated, and the...
Design of Fillet Welds in Plastic State
, M.Sc. Thesis Sharif University of Technology ; Maleki, Shervin (Supervisor)
Abstract
Nowadays, many structural engineers use fillet welds in their designs because of their high strength and affordability. In these welds, eccentric loadings either out-of-plane or in-plane create complex condition in welds from stress point of view. To determine the capacity of such fillet welds different methods have been proposed over time. For instance, the method approved by AISC is the Elastic method. This method when combined with load factors, as required by the LRFD design method, yields very conservative designs for fillet welds. Therefore, in this project, we try to propose the plastic method for welds under eccentric loadings. This method is more economical than the elastic method...
Observer Based Stabilization of Partial Differential Equations Governing Strain Gradient Micro Beams
, M.Sc. Thesis Sharif University of Technology ; Alasti, Aria (Supervisor) ; Fotouhi Firouzabad, Morteza (Co-Advisor)
Abstract
In recent decades, the study of Nano and Micro Electromechanical Systems (NEMS and MEMS) as in micro sensors and actuators or in Atomic Force Microscopes (AFM) attracted considerable attention. Since an indispensable part of such systems is a nano or micro flexible beam, the inevitable undesirable vibrations of the flexible beam necessitate the implementation of vibration control strategies. Recently, some cutting edge experiments on statics and dynamics behavior of micro beams have been conducted that reveal some deviations from the prediction of classical theories, and hence this leads to development of strain gradient elasticity theory. In addition, the often-adopted finite dimensional...
Estimating Price Elasticity of Labor Supply in Ride-sharing Markets (Case Study: Tapsi)
, M.Sc. Thesis Sharif University of Technology ; Madanizadeh, Ali (Supervisor) ; Joshaghani, Hossein (Supervisor)
Abstract
Because of flexibility in labor supply, ride-sharing market is a good platform for estimating drivers’ working hours in response to hourly earning changes. In this research using ride-sharing markets’ data and controlling for geographic effects and time and individual fixed effects, we have estimated 0.0129 for price elasticity of drivers’ working hours. Literature has focused on estimating the elasticity in time horizons shorter than a day (non-stop active hours), while in this paper we have also estimated the elasticity in daily horizon.We have also analyzed the heterogeneity of different types of drivers (Full-Time or Part-Time, Tehran or non-Tehran Plates, Gender and Experience) in...
Estimating The Demand of Freeways in Iran, Using Discreet Choice Model
, M.Sc. Thesis Sharif University of Technology ; Rahmati, Mohammad Hossein (Supervisor) ; Vesal, Mohammad (Supervisor)
Abstract
According to the principle No. 44 of the Constitution of the Islamic Republic of Iran, Roads are in the public domain and are at the discretion of the Government. The result of this rule is that there is always a free route on the side of the freeway and motorists have the right to choose between a freeway and its successor road. This is a perfect laboratory condition which gives the opportunity that can be used with discrete choice models to estimate the demand of freeway versus its successor. In this paper we estimate the determinant parameters of the freeway demand versus the successor road and price elasticity of demand that can be calculated separately for each path. The results show...