Sharif Digital Repository

The price elasticity of gasoline demand is a key parameter in evaluation of various policy options. However, most of the literature uses aggregate data to identify this elasticity. Temporal and spatial aggregation make elasticity estimates unreliable. We employ a unique dataset of all gasoline transactions in Iran during a four-month period around an unexpected exogenous price change to identify price elasticity. After controlling for date and individual fixed effects we estimate a robust significant price elasticity of -0.127. Aggregation of the same data by week, month, and city yields an estimate of -0.3 indicating a significant bias in earlier studies. We also identify a significant... 

A simple control system contains at least an actuator, a controlled link, and a foundation. These structures are not ideally rigid, this flexibility can appear willingly or unwillingly in any parts of the system or the connections between them. As a consequence of this flexibility, the movement of the controlled part will fluctuate unintentionally. In this thesis, a control system with rigid controller and flexible torsional base is investigated and controllers are designed and compared to reduce these unwanted vibrations. Finally, by implementing the controllers on the constructed system, the experimental results are obtained and compared with the analytical results.To fabricate the... 

The dynamic behavior of beams and rectangular plates on elastic foundation under the effect of deterministic and random excitations is investigated in the cases of controlled and uncontrolled systems. The equations of motion are developed in each case in both deterministic and stochastic states. In all cases, the eigenfunction expansion method is used to solve the obtained equations.Moreover, the classical linear optimal control algorithm with displacement-velocity is considered to achieve the required control efforts. The applied dynamic excitations are supposed as moving loads, moving masses accompanied with random lateral excitations of supports and the uniform distributed linear loading... 

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... 

The DNA Molecule carries genetic information in almost all living organisms. The information coded on DNA is an instruction which organizes and conducts all living activities of the living organism. The role of DNA in biological processes is so fundamental that life, as we know, is not possible without DNA. Therefore, studying the biological properties of DNA is crucial for understanding the nature of life. In biological conditions, DNA molecule can be found in highly packed configurations. Since the DNA is a rather stiff molecule, the formation of these configurations cost a considerable amount of energy. The elasticity of DNA plays an important role here. The important question is: how... 

Recent studies show that irregular structures have been damaged more than regular ones during earthquakes. This proves importance of seismic response determination of this type of structures. Today, Codes define irregularity in structures and restrict seismic analysis and design of these types of structures. The Endurance Time (ET) method is a time-history based dynamic pushover procedure for seismic analysis and design of structures that has been recently proposed in Sharif University. This thesis illustrates ET capability in analysis and design of vertically irregular frames. Irregular frames with three, seven and twelve story high were designed with two types of mass and stiffness... 

This work examines the problem of the fully coupled magneto-electro-elastic (MEE) scattering of SH-waves incident upon a heterogeneous MEE scatterer which is embedded in an unbounded medium. The scatterer consists of a circular core and a circular encapsulator with eccentricity. All three regions: the core, encapsulator, and the surrounding matrix have distinct MEE properties and fully coupled constitutive relations. The generated coupled MEE fields coexist simultaneously in all these regions without resort to any simplifying assumptions. The precise description of the multifunctionality involves the solution of three fully coupled partial differential equations in three different regions.... 

Under conventional seismic design strategies, civil engineering structures are designed to undergo inelastic deformation to dissipate earthquake energy, leading to residual displacements and nonlinear deformations in the structure. As a result, there is an essential need for structural health monitoring methods to detect and process these nonlinear behaviors. In this dissertation, a model-free Hysteresis Loop Analysis (HLA) method is developed to identify damage and monitor the structure's performance online, under the earthquake excitations in both severe linear and nonlinear scenarios. The structural models used to validate this method includes three types of one-story, five-story, and... 

In this thesis, We consider a model of a fluid–structure interaction defined on a bounded domain Ω ⊆ R2, that describes a body of elasticity interacting with a fluid. Ω is a bounded simply connected domain, consisting of two open sub-domains Ωs and Ωf .Ωf is the exterior domain with non-overlapping boundaries Γf and Γs, so that ∂Ωs = Γs. Ωs is an interior domain with boundary Γs.Ωs is occupied by an elastic body while Ωf is filled with a fluid.The interaction between the elastic body and the fluid takes place at the interface Γs.The dynamics of the fluid is described by the Navier–Stokes equation and the dynamics of the elastic body is described by an elasto-dynamic system of wave equations.... 

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... 

In this paper, the elastic response of a surface-stiffened transversely isotropic half-space subjected to a surface normal load is addressed. The half-space is reinforced by a Kirchhoff thin plate bonded to its surface. Two different boundary conditions are considered across the plate-half-space interface: (i) the classic approach in which the plate in-plane deformation is neglected by writing the interfacial boundary conditions across the plate mid-plane, and (ii) the refined approach that considers the in-plane deformation of plate due to bending by writing the boundary conditions across the bottom face of plate. By virtue of appropriate displacement potentials, the complete set of elastic... 

In this study, elastic analysis of a functionally graded full-space with quadratic variations under various types of loading is addressed. The elastic responses of the medium are obtained in closed-form under various types of loading including point load, concentrated moment, distributed patch load of rectangular and circular shape, normal ring load, and concentrated torsion. The displacement fields are derived by virtue of the appropriate Green’s functions corresponding to the FGMs with a quadratic variation of elastic moduli and constant poisons ratio of = 0.25 .For the special case of homogeneous medium, the results are verified with available solutions. Furthermore, effects of degree of... 

DNA molecule is one of the most important macromolecules in cell, which carries genetic information for life. DNA is often in confined geometries, such as, packaging in cell and DNA-protein interactions. While DNA is nearly a stiff polymer, its elastic behaviour plays a crucial role on its functionalities.Therefore, investigating the elastic and mechanical properties of DNA is really important.The elastic behaviour of a long and free DNA can be predicted very accurately by ”worm-like chain“ (WLC) model. In WLC model, DNA is assumed as a elastic rod with harmonic potential of local bending and twist.Many structural properties of DNA have been ignored in this model. But in recent years, by... 

In this thesis, we consider a system containing fluid equations, structure equations, and equations of these two materials’ common interface in three dimensions and on the regular domains. We suppose that the solid which is described by the Lamé system of linear elasticity, moves inside an incompressible viscous fluid in three dimensions, and the fluid obeys the incompressible Navier-Stokes equations in a time-dependent domain. At the fluid–solid interface, natural conditions are imposed, continuity of the velocities and of the Cauchy stress forces. The fluid and the solid are coupled through these conditions. By this interaction, the fluid deforms the boundary of the solid which in turn... 

In this thesis an analytical solution is introduced for finding the elastic fields of stress and strain in a confocal elliptic ring at the state of general plane problem. A confocal elliptic ring is a doubly connected region which its external and internal boundaries are ellipses with the same focal points. We used the method of complex variables, the functions of Kolosov-Muskhelishvili potentials, Laurent series expansion for analytical functions, the method of the analytic continuation of Milne-Thomson, elliptic hyperbolic coordinates, and two dimensional conformal mapping to do this study. the importance of this analysis is because we can simulate some problems of the elasticity by... 

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.... 

In order to study the interaction of sloshing and structural vibrations of baffled tanks a reduced order model based on modal analysis of structure model and boundary element method for fluids motion is developed. For this purpose the governing equations of elastic structure and incompressible flow used to derive simple models to simulate both fields. Using the modal analysis technique the structural motions are applied to the fluid model and on the other hand by using boundary element method the fluid loads are applied to the structural model. Based on this formulation a code is developed which is applicable to an arbitrary elastic tank with arbitrary arrangement of baffles. Results... 

In this study, flexural vibration of a functionally graded nanotube under an initial stress is investigated. The small scale effect is taken into consideration based on Eringen’s nonlocal elasticity theory. The material properties are assumed to vary exponentially along the depth direction. The complete effect of the initial stress is taken into account in the problem formulation. The governing equations of motion are derived by using the Hamilton’s principle on the basis of the nonlocal Timoshenko beam theory. An analytical solution of the governing equations, for free vibration of a simply-supported nanotube is presented. Numerical results are presented to investigate the effect of the... 

The seepage through foundation of earth dams causes the serious menaces and the reduction in their efficiency. Therefore essential contrivances must be provided against mentioned problem. One of the common and efficient ways to control the seepage through pervious layers under earth dams is plastic concrete cut off wall which is used as a filling material in dam foundation due to the low permeability, plastic behavior and low enough elastic modulus compatible with the adjusted soil. In addition to the mentioned properties, it is important that plastic concrete have an adequate compressive strength to sustain the lateral and vertical loads. Since the change in the ratio W/C (water to cement)... 

Applying of seismic waves and analysing of its reflections is of effective ways in exploration of the internal structur of the Earth. In this method the Earth is considered as a elastic body that seismic waves are propagated in it. In this thesis the how of creation and propagation of seismic waves is modeld at first and then the inverse problem, exploration of the internal structure of the Earth from observed data, is considered