Sharif Digital Repository

Metallic glasses (MG) are a group of materials that have unique properties such as high yielding strength and high elastic deformation. Because of limitation in the production of these materials, a few industrial materials of MG have been made so far. A few of binary alloys, like binary alloys made of Cu-Zr, have high Glass Forming Ability (GFA) in medium cooling rates. Between two binary systems of Cu-Zr and Ni-Zr, although constituent elements in aspect of atomic radius, electronic structure, physical properties, phase diagrams and intermetallic compounds are so similar to each other, but GFA between them are very different. For example, in Cu-Zr system there are compounds, such as... 

A numerical algorithm for the optimal design of two components functionally graded materials under thermomechanical loadings is introduced in the present study. It is based on the topology optimization method. The objective function, to be minimized, is defined as the weighted combination of the thermal and mechanical compliance of structure. The design variables are defined as the local volume fractions of contributing phases. The set of constraints includes bound constraints on local volume fractions and a global constraint on the total volume fraction of the matrix phase. The corresponding heat and elasticity equations are solved by the finite element method. The local material properties... 

According to current researches, graphene oxide (GO) membranes show promising desalination properties due to ease of synthesis, low production cost, and high efficiency. There are several experimental works to study ionic sieving properties of GO membranes. However, it is difficult to characterize atomistic mechanism of water permeation and ion rejection by experimental approaches. On the other hand, there exist a few reports in which the atomistic picture of water permeation across GO membranes is investigated by means of molecular dynamics (MD) simulation. In the present work, in addition to water desalination, the atomic scale mechanism of ion rejection is studied using large scale MD... 

In order to heat, cool or control the heat transfer in insulation plates, under a certain loading condition, for uniformity temperature distribution and maximum temperature control, it is possible to composite materials with high thermal conductivity and appropriate distribution in Inside the insulation matrix. The purpose of this study is to provide a method for optimally distributing conductive phase inside an insulating plate under a specific thermal loading condition so that the temperature difference between the various points of the plate is minimized in stable conditions. For this purpose, a topology optimization method was used to determine the optimal distribution of conductive... 

The current study is dedicated to free vibration analysis of a thin cylindrical shell with an oblique end. To this end, governing equations of motion and the corresponding boundary conditions are derived using Hamiltonian formulations. The differential form of equations is obtained by applying by part integration to the integral form of equations of motion. Equations of motions have been solved by Galerkin method for two different kinds of boundary conditions. Convergence process for different kinds of conditions has been done and results compared with papers. The effect of different parameters such as, length of cylinder, oblique angle, thickness etc. on the fundamental frequencies has been... 

Polypropylene is a semi-crystalline thermoplastic used in various industries and the second most used polymer globally. Polypropylene is sensitive to degradation by o agents due to having tertiary carbon in its chain. Chlorine-based disinfectants, used to disinfect drinking water, cause the degradation of hot water pipes made of polypropylene random copolymer. The stability of polypropylene against oxidizing chemical agents depends on the type of crystalline phase and polymer morphology. This research investigated the effect of alpha, beta, and gamma crystalline phases and spherulite size on random polypropylene copolymer's chemical stability in chlorine dioxide. Three samples were prepared,... 

Here the differential equations of a Graphene sheet deformation is determined by making use of the most general form of first Strain Gradient Elasticity (SGE) theory. In order to derive the equations of in-plane and out-of-plane deformations, the matrix representation of Strain Gradient constitutive law is used. Vibration of the nano-plate is studied by modeling the plate based on Kirchhoff theory and application of variation of energy, therefor the in-plane and out-of-plane vibration of the nano-plate is found through Navier analytical solution. After all natural frequencies are obtained based on SGE parameters. SGE parameters are determined by calculating the potential of a representative... 

In this research, Mg-Zn bulk metallic glasses have been investigated using molecular dynamics simulation. In order to study the structure of this alloy, coordination number, short and medium order of chemical range, Voronoi analysis, glass conversion temperature and atomic pair distribution function have been used. According to the results, the full icosahedral structure with IS connection type in comparison with other structures has an essential role in the stability of the system during cooling and creating medium-scale areas. The results show that the ability to form glass depends on the chemical composition and cooling rate. In this research, the cooling rate is considered to be 1011 K/s... 

In this project, vibration and stability condition of a pipe conveying flow has been studied for use in firefighting plane. The Plane is a multi-rotor that carries the pipe to a certain height and it does the washing work there, bassed on the fluid flow from the nozzle embedded in the end of the pipe. Due to the flexibility of the pipe in this application, structure modeling is based on cable without bending stiffness. The Galerkin method is used to solve equations by considering the assumed mode shape for structure. At first, by analyzing free vibrations, different boundary conditions were considered for the pipe and the natural frequencies and natural shape modes were extracted in... 

Nanotechnology with the tools, materials and their applications in areas such as engineering mechanics, materials, electronics, computers, and machines at the nanoscale is dealing. The Fnarvy, atoms and molecules as building materials, engineering bricks counts. In mechanical engineering branch, two aspects are discussed in view of nanotechnology, nano-scale structures and analyzing the behavior of phenomena that occur at the nanoscale. In this project, methods to analyze the behavior of nanoscale materials has been studied.
The present thesis examines the natural frequencies of nano graphene sheets on elastic foundation deals. The elastic foundation modeled with two springs.At first The... 

In this study, the nonlinear vibrations of an elastic rotor that is under the elastic support and under the follower force caused by the airflow passing through the rotating plane are investigated. The elastic shaft is modeled by the Timoshenko beam theory, which is connected to a motor through a flexible coupling and the motor increases the rotational speed of the rotor by applying torque. Gibbons’ equations have been used to model the misalignment forces. First, the kinetic energy of the rotating system is calculated nonlinearly to take into account the effect of nonlinear terms due to the rotational inertia of the system, and then the potential energy and The work of external forces on... 

One of the most important factors affecting the performance of the vehicle's brake disc is its stiffening coefficient. To improve this feature, many researches have been carried out by leading automotive companies, whose scientific aspects have not yet been widely disseminated. Brake discs are often made of cast iron and are more likely to produce gray iron with type A graphite. However, according to available resources, factors such as graphite morphology, their length-to-thickness ratios, cast iron and heat treatment on the piece affect this important feature. One of the most important factors that make changes in the above mentioned cases is the chemical composition and freezing rate. In... 

Open data intermediaries, as the key species of the ecosystem, and since they are the primary consumers of open government data, are crucial to the ecosystem's growth. Without them, the data would be useless during the dissemination phase. This study aims to define the roles of open data intermediaries and explain how they are compatible with the value creation and sustainability of the open data ecosystem in order to fill a gap in the literature in this area. Two Iranian open data intermediaries, Rasmio company and Vinsabt group, which have been involved in the field of data pertaining to companies, have been studied for this purpose. The data for this study is qualitative and was gathered... 

The pouring basin is a main part in the gating system. The formation of a vortical flow is a big problem occurs during the discharge of melt from the pouring basin. The vortex formation can enter the floating slag and inclusion into the mold. In the case that the vortex is more stronger, a fully air core to the sprue forms and leads to entraining of the air to the mold. These phenomena can decrease the casting quality significantly. Therefore preventing of the vortex is necessary to produce a sound cast. In this study the mechanism of vortex formation is investigated and several solutions are presented to avoid its detrimental effects. For this purpose discharge of a tank is simulated... 

This study presents the aeroelastic stability and vibration analysis of a sandwich circular cylindrical shells with a constrained viscoelastic layer. Based on the Donnell-Moshtari theory, the structural formulation of the cylinder is obtained using Lagrange method. The Rayleigh-Ritz method is implemented to solve the discretized governing equations. To describe the mechanical properties of the viscoelastic layer, the fractional order standard solid model is applied. The effects of variation of the governing parameters such as the length to radius ratio, radius to total thickness ratio and ratio of core to facing thickness on the stability margins and frequencies of sandwich cylindrical... 

In the current study, stability and nonlinear vibration of bending-torsional extensible beams conveying internal pulsatile and uniform external flow are studied. The internal and external fluid flows are assumed to be incompressible and frictionless. Applying the extensibility to the pipe along its length and using the nonlinear Euler-Bernoulli beam model and including some appropriate additional assumptions, the 3D nonlinear equations of motion of a cantilevered composite pipe is obtained. In order to derive the equations governing the fluid-structure interaction, the internal flow effect is modeled as a distributed load along the pipe which contains the inertia, Coriolis and centrifugal... 

Creating sustainable development in today's society is essential, and one of the most important elements to achieve this is the phenomenon of recycling. Lead-acid batteries are one of the sources of environmental pollution, and their separators contain 50% recyclable silica nanoparticles. In this research, impurities in these separators were removed using two methods: washing with water and sandblasting. The purity of recycled nanoparticles was 85.5% in the first method and 98% in the second method. In addition to the importance of recycling, finding a suitable use for recycled materials is also critical. FDM 3D printing is a new method of producing parts, but polypropylene is not commonly... 

In the present project an analytical model is proposed for the instability of spinning composite cylindrical shells partially filled with fluid. For this purpose, using the linearized Navier-Stokes equation for the incompressible flow, a 2-D model is developed for fluid motion at each section of the cylinder. The resultant pressure exerted on the cylinder wall as the result of the fluid motion, are calculated in terms of elastic displacements of the cylinder. Applying the Hamilton principle, the governing equations of motion of the cylinder are derived and then combined with the equations describing the fluid pressure to obtain the coupled-field equations of the structural-fluid motion.... 

In this study, stability as well as linear and nonlinear vibrations of coaxial rotating cylindrical shells conveying annular incompressible fluid medium are investigated. To this aim the inner isotropic and elastic rotating cylindrical shell along with the rigid and stationary outer cylinder are considered. Equations of motion for the inner cylinder are determined according to the Hamilton’s principle and using the Sanders-Koiter theory assumptions. In order to generalize the boundary condition implementation, some translational and rotational springs are attached to the boundaries at the mid-plane. The final system of equations are solved by means of the extended Galerkin method – being an... 

We establish the existence and uniqueness of the mild solution for stochastic Volterra equation with a non-self-adjoint operator. The specific Volterra equation that we consider is a generalization of the fractional differential equation. To obtain the mild solution for the case of multiplicative problem, the resolvent property of the linear perturbation of a sectorial operator will be considered. Moreover, we establish the existence and uniqueness of the mild solution for semilinear stochastic Volterra equation involving a demicontinuous and semimonotone nonlinearity. The Volterra equation in this case, has a positive-type memory kernel. To obtain the mild solution of the multiplicative...