Sharif Digital Repository

This work numerically simulates pressure drop and heat transfer for flow in a pipe with porous wall. Incompressible two dimensional, ax symmetric laminar or turbulence flow with constant mass flow rate is considered. It is assumed that there is no thermal equilibrium in the porous media region between solid and fluid phase. Effect of porous wall thickness and Darcy number on the rate of heat transfer and pressure drop were investigated. The Darcy number varies from to and porous wall thickness can fill entire pipe. the turbulent model is used to calculate the fluid flow and heat transfer characteristics in turbulent flow. Nusselt number can enhance about ... 

In recent decades, employing fiber-reinforced composite has growing field in various industries due to distinct features like high specific stiffness and strength. Studies in case of this type of composite have not been stopped and nowadays, widespread researches are conducted over optimization of them. As a result, the effect of distributing fiber in this composite by taking the concept of functionally graded materials, on vibrations and buckling behaviors including natural frequencies and minimum axial bulking load under different boundary conditions for a multi-layered cylindrical shell in which volume fraction of fiber along its length varies according to power-law model are investigated... 

Magnesium and its alloys have gained a lot of interest recently in the field of biodegradable implants, particularly in the field of orthopedics, mainly due to their excellent compatibility, low density and similarity of their mechanical properties with the human bone. However, the main weakness of magnesium for such applications is that it corrodes faster than the time required for complete healing of the tissue. Different properties of Mg can be improved by making composites. In this research, 1% and 2% of MgO microparticles were added to the Mg-1Zn-0.2Ag alloy. These composites were made by the stir casting technique, and after that, the samples' microstructure, mechanical... 

In the era of the internet and with the emergence of online stores, the possibility of changing prices for these e-commerce platforms has become simple and virtually cost-free. This allows them to adjust prices optimally in response to environmental and surrounding factors, maximizing their revenue from product sales. This development has led to numerous applications of statistical learning methods, particularly online learning, in these markets. In this thesis, we explore the issue of online pricing from various perspectives. One aspect is that product pricing is based on their features, which can be numerous. This leads us to the use of online learning methods and statistical learning in... 

Magnesium and its alloys are among the new degradable implants due to their characteristics such as biodegradability, low density, elastic modulus close to bone, and biocompatibility, which have received much attention from researchers. However, in most biological applications, the insufficient corrosion resistance of this alloy causes the accumulation of hydrogen gas around the implant, the loss of mechanical strength and its destruction before the completion of the treatment period. In this research, magnesium base alloys Mg–4Sn, Mg–4Sn–0.2Ag and Mg–4Sn–1Ag are investigated to improve mechanical strength and corrosion resistance. Finally, after casting and alloying, microstructural,... 

It is the main idea of present thesis to provide a micromechanical method as a general treatment for several fundamental problems of the piezoelectric inhomogeneities. For initial demonstration of pertinent methodology, a single piezoelectric inhomogeneity of ellipsoidal geometry, under non-uniform far-field loading is considered. Accordingly, it is taken equivalent to elastic and dielectric inclusion problems connected by proper eigenstrain-electric field. This approach is named the electro-mechanical equivalent inclusion method (EMEIM) and requires that the electroelastic fields of the inhomogeneity to be equal to fields of the equivalent inclusions. Afterwards, the complex problem of... 

Laser cladding is a processing technique of layer-by-layer material deposition which is widely used to repair important components. However, tensile residual stresses generated in this process may result in detrimental effects such as crack, undesirable deformation and reduced fatigue life. A thermo-mechanical finite element model is developed to accurately predict residual stresses of the multiple beads laser cladding process with incorporating the cyclic plasticity into the analysis by utilizing the nonlinear kinematic hardening behavior. FE results are presented for Inconel 718, a material for which the laser cladding process is widely used. The FE results are compared with those of... 

Phospholipid vesicles are able to carry drugs or DNA to infected or cancerous cells. The blood flow can carry them to their target positions but their performance will be enhanced if they complete their attack by swimming in final stages of their journey. Vesicles built only by lipid molecules have rotational symmetry and undergo a random motion in their solvents without having a preferred direction. In this project, we break the symmetrical shape of phospholipid vesicles by a cluster of transmembrane proteins. We use a triangulated model of the membrane, apply the method of multi-particle collision dynamics to the motion of solvent particles, and simulate the motility of vesicles for... 

Hard disk drives are the main component of computers for permanent data storage. The security of the stored data is related closely to the air gap between the read-write head and the surface of disk. This gap which is created by the aerodynamic force between head and the disk is altered continually by lateral oscillations of disk. In the extreme condition of zero gap and contact between the protective coating layer and subsequently the magnetic material of the disk with the head, the disk will be scratched and damaged. Therefore, the active or passive control of these vibrations has a particular importance in the technology of manufacturing of hard disks. The first step in active control... 

The Hubbard model is one of the simplest interacting models in theoretical physics, especially condensed matter physics which despite its simplicity, its solutions are highly nontrivial and intractable. After 5 decades since its introduction, its phase diagram is not fully understood and whether or not, it has a high-temperature superconducting phase. In this thesis, we aim to employ the recent advances in machine learning and GPU programming to accelerate the QMC method. By accelerated QMC methods, we can explore the Hubbard model's phase diagram more efficiently. Using massive parallelization of the GPUs can speed up the measuring process by several times. The self-learning quantum... 

As it is known, one of the dangerous consequences of the earthquake is the possibility of fire. In recent years in our country special attention have been paid to design and retrofit buildings against earthquakes, but have not done to understand the behavior and design concepts of structures against fire. One of the reasons is the lack of information and the absence of a specific standard for design of structures against fire. Since the beam-to-column connections play an important role in the performance of structures, in this study, the behavior of the moment frame with flush end plate was investigated by testing on a small scale structural model (half scale). It is observed that, the test... 

In the present study, a high-order accurate numerical solution of steady incompressible slip flow and heat transfer in 2D microchannels is presented. The numerical method used is an alternating direction implicit operator scheme which is efficiently implemented to solve the incompressible Navier-Stokes equations in the primitive variables formulation using the artificial compressibility method. To stabilize the numerical solution, numerical filters are used. The present methodology considers the solution of the Navier-Stokes equations with¬ employing different slip boundary condition¬¬ (Maxwell,¬ ¬¬Hyperbolic tangent function of Knudsen number¬ and Beskok slip models)¬ ¬¬on the wall to model... 

Isogeometric Analysis method is a newly introduced method for the analysis of problems governed by partial differential equations. The method has some features in common with the finite element method and some in common with the mesh-less methods. This method uses the Non-Uniform Rational B-Splines (NURBS) functions as basis function for analysis. With this basis functions, the refinement procedure is much easier than the classical finite element method by eliminating the need to communicate with the CAD model. Modeling cracks in classical finite element method requires very fine mesh near the crack tip. One can model crack propagation by means of classical finite element, using an updating... 

Light has planar wavefront as it propagates in vacuum but in the atmosphere, because it passes through layers with different refractive indices, this planar wavefront is lost. Consequently light is distorted when it enters optical instruments. This issue results in images with low resolution. Adaptive optics is a method used for compensation of these distortions in order to obtain higher resolution. So far adaptive optics systems are successfully used in ground based telescopes and an increasing effort on developing and improving these systems is made. Most of these studies are performed from the optics point of view, but techniques from control theory can be applied to adaptive optics... 

Each of us at some point in our life has been astonished by the observation of the collective motion of certain animals such as birds, fishes or insects. These coherent and synchronized structures are apparently produced without the active role of a leader in the grouping and it has been reported even for some microorganisms such as bacteria or red blood cells. In all the mentioned examples agents are surrounding with the moving fluid which can affect the collective behavior of the system. The collaborative flock of birds in windy conditions and the swimming of fishes in rivers or along oceanic currents are some examples. Moreover, micro-organisms produce different collective behavior in the... 

Attitude control of rigid bodies is a complicated but attractive problem in dynamics. One of its main practical applications is in satellite attitude control and specifically in space telescope orientation control. Using fuel thrusters is not only expensive in most cases, but also it cannot be considered as an appropriate solution from reliability and economic aspects in long-term applications such as space telescopes and telecommunication satellites. On the other hand, magnetic torquers and momentum wheels cannot be utilized for rapid and large maneuvers due to their inability in generating large torques, which are needed in such maneuvers. As a result, another type of attitude control... 

The Hamiltonian of the Hubbard model was introduced by Hubbard in 1963 to model electron correlations in narrow energy bands and it provided an approximate description of electrons in solids.This model provides a simple description of materials, but its exact solution is possible only in one dimension.In the physical examining of this model in quasi two-dimensional systems, the Density Matrix Renormalization Group(DMRG) is used, which is one of the most powerful numerical methods in studying quantum systems. The quantity that is important to solve the systems is the density matrix, which by knowing, many of the observable quantities of the systems can be obtained. Calculating the density... 

The usage of plugin hybrid electric vehicles has environmental benefits. However, the penetration of these components raises important concerns for grid planning. Thus, it is necessary to model the load change due to their charge to investigate the impact of these vehicles on distribution networks. For this reason, it is necessary to determine the specifications of these vehicles, such as battery charge and energy consumption on daily trips. In addition, the study of some behavioral patterns of these vehicles and some experts are necessary to complete the model.In this thesis, an active distribution network is planned using dynamic programming formulation. In this model, some buses are added... 

One of the challenges in predicting the remaining useful life (RUL) of rolling element bearings (REBs) is determining a proper failure threshold (FT). In the literature, the FT is usually assumed to be a constant value of an extracted feature from the vibration signals. In this research, a method was proposed to define the FT of REBs, and the effect of different parameters on the FT was also studied. First, to determine the effective parameters, the variance analysis was applied to the seeded fault dataset of REBs. Afterward, the method based on the principal component analysis (PCA) and the copula models was proposed to estimate the FT. In this method, a proper feature for the FT and a... 

The COVID-19 pandemic has increased environmental risks due to widespread face mask use in production, consumption, and disposal. This study uses surgical single-use as a pyrolysis feedstock due to increased demand. This study investigates the conversion of valuable materials from waste through the recycling of surgical single-use masks in a fluidized bed. The first stage of this study focused on identifying and specifying the main components in the filter layers of disposable surgical masks, which were the compounds in the filter layers made of polypropylene. TGA curves investigated thermal behavior of disposable surgical mask layers, revealing pyrolysis feedstock can produce volatile...