Sharif Digital Repository

Brain diseases like Parkinson’s, ischemia and trauma are among major causes of death worldwide. Axonal swelling is the hallmark of most of these diseases. It is frequently observed that the axonal swelling will not remain homogeneous and shape transformations like forming multiple beads along the axon (or beading) may happen. These focal large swellings can alter or even block the passing action potentials along the axon and hence may have serious cognitive consequences. This research deals with theoretical and numerical modeling of axonal swellings. The proposed model has two parts: the central axoplasm and the surrounding cortical membrane. Instable large deformations, water diffusion,... 

In this study, a fully coupled thermo-hydro-mechanical model for modeling Enhanced geothermal systems (EGS) is introduced using the extended finite method for numerical solution. Enhanced geothermal systems are fractured porous media that in addition to the solid phase usually consist of one or more fluids. Heat extraction from Enhanced geothermal systems involves several Multiphysics coupling processes, including the seepage flow through the fractured porous media, the thermal exchange between the working fluid and the matrix, and the deformation of fractured porous media. modeling of these processes is complex and has several parameters. Therefore, a thermal-hydraulic-mechanical (THM)... 

During the last two decades usage of unstructured grids was very common in the oil reservoir simulators; which is due to free formulation’s structure and independence of the grids to any special boundary lines or surfaces. The use of these types of grids in Computational Fluid Dynamics texts is widely seen in form of Control Volume discretization techniques; and on the other side, Weighted Integral methods known as Galerkin Finite Elements are one of popular methods to approximate displacement differentials quantities. In this study we tried to review application of a new numerical calculation method – which is a combination of Finite Elements and Control Volume methods – in simulation of... 

Processing an alloy can enhance its mechanical properties. Based on repeated radiation of high-power pulsed laser beam, laser shock peening (LSP) is one way to impart favorable residual stress in an alloy and to enhance its damage tolerance property. Study of overlapping LSP is possible through the simulation of limited laser shots. Still, its computational cost is higher than that of a single shot. This research, primarily, is aimed at improving a methodology for reduction of computations in the study of an overlapping LSP and its impacts on fatigue crack growth. Addressing research gaps by utilizing the methodology is the secondary goal. The methodology consists of plastic strain... 

The use of sandwich panels has become very common in recent engineering designs when the weight of the part or structure is important and we are looking to lose weight while maintaining strength. The mechanical properties of this type of structures, including yield stress, fatigue behavior and estimation of their life, failure modes, natural frequencies and resonance phenomena, etc. are affected by various factors, including geometric and environmental factors. Fatigue is one of the most common failures in these structures. Composite materials have complex structures. In these materials, due to the viscoelastic properties, the fatigue behavior changes with changing stress, stress frequency,... 

This study aims to parametric study and model steel joints with side plates. steel joints with continuum plates have been seismically acceptable for years, assuming they are designed to be stronger than beams. After the Northridge earthquake, the belief that the adequacy conditions of flexural frame joints were limited to stiffness and strength factors was challenged for two main reasons. First, at the junction of the beam with the column, high tension is created by the seismic force, and as a result, it buckles and loses its strength before reaching the projected force. The second problem is due to the problem of making such connections that it is difficult to weld. Therefore, the problem... 

With the production from the reservoirs, the amount of in-situ oil storage has decreased and there is a need to increase oil recovery (EOR) from the reservoir. Increased oil recovery (EOR) includes operations such as acidizing and hydraulic fracturing. Considering the economic and high operational costs and geomechanical complexities, as well as the technical progress of hydraulic fracturing and its future; It is necessary to manage hydraulic fracturing operations optimally. This research is about hydraulic fracturing and its main goal is to optimize the parameters of the fracture or the geometry of the fracture. The research study was carried out on the Bangistan Reservoir located in the... 

In the real engineering problems, the existing materials in the nature or human-made materials, contain different heterogeneities from the view of small scale. Reinforced composite materials and porous media containing grains or micro-cracks are some examples of these materials. Due to the large amount of these heterogeneities as well as the small size, direct modelling of these micro-structures requires extremely high computational and memorial cost. Also, the equivalent models introduced in the literature, have strong limitations and therefore, cannot capture accurate behavior of the material. Hence, multiscale methods have been proposed in order to model these heterogeneous media with... 

Shallow geothermal energy is a renewable and sustainable form of energy that has the potential to help alleviate the growing climate and energy crisis. The most common system used to extract shallow geothermal energy is the ground source heat pump (GSHP) system. The concept of using underground structures in exploiting shallow geothermal energy for space heating and cooling has received increasing attention. This study focuses on the use of geothermal tunnels as a means of extracting shallow geothermal energy.This research examines the effects of different heat transfer mechanisms, and highlights the effects of this phenomenon by focusing on the effects of natural convection around the... 

Cylindrical shells play an important role in a wide range of engineering applications such as mechanics, aerospace, marine engineering, and nuclear applications due to their high load-carrying capacity, light structure, and economic advantages. Because these structures are often made of high lengths and thin sheets, they are very prone to vibration, especially under the conditions that they play a role in the rotating state, which can cause failure. For the reasons mentioned, the vibration analysis of rotating cylindrical shells will be essential in engineering designs. In the present study, after introducing general concepts regarding the analysis of structural vibrations, previous research... 

Elevated water tanks are one of the most critical elements in civilized society to provide safe servicing resources of drinking water after natural and human-made disasters. Dynamic analysis plays a vital role in investigating structural behavior of the elevated storage system subjected to the earthquake-induced vibration. The main scope of this paper is to address the structural stability analysis of the Kish Island’s elevated reinforced concrete water tank employing finite element method. A complete solid model of the structure with detailed design was constructed, and finite element analysis was carried out utilizing ABAQUS software. To investigate the dynamic behavior of the structure, a... 

The main goal of this research is to investigate the effects of different types of heterogeneities on fluid flow and solute transport in saturated porous media. These heterogeneities are micro- and macro-fractures and cavities. For modeling micro- and macro-fractures we used an equivalent continuum model and extended finite element, respectively. Also, we modeled the problem by using mass conservation law for both components of the problem – fluid flow and the solute – and Darcy’s law. In modeling vuggy porous media, due to the high velocity of the fluid inside the free flow areas i.e. channels and cavities, we could not model the medium properly using Darcy’s law. Therefore, we had to use a... 

In recent decades, metal nanoparticles have been used in medicine for example in cancer treatment. There have always been debates on the nanoparticles specifications such as particle size, amount of surface charge and the particle material. Meanwhile, the study on selecting appropriate properties of nanoparticles for this purpose is very essential and expensive in medical science. In order to access the best efficiency and the least mortality of the patients in treatments, simulation studies can support the medical scientists. In this thesis, the goal is to study transferring nanoparticles as a drug or included drugs through created hypothetical micro-channels in cancerous cells membrane.... 

Distal humerus fractures commonly take place in adults with low bone mineral density causing major technical challenges upon orthopedic surgeons. Persian fixation method was introduced as a novel technique to stabilize small fragments in comminuted distal humerus fractures using a set of K-wires and reconstruction plate. The objective of the present study is to measure the stiffness and stability of this technique and analyze the effect of influential parameters with numerical simulation and biomechanical testing on a cadaveric specimen. Furthermore, we were able to propose new method to model plastic deformation of implants in surgery.Validation of the finite element (FE) model was... 

Corneal keratoconus is one of the common eye diseases that usually occurs in the teenage years or the beginning of the third decade of life. In this disease, the cornea thins and loses its original shape and becomes conical. To treat this disease, ophthalmologists use different methods such as using glasses, contact lenses (hard and soft), corneal transplantation, and also corneal cross-linking, each of these methods has limitations, on the other hand, considering that The disease progresses and its severity increases, Ophthalmologists use corneal rings to treat this disease in more advanced stages, implanting a suitable ring in the patient's cornea both increases the strength of the... 

Studying the failure mechanics of FGM materials is inevitable due to the increasing use of these materials in various industries. Stress intensity factor and integral-J are important parameters in fracture mechanics. Due to the fragile nature of ceramic components in FGM During the processing of these types of composite materials, cracks are encouraged. Therefore, crack analysis is inevitable in optimizing the design, reliability and durability of FGM materials and structures in innovative engineering applications. In this research, transverse crack growth in beams made of FGM materials has been investigated. First, a MATLAB code was prepared to extract the mechanical properties of these... 

In the present research, a new material model utilizing anisotropic conduction and track-scale heat input model is used to predict the melt pool geometry, material state and thermal history during the selective laser melting process of SS316L in a large range of laser parameters. The model takes into account the phase transition of the material during the process. Furthermore, the phase transition problem in the track-scale model has been analyzed and a solution has been presented. The simulated melt pools in beam-scale and track-scale simulations are compared with experimental measurements in different laser parameters. It is found that the proposed material model is able to maintain... 

The need for position sensors has increased substantially with the development of electric vehicle motion control systems. In industrial applications, encoders are commonly used for positioning, but in polluted industrial environments, with large temperature variation and vibration, the resolver is preferred to optical encoder. Resolver is a two-phase synchronous generator with a high frequency AC excitation voltage instead of DC voltage. Therefore, the output voltages of the resolver are amplitude modulated (AM) voltages which in order to determine the output position, it is necessary to extract the envelope of these signals using R/D converter. In envelope extraction methods, to ensure... 

In the proccess of making key slots in lock parts, broaching is necessary. The only procedure or at least the best procedure for making the slots is broaching. High speed and precision, surface quality and the ability to create complicated surfaces in one step are the advantages that make broaching suitable for this product. The cost of tool maintainance and replacement is very important to make this process efficient economically, therefore, determining the factors affecting tool life are important for industries. The purpose of this study is to increase the life of narrow broaching tools. In other words, in this study, the purpose is to design and manufacture the tool in such a way that... 

The objective of this research is to model the wing structure of a flapping wing MAV and investigate structural dynamic behavior of its wing. in this research, to investigate and identify dynamic instabilities, modeling of the structure based on a nonlinear four-node plane element and aerodynamic modeling based on the strip theory in unsteady flow has been done, and by coupling these two models, the final model is formed. In the model of the wing structure, the displacement and changes angle inside the plane of the wing sections have been ignored and only outside the plane have been assumed for the degrees of freedom. In addition, the veins in the flapping wing have been omitted and the...