Sharif Digital Repository

This research studies the feasibility of the BK7 optical glass milling process with ultrasonic vibrations. Due to the fragility of glasses, especially optical glasses, machining is very sensitive and complex. For this reason, it is necessary to think for the glass machiners to minimize the defects and failures of the process. So far, efforts have been made to reduce the defects caused by machining on brittle materials, such as increasing the speed of the period, reducing the feed rate of the tool, changing the geometry and the type of tool, the type of process lubrication, etc. In addition, other operations performed to improve the surface of the glass are of better quality, using hybrid or... 

In order to prevent deterioration of metallic interconnects in solid oxide fuel cells (SOFC), while interacting with glass-ceramic sealant, a nickel electroplated ferritic stainless steel (UNS 430) was used. After applying a layer of powdered glass (SiO2-B2O3-Al2O3-Na2O-BaO-K2O) with thickness around 300-450 μm on the ferritic stainless steel sheets with dimansion of 0.5 × 60 × 60 mm and 0.5 × 10 × 10 mm, samples were heated at temperatures between 770-850 °C and durations of 1 to 15 hours. To evaluate the effect of the Ni layer, two types of sample (only sanded and only electropolished) were also submitted to the same process, and their results were compared with the coated samples. XRF,... 

Stainless steels have many applications in different industries. Therefore, it was always a main concern to find an appropriate joining method for using these materials in complex structures. In the present investigation, AISI 304 stainless steel was successfully joined by transient liquid phase (TLP) bonding, using a MBF-30 interlayer. The joining process was carried out at 1150 ℃ temperature and for different bonding times. Also joints with complete isothermal solidification were homogenized at 950 ℃ for different holding times. Microstructure and compositional changes of the joints were studied using optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive... 

Hydraulic fracturing process as one of the most important ways to inhanse of production requires careful study and investigation and due to its importance has been studied for decades. The effect of this process on the production at oil and gas industry has many complexities and these complexities with the complex structure of natural gaps, would be multiplied. In this thesis effect of hydraulic fracturing operation on the production of natural fractures at naturaly fractured reservoirs from two aspects of hydraulic and geomechanics will be investigated. First we provide models for fractures network by using UDEC software after that investigate the effect of hydraulic farcture on the natural... 

In this research, the dynamic behavior of a rotating stiffened cylindrical shell has been investigated using the refined finite element method. Refined FEM means decreasing degrees of freedom based on decoupling the structure to longitudinal and layerwise directions. The refined FEM has been used to solve the 3D rotor dynamics equations. The natural frequencies and the corresponding modes have been calculated and verified for some existed data and problems. In addition, the effects of the shell geometry dimensions on the natural frequencies and mode shapes have been studied. Also, the relationship between the length to radius ratio, radius to thickness ratio, rotational speed, Aspect ratio... 

When the human body is subjected to high accelerations, cardiac function and blood supply to the body can be changed. Due to the complex geometrical and mechanical properties of heart, finite element method is useful way for analysis of response of this structure under different load types. Modeling heart using finite element method requires mechanical and geometrical properties of heart. Soft tissues modeling, such as heart muscle using finite element method is one of the most challenging issues in field of biomechanics. In this thesis, the mechanical properties of heart are obtained by performing experimental compression tests on samples of fresh bovine heart. Using obtained experimental... 

This paper presents finite-element simulation results for hydraulic fracture’s initiation, propagation at reservoirs with damaged zone and naturally fractured reservoirs that likely finds in Iranian oil fields. To address this objective, a two-dimensional poro-elastic model was solved and cohesive zone modeling was used as the methodology for simulation fractures. This enables us to assign individual criteria for fracture initiation and propagation in each model. Our results demonstrate that hydraulic fracturing is not useful in reservoir with strongly damaged zone around the wellbore, because pore pressure increases at that zone and plastic flow of fracture wall happens, so it is better to... 

This thesis presents a research on the physical behavior of water inside carbon nanotubes (CNTs). Molecular simulations are carried out using the Monte Carlo method in the canonical and grand canonical ensembles. Due to the difference between the inter-molecular forces in the axial and radial directions, the anisotropic pressure tensor is calculated for water confined inside the CNTs with the diameters of 0.88, 1.08, 1.28, and 1.48 nm at different densities using the Monte Carlo simulations. Using the assumption of effective extended Lennard-Jones interactions between the nearest neighbors, a set of new equations of state for water confined inside the CNTs is derived and shown to be... 

The structural integrity of the sealing material is critical for the reliability of solid oxide fuel/electrolysis stacks. In this study, the mechanical properties of a rapid crystallizing glass of BaO-CaO-SiO2 system were evaluated. The crystallization as a determining factor in the mechanical behavior of the glass-ceramic sealant was investigated via high-temperature X-Ray diffraction spectrometer. Three- and four-point bending tests were carried out to measure the flexural strength (σ) of sealant material bars and head-to-head joined specimens at room- and high-temperatures. In addition, the elastic modulus (E) was measured by impulse excitation test up to 900 ºC. Also, the indentation... 

In today's world, where consumers are increasingly demanding high-quality electricity supply, particularly with minimal outages and the highest continuity of power delivery, considering reliability indices in distribution system expansion planning models is essential. To simultaneously meet the requirements of both economic and reliability criteria for distribution networks, planning models need to assess the reliability of active distribution networks throughout the optimization process. In order to achieve a reliable plan, it is necessary to integrate the reliability evaluation of the network into the distribution planning problem. This thesis presents an effective model for distribution... 

This thesis is divided into three parts: In part I, conformational properties of neutral, anionic, cationic and zwitterionic forms of glutathione tripeptide were investigated by means of DFT-B3LYP method with 6-31+G (d,p) basis set. Results show that glutathione is a very flexible molecule and its conformational energy landscape is strongly influenced by forming intramolecular hydrogen bond and its charge. Conformation of each amino acid in glutathione tripeptide depends on its orientation within the peptide sequence in addition to the conformation of other amino acids within the chain. Investigation of intramolecular hydrogen bonds in these conformers by means of AIM analysis demonstrates...