Sharif Digital Repository

This research is trying to investigate the control algorithms of unknown control direction systems. Since Nussbaum function is the most common method which in used for these systems this research focus on this algorithm to overcome control the effect of unknown control direction. This research study the performance of different control algorithms in controlling such systems followed by analysis of two control modes of continuous and discrete using Nussbam Function. Additionally, in continuous mode, the performance of two methods of backstepping and liding mode has been compared on the given system in variety of situation. Results demonstrate that backstepping method shows better performance... 

Nowadays, modeling the behavior of materials during forming processes is so important. The role of most of them is to investigate and predict the evolutions of microstructure and mechanical properties of materials during plastic deformation. Previous researches have demonstrated that the best parameter to investigate these evolutions is the dislocation density of materials. In this study, first, the dislocation-based models, which investigate the material parameters evolutions during plastic deformation, were investigated and it was revealed that among all presented models, only the two internal variables models can investigate the behavior of materials during severe plastic deformation. ... 

Many researches have been done on the severe plastic deformation of 2024 aluminum alloy, but there is limited information on the effect of severe plastic deformation for this alloy in the over-aged condition. In this study, the effect of severe plastic deformation and annealing heat treatment on the microstructure and strength of the over-aged AA2024 has been investigated. 1, 3, 5 and 7 two-dimensional multi-directional forging passes carried out to the over-aged samples at room temperature as one of the methods of severe plastic deformation process. After applying strain, samples were subjected to annealing heat treatment at 200, 300 and 400 °C for 30 minutes and then quenched in water. For... 

Loess as a kind of collapsible soils is a well-known Aeolian deposit, which is characterized by some specific Engineering properties including high initial void ratio, relatively low initial density and water content and high percentage of fine-grained particles. Collapsible soils such as loess, sustain large stress under dry condition. However, they experience a high and sudden decrease in their volume by reaching to their critical moisture content. As a result, their natural condition is not suitable for construction works if the possibility of the exposure of the soil to excessive water is present. This research presents the utilization of an innovative method for stabilization and... 

Abstract: Fault tolerance in computing systems often depends on the precision of fault detection methods, significantly impacting overall reliability. Classic fault tolerance methods, like task replication, struggle to achieve certain reliability targets with imperfect fault detection, which, unlike perfect detection mechanisms, imposes minimal system overheads. Addressing this, our paper introduces Dynamic Task Replication (DTR), a general fault tolerance technique that dynamically determines the number of replicas at runtime to overcome the limitations of classical task replication. Our primary contribution, Optimal Dynamic Task Replication (ODTR), optimizes DTR for a given task, aiming to... 

Today, due to a massive increase in accuracy of reservoir characterization models, multiphase flow simulation on real permeability fields faces a serious challenge. Using multiscale methods in reservoir flow simulation of a heterogeneous environment has led to huge speed-up of the simulation. In multiscale methods, instead of replacing a heterogeneous medium by an equivalent homogeneous medium, used in upscaling, the problem is solved on the original resolution. In this thesis, multiscale finite volume method (MSFV) has been used to simulate flow and saturation behavior of a black oil model. Unlike the original multiscale finite volume methods that were unable to solve compressible fluid... 

A high percentage of reinforced concrete buildings are not earthquake resistant because they are often designed based on old regulations, which do not satisfy the requirements of new earthquake codes. Construction weaknesses make buildings more vulnerable, and thus, different approaches are needed to strengthen structures to resist lateral forces. 3D Panel system brings together the best qualities of in-situ and precast systems and improves their shortcoming. It includes the advantages of precast systems, such as having relatively low labor costs, less waste material and machinery, reducing implementation time and improving quality control. At the same time, serious problems related to... 

In this project, investigation of C-N internal rotation in ethyl tetrahydro-1(2H)-pyridine carbdithioate and ethyl 1-pyrrolidine carbodithioate were investigated by dynamic nuclear magnetic resonance spectroscopy. The 1HNMR and 13CNMR spectra were taken at the variable tempratures around the coalescence temprature. Thermodynamic parameters were calculated by analysing the spectra and the outcomes were compared by the theoretical results. For ethyl tetrahydro-1(2H)-pyridine carbdithioate ∆G‡ was 14.3 (kcal/mol) and for ethyl 1-pyrrolidine carbodithioate ∆G‡ was 17.0 (kcal/mol) which were in accordance with the theoretical results. The analysis were done by the Spinworks program which... 

Additive manufacturing enables fabricating lattice structures with tailored mechanical responses based on lattice materials. Full exploitation of such a possibility requires reliable and efficient mechanical analysis tools to be explored by topology optimization algorithms for designing the interior architecture of the structures to meet the desired mechanical behavior. However, detailed mechanical analysis of lattice-based structures using the conventional finite element approach is prohibitively expensive due to lattices’ complex and fine features that demand adopting very fine space discretization. As an alternative, equivalent models based on the homogenization principle have widely been... 

In this thesis, the accelerator and cooling equations have been investigated in order to improve the quality of the accelerator by using cooling. With the help of MATLAB software, a cooling method has been proposed that can have a relatively uniform temperature throughout the accelerator. In order to optimize and minimize the number of coolers for each desired temperature difference and each number of coolers, an arrangement of coolers is found so that the temperature difference is minimal. There are different types of charged particle accelerator systems in terms of the structure and energy of the output particles. Linear accelerators are accelerators in which charged particles move along a... 

In nuclear power plants, the fission reaction takes place inside the fuel rods, and the heat generated inside the fuel rods is transferred through the clad wall to the cooling fluid, which is single-phase, subcooled and in the turbulence zone. In the hot channel of the reactor core, where the axial and radial heat flux reaches its maximum state, the fluid leaves the single-phase state and some steam is formed in the area close to the clad wall.Therefore, in some cases, in the hot channel, the steam near the clad wall may reach a point that reduces the heat transfer coefficient, rapidly increases the wall temperature and thus destroys or melts the sheath surface. If this happens, it means... 

Seismic performance analysis is conducted for an isolated three-span continuous highway bridge, which is restrained with shape memory alloy bar. Two series of earthquake ground acceleration, known as ‘pulse records’ and ‘non-pulse records’ are applied to the bridge in three directions. Four types of pier-girder connection are used in the analysis: rigid connection (only for comparison), lead rubber bearing system (LRB), lead rubber bearing along shape memory alloy (SMA) restrainer system and high damping rubber bearing (HDRB) system. SMA bar restrainer is made of Ni-Ti. In the first step of the work, structural properties and analytical models of the bridge segments are introduced. Then, a... 

During the production of crude oil from reservoirs, the production of quantities of formation water along with this oil, causes the crude oil does not have the necessary indicators for transportation, refining and ultimately export. The presence of water and salt along with crude oil causes corrosion of refinery and transmission equipment and makes oil unfavorable in terms of economic efficiency (both for domestic use and for export). water and salt produce stable emulsion with oil that can be stable for a long time and can not be easily separated from crude oil. Therefore, separation of water and salt from crude oil is one of the most important issues in the oil industry. Breaking this... 

AZ91 is the most applicable alloy of magnesium alloys.Semisolid stir welding of AZ91 magnesium alloy was investigated due to its welding problem such oxide formation, hot cracking in weld metal, and high residual stress through solidification with special focus on the effect of the welding temperatures, stirring rates, and tool shape. The interlayer with thickness of 2mm was located between two AZ91 pieces with 7.5mm thickness. Then, they were heated to the desired temperatures (515C, 530C and 540C), the semisolid temperature of both base metal and interlayer. A grooved stirrer with six rotational speeds from 0rpm to 2000rpm was introduced into the stir weld seam and the welded coupons...