Sharif Digital Repository

The dispersed phase holdup is one of the important parameters in the design pulsed column and set the column diameter, height and characteristics of flooding and mass transfer. High efficiency and low space requirements of these columns cause is particularly in the nuclear industry, Due to the possible presence of radiation and the need for protection against radiation, considered and used. In this project, the dispersed phase holdup and mean residence time in a pulsed disc and donut column in a semi-industrial scale using radiotracer and shut down methods compared and presented for water-kerosene system. Also axial dispersion coefficient in the column using radiotracer methods is calculated... 

Many processes in the petroleum engineering industry involve particle transport in oil and gas reservoirs including sand production, fines migration, and nanoparticle injection. In these processes it is important to understand where the particles are travelling in the reservoir and the impact that they have on the formation properties. Large particles can damage the formation and decrease permeability which reduces the productive capacity of the reservoir. During nanoparticle injection, forces at the pore level can cause retention of particles and prevent their recovery. In addition, due to the heterogeneity of typical reservoirs, it is difficult to predict how particles will spread across... 

In this thesis the scattering analysis of periodic rough surfaces is studied using the Spectral Finite Difference Time Domain (SFDTD) method. This method takes advantages of both wideband frequency response and stability criterion for all incident angles compared to other methods in solving the periodic problems. In the SFDTD method a wave with Constant Transverse Wavenumber (CTW) is used as the incident wave. As a result, the problem of time delay in periodic boundary is solved and Periodic Boundary Condition (PBC) can be implemented in time domain directly. Periodic rough surfaces are important part of electromagnetic propagation surfaces. Therefore analysis of scattering from these... 

Hyderogels are hydrophilic polymers with three dimensional network structure, due to their high water absoption, their application to life and industry is increasing from day to day, such as tissue engineering, actuators and sensors, drug delivery and therapeutic treatment. In this project, it has been attempted to produce polyacrylamide/alginate double network hydrogels with the use of graphene oxide nanosheets to indicate that it is possible to combine toughness and self-healing in a hydrogel with the opposite nature of each other. To evaluate mechanical properties, uniaxial tensile test and loading-unloading test were used. The results indicate that increase the weight ratio of acrylamide... 

We study the fundamental and the photometric plane of a sample of 50 dwarf galaxies within the core of Coma cluster observed with DEIMOS on Keck II down to R-band luminosity of -15 Magnitudes. The Calcium triplet lines in the wavelength range between 7500 to 10,000 ˚A, allow us to obtain the velocity dispersion for the sample galaxies with high precision. We also performed a comprehensive error analysis to better estimate the uncertainties of this key observable. We also carried out a galaxy structure modeling using the ACS I-band images for a larger sample. We found larger velocity dispersions for fainter dwarfs than what expected from mass-luminosity trends of brighter Coma galaxies. In... 

The purpose of this research is to investigate the movement and diffusion of pollution transversely around a set of stems of flexible plants with different materials and to observe the effect of resonance on lateral dispersion. Two stem samples of polyurethane and nylon were used under different Reynolds numbers. Vertically uniform dye is injected into the flow, and the evolution of the dye plume along the flow is measured using image processing. By measuring the displacements of selected stems we study the effects of resonance on stem vibration and lateral dispersion. The experiments were also conducted for no-stem dispersion and the results were compared with those with plant samples. The... 

Distributed generation (DG) and its utilization have some benefits and risks for its owner and power network. From owner perspective, benefits of DG include selling energy, reducing costs related to fuel, and other economic benefits. However, there are some risk factors for the owner including risk of supplying fuel, risk of selling generated power, and other risk factors related to establishment of the DG unit. Utilizing risk-reduction tools such as signing agreements for selling power, purchasing fuel, and related economic tools are necessary for risk management of the owners of DG units. The purpose of this thesis is to investigate the economic situation of the DG units and optimize the... 

The importance of rainfall pattern in assessing embankment stability and deformation is widely known. However, many studies have examined an embankment with simple rainfall patterns or used average and maximum ones. The importance of diverse rainfall patterns has also been overlooked in the study of divergent soil stability in the previous study. Therefore, the hydraulic properties of a natural soil with and without salinity potential and the stability analysis of the railway embankment located on this type of soil under various rainfall patterns are investigated. The study area is part of the Zahedan Chabahar National Railway Project, which is located on divergent soil and has high... 

With the increasing penetration of renewable energies as distributed generation (DG) in power systems, technical problems arise in both distribution and transmission system level. Voltage rise is the main barrier for connection of DGs in rural areas, while excessive reactive power demand from transmission system is the major concern for Transmission System Operators (TSO). Here, a centralized control scheme based on the Smart Grid is proposed to reduce the impact on the transmission system voltages and improve its stability, while mitigating the voltage rise issue in the distribution network. Reactive power output of DGs, substation capacitors and tap setting of transmission transformer are... 

In the recent years, there is a worldwide wave of considerable changes in power industries, including the operation of distribution networks. Deregulation, open market, alternative and local energy sources, new energy conversion technologies and other future development of electrical power systems must pursue different goals. Also growth in the demand and change in load patterns may create major bottlenecks in the delivery of electric energy. This would cause distribution system stress.Furthermore, in competitive electricity markets, operators determine the electricity price for specific intervals during a day, taking into account various economical and operational factors. Traditionally, a... 

Tehran air quality is facing a real crisis. Reports of pertinent organizations show air quality is deteriorating in recent years and unhealthy days are increasing. As a result, study and planning in order to change this trend and moving toward improving air quality is a necessity. On the other hand, in order to make proper decisions and choosing effective approaches considering cost-effective attribute and legal, temporal and budget restrictions, selecting the right tool is essential. Air quality models are the tools which in a cost saving manner and reasonable time can provide the required results for researchers, decision makers and legislators. An applicable model correspondent with urban... 

This experimental study investigates the interaction between surface waves and flexible stems in aquatic environments, focusing on the case where the wave frequency is close to the natural frequency of the stems. Aquatic plants have significant structural and ecological effects on aquatic environments, inducing various changes in the flow passing through them. In this research, a polyurethane stem model is used, which is submerged and randomly placed in water. The oscillation amplitude and pollutant dispersion are investigated. The experiments were conducted at four frequencies of 0.7, 0.83, 1, and 1.125 Hz, two wave heights of 2 and 3 cm, and two densities of 0.8 and 1.2%. Image processing... 

In recent decades, particle composite materials have a wide range of applications in engineering. Particle composites are a group of heterogeneous materials with different length scales and are characterized by particles that are randomly distributed in a matrix phase. Geopolymer concrete is a special type of concrete that its binder is made by reacting alumina and silicate carriers with an activating agent and in recent years with the expansion of its use has reduced the amount of cement consumption. In addition to the many advantages of geopolymer concrete, it has disadvantages in terms of setting time. That is why the use of cement has been proposed as a solution to the problem. This... 

Despite the proven advantage of the engineered water flooding technique, a coherent and mechanistic understanding of the fundamental phenomena occurring at pore scale is lacking. Most of the available simulation models have a phenomenological approach and have limited predictive capability. One of the key questions is how to justify and relate large (Darcy) scale observations to effects and phenomena that essentially occur at much smaller scales (i.e. pore and molecular level). Furthermore, two-phase flow dynamics and the effect of complex interplay between wettability, capillary number, and ions dispersion in a heterogeneous porous medium on the trapping and mobilization of oil at pore... 

Different methods of shifting and shaping of space-time electromagnetic pulses are in this work investigated by nonlinearity and/or dispersion. Developing two dimensional (2D) finite difference time domain (FDTD) codes in the nonlinear regime and taking the optical dispersion of ideal metals into account, nanophotonic and plasmonic structures are analyzed in this thesis.
Goos-Hänchen shift, superprism effect, and optical bistability are particularly emphasized. A heuristic approximation is presented to extract the Goos-Hänchen shift at the interface of 1D and 2D photonic crystals. The superprism effect for electric polarization – where the electric field vector is perpendicular to the 2D... 

Obtaining the mechanical properties of body tissues in a non-destructive manner is clinically important and has wide applications in the diagnosis and prevention of diseases. one of non-destructive methods is elastography, which requires proper modeling of the tissue and then analysis of the wave propagation in it and obtaining the propagation relations and the dispersion curves. Study of the literature revealed that many simplifications have been used in most modelings of arteries and so far the anisotropy of the artery and its layers with the effects of surrounding tissues and blood have not been studied Therefore, the aim of this study is to model the artery as a two-layer orthotropic... 

Recent studies have shown that almost 40% of the world's population faces a water crisis, and this amount will reach about 60% by 2025. Due to limited freshwater resources and the increasing world population, we have to use seawater desalination systems to supply water to this growing population. One of the outputs of desalination plants in addition to freshwater is saline effluent or brine water, which is the most important environmental impact of these plants. In this study, an attempt has been made to investigate the various factors affecting the discharge and release of saline effluent from desalination plants and observe its impact on the ecosystem and marine environment. In this... 

The use of distributed generation (DG) units provides several advantages for the utility distribution grid. Mostly power electronics converter is used as an interface to connect a DG unit to a utility grid. A DG unit normally operates in a grid-connected mode. In this mode, the host grid dominantly dictates the voltage amplitude and frequency of the local load at the point of common coupling (PCC) and the DG unit controls its real/reactive power components. Separation of the DG unit and its dedicated load from the host grid is called islanding. Subsequent to the formation of an island, due to the lack of control over the voltage magnitude and frequency, the islanded DG system becomes... 

Over the course of past decade, air pollution has been placed among the top issues chocking capital Tehran. Stationary source of air pollution is among the most important, but, less treated facors. On the year, 2014, Tehran’s air quality company addressed a number of projects in this very field could gain further governmental supports. This announcement could be a sign, showing the importance of this research. These researches in fact, have the potentioal to increase the authority’s decision making abilities in critical situations. As the models prognosticates future with acceptble accuracy, it leads to highly efficient dicissions. The results could also be used in demographic studies as... 

The release of toxic materials causes tragic accidents every year. There are various techniques in order to mitigate the release effect of these materials such as Application of air jets, steam curtains and water curtains. In this study first, previous works are reviewed in order to select the best technique for the mitigation of heavy toxic gas release. Then CFD modeling is used to simulate this technique.
A field situation in which chlorine gas was released upwind of water spray was simulated using the open-source software FDS (Fire Dynamic Simulator), a CFD model. Only mechanical effects of water sprays are considered; hence the effect of absorbtion is neglected. Finally tha...