Sharif Digital Repository

The requirement of reliable relative permeability data is more intensified when the miscibility condition approaches. In this work the relative permeability of CO2 and oil has been measured at different miscibility conditions using conventional methods. Fractured dolomite and sandstone core plugs samples were used in the experiments. Due to some errorful assumptions of conventional methods such as immiscible, incompressible displacement, inverse modeling was used for predicting the reliable relative permeability of oil and gas phases at near miscible condition from measured oil production and pressure drop data. The initial guesses of relative permeabilities were provided from conventional... 

In this paper two methods are presented that can be used to determine the dynamic behavior of viscoelastic beams with different boundary conditions, carrying a moving mass. An analytical-numerical formulation that transforms the governing differential equation in viscoelastic media into a set of ordinary differential equations and thereafter a discrete element model based on assumption that continuous viscoelastic beam can be replaced by a system of rigid bars and joints which resist relative rotation of attached bars. The physical properties of the joints can be found through considering the viscoelastic model of beams material. Correctness of results has been ascertained by a comparison,... 

Double-web angle connection is one of the most rudimentary connections in simple structural systems such as braced frame system. It is essentially presumed in conventional designs that double-web angle connection behaves as a hinge connection. However, in braced frames, due to existence of braces in some bays, in specified locations where gusset plates of brace are placed with beam-to-column connection in one joint, this assumption may not be accurate. This is due to the restraining of the beam from rotation by gusset plates that are placed either on the top and bottom of the beam or only on one side. In such cases, the simple beam-to-column connection may be transformed into a semi-hinge or... 

The oxidation of ferrous iron (Fe2+) in solution using Acidithiobacillus ferrooxidans has industrial applications exclusively in the regeneration of ferric iron (Fe3+) as an oxidizing agent for the removal of hydrogen sulfide from waste gases, desulfurization of coal, leaching of non-ferrous metallic sulfides and treatment of acid mine drainage. The aim of this investigation was to increase the bio-oxidation rate of ferrous sulfate by using immobilized cells. Rate of Fe2+ oxidation was determined in a packed-bed bioreactor configuration with monolithic particles being used as support material. Biooxidation of ferrous iron by immobilized cells was investigated in repeated batch culture and... 

In this work, systems of linear and nonlinear partial differential equations and the reaction-diffusion Brusselator model are handled by applying the variational iteration method. The Variational iteration method has the advantage of being more concise for analytical and numerical purposes. The results reveal that the method is very effective and convenient. © Sharif University of Technology, April 2008  

An analysis of resonant modes in ladder networks is performed using difference equations. Linear and loop configurations are studied and analytical relations are derived for the mode distributions and resonant frequencies of these networks, having arbitrary elements. Furthermore, it is shown that a) Modes with an exponential distribution along network nodes may exist in some cases and b) The mode distributions in loop networks are independent of network elements. Finally, a simple criterion is obtained for a loop structure to control the spacing between resonant frequencies. © Sharif University of Technology, April 2008  

The effect of compressive Residual Stress (RS) on the Stress Intensity Factors (SIFs) of fretting fatigue cracks was studied using semi-analytical methods. The fretting fatigue of a half-plane in contact with a flat rounded pad was taken into consideration, and RS such as those created by shot-peening were added to the model. Studies of several RS profiles were accomplished to consider the effect of changes in RS caused by stress relaxation during service or pretreatment and manufacturing discrepancies regarding parameters. The distribution of dislocations method was applied to the calculation of the SIFs of these cracks and was shown to be capable of dealing with these kinds of problems. It... 

In this paper, distribution of voltage along a general nonuniform transmission line is expanded in an appropriate form, and by employing an approach similar to conventional and modified differential transfer matrix methods already proposed for optical structures, analytical expressions are obtained for voltage/current distributions and reflection/transmission coefficients. This method shows great accuracy in different test cases and has been found to be superior to the well-known analytical method of small reflections. Notwithstanding, the overall accuracy of proposed approach is further improved by introducing the technique of multiple divisions. In particular, lossy/lossless tapered... 

N-Benzyl-DABCO-ammonium tribromide was found to be an efficient and recyclable reagent for the deprotection of dithioacetals in dichloromethane/ methanol at room temperature. The reaction can be performed cleanly, in short time, and in high yield. Copyright © Taylor & Francis Group, LLC  

Theoretical study of arrays of graphene ribbons is currently of high interest due to its potential application in beam splitters, absorbers, and polarizers. In this paper, an analytical method is presented for diffraction analysis of graphene ribbon arrays. Previous analytical studies were carried out in the regime where the lateral separation between the ribbons is much smaller than the wavelength of the incident wave. As such, they cannot be used to calculate the reflection coefficients of higher diffracted orders. In contrast, the method proposed here can predict the electromagnetic response of graphene ribbon arrays even when the array constant is larger than the wavelength. To reach our... 

A general three-dimensional semi-analytical solution of piezocomposite media consisting of various domains of distinct electro-mechanical properties is proposed. The interfaces between the domains may be non-planar. The geometry and boundary conditions may be arbitrary, and the applied loading can be in the form of traction, displacement, voltage, or any combination of them. In this approach, the unknown displacement field u1, u2, u3, and the electric potential φ are taken as appropriate functions in each domain, such that the continuity of the displacement field and the electric potential are exactly satisfied at the interfaces. Also, the continuities of traction stresses and normal... 

A new methodology is presented with which the likely impact of accident in one process unit of an industry on other process units can be forecast and assessed. The methodology is based on Monte Carlo Simulation and overcomes the limitations of analytical methods, used hitherto, which were inherently limited in their ability to handle the uncertainty and the complexity associated with domino effect phenomena. The methodology has been validated and its applicability has been demonstrated with two case studies  

In recent years axial flux permanent magnet (AFPM) machines have found industrial applications because of such characteristics as high power density, compact structure and disc-like shape. Like other electrical machines, prediction of flux density distribution in the air gap of AFPM is essential. In this paper, an analytical method for calculation of air gap flux density caused by armature reaction is presented. The solution is based on Maxwell's equations. Separation of variables method is applied to field equations and 2D distribution of magnetic flux density in the air gap calculated in term of Fourier series. The 2-D distribution of three-phase armature winding is modeled exactly....