Sharif Digital Repository

We consider the application of the Finite Element Method (FEM) for numerical pressure transient analysis under conditions where no reliable analytical solution is available. Pressure transient analysis is normally based on various analytical solutions of the linear one-dimensional diffusion equation under restrictive assumptions about the formation and its boundaries. For example, the formation is either assumed isotropic or a restrictive a priori assumption is made about its heterogeneity. The wellbore storage effect is also often considered without regard to the possibility of phase redistribution. In many practical situations such restrictions are not justified and analytical solutions do... 

This paper investigates the effect of microstructure development on mechanical properties of diffusion brazed IN718 nickel-based superalloy using a Ni-Cr-Si-B-Fe filler metal. The phase transformations during diffusion brazing of IN718/Ni-Cr-Si-B-Fe/IN718, which dictate the microstructure of the bonds are governed by diffusion-induced isothermal solidification, cooling-induced athermal solidification, and diffusion-induced solid-state precipitation. It was found that when partial isothermal solidification occurs at the bonding temperature, the residual liquid is transformed into eutectic-type microconstituents. Considering solute redistribution and segregation behavior of the melting point... 

Shot peening is one of the most effective surface strengthening treatment technologies in which compressive residual stresses are induced beneath the specimen surface. Effects of various factors on the distribution of residual stress profile induced by shot peening have been investigated by many researchers. However, initial residual stresses are one of the important factors which affect the shot peening residual stress.This study is aimed to present comprehensive numerical and experimental study on the effect of initial residual stresses on the shot peened specimen. Initial residual stresses were induced using a four-point bending rig and grinding. Incremental center hole drilling (ICHD)... 

Many technological networks can experience random and/or systematic failures in their components. More destructive situations can happen if the components have limited capacity, where the failure in one of them might lead to a cascade of failures in other components, and consequently break down the structure of the network. In this paper, the tolerance of cascaded failures was investigated in weighted networks. Three weighting strategies were considered including the betweenness centrality of the edges, the product of the degrees of the end nodes, and the product of their betweenness centralities. Then, the effect of the cascaded attack was investigated by considering the local weighted flow... 

A sampling and switching method for a binary weighted digital-to-analogue converter (DAC) in successive approximation register (SAR) analogue-to-digital converters (ADCs) is presented. This sampling method is proposed to reduce the switching energy. Thanks to the proposed switching method, only one reference voltage (Vcm = 1/2 Vref) is required which helps to improve the precision of the DAC along with energy reduction compared with those methods that use more than one reference voltage. The switching energy and area of the DAC reduce by 97.66% and 50% compared with the conventional binary weighted DAC  

Redistribution of alloying elements in the transient liquid phase (TLP) bonding zone of IN738LC/ BNi-3/IN738LC was studied to investigate microstructural evolution in this area. Wavelength dispersive spectrometry and electron probe microanalysis revealed that, during non-isothermal solidification in the TLP bonding zone, enrichment of residual liquid phase with the positive segregating elements caused formation of intermetallic in the bonding zone. Scanning electron microscopy observation Indicated that the redistribution of alloying elements, between TLP bonding zone and base alloy, resulted In formation of a γ′ boundary layer, containing high density of fine γ′, around the bonding zone.... 

A hybrid current/voltage sense amplification scheme is proposed for high speed SRAMs. The scheme includes an offset cancellation technique which makes it robust against the current sense amplifier (CSA) mismatch. The offset cancellation allows for fast open loop operation of the differential CSA. A fourfold reduction of the cell access time is achieved compared to the conventional scheme under similar cell current and bitline capacitance. Thanks to its automatic turn off nature, the proposed CSA incurs zero static power without an auxiliary turn off circuit. The reduction of the charge redistribution on the bitlines offers a low bitline dynamic power consumption as well. In this work, the... 

Construction of underground structures in urban areas is a very challenging work. There are generally two methods of construction, an open cut-and-cover and underground method. To eliminate the subsurface and surface disturbance and street traffic problems, underground method is preferred. The stress redistribution caused by underground excavation induces movements and deformation in the earth mass and ultimately at the ground surface. This is more pronounced in large space excavations. Generally pre-supporting system is used to control ground deformation and thus enhance its stability. In this paper an innovative pre-supporting system is presented. Concrete Arch Pre-supporting System (CAPS)... 

Construction of underground structures in urban areas is a very challenging work. There are generally two methods of their construction, an open cut-and-cover and underground method. To eliminate the subsurface and surface disturbance and street traffic problems, underground method is preferred. The stress redistribution caused by underground excavation induces movements in the earth mass and ultimately at the ground surface. This is more pronounced in large space excavations. Generally pre-supporting system is used to control ground deformation and thus enhance its stability. In this paper an innovative pre-supporting system is presented. Concrete Arch Pre-supporting System (CAPS) is... 

Construction of underground structures in urban areas is a very challenging work. There are generally two methods of their construction, an open cut-and-cover and underground method. To eliminate the subsurface and surface disturbance and street traffic problems, underground method is preferred. The stress redistribution caused by underground excavation induces movements in the earth mass and ultimately at the ground surface. This is more pronounced in large space excavations. Generally pre-supporting system is used to control ground deformation and thus enhance its stability. In this paper an innovative pre-supporting system is presented. Concrete Arch Pre-supporting System (CAPS) is... 

Rock formations are always under in situ stresses due to overburden or tectonic stresses. Drilling a well will lead to stress redistribution around the well. Understanding such a stress redistribution, and adopting a proper failure criterion, play a vital role in predicting any potential wellbore failure. However, most of the published analytical models are based on assumptions that do not satisfy the boundary conditions during production, that is, when the well pressure is less than the pore pressure. This paper is aimed at the modeling of the stress regime around the wellbore through combining the poroelastic model with proper boundary conditions under different flow regimes. As a result,...