Sharif Digital Repository

This work takes a new approach to solving non-hydrostatic equations of layered flows over bottom topography. A perturbation technique is used to find explicit expressions for a flow for different regimes of single- and two-layer flows over a sill. Excellent agreement with previous solutions and experimental data is obtained, and more details of the non-hydrostatic flow over a sill are revealed. The proposed method is simple and compact and removes the need for complex numerical techniques to solve the non-hydrostatic equations. It is shown that in the approach-controlled regime of two-layer flow over a sill, the flow upstream and farther downstream the sill crest can be described by the... 

A simple equation of state (EoS) has recently been introduced (J. Phys. Chem. B2009, 113, 11977-11987) as (Z - 1)v2 = e + f/ρ + gρ2, where Z ≡ pv/RT is the compressibility factor, v = 1/ρ is molar volume, and e, f, and g are temperature dependent parameters. This EoS has been found to be accurate for all types of nano and bulk solids and bulk fluids, in the entire temperature and pressure ranges for which experimental data are reported, except for the isotherms within 1 ≤ T r = T/Tc ≤ 1.1 for the spherical and near spherical species and for a wider temperature range for the cylindrical molecules. The aim of this work is to investigate the validity of a three-term expression similar to the... 

Hyperelastic behavior of isotropic incompressible rubbers are studied to develop a strain energy function. The proposed function includes only three material parameters which are related to physical properties of the material molecular network. Furthermore, the model benefits from well suitting in all ranges of stretch as well as possessing the property of deformation mode independency. This reduces the required number of experimental tests for parameter calibration. Results of the model are compared with results of Mooney-Rivlin, Arruda-Boyce, Gent and Gao models as well as the experimental data  

This paper has described a method to obtain the molecular weight distribution (MWD) of polymeric materials from their rheological data. The method has been developed for linear polymers with log normal molecular weight distribution. The rheological data required to obtain the molecular weight distribution are the shear storage modulus,G' (ω), and shear loss modulus,G' (ω) , extending from the terminal zone to the plateau region. For determining the molecular weight average, the method uses the relationship between stress moduli and relaxation spectrums, with the equation that connects dynamic rheological data with molecular weight distribution, and so it is not necessary to achieve the... 

This work concerns with developing a non-equilibrium model of gravity drainage in a single block. The proposed model which considers both non-equilibrium effects of capillary pressure and relative permeabilities is used for prediction of oil recovery by gravity drainage from a single block. Close agreement observed between the model results and experimental data disclosed that the non-equilibrium assumption is completely reliable for modeling of gravity drainage. The results revealed that when the characteristic time of the saturation variation is comparable with the time required to establish capillary equilibrium, the non-equilibrium effects in gravity drainage must be considered. The... 

In this study, the nonlinear partial differential equations governing two phase flow through porous media are solved using two different methods, namely, finite difference and finite element. The capillary pressure term is considered in the mathematical model. The numerical results on a 2-D test case are then compared with the experimental drainage process and water flooding performed on a glass type micromodel. Based on the obtained results, finite difference technique needs less computational time for solving governing equations of two phase flow, but findings of this method show less agreement with the experimental data. The finite element scheme was found to be more adequate and its... 

In this study, the artificial neural network (ANN) was used for the prediction of WDT. The inputs to network are molar mass and pressure, and the output is WDT at each input. A two-layer network with different hidden neurons and different learning algorithms such as LM, SCG, GDA and BR were examined. The network with 16 hidden neurons and Levenberg-Marquardt (LM) train function showed the best results in comparison with the other networks. Also, the predicted results of this network were compared with the thermodynamic models and better accordance with experimental data for ANN was concluded  

This work concerns with developing a non-equilibrium model of gravity drainage in a single block. The proposed model which considers both non-equilibrium effects of capillary pressure and relative permeabilities is used for prediction of oil recovery by gravity drainage from a single block. Close agreement observed between the model results and experimental data disclosed that the non-equilibrium assumption is completely reliable for modeling of gravity drainage. The results revealed that when the characteristic time of the saturation variation is comparable with the time required to establish capillary equilibrium, the non-equilibrium effects in gravity drainage must be considered. The... 

The effects of laser field and laser pulse width on the dissociation probability of C-H bond of CH4 have been investigated. Calculation of time dependent Schrödinger equation by grid spectral method is carried out and it is produced optimistic results in comparison to the earlier Quasi-classical calculations. The results show that there is an excellent match with experimental data. In this work, a number of results in the emerging field of laser with intensity of I = 8 × 1013 W cm-2 and pulse duration of 100 fs are presented. The present modulated field leads to more than 20% improvement in the dissociation probability  

In the present work, a mathematical model was developed based on finite difference method to predict the microporosity distribution in A356 aluminum alloy casting. Heat, mass, and gas conservation equations were solved in this model. Moreover, Darcy's equation was considered in the mushy zone. Results show that the distribution and concentration of microporosities in cast parts vary with both cooling rate and initial gas content. Simulation results were compared with experimental data where proportionally good agreement with experimental results was found. Finally, a complex cast part was simulated presenting the ability of the model to predict the porosities in industrial cast parts  

Embryogenesis, regeneration and cell differentiation in microbiological entities are influenced by mechanical forces. Therefore, development of mechanical properties of these materials is important. Neural network technique is a useful method which can be used to obtain cell deformation by the means of force-geometric deformation data or vice versa. Prior to insertion in the needle injection process, deformation and geometry of cell under external point-load is a key element to understand the interaction between cell and needle. In this paper the goal is the prediction of cell membrane deformation under a certain force, and to visually estimate the force of indentation on the membrane from... 

We present the kinetic parameters and equilibrium constant of the enzymatic glucose-fructose isomerization reaction with an immobilized glucose isomerase (IGI), Sweetzyme IT, using a batch stirred-tank reactor following the procedure developed by Dehkordi et al. (AIChE J. 2008, 54, 1333). The model predictions were compared with the experimental data and fair agreements were found. The influence of temperature on the equilibrium constant and kinetic parameters of glucose to fructose isomerization reaction was investigated. In addition, the frequency factors and the activation energies were determined by using Arrhenius-like expressions. Furthermore, correlations were found for the maximum... 

A unified model composed of the flow function model, dislocation model and Taylor theory is used to investigate the evolution of dislocation density, cell size, and strength of tantalum during ECAP process. From the flow function model, strain and strain rate distributions are achieved and then using a modified version of three-dimensional ETMB model, the dislocation density, cell size, and strength are predicted. The predicted dislocation density, cell size, and strength are compared with the experimental data and a remarkable agreement is obtained. In addition, the effect of dynamic recovery on the strength of the processed tantalum is modeled and compared with other materials. © 2008... 

Using a mechanical model and dislocation density based model, the evolutions of dislocation density and flow stress of pure copper during constrained groove pressing (CGP) process are investigated. In this regard, the strain and strain rate are achieved from the mechanical model and then input into the dislocation model. To verify the predicted flow stress, the process of constrained groove pressing is performed on the sheets of pure copper from one to three passes. The predicted flow stresses are compared with the experimental data and a good agreement is observed. Also, it is found that during the straining of the copper sheet in CGP process, the dislocation density and strength dropping... 

A feed forward multi-layer perceptron neural network was developed to predict carbon dioxide loading capacity of chemical absorbents over wide ranges of temperature, pressure, and concentration based on the molecular weight of solution. To verify the suggested artificial neural network (ANN), regression analysis was conducted on the estimated and experimental values of CO2 solubility in various aqueous solutions. Furthermore, a comparison was performed between results of the proposed neural network and experimental data that were not previously used for network training, as well as a set of data for binary solutions. Comparison between the proposed multi-layer perceptron (MLP) network and... 

An important aspect of corrosion prediction for oil/gas wells and pipelines is to obtain a realistic estimate of the corrosion rate. Corrosion rate prediction involves developing a predictive model that utilizes commonly available operational parameters, existing lab/field data, and theoretical models to obtain realistic assessments of corrosion rates. This study presents a new model to predict corrosion rates by using artificial neural network (ANN) systems. The values of pH, velocity, temperature, and partial pressure of the CO2 are input variables of the network and the rate of corrosion has been set as the network output. Among the 718 data sets, 503 of the data were implemented to find... 

In tube hydroforming, the inverse finite element method (IFEM) has been used for estimating the initial length of tube, axial feeding and fluid pressure. The already developed IFEM algorithm used in this work is based on the total deformation theory of plasticity. Although the nature of tube hydroforming is three-dimensional deformation, in this paper a modeling technique has been used to perform the computations in two-dimensional space. Therefore, compared with conventional forward finite element methods, the present computations are quite fast with no trial and error process. In addition, the solution provides all the components of strain. Using the forming limit diagram (FLD), the... 

In this study, the microstructural and mechanical features of monolithic pure Cu and Cu matrix nanocomposites reinforced with three different fractions (2, 4, and 6. vol%) of SiC nanoparticles (n-SiC) fabricated via a combination of high energy mechanical milling and hot pressing techniques were investigated. The fabricated composites exhibited homogeneous distribution of the n-SiC with few porosities. It was found that the grain refinement, the planar features within the grains, and the lattice strains increase with increase in the n-SiC content. The yield and compressive strengths of the nanocomposites were significantly improved with increases in the n-SiC content up to 4. vol%; then they... 

A general flow line model is developed to investigate the deformation behavior of Cu and Al through Bc route of Equal Channel Angular Pressing process at curved and sharp dies. Considering the Taylor theory, the obtained strain and strain rate from the flow line model and also using a modified version of ETMB model, the evolutions of nano-structure in the processed Cu and Al are predicted. Comparison between the modeling results and experimental data is carried out and a reasonable agreement is achieved. The results show that the deformation in the sharp die occurs in a narrow zone with higher strain rate than that in the curved die. Also, the cell size of the processed Cu is smaller than... 

A novel combination of discontinuous molecular dynamics and the Langevin equation, together with an intermediate-resolution model of proteins, is used to carry out long (several microsecond) simulations in order to study transport of proteins in nanopores. We simulated single-domain proteins with the α-helical native structure. Both attractive and repulsive interaction potentials between the proteins and the pores' walls are considered. The diffusivity D of the proteins is computed not only under the bulk conditions but also as a function of their "length" (the number of the amino-acid groups), temperature T, pore size, and interaction potentials with the walls. Compared with the...