Sharif Digital Repository

In this research, an extended finite element model has been investigated. Investigation of opening and closure stress always has been one of the difficult parameters to analysis of results; therefore, the utilization of finite element methods would be a good and logical alternative for this purpose. In addition, linear elastic fracture criteria are used for validation of numerical results from the simulation. In this work, a detailed analysis of the influence of different parameters in the results of a specific specimen with a semi-elliptical tooling groove in terms of closure and opening stress is presented, and the impact of optimum element size in fracture characteristic in various load... 

The capability of backward extrusion (BE) method was assessed to achieve modified structures in AZ80 magnesium alloy. At first, 3D-Deform was employed to simulate the deformation flow through the deformed cup which gives an evidence from the flow behavior of the material. The material was processed via BE method at various temperatures of 250, 350, and 450 °C. Metallographic investigations were conducted in three different regions of the BE-processed cup (wall, bottom, and flow channel). The main feature observed at the wall of the BE cup was the presence of mechanical twins, the frequency of which was reduced by raising the process temperature. The flow localization in the form of shear... 

The capability of backward extrusion (BE) method was assessed to achieve modified structures in AZ80 magnesium alloy. At first, 3D-Deform was employed to simulate the deformation flow through the deformed cup which gives an evidence from the flow behavior of the material. The material was processed via BE method at various temperatures of 250, 350, and 450 °C. Metallographic investigations were conducted in three different regions of the BE-processed cup (wall, bottom, and flow channel). The main feature observed at the wall of the BE cup was the presence of mechanical twins, the frequency of which was reduced by raising the process temperature. The flow localization in the form of shear... 

The free vibration analysis of rotating axially functionally graded nanobeams under an in-plane nonlinear thermal loading is provided for the first time in this paper. The formulations are based on Timoshenko beam theory through Hamilton’s principle. The small-scale effect has been considered using the nonlocal Eringen’s elasticity theory. Then, the governing equations are solved by generalized differential quadrature method. It is supposed that the thermal distribution is considered as nonlinear, material properties are temperature dependent, and the power-law form is the basis of the variation of the material properties through the axial of beam. Free vibration frequencies obtained are... 

The original version of this article unfortunately contained a mistake. The affiliation 3 was incorrect. The correct affiliation 3 is: Department of Mechanical Engineering, Payame Noor University (PNU), P. O. Box 19395-3697, Tehran, Iran. © 2016, Indian Society of Haematology & Transfusion Medicine  

The effect of graphene (G) and graphene oxide (GO), used as the nanofiller in polymer nanocomposites (NC), on the structural and dynamic properties of polymer chains, has been studied by means of molecular dynamics (MD) simulations. Two polymers, i.e., poly(propylene) and poly(vinyl alcohol), are employed as matrices to cover a wider range of polymer–filler interactions. The local structural properties, e.g., density profile, average Rg, and end-to-end distance as well as dynamic properties, e.g., estimated translational and orientational relaxation times, of polymer chains are studied. In addition, the interaction energies are estimated between polymers and nanofillers for different hybrid... 

The vibration analysis of rotating, functionally graded Timoshenko nano-beams under an in-plane nonlinear thermal loading is studied for the first time. The formulation is based on Eringen's nonlocal elasticity theory. Hamilton's principle is used for the derivation of the equations. The governing equations are solved by the differential quadrature method. The nano-beam is under axial load due to the rotation and thermal effects, and the boundary conditions are considered as cantilever and propped cantilever. The thermal distribution is considered to be nonlinear and material properties are temperature-dependent and are changing continuously through the thickness according to the power-law... 

The feasibility of a mesophilic anaerobic treatment of an alcohol distillery wastewater (beet molasses stillage) was studied in a 1300 I Upflow Anaerobic Sludge Blanket (UASB) reactor for a period of 180 days. The system was seeded with 600 L of mesophilic anaerobic sludge harvested from the bottom of a dairy anaerobic lagoon. Nutrients were added to acidified effluent and after adjusting the pH in an equalization tank, the system was fed with a diluted effluent containing COD in the range of 1000-11000 mg/L at 30°C. Initially, the system had an OLR of 1 kg COD m-3 d-1 and upflow velocity was maintained at 0.6 m/h (HRT= 6 h) throughout the study. A gradual increase in OLR, through increased... 

A cell migration numerical simulation is presented to mimic the motility of endothelial cells subjected to the concentration gradients of a Forebrain embryoniccortical neuron Conditioned Medium (CM). This factor was previously shflown to induce the directional chemotaxis of endothelial cells with an over-expressed G protein coupled receptor 124 (GPR 124). A cell simulator program incorporates basic elements of the cell cytoskeleton, including membrane, nucleus and cytoskeleton. The developed 2D cell model is capable of responding to concentration gradients of biochemical factors by changing the cytoskeleton arrangement. Random walk force, cell drag force and cell inertial effects are also... 

A new approach for attaining numerical solution to sinusoidal steady-state Maxwell's equations is developed. This approach is based on Yee's method, and can be applied on unstructured grids. A problem is solved by the method and the results show good agreement with the available analytical solution. This method can be improved to be applicable for general unsteady problems. © 2018 Sharif University of Technology. All rights reserved  

The present work was conducted to study the effects of microstructural evolutions on the mechanical and wear behavior of an accumulative back extruded aluminum-based in-situ composite. The mechanical fragmentation and thermal disintegration of the primary and secondary Mg2Si particles were found as the main microstructural changes. For that reason, the particle interspacing was decreased, the sharp ends were modified, and the reinforcements were more uniformly distributed. Surprisingly, the wear loss was dramatically decreased in processed materials in comparison to the as-received one. Oxidation and delamination were identified as the dominant wear mechanisms. These were addressed... 

Comprehensive two-dimensional gas chromatography and flame ionization detection combined with unfolded-partial least squares is proposed as a simple, fast and reliable method to assess the quality of gasoline and to detect its potential adulterants. The data for the calibration set are first baseline corrected using a two-dimensional asymmetric least squares algorithm. The number of significant partial least squares components to build the model is determined using the minimum value of root-mean square error of leave-one out cross validation, which was 4. In this regard, blends of gasoline with kerosene, white spirit and paint thinner as frequently used adulterants are used to make... 

We study critical properties of the continuous Abelian sandpile model with anisotropies in toppling rules that produce ordered patterns on it. Also, we consider the continuous directed sandpile model perturbed by a weak quenched randomness, study critical behavior of the model using perturbative conformal field theory, and show that the model has a random fixed point. © 2009 The American Physical Society  

The vibration analysis of rotating, functionally graded Timoshenko nano-beams under an in-plane nonlinear thermal loading is studied for the first time. The formulation is based on Eringen's nonlocal elasticity theory. Hamilton's principle is used for the derivation of the equations. The governing equations are solved by the differential quadrature method. The nano-beam is under axial load due to the rotation and thermal effects, and the boundary conditions are considered as cantilever and propped cantilever. The thermal distribution is considered to be nonlinear and material properties are temperature-dependent and are changing continuously through the thickness according to the power-law... 

Ground reaction force (GRF) characteristics of amputee walking are important for the analysis of clinical gait data, and also to update model reference adaptive impedance (MRAI) controllers. GRF estimation is a better alternative than direct GRF measurement because of the disadvantages of load cells, such as high cost, integration difficulties due to weight and physical dimensions, the possibility of overload, and measurement noise. This paper presents four robust MRAI observer/controller combinations for GRF estimation-based control of a prosthesis and a legged robot model in the presence of parametric uncertainties and unmodeled dynamics, in which the robot model is employed to mimic... 

The soil slurry-sequencing bath reactor (SS-SBR) was studied to treat poorly graded sand with clay (SP-SC) contaminated by aged petroleum hydrocarbons and polycyclic aromatic hydrocarbons (PAHs) with concentrations of 23000 mg/kg and 750 mg/kg respectively. An 8 L bioreactor was operated with a 10% solid concentration (0.1 kg dry soil/L slurry). The fill period was relatively instantaneous, and the draw period lasted approximately 1 minute so the react period comprised essentially the entire cycle time. In the draw period a fraction of slurry (10%) was removed from the SS-SBR weekly and it was replaced with untreated slurry. This volumetric replacement strategy provided 70 days hydraulic... 

The objective of this article is to study the performance of iterative parameter and function estimation techniques to solve simultaneously two unknown functions (quadratic in time, and linear in time and space) using transient inverse heat conduction method in conjunction with a geometrical domain decomposition approach, in cylindrical coordinates. For geometrical decomposition of physical domain, a multi-block method has been used. The numerical scheme for the solution of the governing partial differential equations is the finite element method. The results of the present study for a configuration composed of two joined disks with different heights are compared to those of exact heat... 

The aim of this study is to develop iterative regularization algorithms based on parameter and function estimation techniques to solve two-dimensional/axisymmetric transient inverse heat conduction problems in curvilinear coordinate system. The multiblock method is used for geometric decomposition of the physical domain into regions with patched-overlapped interface grids. The central finite-difference version of the alternating-direction implicit technique together with structured body-fitted grids is implemented for numerical solution of the direct problem and other partial differential equations derived by inverse analysis. The approach of estimating unknown parameters and functions is... 

In this study a structured multiblock grid is used to solve two-dimensional transient inverse heat conduction problems. The multiblock method is implemented for geometric decomposition of the physical domain into regions with blocked interfaces. The finite-element method is employed for direct solution of the transient heat conduction equation in a Cartesian coordinate system. Inverse algorithms used in this research are iterative Levenberg-Marquardt and adjoint conjugate gradient techniques for parameter and function estimations. The measured transient temperature data needed in the inverse solution are given by exact or noisy data. Simultaneous estimation of unknown linear/nonlinear... 

In this paper, the transient motion of a three unit intelligent Pipe Inspection Gauge (PIG) while moving across anomalies and bends inside gas/oil pipeline has been investigated. The pipeline fluid has been considered as isothermal and compressible. In addition, the pipeline itself has also been considered to be flexible. The fluid continuity and momentum equations along with the 3D multi body dynamic equations of motion of the pig comprise a system of coupled dynamic differential equations which have been solved numerically. Pig's position and velocity profiles as well as upstream and downstream fluid's pressure waves are presented as simulation results which provide a better understanding...