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Nonlinear interstory drift contours for idealized forward directivity pulses using "modified fish-bone" models
, Article Advances in Structural Engineering ; Volume 18, Issue 5 , May , 2015 , Pages 603-627 ; 13694332 (ISSN) ; Khosravi, H ; Jamnani, H. H ; Sharif University of Technology
Multi-Science Publishing Co. Ltd
2015
Abstract
Four 5-, 10-, 20- and 30-story moment frames, representing low-, mid-, and two high-rise structures, were subjected to a great number of idealized directivity pulses. The amplitudes and periods of pulses vary from 0.02 g to 1.0 g and 0.5 to 12 sec, respectively. Over 1400 nonlinear dynamic analyses of low- to high-rise moment frames were performed which were feasible through using modified fish-bone model. The distribution of interstory drift along the height was studied and two applied contours were proposed: (i) the maximum interstory drift contour, and (ii) the critical story contour. These contours were demonstrated versus the ratio of natural period of the structure to the pulse period...
Performance of RC Shear Walls Strengthened by Diagonal Strips of Steel Plates under Seismic Loading
, M.Sc. Thesis Sharif University of Technology ; khalo, Alireza (Supervisor)
Abstract
Even though a considerable amount of research has been conducted on composite wall system during past years, very limited research has been reported on shear walls strengthened by steel plates. In 2008, the composite shear wall, which consisted of reinforced concrete wall, retrofitted by steel plates, attached to both sides of RC walls using mechanical connectors in form of shear studs, bolts or lateral ties tested under axial load and lateral force. In this research, seismic behavior of RC shear walls strengthened by diagonal strips of steel plates is going to be studied. The result will be compared with RC shear wall which fully covered by steel plates.The behavior of RC shear wall will be...
Numerical Modeling and Optimization of Cold and Hot Powder Forming Processes
, Ph.D. Dissertation Sharif University of Technology ; Khoei, Amir Reza (Supervisor) ; Khalo, Ali Reza (Supervisor)
Abstract
In this thesis, a shape optimization technique is presented for powder forming processes based on the genetic algorithm approach. The numerical modeling of powder compaction simulation is applied based on a large deformation formulation, powder plasticity behavior, and frictional contact algorithm. A Lagrangian finite element formulation is employed for large powder deformations. A cap plasticity model is used in numerical simulation of nonlinear powder behavior. The influence of powder-tool friction is simulated by the use of penalty approach in which a plasticity theory of friction is incorporated to model sliding resistance at the powder-tool interface. For hot compaction process coupled...
SUT-DAM: An integrated software environment for multi-disciplinary geotechnical engineering
, Article Advances in Engineering Software ; Volume 37, Issue 11 , 2006 , Pages 728-753 ; 09659978 (ISSN) ; Gharehbaghi, S. A ; Azami, A. R ; Tabarraie, A. R ; Sharif University of Technology
Elsevier Ltd
2006
Abstract
As computer simulation increasingly supports engineering design, the requirement for a computer software environment providing an integration platform for computational engineering software increases. A key component of an integrated environment is the use of computational engineering to assist and support solutions for complex design. In the present paper, an integrated software environment is demonstrated for multi-disciplinary computational modeling of structural and geotechnical problems. The SUT-DAM is designed in both popularity and functionality with the development of user-friendly pre- and post-processing software. Pre-processing software is used to create the model, generate an...
Contact friction simulation in powder compaction process based on the penalty approach
, Article Materials and Design ; Volume 29, Issue 6 , 2008 , Pages 1199-1211 ; 02613069 (ISSN) ; Khoei, A. R ; Khaloo, A. R ; Sharif University of Technology
Elsevier Ltd
2008
Abstract
In this paper, the influence of powder-tool friction on the mechanical properties of the final product is investigated in pressing metal powders. A computational algorithm is presented for simulation of frictional contact in the compaction process of powder. The large deformation finite element (FE) formulation is characterized by the use of penalty approach in which a plasticity theory of friction is incorporated to simulate sliding resistance at the powder-tool interface. The constitutive relations for friction are derived from a Coulomb friction law. A double-surface cap plasticity model is employed together with the nonlinear contact friction behavior in numerical simulation of powder...
An atomistic–continuum multiscale analysis for heterogeneous nanomaterials and its application in nanoporous gold foams
, Article Applied Mathematical Modelling ; Volume 107 , 2022 , Pages 353-378 ; 0307904X (ISSN) ; Sameti, A. R ; Khoei, A. R ; Sharif University of Technology
Elsevier Inc
2022
Abstract
In this paper, an atomistic–continuum homogenization multiscale method is developed to study the nonlinear behavior of heterogeneous nanomaterials. The atomistic representative volume element (RVE) with vacancy and/or void defects are analyzed by employing the fully atomistic method, in which the nucleation, migration, and elimination of dislocation, as well as the dislocation-vacancy interaction, are captured. The coarse-scale material domain is modeled within the framework of the nonlinear finite element method, and the impression of nanoscale material defects is investigated by upscaling the stress tensor and tangent modulus from the atomistic RVE based on the Hill-Mandel principle. The...
Improved passivity criterion in haptic rendering: influence of coulomb and viscous friction [electronic resource]
, Article Advanced Robotics ; 2014 Volume 28, Issue 10 ; R. Bozorgmehry, R ; Nahvi, A ; Meghdari, A ; Asgari, P ; Sharif University of Technology
Abstract
In this paper, a new criterion for passivity of haptic devices is obtained. This criterion creates a relationship between Coulomb friction coefficient, viscous friction coefficient, sampling rate, and the maximum simulated stiffness. The process of derivation of the passivity criterion is described in detail. This criterion is improved compared with other existing criteria and predicts passivity in haptic rendering more accurately. In particular, for speeds of less than 5 cm/s, the new passivity criterion should replace the previous criteria to avoid unwanted vibrations of stiff virtual walls. Analytical and numerical investigations are presented to validate the new criterion. A specific...
Growth and field emission study of molybdenum oxide nanostars
, Article Journal of Physical Chemistry C ; Volume 113, Issue 44 , 2009 , Pages 19298-19304 ; 19327447 (ISSN) ; Azimirad, R ; Zavarian, A. A ; Zaker Moshfegh, A. R ; Sharif University of Technology
2009
Abstract
The field emission properties of MoO2 nanostars grown on a silicon substrate and their emission performance in various vacuum gaps are reported in this article. A new structure of molybdenum oxides, named a nanostar, is grown by thermal vapor deposition with a length of ̃1 μm, a thickness of ̃50 nm, and its width in the range of 500-700 nm. The morphology, structure, composition, and chemical states of the prepared nanostars were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). According to XRD analysis, the grown nanostructures are composed of both crystalline Mo4O11 and...
Design and control of an assistive exoskeleton with passive toe joint
, Article International Journal of Mechatronics and Automation ; Volume 6, Issue 2-3 , 2018 , Pages 83-93 ; 20451059 (ISSN) ; Shariat, A ; Khezrian, R ; Zibafar, A ; Rashidi, A. R ; Rostami, H ; Vossoughi, G. R ; Selk Ghafari, A ; Sharif University of Technology
Inderscience Enterprises Ltd
2018
Abstract
Several exoskeletons with various configurations and degrees-of-freedoms (DOFs) have been introduced in the literature, but not many have addressed the optimal selection of the mechanism's DOFs. In the proposed system a semi-passive toe joint is introduced to achieve several advantages. The performance of the proposed novel passive toe joint is evaluated experimentally. In addition, the semi-passive abduction/adduction DOFs in the hip joint and eversion/inversion DOFs in ankle joint is proposed to facilitate turning while providing more comfort during normal walking. The effect of passive DoFs existence on the user comfortability is studied with the aid of three kinematic indices. In the...
Theoretical investigation of dielectric corona pre-ionization TEA nitrogen laser based on transmission line method
, Article Optics and Laser Technology ; Volume 39, Issue 5 , 2007 , Pages 1014-1019 ; 00303992 (ISSN) ; Fallah, R ; Ganjovi, A. R ; Bahrampour, A ; Sharif University of Technology
2007
Abstract
This paper models the dielectric corona pre-ionization, capacitor transfer type of flat-plane transmission line traveling wave transverse excited atmospheric pressure nitrogen laser by a non-linear lumped RLC electric circuit. The flat-plane transmission line and the pre-ionizer dielectric are modeled by a lumped linear RLC and time-dependent non-linear RC circuit, respectively. The main discharge region is considered as a time-dependent non-linear RLC circuit where its resistance value is also depends on the radiated pre-ionization ultra violet (UV) intensity. The UV radiation is radiated by the resistance due to the surface plasma on the pre-ionizer dielectric. The theoretical predictions...
A study of the reliability of various types of the electric vehicles
, Article 2012 IEEE International Electric Vehicle Conference, IEVC 2012 ; 2012 ; 9781467315623 (ISBN) ; Ghahnavieh, A. R ; Mobarakeh, A. S
2012
Abstract
The reliability Studies are done in order to determine the probability of functioning or availability of different engineering systems. These studies can also provide a basis for comparing different structures of a system and can be used as a tool to improve the system design. Also, reliability is an important consideration in the planning, design and operation of transit system. Since the issue of the reliability of electric vehicles has not been sufficiently and seriously evaluated yet, so in this paper, the reliability of the various types of these kinds of vehicles will be discussed and then the reliability indices of them will be compared with each other and with the conventional cars
A new wideband MIMO channel model for simulating 5-GHz band indoor WLANs
, Article 2006 IEEE 64th Vehicular Technology Conference, VTC-2006 Fall, Montreal, QC, 25 September 2006 through 28 September 2006 ; 2006 , Pages 2298-2303 ; 15502252 (ISSN); 1424400635 (ISBN); 9781424400638 (ISBN) ; Golparvar Roozbahani, M ; Shishegar, A. A ; Enayati, A. R ; Alihemmati, R ; Sharif University of Technology
2006
Abstract
Considerable interest in the indoor applications of wireless local-area networks (WLANs) demands some powerful simulation methods of these systems. Proper modeling of the physical propagation channel is crucial in this context. A novel simulation method for indoor wideband multi-input multi-output (MIMO) channel at the operating frequency band of IEEE 802.11a, HIPERLAN/2, and the emerging IEEE 802.11n standards is presented in this paper which is suitable for performance analysis of MIMO techniques in these systems. The presented model is developed on the basis of a previously proposed channel representation at the same frequency band. Simulation results for MIMO channel capacity are...
Modified carrageenan. 4. Synthesis and swelling behavior of crosslinked kappa C-g-AMPS superabsorbent hydrogel with antisalt and pH-responsiveness properties [electronic resource]
, Article Journal of Applied Polymer Science ; Vol.98, No.1, 255-263, 2005 ; Hosseinzadeh, H ; Mazidi, R
Abstract
To synthesize a novel biopolymer-based superabsorbent hydrogel, 2-acrylamido-2-methylpropanesulfonic acid (AMPS) was grafted onto kappa-carrageenan (KC) backbones. The graft copolymerization reaction was carried out in a homogeneous medium and in the presence of ammonium persulfate (APS) as an initiator, N,N,N',N'-tetramethyl ethylenediamine (TMEDA) as an accelerator, and N,N'-methylene bisacrylamide (MBA) as a crosslinker. A proposed mechanism for KC-g-AMPS formation was suggested and the hydrogel structure was confirmed using FTIR spectroscopy. The affecting variables on swelling capacity, i.e., the initiator, the crosslinker, and the monomer concentration, as well as reaction temperature,...
Effect of TiO2 nanofiber density on organic-inorganic based hybrid solar cells
, Article International Journal of Engineering, Transactions A: Basics ; Vol. 27, issue. 7 , 2014 , p. 1133-1138 ; Kasaeian, A. B ; Nikfarjam, A. R ; Mohammadpour, R ; Sharif University of Technology
2014
Abstract
In this work, a comparative study of hybrid solar cells based on P3HT and TiO2 nanofibers was accomplished. Electrospinning, a low cost production method for large area nanofibrous films, was employed to fabricate the organic-inorganic hybrid solar cells based on poly (3-hexylthiophene) and TiO2 nanofibers. The performance of the hybrid solar cells was analyzed for four density levels of TiO2 nanofibers which resulted in the average power conversion efficiency of about 0.0134% under AM 1.5 simulated illuminations (100 mWcm-2). It is found that the higher densities of TiO2 lead to more interface area and generating exciton, so the power conversion efficiency will be increased till the active...
Forming limit diagrams by including the M–K model in finite element simulation considering the effect of bending
, Article Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications ; Volume 232, Issue 8 , 2018 , Pages 625-636 ; 14644207 (ISSN) ; Hashemi, R ; Ghazanfari, A ; Naghdabadi, R ; Assempour, A ; Sharif University of Technology
SAGE Publications Ltd
2018
Abstract
Forming limit diagram is often used as a criterion to predict necking initiation in sheet metal forming processes. In this study, the forming limit diagram was obtained through the inclusion of the Marciniak–Kaczynski model in the Nakazima out-of-plane test finite element model and also a flat model. The effect of bending on the forming limit diagram was investigated numerically and experimentally. Data required for this simulation were determined through a simple tension test in three directions. After comparing the results of the flat and Nakazima finite element models with the experimental results, the forming limit diagram computed by the Nakazima finite element model was more convenient...
Residual stresses in radial and indentation forging of tubes
, Article 2005 SAE World Congress, Detroit, MI, 11 April 2005 through 14 April 2005 ; 2005 ; 01487191 (ISSN) ; Ameli, A ; Movahhedy, M. R ; Mashregi, A. R ; Sharif University of Technology
SAE International
2005
Abstract
Radial forging and indentation forging processes are two processes used for sizing and/or internal profiling of tubes. In this paper, the two processes are simulated using finite element method and their results are compared with Experimental results. The purpose of this paper is to compare the pattern of residual stresses in both processes. Copyright © 2005 SAE International
Full scale analysis of apple juice ultrafiltration and optimization of diafiltration
, Article Separation and Purification Technology ; Volume 47, Issue 1-2 , 2005 , Pages 52-57 ; 13835866 (ISSN) ; Tabatabaeenezhad, A. R ; Roostaazad, R ; Khoshfetrat, A. B ; Sharif University of Technology
2005
Abstract
Declining permeate flux and increasing retentate solute concentration during a full scale apple juice ultrafiltration process was investigated. A modified equation and procedure was used for predicting retentate solute concentration (pectin) in the system. Solute concentration in the retentate was indirectly evaluated using the measured values of viscosity, temperature and Brix. The gel-polarization model was then used to analyze the collected data and a good agreement was observed between the experimental data and the model predictions. Fitted model parameters were very close to the published literature values for similar studies in pilot scale systems. According to the model, the optimum...
Modeling of pressure-sensitive materials using a cap plasticity theory in extended finite element method
, Article AMPT/ANMEOS Part 2 ; Volume 164-165 , 2005 , Pages 1248-1257 ; 09240136 (ISSN) ; Azami, A. R ; Khoei, A. R ; Dobrzanski L ; Sharif University of Technology
2005
Abstract
In this paper, a new computational technique based on the extended finite element method (X-FEM) is presented in elasto-plastic behavior of pressure-sensitive material. The cap plasticity model is employed within the X-FEM framework in numerical simulation of powder die pressing. The double-surface plasticity model includes a failure surface and an elliptical yield cap, which closes the open space between the failure surface and hydrostatic axis. The yield cap expands in the stress space according to a specified hardening rule. Application of the X-FEM in simulation of two phase plasticity continuums is presented in an incremental manner and the role of sub-elements in the partition of unity...
Rapid microwave-assisted synthesis of PVP-coated ultrasmall gadolinium oxide nanoparticles for magnetic resonance imaging
, Article Chemical Physics ; Volume 453-454 , May , 2015 , Pages 35-41 ; 03010104 (ISSN) ; Madaah Hosseini, H. R ; Khodaei, A ; Montazerabadi, A. R ; Irajirad, R ; Oghabian, M. A ; Delavari,H. H ; Sharif University of Technology
Elsevier
2015
Abstract
Synthesis of polyvinyl pyrrolidone (PVP) coated ultrasmall Gd2 O3 nanoparticles (NPs) with enhanced T1 -weighted signal intensity and r2 /r1 ratio close to unity is performed by a microwave-assisted polyol process. PVP coated Gd2 O3 NPs with spherical shape and uniform size of 2.5 ± 0.5 nm have been synthesized below 5 min and structure and morphology confirmed by HRTEM, XRD and FTIR. The longitudinal (r1 ) and transversal relaxation (r2 ) of Gd2 O3 NPs is measured by a 3 T MRI scanner. The results showed considerable increasing of relaxivity for Gd2 O3 NPs in...
Three-dimensional forced Burgers turbulence supplemented with a continuity equation
, Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 63, Issue 5 II , 2001 , Pages 563081-5630813 ; 15393755 (ISSN) ; Masoudi, A. A ; Rahimi Tabar, M. R ; Rastegar, A. R ; Shahbazi, F ; Sharif University of Technology
2001
Abstract
The turbulent limit of three dimensional Burger equation was studied. An adjusting parameter emerged through the calculations, based on mean field analysis, that was the scaling exponent of conditional density-density correlations. Two kinds of solutions were also shown for velocity-increment probability density function (PDF)