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finite-difference-methods
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Electrokinetic and aspect ratio effects on secondary flow of viscoelastic fluids in rectangular microchannels
, Article Microfluidics and Nanofluidics ; Volume 20, Issue 8 , 2016 ; 16134982 (ISSN) ; Saidi, M. H ; Firoozabadi, B ; Saidi, M. S ; Sharif University of Technology
Springer Verlag
2016
Abstract
The secondary flow of PTT fluids in rectangular cross-sectional plane of microchannels under combined effects of electroosmotic and pressure driving forces is the subject of the present study. Employing second-order central finite difference method in a very refined grid network, we investigate the effect of electrokinetic and geometric parameters on the pattern, strength and the average of the secondary flow. In this regard, we try to illustrate the deformations of recirculating vortices due to change in the dimensionless Debye–Hückel and zeta potential parameters as well as channel aspect ratio. We demonstrate that, in the presence of thick electric double layers, significant alteration...
Pure axial flow of viscoelastic fluids in rectangular microchannels under combined effects of electro-osmosis and hydrodynamics
, Article Theoretical and Computational Fluid Dynamics ; Volume 32, Issue 1 , 2018 ; 09354964 (ISSN) ; Saidi, M. H ; Ebrahimi, A ; Sharif University of Technology
Springer New York LLC
2018
Abstract
This paper presents an analysis of the combined electro-osmotic and pressure-driven axial flows of viscoelastic fluids in a rectangular microchannel with arbitrary aspect ratios. The rheological behavior of the fluid is described by the complete form of Phan-Thien–Tanner (PTT) model with the Gordon–Schowalter convected derivative which covers the upper convected Maxwell, Johnson–Segalman and FENE-P models. Our numerical simulation is based on the computation of 2D Poisson–Boltzmann, Cauchy momentum and PTT constitutive equations. The solution of these governing nonlinear coupled set of equations is obtained by using the second-order central finite difference method in a non-uniform grid...
Analytical investigation of composite sandwich beams filled with shape memory polymer corrugated core
, Article Meccanica ; Volume 54, Issue 10 , 2019 , Pages 1647-1661 ; 00256455 (ISSN) ; Baghani, M ; Zakerzadeh, M. R ; Shahsavari, H ; Sohrabpour, S ; Sharif University of Technology
Springer Netherlands
2019
Abstract
Shape memory polymers (SMPs) are a class of smart materials which can recover their shape even after many shape changes in application of an external stimulus. In this paper, flexural behavior of a composite beam, constructed of a corrugated part filled with SMPs, is studied. This composite beam is applicable in sensor and actuator applications. Since the corrugated profiles display higher stiffness-to-mass ratio in the transverse to the corrugation direction, the beams with a corrugated part along the transverse direction are stiffer than ones with a corrugated part along the length. Employing a developed constitutive model for SMPs and the Euler–Bernoulli beam theory, the behavior of the...
Numerical modeling and experimental validation of microstructure in gray cast iron
, Article International Journal of Minerals, Metallurgy and Materials ; Volume 19, Issue 10 , 2012 , Pages 908-914 ; 16744799 (ISSN) ; Davami, P ; Varahram, N ; Sharif University of Technology
Springer
2012
Abstract
To predict the amount of different phases in gray cast iron by a finite difference model (FDM) on the basis of cooling rate (R), the volume fractions of total γphase, graphite, and cementite were calculated. The results of phase composition were evaluated to find a proper correlation with cooling rate. More trials were carried out to find a good correlation between the hardness and phase composition. New proposed formulas show that the hardness of gray cast iron decreases as the amount of graphite phase increases, and increases as the amount of cementite increases. These formulas are developed to correlate the phase volume fraction to hardness. The results are compared with experimental data...
Simultaneous measurement of refractive index and thickness of multilayer systems using Fourier domain optical coherence tomography, part 2: Implementation
, Article Journal of Biomedical Optics ; Volume 22, Issue 1 , 2017 ; 10833668 (ISSN) ; Schriemer, H ; Amjadi, A ; Munger, R ; Sharif University of Technology
SPIE
2017
Abstract
We introduce a theoretical method for simultaneous measurement of refractive index and thickness of multilayer systems using Fourier domain optical coherence tomography (FD-OCT) without any auxiliary arrangement. The input data to the formalism are the FD-OCT measured optical path lengths (OPLs) and properly selected spectral components of FD-OCT interference spectrum. The outputs of the formalism can be affected significantly by uncertainty in measuring the OPLs. An optimization method is introduced to deal with the relatively large amount of uncertainty in measured OPLs and enhance the final results. Simulation result shows that by using the optimization method, indices can be extracted...
A numerical study on fluid flow and acoustic characteristics of a supersonic impinging jet using vorticity confinement
, Article Acta Acustica united with Acustica ; Volume 105, Issue 6 , 2019 , Pages 1127-1136 ; 16101928 (ISSN) ; Hejranfar, K ; Ebrahimi, M ; Sharif University of Technology
S. Hirzel Verlag GmbH
2019
Abstract
The objective of this work is to numerically study the fluid flow and acoustic field of a supersonic impinging jet by applying the vorticity confinement (VC) method. For this aim, the three-dimensional compressible Navier-Stokes equations with the incorporation of the VC method are considered and the resulting system of equations is solved by using the sixth-order compact finite-difference scheme. To eliminate the numerical instability, a low-pass high-order filter is used. The nonreflective boundary conditions are applied for all the free boundaries and the radiated sound field is obtained by the Kirchhoff surface integration. Comparisons of the present results with the experimental data...
A numerical study on fluid flow and acoustic characteristics of a supersonic impinging jet using vorticity confinement
, Article Acta Acustica united with Acustica ; Volume 105, Issue 6 , 2019 , Pages 1127-1136 ; 16101928 (ISSN) ; Hejranfar, K ; Ebrahimi, M ; Sharif University of Technology
S. Hirzel Verlag GmbH
2019
Abstract
The objective of this work is to numerically study the fluid flow and acoustic field of a supersonic impinging jet by applying the vorticity confinement (VC) method. For this aim, the three-dimensional compressible Navier-Stokes equations with the incorporation of the VC method are considered and the resulting system of equations is solved by using the sixth-order compact finite-difference scheme. To eliminate the numerical instability, a low-pass high-order filter is used. The nonreflective boundary conditions are applied for all the free boundaries and the radiated sound field is obtained by the Kirchhoff surface integration. Comparisons of the present results with the experimental data...
Effects of viscoelastic supports on the behavior of bridges under moving vehicles
, Article Scientia Iranica ; Volume 24, Issue 4 , 2017 , Pages 1751-1769 ; 10263098 (ISSN) ; Vafai, H ; Sharif University of Technology
Sharif University of Technology
2017
Abstract
One of the most important problems facing structural engineers is the analysis of dynamic behavior of bridges subjected to moving vehicles. In addition, viscoelastic supports under bridges change their dynamic behavior under passing traffic loads. This paper presents how to model a bridge with viscoelastic supports and how the maximum dynamic stress of bridges changes during the passing of moving vehicles. Furthermore, this paper presents an algorithm to solve the governing equation of the bridge with viscoelastic supports as well as the equation of motion of a real European truck with different speeds, simultaneously. Using viscoelastic supports with appropriate characteristics can make a...
The size-dependent electromechanical instability of double-sided and paddle-type actuators in centrifugal and Casimir force fields
, Article Scientia Iranica ; Volume 24, Issue 3 , 2017 , Pages 1077-1090 ; 10263098 (ISSN) ; Farahani, M ; Kanani, A ; Rach, R ; Keivani, M ; Abadyan, M ; Sharif University of Technology
Sharif University of Technology
2017
Abstract
The present research is devoted to theoretical study of the pull-in performance of double-sided and paddle-type NEMS actuators fabricated from cylindrical nanowire operating in the Casimir regime and in the presence of the centrifugal force. D'Alembert's principle was used to transform the angular velocity into an equivalent static, centrifugal force. Using the couple stress theory, the constitutive equations of the actuators were derived. The equivalent boundary condition technique was applied to obtain the governing equation of the paddle-type actuator. Three distinct approaches, the Duan-Adomian Method (DAM), Finite Difference Method (FDM), and Lumped Parameter Model (LPM), were applied...
Development of a saturation-based μ(I)-rheology for wet granular materials using discrete element method
, Article Scientia Iranica ; Volume 28, Issue 5 B , 2021 , Pages 2719-2732 ; 10263098 (ISSN) ; Taghizadeh Manzari, M ; Hajilouy Benisi, A ; Sharif University of Technology
Sharif University of Technology
2021
Abstract
The present study employs Discrete Element Method (DEM) to establish a rheological model that relates the apparent viscosity of a granular material to shear rate, normal stress, and water saturation. In addition, a theoretical model was developed to determine water distribution and water-induced forces between particles for different saturations. The resulting forces were embedded in a 3D shear cell as a numerical rheometer, and a wet specimen was sheared between two walls. A power law rheological model was then obtained as a function of inertia number and saturation. It was found that up to a critical saturation, the apparent viscosity increased with saturation that was higher than that of...
Computation of three-dimensional supersonic turbulent flows over wrap-around fin projectiles using personal computers
, Article Scientia Iranica ; Volume 12, Issue 2 , 2005 , Pages 217-228 ; 10263098 (ISSN) ; Azimi, A ; Farhanieh, B ; Sharif University of Technology
Sharif University of Technology
2005
Abstract
The three-dimensional supersonic turbulent flows over wrap-around fin missiles have been computed using the Thin Layer Navier-Stokes (TLNS) equations to reduce the computational efforts compared to those of the Full Navier-Stokes (FNS) equations. In this research, the missile configuration is divided into multi regions to enable fluid flow simulation using Personal Computers (PC). It also makes it possible to use a different number of nodes and distribution of grids in each region to enhance the accuracy. The Thin Layer Navier-Stokes equations in the generalized coordinate system were solved using an efficient, implicit, finite-difference factored algorithm of the Beam and Warming. For the...
Dynamic modeling of the turning process of slip-cast fused silica ceramics using the discrete element method
, Article Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture ; Volume 234, Issue 3 , 2020 , Pages 629-640 ; Movahhedy, M. R ; Sharif University of Technology
SAGE Publications Ltd
2020
Abstract
Simulation of brittle regime machining of materials (such as ceramics) is often difficult because of the complex material removal mechanisms involved. In this study, the discrete element method is used to simulate the dynamic process for machining of slip-cast fused silica ceramics. Flat-joint contact model is exploited to model contacts between particles in synthetic discrete element method models. This contact model is suitable for modeling of brittle materials with high ratios (higher than 10) of unconfined compressive strength to tensile strength. The discrete element method has the ability to simulate initiation, propagation, and coalescence of cracks leading to chip formation in the...
Exponential stabilization of flexural sway vibration of gantry crane via boundary control method
, Article JVC/Journal of Vibration and Control ; Volume 26, Issue 1-2 , 2020 , Pages 36-55 ; Najafi Ardekany, A ; Alasty, A ; Sharif University of Technology
SAGE Publications Inc
2020
Abstract
This paper aims to develop a boundary control solution for complicated gantry crane coupled motions. In addition to the large angle sway motion, the crane cable has a flexural transverse vibration. The Hamilton principle has been utilized to derive the governing partial differential equations of motion. The control objectives which are sought include: moving the payload to the desired position; reducing the payload swing with large sway angle; and finally suppressing the cable transverse vibrations in the presence of boundary disturbances simultaneously. These simultaneous boundary control objectives make the problem challenging. The proposed control approach is based on the original...
Effects of slip condition on the characteristic of flow in ice melting process
, Article International Journal of Engineering, Transactions B: Applications ; Volume 18, Issue 3 , 2005 , Pages 253-261 ; 1728-144X (ISSN) ; Rad, M ; Borujerdi, A. N ; Sharif University of Technology
Materials and Energy Research Center
2005
Abstract
In this paper a laminar flow of water on an ice layer subjected to a slip condition is considered numerically. The paper describes a parametric mathematical model to simulate the coupled heat and mass transfer events occurring in moving boundary problems associated with a quasi steady state steady flow process. The discretization technique of the elliptic governing differential equations of mass, momentum and energy is based on the control volume finite difference approach and enthalpy method, the results illustrate, the distribution of heat transfer coefficient, ice melting thickness, slip velocity at solid moving boundary and boundary layer thickness for some values of slip velocity...
Application of a preconditioned high-order accurate artificial compressibility-based incompressible flow solver in wide range of Reynolds numbers
, Article International Journal for Numerical Methods in Fluids ; Volume 86, Issue 1 , 2018 , Pages 46-77 ; 02712091 (ISSN) ; Parseh, K ; Sharif University of Technology
John Wiley and Sons Ltd
2018
Abstract
In the present study, the preconditioned incompressible Navier-Stokes equations with the artificial compressibility method formulated in the generalized curvilinear coordinates are numerically solved by using a high-order compact finite-difference scheme for accurately and efficiently computing the incompressible flows in a wide range of Reynolds numbers. A fourth-order compact finite-difference scheme is utilized to accurately discretize the spatial derivative terms of the governing equations, and the time integration is carried out based on the dual time-stepping method. The capability of the proposed solution methodology for the computations of the steady and unsteady incompressible...
Simulation of three-dimensional incompressible flows in generalized curvilinear coordinates using a high-order compact finite-difference lattice Boltzmann method
, Article International Journal for Numerical Methods in Fluids ; 2018 ; 02712091 (ISSN) ; Hejranfar, K ; Sharif University of Technology
John Wiley and Sons Ltd
2018
Abstract
In the present study, a high-order compact finite-difference lattice Boltzmann method is applied for accurately computing 3-D incompressible flows in the generalized curvilinear coordinates to handle practical and realistic geometries with curved boundaries and nonuniform grids. The incompressible form of the 3-D nineteen discrete velocity lattice Boltzmann method is transformed into the generalized curvilinear coordinates. Herein, a fourth-order compact finite-difference scheme and a fourth-order Runge-Kutta scheme are used for the discretization of the spatial derivatives and the temporal term, respectively, in the resulting 3-D nineteen discrete velocity lattice Boltzmann equation to...
Simulation of three-dimensional incompressible flows in generalized curvilinear coordinates using a high-order compact finite-difference lattice boltzmann method
, Article International Journal for Numerical Methods in Fluids ; Volume 89, Issue 7 , 2019 , Pages 235-255 ; 02712091 (ISSN) ; Hejranfar, K ; Sharif University of Technology
John Wiley and Sons Ltd
2019
Abstract
In the present study, a high-order compact finite-difference lattice Boltzmann method is applied for accurately computing 3-D incompressible flows in the generalized curvilinear coordinates to handle practical and realistic geometries with curved boundaries and nonuniform grids. The incompressible form of the 3-D nineteen discrete velocity lattice Boltzmann method is transformed into the generalized curvilinear coordinates. Herein, a fourth-order compact finite-difference scheme and a fourth-order Runge-Kutta scheme are used for the discretization of the spatial derivatives and the temporal term, respectively, in the resulting 3-D nineteen discrete velocity lattice Boltzmann equation to...
Interpretation of CPT in unsaturated sands under drained conditions: A numerical study
, Article International Journal for Numerical and Analytical Methods in Geomechanics ; Volume 45, Issue 18 , 2021 , Pages 2732-2755 ; 03639061 (ISSN) ; Ahmadi, M. M ; Sharif University of Technology
John Wiley and Sons Ltd
2021
Abstract
A finite difference-based numerical model simulating the cone penetration process in unsaturated sands is presented. Mohr–Coulomb model (MCM) with simple modifications and Sun model (SM) were implemented to capture the unsaturated sand behaviour. It was shown that the cone tip resistance values resulting from the two models were fairly comparable. Predicted cone tip resistance values in dry, saturated and unsaturated sands using MCM were validated by the results of field and calibration chamber tests. Sensitivity analyses were performed, and the influence of parameters including relative density, mean effective stress and apparent cohesion due to suction on the tip resistance was...
Neural implant stimulation based on TiO2 nanostructured arrays; A multiphysics modeling verification
, Article IECBES 2014, Conference Proceedings - 2014 IEEE Conference on Biomedical Engineering and Sciences: "Miri, Where Engineering in Medicine and Biology and Humanity Meet", 8 December 2014 through 10 December 2014 ; December , 2015 , Pages 677-680 ; 9781479940844 (ISBN) ; Mohammadpour, R ; Amiri, K ; Silterra; University of Malaya ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2015
Abstract
Exploiting of the nanostructure arrays as a promising candidate for excitation of neural cells has been analyzed. Based on the importance of the coupling effect between electrode and neuron, a multiphyscis modeling approach has been proposed. The model incorporates theoretically both structural effects (size, geometry) and electrophysiological effects. The system of equations for proposed model has been solved numerically using Finite Element Method for Poisson equation and Finite Difference Method for Cable equation. In this regards we have combined the system of equations in COMSOL platform with Matlab interface accordingly. We have analyzed the effect of excitation of neuron with an extra...
Enhancement of full-duplex efficiency in an asymmetric IEEE 802.11-based WLAN
, Article IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC, 4 September 2016 through 8 September 2016 ; 2016 ; 9781509032549 (ISBN) ; Ashtiani, F ; Mirmohseni, M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2016
Abstract
In this paper, we propose a new packet prioritization scheme in order to exploit the full-duplex (FD) capability of the access point (AP) more efficiently, in an asymmetric IEEE 802.11-based WLAN, i.e., only the AP has the in-band FD communications capability. In this respect, we consider a modified version of IEEE 802.11 MAC protocol such that at any transmission opportunity in which AP has the role of the transmitter or the receiver, it does the best to select a partner packet to be simultaneously received or transmitted, respectively. The key feature of our proposed partner packet selection scheme is to reduce the idle time intervals that in an FD transmission opportunity, due to...