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finite-difference-method
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Open-and short-circuit switch fault diagnosis for nonisolated DC-DC converters using field programmable gate array
, Article IEEE Transactions on Industrial Electronics ; Volume 60, Issue 9 , October , 2013 , Pages 4136-4146 ; 02780046 (ISSN) ; Jamshidpour, E ; Poure, P ; Saadate, S ; Zolghadri, M. R ; Sharif University of Technology
2013
Abstract
Fault detection (FD) in power electronic converters is necessary in embedded and safety critical applications to prevent further damage. Fast FD is a mandatory step in order to make a suitable response to a fault in one of the semiconductor devices. The aim of this study is to present a fast yet robust method for fault diagnosis in nonisolated dc-dc converters. FD is based on time and current criteria which observe the slope of the inductor current over the time. It is realized by using a hybrid structure via coordinated operation of two FD subsystems that work in parallel. No additional sensors, which increase system cost and reduce reliability, are required for this detection method. For...
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...
The dynamic pull-in instability and snap-through behavior of initially curved microbeams
, Article Mechanics of Advanced Materials and Structures ; Volume 19, Issue 6 , Jul , 2012 , Pages 485-491 ; 15376494 (ISSN) ; Sharif University of Technology
T&F
2012
Abstract
In this study, dynamic pull-in instability and snap-through buckling of initially curved microbeams are investigated. The microbeams are actuated by suddenly applied electrostatic force. A finite element model is developed to discretize the governing equations, and Newmark time discretization is employed to solve the discretized equations. The static pull-in behavior is investigated to validate the model. The results of the finite element model are compared with finite difference solutions and their convergence is examined. In addition, the influence of different parameters on dynamic pull-in instability and snap-through buckling is explored
Upwind compact implicit and explicit high-order finite difference schemes for level set technique
, Article International Journal of Computational Methods in Engineering Science and Mechanics ; Volume 13, Issue 4 , 2012 , Pages 308-318 ; 15502287 (ISSN) ; Kebriaee, A ; Sharif University of Technology
2012
Abstract
This paper investigates implementation of upwind compact implicit and explicit high-order finite difference schemes for solution of the level set equation. The upwind compact implicit and explicit high-order finite difference schemes are well-known techniques to descritize spatial derivatives for convection term in hyperbolic equations. Applying of upwind high-order schemes on the level set equation leads to less error and CPU time reduction compared to essential non-oscillatory (ENO), weighted essential non-oscillatory schemes (WENO), and even different particle level set methods. The results indicate the error based on area loss decreases drastically with applying high-order upwind,...
Mixed electroosmotically and pressure-driven flow with temperature- dependent properties
, Article Journal of Thermophysics and Heat Transfer ; Volume 25, Issue 3 , Sep , 2011 , Pages 432-442 ; 08878722 (ISSN) ; Yavari, H ; Saidi, M. H ; Chakraborty, S ; Sharif University of Technology
2011
Abstract
The present work reports the outcome of a comprehensive parametric study on mixed electroosmotically and pressure-driven flow in slit microchannels with constant wall heat fluxes. Special attention is given to disclose the applicability ranges of usual assumptions in simplified analyses. The governing equations for fully developed conditions are first made dimensionless and then solved by means of an implicit finite difference method. The results reveal that the assumption of constant thermophysical properties does not leadto significant errors in practical applications. Although the Debye-Huckel linearization may successfully be used to evaluate velocity profiles up to the zeta potentials...
The effect of normal stress on hydro-mechanical deep drawing process
, Article International Journal of Mechanical Sciences ; Volume 53, Issue 6 , 2011 , Pages 407-416 ; 00207403 (ISSN) ; Taghipour, E ; Sharif University of Technology
2011
Abstract
Normal stress has some role in the deformation analysis of hydroforming processes. In this study, analytical modeling is pursued to evaluate the effect of normal stress on the hydro-mechanical deep drawing (HDD) process. Analyses are carried out for axisymmetric elements of the formed cup-shaped part for increments of the punch travel. The formulations are obtained using mechanical and geometrical relations and the finite difference method, thereby being solved by proper numerical algorithms. Furthermore, in the present work, part thickness is variable, the loading and straining are non-proportional, and bending/unbending effects over the part curvature are considered. The results show that...
Numerical modeling of incline plate LiBr absorber
, Article Heat and Mass Transfer/Waerme- und Stoffuebertragung ; Volume 47, Issue 3 , November , 2011 , Pages 259-267 ; 09477411 (ISSN) ; Farhanieh, B ; Sharif University of Technology
2011
Abstract
Among major components of LiBr-H 2O absorption chillers is the absorber, which has a direct effect on the chillier size and whose characteristics have significant effects on the overall efficiency of absorption machines. In this article, heat and mass transfer process in absorption of refrigerant vapor into a lithium bromide solution of water-cooled incline plate absorber in the Reynolds number range of 5
Comparison between triangular and hexagonal modeling of a hexagonal-structured reactor core using box method
, Article Annals of Nuclear Energy ; Volume 38, Issue 2-3 , February–March , 2011 , Pages 371-378 ; 03064549 (ISSN) ; Moghaddam, N. M ; Zahedinejad, E ; Sharif University of Technology
2011
Abstract
A hexagonal-structured reactor core (e.g. VVER-type) is mostly modeled by structured triangular and hexagonal mesh zones. Although both the triangular and hexagonal models give good approximations over the neutronic calculation of the core, there are some differences between them that seem necessary to be clarified. For this purpose, the neutronic calculations of a hexagonal-structured reactor core have to be performed using the structured triangular and hexagonal meshes based on box method of discretisation and then the results of two models should be benchmarked in different cases. In this paper, the box method of discretisation is derived for triangular and hexagonal meshes. Then, two 2-D...
Contact time study of electrostatically actuated microsystems
, Article Scientia Iranica ; Volume 17, Issue 5 B , SEPTEMBER-OCTOBER , 2010 , Pages 348-357 ; 10263098 (ISSN) ; Rashidian, B ; Ahmadian, M. T ; Sharif University of Technology
2010
Abstract
This paper presents a model to analyze contact phenomenon in microsystems actuated by ramp voltages, which has applications in frequency sweeping. First-order shear deformation theory is used to model dynamical system using finite element method, while finite difference method is applied to model squeeze film damping. The model is validated by static pull-in results. The presented hybrid FEMFDM model is utilized to compute values of contact time and dynamic behavior. Considering this model, effects of different geometrical and mechanical parameters on contact time are studied. The influence of imposing the additional reverse voltage on dynamic characteristics of the system is also...
Comparison of numerical formulations for Two-phase flow in porous media
, Article Geotechnical and Geological Engineering ; Volume 28, Issue 4 , 2010 , Pages 373-389 ; 09603182 (ISSN) ; Raeesi Ardekani, D ; Sharif University of Technology
2010
Abstract
Numerical approximation based on different forms of the governing partial differential equation can lead to significantly different results for two-phase flow in porous media. Selecting the proper primary variables is a critical step in efficiently modeling the highly nonlinear problem of multiphase subsurface flow. A comparison of various forms of numerical approximations for two-phase flow equations is performed in this work. Three forms of equations including the pressure-based, mixed pressure-saturation and modified pressure-saturation are examined. Each of these three highly nonlinear formulations is approximated using finite difference method and is linearized using both Picard and...
Wideband maximally flat fractional-delay allpass filters
, Article Electronics Letters ; Volume 46, Issue 10 , May , 2010 , Pages 722-723 ; 00135194 (ISSN) ; Sharif University of Technology
2010
Abstract
The maximally flat (MF) fractional-delay (FD) allpass filter, also known as Thiran's allpass filter, is one of the most popular IIR FD systems which is typically deployed in its causal forms. It is shown that if this causality constraint is removed, MFFD allpass filters with considerably wider bandwidths can be obtained. In many applications this extra bandwidth is worth having a non-causal system
Comparing sloshing phenomena in a rectangular container with and without a porous medium using explicit nonlinear 2-D BEM-FDM
, Article Scientia Iranica ; Volume 17, Issue 2 B , 2010 , Pages 93-101 ; 10263098 (ISSN) ; Ghodsi Hassanabad, M ; Sharif University of Technology
2010
Abstract
The sloshing phenomena in a partially filled tank can affect its stability. Modifications of tank instability due to the movement of the tank carrier, are key design points for the stability of a carrier. Even though the sloshing phenomenon has already been investigated using the BEM-FDM technique, the research in this paper covers this phenomenon in a porous media, which is new in 2-D coordinates. For this purpose, a Laplace equation has been used for potential flow, and kinematic and dynamic boundary conditions have been applied to the free surface. Also, a formulation has been developed for a free surface in porous media. BEM has been used for solving the governing equation and FDM...
Computational simulation of marangoni convection under microgravity condition
, Article Scientia Iranica ; Volume 16, Issue 6 B , 2009 , Pages 513-524 ; 10263098 (ISSN) ; Taeibi Rahni, M ; Asadi, B ; Ahmadi, G ; Sharif University of Technology
2009
Abstract
In this work, the rising of a single bubble in a quiescent liquid under microgravity condition was simulated. In addition to general studies of microgravity effects, the initiation of hydrodynamic convection, solely due to the variations of interface curvature (surface tension force) and thus the generation of shearing forces at the interfaces, was also studied. Then, the variation of surface tension due to the temperature gradient (Marangoni convection), which can initiate the onset of convection even in the absence of buoyancy, was studied. The related unsteady incompressible full Navier-Stokes equations were solved using a finite difference method with a structured staggered grid. The...
Comparison of finite difference schemes for water flow in unsaturated soils
, Article World Academy of Science, Engineering and Technology ; Volume 40 , 2009 , Pages 21-25 ; 2010376X (ISSN) ; Ataie Ashtiani, B ; Sharif University of Technology
2009
Abstract
Flow movement in unsaturated soil can be expressed by a partial differential equation, named Richards equation. The objective of this study is the finding of an appropriate implicit numerical solution for head based Richards equation. Some of the well known finite difference schemes (fully implicit, Crank Nicolson and Runge-Kutta) have been utilized in this study. In addition, the effects of different approximations of moisture capacity function, convergence criteria and time stepping methods were evaluated. Two different infiltration problems were solved to investigate the performance of different schemes. These problems include of vertical water flow in a wet and very dry soils. The...
Influence of Darcy number on the onset of convection in a porous layer with a uniform heat source
, Article International Journal of Thermal Sciences ; Volume 47, Issue 8 , August , 2008 , Pages 1020-1025 ; 12900729 (ISSN) ; Noghrehabadi, A. R ; Rees, D. A. S ; Sharif University of Technology
2008
Abstract
This note considers the effect of different Darcy numbers on the onset of natural convection in a horizontal, fluid-saturated porous layer with uniform internal heating. It is assumed that the two bounding surfaces are maintained at constant but equal temperatures and that the fluid and porous matrix are in local thermal equilibrium. Linear stability theory is applied to the problem, and numerical solutions obtained using compact fourth order finite differences are presented for all Darcy numbers between Da = 0 (Darcian porous medium) and Da → ∞ (the clear fluid limit). The numerical work is supplemented by an asymptotic analysis for small values Da. © 2007 Elsevier Masson SAS. All rights...
Optimal riser design in sand casting process by topology optimization with SIMP method I: poisson approximation of nonlinear heat transfer equation
, Article Structural and Multidisciplinary Optimization ; Volume 36, Issue 2 , 25 January , 2008 , Pages 193-202 ; 1615147X (ISSN) ; Davami, P ; Sharif University of Technology
2008
Abstract
The optimal design of a casting feeding system is considered. The problem is formulated as the volume constrained topology optimization and is solved with the finite element analysis, explicit design sensitivity, and numerical optimization. In contrast to the traditional topology optimization where the objective function is defined on the design space, in the presented method, the design space is a subset of the complement of the objective function space. To accelerate optimization procedure, the nonlinear unsteady heat transfer equation is approximated with a Poisson-like equation. The feasibility of the presented method is supported with illustrative examples. © 2007 Springer-Verlag
The application of corrugated parallel bundle model to immobilized cells in porous microcapsule membranes
, Article Journal of Membrane Science ; Volume 311, Issue 1-2 , 2008 , Pages 159-164 ; 03767388 (ISSN) ; Zarrabi, A ; Khosravi, A ; Sharif University of Technology
2008
Abstract
To describe immobilized cells in porous microcapsule membranes with straight pores, a novel model called corrugated parallel bundle model (CPBM) was utilized. In this model, a network was developed with 10 main pores each composing 10 pore elements. Cell growth kinetic in the network was examined using non-structural models. Effectiveness factor and pore plugging time were calculated by solving reaction-diffusion equation set via finite difference method. The findings revealed that diffusion coefficient for lower order reactions will create a lesser impact on the reduction of effectiveness factor. These findings also indicated that the use of such supporting carrier for cell immobilization...
Implementation of high-order compact finite-difference method to parabolized Navier-Stokes schemes
, Article International Journal for Numerical Methods in Fluids ; Volume 58, Issue 6 , 2008 , Pages 659-685 ; 02712091 (ISSN) ; Hejranfar, K ; Mahmoodi Darian, H ; Sharif University of Technology
2008
Abstract
The numerical solution to the parabolized Navier-Stokes (PNS) and globally iterated PNS (IPNS) equations for accurate computation of hypersonic axisymmetric flowfields is obtained by using the fourth-order compact finite-difference method. The PNS and IPNS equations in the general curvilinear coordinates are solved by using the implicit finite-difference algorithm of Beam and Warming type with a high-order compact accuracy. A shock-fitting procedure is utilized in both compact PNS and IPNS schemes to obtain accurate solutions in the vicinity of the shock. The main advantage of the present formulation is that the basic flow variables and their first and second derivatives are simultaneously...
A moving-mesh finite-volume method to solve free-surface seepage problem in arbitrary geometries
, Article International Journal for Numerical and Analytical Methods in Geomechanics ; Volume 31, Issue 14 , 2007 , Pages 1609-1629 ; 03639061 (ISSN) ; Torabi, S. O ; Saadat, M ; Daghighi, Y ; Jarrahbashi, D ; Sharif University of Technology
2007
Abstract
The main objective of this work is to develop a novel moving-mesh finite-volume method capable of solving the seepage problem in domains with arbitrary geometries. One major difficulty in analysing the seepage problem is the position of phreatic boundary which is unknown at the beginning of solution. In the current algorithm, we first choose an arbitrary solution domain with a hypothetical phreatic boundary and distribute the finite volumes therein. Then, we derive the conservative statement on a curvilinear co-ordinate system for each cell and implement the known boundary conditions all over the solution domain. Defining a consistency factor, the inconsistency between the hypothesis...
A higher-order two-dimensional Boussinesq wave model
, Article Journal of Coastal Research ; Issue SPEC. ISSUE 50 , 2007 , Pages 1183-1187 ; 07490208 (ISSN) ; Najafi Jilani, A ; Sharif University of Technology
2007
Abstract
A two-dimensional Boussinesq-type model is presented accurate to O(μ)6 , μ = h0/l0, in dispersion and all consequential order for non-linearity with arbitrary bottom boundary, where h0 is the water depth and l0 is the characteristic wave length. The mathematical formulation is an extension of (4,4) the Padé approximant to include varying bottom boundary in two horizontal dimensions. A higher order perturbation method is used for mathematical derivation of the presented model. A two horizontal dimension numerical model is developed based on derived equations using the Finite Difference Method in higher-order scheme for time and space. The numerical wave model is verified successfully in...