Search for: finite-difference-methods
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    A Monte Carlo Method for Neutron Noise Calculation in the Frequency Domain

    , M.Sc. Thesis Sharif University of Technology Ghorbani Ashraf, Mahdi (Author) ; Vosoughi, Naser (Supervisor)
    Neutron noise equations, which are obtained by assuming small perturbations of macroscopic cross sections around a steady-state neutron field and by subsequently taking the Fourier transform in the frequency domain, have been usually solved by analytical techniques or by resorting to diffusion theory, but in this thesis, in order to increase of accuracy of neutron noise calculation, has been used transport approximation for neutron noise calculation and the Monte Carlo method has been used to solve transport equation of the neutron noise in the frequency domain. Since the transport equation of the neutron noise is a complex equation, a new Monte Carlo technique for treating complex-valued... 

    Numerical solution of homogeneous double pipe heat exchanger: Dynamic modeling

    , Article Scientia Iranica ; Volume 21, Issue 2 , 2014 , pp. 449-455 ; ISSN: 10263098 AliHosseinpour, H ; Kazemi, Y ; Fattahi, M ; Sharif University of Technology
    Dynamic modeling of a double-pipe heat exchanger is the subject of the current study. The basis of this study is the same velocity of vapor and liquid phases or, in other words, homogeneous phase, in the annulus part of the exchanger. The model can predict the temperature and vapor quality along the axial pipe from the pipe inlet up to a distance where steady state conditions are achieved. The simulation is conducted for two modes of co- and counter-flow in a one dimensional transient system. The physical properties of water are estimated from empirical correlation and a saturated vapor table with cubic spline interpolation. The exchanger model, which is a set of Ordinary Differential... 

    An experimental-based numerical simulation of two phase flow through porous media: A comparative study on finite element and finite difference schemes

    , Article Petroleum Science and Technology ; Volume 31, Issue 18 , 2013 , Pages 1881-1890 ; 10916466 (ISSN) Tavakkoli, M ; Kharrat, R ; Ghazanfari, M. H ; Sharif University of Technology
    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... 

    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) Jabbari, M ; Davami, P ; Varahram, N ; Sharif University of Technology
    Springer  2012
    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... 

    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) Sadeghi, A ; Yavari, H ; Saidi, M. H ; Chakraborty, S ; Sharif University of Technology
    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) Assempour, A ; Taghipour, E ; Sharif University of Technology
    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... 

    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) Malmir, H ; Moghaddam, N. M ; Zahedinejad, E ; Sharif University of Technology
    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... 

    On application of high-order compact finite-difference schemes to compressible vorticity confinement method

    , Article Aerospace Science and Technology ; Volume 46 , October–November , 2015 , Pages 398-411 ; 12709638 (ISSN) Sadri, M ; Hejranfar, K ; Ebrahimi, M ; Sharif University of Technology
    Elsevier Masson SAS  2015
    The main goal of this study is to assess the application of high-order compact finite-difference schemes for the solution of the Euler equations in conjunction with the compressible vorticity confinement method on both uniform Cartesian and curvilinear grids. Here, the spatial discretization of the governing equations is performed by the fourth-order compact finite-difference scheme and the temporal term is discretized by the fourth-order Runge-Kutta method. To stabilize the numerical solution, appropriate dissipation terms are applied and a detail assessment is performed to study the effects of the values of confinement and dissipation coefficients on the solution to reasonably preserve the... 

    Propagation noise calculations in VVER-type reactor core

    , Article Progress in Nuclear Energy ; Volume 78 , January , 2015 , Pages 10-18 ; 01491970 (ISSN) Malmir, H ; Vosoughi, N ; Sharif University of Technology
    Elsevier Ltd  2015
    Neutron noise induced by propagating disturbances in VVER-type reactor core is addressed in this paper. The spatial discretization of the governing equations is based on the box-scheme finite difference method for triangular-z geometry. Using the derived equations, a 3-D 2-group neutron noise simulator (called TRIDYN-3) is developed for hexagonal-structured reactor core, by which the discrete form of both the forward and adjoint reactor dynamic transfer functions (in the frequency domain) can be calculated. In addition, both types of noise sources, namely point-like and traveling perturbations, can be modeled by TRIDYN-3. The results are then benchmarked in different cases. Considering the... 

    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) Sasanpour, P ; Mohammadpour, R ; Amiri, K ; Silterra; University of Malaya ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2015
    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... 

    Active vibration control of a cmos-mems nano-newton capacitive force sensor for bio application using PZT

    , Article Advanced Materials Research, San Diego, CA ; Volume 628 , 2013 , Pages 317-323 ; 10226680 (ISSN) ; 9783037855706 (ISBN) Mozhdehi, R. J ; Selkghafari, A ; Zabiholah, A ; Meghdari, A ; Sharif University of Technology
    This paper reports the design of an optimal controller to prevent suppressvertical vibration due to undesired out of plane excitations generated by environment or gripper during manipulation for a CMOS-MEMS Nano-Newton capacitive force sensor applied for biomedical applications. Undesired out of plane excitations generated by environment or gripper during manipulation is the most prevalent source of vertical vibration in this type of sensors. To suppress the vibrational movement a PZT 5A is used as actuation mechanism. Discrete element method DEM model and Modal analysis were used to find dominant natural frequencies and mode shape vectors. To eliminate out of plane excitation an optimal... 

    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) Goshtasbpour, S ; Ashtiani, F ; Mirmohseni, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2016
    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... 

    New insight into H2S sensing mechanism of continuous SnO2-CuO bilayer thin film: A theoretical macroscopic approach

    , Article Journal of Physical Chemistry C ; Volume 120, Issue 14 , 2016 , Pages 7678-7684 ; 19327447 (ISSN) Boroun, Z ; Ghorbani, M ; Moosavi, A ; Mohammadpour, R ; Sharif University of Technology
    American Chemical Society  2016
    SnO2-CuO is one the most promising systems for detection of detrimental H2S gas. Although previous experimental research has suggested a sulfidation reaction to explain selectivity toward H2S, little is known about the origin of change of electrical response of this system by changing the H2S gas concentration. In this study the relation between sensing response of continuous SnO2-CuO bilayer thin film and H2S gas concentration is computed based on changeability of chemical composition of covellite CuxS. For this purpose, chemical activity of sulfur as a function of atomic fraction in covellite copper sulfide is estimated using Gibbs energies of formation and chemical thermodynamics. By... 

    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) Samanipour, K ; Vafai, H ; Sharif University of Technology
    Sharif University of Technology  2017
    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... 

    Assessment of characteristic boundary conditions based on the artificial compressibility method in generalized curvilinear coordinates for solution of the Euler equations

    , Article Computational Methods in Applied Mathematics ; Volume 18, Issue 4 , 2018 , Pages 717-740 ; 16094840 (ISSN) Parseh, K ; Hejranfar, K ; Sharif University of Technology
    De Gruyter  2018
    The characteristic boundary conditions are applied and assessed for the solution of incompressible inviscid flows. The two-dimensional incompressible Euler equations based on the artificial compressibility method are considered and then the characteristic boundary conditions are formulated in the generalized curvilinear coordinates and implemented on both the far-field and wall boundaries. A fourth-order compact finite-difference scheme is used to discretize the resulting system of equations. The solution methodology adopted is more suitable for this assessment because the Euler equations and the high-accurate numerical scheme applied are quite sensitive to the treatment of boundary... 

    Delayed data offloading based on full-duplex D2D communications in a cellular network

    , Article 2018 Iran Workshop on Communication and Information Theory, IWCIT 2018, 25 April 2018 through 26 April 2018 ; 2018 , Pages 1-6 ; 9781538641491 (ISBN) Karami, F ; Mirmohseni, M ; Ashtiani, F ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2018
    In this paper, we propose a new delayed data offloading scheme by exploiting full-duplex (FD) device-to-device (D2D) communications. To this end, we consider a scenario in which a common file is requested by a subset of users in different times and with different maximum tolerable delays. Moreover, a maximum specific bandwidth is dedicated for data transmission. In order to send the file in the specific bandwidth, we use multicasting alongside FD D2D communications. Thanks to the fact that users have different deadlines, we divide them into non-overlapping groups, i.e., coalitions, to receive the file in distinct intervals. In order to guarantee the tolerable delay of all users, a coalition... 

    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) Akbari Azar, S ; Baghani, M ; Zakerzadeh, M. R ; Shahsavari, H ; Sohrabpour, S ; Sharif University of Technology
    Springer Netherlands  2019
    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... 

    Secrecy performance of friendly jammer assisted cooperative NOMA systems with internal eavesdroppers

    , Article 31st IEEE Annual International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC 2020, 31 August 2020 through 3 September 2020 ; Volume 2020-August , 2020 Abolpour, M ; Aissa, S ; Mirmohseni, M ; Aref, M. R ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2020
    In non-orthogonal multiple access (NOMA) systems, serving multiple users in shared resource blocks can allow untrusted users to overhear the messages of other users. In this context, we study a network consisting of a base station (BS), a near user and a far user, where the latter attempts to overhear the message of the former. The near user is a full-duplex (FD) node that can also act as a relay. Two operating scenarios are considered: 1) friendly jammer (FJ), where the FD node broadcasts noise for degrading the channel between the BS and the far user, while receiving data from the BS; and 2) friendly jammer relay (FJR), where, in addition to degrading the channel between the BS and the far... 

    Delay-Optimal cooperation policy in a slotted aloha full-duplex wireless network: static approach

    , Article IEEE Systems Journal ; Volume 14, Issue 2 , 2020 , Pages 2257-2268 Vaezi, K ; Ashtiani, F ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2020
    We consider a cooperative wireless communication network comprising two full-duplex (FD) nodes transmitting to a common destination based on slotted Aloha protocol. Each node has exogenous arrivals and also may relay some of the unsuccessfully transmitted packets of the other node. In this article, we find the optimal static policies of nodes in order to minimize the sum of the average transmission delays, while the average transmission delay of each node is constrained. The static policy of each node specifies the probability of accepting an unsuccessfully transmitted packet of the other node and how the node prioritizes its transmissions. We show that in the optimal policies, just the node... 

    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) Biria, D ; Zarrabi, A ; Khosravi, A ; Sharif University of Technology
    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...