Search for: comsol-multiphysics
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    3-D electrical model of a neuroprosthesis stimulator based on the concept of stimulus router system

    , Article 2013 20th Iranian Conference on Biomedical Engineering, ICBME 2013 ; 2013 , Pages 265-268 Ashiri, M ; Zahedi, E ; Sharif University of Technology
    IEEE Computer Society  2013
    Lost sensory or motor functions can be restored using electrical neural prostheses (NP), which include surface NPs, implanted or subcutaneous NPs and the more recent Stimulus Router System (SRS). The latter type of NP outperforms the other types in its selective excitation and least invasiveness. In each case, the achieved performance depends on a multitude of design factors among which the electrical excitation waveform shape, frequency, duration of pulses, configuration of electrodes, number of intervals, thermal conditions and electrode material. To investigate the effects of these parameters on the distribution of electric current inside biological tissues, numerical modeling can be... 

    Study of the effect of thermal dispersion on internal natural convection in porous media using fourier series

    , Article Transport in Porous Media ; Volume 131, Issue 2 , 2020 , Pages 537-568 Fahs, M ; Graf, T ; Tran, T. V ; Ataie Ashtiani, B ; Simmons, C. T ; Younes, A ; Sharif University of Technology
    Springer  2020
    Natural convection in a porous enclosure in the presence of thermal dispersion is investigated. The Fourier–Galerkin (FG) spectral element method is adapted to solve the coupled equations of Darcy’s flow and heat transfer with a full velocity-dependent dispersion tensor, employing the stream function formulation. A sound implementation of the FG method is developed to obtain accurate solutions within affordable computational costs. In the spectral space, the stream function is expressed analytically in terms of temperature, and the spectral system is solved using temperature as the primary unknown. The FG method is compared to finite element solutions obtained using an in-house code... 

    On the use of COMSOL Multiphysics for seawater intrusion in fractured coastal aquifers

    , Article 25th Salt Water Intrusion Meeting, SWIM 2018, 17 June 2018 through 22 June 2018 ; Volume 54 , 2018 ; 22671242 (ISSN) Mozafari, B ; Fahs, M ; Ataie Ashtiani, B ; Simmons, C. T ; Younes, R ; Sharif University of Technology
    EDP Sciences  2018
    COMSOL Multiphysics is a comprehensive simulation software environment for a wide range of applications. COMSOL has an interactive interface that facilitates the modeling procedure and allows an easy coupling of different physical processes. The Subsurface Flow module extends the COMSOL modeling environment to applications related to fluid flow in saturated and variably saturated porous media. COMSOL is increasingly used in the investigation of geophysical, hydrogeological and environmental phenomena. The main goal of this work is to explore the ability of COMSOL for simulating seawater intrusion (SWI) in fractured coastal aquifers. Numerical modeling of such a problem is of high interest as... 

    Proposing a high-efficiency dielectrophoretic system for separation of dead and live cells

    , Article Scientia Iranica ; Volume 25, Issue 1 , 2018 , Pages 186-195 ; 10263098 (ISSN) Shayestehpour, H ; Nassiri Nazif, K ; Soufi, A. M ; Saidi, M. S ; Sharif University of Technology
    Sharif University of Technology  2018
    Recently, electrode-based Dielectrophoresis (eDEP) has been used for particle manipulation by means of triangular electrodes. In this theoretical and numerical study, a microchannel with quarter-of-ellipse electrodes is presented and a detailed comparison with triangular electrodes is provided. Electric field, resultant DEP force, and particle trajectories for each microchannel are evaluated by means of COMSOL Multiphysics 4.4. Afterwards, focusing and separation efficiencies of the systems are assessed and compared. Finally, separation efficiency of our proposed model for live and dead cells is compared with that of our previous model published in the literature [1]. It is demonstrated that... 

    Experimental and modelling study of gravity drainage in a three-block system

    , Article Transport in Porous Media ; 2020 Erfani, H ; Karimi Malekabadi, A ; Ghazanfari, M. H ; Rostami, B ; Sharif University of Technology
    Springer Science and Business Media B.V  2020
    Gravity drainage is known as the controlling mechanism of oil recovery in naturally fractured reservoirs. The efficiency of this mechanism is controlled by block-to-block interactions through capillary continuity and/or reinfiltration processes. In this study, at first, several free-fall gravity drainage experiments were conducted on a well-designed three-block apparatus and the role of tilt angle, spacers’ permeability, wettability and effective contact area (representing a different status of the block-to-block interactions between matrix blocks) on the recovery efficiency were investigated. Then, an experimental-based numerical model of free-fall gravity drainage process was developed,... 

    Hybrid anisotropic pentamode mechanical metamaterial produced by additive manufacturing technique

    , Article Applied Physics Letters ; Volume 117, Issue 6 , 2020 Mohammadi, K ; Movahhedy, M. R ; Shishkovsky, I ; Hedayati, R ; Sharif University of Technology
    American Institute of Physics Inc  2020
    Pentamode metamaterials are a type of extremal designer metamaterials, which are able to demonstrate extremely high rigidity in one direction and extremely high compliance in other directions. Pentamodes can, therefore, be considered as building blocks of exotic materials with any arbitrarily selected thermodynamically admissible elasticity tensor. The pentamode lattices can then be envisioned to be combined to construct intermediate extremal materials, such as quadramodes, trimodes, and bimodes. In this study, we constructed several primary types of anisotropic pentamode lattices (with midpoint positioning of 10%, 15%, 20%, 25%, 30%, 35%, and 42% of the main unit cell diagonal) and then... 

    Elimination of the effect of bottom-plate capacitors in C-2C DAC using a layout technique

    , Article Microelectronics Journal ; Volume 46, Issue 12 , 2015 , Pages 1275-1282 ; 00262692 (ISSN) Khorami, A ; Sharifkhani, M ; Sharif University of Technology
    An efficient layout technique is proposed to eliminate the effect of the bottom-plate capacitors in a C-2C Digital to Analog Converter (DAC). Using this technique, the bottom-plate capacitors of 2C capacitors in the C-2C structure are placed in parallel with 1C capacitors. Then, the effect of the bottom plate capacitors is nulled by modifying the size of the main 1C capacitors. Hence, avoiding the complexity of calibration, this technique can preclude the effect of the bottom-plate to ground capacitance. Statistical simulations prove that the proposed technique is robust to non-ideal effects such as mismatch or parasitic capacitors. A 10-bit C-2C DAC is modeled in COMSOL Multiphysics using... 

    Numerical analysis of heat conduction treated with highly conductive copper oxide nanoparticles In porous media

    , Article Special Topics and Reviews in Porous Media ; Volume 7, Issue 2 , 2016 , Pages 149-160 ; 21514798 (ISSN) Rokhforouz, M. R ; Rabbani, A ; Ayatollahi, S ; Taghikhani, V ; Sharif University of Technology
    Begell House Inc  2016
    In this paper, the effect of highly conductive copper oxide nanoparticles on the effective thermal conductivity (ETC) of rock samples was mathematically investigated. To solve the governing conservation equations for the ETC a commercial finite element package (COMSOL Multiphysics) was used. It should be stressed that the single-phase approach was employed to mathematically model the effect of nanofluid on the heat transfer improvement. The computational geometry of the rock samples was obtained by analyzing the microscopic images of the limestone rock samples. The results obtained from the mathematical modeling of the rock samples showed that the conductive heat transfer through porous... 

    HTS transformer’s partial discharges raised by floating particles and nitrogen bubbles

    , Article Journal of Superconductivity and Novel Magnetism ; Volume 33, Issue 10 , 6 July , 2020 , Pages 3027-3034 Moradnouri, A ; Vakilian, M ; Hekmati, A ; Fardmanesh, M ; Sharif University of Technology
    Springer  2020
    Presence of defects, conducting particles, nonconducting particles, and nitrogen gas bubbles in the insulation system of high-temperature superconducting (HTS) transformers, mainly inside the liquid nitrogen as its major insulation, can create local field enhancement and consequently partial discharges which eventually lead to the catastrophic failure of the transformer. In this paper, two-dimensional (2D) axisymmetric finite element method (FEM) modeling via COMSOL Multiphysics software has been utilized for the investigation of the impact of size and shape of conducting particles and nitrogen gas bubbles on partial discharge (PD) activities in liquid nitrogen. Conducting particles of... 

    HTS transformers leakage flux and short circuit force mitigation through optimal design of auxiliary windings

    , Article Cryogenics ; Volume 110 , September , 2020 Moradnouri, A ; Vakilian, M ; Hekmati, A ; Fardmanesh, M ; Sharif University of Technology
    Elsevier Ltd  2020
    Mitigation and control of leakage fluxes and short circuit forces needs much more attention, for a high-temperature superconducting (HTS) transformer, than for a conventional one. Different methods such as the application of auxiliary windings, multi-segment winding, and flux diverter have been presented in the literatures for leakage magnetic field reduction in HTS transformers. In this paper, for the first time, optimal design of auxiliary windings has been performed for a 132/13.8 kV, 50 MVA three phase core type HTS transformer. Genetic algorithm (GA) has been used for the optimization process. Induced current in auxiliary windings which is inversely proportional to the leakage fluxes... 

    Influence of lakebed sediment deposit on the interaction of hypersaline lake and groundwater: A simplified case of lake Urmia, Iran

    , Article Journal of Hydrology ; Volume 588 , 2020 Sheibani, S ; Ataie Ashtiani, B ; Safaie, A ; Simmons, C. T ; Sharif University of Technology
    Elsevier B.V  2020
    Lake Urmia, which was once the second-largest saline lake in the world, has been shrinking dramatically. Moreover, Lake Urmia has become supersaturated with total salinity averaging more than 350 g/l. Salt precipitation and dissolved materials brought by inflowing rivers have formed a layer of sediment with low hydraulic conductivity on the lakebed. Considering the flat bathymetry of Lake Urmia, we conducted a series of numerical simulation scenarios to study the groundwater flow pattern in the vicinity of the hypersaline Lake Urmia using COMSOL Multiphysics®. In the first step, we performed the simulations in steady-state conditions. Secondly, we simulated the lake level fall in 10 years at...