Search for: aspect-ratio
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    Simulation of a falling droplet in a vertical channel with rectangular obstacles

    , Article European Journal of Mechanics, B/Fluids ; Volume 68 , March-April , 2018 , Pages 108-117 ; 09977546 (ISSN) Merdasi, A ; Ebrahimi, S ; Moosavi, A ; Shafii, M. B ; Kowsary, F ; Sharif University of Technology
    Elsevier Ltd  2018
    Droplet microfluidic systems have attracted a large amount of research due to their numerous applications in biomedical micro-devices and drug discovery/delivery platforms. One of the most important problems in such systems is to investigate deformation, coalescence, and breakup of droplets within the channel. The present study demonstrates numerical simulation of a falling droplet subject to gravitational force in a channel with embedded rectangular obstacles. The lattice Boltzmann method incorporated using He–Chen–Zhang method for two phase flow is employed. Two rectangular obstacles with inverse aspect ratios are introduced to investigate the mechanism of breakup and deformation of the... 

    MHD equilibrium and kink stability in Damavand tokamak

    , Article Journal of Fusion Energy ; Volume 28, Issue 3 , 2009 , Pages 282-289 ; 01640313 (ISSN) Dini, F ; Khorasani, S ; Sharif University of Technology
    Magnetohydrodynamic (MHD) equilibrium is vulnerable to numerous destabilizing mechanisms. Instabilities introduce distortions to the plasma magnetic surfaces and its boundaries, their driving force being the radial gradient of plasma toroidal current density. For certain modal numbers, internal kink modes may develop, and their study is feasible according to the energy principle, in which the change in total potential energy due to the disturbance is evaluated. In this article, we present a totally new analysis of MHD equilibrium and stability, and apply it to Damavand tokamak which has a large aspect ratio. For this purpose, we combine perturbation and Green's function methods to solve for... 

    Performance optimization of a long rod penetrator penetrating into a semi-infinite target considering bending characteristics

    , Article Turkish Journal of Engineering and Environmental Sciences ; Volume 33, Issue 1 , 2009 , Pages 9-20 ; 13000160 (ISSN) Vahedi, K ; Zohoor, H ; Nezamabadi, A ; Zolfaghari, M ; Sharif University of Technology
    In this article a new parameter is introduced that optimizes penetration depth of a long rod penetrating into a semi-infinite target. This parameter helps to optimize penetration depth when the projectile is subjected to transverse loading. This parameter is defined using a simple assumption governing bending moment and deflection of the rod as well as the experimental observation of long rod penetrators having aspect ratios (L/D) of greater than 30. In this article the length of the rod that sustains allowable bending stress but does not fail is calculated. Using the results of the bending analysis and solution of the Alekseevskii & Tate (AT) equation, an analytical method to optimize... 

    The role of mixed reaction promoters in polyol synthesis of high aspect ratio ag nanowires for transparent conducting electrodes

    , Article Journal of Electronic Materials ; Volume 49, Issue 8 , 2020 , Pages 4822-4829 Amiri Zarandi, A ; Khosravi, A ; Dehghani, M ; Tajabadi, F ; Taghavinia, N ; Sharif University of Technology
    Springer  2020
    In recent years, thin silver nanowires (Ag NWs) with diameters smaller than 150 nm have been synthesized by implementation of NaCl or FeCl3 as reaction promoters and high molecular weight polyvinylpyrrolidone (PVP) as the capping agent. However, the yield of Ag NWs still remains low, mostly due to the insufficient aspect ratio (AR) of the synthesized nanostructures and the production of Ag nanoparticles, which is an undesirable by product. This study proposes a modified technique to alleviate the problem by using a mixture of FeCl3/CuCl2 as the reaction promoter and two different types of PVP with molecular weight of 360 k and 40 k as the capping agents. The appropriate mixtures of... 

    Multi-objective robust design optimization (MORDO) of an aeroelastic high-aspect-ratio wing

    , Article Journal of the Brazilian Society of Mechanical Sciences and Engineering ; Volume 42, Issue 11 , 2020 Elyasi, M ; Roudbari, A ; Hajipourzadeh, P ; Sharif University of Technology
    Springer Science and Business Media Deutschland GmbH  2020
    In this paper, a new approach for multi-objective robust optimization of flutter velocity and maximum displacement of the wing tip are investigated. The wing is under the influence of bending–torsion coupling and its design variables have different levels of uncertainty. In designing and optimizing wings with a high aspect ratio, the optimization process can be done in such a way to increase the flutter velocity, but this can increase the amplitude of the wing tip displacement to a point that leads to the wings damage and structural failure. Therefore, single-objective design optimization may lead to infeasible designs. Thus, for multi-objective optimization, modeling is based on the... 

    Parametric study of buckling and post-buckling behavior for an aluminum hull structure of a high-aspect-ratio twin hull vessel

    , Article Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment ; Volume 234, Issue 1 , 2020 , Pages 15-25 Soleimani, E ; Tabeshpour, M. R ; Seif, M. S ; Sharif University of Technology
    SAGE Publications Ltd  2020
    Metal plates are essential parts of structures such as ship hulls and offshore oil platforms. These plates are typically under compressive axial forces. Hence, one of the main mechanisms for failure and collapse of such structures is buckling of plates. Thus, for safe and secure design, buckling strength of plates should be evaluated. Finite element analysis techniques are perfect tools for this purpose because of the accuracy and flexibility for performing simulations with different variables. In this study, the strength of aluminum plates has been studied using finite element analysis software and it was tried to study the influence of variables such as initial imperfections, plate... 

    Geometrically non-linear vibration of concrete shallow funicular shells

    , Article Proceedings of the Institution of Civil Engineers: Structures and Buildings ; Volume 174, Issue 3 , 2021 , Pages 169-180 ; 09650911 (ISSN) Sabermahany, H ; Mofid, M ; Daneshmand, N ; Sharif University of Technology
    ICE Publishing  2021
    This study deals with the geometrically non-linear vibration analysis of concrete shallow funicular shells of rectangular plan with four clamped edges under impulse loads. The shape of a concrete funicular shell is such that the shell is subjected to pure compression under its dead weight. Following the existing method presented for the linear vibration analysis, the geometrically non-linear vibration analysis is considered through the use of non-linear shallow shells theory. Each displacement component is expanded in a double Fourier series and the kinetic energy, the elastic strain energy and the virtual work done by external forces are calculated in terms of the displacement components.... 

    Investigation of Effect of the Initial Bubble Shape on Rising Bubble Behaviour

    , M.Sc. Thesis Sharif University of Technology Ghamangiz Khararodi, Mohammad (Author) ; Bastani, Daruoosh (Supervisor)
    In this experimental work terminal velocity, velocity profile and aspect ratio of bubble with 1.49 mm diameter which ascend in pure water and infected by surfactant nonionic C10DMPO and surfactant ionic SDS in regime that surface tension is dominant, have been considered. Observations showed that with respect to entering nozzle, bubbles with this diameter have two initial stable shape; spherical and extended form on surface for horizontal needle and vertical nozzle. Results are (1) Bubbles with initial spherical shape had lower terminal velocity and higher aspect ratio with respect to bubbles with initial extended form, (2) Spherical bubble had aspect ratio about 1 at whole bubble column... 

    Application of Experimental Design for Synthesis and Controlling Aspect Ratio of Metallic Nanorods

    , M.Sc. Thesis Sharif University of Technology Robatjazi, Hossein (Author) ; Jalali-Heravi, Mehdi (Supervisor) ; ormozi Nezhad, Mohammad Reza (Supervisor)
    Aspect ratio dependant optical properties of silver and gold nanorods is responsible for great attention toward controlling the aspect ratio of this class of the nanostructure for their application in variety of area, such as medical diagnosis, drug delivery, biosensing and treatment. In this research, gold and silver nanorods have been synthesized using chemical reducation and growth based on seed mediated method, which is the newest and one of the best methods with less difficulty for producing silver and gold nanorods. Absorption of the visible light by gold and silver nanorods results in appearing the longitudinal and transverse Plasmon bands in their absorption spectra which is related... 

    Non-Equilibrium Interfacial Behavior of Dynamic Interfaces in Presence of Surfactants and Nanoparticles; Experimental and Computational Fluid Dynamic Investigations

    , Ph.D. Dissertation Sharif University of Technology Fayzi, Pouyan (Author) ; Bastani, Dariush (Supervisor) ; Lotfi, Marzieh (Supervisor)
    The present study has been performed for better understanding about the dynamic behavior of fluid interfaces in presence of surfactants, nanoparticles and their interactions in gas-liquid dispersion systems. One of the main purposes of this work is to investigate the influence of surface modified nanoparticles on the dynamic behavior of gas-liquid interfaces. For this purpose, the rising bubble experiment was used as one of the most conventional procedures. Local velocities of bubbles rising in nanoparticle solutions were determined experimentally. Influences of silica nanoparticles which were modified via three approaches were investigated in these experiments. Heat treatment was applied to... 

    A novel field ionization gas sensor based on self-organized CuO nanowire arrays

    , Article Sensors and Actuators, A: Physical ; Vol. 216 , 2014 , pp. 202-206 ; ISSN: 09244247 Mohammadpour, R ; Ahmadvand, H ; Iraji Zad, A ; Sharif University of Technology
    In this study, we present fabrication and characterization of a gas ionization sensor based on high aspect ratio one-dimensional CuO nanowires as the field enhancing medium. Self-organized arrays of CuO nanowires have been synthesized based on a low-cost thermal oxidation method and integrated into a gas ionization sensor (GIS). The self-organized arrays of CuO nanowires have been employed to detect the identity of several gas species such as He, Ar and CO at ambient temperature and pressure. The sharp nanoscale size of CuO tips provide very high electric fields at moderate voltages (less than 100 V) and provoke the breakdown of different gases. The reduced breakdown current of the metal... 

    The study of magnetic field implementation on cylinder quenched in boiling ferro-fluid

    , Article Applied Thermal Engineering ; Volume 64, Issue 1-2 , March , 2014 , Pages 331-338 ; ISSN: 13594311 Habibi Khoshmehr, H ; Saboonchi, A ; Shafii, M. B ; Jahani, N ; Sharif University of Technology
    It has been shown that nanofluids in different investigations increase or decrease heat transfer rate in boiling phenomenon. The present study examined the effects of ferro-fluid concentrations and magnetic field implementation on the fluid throughout the boiling process. Obtained are the quenching curve and boiling curve on specified surface roughness in both water and ferro-fluid with two different concentrations. A silver cylinder with Aspect ratio of 10, and surface roughness of 689 nm was heated up to 350 C and then was overwhelmed in the fluid under study. Temperatures were measured by a thermocouple which installed in the center of the cylinder. The test was carried out 5 times. The... 

    Simulation and control of multidimensional crystallization Processes

    , Article Chemical Engineering Communications ; Vol. 201, Issue. 7 , 2014 , pp. 870-895 ; ISSN: 0098-6445 Orkomi, A. A ; Shahrokhi, M ; Sharif University of Technology
    In this article, solving the population balance equation (PBE) and controlling the final particle size for crystallization problems have been addressed. For solving the general form of multidimensional PBE, a numerical method called conservation element and solution element (CE/SE) has been used. By applying this method to one- and two-dimensional crystallization problems, it has been shown that this technique can handle all types of source terms in the PBE. Model accuracy has been checked with experimental data reported in the literature and also with the analytical solution of PB-type equations. Control of final particle size was formulated in an optimization framework. To obtain a desired... 

    Laminar falling film flow of aqueous Li Br solution on a horizontal elliptical tube

    , Article International Journal of Fluid Mechanics Research ; Volume 40, Issue 4 , 2013 , Pages 324-343 ; 10642277 (ISSN) Abyaneh, M. H. J ; Saidi, M. H ; Sharif University of Technology
    Flow hydrodynamics of laminar falling film of aqueous Li Br solution (Li Br - H2O) on a horizontal elliptical tube has been investigated in this research. The film velocity distribution and film thickness, namely, the flow characteristics are determined by solving analytically simultaneous simplified Navier - Stokes equations and continuity equation in polar and Cartesian coordinates. The analysis is based on steady state laminar flow of falling liquid film of Li Br - H2O on a horizontal elliptical tube in polar model and Cartesian model (CM), for cases in which traction on the film surface is considered negligible. Models are compared with each other in three cases of aspect ratios (Ar),... 

    Effective behavior of porous elastomers containing aligned spheroidal voids

    , Article Acta Mechanica ; Volume 224, Issue 9 , September , 2013 , Pages 1901-1915 ; 00015970 (ISSN) Avazmohammadi, R ; Naghdabadi, R ; Sharif University of Technology
    The theoretical need to recognize the link between the basic microstructure of nonlinear porous materials and their macroscopic mechanical behavior is continuously rising owing to the existing engineering applications. In this regard, a semi-analytical homogenization model is proposed to establish an overall, continuum-level constitutive law for nonlinear elastic materials containing prolate/oblate spheroidal voids undergoing finite axisymmetric deformations. The microgeometry of the porous materials is taken to be voided spheroid assemblage consisting of confocally voided spheroids of all sizes having the same orientation. Following a kinematically admissible deformation field for a... 

    Bending-torsional flutter of a cantilevered pipe conveying fluid with an inclined terminal nozzle

    , Article Journal of Sound and Vibration ; Volume 332, Issue 12 , 2013 , Pages 3002-3014 ; 0022460X (ISSN) Firouz Abadi, R. D ; Askarian, A. R ; Kheiri, M ; Sharif University of Technology
    Stability analysis of a horizontal cantilevered pipe conveying fluid with an inclined terminal nozzle is considered in this paper. The pipe is modelled as a cantilevered Euler-Bernoulli beam, and the flow-induced inertia, Coriolis and centrifugal forces along the pipe as well as the follower force induced by the jet-flow are taken into account. The governing equations of the coupled bending-torsional vibrations of the pipe are obtained using extended Hamilton's principle and are then discretized via the Galerkin method. The resulting eigenvalue problem is then solved, and several cases are examined to determine the effect of nozzle inclination angle, nozzle aspect ratio, mass ratio and... 

    Modified multiscale finite volume method for two phase flow in porous media

    , Article ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) ; Volume 7 A , 2013 ; 9780791856314 (ISBN) Saeidimanesh, M ; Eksiri, H ; ASME ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2013
    Multiscale finite volume (MSFV) method have been developed and applied in various complicated physics. The most important advantage of MSFV method is its computational efficiency. In this paper we present a new set of boundary condition for calculation of basis and correction functions which leads to further reduction in computational time in problems with medium heterogeneity and therefore improves computational efficiency. In standard MSFV (sMSFV) method reduced boundary condition is used to determine the basis and correction functions which is based on local information, however in modified MSFV (mMSFV) method global information is used at initial time for constructing boundary condition... 

    The influence of grain size and grain size distribution on sliding frictional contact in laterally graded materials

    , Article Mechatronics and Applied Mechanics, Hong Kong, 27 December 2011 through 28 December 2011 ; Volume 157-158 , 2012 , Pages 964-969 ; 16609336 (ISSN); 9783037853801 (ISBN) Khajehtourian, R ; Adibnazari, S ; Tashi, S ; 2011 International Conference; on Mechatronics and Applied Mechanics, ICMAM2011 ; Sharif University of Technology
    The sliding frictional contact problem for a laterally graded half-plane has been considered. Two finite element (FE) models, in macro and micro scales have been developed to investigate the effective parameters in contact mechanics of laterally graded materials loaded by flat and triangular rigid stamps. In macro scale model, the laterally graded half-plane is discretized by piecewise homogeneous layers for which the material properties are specified at the centroids by Mori-Tanaka method. In micro scale model, functionally graded material (FGM) structure has been modeled as ideal solid quadrant particles which are spatially distributed in a homogeneous matrix. Boundary conditions and... 

    Colorimetric detection of glutathione based on transverse overgrowth of high aspect ratio gold nanorods investigated by MCR-ALS

    , Article RSC Advances ; Volume 5, Issue 101 , 2015 , Pages 82906-82915 ; 20462069 (ISSN) Fahimi Kashani, N ; Shadabipour, P ; Hormozi-Nezhad, M. R ; Sharif University of Technology
    Royal Society of Chemistry  2015
    In this paper, we present a simple platform for colorimetric detection of glutathione using gold nanorods (AR ∼ 6.5 ± 0.2) as a plasmonic sensor. The functional mechanism of the sensor is based on shifts of longitudinal plasmon resonance during selective transverse overgrowth induced by preferential binding of glutathione at the nanorod tips. Under the optimum conditions, a calibration curve showed two linear regimes at the range of 50 nM to 20 μM of glutathione with a detection limit as low as 40 nM. The nanosensor maintains relatively high selectivity for determination of glutathione in the presence of several other amino acids. However, cysteine at similar concentration levels strongly... 

    Equilibrium state of a cylindrical particle with flat ends in nematic liquid crystals

    , Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 91, Issue 1 , January , 2015 ; 15393755 (ISSN) Hashemi, S. M ; Ejtehadi, M. R ; Sharif University of Technology
    American Physical Society  2015
    A continuum theory is employed to numerically study the equilibrium orientation and defect structures of a circular cylindrical particle with flat ends under a homeotropic anchoring condition in a uniform nematic medium. Different aspect ratios of this colloidal geometry from thin discotic to long rodlike shapes and several colloidal length scales ranging from mesoscale to nanoscale are investigated. We show that the equilibrium state of this colloidal geometry is sensitive to the two geometrical parameters: aspect ratio and length scale of the particle. For a large enough mesoscopic particle, there is a specific asymptotic equilibrium angle associated to each aspect ratio. Upon reducing the...