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CFD modeling of natural convection in right-angled triangular enclosures
, Article International Journal of Heat and Technology ; Volume 34, Issue 3 , 2016 , Pages 503-506 ; 03928764 (ISSN) ; Sharif University of Technology
Edizioni ETS
2016
Abstract
Two-dimensional numerical simulations have been performed to study natural convection in right-angled triangular enclosures filled with water considering different aspect ratios. Continuity, momentum and energy equations are solved assuming Boussinesq approximation utilizing COMSOL. Effect of Rayleigh number, Ra, on heat transfer rate is investigated by showing Nusselt number, Nu, for a range from 1 × 104 to 1 × 107 . It is shown that increasing aspect ratio of the cavity increases averaged Nusselt number in a cavity heated from below. Finally, a correlation for heat transfer rate is developed considering the effect of aspect ratio using simulation results
Influence of main and outer wings on aerodynamic characteristics of compound wing-in-ground effect
, Article Aerospace Science and Technology ; Volume 55 , 2016 , Pages 177-188 ; 12709638 (ISSN) ; Seif, M. S ; Sharif University of Technology
Elsevier Masson SAS
Abstract
A practical mathematical model with low computational time and good accuracy is applied to investigate theaerodynamic characteristics and static height stability of the compound wing-in-ground effect (WIG). The compound WIG consists of a main wing with low aspect ratio and an endplate, and anouter wing with high aspect ratio. To validate the present mathematical model, a numerical simulation is performed so thatnumerical results had a good agreement with the experimental data. The analysis shows that the main wing is useful in the extreme ground effect zone and the outer wing enhances performance of the compound WIG in the weak ground effect zone. In order to satisfy the static height...
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...
Investigation of CFS shear walls with one and two-sided steel sheeting
, Article Journal of Constructional Steel Research ; Volume 122 , 2016 , Pages 292-307 ; 0143974X (ISSN) ; Alizadeh, S ; Hadidi, S ; Sharif University of Technology
Elsevier Ltd
2016
Abstract
In this study six Cold-Formed Steel shear wall (CFS) with one and two side steel sheeting are tested under reversed cyclic loading. Besides, thirteen numerical models are simulated, using nonlinear finite element method, and analyzed under monotonic pushover loading. The studied parameters are the comparison of one and two side steel sheeting, the nominal thickness of steel sheet and boundary elements, and height to width aspect ratios of the wall. The performance of tested specimens is investigated in terms of lateral load-story drift response, failure modes and ultimate strength of shear walls. Based on AISI S213 the available strength of two-sided steel-sheathed walls is cumulative but...
Broadband and low-loss plasmonic Light trapping in dye-sensitized solar cells using micrometer-scale rodlike and spherical core-shell plasmonic particles
, Article ACS Applied Materials and Interfaces ; Volume 8, Issue 25 , 2016 , Pages 16359-16367 ; 19448244 (ISSN) ; Nemati Kharat, A ; Taghavinia, N ; Dabirian, A ; Sharif University of Technology
American Chemical Society
2016
Abstract
Dielectric scattering particles have widely been used as embedded scattering elements in dye-sensitized solar cells (DSCs) to improve the optical absorption of the device. Here we systematically study rodlike and spherical core-shell silica@Ag particles as more effective alternatives to the dielectric scattering particles. The wavelength-scale silica@Ag particles with sufficiently thin Ag shell support hybrid plasmonic-photonic resonance modes that have low parasitic absorption losses and a broadband optical response. Both of these features lead to their successful deployment in light trapping in high-efficiency DSCs. Optimized rodlike silica@Ag@silica particles improve the power conversion...
Analytical solutions for the size dependent buckling and postbuckling behavior of functionally graded micro-plates
, Article International Journal of Engineering Science ; Volume 100 , 2016 , Pages 45-60 ; 00207225 (ISSN) ; Sharif University of Technology
Elsevier Ltd
2016
Abstract
In this study, the buckling and postbuckling analysis of FG micro-plates under different kinds of traction on the edges is investigated based on the modified couple stress theory. The static equilibrium equations of an FG rectangular micro-plate as well as the boundary conditions are derived using the principle of minimum total potential energy. The analytical solutions are developed for three case studies including: simply supported micro-plates subjected to uniform transverse load and biaxial tractions, clamped-simply supported micro-plates under uniform transverse load and axial traction, and simply supported micro-plates subjected to shear traction. All plate properties except the length...
Laminar forced convection in annular microchannels with slip flow regime
, Article 7th International Conference on Nanochannels, Microchannels, and Minichannels, 22 June 2009 through 24 June 2009 ; Issue PART A , 2009 , Pages 353-361 ; 9780791843499 (ISBN) ; Asgarshamsi, A. H ; Saidi, M. H ; Sharif University of Technology
Abstract
Fluid flow and heat transfer at microscale have attracted an important research interest in recent years due to the rapid development of microelectromechanical systems (MEMS). Fluid flow in microdevices has some characteristics which one of them is rarefaction effect related with gas flow. In this research, hydrodynamically and thermally fully developed laminar rarefied gas flow in annular microducts is studied using slip flow boundary conditions. Two different cases of the thermal boundary conditions are considered, namely: uniform temperature at the outer wall and adiabatic inner wall (Case A) and uniform temperature at the inner wall and adiabatic outer wall (Case B). Using the previously...
Second law analysis of slip flow heat transfer in annulus microchannel
, Article Proceedings of the ASME Summer Heat Transfer Conference 2009, HT2009, 19 July 2009 through 23 July 2009, San Francisco, CA ; Volume 1 , 2009 , Pages 321-330 ; 9780791843567 (ISBN) ; Asgarshamsi, A ; Saidi, M. H ; Sharif University of Technology
Abstract
In the present work, the second law of thermodynamics analysis has been carried out for steady state hydrodynamically and thermally fully developed laminar gas flow in annulus microchannels with asymmetrically heated walls. The rarefaction effects are taken into consideration using first order slip velocity and temperature jump boundary conditions. Viscous heating is also included for both the hot wall and the cold wall cases. Using the velocity distribution obtained in earlier works, the energy equation is solved to get analytically the temperature distribution and consequently to compute the entropy generation rate. The effects of rarefaction and the annulus geometrical aspect ratio on...
Coanda surface geometry optimization for multi-directional co-flow fluidic thrust vectoring
, Article Proceedings of the ASME Turbo Expo: Power for Land, Sea, and Air ; Volume 5 , 2009 , Pages 183-189 ; 9780791848869 (ISBN) ; Banazadeh, A ; Sharif University of Technology
Abstract
The performance of Co-flow fluidic thrust vectoring is a function of secondary flow characteristics and the fluidic nozzle geometry. In terms of nozzle geometry, wall shape and the secondary slot aspect ratio are the main parameters that control the vector angle. The present study aims to find a high quality wall shape to achieve the best thrust vectoring performance, which is characterized by the maximum thrust deflection angle with respect to the injected secondary air. A 3D computational fluid dynamics (CFD) model is employed to investigate the flow characteristics in thrust vectoring system. This model is validated using experimental data collected from the deflection of exhaust gases of...
Time-average drag coefficient and void fraction in gas-liquid two phase flow
, Article Proceedings of the ASME Fluids Engineering Division Summer Conference 2009, FEDSM2009, 2 August 2009 through 6 August 2009, Vail, CO ; Volume 1, Issue PART B , 2009 , Pages 1083-1094 ; 9780791843727 (ISBN) ; Hanafizadeh, P ; Saidi, M. H ; Sharif University of Technology
Abstract
Two-phase flow simulations around a body were not studied before and considering these flows can play a significant role in long-term reliability and safety of industrial systems. In this paper, flow regimes, drag coefficient and void fraction around different cross-section prisms were considered. To achieve this aim, main equations of flow have been developed for investigation of drag coefficient in air-water two phase. Our numerical analyses were performed by a designed and written CFD package which is based on Eulerian-Eulerian approach. Geometries, which have been studied in this article, are: circle, rectangle and triangle, for different aspect ratio (length over width) and leading edge...
Flow field analysis around the ship fin stabilizer including free surface
, Article Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE, 31 May 2009 through 5 June 2009, Honolulu, HI ; Volume 4, Issue PART A , 2009 , Pages 603-608 ; 9780791843444 (ISBN) ; Ghassemi, H ; Ghadimi, P ; Ommani, B ; Sharif University of Technology
Abstract
Fin stabilizers are very important device for controlling the ship roll motion against the external moments due to wave. This paper presents numerical results for flow field simulation and the hydrodynamic performance of fin stabilizer attached to a ship hull with free surface effects. Combination of CFD and RANS method has been used for this study. The fin is nonrectangular NACA0015 profile section with a finite aspect ratio. The numerical results include pressure distributions and flow field around the fin which are used to calculate lift coefficients and free surface elevation as the main interest. Some results are compared with available experimental and numerical data in literature and...
Geometry effect on electrokinetic flow and ionic conductance in pH-regulated nanochannels
, Article Physics of Fluids ; Volume 29, Issue 12 , 2017 ; 10706631 (ISSN) ; Saidi, M. H ; Moosavi, A ; Sadeghi, A ; Sharif University of Technology
Abstract
Semi-analytical solutions are obtained for the electrical potential, electroosmotic velocity, ionic conductance, and surface physicochemical properties associated with long pH-regulated nanochannels of arbitrary but constant cross-sectional area. The effects of electric double layer overlap, multiple ionic species, and surface association/dissociation reactions are all taken into account, assuming low surface potentials. The method of analysis includes series solutions which the pertinent coefficients are obtained by applying the wall boundary conditions using either of the least-squares or point matching techniques. Although the procedure is general enough to be applied to almost any...
Reduction of production rate in y-shaped microreactors in the presence of viscoelasticity
, Article Analytica Chimica Acta ; Volume 990 , 2017 , Pages 121-134 ; 00032670 (ISSN) ; Saidi, M. H ; Sadeghi, A ; Sharif University of Technology
Abstract
The viscoelasticity effects on the reaction-diffusion rates in a Y-shaped microreactor are studied utilizing the PTT rheological model. The flow is assumed to be fully developed and considered to be created under a combined action of electroosmotic and pressure forces. In general, finite-volume-based numerical simulations are conducted to handle the problem; however, analytical solutions based on the depthwise averaging approach are also obtained for the case for which there is no reaction between the inlet components. The analytical solutions are found to predict accurate results when the width to height ratio is at least 10 and acceptable results for lower aspect ratios. An investigation...
Engineered cost-effective growth of Co-based nanoflakes as a sustainable water oxidation electrocatalyst
, Article Journal of Physics D: Applied Physics ; Volume 50, Issue 47 , 2017 ; 00223727 (ISSN) ; Naseri, N ; Sharif University of Technology
Abstract
Developing low-cost, scalable and reproducible synthesis methods for water oxidation reaction (WOR) catalysts is highly desirable and also challenging in energy, environmental and industrial applications. In this context, electrochemical deposition is known as an easy and cost-effective technique in nanomaterial growth. Herein, cobalt-based nanoflakes were grown on a flexible and commercially available steel mesh substrate by electrodeposition approach with a crystalline structure as a mixture of oxide, hydroxide and oxyhydroxide phases. For the first time, the correlation between electrodeposition parameters, time and current density, and morphological characteristics of the grown...
Geometrical influence of a deposited particle on the performance of bridged carbon nanotube-based mass detectors
, Article Physica E: Low-Dimensional Systems and Nanostructures ; Volume 94 , 2017 , Pages 31-46 ; 13869477 (ISSN) ; Ceballes, S ; Abdelkefi, A ; Sharif University of Technology
Abstract
A nonlocal continuum-based model is derived to simulate the dynamic behavior of bridged carbon nanotube-based nano-scale mass detectors. The carbon nanotube (CNT) is modeled as an elastic Euler-Bernoulli beam considering von-Kármán type geometric nonlinearity. In order to achieve better accuracy in characterization of the CNTs, the geometrical properties of an attached nano-scale particle are introduced into the model by its moment of inertia with respect to the central axis of the beam. The inter-atomic long-range interactions within the structure of the CNT are incorporated into the model using Eringen's nonlocal elastic field theory. In this model, the mass can be deposited along an...
Probabilistic evaluation of 2015 NEHRP soil-structure interaction provisions
, Article Journal of Engineering Mechanics ; Volume 143, Issue 9 , 2017 ; 07339399 (ISSN) ; Mahsuli, M ; Ghannad, M. A ; Sharif University of Technology
Abstract
This paper reveals the consequences of practicing the 2015 National Earthquake Hazards Reduction Program (NEHRP) soilstructure interaction (SSI) provisions, which form the basis of the 2016 edition of the seismic design standard provided by the ASCE. For this purpose, the probability that the practice of SSI provisions, in lieu of fixed-base provisions, increases the ductility demand of the structure computed. It is subsequently investigated whether the NEHRP provisions are indeed an improvement upon the SSI provisions of the current ASCE seismic design standard. To this end, 720 soil-structure systems with different numbers of stories, structural systems, aspect ratios, and foundation...
Viscous damping effect on the aeroelastic stability of subsonic wings: Introduction of the U–K method
, Article Journal of Fluids and Structures ; Volume 73 , 2017 , Pages 1-15 ; 08899746 (ISSN) ; Dehghani Firouz Abadi, R ; Rahmanian, M ; Sharif University of Technology
Abstract
This study aims at introduction of a novel method for evaluating the effect of viscous damping on the aeroelastic stability boundaries. The K-method is well-known for being one of the fastest methods in determining the instability conditions (i.e. critical speed and its corresponding frequency). However, formulation of the K-method is developed for aeroelastic systems without viscous damping and solution is valid where the introduced artificial damping is zero. Taking into account the framework of the K-method in general, this study has tried to remove the major shortcoming of the K-method, i.e. investigation of the effect of viscous damping on the aeroelastic stability boundaries. The...
Thermo-mechanical vibration of orthotropic cantilever and propped cantilever nanoplate using generalized differential quadrature method
, Article Mechanics of Advanced Materials and Structures ; Volume 24, Issue 8 , 2017 , Pages 636-646 ; 15376494 (ISSN) ; Shafiei, N ; Alavi, H ; Sharif University of Technology
Abstract
In this article, the vibration frequency of an orthotropic nanoplate under the effect of temperature change is investigated. Using nonlocal elasticity theory, governing equations are derived. Based on the generalized differential quadrature method for cantilever and propped cantilever boundary conditions, the frequencies of orthotropic nanoplates are considered and the obtained results are compared with valid reported results in the literature. The effects of temperature variation, small scale, different boundary conditions, aspect ratio, and length on natural nondimensional frequencies are studied. The present analysis is applicable for the design of rotating and nonrotating nano-devices...
Electroosmotic flow and ionic conductance in a pH-regulated rectangular nanochannel
, Article Physics of Fluids ; Volume 29, Issue 6 , 2017 ; 10706631 (ISSN) ; Saidi, M. H ; Sadeghi, A ; Sharif University of Technology
Abstract
Infinite series solutions are obtained for electrical potential, electroosmotic velocity, ionic conductance, and surface physicochemical properties of long pH-regulated rectangular nanochannels of low surface potential utilizing the double finite Fourier transform method. Closed form expressions are also obtained for channels of large height to width ratio for which the depthwise variations vanish. Neglecting the Stern layer impact, the effects of EDL (Electric Double Layer) overlap, multiple ionic species, and association/dissociation reactions on the surface are all taken into account. Moreover, finite-element-based numerical simulations are conducted to account for the end effects as well...
Nonlinear dynamics of extensible viscoelastic cantilevered pipes conveying pulsatile flow with an end nozzle
, Article International Journal of Non-Linear Mechanics ; Volume 91 , 2017 , Pages 22-35 ; 00207462 (ISSN) ; Haddadpour, H ; Dehghani Firouz Abadi, R ; Abtahi, H ; Sharif University of Technology
Elsevier Ltd
2017
Abstract
Nonlinear dynamics of an extensible cantilevered pipe conveying pulsating flow is considered in this paper. The fluid flow fluctuates harmonically and exhausts via a nozzle attached to the end of the pipe. Taking into account the extensibility assumption, the coupled nonlinear lateral–longitudinal equations of motion are derived using Hamilton's principle and discretized via Galerkin's method. The adaptive time step Adams algorithm is applied to extract the time response, and then the bifurcation, power spectral density and phase plane maps are plotted for some case studies. Effects of some geometrical parameters such as flow mass, pulsating flow frequency, gravity, nozzle mass and nozzle...