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Total 217 records

    Dynamic instability of cantilevered composite pipe conveying flow with an end nozzle

    , Article 21st International Congress on Sound and Vibration 2014, ICSV 2014 ; Vol. 4, issue , 13- 17 July , 2014 , pp. 3564-3571 ; ISBN: 9781634392389 Askarian, A ; Abtahi, H ; Haddadpour, H ; Sharif University of Technology
    Abstract
    In this paper, the instability of cantilevered horizontal composite pipes is investigated. To this aim, the lateral flow forces are modelled as a distributed lateral force and the nozzle effect is modelled as a compressive axial follower force and a concentrated end mass. The coupled bending-torsional equations of motion are derived using Hamilton's principal and Galerkin method. In order to obtain the stability margin of the pipe, the standard Eigen value problem is solved. Finally, effects of elastic coupling parameter and nozzle aspect ratio are considered on the stability margin of the pipe and some conclusions are drawn  

    An analysis of carbone monoxide distribution in large tunnel fires

    , Article Journal of Mechanical Science and Technology ; Vol. 28, Issue. 5 , 2014 , pp. 1917-1925 ; ISSN: 1738494X Sojoudi, A ; Afshin, H ; Farhanieh, B ; Sharif University of Technology
    Abstract
    Fire events and the related toxicants such as CO are responsible for many fatalities in the current century. These hazardous events are much more dangerous when they occur in enclosed spaces. In the present study, a theoretical relation is developed for horizontal distribution of CO in a large tunnel fire. Then, the developed criterion is used to study the effect of some rudimentary parameters such as the heat release rate (HRR) of fire and tunnel's aspect ratio (AR) on CO and temperature stratification. Theoretical results of various heat release rates and aspect ratios for horizontal distribution of CO are compared with numerical results using fire dynamics simulator (FDS5.5). It is found... 

    Modeling of dislocation density and strength on rheoforged A356 alloy during multi-directional forging

    , Article Computational Materials Science ; Vol. 81 , 2014 , pp. 284-289 Kavosi, J ; Saei, M ; Kazeminezhad, M ; Dodangeh, A ; Sharif University of Technology
    Abstract
    In this study, a hybrid model is presented to predict the dislocation density and strength evolution of the rheoforged non-dendritic A356 alloy during multi-directional forging. Regarding the characteristics of non-dendritic A356 alloy, combination of Shear Lag and Nes models is used for the eutectic structure, and Nes model is used for the α-Al globular phase. The aspect ratio variations of Si particles in eutectic structure during 3 passes of multi-directional forging do not change the model predictions, significantly. Model predictions on shear stress are in good agreement with experimental results of shear punch test  

    Towards defining new nano-descriptors: Extracting morphological features from transmission electron microscopy images

    , Article RSC Advances ; Vol. 4, issue. 104 , Nov , 2014 , p. 60135-60143 Bigdeli, A ; Hormozi-Nezhad, M. R ; Jalali-Heravi, M ; Abedini, M. R ; Sharif-Bakhtiar, F ; Sharif University of Technology
    Abstract
    Due to the important role of surface-related properties of NPs in their biological behavior, simple and fast methods that could precisely demonstrate accurate information about NPs' surface, structure and morphology are highly desirable. In this study a set of surface morphological nano-descriptors (size, shape, surface area, agglomeration state, curvature, corner count and aspect ratio) have been defined and extracted from Transmission Electron Microscopy (TEM) images of nanoparticles (NPs) by Digital Image Processing methods. The extracted data represent a thorough description of the surface and morphologies of NPs lying beyond their TEM images and can supply the data required for a... 

    A study on the axial stresses of P-FGM, SFGM and E-FGM plates under pressure loading using the energy concept

    , Article 27th Congress of the International Council of the Aeronautical Sciences 2010, ICAS 2010, 19 September 2010 through 24 September 2010, Nice ; Volume 3 , 2010 , Pages 2060-2068 ; 9781617820496 (ISBN) Dastoom Laatleyli, H ; Abedian, A ; Sharif University of Technology
    2010
    Abstract
    In this study the energy concept along with the classical plate theory (CPT), first and third order shear deformation theories (FSDT and TSDT) are used to predict the large deflection and through the thickness stresses of a FGM plate. For defining the volume fraction of the FGM constituent materials three different functions are considered; simple power-law (PFGM), exponential (E-FGM) and sigmoid (S_FGM) functions. Power-law and exponential functions are commonly used tocontrol the variations of properties of FGMs. However, with both functions, a stress concentration appears due to abruptchange of the volume fraction of the constituents. Therefore, a sigmoid FGM is used to define a new... 

    Effect of anisotropy on the scaling of connectivity and conductivity in continuum percolation theory

    , Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 81, Issue 6 , June , 2010 ; 15393755 (ISSN) Sadeghnejad, S ; Masihi, M ; King, P. R ; Shojaei, A ; Pishvaei, M ; Sharif University of Technology
    2010
    Abstract
    We investigate the effects of anisotropy on the finite-size scaling of connectivity and conductivity of continuum percolation in three dimensions. We consider a system of size X×Y×Z in which cubic bodies of size a×b×c are placed randomly. We define two aspect ratios to request anisotropy then we expect that the displacement of average connected fraction P (averaged over the realizations), about the isotropic universal curves will be a function of the two aspect ratios. This is accounted by considering an apparent percolation threshold in each direction which leads to 50% of realizations connecting in that direction. We find the aspect ratios' dependency of the apparent threshold and... 

    Solar radiation on domed roofs

    , Article Energy and Buildings ; Volume 41, Issue 11 , 2009 , Pages 1238-1245 ; 03787788 (ISSN) Faghih Khorasani, A. R ; Bahadori, M.N ; Sharif University of Technology
    2009
    Abstract
    Solar radiation received and absorbed by four domed roofs was estimated and compared with that of a flat roof. The domed roofs all had the same base areas, and equal to that of the flat roof. One of the roofs considered was the dome of the St. Peter's Church in Rome. Compared with the other roofs considered, this dome had a higher aspect ratio. It was found that all domed roofs received more solar radiation than the flat roof. Considering glazed tiles to cover a selected dome in Iran and the dome of the St. Peter's Church, it was found that the solar radiation absorbed by these roofs is reduced appreciably. In the case of the dome of St. Peter's Church, the amount of radiation absorbed was... 

    Water drop impact on a semi-cylindrical convex hot surface for a diameter ratio of unity

    , Article Experimental Thermal and Fluid Science ; Volume 106 , 2019 , Pages 68-77 ; 08941777 (ISSN) Jowkar, S ; Morad, M. R ; Sharif University of Technology
    Elsevier Inc  2019
    Abstract
    When a liquid drop impacts on a hot non-flat surface the curvature of the surface and its geometrical characteristics transmute the physical regimes and their boundary compared to a flat surface impact. The present experimental study is focused on water drop impingement on a mimetic solid semi-cylindrical convex hot surface, with a size equal to the drop. The thermal versus inertia map of generated regimes is obtained, while some well-known regimes associated with a flat surface are not observed for the present non-flat impacts. These include rebounding of the main drop and atomization which are common observed phenomena when the hot surface is flat. The maximum spreading of the droplet is... 

    Penetration of elliptical liquid jets in low-speed crossflow

    , Article Journal of Fluids Engineering, Transactions of the ASME ; Volume 141, Issue 1 , 2019 ; 00982202 (ISSN) Morad, M. R ; Khosrobeygi, H ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2019
    Abstract
    Trajectory and penetration of elliptical liquid jets emerged into a low-speed crossflow of air are studied. The jets are introduced to the crossflow at different momentum ratios ranging from 1 to 300. The images are analyzed to obtain the trajectories of the outer boundary of the jets for two different aspect ratios. An empirical correlation is proposed for the present injector geometries and for the range of momentum ratio, Weber, and Reynolds numbers used in this study. Finally, a theoretical model for the trajectory of the liquid column for an initially elliptical liquid emerging into a crossflow is presented, and the associated drag coefficients are obtained for a precise trajectory... 

    Microstructural investigation of semisolid aluminum a356 alloy prepared by the combination of electromagnetic stirring and gas induction

    , Article 15th International conference on Semi-Solid Processing of Alloys and Composites, S2P 2018, 22 October 2018 through 24 October 2018 ; Volume 285 SSP , 2019 , Pages 290-295 ; 16629779 (ISSN); 9783035713732 (ISBN) Nafari, N ; Yekani, F ; Aashuri, H ; Sharif University of Technology
    Trans Tech Publications Ltd  2019
    Abstract
    A three phase electromagnetic stirrer was used to agitate aluminum A356 slurry and a dry and oxygen free argon gas was introduced in to the slurry by a porous graphite core at a same time. The prepared semi-solid slurry was then transferred into a metallic mold and was compacted by a drop weight. Results demonstrated a favorable increase in shape factor, decrease in aspect ratio and average diameter size at different intensities of stirring. The intensity of stirring was changed by altering the current passed through the magnetic coil and also bubbling intensity via the porous graphite diffuser. Different time intervals for electromagnetic stirring and gas induction were applied. Agitating... 

    The effects of bubble detachment shape on rising bubble hydrodynamics

    , Article Scientia Iranica ; Volume 26, Issue 3 C , 2019 , Pages 1546-1554 ; 10263098 (ISSN) Fayzi, P ; Bastani, D ; Lotfi, M ; Ghamangiz Khararoodi, M ; Sharif University of Technology
    Sharif University of Technology  2019
    Abstract
    Local velocities and aspect ratios of rising bubbles were measured to investigate the effects of bubble detachment shape on rising bubble hydrodynamics. Two types of capillary were employed to generate bubbles of identical volume: one glassy nozzle aligned vertically and the other stainless steel needle aligned horizontally. Horizontally injected bubbles have a spherical initial shape, and their values of aspect ratio slightly fluctuate around unity. However, vertically injected bubbles have a surface-stretched initial shape, and their values of aspect ratios decrease sharply from 1.1 to 0.65. There is a notable correspondence between the variation of local velocities and aspect ratios that... 

    Penetration of elliptical liquid jets in low-speed crossflow

    , Article Journal of Fluids Engineering, Transactions of the ASME ; Volume 141, Issue 1 , 2019 ; 00982202 (ISSN) Morad, M. R ; Khosrobeygi, H ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2019
    Abstract
    Trajectory and penetration of elliptical liquid jets emerged into a low-speed crossflow of air are studied. The jets are introduced to the crossflow at different momentum ratios ranging from 1 to 300. The images are analyzed to obtain the trajectories of the outer boundary of the jets for two different aspect ratios. An empirical correlation is proposed for the present injector geometries and for the range of momentum ratio, Weber, and Reynolds numbers used in this study. Finally, a theoretical model for the trajectory of the liquid column for an initially elliptical liquid emerging into a crossflow is presented, and the associated drag coefficients are obtained for a precise trajectory... 

    Numerical modeling of instability and breakup of elliptical liquid jets

    , Article AIAA Journal ; Volume 58, Issue 6 , June , 2020 , Pages 2442-2449 Morad, M. R ; Nasiri, M ; Amini, G ; Sharif University of Technology
    American Institute of Aeronautics and Astronautics Inc  2020
    Abstract
    Numerical simulations are performed to provide an in-depth insight into the effect of instabilities on liquid jets discharging from elliptical orifices. The axis-switching phenomenon and breakup are simulated and characterized under the effect of disturbances imposed at the nozzle exit. The simulations are based on the volume of fluid approach and an adaptive meshing. A range of orifice aspect ratios from 1 to 4 at the Rayleigh breakup regime is considered. The evolution of the jet cross section and axis switching under the influence of disturbances is compared with that of nonperturbed elliptical jets. It is found that the axis-switching repetition and breakup length exponentially decrease... 

    Identification of nonlinear model for rotary high aspect ratio flexible blade using free vibration response

    , Article Alexandria Engineering Journal ; Volume 59, Issue 4 , August , 2020 , Pages 2131-2139 Mahariq, I ; Kavyanpoor, M ; Ghalandari, M ; Nazari, M. A ; Bui, D. T ; Sharif University of Technology
    Elsevier B. V  2020
    Abstract
    Nonlinear identification of a narrow cantilever blade undergoing free vibration was studied. In the absence of forced excitation and because of general data deficiency of this system, the current identification methods cannot be applied with sufficient accuracy. A new identification approach was introduced in the present study based on nonlinear free vibration decay. Nonlinear free response of the presented system is determined by the coupling of generalized variation iteration and the modified differential transformation methods. The comparisons between the experiments and calculations is highlighted the good accuracy of the identified nonlinear model. © 2020 Faculty of Engineering,... 

    Numerical study of flow and heat in long micro and nano channels

    , Article 1st ASME Micro/Nanoscale Heat Transfer International Conference, MNHT08, Tainan, 6 January 2008 through 9 January 2008 ; Volume Parts A and B , 2008 , Pages 1299-1307 ; 0791842924 (ISBN); 9780791842928 (ISBN) Darbandi, M ; Vakilipour, S ; Sharif University of Technology
    2008
    Abstract
    In this work, we extend a numerical tool capable of solving compressible and incompressible gas flows to study the momentum and heat transfer rates in micro/nano channels with high aspect ratio (L/H = 8000), where the compressibility effect is dominant. The constant heat flux thermal boundary condition is firstly applied at the wall. Next, the flow regime is extended to the early transition regime employing a high order slip velocity boundary condition based on the kinetic theory assumptions. The accuracy of the present results in the slip flow regimes is evaluated against other available theoretical and experimental results. The thermal and compressibility effects on the pressure and... 

    Applications of single-layered graphene sheets as mass sensors and atomistic dust detectors

    , Article ASME 2007 International Mechanical Engineering Congress and Exposition, IMECE 2007, 11 November 2007 through 15 November 2007 ; Volume 11 , 2007 , Pages 99-104 ; 079184305X (ISBN) Sakhaee-Pour, A ; Ahmadian, M. T ; Vafai, A ; ASME ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2007
    Abstract
    Molecular structural mechanics is implemented to model vibrational behavior of defect free single-layered graphene sheets (SLGSs) at constant temperature. To mimic these two-dimensional layers, zigzag and armchair models with cantilever and bridge boundary conditions are adopted. Fundamental frequencies of these nano structures are calculated, and it is perceived that they are independent of the chirality and aspect ratio. Effects of point mass and atomistic dust on the fundamental frequencies are also considered in order to investigate the possibility of using SLGSs as sensors. Results of exhibit the principle frequencies are highly sensitive to the added mass in the order of 10-6 fg.... 

    Effective anti-plane moduli of couple stress composites containing elliptic multi-coated nano-fibers with interfacial damage and variational bounds

    , Article International Journal of Damage Mechanics ; Volume 30, Issue 9 , 2021 , Pages 1351-1376 ; 10567895 (ISSN) Hashemian, B ; Shodja, H. M ; Sharif University of Technology
    SAGE Publications Ltd  2021
    Abstract
    Prediction of the anti-plane moduli of solids consisting of a given distribution of unidirectionally aligned elliptic multi-coated fibers with interfacial damage is the focus of this paper. The fibers and their coating layers may be in the order of nano or micro scales. All the constituent phases of the composite are supposed to be described in terms of couple stress elasticity. Accordingly, the bounds for the overall shear moduli of the aforementioned composites are provided by employing the principles of minimum potential and complementary energies. Certain subtleties associated with the elliptic multi-coated fibers for three cases of pure sliding (completely damaged), imperfect (partially... 

    Effects of wing geometry on wing-body-tail interference in subsonic flow

    , Article Scientia Iranica ; Volume 18, Issue 3 B , 2011 , Pages 407-415 ; 10263098 (ISSN) Davari, A. R ; Soltani, M. R ; Askari, F ; Pajuhande, H. R ; Sharif University of Technology
    Abstract
    Extensive wind tunnel tests were performed on several wing- body-tail combinations in subsonic flow to study the effects of wing geometric parameters on the flow field over the tail. For each configuration, tail surface pressure distribution, as well as the velocity contour at a plane perpendicular to the flow direction behind the wing was measured. The results show a strong effect of wing to tail span ratio, as well as wing aspect ratio, on the flowfield downstream of the wing. For low sweep wings, as those considered here, wing and body interference effects on the tail are associated with the wing tip vortex and nose-body vortex  

    Electrokinetic mixing at high zeta potentials: Ionic size effects on cross stream diffusion

    , Article Journal of Colloid and Interface Science ; Volume 442 , 2015 , Pages 8-14 ; 00219797 (ISSN) Ahmadian Yazdi, A ; Sadeghi, A ; Saidi, M. H ; Sharif University of Technology
    Academic Press Inc  2015
    Abstract
    The electrokinetic phenomena at high zeta potentials may show several unique features which are not normally observed. One of these features is the ionic size (steric) effect associated with the solutions of high ionic concentration. In the present work, attention is given to the influences of finite ionic size on the cross stream diffusion process in an electrokinetically actuated Y-shaped micromixer. The method consists of a finite difference based numerical approach for non-uniform grid which is applied to the dimensionless form of the governing equations, including the modified Poisson-Boltzmann equation. The results reveal that, neglecting the ionic size at high zeta potentials gives... 

    Numerical investigation of turbulent free jet flows issuing from rectangular nozzles: The influence of small aspect ratio

    , Article Archive of Applied Mechanics ; Volume 80, Issue 7 , 2010 , Pages 727-745 ; 09391533 (ISSN) Faghani, E ; Maddahian, R ; Faghani, P ; Farhanieh, B ; Sharif University of Technology
    2010
    Abstract
    In this research, the fluid and thermal characteristics of a rectangular turbulent jet flow is studied numerically. The results of three-dimensional jet issued from a rectangular nozzle are presented. A numerical method employing control volume approach with collocated grid arrangement was employed. Velocity and pressure fields are coupled with SIMPLEC algorithm. The turbulent stresses are approximated using k-ε model with two different inlet conditions. The velocity and temperature fields are presented and the rates of their decay at the jet centerline are noted. The velocity vectors of the main flow and the secondary flow are illustrated. Also, effect of aspect ratio on mixing in...